CREATING METHODS FOR VALUE-ADDED BOTTLE-GRADE POLY (ETHYLENE TER- EPHTHALATE) FROM BLENDS OF BOTTLE-GRADE AND THERMOFORM-GRADE POLY (ETHYLENE TEREPHTHALATE) By Anurag Ganapathi A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Packaging – Master of Science 2023 ABSTRACT One of the widely used plastics in food, consumer goods, beverage, and pharmaceutical industries is poly (ethylene terephthalate) (PET). On a global scale, PET is renowned as the most frequently recycled polymer. Thermoform PET (PET-T) must be separated from bottle-grade PET (PET-B) streams due to variations in their intrinsic viscosity (IV). This research aims to create commercial bottle-grade pellets by blending recycled PET-B and recycled PET-T. Three techniques were used to rebuild PET-B characteristics with 10-20 wt% PET-T: solid-state polymerization (SSP), chain extension, and chain extension combined with SSP. The IV values for PET-B containing 10-20% PET-T were determined. Mechanical parameters like impact strength, tensile modulus, tensile strength, and elongation at break were also tested. Furthermore, thermal characteristics like ther- mal degradation, crystallinity, glass transition temperature (Tg), and melting temperature (Tm) were studied. The implementation of SSP treatment and a chain extender improves the IV values of rPET blends. The use of SSP treatment and a chain extender also improved the thermo-mechanical behavior of recycled PET blends from PET-B and PET-T. The tensile strengths and Izod impact strengths of blends that had undergone chain extension and SSP were greater than those of un- treated PET blends. Meanwhile, the thermal properties, such as the Tg and Tm remained unaffected by adding the chain extender and the SSP treatment. Keywords: Recycled PET, Solid-State Polymerization, Chain extenders, Reactive extrusion ACKNOWLEDGMENTS I want to express my heartfelt gratitude to Dr. Muhammad Rabnawaz, my mentor, for granting me the chance to be a part of his esteemed Sustainable Materials Group for this project. His consistent encouragement and expert direction were pivotal in the successful culmination of this research endeavor. My gratitude also goes to Dr. Shiwang Cheng and Dr. Mohammad Mohiuddin for their significant contributions and invaluable guidance in their roles as committee members. Thanks for the valua- ble time and suggestions they provided throughout the research. I extend my appreciation to Dr. Mohamed Abdelwahab and Naveed Muhammad for generously dedicating their valuable time to train me on various equipment and analysis software tools. I got erudite with the process of experimentation, technical writing, and presentation skills from the research group. I am grateful to the members of the sustainable material group for their constant support during the research period. I am grateful to Aaron Walworth and the School of Packaging (SOP) for helping with the training of equipment and the use of facilities available in the SOP throughout the research and development of my project. Finally, I deeply appreciate the love and support my family and friends extended to me. My parents and elder brother have always motivated and encouraged me to push to extreme limits during my research. Also, I will never forget the support from my friends, who have been helpful throughout the graduation program. iii TABLE OF CONTENTS CHAPTER 1: INTRODUCTION ................................................................................................ 1 1.1 Introduction .................................................................................................................... 1 1.2 Objectives ........................................................................................................................ 4 1.3 Thesis Work Scope ......................................................................................................... 5 1.4 Hypothesis ....................................................................................................................... 5 Structure of the Thesis ................................................................................................... 6 1.5 REFERENCES .......................................................................................................................... 7 CHAPTER 2: REVIEW OF LITERATURE ........................................................................... 10 PET ................................................................................................................................ 10 2.1 2.2 Recycling ....................................................................................................................... 14 2.3 Recycled PET content .................................................................................................. 19 2.4 Challenges in Mechanical and Chemical Recycling of PET ..................................... 22 2.5 Solid-State Polymerization (SSP) ................................................................................ 26 2.6 Chain Extenders (CE) .................................................................................................. 27 REFERENCES ........................................................................................................................ 31 CHAPTER 3: EXPERIMENTAL ............................................................................................. 38 3.1 Materials ....................................................................................................................... 38 3.2 Methods ......................................................................................................................... 42 REFERENCES ........................................................................................................................ 46 CHAPTER 4: RESULTS AND DISCUSSION ........................................................................ 47 SSP and Reactive Extrusion ........................................................................................ 47 4.1 4.2 Characterization ........................................................................................................... 48 REFERENCES ........................................................................................................................ 58 CHAPTER 5: CONCLUSION AND FUTURE WORK ......................................................... 61 5.1 Conclusion ..................................................................................................................... 61 Future Work ................................................................................................................. 62 5.2 iv CHAPTER 1: INTRODUCTION 1.1 Introduction PET (Polyethylene terephthalate) is a commonly utilized plastic within the food and beverage in- dustry, where it is used in packaging such as trays, bottles, bottle caps, cups, clamshell containers, and cartons. Every year the utilization of PET in the form of beverage bottles, textiles, and pack- aging has exceeded 18 billion pounds globally. Nearly 3 million tons out of 51 million tons of recovered PET bottles are recycled. With the increasing demand for PET packaging, it is expected that 63 million pounds of waste will be generated in 2023, with rising yearly consumption to 6.9 million from 5.1 million since 2020 [0-2]. The demand for PET in various applications is driving the growth of the PET market. Conversely, the substantial volume of PET waste underscores the significance of circular economies like mechanical recycling. However, only bottle-grade PET (PET-B) is recycled at a rate of 30%, whereas Thermoform PET (PET-T) is not recycled at all, even though PET-T accounts for roughly 10% of the recycled PET stream [3]. PET-T operates differently from PET-B due to the many fundamental characteristics of the Ther- moforming material and other associated components in the stream. The key distinction is that typical PET reclamation processes are designed for bottles and have only recently begun to treat thermoforms. One of the primary reasons thermoforms are only sometimes used is due to the in- consistency of the plastic resins used in their fabrication [4]. Other thermoform manufacturers employ PET-like materials, such as (polylactic acid) (PLA) which is used in thermoform clam- shells and trays, and (polyethylene terephthalate glycol) (PETG) which is used in thermoform clamshells and trays [5] The adhesives used on thermoforms are significantly abrasive than the labels used on bottle labels. Because the adhesive covers the whole label in many cases, removing the label from PET-T or PET-G containers (or crushed PET flakes) is frequently more difficult [0]. 1 Furthermore, the aqueous solution used to wash the PET flakes is prone to becoming contaminated with adhesive residue. When PET bottles and clamshells are produced concurrently, problems arise because the intrinsic viscosity (IV), tensile strength, or elasticity of PET-T are frequently lower than those of PET-B. Due to thermal degradation and possible contamination, the mechanical prop- erties and molecular weight frequently diminish over several repeated processing cycles. When PET is reprocessed with extreme temperatures, oxygen, and moisture, the polymer degrades [5]. Because the polymer is made at high temperatures, it contains degradation products such as cyclic oligomers [4,6]. It is a well-established fact that the mechanical, thermal, and rheological charac- teristics of a polymer are influenced by its molecular weight. The IV range for PET-B and other high-value plastics is 0.72-0.85 dL/g [7-9]. There are several techniques for increasing the IV and molecular weight of PET. First, additives such as chain extenders can be incorporated to generate interlinking bonds between polymer chains and thus enhance the polymer’s chain length. The second approach would be to continue the PET chain's melt repolymerization with a chemical recycling process, which would be a costly opera- tion. The third choice is the Solid-State Polymerization (SSP) method for PET. This involves heating the prepolymer with low molecular weight to temperatures below its Tm but above its Tg. To elim- inate byproducts of condensation, a vacuum or inert gas can be employed after the condensation reaction takes place [9]. The polymer becomes more tightly intertwined, and its molecular weight increases. The temperature at which the reaction is done is often lower than the polyester's melting temperature, and thus thermal degradation is dramatically reduced. Side products such as water and ethylene glycol can be eliminated under vacuum or by flushing the polymer with an inert gas. 2 One of the main issues linked with PET is its elevated melting point, around 250 ⁰C. The melting points of PET-T and recycled PET-B are lower in contrast to virgin PET-B. All these issues may be addressed by using a chain extender prior to SSP and melting the recycled PET material [9]. The method of chain extensions is widely employed in the process of extending and modifying PET chains, primarily due to its relatively gentle reaction conditions. This approach offers ad- vantages such as minimal energy consumption during flow and a high level of efficiency. Through the utilization of chain extenders, polymers can create covalent chemical bonds, creating the elon- gation of polymer chains and a subsequent rise in the overall molecular weight of the polymer. [10]. Polymer chains that have undergone degradation can be reconnected through the application of chain extenders. The reactions that occur are impacted by both the functional properties of the selected chain extender and the proportion of the same in relation to the polymer [11]. The characteristics of the utilized chain extender and the quantity of polymer in the mixture deter- mine the formation of branched chains. Joncryl ADR is a family of epoxy-based multifunctional oligomer chain extender that is formulated to react with the terminal group of polyesters [12-13]. Joncryl® ADR 4468 (J) is a multi-functional reactive polymer with high thermal stability that is utilized in food and beverage application involving polycondensation polymers such as PET, PLA, and poly (butylene terephthalate) (PBT). Many prior studies have shown that adding a chain extender or performing the SSP procedure can increase the IV values and enhance the mechanical characteristics of post-consumer PET. Adding a chain extender to PET raises the molecular weight of the rPET component by simultaneously broadening and lengthening the chains in the polymer [14]. It has been shown that adding J in- creases the IV and molar mass of recycled PET to greater values than are observed for virgin PET. 3 Some investigations have investigated whether J may increase the crystallization rate of thermo- plastics with sluggish crystallization, such as PET and PLA [15,16]. A few studies have revealed that reactions performed under vacuum conditions improve the IV of PET. As reported by Ma et al., the elimination of water and ethylene glycol using the SSP process enhances the IV of PET [17]. With SSP at 240-245 °C for 3-5 h, the IV may be raised to 0.72 dL/g and the terminal group of PET can be reduced to less than 20 meq/kg [9,18]. Various studies indi- cate that the IV of PET is influenced by its molecular weight and moisture content. By-products are eliminated during the SSP process, which raises the molecular weight of recovered PET [19- 21]. In this work, three techniques were utilized to rebuild the IV characteristics of post-consumer PET- B with 10-20 wt% PET-T to performance matching that of virgin PET. These techniques included SSP, chain extension, and chain extension coupled with SSP. Thermal, rheological, and mechanical characteristics of post-consumer PET-B with 10-20 wt% PET-T were also examined following various treatments. 