The present investigation aims to study the wetting and physicochemical characteristics of Polypropylene (PP) sheet when exposed to a DC glow discharge through air across different electrodes such as copper, nickel and stainless steel at 13 W power level of DC glow discharge under an electrode size of 64 cm2. In order to estimate the extent of surface modification, the surface energies of the polymer surfaces exposed to DC glow discharge have been determined by measuring contact angles using two standard test liquids of known surface energies. It is observed that surface energy and its polar component increases with increasing exposure time, attains maximum and then decreases. The increase in surface energy and its polar component is relatively higher when the polymer is exposed under stainless steel electrode followed by nickel and then copper electrode. The dispersion component of surface energy remains almost unaffected. The surfaces have also been studied by optical microscopy and electron spectroscopy for chemical analysis (ESCA). It is observed that when the PP is exposed under these electrodes, single crystals of shish kebab structure forms and the extent of formation of crystals are higher under stainless steel electrode followed by nickel and then copper electrodes. Exposure of the polymer under DC glow discharges has essentially incorporated oxygen functionalities on the polymer surface as detected by ESCA. It is noted that higher incorporation of oxygen functionalities have been obtained, when the polymer is exposed to DC glow discharge under stainless steel electrode followed by nickel and copper electrodes as evident from ESCA studies. These oxygen functionalities have been transformed into various polar functional groups and which has been attributed to increase the polar component of surface energy of the polymer. Therefore, maximum increase in surface energy is obtained when the PP sheet is exposed under a stainless steel electrode rather than nickel or copper electrodes.
Shantanu Bhowmik, Jana, P., Chaki, T. K., and Ray, S., “Surface modification of PP under different electrodes of DC glow discharge and its physicochemical characteristics”, Surface and Coatings Technology, vol. 185, pp. 81–91, 2004.