Biocide-encapsulated core–shell polymer microspheres: A novel approach for preparing long-lasting antimicrobial coatings

Abstract

Antimicrobial coatings play a crucial role in combating pathogenic microorganisms. However, developing long-lasting antimicrobial coatings presents substantial challenges. In this study, we developed a robust method for fabricating durable antimicrobial coatings using crosslinked, biocide-encapsulated core–shell polymer microspheres. These microspheres were prepared by emulsion polymerization, facilitating simultaneous synthesis and biocide loading. Designed with a hydrophilic shell and a hydrophobic core, the microspheres predominantly stored the hydrophobic biocides within the core, thus reducing the biocide concentration at the shell. This design, which is governed by Fickian diffusion, substantially slowed the rate of biocide migration from the shell to the external environment, thereby enhancing the coating's antimicrobial longevity. The synthetic process for these biocide-encapsulated microspheres was optimized to encapsulate biocides with a Log P range of 1–3, achieving an encapsulation efficiency exceeding 85 % for all tested biocides. Specifically, microspheres containing N-butyl-1,2-benzisothiazolin-3-one (BBIT) were used to develop an antimicrobial coating. The coating can be applied to various substrates, including glass, metal, wood, ceramics, and plastics. It exhibits excellent hardness, adhesion, mechanical strength, and solvent resistance on these surfaces. Antimicrobial tests and release analyses demonstrated that the coating maintains high biological activity for at least 10 months, effectively inhibiting bacterial and fungal growth. The release behavior of the coating adhered to the Peppas–Sahlin model, with diffusion as the predominant mechanism. The model predicted an antimicrobial retention rate of over 66 % after 1 year, confirming its sustained antimicrobial effectiveness.