WW E ‘. a a Uta-r ”J 4 fliihifrflflflgiflifiji L, This is to certify that the thesis entitled The Effects of Tensile Strain on the Performance of High- Barrier Retortabie Pouch Material presented by Scott Alian Morris has been accepted towards fulfillment of the requirements for M-S- degree in PackaqinL ///m.,_ 1/.» Major professor, Date 2‘/2“JD7 / 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution MSU RETURNING MATERIALS: P1ace in book drop to LJBRARJES remove this checkout from “ your record. FINES will be charged if book is returned after the date stamped be10w. ' .DEC 0 S 1931 ’35 a‘ (‘ \ x”. ‘ ‘. . . I. 1’ ~ ' - J‘ W o) ," f'» THE EFFECTS OF TENSILE STRAIN ON THE PERFORMANCE OF HIGH-BARRIER RETORTABLE POUCH MATERIAL By ‘Scott Allan Morris A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE School of Packaging 1987 ABSTRACT THE EFFECTS OF TENSILE STRAIN ON THE PERFORMANCE OF HIGH-BARRIER RETORTABLE POUCH MATERIAL By Scott Allan Morris The oxygen permeation rate of some materials can be shown to vary in proportion to mechanical strain. The oxygen permeation rate affects the shelf-life of packaged foodstuffs and other products. lt follows that the amount of strain that a package encounters will relate to some degree of quality reduction due to an increase in oxygen permeation rates. This study investigated the effect of tensile strain on the barrier properties of the composite material used in retortable food pouches. The effects of variations in material orientation, strain-rate, and degree of strain on changes in the material’s oxygen permeation rate were investigated. Additionally, a finite element model of the test samples was constructed to estimate the stress in the sample structure. The data gathered during this experiment conclusively showed that straining the material did 'increase the material’s oxygen transmission rate, which is crucial in the long-term storage of oxygen-sensitive products. Copyright by SCOTT ALLAN MORRlS 1987 ii DEDICATION This brief tome is dedicated to my parents, Dr. Allan J. Morris and Frances M. Stearns-Morris and my sole sibling, Pamela, whose patience and generosity have not always been reciprocated. ACKNOWLEDGEMENTS None of this would have been possible without the continued support and good humor of the thesis committee: Rick Brandenburg, Bruce Harte, and my major advisor, Julian Lee. Assistance ,from Larry Segerlind with the numerical model, and John Gill with the statistics is also gratefully acknowledged. The rest of the staff and faculty at the School of Packaging also recieve my heartfelt thanks for their assistance in everything, period. Finally, all of my fellow students, past and present,(and everyone else) that l have had the pleasure of associating with are acknowledged for the enriching of my life...there isn’t room for everyone’s name, but I haven’t forgotten. iv TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES INTRODUCTION FAILURE MECHANISMS EXPERIMENTAL PROCEDURES Initial Tensile Measurements Tensile Treatment Oxygen Transmission Rate Testing The Numerical Model RESULTS CONCLUSIONS APPENDIX A: DATA ON THE PROPERTIES OF THE RETORT POUCH FILM USED IN THE PERMEATION STUDY APPENDIX B: DETERMINATION OF THE MECHANICAL PROPERTIES OF THE FILM USED IN THE NUMERICAL MODEL LIST OF REFERENCES Page vi vii 21 25 28 4O 42 LIST OF TABLES 10. 11. 12. 13. 14. 15. 16. Tabulated Mean Permeation Data Statistical Summary Tensile Failure Data: Cross-machine direction 10.0 in/min. Tensile Failure Data: Cross-machine direction 1.0 in/min. Tensile Failure Data: Cross-machine direction 0.1 in/min. Tensile Failure Data: Machine direction 10.0 in/min. Tensile Failure Data: Machine direction 1.0 in/min. Tensile Failure Data: Machine direction 0.1 in/min. Permeation Rate Data: Cross-machine direction 0.1 in/min. Permeation Rate Data: Cross-machine direction 1.0 in/min. Permeation Rate Data: Cross-machine direction 10.0 in/min. Permeation Rate Data: Machine direction 0.1 in/min. Permeation Rate Data: Machine direction 1.0 in/min. Permeation Rate Data: Machine direction 10.0 in/min. Data used for the determination of Poisson’s ratio. Calculation of the modulus of elasticity vi 22 24 28 29 30 31 32 33 34 35 36 37 38 39 40 41 Figure 1. 