DEVELOPMENT OF A POLY(LACTIC ACID) PACKAGING MATERIAL ABLE TO SCAVENGE CARBON DIOXIDE AND ETHYLENE BY INCORPORATION OF ZEOLITES B y Anna DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Packaging - Doctor of Philosophy 2015 ABSTRACT DEVELOPMENT OF A POLY(LACTIC ACID) PACKAGING MATERIAL ABLE TO SCAVENGE CARBON DIOXIDE AND ETHYLENE BY INCORPORATION OF ZEOLITES B y Anna Poly(lactic acid) is a biobased polymer and known to biodegrade reasonably quickly in commercial compost. There has been a growing interest in using it as a replacement for petrochemical based polymers due to its environmental - friendliness. Zeolites are crystalline hydrated aluminosilicates of alkali and alkaline earth elements. They can be natural minerals or produced synthetically. Depending on their framework they can have different structures and different pore sizes which makes them sorption - specific systems for various volatiles. There is a growing interest in their application in food packaging as they can adsorb and absorb gases crucial for extending shelf life of fresh produce, like ethylene and CO 2 . Active packaging systems are efficiently used in food packaging. Studies show that PLA and zeolites can be combined into one material by extrusion. Now the question is if they can act as an efficient active packaging system. Results obtained showed that t wo chosen zeolites, natural clinoptilolite and synthetic type 4A, have high sorption capacities for ethylene and carbon dioxide. Experimental conditions were varied, of varying combinations and concentrations of ethylene, carbon dioxide, nitrogen, and oxygen. Although low temperature and the presence of water in the system decreased sorption capacities of the zeolites, most measured amounts of ad sorbed ethylene and carbon dioxide were relevant to concentrations produced and higher than concentrations tolerated by fresh produce, and were promising enough to continue investigating these two zeolites when incorporated into/onto PLA films. Two techni ques to produce PLA/zeolite films were tested, extrusion (followed by injection molding and compression) and bar solution coating. The second method resulted in films with higher sorption potential for the two investigated gases since extrusion resulted in the zeolites being too deeply incorporated into the polymer matrix and having PLA as the polymer with good barrier properties towards ethylene did limit their sorption capacities. Further development of the most efficient coating solution and coating metho d resulted in production of two zeolite coated PLA films. The newly developed films were compared in sorption studies to two commercially available bags that are claimed to be ethylene scavengers and as a result to extend fresh produce shelf life. PLA fi lms proved to be comparable to one of the commercial bags comprised of LDPE impregnated with zeolites. The second commercial product did not show significant sorption of either of the two gases of interest. All film samples were tested in two conditions (2 both cases sorption of ethylene and carbon dioxide was smaller than for powder zeolites, with even higher decrease in low temperature and in the presence of water, the resulting sorbed amounts were still relevant to real life situations. Experiments designed to determine whether those films could be reused showed that both zeolite coated PLA films could be successfully reused in room temperature, the same as for the commercial film. Copyright by 2015 v ACKNOWLEDGMENTS I would like to thank Dr. Susan Selke for being my advisor. You were my fourth one, but the best one. You gave me a chance when I applied to School of Packaging, without you I would not be where I am now, with a Ph.D. You always had time for me and helped me with everything, giving me advice not only with this research but also anything else I needed. Thank you for everything. Dr. Eva Almenar, thank you for all your time and help. Without you thi s project would not go this far. Your comments and suggestions made me think more about food packaging than materials, which was always challenging for a person with chemistry background. Dr. Maria Rubino and Dr. Rafael Auras, thank you for finding time a nd helping me when I asked. Also thank you for your comments and suggestions during comprehensive exam and defense. They made this dissertation and whole project much better. Dr. Ramani Narayan, thank you for all your comments and suggestions. They were v ery useful in improving my work. vi TABLE OF CONTENTS LIST OF TABLES ................................ ................................ ................................ ................................ ............. ix LIST OF FIGURES ................................ ................................ ................................ ................................ .......... xiv CHAPTER 1 Research Motivation and Goals ................................ ................................ ................................ . 1 CHAPTER 2 Literature review ................................ ................................ ................................ ........................ 3 2.1. Active Packaging ................................ ................................ ................................ ............................. 3 2.2. Ethylen e (C 2 H 4 ) ................................ ................................ ................................ ............................... 7 2.3. Carbon dioxide (CO 2 ) ................................ ................................ ................................ .................... 12 2.4. Z eolites ................................ ................................ ................................ ................................ ......... 15 2.4.1. Clinoptilolite as the chosen natural zeolite ................................ ................................ ....... 22 2.4.2. Type 4A zeolite as the chosen synthetic zeolite ................................ ................................ 23 2.5. Application of zeolites in active packaging ................................ ................................ .................. 23 2.6. Polymer/zeolite systems ................................ ................................ ................................ .............. 25 2.7. Poly(lactic acid) (PLA) ................................ ................................ ................................ ................... 28 2.8. Measurements of ethylene ................................ ................................ ................................ .......... 32 REFERENCES ................................ ................................ ................................ ................................ ................ 36 CHAPTER 3 Ethylene and ca rbon dioxide sorption of natural and sy nthetic zeolites as affected by fresh produce conditions ................................ ................................ ................................ .................. 44 3.1. Introduction ................................ ................................ ................................ ................................ . 44 3.2. Experimental section ................................ ................................ ................................ .................... 46 3.2.1. Materials ................................ ................................ ................................ ........................... 46 3.2.1.1. Zeolites ................................ ................................ ................................ ........................... 46 3.2.1.2. Gases ................................ ................................ ................................ .............................. 46 3.2.2. Methods ................................ ................................ ................................ ............................ 47 3.2.2.1. Gas Chrom atography with Flame Ionization Detector (GC FID) ............................. 47 3.2.2.2. Gas Chromatography with Thermal Conductivity Detector (GC TCD) ................... 47 3.2.3. Sampling system and measuring conditions ................................ ................................ ..... 47 3.2.4. Adsorption measurements ................................ ................................ ................................ 48 3.2.5. Characterization of zeolites ................................ ................................ ............................... 49 3.2.5.1. Automated Gas Sorption Analyzer (Quantachrome) ................................ ............. 49 3.2.5.2. Scanning Electron Microscopy (SEM) ................................ ................................ ..... 50 3.2.6. Statistical methods ................................ ................................ ................................ ............ 50 3.3. Results and discussion ................................ ................................ ................................ .................. 50 3.3.1. Surface characteristics ................................ ................................ ................................ ...... 50 3.3.2. Adsorption measurements ................................ ................................ ................................ 53 3. 4. Conclusions ................................ ................................ ................................ ................................ .. 74 APPENDIX ................................ ................................ ................................ ................................ .................... 7 6 REFERENCES ................................ ................................ ................................ ................................ ................ 92 vii CHAPTER 4 Effect of the processing method on the adsorbing gas capability of active films made of PLA/zeolite ................................ ................................ ................................ .............................. 95 4.1. Introduction ................................ ................................ ................................ ................................ . 95 4.2. Experimental ................................ ................................ ................................ ................................ 96 4.2.1. Materials ................................ ................................ ................................ ........................... 96 4.2.1.1. Zeolites and Gases ................................ ................................ ................................ .. 96 4.2.1.2. Poly(lactic acid) ................................ ................................ ................................ ....... 96 4.2.2. Methods of thin film production ................................ ................................ ....................... 96 4.2.2.1. Extrusion, followed by injection molding and compression molding .................... 96 4.2.2.2. Bar coating ................................ ................................ ................................ .............. 98 4.2.2.3. Sample preparation ................................ ................................ ................................ 99 4.2.3. Adsorption measurements ................................ ................................ ................................ 99 4.2.3.1. Gas Chromatography with Flame Ionization Detector (GC FID) ............................. 99 4.2.3.2. Gas Chromatography with Thermal Conductivity Detector (GC TCD) ................. 100 4.2.4. Characterization of produced films ................................ ................................ ................. 100 4.2.4.1. Thermogravimetric Analysis (TGA) ................................ ................................ ....... 100 4.2.4.2. Scanning Electron Microscopy (SEM) ................................ ................................ ... 101 4.2.5. Statistical methods ................................ ................................ ................................ .......... 101 4.3. Results and discussion ................................ ................................ ................................ ................ 101 4.3.1. Melt processing ................................ ................................ ................................ ............... 101 4.3.2. S urface characteristics ................................ ................................ ................................ .... 104 4.3.3. Solution coating ................................ ................................ ................................ ............... 105 4.4. Conclusions ................................ ................................ ................................ ................................ 115 APPENDIX ................................ ................................ ................................ ................................ .................. 116 REFERENCES ................................ ................................ ................................ ................................ .............. 123 CHAPTER 5 New active packaging materials made of PLA films coated with solutions of PLA and natural or synthetic zeolites characterized as ethylene and carbon dioxide scavengers ................. 125 5.1. Introduction ................................ ................................ ................................ ............................... 125 5.2. Experimental ................................ ................................ ................................ .............................. 127 5.2.1. Materia ls ................................ ................................ ................................ ......................... 127 5.2.1.1. Zeolites and gases ................................ ................................ ................................ 127 5.2.1.2. Poly(lactic acid) ................................ ................................ ................................ ..... 127 5.2.1.3. Commercial bags ................................ ................................ ................................ .. 127 5.2.2. Bar coating ................................ ................................ ................................ ....................... 127 5.2.3. Adsorption measurements ................................ ................................ .............................. 128 5.2.4. Desorption measurements ................................ ................................ .............................. 128 5.2.5. Sample preparation ................................ ................................ ................................ ......... 128 5.2.6. Characterization of produced films ................................ ................................ ................. 130 5.2.6.1. Thermogravimetric Analysis (TGA) ................................ ................................ ....... 130 5.2.6.2. Differential Scanning Calorimetry (DSC) ................................ ............................... 130 5.2.6.3. Scanning Electron Microscopy (SEM) ................................ ................................ ... 130 5.2.6.4. Tensile Testing ................................ ................................ ................................ ...... 131 5.2.6.5. Fourier Transform Infrared Spectroscopy (FTIR) ................................ .................. 131 5.2.7. Statistical methods ................................ ................................ ................................ .......... 131 5.3. Results and discussion ................................ ................................ ................................ ................ 132 5.3.1. Adsorption measurements ................................ ................................ .............................. 132 5.3.2. Desorption studies ................................ ................................ ................................ .......... 148 viii 5.3.3. Thermal analysis ................................ ................................ ................................ .............. 148 5.3.4. FTIR analysis ................................ ................................ ................................ .................... 152 5.3.5. Mechanical characterization ................................ ................................ ........................... 155 5.3.6. Surface characteristics ................................ ................................ ................................ .... 158 5.4. Conclusions ................................ ................................ ................................ ................................ 159 APPENDIX ................................ ................................ ................................ ................................ .................. 161 REFERENCES ................................ ................................ ................................ ................................ .............. 1 70 CHAPTER 6 Summary, general conclusions and recommendations for future work ............................... 173 ix LIST OF TABLES Table 2.1. Some examples of active packaging systems, adapted from [4]. ................................ ................ 5 Table 2.2. Fresh produce classification based on respiratory behavior during ripening, adapted from [13]. . ................................ ................................ ................................ ................................ ............ 8 Table 2.3. Commodities classified according to ethylene production rates, adapted from [13]. ................ 9 Table 2.4. Ethylene production and sensitivity of some fresh produce, adapted from [13]. ....................... 9 Table 2.5. Positive and negative effects of the same ethylene response, adapted from [13]. .................. 10 Table 2.6. Commercially available ethylene scavenger systems, adapted from [16]. ................................ 11 Table 2.7. Fresh p roduce listed in groups according to their respiration rates, adapted from [13]. ......... 13 Table 2.8. Commodities grouped according to thei r tolerance to CO 2 concentrations, adapt ed from [13]... ................................ ................................ ................................ ................................ ......... 14 Table 2.9. Commercial CO 2 active packaging systems with possible O 2 scavenging activity, adapted from [7]. ................................ ................................ ................................ ................................ ............. 15 Table 2.10. Kinetic diameters of some gases, adapted from [74]. ................................ ............................. 19 Table 2.11. Physical properties of zeolites used commercially [28, 81]. ................................ .................... 22 Table 2.12. CO 2 ................................ ...... 30 Table 2.13. O 2 ................................ ............ 30 Table 2.14. N 2 ................................ ................................ ................ 30 Table 2.15. H 2 O vapor ................................ ........... 31 Table 2.16. C 2 H 4 permeability coefficients [61]. ................................ ................................ ......................... 31 Table 3.1. Surface characteristics of investigated zeolites. ................................ ................................ ........ 50 Table 3.2. Total times for ethylene adsorption measurements. ................................ ................................ 5 4 Table 3.3. Total times for carbon dioxide adsorption measurements. ................................ ....................... 5 4 Table A3 .1. Ethylene calibration data for GC FID. ................................ ................................ ....................... 78 Table A3 .2. Oxygen calibration data for GC TCD. ................................ ................................ ....................... 81 x Table A3 .3. Nitrogen calibration data for GC TCD. ................................ ................................ ..................... 81 Table A3 .4. Carbon dioxide calibration data for GC TCD. ................................ ................................ ........... 82 Table A3.5 . Summary of ethylene (ppm) measurements taken for powder zeolites in chapter 3. ........... 82 Table A3.6 . Summary of ethylene (%) measurements taken for powder zeolites in chapter 3. ................ 83 Table A3.7 . Summary of ethylene (nL) measurements taken for powder zeolites in chapter 3. ............... 84 Table A3.8 . Summary of carbon dioxide (%) measurements taken for powder zeolites in chapter 3 . ...... 85 Table A3.9 . Amount of ethylene adsorption (ppm) at room temperature and 0% RH. ............................. 85 Table A3.10 . Amount of ethylene adsorption (%) at room temperature and 0% RH. ................................ 85 Table A3.11 . Amount of ethylene adsorption (ppm) a t room temperature and 0% RH with carbon dioxid e present. ................................ ................................ ................................ ................................ ..... 86 Table A3.12 . Amount of ethylene adsorption (%) at room temperature and 0% RH with carbon dioxide present. ................................ ................................ ................................ ................................ ..... 86 Table A3.13 . present. ..... 87 Table A3.14 . .......... 88 Table A3.15 . Amount of ethylene adsorption (ppm) at room temperatur e and 100% RH. ....................... 88 Table A3.16 . Amount of ethylene adsorption (%) at room temperat ure and 100% RH. ............................ 89 Table A3.17 . ................................ ................ 89 Table A3.18 . ................................ .................... 89 Table A3.19 . Amount of carbon dioxide adsorption (%) at room temperature and 0% RH. ...................... 89 Table A3.20 . Amount of carbon dioxide adsorption (%) at room temperature and 0% RH in presence of ethylene. ................................ ................................ ................................ ................................ ... 90 Table A3.21 . Amount of carbon dioxide adsorption (%) at room temperature and 0% RH in presence of oxygen. ................................ ................................ ................................ ................................ ...... 90 Table A3.22 . Amount of carbon dioxide adso rption (%) at room temperature and 100% RH. .................. 90 Table A3.23 . ........ 90 Table A3.24 . Amount of carbon dioxide adsorption ( ................................ .......... 91 x i Tabl e 4.1 . List of combination of wt% of zeolite in coating solution and bar used for coating and % of zeolite in obtained film. ................................ ................................ ................................ .......... 108 Table 4.2 . List of combination of PLA and zeolite weights in coating solution along with bar used for coating and % of zeolite in obtained film. ................................ ................................ ............. 111 Table A4 .1. Amount of ethylene (%) adsorbed by film samples at two different times. ......................... 117 Table A4 .2. Amount of ethylene (nL) adsorbed by film samples at two different times. ........................ 117 Table A4 .3. Amount of carbon dioxide (%) adsorbed by film samples at two different times. ................ 117 Table A4 .4. Amount of carbon dioxide (%) adsorbed by film samples at two different times. ................ 117 Table A4 .5. Amount of ethylene (%) adsorbed by extruded and coat ed film samples. ........................... 118 Table A4 .6. Amount of ethylene (nL) adsorbed by extruded and coated film samples. .......................... 118 Table A4 .7. Amount of carbon dioxide (%) adsorbed by extruded and coated film samples. ................. 118 Table A4 .8. Amount of carbon dioxide (mL) adsorbed by extr uded and coated film samples. ............... 118 Table A4 .9. Amount of ethylene (%) adsorbed by coated film samples prepared using different coating solutions and dif ferent coating bars. ................................ ................................ ...................... 119 Table A4 .10. Amount of ethylene (nL) adsorbed by coated film samples prepared us ing different coating solutions and different coating bars. ................................ ................................ ...................... 119 Table A4 .11. Amount of carbon dioxide (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars. ................................ ................................ ......... 1 20 Table A4 .12. Amount of carbon dioxide (mL) adsorbed by coated film samples prepared using different coating solutions and different coating bars. ................................ ................................ ......... 120 Table A4 .13. Amount of ethylene (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four dif ferent times. ................................ ................. 121 Table A4 .14. Amount of ethylene (nL) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four different times. ................................ ................. 121 Table A4 .15. Amount of carbon dioxide (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four different times. ................................ .... 121 Table A4 .16. Amount of carbon dioxide (mL) adsorbed by coated film samples prepared using different coating solutions and different coating bars at f our different times. ................................ .... 122 xii Table 5.1. Percent of zeolite content in investigated films measured by TGA. ................................ ........ 149 Table 5.2. Thermal properties of investigated PLA films coated with zeolites along with standard samples. ................................ ................................ ................................ ................................ .. 15 2 Table 5.3. Tensile properties of standard samples and PLA films coated with zeolites. .......................... 157 Table A5 .1. Amount of carbon dioxide (%) adsorbed by commercial and coated films and values for ................................ ................................ 16 2 Table A5 .2. Amount of carbon dioxide (mL) adsorbed by commercial and coated films and values for ................................ ................................ 16 2 Table A5 .3. Amount of ethylene (ppm) adsorbed by commercial and coated films and values for control ................................ ................................ ............ 16 3 Table A5 .4. Amount of ethylene (%) adsorbed by commercial and coated films and values for control a t ................................ ................................ ................ 16 3 Table A5 .5. Amount of ethylene (nL) adsorbed by commercial and coated films and values for control a t four dif ................................ ................................ ................ 16 3 Table A5 .6. Amount of carbon dioxide (%) adsorbed by commercial and coated films and values for ................................ .............................. 16 4 Table A5 .7. Amount of carbon dioxide (mL) adsorbed by commercial and coated films and values for ................................ .............................. 16 4 Table A5 .8. Amount of ethylene (ppm) adsorbed by commercial and coated films and values for control ................................ ................................ .......... 16 4 Table A5 .9. Amount of e thylene (%) adsorbed by commercial and coated films and values for control at ................................ ................................ .............. 16 5 Table A 5 .10. Amount of ethylene (nL) adsorbed by commercial and coated films and values for control nd 100% RH. ................................ ................................ .......... 16 5 Table A5 .11. Amount of carbon dioxide (%) adsorbed by the same commercial and coated films and values for control, used first time after coating and second time after degassing, at four ................................ ................................ ........................ 