Grafting of polyhedral oligomeric silsesquioxanes on a carbon fiber surface: novel coupling agents for fiber/polymer matrix composites

A new application of polyhedral oligomeric silsesquioxanes (POSS) as coupling agents to functionalize conventional carbon fibers was reported. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and dynamic contact angle analysis were used to characterize the carbon fiber surface. AFM images showed that POSS was grafted uniformly on the fiber surface and the surface roughness increased significantly. XPS and FTIR results indicated that polar groups on the fiber surface increased after modification. Dynamic contact angle measurements, before and after functionalization, demonstrated an improvement in the surface energy and wettability that related to the increase of the polarity of the modified fiber surface. Single fiber pull-out testing, dynamic mechanical analysis (DMA) and impact testing were carried out to evaluate the effect of the POSS coupling agent on the mechanical properties of the composites. Experimental results indicated that the interfacial strength under both static and dynamic loads had a dramatic improvement, and the impact toughness was increased simultaneously. Moreover, reinforcing and toughening mechanisms of the POSS coupling agent were also discussed.