2. LIST OF FIGURES Diagram of sample-cutting template. Diagram of clamp-extension assembly. Graph of oxygen orientation and Graph of oxygen orientation and Graph of oxygen orientation and Graph of oxygen and rate in the Graph of oxygen strain and rate permeation rates versus strain at 0.1 in/min. permeation rates versus strain at 1.0 in/min. permeation rates versus strain at 10.0 in/min. permeation rates versus strain cross-machine direction. permeation rates versus strain in the machine direction. Diagram of finite-element grid for numerical analysis of strain in samples. Plot of stress in isoparametric finite- element model. vii £9.19. 11 14 15 16 17 19 20 INTRODUCTION The Development of high-barrier flexible packaging materials has resulted in flexible packages that may be thermally processed in a manner similar to the metal cans and glass bottles that they are intended to supplant. These retortable packages (pouches, trays, and the like) are capable of providing a low-cost, lightweight package with good shelf-life and the potential of replacing cans and jars in specific applications. Their widespread acceptance by food companies, to date, has been hampered by the cost of production equipment, and the slow production speed of filling lines. Little is known about the survivability of these new types of containers in production and distribution. Their predecessors--cans, jars, and bottles--will usually give a clear indication of the loss of integrity by either the loss of internal vacuum or the destruction of the package structure. Unlike the cans, jars and bottles that they replace, these retortable containers have the possibility of partial loss of their barrier properties in localized areas with attendant quality or safety deterioration. The results of this may be premature nutrient loss, contamination, or flavor deterioration. Thus, a flexible retortable pouch that has been subtly damaged may be as ineffective a barrier as a container that is leaking its contents, yet will give no overt indication of damage. In this study, the exhibited changes of barrier capability as a function of simple uniaxial strain give a clearer notion of the mechanisms by which the material degrades before failure, and the sorts of damage mechanisms one might expect to be present as a result of handling and transportation. FAILURE MECHANISMS In most applications, a barrier film that is subjected to mechanical stresses can reasonably be expected to fail, given severe enough levels of abuse. What is not so clear are the effects of ”sublimital" damage--damages that have no overt effect but will reduce the efficacy of the barrier material involved. The implication of this type of failure is that a product contained in a polymeric or a polymer-laminate composite is at risk of losing its protection from potentially damaging elements without any externally evident indication of failure. In most situations, failure is usually associated with breaking or rupture of the container material, yet a packaging material that has lost its necessary barrier qualities has failed just as badly. Further, since there is no obvious indication that the contents have degraded, there is the risk of the contents being used after their shelf-life has prematurely expired. In the case of a food product that will visibly show quality changes (such as the oxidation browning of catsup), the harm to the consumer is