Review - Environmentally friendly coatings using carbon dioxide as the carrier medium

The use of supercritical or liquid carbon dioxide as a medium for delivering coating systems is attracting much interest because of concerns over the environmental effects of volatile organic compound (VOC) emissions from conventional coatings. Significant reductions in VOC emissions can be achieved by replacing some or all of the organic solvent by CO2 in spray coatings. Technical and commercial benefits are also claimed for these systems, including improved coating efficiency and operating cost savings. In this review, the range of current and potential applications achievable using CO2-based coatings is discussed. In addition to spray coatings onto a variety of substrate surfaces, CO2 processes can be used to produce controlled particle size powders for use in powder coatings and also for the coating of preformed particles such as metal powders and pharmaceuticals for controlled release in drug delivery. Use of CO2 in spin coating and microlithography offers the potential for significant waste reduction. Specific substrates where use of CO2 can be beneficial include the treatment of building stone and wood treatment. CO2 can aid surface impregnation of substrates because of its high diffusivity and the potential for substrate swelling. (C) 2002 Kluwer Academic Publishers.