Trends in Polyester Upcycling for Diversifying a Problematic Waste Stream

Abstract

We are facing a rapidly growing plastic pollution crisis, which is adversely affecting communities and ecosystems across the globe. Polymer scientists have an urgent obligation to develop and implement strategies for reutilizing plastic waste streams instead of continually relying on virgin feedstocks in plastic manufacturing. Postconsumer and postindustrial plastic items should be treated as valuable resources instead of discarding them. In order to do this, technological outlets must be developed to produce renewed materials using plastic waste as an input. Polyesters represent one of the largest plastic waste streams because they are commonly used in single-use beverage and food containers as well as textiles. Polyesters are also ideal candidates to exploit through chemical diversification, owing to the wide variety of functional derivatives that can be synthetically accessed via ester reactivity. This work highlights some recent developments related to diversifying polyester waste, with a focus on poly(ethylene terephthalate) (PET) as waste stream. The strategies encompass the production of both valuable small molecules prepared via degradation of PET and high-performance polymeric scaffolds derived from reactions with PET. Taking the recent ingenuity into consideration, based on these technological developments, an outlook is provided for the future of polyester waste streams. What are the next steps that are needed? Where are these trends headed? What gaps still exist, particularly with respect to assessment of sustainability and life cycle analysis? Collectively considering the examples highlighted here, there is great promise in the field of reutilizing waste streams as feedstocks for value-added materials.

Solvent-Promoted Catalyst-Free Recycling of Waste Polyester and Polycarbonate Materials

“…PET is extensively used in packaging and textiles, while BPA-PC finds applications in electronic, constructional, and optical applications. For PET, several typical depolymerization methods, including alcoholysis, glycolysis, aminolysis, and hydrolysis, were well reviewed. ,, In our work, the methanolysis of PET required a higher temperature (Table ) compared with PLA. For example, PLA could be fully depolymerized at 140 °C by methanolysis.…”

Upcycling of Plastic Waste Using Photo-, Electro-, and Photoelectrocatalytic Approaches: A Way toward Circular Economy

“…Chemical upcycling primarily involves the conversion of plastic polymers into their monomers or some short chains which can therefore be used as fuels or feedstock for polymerization reactions and the further production of VAP. , As a result, plastic waste can be converted into solid carbonaceous materials, liquids including acids and fuels, and gaseous fuels such as hydrogen and syngas. − The separation of various plastics, contamination, the potential creation of corrosive gases, and the typical low selectivities of products are some of the practical issues that currently plague chemical upcycling operations. , Although conventional chemical upcycling uses more energy, it is a promising strategy since it may produce a wide range of readily available compounds with the judicious development of catalysts and reaction conditions. Further, biological upcycling mainly focuses on microorganisms and enzymatic activity for the valorization of plastics with some review articles published. − Ru et al revealed that the enzymatic reactions are inefficient after reviewing the microbial valorization of plastic waste . The expense of utilizing or maintaining enzymes and bacteria, the constrained variety of reaction conditions, and the narrow scope to mostly condensation polymers are further issues with biological techniques for upcycling plastics …”

Semi-Crystalline and Amorphous Polyesters Derived from Biobased Tri-Aromatic Dicarboxylates and Containing Cleavable Acylhydrazone Units for Short-Loop Chemical Recycling

“…Poly­(ethylene terephthalate) (PET) is the most important aromatic polyester available today, widely used in film and beverage packaging and textiles. , However, the fossil-based nature of terephthalic acid (TPA) or its dimethyl ester (dimethyl terephthalate) used in PET production has raised serious questions concerning its sustainability. − Consequently, there has been an enormous interest recently in the industry and academia to develop alternative biobased aromatic dicarboxylic acids and dicarboxylates as a potential substitute for TPA in aromatic polyesters. − One significant achievement in this direction is the development of 2,5-furandicarboxylic acid (FDCA) derived from a sugar-based building block. The polycondensation of FDCA with ethylene glycol yields a 100% biobased polyester known as poly­(ethylene 2,5-furandicarboxylate), or PEF, which possesses comparable or even slightly better properties than PET. , Inspired by this successful example, several alternative biobased aromatic diacid or dicarboxylates have been reported for polyester synthesis, particularly using the phenolic and furanic building blocks obtained from lignocellulosic biomass. − …”