Effects of particle size and distribution of the sizing agent on carbon fiber/epoxy composites interfacial adhesion

Abstract

This article aims to study the effects of particle size and distribution (PSD) of sizing agent on surface physical and chemical properties of the carbon fiber. Five kinds of sizing agents with various PSD named P‐1 to P‐5 sizing were applied in order to investigate the influences on interfacial properties between the carbon fiber and the matrix. The surface characteristics of carbon fibers were investigated to determine morphology, chemical composition, surface energy, interfacial thickness, and interlaminar shear strength (ILSS). The results revealed that, as the particle size decreasing, the O1s/C1s composition ratios, surface energy and the interfacial thickness show a growing trend whereas the surface roughness reduces mildly. Similarly, the ILSS of the carbon fiber/epoxy composites have also increased by more than 8% with the decreased particle size. This demonstrates that small particle size with multimodal PSD in sizing is advantageous for effective wetting and force transition in the interfacial adhesion. Actually, when the mean particle size is around 110 nm (P‐3 sizing), the emulsion droplets can repair the surface irregularity and hold back excessive stress most remarkably, leading to optimal contributions to the improvement of ILSS. Based on these results, a mechanism concerning particle arrangement in sizing and interfacial strengthening in carbon fiber/epoxy composites was proposed, which provided a reasonable explanation to analyze the effects of PSD in sizing and interfacial bonding. POLYM. COMPOS., 39:E2036–E2045, 2018. © 2017 Society of Plastics Engineers