Preparation of L-PLA Submicron Particles by a Continuous Supercritical Antisolvent Precipitation Process

Submicron particles of L-polylactic acid (L-PLA) without residual solvent were prepared by a continuous supercritical antisolvent (SAS) recrystallization process. Methylene chloride (CH₂Cl₂) was used as a carrier solvent of L-PLA. Experiments were performed with changing process parameters such as pressure and temperature at constant concentration. Also, L-PLA initial concentrations in methylene chloride were varied from 0.3 to 4 wt%. The flow rates of CO₂ and solution, which were introduced into the precipitator, and nozzle diameter were kept unchanged in all of the experiments. It was found that the SAS process gives fine tuning of particle size and particle size distribution (PSD) by simple manipulations of the process parameters. In all cases of SAS recrystallization experiments, the formed spherical fine particles with a smooth surface were non-agglomerated and free flowing. Mean particle size of the L-PLA microparticles formed was varied from 0.1 to 1 μm by means of adjusting the system pressure and/or temperature.