Efficient enzymatic degradation of poly(ε-caprolactone) by a commercial lipase

The production and use of plastics have been growing in the past decades. Most of these plastics are fossil fuel-based and non-degradable, thus they accumulate in the environment causing severe problems. The use of plastic-degrading enzymes in the treatment of plastic waste, thus the use of biodegradable polymers has gained growing attention in different fields, including packaging, agriculture and medicine. 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. Among them, poly(ε-caprolactone) (PCL) is a semicrystalline aliphatic polyester, widely used in biomedical and packaging applications, because of its biocompatibility and biodegradability. This study investigates the degradation mechanism of two commercial PCL with different molecular weights (150*10³ and 215*10³ g/mol) by a commercial lipase from Candida sp. (CALB). The degradation mechanism is studied through weight loss measurements of polyester films combined to other analyses (i.e., GPC, ¹H NMR and DSC) performed on the residual solids after incubation with the enzyme, in order to understand molecular and chemical modifications induced by lipase. Moreover, a cleaving action mode for the enzyme (endo- and/or exo-type) on both PCL was also proposed based on the identification and quantification, via GPC, ¹H NMR and HPLC-RID analyses, of residual oligomers and monomers released as degradation products in the liquid fraction. Results showed that lipase CALB degrade the polymers homogeneously from the surface through an erosion mechanism, with an exo-type cleaving action mode, and the degradation rate is slower with a higher molecular weight.