1.2 Objectives The objective of the research was to create and develop commercial bottle-grade PET from recy- cled pellets composed of PET-B and PET-T. To achieve this objective, two specific research tasks were pursued in this investigation. Firstly, we investigated the consequence of using SSP on the thermomechanical characteristics of an rPET blend created in pellet form from PET-B and PET-T. Secondly, we evaluated the effect of the chain extender (CE) on rPET pellet blend characterizations like its physical shape, and rheological and thermomechanical properties. 4 1.3 Thesis Work Scope The scope of the research is to create commercial bottle-grade pellets from recycled PET-B and PET-T. PET is the most recycled and widely used plastic. Almost 2.91 million tons of PET bottles were recycled in 2022 but that process required the separation of PET-T from bottle streams [0]. This research will help in incorporating PET-T along with PET-B. The research will create ther- moform and bottle PET blend pellets from recycled material with the help of SSP and chain ex- tension and enhance the thermal and mechanical characteristics of these rPET blends so that they are equivalent to those of bottles created from virgin pellets. In addition, we can create a consistent recycling stream that includes both bottle-grade and thermoform materials. 1.4 Hypothesis The first hypothesis is that adding the commercial chain extender Joncryl ADR to a recycled PET blend made of PET-B and PET-T is necessary for bottle making while retaining or improving the desirable thermal and mechanical properties. The second hypothesis is that the combination of chain extension with SSP is likely to increase the intrinsic viscosities necessary for bottle-making purposes while retaining or improving the de- sirable thermal and mechanical properties. 5 Figure 1.1: Schematic representation of a process for recycled PET-B and PET-T blends using chain extension and SSP to create commercial bottle-grade pellets. 1.5 Structure of the Thesis This thesis is divided into five chapters, and the contents of these chapters are outlined below: Chapter 1 introduces the hypothesis, scope, and objectives of this work. Chapter 2 lays out the literature review on PET recycling techniques, chain extenders, and SSP processes. Chapter 3 discusses the materials and methodology used in this study. Chapter 4 provides the results obtained during this research. Chapter 5 summarizes the overall conclusions and discusses the future scope of the research con- ducted. 6 REFERENCES 1. Alves, B. U.S. plastic bottle recycling rates by type 2020. Association of Plastic Recyclers, 2023. https://www.statista.com/statistics/623553/plastic-bottle-recycling-rates-in-the-us-by- material-type/ (accessed 2023 May 5th, 2023). 2. Kasmi, N.; Bäckström, E.; Hakkarainen, M. Open-loop recycling of post-consumer PET to closed-loop chemically recyclable high-performance polyimines. Resources, Conservation and Recycling 2023, 193, 106974. DOI: https://doi.org/10.1016/j.resconrec.2023.106974. 3. Jang, J. Y.; Sadeghi, K.; Seo, J. Chain-Extending Modification for Value-Added Recycled 860-889. DOI: Reviews 2022, (4), 62 PET: A Polymer 10.1080/15583724.2022.2033765. Review. 4. Steve Navedo, R. D. a. C. G. Thermoform recycling realities. Resource Recycling, Inc 2022. https://resource-recycling.com/plastics/2021/11/24/thermoform-recycling-realities/ (accessed 2023 5/18/2023). 5. Selke Susan E M, J. D. C., Rafael Auras, Muhammad Rabnawaz. Plastics packaging: Proper- ties, processing, applications, and regulations. ; Hanser Publishers, 2021. 6. Agostinho, B.; Silvestre, A. J. D.; Sousa, A. F. From PEF to rPEF: disclosing the potential of deep eutectic solvents in continuous de-/re-polymerization recycling of biobased polyes- ters††Electronic supplementary information (ESI) available: Experimental details, synthetic procedures, characterization data, NMR spectra. See DOI: 10.1039/d2gc00074a. Green Chem- istry 2022, 24 (8), 3115-3119. DOI: https://doi.org/10.1039/d2gc00074a. 7. Polymers: Intrinsic viscosity measurements for quality control of pet. Anton Paar. (n.d.). https://www.anton-paar.com/corp-en/services-support/document-finder/application-re- ports/polymers-intrinsic-viscosity-measurements-for-quality-control-of- pet/#:~:text=The%20intrinsic%20viscosity%20is%20dependent,grades%20(see%20Ta- ble%201). 8. Dulio, V.; Po, R.; Borrelli, R.; Guarini, A.; Santini, C. Characterization of low-molecular- weight oligomers in recycled poly(ethylene terephthalate). Die Angewandte Makromolekulare Chemie 1995, 225 (1), 109-122. DOI: https://doi.org/10.1002/apmc.1995.052250110. 9. Chang, S.; Sheu, M.-F.; Chen, S.-M. Solid-state polymerization of poly(ethylene tereph- thalate). Journal of Applied Polymer Science 1983, 28 (10), 3289-3300. DOI: https://doi.org/10.1002/app.1983.070281023 (accessed 2023/06/20). 10. Liu, B.-C.; Xu, Q. Effects of Bifunctional Chain Extender on the Crystallinity and Thermal Stability of PET. Journal of Materials Science and Chemical Engineering 2013, 2013, 9-15. 7 11. Arruda, L. C.; Magaton, M.; Bretas, R. E. S.; Ueki, M. M. Influence of chain extender on mechanical, thermal and morphological properties of blown films of PLA/PBAT blends. Pol- ymer Testing 2015, 43, 27-37. DOI: https://doi.org/10.1016/j.polymertesting.2015.02.005. 12. Corre, Y.-M.; Duchet, J.; Reignier, J.; Maazouz, A. Melt strengthening of poly (lactic acid) through reactive extrusion with epoxy-functionalized chains. Rheologica Acta 2011, 50 (7), 613-629. DOI: 10.1007/s00397-011-0538-1. 13. Saabome, S. M.; Lee, J. E.; Hong, J. S.; Kim, D. H.; Ahn, K. H. ``Mechanical degradation of poly(ethylene terephthalate) and its structural modification by chain extender. Korea-Australia Rheology Journal 2023. DOI: 10.1007/s13367-023-00059-w. 14. Incarnato, L.; Scarfato, P.; Di Maio, L.; Acierno, D. Structure and rheology of recycled PET (18), 6825-6831. DOI: extrusion. Polymer 2000, 41 reactive modified by https://doi.org/10.1016/S0032-3861(00)00032-X. 15. Tavares, A. A.; Silva, D. F. A.; Lima, P. S.; Andrade, D. L. A. C. S.; Silva, S. M. L.; Canedo, E. L. Chain extension of virgin and recycled polyethylene terephthalate. Polymer Testing 2016, 50, 26-32. DOI: https://doi.org/10.1016/j.polymertesting.2015.11.020. 16. Standau, T.; Nofar, M.; Dörr, D.; Ruckdäschel, H.; Altstädt, V. A Review on Multifunctional Epoxy-Based Joncryl® ADR Chain Extended Thermoplastics. Polymer Reviews 2022, 62 (2), 296-350. DOI: 10.1080/15583724.2021.1918710. 17. Ma, Y.; Agarwal, U. S.; Sikkema, D. J.; Lemstra, P. J. Solid-state polymerization of PET: influence of nitrogen sweep and high vacuum. Polymer 2003, 44 (15), 4085-4096. DOI: https://doi.org/10.1016/S0032-3861(03)00408-7. 18. Jabarin, S. A.; Lofgren, E. A. Solid state polymerization of poly(ethylene terephthalate): Ki- netic and property parameters. Journal of Applied Polymer Science 1986, 32 (6), 5315-5335. DOI: https://doi.org/10.1002/app.1986.070320607 (accessed 2023/06/20). 19. Qiu, G.; Huang, N.-X.; Tang, Z.-L.; Gerking, L. Modelling of solid state polycondensation of poly(ethylene terephthalate). Chemical Engineering Science 1997, 52 (3), 371-376. DOI: https://doi.org/10.1016/S0009-2509(96)00414-9. 20. Karayannidis, G. P.; Kokkalas, D. E.; Bikiaris, D. N. Solid-state polycondensation of poly(eth- ylene terephthalate) recycled from postconsumer soft-drink bottles. II. Journal of Applied Pol- ymer Science 1995, 56 (3), 405-410. DOI: https://doi.org/10.1002/app.1995.070560311 (ac- cessed 2023/06/20). 21. Karayannidis, G. P.; Psalida, E. A. Chain extension of recycled poly(ethylene terephthalate) with 2,2′-(1,4-phenylene)bis(2-oxazoline). Journal of Applied Polymer Science 2000, 77 (10), 8 2206-2211,. APP14>3.0.CO;2-D (acccessed 2023/06/20). DOI: https://doi.org/10.1002/1097-4628(20000906)77:10<2206::AID- 9 CHAPTER 2: REVIEW OF LITERATURE 2.1 PET Polyethylene terephthalate (PET), a type of polycondensation polymer, is synthesized from eth- ylene glycol (EG) and terephthalic acid (TPA) or terephthalic ester. PET is widely employed in the packaging industry due to its favorable attributes, including strong mechanical properties, impres- sive optical and thermal characteristics, and effective barrier properties [1]. PET was first created by the USSR and Great Britain in 1941 through the polycondensation process of EG and TPA. In the 1970s, the large-scale production of PET bottles and containers commenced. By 2019, the worldwide yearly manufacturing capacity for polyethylene terephthalate (PET) had reached approximately 30.5 million metric tons. This capacity is projected to rise to 35.3 million metric tons per annum by 2024. PET is the dominant polymer utilized in the production of bottles. [2]. The Global waste generated by PET plastics waste accounts for 12% of global plastic waste produced. 30% of PET bottles are recycled today, while 70% are sent to landfills. There is a strong interest in further increasing PET recycling. However, the rPET (post-consumer recycled or post- consumer resin PET) ends up mostly in fibers and some in bottles, despite there being an interest in bottle-to-bottle PET. 2.1.1 Structure and Properties Figure 2.1: Chemical structure of PET. PET is formed through the polycondensation of dimethyl terephthalate (DMT) or terephthalic acid (TPA) with ethylene glycol (EG). PET possesses ester bonds within its backbone structure and has 10 a melting point ranging between 250-260⁰C. The density of PET varies based on its level of crys- tallinity, with crystal PET exhibiting a density of 1.455 g/cm³, while amorphous PET has a density of 1.333 g/cm³ [3]. Bottle-grade PET is often produced in 3 stages: i) transesterification, ii) pre-polymerization, iii) polymerization, and iv) SSP. The esterification of EG and TPA at 180⁰C creates BHET bis(hydrox- yethyl)terephthalate. Then BHET is further polymerized at 220 ⁰C under vacuum. Then the melt condensation of the polymer is done at 150-2200⁰C up to the degree of polymerization of about 100 [4]. With the help of a catalyst like antimony triacetate in a helical screw reaction, the SSP process is executed at 200-230⁰C below melting temperature 240-260⁰C where the PET polymer pellets are created. Most of the PET have CEs when the pellets are made. The application of these chain extenders (CEs) accelerates the production rate, thereby raising the molecular weight of PET [5]. Figure 2.2: PET synthesis from TPA and EG [6]. The benzene ring in the main chain of PET polymer gives stiffness to the polymer. Tg for PET ranges from 67-81⁰C depending on its crystallinity and the melting point for PET is 256-260⁰C [7,8]. 11 Figure 2.3: Properties of PET polymer. Table is taken from ref. [3]. Selke Susan E M, J. D. C., Rafael Auras, Muhammad Rabnawaz. Plastics packaging: Properties, processing, applications, and regulations.; Carl Hanser Verlag Munich, 2021.with permission from the publisher. The above table shows the typical properties of a PET polymer. The tensile strength of the virgin polyethylene terephthalate polymer comes in the range of 48.2-72.3Mpa and the elongation varies from 30-3000% depending on the long chain of PET and the crystals of the PET. The PET polymer has a good O2 and CO2 barrier but poor water vapor and water barrier. Most PET containers or bottles are clear and transparent due to high crystallinity but can also be found in a hazy color if the amorphous regions are present in the structure [3]. 2.1.2 Different Types of Commercial PET PET is one of the most utility plastics that is being used globally. Due to its versatility, it can be used as a thermoplastic polymer, or when processed it can be created as strong and as functional as a thermosetting polymer. 5 different types of PET can be seen in use widely Oriented Polyeth- ylene terephthalate (OPET), Polyethylene terephthalate glycol (PETG), Extrudable Polyethylene 12 terephthalate EPET, Cyclohexylenedimethylene Terephthalate (PCTG), and Polyethylene tereph- thalate (PET) [9]. PETE or PET: It is a semicrystalline PET homopolymer. it can be rigid or semi-rigid. This PET can find utilization in sophisticated applications including industrial components, pharmaceutical and medical device components, automotive parts, and electrical circuit elements. OPET: Oriented PET is used for high-end applications because of its high tensile properties and stability. OPET is used for fiber and films. OPET is created by heating and stretching the unbal- anced chains in the polymer molecules and then arranged in a parallel way in the stretched direc- tion. This helps to increase the clarity and barrier properties of PET [1,3]. EPET: Extrudable PET (EPET) resins have very high melt viscosity and slow crystallization rate, which makes the processing of PET resins easier for extrusion blown film and extruded blow molded bottle applications. APET: Amorphous PET is the PET resins made so that the polymer remains amorphous using the copolymerization technique. There are two types of amorphous PET. PETG and PCTG. PETG is a copolymer made from EG and TPA in the presence of isophthalic acid and diethylene glycol [10]. The modifier makes sure it reduces the crystallization rate and melting point of the polymer. They also make sure that no orientations in crystals take place. PCTG is a type of PETG made from the copolymerization of TPA and EG by adding a few mol percent of cyclohexane di-methanol in the PET structure to create a copolymer. Both PETG and PCTG have good chemical resistance and clarity. PCTG is known for its excellent impact resistance and is majorly used in cosmetic indus- tries. PETG is used in food industries for trays and in medical sectors for making thermoforms due to its excellent clarity [9-11]. 