usually minor even though the likelihood of a repeat purchase is reduced. If the product is a pharmaceutical or a medical diagnostic item, the harm to the ”consumer" might well be more severe than an affront to his palate. The relationship between strain-induced orientation changes, and changes in the permeation and sorption values for a polymer film under various conditions is well known, although there is no precise predictive model for these changes under most circumstances‘v’v3"v’. Similarly, there is a wealth of data relating the morphological changes in polymeric materials to the variables involved in plastic deformation and reorientation from very low levels of strain to failure‘~’v'. There is little information relating barrier failure to the morphological changes which occur in the areas where strain will induce discontinuities in the material. The strain-induced morphological changes in semicrystalline polymers, and the attendant failure mechanisms are known to be dependent on the rate as well as the magnitude of the strain'. It has been shown that failure mechanisms of simple polymer sheets will fall into three broad classes which are contingent on the strain rate“. At very low strain rates, the polymer is able to reorient itself in the direction of the applied stress, changing its morphology from semicrystalline spherulites to highly oriented fibrillar strands with an attendant decrease in permeation and sorption rates and an increase in unit strength. This decrease in permeation has been exploited in the production of some types of biaxially oriented beverage containers for the soft-drink industry. As the rate of strain increases, the material in the spherulites does not have the time to reorient itself, and the spherulites will begin to pull apart (a phenomenon termed ”crazing")‘°. This process will generate microscopic voids in the interspherulitic boundaries, and it is at this point that some researchers consider their investigation into strain-related permeation changes at an end because the permeation mechanism diverges from a strict sorption-d1ffusion-desorption model. This is unfortunate because at this point that a large number of practical applications begin to surface. At still higher rates of strain there is insufficient time for the spherulites to reorient their internal structure and intraspherulitic fracturing begins to occur. This fracturing will also cause a significant decrease in the barrier capability of the polymer due to its increasing porosity. It must be mentioned that a panoply of other factors will affect the effects of strain rate. Most noteworthy of these is temperature, which directly affects the segmental mobility of the polymer matrix, and thus mediates the modes of failure described above“. Additionally these temperature effects will cause the thermally processed containers to exhibit changes during and after processing which will affect the physical stability of containers. The destruction of barrier properties in a metallic laminate has an additional set of complications. The first of these is the adhesion between the layers. Since the adhesive is a polymeric substance as well there may be additional strain-dependent effects exhibited in the adhesive layers. Poor bonding, or a significant shift in the bonding characteristics of the adhesive layer will affect the isotropic nature of the laminate‘. Moreover, the metallic layer provides most of the barrier properties in the laminate. The ultimate plastic deformation for aluminum foils is approximately 35%‘3 while for most polyolefin polymers the minimum (at sufficiently low strain rates) is several hundred percent“. In the event that the metallic layer is well bonded, the metallic layer should fragment in the area where the strain occurs, negating a large portion of the foil’s