Microcapsule-Type Self-Healing Protective Coating That Can Maintain Its Healed State upon Crack Expansion

Abstract

The purpose of this study was to develop a microcapsule-type self-healing coating system that could self-heal cracks and then maintain the healed state even upon crack expansion. Mixtures consisting of a photoinitiator and two methacrylate components, bismethacryloxypropyl-terminated polydimethylsiloxane (BMT-PDMS) and monomethacryloxypropyl-terminated PDMS (MMT-PDMS), were transformed into viscoelastic semi-solids through photoreaction. The viscoelasticity of the reacted mixtures could be controlled by varying the mass ratio of the two methacrylates. Through a stretchability test, the optimal composition mixture was chosen as a healing agent. Microcapsules loaded with the healing agent were prepared and dispersed in a commercial undercoating to obtain a self-healing coating formulation. The formulation was applied onto mortar specimens, and then cracks were generated in the coating by using a universal testing machine (UTM). Cracks with around a 150-μm mean width were generated and were allowed to self-heal under UV light. Then, the cracks were expanded up to 650 μm in width. By conducting a water sorptivity test at each expanded crack width, the self-healing efficiency and capability of maintaining the healed state were evaluated. The B-M-1.5-1-based coating showed a healing efficiency of 90% at a 150-μm crack width and maintained its healing efficiency (about 80%) up to a 350-μm crack width. This self-healing coating system is promising for the protection of structural materials that can undergo crack formation and expansion.

Repeatable Self-Healing of a Protective Coating Based on Vegetable-Oil-Loaded Microcapsules

“…Finally, the healing agent solidifies through a chemical reaction, and self-healing is achieved. Compared with the intrinsic system, the microcapsule-type system has the advantage of healing a larger damaged volume [ 1 , 6 , 7 ]; however, these microcapsule-type systems have the limitation of single local self-healing [ 1 , 8 , 9 ]; when the healed region is damaged again, repeated self-healing cannot occur because healing agent-loaded microcapsules are depleted and the released healing agent transforms into a hard solid without the self-healing capability. To solve this limitation, vascular type self-healing materials having multiple local healing abilities have been developed [ 8 , 10 ]; however, such systems have disadvantages based on the difficulty in vascular structure fabrication and the need to use an external healing agent supply.…”