Antibacterial, Antiviral and Antifungal Activity of Zinc Oxide Tetrapod in Polypropylene Compared to Other Zinc Based Additives

Polypropylene (PP) was compounded with 3 different zinc-based additives, zinc oxide tetrapod (t-ZnO), zinc oxide, and zinc pyrithione (ZPT) at different concentrations (0.1–2 wt%) and their antimicrobial (AM) efficacy toward bacteria, virus, and fungi was assessed. Additionally, caprylic acid (CA), aimed to be used as a promoter, showed inherent AM properties when compounded in PP (at 2 wt% loading, log R = 2.5 and 4.1 against Escherichia coli and Staphylococcus aureus , respectively) and a synergistic effect with zinc additives. CA enhanced AM performance, thus effectively requiring less overall concentration of Zn to provide the same effect (additives loadings down to 0.1 wt% for ZPT and down to 0.4 wt% for tZnO when CA was used in equal amount). The antiviral properties against H₁N₁ of selected PP materials showed the superiority of ZPT compared to t-ZnO, with up to 93% viral reduction after 6 h for ZPT versus 85% for t-ZnO. Similarly, ZPT showed superior antifungal properties, with almost no fungal growth after 28 days incubation, while some growth was visible with a microscope on PP with t-ZnO additive at the same loading. The morphology of the zinc particles was assessed using different visualization techniques (CT-scan and SEM–EDX). A similar overall distribution with or without CA was obtained, yet with a different shape of the zinc particles in both cases (ZPT and t-ZnO). At high concentration in the PP matrix, CA may act as a plasticizer during extrusion and would thus help in retaining the inherent morphology of the zinc particles.