Research Progresses in Self-Healing Polymer Materials

Self-healing was put forward to cope with slight damages in polymer materials which are difficult to detect. Research progress in self-healing polymer materials in recent years is summarized in this paper. According to the healing agents employing or not, self-healing methods in polymer materials or polymer composites can be classified into two categories, namely, extrinsic and intrinsic. The extrinsic self-healing polymer materials accomplish self-healing with the aid of self-healing agents incorporated in microcapsules or hollow-fibers. The self-healing agents are released when microcapsules or hollow-fibers are attacked by microcracks, and then reactions involved self-healing take place and the crack surfaces are bonded together to achieve self-healing. This method performs easily and efficiently, but the self-healing process can not be repeated and the candidates of self-healing agents are limited. On the other hand, the intrinsic self-healing polymers bring into effect with the help of Diels-Alder reactions, dynamic covalent chemistry, disulfide-bond reactions, supramolecular structure with hydrogen-bond, pi-pi stacking, ionomes and so on. Furthermore, the chemical reactions related to these special molecular structures are reversible. Though the preparation of intrinsic self-healing polymers is more complicated, the self-healing process is efficient in repeatable manner. So, the durability of polymer materials can be extended. This paper reviews mainly on the specialities and applications of the above self-healing methods in polymer materials.