Improvements in fatigue life of amine-functionalized multi-walled carbon nanotube-reinforced epoxy composites: Effect of functionalization degree and microwave-assisted precuring

Abstract

In this study, the effects of functionalization degree and precuring process were studied on the fatigue life of amine-functionalized multi-walled carbon nanotube-reinforced epoxy composites. The multi-walled carbon nanotubes were highly functionalized by ethylenediamine through a microwave-assisted method. The grafted amine moieties on the multi-walled carbon nanotubes could react with the epoxy chains of the matrix and consequently form covalent bonds between the multi-walled carbon nanotubes and the epoxy matrix. It has been found that higher functionalization degrees can lead to considerable enhancement on fatigue life of reinforced composites by increasing the dispersibility of multi-walled carbon nanotubes in the epoxy matrix and also improving the interfacial interactions between the reinforcing phase and the matrix. In the next step, the precuring process was performed by three apparatuses: oven, stirrer and microwave. While the precuring process with all three apparatuses resulted in higher mechanical properties of reinforced composites, the microwave-assisted precuring was more successful than the other two apparatuses. The reinforced composites prepared by microwave-assisted precuring experienced more than 19% improvement in the tensile strength in comparison to the non-precured composite; such improvements in the mechanical properties of reinforced composites were attributed to higher reactivity of amine moieties with the epoxy chains due to sufficient activation energy provided by microwave radiations. Observations with scanning electron microscopy indicated that highly functionalized multi-walled carbon nanotubes were uniformly distributed in the epoxy matrix; this can lead to uniform distribution of applied stress in the composites and consequently improve mechanical properties of the reinforced composites.