Mishima, Kenji, Kiyoshi Matsuyama, Takuji Hirabaru, Masayoshi Baba, Hideharu Ishikawa, Ken-ichiro Hayashi. CONTROL OF POLYMER COATING THICKNESS OF MICROCAPSULES CONTAINING INORGANIC MICROPARTICLES
8-19-1 Nanakau, Jonanku, Fukuoka, Fukuoka, 814-0180, Japan (mishima@fukuoka-u.ac.jp)
A novel control method of coating thickness of microcapsules is reported for forming polymer microcapsules containing inorganic microparticles, in this case silica and polymer using gas-liquid cosolvency of supercritical carbon dioxide. A suspension of silica in CO2 containing a cosolvent and dissolved polymer is sprayed through a nozzle to atmospheric pressure. The polymers are poly(styrene)-poly(methyl methacylate)-poly(glycidyl methacylate) triblock copolymer (PS-PMMA-PGMA; Mw= 5,000), poly(ethylene glycol) (PEG; M.W.=7,500), poly(L-lactic acid)(PLA; M.W.=5,000). The solubilities of these polymers in CO2 increase significantly with the use of low molecular weight alcohols as cosolvents. After expansion, the particles do not tend to agglomerate, since the pure cosolvent is a nonsolvent for the polymer. The thickness of the polymer coating about the silica, and likewise, the mean particle diameter and particle size distribution, could be controlled by changing the feed composition of the polymer.