Enhancing cryogenic mechanical properties of epoxy resins toughened by biscitraconimide resin

The demand for lightweight carbon fibre-reinforced polymer matrix composites (CFRPs), which typically have an epoxy resin (EP) matrix, have been increasing in cryogenic fields. The mechanical properties of CFRPs depend largely on the mechanical properties of their EP matrix, particularly in cryogenic environments. To date, however, no commercially available EP can comprehensively fulfil the demands. In this study, biscitraconimide resin (BCI) was introduced to enhance the mechanical properties of EP. Results indicated that cryogenic tensile strength, bending strength, impact strength and fracture toughness (K_IC) were enhanced for the modified epoxy system at appropriate BCI contents. The tensile strength (144.57 MPa) of EP increased by 67.6%, and its bending strength (229.53 MPa) increased by 94.9% at 77 K. Impact strength (41.16 kJ·m⁻²) was improved by 195.7% and K_IC (2.72 MPa·m^1/2) increased by 65.9% at 77 K compared with that of pure EP. The results were properly explained via scanning electron microscopy observation, and the mechanism of the improved mechanical properties was analysed in detail.