Electrospraying technique under pressurized carbon dioxide for hollow particle production

Fabrication of polyvinylpyrrolidone (PVP)particles by an electrospraying process under pressurized carbon dioxide (CO₂)used as an anti-solvent was studied. The process was carried out at a constant temperature with CO₂ pressures ranging from 1 to 6 MPa. A fixed applied voltage (17 kV)was employed to generate electric field. PVP powder dissolved in dichloromethane (DCM)at concentrations of 4, 6, and 8 wt% was used as the starting material. Scanning electron microscopy observations indicated that the electrosprayed PVP particles produced at 1–3 MPa using 8 wt% PVP solutions have spherical morphologies. At a similar concentration, increasing the CO₂ pressure up to 6 MPa resulted in particle strings and strings as major products. Interestingly, hollow core particles formed when ethanol was added as a secondary solvent for controlling the evaporation rate of DCM during the electrospraying process under pressurized CO₂. The FT–IR spectra revealed that the structural properties of PVP did not change after the electrospraying process. This work demonstrates that electrohydrodynamic processes under pressurized CO₂ are likely to be fruitful for the fabrication of organic polymers with hollow cores.