Effect of type and aspect ratio of different carbon nanotubes on cure behavior of epoxy-based nanocomposites

Abstract

Effect of incorporation of carbon nanotubes (CNTs) into diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin (HY5052/LY5052 system) on cure reaction was investigated via thermal analysis. Keeping their length constant, CNTs of different diameters were chosen. Samples based on epoxy resin and different type and content of CNTs were prepared and characterized. The cure behavior of epoxy matrix in the presence of CNTs was studied in both glassy and rubbery states. The results indicated that the final cure characteristics of epoxy nanocomposites were controlled by the competition of viscosity-increasing effect and heat-sink effect of CNTs. Isothermal analysis showed that accelerating or decelerating effect of CNTs on the cure process depends on CNT content, its aspect ratio and temperature of isothermal cure. The presence of the CNTs physically hindered the mobility of the epoxy and hardener monomers preventing the cure reaction (viscosity-increasing effect). In contrast, inherent high thermal conductivity of CNTs can act as a heat sink to accelerate the heat absorption of the epoxy (heat-sink effect). Below glass–rubber transition temperature (Tg), heat-sink effect of CNTs was dominant due to the restricted mobility of polymer chains in glassy state, whereas at temperatures higher than Tg, viscosity-increasing effect was dominant. CNTs physically hindered the mobility of reactive species despite the inherent tendency of polymer chains for long-range molecular motions.