Grafting of amine-capped cross-linked polyphosphazenes onto carbon fiber surfaces: a novel coupling agent for fiber reinforced composites

The performance of carbon fiber reinforced composites is to a great extent dictated by the interfacial adhesion strength between the fibers and matrix. In order to improve the interfacial properties of carbon fiber/polypropylene (PP) composites, a new surface treatment has been developed to graft the amine-capped cross-linked polyphosphazenes (ACP) onto carbon fibers as a novel coupling agent through in situ polycondensation between hexachlorocyclotriphosphazene (HCCP) and 4,4'-diaminodiphenyl ether (DDE) under mild reaction conditions, and maleic anhydride grafted PP (M-PP) was used as the matrix. The chemical composition of the modified carbon fibers was verified by Fourier-transform infrared (FTIR) spectra and X-ray photoelectron spectra (XPS). The surface morphologies of the modified carbon fibers were detected by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The interfacial shear strength (IFSS) between carbon fibers and the matrix was investigated by a microbond test. The grafted ACP with a quantity of amine groups uniformly covered the carbon fiber surfaces, which results in strong interfacial adhesion between the modified carbon fibers and M-PP. The results of the test reveal a significant improvement of IFSS in the ACP grafted carbon fiber composites with an increase of 223.0% compared to the unmodified carbon fiber composites. In this work, we propose a facile and effective method for improving the interfacial properties of carbon fiber composites by grafting a novel coupling agent.