Effects of Fluorinated Silane Coupling Agent on Properties of Microcapsules for Self-Healing Materials

Urea–formaldehyde (UF) microcapsules used as self-healing materials were facilely prepared by a sonication technique using epoxy resin (E-51) and UF resin as core and shell materials, respectively. Fluorinated silane coupling agent (KBM-7803) was used to modify the surface of the UF microcapsules. The as-prepared microcapsules were investigated by Fourier transform infrared spectroscopy, which indicated the formation of UF polymer with successful encapsulation of the core materials in UF shell and effective absorption of KBM-7803 on the surface of the microcapsules. Analysis of the mechanical properties revealed that the modification using KBM-7803 improved the tensile properties and decreased the elasticity of the microcapsules. The results of scanning electron microscopy illustrated that KBM-7803 modified microcapsules had thin shells, indicating that the microcapsules were capable of being ruptured easily which resulted in the effective release of the curing agent into the crack planes to form a polymer that bonded the crack faces and restored the structural continuity of the composite, leading to effective self-healing.