barrier contribution. If the foil layer is poorly bonded the material will exhibit a large degree of anisotropicity, and the metallic layer will fracture in a direction approximately normal to the applied stress, as if it were an isolated piece of foil being supported by the polymer layers‘. In either case the inelasticity of the metallic layer relative to its polymeric companions would lead to the expectation of failure in the metallic layer after a relatively small degree of strain, and that this failure should be relatively rate independent. The resulting combination of effects that one finds in the laminate material examined in this study points to the expectation that there would be a mode of barrier degradation that would vary according to both the degree and rate of strain applied. The degradation should result from two types of effects; Those related to the destruction of the foil layer at a (relatively) low degree of strain, and those related to the previously described rate-dependent failure of the polymer layers occurring at higher percentages of strain than that which fragments the foil layer. It should be noted that newer types of laminates (where a high-barrier polymer film replaces the foil layer) for thermally processed food applications may not exhibit the same effects because of the substitution of a plasticized polymeric barrier layer for the foil layer. However this makes the rate dependent effects, as well as the thermal history of the material more important. EXPERIMENTAL PROCEDURES Initial Tensile Measurements Samples of American Can Co. retort pouch material (Material Number K125 44-050) were cut to shape using a template (Figure 1) and then subjected to tensile stress in an Instron Tensile Tester (Model #1114). The failure points were determined for each rate and orientation of the material and the average strains at failure were used in the calculation of the 10%,50M, and 90% of failure strain extension (Appendix A, Tables 3-8). Tensile Treatment The experimental samples were stored at 73°F and 50% relative humidity for at least 48 hours prior to testing. Samples were then cut from the stock to be tested using a template (Figure 1) to ensure uniform and symmetrical dimensions in the sample. The shape of this template differs from most of those used in ASTM tensile tests of flat materials. The reason for a sample shape of this type is to concentrate the stress in the sample along a single transverse band in the center of the sample material rather than along the length of a long strip of material. This, in turn, allows a 3a JL. : :- —OI| :6— l/ KI so .mam_aemu acmuuzu-m_a5mm Co Encampo ._ mgam_a 10 sample to have the resultant strain placed in a relatively specific area for the later testing of oxygen transmission rates. The cut samples of flat stock were then placed in the jaws of the Instron tensile-tester and subjected to strain amounting to 10%, 50%, and 90% of the mean failure strain extension as calculated above. Additionally, samples at each of the above strain levels were strained at 0.1, 1.0, and 10.0 inches per minute. The materials thus tested were sampled from the machine direction (tensile force applied along the length of the spooled material) and the cross machine direction (in a direction planar-normal to the first). This was done to determine any effects of material pre-orientation on the stress-related barrier failure. Three samples of each direction, rate, and orientation were tested, for a total of 54 tested samples. Because of the extreme width of the samples at each end, the jaws of the tensile tester had to be widened by means of a set of extension clamps (Figure 2). Once the samples had been strained, crosshead travel was immediately reversed so that the reorientation time of the material would be limited to approximately