13 2.1.3 PET Application Because of its adaptable nature and favorable physical and chemical attributes, PET finds exten- sive application in sectors like food and beverage, pharmaceuticals and medical fields, automotive manufacturing, electronics, power tools, as well as clothing and textiles. [10]. If we use CPET (crystallized PET) we can use it in applications like packaged frozen food, microwaveable con- tainers, and toiletries. Oriented PET in film and sheet forms can be used for laminations in food packaging, cheese, and meat packaging, creating boil-in-bags. Oriented PET is also used in the medical industry as sterilizable pouches and thermoform trays [3]. PETG is specially used in med- ical industries as it can be sterilized with gamma radiation and ethylene oxide. Also, due to its semi-crystalline nature and high thermal degradation temperature PETG can be used in 3D printing industries [11-12]. 2.2 Recycling Recycling of plastic is the collecting of plastic material or waste generated from either post-con- sumer or post-industrial use and using the recovery of the material in use to make the same product or different end-use product. Addressing the environmental repercussions of plastic waste has made polymer waste recycling a vital solution. Recycling can be classified into four distinct cate- gories: primary recycling (mechanical recycling of industrial waste), secondary recycling (me- chanical recycling of consumer plastics), tertiary recycling (chemical recycling), and quaternary recycling (energy recovery). [13]. Primary recycling includes recycling and creating similar qual- ity products from post-industrial materials. Mechanical recycling of rPET is secondary recycling, which involves cleaning and reprocessing of the material. Often down-cycling, such as creating textiles from bottle-grade material or creating plastic lumber from the material. Sometimes the 14 polymer or material is depolymerized in monomers and remade again. The last type of recycling is quaternary recycling, where the polymer is converted into energy from the waste generated [14]. Recycling is broadly categorized into two main types: chemical recycling and mechanical recy- cling. Most of the thermoplastics can be mechanically recycled [13]. The recycling process follows collection, sorting, cleaning, and grinding before melt-reprocessed into pellets (mechanical recy- cling) [15] or contaminated plastics are converted into flakes and depolymerized into small mole- cules (chemical recycling). 2.2.1 PET Recycling As PET is extensively recycled, to boost waste management and reduce the price of PET pellet creation of rPET pellets was started in 1977 [16-17]. PET soft drink bottles were the first post- consumer plastic containers to be recycled on a wide scale in the United States. As previously stated, they benefitted from the existence of bottle deposit legislation in several states. The use of PET in packaging applications has expanded fast. Fiber applications of different sorts have been the greatest end-use market for recovered PET, ranging from fiberfill for ski coats and sleeping bags to face yarn for polyester carpets. Over the last decade, the utilization of rPET in food and beverage bottles has grown considerably [3]. In the last few years, the creation of packaging ma- terial from post-consumer recycled material (RPET) has increased dramatically [18-19]. In recent years the utilization of bottle PET for recycling has become significant due to the production ac- cessibility, and purity of PET material in bottle packaging. Furthermore, the recycling of PET from bottles and PET used in food packaging holds significance, as other recycled PET materials tend to contain higher levels of contaminants and are typically limited to non-food contact applications. [16]. 15 2.2.2 Mechanical Recycling Mechanical Recycling of PET means reprocessing either post-consumer or post-industrial PET by shear force and extreme heating conditions without changing the polymer structure and chemical properties [20]. The steps for mechanical recycling are getting the materials separated according to their polymeric system. Followed by the cleaning process, which involves washing dirt and other contaminants, then grinding and shredding polymeric products into smaller flakes, cleaning the flakes from contaminants, and subsequent extrusion of the flakes into PET pellets, after creat- ing the pellets the pellets are converted into PET products like bottles, textiles, straps and other packaging materials [20]. Currently, mechanical recycling remains the most commercially viable option due to its cost-effectiveness and energy efficiency. 2.2.2.1 Method of Creating Mechanically Recycled Pellets Mechanical recycling of PET involves collection, flaking, cleaning, drying, and palletization [21]. These pellets are then enhanced into desired pellets for various applications. PET bottle mono- collection systems produce high-purity rPET [22]. The technique and sorting equipment employed are critical to have good quality rPET. The separation process is based on identifying a feature that distinguishes between PET and a specific adulterant or impurities, such as density, melting tem- perature, and the NIR (near-infrared) spectrum. Based on these distinctions, identification, and separation are performed [23]. The first method is to start manual sorting. The garbage is placed on a conveyor belt before entering the recycling line. Workers are stationed along the conveyor belt to gather and discard things that do not need to be introduced into the recycling process [24]. Automated sorting is considered to be more reliable, efficient, and proficient in handling substan- tial waste volume compared to manual sorting. In cases where recycling facilities manage larger 16 waste quantities, the initial costly investment can be recovered over time. However, for certain tiny plants, this may not be possible. Various systems, such as machine vision or NIR sorting, can be employed [24-25]. Flotation is a widely used separation method that relies on the principle of density variations. It's a straightforward and cost-effective technique. In this process, the mixed plastic flakes are placed in a tank with a floating medium. Plastics with densities more than the medium sink to the tank's bottom, while those with lower densities float. Typically, water is utilized as the flotation medium. In this setup, PET sinks while the remaining plastics float, allowing for effective separation [26]. For full bottles and powdered PET flakes, NIR sorting technologies are commonly utilized. The reason for this is that near-infrared sensors can identify a series of different materials quickly and consistently, allowing for larger throughputs. NIR, on the other hand, this method struggles to differentiate between different types of packaging waste made from identical polymer (like PET bottles and PET trays), as well as polymers with similar spectral characteristics, such as polyeth- ylene terephthalate glycol (PETG) and polyethylene terephthalate [25-26]. 2.2.2.2 Cleaning and Drying Process Before shredding PET, bottles, or thermoform, they are washed to remove labels and adhesives using hot water, scrubs, and brake cleaning solutions. When all rPET is cleaned, the cap and the safety seal must be removed and then cut into flakes. The incoming flake might be clean or un- clean; all reclaimed flakes are cleaned as part of the reclaimer processing procedures. This proce- dure can be carried out using a caustic wash; however, other recyclers have mentioned the utiliza- tion of various washing products like defoamers, surfactants, and wetting agents. [27]. The PET flakes are washed three times in the following order: clean using water for 10 minutes, using 1% aqueous sodium hydroxide solution for five minutes, and again clean using water for 10 minutes. 17 PET flakes, after washing, are dried in a regular oven at 160 ⁰C for 6 hours or at 80 ⁰C for 12 hours [28]. PET bottles that have been used for non-food purposes, possibly containing hazardous mate- rials, are consistently gathered and introduced into the recycling system. Consequently, these non- food containers could potentially introduce contaminants into the recycled PET (rPET) product. It's essential to keep these non-food PET bottles separate in the collection process. To enhance the decontamination effectiveness of rPET bottles intended for direct food contact packaging, a tech- nique known as super-clean recycling or deep-clean recycling has been adopted. This process in- volves three main phases: (1) high-temperature cleaning, (2) gas-based cleaning, and (3) chemical cleaning [16,29]. 2.2.2.3 Extrusion Process Shredded and dried PET flakes are fed into an extruder for pelletization/granulation. Extrusion involves the melting of PET flakes for palletization. The extrusion also helps to get rid of leftover contamination (volatiles by venting and pigments/dirt by screening), particularly regarding food- grade rPET [30-31]. Although washing and sorting processes effectively eliminate a substantial portion of contaminants, they are inadequate in addressing organic impurities that may be embed- ded within the plastic structure. Additionally, PET flakes are transformed into pellets for easier handling during the extrusion phase. Following extrusion, these solid rPET pellets undergo solid- state polymerization (SSP). The pellets are exposed to temperatures ranging from 180 to 220 °C, which is above the glass transition temperature of PET but below its melting point, ensuring the pellets remain in a non-melted state. The prescribed conditions prevent thermal degradation and facilitate polymer condensation. This condensation process leads to the formation of longer PET chains and an increase in intrinsic viscosity (IV) [32]. 18 rPET flakes are heated until they melt in the process at 280 °C. The molten plastic is then forced through a die, resulting in cylindrical pellets. These pellets may be recycled as raw materials in manufacturing operations, lowering raw material prices. The strand pelletizer forms pellets from molten plastic strands, whereas the underwater pelletizer immerses the plastic melt in water to cool and solidify the pellets. Before cutting the plastic melt into pellets, the water ring pelletizer cools and hardens it in a ring of water [33-34]. 2.2.3 Chemical Recycling The hydrolysis of ester linkages can lead to the breakdown of PET into monomers, oligomers, and various other compounds [35]. Chemical recycling of PET has numerous advantages, including providing a true closed-loop approach (e.g., bottle-to-bottle recycling for an almost infinite cycle of recycling), providing mechanical and thermal properties which is equivalent to virgin polymer, the absence of contaminants, and thus yielding polymer suitable for applications like food contact packaging material. Chemical recycling is the sole method that aligns with the principles of 'sus- tainability' as it generates new raw materials. Moreover, additional resources for PET production are unnecessary when employing chemical recycling for PET. Multiple techniques are utilized for the chemical recycling of PET, including hydrolysis, glycolysis, and methanolysis [36-37]. PET can also be chemically recycled to feedstock for polyurethane and unsaturated polyester resins. Glycolysis is the most widely employed, as the resulting BHET can be utilized to produce PET. However, the downside of chemical recycling is its elevated cost. 2.3 Recycled PET content 2.3.1 Demand for Recycled PET The projected value of rPET demand is anticipated to rise from 11 billion USD to 15 billion USD within 5 years. Because of the demand for sustainable packaging materials and products, the 19 people find alternative ways to reduce the use of a virgin polymer that comes from non-renewable resources, as efforts to save the environment the demand for recycling is growing even higher. Also, government regulations and policies focus on the use of recyclable materials and circular economy [38]. However, even with ambitious goals for incorporating recycled materials in the long run, the demand for recycled polyethylene terephthalate (rPET) is forecasted to maintain a relatively modest trend in 2023. This could potentially lead to downward pricing pressures in the United States. Around 80% of the rPET capacity in the United States originates from post-con- sumer sources, primarily bottles, while the remaining 20% is sourced from post-industrial feed- stock [39]. During the forecast period, bottles are predicted to be the most significant and fastest- growing application in the rPET Market. The momentum behind PET recycling is anticipated to stem from its minimal energy requirements and the straightforward bottle-to-bottle recycling process. Throughout the projected timeframe, the utilization of PET in food, beverage, and bottle applications is predicted to exhibit the highest compound annual growth rate (CAGR). The Asia Pacific region emerged as the global leader in terms of revenue, and this region is projected to sustain a steady CAGR during the forecast period [40]. 2.3.2 Effect of Contamination One of the significant issues with rPET content is the presence of unwanted contamination in it. rPET tends to get moisture content to it faster than virgin PET material, which creates problems of sticking, and clogging, and degradation during the processing. Also, during the drying of rPET, contaminants like vinyl ester are produced [6,41]. During reprocessing and extrusion at high tem- peratures, acidic compounds are generated from polyethylene vinyl acetate (PVA) lines, adhesives, and labels. Also, by-products like acetaldehyde produce vinyl ester, which affects PET polymer 20 and is volatile and harmful for bottles and food packaging applications [42]. The presence of metal ions also affects the rPET content. Metal ion contaminants affect the melting behavior of polymers [43]. 