Grape Pomace as a Biofiller in PLA ‐ and PBAT ‐Based Composites: Effects on Processing, Properties, and Compost Disintegration

Biocomposites offer a key solution for managing food waste and replacing non‐biodegradable plastics. In this study, grape pomace (GP) was incorporated at 10 and 20 wt.% into poly(butylene adipate‐co‐butylene terephthalate) (PBAT) and polylactide (PLA) through melt compounding to investigate the effect of the filler on different properties. The influence of GP on morphology, mechanical, thermal, and rheological properties was evaluated. The results revealed a strongly matrix‐dependent effect of GP. GP has opposite effects on viscosity: it increases in PBAT‐based composite (especially at 20% loading), but reduces it in PLA‐based ones. SEC analyses showed a progressive decrease in PLA molecular weight from Mw about 245,000 g mol −1 for neat PLA to ~147,000 g mol −1 for PLA/GP20, while only limited variations were observed for PBAT‐based samples. For both matrices, GP enhanced stiffness while reducing tensile strength and elongation at break. The comparative performance assessment provided the appropriate information for selecting the PBAT‐based biocomposite as the most suitable formulation for further degradation testing in compost. Degradation tests in compost (58°C, 90 days) demonstrate that GP accelerates disintegration kinetics with PBAT‐based biocomposites showing significantly higher weight loss and surface deterioration than neat PBAT. Grape pomace promotes microbial colonization and enzyme activity, specifically driven by Streptomyces thermoviolaceus and Bradyrhizobium elkanii , which accelerates PBAT depolymerization. Overall, GP effects depend on the polymer: it worsens PLA chain degradation during processing, whereas in PBAT it preserves molecular integrity while accelerating composting disintegration. Further studies measuring CO 2 and O 2 are needed to confirm ultimate biodegradation and mineralization.