the amount of time that the material was actually under extension in the tensile tester. II \xnm= mmumg cowummeLma :mmxxo so sauce .m we:m_m Sch—m 0.24:0“. c002 Don—0.3200 $0 uCOOLOQ m0 Epfim 2: cm on on cm on 9. on ON o. c .IbrbrL......T.L....o T H" In mm 1%“ r m 2... Ion low T.oo— e O .. m on. 2 . W 2o: 27.. e w c.5085 echaZIoaoS 9 1.3— w 53026 05:00: 0 2 rom— ioauuad U! DO! I!W*OO 15 .cwe\:w o._ um seesaw ucm cowpmucmwso mamsm> mono; cowummELma :mmxxo co cameo .e meam_m Spam 95:0... coo: 83.30.00 20 acoSod mo Eobw cop om on on on on 0* on ON OF 9 PLLp—LBL - b b b h LI - D h I - P o H" , I. 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O l m Tom H -9 .00 r .00 r200.. lou— i r0...— 563 0.2 .8085 2.28: 2 . c.E\c. 0.. 60:02.0 00.500: 0 r00— 55}. to .8285 228: o . wiva: W‘s/(co .:o_puoawu mcwcume 0:0 c. was; new cpmaum mzmsm> mecca :o_um02200 cmmxxo mo Emcee .N mgzm_m Z ”WOO ioeuuad til IJCJI 19 .mmPaEmm c. mcwmcum mo mwmx—mcc PMUPLme:: 200 0.20 acmempmump_cwm mo Emammwo .m 0230.0 \\\\\\\\ ._0uoe acmemP0200wcwm u_guoEmgmqomw :_ mmmgum so pop; .0 mesmFE 3. 5a e. «as?» .5303 :< nun , 17IIIJNH ./L HN\— / /1/ flwb // 7H a \/ b/I \/ —--—mo ugmucmum mPQSmm _. Sing}... AF PFE\00 c. can; cowumoegma: waspwmm came umumpzupmo co momucwugma a mo mmgmmom 0mm.m_ Pm0.0~ pwm.m0— «Fm.mp —m0.¢~ mmw.mn 000.m_ mum.0~ o~0.mm mmw.n— unm.0p Nm~.mp 0~0.mp cvm.vp www.0P ~0~.mp 0pm.wp mmm.mp :mpwm cowum052ma cam: .mu::.e\mmzucw :. macaw cowuumgwa mcwgumz ”a: covuuws_0 0=_;0mE-mmoLu ”zxH fiop Rom x00 fic— Rom $00 no— Rom N00 xop Rom N00 xop xom Rom flop New wow mmmgmmo mama cowummegma cam: 000o_=aah o.o_ 0.P _.o 0.0_ 0.P P.0 «mama 0: 2x .cowuomgwo ._ 2...: 23 summarized in Table 2. It is clear from the calculated F-values--all of which exceed the required values for significant effect-~that all of the variables (both singly and in combination) to which the samples were subjected had a significant effect on the permeation rates through the samples. This relates well to the relationships between the strain variables and changes in permeation afforded by preliminary inspection of the data. Further statistical analysis of the data, such as the establishment of a correlation coefficient between some particular strain variable, and the resultant change in permeation rates, would be hindered by the simplicity of the model used in determining the strain occurring within the deformed areas of the sample as well as the lack of data from a complete spectrum of strain and direction variables. Thus, although an approximate notion of the applied strain can be garnered from this experiment, and although the resulting significant shifts in the permeation can be experimentally obtained, a comprehensive quantitative relationship between the strain in the sample and changes in permeation requires the development of the stress-strain relationships occurring in an asymetrical composite system undergoing elastic and plastic deformation within a single sample--and is beyond the scope of this study. 24 mm.m 00.0 00.0 00.0 00.0 0N.m 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 x— 00 0:00> 0 00200000 00.00 00.00 m0.~0~ 00.00 00.000 00.00 0_.0m_ 0 .mno “0.0 00.000 00.00— N_.000P 00.000 P0.momp 00.000 0m.~m0_ 0: 00.000 00.0000 00.000 0_.00Nm 00.000 0F.m~00 00.000 00.0000 00.00000 .00 0m 20220 002000 a .0000 .000000200 002000 0 0000 002000 0 000000200 0000 0 000000200 000200 00 .00 002000 000200 00 0000 000200 00 000000200 00000 00000020> 00 002000 Mr—NNNNVQ’ LO 'I u. 22mse=m .202002020m .N 0.0.0 CONCLUSIONS In this study, samples of a single type of material were subjected to different, focused tensile strains and the resulting changes in oxygen transmission rates were measured and compared. The rate, degree, and direction of the applied strain, both singly and in combination, were shown to be significant