Precipitation kinetics of PMMA sub-micrometric particles with a supercritical assisted-atomization process

Sub-micrometric particles of PMMA were successfully prepared via a supercritical assisted-atomization (SAA) process using acetone as a solvent and supercritical carbon dioxide as a spraying medium. The effects of several key factors on the particle size were investigated. These factors included the concentration of polymer solution, temperature in saturator and volumetric flow rate ratio of carbon dioxide to polymer solution. The shape of the polymer's primary particles is spherical with the arithmetic mean size ranging from 82 nm to 176 nm and the mass-weighted mean size ranging from 127 nm to 300 nm. As evidenced from the experimental results, the lower concentrations of polymer solution, optimized volumetric flow rate ratios, and higher temperatures in saturator can effectively reduce the mean particle size. The precipitation kinetic parameters were determined from the particle size distributions with the aid of the population balance theory. This study found the primary nucleation to be dominant in the precipitation and diffusion may govern particle growth.

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► The lower concentrations of polymer solution and higher temperatures in the saturator favor to reduce the particles size.
► At the optimized volumetric flow rate ratios, the composition of CO2 in the feed streams was near the bubble points of the saturator temperatures.
► The MSMPR population balance equation is capable of representing the precipitation kinetics of SAA process.