Activation of silver nanoparticles by hydrophilic encapsulation for antimicrobial powder coated surfaces

Silver nanoparticles (AgNP) are known as an antimicrobial agent, but they cannot be efficiently converted to active silver ions due to the lack of hydrophilic reaction environment when incorporated into a dry powder coating film. To make these agents effective in the powder coated surface, a novel encapsulation approach was proposed. Silver nanoparticles were first synthesized on the surface of synthetic zeolite A by in-situ chemical reduction method, which was followed by the addition of copper ions through ion exchange. The functionalized zeolite was then encapsulated with different water-soluble hydrophilic polymers to facilitate the generation of silver ions from nanoparticles. The encapsulated additives were incorporated into the resin system for making the antimicrobial powder coating film. The properties of the additives and films were carefully analyzed, and results show that appropriate loading of silver guarantees a high concentration and uniform distribution of silver nanoparticles on the zeolite surface. The strength of the encapsulation with the additive is found to depend on the cations present in the additives. Anionic polymer encapsulation is the most effective solution for releasing silver ions from antimicrobial coated surface. Excessive hydrophilicity is not beneficial to antimicrobial ability and brings cracks on the surface. Additives with non-polymeric hydrophilic encapsulation made from the precipitation of calcium nitrate and sodium phosphate also shows acceptable antimicrobial efficiency. The proposed hydrophilic encapsulation method can well facilitate the activation of silver nanoparticles and ensure an effective antimicrobial property of the powder coating film.