Simultaneously enhanced cryogenic tensile strength and fracture toughness of epoxy resins by carboxylic nitrile-butadiene nano-rubber

Epoxy resins are important matrices for composites. Carboxylic nitrile-butadiene nano-rubber (NR) particles are employed to improve the tensile strength and fracture toughness at 77 K of diglycidyl ether of bisphenol-F epoxy using diethyl toluene diamine as curing agent. It is shown that the cryogenic tensile strength and fracture toughness are simultaneously enhanced by the addition of NR. Also, the fracture toughness at room temperature (RT) is enhanced by the addition of NR. On the other hand, the tensile strength at RT first increases and then decreases with further increasing the NR content up to 5 phr. 5 phr NR is the proper content, which corresponds to the simultaneous enhancements in the tensile strength and fracture toughness at RT. Moreover, the comparison of mechanical properties between 77 K and room temperature indicates that the tensile strength, Young’s modulus and fracture toughness at 77 K are higher than those at RT but the failure strain shows the opposite results. The results are properly explained by the SEM observation.