In nature, self-healing allows many biological materials to meet their required function and exhibit many of the resilient properties we expect in emerging applications for polymers. Inspired by nature, several routes to achieve self-healing in synthetic polymers have been devised. One approach is to make polymer composite materials where microscopic capsules and capillary tubes that carry a “healing agent” are embedded within a polymer matrix. Isocyanates in particular have attracted focus as a healing agent because the polymerization reaction is achieved without the need for a catalyst, UV light, or increased temperature. Isocyanates healing agents are polymerized through exposure to water, which makes them attractive for applications in protective coatings, water filtration membranes, and other environmentally relevant materials. In this study, we studied the release of diisocyanate healing agent from microcapsules that are used in extrinsic self-healing materials in contact with water. Our results show that the reaction of bulk IPDI with water to form polyurea does not go to completion and some unreacted diisocyanate can remain in water for multiple days. However, IPDI released from microcapsules has a high surface area to volume ratio and all the released isocyanate is converted into polyurea within our experimental timeframe of hours. The results suggest that release of core components from microcapsules into flowing water is possible, but the released particles are in the form of polyurea microparticles rather than the diisocyanate healing agent. These results will have implications for the self-healing performance of self-healing materials that are to be used in contact with flowing liquid since they suggest that the healing agent can be carried away from its original location.

Release of polyurea microparticles from self-healing materials

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