Biocides are necessary to prevent the microbial deterioration of many industrial coatings. The two main applications of biocides are (a) to prevent spoilage of the wet-state product during storage and transport (in-can protection), and (b) to ensure long-term performance of the coating (dry-film protection).(1)
Upon drying, both water- and solvent-based coatings are susceptible to colonization by fungi and/or algae. The growth of microorganisms on dry film not only affects the appearance of the coating (discoloration), but it may also compromise its performance (biodeterioration). Fungi can penetrate coatings, resulting in cracking, blistering and loss of adhesion, leading to decay or corrosion of the underlying substrate. Algae colonies, which seem to grow more rapidly on porous substrates such as stucco, cement and bricks, have the ability to occlude water. The freezing and thawing of this entrapped water may induce cracking or increase the permeation properties of the coating, leading to failure. The presence of water may also encourage colonization by other microorganisms that, in turn, may cause biodeterioration.(2) The type of microorganism that can colonize the coating will depend on several factors, including moisture content of the surface, presence of nutrients, substrate and coating composition.(3)
In order to be most effective, the biocide needs to be present at the coating interface. This makes it susceptible to water leaching. Controlling the release of the biocide through encapsulation could ensure that a minimum concentration of biocide is always maintained at the surface interface, extending the shelf life of the coating. Additionally, this controlled release could reduce the amount of biocide that is released to the environment over a period of time.
This paper describes the controlled release of IPBC (3-iodo-2-propynyl butylcarbamate) through encapsulation. Long-term protection of the surface is enabled through the adsorption interaction between the biocide and the carrier.(4,5) This renders the biocide more resistant to leaching. Encapsulated IPBC was released more slowly than non-encapsulated, as measured by analytical and microbiological methods. The encapsulated biocide was also more resistant to environmental degradation from UV/heat. Furthermore, outdoor exposure tests of paints containing encapsulated IPBC showed enhanced dry-film protection.