factors in the breakdown of the barrier material. Analysis of the data showed that the tested material has incipient failure characteristics which render it capable of an order of magnitude increase in permeation--without rupturing the material or giving an immediate indication of having been damaged. More specifically, the combination of strain in the machine-direction and a degree of strain at the 90% level (near the failure point of the material) seemed to afford the most significant change in permeation values. Further, permeation rates within these specific variables of strain increased in tandem with increasing rates of strain (Figure 6). The explanation of the ispecific causes of this behavior is difficult since the mechanisms of failure are, as previously described, quite complex and must take into account a plethora of interdependent variables. The simplest explanation for the behavior exhibited by this particular material would relate the permeation change to 25 26 the extensibility of the pouch material’s polyester layer although there is no specific data to support this notion. Ultimately, the best conclusion that can be drawn from this study is that there is a highly significant qualitative relationship between the variables of strain-rate, degree of strain, material orientation and a highly significant shift in oxygen permeation values. These shifts of permeation rates, in turn, represent a potential for the causation of quality loss in a product that depends on an intact oxygen barrier for quality maintenance. Additionally, a quantitative relationship might be attempted from the data garnered in this study but, as the specific amount of strain in all regions of each sample is not known in a simple experiment of this type any correlations might be misleading. The utility of these types of studies lies in the development of methods for the analysis and design of high-barrier packages that can survive the mechanical stresses and strains inherent in their production and distribution. Predictive knowledge of the changes that can occur in a package will allow design of materials and structures that meet the needs of the package system without extensive "try it and see” prototyping that is both time-consuming and expensive. A good correlation between permeation changes and strains in a packages’ structure will allow the package 27 designer to utilize computer-based predictive models in the design process, as is done in other fields of engineering. The extension of the shelf-life and an increase in safety resulting from a ‘more complete understanding of the necessary design factors should allow a more confident implementation of newer, more highly engineered types of packaging systems with a reduced pre-production lead time for prototyping and testing. APPENDIX A DATA ON THE PROPERTIES OF THE RETORT POUCH FILM USED IN THE PERMEATION STUDY. 28 TABLE 3: Tensile Failure Data. Orientation: Cross4Machine Direction. Rate of Strain: 10 in/min. Samplg Extension at Failugg XMi 2.00 in. XM2 2.50 XM3 3.00 XM4 2.07 XMS 3.13 XMS 2.69 Mean = 2.57 in. Sample Standard Deviation: 0.467 in. 29 TABLE 4: Tensile Failure Data. Orientation: Cross0Machine Direction. Rate of Strain: 1.0 in/min. Samplg ggtgngion gt Failure XM7 2.80 in. XM8 2.31 XM9 2.86 XM10 2.31 XMii 2.44 XM12 2.50 Mean: 2.50 in. Sample Standard Deviation: 2.44 in. 30 TABLE 5: Tensile Failure Data. Orientation: CrossSMachine Direction. Rate of Strain: 0.1 in/min. Samplg Exiengion at Failurg XM14 2.25 XM15 1.63 XM16 1.75 XMiB 1.75 XM19 2.25 XM20 1.50 Mean: 1.85 in. Sample Standard Deviation: 0.32 in. 31 TABLE 6: Tensile Failure Data. Orientation: Machine Direction. Rate of Strain: 10 in/min. m le xtensi n t a lure MDi 2.25 MD2 2.19 MD3 2.25 MD4 2.34 MDS 2.31 MD6 2.34 Mean: 2.28 in. Sample Standard Deviation: 0.06 in. 