No abstract

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 CO 2 evolution in compost media at 58 and 37 °C, and the number average molecular weight (M n ) 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 M n 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.

The hydrolysis of poly(lactic acid), PLA, was investigated considering the changes in the three-phase model structures, the mobile amorphous, crystalline (CF), and rigid amorphous fractions (RAF). Amorphous PLA films with different L-lactide were crystallized by cold-crystallization and meltstretching crystallization to promote the three-phase structural variation in the PLA films. The changes in the phase structure and molecular weight during hydrolysis were investigated. As a result, PLA with higher CF had a slow hydrolysis rate due to limited water diffusion into the crystalline structure. Conversely, the initial amount of RAF fasten the hydrolysis affected by the higher water diffusion and more hydrophilic end groups at the early stage. Moreover, the distinct structure of the nanoconfined crystals from the melt-stretching method could limit the diffusion of water molecules into the PLA film and accordingly add more stability to the hydrolysis.