Enzymatic degradation of a commercial bio-based polyester and evaluation of the mechanism involved

Aliphatic polyesters are the most promising biodegradable plastics because of their high susceptibility to the attack of hydrolytic
enzymes and of many microorganisms naturally occurring in the environment. Poly(butylene succinate-co-adipate) (PBSA) is a biobased semicrystalline copolymer of poly(butylene succinate) (PBS), with adipic acid as co-monomer. It is highly biodegradable
because of its lower crystallinity and higher flexibility of polymer chains compared to PBS. In the present study, the biodegradability mechanism of PBSA was evaluated using cutinase from Humicola insolens, which is a commercial hydrolytic enzyme presenting both lipase and esterase features. The polyester degradation is based on weight loss measurements combined to other analyses (i.e., GPC, ¹H NMR, and DSC) performed on the residual solids of PBSA films, in order to understand the molecular and chemical modifications induced at the surface and/or in the bulk of polymer materials over time. The results showed that the enzymatic degradation mechanism of cutinase proceed by degrading the polymer from the surface of the film. An exo-type cleaving action mode was proposed based on the identification of the oligomers and monomers released as degradation products.