An effective non‐covalent grafting approach to functionalize carbon fiber with polyethyleneimine in supercritical fluid to enhance the interfacial strength of carbon fiber/epoxy composites

A facile and effective approach to functionalize carbon fiber (CF) by non‐covalent grafting branched polyethyleneimine (PEI) in conventional and supercritical methods was proposed. Fourier transform infrared (FTIR) spectrometry, X‐ray photoelectron spectroscopy, Raman, scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic contact angle analysis (DCA), and single fiber tensile testing were carried out to characterize the CF reinforcements. Interfacial shear strength (IFSS) and transmission electron microscopy were performed to investigate the composites interfacial properties. Experimental results indicated that the non‐covalent grafting polyethyleneimine on CF–COOH increased the polarity, wettability, and roughness of carbon fiber surface. The interfacial shear strength improved significantly using the two methods, especially in supercritical methanol, which further confirmed the previous study. Single fiber tensile strength did not deteriorate owing to the green modification. Moreover, this convenient project was believed to have widely potential applications in high performance composites. POLYM. COMPOS., 39:E2381–E2389, 2018. © 2017 Society of Plastics Engineers