Evaluation of the Mechanical Properties of Polyether Sulfone-Toughened Epoxy Resin for Carbon Fiber Composites

Abstract

Polyether sulfone (PES), which is a thermoplastic polymer, was added as a toughening agent to a bisphenol-A type epoxy resin to form a matrix of carbon-fiber-reinforced composites (CFRPs). For benchmarking, carboxyl-terminated butadiene acrylonitrile (CTBN), which is a rubber-based toughening agent, was added to the epoxy resin. The mechanical and thermal properties of the PES- and CTBN-toughened epoxy resins were compared. Dicyandiamide (DICY) was used as the hardening agent, whereas 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) was used as the hardening accelerator. In addition, 4,4 '-diamino diphenyl sulfone (DDS) was added to improve the dispersibility of PES in the epoxy resin. The CTBN-toughened epoxy resin exhibited improved impact strength and fracture toughness, but decreased tensile strength, tensile modulus, and glass transition temperature (T-g). The fracture toughness and T-g values of the PES-toughened epoxy resins increased with increasing amount of added PES. However, the tensile moduli and T-g values of the epoxy decreased upon addition of CTBN. The tensile and impact strengths of the specimen toughened with 10 phr PES increased by 14 % and 106 %, respectively, compared to those of the PES un-toughened epoxy resin. The ductility factor of the resin improved with increasing PES content. CTBN formed microvoids and CTBN particles within the epoxy matrix, which improved the fracture toughness of the resin, but deteriorated its tensile properties by stress concentration. In contrast, PES improved the properties of the epoxy resin. This was attributed to PES being well dispersed within the epoxy matrix, thereby absorbing the energy required for crack propagation. Hence, owing to their excellent mechanical properties, the PES-toughened epoxy resins were determined suitable for use as matrices for CFRPs.