Comparative study of hydrophilic modification of polyacrylonitrile membranes by nitrogen and carbon dioxide RF plasma

Abstract

Low temperature plasma treatment using radio frequency (RF) discharge of nitrogen and carbon dioxide gases was employed to enhance hydrophilicity of the polyacrylonitrile copolymer membrane surface. Influence of various plasma operating conditions, namely, power and exposure time on improvement of surface energy, permeability, and hydrophilicity of the membrane was investigated. Surface energy of RF nitrogen plasma-treated membrane (70 W, 8 min) was enhanced by 70%. Surface etching due to plasma treatment was confirmed by weight loss of the treated membranes. About 78% increase in average pore size was obtained using RF carbon dioxide plasma treatment due to surface etching. Hydrophilicity of nitrogen plasma modified membrane was enhanced by 32% and it was maintained up to 100 days. The pore enlargement due to plasma etching is more effective compared to surface energy in enhancing permeability (70%) of RF carbon dioxide modified (70 W, 6 min) membrane throughout the aging period. The permeability of nitrogen RF plasma-treated membrane is affected by surface energy and pore enlargement for initial 20 days of aging. After that, the permeability of treated PAN only depends on pore enlargement due to plasma etching. The nitrogen plasma modified surfaces appear to retain their functionality better than carbon dioxide plasma-treated samples. Oxygen and nitrogen functional groups were identified to be responsible for surface hydrophilicity. POLYM. ENG. SCI., 59:2148–2158, 2019. © 2019 Society of Plastics Engineers