2.3.3 End-use Application This industry's expansion may be due to the coordinated development of food and beverage, do- mestic applications, personal care goods, and other consumer packaged goods. rPET flakes are used in fibers to make a variety of apparel items, such as polyester clothing. They are also utilized in the production of automotive seat coverings, furniture textiles, carpets, and so on. The cost- effectiveness of producing clothing from recycled polyethylene terephthalate pellets is anticipated to drive a surge in global usage for rPET pellets. The presence of a robust manufacturing industry, in which rPET is widely employed across a variety of applications, can be attributed to the expan- sion [3]. The increasing investments in manufacturing facilities focused on recycling, particularly in the Asia Pacific region, are foreseen to boost the demand for recycled polyethylene terephthalate (rPET) flakes, particularly for the production of non-food bottles and containers [38,40]. The es- tablishment of advanced bottled water production plants and the rise in tourism, particularly in Asia Pacific, are projected to stimulate the demand for bottled water, consequently driving the utilization of recycled polyethylene terephthalate flakes for the creation of food and beverage bot- tles and containers. The United States recovers over 1.5 billion pounds of discarded PET plastic bottles and containers (such as beverage bottles and cosmetic containers) for recycling each year. Recycled PET (rPET) plastic serves as a versatile material for crafting bottles, clamshell food containers, trays, cups, carpets, garments, and fiberfill, among other items. A notable aspect of PET plastic is its recyclability, as recycling facilities can incorporate additives to enhance the 21 intrinsic viscosity (IV) of rPET during the recycling process. IV signifies the polymer's molecular weight, encompassing its melting point, crystallinity, and tensile strength. Both PET and rPET plastics are secure and practical for food packaging. Nevertheless, obstacles in the bottled water sector's adoption of rPET plastic arise from cost considerations, contamination issues, and supply constraints [40]. 2.4 Challenges in Mechanical and Chemical Recycling of PET The challenge of generating recycled resins from plastic waste stems from the intrinsic immisci- bility of most distinct plastic types at the molecular level, coupled with differences in processing requirements on a larger scale. The presence of even a small amount of non-compatible plastic in a PET recycling stream can lead to damage to the recovered PET resin. This occurs due to the generation of by-products at higher temperatures required for melting and reprocessing PET. In- corporating recovered plastic into new polymers often presents physical limitations without com- promising certain qualities of virgin plastic, including color, clarity, or mechanical properties like impact strength. The feasibility of substituting recycled plastic for virgin polymer is primarily in- fluenced by the purity of the recycled plastic feed and the specific property demands of the end plastic product. Consequently, contemporary recycling systems for post-consumer waste prioritize the recycling of packaging that can be easily separated, such as PET soft drinks and water bottles. [13,44]. The major difficulty of mechanical recycling of PET is its lower purity. PET is often combined with additives and composite material to enhance its physical and chemical properties. Also, PET can be chemically recycled but currently, chemical recycling is not much done at the commercial level [14-15]. One of the major issues with using recycled content is the degradation of IV during chemical and mechanical recycling. Due to shear force and high heating conditions in chemical 22 and mechanical recycling, the IV of the plastic reduces. Also, sometimes the catalyst used for depolymerization during chemical recycling negatively affects the PET polymer during repro- cessing. 2.4.1 The Challenge of Thermoforming in Bottle-Grade PET The variability of PET resins used in thermoform manufacture is the primary concern, ther- moforms are not routinely recycled. Even though PET is the favored material in the recycling sector, thermoforms constructed from OPS (oriented polystyrene) continue to be popular. Further- more, some thermoform producers employ PET substitutes such as PLA, PVC, and PETG [45]. Another significant technological problem is labels and adhesives. The labels used in clamshell PET containers vary widely, including the ongoing use of recycling with contaminated paper la- bels. The most favorable label substrates for PET recycling are polyolefin-based, the most often used label is polypropylene. In the reclamation process, the thinness of thermoform trays poses a "bulk density" concern (clogging of the polymer thermoform samples into the recycling stream). Before washing, Plastic bottles and containers are transformed into chips by crushing, and if these chips are too lightweight, they may encounter challenges in smoothly traversing through the wash- ing process. [46]. When bottles and thermoforms are melted together, the intrinsic viscosity of PET thermoforms is often less compared to that of PET bottles, posing complications. Following washing, the intrinsic viscosity of post-consumer thermoforms regrind can be improved through solid-state processing during decontamination and reprocessing. This enhancement is geared towards tailoring the mate- rial for specific end-use applications, like PET bottles, which demand a higher intrinsic viscosity compared to the initial sheets used in producing the thermoforms [45-46]. PETG should be omitted from the input materials in the recycling stream of PET bottles due to its 23 incompatibility with PET. However, this situation becomes more complicated. It has been chal- lenging to distinguish PETG from PET as they have similar morphologically and density. Due to these factors, recycling companies urge PET bottle manufacturers to explore substitute materials. Nevertheless, PET bottle producers are reluctant to relinquish the advantages of this superior material. The inclusion of PETG leads to notable challenges during the granulation pro- cess. Additionally, owing to PETG's lower melting point compared to PET, it can result in the formation of an adhesive mass during drying and transfer operations. Furthermore, it can cause blockages of the PETG polymer within the extruder's mandrels before extrusion. Another unfavor- able consequence is rPET browning [6,47]. Furthermore, PETG contains glycol. EG is utilized in the chemical recycling of PET (glycolysis) to break polymeric chains. Depending on the circumstances, a similar effect might occur when glycol is eliminated during granulation, influencing the intrinsic viscosity of rPET [48]. 2.4.2 Intrinsic Viscosity of PET and its Relevance for Processing In a cost-efficient manner, Intrinsic Viscosity (IV) serves as a rheological measurement indicating the polymer's average molecular weight. Fundamentally, PET's IV is indicative of its molecular weight. Typically, virgin PET boasts a higher IV than rPET, given that the latter is subjected to degradation processes including elevated temperatures, shear forces, hydrolysis, and the influence of contaminants and moisture [49]. When PET is recycled at a higher temperature than its melting temperature, volatile compounds are generated with a decrease in the IV of the polymers. The IV of a polymer increases with the polymer’s molecular weight and high IV values are essential for better Thermo-mechanical characteristics. The IV of the polymers is directly proportional to the length of the polymer chains. The more chain entanglement, the higher the viscosity. Different applications of PET have different grades of pellets. Each pellet has a different intrinsic viscosity. 24 The inherent viscosity is impacted by the length of polymer chains. Longer polymer chains lead to increased entanglements between them, resulting in higher viscosity values. PET's intrinsic vis- cosity is determined by its use and is divided into the following grades. Table 2.1: IV values of different PET grades [31,49]. Application IV (dl g-1) Bottle Grade Carbonated Drinks Film Grade Tape Grade Fiber Grade 0.70 – 0.78 0.78 – 0.85 0.70 – 1.00 0.60 0.40 – 0.70 The critical feature of intrinsic viscosity arises where the properties of the rPET need to be con- trolled. IV is important for PET to have consistent production of the PET or rPET bottle, pipes, and caps in processing conditions, it is important to maintain and control the quality in the PET manufacturing sector [50]. As PET loses the metallic catalyst used for polymerization during recycling, it leads to a reduction in the intrinsic viscosity of rPET. To increase the intrinsic viscosity various techniques have been used. One approach involves employing thorough drying alongside vacuum degassing to eliminate moisture from the polymer, thereby enhancing the molecular weight of rPET. Another technique is to implement solid-state polymerization, leading to an increase in both Mw (molecular weight) and IV (intrinsic viscosity) of the polymers. A less expensive option for increasing the IV of the polymer for processing is to add a stabilizer or CE to the polymer to increase the Mw thereby increasing the IV of the polymer [50-51]. 25 2.5 Solid-State Polymerization (SSP) Solid-state Polymerization (SSP) is an approach to increase the molar mass of the polymer by enabling a reaction between the terminal group in a solid state [53-54]. For SSP treatment, PET is heated at temperature below Tm of the plastic and above the (Tg) to increase its molecular weight. SSP is usually done in the presence of inert gases under a vacuum [54]. The SSP process helps the amorphous phase of the polymer mobile enough so that it can react with the terminal group and crystalline phase with restricted mobility [55]. With the process of SSP under vacuum or inert gases, the unwanted by-products are removed, and the molecular weight of the polymer increases. The SSP process can be integrated into the recycling process to enhance the molecular weight of the recycled material, SSP also enhances the properties of rPET which deteriorated during the reprocessing the post-consumer polymer [56]. 2.5.1 Types of SSP The two procedures used for SSP include batch and continuous process. In the continuous process of SSP, the polymer is heated and mechanically agitated in glass tubes, rotating flasks, or vertical reactors. The weight of the reacting mass is continuously checked for water being formed [57]. One process of SSP is to heat the polymer at a temperature higher than 200 ⁰C under vacuum conditions. SSP under vacuum is less time-consuming to attain a higher molecular weight polymer. SSP under vacuum also helps the polymer create proper orientation amongst the chains. But SSP under vacuum can cause oxidation and discoloration of the PET plastic. Another drawback of SSP under vacuum is low polymerization rates, so it is feasible for large batches to create a good yield of polymer [58]. The other technique of SSP under high temperatures inside an oven is to pass inert gases through the polymeric sample. Nitrogen (N2), Helium (He), and Carbon Dioxide (CO2) are used for SSP 26 treatment of PET. The benefit of using SSP under inert gases is, it suppresses deterioration and discoloration. This is also a little quicker [58-59]. When both techniques are combined, it provides proper monomer maintenance in reactors and the removal of unintentional by-products to have an appropriate polymerization. 2.5.2 Effect of SSP on PET SSP of PET increases crystallinity in a polymer due to monomer cyclization, and undesired reac- tions are prevented. The process improves the stability of PET under higher heating temperatures which is useful for processing the recycled material under an extruder. Also, SSP helps in improv- ing the linearity in the chain than can prevent ultra cross-linking of the polymer during reactive extrusion and other processing. Another advantage of SSP is that it removes unwanted monomer and volatile byproducts and moisture, and thus improves the processing of PET resin and the qual- ity of rPET [53,60]. 2.6 Chain Extenders (CE) Chain Extenders (CE) are additives that can adjust the rheological properties of the polymer with chemical modifications done in reactive melt processing conditions. CEs are usually used to im- prove the characteristics of mechanically recycled PET and reduce the amount of chain scission in rPET [61]. The objective of using chain extenders (CEs) is to interact with the terminal groups of polyethylene terephthalate (PET), elongating the PET chains and minimizing the likelihood of material decomposition. This process helps maintain the desired molecular weight [62-63]. CEs are usually used in polymer and recycled contents of PET polyethylene terephthalate (PET), pol- yamides (PA), polyoxymethylene (POM), thermoplastic polyurethanes (TPU), polybutylene ter- ephthalate (PBT), bisphenol A-based polycarbonates (PC) to reduce the degradation of these 27 polymeric materials. Different CEs have other purposes; some CEs are plasticizers, and some im- prove melt-processing and dispersion of fillers in plastics [64]. Different types of CE can be found according to the functional group. Epoxy CE which promotes an increase in the chemical resistance and mechanical characteristics. The chain extender have epoxy functional groups which react with polymers terminal groups. Usually, they are used for food contact material and mainly used with PBAT, PET and PLA which react with the carboxyl group of the polymer and increase the number of chains. Isocyanates are used during pre-polymer- ization process of material like PU, PLA, and PET, it is used to enhance the molecular weight and IV of polymers like PET and PLA and increase the elongation at break from 5-300%. Oxazolines are low toxic and transparent materials. Oxazolines are capable of forming ester-amide bonds by undergoing ring-opening reactions with carboxyl groups. Oxazolines are commonly utilized with oligomers in solution reactions, although melt processing has also been observed to result in higher molecular weight and melt strength. Anhydride has a reactive functional group with a high affinity for PET, which can increase rPET performance [64]. 