Bio-Based Upcycling of Poly(ethylene terephthalate) Waste for the Preparation of High-Performance Thermoplastic Copolyesters

Abstract

Thermoplastic copolyesters occupy an important segment in the materials market, finding use in a wide range of engineering plastic applications. This fact owes itself to the versatility underlying the synthetic preparation. However, the industry relies nearly exclusively on virgin feedstocks that are derived from fossil-based resources. With a keen interest in improving the deleterious environmental impact of this material class, we combine postconsumer recycled PET (rPET) with a bioderived dimer fatty acid (DFA) building block for the synthesis of segmented thermoplastic copolyesters (TPCs) via solvent-free melt polycondensation. The influence of (i) catalyst type, (ii) hard block (i.e., PET) precursor, and (iii) soft block (i.e., DFA) content on the microstructure and mechanical properties of TPCs was assessed. Samples that exhibit equivalent mechanical strength and segment distribution are accessible using either pristine bis-hydroxy ethylene terephthalate (BHET) or rPET as starting materials. Screening of reaction conditions and composition space within this context was performed with small-scale (2 g) reactions. Further optimization of reaction conditions in terms of catalyst concentration and ethylene glycol deconstruction agent content allowed for the upscaled synthesis (100 g) of engineering-grade TPCs in a custom-built reactor. We believe that our results contribute to a new paradigm in the efforts for more responsible manufacturing practices for TPCs and provide an additional outlet for the efficient handling of end-of-life, recyclable plastics.