Effect of Epoxy Functional Groups on the Properties of Carbon Fiber-Epoxy Composites

Matrix resins of carbon fiber-epoxy composites with different numbers of epoxy functional groups were prepared, and their properties were compared to optimize the matrix resin composition. To understand the bonding strengths between the carbon fiber and epoxy resins in monofilaments and micro-sized resin beads, the interfacial shear strength (IFSS) was measured using the microdroplet technique. The bonding strength for the T800SC carbon fibers was maximized for a 50:50 (wt/wt) ratio of epoxy resins containing four and three epoxy groups per molecule, respectively, and that for the IMS60 carbon fibers was maximized for a 70:25:5 (wt/wt/wt) ratio of epoxy resins containing four, three, and two epoxy groups per molecule, respectively. The transverse tensile, in-plane shear, interlaminar shear, and compression strengths were higher for the interfacial-shear-strength-optimized T800SC-epoxy mixture than for the T800SC-100% basic bisphenol A epoxy material. These composite materials exhibit a potential to be used in applications such as automobiles and aircraft as lightweight, high-strength, and rigid materials.