Effect of surface modification of high-density polyethylene by direct current and radio frequency glow discharge on wett
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1/30/04
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Effect of Surface Modification of High-Density Polyethylene by Direct Current and Radio Frequency Glow Discharge on Wetting and Adhesion Characteristics S. BHOWMIK, T.K. CHAKI, S. RAY, F. HOFFMAN, and L. DORN The present investigation aims to optimize the process parameters of Direct Current (DC) and Radio Frequency (RF) glow discharge treatment through air in terms of discharge power and time of exposure for the surface modification of high-density polyethylene (HDPE) 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 increase with increasing exposure time, attaining a maximum and then decreasing. In the case of RF glow discharge, surface energy and its polar component increase with increasing exposure time and then saturate. Surface modification by DC glow discharge increases the surface energy of HDPE 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). A significant oxygen peak is observed for surface-modified polymer as detected by ESCA and EDS. Lap shear tensile test of an adhesive (Araldite AY 105) joint of HDPE with mild steel has been carried out in optimizing the parameters of DC and RF glow discharge for maximum joint strength. When HDPE is exposed to DC glow discharge, improvement of adhesive joint strength of HDPE to mild steel is found to be by a factor more than 7. On the other hand, when HDPE is exposed to RF glow discharge, results in improvement of adhesive joint strength of HDPE to mild steel by a factor nearer to 7 are found. Thus, DC glow discharge is more capable for increasing wetting and adhesion characteristics of the polymer.
I. INTRODUCTION
IN recent years, a remarkable growth in the use of organic polymers has been observed both for technological and consumer product applications. Major industrial sectors such as automotive industries, aircraft industries, chemical industries, railways, as well as many civil construction works are increasingly using polymers bonded with adhesives in the secondary structures replacing traditional engineering materials such as steel and aluminum. Unique physical and chemical characteristics of polymers such as high strengthto-weight ratio, resistance to corrosion, and relatively low cost make them attractive. Among the polymers used in engineering applications, high-density polyethylene (HDPE) and polypropylene (PP) are popular due to their superior mechanical, physical, and chemical properties and their relatively lower weight, high corrosion resistan
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