Preparation of poly(L-lactide) microparticles by a supercritical antisolvent process with a mixed solvent

Poly(L-lactide) (PLLA) microparticles were prepared by a supercritical antisolvent (SAS) process with a mixed solvent. Five factors, namely, the molar percentage of acetone, pressure, temperature, flow rate, and concentration of the solution, were optimized by a four-level orthogonal array design. By analysis of variance, the concentration of the solution showed a significant effect on the PLLA microparticle size. The effects of the mixed solvent (dichloromethane/acetone) at different mixing ratios, pressures, and temperatures on the morphology of the PLLA microparticles were also investigated. The thermal properties of PLLA before and after the SAS process were studied by differential scanning calorimetry. The results indicate that the molar percentage of acetone had a significant effect on the morphology of the PLLA microparticles. The microparticles prepared with the mixed solvent were much smaller than those prepared with dichloromethane alone under the same conditions. Furthermore, the particle size distribution was more uniform in the case of the mixed solvent. The particle size decreased with increasing pressure, whereas it showed no significant change with increasing temperature. The results also show that the thermal properties of PLLA could be improved through the SAS process. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012