Enhancing antimicrobial properties and hydrophilicity of environmentally biodegradable plastic using sparking-deposited ZnO nanoparticles

Biodegradable plastics such as polylactic acid (PLA), polybutylene succinate (PBS), and polybutylene adipate-co-terephthalate (PBAT) are sustainable alternatives to petroleum-based packaging, but their limited antimicrobial properties hinder broader applications in food packaging. This study presents a solvent-free sparking discharge method to deposit zinc oxide (ZnO) nanoparticles onto bioplastic surfaces to enhance antimicrobial and hydrophilic properties. ZnO was deposited on PLA, PBS, and PBAT films through 10 to 60 sparking cycles. Structural and surface characterizations were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and water contact angle. Antibacterial activity against Escherichia coli and Staphylococcus aureus and antifungal activity against Aspergillus flavus spores were evaluated by plate count methods. LIVE/DEAD BacLight staining with fluorescence microscopy confirmed microbial viability. PLA showed the most uniform ZnO distribution among the films, with 16.63 wt% Zn detected after 60 sparking cycles. This treatment reduced the water contact angle from 96.67° to 37.93°, indicating improved surface wettability. Zn-PLA-60X achieved the highest antimicrobial performance, reducing E. coli and S. aureus by 1.44 and 1.01 log CFU/25 cm² (96 % and 90 % reduction) and reducing A. flavus spores by 2.16 log (∼99 %). Fluorescence imaging confirmed increased membrane damage and cell death. These results demonstrated that the sparking method offered a practical, scalable, and environmentally friendly approach for producing antimicrobial biodegradable films, with Zn-PLA-60X showing potential for food packaging and biomedical applications.