Comparative degradation study of a biodegradable composite based on polylactide with halloysite nanotubes and a polyacrylic acid copolymer

Abstract

This study investigates the optimal composition of two additives to accelerate the degradation mechanism of polylactide (PLA) material under different conditions: abiotic hydrolysis, biotic degradation and composting conditions at the laboratory scale level. The composites were prepared from a PLA matrix with a synthesised additive based on a copolymer of polylactic acid and polyacrylic acid (PLA-g-PAA) with inorganic filler halloysite (HNT). The aim was to design a composite material with improved physical and chemical properties and accelerated degradability than conventional PLA, which would apply to products incapable of mechanical or chemical recycling. The addition of HNT alone helped increase Young's modulus by 15-25 % but worsened the elongation, which was compensated by adding a second additive in the composite. The experimental data from abiotic hydrolysis and biodegradation were processed using appropriate kinetic models. Abiotic hydrolysis was recorded by changes in molecular weights and released carbon (GPC, TOC-L), confirming its acceleration in PLA/ 5H/20PLA-g-PAA composites by a faster release of ester bonds in PLA. A similar effect was observed during biotic degradation using the measured CO2 content (GC instrument), which was demonstrated by accelerating from 0.0238 day-1 for neat PLA to 0.0397 day-1. In composting conditions, the course was the fastest up to 45 days; samples containing additives were disintegrated by 94.1-99.8 %, without depreciating the properties of compost and plant germination.