The present investigation aims to optimise the process parameters of DC and RF glow discharge treatment through air in terms of discharge power and time of exposure for the surface modification of PP sheet, for attaining best adhesive joint of the polymer to mild steel. In order to estimate the extent of surface modification, the surface energies of the polymer surfaces exposed to glow discharge have been determined by measuring contact angles using two standard test liquids of known surface energies. It is observed that at a given power level of DC glow discharge, surface energy and its polar component increases with increasing exposure time which attains maximum and then decreases. In the case of RF glow discharge, surface energy and its polar component increases with increasing exposure time and then saturate before reaching to maximum level. Surface modification by DC glow discharge increases the surface energy of PP relatively more at a lower power compared to that observed for RF glow discharge. The dispersion component of surface energy remains almost unaffected. The surfaces have also been studied by Electron Spectroscopy for Chemical Analysis (ESCA) and Energy Dispersive Spectra (EDS). Significant oxygen peak is observed for surface modified polymer as detected by ESCA and EDS. Lap shear tensile test of adhesive (Araldite AY 105) joint of PP with mild steel has been carried out in optimising the parameters of DC and RF glow discharge for maximum joint strength. When PP is exposed to DC glow discharge, improvement of adhesive joint strength of PP to mild steel is found to be by a factor nearer to 6. On the otherhand, when PP is exposed to RF glow discharge, results in improvement of adhesive joint strength of PP to mild steel by a factor lower than 5 is found. Thus, DC glow discharge is more capable for increasing wetting and adhesion characteristics of the polymer.
Shantanu Bhowmik and Chaki, T. K., “Wetting and Adhesion Characteristics of DC and RF Glow Discharge Exposed PP”, in Fourth International Symposium on Polymer Surface Modification: Relevance to Adhesion, Novotel, Toronto Centre, Toronto, Canada, 2003.