Biodegradation and hydrolytic degradation of poly(butylene terephthalate) copolyesters containing cyclic sugar units

The hydrolytic and enzymatic degradation of PBT copolyesters obtained by replacing partially the diol or the diacidic monomers by bicyclic acetalized carbohydrate-based monomers from galactaric acid was studied. Changes taking place in sample weight, molecular weight, chemical constitution, crystallinity and morphology of the polyesters were evaluated. The partial replacement of 1,4-butanediol by 2,3:4,5-di-O-methylene-galactitol resulted in copolyesters with enhanced hydrodegradability compared to PBT. On the other hand, copolyesters obtained by partial replacement of dimethyl terephthalate by dimethyl 2,3:4,5-di-O-methylene-galactarate were biodegradable in the presence of lipases, and were hydrodegraded at a rate that increased with the content in galactarate units.