16 6 Table A5 .12. Amount of carbon dioxide (mL) adsorbed by the same commercial and coated films and values for control, used first time after coating and second time after degassing, at four ................................ ................................ ........................ 16 6 Table A5 .13. Amount of ethylene (ppm) adsor bed by the same commercial and coated films and values for control, used first time after coating and second time after degassing, at four different ................................ ................................ ................................ ....... 16 7 xiii Table A5 .14. Amount of ethylene (%) adsorbed by the same commercial and coated films and values for control, used first time after coating and second time after degassing, at four different times ................................ ................................ ................................ ................. 16 7 Table A5 .15. Amount of ethylene (nL) adsorbed by the same commercial and coated films and values for control, used first time after coating and second time after degassing, at four different times ................................ ................................ ................................ ................. 16 8 Table A5 .16. Amount of ethylene (%, ppm, nL) adsorbed by coated films in permeation cells at four ................................ ................................ ........................ 16 9 Table A5 .17. Am ount of ethylene (%, ppm, nL) adsorbed by coated films in permeation cells at four ................................ ................................ .......................... 16 9 xiv LIST OF FIGURES Figure 2.1. Global market value (million US $) of active and intelligent packaging [7]. ............................... 6 Figure 2.2. Global market share (%) of active and intelligent packaging [7]. ................................ ............... 7 Figure 2.3.Types of sorption isotherms, adapted from [86]. ................................ ................................ ...... 20 Figure 2.4. Poly(lactic acid). ................................ ................................ ................................ ........................ 28 Figure 3.1. Images of natural clinoptilolite (on left) and synthetic type 4A (on right ) zeolites. ................. 46 Figure 3.2. Nitrogen sorption isotherm for clinoptilolite. ................................ ................................ ........... 52 Figure 3.3. Nitrogen sorption isotherm for type 4A zeolite. ................................ ................................ ....... 52 Figure 3.4. SEM images of clinoptilolite (on left) and type 4A zeolite (on right). ................................ ....... 53 Figure 3.5. Amount of ethylene (ppm) adsorbed by zeolites after 2 days. ................................ ................ 55 Figure 3.6. Amount of ethylene (%) adsorbed by zeolites after 2 days. ................................ ..................... 5 6 Figure 3.7. Amount of ethylene (nL) adsorbed by zeolites after 2 days. ................................ .................... 5 6 Figure 3.8. Amount of ethylene (ppm) adsorbed by zeolites after 5 days. ................................ ................ 57 Figure 3.9. Amount of ethylene (%) adsorbed by zeolites after 5 days. ................................ ..................... 57 Figure 3.10. Amount of ethylene (nL) adsorbed by zeolites after 5 days. ................................ .................. 5 8 Figure 3.11. Amount of ethylene (ppm) adsorbed by zeolites after total measurement time. ................. 58 Figure 3.12. Amount of ethylene (%) adsorbed by zeolites after total measurement time. ...................... 59 Figure 3.13. Amount of ethylene (nL) adsorbed by zeolites after total time. ................................ ............ 59 Figure 3.14. Amount of carbon dioxide (%) adsorbed by zeolites after 5 hours. ................................ ....... 61 Figure 3.15. Amount of carbon dioxide (mL) adsorbed by zeolites after 5 hours. ................................ ..... 61 Figure 3.16. Amount of carbon dioxide (%) adsorbed by zeolites after total measurement time. ............ 62 Figure 3.17. Amount of carbon dioxide (mL) adsorbed by zeolites after total measurement time. .......... 62 Figure 3.18. Amount of ethylene sorption (ppm) at room temperature and 0% RH. ................................ 64 xv Figure 3.19. Amount of ethylene sorption (%) at room temperature and 0% RH. ................................ ..... 65 Figure 3.20. Amount of ethylene sorption (ppm) at room temperature and 0% RH with carbon dioxide present. ................................ ................................ ................................ ................................ ..... 66 Figure 3.21. Amount of ethylene sorption (%) at room temperature and 0% RH with carbon dioxide present. ................................ ................................ ................................ ................................ ..... 66 Figure 3.22. Amount .......... 67 Figure 3.23. Amount of ............... 67 Figure 3.24. Amount of ethylene sorption (ppm) at room temperature and 100% RH. ............................ 68 Figure 3.25. Amount of ethylene sorption (%) at room temperature and 100% RH. ................................ . 69 Figure 3.26. Amount ................................ ..................... 69 Figure 3.27. Amount ................................ ............................. 70 Figure 3.28. Amount of carbon di oxide sorption (%) at room temperature and 0% RH. ........................... 70 Figure 3.29. Amount of carbon dioxide sorption (%) at room temperature and 0% RH in presence of ethylene. ................................ ................................ ................................ ................................ ... 71 Figure 3.30. Amount of carbon dioxide sorp tion (%) at room temperature and 0% RH in presence of oxygen. ................................ ................................ ................................ ................................ ...... 72 Figure 3.31. Amount of carbon dioxide sorption (%) at room tempera ture and 100%RH. ........................ 72 Figure 3.32. Amount ............. 73 Figure 3.33. Amount ................................ ............... 74 Figure A 3 .1. Ethylene calibration curve for GC FID. ................................ ................................ .................... 77 Figure A 3 .2. Oxygen calibration curve for GC TCD. ................................ ................................ .................... 79 Figure A3 .3. Nitrogen calibration curve for GC TCD. ................................ ................................ .................. 79 Figure A3 .4. Carbon dioxide calibration curve for GC TCD. ................................ ................................ ........ 80 Figure 4. 1 . Injection molded PLA, PLA/30% type 4A zeolite, PLA/30% clinoptilolite discs. ....................... 97 Figure 4.2 . Heated press used to produce films from injection molded discs. ................................ .......... 98 Figure 4. 3 . Multicoater used to produce coated films. ................................ ................................ .............. 99 xvi Figure 4.4 . Amount of ethylene (%) adsorbed by film samples at 2 different times. ............................... 102 Figure 4.5 . Amount of ethylene (nL) adsorbed by film samples at 2 different times. .............................. 102 Figure 4.6 . Amount of carbon dioxide (%) adsorbed by film samples at 2 different times. ..................... 103 Figure 4. 7 . Amount of carbon dioxide (mL) adsorbed by film samples at 2 different times. ................... 103 Fi gure 4.8 . SEM images of PLA/30 wt% CL (on left) and PLA/30 wt% 4A (on right). ................................ 104 Figure 4.9 . Amount of ethylene (%) adsorbed by extruded (ext) and coated (coat)film samples. .......... 105 Figure 4.10 . Amount of ethylene (nL) adsorbed by extruded and coated film samples. ......................... 106 Figure 4.11 . Amount of carbon dioxide (%) adsorbed by extruded and coated film samples. ................ 106 Figure 4.12 . Amount of carbon dioxide (mL) adsorbed by extruded and coated film samples. .............. 107 Figure 4.13 . Amount of ethylene (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars. ................................ ................................ ...................... 109 Figure 4.14 . Amount of ethylene (nL) adsorbed by coated film samples prepared using different coating solutions and different co ating bars. ................................ ................................ ...................... 109 Figure 4.15 . Amount of carbon dioxide (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars. ................................ ................................ ......... 110 Figure 4.16 . Amount of carbon dioxide (mL) adsorbed by coated film samples prepared using different coating solutions and different coating bars. ................................ ................................ ......... 110 Figure 4.17 . Amount of ethylene (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars at f our sampling times. ................................ ................. 112 Figure 4.18. Amount of ethylene (nL) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four sampling times. ................................ ............... 112 3 Figure 4.19. Amount of carbon dioxide (%) adsorbed by coated film samples prepared using different coat ing solutions and different coating bars at four sampling times. ................................ .... 113 Figure 4.20. Amount of carbon dioxide (mL) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four sampling times. ................................ .... 11 4 Figure 5.1. Amount of ethylene (%) adsorbed by commercial and coated fi lms and values for control at ................................ ................................ ................ 133 Figure 5.2. Amount of ethylene (ppm) absorbed by commercial and coated films and values for control ................................ ................................ ............ 133 Figure 5.3. Amount of ethylene (nL) absorbed by commercial and coated films and values for control at ................................ ................................ ................ 134 xvii Figure 5.4. Amount of carbon dioxide (%) adsorbed by commercial and coated films and values for ................................ ............................... 135 Figure 5.5. Amount of carbon dioxide (mL) adsorbed by commercial and coated films and values for ................................ ............................... 135 Figure 5.6. Amount of ethylene (%) adsorbed by commercial and coated films and values for control at ................................ ................................ .............. 13 6 Figure 5.7. Amount of ethylene (ppm) adsorbed by commercial and coated films and values for control and 100% RH. ................................ ................................ .......... 137 Figure 5.8. Amount of ethylene (nL) adsorbed by commercial and coated films and values for control at ................................ ................................ .............. 137 Figure 5.9. Amount of carbon dioxide (%) adsorbed by commercial and coated films and values for ................................ ............................. 138 Figure 5.10. Amount of carbon dioxide (mL) adsorbed by commercial and coated films and values for ................................ ............................. 139 Figure 5.11. Amount of ethylene (%) adsorbe d by the same commercial and coated films and values for control, used first time after coating and second time after drying, at four sampling times at ................................ ................................ ................................ ..................... 1 4 0 Figure 5.12. Amount of ethylene (ppm) adsorbed by the same commercial and coated films and values for control, used first time after coating and second time after drying, at four sampling times ................................ ................................ ................................ ................. 141 Figure 5.13.Amount of ethylene (ppm) adsorbed by the same commercial and coated films and values for control, used first time after coating and second time after drying, at four sampling times ................................ ................................ ................................ ................. 141 Figure 5.14. Amount of carbon dioxide (%) adsorbed by the same commercial and coated films and val ues for control, used first time after coating and second time after drying, at four sampling ................................ ................................ ................................ ....... 142 Figure 5.15. Amount of carbon dioxide (mL) adsorbed by the same commercial and coated films and values for control, used first time a fter coating and second time after drying, at four sampling ................................ ................................ ................................ ....... 143 Figure 5.16. Amount of ethylene (%) adsorbed by coated films in permeation cells at four sampling times ................................ ................................ ................................ ................. 144 Figure 5.17. Amount of ethylene (ppm) absorbed by coated films in permeation cells at four sampling ................................ ................................ ................................ ....... 144 Figure 5.18. Amount of ethylene (nL) absorbed by coated films in permeation cells at four sampling ................................ ................................ ................................ ....... 145 xviii Fig ure 5.19 . Amount of ethylene (%) adsorbed by coated films in permeation cells at four sampling times ................................ ................................ ................................ ................... 146 Figure 5.20 . Amount of ethylene (ppm) adsorbed by coated films in permeation cells at four sampling ................................ ................................ ................................ ......... 146 Figure 5.21 . Amount of ethylene (nL) adsorbed by coated films in permeation cells at four sampling ................................ ................................ ................................ ......... 1 47 Figure 5.22. TGA thermograms of two zeolite coated films and two commercial films. ......................... 150 Figure 5.23. DSC thermograms (1st cycle) of standard samples and PLA films coated with zeolites. ..... 151 Figure 5.24. FTIR spectra of PLA film coated with clinoptilolite, after adsorption of ethylene and after degassing. ................................ ................................ ................................ ............................... 153 Figure 5.25. FTIR spectra of PLA film coated with type 4A zeolite, after adsorption of e thylene and after degassing. ................................ ................................ ................................ ............................... 155 Figure 5.26. SEM images of PLA films coated with clinoptilolite. ................................ ............................. 15 8 Figure 5.27. SEM images of PLA films coated with type 4A zeolite. ................................ ......................... 159 1 CHAPTER 1 Research Motivation and Goals Researchers working in food packaging have always been concerned about using proper packaging materials and systems to minimize food losses and result in safe food products. Lately, there has been a growing interest in providing better quality foods that can stay fresh - like for a much longer time without looking or tasting as if they were packed awhile ago. This resulted in development of active packaging technologies. In perishables packaging, headspace gas content and its changing concentra tion are very important in keeping the product fresh like and safe for as long as possible. Gases used during the packaging process (O 2 , CO 2 , N 2 ) as well as those produced by food (C 2 H 4 , CO 2 ) play an important role in shelf life. Recently zeolites have bee n a subject of study as absorbers for many different gases. Since they can act as ethylene and CO 2 scavengers, researchers are investigating their possible utilization in active packaging systems. Poly(lactic acid) as a biobased and certified compostable in industrial compost systems alternative to petrochemical based polymers is also receiving growing attention in food packaging. For fresh produce purposes it should be modified by additives that will help with sorption of specific gases. Since zeolite/PL A composite materials have been successfully produced in the past, natural development suggests extrapolating their use to food packaging. Zeolites, crystalline aluminosilicates of alkali and alkaline earth elements that are characterized by unique three - dimensional framework structures composed of SiO 4 and AlO 4 , have been successfully used as ethylene and CO 2 scavengers. They have also been used to produce polymer/zeolite films and 2 their adsorption capacities have been investigated. Polymers commonly mixe d with zeolites include LDPE, HDPE, PP, PC, and PS but they can also be successfully incorporated into PLA films. The main goal of this project was to develop a new active packaging system composed of zeolites and PLA, which will be able to act as an eth ylene and CO 2 scavenger. The specific objectives were to measure ethylene and CO 2 sorption capacities of two chosen zeolites in the form of powders and to produce and evaluate PLA films coated with zeolites as ethylene and CO 2 scavengers. The following st eps were involved in accomplishing the pursued goals. First, a method and system that could be applied to measuring ethylene and CO 2 sorption for both powder zeolites and PLA films coated with zeolites were developed. This was followed by determination of zeolite sorption of ethylene and CO 2 at various concentrations, temperatures and relative humidities, and also in the presence of additional gases. Then the natural step was to move to producing PLA zeolite films. Coating of PLA film with zeolites was the most successful of the attempted methods. Lastly, these films were investigated as to ethylene and CO 2 sorptionat various concentrations, temperatures and relative humidities, and also in the presence of additional gases. This project was designed to provi de information about how to produce a desired wt% combination of zeolite on PLA film so that the sorption capacity of the zeolites is not inhibited by the high barrier of PLA to ethylene. The goal was to produce not a system that absorbs the most, but rath er one that is most efficient in ad sorbing concentrations that are most relevant to real life situations, and to compare it to commercially available packages that are claimed to be ethylene scavengers that extend fresh produce shelf life. 3 CHAPTER 2 Literature review 2.1. Active Packaging The main concern of food packaging has always been to use appropriate packaging materials and methods to ensure the safety and health of food products, but also to minimize product losses. As consumers expect high quality, fresh - like quality and easy to access fresh produce, the industry must match these demands. One way to achieve it is by using active packaging technology for perishables. Active packaging (AP) can be described as a packaging system that enhances shelf life by doing more than simply contain the product. For foods, often this involves incorporating additives as a part of the packaging material or plac ing them inside of a container to modify or to interact with the headspace in the package and extend the product s shelf life. AP has to fulfill consumer demands of high quality, fresh - like quality and safety of food products. This technology involves interactions between the package or package component and the food or internal gas atmosphere. The m ain p urpose of many active packaging technologies is to extend the shelf life of fresh produce while preventing loss of nutritional quality and freshness, and at the same time inhibiting the growth of pathogens and spoilage microorganisms. The market for active packages has been rapidly growing in the last several decades[1 - 3 , 89 ]. Two mechanisms by which active packaging works are based on where and how the active element is incorporated . It can be placed inside the package but separate from the food, for exam ple as a sachet, or it can be incorporated into the packaging material [1,4 - 5]. 4 The classification of active packaging systems depends on their principle of operation. They might be scavenging or emitting systems. Within these two actions, AP might work w ith different gases (oxygen, carbon dioxide, ethylene, ethanol, etc.) by both absorption and release. But also moisture control, antimicrobial and antioxidant releasing, flavor releasing and absorbing, light absorbing or regulating, and color containing sy stems are known. Advanced AP systems might have dual or multiple functionality since fresh produce will be influenced by many factors and will need or produce more than one gas. For instance, a popular combination is oxygen scavengers with carbon dioxide e mitters, or sometimes also releasing antimicrobials. Often these combined systems will complement each other. For example, an oxygen absorber when combined with ethanol ( C 2 H 5 OH) and antimicrobial release will be more effective than the oxygen scavenger alone [1 - 8]. Until now, the most popular way of creating an active packaging system was to place additives in the form of a sachet, sheet, label or closure liner inside of a packa ge. Sachets may not be the safest due to the danger of being eaten or ruptured and allowing active components to contact the food. Also contents of these sachets have not always been safe. For example, the most common ethylene absorbing system consists of potassium permanganate imbedded in silica. First silica absorbs ethylene which is then oxidized by potassium permanganate to ethylene glycol. It is a very popular scavenger due to its low cost and the ease of placing a sachet with an active compound inside a package. Unfortunately, potassium permanganate is toxic, so it should not be in direct contact with any food products [1, 7 - 8]. The newer option is to incorporate active elements directly into the material or on the surface of it. The choice of proper polymer will also play a critical role in the efficiency of such a system. If a polymer has high barrier properties to the gas which is to be absorbed, having an active element too deep into the polymer matrix will inhibit its sorption capacity. But having the element on the surface will 5 permit adsorption. This way the characteristics of the active element will be the least affected by the polymer material itself. Incorporating of active elements, for example zeolites, into polymer film might be done by usi ng different production processes, extrusion from a masterbatch, lamination or coating, etc [1,7 - 8]. Table 2.1 shows a variety of active packaging systems with their mechanism of action (active element) and food applications. It can be seen that with thes e already known systems we can successfully control concentrations of headspace gases along with moisture content, temperature, etc. Foods for which those AP systems can be applied seem to be very vast. Table 2 . 1 . Some examples of active packaging systems, adapted from [4]. AP system Active element Food Oxygen scavengers Iron based Bread, cakes, cooked rice, Metal/acid biscuits, pizza, pasta, Nylon MXD6 cheese, cured meats and Metal (e.g. platinum) catalyst fish, coffee, snack foods, Ascorbate/metallic salts dried foods and beverages Enzyme based Carbon dioxide Iron oxide/calcium hydroxide Coffee, fresh meats and fish, scavengers/emitters Ferrous carbonate/metal halide N uts Calcium oxide/activated charcoal Ascorbate/sodium bicarbonate Ethylene scavengers Potassium permanganate Fruit, vegetables Activated carbon Activated clays/zeolites Ethanol emitters Encapsulated ethanol Pizza crusts, cakes, bread, biscuits, fish and bakery products Moisture absorbers Activated clays and minerals Fish, meats, poultry, snack Silica gel foods, cereals, dried foods, sandwiches, fruits and V egetables Flavor/odor Acetylated paper Fruit juices, fish, cereals, A bsorbers Citric acid poultry, dairy products Ferrous salt/ascorbate and fruit Activated carbon/clays/zeolites 6 Active packaging technology is still developing and will be based on advances in packaging material science but also on new consumer demands. Although active and intelligent packaging was first introduced in Japan in the mid 70s and 20 years later became a n interest in industry in Europe and in the USA, this market is still growing. In 2001, active and intelligent packaging was worth 1.1 M US$ with only two technologies accounting for80% of it - oxygen scavenging and moisture absorbents. The global value in creased to 1.8 M US$ by 2005 with 40% still taken by oxygen scavengers. Predictions for 2010 (forecasted in 200 7 ) showed a growing trend in global market value, shown in figure 2.1. It should be also noticed that ethylene and CO 2 scavenging are still one o f the smallest market shares, with just a few percent of the total, presented in figure 2.2 [7 - 8]. Figure 2 . 1 . Global market value (million US $) of active and intelligent packaging [7]. 0 100 200 300 400 500 600 700 800 900 1000 million US $ 2001 2005 2010 (forecasted in 2007) 7 Figure 2 . 2 . Global market share (%) of active and intelligent packaging [7]. M any of the AP systems used nowadays are still expensive and do not compensate for the cost with the benefits they bring. Handling of these packages can also cause issues, because having limited sorption/emission capacity of active components, it is not desirable for them to start to work before the product is packed. And most of all, consumers have to accept industrially applied solutions. Sachets and oth er foreign bodies inside the package may be a concern for consumers, especially with small children. AP with the active element incorporated into the polymer might be a more acceptable option [7 - 8]. 2.2. Ethylene (C 2 H 4 ) Ethylene is a naturally occurring g as that works as a plant hormone and can cause different physiological effects in fresh produce. Ethylene accelerates ripening and senescence, and causes early maturity and softening of climacteric fruits and vegetables by increasing their respiration rate . It is a colorless gas, which is produced by plants. It can also induce yellowing of green vegetables. Too high levels of ethylene during storage can shorten shelf life and also produce some defects of the harvest like Oxygen scavengers Ethylene scavengers Carbon dioxide scavengers/emitters Moisture scavengers Ethanol emitters Flavor/odor absorbers Antioxidants Self - venting Susceptor laminates Temperature control 8 textural and color changes or even t issue degradation, for example russet spotting on lettuce and scald on apples. Not all ethylene effects are unwanted; some can be positive like degreening of citrus fruits or induction of flowering in pineapples [1 - 4, 9, 13 - 14]. Although ethylene is natu rally occurring in plant tissues, the main sources of ethylene in the atmosphere are climacteric fruits and damaged or rotten produce. It is also produced by internal combustion engines, smoke and other sources of pollution. Climacteric fruits are fruits w ith high respiration rates that after harvest increase very rapidly during ripening and decrease during senescence. An increase in ethylene production is observed as the fruits ripen. Non - climacteric fruits have low respiration rates after harvest, which also decrease over time and are not influenced much by the presence of ethylene. Table 2.2 provides a list of climacteric and non - climacteric fruits and vegetables [9, 13 - 14]. Table 2 . 