SURFACE MODIFICATION OF POLYIMIDE BY ATMOSPHERIC PRESSURE PLASMA FOR ADHESIVE BONDING WITH TITANIUM AND ITS APPLICATION TO AVIATION AND SPACE

摘要

It is noted that in search of long term and efficient service performance in the context of future generation of aerospace materials, there is increasing need of metal-high performance polymer composite. Based on these considerations, high temperature resistant polymeric sheet such as Polyimide Meldin7001 sheet, is joined with Titanium sheet by employing ultra high temperature resistant Polyimide adhesive. In order to increase surface energy of Polyimide surface, atmospheric pressure plasma treatment is used to modify the Polyimide surface. Atmospheric pressure plasma treatment creates physical and chemical changes such as cross linking, formation of free radicals and oxygen functionalization in the form of polar groups on polymer surface resulting in improvement of wetting and adhesion characteristics. Surface of Polyimide (PI) sheet is treated with atmospheric pressure plasma for different exposure periods. Surface energy of PI sheet increases with increase in exposure time. However, after a certain exposure time of plasma, deterioration of surface layer of PI substrate results in degradation and embitterment of PI which is not suitable for adhesive bonding. Optical microscopic, SEM (EDS), analysis of treated and untreated specimen is carried out to examine the surface characteristics. Treated samples and untreated samples of Polyimide are bonded together with overlap joints. Lap shear bond strength of treated and untreated samples was measured by tensile test to study the effect of treatment on adhesive bond strength. The optimized time of plasma treatment suggested in this investigation results in maximum adhesive bond strength and consequently, this technology is highly acceptable for aviation and space applications.