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.

Automated summary

In this study, naphthalenediimide copolymers with different flexible chain lengths were used to construct a rigid-flexible interphase on high modulus carbon fiber (HMCF) surface. The interfacial performance and interphase reinforcing mechanism of the composites were investigated. It was found that the surface activity and roughness of HMCF increased gradually with the introduction of LN, MN, and SN copolymers. HMCF-SN composites showed wider transit-modulus platform, increased interphase thickness, improved deformation, and decreased thermal residual stress compared to HMCF-LN and HMCF-MN composites. The highest improvement in transverse fiber bundle test strength (TFBT) and interfacial shear strength (IFSS) was achieved in HMCF-SN composites due to the reduced flexible chain lengths and increased functionality of SN copolymers, resulting in effective relaxation of interfacial stress and stronger chemical interaction with the matrix.