Formation of l-poly(lactic acid) microspheres by rapid expansion of CO 2 saturated polymer suspensions

Abstract

l-Poly(lactic acid) (PLA) microspheres were produced by rapid expansion of carbon dioxide (CO 2) saturated polymer suspensions. The suspensions of CO 2 saturated polymer solution containing ethanol were sprayed through a nozzle to the atmosphere or into water. In this work, to control the particle morphology, the gas-saturated polymer suspensions were expanded through the nozzle to water. After spraying solutions through a nozzle to the atmosphere, polymeric fibers and/or coalesced particles were obtained. On the other hand, polymeric microspheres were obtained after spraying through a nozzle to water. The obtained particles were smaller than those produced by expansion to atmosphere. The expansion of polymer suspensions to water impedes particle's growth and agglomeration. The particles do not tend to agglomerate after expansion, since the ethanol used as co-solvent on the surface of particles diffuses through the water phase. Furthermore, the interfacial tension between the polymer droplets and water phase contributes to the microspheres formation. Changing the pre-expansion pressure and injection distance between the nozzle and water interface, controls the particle size distribution and morphology of microparticles.