Thermal and mechanical investigation of toughened epoxy resins having auto-repair ability based on supramolecular chemistry

Drawing inspiration from biological systems, nowadays researchers are trying to develop a new class of synthetic materials known as self-healing materials that can automatically repair damages, with the aim to increase the durability of the same materials and reduce their maintenance cost. Many efforts have been effectively directed to impart self-healing properties to a broad variety of materials, including polymers or composites. In this work, we propose a formulation based on supramolecular chemistry capable to give auto-repair functionality to epoxy nanocomposites. In particular, in order to develop materials suitable for aeronautical applications, a tetrafunctional epoxy resin has been toughened by a functionalization procedure, which allowed to covalently bond a rubber phase to the epoxy matrix. The performed functionalization was found to be effective in reducing the rigidity of the resin and favouring the activation of self-healing mechanisms. The intrinsic healing ability of the functionalized epoxy matrix has been improved by the addition of “self-healing fillers” which are endowed with hydrogen bonding donor and acceptor sites able to interact with the hydroxyl and carboxyl functional groups of the hosting matrix, through the formation of non-covalent reversible H-bond. Furthermore, multiwall carbon nanotubes have been dispersed into the matrix with the aim to obtain electrically conductive composites. The formulated epoxy samples have shown conductivity values beyond the Electrical Percolation Threshold (EPT) and healing efficiency values higher than 60%, at room temperature. Thermal and mechanical investigations demonstrated the success of the proposed self-healing strategy which made it possible to take a further step forward the development of smart structural composites.