Antimicrobial PLA-Based Composite Gels with Improved Functional Properties for Food Packaging

Biodegradable polymeric materials with antimicrobial functionality are increasingly explored as sustainable alternatives for food packaging. This study developed multifunctional PLA-based composite films containing controlled concentrations of active agents and evaluated their structural, mechanical, thermal, and antimicrobial properties. Five formulations were prepared: a reference PLA/glycerol diacetate blend (85/15 wt. %) and four composites with 0.5 wt. % functional fillers—grape pomace, silver–graphene oxide (GO-Ag), titanium dioxide–graphene oxide (GO-TiO2), or graphene oxide (GO)—with PLA adjusted to 84.5 wt. %. The films were characterized for antimicrobial activity, tensile strength, hardness (Vickers test), morphology (SEM), and thermal behavior (DSC). Mechanical testing revealed statistically significant differences (p < 0.05), with Vickers hardness increasing from neat PLA (13.77) to 0.5% grape pomace (16.30) and nanofiller composites (GO–Ag 18.59, GO 19.56, GO–TiO2 22.7), demonstrating enhanced stiffness and efficient load transfer. Incorporation of Ag and TiO2 shifted endothermic transitions to higher temperatures, particularly in PLA-GT (~140 °C), indicating improved thermal stability, while neat PLA and PLA-GP showed multiple or intermediate transitions (86–92 °C). Antibacterial performance was strongly influenced by composition and surface characteristics, with PLA-GA, PLA-GT, and PLA-GO showing the greatest efficacy. These findings demonstrate that bioactive and nanostructured fillers can effectively enhance the mechanical, thermal, and antimicrobial properties of PLA, highlighting their potential for sustainable, functional food packaging applications.