2 . Fresh produce classification based on r espiratory behavior during ripening, adapted from [13]. Climacteric Non - climacteric Apple Blackberry Blueberry Cherry Nectarine Cranberry Peach Cucumber Pear Grape Plum Raspberry Tomato Strawberry Watermelon For climacteric fruits, lowering ethylene concentration can delay ripening, but without it normal ripening cannot occur. For instance, tomatoes need ethylene to develop a red color and to soften. Although different fruits have different production rates of ethylene, when stored together w ith other fruits they can be affected by high ethylene levels produced by the other fruits. Table 2.3 shows differing ethylene production rates of fruits and vegetables [9, 13 - 15]. 9 Table 2 . 3 . Commodities classified according to ethylene production rates, adapted from [13]. Class Fresh produce 2 H 4 /kg h ) Very low Less than 0.1 Cauliflower, cherry, citrus fruits, grape, strawberry, pomegranate, potato Blackberry, blueberry, cranberry, Low 0.1 - 1.0 cucumber, pineapple, pumpkin, raspberry, watermelon Moderate 1.0 - 10.0 Banana, fig, mango, tomato High 10.0 - 100.0 Apple, avocado, nectarine, papaya, peach, pear, plum Very high more than 100.0 Mammee apple, passion fruit Even very low concentrations of ethylene, at the level of parts per billion (ppb) and parts per million (p pm), can be critical. Table 2.4 shows how small amounts of ethylene are produced by given perishables and also lists their ethylene sensitivity [13]. Table 2 . 4 . Ethylene production and sensitivity of some fresh produce, adapted from [13]. Fresh produce Ethylene production Ethylene sensitivity (ppm) Climacteric Fruit Apple, kiwifruit, pear H igh high (0.03 - 0.1) Avocado, passion fruit H igh medium (> 0.4) Banana, mango M edium high (0.03 - 0.1) Nectarine, papaya, peach, plum, tomato M edium medium (> 0.4) Vegetables and non - climacteric fruit Broccoli, Brussels, cabbage, carrot, L ow high (0.01 - 0.02) cauliflower, cucumber, lettuce, potato, spinach, strawberry Asparagus, celery , citrus L ow medium (0.04 - 0.2) Berries, cherry, grape, pineapple L ow low (> 0.2) Exposure to ethylene can bring positive or negative effects. The effect may also depend on when exposure to this plant hormone occurs. Ethylene effects can be very different like physiological disorders (chilling injury, russet spotting, superficial scald, internal browning), abscission, bitterness, 10 toughness, off - flavo rs, sprouting, color changes (yellowing or discoloration) and softening [9, 13 - 14, 16]. Some examples are listed in table 2.5. Table 2 . 5 . Positive and negative effects of the same ethylene response, adapted from [13]. Ethylene response Positive effect Negative effect Accelerates chlorophyll loss Degreening of citrus Yellowing of green vegetables Promotes ripening Ripening of climacteric fruit Overly soft and mealy fruit In the horticultural industry different methods have been applied to reduce ethylene's impact on fresh produce during both storage and distribution. The most common ones are low temperatures and controlled atmospheres but also using filters/scrubbers to remove ethylene present around stored fruits and vegeta bles. Low temperature is proven to lower the respiration rate of fresh produce, and controlled atmosphere utilizes low oxygen and high carbon dioxide concentrations which will also result in lowering respiration rates. But not all of these technologies can be used when dealing with closed packages where ethylene will be accumulating [1 - 4, 9]. Packaging technologies involving control of ethylene inside packages are based on scavenging it. The most widely used systems involve sachets. As mentioned before, t hese might contain potassium permanganate, which is toxic and causes concerns about KMnO 4 migration into the produce. The second most common sachet - based C 2 H 4 scavenging system involves activated carbon with a metal catalyst. These systems can effectively r emove ethylene from air passing over the sachet. Unfortunately , they require heat and moving gases, so they are not appropriate for closed packages. However activated charcoal impregnated with a palladium catalyst inside a paper sachet was proven to scaven ge ethylene from kiwi, banana, broccoli and spinach [16]. Recently, there has been a focus on replacing sachets by incorporating active compounds directly into the package. Many of these newly developed polymer films consist of polyethylene 11 impregnated wi th finely dispersed minerals. Often these minerals are local kinds of clay, zeolites or Japanese oya stone. They are produced as bags and are commercially available. Many of these companies are Japanese or Korean, but there are also some from the United St ates and Australia. A few of these companies and their packaging systems are listed in table 2.6 [9, 16]. Table 2 . 6 . Commercially available ethylene scavenger systems, adapted from [16]. Producer Country Market name Active element Packaging form Air repair Products, Inc. USA N/A Potassium permanganate Sachets/blankets Ethylene Control, Inc. USA N/A Potassium permanganate Sachets/blankets Extenda Life Systems USA N/A Potassium permanganate Sachets/blankets Mitsubishi Gas Chem. Co. Ltd Japan Sendo - Mate Activated carbon Plastic film Cho Yang Heung San Co. Ltd Korea Orega Activated clays/zeolites Plastic film Evert - Fresh Corporation USA Evert - Fresh Activated zeolites Plastic film Odja Shoji Co. Ltd Japan BO Film Crysburite ceramic Plastic film Peak f resh Products Ltd Australia Peak f resh Activated clays/zeolites Plastic film Grofit Plastics Israel Bio - fresh Activated clays/zeolites Plastic film Food Science Australia Australia N/A Tetrazine derivatives Plastic film Manufacturers offering bags made of minerals dispersed within the film advertise their products as ethylene adsorbing products, often reusable ones. To prove that their product works as described they provide results from shelf life experiments where norm al polyethylene bags are compared to their mineralized bags. Often the results presented show extension of shelf life or lowering of the ethylene concentration in the headspace. The explanation might not be so obvious as ethylene absorption by the minerals . As is the case for any finely distributed material within the bag, these minerals will also open pores in the plastic and influence barrier properties for different gases, including ethylene. Ethylene as a small molecule will diffuse more easily through open pores in the plastic than through the plastic itself. Also exchange of oxygen and carbon dioxide will be altered by the pores. O 2 will enter the bags while CO 2 will leave them. All of these processes will extend shelf life and decrease the concentrati on of ethylene inside the package, no matter the sorption activity of the mineral dispersed within the plastic 12 bag. Even though many minerals have sorption capacity for ethylene, the biggest challenge is not to inhibit it when dispersing the minerals withi n the polymer matrix. Polymers with high barriers for ethylene will not allow any ethylene to get into such a mineral fast enough to extend the shelf life of fresh produce. This is why it is important to focus on methodologies of incorporating ethylene sca vengers as close to the surface of the plastic as possible. Also experiments which are supposed to support ethylene absorption of a given system should be run in closed systems where part of plastic bag is placed and there will be no doubt that such a prod uct removes ethylene from the headspace. Also conditions of such tests should mimic real conditions applied when packing perishables, i.e. low temperatures and high humidity, since it is known that temperature and humidity influences not only the productio n of ethylene by fruits but also influences sorption capacities of active compounds [1 - 4, 9, 13 - 14]. PeakFresh bags are marketed as ethylene absorbers. These polyethylene bags impregnated with humidity of at least 40%. During a 24h period they did not absorb any measurable amount of ethylene [17 - 18]. 2.3. Carbon dioxide (CO 2 ) Respiration is a metabolic process where organic substrates (carbohydrates, lipids and organic acids) are oxidized to c arbon dioxide and water. During respiration O 2 will be consumed and CO 2 will be produced [21]. Different perishables have different respiration rates, which are listed in the table 2.7. In general, after harvesting the respiration rates will determine how fast or slowly given fruits and vegetables will deteriorate. For commodities with high and very high respiration rates, concentrations of CO 2 inside the package can increase substantially after the packaging process is completed [3, 19 - 21]. 13 Table 2 . 7 . Fresh produce listed in groups according to their respiration rates, adapted from [13]. Class Fresh produce (mg CO 2 /kg h ) Very low Less than 5 Dates, dried fruits and vegetables, nuts Low 5 - 10 Apple, celery, cranberry, garlic, grape, onion, papaya, potato (mature), sweet potato, watermelon Banana, blueberry, cabbage, cherry, cucumber, fig, Moderate 10 - 20 lettuce (head), nectarine, olive, peach, pear, plum, potato (immature), tomato High 20 - 40 Blackberry, carrot (with tops), cauliflower, lettuce (leaf), raspberry, strawberry Very high 40 - 60 Broccoli, Brussels sprouts, green onions Extremely high More than 60 Asparagus, mushroom, parsley, peas, spinach, sweet corn High levels of CO 2 in the headspace are in general beneficial in many cases due to slowing down respiration and lipid oxidation, reducing color change, and inhibiting growth of molds, yeasts and bacteria. Keeping a high concentration of CO 2 in the package can also prevent it from collapsing. This is why there have been many carbon dioxide emitters used in active packaging systems [1,3]. However, excessive concentrations of CO 2 inside the package might reduce the pH of the product, which will result in developm ent of an acid taste or cause flavor tainting and drip loss. Also if the wrong packaging material is used, especially with high respiration classes of perishables, there is a danger of blowing up the package by excessive package expansion, which is very pr oblematic with packaging of freshly roasted or ground coffee. For rigid packaging, carbon dioxide scavengers will inhibit increasing gas pressure while for flexible packaging . T hey will reduce volume expansion [23 - 24]. All perishables have a safe range of oxygen and carbon dioxide, based on tolerances to each gas. Tolerances for CO 2 are listed in the table 2.8. If concentrations of carbon dioxide are too high around fresh produce then damage to the commodities may happen, like unfavorable physiological dis order, for 14 example breakdown of internal tissues. To avoid those changes, keeping CO 2 concentrations below the CO 2 tolerance limits is desired [3, 9, 21]. Table 2 . 8 . Commodities grouped according to their tolerance to CO 2 concentrations, adapted from [13]. Maximum CO 2 concentration Fresh produce tolerated (%) Apple (Golden Delicious), Asian pear, European 2 pear, grape, olive, tomato, pepper (sweet), lettuce, Chinese cabbage, celery, sweet potato 5 Apple (most cultivars), peach, nectarine, plum, orange, avocado, banana, mango, papaya, kiwifruit, cranberry, pea, pepper (chili), cauliflower, cabbage, Brussels sprouts, carrot Grapefruit, lemon, lime, pineapple, cucumber, 10 asparagus, broccoli, parsley, green onion, dry onion, garlic, potato 15 Strawberry, raspberry, blackberry, blueberry, cherry, fig, sweet corn, mushroom, spinach Carbon dioxide emitters or scavengers are provided mostly in the form of sachets or labels. CO 2 absorbers are not only important for coffee but also for battered goods, cheese, fresh and dehydrated meat and poultry products. Most carbon dioxide scavengers just scavengeCO 2 , but there are also many dual action scavengers that will at the same time sca venge CO 2 and O 2 .The most common carbon dioxide scavengers are composed of calcium hydroxide, sodium hydroxide, potassium hydroxide, calcium oxide or silica gel. When CO 2 reacts with hydroxides, it produces carbonates. Polyethylene - lined coffee pouches wit h mixtures of calcium oxide and activated charcoal have been used as CO 2 scavengers but the more common systems in Japan and the USA are the dual - action scavengers [19 - 25]. These sachets and labels are commercially available for canned and foil pouched coffees [22]. Such systems will contain iron powder to scavenge O 2 and calcium hydroxide to scavenge CO 2 [3]. 15 Active packaging systems involving carbon dioxide are a relatively small part of the AP market. There is a growing interest in CO 2 scavengers an d emitters, especially for dual action scavengers [5]. A list of commercially available single or dual action CO 2 s cavengers is given in table 2.9 [7]. Table 2 . 9 . Commercial CO 2 active packaging systems with possible O 2 scaven ging activity, adapted from [7]. Producer Market name Country Mechanism of action Mitsubishu Gas Chem. Freshlock/Ageless E Japan CO 2 scavenging (Ca(OH) 2 )/O 2 scavenging (iron powder) Mitsubishu Gas Chem. Ageless G Japan CO 2 generating (ascorbic acid)/O 2 scavenging Toppan Printing Co Fertilizer CV Japan CO 2 s and O 2 scavenging (non - ferrous metal) Toppan Printing Co Fertilizer C and CW Japan CO 2 generating/O 2 scavenging Multisorbtechn. Freshpax M USA CO 2 generating/O 2 scavenging S.A.R.L. Codimer Verifrais France CO 2 generating Toagosei Chem. Ind. Co. Vitalon G Japan CO 2 generating/O 2 scavenging 2.4. Zeolites Zeolites are microporous crystalline aluminosilicates of alkali and alkaline earth elements. We can differentiate naturally occurring and synthetic zeolites. They are characterized by unique three - dimensional framework structures composed of tetrahedral SiO 4 and AlO 4 . Within zeolites, we can differentiate types based on the framework structure. Many zeolites are also modified by exchangi ng cations, in order to increase their specific activity[27 - 28]. Zeolites are composed of metal extraframework cations, framework (SiO 4 and AlO 4 ) and sorbed phase (H 2 O molecules). The extraframework metal cations are ion exchangeable. The framework can va ry a lot in number of Al. The ratio between silicon and aluminum can be between 1 and infinity. Framework composition is controlled during synthesis for synthetic zeolites. With increasing Si/Al ratio, 16 hydrothermal stability and hydrophobicity increases. D uring synthesis water will fill the internal voids of a zeolite. To remove water, thermal treatment is used which results in making the intracrystalline space available. Loss of water does not change the structural integrity. Having crystalline frameworks will result in uniform pore openings within a crystal. Substitution of Si by Al will result in negative charge density in the lattice of the zeolite. Neutralization of that charge is done by introduction of exchanged monovalent, divalent or trivalent catio ns in the structural sites of the zeolite. Metal cations occupy cavities in the channel walls and are coordinated with H 2 O molecules within the channel. If small cations are replaced by high molecular weight cations (e.g. cationic surfactants), exchange will occur at the external surface since the surfactants are too large to enter the zeolite pores. The most common applicat ions of zeolites as molecular sieves and ion exchangers are due to different chemical, physical and structural properties within known zeolites. Using different concentrations of surfactants, such a modified zeolite can adsorb any of three major types of a dsorbates, i.e. cations, anions and non - polar organics [11 - 12, 27 - 29]. Most natural zeolites are formed from volcanic glass. When saline ground water attacks the surface of the glass, it will leach soluble oxides and salts, which will leave zeolite cryst als on the glass surface. Volcanic eruptions produce very reactive glasses, in the fly ash. To start nucleation of the crystals, relatively low heat is required so no excessive depth or volcanic activity is necessary for synthesis. Higher temperatures will result in production of quartz. Most natural zeolites will contain potassium since it is the most common cation in alkaline ground waters. About 40 natural zeolites are known. Most of them have lower Si/Al ratios than synthetic zeolites due to the absence of organic structure - directing agents. The two most commonly used natural zeolites are clinoptilolite and mordenite. They are extensively used for ion - exchange and sorption [27 - 28, 30]. 17 There are over 150 known synthetic zeolites. Most of them have no na tural analogues. When compared to natural zeolites, they are characterized by high purity, uniform pore size and better ion - exchange abilities. Manufacture of synthetic zeolites requires specifically controlled temperature, pressure and time. In general, s uch a synthesis will be as follows: reactants (i.e. silica, alumina) will be mixed with the cation source (often in a high pH water - based medium), then the aqueous reaction mixture will be heated, usually above 100 C, in a sealed autoclave. During that tim e reactants will remain amorphous and after a specific time, crystalline zeolites will be present. At the end of the synthesis process, all amorphous material will be replaced by product crystals which will be recovered by filtration, washing and drying. S ynthetic zeolites are also mostly applied in adsorption, ion exchange and catalysis [30 - 32]. Unique properties such as thermal stability, acidity, surface hydrophobicity or hydrophilicity, large ion - exchange capacity, low density, large void volume, unif orm molecular sized channels, sorption of many different gases and vapors and catalytic properties make zeolites available for many applications. Although they are mostly used in catalysis, ion exchange and adsorption, they have become materials of interes t also in other fields. For example, in environmental aspects they can be used for water purification, where they are capable of removing ammonia, heavy metals, radioactive species and organic substances. In industry, zeolites are applied in petroleum refi ning, petrochemical, coal and fine chemical industries. There is also a growing interest in using zeolites in more special application fields which can be as vast as process intensification, green chemistry, hybrid materials, medicine, animal food uses, op tical and electrical based applications, multifunctional fabrics and nanotechnology [27 - 33]. Separation and purification of gas mixtures by selective adsorption is one of the most important and popular application of zeolites. It is utilized in the chemic al, petrochemical, environmental, medical 18 and electronic gas industries. A multitude of both natural and synthetic zeolites characterized by sorption capacities versus different gases are of growing interest also in other fields, like packaging. A variety of synthetic zeolites with high purities and the abundance of natural zeolites in some volcanic areas, together with their high sorption capacities, make them new and competitive alternatives to commercial sorption systems used nowadays [27 - 33]. Although not specifically for packaging applications, many zeolites have been proven to adsorb gases that play crucial roles in perishables and other products packaging. These studies included ethylene, carbon dioxide, ethane, propane, etc. Most of them were perfor med on zeolites themselves, not incorporated in any kind of material. ZSM - 5 zeolite was proven to adsorb CO 2 and C 2 H 4 , with increasing preference for those polar molecules with a decrease of the Si/Al ratio [33]. Engelhard titanosilicate (ETS - 10) had isoth erms measured for ethylene and ethane adsorption. When ETS - 10 was exchanged with Na - , K - and Ag - cations, it was found that all of them had a strong absorption for both gases [34 - 35]. Large zeolite NaX crystals when dispersed with CuCl crystals demonstrate d effective separation of ethylene and ethane mixtures through adsorption [36].Adsorption kinetics and equilibria of carbon dioxide, ethylene and ethane were investigated for type 4A(CECA) commercial zeolite. There was decreasing adsorption affinity proven in the order CO 2 >C 2 H 4 >C 2 H 6 which makes 4A zeolite capable of separating binary mixtures of the three gases [29]. Also 13X zeolite could be a good candidate for separation of ethylene from CO 2 , as it was reported to have ethylene adsorption properties [37] . G5 zeolite was investigated as a possible ethylene adsorbent. An automated apparatus recorded adsorption isotherms for methane, ethane and ethylene. It was discovered that G5 increases adsorption with increase in carbon number and amount of unsaturation (methane90% then PLA wi ll be crystalline while a decrease in PLLA content will result in more amorphous polymers, but also lower melting and glass transition temperatures [59 - 61 , 9 1 ]. PLAs high cost of production used to limit its application as a packaging material in general. But as the cost has continued to decrease, PLA is more and more used. As it can be used in different manufacturing processes (extrusion molding, injection molding, blow molding, extrusion foaming, etc) its potential applications in the packaging industry are vast. Nowadays it is commercially used as a retail package for fresh food in the form of clamshell containers, thermoformed foam trays or pouches made of film, but also as beverage bottles or blister packages. With growing public concern about eliminat ing petrochemical based polymers from the food industry, PLA has become a material of interest [56 - 60]. Barrier properties of packaging materials are crucial when decisions are made about products. In the fresh produce industry concentrations of headspace gases (carbon dioxide, oxygen, nitrogen, ethylene) and moisture content inside the package will determine how fresh and safe, and for how long, perishables will be. Barrier properties of commercially available polymers used in the packaging industry have been measured at many different conditions. Permeabilities of several common gases in polymers are presented in the tables 2.1 3 - 2.1 7 . PLA has lower CO 2 permeability coefficients than many petroleum - based polymers, which makes it a better car bon dioxide barrier (table 2.12 ) [ 9 2 ]. 30 Table 2 . 12 . CO 2 92 ]. CO 2 Permeability (10 - 17 kg m/m 2 s Pa) Polymer Poly(lactic acid) - 1.52 High - density polyethylene 4.44 - 6.31 5.25 Low - density polyethylene 6.31 - 13.5 52.82 Poly(ethylene terephthalate) 0.18 - 0.44 0.02 Polypropylene 9.0 - 18.0 13.8 Polystyrene - 13.2 Oxygen permeability values show that barrier properties of PLA and many petroleum - based polymers are similar (table 2.13). PLA, polyolefins and polystyrene are poor oxygen barriers [ 92 ]. Table 2 . 13 . O 2 92 ]. O 2 Permeability (10 - 17 kg m/m 2 s Pa) Polymer Cellophane 0.0013 - Poly(vinyl alcohol) 0.0001 - Poly(ethylene terephthalate) 0.0540 0.0333 Poly(lactic acid) - 0.4948 High - density polyethylene - 1.5924 Low - density polyethylene 4.3183 8.2498 Polypropylene 1.3490 3.4540 Polystyrene 3.7780 1.6464 PLA value is much larger than for PET , but very similar to N 2 permeability coefficients of PS and LDPE [63]. Table 2 . 14 . N 2 N 2 Permeability (10 - 14 kg m/m 2 s Pa) Polymer Poly(lactic acid) 1.93 Poly(ethylene terephthalate) 0.0119 Polystyrene 3.27 Low - density polyethylene 2.82 31 Table 2.15 lists water vapor permeabilities. High values for PLA show that it is a poor barrier to H 2 O [ 9 2 ]. Table 2 . 15 . H 2 92 ]. H 2 O vapor Permeability (10 - 13 kg m/m 2 s Pa) Polymer Poly(lactic acid) 80 - 360 Cellulose nitrate 472 Poly(ethylene terephthalate) 110 Polystyrene 670 High - density polyethylene 225 Polypropylene 225 Low - density polyethylene 670 Ethylene permeability of amorphous PLA and couple of conventional polymers are listed in table 2.16. A decrease in ethylene permeability was associated with increasing crystallinity of PLA. All three materials are good barriers for ethylene, which makes it undesired for fresh produce packaging since accumula tion of C 2 H 4 inside the package will occur resulting in senescence, ripening and decrease of shelf life [61]. Table 2 . 16 . C 2 H 4 permeability coefficients [61]. Polymer C 2 H 4 Permeability (10 - 18 m 3 m/m 2 s Pa) Poly(lactic acid) 6.8 Poly(ethylene terephthalate) 0.03 Low - density polyethylene 22 Based on the barrier properties discussed above, but also its low thermal stability and impact resistance, PLA in order to be used as a competitive material against conventional polymers in thermoplastic applications has to be modified. Obtaining desired p roperties of poly(lactic acid) packaging materials can be achieved by producing copolymers, PLA blends, composites and 32 nanocomposites or by laminating or coating the PLA surface. Blending PLA with other polymers is the easiest method of improving desired p roperties. PLA has been successfully blended with polymers from renewable resources like chitosan or starch, but also with petrochemical - based ones (PVA, PCL or PEG) [75 - 76]. Also blending with cyclodextrins (CDs) resulted in changes in polymer barrier and mechanical properties. Permeability was increased while tensile strength and elongation at break were decreased [77 - 78]. Degradation of PLA may occur through hydrolytic degradation, enzymatic degradation, thermal degradation, photodegradation and radiat ive degradation or biodegradation. Hydrolytic degradation is a primary degradation process for poly(lactic acid) which happens in two steps. The first step involves random non - enzymatic chain scission of the ester groups, which as a result reduces molecula r weight. In the second step, low molecular weight PLA will diffuse from the bulk and microorganisms can metabolize it and produce CO 2 , H 2 O and humus [59]. 2. 8 . Measurements of ethylene The importance of achieving a proper concentration of ethylene inside the package has been explained already. For optimal freshness, safety and shelf life, the amounts of ethylene need to be controlled at levels of ppm and ppb, so a properly sensitive and reliable analytical method of monitoring and quantification is requir ed. Attempts at measuring ethylene go back to 1934 and include techniques like bioassays, gravimetric analyses, manometric techniques after mercury complexation/decomposition and physico - chemical colorimetric assays. Although detection limits were down to 10ppb, none of these methods were easily automated [64 - 65]. 