32 TABLE 7: Tensile Failure Data. Orientation: Machine Direction. Rate of Strain: 1.0 in/min. Samele Exteneien at Failure MD7 1.75 in MD8 1.63 MDQ 1.75 MD10 1.50 MDii 1.86 MD12 1.25 Mean: 1.62 in. Sample Standard Deviation: 0.22 in. 33 TABLE 8: Tensile Failure Data. Orientation: Machine Direction. Rate of Strain: 0.1 in/min. Samele Extension at Failuee MD13 1.50 MD14 1.44 MDiS 1.75 MD16 1.38 MD17 1.56 MD19 1.62 Mean: 1.54 in. Sample Standard Deviation: 0.13 in. 34 Table 9. PERMEATION RATE DATA Orientation: Cross-Machine Direction Rate: 0.1 in/min Calibration Value”: 17.390 xt n on Samele Reeding Permeatien ean D 90% X20 0.21 mV 20.0862 X21 0.18 17.215 X318.332 X22 0.185 17.694 s81.540 50% X24 0.17 16.258 X25 0.21 20.086 X818.810 X26 0.21 20.086 s82.211 10% X27 0.20 19.129 X28 0.21 20.086 X819.767 X29 0.21 20.086 s80.550 ‘ Calibration values in CC/M’lDay/Mil/Atm per Millivolt. Taken from NBS-1470 Standard Polyester Film. ’ Permeation in CC/M'lDay/Mil/Atm. 35 Table 10. PERMEATION RATE DATA Orientation: Cross-flachine Direction Rate: 1.0 in/min Calibration Value“: 17.390 Extgggign gamglg Reading 90% X32 X33 X34 50% X36 X37 X38 10% X39 X40 X41 ‘Calibration values 0.16mV 0.17 0.16 0.16 Permeation Mgan & SD 15.301 16.258 12.236 14.344 15.301 13.393 16.256 15.301 15.301 in CC/m3/Day/Mil/Atm Taken from NBS-1470 Standard Polyester Film. aPermeation in CC/Ha/Day/Hil/Atm. X814.828 s=2.065 X=14.344 s=0.957 X315.620 s=0.550 per Millivolt. 36 Table 11. PERMEATlON RATE DATA Orientation: Cross-Haohine Rate: 10.0 in/min Calibration Value“: W“ 1 fl mm 90% X42 X43 X44 50% X45 X37 X38 10% X39 X40 X41 ‘Calibration values Direction Easting 0.17mV 0.15 0.175 0.165 0.18 0.175 0.16 0.19 0.21 CC/m’lDay/Mil/Atm Permeation 15.3012 14.350 11.237 15.780 17.215 16.737 15.301 18.172 20.086 Taken from NBS-i470 Standard Polyester Film. aPermeation in CC/H’lDay/Hil/Atm. per Mgan & SQ X=15.752 381.265 X=16.577 s=0.732 X=17.853 s=i.914 Millivolt. 37 Table 12. PERMEATION RATE DATA Orientation: Hachine Direction Rate: 0.1 in/min Calibration Value': 17.724 Extonoion fiaeole Reaoing Permeation Hean & SD 90% H43 0.380mV 37.043a H42 0.400 38.995 XI35.420 H41 0.310 30.217 s83.762 50% H46 0.170 16.572 H45 0.165 16.082 X=16.573 H44 0.175 17.061 s=0.490 10% H50 0.165 16.082 H49 0.105 10.234 X=13.640 H48 0.150 14.625 s=3.042 ‘Calibration values in CC/m‘lDay/Hil/Atm per Hillivolt. Taken from NBS-1470 Standard Polyester Film. aPermeation in CC/H'lDay/Hil/Atm. 38 Table 13. PERMEATION RATE DATA Orientation: Hachine Rate: 1.0 in/min Calibration Value”: 17.390 Extongion Samolo Beoding EQLQQQLLQE 90% H22 0.475mV 45.430” H21 0.970_ 92.774 H20 0.840 80.334 50% M25 0.150 14.350 H24 0.150 14.350 H23 0.140 13.393 10% H28 0.150 14.350 H27 0.150 14.350 H26 0.130 12.436 ‘Calibration values Direction in CC/m”/Day/Hil/Atm per Taken from NBS-1470 Standard Polyester Film. ”Permeation in CC/H”/Day/Hil/Atm. H n & X=73.838 s=24.547 X=14.031 330.550 X=13.712 s=1.128 Hillivolt. 39 Table 14. PERHEATION RATE DATA Orientation: Hachine Direction Rate: 10.0 in/min Calibration Value”: 17.390 Exten on goooio Reading Pogmoation 90% H32 1.800mV 172.161” H31 31.302 172.161 H30 27.824 153.032 50% H35 0.170 16.258 H34 0.205 19.608 H33 0.200 19.129 10% H38 0.150 14.350 H37 0.170 16.258 H36 0.180 17.270 ‘Calibration values in CC/m”/Day/Hil/Atm per Taken from NBS-1470 Standard Polyester Film. ”Permeation 1n CC/H”/Day/Hil/Atm. M X8165.781 9811.044 X=14.031 380.550 X=15.956 381.485 Hillivolt. APPENDIX 8 DETERMINATION OF THE MECHANICAL PROPERTIES OF THE FILM USED IN THE NUMERICAL MODEL 40 potogmination of Poisson’s ratio. Poisson’s ratio is the ratio of lateral strain to axial strain“. For the purposes of this study, a simple determination is sufficient for use in the numerical model. Sample strips of retort pouch material 1” x 10” were stretched 1" in an