Breaking It Down: How Thermoplastic Starch Enhances Poly(lactic acid) Biodegradation in Compost─A Comparative Analysis of Reactive Blends

Poly(lactic acid) (PLA) is a sustainable, bio-based, and industrially compostable polymer with a recalcitrant abiotic degradation phase, limiting its organic recovery to well-managed industrial composting facilities. We present a methodology to fully biodegrade PLA in industrial and home composting settings. Thermoplastic starch (TPS) and PLA were reactively blended by adding a chemical modifier and peroxide radicals to obtain a PLA-g-TPS blend by twin screw extrusion and later processed into films by cast extrusion. Biodegradation of the films was investigated using a direct measurement respirometer for 180 days by tracking the CO2 evolution in compost media at 58 and 37 °C, and the number average molecular weight (Mn) reduction was measured by size exclusion chromatography. The hydrophilic nature of TPS and its role as a nutrient source accelerated the degradation of PLA in both abiotic and biotic phases of the composting process. The kinetic curve of Mn reduction showed the positive effect of TPS on accelerating PLA hydrolysis during the lag phase in both mesophilic and thermophilic conditions due to increased chain mobility. This work unlocks the capability of PLA-based films to be successfully composted in industrial and home composting without compromising their desired properties for applications in everyday life.