Enhancement of interfacial properties of HMCF composites by constructing of rigid-flexible interphase through naphthalenediimide with different flexible chain lengths

Naphthalenediimide copolymers with long, middle and short flexible chain lengths (LN, MN and SN) were designed and used to construct rigid-flexible interphase on high-modulus carbon fiber (HMCF) surface, and the interfacial performance and interphase reinforcing mechanism of composites were explored. Compared with desized HMCF (HMCF-desized), the surface activity and roughness of HMCF-LN, HMCF-MN and HMCF-SN were gradually increased. In contrast to HMCF-LN and HMCF-MN composites, wider transit-modulus platform and increased interphase thickness were detected in HMCF-SN composites, the improved deformation and decreased thermal residual stress from rigid-flexible interphase were obtained. The highest improvement of transverse fiber bundle test strength (TFBT) and interfacial shear strength (IFSS) of HMCF-SN composites were achieved, which was ascribed to the effective relaxation of interfacial stress and stronger chemical interaction of HMCF-SN with matrix by the reduced flexible chain lengths and the increased functionality of SN copolymers. Highlights Rigid-flexible interphase was constructed by naphthalenediimide copolymers. Wider transit-modulus platform was detected in HMCF-SN composites. Improved deformation and decreased residual stress of interphase were obtained. The interfacial performance of HMCF-SN composites were greatly improved.