2.6.1 Reactive Extrusion Method Polycondensation polymer like PET, PBT, PU tend to deteriorate during the extrusion process by acid hydrolysis and thermal degradations. This leads to decrease in the Mw and IV reduction and loss of the mechanical performance of the material [63,65]. To overcome the degradation, reactive extrusion is done where the polymer is extruded along with a CE in a single or twin-screw extruder [65]. For PET, the temperature set during the reactive extrusion is above 260 ⁰C and the concen- tration of the CE is kept below 2% wt. of the polymer. If the weight of the CE is increased, it increases the IV and Mw. Still, the polymer degrades inside the extruder due to the torque gener- ated, and the increasing shear force tends to degrade the polymer. 28 2.6.2 Effect of Chain Extender on the PET- CHEMISTRY Figure 2.4: Composition of epoxy based Joncryl chain extender taken from source [66] page 2 figure1 with permission from the Taylor francis. When PET goes through the process of mechanical recycling, the polymer tends to degrade thermo-mechanically during reprocessing in extruder due to shear force and high heating temper- ature. Thermal degradation decreases the Mw and IV of the polymers, which affects the mechanical properties of the material. The use of CEs like Joncryl® shows an increase in the Mw of the PET polymer. It also tends to increase the mechanical characteristics like tensile strength of the material. In the reactive extrusion of CE and PET, It has been shown that even with increased concentrations, the system can remain reactive after compounding. [66]. Different functional groups of CEs have different effects on PET chemistry. The utilization of epoxy groups can be attributed to their in- volvement in transesterification reactions with the carboxyl and hydroxyl end groups of PET. This chemical process generates additional hydroxyl groups, which in turn can interact with other epoxy groups [67]. The epoxy groups can react with the terminal groups of PET polymer to form extended chains. The ring-opening reaction of epoxy with PET follows two distinct pathways. The first involves a general interaction between the oxirane ring and PET's carboxyl groups, while the second pathway 29 involves a reaction with hydroxyl groups [68]. Through these chain extension methods, the inclu- sion of CE with the epoxy functional group to the processing will increase the rPET characteristics. The isocyanate's reactivity with the hydroxyl groups in rPET was observed to be faster compared to its reaction with the carboxyl groups. The initial reaction led to the formation of urethane groups, while the reaction between PET's carboxyl and isocyanate groups resulted in the creation of amide groups. Both of these PET branching reactions occurred within the temperature range of 250 to 280 ⁰C during processing. When subjected to extrusion temperatures within the range of 250-280 ⁰C, the OXA interacted with the carboxyl end-groups of the two PETs, resulting in the formation of a by-product known as an ester amide group [69,70] 30 REFERENCES 1. Berg, D., Schaefer, K., & Moeller, M. (2018). Impact of the chain extension of poly(ethylene terephthalate) with 1,3‐phenylene‐bis‐oxazoline and n, n′ carbonylbiscaprolactam by reactive extrusion on its properties. Polymer Engineering & Science, 59(2), 284–294. https://doi.org/10.1002/pen.24903 2. Tiseo, J. Production Capacity of Polyethylene Terephthalate Worldwide from 2014 to 2024. Available online: https://www.statista.com/statistics/242764/global-polyethylene-tereph- thalate-production-capacity/ (accessed on 10 January 2023). 3. Selke Susan E M, J. D. C., Rafael Auras, Muhammad Rabnawaz. Plastics packaging: Proper- ties, processing, applications, and regulations. ; Hanser Publishers, 2021. 4. https://www3.epa.gov/ttnchie1/ap42/ch06/final/c06s06-2.pdf. 5. K. Ravindranath, R.A. Mashelkar, Polyethylene terephthalate—I. Chemistry, thermodynamics and transport properties, Chem. Eng. Sci. 41 (9) (1986) 21972214. 6. Benyathiar, P., Kumar, P., Carpenter, G., Brace, J., & Mishra, D. K. (2022). Polyethylene ter- ephthalate (PET) bottle-to-bottle recycling for the beverage industry: A Review. Polymers, 14(12), 2366. https://doi.org/10.3390/polym14122366 7. Groeninckx, G., Berghmans, H., Overbergh, N., & Smets, G. (1974). Crystallization of poly (ethylene terephthalate) induced by inorganic compounds. i. crystallization behavior from the glassy state in a low-temperature region. Journal of Polymer Science: Polymer Physics Edition, 12(2), 303–316. https://doi.org/10.1002/pol.1974.180120207 8. Smirnov, P.V., Repina, L.P., Bunigina, N.S. et al. Transesterification of dimethyl terephthalate with ethylene glycol. Fibre Chem 15, 332–336 (1984). https://doi.org/10.1007/BF00548126 9. Edward. (2018, June 25). What’s the difference between pet, Opet, EPET, PETG and PCTG?: - O.Berk®. O.berk. Glass, Plastic, Metal Bottles https://www.oberk.com/packaging-crash-course/differences-in-pet and Caps Wholesale 10. Comprehensive guide on polyethylene terephthalate (PET). Polyethylene Terephthalate (PET) - Uses, Properties & Structure. (n.d.). https://omnexus.specialchem.com/selection-guide/poly- ethylene-terephthalate-pet-plastic 11. Guessasma, S., Belhabib, S., & Nouri, H. (2019). Printability and tensile performance of 3D printed polyethylene terephthalate glycol using fused deposition modelling. Polymers, 11(7), 1220. https://doi.org/10.3390/polym11071220 31 12. European Commission. Communication from the Commission to the Council, the European Parliament, the European Economic and Social Committee and the Committee of the Regions: Civil Society Dialogue Between the EU and Candidate Countries; European Commission: Brussels, Belgium, 2005; Volume 290. 13. Hopewell, J., Dvorak, R., & Kosior, E. (2009). Plastics recycling: Challenges and oppor- tunities. Philosophical Transactions of the Royal Society B: Biological Sciences, 364(1526), 2115–2126. https://doi.org/10.1098/rstb.2008.0311 14. Shen, L., & Worrell, E. (2014). Plastic recycling. Handbook of Recycling, 179–190. https://doi.org/10.1016/b978-0-12-396459-5.00013-1 15. Chanda, M., & Roy, S. K. (2007). Plastics technology handbook. CRC Press. 16. Welle, F. (2011). Twenty years of pet bottle to Bottle Recycling—an overview. Resources, https://doi.org/10.1016/j.rescon- and Recycling, 865–875. 55(11), Conservation rec.2011.04.009 17. Park, S. H., & Kim, S. H. (2014). Poly (ethylene terephthalate) recycling for high value added textiles. Fashion and Textiles, 1(1). https://doi.org/10.1186/s40691-014-0001-x 18. Nkwachukwu, O., Chima, C., Ikenna, A., & Albert, L. (2013). Focus on potential environmen- tal issues on plastic world towards a sustainable plastic recycling in developing countries. In- ternational Journal of Industrial Chemistry, 4(1), 34. https://doi.org/10.1186/2228-5547-4-34 19. Mackey, G. (1995). A review of Advanced Recycling Technology. ACS Symposium Series, 161–169. https://doi.org/10.1021/bk-1995-0609.ch014. 20. Mishra, M. (2019). Encyclopedia of polymer applications. Taylor et Francis, CRC Press. 21. Bartolome, L., Imran, M., Gyoo, B., A., W., & Hyun, D. (2012). Recent developments in - Trends and Perspectives. recycling of pet. Material Recycling the chemical https://doi.org/10.5772/33800 22. Brouwer, M. T., Alvarado Chacon, F., & Thoden van Velzen, E. U. (2020). Effect of recycled content and Rpet quality on the properties of PET bottles, part III: Modelling of Re- petitive Recycling. 373–383. https://doi.org/10.1002/pts.2489 Packaging Technology Science, 33(9), and 23. Forrest, M. J. (2019). 5. Separation and Sorting Technologies. Recycling of Polyethylene Ter- ephthalate, 75–100. https://doi.org/10.1515/9783110640304-005 32 24. Wahab, D. A., Hussain, A., Scavino, E., Mustafa, M. M., & Basri, H. (2006). Develop- ment of a prototype automated sorting system for Plastic Recycling. American Journal of Ap- plied Sciences, 3(7), 1924–1928. https://doi.org/10.3844/ajassp.2006.1924.1928 25. Ji, T., Fang, H., Zhang, R., Yang, J., Fan, L., & Li, J. (2022). Automatic sorting of low- value recyclable waste: A Comparative Experimental Study. Clean Technologies and Environ- mental Policy, 25(3), 949–961. https://doi.org/10.1007/s10098-022-02418-7 26. Bauer, M., Lehner, M., Schwabl, D., Flachberger, H., Kranzinger, L., Pomberger, R., & Hofer, W. (2018). Sink–float density separation of post-consumer plastics for feedstock recy- cling. Journal of Material Cycles and Waste Management, 20(3), 1781–1791. https://doi.org/10.1007/s10163-018-0748-z 27. Life cycle impacts for postconsumer recycled resins: Pet ... (n.d.). Retrieved March 6, 2022, from https://plasticsrecycling.org/images/library/2018-APR-LCI-report.pdf. 28. Mancini, S. D., Schwartzman, J. A., Nogueira, A. R., Kagohara, D. A., & Zanin, M. (2010). Additional steps in mechanical recyling of pet. Journal of Cleaner Production, 18(1), 92–100. https://doi.org/10.1016/j.jclepro.2009.09.004 29. Welle, F. (2007). Decontamination efficiency of a new post-consumer poly(ethylene tereph- thalate) (PET) recycling concept. Food Additives &amp; Contaminants: Part A, 25(1), 123–131. https://doi.org/10.1080/02652030701474227 30. Welle, F. (2012). Simulation of the decontamination efficiency of pet recycling processes based on solid-state polycondensation. Packaging Technology and Science, 27(2), 141–148. https://doi.org/10.1002/pts.2013 31. Awaja, F.; Pavel, D. Recycling of PET. European Polymer Journal 2005, 41 (7), 1453-1477. DOI: https://doi.org/10.1016/j.eurpolymj.2005.02.005. 32. Qiu Gao, Huang Nan-Xun, Tang Zhi-Lian, & Gerking, L. (1997). Modelling of solid state polycondensation of poly(ethylene terephthalate). Chemical Engineering Science, 52(3), 371– 376. https://doi.org/10.1016/s0009-2509(96)00414-9 33. 3devo. (n.d.). Recycling pet bottles into filament: Shredding and extrusion walkthrough. Sup- port. https://support.3devo.com/pet-recycling 34. PET extrusion pelletizing line. Nicety Plastic Machinery Co., Ltd. (n.d.). https://nicety- machine.com/pet-extrusion-pelletizing-line/#:~:text=The%20process%20involves%20cut- ting%20plastic,thereby%20reducing%20raw%20material%20costs. 33 35. Shojaei, B., Abtahi, M., & Najafi, M. (2020). Chemical recycling of(PET) : A stepping‐ stone toward sustainability. Polymers for Advanced Technologies, 31(12), 2912–2938. https://doi.org/10.1002/pat.5023 36. Chen, C.-H., Chen, C.-Y., Lo, Y.-W., Mao, C.-F., & Liao, W.-T. (2001). Studies of gly- colysis of poly(ethylene terephthalate) recycled from postconsumer soft-drink bottles. I. Influ- ences of glycolysis conditions. Journal of Applied Polymer Science, 80(7), 943–948. https://doi.org/10.1002/app.1174 37. Bartolome, L., Imran, M., Gyoo, B., A., W., & Hyun, D. (2012a). Recent developments in the chemical recycling of pet. Material Recycling - Trends and Perspectives. https://doi.org/10.5772/33800 38. Recycled pet market, global industry forecast, [latest]. MarketsandMarkets. (n.d.). https://www.marketsandmarkets.com/Market-Reports/recycled-pte-market- 248965407.html#:~:text=The%20global%20Recycled%20PET%20market%20is%20esti- mated%20to%20be%20USD,growth%20of%20the%20rPET%20market. 39. 05, P. L. | J. (2023, June 5). Recycled pet prices trending down amid weak US demand. plas- ticstoday.com. https://www.plasticstoday.com/packaging/recycled-pet-prices-trending-down- amid-weak-us-demand 40. Recycled pet flakes market share & trends report, 2030. Recycled PET Flakes Market Share & Trends Report, 2030. (n.d.). https://www.grandviewresearch.com/industry-anal- ysis/recycled-pet-flakes-market-report 41. Koo, Hyun Jin, et al. “Effects of Recycling Processes on Physical, Mechanical and Degrada- tion Properties of Pet Yarns.” Fibers and Polymers, vol. 14, no. 12, 2013, pp. 2083–2087, https://doi.org/10.1007/s12221-013-2083-2. 42. Villain, F., Coudane, J., & Vert, M. (1995). Thermal degradation of polyethylene tereph- thalate: Study of Polymer Stabilization. Polymer Degradation and Stability, 49(3), 393–397. https://doi.org/10.1016/0141-3910(95)00121-2 43. Scheirs, J. (2001). Polymer recycling: Science, technology and applications. John Wiley & Sons. 44. Zander, N. E., Gillan, M., & Lambeth, R. H. (2018). Recycled Polyethylene terephthalate feedstock material. Additive Manufacturing, 21, 174–182. a new FFF as https://doi.org/10.1016/j.addma.2018.03.007 45. Steve Navedo, R. D. a. C. G. Thermoform recycling realities. Resource Recycling, Inc 2022. https://resource-recycling.com/plastics/2021/11/24/thermoform-recycling-realities/ (accessed 2023 5/18/2023). 34 46. Carlin, C. (2020). A New Landscape for PET Recycling: It’s not just for bottles anymore. https://go-gale-com.proxy2.cl.msu.edu/ps/log- Shibboleth out.do?userGroupName=msu_main&page=true&prodId=AONE authentication request. 47. Rigid pet thermoform recycling finds a continued strong supporter in Placon. Placon. (n.d.). https://www.placon.com/resources/news/rigid-pet-thermoform-recycling-finds-a-continued- strong-supporter-in-placon/ 48. EPBP. European PET Bottle Platform Technical Opinion: Glycol-modified polyethylene ter- ephthalate (PETG). In: EPBP [online]. Brussels, 2020. [Accessed 26 June 2023]. Available from: https://www.epbp.org/download/333/non-endorsement-petg-components 49. Polymers: Intrinsic viscosity measurements for quality control of pet. Anton Paar. (n.d.). https://www.anton-paar.com/corp-en/services-support/document-finder/application-re- ports/polymers-intrinsic-viscosity-measurements-for-quality-control-of- pet/#:~:text=The%20intrinsic%20viscosity%20is%20dependent,grades%20(see%20Ta- ble%201). 