Triggered-Release Biocidal Nanocomposite Coatings

Biocidal additives are vital for both the preservation of coatings in the can and for long-term coating integrity after applications. Antifungal additives are critical for delaying attack by fungal and algal growth once an architectural coating is in place. Biocidal coatings are designed to kill microbes and fungi by slowly and steadily releasing biocide from the dried film. Unfortunately, this mechanism also is responsible for the ultimate deactivation of the biocidal activity; once the biocide has leached out or washed out of the coating, all protection against microbes is lost. The protection of the coating by the biocide typically lasts only around 18 months and even less in hot, humid environments like the South and Southeast United States. Once the biocides have leached out, a new coating must be reapplied, often after a labor-intensive washing or removal of the previous coating. This process creates a variety of undesirable environmental impacts, from the contamination of surrounding areas by nonspecific biocide leaching to the increased volatile organic compounds (VOC) emitted during the reapplication of the coating. A system that prolongs biocidal coating lifetime and decreases the environmental impacts of the current system would benefit both the environment and property owners. TDA Research, Inc., will develop a new biocidal-coating system that prolongs biocidal activity by immobilizing biocidal additives in a coating. Biocides are largely wasted because they are emitted continuously but slowly, which contaminates the surrounding area. A nonleaching biocide, however, would eliminate the undesired contamination of the surrounding area and it would stay within a coating for longer time periods. A coating that retains biocidal activity for twice as long, for example, would require repainting only half as often, also leading to a decrease in VOC emissions and waste production during painting. Such a biocide also would prevent the formation of biocide-resistant bacteria that can form from a traditional slow-release biocide.