Mechanical recycling is the least energy intensive and most widely implemented means of recovering value from plastic waste. To ensure a more robust and efficient circular plastics economy, it is imperative that efforts to improve mechanical recycling continue. The associated challenges span many dimensions, including social (e.g. consumer behavior), infrastructural (e.g. waste collection), and technological (e.g. sorting and reprocessing). For reprocessing, a pivotal obstacle is degradation of the plastic during extrusion, as this can severely limit the quality of the obtained recyclate. The thermo-oxidative processes that cause this degradation can be ‘reversed’ or mitigated by using appropriate additives such as chain extenders or antioxidants, which effectively increase the number of recycles that a plastic can ultimately undergo. In this work, we demonstrate the synthesis of novel polymeric additives targeted toward mechanical recycling of condensation polymers, with particular focus on poly(ethylene terephthalate) [PET]. The polymeric additives are synthesized by free radical terpolymerization of antioxidant- and chain-extender-containing monomers with styrene. By varying the monomer feed ratios, a suite of dual-functional polymer additives were prepared and purified. The efficacy of these polymers was tested by mixing ~1 wt% of each with PET and subjecting this mixture to oscillatory shear rheology measurements over extended periods of time. The optimal candidates were then translated to extrusion trials with pre-extruded PET and actual post-consumer waste PET. The successful performance of these additives was assessed by subjecting the obtained recyclate to size exclusion chromatography, thermal characterization methods, and tensile testing. The performance of the novel additives was benchmarked against currently available commercial additives (chain extender or antioxidant).

Dual-functional polymeric additives for mechanical recycling of PET

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ACS Fall 2022

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