Helicteres isora Fiber-Reinforced PLA Biocomposites: Investigation of Biodegradability in Soil and Compost Environments and Antimicrobial Surface Coating to Increase Microbial Inhibition Ability

Natural fiber-reinforced polymer composites are gaining significant momentum in sustainable engineering applications. This study investigates the biodegradability and antimicrobial property enhancement of Helicteres isora fiber-reinforced polylactic acid (PLA) biocomposites. Biodegradation was assessed via controlled soil and vermicompost burial tests simulating natural disposal environments. Composite specimens were monitored for weight loss and surface morphological changes over 90 days at ambient temperature and 45 days in compost at 60 °C. Degradation was substantially higher in compost due to elevated microbial activity and moisture. Thermophilic composting accelerated the breakdown, yielding 22–27% weight loss within 45 days. Antimicrobial functionality was evaluated by coating composite surfaces with zinc oxide and silver nanoparticles (AgNPs; hydrodynamic size 45.23 nm, crystallite size 6.21 nm) against Staphylococcus aureus and Escherichia coli. A 1 wt % AgNP coating produced distinct bacterial inhibition zones against both strains, whereas zinc oxide coatings showed negligible efficacy. The developed biocomposites demonstrate dual functionality: proven industrial compostability and potent broad-spectrum antibacterial resistance without compromising core matrix biodegradability. These functionalized materials offer significant potential for eco-friendly, antimicrobial food packaging, agricultural films, and single-use hygienic goods.