Effect of atmospheric plasma treatment and wet blast on adhesion characteristics of carbon fiber reinforced LM-PAEK thermoplastic composites

Surface characteristics of polymeric materials are quite challenging for adhesion especially thermoplastics, requiring specific surface preparation operations before reaching successful bonding. These processes are principally aimed to increase the low surface energy of the material, bonding agent contact area and wetting characteristics to provide proper and strong adhesion. In this study, two different surface treatments with different processing parameters were applied to CF/LM-PAEK thermoplastic composites in order to examine the changes on surface characteristics and adhesion strengths. Apart from desired surface treatments for thermoplastics indicated in previous studies and backgrounds, wet blasting method is used to prepare surfaces before bonding. Separately prepared surfaces, applying wet blasting and atmospheric plasma treatment, were adhered using epoxy-based film adhesive to be subjected to single lap shear testing to examine adhesion strength under tensile loading. According to the results of experimental study, it was observed that both surface treatments increased the adhesion strength of the bonded pre-consolidated CF/LM-PAEK thermoplastic composites compared to specimens having untreated surfaces. Atmospheric plasma treatment increased the surface energy by 18.24% and showed higher strength up to 14.93% compared to the untreated specimens. On the other hand, surprisingly, wet blasted specimens with lower surface energies showed high strength up to 6.48% compared to the untreated specimens. In addition to surface energies and lap shear strengths, roughness measurements and SEM surface evaluations were also issued to enlighten obtained test results accordingly.