Supercritical fluid assisted melting of poly(ethylene glycol): a new solvent-free route to microparticles

Liquefying a polymer with supercritical carbon dioxide (scCO2) and then spraying the polymer/CO2 melt through a nozzle is a promising way to generate polymeric particles. This technique is of particular interest since the processing can be performed at lowered temperatures and in the absence of organic solvents. We use poly(ethylene glycol) (PEG) as the processing polymer to explore the general control principles for particle size and morphology for crystalline polymers. The morphology for sprayed particles can be controlled by manipulating the processing conditions. For example, decreasing processing pressure and increasing temperature favour the production of spherical particles. Furthermore, decreasing the bore diameter of the nozzle can increase the percentage of spherical particles in the product. Compared to particle morphology, the effect on particle size is less dramatic when either temperature, pressure or the bore diameter of the nozzle are altered. The spherical particles produced are mostly hollow in structure with a singe internal void and a thin outer crust.