Instron Tensile Tester (Hodel #1116) and the change in the width of the sample was recorded. Orientation was found not to be a factor, and thinning effects were not considered. The value of 0.42 is similar to nylon, and is in the right range for materials of this type". Table 15. Data used for the determination of Poisson’s ratio. Samole Ogientation Latoral Stgain 1 Cross Machine Direction 0.04 2 ” 0.04 3 ” 0.04 4 " 0.04 5 ” 0.06 6 Machine Direction 0.02 7 ” 0.04 8 ” 0.06 9 " 0.04 10 ” 0.04 Mean Lateral Strain: 0.042 Sample Standard Deviation: 0.011 Axial Strain: 1"/10”=0.1 Poisson’s Ratio=Lateral Strain/Axial Strain =(0.042)/(0.1)=0.42 41 Determination of the Modulus of Elasticity. The modulus of elasticity (E) is the ratio of applied load to resultant deflection, and is usually determined to be the slope of a .stress-strain curve in the linearly elastic portion of the curve“. For the purposes of the numerical simulation, a simple determination of E is sufficient. Ten samples (five from each orientation) were placed under tensile stress (rate81.0 in/min), and the slope of each curve’s elastic region was determined, giving the coefficient of elasticity. Table 16. Calculation of the Hodulus of Elasticity. In this case all of the sample’s slopes were identical within the limits of the recording device attached to the tensile tester. Number of Samples: 10 (5 from each orientation) Sample width: 1.0 in. Load: 13.3 lbs. Thickness: 0.052 in. Measured strain: (0.1 in./8.333 in.)= 0.012 (Load/Thickness) E= (Heasured Strain) =2.137 x 10' psi. LIST OF REFERENCES Schrenk, U.J. and Alfrey, T. Jr., 1969. ”Physical Properties of Hultilayered Films”. Eolymor Engineering and Science, Vol. 9, No.6, pp.393-399. Rogers, C.E., 1985. ”Permeation of Gasses and Vapors in Polymers”. Polymo; Pormeabilitx, J. Comyn, Editor. Chapter 2, pp. 55-56. Smith, Thor L. and Adam, Randall 5., ”Effect of Tensile Deformations in Glassy Polymer Films”. Polymoo, Vol 22, No.3, pp.299. . Yasuda,H. and Peterlin, 4., "Gas Permeability of Deformed Polyethylene Films”. Joogool o1 Aoolied Rosen, Bernard. "Time-Dependent Tensile Properties. Part ll. Porosity of Deformed Glasses”. Jougool of Polymor Science, Vol. XLVll, pp.19-27 (1960). Schultz, J.H., ”Hicrostructural Aspects of Failure in Semicrystalline Polymers”. Pol mer n i eri n Science, Vol. 24, No. 10 pp.770-785. Hark, Herman F. ”Strength of Polymers”. Eolxoeg §oioooo_ooo_flo£ooiolo. Eds. Tobolsky, Arthur V. and Hark, Herman F., New York: Uiley-lnterscience, 1971. pp.231-246. Samuels, Robert J. ”Application: Quantitative Correlation of Polymer Structure with End-Use Properties”. Structured Polyoor Prooertioo. New York: John Wiley & Sons, 1974. pp. 160-242. Vincent, P.l., ”Fracture”. Hechanica o t e f Polymo: . New York: John Wiley & Sons, 1971. pp.136- 141. 42 10.) 11.) 12.) 13.) 14.) 15.) 16.) 17.) 43 LIST OF REFERENCES (Cont’d.) Jang, B.Z. et a], ”Grazing in Polypropylene". Polymor- Eogineozing and Scionco, Vol. 25, No.2 pp.98-104. Deanin, R.D. ”The Science of Plastics”. P m C no and Hatooialo Eds. Tobolsky, Arthur V. and Hark, Herman F., New York: Wiley-Interscience, 1971. p.318 Harks, Lionel 5., H chan al n i eer ’ a ho k. 5th ed. New York: HcGraw-Hill, 1951 ”Properties of Packaging Films”, Hooorn Packaging gooyclooeoia & Buyers Guide. 1977. Segerlind, Larry J.”lsoelastic", Computer Prograe, HHH809 Course Material. unsupported FORTRAN source code available from the author c/o Department of Agricultural Engineering, Michigan State University, East Lansing, HI 48823. . Little, T.M. and Hills, F.J., Sta t a th d Aggicultugal Researoh. University of California, Davis Book Store, 1972. pp.36-40. Gere, J.H. and Timoshenko, S., Hechonical Prooegtioo of Materials. Boston: PUS Publishers, 1984. pp.18-24. Gere, J.H. and Timoshenko, S., op. cit. p.744. "THJWETTMITMTETVS