Environmentally benign formation of polymeric microspheres by rapid expansion of supercritical carbon dioxide solution with a nonsolvent

A novel method is reported for forming polymer microparticles, which reduce atmospheric emissions of environmentally harmful volatile organic compound s such as toluene and xylene used as paint solvent in paint industry. The p olymer microparticles have formed through rapid expansion from supercritica l solution with a nonsolvent (RESS-N). Solubilization of poly(styrene)-b-(p oly(methyl methacrylate)-co-poly (glycidyl methacrylate)) copolymer (PS-b-( PMMA-co-PGMA), MW = 5000, PS/PMMA/PGMA = 2/5/3), poly(ethylene glycol) (PEG , M. W = 4000), bisphenol A type epoxy resin (EP, MW = 3000), poly(methyl m ethacrylate) (PMMA; MW = 15 000, 75 000, 120 000), and poly(oxyalkylene) al kylphenyl ether (MW 4000) in carbon dioxide (CO2) was achieved with the use of small alcohols as cosolvents. The solubility of the PS-b-(PMMA-co-PGMA) is extremely low in either CO2 or ethanol but becomes 20 wt % in a mixture of the two. Because ethanol is a nonsolvent for the polymer, it can be use d as a cosolvent in rapid expansion from supercritical solution to produce 1-3 mum particles that do not agglomerate. Obtained polymer particles by RE SS-N were applied as powder coatings. The resulting coatings have a smooth and coherent film. The particle size distribution of microspheres was contr olled by changing the polymer concentration, preexpansion pressure, tempera ture, and injection distance. The feed compositions were more effective tha n the other factors in controlling the particle size. The polymeric micropa rticles formed by RESS-N method can be utilized to make the thin coating fi lm without any toxic organic solvents and/or surfactants.