50. Shah, J. (n.d.). The importance of controlling intrinsic viscosity in extruded pet. Industry In- https://blog.icpg.co/the-importance-of-controlling-intrinsic-viscosity-in-extruded- sights. pet#:~:text=A%20measure%20of%20the%20polymers,length%20of%20the%20poly- mer%20chains. 51. The importance of (n.d.). https://www.ametektest.com/learningzone/library/articles/the-importance-of-intrinsic-viscos- ity-measurement intrinsic viscosity measurement ametek test. - 52. Goje, A. S., & Mishra, S. (2003). Chemical Kinetics, simulation, and thermodynamics of glycolytic depolymerization of poly(ethylene terephthalate) waste with catalyst optimization for recycling of value added monomeric products. Macromolecular Materials and Engineering, 288(4), 326–336. https://doi.org/10.1002/mame.200390034 53. Chang, S.; Sheu, M.-F.; Chen, S.-M. Solid-state polymerization of poly(ethylene tereph- (10), 3289-3300, Journal of Applied Polymer Science 1983, 28 thalate). https://doi.org/10.1002/app.1983.070281023. 54. Papaspyrides, C. D., & Vouyiouka, S. N. (2009). Solid state polymerization. Wiley- Blackwell. 55. Shi, C., DeSimone, J. M., Kiserow, D. J., & Roberts, G. W. (2001). Reaction kinetics of the solid-state polymerization of poly(bisphenol A carbonate) facilitated by supercritical car- bon dioxide. Macromolecules, 34(22), 7744–7750. https://doi.org/10.1021/ma011068h 35 56. Ravindranath, K., & Mashelkar, R. A. (1990). Modeling of poly(ethylene terephthalate) reactors. ix. solid state polycondensation process. Journal of Applied Polymer Science, 39(6), 1325–1345. https://doi.org/10.1002/app.1990.070390610 57. Beaton D. Continuous, solid-phase polymerization of polyamide granules (E.I. du Pont de Nemours and Company) US Patent 3,821,171; 1974. 58. Ma, Y., Agarwal, U. S., Sikkema, D. J., & Lemstra, P. J. (2003). Solid-state polymeriza- tion of pet: Influence of nitrogen sweep and high vacuum. Polymer, 44(15), 4085–4096. https://doi.org/10.1016/s0032-3861(03)00408-7 59. Mallon, F., Beers, K., Ives, A., & Ray, W. H. (1998). The effect of the type of purge gas on the solid-state polymerization of polyethylene terephthalate. Journal of Applied Polymer Science, 69(9), 1789–1791. https://doi.org/10.1002/(sici)1097-4628 (19980829) 69:9 < 1789::aid-app13>3.0.co;2-h 60. Mendes, L. C., Mallet, I. A., Cestari, S. P., Dias, F. G., & Pereira, P. S. (2014). Solid state polymerization of PET/PC extruded blend: Effect of reaction temperature on thermal, morpho- logical and viscosity properties. Polímeros, 24(4), 422–427. https://doi.org/10.1590/0104- 1428.1518 61. Makkam, S., & Harnnarongchai, W. (2014). Rheological and mechanical properties of reactive extrusion. Energy Procedia, 56, 547–553. recycled PET modified by https://doi.org/10.1016/j.egypro.2014.07.191 62. Bimestre, B. H., & Saron, C. (2012). Chain extension of poly (ethylene terephthalate) by reactive extrusion with secondary stabilizer. Materials Research, 15(3), 467–472. https://doi.org/10.1590/s1516-14392012005000058 63. Awaja, F., Daver, F., & Kosior, E. (2004). Recycled poly(ethylene terephthalate) chain extension by a reactive extrusion process. Polymer Engineering and Science, 44(8), 1579– 1587. https://doi.org/10.1002/pen.20155 64. Standau, T., Nofar, M., Dörr, D., Ruckdäschel, H., & Altstädt, V. (2021). A review on multifunctional epoxy-based Joncryl® ADR chain extended thermoplastics. Polymer Reviews, 62(2), 296–350. https://doi.org/10.1080/15583724.2021.1918710 65. Liu, B., & Xu, Q. (2013). Effects of bifunctional Chain Extender on the  crystal- linity and thermal stability of pet. Journal of Materials Science and Chemical Engineering, 01(06), 9–15. https://doi.org/10.4236/msce.2013.16002 66. Villalobos, M., et al. “Oligomeric Chain Extenders for Economic Reprocessing and Recycling of Condensation Plastics.” Energy, vol. 31, no. 15, 2006, pp. 3227–3234, 36 https://doi.org/10.1016/j.energy.2006.03.026. May, C. A. (1988). Epoxy resins: Chemistry and Technology. Marcel Dekker. 67. May, C. A. (1988). Epoxy resins: Chemistry and Technology. Marcel Dekker. 68. Japon, S., Boogh, L., Leterrier, Y., & Månson, J.-A. E. (2000). Reactive processing of poly(ethylene terephthalate) modified with multifunctional epoxy-based additives. Polymer, 41(15), 5809–5818. https://doi.org/10.1016/s0032-3861(99)00768-5 69. Torres, N., Robin, J. J., & Boutevin, B. (2001). Chemical modification of virgin and re- cycled poly(ethylene terephthalate) by adding of chain extenders during processing. Journal of Applied https://doi.org/10.1002/1097- Science, 4628(20010307)79:10<1816::aid-app100>3.0.co;2-r 1816–1824. Polymer 79(10), 70. Lee, T., Lee, C., Cho, S., Lee, D., & Yoon, K.-B. (2010). Enhancement of physical prop- erties of thermoplastic polyether-ester elastomer by reactive extrusion with chain extender. Polymer Bulletin, 66(7), 979–990. https://doi.org/10.1007/s00289-010-0405-8 37 CHAPTER 3: EXPERIMENTAL 3.1 Materials 3.1.1 Preparation of PET bottle pellets Feedstocks of post-consumer and waste bottles, thermoform, and clamshells PET (PET-T) were from the Michigan State University recycling facility (Michigan, USA). The bottles, thermoform, and clamshells PET (PET-T) were first cleaned by rinsing them with warm water and a detergent bath to eliminate labels, impurities, and contaminants from the bottles and vacuum dried at 80⁰C overnight in a oven. The bottles and thermoforms were then shredded as small flakes using a plastic granulator (polymer machinery B.T.P granulator, Michigan, USA) and washed in a detergent bath again to remove any impurities present. These flakes are then dried and extruded in a twin-screw extruder (Leistritz Extruder, Michigan, USA) at 250⁰C at 100 rpm to create recycled PET-B pellets [1]. 38 3.1.2 Chain Extender Joncryl® ADR 4468 Joncryl® ADR 4468 was acquired from BASF. It was used to enhance the thermal stability of recycled PET blends and increase melting strength [2]. Table 3.1: Specification data for Joncryl® ADR 4468 {[3-4]}. Appearance Solid flakes Specific gravity, 25° C Mw Tg (°C) Non-volatile by GC (%) Epoxy equivalent weight (g/mol) Typical dosage (%) Processing temperature range (℃) 1.08 7250 59 >99 310 0.1-1.0% 170-330 3.1.3 Preparation of PET Bottle/Thermoform Blends Both PET-T and PET-B were vacuum dried conditions at 80 ⁰C for 12 hours to eliminate moisture content to prevent hygroscopic reaction during the extrusion process and reactive extrusion. PET- B and PET-T were manually combined in 90:10 and 80:20 ratios to produce PET-B/10% PET-T and PET-B/20% PET-T. Yielding a total of four distinct Pellet form samples. These pellets were 39 produced in a micro-compounder (DSM Xplore 15 cc, Netherlands) at 280⁰C and 100 rpm with a two minute residence duration. 3.1.4 Preparation of the Joncryl ADR (J) blends The rPET blends with chain extender Joncryl ADR (J) were prepared by taking the blends created in subtopic (3.1.3)and 0.5 phr of Joncryl ADR (J) in a reactive extrusion process. These pellets were produced in a micro-compounder (DSM Xplore 15 cc, Netherlands) at 280⁰C and 100 rpm with a two-minute residence duration. Two distinct pellets with chain extenders were created. 40 Table 3.2: Designation and formulation composition of the neat polymer and the blend. Samples PET-B PET-T 10%PET-T 20%PET-T 10%PET-T+J 20%PET-T+J PET-B (wt.%) 100 --- 90 80 90 80 PET-T (wt.%) ---- 100 10 20 10 20 J (phr) ---- --- ---- ---- 0.5 0.5 * PET-B: PET wastewater bottles, PET-T: PET thermoforming clamshells, J: Joncryl ADR4468 3.1.5 Preparation of SSP (Solid State Polymerization Samples) Each of the compositions in Table 3.2 was placed and vacuum dried in a oven for a reaction time of 8 h in between 3-4 Pa at 220 ⁰C and then cooled at room temperature. The resulting samples with the samples before the solid-state polymerization were analyzed for their thermo-mechanical behavior and intrinsic viscosity. 41 3.1.6 Preparation of Tensile T-bones and Izod Impact Bars The compositions from Table 3.2 were melt processed in a micro compounder (DSM Xplore 15 cc, Netherlands) at 280⁰C and 100 rpm with a two-minute residence duration. The molten compo- sition from the extruder was then injected into a mold of T-bone and impact bar to create samples for tensile testing and Izod impact testing according to ASTM D638 and ASTM D625 in a micro- Injector at 30 ⁰C mold temperature and vacuum pressure of 0.8 MPa for 10 secs. 3.2 Methods 3.2.1 Intrinsic Viscosity Analysis and Molecular Weight Determination The Intrinsic Viscosity (IV) was analyzed by the ASTM standard of D4603. The flow time for different PET blend compositions from Table 3.2 and in subsection 3.1.6 was determined by using a (1 C Ubbelohde-Type) viscometer (Appx. constant: 0.03mm2/s, Kinematic viscosity range: 6 to 30 mm2/s) at 25 ± 0.2 ⁰C in a solution of 60/40 w/w Phenol/1,1,2,2-tetrachloroethane (Sigma– Aldrich, St. Louis, MO) solution at a polymer concentration of 0.25 g/dl. Six distinct solutions of recycled PET composition were created and tested for their flow rate. Using Bill Meyer’s Rela- tionship [5]. η = 0.25( η𝑟 − 1 + 3 ln η𝑟)/𝐶. Eq. 1 Where: η = intrinsic viscosity, ηr = relative viscosity = t/to, t = average solution flow time (sec), to = average solvent flow time (sec), and C = polymer solution concentration, g/dL. • All the composition of PET blends and its SSP samples are dried in vacuum condition for 2hrs at 65°C to remove any kind of moisture present in the polymer pellets. • recycled PET composition of 0.2475 g to 2.2525 g were completely dissolved in the 25 ml solvent at 110°C to create a solution of 50 ml for each blend. • The solution was filled in the Ubbelholde viscometer. 42 • The viscometer was positioned within a temperature-controlled bath set at a constant 30°C. After reaching equilibrium pull the solution to the top mark of the Ubbelohde bulb. Measure the flow time. By repeating the steps 3-4 times to get an average range. 3.2.2 Mechanical Properties 3.2.2.1 Tensile Strength Testing Five Specimens each of T bone tensile were created for the six different compositions and their SSP pellets. Each of the specimens was kept for 48 hours at standard laboratory conditions of 23°C and 50% relative humidity after being processed in the injection molding process. To measure the tensile strength Instron model 5565 (Massachusetts, USA) having tensile grips and a load cell was used with a parameter of testing speed of 30 mm/min. the test was done according to ASTM stand- ards D638-14 (Type V) for rigid plastic specimens. The gauge length for the specimens was 10 mm and the distance between the grip was 25 mm. The specimen is loaded between the grips and tested for the force required by the machine to stretch and break the specimen at the center [6]. 43 3.2.2.2 Izod Impact Testing Five Specimens each of Izod Impact were created for the Six different compositions and their SSP Pellets. Each of the specimens was kept for 48 hours at standard laboratory conditions of 23°C and 50% Relative Humidity for conditioning after being processed in the injection molding process. A Ray-Ray impact test was used to test the Izod impact for the specimens. The parameter for the hammer impact energy was 5.417J testing according to ASTMD256 standards for notched sam- ples. The notching of 1mm was done using the notch-cutting tool TMI 22-05 (Michigan, USA). The specimen was placed vertically in between the grips in the Ray-Ray impact tester. The speci- men was struck with a single swing of the hammer pendulum and the absorbed energy by the specimen was measured. The average of the Five specimens was recorded and reported in KJ/m2 [7]. 3.2.3 Thermal Properties 3.2.3.1 Differential Scanning Calorimetry (DSC) DSC (Differential Scanning Calorimetry) was performed using a DSC Q100 Analyzer (TA Instru- ments, DE, USA). 6-12 mg of PET samples were sealed in hermetic aluminum pans. Each speci- men was pre-conditioned at 65⁰C for 12hr prior to testing to remove moisture. Each Recycled PET composition was examined under nitrogen of flow rate of 70 ml/min at a heating rate of 10°C/min and utilizing the heat-cool-heat cycle technique. Two replications were tested for each specimen. All samples were equilibrated at -20°C before being heated to 280 °C. The first heating cycle was performed to eliminate the thermal history of the polymer -20°C to 280°C. the cooling 280°C to - 20°C was used to determine the crystallization temperature and the last heating cycle was used to determine the Tg, Tm, ΔHm, and Xc. The characterization data were collected from the integration 44 of the curve, and the step change formed in the cooling and second heating cycle. TA Instruments Universal Analysis 2000 version 4.5A (TA Instruments) was used to analyze the data [8]. Tm and Tc are the melting and cooling temperatures, respectively; Tg is the glass transition temper- ature; Xc is the degree of crystallinity; and ΔHm is the melting enthalpy. The equation used to calculate the degree of crystallinity is given by: - %𝑋𝑐 = ( ΔHm (1−Ø)∗ΔHm∗) ∗ 100 Eq.3 Where Ø is the chain extender's weight percentage and ΔHm* is the expected melting enthalpy of 100% crystalline PET (140 J/g) [9]. 3.2.3.2 Thermogravimetric Analysis (TGA) The thermal stability and degradation analysis of the recycled PET compositions were determined from TA Q50 (TA instruments, DE, USA). Each specimen was pre-conditioned at 65⁰C for 12hr prior to testing to remove moisture. All the samples weighed around 6-12 mg were characterized at 10⁰C/min up to 600⁰C under a nitrogen flow of 40 mL/min. The average value of two TGA is reported. TA Instruments Universal Analysis 2000 version 4.5A (TA Instruments) was used to an- alyze the data of the thermograms and first-order derivative thermograms curve [10]. 