33 Currently, many methods are more or less successfully utilized. The variety of methods may be due to the vastness of ethylene sources (i.e. plants, fruits or cylinders), sampling systems (i.e. s eparate systems for keeping samples vs. those incorporated into analytical instruments) and what is exactly to be determined (i.e. adsorption, permeability, etc . ). Each of these methods will have its advantages and limitations which makes it very difficult but also important to match exactly to a specific research project. Nowadays, the most commonly used method for separation and analysis of volatile compounds is gas chromatography. This detection technique can separate, analyze and quantify individual co mponents from complex mixtures by using appropriate columns and detectors. Thermal conductivity detectors (TCD) were first used in GC systems for ethylene detection, but due to poor detection limits (10 - 100 µL/L) it was not a very effective method. Develop ment of flame ionization detection (FID) and later photoionization detection (PID) significantly improved detection limits for ethylene to tens of nL/L for FID and sub - nL/L for PID. Besides good detection limits, GCs offer more advantages over other techni ques, like small sample requirements, high selectivity, fast analysis with minute time scales and relatively easy operation. The main disadvantages are high costs and limited sensitivity [10,18, 64 - 71]. Recent advances in electrochemical sensor technolog y have allowed these techniques to be applied to an even wider range of compounds, including ethylene. In general, such a sensor will transform a gas concentration into a detectable physical signal. Classification of electrochemical sensors is based on the physical change measured. Amperometric sensors will measure current (A), of these sensors are as follows: ethylene detection limits between µL/L and te ns of nL/L, good repeatability and accuracy, response time below 1 min, low power consumption, and low cost. Disadvantages include: sensitivity to interfering gases and to temperature and humidity changes, limited 34 temperature range and lifetime dramaticall y reduced when exposed to higher ethylene concentrations [65]. Interaction between ethylene molecules and light can result in its absorption, emission or scattering. This interaction allows for optical sensors to be used for ethylene measurements. The str ongest absorption characteristics of C 2 H 4 are in the mid - infrared (IR) region (2 - 12 µm). Quantification of ethylene concentration can be achieved by knowing the absorption strength of ethylene at a specific IR light frequency. In non - dispersive infrared (N DIR) instruments all wavelengths from a broadband source will not be separated but considered at the same time and the resulting spectrum will not be resolved. This is why band - pass filters are very important in NDIR sensors. Using filters will increase se nsitivity for ethylene which is relatively little without filters and attenuate undesired absorbents. Being simple and robust instruments does not overcome their limited sensitivity and lack of selectivity [65, 67]. A novel approach in ethylene detection is the use of laser - based detectors. They utilize laser photothermal deflection or laser - driven intracavityphotoacoustic spectroscopy. Laser - based sensors have the highest sensitivities (below nL/L) and selectivities for ethylene with detection limits of 0 .5ppb for laser photothermal deflection and 10ppt for laser - driven intracavityphotoacoustic spectroscopy. Laser response time is within seconds, which makes them applicable in real - time monitoring, and measurements can be made directly and almost continuou sly. In spite of all the advantages, the disadvantages are difficult to overcome: lasers are very expensive and provide only single gas detection [64 - 65]. For the purpose of surface area and pore size characterization, volumetric sorption analyzers have b een developed. They are called quantasorb sorption analyzers, or in short quantachromes. Their principle of operation is based on a volumetric method. 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Too high levels of C 2 H 4 during storage can shorten shelf life and also produce physiological defects of the harvest ( textural and color changes or even tissue degradation, for example russet spotting on lettuce and scald on apples). C 2 H 4 ,by increasing the respiration rate, causes early maturity and softening of climacteric fruits and vegetables. It can also induce yellowing of green vegetables. Even very low concentrations of C 2 H 4 , at the level of parts per billion (ppb) and parts per million (ppm), can be critical. Commodities can be grouped based on their C 2 H 4 production rates, which usually range between 0.1 - 100 µ C 2 H 4 /kg h C 2 H 4 sensitivity of these groups might or might not be proportional to their production rates, and has been determined to be significant at levels as small as 0.01 and as large as 0.4 ppm [ 1 - 13 , 17 ]. During respiration, a metabolic process, organic substrates (carbohydrates, lipids and organic acids) are oxidized and carbon dioxide ( CO 2 ) and water are produced. Although high levels of CO 2 in the fresh produce package headspace might be beneficial in many cases (slow down respiration and lipid oxidation, reduce color change, inhibit growth of molds, yeasts and bacteria), excessive concentrations of CO 2 inside the package might reduce the pH of the product, which will result in development of an acid taste or cause flavor tainting and drip loss. Also if the wrong packaging material is used, especially with high respiration classes of perishables, there is a danger of blowing up the package by excessive 45 package expansion. Depending on the fresh produce group, respiration rates between 5 - 60 mg CO 2 /kg h e observed, while the maximum CO 2 tolerance can vary between 5 - 15 %. This means many commodities produce more carbon dioxide than they can tolerate [14 - 17 ]. Zeolites are crystalline aluminosilicates of alkali and alkaline earth elements that are charact erized by unique three - dimensional framework structures composed of SiO 4 and AlO 4 . Zeolites can be grouped into different types based on their framework structure. Since zeolites can be applied in many disciplines, for example gas adsorption and separation, and removal of odors, they are often modified by exchanging cations so that their activity toward specific molecules increases [3 - 4]. There are few reported cases when zeolites have been used as C 2 H 4 and CO 2 scavengers [2,19 - 20]. The purpose o f this study wa s to investigate C 2 H 4 and CO 2 sorption characteristics (capacities, time) of two types of zeolites - natural clinoptilolite and synthetic - type 4A at conditions relevant to fresh produce . These include two different conditions of temperature, relative humidity and a few combinations of headspace gases in the sampling systems. Similar studies of sorption capacities for zeolites have been done but not in a closed system and with so many variations of conditions inside the system. Results obtaine d in this study were treated as preliminary data for further studies that involve d production of polymer/zeolite composite films that could be new alternatives to current active packaging systems available in the market. 46 3.2. Experimental section 3 .2.1. Materials 3.2.1.1. Zeolites Zeolites in form of fine powders have been purchased from following companies, clinoptilolite ( the Liquid Zeolite Company Inc. , Cedar Grove, NJ, US) and type 4A zeolite (UOP LLC, A Honeywell Company (Des Plaines, IL, US) . Prior to using, both zeolites were activated by drying in vacuum oven (4h Figure 3.1 shows the physical appearance of both zeolites. CL is beige and 4A is white. Figure 3 . 1 . Images of natural clinoptilolite (on left) and synthetic type 4A (on right) zeolites. 3.2.1.2. Gases Adsorbent gases were provided by Airgas (Radnor, PA, US) as size 200 certified cylinders. Three cylinders used were as follows: 500ppm of C 2 H 4 balanced in N 2 , 100% CO 2 and a mixture of headspace gases (5% O 2 , 15% CO 2 and 80% N 2 ). 47 3.2.2. Methods All gases were detected by gas chromatography. 3.2.2.1. Gas Chromat ography with Flame Ionization Detector (GC FID) For C 2 H 4 Flame Ionization Detector (FID) was chosen (Hewlett Packard GC 6890, Agilent Technologies, Santa Clara, CA, US) and oven temperature was kept constant through the 13 min Ethylene peaks were detected at 11 min. 3.2.2.2. Gas Chromatography with Thermal Conductivity Detector (GC TCD) While for CO 2 , O 2 and N 2 Thermal Conductivity Detector (TCD) was utilized (ThermoScient ific Trace GC Ultra GC with FID/TCD, Waltham, MA, US) . The init i a l temperature of was he ld for 4 min and was used to reach where it was he ld for 1.3 min . A s econd ramp of continued to and was he ld for 1 min to clean the column. The i and the During the total run time of 9 min the following retention times were recorded: 3.4 min for O 2 , 3.6 min for N 2 and 7.2 min for CO 2 . For all gases the same columns were appropriate, SupelcoCarboxen 1010 PLOT, L x I.D. 30m x 0.53 mm , packed with fused silica. Calibration curves for all gases can be found in appendix below . 3.2.3. Sampling system and measuring conditions One g of each zeolite was placed into 250 m L glass jars with aluminum closures. Each jar had a small hole drilled in the closure to allow flushing with the chosen gases directly from the cylinder and 48 also for further withdrawal of sample gas. The hole was closed with a gray butyl rubber septum. A 10 0µ L gas tight syringe with needle valve (Supelco SGE , Australia ) was used to withdraw 50 µ L gas from jars. Depending on what gases were present in the system, samples were injected into the GC TCD or the GC FID for single gas detection or simultaneously in to both instruments if both gases of interest were present. To provide the different temperatures the jars were kept in a controlled condition room or in an environmental chamber. Two temperatures were chosen - room temperature (23 ) and low temperature (7 ± 1 C in a cha mber ) to mimic the two temperatures at which produce would likely be kept. To reach 100% relative humidity in the jar, a small vial with deionized water was placed inside. When the jars were closed without water, it was assume d to be 0% RH. Since dry gases were used to fill the jars and experiments with desiccant placed inside the jars gave similar results to those without desiccant , the assum ption of 0% RH was reasonable . Variations of headspace gases included: 500 ppm C 2 H 4 , 1 00% CO 2 , 250 ppm ethylene and 50% CO 2 together, and 15% CO 2 with 5% O 2 . In all cases, when the investigated gases were not pure, they were balanced with N 2 . 3.2.4. Adsorption measurements Depending on the rate of ad sorption, samples were tested every 2.5 hours in the beginning of the experiments for CO 2 and C 2 H 4 , for up to 18 hours ; every 24 hours after initial measurements were done for CO 2 and C 2 H 4 , or weekly for C 2 H 4 after sorption of CO 2 was complete . Sampling was stopped when the maximum sorption was reached or there was a suspicion of leakage based on results from control jars with no zeolite but all the gases inside. Each sample type had three replicates. Ethylene adsorption is pres ented in three w ays, in concent r a tion units of ppm and % and volume units of µL and nL . Concent ration in ppm and volume in nL for C 2 H 4 and volume in mL for CO 2 is intended to show the exact amount of adsorbed gas , while concentration in % for CO 2 and C 2 H 4 is provided to sho w the change in total concentration due to gas adsorption . 49 All % results were normalized to mass as in equation 3. 1. ( 3. 1) For ppm results, they were normalized as in equation 3.2. (3.2) V olume results (n L , mL ) were normalized according to equation 3.3. (3.3) To compare all data sets measured at different conditions of temperature, relative humidity and composition of headspace gases, specific t imes were chosen. For C 2 H 4 there were three times of comparison: 2 days when the largest and fastest sorption occurred, 5 days when some of the sets had reached equilibrium, and total time which was treated as the highest measured sorption (based on the c ontrol samples). When the control samples were suspected of leakage, measurements ended. For CO 2 two times were chosen: 5 hours when rapid sorption happened, and total time when all sets reached maximum sorption. 3.2. 5 . Characterization of zeolites 3.2.5.1. Automated Gas Sorption Analyzer (Quantachrome) A Quantachrome Autosorb iQ2 (Quantachrome Instruments , Boynton Beach, FL , USA ) was used to determine zeolite surface areas and pore characteristics. Forty mg of each sample was degassed to 1 torr pri or to measurements to remove H 2 O ; zeolites were kept Surface areas were obtained by applying Brunauer - 50 Emmet - Teller and Langmuir sorption isotherm equations to measure ad sorption of N 2 at standard temperature and pressure. 3.2.5.2. Scanning Electron Microscopy (SEM) Scanning Electron Microscopy (SEM) (Carl Zeiss Variable Pressure SEM EVO LS25, Germany) was used to determine the particle size and shape of the zeolites. Samples were coated with tungsten. Images were acquired with an accelerating voltage of 20 kV and a working distance of 10mm at 6k and 11k x magnification. 3.2. 6 . Statistical methods Analysis of variance (ANOVA) was performed in the analytical software SP SS version 22 (SPSS Inc., Chicago, IL, US). Means were separated using the Tukey honestly significant difference (HSD) test (p < 0.05). 3.3. Results and discussion 3.3.1. Surface characteristics Both zeolites were characterized by Quantachrome to determin e their external and internal surface characteristics. Results are listed in table 3.1. Table 3 . 1 . Surface characteristics of investigated zeolites. sample BET surface area [m 2 /g] Langmuir surface area [m 2 /g] average pore radius [Å] total pore volume [cm 3 /g] CL 31. 4 ± 5. 4 a* 169.8 ± 17.8 a 5.5 ± 0.8 a 0.85 ± 0.08 a 4A 4 8.0 ± 26.0 a 171. 3 ± 79.4 a 2. 3 ± 0. 7 b 0.41 ± 0.28 b * means followed by the same lower case letter in column are not statistically different from each 51 Recorder results have larger standard deviations for 4A than for CL due to the framework structure of the zeolites. The c ubic LTA in 4A can result in more possible combinations than those of HEU in natural zeolite (CL). Average pore radius and total pore volumes are larger for CL than 4A which might suggest that physisorption on the external surface will be more probable for 4A and inside cages and cavities for CL. Compar ing recorde d result s to values in the literature, it can be seen that CL had a pore radius larger than reported (5.5 ± 0.8 Å vs. 3.5 Å), while 4A had a smaller one (2.3 ± 0.7 Å vs. 4 Å) [24, 26]. A s imilar situation can be observed for pore volumes. The measured volume of CL, 0.85 ± 0.01 cm 3 /g is larger than in th e liter ature , 0.279 cm 3 /g, while for 4A the measured value of 0.41 ± 0.28 cm 3 /g is smaller than the literature value of 0.508 cm 3 /g [24. 26]. BET surface areas for both investigated zeolites ( 31.4 ± 5.4 m 2 /g for CL and 48.0 ± 26.0 m 2 /g for 4A) are within the range found in literature, 28 - 60 m 2 /g [4]. Differences between zeolites are due to frameworks, cavities and cages. C L is composed of a single building block and has both 10 - and 8 - ring channels, while type 4A zeolite is composed o f three different building blocks of varying sizes and dimen sions. A lso both the 4 - and 8 - ring c hannels are smaller . BET and Langmuir surface areas are comparable for both zeolites (p > 0.05), while there are significant differences for pore radius and pore volume (p < 0.05). Data listed in table 3.1 are based on sorption isotherms determined by Quantachrome. Figures 3.2 and 3.3 present N 2 sorption iso therms for CL and 4A zeolites. Both sorption isotherms resemble type I V isotherm s with visible presence o f two separate surface layers on a surface or in the pores. . A T ype IV isotherm is displayed when intermolecular attractions are large. N 2 has a kinetic diameter of 3.64 Å [24 ], which is larger than the pore openings in 4A (2.3± 0.7 Å) but smaller than in CL (5.5 ± 0.8 Å) , so there is a possibility for adsorbent molecule s to enter pores in CL, but not in 4A. 52 Figure 3.2. Nitrogen sorption isotherm for clinoptilolite. Figure 3.3 . Nitrogen sorption isotherm for type 4A zeolite. To understand more if there is any effect of surface characteristics on adsorption taking place in both zeolites of interest, SEM images of C L and 4A were taken (figure 3.4 ). It can be seen that the synthetic particles are very symmetrical in their shape , and the size distribut ion is much smaller when compared to the natural zeolite. In clinoptilolite , we can see non - regular molecules with relatively broad 0 5 10 15 20 25 30 35 40 45 50 0 0.2 0.4 0.6 0.8 1 volume [cm 3 /g] relative pressure [p/p 0 ] 0 2 4 6 8 10 12 14 0 0.2 0.4 0.6 0.8 1 volume [cm 3 /g] relative pressure [p/p 0 ] 53 size distribution. For 4A the particle size range was between 0.971 µm and 3.5 µm, while for clinoptilolite it was between 0 .219 µm and 4.8 µm. Figure 3. 4 . SEM images of clinoptilolite (on left) and type 4A zeolite (on right). Supporting data for this chapter can be found in appendi x below . 3.3.2. Adsorption measurements Tables 3.2 and 3.3 list total times for all measurements carried out . It can be seen that depending on conditions (temperature, relative humidity and headspace ga s es) inside the jars, the end times for measurements could change from 5 to 18 days for C 2 H 4 and from 7.5 to 48 hours for CO 2 . Longer time s for C 2 H 4 and CO 2 were observed in the presence of both gases in the systems. Reasons for increase s in adsorption times might be due to competition between C 2 H 4 and CO 2 for adsorption sites and inhibiting sites for the other gas in the process. 54 Table 3. 2. Total times for ethylene adsorption measurements. system total time [h/d] C 2 H 4 96/5 C 2 H 4 + CO 2 288/13 C 2 H 4 2 O) 96/5 C 2 H 4 + CO 2 432/18 C 2 H 4 2 O) 96/5 Table 3.3. Total times for carbon dioxide adsorption measurements. system total time [h] CO 2 10 CO 2 + C 2 H 4 48 CO 2 + O 2 15 CO 2 2 O) 7.5 CO 2 + C 2 H 4 48 CO 2 2 O) 12.5 Data shown in figures 3. 5 - 3.1 9 indicates superior performance of the synthetic zeolite - type 4A when compared to the natural one - clinoptilolite (CL), in all studied cases. Differences in amount of C 2 H 4 adsorbed were as low as 20% for C 2 H 4 and up to 100% for C 2 H 4 100% RH). For CO 2 adsorption the differences we re smaller, but still relatively important, 20% for CO 2 + O 2 a maximum of 50% for CO 2 + O 2 Focusing first on C 2 H 4 adsorption, figures 3. 5 - 3.1 3 are relevant. No matter which units of adsorbed C 2 H 4 are presented (ppm, % or n L ), all show the same trends. The presence of CO 2 in the headspace had an inhibiting effect on C 2 H 4 sorption for CL (p <0.05) , while it did not influence 4A performance. Selectivities towards gases, CO 2 or C 2 H 4 in our case, are due to predominant interaction energies, which are dependent on physical properties of the gases (i.e. q uadrupole moment, polarizabilit ies, etc.). In 4A zeolite, CO 2 and C 2 H 4 have to compete for adsorption sites . Molecules with 55 bigger qu a drupole moment ( CO 2 - 0.64 Å, C 2 H 4 - 0.48 Å) will have stronger interaction [24]. Also a decrease in temperature and increase of relative humidity significantly decreased the adsorption capacity of CL (p < 0.05) . In sets where high humidity was applied, the initial high sorption data for 4A decreased over time (p < 0.05). It is suspected that water was replacing C 2 H 4 in the zeolite matrix and C 2 H 4 was released back to the headspace after 5 days. Low temperature tended to have a smaller effect on C 2 H 4 sorp tion of 4A than CL . Looking at total measurement times (figures 3. 5 - 3.1 3 ), showed that the presence of CO 2 in the headspace increased sorption time about 3 fold when compared to sets with just C 2 H 4 in the jar for 4A . High humidity had the opposite effec t; it decreased the total time over which zeolites adsorbed. Lowering the temperature did not seem to have any critical effect on time in both zeolites . Figure 3 . 5 . Amount of ethylene (ppm) adsorbed by zeolites after 2 days. C 2 H 4 C 2 H 4 + CO 2 C 2 H 4 2 O) C 2 H 4 + CO 2 C 2 H 4 2 O) 0 50 100 150 200 250 300 350 400 450 adsorbed ethylene [ppm]/g zeolite controls clinoptilolite 4A 56 Figure 3 . 6 . Amount of ethylene (%) adsorbed by zeolites after 2 days. Figure 3. 7 . Amount of ethylene (nL) adsorbed by zeolites after 2 days. C 2 H 4 C 2 H 4 + CO 2 C 2 H 4 2 O) C 2 H 4 + CO 2 C 2 H 4 2 O) 0 10 20 30 40 50 60 70 80 90 100 adsorbed ethylene [%]/g zeolite controls clinoptilolite 4A C 2 H 4 C 2 H 4 + CO 2 C 2 H 4 2 O) C 2 H 4 + CO 2 C 2 H 4 2 O) 0 2 4 6 8 10 12 14 16 18 20 adsorbed ethylene [nL]/g zeolite controls clinoptilolite 4A 57 Figure 3 . 8 . Amount of ethylene (ppm) adsorbed by zeolites after 5 days. Figure 3 . 9 . Amount of ethylene (%) adsorbed by zeolites after 5 days. C 2 H 4 C 2 H 4 + CO 2 C 2 H 4 2 O) C 2 H 4 + CO 2 C 2 H 4 2 O) 0 50 100 150 200 250 300 350 400 adsorbed ethylene [ppm]/g zeolite controls clinoptilolite 4A C 2 H 4 C 2 H 4 + CO 2 C 2 H 4 2 O) C 2 H 4 + CO 2 C 2 H 4 2 O) 0 10 20 30 40 50 60 70 80 90 adsorbed ethylene [%]/g zeolite controls clinoptilolite 4A 58 Figure 3. 10 . Amount of ethylene (nL) adsorbed by zeolites after 5 days. Figure 3 . 11 . Amount of ethylene (ppm) adsorbed by zeolites after total measurement time. C 2 H 4 C 2 H 4 + CO 2 C 2 H 4 2 O) C 2 H 4 + CO 2 C 2 H 4 2 O) 0 2 4 6 8 10 12 14 16 18 20 adsorbed ethylene [nL]/g zeolite controls clinoptilolite 4A C 2 H 4 C 2 H 4 + CO 2 C 2 H 4 2 O) C 2 H 4 + CO 2 C 2 H 4 2 O) 0 50 100 150 200 250 300 350 400 adsorbed ethylene [ppm]/g zeolite controls clinoptilolite 4A 59 Figure 3 . 12 . Amount of ethylene (%) adsorbed by zeolites after total measurement time. Figure 3. 1 3 . Amount of ethylene (nL) adsorbed by zeolites after total time. Figures 3.14 - 3.17 present CO 2 adsorption results for bot h %RH, gases in jars) and two times (5h and total). Adsorption of CO 2 was much faster than sorption of C 2 H 4 in all cases. Based on the Quantachrome results, it is more probable for CO 2 to adsorb on the external surfaces, especially for 4A , than for C 2 H 4 to get into the cavities and cages, especially in CL. Equilibrium for all CO 2 adsorption studies C 2 H 4 C 2 H 4 + CO 2 C 2 H 4 2 O) C 2 H 4 + CO 2 C 2 H 4 2 O) 0 10 20 30 40 50 60 70 80 90 adsorbed ethylene [%]/g zeolite controls clinoptilolite 4A C 2 H 4 C 2 H 4 + CO 2 C 2 H 4 2 O) C 2 H 4 + CO 2 C 2 H 4 2 O) 0 2 4 6 8 10 12 14 16 18 20 adsorbed ethylene [nL]/g zeolite controls clinoptilolite 4A 60 was reached after a maximum of 2 days while adsorption of C 2 H 4 continued sometimes until 18 days. This suggests that there are different parts of the zeolites within their st ructure/framework that are responsible for sorption of these two gases , CO 2 and C 2 H 4 . This difference might be due to an increase in ionic radius, which is associated with higher polarizability of the larger ionic radius. Also, type 4A zeolites for both CO 2 and C 2 H 4 , showed superior performance when compared to CL , although CL showed much more ad sorption capacity for CO 2 than for C 2 H 4 .The presence of additional gases in the headspace increased sorption potential of both zeolites (p < 0.05) . More CO 2 was adsorbed when C 2 H 4 was present, but also when O 2 was present in the absence of C 2 H 4 . High humidity had an effect on both gases. As shown above in figures 3. 5 - 3.17 for C 2 H 4 and also for CO 2 it decreased the sorption (p < 0.05) . After initial C 2 H 4 so rption, water replaced C 2 H 4 in both zeolites and sorption was reversed in 4A. For CL (figures 3. 5 - 3.13 ) , at both temperatures in the presence of water, there was no sorption of C 2 H 4 (p < 0.05) . A decrease in temperature did not affect the sorption as much as high humidity, although it decreased ad sorption of C 2 H 4 in both zeolites and increased CO 2 ad sorption in CL, but decreased it in 4A. This might be explained by the endothermic character of C 2 H 4 adsorption in both zeolites an d CO 2 adsorption in 4A, and the exothermic character of CO 2 adsorption in CL. 61 Figure 3. 14 . Amount of carbon dioxide (%) adsorbed by zeolites after 5 hours. Figure 3. 15 . Amount of carbon dioxide (mL) adsorbed by zeolites after 5 hours. CO 2 CO 2 + C 2 H 4 CO 2 + O 2 CO 2 2 O) CO 2 + C 2 H 4 CO 2 2 O) 0 10 20 30 40 50 60 70 adsorbed carbon dioxide [%]/g zeolite controls clinoptilolite 4A CO 2 CO 2 + C 2 H 4 CO 2 + O 2 CO 2 2 O) CO 2 + C 2 H 4 CO 2 2 O) 0 20 40 60 80 100 120 140 160 180 adsorbed carbon dioxide [mL]/g zeolite controls clinoptilolite 4A 62 Figure 3 . 16 . Amount of carbon dioxide (%) adsorbed by zeolites after total measurement time. Figure 3. 17 . Amount of carbon dioxide (mL ) adsorbed by zeolites after total measurement time. Although not determined in this research but based on literature, it is known that adsorption isotherms for C 2 H 4 and CO 2 in clinoptilolite have a classic isotherm form ( Langmuir ). These isotherms are CO 2 CO 2 + C 2 H 4 CO 2 + O 2 CO 2 2 O) CO 2 + C 2 H 4 CO 2 2 O) 0 10 20 30 40 50 60 70 80 adsorbed carbon dioxide [%]/g zeolite controls clinoptilolite 4A CO 2 CO 2 + C 2 H 4 CO 2 + O 2 CO 2 2 O) CO 2 + C 2 H 4 CO 2 2 O) 0 20 40 60 80 100 120 140 160 180 200 adsorbed carbon dioxide [mL]/g zeolite controls clinoptilolite 4A 63 often observed in the case of adsorbents with a wide ran ge of pore sizes, like natural zeolites. Type II isotherms are observed when adsorbate molecules are small enough to enter zeolite micropore systems. The kinetic diameters of CO 2 (3.3 Å) and C 2 H 4 (3.9 Å) are both smaller than the measured average pore radi us in clinoptilolite (5.5 ± 0.8 Å), which was actually larger than the literature value (3.5 Å) [24 - 25 ]. This suggests that both gases could get inside the cages and cavities in the zeolite framework. Since physisorption was happening not only on external but also on internal surface s , it was characterized by a higher adsorption energy but a l low adsorption rate [3 - 4, 20 ]. For type 4A zeolite it was found that the adsorption isotherm for CO 2 also ha d a characteristic type II shape while the one f or C 2 H 4 ha d a type I shape and follow ed Henry's law [21 - 22] . Type I isotherm s are normal for microporous adsorbents that have pore size s similar to the diameter of the molecules t hat will be sorbed. Adsorbents with a wide range of pore sizes, like in this case the 4A zeolite, will display type I isotherm s , which are often associated with continuous progression from monolayer to multilayer adsorption [21 - 22] . Again comparing pore openings in 4A measured by Q uantachrome (2. 3 ± 0. 7 Å) to those found in the literature (4 Å) shows that the actual pore radius is much smaller , probably due to different cations occupying the corner sites in cavities and cages and therefore reducing the channel. This might suggest that all physisorption took place on the external surface of the zeolite (mesopores or larger) and was characterized by low adsorption energy and high adsorption rate [21 - 22 ]. Ads orption of both gases in all cases in the type 4A zeolite was much faster and adsorption capacities were higher than in clinop tilolite. As for water (2.65 Å) when compared to the pores in both zeolites, again it is possible for H 2 O to enter the pores in clinoptilolite and block adsorption sites for C 2 H 4 and CO 2 , while it is often too large for 4A zeolite pores and this is why the effect of water was not as critical to sorption as in the case of the natural zeolite. Increased sorption of CO 2 when compared to C 2 H 4 could be due to higher polarizability associa ted with the larger ionic radius [23, 25 ]. All of the above shows a potential for all three molecules to pass through natur al zeolite pore openings and all except H 2 O to not be able to go inside the cages 64 and cavities inside the synthetic zeolite. For all three molecules, CO 2 , C 2 H 4 , H 2 O, physisorption in both zeolites can occur on the surface (adsorption) while for CL having larger pore sizes there is also a possibility for all molecules to have absorption occur inside the zeolite framework. Figures 3.1 8 - 3. 33 show the sorption for both gases as they were measured during the experiments. For C 2 H 4 all data are shown in ppm , % and nL , while for CO 2 only % and mL are presented. In all cases the greatest increase in sorption occurred in the beginning and the rate of increase slowed as the experiment continued. Figure 3 . 1 8 . Amount of ethylene sorption (ppm) at room temperature and 0% RH. 0 50 100 150 200 250 300 350 400 450 0 20 40 60 80 100 conc in zeolite [ppm]/g zeolite time [h] 4A CL control 65 Figure 3 . 1 9 . Amount of ethylene sorption (%) at room temperature and 0% RH. Comparing figures 3.1 8 - 3. 21 we can observe the effect of the second gas present in the headspace. In the first case, with just C 2 H 4 present , the whole process reached equilibrium within 100 hours, while in the presence of CO 2 , the time for equilibrium wa s extended to roughly 300 hours, while the percent of total sorption increase d by 15% in presence of CO 2 . But a fter 20h, more C 2 H 4 wa s adsorbed in the presence of CO 2 . 0 10 20 30 40 50 60 70 80 90 0 20 40 60 80 100 conc in zeolite [%]/g zeolite time [h] 4A CL control 66 Figure 3 . 20 . Amount of ethylene sorption (ppm) at room temperature and 0% RH with carbon dioxide present. Figure 3 . 2 1 . Amount of ethylene sorption (%) at room temperature and 0% RH with carbon dioxide present. Decreasing the temperature (figures 3. 20 - 3. 23 ) extended the ad sorption from about 100 h to over 400 h and significantly affected the total percent of ad sorption in CL . Lower temperature increased it significantly by more than 50% (p < 0.05). 0 20 40 60 80 100 120 140 160 0 50 100 150 200 250 300 conc in zeolite [ppm]/g zeolite time [h] 4A CL control 0 10 20 30 40 50 60 70 0 50 100 150 200 250 300 conc in zeolite [%]/g zeolite time [h] 4A CL control 67 Figure 3 . 