Reinforcement of epoxy resins with multi-walled carbon nanotubes for enhancing cryogenic mechanical properties

Epoxy resins are widely applied in cryogenic engineering and their cryogenic mechanical properties as important parameters have to be improved to meet the high requirements by cryogenic engineering applications. Carbon nanotubes (CNTs) are regarded as exceptional reinforcements for polymers. However, poor carbon nanotube (CNT)-polymer interfacial bonding leads to the unexpected low reinforcing efficiency. This paper presents a study on the cryogenic mechanical properties of multi-walled carbon nanotube reinforced epoxy nanocomposites, which are prepared by adding multi-walled carbon nanotubes (MWCNTs) to diglycidyl ether of bisphenol-F epoxy via the ultrasonic technique. When the temperature decreases from room temperature to liquid nitrogen temperature (77 K), a strong CNT-epoxy interfacial bonding is observed due to the thermal contraction of epoxy matrix because of the big differences in thermal expansion coefficients of epoxy and MWCNTs, resulting in a higher reinforcing efficiency. Moreover, synthetic sequence leads to selective dispersion of MWCNTs in the brittle primary phase but not in the soft second phase in the two phase epoxy matrix. Consequently, the cryogenic tensile strength, Young's modulus, failure strain and impact strength at 77 K are all enhanced by the addition of MWCNTs at appropriate contents. The results suggest that CNTs are promising reinforcements for enhancing the cryogenic mechanical properties of epoxy resins that have potential applications in cryogenic engineering areas.