For the purpose of developing self-healing skin layers of instrument panels in automobiles, mechanically and thermally stable microcapsules containing healing agents were prepared and incorporated into a polyurethane (PU) matrix. Two different poly(urea-formaldehyde) (PUF) microcapsules containing either a polydimethylsiloxane (PDMS)/Pt catalyst (Pt) blend or crosslinker were synthesized using in situ emulsion polymerization. However, the resulting microcapsules were mechanically and thermally weak. More than 40% of the microcapsules were broken during the washing/drying process, and capsule decomposition began at 200 ◦C. These properties of microcapsules were greatly enhanced by decreasing the capsule size and depositing an additional urea-formaldehyde (UF) layer onto pre-formed PUF microcapsules. The former was accomplished by tuning the stirring speed during the reaction and the latter by adding more urea components. Under optimized conditions, only approximately 10% of microcapsules were broken after the same washing/drying process, and the decomposition temperature was raised to 250 ◦C. The two different optimized microcapsules were successfully embedded in a PU matrix and could be broken upon matrix cracking, thereby releasing the healing agent to the target areas via capillary effects. Subsequently, it was confirmed that the cracked portions were repaired through chemical and/or physical interactions within the healing system.
