Investigation of the thermal self-healing mechanism in a cross-linked epoxy system

Abstract

The mechanism of self-healing of a cross-linked epoxy system based on the diglycidyl ether of bisphenol A (DGEBA) and a new diamine cross-linker with two Diels–Alder (DA) adducts has been investigated. The location of the DA adducts on the diamine means that the cross-linker is the structural element that can be thermally cleaved and reformed, thereby allowing the cross-linked polymer to flow and fill or heal cracks and scratches. Since the stimulus for opening up the cross-linked network to allow flow and heal is heat, the temperature of the original network cure also becomes an important variable, and in this work different curing conditions have been explored to find suitable curing conditions which can cause the epoxy–amine to react, whilst avoiding initial scission of the DA adducts. The thermal self-healing mechanism of cured samples was studied by following the effect of scission on a range of properties such as the chemistry of the adducts, the glass transition of the polymer network, the size of units into which the network fragments upon scission and the ability of the network to swell. The appropriate conditions required to heal surface scratches of a micrometre size-scale were also studied.