45 REFERENCES 1. Life cycle impacts for postconsumer recycled resins: Pet ... (n.d.). Retrieved March 6, 2022, from https://plasticsrecycling.org/images/library/2018-APR-LCI-report.pdf. 2. Joncryl ADR 4468. Azelis Americas. (2020, November 27). https://azelisamericas- case.com/product/joncryl-adr-4468/ 3. BASF Joncryl® ADR-4400/ ADR-4468. BASF Joncryl® ADR-4400/ ADR-4468, Chain Ex- tender. (n.d.). http://www.lithlon.com/en/ProductDetail/2887400.html 4. Joncryl® ADR 4468. Joncryl® ADR 4468 - BASF- Technical Datasheet. (n.d.-a). https://pol- ymer-additives.specialchem.com/product/a-basf-joncryl-adr-4468 5. (N.d.). Test Method for Determining Inherent Viscosity of Poly (Ethylene Terephthalate) (PET) by Glass Capillary Viscometer. https://doi.org/10.1520/d4603-18 6. Test method for tensile properties of plastics. (n.d.). https://doi.org/10.1520/d0638-14 7. Test methods for determining the Izod pendulum impact resistance of plastics. (n.d.). https://doi.org/10.1520/d0256-10r18 8. Test method for transition temperatures and enthalpies of fusion and crystallization of poly- mers by differential scanning calorimetry. (n.d.). https://doi.org/10.1520/d3418-15 9. Starkweather, H. W., Jr.; Zoller, P.; Jones, G. A. The heat of fusion of poly(ethylene tereph- thalate). J. Polym. Sci., Polym. Phys. Ed.1983, 21, 295−299. 10. Practice general techniques of thermogravimetric analysis (TGA) coupled with infrared anal- ysis (TGA/IR). (n.d.). https://doi.org/10.1520/e2105-00r16 46 CHAPTER 4: RESULTS AND DISCUSSION This chapter presents and exhibits the effect of the SSP process and the addition of a chain extender on the recycled polyethylene terephthalate blends. The rheological and thermos-mechanical prop- erties of the recycled PET-B and PET-T blends were investigated before and after the SSP process and reactive extrusion with chain extenders. 4.1 SSP and Reactive Extrusion The acquired bottle PET and thermoform PET were converted into pellet forms and blended into the different compositions as designated in Table 3.2. The blends were then exposed to form ground flakes with SSP. It was observed that due to the SSP process, the recycled polymer was stuck together after 8 h of SSP. The addition of a chain extender to the polymer helped create the non-sticking of the polymer due to SSP. Recycled polymer when processed mechanically tends to degrade and starts melting at lower temperatures and starts sticking to the other pellets of the pol- ymer, this can happen due to the polydispersity of the polycondensation polymer [1]. The reason for caking in recycled PET blends is the chemical compounds found in the thermoform and the blend composition, which is glycol content. If there is the presence of PET-G in the thermoform trays, the glycol content in the polymer increases and decreases the melting point hence creating caking and stickiness [2]. The chain extender is used to prevent the caking and stickiness of the polymer blend pellets. The temperature needed for the melt extrusion process was 280 ⁰C and the torque resistance in- creased when reactive extrusion was done using the chain extender suggesting an increase in the melt viscosity and the molecular weight of the polymer. The chain extender use help in the reduc- tion of degradation during processing for the recycled PET blends and the non-sticking of the polymer blend when the SSP process is performed [3]. 47 4.2 Characterization 4.2.1 Intrinsic Viscosity and Molecular Weight Figure 4.1: Intrinsic Viscosity of PET samples with different composition ratios PET-B and its blends. Intrinsic Viscosity of the polymer exhibits its physical and rheological characteristics. This IV of the polymers is important for the processing of the polymer at varied temperatures and systems. The bottles and thermoform were recycled and the IV is characterized by Bill-Meyer’s relationship in Ubbelohde glass capillary. Figure 4.1 exhibits the IV of the recycled PET-B and its blends. The IV of PET-B was determined to be 0.74 g/dl. This number is consistent with the literature, which states that the IV of the pellets found in the market for PET water bottles ranges between 0.73 and 0.8 dl/g [2]. Meanwhile, virgin 48 PET-B exhibits IV values in the range of 0.8-0.85 dl/g, but these values drop to 0.73-0.8 dl/g during bottle manufacture due to hydrolytic degradation of PET during this process. SSP treatment of PET increased the IV to 1.05 dl/g, which was higher than before the bottle forming procedure. Prior to SSP, recycled PET-T had an IV of 0.79 dl/g, and SSP assisted in increasing the IV of PET- T to 0.91 dl/g [4]. In Figure 4.1, we can observe that the IV reduces and goes below (<0.73-0.8 dl/g) when the recycled PET-B and PET-T are blended in an extrusion process, this reduction in IV happens due to the thermo-oxidative degradation that takes place in the extruder processing at 280 ⁰C when the blend pellets are created [5]. Also, the more the presence of thermoform PET in the blend pellet, the more is the reduction in IV which can be observed in 20%PET-T/PET-B, the IV reduces by 11% and reduces up to 0.66 dl/g [1]. Following that, we evaluated the IVs of PET-B samples with PET-T contents of 10 and 20% by weight. Prior to SSP treatment, a sample containing 10% PET-T had an IV of 0.73 dl/g, which was lower than the necessary IV for making PET bottles. The 10 wt %PET-T an IV of 0.79 dl/g after SSP treatment, which was extremely near to the value necessary for bottle manufacture. Sim- ilarly, before SSP, the 20 wt% PET-T system had an IV of 0.66 dl/g, which is lower than the needed IV for producing PET bottles. The 20 wt% PET-T system had an IV of 0.76 dl/g after SSP treat- ment, which was very near to the IV necessary for bottle manufacture (IV 0.8 dl/g) [6-7]. Even after SSP, the IV values for both the 10% and 20% PET-T samples are in the lower range of what is necessary for plastics. As a result, we chose to combine SSP therapy with chain extenders. Both the 10 wt% and 20 wt% PET-T compounds were evaluated first with a chain extender, 0.5 phr Joncryl 4468. Both demonstrated increases in their IVs to values greater than 0.8 dl/g with the addition of chain extenders, and these values rose further after the SSP therapy. For example, the 20 wt% PET-T had an IV of 0.85 after adding the chain extender, and this value climbed to nearly 49 1.0 after SSP treatment [8]. The findings indicate that SSP treatment may be insufficient for recy- cled PET with a PET-T concentration of roughly 20% by weight. On the other hand, the chain extender alone is sufficient to raise the IV over 0.8, and following SSP treatment, the values ap- proach 1 dl/g, matching those of SSP-treated 100 wt% PET-B. Figure 4.1 also exhibits the difference in the intrinsic viscosity before and after the process of solid-state polymerization. There is a significant increase in the IV and molecular weight in the recycled PET blends after the SSP process. It was observed that the IV increased by 10-25% for all the recycled PET compositions. It was observed that after SSP of 8hr at 220 ⁰C tends to improve the esterification in recycled PET blends which removes the by-products group in the PET and thereby increases the IV and molecular weight. The enhancement occurs due to the crystallization of recycled PET blends at 180-190 ⁰C for 1-2hr and the inherent viscosity tends to increase from 0.6 to 0.72dL/g after 3-5hrs, This happens due to the reduction of carboxyl content to less than 20meq/kg during SSP [1]. The addition of PET-T to the PET-B blends at a loading of 20% lowered the IV by 11% to 0.66 g/dl. Figure 4.1 demonstrates that adding 1 phr of chain extender J to the blend increased the IV of the PET-B and its blends somewhat. In comparison to PET-B, the SSP procedure at 220 0C and integration of 0.5 phr of J increased the IV by 10-30%. The insertion of 0.5 phr of J may raise the IV of recycled PET, implying that chain extenders successfully connected various PET chains, increasing their IV (Figure 4.1).[9-11]. As shown in Figure 4.1, there was a significant enhance- ment in the viscosity properties of the recycled PET-B and its blends. The SSP process caused the IV values to increase by 10-25% in IV. It was observed that SSP at 220 ⁰C for 8 h improved the esterification in PET-B and its blends and, indeed reduced the by-product groups in the PET-B and its blends and thereby increasing the IV. 50 4.2.2 Mechanical Properties We evaluated their mechanical characteristics after generating desirable IV values using the chain extender alone and the chain extender combined with SSP treatment. The mechanical characteris- tics of PET-B, PET-T, and their mixtures are depicted in Figure 4.2 Figure 4.2: Mechanical Properties of neat PET-B, neat-T, and its blends with PET-T before and after SSP including the (A) tensile strength, (B) tensile modulus, (C) elongation at break, and (D) notched impact strength. 4.2.2.1 Tensile Properties Figure 4.2 exhibits the mechanical characteristics namely young modulus, tensile strength, and elongation at break before the SSP process and addition of chain extender (J) and after the SSP 51 process and reactive extrusion. The tensile properties of PET-B like tensile strength of 52 MPa and tensile modulus of 2150 MPa were observed. It was also observed that the elongation at the break of the recycled PET-B was 396%. The blending of 10% and 20% PET-T with PET-B did not have much effect on the tensile strength and tensile modulus. But it was observed that there was a slight reduction in 10% blends and then an increase in elongation at break at 20% blend. This increase in elongation is due to a reduction in the molecular weight of the polymer during the extrusion process. This can also happen due to the realignment of orientation in the crystals during the ex- trusion process. The reduction of Mw leads to an increase elongation at break can be observed due to the hydrolysis and transesterification process which reduces and shortens the chains of recycled PET blends during the extrusion process [12-14]. Also, we can observe that tensile strength and tensile modulus are directly proportional to the molecular weight of the polymer, which can be seen in Figure 4.1 and Figure 4.2 [13-15]. SSP process and chain extender tend to increase the Mw of recycled PET thereby increasing the tensile strength of recycled PET blends. The process of SSP and chain extension increases the Mw of the rPET blends. The elongation at break can be observed to be much lower after the addition of a chain extender, the reduction in elongation at break is down at least by (50-100%) elongation in 10% and 20% of PET-B/PET-T blends. This can happen due to cross-linking of chains between the chain extender (J) and the functional group of recycled PET blends [16-18]. 4.2.2.2 Izod Impact The Izod Impact test is done to calculate the impact resistance and toughness of recycled PET blends. The Izod impact of PET-B was found to be 2.8 KJ/m2. It can be observed that with the SSP process there is a 5-10% increase in the impact resistance of the recycled PET blends. Also, the addition of chain extender (J) to 10% and 20% PET-T/PET-B blend shows a significant increase 52 in the impact resistance of the specimens of those PET blends [19]. This can happen due to an increase in the chain length and molecular weight of the recycled PET. There is also increase in the impact resistance of the polymer [19-20]. Some anomalies that can be found in the results on Izod impact from Figure 4.2 are that reduction of impact resistance for PET-T and 20%PET- T/PET-B added with chain extender (J) post the SSP treatment. This may have occurred due to heavy crosslinking of the polymer chain which is determinantal to the mechanical properties and thermal stability of recycled PET blends [12,20]. 4.2.3 Thermal Properties The thermal properties were determined by DSC and TGA. DSC and TGA were used to investigate the recycled PET blend processing temperature, its crystallization temperature, and its degradation temperature. These properties are extremely important for processing bottles and pellets from an extrusion machine or creating specimens from an injection molding machine. 