Two-step method to realize continuous multi-wall carbon nanotube grafted on the fibers to improve the interface of carbon fibers/epoxy resin composites based on the Diels-Alder reaction

A new simple and continuous method was developed for chemically grafting multi-wall carbon nanotubes (MWCNTs) onto the surface of carbon fibers (CF) to improve the interlaminar properties of composites. In this method, maleimide-grafted waterborne polyurethane emulsion and furan functionalized MWCNTs were prepared. Then, based on the Diels-Alder reaction under mild reaction conditions (60 °C), CF/MWCNTs multi-scale reinforcements (MSCF) were successfully prepared through a two-step method of MWPU sizing and MWCNTs ultrasonic grafting, which overcame the complex process flow, greatly shortened the preparation time and avoided damage to fibers. The successful grafting of MWCNTs was proved by the results of SEM and HRTEM. After grafting MWCNTs, the interface between the matrix and fibers was enhanced. The interlaminar shear strength (ILSS) and flexural strength of MSCF/epoxy reinforced composites were promoted to 64.54 MPa and 981.95 MPa, which was prominently increased by 52.84% and 32.32%, respectively. In addition, this process could match the current production of carbon fibers for commercialization, but further research was expected to control the grafting amount of MWCNTs and their impact on performance.