Improving film adhesive joining performance of poly(phenylene sulfide)/carbon fiber thermoplastic composite laminates by plasma surface treatment

The main purpose of this study was to observe the degree of the improvement on the film adhesive joining performance of Poly(phenylene sulfide)/Carbon Fiber (PPS/CF) thermoplastic composite laminates when their surfaces were treated by atmospheric plasma technique. For this purpose, plasma treated surfaces were compared with untreated and the traditional grit-blasted surfaces. Treated surfaces were characterized by various techniques including contact angle, surface energy, surface roughness, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. Then, joining performance of the PPS/CF composite samples bonded by an epoxy-based film adhesive was determined by using three different mechanical tests; single-lap shear strength, mode-I interlaminar fracture toughness energy, and drop-weight impact toughness. Grit-blasting surface treatment increased surface roughness of the specimens enormously (7 times more), leading to mechanical interlocking as the dominant bonding mechanism. Contrarily, plasma surface treatment resulted in formation of chemically reactive sites, thus dominant bonding mechanisms in the film adhesive joining were certain polar interactions and chemical bonding. Mechanical tests pointed out that compared to grit-blasting, plasma surface treatment resulted in considerably higher joint performance regarding interlaminar shear strength (35% more), interlaminar fracture toughness (67% more) and impact toughness (28% more), with the cohesive failure mode. Accordingly, it could be stated that traditional grit-blasting could be replaced with plasma surface treatment applied before film adhesive joining of PPS/CF composite parts in aircraft industry.