Direct polymer-to-polymer upcycling of mixed PET/PBT wastes into biodegradable plastics: an environmental techno-economic assessment

초록

Upcycling of post-consumer poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) typically relies on depolymerization. However, depolymerization can be energy-intensive and operationally complex, undermining the benefits of upcycling. In this study, we designed a direct polymer-to-polymer copolymerization process that converts mixed PET/PBT waste into biodegradable copolyesters. We evaluated the effects of poly (tetramethylene glycol) (PTMG) loading (20-40 wt%) and the inclusion of a glass fiber removal step on process performance. To this end, we conducted an environmental techno-economic assessment of the proposed process to quantify its environmental and economic viability. Increasing PTMG loading generally increased both cost ($324-539/ton-product)andgreenhouse-gasemissions(from-1.24to1.03kgCO2eq./kg-product),indicatingthatPTMGloadingisaprimarylevergoverningthetradeoffbetweeneconomicandclimateperformance.Moreover,glassfiberremovalincreasedtheminimumsellingpricefrom$1335-1588/ton to $1717-1807/tonowingtosolventhandlingandrecovery.However,glassfiberremovalenablesfiber-freespecificationswhenrequired,andthisquality-costtradeoffcanbemitigatedbyminimizingsolventlossesandrecoveryduty.Applyingacarbonpriceof$22.04/ton to monetize greenhouse gas reductions lowered the break-even price by $34-155/ton across cases. Overall, PTMG loading and glass fiber management emerged as explicit and controllable levers, enabling flexible, grade- and specification-dependent operation within a single plant.

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