Effects of silsesquioxane coating structure on mechanical interfacial properties of carbon fibre/polyarylacetylene composites

Carbon fibres (CF) were treated with different coatings, including [3-(methacryloxy)propyl]trimethoxylsilane (MPMS), [3-(methacryloxy)propyl]silsesquioxane (MPMS-SSO), and (methacryloxy)propyl polyhedral oligomeric silsesquioxane (Methacryl-POSS), to improve the interfacial properties of carbon fibre reinforced polyarylacetylene (PAA) matrix composites. MPMS-SSO was obtained from the hydrolytic condensation of MPMS. The complicated structure, including cage and ladder one, of MPMS-SSO may be assigned by Fourier transforms infrared (FT-IR) spectra, 1H, 13C and 29Si nuclear magnetic resonance (NMR) and ultraviolet matrix-assisted laser desorption ionization time-of-flight mass spectrometry (UV-MALDI-TOF MS). Interlaminar shear strength (ILSS) was tested to investigate the effect of coating structure on the interfacial bonding. The values of ILSS of untreated and treated CF/PAA composites with different coatings (MPMS, MPMS-SSO and Methacryl-POSS) show that the treatment effect of Methacryl-POSS coating is the best one and the MPMS-SSO coating is better than that of MPMS coating. SEM micrographs of shear fracture of CF/PAA composites also suggested the different coating treatment effects. The differences of increasing degrees of ILSS indicate that the structure of coating is important when silsesquioxanes are used as coatings to treat fibre surface for building up the adhesion and improving interfacial properties of fibre reinforced polymer matrix composites.