53 Table 4.1: Thermal Characteristics Determined by TGA and DSC of ratios PET-B and its blends. TGA DSC Sample PET-T PET-B PET-B(SSP) PET-B /10% PET-T PET-B /20% PET-T PET-B /10% PET-T+J PET-B /20% PET-T +J Tg (°C) 82.71 (1.95) 79.36 (0.23) 80.34 (1.88) 79.92 (0.24) 80.15 (0.05) 80.89 (1.21) 79.28 (0.30) 81.34 (0.52) 81.85 (1.49) 80.40 (0.05) 82.42 (0.66) 80.88 (1.21) Tmax (°C) 429.95 (1.40) 430.54 (1.06) 429.21 (0.63) 425.89 (1.58) 429.89 (3.12) 430.37 (1.12) 430.37 (1.43) 429.40 (0.92) 429.94 (3.05) 428.90 (0.24) 430.50 (3.48) 429.01 (1.38) T10 (°C) 400.99 (0.028) 402.85 (0.36) 401.28 (0.66) 402.91 (1.09) 401.35 (1.08) 400.94 (1.27) 400.94 (1.27) 400.30 (0.44) 401.58 (2.44) 400.74 (1.66) 401.85 (2.92) 400.14 (1.02) Tc (°C) 204.44 (2.72) 206.07 (0.18) 208.64 (4.67) 213.32 (1.06) 209.18 (0.68) 204.16 (6.81) 199.25 (4.74) 203.82 (1.65) 207.85 (1.65) 203.86 (1.48) 202.89 (2.58) 207.00 (2.46) * Tm and Tc are the melting and cooling temperatures, respectively; Tg is the glass transition tem- perature; Xc is the degree of crystallinity; ΔHm is the enthalpy of melting. The formula Xc= [(ΔHm)/((1-Ø) ΔHm*)]100 was used to determine Xc, where Ø is the weight percentage of the chain extender and ΔHm* is the predicted melting enthalpy of 100% crystalline PET (140J/g). According to TGA measurements, T10 and Tmax are the breakdown temperatures at 10% weight loss and the maximum derivative peaks, respectively. Tm (°C) 244.19 (1.35) 250.21 (0.66) 243.85 (1.68) 245.25 (0.25) 244.79 (0.07) 248.91 (0.06) 244.18 (1.95) 249.41 (0.51) 245.13 (1.13) 246.54 (3.52) 246.00 (0.43) 248.29 (1.77) ΔHm (J/g) 35.68 (0.47) 39.09 (0.22) 48.045 (2.66) 39.84 (0.61) 39.52 (3.03) 35.56 (1.35) 39.19 (0.72) 35.34 (2.23) 38.75 (3.89) 38.38 (3.88) 37.92 (1.29) 35.14 (3.27) Xc (%) 25.48 (0.33) 27.93 (0.15) 34.31 (1.90) 28.46 (0.43) 28.37 (2.17) 25.52 (0.97) 27.99 (0.51) 25.24 (1.60) 27.68 (2.79) 27.41 (2.76) 27.22 (0.90) 25.23 (3.07) PET-B /10% PET-T(SSP) PET-B /20% PET-T(SSP) PET-B /10% PET-T+J(SSP) PET-B /20% PET-T +J(SSP) PET-T(SSP) 54 4.2.3.1 Differential Scanning Calorimetry (DSC) Figure 4.3: DSC 2nd heating curve of PET-B, PET-T and PET-B/PET-T blends. The glass transition temperature (Tg), melting temperature (Tm), and crystallization temperature. (Tc) of the recycled blend composition were measured and analyzed with DSC. DSC helped in establish the miscibility of the blend. Figure 4.3 and Table 4.1 illustrate the second heating cycle and cooling cycle of the recycled PET blends. There was no significant change in the Tg and Tm of the recycled PET blend pellets before and after the SSP process [21-22]. The addition of a chain extender helped reduce the processing temperature by 1°C. We observed that the melting temper- ature Tm for PET-T is higher than the rest of all recycled PET compositions. The heating cycle was 55 found to be in the range of 244-250°C. The Tg of all the samples was between 79-83°C. Figure 4.3 showed two melting peaks. This may be due to the restructuring of the crystals during the heating cycle due to the higher molecular weight present due to the addition of a chain extender in the blend samples [23]. We can observe a reduction in the melting temperature of recycled PET blend and its compositions after the SSP process. Which may be due to the SSP process at higher temperatures raising the melting point of the final polymer. But we see a shift towards lower temperature, this may be due to heavy cross-linking of the polymer during SSP and reactive extrusion with chain extender, mak- ing the polymer requires less energy and less temperature to break the chain and create a melt flow during extrusion [24-25]. We also observed that the crystallization temperature for PET-B is 204.4°C. The study discovered that employing the SSP procedure requires less heat and takes less time to crystallize PET-B. Fur- thermore, the heating curve shows that as molecular weight increases, chain-extending PET's crys- tallinity decreases significantly. This is because, given the same crystallization setting, the molec- ular weight is more, and the melt viscosity is greater. As a result of the crystallization setting the aligning links often form a highly ordered lattice, which is easier to break. As less energy is re- quired to break the lattice during melting, we observed that the melting peak moves to a lower temperature as crystallinity decreases [26]. Also, it can be observed that during the reactive extru- sion, the polymer chains tend to reorganize and form crystals reducing the branching in the chains and increasing the Mw with the addition of a chain extender which decreases the Tc of the polymer [10-11,25]. 56 4.2.3.2 Thermogravimetric analysis (TGA) The Thermal Stability of the recycled PET blends was measured using TGA and was listed in Table 4.1. Table 4.1 depicts the degradation temperature of the recycled PET blends. As observed, the thermograms for all the recycled PET blends were similar and the thermal stability of all the polymer blends remained intact till the range of (425-430°C). There was no significant variation in the thermal stability of recycled PET blends even after the SSP process and the addition of the chain extender. As the thermal degradation temperature is higher than the degradation temperature of recycled PET-B and recycled PET-T we can say that the polymer will not degrade while pro- cessing. 57 REFERENCES 1. Capone, C., Di Landro, L., Inzoli, F., Penco, M., & Sartore, L. (2007). Thermal and mechanical degradation during polymer extrusion processing. Polymer Engineering & Science, 47(11), 1813–1819. https://doi.org/10.1002/pen.20882 2. Chang, S.; Sheu, M.-F.; Chen, S.-M. Solid-state polymerization of poly(ethylene tereph- (10), 3289-3300, Journal of Applied Polymer Science 1983, 28 thalate). https://doi.org/10.1002/app.1983.070281023. 3. Bimestre, B. H., & Saron, C. (2012b). Chain extension of poly (ethylene terephthalate) by reactive extrusion with secondary stabilizer. Materials Research, 15(3), 467–472. https://doi.org/10.1590/s1516-14392012005000058 4. Awaja, F.; Pavel, D. Recycling of PET. European Polymer Journal 2005, 41 (7), 1453-1477. DOI: https://doi.org/10.1016/j.eurpolymj.2005.02.005. 5. Badía, J. D.; Vilaplana, F.; Karlsson, S.; Ribes-Greus, A. Thermal analysis as a quality tool for assessing the influence of thermo-mechanical degradation on recycled poly(ethylene tereph- thalate). DOI: 2009, https://doi.org/10.1016/j.polymertesting.2008.11.010. 169-175. Polymer Testing (2), 28 6. Standau, T., Nofar, M., Dörr, D., Ruckdäschel, H., & Altstädt, V. (2021). A review on multi- functional epoxy-based Joncryl® ADR chain extended thermoplastics. Polymer Reviews, 62(2), 296–350. https://doi.org/10.1080/15583724.2021.1918710 7. Nofar, M., & Oğuz, H. (2019). Development of PBT/recycled-pet blends and the influence of using Chain Extender. Journal of Polymers and the Environment, 27(7), 1404–1417. https://doi.org/10.1007/s10924-019-01435-w 8. Guclu, M., Alkan Göksu, Y., Özdemir, B., Ghanbari, A., & Nofar, M. (2021). Thermal stabilization of recycled pet through chain extension and blending with PBT. Journal of Poly- mers and the Environment, 30(2), 719–727. https://doi.org/10.1007/s10924-021-02238-8 9. Qiu, G.; Huang, N.-X.; Tang, Z.-L.; Gerking, L. Modelling of solid state polycondensation of poly(ethylene terephthalate). Chemical Engineering Science 1997, 52 (3), 371-376. DOI: https://doi.org/10.1016/S0009-2509(96)00414-9. 10. Karayannidis, G. P.; Kokkalas, D. E.; Bikiaris, D. N. Solid-state polycondensation of poly(ethylene terephthalate) recycled from postconsumer soft-drink bottles. II. Journal of Applied Polymer Science 1995, 56 (3), 405-410, https://doi.org/10.1002/app.1995.070560311. DOI: https://doi.org/10.1002/app.1995.070560311 (acccessed 2023/06/20). 11. Karayannidis, G. P.; Psalida, E. A. Chain extension of recycled poly(ethylene terephthalate) with 2,2′-(1,4-phenylene)bis(2-oxazoline). Journal of Applied Polymer Science 2000, 77 (10), 58 2206-2211,https://doi.org/10.1002/1097-4628(20000906)77:10<2206::AID- APP14>3.0.CO;2-D. DOI: https://doi.org/10.1002/1097-4628(20000906)77:10<2206::AID- APP14>3.0.CO;2-D (acccessed 2023/06/20). 12. Paci, M.; La Mantia, F. P. Influence of small amounts of polyvinylchloride on the recycling of polyethyleneterephthalate. Polymer Degradation and Stability 1999, 63 (1), 11-14. DOI: https://doi.org/10.1016/S0141-3910(98)00053-6. 13. Al-Itry, R.; Lamnawar, K.; Maazouz, A. Improvement of thermal stability, rheological and me- chanical properties of PLA, PBAT and their blends by reactive extrusion with functionalized (10), 1898-1914. DOI: epoxy. Polymer Degradation and Stability 2012, 97 https://doi.org/10.1016/j.polymdegradstab.2012.06.028. 14. Awaja, F.; Daver, F.; Kosior, E. Recycled poly(ethylene terephthalate) chain extension by a reactive extrusion process. Polymer Engineering & Science 2004, 44 (8), 1579-1587, https://doi.org/10.1002/pen.20155. DOI: https://doi.org/10.1002/pen.20155 15. Kong, Y.; Hay, J. N. Multiple melting behaviour of poly(ethylene terephthalate). Polymer 2003, 44 (3), 623-633. DOI: https://doi.org/10.1016/S0032-3861(02)00814-5. 16. Inata, H.; Morinaga, T.; Matsumura, S. Postcrosslinking of linear polyesters. I melt-blend-type UV-induced crosslinking agents. Journal of Applied Polymer Science 1988, 35 (7), 1705- 1714,https://doi.org/10.1002/app.1988.070350701.DOI:https://doi.org/10.1002/app.1988.070 350701 (acccessed 2023/06/20). 17. Abdelwahab, M. A., Taylor, S., Misra, M., & Mohanty, A. K. (2015). Thermo-mechanical characterization of bioblends from polylactide and poly(butylene adipate-co-terephthalate) and 299–311. lignin. Macromolecular Materials https://doi.org/10.1002/mame.201400241 Engineering, 300(3), and 18. Bocz, K., Molnár, B., Marosi, G., & Ronkay, F. (2018). Preparation of low-density mi- crocellular foams from recycled PET modified by solid state polymerization and chain exten- sion. 343–351. of https://doi.org/10.1007/s10924-018-1351-z Environment, Polymers Journal 27(2), and the 19. Kaci, M., Benhamida, A., Cimmino, S., Silvestre, C., & Carfagna, C. (2005). Waste and virgin LDPE/PET blends compatibilized with an ethylene-butyl acrylate-glycidyl methacrylate (EBAGMA) terpolymer, 1. Macromolecular Materials and Engineering, 290(10), 987–995. https://doi.org/10.1002/mame.200500217 20. Makkam, S.; Harnnarongchai, W. Rheological and Mechanical Properties of Recycled PET Modified by Reactive Extrusion. Energy Procedia 2014, 56, 547-553. DOI: https://doi.org/10.1016/j.egypro.2014.07.191. 59 21. López, M. d. M. C.; Ares Pernas, A. I.; Abad López, M. J.; Latorre, A. L.; López Vilariño, J. M.; González Rodríguez, M. V. Assessing changes on poly(ethylene terephthalate) properties after recycling: Mechanical recycling in laboratory versus postconsumer recycled material. DOI: Materials https://doi.org/10.1016/j.matchemphys.2014.06.034. Chemistry 884-894. Physics 2014, and 147 (3), 22. Dombre, C.; Marais, S.; Chappey, C.; Lixon-Buquet, C.; Chalier, P. The behaviour of wine aroma compounds related to structure and barrier properties of virgin, recycled, and active PET membranes. 215-225. DOI: https://doi.org/10.1016/j.memsci.2014.03.066. of Membrane Journal Science 2014, 463, 23. Holdsworth, P. J.; Turner-Jones, A. The melting behavior of heat-crystallized poly(ethylene terephthalate). Polymer 1971, 12 (3), 195-208. DOI: https://doi.org/10.1016/0032-3861(71 )90045-0. 24. Jie, Z.; Fa-xue, L.; Jiang-yong, Y. Multiple melting behavior of biodegradable poly(butylene succinate-co-terephthalate) (PBST) copolyester. Journal of Thermal Analysis and Calorimetry 2013, 111 (1), 711-715. DOI: 10.1007/s10973-012-2229-2. 25. Zhao, Z.; Wu, Y.; Wang, K.; Xia, Y.; Gao, H.; Luo, K.; Cao, Z.; Qi, J. Effect of the Trifunctional Chain Extender on Intrinsic Viscosity, Crystallization Behavior, and Mechanical Properties of (30), 19247-19254. DOI: Poly(Ethylene Terephthalate). ACS Omega 2020, 5 10.1021/acsomega.0c02815. 26. Rinehart, V. R. Solid state polymerization of polyester prepolymers. USA 1988. 60 CHAPTER 5: CONCLUSION AND FUTURE WORK 5.1 Conclusion In conclusion, we have shown that blends of PET-B with 10-20 wt% PET-T content may be recy- cled back to bottle-grade PET. Among the three studied techniques, chain extension and the com- bination of chain extension with SSP completely recovered the desired inherent viscosity values for PET-B blends containing 10-20 wt% PET-T. The SSP process was used to enhance the intrinsic viscosity (IV) of the polymer blends. Through the implementation of solid-state polymerization (SSP), the polymer's chain extension was enhanced, leading to a diminished level of degradation during the treatment of PET blends using processes like extrusion and injection molding. The IV of the recycled blends was increased by 0.05-0.3 dl/g. Meanwhile, the tensile strength has increased by 5-10% after SSP and the tensile strength had also increased. The Izod impact strengths of the PET-B/PET-T blends containing 10 and 20 wt% PET-T had increased by 0.5 and 0.2 kJ/m2, respectively. This increase in overall impact strength can be attributed to the SSP process. In this study, a chain extender was employed to improve the thermal stability of the polymer and enhance the melt processability of recycled PET in the extrusion procedure. The application of the chain extender Joncryl ADR (J) within the reactive extrusion process mitigated the degradation of recycled PET while elevating molecular weights. The addition of J enhanced the polymer’s vis- cosity and thermos-mechanical properties. The addition of J to the 10 and 20 wt% PET-B/PET-T blends enhanced the IV by 0.82 and 0.86 dL/g, respectively, which indicates that the Mw of the polymer blend had increased after the implementation of the chain extender. TGA and DSC data showed that the chain extension and SSP treatment did not have much of an impact on the recycled 61 PET blend’s thermal characteristics. The thermal characteristics were like that of a 100% recycled PET material. The hypothesis was thus proven, demonstrating an elevation in IV, it was shown that the incorpo- ration of the chain extender and subsequent SSP process led to improvements that could be applied for bottle production. This investigation also confirmed our hypothesis that there would be no degradation in the thermomechanical characteristics of the rPET blends made from the reactive extrusion process and via SSP pre-processing. This project will help create a streamlined system in which post-consumer PET bottles and PET thermoforms can be recycled together to create 100% recycled bottles from these blends, thus creating a bottle-bottle recycling system and reduc- ing landfilling and reducing the need for a separate recycling process to handle thermoform PET. 5.2 Future Work The research provided insight into improving the IV values and thermal characteristics of rPET blends of PET-B and PET-T using chain-extension and a SSP process. There are a few points that can be considered for further research in more depth in characterizing the polymer blend material. UV-visible spectroscopy can be employed to analyze the polymer blend for color presence and assess material transparency, facilitating the potential use of recycled material for producing clear bottles. However, it's important to note that this study didn't verify the material's barrier properties, a crucial factor in practical applications. Hence, evaluating the PET blends for oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) would be valuable. In addition, the perfor- mance of the recycled PET blend pellet should be compared with those of commercially available recycled pellets in a future investigation. Also, the homogeneity of the blends can be verified by visual inspection and microscopic analysis. 62