Poly(ethylene Terephthalate) Waste Heterogeneity and Recycling Pathways: Evaluating Mechanical and Chemical Recycling Technologies in the Context of the Poly(ethylene Terephthalate) Supply Chain
Adam McNeeley, Y. A. Liu, Kiyan Vadoudi
Abstract
High Resolution Image Download MS PowerPoint Slide Poly(ethylene terephthalate) (PET) is a common thermoplastic used in a variety of applications. PET is one of the most highly recycled plastics, and mechanical recycling of PET bottles has been practiced for over 30 years, with large and robust collection and processing supply chains. Even with this success, there are challenges and opportunities to improve PET bottle recycling. Other PET materials, such as textiles, the largest PET end use, are not compatible with the existing mechanical recycling technologies. Development and improvement of PET recycling technology are necessary to expand the scope of recyclable wastes, such as textiles, and improve the circularity and sustainability of PET as a material. A detailed understanding is required of PET products and compositional characteristics, and how they influence the characteristics and composition of PET waste. This needs to complement an understanding of the technological nuances of different PET recycling technologies that cause processing or reliability limitations and provide fundamental advantages and disadvantages. The purpose of this work is to tie together the product and compositional variation of PET products and PET waste feedstocks to the fundamentals of different recycling pathways to determine the advantages and limitations of current and developing technologies. Mechanical recycling technologies should be used to the broadest extent possible, but purification limitations related to mechanical recycling reduce the scope of recyclable material to heavily sorted or monocollected, clear feedstocks, requiring support from upstream supply chain improvements and design-for-circularity initiatives. Chemical recycling pathways provide a way to considerably expand the scope of recoverable PET waste by enabling purification capabilities at a molecular level. Separations and purification capabilities are the primary factors impacting the energy demand and complexity of chemical recycling technologies. The development of consistent and reliable supply chains for the collection of polyester textile waste encourages the investment and development of large-scale textile-based chemical recycling plants. Understanding the material quality and compositional variance of textile waste in the supply chain is necessary to tailor the design of chemical recycling processes to specific types of waste, which further improves the efficiency and economics. Identification of processing issues or inefficiencies in recycling low-quality waste motivates changes in product design or collection, which further reduce recycling costs and improve recycling efficiency.