Comparison of rigid and flexible structural daimines grafted carbon fiber for enhancing the interfacial and mechanical properties of carbon fiber/epoxy composites

Interfacial strength between fiber and matrix is an important factor affecting the mechanical properties of carbon fiber composites. Different daimines, ethylenediamine (EDA) and p-phenylenediamine (PPD), were grafted on carbon fiber to enhance interfacial strength of composites. Functional groups and chemical composition were tested by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Thermaogravimetric analysis and Roman spectroscopy. Scanning electron microscope was used to characterized surface morphology. Results revealed that EDA with flexible structure was more easily grafted onto surface. In contrast, PPD with rigid structure could improve the interfacial performance better. More importantly, carbon fiber grafted on both EDA and PPD had the highest wettability and interlaminar shear strength owing to the presence of sufficient functional groups on carbon fiber surface. Compared with untreated carbon fibers, the surface energy and the interlaminar shear strength of the grafted EDA and PPD carbon fibers increased by 38.57% (50.98 mN/m) and 44.81% (69.8 MPa) respectively. The investigation provides an approach to enhance the mechanical properties of fiber composites by controlling the structure of grafted components.