Chemical recycling of all-polyester vehicle interior solutions

Abstract

Increased circularity in the plastic industry is key to decrease oil-dependence and find more sustainable solutions. In addition to the most widely used method, mechanical recycling, others are possible which could enable more complex material streams to be recycled. One such route is chemical recycling where depolymerisation yields monomers of virgin quality, which can be used to synthesise new polymer chains. Typical vehicle flooring solutions results in waste consisting of various different polymeric fibres and foams adhered together, resulting in low recyclability and the waste is either incinerated or sent to landfills. In response to the low recyclability of conventional soulutions, new solutions based on polyester and comonomers have been developed, as the most commonly used polyester, poly(ethylene terephthalate) (PET), has good recyclability. However, the recyclability of an all-polyester solution, containing different polyesters and comonomers has not been investigated and that will therefor be done in this project. In the project, PET, poly(butylene terephthalate) (PBT), polyester based components for vehicle flooring, and a complete all-polyester vehicle flooring solution were depolymerised by glycolysis. Analyses showed that the components in the polyester based vehicle flooring consisted mainly of either PET or PBT. Glycolysis of neat PBT gave a crystallised yield of 38 mol% of bis(2-hydroxyethyl)terephthalate (BHET), PET monomer, compared to 79 mol% from neat PET. Several of the components yielded similar amounts as neat PET, whilst lower yields were obtained from components which consisted mainly of PBT, where co-polyester glue appeared most challenging. The glycolysis of the full vehicle flooring solution yielded white crystalline BHET with a purity above 97 % and a crystallised yield of 60 mol% confirming that the product is recyclable. The origin of the low yield of BHET crystals from PBT, compared to PET, was further studied using HPLC. It was shown that the yields of BHET in the reaction solution was significantly higher compared to the crystallised yield after workup. This indicates that for the flooring, and other PBT containing mixes, the separation process needs adjusting as compared to that used for neat PET, likely due to additional byproducts forming. The results showed that the polyester based vehicle flooring solution, and PET and PBT blends, can be chemically recycled by glycolysis to BHET which could help close the material loop as a more circular solution.