Polyesters with inbuilt photolabile units for degradation of PET in the natural environment

Abstract

The proliferation of waste plastic is a growing environmental concern due to its harmful effects on ecosystems, wildlife and human health. Here we have investigated the introduction of photolabile carbonyl and dicarbonyl units into polyethylene terephthalate (PET) with the aim to enhance the degradability of PET in the natural environment. Single carbonyl units have been introduced using 1,3-dihydroxyacetone as the diol component in place of ethylene glycol. Studies on the thermal behaviour of molecular polymer models have shown insufficient stability of the dihydroxyacetone unit under typical PET polymerisation conditions (∼270 °C). The introduction of dicarbonyl units into PET was achieved using a dimethyl dicarbonyl ester (DDE) or di(hydroxyethyl) dicarbonyl ester (BHEDE) which have been incorporated into PET through transesterification methods. Effective removal of methanol or glycol is extremely difficult under these conditions and can lead to reductions in molecular weight due to transesterification. A series of copolymers using various ratios of additive/PET has been prepared through melt processing. The degradability of the resulting polymer films has been investigated using artificial weathering during a 14-day cycle with controlled temperature, humidity and UV irradiation. A lowering of the molecular weight was observed in all cases, most likely due to hydrolysis of the ester linkages, although oxidative cleavage of the dicarbonyl units could also have taken place, but the end-groups would be indistinguishable.