Effect of Copper-Modified ZSM-5 Zeolite Concentration on the Thermomechanical and Antimicrobial Properties of...

The development of multifunctional biodegradable materials with improved structural performance and antimicrobial functionality is essential for advancing sustainable packaging. This study evaluates the effect of copper-modified ZSM-5 zeolite (ZCu) concentration (0, 1, and 5 wt%) on thermoplastic starch/polylactic acid (TPS/PLA) blends. The TPS was derived from Ipomoea batatas (sweet potato, SP) and Dioscorea rotundata (diamond yam, DY) starches and compatibilized with 1 wt% citric acid. The ZCu response depended on both ZCu loading and the botanical starch source. Structural analyses showed that SP-based composites reached their highest crystallinity at 1 wt% ZCu (13.70%), whereas DY-based systems exhibited an initial decrease at 1 wt% followed by an increase to 12.75% at 5 wt%, reflecting distinct concentration-dependent crystallization trends. Thermal analyses demonstrated a substantial increase in the degradation onset temperature of SP-based composites, from 132.9 °C to 185.1 °C at 1 wt% ZCu, indicating an effective thermal barrier effect. Nanomechanical mapping revealed concentration- and starch-source-dependent changes in local hardness, reduced modulus, and elastic recovery, without evidence of uniform mechanical reinforcement across all formulations. Antibacterial activity was observed exclusively in composites containing 5 wt% ZCu, with inhibition zones of 5.3 mm against Staphylococcus aureus and 1.0 mm against Escherichia coli. These findings highlight how the structural, thermal, nanomechanical and antimicrobial responses of TPS/PLA blends vary with ZCu concentration and the botanical origin of the starch.