The effect of organocatalytic acetylation on water sensitivity and mechanical performance in starch Acetate/Polylactide composites

Abstract The integration of starch with polylactide often leads to suboptimal compatibility and compromises in mechanical properties, especially when processed using conventional melt processing methods. Although the property profile of the polyester can be effectively tailored by the incorporation of starch, the limited thermal stability and hygroscopic nature of the latter present considerable challenges. Heterogeneous organocatalytic acetylation addresses both shortcomings and yields high degrees of substitution (up to 1.6) without drastically changing the granular structure of the polysaccharide. The primary aim of this work was to determine the effect of esterification on interfacial adhesion in composites made of unplasticized, organocatalytically acetylated corn starch and polylactide. Contrary to widely accepted earlier claims, acetylation clearly hinders interfacial adhesion with the less polar matrix polymer. This effect cannot be overcome by the addition of a reactive polymer, maleic anhydride-grafted polylactide, necessitating other means of compatibilization. On the other hand, less humidity-dependent mechanical properties could be achieved, as the hydrophobic modification reduces the equilibrium water content (4.0 to 1.2 wt%) of the composites. The originality of this work lies in its systematic evaluation of the interplay between chemical modification, material formulation, and resulting morphological and mechanical properties. Our study provides evidence for organocatalytic esterification being a scalable and industrially relevant route toward moisture-resistant biodegradable composites, contributing to the advancement of sustainable materials for a range of applications.