Relationship between Particle Size, Anti-Microbial Activity and Leachability of Copper Particles in Liquid Suspension and Compounded in Polypropylene

Abstract

Testing the antimicrobial efficiency of plastics with good precision and repeatability remains a challenge in the plastic industry, as commonly used standards can provide unreliable data. In this paper, we show that the “Bacterial Liquid Suspension Test” is a reliable method that allows for the measurement of antimicrobial activity of poor to very potent biocides. We used this technique to discriminate the performance of two Cu-based biocides, either in nanoparticle (NP) or macroparticle (MP) size, at three different loadings (0.02, 0.2 and 2 wt.%) in PP. With this technique, we also tested the antibacterial performance of PP as powders, pellets, and injection molded disks. As anticipated, the technique shows that both the increased loading and the smaller particle size showed higher antimicrobial activity than the larger particle size due to their increased surface area. Also, PP powders showed greater bacterial reduction than pellets and disks. While the PP with 2 wt.% Cu NPs showed the best antimicrobial performance, the detection of Cu at the surface (using SEM-EDX) and in the water leachate (using ICP-MS) were below the LODs, indicating their ability to kill bacteria.