Extraction and precipitation particle coating using supercritical CO₂

A modified RESS process for particle coating with a solution of polymer in supercritical CO₂ was studied in this research. This technique involves extracting the polymer with supercritical CO₂, with or without a cosolvent in an extraction vessel, and then precipitating the polymer onto the surface of host particles in a second precipitation vessel by adjusting the pressure and temperature inside the precipitator to lower its solubility. The research was performed using a pilot-scale supercritical apparatus, glass beads as host particles and two different polymers as coating materials. Experiments showed that the coating of glass beads with polyvinyl chloride-co-vinyl acetate (PVCVA) and hydroxypropyl cellulose (HPC) was successfully achieved. Scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), energy dispersive X-ray mapping and thermogravimetric analysis (TGA) were used to characterize the coatings obtained. The results indicate that the process of particle coating with supercritical solution is a promising environmentally friendly, alternative coating method with little or no organic solvents required.