Change in Surface Free Energy and Surface Resistivity of Polycarbonate and Polypropylene Sheets after Plasma Exposure

Abstract

Sheets of polypropylene (PP) and polycarbonate (PC) of thickness 2 mm have been exposed to direct current (DC) plasma. Glow discharge plasma was generated at a pressure 200 Pa to modify the surface of polymer sheets at room temperature. Low pressure allows a relatively long free path for accelerated electrons and ions inside the chamber. The measurements of surface energy and surface resistivity were carried out for the thin sheets which were exposed at different discharge powers and exposure time in oxygen plasma. It has been observed that for lowest discharge power (1 watt), the variations in surface energy (along with its components) for PC are small then that for PP sheet, while at 5 watt of discharge power no significant difference has been observed. The resistivity has been found to decrease with the exposure time as well as with the discharge power for both the samples. The surface free energy of PP has been found to increase to 50 mJ/m2 and in case of PC 52 mJ/m2 For maximum power (i.e. 5 watt used in this study) the surface resistivity of PP has been found to decrease to 1.26x109 Ω/cm2 and for PC it decreased to 1.83x1011Ω/cm2. Before the treatment the resistivity of PP and PC were measured 1.24x1012Ω/cm2 and 1.32x1015Ω/cm2 respectively.