Polymer Micronization using Batch Supercritical Antisolvent Process

In this paper, different polymers were processed using a Batch Supercritical AntiSolvent precipitation (BSAS) to evaluate the possibility of producing nanoparticles and microparticles of controlled size and distribution. Liquid solutions of a polymer in dimethylsulfoxide (DMSO) or acetone were charged in a vessel; then, supercritical CO2 with the role of antisolvent was pumped up to the desired pressure. The process was performed in two steps: in batch mode for a time t1 and in continuous mode for a time t2, with a constant CO2 flow rate. All the experiments were carried out at a final pressure of 100 bar and a final temperature of 40 °C, whereas the concentration of the liquid solution was varied from 0.1 to 5 mg/mL. SEM images of the processed material were used to study morphology, mean particle size and particle size distribution. Amorphous particles were obtained at all successful BSAS conditions, whereas crystals were sometimes observed when the micronization process failed. Polymers solubilized in acetone, such as cellulose acetate, ethyl cellulose, polymethyl methacrylate (PMMA) and Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) prevalently precipitated in form of nanoparticles in the range 50-200 nanometers, whereas polymers solubilized in DMSO, such as Poly-vinyl-alcohol (PVA), dextran and inulin precipitated in form of nanoparticles at lower concentrations (in the range 100-200 nanometers) and in form of microparticles at higher concentrations (in the range 0.7-2 µm).