Improved PCA process for the production of nano- and microparticles of polymers

The system dextran-DMSO-CO₂ has been chosen as a model system to study the fundamentals of the precipitation of biodegradable polymers, using the precipitation with a compressed antisolvent (PCA) process. At conditions of completely miscibility between the organic solvent (DMSO) and CO₂, it is proposed that the formation of droplets in the system is not the consequence of atomization of the DMSO solution, but rather the result of the occurrence of a liquid-liquid phase split when the DMSO-solution and CO₂ are intimately mixed. Penetration of CO₂ into the droplets and stripping of DMSO induces the solidification of these droplets. A new device was designed to separate the three steps involved in the process: mixing of CO₂ and solution, liquid- liquid phase split, and stripping of the solvent. This new device eliminates agglomeration of particles, and yields reproducible results. The particle size can be easily manipulated over a size range from several nanometers to tenths of microns by changes in the operating conditions. The influence of these operating conditions (pressure, temperature, polymer concentration, and solution/CO₂ composition ratio) on particle morphology has been studied.