Investigation on the synergistic effect mechanism of hydroxyl-terminated PES/Nano-SiO2 on the mechanical properties of epoxy resin at ultra-low temperatures

The mechanical properties of resin matrixes are predominant factors influencing the overall performance of fiber-reinforced composites. In this study, the high brittleness and low toughness of epoxy resin (EP) are addressed by incorporating hydroxyl-terminated polyether-sulfone (PES-OH) and nano-silica (Nano-SiO₂) into the EP. The incorporation of PES-OH into EP led to a 22.6 % increase in tensile strength and a 27.8 % improvement in elongation at break at ultra-low temperatures. These enhancements are attributed to the formation of a semi-interpenetrating polymer network (SIPN) during the curing process, which strengthens the molecular network of the epoxy resin matrix through physical entanglement, interfacial reinforcement, and stress dispersion, enhancing crack resistance. The simultaneous introduction of PES-OH and Nano-SiO₂ synergistically improves the mechanical properties of EP at ultra-low temperatures (90 K). Specifically, the tensile strength, elongation at break, and modulus of elasticity of the modified EP were increased by 30.63 %, 19.6 %, 20.9 % and a 65.61 % improvement in fracture toughness (K_IC), respectively, compared to the pure EP. The synergistic effect arises from the covalent bonding between the hydroxyl groups on Nano-SiO₂ and those in PES-OH and EP, thereby toughening and strengthening the epoxy molecular structure. Additionally, microdroplet debonding tests of carbon fiber with EP showed a 25.22 % increase in interfacial shear strength after introducing PES-OH and Nano-SiO₂. Dynamic thermo-mechanical analysis confirmed that the incorporation of PES-OH and Nano-SiO₂ does not compromise the thermal stability of EP.