Enzymatic Degradation of Poly(Butylene Adipate-co-Terephthalate)/Poly(Lactic Acid) Blends

Poly(lactic acid) (PLA) is regularly blended with poly(butylene adipate-co-terephthalate) (PBAT) to produce compostable plastic films used in packaging applications, for example. Since PLA and PBAT both contain ester bonds, these PBAT/PLA blends are interesting candidates for enzymatic recycling. This is a new, green recycling technique that allows the use of mild processing conditions to regenerate the pure building blocks of polymers, thereby enabling repolymerization to virgin-quality plastic. In this work, various PBAT/PLA blends are prepared (20, 40, 60, and 80 wt% PBAT) and incubated with a cutinase enzyme from Humicola insolens (HiC). Enzymatic degradation is characterized by weight loss, scanning electron microscopy (SEM), and proton nuclear magnetic resonance (¹H NMR) spectroscopy. Blends rich in PBAT are effectively degraded by HiC (up to 40% weight loss after 7 days of incubation at 70°C), while PLA-rich blends are degraded to a lesser extent. HiC is capable of degrading both polymers, although for PLA, the extent of degradation is similar to control experiments without HiC. Furthermore, in the absence of an enzyme, a “shielding” effect is found for nonenzymatic degradation, where a hydrolytically stable PBAT matrix prevents the degradation of the PLA domains. This work provides insight into the enzymatic degradation of uncompatibilized polymer blends and opens up the possibility for the enzymatic recycling of commercial PBAT/PLA blends.