Sanghvi and Nairn (1991,1992) investigated the formation of microcapsules using cellulose acetate trimellitate. Three-component phase diagrams were prepared to show the region of microcapsule formation for the system polymer, light mineral oil and the solvent acetone-ethanol. Chloroform was used as the hardening agent. Microcapsules were only formed when the polymer concentration was in the 0.5-1.5% range and the solvent concentration in the 5-10% range. The addition of surfactants such as sorbitan trioleate or sorbitan oleate to the mineral oil altered and/or increased the region of microencapsulation. Surfactants with higher hydrophile-lipophile balance values tended to decrease the area of microcapsules on the phase diagram. Sorbitan monooleate 1% in mineral oil gave products with smoother coats and a more uniform particle size. Tartrazine-containing microcapsules were prepared and the smallest microcapsule size was obtained when sorbitan monooleate 3% was used and these microcapsules had the slowest rate of release in an acidic medium. As a result of the removal of acetone from the polymer solution by the mineral oil, a polymer-rich phase is formed and after combining with other droplets and/or the core material, the microcapsules are formed which are hardened by further loss of solvent to the dispersion medium and also by the addition of chloroform.
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