Effect of mesoporous SiO₂ on the mechanical properties of epoxy resin at ultra-low temperature and the interface properties of resin/carbon fiber

Carbon fiber reinforced epoxy matrix composites are increasingly used in ultra-low temperature environments. However, due to the mismatch of the thermal expansion coefficient between the epoxy resin matrix and the carbon fiber, the carbon fiber composite material will produce significant temperature stress in the ultra-low temperature environment, which will affect its service performance. Mesoporous SiO₂ with a particle size of 100 to 160 nm and an average pore size of 4.24 nm was successfully prepared by sol-gel method, and mesoporous SiO₂/epoxy resin composites were prepared by adding them to epoxy resin by three-roller grinding method. The test results show that the addition of mesoporous SiO₂ effectively reduces the thermal expansion coefficient of epoxy resin and improves its mechanical properties. Specifically, at room temperature and 90 K, the tensile strength of epoxy resin with 10 wt.% mesoporous SiO₂ reached about 98 MPa and 160 MPa, respectively, which was 27.07% and 26.02% higher than that of pure epoxy resin, respectively. In addition, with the increase of mesoporous SiO₂ content, the thermal expansion coefficient of epoxy resin decreases gradually, and when 20wt.% mesoporous SiO₂ is added, the thermal expansion coefficient of mesoporous SiO₂/epoxy resin composites decreases by 26.31% compared with that of pure epoxy resin. The TFBT test results showed that the TFBT strength of epoxy resin with 5 wt.% mesoporous SiO₂ content was increased by 41.07% compared with that of pure epoxy resin, indicating that mesoporous SiO₂ could effectively improve the interfacial bonding properties of resin/carbon fiber.