Sodium Pyrithione-Modified PCL/PLA Blends as Active Antimicrobial Biodegradable Packaging Materials

Introduction
The development of biodegradable polymers with antimicrobial properties is an important direction in sustainable food packaging. Poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) are widely used due to their biodegradability and favorable properties. This study aimed to develop PCL/PLA blends modified with sodium pyrithione as active packaging materials to improve food safety by inhibiting microbial growth.

Methods
Composite films based on PCL and PLA containing different concentrations of sodium pyrithione were prepared and evaluated for antimicrobial activity. Tests were performed against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa according to PN-EN ISO 20645, and against a mixed fungal culture according to PN-EN ISO 846. Bacterial tests were conducted after incubation at 37 °C for 24 h, while antifungal tests were performed after incubation at 22 °C for 28 days. Antimicrobial activity was evaluated according to the criteria specified in the respective standards. All experiments were performed in duplicate.

Results
Control samples showed intensive microbial growth without inhibition. All sodium pyrithione-modified films demonstrated strong inhibition of bacterial growth against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. According to the PN-EN ISO 20645 evaluation criteria, all tested variants exhibited a pronounced antibacterial effect, regardless of sodium pyrithione concentration. No clear concentration-dependent differences were observed among the tested formulations. Antifungal testing confirmed sustained inhibitory activity throughout the 28-day incubation period. Clear zones of fungal growth inhibition were maintained around the modified films during the entire incubation period, indicating strong and persistent antifungal effectiveness.

Conclusions
PCL/PLA blends modified with sodium pyrithione exhibited broad-spectrum antimicrobial activity against both bacteria and fungi. The obtained results demonstrate the potential of these materials for application in active biodegradable food packaging. Further studies are required to optimize the additive concentration and to better understand the mechanisms responsible for the antimicrobial activity.

Financed by the Minister of Science and Higher Education under the “Excellence Initiative – Research University” program for the Priority Research Team at Nicolaus Copernicus University in Toruń, “EPIBIOMAT Research Group – Epibiocompatible Materials for Medicine and One Health”.