Capsule-based healing systems in composite materials: a review

Composites are used in a variety of applications due to their excellent properties. However, structural polymers are sensitive and susceptible to thermal and mechanical damage in form of micro-cracks, which are onset to grow deep within the structure where detection and repair are practically impossible. To overcome these problems, broad range of self-healing structures have emerged. This technology has led to an increase in the material’s lifetime and safety while reducing the repair and replacement costs. Capsule-based healing systems are a well-known technology that has many uses in smart protective coatings, dental composites, concrete components, and generally for polymer and fiber-reinforced composites. This article summarizes the research work on the capsule-based self-healing system over the last two decades. In this regard, after a brief introduction, various types of microencapsulation-based methods used in healing systems are classified. After explaining the manufacturing process of capsules, parameters affecting the microencapsulation quality particularly, agitation rate, core to shell weight ratio, monomer viscosity, solvent property, reaction time, temperature, pH, and U/F ratio are explained in detail. Finally, the most common healing efficiency evaluation methods are described. This review provides the reader with an overview of achievements to date, and insight into future development for industrial and engineering applications.