Development of a novel silver ions-nanosilver complementary composite as antimicrobial additive for powder coating

Applying silver into coatings has become a prevalent method in fabricating antimicrobial surfaces. However, the concerns about durability always exist and limit its applications. Here, a highly inhibitory, active, durable, and easy-to-use silver ions-nanosilver antimicrobial additive for powder coatings was fabricated in this study. Silver nanoparticles were chemically bonded to the Ag, Cu, and Zn-ternary ion-exchanged zeolite by $$ -lipoic acid, which was then encapsulated by hydrophilic polymers. The fabricated silver ions and silver nanoparticles (Ag⁺-AgNPs) complementary structure provides a synergistic effect. Ag⁺ is the main antimicrobial agent, while AgNPs act as a supplementary reservoir of Ag⁺. As well, the formed thin layer of silver nanoparticles and hydrophilic film prolongs the release of active Ag⁺ from zeolite, and Ag⁺ facilitates the activation of AgNPs. The results show that this additive indicates excellent antimicrobial activity to E. coli, S. aureus, P. aeruginosa, and C. albicans, and that the coatings with the additive exhibit over 99.99% reduction rate for the tested bacteria and fungi. The coating film is able to maintain over 99% antimicrobial reduction even after 1200 repeated solution wipings, or over 30 wash cycles of artificial sweat solution, indicating high durability. Furthermore, the yellowness of the coating is not evident (Δb < 2) despite the high loading of silver, and the silver nanoparticles have little impact on gloss, haze, and distinctness of the coating film image.