22 . Amount Figure 3 . 23 . Amount of carbon dioxide present. 0 20 40 60 80 100 120 140 160 0 100 200 300 400 500 conc in zeolite [ppm]/g zeolite time [h] 4A CL control 0 10 20 30 40 50 60 70 0 100 200 300 400 500 conc in zeolite [%]/g zeolite time [h] 4A CL control 68 The presence of water in the system ( 100% RH) significantly decreased the total time of ad sorption (p < 0.05) (figures 3. 24 and 3. 2 5 ). For CL there wa s no significant ad sorption of C 2 H 4 during the whole experimental time (p < 0.05) , while for 4A type zeolite the initial high ad sorption decrease d over time. All of this suggests that H 2 O act ed as a competitive molecule to C 2 H 4 and block ed the sorption sites in both zeolites. In clinoptilolite , it wa s more prone to do so from the very beginning while in 4A, it appear ed to reverse the initial sorption of C 2 H 4 after about 48 hours. Figure 3 . 24 . Amount of ethylene sorption (ppm) at room temperature and 100% RH. 0 20 40 60 80 100 120 140 160 180 0 20 40 60 80 100 120 conc in zeolite [ppm]/g zeolite time [h] 4A CL control 69 Figure 3 . 25 . Amount of ethylene sorption (%) at room temperature and 100% RH. Lowering the temperature in the presence of water in the system (figures 3.26 - 3.27 ) cause d desorption of C 2 H 4 to continue over time in the synthetic zeolite. At room temperature the initial drop C 2 H 4 continued to be desorbed until the end of the experiment. Figure 3 . 26 . Amount 0 5 10 15 20 25 30 35 40 0 20 40 60 80 100 120 conc in zeolite [%]/g zeolite time [h] 4A CL control 0 50 100 150 200 250 300 350 400 0 20 40 60 80 100 conc in zeolite [ppm]/g zeolite time [h] 4A CL control 70 Figure 3 . 27 . Amount As for CO 2 ad sorption (figures 3.2 8 - 3. 33 ), in general, the final ad sorption capacities were reached much faster than for any C 2 H 4 case . Again the synthetic type 4A zeolite was superior in all cases (p < 0.05) . Figure 3 . 28 . Amount of carbon dioxide sorption (%) at room temperature and 0% RH. 0 10 20 30 40 50 60 70 80 0 20 40 60 80 100 conc in zeolite [%]/g zeolite time [h] 4A CL control 0 5 10 15 20 25 30 0 2 4 6 8 10 12 conc in zeolite [%]/g zeolite time [h] 4A CL control 71 The same situation as with C 2 H 4 can be observed; the presence of a second gas in the headspace slowed down the ad sorption process (p < 0.05) (figures 3.2 8 and 3.2 9 ). A few percent decrease in sorption for the 4A zeolite was observed, while in the natural zeolite there was no significant difference (p < 0.05) . Figure 3 . 29 . Amount of carbon dioxide sorption (%) at room temperature and 0% RH in presence of ethylene. Decreasing the concentration of CO 2 from 35% (figu re 3.2 9 ) to 15% and the presence of 5% O 2 did not result insignificant differences when compared to the other cases (p > 0.05) (figure 3. 30 ). CL immediately reached its maximum sorption capacity a nd maintained it on the same level to the end of the measurements. In the case of the synthetic ze olite, the behavior was similar to many other cases, sorption increas ed for a long time and reached equilibrium after 12.5h . The ad sorption was still relatively fast and the maximum capacities were reached much faster than in any case involving C 2 H 4 ad sorption. 0 5 10 15 20 25 0 10 20 30 40 50 60 conc in zeolite [%]/g zeolite time [h] 4A CL control 72 Figure 3 . 30 . Amount of carbon dioxide sorption (%) at room temperature and 0% RH in presence of oxygen. The presence of water at either temperature (figure s 3. 31 and 3.3 3 ) did not affect ad sorption of CO 2 . No significant desorption was observed and the maximum sorption capacity was reached quite quickly (between 8 h and 12h) (p <0.05). Figure 3 . 31 . Amount of carbon dioxide sorption (%) at room temperature and 100%RH. 0 2 4 6 8 10 12 0 5 10 15 conc in zeolite [%]/g zeolite time [hours] CL 4A control 0 5 10 15 20 25 30 35 0 2 4 6 8 conc in zeolite [%]/g zeolite time [h] 4A CL control 73 Both decreasing temperature and the presence of C 2 H 4 in the headspace as well as absence of H 2 O incre ased ad sorption time but also significantly increased adsorption of CO 2 for both zeolites (p < 0.05) (figure s 3. 31 and 3. 32 ). As was discussed, lower temperature result ing in increased adsorption suggests that this process is exothermic in nature. Also the absence of wate r means absence of competiti ve molecule s that can block available adsorption sites for the other two gases, CO 2 and C 2 H 4 . Figure 3 .32 . Amount RH in presence of ethylene. The presence of water significantly decreased the sorption time and sorption capacity (figure 3. 33 ), s uggesting again that H 2 O acts as a competitive molecule to CO 2 . 0 10 20 30 40 50 60 0 10 20 30 40 50 conc in zeolite [%]/g zeolite time [h] 4A CL control 74 Figure 3 . 33 . Amount 3 .4. Conclusion s All of the investigated cases with changing headspace gases, temperatures and humidities showed promising sorption capacities for zeolites that can be applied to packaging of perishables. Even though the most relevant conditions of storage of fresh produce smallest sorption capacities for both zeolites, it must be remembered that fruits and vegetables produce small concentrations of these gases and are only going to be stored for a few days. Lowering increased sorption of CO 2 in CL but decreased it in 4A, which means that we have exothermi c and endothermic adsorptions, respectively. In case of ethylene adsorption the same situation happened for both zeolites, adsorption was decreased due to the endoth ermic character of this process. Presence of H 2 O had an effect on both zeolites. Due to the hydrophilicity of CL it inhibited its adsorption ofCO 2 and C 2 H 4 , while for 4A the initial high adsorption of C 2 H 4 was reversed and H 2 O molecules were exchanged wit h C 2 H 4 on the adsorption sites, showing that H 2 O is a competitive molecule to the other two gases. Adsorption of CO 2 was not affected in 4A, which is in accord with the 0 5 10 15 20 25 30 0 5 10 15 conc in zeolite [%]/g zeolite time [h] 4A CL control 75 ze olite's hydrophobic character. The p resence of additional gases as compared to pure si ngle component systems showed increased adsorption capacities. Higher polarizabilitie s and quadrupole moments of ion s with larger radii cause them to adsorb first. After the sorption capacities of the two zeolites in the form of powder were determined in conditions relevant to fresh produce , the next step was to produce a polymer film with zeolites incorporated in it, which could work as a new active packaging material for fresh produce. This will be reported in the next chapter . 76 APPENDIX 77 Figure A3 . 1 . Ethylene calibration curve for GC FID. y = 4.1219E - 08x R² = 9.9865E - 01 0 0.01 0.02 0.03 0.04 0.05 0.06 0 200000 400000 600000 800000 1000000 1200000 1400000 ethylene [ul] chromatographic area [uV*sec] 78 Table A3 . 1 . Ethylene calibration data for GC FID. area [µV*s] ethylene [µL] 1198424 0.05 1208126 0.05 1179961 0.05 1240137 0.05 1205877 0.05 989736 0.04 971170 0.04 971578 0.04 964135 0.04 964614 0.04 616687 0.025 616902 0.025 618923 0.025 622984 0.025 624110 0.025 231309 0.01 238529 0.01 234532 0.01 225987 0.01 223184 0.01 0 0 79 Figure A 3 .2. Oxygen calibration curve for GC TCD. Figure A3 .3. Nitrogen calibration curve for GC TCD. y = 1.1301E - 05x R² = 9.9406E - 01 0 20 40 60 80 100 120 0 2000000 4000000 6000000 8000000 10000000 oxygen [%] chromatographic area [counts] Oxygen % Linear (Oxygen %) y = 9.0489E - 06x R² = 9.9973E - 01 0 20 40 60 80 100 120 0 5000000 10000000 15000000 nitrogen [%] chromatographic area [counts] Nitrogen % Linear (Nitrogen %) 80 Figure A 3 .4. Carbon dioxide calibration curve for GC TCD. y = 4.8549E - 06x R² = 9.9965E - 01 0 20 40 60 80 100 120 0 5000000 10000000 15000000 20000000 25000000 carbon dioxide [%] chromatographic area [counts] Carbon dioxide Linear (Carbon dioxide) 81 Table A 3 .2. Oxygen calibration data for GC TCD. oxygen [%] area [counts] (nitrogen) 0 0 (nitrogen) 0 0 (nitrogen) 0 0 (carb. diox.) 0 0 (carb. diox.) 0 0 (carb. diox.) 0 0 (mix) 5 0 (mix) 5 0 (mix) 5 0 (air) 20.9476 0 (air) 20.9476 0 (air) 20.9476 0 (oxygen) 100 0 (oxygen) 100 0 (oxygen) 100 0 Table A3 .3. Nitrogen calibration data for GC TCD. nitrogen [%] area [counts] (carb. diox.) 0 0 (carb. diox.) 0 0 (carb. diox.) 0 0 (oxygen) 0 0 (oxygen) 0 0 (oxygen) 0 0 (air) 78.084 8493546 (air) 78.084 8512040 (air) 78.084 8555943 (mix) 80 8809718 (mix) 80 8917720 (mix) 80 8917346 (nitrogen) 100 11048430 (nitrogen) 100 11006169 (nitrogen) 100 11246913 82 Table A 3 .4. Carbon dioxide calibration data for GC TCD. carbon dioxide [%] area [counts] (oxygen) 0 0 (oxygen) 0 0 (oxygen) 0 0 (nitrogen) 0 0 (nitrogen) 0 0 (nitrogen) 0 0 (air) 0 0 (air) 0 0 (air) 0 0 (mix) 15 2802832 (mix) 15 2832167 (mix) 15 2858897 (carb. diox.) 100 20462952 (carb. diox.) 100 20508062 (carb. diox.) 100 20922885 Table A3.5 . Summary of ethylene (ppm) measurements taken for powder zeolites in chapter 3. conditions sample CO 3.3 ± 0.8 aA* 6.6 ± 1.7 aA 6.6 ± 1.7 aA C 2 H 4 CL 221.3 ± 21.0 dA 267.7 ± 24.9 eB 267.7 ± 24.9 eB 4A 342.7 ± 43.0 eA 357.8 ± 34.6 fA 357.8 ± 34.6 fA CO 2.2 ± 0.7 aA 4.4 ± 0.3 aB 7.7 ± 7.5 aC C 2 H 4 + CO 2 CL 15.4 ± 5.2 aA 22.3 ± 7.8 aAB 37.0 ± 9.8 aB 4A 113.3 ± 12.9 cA 122.9 ± 14.9 cA 130.2 ± 14.4 cA CO 1.3 ± 1.6 aA 2.4 ± 3.4 aA 2.4 ± 3.4 aA C 2 H 4 2 O) CL 9.9 ± 9.3 aA 9.5 ± 13.8 aA 9.5 ± 13.8 aA 4A 127.6 ± 1.9 cA 116.0 ± 13.2 bcA 116.0 ± 13.2 cA CO 2.5 ± 4.3 aA 2.2 ± 1.7 aA 22.7 ± 38.3 aB C 2 H 4 + CO 2 CL 33.7 ± 13.0 abA 24.2 ± 7.2 aA 46.6 ± 9.0 aA 4A 64.6 ± 9.5 bA 90.1 ± 4.9 bB 131.1 ± 6.8 cC CO 3.9 ± 2.4 aA 6.8 ± 5.7 aA 6.8 ± 5.7 aA C 2 H 4 2 O) CL 10.1 ± 0.9 aA 6.9 ± 1.7 aA 6.9 ± 1.7 aA 4A 433.6 ± 8.9 fA 220.2 ± 15.7 dB 220.2 ± 15.7 dB * means followed by the same lower case letter in column, upper case in rows, are not statistically 0.05) 83 Table A 3.6 . Summary of ethylene (%) measurements taken for powder zeolites in chapter 3. conditions sample CO 0.6 ± 0.2 aA* 1.2 ± 0.3 aA 1.2 ± 0.3 aA C 2 H 4 CL 42.1 ± 3.9 dA 50.9 ± 4.6 eB 50.9 ± 4.6 deB 4A 66.5 ± 8.5 Ea 69.4 ± 6.9 Fa 69.4 ± 6.9 Fa CO 0.9 ± 0.3 aA 1.8 ± 0.6 abA 3.2 ± 3.2 aB C 2 H 4 + CO 2 CL 6.2 ± 1.3 abA 8.9 ± 1.9 abA 14.9 ± 2.1 bB 4A 69.4 ± 1.4 eA 75.3 ± 1.9 gB 79.8 ± 1.9 gC CO 0.3 ± 0.4aA 0.5 ± 0.7 aA 0.5 ± 0.7 aA C 2 H 4 2 O) CL 2.2 ± 2.0 aA 2.1 ± 3.0 abA 2.1 ± 3.0 aA 4A 96.1 ± 1.0 fA 25.3 ± 3.0 cB 25.3 ± 3.0 cB CO 1.1 ± 1.8aA 1.0 ± 0.7 aA 4.4 ± 1.8 aB C 2 H 4 + CO 2 CL 13.6 ± 4.5 bA 9.8 ± 2.4 bA 19.3 ± 5.4 bcA 4A 28.8 ± 3.6cA 40.2 ± 1.5 dB 58.5 ± 1.4 eC CO 1.0 ± 0.4 aA 1.7 ± 1.2 abA 1.7 ± 1.2 aA C 2 H 4 2 O) CL 2.2 ± 0.2 aA 1.5 ± 0.4 abA 1.5 ± 0.4 aA 4A 95.3 ± 1.2 fA 48.4 ± 3.8 deB 48.4 ± 3.8 dB * means followed by the same lower case letter in column, upper case in rows, are not statistically 84 Table A3.7 . Summary of ethylene (nL) measurements taken for powder zeolites in chapter 3. conditions sample CO 0.3 ± 0.1 aA* 0.3 ± 0.0 aA 0.3 ± 0.0 aA C 2 H 4 CL 11.1 ± 1.0 dA 13.4 ± 1.2 eB 13.4 ± 1.2 eB 4A 17.1 ± 2.1 eA 17.9 ± 1.7 fA 17.9 ± 1.7 fA CO 0.0 ± 0.1 aA 0.2 ± 0.1 aB 0.4 ± 0.4 aC C 2 H 4 + CO 2 CL 0.8 ± 0.3 aA 1.1 ± 0.4 aAB 1.8 ± 0.5 aB 4A 5.7 ± 0.6 cA 6.1 ± 0.7 cA 6.5 ± 0.7 cA CO 0.1 ± 0.1 aA 0.1 ± 0.1 aA 0.1 ± 0.1 aA C 2 H 4 2 O) CL 0.5 ± 0.5 aA 0.5 ± 0.7 aA 0.5 ± 0.7 aA 4A 5.8 ± 0.5 cA 5.8 ± 0.7 bcA 5.8 ± 0.7 cA CO 0.6 ± 0.1 aA 0.5 ± 0.1 aA 1.8 ± 1.7 aB C 2 H 4 + CO 2 CL 1.8 ± 0.7 abA 1.2 ± 0.4 aA 2.3 ± 0.4 aA 4A 3.2 ± 0.5 bA 4.5 ± 0.2 bB 6.6 ± 0.3 cC CO 0.2 ± 0.1 aA 0.1 ± 0.1 aA 1.1 ± 0.2 aA C 2 H 4 2 O) CL 0.4 ± 0.2 aA 0.5 ± 0.2 aA 3.6 ± 0.6 aA 4A 2.9 ± 1.2 fA 4.1 ± 1.2 dB 6.6 ± 1.1 dB * means followed by the same lower case letter in column, upper case in rows, are not statistically 85 Table A3 . 8 . Summary of carbon dioxide (%) measurements taken for powder zeolites in chapter 3. conditions sample CO 0.6 ± 0.5 aA* 3.7 ± 0.5 aB CO 2 CL 3.9 ± 0.4 abA 6.6 ± 0.6 aB 4A 28.6 ± 2.4 efA 30.1 ± 1.9 dA CO 2.1 ± 0.5 abA 3.0 ± 1.1 aA CO 2 + C 2 H 4 CL 12.0 ± 0.9 cA 14.9 ± 0.9 bA 4A 48.6± 3.0 hA 63.9 ± 5.5 eB CO 4.8 ± 1.4 abA 3.5 ± 0.1 aA CO 2 + O 2 CL 21.1 ± 1.9 dA 21.3 ± 0.9 cA 4A 59.3 ± 2.3 iA 73.0 ± 1.0 fB CO 1.0 ± 1.0 aA 1.3 ± 1.2 aA CO 2 2 O) CL 4.2 ± 2.4 abA 4.3 ± 0.6 aA 4A 31.5 ± 0.7 fA 30.3 ± 0.9 dA CO 1.7 ± 1.4 aA 2.2 ± 0.8 aA CO 2 + C 2 H 4 CL 14.1 ± 0.3 cA 18.6 ± 0.8 bcB 4A 37.7 ± 2.4 gA 63.1 ± 2.4 eB CO 1.7 ± 0.7 aA 1.3 ± 0.6 aA CO 2 2 O) CL 6.9 ± 1.3 bA 4.8 ± 0.8 aA 4A 24.2 ± 1.1 deA 27.2 ± 2.4 dA * means followed by the same lower case letter in column, upper case in rows, are not statistically Table A3.9 . Amount of ethylene adsorption (ppm) at room temperature and 0% RH. time [h] CO [ppm] CL [ppm] 4A [ppm] 0 0 0 0 24 3.7 ± 2.5 172.2 ± 20.8 322.8 ± 48.7 48 5.1 ± 2.7 221.3 ± 21.0 342.7 ± 43.0 72 1.9 ± 1.3 249.4 ± 23.6 352.0 ± 37.7 96 5.9 ± 0.5 267.7 ± 24.9 357.8 ± 34.6 Table A3.10 . Amount of ethylene adsorption (%) at room temperature and 0% RH. time [h] CO [%] CL [%] 4A [%] 0 0 0 0 24 0.7 ± 0.5 32.7 ± 3.8 62.6 ± 9.6 48 1.0 ± 0.5 42.1 ± 3.9 66.5 ± 8.5 72 0.4 ± 0.3 47.4 ± 4.3 68.3 ± 7.5 96 1.1 ± 0.1 50.9 ± 4.6 69.4 ± 6.9 86 Table A3.11 . Amount of ethylene adsorption (ppm) at room temperature and 0% RH with carbon dioxide present. time [h] CO [ppm] CL [ppm] 4A [ppm] 0 0 0 0 2.5 2.1 ± 0.8 3.6 ± 2.8 50.3 ± 3.7 5 1.3 ± 1.0 5.1 ± 2.2 64.7 ± 5.0 7.5 1.0 ± 0.8 6.6 ± 2.3 73.7 ± 5.5 24 2.2 ± 1.6 9.7 ± 2.5 99.7 ± 10.0 48 1.5 ± 0.6 15.4 ± 5.2 113.3 ± 12.9 72 3.7 ± 2.4 17.9 ± 4.3 117.8 ± 13.1 96 3.6 ± 2.4 22.3 ± 7.8 122.9 ± 14.9 240 5.1 ± 5.9 29.7 ± 11.2 128.8 ± 15.4 264 3.3 ± 5.1 34.8 ± 9.6 129.8 ± 14.4 288 8.8 ± 7.8 37.0 ± 9.8 131.2 ± 15.6 Table A3.12 . Amount of ethylene adsorption (%) at room temperature and 0% RH with carbon dioxide present. time [h] CO [%] CL [%] 4A [%] 0 0 0 0 2.5 0.9 ± 0.3 1.3 ± 0.9 21.6 ± 0.1 5 0.6 ± 0.4 2.0 ± 0.6 27.7 ± 0.2 7.5 0.4 ± 0.3 2.6 ± 0.5 31.6 ± 1.0 24 0.9 ± 0.7 3.8 ± 0.4 42.7 ± 1.4 48 0.6 ± 0.3 6.0 ± 1.2 48.5 ± 2.1 72 1.6 ± 1.0 7.1 ± 0.7 50.4 ± 2.1 96 1.5 ± 1.0 8.7 ± 1.8 52.6 ± 2.6 240 2.1 ± 2.5 11.6 ± 2.8 55.1 ± 2.7 264 1.4 ± 2.2 13.7 ± 2.1 55.2 ± 2.4 288 3.7 ± 3.3 14.6 ± 2.0 55.6 ± 2.4 87 Table A3.13 . present. time [h] CO [ppm] CL [ppm] 4A [ppm] 0 0 0 0 2.5 11.6 ± 8.9 22.99 ± 8.4 27.0 ± 2.5 5 4.3 ± 3.0 23.24 ± 11.8 25.8 ± 8.1 7.5 30.7 ± 35.0 26.08 ± 20.3 65.6 ± 25.9 10 26.1 ± 17.4 9.67 ± 6.6 25.4 ± 10.0 24 22.4 ± 3.6 21.25 ± 8.2 67.2 ± 20.2 48 12.8 ± 2.6 33.74 ± 13.0 64.6 ± 9.5 72 8.5 ± 3.5 23.55 ± 9.5 78.8 ± 8.4 96 9.3 ± 2.5 24.2 ± 7.2 90.1 ± 4.9 120 0.0 ± 2.3 18.63 ± 4.8 89.6 ± 6.5 144 0.6 ± 2.4 21.31 ± 7.5 97.6 ± 9.3 168 4.7 ± 2.3 26.18 ± 5.4 102.3 ± 7.3 192 3.9 ± 4.1 23.69 ± 6.5 104.4 ± 5.9 216 8.5 ± 9.6 27.43 ± 4.7 108.8 ± 5.9 240 12.7 ± 9.1 35.76 ± 3.7 112.1 ± 6.3 264 11.3 ± 10.4 30.95 ± 2.5 113.0 ± 5.7 288 13.3 ± 12.0 34.55 ± 7.4 115.8 ± 4.3 312 19.1 ± 13.3 36.68 ± 2.1 117.1 ± 4.7 336 17.5 ± 21.5 37.31 ± 5.6 119.8 ± 6.2 360 24.2 ± 25.4 40.12 ± 6.3 121.5 ± 6.1 384 27.1 ± 31.2 44.20 ± 7.4 126.1 ± 7.6 408 29.5 ± 32.2 44.95 ± 7.3 126.6 ± 8.8 432 35.8 ± 33.5 46.55 ± 90. 131.0 ± 6.8 88 Table A3.14 . present. time [h] CO [%] CL [%] 4A [%] 0 0 0 0 2.5 5.2 ± 3.8 9.3 ± 3.0 12.0 ± 0.8 5 1.9 ± 1.3 9.3 ± 3.9 11.5 ± 3.3 7.5 13.3 ± 13.6 10.2 ± 7.2 29.1 ± 10.6 10 11.2 ± 7.2 4.0 ± 2.7 11.2 ± 4.1 24 9.8 ± 1.9 8.7 ± 3.3 29.9 ± 8.6 48 5.6 ± 1.4 13.6 ± 4.5 28.8 ± 3.6 72 3.7 ± 1.6 9.4 ± 3.1 35.1 ± 3.3 96 4.0 ± 1.0 9.7 ± 2.4 40.2 ± 1.5 120 0.0 ± 1.0 7.5 ± 1.3 40.0 ±2.0 144 0.3 ± 1.1 8.6 ± 2.8 43.5 ± 3.5 168 2.0 ± 1.0 10.6 ± 1.7 45.6 ± 2.4 192 1.7 ± 1.8 9.6 ± 2.3 46.5 ± 1.7 216 3.7 ± 4.1 11.1 ± 1.3 48.5 ± 1.8 240 5.5 ± 3.9 14.6 ± 1.4 50.0 ± 1.5 264 4.9 ± 4.4 12.6 ± 0.9 50.4 ± 1.5 288 5.8 ± 5.1 14.2 ± 3.4 51.7 ± 0.5 312 8.3 ± 5.6 15.0 ± 1.7 52.2 ± 0.6 336 7.6 ± 9.2 15.3 ± 3.0 53.5 ± 1.2 360 10.5 ± 10.8 16.6 ± 3.8 54.2 ± 1.2 384 11.7 ± 13.3 18.3 ± 4.5 56.3 ± 1.8 408 12.7 ± 13.7 18.6 ± 4.5 56.4 ± 2.4 432 15.4 ± 14.3 19.3 ± 5.4 58.4 ± 1.4 Table A3 .1 5 . Amount of ethylene adsorption (ppm) at room temperature and 100% RH. time [h] CO [ppm] CL [ppm] 4A [ppm] 0 0 0 0 24 1.5 ± 0.6 5.8 ± 8.4 165.4 ± 1.7 48 1.8 ± 2.6 9.8 ± 9.1 116.3 ± 10.4 72 2.3 ± 2.7 10.9 ± 8.8 113.1 ± 11.7 96 3.0 ± 2.9 9.4 ± 13.6 116.0 ± 13.2 89 Table A3 .1 6 . Amount of ethylene adsorption (%) at room temperature and 100% RH. time [h] CO [%] CL [%] 4A [%] 0 0 0 0 24 0.3 ± 0.1 1.3 ± 1.8 36.1 ± 0.6 48 0.4 ± 0.6 2.1 ± 2.0 25.4 ± 2.4 72 0.5 ± 0.6 2.4 ± 1.9 24.7 ± 2.7 96 0.6 ± 0.6 2.0 ± 3.0 25.3 ± 3.0 Table A3 .1 7 . time [h] CO [ppm] CL [ppm] 4A [ppm] 0 0 0 0 24 5.3 ± 5.9 22.8 ± 5.3 324.5 ± 16.1 48 12.5 ± 9.7 10.1 ± 0.9 293.6 ± 19.2 72 7.4 ± 4.9 5.8 ± 2.8 246.8 ± 16.3 96 8.3 ± 7.0 6.9 ± 1.7 220.2 ± 15.7 Table A3 .1 8 . time [h] CO [%] CL [%] 4A [%] 0 0 0 0 24 1.1 ± 1.3 4.9 ± 1.2 71.4 ± 4.2 48 2.7 ± 2.1 2.2 ± 0.2 64.6 ± 4.9 72 1.6 ± 1.0 1.3 ± 0.6 54.3 ± 4.1 96 1.8 ± 1.5 1.5 ± 0.4 48.4 ± 3.8 Table A3 . 19 . Amount of carbon dioxide adsorption (%) at room temperature and 0% RH. time [h] CO [%] CL [%] 4A [%] 0 0 0 0 2.5 0.8 ± 0.7 1.8 ± 1.9 19.9 ± 0.7 5 0.5 ± 0.5 1.6 ± 1.8 24.0 ± 2.1 7.5 1.3 ± 0.5 2.6 ± 2.1 24.8 ± 2.1 10 3.2 ± 0.5 4.2 ± 1.6 25.2 ± 1.8 90 Table A3.20 . Amount of carbon dioxide adsorption (%) at room temperature and 0% RH in presence of ethylene. time [h] CO [%] CL [%] 4A [%] 0 0 0 0 2.5 0.8 ± 0.5 3.1 ± 0.5 10.1 ± 1.5 5 1.0 ± 0.4 3.2 ± 0.4 14.6 ± 1.3 7.5 0.6 ± 0.7 3.3 ± 0.7 16.6 ± 1.3 10 0.8 ± 0.2 3.3 ± 0.8 17.8 ± 1.2 12.5 0.7 ± 0.5 3.6 ± 0.8 18.7 ± 1.4 24 0.8 ± 0.4 3.9 ± 0.8 19.4 ± 0.9 48 0.9 ± 0.3 4.3 ± 0.3 20.2 ± 0.9 Table A3.21 . Amount of carbon dioxide adsorption (%) at room temperature and 0% RH in presence of oxygen. time [h] CO [%] CL [%] 4A [%] 0 0 0 0 2.5 0.3 ± 0.3 11.0 ± 0.2 7.7 ± 0.3 5 0.5 ± 0.1 11.0 ± 0.7 5.8 ± 0.3 7.5 0. ± 0.2 11.0 ± 0.3 4.7 ± 0.2 10 0.2 ± 0.1 11.1 ± 0.5 4.2 ± 0.3 12.5 0.3 ± 0.2 11.1 ± 0.4 3.8 ± 0.3 15 0.3 ± 0.2 11.0 ± 0.4 3.8 ± 0.3 Table A3.22 . Amount of carbon dioxide adsorption (%) at room temperature and 100% RH. time [h] CO [%] CL [%] 4A [%] 0 0 0 0 2.5 3.0 ± 1.4 4.6 ± 3.1 28.8 ± 1.9 5 0.9 ± 1.0 4.1 ± 2.4 30.8 ± 0.6 7.5 1.3 ± 1.1 4.1 ± 0.3 29.7 ± 0.8 Table A3.23 . time [h] CO [%] CL [%] 4A [%] 0 0 0 0 2.5 1.2 ± 0.8 8.0 ± 1.5 18.8 ± 1.2 5 1.1 ± 1.1 9.4 ± 1.1 27.6 ± 1.5 7.5 1.2 ± 0.6 10.3 ± 1.5 36.1 ± 2.3 10 1.1 ± 0.9 8.1 ± 2.3 36.7 ± 0.7 24 2.1 ± 1.0 10.6 ± 1.1 45.7 ± 2.3 48 1.0 ± 1.6 12.4 ± 1.9 46.1 ± 1.0 91 Table A3 . 24 . Amount of carbon dioxide adsorption time [h] CO [%] CL [%] 4A [%] 0 0 0 0 2.5 0.8 ± 0.7 6.2 ± 1.3 15.1 ± 1.3 5 1.4 ± 0.6 5.9 ± 1.1 20.8 ± 0.9 7.5 1.1 ± 1.1 5.3 ± 0.7 22.6 ± 1.7 10 1.3 ± 0.8 5.0 ± 0.4 23.4 ± 1.5 12.5 1.1 ± 0.5 4.2 ± 0.7 23.4 ± 2.0 92 REFERENCES 93 R E F E R E N C E S 1. 2012 Production guide for Storage of Organic Fruits and Vegetables NYS IPM Publication no.10 2. Coloma A., Rodriguez F.J., Bruna J.E., Guarda A., Galotto M.J. Development of an Active Film with Natural Zeolite as Ethylene Scavenger , J ournal of the Chilean Chemical Society 2014 (49) 2409 - 2414 3. Patdhanagul N., Srithanratana T., Rangsriwatananon K., Hengrasmee S. Ethylene adsorption on cationic surfactant modified zeolite NaY , Microporous and Mesoporous Materials 2010 (131) 97 - 102 4. Erdoga n B., Sakizci M., Yorukogullari E. Characterization and ethylene adsorption of natural and modified clinoptilolites , Applied Surface Science 2008 (254) 2450 - 2457 5. 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Adsorption Kinetics of CO 2 , O 2 , N 2 , and CH 4 in Cation - Exchanged Clinoptilolite , Journal of Physical Chemistry B 2001 (105) 1313 - 1319 26. http://helios.princeton.edu/zeomics/ 95 CHAPTER 4 Effect of the processing method on the adsorbing gas capability of active films made of PLA/zeolite 4.1. Introduction In cha pter 3 sorption characteristics of two zeolites were investigated. Natural clinoptilolite (CL) and synthetic type 4A zeolites in the form of powder were p roven to have simultaneous sorption capacities for ethylene and carbon dioxide. The next step was to incorporate them into plastic films so that they could be used as packaging materials for fresh produce. But first an appropriate method of production wa s needed. This method should not only result in a composite material made of PLA and zeolites but should not limit the sorption capacities of zeolites due to their incorporation into the polymer materials. PLA was chosen due to it being biobased and known to biodegrade reasonably quickly in commercial compost , and so it provides an alternative to commonly used petrochemical based polymers. A commonly used technology for mixing polymers with additives is extrusion, preceded by production of a masterbatch [1] . Two zeolites, synthetic type 4A and natural chabazite, were used. First PLA and zeolites were placed in a micro extruder with co - rotating twin - screws; then the extrudate was transferred to a mini - injection molder and small discs were formed. To obtain th in films, the discs were compressed. No compatibilizer was needed [2 - 3]. Solvent coating is a known method of incorporating different materials on the surface of extruded films. Although it has not been commonly used for zeolites, it has been utilized in PLA production. 96 This chapter will show how different processing methods can produce films of varying sorption capacities for the two gases of interest. It will also show how small modifications within a given process can significantly change the sorption characteristics of a given film. 4.2. Experimental 4.2.1. Materials 4.2.1.1. Zeolites and Gases Two zeolites were chosen, one synthetic - type 4A a nd one natural - clinoptilolite, and two adsorbents, ethylene and car bon dioxide, a s described in chapter 3. 4.2.1.2. Poly(lactic acid) PLA was used in two different forms - pellets and film. Pellets of PLA resin 4060 D were obtained from Nature Works LLC (Blair, NE, US) . Film was purchased as a roll from Evlon (Wingham, Ontario, C anada) - F40EVHS, biaxially oriented with outside corona treatment to improve the surface adhesion of the coating. coated with a zeolite/PLA coating solution on the outside. 4.2.2. Methods of thin film production 4.2.2.1. Extrusion, followed by injection molding and compression molding PLA composites with 30 wt% of one of the zeolites, clinoptilolite or type 4A, were produced in the Composite Materials and Structures Center at Michigan Sta te University. Both PLA and zeolites were 97 dried in a vacuum oven before processing, as previously described, cooled and stored in a desiccator prior to use. A DSM microextruder with co - rotating twin - scr ews (DSM Research, Netherlands) was used to mix PLA with the zeolites. Processing temperatures in the microextruder (top, middle, bottom) were all The resulting extrudate was collected from the die into a preheat transferred into a mini injection molder (DSM Research, Netherlands). The applied injection pressure Round micro discs were molded (figure 4.1 ). Dry ice was used to remove the discs f rom the mold. Figure 4 . 1 . Injection molded PLA, PLA/30% type 4A zeolite, PLA/30% clinoptilolite discs. thin films in a PHI Heated Press (model no. QL438 - C , City of Industry, CA, US ) (figure 4.2 applying a force of 25 tons for 5 minutes. 98 Figure 4 . 2 . Heated press used to produce films from injection molded discs . The resulting films had a thickness between 0.09 and 0.05 mm. In a similar manner PLA films with no additives were produced. D ifferences in thicknesses of res ulting composite films might influence sorption measurements. Thicker films will have a larger barrier of PLA between the gases and the zeolites that might inhibit adsorption. 4.2.2.2. Bar coating For bar coating, a n instrument that allows accurate and reproducible prints was used (RK K303 Multicoater , United Kingdom ) (figure 4.3 ). All coating solutions were prepared at room temperature and a mixing time of 45 minutes. The coating solu tion was 20 m L of acetone and various combinations of PLA and zeolites , as detailed in the results and discussion section. With this method, the thickness of the final film can be controlled by using different coating bars. The lower the number of the coat ing bar, the smaller is the thickness. Bars with numbers between 0 and 8 were used with speed set to 4 m/min. Coated films were dried in air and kept overnight in a desiccator before testing. Although PLA wa s coated with a solution containing both PLA and zeolites, the nomenclature has been shortened to PLA/zeolite coated film for simplicity. 99 Figure 4 . 3 . Multicoater used to produce coated films . 4.2.2.3. S ample preparation All films were cut into the same size samples (17.5 x 8 cm) , stapled on the end to prevent rolling, and placed into 250 mL glass jars with metal closures. For filling and sampling purposes, holes were drilled in the lids and septa made of gray butyl rubber were insert ed. The headspace was flushed with both gases ( C 2 H 4 and CO 2 ) and pla 4.2.3. Ads orption measurements 4.2.3.1. Gas Chromatography with Flame Ionization Detector (GC FID) GC FID (Hewlett Packard GC 6890, Agilent Technologies, Santa Clara, CA, US) is used to detect C 2 H 4 concentration in the sampling systems (glass jars with aluminum closures and septa). The column used is Supelco Carboxen 1010 PLOT, L x I.D. 30m x 0.53 mm , p acked with fused silica. The measuring method for C 2 H 4 was as fo llows: d a continuous run of 13 min , the retention time for a clear and symmetrical C 2 H 4 peak wa s 11 min . Both inlet and detector temperatures 100 4.2.3.2. Gas Chromatography with Thermal Conductivity Detector (GC TCD) GC TCD (ThermoScientific Trace GC Ultra GC with FID/TCD , Waltham, MA, US ) wa s used to detect CO 2 , O 2 and N 2 concentrations in the sampling systems ( same jars ). The column used wa s as mentioned above. For detection of headspace gases (O 2 , N 2 and CO 2 ) the measuring method was as follows: tem th a total run time of 9 min and retention times of 3.4 min for O 2 , 3.55 min for N 2 and 7.2 min for CO 2 . Inlet and detector temperatures into the GC using a 100 µL gas tight syringe with needle valve (Supelco SGE , Australia ). Ads orption measurements were compared after 48 hours and after one week for all samples. Three repl icates of each type of samples we re tested. Results for C 2 H 4 are pre sented in % to show the proportion of the total headspace gas that wa s adsorbed and in nL to show the exact adsorbed volumes. For CO 2 , % and mL results are presented for the same reasons. Calibration c urves can be found in appendix in chapter 3 . 4.2.4. Characterization of produced films 4.2.4.1. Thermogravimetric Analysis (TGA) A TGA Q50 (TA Instruments , New Castle, DE, US ) was used to determine the zeolite content in the PLA films. From five to ten g per C with constant N 2 flow of 70 mL/min. Zeolite content was measured for each sample. 101 4.2.4.2. Scanning Electron Microscopy (SEM) SEM (Carl Zeiss Variable Pressure SEM EVO LS25 , Germany ) was used to determine how zeolites we re distributed in /on the PLA surface. Images were acquired with an accelerating voltage of 20 kV and a working distance of 10 mm at 6 k and 11 k x magnification. 4.2.5. Statistical methods Analysis of variance (ANOVA) was performed in the analytical software SPSS version 22 ( SPSS Inc., Chicago, IL, US). Means were separated using the Tukey honestly significant difference (HSD) test (p < 0.05). 4.3. Results and discussion 4.3.1. Melt processing Figure s 4.4 and 4.5 show results for plain PLA and PLA/30 wt% zeolite composites wi th both zeolites. The first measurement was taken 48 hours after filling the jars with C 2 H 4 and CO 2 , while the final measurement was taken after 6 weeks of storage. The ad sorption percentage wa s calculated using equation 4.1. (4.1) While volume results (nL , mL ) were no rmalized according to equation 4.2. (4 .2) 102 Figure 4 . 4 . Amount of ethylene (%) adsorbed by film samples at 2 different times. Figure 4. 5 . Amount of ethylene (nL) adsorbed by film samples at 2 different times. 0 1 2 3 4 5 6 7 8 PLA PLA + 30% CL PLA + 30% 4A adsorbed ethylene [%]/g zeolite 2 days final 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 PLA PLA + 30% CL PLA + 30% 4A adsorbed ethylene [nL]/g zeolite 2 days final 103 Figure 4 . 6 . Amount of carbon dioxide (%) adsorbed by film samples at 2 different times. Figure 4. 