Effect of silane coupling treatment on the adhesion between polyamide and epoxy based composites reinforced with carbon fibers

The increasing efforts aimed to design structures with reduced weight and better mechanical performances has led in recent years to a growing use of fiber reinforced polymer materials in several fields such as marine. However, these materials can be composed of chemically very different elements and, hence, may be difficult to joint. This research aims to improve the adhesion between a thermoplastic matrix of polyamide reinforced with short carbon fibers (PA12-CR) and a carbon fiber reinforced epoxy matrix (CFRP). Two different silane coupling agents, (3-Aminopropyl)trimethoxysilane (AM) and (3-Glycidyloxypropyl)trimethoxysilane (EP), were applied, through the spray deposition method, on the PA12-CR substrate to create a reactive layer between the adherents. Different deposition methods and coupling agents curing conditions were also investigated. The wettability of the PA12-CR surface as well as the chemical modifications induced by silane treatments were investigated through contact angle and Fourier Transform Infrared spectroscopy (FTIR) analyses. Furthermore, the interfacial adhesion between PA12-CR and CFRP substrates was evaluated through Mode I delamination tests (DCB). The effectiveness of the most promising treatment was finally verified on sandwich structures, having PA12-CR printed as internal core and CFRP laminates as external skins, through quasi-static three-point bending mechanical tests. Overall, the epoxy-based silane (EP) allowed significantly better resistance to the delamination up until the tensile failure of the CFRP substrate.