Mechanical improvement of carbon fiber/epoxy composites by sizing functionalized carbon nanotubes on fibers

Abstract A sizing agent mainly consisting of polyethersulfone and acidified multi‐walled carbon nanotubes (MWCNT) was developed for surface modification of carbon fibers (CF) to enhance the interfacial bond and to form carbon fiber‐carbon nanotube (CF‐MWCNT) multiscale reinforcements. To prepare the modified carbon fiber/epoxy resin composites (CFRP), a vacuum molding technique was used in this study. The effects of the MWCNT‐containing sizing agent on the morphology and chemical structure of the CF surface were observed by scanning electron microscopy and Fourier transform infrared spectroscopy. The influence of MWCNT length and content on the mechanical properties of CFRP were also studied. The experimental results showed that the strength of the CFRP decreased with the increase of MWCNT length, and the MWCNT with a content of 0.05 wt% had a good reinforced effect on the CFRP. After the sizing treatment, the interlaminar shear strength (ILSS) of the CFRP is increased. These enhancements are attributed to the improved mechanical bonding and chemical bonding between CF and resin matrix. The MWCNT provides nanosized rough surface to CF and these acidified MWCNTs attached to the surface of CF with polar oxygen‐containing functional groups improve the compatibility with reinforcement and resin matrix. Highlights Carbon fiber was modified by a sizing agent mainly consisting of polyethersulfone and acidified carbon nanotube (CNT). CNTs enhance the interfacial chemical bonding and mechanical bonding. The CNT length affects the mechanical properties of the carbon fiber/epoxy resin composites (CFRP). The modified carbon fiber has enhanced the mechanical properties of the CFRP.