Fracture Toughness Properties of CF/EPOXY Resin Toughened by Polyether Sulfone

Abstract

Polyether sulfone (PES), which is a thermoplastic polymer, was added as a toughening agent to a bisphenol A type epoxy for a matrix of carbon fiber reinforced composites. For comparison, a rubber-based toughening agent, carboxyl-terminated butadiene acrylonitrile (CTBN), was also added to the epoxy. The mechanical and thermal stabilities of PES and CTBN were compared. Dicyandiamide (DICY) was used as the hardening agent, while 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. The epoxy with CTBN showed improved impact strength and fracture toughness, but showed decreasing tensile strength, tensile modulus, and glass transition temperature. In the case of the epoxy with PES, the fracture toughness and glass transition temperature increased with increasing amount of PES. However, the tensile modulus and glass transition temperature of the epoxy decreased with the addition of CTBN. The tensile and impact strengths of the specimen with 10 phr of PES have improved by 14% and 106%, respectively, compared to those of the pure epoxy. The ductility factor of the resin improved with increasing PES content. CTBN formed microvoids within the epoxy, deteriorating its mechanical properties. On the other hand, PES improved the properties of the epoxy. This is because PES was well dispersed within the epoxy, absorbing the energy required for crack propagation. After PES shows better properties when incorporated in epoxy, two types of carbon fiber reinforced plastics (CFRPs), using matrix with PES0 and PES10, were compared for its mechanical properties and fracture delamination toughness (Dual cantilever Beam (DCB)). The CF/PES toughened epoxy composites show improved 0˚, 90˚ tensile strength and ILSS by 4.7%, 14.5% and 5.6%, respectively. Throughout the test, it was found that the fracture toughness has improved when using CF/PES toughened epoxy compared to that of CFRP without PES. The fracture delamination behavior of bridging and fiber breakage was observed during fracture toughness tests. Hence, the PES-added epoxy was found to be suitable to be used as the matrix for carbon fiber composites owing to its excellent mechanical properties.