Optimization of interfacial properties of different high modulus carbon fiber composites by tailored interphase stiffness with MWNT-EP/epoxy sizing

Abstract

Based on the physicochemical properties of high modulus carbon fibers (HMCF, p-CCM40J, p-CCM50J and p-CCM55J), the interphases of various gradient modulus were designed and constructed via epoxy suspension with epoxide functionalized muti-wall carbon nanotubes (MWNT-EP), and the relations and mechanisms of optimized interfacial properties with different interphase structures of HMCF composites were explored. Due to the increased degree of surface graphitization of pristine HMCFs, a smoother and more inert surface structure was exhibited. As the elevated sizing concentration of MWNT-EP, the HMCF morphology displayed a tendency from sparseness to uniformity then agglomeration with a slackened ascent of chemical activity, which indicated the various thresholds of MWNT-EP on different HMCF surface. Compared to pristine HMCF composites, the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of CCM40J, CCM50J and CCM55J composites at the threshold concentration (0.7 wt%, 0.5 wt%, 0.3 wt%) showed remarkable enhancements by 58.46%, 54.39%, 34.92% and 25.19%, 24.43%, 17.95%, respectively, which was attributed to the modulus transition layer. Schematic models of tailored interfacial reinforcing mechanism were proposed to illustrate the various optimal content of MWNT-EP applied to buffer the exterior load and achieve smooth modulus transition at the interphase, which was ascribed to the corresponding matching of the MWNT-EP threshold with the intrinsic structure and modulus of HMCFs.