Atmospheric plasma modification of polyimide sheet for joining to titanium with high temperature adhesive

This investigation highlights the rationale of adhesive bonding of atmospheric pressure plasma treated high temperature resistant polymeric sheet such as polyimide sheet (Meldin 7001), with titanium sheets. The surface of polyimide (PI) sheet was treated with atmospheric pressure plasma for different exposure times. The surface energy was found to increase with increase in exposure time. However, longer exposure time of plasma, results in deterioration of the surface layer of PI resulting in degradation and embrittlement.Contact angle measurements with sessile drop technique were carried out for estimation of surface energy. SEM (EDS) and AFM analyses of treated and untreated specimens were carried out to examine the surface characteristics and understanding morphological changes following surface treatment. Untreated samples and atmospheric pressure plasma treated samples of polyimide Meldin 7001 sheet were bonded together as well as with titanium substrates to form overlap joints. Single lap shear tensile testing of these adhesively bonded joints was performed to measure bond strength and to investigate the effect of surface treatment on adhesive bond strength. An optimized plasma treatment time results in maximum adhesive bond strength and consequently, this technology is highly acceptable for aviation and space applications.