7 . Amount of carbon dioxide (mL) adsorbed by film samples at 2 different times. Comparing all collected data (figures 4. 4 - 4.7 ) , it was shown that for both gases there was no significant amount ad sorbed within the first two days (p < 0.05) . C 2 H 4 ad sorption of about 2% was observed for the composite materials and about 1% for plain PLA (figures 4. 4 - 4.5 ) . For CO 2 only 1% was sorbed by all the samples, with no significant difference whether samples contained zeolite or not (p > 0 1 2 3 4 5 6 7 8 9 PLA PLA + 30% CL PLA + 30% 4A adsorbed carbon dioxide [%]/g zeolite 2 days final 0 5 10 15 20 25 PLA PLA + 30% CL PLA + 30% 4A adsorbed carbon dioxide [mL]/g zeolite 2 days final 104 0.05) (figures 4.6 - 4.7 ) .Measurements carried out for multiple weeks showed almost no change in ad sorption of C 2 H 4 for samples with zeolites incorporated int o PLA. But the PLA itself seemed to sorb more than the investigated composites. For CO 2 , a similar situation was observed. PLA sorbed more than the zeolite composites. This time there was a significant difference between performance of the zeolites (p < 0.05) ; type 4A zeolite resulted in higher ad sorption of CO 2 when compared to CL. Supporting data for this ch apter can be found in appendix below . 4.3.2. Surface characteristics At that point it was suspected that zeolites that are incorporated too deepl y into the polymer matrix have inhibited ad sorption capacity for C 2 H 4 . To investigate, SEM images of both m aterials were taken (figure 4. 8 ). Figure 4 . 8 . SEM images of PLA/30 wt% CL (on left) and PLA/30 wt % 4A (on right). Figure 4. 8 shows that in both cases zeolites are not on the surface of PLA but inside its matrix. Since PLA is a good barrier to C 2 H 4 , it blocks the ad sorption capacities of both zeolites. 105 4.3.3. Solution coating There was a need for a new method that would allow zeolites to be deposited as much on the surface of the PLA as possible. Methods considered included bar coating, spin coating, knife coating, plasma application, cast extrusion, blown film and extrusion of a bilayer. It was decided to start with bar coatin g as a widely used method that could be evaluated relatively quickly. When comparing all samples, extruded and coated , after 2 days increased ad sorption in the coated films compared to the extruded films was observed (figures 4. 9 and 4. 12 ). It should be al so noted that although both zeolites were coated similarly on the PLA surface they displayed different ad sorption behavior . Natural clinoptilolite was more active with CO 2 , while synthetic 4A was more active for C 2 H 4 . Figure 4 . 9 . Amount of ethylene (%) a d sorbed by extruded (ext) and coated (coat) film samples. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 PLA (ext) PLA + 30% CL (ext) PLA + 30% 4A (ext) PLA + 30% CL (coat) PLA + 30% 4A (coat) adsorbed ethylene [%]/g zeolite 2 days 106 Figure 4. 10 . Amount of ethylene (nL) adsorbed by extruded and coated film samples. Figure 4 . 11 . Amount of carbon dioxide (%) a d sorbed by extruded and coated film samples. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 PLA (ext) PLA + 30% CL (ext) PLA + 30% 4A (ext) PLA + 30% CL (coat) PLA + 30% 4A (coat) adsorbed ethylene [nL]/g zeolite 2 days 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 PLA (ext) PLA + 30% CL (ext) PLA + 30% 4A (ext) PLA + 30% CL (coat) PLA + 30% 4A (coat) adsorbed carbon dioxide [%]/g zeolite 2 days 107 Figure 4. 12 . Amount of carbon dioxide (mL) adsorbed by extruded and coated film samples. As those initial measurements showed promise that coating was a more appropriate method of production for PLA/zeolite composites than extrusion, it was further investigated. The next step was to try different coating solutions, to determine if an increase in wt% of zeolite would increase ad sorption. Solutions of 30, 60 and 90 wt% of both zeolites were prepared and tested. Coating solutions were modified only by adding more zeolites, 2 0 m L of acetone, 1 g of PLA and 0.3, 0.6 or 0.9 g of zeolite, respectively. Also different coating bars were used, to see how the thickness of the resulting film influenced wt% and ad sorption capacity, all with the goal of increasing the exposure of zeolit es on the surface of the PLA film. Tested combinations of coating solutions and bars used for coating are listed in table 4.1. 0 2 4 6 8 10 12 PLA (ext) PLA + 30% CL (ext) PLA + 30% 4A (ext) PLA + 30% CL (coat) PLA + 30% 4A (coat) adsorbed carbon dioxide [mL]/g zeolite 2 days 108 Table 4 . 1 . List of combination of wt% of zeolite in coating solution and bar used for coating and % of zeolite in obtained film. sample bar % zeolite PLA+30%CL 0 0.9 8 PLA+30%CL 7 2.6 9 PLA+30%CL 8 3.14 PLA+60%CL 7 5.07 PLA+60%CL 8 5.93 PLA+90%CL 8 7.0 2 PLA+30%4A 7 3.34 PLA+60%4A 7 4.33 PLA+60%4A 8 2.37 PLA+90%4A 8 7.48 Mixing different coating solutions and using different bars for coating did not give conclusive results , as shown in figures 4.1 3 and 4.1 6 . There was too much variation in preparation of film samples. Since two variables were changed at the same time, the coating solution together with the bar, it was not easy to see which of these had the actual effect on ad sorption capacity of the investigated samples. Nevertheless, for most samples it was observed that after a week their ad sorption capacity was significantly in creased when compared to data collected after 48 hours (p < 0.05) . What was interesting is that natural zeolite (CL), which when investigated as powder always displayed worse ad sorption capacity than synthetic one (4A), this time, when incorporated into fi lm, CL could compete with 4A and in few cases be a more active compound. This was noted for both C 2 H 4 and CO 2 . The main difference between CL and 4A is that natural zeolite is hydrophilic and the synthetic one is hydrophobic. Due to having PLA on the surface, covering the zeolites, any H 2 O molecules have to get through the PLA first before getting into the zeolites and this way , sorption sites in CL are not blocked by moisture. 109 Figure 4 . 13 . Amount of ethylene (%) adsorbed by coated film samples prepa red using different coating solutions and different coating bars. Figure 4. 14 . Amount of ethylene (nL) adsorbed by coated film samples prepared using different coating solutions and different coating bars. 0 1 2 3 4 5 6 7 8 9 10 adsorbed ethylene [%]/g zeolite 2 days week 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 adsorbed ethylene [nL]/g zeolite 2 days week 110 Figure 4 . 15 . Amount of carbon dioxide (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars. Figure 4. 16 . Amount of carbon dioxide (mL) adsorbed by coated film samples prepared using different coating solutions and diffe rent coating bars. Due to the inconclusiveness of the data shown in figures 4.1 3 - 4.1 6 , it was decided to try to use as little PLA and as much zeolite in the coating solution as possible, so that the PLA would not block the 0 1 2 3 4 5 6 7 8 adsorbed carbon dioxide [%]/g zeolite 2 days week 0 2 4 6 8 10 12 14 16 18 20 adsorbed carbon dioxide [mL]/g zeolite 2 days week 111 zeolites but still enough PLA so that a uniform coating was obtained. Different combinations of PLA and zeolite weights that were tested in coating solutions are listed in table 4.2. TGA was used to determine the zeolite % in each film. Using a bar with a smaller number resulted in a thinner layer of PLA on top of the zeolites, allowing for less coverage of the particles with PLA. Ads orption measurements were carried out for a maximum of three weeks so that ad sorption characteristics of all materials could be fully discovered. Re sults are shown in figures 4.1 7 - 4. 20 . Table 4 . 2 . List of combination of PLA and zeolite weights in coating solution along with bar used for coating and % of zeolite in obtained film. sample bar % zeolite PLA+ CL (1g + 0.3g) 8 3.67 PLA + CL (0.2g + 1g) 2 2.55 PLA + CL (0.2g + 1g) 3 3.56 PLA+ 4A (1g + 0.3g) 8 3.79 PLA + 4A (0.2g + 1g) 2 2.05 PLA + 4A (0.2g + 1g) 3 3.49 PLA + 4A (0.8g + 1g) 3 4.26 Analyzing samples with CL, it can be seen that although initially (after 2 days) there wa s no significant difference between the four samples (p < 0.05) , after one week one of the combinations ( PLA + CL (0.2 g + 1 g) and B3) started to show superior behavior due to the higher amount of CL and lower amount of PLA , which continue d in the next two weeks. This happen ed for both gases, which also proves that ad sorption wa s not selective to only one gas at a time but happen ed simultaneousl y for C 2 H 4 and CO 2 . Results for 4A composites seemed similar to what was observed for CL. For the 2 - day measurement, there was no significant difference between the samples for both gases (p > 0.05) . But it gets more interesting when comparing data after o ne, two and three weeks. One sample ( PLA+ 4A (1 g + 0.3 g) and B8) seemed more prone to a d sorb C 2 H 4 and a little bit less CO 2 while another ( PLA + 4A (0.2 g + 1 g) and B2) was exactly the opposite. All of this happen ed because of the processing differences. Bar 8 resulted in a higher thickness of the final material than bar 2, so larger CO 2 molecule s will have more 112 issues in getting to the zeolites. The s ame goes for having 5 times higher content of PLA in the coating s olution. Remembering that PLA is a good barrier to C 2 H 4 and CO 2 is also important [4 - 5] . A h igher content of zeolite means more available adsorption sites. Since in active packaging of fresh produce, C 2 H 4 has more negative effects than CO 2 does, the better option here is the first sample. Figure 4 . 17 . Amount of ethylene (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four sampling times. 0 2 4 6 8 10 12 14 adsorbed ethylene [%]/g zeolite 2 days week 2 weeks 3 weeks 113 Figure 4. 18 . Amount of ethylene (nL) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four sampling times. Figure 4 . 1 9 . Amount of carbon dioxide (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four sampling times. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 adsorbed ethylene [nL]/g zeolite 2 days week 2 weeks 3 weeks 0 2 4 6 8 10 12 14 16 18 20 adsorbed carbon dioxide [%]/g zeolite 2 days week 2 weeks 3 weeks 114 Figure 4. 20 . Amount of carbon dioxide (mL) adsorbed by coated film samples prepared using different coati ng solutions and different coating bars at four sampling times. Based on the results shown in figures 4.1 7 to 4. 2 0 and visual evaluation of the homogeneity of the coating, it was concluded that for each zeolite different combinations of coating solution and bar were optimal. For CL the best results were obtained with 0.2 g of PLA and 1 g of zeolite and bar no. 3, whil e for type 4A more PLA was required in solution, 1g of PLA mixed with 0.3 g of zeolite and coated with bar no. 8. Measured using TGA, both options resulted in a similar wt% of zeolite, 3.56% of CL and 3.7 9 % of 4A. Both values are smaller than the wt% for c ommercially available film that was tested in the same manner, LDPE with 5 wt% of zeolite as determined by TGA. For this film, the producer does not provide information about what zeolite is used or by what process the film is produced. 0 5 10 15 20 25 30 35 40 45 50 adsorbed carbon dioxide [mL]/g zeolite 2 days week 2 weeks 3 weeks 115 4.4. Conclusions B ar coating is a superior method for preparing PLA/zeolite composite materials for ad sorption of C 2 H 4 and CO 2 compared to extrusion followed by injection molding and compression. Films obtained by the first method allow zeolites to be more on the surface of the films rather than being too deeply incorporated into the polymer matrix, which eventually blocks their ad sorption capacity due to PLA being a good barrier to C 2 H 4 . Varying the composition of coating solution (amounts of PLA and zeolites) but also changing the thickness of the coating by using different bars strongly influence d the ad sorption capacities of the resulting films. Natural clinoptilolite needs much less PLA and a thinner coating layer than does synthetic 4A, which suggests that CL blends better with PLA. Further studies should be done to evaluate the ad sorption capacities of the investigated fi lms in real life situations relevant to packing fresh produce (low temperature and high relative humidity). 116 APPENDIX 117 Table A4 . 1 . Amount of ethylene (%) adsorbed by film samples at two different times. % eth 2 days 6weeks PLA 0.9 ± 0.3 a1* 5.1 ± 2.2 a2 PLA+30%CL 2.1 ± 0.6 a1 2.7 ± 1.2 a1 PLA+30%4A 2.4 ± 1.2 a1 2.7 ± 1.9 a1 * means followed by the same lower case letter in column, numbers between times, are not Table A4 . 2 . Amount of ethylene (nL) adsorbed by film samples at two different times. % eth 2 days 6 weeks PLA 0.2 ± 0.1 a1* 0.5 ± 0.3 a2 PLA+30%CL 0.4 ± 0.2 a1 0.4 ± 0.2 a1 PLA+30%4A 0.4 ± 0.2 a1 0.5 ± 0.3 a1 * means followed by the same lower case letter in column, numbers between times, are not Table A4 . 3 . Amount of carbon dioxide (%) adsorbed by film samples at two different times. % CO 2 2 days 6 weeks PLA 1.1 ± 0.4 a1* 5.7 ± 2.6 ab2 PLA+30%CL 1.3 ± 0.7 a1 2.2 ± 1.6 b1 PLA+30%4A 1.5 ± 1.8 a1 3.8 ± 0.2 a2 * means followed by the same lower case letter in column, numbers between times, are not Table A4 . 4 . Amount of carbon dioxide (%) adsorbed by film samples at two different times. % CO 2 2 days 6 weeks PLA 2.7 ± 0.9 a1* 14.3 ± 6.6 ab2 PLA+30%CL 3.2 ± 1.7 a1 5.6 ± 3.9 b1 PLA+30%4A 3.6 ± 4.5 a1 3.4 ± 0.4 a2 * means followed by the same lower case letter in column, numbers between times, are not 118 Table A4 . 5 . Amount of ethylene (%) adsorbed by extruded and coated film samples. % eth 2 days PLA (ext) 0.9 ± 0.3 a* PLA+30%CL (ext) 2.1 ± 0.6 a PLA+30%4A (ext) 2.4 ± 1.2 a PLA+30%CL (coat) 2.0 ± 0.6 a PLA+30%4A (coat) 3.0 ± 1.0 a * means followed by the same lower case letter in column are not statistically different from each Table A4 . 6 . Amount of ethylene (nL) adsorbed by extruded and coated film samples. nL eth 2 days PLA (ext) 0.2 ± 0.1 a* PLA+30%CL (ext) 0.4 ± 0.2 a PLA+30%4A (ext) 0.4 ± 0.2 a PLA+30%CL (coat) 0.3 ± 0.1 a PLA+30%4A (coat) 0.5 ± 0.2 a * means followed by the same lower case letter in column are not statistically different from each Table A4 . 7 . Amount of carbon dioxide (%) adsorbed by extruded and coated film samples. % CO 2 2 days PLA (ext) 1.1 ± 0.4 a* PLA+30%CL (ext) 1.3 ± 0.7 a PLA+30%4A (ext) 1.5 ± 1.8 a PLA+30%CL (coat) 3.2 ± 1.3 a PLA+30%4A (coat) 1.7 ± 0.2 a * means followed by the same lower case letter in column are not statistically different from each Table A4 . 8 . Amount of carbon dioxide (mL) adsorbed by extruded and coated film samples. mL CO 2 2 days PLA (ext) 2.7 ± 0.9 a* PLA+30%CL (ext) 3.2 ± 1 .7 a PLA+30%4A (ext) 3.6 ± 4.5 a PLA+30%CL (coat) 8.0 ± 3 .3 a PLA+30%4A (coat) 4.3 ± 0.5 a * means followed by the same lower case letter in column are not statistically different from each other (Tukey, 119 Table A4 . 9 . Amount of ethylene (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars. % eth 2 days week PLA+PLA B3 0.6 ± 0.1 a1* 2.0 ± 1.5 a2 PLA+30%CL B0 0.8 ± 0.5 a1 4.5 ± 1.0 a2 PLA+30%CL B7 1.8 ± 0.9 a1 4.1 ± 0.4 a2 PLA+30%CL B8 2.0 ± 0.6 a1 7.4 ± 1.2 a2 PLA+60%CL B7 1.4 ± 0.3 a1 3.8 ± 1.3 a2 PLA+60%CL B8 2.6 ± 0.7 ab1 2.6 ± 0.7 a1 PLA+90%CL B8 4.0 ± 1.1 b1 4.9 ± 1.3 a1 PLA+30%4A B7 3.0 ± 1.0 ab1 5.1 ± 2.3 a1 PLA+60%4A B7 1.4 ± 0.5 a1 5.7 ± 3.2 a2 PLA+60%4A B8 1.7 ± 0.6 a1 4.2 ± 1.1 a2 PLA+90%4A B8 2.8 ± 1.0 ab1 5.5 ± 1.0 a2 * means followed by the same lower case letter in column, numbers between times, are not Table A4 .1 0 . Amount of ethylene (nL) adsorbed by coated film samples prepared using different coating solutions and different coating bars. nL eth 2 days week PLA+PLA B3 0.1 ± 0.0 a1* 0.2 ± 0.2 a2 PLA+30%CL B0 0.1 ± 0.1 a1 0.5 ± 0.1 a2 PLA+30%CL B7 0.2 ± 0.1 a1 0.5 ± 0.0 a2 PLA+30%CL B8 0.2 ± 0.1 a1 0.8 ± 0.1 a2 PLA+60%CL B7 0.2 ± 0.0 a1 0.4 ± 0.1 a2 PLA+60%CL B8 0.3 ± 0.1 ab1 0.3 ± 0.1 a1 PLA+90%CL B8 0.4 ± 0.1 b1 0.5 ± 0.1 a1 PLA+30%4A B7 0.3 ± 0.1 ab1 0.6 ± 0.3 a1 PLA+60%4A B7 0.2 ± 0.1 a1 0.6 ± 0.4 a2 PLA+60%4A B8 0.2 ± 0.1 a1 0.5 ± 0.1 a2 PLA+90%4A B8 0.3± 0.1 ab1 0.6 ± 0.1 a2 * means followed by the same lower case letter in column, numbers between times, are not 120 Table A 4 . 1 1 . Amount of carbon dioxide (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars. % CO 2 2 days week PLA+PLA B3 1.6 ± 0.5 a1* 3.0 ± 0.1 a2 PLA+30%CL B0 0.8 ± 0.5 a1 4.0 ± 0.7 a2 PLA+30%CL B7 3.2 ± 1.3 b1 5.3 ± 1.4 a1 PLA+30%CL B8 2.1 ± 0.7 ab1 6.1 ± 1.0 a2 PLA+60%CL B7 2.6 ± 0.4 ab1 3.6 ± 0.7 a1 PLA+60%CL B8 3.5 ± 0.2 b1 3.9 ± 1.5 a1 PLA+90%CL B8 2.1 ± 0.7 ab1 4.2 ± 1.5 a1 PLA+30%4A B7 1.7 ± 0.2 ab1 3.8 ± 1.3 a1 PLA+60%4A B7 2.4 ± 1.5 ab1 5.3 ± 1.8 a1 PLA+60%4A B8 2.7 ± 1.3 ab1 3.7 ± 1.0 a1 PLA+90%4A B8 1.6 ± 1.0 ab1 4.4 ± 1.8 a1 * means followed by the same lower case letter in column, numbers between times, are not Table A4 .1 2 . Amount of carbon dioxide (mL) adsorbed by coated film samples prepared using different coating solutions and different coating bars. mL CO 2 2 days week PLA+PLA B3 4.0 ± 1.2 a1* 7.4 ± 0.3 a2 PLA+30%CL B0 2.0 ± 1.2 a1 9.9 ± 1.6 a2 PLA+30%CL B7 8.0 ± 3.3 b1 13.3 ± 3.6 a1 PLA+30%CL B8 5.3 ± 1.7 ab1 15.2 ± 2.4 a2 PLA+60%CL B7 6.5 ± 1.0 ab1 8.9 ± 1.8 a1 PLA+60%CL B8 8.8 ± 0.6 b1 9.7 ± 3.7 a1 PLA+90%CL B8 5.2 ± 1.7 ab1 10.5 ± 3.6 a1 PLA+30%4A B7 4.3 ± 0.5 ab1 9.4 ± 3.2 a1 PLA+60%4A B7 5.9 ± 3.8 ab1 13.1 ± 4.5 a1 PLA+60%4A B8 6.6 ± 3.3 ab1 9.2 ± 2.4 a1 PLA+90%4A B8 4.0 ± 2.5 ab1 10.9 ± 4.4 a1 * means followed by the same lower case letter in column, numbers between times, are not 121 Table A4 . 1 3 . Amount of ethylene (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four different times. % eth 2 days week 2 weeks 3 weeks PLA + PLA (1g) B3 0.5 ± 0.3 a1* 1.0 ± 0.7 a1 2.3 ± 1.1 a2 3.5 ± 1.4 a2 PLA+ CL (1g + 0.3g) B8 2.4 ± 0.3 a1 2.3 ± 0.7 a1 2.7 ± 0.5 a1 6.1 ± 0.3 a2 PLA + CL (0.2g+1g) B2 1.8 ± 0.8 a1 2.5 ± 0.3 a1 4.7 ± 0.7 b2 7.8 ± 1.0 a3 PLA + CL (0.2g+1g) B3 3.1 ± 1.3 a1 5.1 ± 0.6 b1 8.6 ± 0.8 c2 10.4 ± 1.6 b2 PLA+ 4A (1g + 0.3g) B8 2.5 ± 1.2 a1 4.5 ± 0.6 b12 6.1 ± 0.6 d23 7.3 ± 0.6 a3 PLA + 4A (0.2g+1g) B2 1.2 ± 0.2 a1 2.2 ± 0.2 a1 4.2 ± 0.3 b2 6.9 ± 1.0 a3 PLA + 4A (0.2g+1g) B3 1.8 ± 0.7 a1 2.2 ± 0.4 a1 4.5 ± 0.4 b2 6.5 ± 0.5 a3 PLA + 4A (0.8g+1g) B3 1.8 ± 0.3 a1 3.3 ± 0.1 a2 3.4 ± 0.3 ab2 3.6 ± 0.1 c2 * means followed by the same lower case letter in column, numbers between times, are not statistically Table A4 .1 4 . Amount of ethylene (nL) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four different times. nL eth 2 days week 2 weeks 3 weeks PLA + PLA (1g) B3 0.1 ± 0.0 a1* 0.1 ± 0.1 a1 0.3 ± 0.1 a2 0.4 ± 0.2 a2 PLA+ CL (1g + 0.3g) B8 0.3 ± 0.0 a1 0.3 ± 0.1 a1 0.3 ± 0.1 a1 0.7 ± 0.0 a2 PLA + CL (0.2g+1g) B2 0.2 ± 0.1 a1 0.3 ± 0.0 a1 0.5 ± 0.1 b2 0.9 ± 0.1 a3 PLA + CL (0.2g+1g) B3 0.3 ± 0.1 a1 0.6 ± 0.1 b1 1.0 ± 0.1 c2 1.1 ± 0.2 b2 PLA+ 4A (1g + 0.3g) B8 0.3 ± 0.1 a1 0.5 ± 0.1 b12 0.7 ± 0.1 d23 0.8 ± 0.1 a3 PLA + 4A (0.2g+1g) B2 0.1 ± 0.0 a1 0.2 ± 0.0 a1 0.5 ± 0.0 b2 0.8 ± 0.1 a3 PLA + 4A (0.2g+1g) B3 0.2 ± 0.1 a1 0.3 ± 0.0 a1 0.5 ± 0.0 b2 0.7 ± 0.1 a3 PLA + 4A (0.8g+1g) B3 0.2 ± 0.0 a1 0.4 ± 0.0 a2 0.4 ± 0.0 ab2 0.4 ± 0.0 c2 * means followed by the same lower case letter in column, numbers between times, are not statistically Table A4 . 1 5 . Amount of carbon dioxide (%) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four different times. % CO 2 2 days week 2 weeks 3 weeks PLA + PLA (1g) B3 0.7 ± 0.6 a1* 1.8 ± 0.2 a2 1.2 ± 1.1 a12 1.8 ± 1.0 a1 PLA+ CL (1g + 0.3g) B8 2.2 ± 0.6 a1 2.8 ± 0.4 a1 5.3 ± 0.0 ab2 9.4 ± 0.7 ab3 PLA + CL (0.2g+1g) B2 2.7 ± 0.5 ab1 3.7 ± 0.4 ab1 7.0 ± 0.8 ac2 11.3 ± 0.6 a3 PLA + CL (0.2g+1g) B3 4.2 ± 0.5 b1 8.9 ± 0.8 c2 12.4 ± 0.9 d3 16.5 ± 0.7 c4 PLA+ 4A (1g + 0.3g) B8 2.6 ± 0.8 ab1 4.5 ± 0.2 bd2 7.9 ± 0.8 ce3 11.6 ± 0.8 a4 PLA + 4A (0.2g+1g) B2 2.8 ± 0.7 ab1 2.9 ± 0.7 a1 6.4 ± 0.3 abc2 8.7 ± 0.9 b3 PLA + 4A (0.2g+1g) B3 4.2 ± 1.1 b1 5.5 ± 0.6 d1 9.7 ± 0.9 e2 11.7 ± 0.6 a2 PLA + 4A (0.8g+1g) B3 2.8 ± 0.3 ab1 3.3 ± 0.2 ab12 4.7 ± 1.0 b2 5.0 ± 0.5 d2 * means followed by the same lower case letter in column, numbers between times, are not statistically 122 Table A4. 16 . Amount of carbon dioxide (mL) adsorbed by coated film samples prepared using different coating solutions and different coating bars at four different time s. mL CO 2 2 days week 2 weeks 3 weeks PLA + PLA (1g) B3 1.7 ± 1.4 a1* 4.5 ± 0.5 a2 3.0 ± 2.6 a12 4.6 ± 2.5 a1 PLA+ CL (1g + 0.3g) B8 5.5 ± 1.5 a1 7.0 ± 0.9 a1 13.1 ± 0.0 ab2 23.6 ± 1.8 ab3 PLA + CL (0.2g+1g) B2 6.7 ± 1.3 ab1 9.2 ± 1.0 ab1 17.5 ± 2.0 ac2 28.1 ± 1.6 a3 PLA + CL (0.2g+1g) B3 10.6 ± 1.3 b1 22.2 ± 2.1 c2 31.0 ± 2.3 d3 41.2 ± 1.7 c4 PLA+ 4A (1g + 0.3g) B8 6.5 ± 2.0 ab1 11.2 ± 0.5 bd2 19.7 ± 2.0 ce3 28.9 ± 2.1 a4 PLA + 4A (0.2g+1g) B2 7.1 ± 1.8 ab1 7.3 ± 1.7 a1 16.0 ± 0.6 abc2 21.8 ± 2.3 b3 PLA + 4A (0.2g+1g) B3 10.4 ± 2.6 b1 13.6 ± 1.6 d1 24.2 ± 2.1 e2 29.3 ± 1.6 a2 PLA + 4A (0.8g+1g) B3 7.0 ± 0.8 ab1 8.2 ± 0.4 ab12 11.7 ± 2.4 b2 12.5 ± 1.2 d2 * means followed by the same lower case letter in column, numbers between times, are not statistically 123 REFERENCES 124 R E F E R E N C E S 1. Coloma A., Rodriguez F.J., Bruna J.E., Guarda A., Galotto M.J. Development of an Active Film with Natural Zeolite as Ethylene Scavenger , Journal of the Chilean Chemical Society 2014 (49) 2409 - 2414 2. Yuzay I. E., Auras R., Selke S. Poly(lactic acid) and Zeolite Composites Prepared by Melt Processing: Morphological and Physical Mechanical Properties , Journal of Applied Polymer Science 2009 (115) 2262 2270 3. Yuzay, I. E., Auras R., Soto - Valdez H., Selke S. Effects of synthetic and natural zeolites on morphology and thermal degradation of poly(lactic acid) composites , Polymer Degradation and Stability 201 0 (95) 1769 1777 4. Domenek S., Courgneau C., Ducruet V. Characteristics and Applications of PLA in Kalia S., Averous L. (ed.) Biopolymers: Biomedical and Environmental Applications (183 - 223) Wiley - Scrivener 2011 5. Almenar E., Auras R. Permeation, sorption, and diffusion in poly(lactic acid) in Auras R., Lim L. - T., Selke S., Tsuji H. (ed.) Poly(lactic acid) Synthesis, Structures, Properties, Processing and Applications (155 - 179) John Willey and Sons 2010 125 CHAPTER 5 New active packaging materials made of PLA films coated with solutions of PLA and natural or synthetic zeolites characterized as ethylene and carbon dioxide scavengers 5.1. Introduction One type of a ctive packaging (AP) involves additives incorporated as a part of the packaging material or placed inside of a container to modify or to interact with the headspace and extend product shelf life. It is very important in fresh produce packaging. The m ain purpose of many AP systems is to extend the shelf life of fresh produce while preventing loss of nutritional quality and freshness, and at the same time inhibit the growth of pathogens. The market for active packages has been growing in the last several decades [1 - 3]. Until now, the m ost popular way of creating an active packaging system was to place additives in the form of a sachet inside of a package. Sachets may not be the safest due to the danger of being eaten or ruptured and allowing active components to contact the food. The ne wer option is to incorporate active elements directly into the material or on the surface of it [1 - 3]. Ethylene is a plant hormone that accelerates ripening and senescence of climacteric fruits and vegetables by increasing their respiration rate. It is a colorless gas which is produced by plants as they ripen. Too high levels of ethylene during storage can shorten shelf life and also produce physiological defects of the harvest. Even a very low concentration of ethylene, at the level of parts per billion ( ppb) and parts per million (ppm), can be critical [4 - 7]. Although high levels of CO 2 in the headspace might be beneficial in many cases (slow down respiration and lipid oxidation, reduce color change, inhibit growth of molds, yeasts and bacteria), 126 excessi ve concentrations of CO 2 inside the package might reduce the pH of the product, which will result in development of an acid taste or cause flavor tainting and drip loss. Also if the wrong packaging material is used, especially with high respiration classes of perishables, there is a danger of blowing up the package by excessive package expansion [4]. Zeolites are crystalline aluminosilicates of alkali and alkaline earth elements. They are characterized by unique three - dimensional framework structures compo sed of SiO 4 and AlO 4 . Within zeolites, we can differentiate types based on the framework structure. Many zeolites are also modified by exchanging cations, in order to increase their specific activity. Zeolites have been commonly used for a variety of purpo ses, including gas separation, gas adsorption, antimicrobials, removal of odors, etc. [6 - 7]. Zeolites have been successfully used as C 2 H 4 and CO 2 scavengers. They have also been used to produce polymer/zeolite films and their adsorption capacities have bee n investigated. Polymers commonly mixed with zeolites include LDPE, HDPE, PP, PC, and PS [1,5,11]. Poly(lactic acid) is a biobased polymer , which can be obtained from renewable resources like corn, potato or sugar beets. Its high cost of production used to limit its application as a packaging material in general. But as the cost has been continuing to decrease, PLA is more and more used. Nowadays it is commercially used as a retail package in the form of clamshell containers, thermoformed foam trays or po uches made of film. With growing public concern about eliminating petrochemical based polymers from the food industry, PLA has become a material of interest [8 - 9]. PLA is a good barrier to CO 2 , O 2 , and ethanol but a poor barrier to H 2 O [9]. This is why if PLA is to be used as an active packaging material, it has to be modified. It has been proved that PLA/zeolite composite materials can be produced by melt processing without compatibilizers [10]. 127 The objective of this study wa s to determine how well newly developed PLA films coated with PLA/zeolite solutions can be used as ethylene and carbon dioxide scavengers in conditions relevant to fresh produce. 5.2. Experimental 5.2.1. Materials 5.2.1.1. Zeolites and gases Synthetic type 4A and natural clino ptilolite, and ethylene and carbon dioxide, as described in chapter 3 . 5.2.1.2. Poly(lactic acid) PLA was used in two different forms - pellets and film , as described in chapter 4 . 5.2.1.3. Commercial bags Two commercial materials were chosen for compar ison, PeakFresh (PeakFresh Produce Bags, Australia) and Green bags (Evert - Fresh Corporation, Katy, TX, US). 5.2.2. Bar coating A multicoater (RK K303, United Kingdom) was used as described in chapter 4. For CL the coating solution contained 0.2 g of PLA, 1 g of zeolite and bar no. 3 was used for distributing it on the polymer surface, while for type 4A the coating solution was composed of 1 g of PLA mixed with 0.3 g of zeolite and coated with bar no. 8. 128 Coated film s were dried in air and kept overnight in a desiccator before testing. 5.2.3. Ads orption measurements Gas Chromatography with Flame Ionization Detector (GC FID) and Gas Chromatography with Thermal Conductivity Detector (GC TCD) were used to quantify C 2 H 4 and CO 2 , as described in chapters 3 and 4. To validate if acetone was still present in the PLA films coated with PLA/zeolite solutions (PLA/zeolite coated films in short) the headspace of PLA/coated film was injected into GC FID equip p ed with an HP - The s ame was done with headspace coming from a bottle of acetone. Retention time for acetone wa s 2.1 min. Three replicates of each sample type were measured. Calibratio n curves for C 2 H 4 , CO 2 , O 2 and N 2 are in appendix in chapter 3 . 5.2.4. Desorption measurements For the purpose of reusing samples, desorption studies were carried out . After adsorption studies were completed , film samples were placed into new jars with n o headspace gases present (C 2 H 4 or CO 2 A s econd set of desorption jars involved the same handling of the 5.2.5 . Sample preparation Some standard samples were chosen to compare performance of investigated PLA films coated with the two types of zeolites. An empty jar flushed with the same gases as all the other samples was used as a control. The designation PLA indicates a piece of film cut from the same roll as the coated 129 films. 