Compostable Multilayer Films with Tailored Gas Barrier and Biodegradation

This study investigates the barrier and biodegradation performance of reactive blends (reactive melt mixing inside the extruder) of poly-(lactic acid) [PLA] and thermoplastic cassava starch (TPCS). Two PLA-g-TPCS, plasticized with either glycerol (Gly) or poly-(ethylene glycol) (PEG), were prepared by twin-screw extrusion and processed into multilayer films through cast coextrusion. The films were characterized to assess structural, mechanical, thermal, optical, barrier, and surface properties, with emphasis on the effects of plasticizers. The biodegradation of these multilayer films was evaluated over 90 days using a direct-measurement respirometer system, tracking the evolution of CO₂ in compost under thermophilic conditions. Fourier transform infrared spectroscopy (FTIR) analysis confirmed the successful grafting between PLA and TPCS. Reactive blending of PLA with TPCS significantly reduced tensile strength (TS) and Young's modulus (YM) by over 50%, while elongation at break (EAB) increased by 70-80%. Incorporating the PLA-g-TPCS layer into a multilayer design tripled tensile strength and modulus compared to monolayers. TPCS enhanced chain mobility, lowering glass transition and melting temperatures. Gly-plasticized TPCS reduced oxygen permeability by 50%, whereas both plasticizers increased water vapor transmission and surface hydrophilicity. The hydrophilic TPCS accelerated abiotic degradation (hydrolysis of ester bonds due to humidity and temperature before biodegradation) of PLA under thermophilic conditions. Conversely, the PLA outer layers slowed the overall biodegradation rate in multilayer films, influenced significantly by the type of plasticizer used. Overall, PLA-g-TPCS multilayer films combine composability (in industrial facilities and possibly also in home composting environments) with functional performance, offering promise for sustainable packaging.