Toward improved mechanical performance of multiscale carbon fiber and carbon nanotube epoxy composites

A novel class of multiscale epoxy composites was developed containing carbon fibers (CFs) and multiwalled carbon nanotubes (MWCNTs) to explore their mutual effect on the mechanical performance of composites. The loading of CFs in composites was kept constant at ～60 wt%, while the contents of MWCNTs were increased from 0.5 to 2.0 wt%. MWCNTs were functionalized through acid treatment before incorporating into epoxy matrix to promote dispersion quality. The developed composites were characterized microstructurally by scanning electron microscopy and mechanically by tensile, flexural, edgewise compression, and hardness tests. Homogeneous dispersion of MWCNTs was observed until their loading of 1.5 wt%, which enhanced the mechanical performance of composites. Hardness increased up to 47% while tensile, flexural, and edgewise compressive moduli increased to 40%, 16.3%, and 164%, respectively. Moreover, tensile, flexural, and edgewise compressive strengths showed rises of 45%, 15.2%, and 43%, respectively. The fracture strain increased in both the tensile and flexural tests while it decreased in edgewise compressive tests. Increasing the MWCNTs in composites to 2.0 wt% produced their agglomerates and reversed the rising trend in mechanical properties. POLYM. COMPOS., 38:1519–1528, 2017. © 2015 Society of Plastics Engineers