2PLA denotes film prepared by coating PLA with a coating solution that contained PLA but no zeolite. PLA+CL and PLA+4A denote films coated with natural and synthetic zeolites, respectively. Commercial films chos en for evaluation were Green Bags and Peakfresh bags, both made of LDPE and zeolites. Standard neat LDPE film was evaluated for comparison. For the adsorption/desorption experiments, films were cut into the same size samples (17.5 x 8 cm) , stapled on end to prevent rolling, and placed into 250 m L glass jars with metal closures. For filling and sampling purposes, holes were drilled in the lids and septa made of gray butyl rubber were inserted. The headspace was flushed with both gases ( C 2 H 4 and CO 2 ). For the adsorption/permeation experiments, samples were cut into circles of 10 cm diameter and placed into the middle of 150 mL permeation cells. The permeation cells were divided into two separate compartments by placing the film in between. The bottom of the cells was flushed with C 2 H 4 (500 ppm in N 2 ) for 30 seconds, while the top was left containing room air. The coated side of the film was exposed to the flushed side of the cell. Septa placed on the sides of the cells were used for sampling purposes. In an attempt to obtain permeability data, gas concentrations in two of the four available cells were measured at selected times (K1 and K4), the same as with the jars (2, 7, 14 and 21 days). Two cells were measured only during the first and last week (K2 and K3 ) to avoid any leakage that might be associated with repeated measurements. PLA coated films were prepared according to the same method as before. Two cells contained CL coated films (K3 and K4), and the remaining two contained 4A coated films (K1 and K2). assure 100% relative humidity. Adsorption measurements w ere carried out at set intervals: after 48 hours, one, two and three weeks for all samples. 130 Adsorption measurements carried out in jars had three replicates of each sample type, while measurements done in permeation cells were performed in single cells. R esults for C 2 H 4 are presented as %, ppm and nL ; those for CO 2 are given in % and mL. Calibration cu rves can be found in appendix in chapter 3 5.2. 6 . Characterization of produced films 5.2.6.1. Thermogravimetric Analysis (TGA) A TGA Q50 (TA Instruments , New Castle DE, US ) was used to determine the % content of zeolite in coated PLA films , as described in chapter 4. 5.2.6.2. Differential Scanning Calorimetry (DSC) A DSC Q100 (TA Instruments , New Castle DE, US ) was used to determine the glass transition te mperature (T g ), melting temperature (T m m ). Between 5 and 10g of sample were heated from N 2 flow of 70mL/min. The degree of crystallinity (X c ) of all samples was calculated using equation 5.1. (5.1) where m c and X PLA are melting enthalpy, crystallization enthalpy and PLA content, respectively. 93.1 J/g is the literature value for the melting enthalpy for 100% crystalline PLA [12]. 5.2.6.3. Scanning Electron Microscopy (SEM) A scanning electron microscope (Carl Zeiss Variable Pressure SEM EVO LS2 , Germany ) was used to determine the particle size of the zeolites and their size and distribution on the PLA surface. To 131 prevent PLA melting under the electron beam, the sample holder was cooled down to - measurements. Images were acquired with an acceler ating voltage of 20 kV and a working distance of 10 mm at 6 k and 11 k x magnification. 5.2.6.4. Tensile Testing An Instron Universal Testing Machine (Model 5567 , Instron, Norwood, MA, US ) was used to test the tensile properties of the PLA/zeolite films. ASTM D 882 (2002) was followed as a standard test method for determination of tensile properties of plastics in the form of thin sheeting. 5.2.6.5. Fourier Transform Infrared Spectroscopy (FTIR) A Shimadzu IRPrestige - 21 spectrometer (Shimadzu, Japan) was used in the attenuated total reflection mode to examine the surface structure of PLA films coated with clinoptilolite and type 4A zeolite. Spectra were collected at a 4cm - 1 resolution, a scan rate of 40 and wavenumber 400 - 4000 cm - 1 . Exactly the same s amples were used for measurements after ad sorption tests were completed and they were remeasured after overnight degassing in vacuum oven at room temperature. 5.2. 7 . Statistical methods Analysis of variance (ANOVA) was performed in the analytical software SPSS version 22 (SPSS Inc., Chicago, IL, US). Means were separated using the Tukey honestly significant difference (HSD) test (p < 0.05). 132 5.3. Results and discussion 5.3.1. Adsorption measurements All % results were normalized to mass as in the equation 5. 2 below: (5. 2 ) For pp m results, they were normalized as in equation 5. 3 : (5. 3 ) While volume results (nL, mL) were normalized according to equation 5.4. (5.4) Figures 5.1 - 5.3 compare C 2 H 4 ad sorption of all tested materials in % of total concentration of C 2 H 4 in the jar and specific ppm and nL c orresponding to those concentrations. It is apparent that there was no significant difference between the co ntrol, PLA, 2PLA, LDPE and Peakf resh samples for any of th e times investigated (p > 0.05) . Only the G reen bags have ad sor p tion comparable to the PLA /zeolite materials. There is no significant difference between any of three materials ; CL and 4A coatings on PLA gave similar results of C 2 H 4 ad sorption to commercial G reen bags (p > 0.05) . Supporting data for this chapter can be found in appendix below. 133 Figure 5 . 1 . Amount of ethylene (%) adsorbed by commercial and coated films and values for control at Figure 5 . 2 . Amount of ethylene (ppm) absorbed by commercial and coated films and values for control 0 2 4 6 8 10 12 14 16 control PLA 2PLA PLA+CL PLA+4A LDPE Green bags PeakFresh adsorbed ethylene [%]/g zeolite 2 days 7 days 14 days 21 days 0 5 10 15 20 25 30 35 40 control PLA 2PLA PLA+CL PLA+4A LDPE Green bags PeakFresh adsorbed ethylene [ppm]/g zeolite 2 days 7 days 14 days 21 days 134 Figure 5. 3 . Amount of ethylene (nL) absorbed by commercial and coated films and values for control Looking at a similar set of data (figure s 5. 4 - 5.5 ), this time measuring CO 2 ad sorption, superior performance of the new - coated fi lms can be observed. Starting with the initial measurement after 48 hours of flushing the jars with both gases, both zeolites significantly increased the ad sorption capacities of the PLA (p < 0.05) . Again most control samples showed no signif icant ad sorpti on (p > 0.05) , except for the G reen bags (p < 0.05) . There was also a noticeable increase in ad sorption in the 4A coated material after 2 weeks (p < 0.05) , showing that the PLA coating may be causing a delay in reaching the total ad sorption capacity of the synthetic zeolites. The higher PLA content in the coating solution for the 4A material and the higher thickness of the final film (2 mils compared to 1.7 mils for CL coated and 1.6 mil s for neat PLA film), may explain that result, especially since PLA is known for its good barrier properties towards C 2 H 4 (6.8·10 - 18 m 3 m/m 2 s Pa) [13]. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 control PLA 2PLA PLA+CL PLA+4A LDPE Green bags PeakFresh adsorbed ethylene [nL]/g zeolite 2 days 7 days 14 days 21 days 135 Figure 5 . 4 . Amount of carbon dioxide (%) adsorbed by commercial and coated films and values for contro Figure 5. 5 . Amount of carbon dioxide (mL) adsorbed by commercial and coated films and values for 0 2 4 6 8 10 12 control PLA 2PLA PLA+CL PLA+4A LDPE Green bags PeakFresh adsorbed carbon dioxide [%]/g zeolite 2 days 7 days 14 days 21 days 0 5 10 15 20 25 30 control PLA 2PLA PLA+CL PLA+4A LDPE Green bags PeakFresh adsorbed carbon dioxide [mL]/g zeolite 2 days 7 days 14 days 21 days 136 A similar set of materials was used for testing in more realistic fresh produce 100% RH (figures 5.6 - 5.8) . The presence of water could be responsible for the higher ad sorption capacities measured for both gases for all investigated cases. It is suspected that C 2 H 4 and CO 2 were soluble in t he deionized water used to fill the small vials in the jars, evidenced by the apparent ad sorption in the control jars. Only three materials had noticeably higher C 2 H 4 ad sorption (p < 0.05) . These are again PLA films coated with synthetic and natural zeolit es and G reen bags. Although there were no significant differences between the samples for the first two time periods, 2 and 7 days (p > 0.05) , there was a significant difference for the last two samplings at 2 and 3 weeks (p < 0.05) . In chapter 3 it was sh own that presence of H 2 O molecules inhibited adsorption of C 2 H 4 in CL and caused desorption of initially adsorbed C 2 H 4 in 4A. In the coated films the situation was the opposite in the presence of H 2 O there was no desorption of adsorbed gases, moreover adsorption continue d until the experiment was stopped. All of this wa s likely due to presence of the polymer in the samples . A dsorption of C 2 H 4 in both powder zeolites decreased when the temperature was decreased, while in coated films it actually increas ed , although in general increase in temperature increases permeability of polymers. Figure 5 . 6 . Amount of ethylene (%) adsorbed by commercial and coated films and values for control at 0 5 10 15 20 25 30 control PLA 2PLA PLA+CL PLA+4A LDPE Green bags PeakFresh adsorbed ethyene [%]/g zeolite 2 days 7 days 14 days 21 days 137 Figure 5 . 7 . Amount of ethylene (ppm) adsorbed by commercial and coated films and values for control nd 100% RH. Figure 5. 8 . Amount of ethylene (nL) adsorbed by commercial and coated films and values for control A little different situation can be noticed for the CO 2 ad sorption data (fig ure s 5. 9 - 5.10 ). Already within the first week, the experimental PLA film s coated with zeolites and the G reen bags had superior 0 10 20 30 40 50 60 70 80 control PLA 2PLA PLA+CL PLA+4A LDPE Green bags PeakFresh adsorbed ethylene [ppm]/g zeolite 2 days 7 days 14 days 21 days 0 0.5 1 1.5 2 2.5 3 3.5 4 control PLA 2PLA PLA+CL PLA+4A LDPE Green bags PeakFresh adsorbed ethylene [nL]/g zeolite 2 days 7 days 14 days 21 days 138 performance compared to any other samples (p < 0.05) . As expected from previous experiments carried out with only zeolites present in the jars, t he initial high ad sorption became steady over time, indicating that low temperature and high relative humidity limit the CO 2 ad sorption capacities of the zeolites in any material in which they are incorporated. Figure 5 . 9 . Amount of carbon dioxide (%) adsorbed by commercial and coated films and values for 0 2 4 6 8 10 12 14 16 18 20 control PLA 2PLA PLA+CL PLA+4A LDPE Green bags PeakFresh adsorbed carbon dioxide [%]/g zeolite 2 days 7 days 14 days 21 days 139 Figure 5. 10 . Amount of carbon dioxide (mL) adsorbed by commercial and coated films and values for H. The producers of the commercially available films advertised them as reusable packaging materials. Following the same thinking, two of the previously tested films, each with different zeolites, along with one of the commercial films that showed simila r ad sorption capacities, were reused. Prior to the ad and kept in a desiccator prior to testing. And finally, the same testing conditions were applied as when they were tested the first time( the same jars, same gases and environmental conditions). C 2 H 4 and CO 2 The results presented in figures 5. 11 - 5. 13 show that for most investigated samples, the ad sorption capacity did not change. Also, the rate of ad sorption was similar since the % changes at equal times were very similar. Natural zeolite (CL) had no significant differences within the first three measu rements. Only the last measurement, after three weeks, showed a significant increase for the used material. It is suspected that degassing in the vacuum oven removes more of the H 2 O than keeping 0 5 10 15 20 25 30 35 40 45 50 control PLA 2PLA PLA+CL PLA+4A LDPE Green bags PeakFresh adsorbed carbon dioxide [mL]/g zeolite 2 days 7 days 14 days 21 days 140 the material in the desiccator right after production. Moistu re might be getting into the zeolites during the coating process and cannot be removed without degassing in vacuum oven. There is no doubt these PLA/zeolite films can be reused. Very similar situations can be observed for the synthetic zeolite (4A) and th e commercial films. There were no significant differences for the 2, 7 and 14 day measurements (p < 0.05) with a significant increase in ad sorption at 3 weeks (p > 0.05) . The explanation seems to be the same as in the case of clinoptilolite. Figure 5 . 11 . Amount of ethylene (%) adsorbed by the same commercial and coated films and values and 0% RH. 0 2 4 6 8 10 12 14 16 18 control 1st control 2nd PLA+CL 1st PLA+CL 2nd PLA+4A 1st PLA+4A 2nd Green 1st Green 2nd adsorbed ethylene [%]/g zeolite 2 days week 2 weeks 3 weeks 141 Figure 5 . 12 . Amount of ethylene (ppm) adsorbed by the same commercial and coated films and values and 0% RH. Figure 5. 13 . Amount of ethylene ( ppm ) adsorbed by the same commercial and coated films and values and 0% RH. As for CO 2 , different observations can be drawn from figure s 5. 14 and 5.15 . The natural zeolite and the commercial film had similar ad sorption capacities for both uses. There was no significant 0 5 10 15 20 25 30 35 40 control 1st control 2nd PLA+CL 1st PLA+CL 2nd PLA+4A 1st PLA+4A 2nd Green 1st Green 2nd adsorbed ethylene [ppm]/g zeolite 2 days week 2 weeks 3 weeks 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 control 1st control 2nd PLA+CL 1st PLA+CL 2nd PLA+4A 1st PLA+4A 2nd Green 1st Green 2nd adsorbed ethylene [ppm]/g zeolite 2 days week 2 weeks 3 weeks 142 difference between the first and second use at any time point (p < 0.05) , while the synthetic zeolite (4A) seemed to be losing its ad sorption capacity when reused (p > 0.05) . This could be due t o stronger interactions between the type 4A zeolite and CO 2 than was observed for the natural zeolite and commercial film. Probably degassing in vacuum oven did not remove all the previously ad sorbed CO 2 and H 2 O, which limited the ad sorption capacity when r eusing the film. Figure 5 . 14 . Amount of carbon dioxide (%) adsorbed by the same commercial and coated films and values for control, used first time after coating and second time after drying, at four sampling times at 0 2 4 6 8 10 12 control 1st control 2nd PLA+CL 1st PLA+CL 2nd PLA+4A 1st PLA+4A 2nd Green 1st Green 2nd adsorbed carbon dioxide [%]/g zeolite 2 days week 2 weeks 3 weeks 143 Figure 5. 15 . Amount of carbon dioxide (mL) adsorbed by the same commercial and coated films and values for control, used first time after coating and second time after drying, at four sampling times at Figures 5 .1 - 5 .1 8 present data collected at roo m temperature, while f igures 5 .1 9 - 5 . 21 present C 2 H 4 ad sorption taking place at room temperature showed a steady increase in ad sorption for both zeolites during the first two weeks of the experiment. A higher increase was noted for the synthetic zeolite at 3 weeks. This could be explained again by more PLA covering and blocking the type 4A zeolite from reaching its maximum ad sorpt ion capacity. 0 5 10 15 20 25 30 control 1st control 2nd PLA+CL 1st PLA+CL 2nd PLA+4A 1st PLA+4A 2nd Green 1st Green 2nd adsorbed carbon dioxide [mL]/g zeolite 2 days week 2 weeks 3 weeks 144 Figure 5 . 1 6 . Amount of ethylene (%) adsorbed by coated films in permeation cells at four sampling Figure 5 . 1 7 . Amount of ethylene (ppm) absorbed by coated films in permeation cells at four sampling 0 2 4 6 8 10 12 14 4A (K1) 4A (K2) CL (K3) CL (K4) adsorbed ethylene [%]/g zeolite 2 days 7 days 14 days 21 days 0 10 20 30 40 50 60 4A (K1) 4A (K2) CL (K3) CL (K4) adsorbed ethylene [ppm]/g zeolite 2 days 7 days 14 days 21 days 145 Figure 5. 18 . Amount of ethylene (nL) absorbed by coated films in permeation cells at four sampling What is interesting when looking at a similar experiment carried out at low temperature (figures 5.12 - 5.13), is that C 2 H 4 ad sorption wa s higher but also grew more steadily with time than at room temperature. Again, two types of cells, those measured periodically and just at the beginning and end, showed very similar results for both zeolites, which means the conditions were repeatable . Also, even a small amount of water ca n have a large impact on the ad sorption capacities of both zeolites. Water seems to work as a competitive molecule to C 2 H 4 and CO 2 (figures 5.6 - 5.9) . There is no similar set of con di tions in the experiments reported in chapter 3 to compare to these data, so it cannot be stated how lowering temperature influence adsorption in zeolites when used as fine powders versus when they we re incorporated onto the PLA film. 0 0.5 1 1.5 2 2.5 3 4A (K1) 4A (K2) CL (K3) CL (K4) adsorbed ethylene [nL]/g zeolite 2 days 7 days 14 days 21 days 146 Figure 5 . 1 9 . Amount of ethylene (%) adsorbed by coated films in permeation cells at four sampling Figure 5 . 20 . Amount of ethylene (ppm) adsorbed by coated films in permeation cells at four sampling 0 5 10 15 20 25 30 35 40 4A (K1) 4A (K2) CL (K3) CL (K4) adsorbed ethylene [%]/g zeolite 2 days 7 days 14 days 21 days 0 20 40 60 80 100 120 140 160 180 4A (K1) 4A (K2) CL (K3) CL (K4) adsorbed ethylene [ppm]/g zeolite 2 days 7 days 14 days 21 days 147 Figure 5. 21 . Amount of ethylene (nL) adsorbed by coated films in permeation cells at four sampling As found in the literature, the adsorption isotherms for C 2 H 4 and CO 2 in clinoptilolite have a classic isotherm form (type II) as is characteris tic for adsorbents with a wide range of pore sizes, such as natural zeolites. These isotherms are observed when adsorbate molecules are small enough to enter the zeolite micropore systems. Literature kinetic diameters of CO 2 (3.3 Å) and C 2 H 4 (3.9 Å) are bo th smaller than the average pore radius measured in clinoptilolite (5.5 ± 0.8 Å), which was actually larger than literature reports (3.5 Å) [ 22 - 23 ]. This allows both gases to get inside the cages and cavities in the zeolite framework. P hysisorption taking place inside zeolites resulted in higher adsorption energy and low er adsorption rate than if it occurred only on the external surface [6 - 7, 18 ]. For t ype 4A zeolite , the adsorption isotherm for CO 2 also has the characteristic type II shape while the one for C 2 H 4 has the type I shape and follows Henry's law. Again comparing pore openings in 4A measured by Q uantachrome and listed in chapter 3 (2. 3 ± 0. 7 Å) to those found in literature (4 Å) shows that the actual pore radius was much smaller , probably due to different cations occupying the corner sites in cavities and cages resulting in channel size reduction . This could result in all physisorption happening on the external surface of the zeolite and be characterized by low adsorption energy and high adsorpti on rate [19 - 20]. All of the above 0 1 2 3 4 5 6 7 8 9 4A (K1) 4A (K2) CL (K3) CL (K4) adsorbed ethylene [nL]/g zeolite 2 days 7 days 14 days 21 days 148 supports the experimental results. Water having the smallest kinetic diameter of all investigated gases (2.65 Å) makes it even easier for H 2 O to enter the pores in clinoptilolite and block adsorption sites for C 2 H 4 and CO 2 , while it is often too large for 4A zeolite pores and this is why the effect of water is not as critical to ad sorption as in the case of the natural zeolite. Decreased ad sorption of C 2 H 4 when compared to CO 2 could be due to lower polarizability associ ated with smaller ionic radius [21 , 2 3 ]. Injection of samples of the headspace into the GC FID in order to determine if there wa s any acetone content left after coated samples were dried i n air showed small amounts of acetone was present after the film sample s were stored for about two months inside the jar. One way to remove acetone would be to heat the sample , which in case of PLA would not be recommended. PLA is not very heat resistant ; its melting temperatures are between 150 - Although the amount was not quantified, even trace amounts of acetone are not tolerated in food packaging, which means that a different solvent should be investigated if the coating approach is used . 5.3.2. Desorption studies For coated samples after adsorption studies were done, no desorption was noticed, since no significant amounts of C 2 H 4 or CO 2 C. This was the reason for degassing the samples in a vacuum oven before reusing. 5.3.3. Thermal analy sis TGA analysis was performed to determine the percent of zeolites in both the newly developed films and the commercially available ones. For all samples it was observed that coating or impregnation did not result in very uniform distribution of the zeol ites. However, a more uniform distribution was achieved in the experimental samples than in the commercial ones . The data are listed in table 5. 1 and show that the % zeolites in all samples were similar. 149 Table 5 . 1 . Percent of zeolite content in investigate d films measured by TGA. sample % zeolite PLA + CL 3.40 ± 0.40 PLA + 4A 4.4 5 ± 1.44 Peakf resh 3.30 ± 2.1 6 Green bags 4.55 ± 2.9 5 Sample thermograms for zeolite coated films and commercial bags are shown in figure 5.22 . Since coated films are PLA and commercial ones are LDPE there are obvious differences in the thermograms between these two polymers. Both commercial films display similar thermograms, with both having onset temperatures higher than those for coated films for PLA , meaning LDPE is a m ore thermally stable polymer than PLA. Comparing the effect of the coating on PLA shows that the onset temperature of degrad ation of PLA in the 4A sample was Degradation of PLA ended This m eans that PLA coated with 4A had lower thermal stability than PLA coated with CL. 150 Figure 5 . 2 2 . TGA thermograms of two zeolite coated films and two commercial films. To further investigate the influence of zeolite coatings on PLA, DSC analysis was done. The resulting thermograms are shown in figure 5.2 3 , and thermal properties are listed in table 5. 2 . The most obvious difference in the DSC thermograms is that all the s amples except the PLA pellets had two glass transition temperatures and both were higher than the T g of the pellets. On the website for Evlon [14], producer of our PLA film, it can be found that the one side heat sealable polylactide film is composed of th ree parts: the PLA treated surface, the PLA sealant layer and the PLA core. All coatings were applied to the treated surface and their interaction with PLA might have caused some changes in the first T g and the presence of an apparent second T g . For three of the investigated samples, PLA film, PLA film coated with PLA and PLA film coated with CL, there was no difference between T g values (p < 0.05) . In the case of PLA coated with 4A, the T g value was very close to the PLA pellet T g , and both were significan tly different than those for the other films (p < 0.05) . There was no significant difference between the 151 melting temperatures (T m ) for any of the samples tested (p > 0.05) . But the % crystallinity of the films coated with 4A zeolite was significantly diffe rent than that of all other samples (p < 0.05) , having the lowest crystallinity, except for the pellets having no crystallinity. Changes in T g values can be related to permeabilities of gases. Increase of T g means chain separation and mobility in the polymer chain is decreased which can make it more challenging for C 2 H 4 and CO 2 molecules to pass through PLA and get close to the zeolites. Within all film samples, PLA coated with 4A ha d the lowest T g , and this is in accord with those materials being ofte n the most effective scavengers of C 2 H 4 and CO 2 . Figure 5 . 2 3 . DSC thermograms (1st cycle) of standard samples and PLA films coated with zeolites. 0 20 40 60 80 100 120 140 160 180 200 heat flow exo [W/g] PLA pellet PLA film 2PLA CL 4A 152 Table 5 . 2 . Thermal properties of investigated PLA films coated with zeolites along with standard samples. sample T g1 T g2 T m m [J/g] %X c PLA pellet 59. 1 ± 0.0 a* - - - 0 PLA film 65. 1 ± 0.1 b 71. 2 ± 0. 2 a 165.8 ± 0. 2 a 35. 7 ± 0.8 ab 38.3 ± 0. 9 a 2PLA 65.1 ± 0. 1 b 71.3 ± 0. 2 a 166.3 ± 0.1 a 36. 1 ± 0.4 a 39.6 ± 0.5 a PLA + CL 6 5.0 ± 0.0 b 71.3 ± 0.1 a 165.8 ± 0.2 a 35. 1 ± 0.3 b 38. 3 ± 0.3 a PLA + 4A 60.4 ± 1.0 c 70.1 ± 0.7 b 165.9 ±0. 2 a 32. 2 ± 0. 2 c 35 .0 ± 0. 2 a * means followed by the same lower case letter in column are not statistically different from each other 5.3.4. FTIR analysis FTIR spectra were recorded to determine whether or not C 2 H 4 was absorbed on the zeolite coated films. The FTIR spectra of the same films exposed to C 2 H 4 and after degassing after ad sorption were compared. Different peaks observed for the differing zeolites suggest that ad sorption happened differently depending on the zeolite involved. Recorded spectra were compared to literature spectra fo r C 2 H 4 [15 - 16]. Figure s 5.2 4 a and b shows the effects in CL coated film s . The intensive absorption band at 1000 cm - 1 is even more intense when C 2 H 4 is present (figure 5.2 4 b) , which could suggest that it is resulting from the CH 2 twist in the C 2 H 4 molecules . This suggests that C 2 H 4 molecules are free to twist which can be possible more on the external surface of the zeolite than inside pores and cavities. 153 Figure 5 . 2 4 . FTIR spectra of PLA film coated with clinoptilolite, after ad sorption of ethylene and after degassing. 60 65 70 75 80 85 90 95 100 105 110 600 1100 1600 2100 2600 3100 %T wavenumber [cm - 1 ] CL no eth CL eth a 55 60 65 70 75 80 85 90 95 900 1000 1100 1200 %T wavenumber [cm - 1 ] CL no eth CL eth b 154 Figure 5.2 5 (a - d) shows what happened in the type 4A coated PLA film s . Here the opposite situation was observed; the absorption band right after 1000 cm - 1 decreased in the presence of C 2 H 4 (figure 5.2 5 d) , meaning that C 2 H 4 limited the stretching of the Si - O and Al - O bonds belonging to the SiO 4 and AlO 4 tetrahedra, which are associated with those bands [17]. Also , new absorption peaks at 1200 cm - 1 and 1300 cm - 1 appeared in the spectra of the exposed sample (figure 5.25 c) , whic h could be attributed to CH 2 rock and CH 2 scissor vibrations in the C 2 H 4 molecules, respectively. The increased intensity of the 1700 cm - 1 peak could be explained by the C - C stretch in the C 2 H 4 molecules (figure 5.2 5 b) . Relatively high intensity changes in some peaks in the case of both zeolite coated films might suggest that C 2 H 4 molecules are adsorbed rather than absorbed, due to their possible movements and limiting movements of zeolites, since the pore openings in the zeolites are very close to the size of the C 2 H 4 molecules. 155 Figure 5 . 2 5 . FTIR spectra of PLA film coated with type 4A zeolite, after ad sorption of ethylene and after degassing. 5.3.5. Mechanical characterization Results for the mechanical properties of the uncoated and coated samples are provided in table 5. 3 . Data were recorded for the samples in the machine direction (MD) and cross machine direction 80 85 90 95 100 105 110 600 1100 1600 2100 2600 3100 %T wavenumber [cm - 1 ] 4A no eth 4A eth a 90 95 100 105 110 1650 1750 1850 %T wavenumber [cm - 1 ] b 85 90 95 100 105 1000 1200 1400 %T wavenumber [cm - 1 ] c 80 85 90 95 100 800 900 1000 1100 %T wavenumber [cm - 1 ] d 156 (CD). In general, most mechanical properties of the PLA film changed with coating, having different change s associated with diff erent coating solution composition s . Tensile strength in all cases but one (PLA coated with PLA in CD) decreased, with the lowest values for the 4A coatings, and the highest for the PLA coating. A decrease in the modulus of elasticity, break strength, and tensile stress at yield was observed for all samples. The maximum load was the only property that was not changed with coating (p > 0.05) , while elongation at break was the only one that increased with coating, being highest for 4A and lowest for PLA coati ng. These changes could be due to the different characteristic s of the materials involved. PLA is hydrophobic and the zeolites are hydrophilic. The coating made PLA films less breakable (due to lower values of energy to break) and more flexible. 157 Table 5 . 3 . Tensile properties of standard samples and PLA films coated with zeolites. sample tensile strength [MPa] elongation at break [%] modulus of elasticity [GPa] maximum load [N] break strength [MPa] energy to break [in - lbf/in 3 ] extension at yield ( zero slope) [mm] tensile stress at yield (zero slope) [MPa] MD PLA 143. 3 ± 5. 2 a* 55.5 ± 2. 5 a 5.0 ± 0.1 a 93.7 ± 1.0 a 90. 1 ± 33.3 ab 577.7 ± 273.8 a 3.9 ± 0.1 a 134.4 ± 24.7 a 2PLA 100.6 ± 24.7 bc 124.4 ± 1.4 de 3.2 ± 0. 6 a 87.1 ± 3. 3 a 81.9 ± 19.6 a 1362. 9 ± 260.9 de 7.0 ± 0. 3 b 92.5 ± 23. 4 b PLA + CL 84. 7 ± 2.2 bd 103. 5 ± 25. 9 cd 3. 1 ± 0. 1 a 92. 9 ± 2.4 a 65. 1 ± 4. 1 a 807.6 ± 260. 4 ab 4. 1 ± 0. 2 7 a 84. 7 ± 2.2 b PLA + 4A 71.2 ± 1.9 cd 141.6 ± 5.3 e 2.6 ± 0. 1 a 91.9 ± 2. 5 a 67. 3 ± 6. 4 a 1010.0 ± 42. 2 bcd 4. 5 ± 0. 1 a 70.7 ± 1. 5 b CD PLA 180. 2 ± 10. 5 e 75.8 ± 4.2 ab 6.8 ± 0.3 b 116. 3 ± 6. 8 a 175.1 ± 20.0 c 1300.6 ± 100. 1 cde 3.0 ± 0. 1 a 155.4 ± 1.4 a 2PLA 188.2 ± 7. 5 e 96.4 ± 12.1 bc 6.6 ± 0. 5 b 121.4 ± 4.8 ab 184.6 ± 10. 7 c 1648. 7 ± 198.8 e 3. 1 ± 0.2 a 150.2 ± 2. 8 a PLA + CL 116. 4 ± 4. 2 c 88.0 ± 4.5 bc 4. 1 ± 0. 2 a 127. 7 ± 4.6 b 116. 9 ± 4.0 b 95 9.0 ± 36. 7 bc 2.9 ± 0. 1 a 91.8 ± 2.0 b PLA + 4A 96.6 ± 3. 7 bc 95. 4 ± 8.4 bc 3.3 ± 0.2 a 124. 7 ± 4.7 ab 94. 2 ± 3. 9 ab 827. 1 ± 59.4 ab 3.9 ± 0. 2 a 76. 3 ± 1.4 b * means followed by the same lower case letter in column are not statistically different from each other (Tukey, 158 5.3.6. Surface characteristics SEM images of the zeolite - coated films were taken to help understand if there might be any surface reasons for aff ecting ad sorption in these films. Figures 5. 26 and 5. 27 show how differently the coated surfaces appeared, depending on the type of zeolite. Clinoptilolite blended very well with PLA and formed a uniform layer on the surface of the PLA film with almost no uncovered spaces, while type 4A zeolites formed cluster s of particl es. The images show how uniformly the zeolites were dispersed throughout the surface and also how much the zeolite molecules were covered by the PLA. Those images are in concordance with the previously discussed ad sorption capacities and behavi or of the investigated films. CL was more exposed to the headspace gases and so the ad sorption was not as much influenced by PLA as in the case of 4A. Cubic 4A molecules were not only blocked by the PLA but also by other 4A molecules, so ad sorption of C 2 H 4 and CO 2 did not occur as fast as in CL. Figure 5 . 26 . SEM images of PLA films coated with clinoptilolite. 159 Figure 5 . 27 . SEM images of PLA films coated with type 4A zeolite. 5.4. Conclusions Zeolite coatings allowed PLA films to be successful C 2 H 4 and CO 2 scavengers in two sets of conditions for packing of fresh produce The lat t er is the more relevant to commodities and it was showed that lowerin g temperature actually increased adsorption of both gases, by a factor o f 2 for C 2 H 4 and by a few percent for CO 2 . One of the commercial films did not appear to work, while the other one was comparable to the coated films in sorption capacities and %wt zeolite content . There is a possibility of reusing two zeolite coated films in the same manner and efficiency as the commercial Green bags. Solution coating was more repeatable than commercial impregnation with zeolites, as the stan d ard deviations of the %wt of zeolites were smaller. SEM images showed that there is a better distr ibution of CL coating than 4A which , as show n in the adsorption measurements , greatly improve d the sorption capacities of the resulting films. The r mal and tensile properties were not greatly affected by the zeolite coatings. 160 While the mechanism of action of the zeolites as gas scavengers is still not fully known, PLA films coated with zeolites show promise in providing a new biobased and biodegradable alternative to commercially available bags and should be further investigate d . 161 APPENDIX 162 Table A5 . 1 . Amount of carbon dioxide (%) adsorbed by commercial and coated films and values for % CO 2 2 days 7 days 14 days 21 days C ontrol 0.7 ± 0.5 aA* 0.8 ± 0.5 aA 1.8 ± 0.6 aA 1.2 ± 0.1 aA PLA 0.6 ± 0.9 aA 1.1 ± 0.7 aA 1.5 ± 0.5 aA 2.4 ± 1.1 abA 2PLA 0.7 ± 0.6 aA 1.8 ± 0.2 aA 1.2 ± 1.1 aA 1.8 ± 1.0 abA CL 1.9 ± 0.7 aA 3.5 ± 0.3 bB 5.2 ± 0.6 bC 5.1 ± 0.4 bC 4A 3.1 ± 0.8 bA 4.3 ± 0.8 bA 8.9 ± 0.5 cB 9.9 ± 1.3 cB LDPE 1.2 ± 0.8 aA 1.6 ± 0.5 aA 1.7 ± 0.9 aA 2.2 ± 1.5 abA Green bags 0.4 ± 0.3 aA 1.7 ± 0.1 aA 2.2 ± 1.5 aA 3.9 ± 2.2 abA Peakfresh 1.4 ± 0.6 aA 1.7 ± 0.4 aA 1.9 ± 0.5 aA 2.5 ± 1.5 abA * means followed by the same lower case letter in column, upper case in rows are not statistically Table A5 . 2 . Amount of carbon dioxide (mL) adsorbed by commercial and coated films and values for mL CO 2 2 days 7 days 14 days 21 days C ontrol 1.6 ± 1.2 aA* 2.0 ± 1.3 aA 4.4 ± 1.6 aA 3.0 ± 0.3 aA PLA 1.5 ± 2.3 aA 2.7 ± 1.7 aA 3.9 ± 1.2 aA 5.9 ± 2.9 abA 2PLA 1.7 ± 1.4 aA 4.5 ± 0.5 aA 3.0 ± 2.6 aA 4.6 ± 2.5 abA CL 4.7 ± 1.7 aA 8.8 ± 0.7 bB 13.1 ± 1.6 bC 12.8 ± 1.1 bC 4A 7.7 ± 2.1 bA 10.6 ± 2.1 bA 22.2 ± 1.3 cB 24.6 ± 3.2 cB LDPE 3.1 ± 2.0 aA 3.9 ± 1.2 aA 4.3 ± 2.3 aA 5.6 ± 3.6 abA Green bags 1.1 ± 0.7 aA 4.1 ± 3.1 aA 5.5 ± 3.8 aA 9.8 ± 5.4 abA Peakfresh 3.6 ± 1.4 aA 4.3 ± 1.0 aA 4.7 ± 2.2 aA 6.3 ± 3.7 abA * means followed by the same lower case letter in column, upper case in rows are not statistically 163 Table A5 . 3 . Amount of ethylene (ppm) adsorbed by commercial and coated films and values for control at four ppm eth 2 days 7 days 14 days 21 days C ontrol 3.2± 2.3 aA* 2.5 ± 0.8 aA 3.1 ± 1.6 aA 4.9 ± 1.1 aA PLA 3.3 ± 0.8 aA 1.0 ± 1.3 aA 3.1 ± 1.5 aA 4.8 ± 4.2 aA 2PLA 1.3 ± 0.8 aA 2.2 ± 1.5 aA 5.4 ± 2.4 aAB 8.2 ± 2.6 aB CL 5.3 ± 1.5 aA 8.6 ± 1.6 bA 13.2 ± 0.8 bB 22.8 ± 0.5 bC 4A 4.2 ± 1.1 aA 10.7 ± 1.1 bB 13.6 ± 2.7 bB 26.9 ± 6.8 bC LDPE 4.9 ± 1.8 aA 5.6 ± 1.8 aA 6.2 ± 1.6 aA 8.3 ± 0.8 aA Green bags 3.3 ± 0.8 aA 3.0 ± 0.5 aA 11.8 ± 3.6 bB 23.8 ± 8.7 bC Peakfresh 3.0 ± 2.1 aA 0.5 ± 0.5 aA 2.6 ± 0.2 bA 4.1 ± 5.8 aA * means followed by the same lower case letter in column, upper case in rows are not statistically Table A5 . 4 . Amount of ethylene (%) adsorbed by commercial and coated films and values for control % eth 2 days 7 days 14 days 21 days control 1.3 ± 0.8 aA* 1.1 ± 0.4 aA 1.3 ± 0.7 aA 2.1 ± 0.5 aA PLA 1.4 ± 0.1 aA 0.4 ± 0.5 aA 1.3 ± 0.7 aA 2.1 ± 1.9 aA 2PLA 0.5 ± 0.3 aA 1.0 ± 0.7 aA 2.3 ± 1.1 aAB 3.5 ± 1.4 aB CL 2.2 ± 0.5 aA 3.6 ± 0.8 bB 5.5 ± 0.4 bC 9.6 ± 0.4 bD 4A 1.8 ± 0.4 aA 4.5 ± 0.5 bB 5.8 ± 1.4 bB 11.5 ± 3.4 bC LDPE 2.0 ± 0.8 aA 2.3 ± 0.8 aA 2.5 ± 0.7 aAB 3.3 ± 0.5 aB Green bags 1.4 ± 0.1 aA 1.2 ± 0.9 aB 5.1 ± 0.9 bC 10.1 ± 2.2 bD Peakfresh 1.2 ± 0.8 aA 1.2 ± 1.6 aA 3.2 ± 3.6 aA 1.7 ± 2.4 aA * means followed by the same lower case letter in column, upper case in rows are not statistically Table A5.5 . Amount of ethylene (nL) adsorbed by commercial and coated films and values for control nL eth 2 days 7 days 14 days 21 days control 0.2 ± 0.1 aA* 0.1 ± 0.0 aA 0.2 ± 0.1 aA 0.2 ± 0.1 aA PLA 0.2 ± 0.1 aA 0.0 ± 0.1 aA 0.2 ± 0.1 aA 0.2 ± 0.2 aA 2PLA 0.1 ± 0.0 aA 0.1 ± 0.1 aA 0.3 ± 0.1 aAB 0.4 ± 0.1 aB CL 0.3 ± 0.1 aA 0.4 ± 0.1 bB 0.7 ± 0.0 bC 1.1 ± 0.0 bD 4A 0.2 ± 0.1 aA 0.5 ± 0.1 bB 0.7 ± 0.1 bB 1.3 ± 0.3 bC LDPE 0.2 ± 0.1 aA 0.1 ± 0.1 aA 0.2 ± 0.2 aAB 0.3 ± 0.2 aB Green bags 0.2 ± 0.0 aA 0.1 ± 0.1 aB 0.6 ± 0.2 bC 1.2 ± 0.4 bD Peakfresh 0.1 ± 0.0 aA 0.1 ± 0.1 aA 0.2 ± 0.2 aA 0.1 ± 0.1 aA * means followed by the same lower case letter in column, upper case in rows are not statistically 0.05) 164 Table A5 . 6 . Amount of carbon dioxide (%) adsorbed by commercial and coated films and values for % CO 2 2 days 7 days 14 days 21 days control 3.9± 0.4 aA* 4.2 ± 0.9 aA 5.5 ± 1.3 aA 5.5 ± 1.8 aA PLA 2.2 ± 0.6 aA 4.5 ± 0.3 aB 6.0 ± 0.7 aC 5.4 ± 2.9 aC 2PLA 4.2 ± 0.9 aA 4.0 ± 1.0 aA 6.0 ± 1.2 aBC 7.5 ± 1.5 aC CL 9.9 ± 0.5 bA 13.1 ± 1.4 bB 13.3 ± 1.7 bB 14.7 ± 1.4 bB 4A 8.4 ± 0.8 bA 12.1 ± 1.1 bB 13.3 ±1.4 bB 14.3 ± 1.1 bB LDPE 2.4 ± 0.6 aA 4.8 ± 1.6 aB 6.0 ± 2.2 aB 6.2 ± 2.4 aB Green bags 11.4 ± 0.2 bA 9.5 ± 2.1 bA 12.0 ± 1.6 bA 14.4 ± 3.8 bA Peakfresh 3.1 ± 2.0 aA 6.2 ± 2.3 a 5.4 ± 2.7 a 5.8 ± 1.0 aA * means followed by the same lower case letter in column, upper case in rows are not statistically Table A5 . 7 . Amount of carbon dioxide (mL) adsorbed by commercial and coated films and values for mL CO 2 2 days 7 days 14 days 21 days control 9.7 ± 1.0 aA* 10.4 ± 2.2 aA 13.8 ± 3.2 aA 13.9 ± 4.6 aA PLA 5.5 ± 1.6 aA 11.2 ± 0.8 aB 15.1 ± 1.6 aC 13.5 ± 7.2 aC 2PLA 10.5 ± 2.3 aA 9.9 ± 2.5 aA 15.1 ± 2.9 aBC 18.8 ± 3.8 aC CL 24.7 ± 1.3 bA 32.6 ± 3.5 bB 33.2 ± 4.1 bB 36.7 ± 3.6 bB 4A 21.1 ± 2.1 bA 30.3 ± 2.8 bB 33.3 ± 3.4 bB 35.8 ± 2.9 bB LDPE 6.0 ± 1.4 aA 11.9 ± 4.1 aB 14.9 ± 5.4 aB 15.6 ± 6.1 aB Green bags 28.5 ± 0.5 bA 23.7 ± 5.2 bA 30.0 ± 4.0 bA 36.0 ± 9.4 bA Peakfresh 7.8 ± 4.9 aA 15.6 ± 5.7 a 13.6 ± 6.8 a 14.4 ± 2.4 aA * means followed by the same lower case letter in column, upper case in rows are not statistically Table A 5 . 8 . Amount of ethylene (ppm) adsorbed by commercial and coated films and values for and 100% RH. ppm eth 2 days 7 days 14 days 21 days control 11.9 ± 2.1aA* 15.7 ± 1.9 aA 11.1 ± 3.0 aA 13.5 ± 4.1 aA PLA 12.7 ± 4.2 aA 14.8 ± 1.8 aA 18.5 ± 1.9 aB 22.6 ± 3.8 aB 2PLA 14.0 ± 5.4 aA 17.5 ± 3.8 aA 20.2 ± 5.5 aA 18.4 ± 6.0 aA CL 17.2 ± 3.7 aA 23.9 ± 3.2 bA 47.9 ± 3.1 bB 50.7 ± 2.6 bB 4A 16.1 ± 4.4 aA 26.5 ± 8.4 bA 51.2 ± 11.4 bB 55.2 ± 16.6 bB LDPE 12.8 ± 1.3 aA 14.5 ± 0.3 aA 14.9 ± 6.3 aA 17.4 ± 5.3 aA Green bags 11.3 ± 0.6 aA 15.5 ± 1.9 aA 34.7 ± 2.3 bB 40.2 ± 2.1 bB Peakfresh 13.0 ± 2.8 aA 15.1 ± 0.7 aA 19.0 ± 6.3 aA 19.9 ± 8.0 aA * means followed by the same lower case letter in column, upper case in rows are not statistically 165 Table A5 . 9 . Amount of ethylene (%) adsorbed by commercial and coated films and values for control % eth 2 days 7 days 14 days 21 days control 5.4 ± 1.1 aA* 7.1 ± 1.1 aA 5.0 ± 1.4 aA 6.1 ± 2.0 aA PLA 5.7 ± 1.8 aA 6.7 ± 0.6 aA 8.4 ± 0.6 aB 10.2 ± 1.4 aB 2PLA 6.3 ± 2.2 aA 8.0 ± 1.4 aA 9.2 ± 2.1 aA 8.3 ± 2.4 aA CL 7.6 ± 1.3 aA 10.5± 0.9 bB 21.2 ± 0.8 bC 22.4 ± 0.9 bC 4A 6.7 ± 1.3aA 11.0 ± 2.8 bB 21.3 ± 3.0 bC 22.9 ± 5.1 bC LDPE 5.8 ± 0.8 aA 6.6 ± 0.1 aA 6.7 ± 2.6 aA 7.9 ± 2.3 aA Green bags 5.6 ± 0.5 aA 7.8 ± 1.8 aA 17.2 ± 1.2 bB 20.0 ± 3.1 bB Peakfresh 5.6 ± 1.0 aA 6.4 ± 0.3 aA 8.0 ± 2.3 aA 8.4 ± 3.0 aA * means followed by the same lower case letter in column, upper case in rows are not statistically Table A 5 .1 0 . Amount of ethylene (nL) adsorbed by commercial and coated films and values for nL eth 2 days 7 days 14 days 21 days control 0.6 ± 0.1 aA* 0.8 ± 0.1 aA 0.6 ± 0.2 aA 0.7 ± 0.2 aA PLA 0.6 ± 0.2 aA 0.7 ± 0.1 aA 0.9 ± 0.1 aB 1.1 ± 0.2 aB 2PLA 0.7 ± 0.3 aA 0.9 ± 0.2 aA 1.0 ± 0.3 aA 0.9 ± 0.3 aA CL 0.9 ± 0.2 aA 1.2 ± 0.2 bB 2.4 ± 0.2 bC 2.5 ± 0.1 bC 4A 0.8 ± 0.2 aA 1.3 ± 0.4 bB 2.6 ± 0.6 bC 2.8 ± 0.8 bC LDPE 0.6 ± 0.1 aA 0.7 ± 0.0 aA 0.7 ± 0.3 aA 0.9 ± 0.3 aA Green bags 0.6 ± 0.0 aA 0.8 ± 0.1 aA 1.7 ± 0.1 bB 2.0 ± 0.1 bB Peakfresh 0.7 ± 0.1 aA 0.8 ± 0.0 aA 1.0 ± 0.3 aA 1.0 ± 0.4 aA * means followed by the same lower case letter in column, upper case in rows are not statistically 0.05) 166 Table A5 . 1 1 . Amount of carbon dioxide (%) adsorbed by the same commercial and coated films and values for control, used first time after % CO 2 2 days week 2 weeks 3 weeks 1st time 2nd time 1st time 2nd time 1st time 2nd time 1st time 2nd time CO 0.7 ± 0.5aA1* 0.5 ± 0.2aA1 0.8 ± 0.5aA1 1.3 ± 0.7aA1 1.8 ± 0.6aA1 1.4 ± 0.7aA1 1.2 ± 0.1aA1 1.6 ± 1.1aA1 CL 1.9 ± 0.7aA1 3.9 ± 0.9bA2 3.5 ± 0.3bB1 4.1 ± 0.7bA1 5.2 ± 0.6bC1 5.2 ± 1.0bA1 5.1 ± 0.4bC1 6.2 ± 2.2bA1 4A 3.1± 0.8bA1 2.2 ± 1.2bA1 4.3 ± 0.8bA1 3.8 ± 1.9bcAB1 8.9 ± 0.5cB1 5.0 ± 1.3bB2 9.9 ± 1.3cB1 5.8 ± 1.7bB2 Green bags 0.4 ± 0.3aA1 0.9 ± 0.5aA1 1.7 ± 1.2aA1 1.9 ± 0.8acA1 2.2 ± 1.5aA1 2.2 ± 1.4aA1 3.9 ± 2.2abA1 6.3 ± 2.2bB2 * means followed by the same lower case letter in column, upper case in rows, numbers between times, are not statistically Table A 5 .1 2 . Amount of carbon dioxide (mL) adsorbed by the same commercial and coated films and values for control, used first time after mL CO 2 2 days week 2 weeks 3 weeks 1st time 2nd time 1st time 2nd time 1st time 2nd time 1st time 2nd time CO 1.6 ± 1.2 aA1* 1.3 ± 0.5 aA1 2.0 ± 1.3 aA1 3.3 ± 1.7 aA1 4.4 ± 1.6 aA1 3.6 ± 1.7 aA1 3.0 ± 0.3 aA1 4.1 ± 2.7 aA1 CL 4.7 ± 1.7 aA1 9.6 ± 2.2 bA2 8.8 ± 0.7 bB1 10.2 ± 1.8 bA1 13.1 ± 1.6 bC1 13.1 ± 2.4 bA1 12.8 ± 1.1 bC1 15.5 ± 5.4 bA1 4A 7.7 ± 2.1 bA1 5.5 ± 3.1 bA1 10.6 ± 2.1 bA1 9.4 ± 4.8 bcAB1 22.2 ± 1.3 cB1 12.5 ± 3.3 bB2 24.6 ± 3.1 cB1 14.5 ± 4.2 bB2 Green bags 1.1 ± 0.7 aA1 2.3 ± 1.3 aA1 4.1 ± 3.1 aA1 4.8 ± 1.9 acA1 5.5 ± 3.8 aA1 5.4 ± 3.5 aA1 9.8 ± 5.4 abA1 15.8 ± 5.5 bB2 * means followed by the same lower case letter in column, upper case in rows, numbers between times, are not statistically 167 Table A5 . 1 3 . Amount of ethylene (ppm) adsorbed by the same commercial and coated films and values for control, used first time after ppm eth 2 days week 2 weeks 3 weeks 1st time 2nd time 1st time 2nd time 1st time 2nd time 1st time 2nd time CO 3.2 ± 2.3 aA1* 3.1 ± 1.3 aA1 2.5 ± 0.8 aA1 2.8 ± 1.6 aA1 3.1 ± 1.6 aA1 3.1 ± 4.2 aA1 4.9 ± 1.1 aA1 5.5 ± 3.2 aA1 CL 5.3 ± 1.5 aA1 7.7 ± 0.4 bA2 8.6 ± 1.6 bA1 8.8 ± 0.9 bA1 13.2 ± 0.8 bB1 12.5 ± 1.0 bB1 22.8 ± 0.5 bC1 33.5 ± 0.7 bC2 4A 4.2 ± 1.1 aA1 7.1 ± 0.3 bA2 10.7 ± 1.1 bB1 11.4 ± 2.1 bB1 13.6 ± 2.7 bB1 14.2 ± 2.2 bB1 26.9 ± 6.8 bC1 33.0 ± 2.4 bC1 Green bags 3.3 ± 0.8 aA1 4.6 ± 0.6 aA1 3.0 ± 0.5 aA1 3.5 ± 2.0 aA1 11.8 ± 3.6 bB1 12.4 ± 0.7 bB1 23.8 ± 8.7 bC1 31.2 ± 2.8 bC1 * means followed by the same lower case letter in column, upper case in rows, numbers between times, are not statistically Table A5 . 1 4 . Amount of ethylene (%) adsorbed by the same commercial and coated films and values for control, used first time after coating % eth 2 days week 2 weeks 3 weeks 1st time 2nd time 1st time 2nd time 1st time 2nd time 1st time 2nd time CO 1.3 ± 0.8 aA1* 1.4 ± 0.5 aA1 1.1 ± 0.4 aA1 1.2 ± 0.7 aA1 1.3 ± 0.7 aA1 1.4± 1.8 aA1 2.1 ± 0.5 aA1 2.5 ± 1.4 aA1 CL 2.2 ± 0.5 aA1 3.5 ± 0.3 bA2 3.6 ± 0.8 bB1 4.3 ± 0.6 bA1 5.5 ± 0.4 bC1 4.6 ± 0.9 bA1 9.6 ± 0.4 bD1 15.1 ± 0.4 bB2 4A 1.8 ± 0.4 aA1 3.2 ± 0.1 bA2 4.5 ± 0.5 bB1 4.2 ± 1.0 bA1 5.8 ± 1.4 bB1 5.5 ± 3.0 bA1 11.5 ± 3.4 bC1 14.9 ± 1.2 bB1 Green bags 1.4 ± 0.1 aA1 2.1 ± 0.2 aA2 1.2 ± 0.9 aB1 1.6 ± 1.0 aA1 5.1 ± 0.9 bC1 5.3 ± 0.7 b1 10.1 ± 2.2 bD1 14.1 ± 1.2 bC2 * means followed by the same lower case letter in column, upper case in rows, numbers between times, are not 168 Table A5 .1 5 . Amount of ethylene (nL) adsorbed by the same commercial and coated films and values for control, used first time after coatin g and second time after nL eth 2 days week 2 weeks 3 weeks 1st time 2nd time 1st time 2nd time 1st time 2nd time 1st time 2nd time CO 0.2 ± 0.1 aA1* 0.2 ± 0.1 aA1 0.2 ± 0.1 aA1 0.2 ± 0.2 aA1 0.2 ± 0.1 aA1 0.2 ± 0.2 aA1 0.2 ± 0.1 aA1 0.3 ± 0.2 aA1 CL 0.3 ± 0.1 aA1 0.4 ± 0.0 bA2 0.7 ± 0.0 bB1 0.6 ± 0.1 bA1 0.7 ± 0.0 bC1 0.6 ± 0.1 bA1 1.1 ± 0.0 bD1 1.7 ± 0.0 bB2 4A 0.2 ± 0.1 aA1 0.4 ± 0.0 bA2 0.7 ± 0.1 bB1 0.7 ± 0.3 bA1 0.7 ± 0.1 bB1 0.7 ± 0.3 bA1 1.3 ± 0.3 bC1 1.6 ± 0.1 bB1 Green bags 0.2 ± 0.0 aA1 0.2 ± 0.0 aA2 0.6 ± 0.2 aB1 0.6 ± 0.1 aA1 0.6 ± 0.2 bC1 0.6 ± 0.1 b1 1.2 ± 0.4 bD1 1.6 ± 0.1 bC2 * means followed by the same lower case letter in column, upper case in rows, numbers between times, are not statistically 169 Table A5 . 16 . Amount of ethylene (%, ppm, nL) adsorbed by coated films in permeation cells at four 2 days % eth ppm eth nL eth 4A (K1) 0.4 1.7 0.1 CL (K4) 0.2 4.0 0.0 7 days % eth ppm eth nL eth 4A (K1) 2.7 12.4 0.6 CL (K4) 2.5 15.7 0.6 14 days % eth ppm eth nL eth 4A (K1) 3.5 15.9 0.8 CL (K4) 4.6 21.0 1.0 21 days % eth ppm eth nL eth 4A (K1) 12.1 55.4 2.7 4A (K2) 12.1 52.7 2.7 CL (K3) 10.3 35.8 2.3 CL (K4) 9.2 31.6 2.1 Table A5 . 17 . Amount of ethylene (%, ppm, nL) adsorbed by coated films in permeation cells at four 2 days % eth ppm eth nL eth 4A (K1) 9.9 44.3 2.2 CL (K4) 10.5 47.2 2.4 7 days % eth ppm eth nL eth 4A (K1) 19.5 86.8 4.3 CL (K4) 16.4 73.4 3.7 14 days % eth ppm eth nL eth 4A (K1) 29.3 143.2 7.1 CL (K4) 24.9 124.2 6.2 21 days % eth ppm eth nL eth 4A (K1) 33.4 161.6 8.0 4A (K2) 32.1 154.2 7.7 CL (K3) 28.4 137.1 6.9 CL (K4) 26 129.4 6.5 170 REFERENCES 171 R E F E R E N C E S 1. Ozdemir M., Floros J. D. Active Food Packaging Technologies Critical Reviews in Food Science and Nutrition, 2004 (44) 185 - 193 2. Wilson C. L. (ed.) Intelligent and Active Packaging for Fruits and Vegetables CRC Press 2007 (57 - 71) 3. Zagory D. Ethylene - removing packaging in Rooney M.L. (ed.) Active Food Packaging (38 - 54) 4. Chapman& Hall 1995 2012 Production guide for Storage of Organic Fruits and Vegetables NYS IPM Publication no.10 5. Coloma A., Rodriguez F.J., Bruna J.E., Guarda A., Galotto M.J. Development of an Active Film with Natural Zeolite as Ethylene Scavenger , J ournal of Chilean Chemical Society 2014 (49) 2409 - 2414 6. Patdhanagul N., Srithanratana T., Rangsriwatananon K., Hengrasmee S. Ethylene adsorption on cationic surfactant m odified zeolite NaY , Microporous and Mesoporous Materials 2010 (131) 97 - 102 7. Erdogan B., Sakizci M., Yorukogullari E. Characterization and ethylene adsorption of natural and modified clinoptilolites , Applied Sur face Science 2008 (254) 2450 - 2457 8. Sodergard A. , Stolt M. Industrial production of high molecular weight poly(lactic acid) in Auras R., Lim L. - T., Selke S., Tsuji H. (ed.) Poly(lactic acid) Synthesis, Structures, Properties, Processing and Applications (27 - 41) John Willey and Sons 2010 9. Gonzales - Buesa J., Page N., Kaminski C., Ryser E.T., Beaudry R., Almenar E. Effect of non - conventional atmospheres and bio - based packaging on the quality and safety of Listeria monocytogenes - inoculated fresh - cut celery ( Apiumgraveolens L. )during storage Postharvest Biol ogy and Technology 2014 (93) 29 - 37 10. Yuzay I.E., Auras R., Selke S. Poly(lactic acid) and synthetic zeolite composites prepared by melt processing , Journal of Applied Polymer Science 2009 (115) 2262 - 2270 11. Esturk O., Ayhan Z., Gokkurt T. Production and Applica tion of Active Packaging Film with Ethylene Adsorber to Increase the Shelf Life of Broccoli ( Brassica oleracea L. var. Italica) , Packaging Technology and Science 2013 (27) 179 - 191 12. Mohanty A. , Misra M. , Drzal L. (ed.) Natural Fibers, Biopolymers, and Biocomposites CRC Press 2005 13. Domenek S., Courgneau C., Ducruet V. Characteristics and Applications of PLA in Kalia S., Averous L. (ed.) Biopolymers: Biomedical and Environmental Applications (183 - 223) Wiley - Scrivener 2011 14. ht tp://evlon.ca/specifications.php 172 15. http://vpl.astro.washington.edu/spectra/c2h4.htm 16. http://webbook.nist.gov/cgi/cbook.cgi?ID=C74851&Units=SI&Type=IR - SPEC&Index=0#IR - SPEC 17. Aronne A., Esposito S., Ferone C., Pansini M., Pernice P. FTIR study of the thermal transformation of barium - exchanged zeolite A to celsian , J ournal of Mater ials Chem istry 2002 ( 12 ) 3039 - 3045 18. Elaiopoulos E. Operations involving organic gases and vapors in Inglezakis V. J., Zorpas A. A. (ed.) Handbook of Natural Zeolites (246 - 252) Bentham Science Publishers 2012 19. Romero - Perez A., Aguilar - Armenta G. Adsorption kinetics and equilibria of carbon dioxide, ethylene and ethane on 4A (CECA) zeolite , Journal of Chemical and Engineering Data 2010 ( 55 ) 3625 3630 20. Adsorption by Clays, Pillared Clays, Zeolites and Aluminophosphates in Rouquerol F., Rouquerol J., Sing K. Adsorption by Powders and Porous Solids. Principles, Methodology and Applications (490 - 519) Elsevier 1999 21. Jinqu W., Yongchun Z. Adsorption equilibrium of ethylene - carbon dioxide mixture on zeolite ZSM5 and its correlation , Journal of Chemical Industry and Engineering (China) 1992 (7) 208 - 215 22. Sircar S., Myers A. L. Gas Separation by Zeolites in Auerbach S. M., Carrado K. A., Dutta P. K. (ed.) Handbook of Zeolite Science &Technology (1354 - 1406) Dekker 2003 23. Aguilar - Armenta G., Hernandez - Ramirez G., Flores - Loyola E., Ugarte - Castaneda A., Silva - Gonzalez R., Tabares - Munoz C., Jimenez - Lopez A., Rodriguez - Castellon E. Adsorption Kinetics of CO 2 , O 2 , N 2 , and CH 4 in Cation - Exchanged Clinoptilolite , Journal of Physical Chemistry B 2001 (105) 1313 - 1319 173 CHAPTER 6 Summary, g eneral conclusions and recommendations for future work In food packaging, the composition and relative concentrations of headspace gases play an important role in extending the shelf life of perishables. Some gases, like oxygen, nitrogen or carbon dioxide, will be placed in the packages during the packaging process; others (especially ethylene but also carbon dioxide) will b e produced by the fresh produce itself. Presence of specific gases or too high concentrations of already present gases will play a critical role in keeping fruits and vegetables both fresh and safe. Active packaging systems are efficiently used in food p ackaging. Due to growing interest in using PLA as a replacement packaging material for petrochemical based polymers, there is also a question if PLA can be used as a part of active packaging systems. Zeolites, having many different structures and framework s, make themselves ideal sorbents for many volatiles. They have been proven to act as ethylene and CO 2 scavengers. Studies show that PLA and zeolites can be combined into one material by extrusion. Now the question is if they can act as an efficient active packaging system. In chapter 3, two zeolites were chosen for investigation, due to their popularity and common utilization in many fields. These were natural clinoptilolite (CL) and synthetic type 4A zeolite. Experiments were focused on determination of their ad sorption capacities for ethylene (C 2 H 4 ) and carbon dioxide (CO 2 ) at different conditions (temperature, humidity, composition of headspace gases). It was proven that both zeolites can be successfully used as ethylene and carbon dioxide scavengers a nd are promising alternatives to currently used materials. The largest ad sorption capacities were recorded for room temperature and 0% relative humidity and the smallest for the conditions most relevant to 174 ted cases showed that the amounts ad sorbed are in a range that corresponds to concentrations produced and are above amounts tolerated by fresh produce. Zeolites were active for different times, between 2 days for carbon dioxide and up to three weeks for et hylene. Commodities are not usually stored this long. All of those results proved that zeolites could be used for the purpose needed in this research. Chapter 4 describes two ways of incorporating zeolites into/onto poly(lactic acid). The first processin g method was based on research done before at the School of Packaging and involved extrusion, injection molding and compression. Ethylene and carbon dioxide ad sorption of the produced films were investigated and no significant ad sorption was observed. This was due to the zeolites being too deeply incorporated into the PLA matrix. Since PLA is a good barrier to ethylene, it was blocking the zeolites. The second method tried was solution coating. This method proved to be successful in incorporating zeolites o n the surface of the PLA film and also not blocking their activity as a gas scavenger. Different combinations of zeolite and polymer contents were investigated in the ad sorption studies. At the end, two coating solutions and conditions were developed for e ach zeolite and were proven to be most effective for further studies. In chapter 5 details about ad sorption characteristics, thermal and tensile properties of the newly developed zeolite coated PLA films are provided. For the ad sorption studies, also two co mmercially available bags, PeakFresh and Green bags, which are claimed to be ethylene scavengers that extend fresh produce shelf life , were evaluated. There were also several control samples: PLA film without coating, PLA film coated with the same coati ng solution just not containing zeolit es, and LDPE film as a control f or the commercial films, since they are LDPE with impregnated zeolites. Ads orption studies were run did not s how significant ad sorption of the two investigated gases, while coated films and Green bags did. In both 175 testing conditions our films were comparable to each other and one of commercial bags in ad sorption of ethylene and carbon dioxide. Since producers of commercial films advertise them as reusable bags, an experiment was performed to compare the reusability of coated films and one of the commercial bags that was comparable in ad sorption capacity to our samples. It was proven that at room temperature all sa mples could be successfully reused after proper desorption in vacuum oven. Experiments involving permeation cells also proved that zeolite coated PLA films can be successful in scavenging C 2 H 4 minimally changed when compared to PLA films that were uncoated or coated without zeolite. Tensile properties were more significantly affected by the presence of zeolites. Tensile strength and modulus of elasticity were decreased while elongation at break was increased, meaning our films were less breakable and more flexible. In conclusion, this research has show n that zeolites in the form of powder are powerful ethylene and carbon dioxide scavengers in different conditions of temperature, relative humidi ty and headspace gases. Decreas ing the temper sorption of ethylene for both zeolites, and decreased sorption of carbon dioxide in 4A, while increasing sor ption of carbon dioxide in CL. The presence of water inhibited adsorpt ion of ethylene in CL, decreased adsorption of carbon dioxide in CL, and reverse d ethylene adsorption in 4A but d id not affect adsorption of carbon dioxide in 4A. The p resence of additional headspace gases in most cases increased sorption of larger molecules and extended adsorption times for smaller molecules. Since fresh produce is usually kept at low temperatures and with high humidities inside packages with few gases present inside the headspace, all those changes are relevant. Decrease d temperature will have a positive effect while increased RH and more headspace gases might have detrimental effects. Further, solution coating is a method of choice to incorporate zeo lites on the surface of PLA films without blocking their ad sorption capacities by incorporating them too deeply into the polymer 176 matrix. Zeolite coated PLA films demonstrated lower ad sorption capacities than zeolites by themselves but were still relevant f or the concentrations produced and are above amounts tolerated by fresh produce, with the length of action longer than would be typical in applications. While the mechanism of action of zeolites as gas scavengers is still not fully known, PLA films coated with zeolites should be further investigated as a new biobased and biodegradable alternative to commercially available LDPE bags. Many questions have been answered by this research , but there are still more questions to be asked. It would be definitely b eneficial to investigate more different zeolites. There are over 150 synthetic and 40 natural zeolites and we have tested only two of them. Depending on the type of framework, zeolites can have different pore openings; modified zeolites can also have varia ble ions. All of these will definitely change their ad sorption capacities. As for the production method, only extrusion with injection molding followed by compression and solution coating have been tried. There are also other methods available like spin co ating, knife coating, bilayer cast film extrusion on PLA film, etc. To improve the homogen e ity of coating solutions , sonication could be utilized. No matter the method, the ad sorption mechanism should be further investigated . Experiments involving kinetics characterization as well as building sorption isotherms for the new films should be carried out. As much as ad sorption is very important in extending the shelf life of fresh produce, desorption measurements could help in developing films that could be uti lized as reusable packages, which would help in being a competitive alternative to commercially available systems.