A Self-Healing Material Based on Microcapsules of Poly(Urea-Formaldehyde)/Bis-Propargyl-Succinate Containing in Polyurethane Matrix

With the development of current technology, several concepts of self-healing materials (SHMs) have recently been proposed, and capsule-based SHMs are explored. In our study, a terminal alkyne compound (bis-propargyl-succinate, BPS) is concerned as a healing agent to be used as a core material, and poly(urea-formaldehyde) (PUF) is employed as a wall shell. Besides, the chemical, morphological and thermal properties of the microcapsules (MCs) are also determined by Fourier-transform infrared spectroscopy (FTIR), gas chromatography (GC), thermogravimetric analysis (TGA), and optical microscopy (OM). Additionally, the MCs have better thermal stability up to 257 °C with the rough outer surface. The MCs have successfully encapsulated 75.0% of BPS with a size range of 63 – 125 μm and PUF shell thickness range of 5.72 – 11.35 μm; moreover, the stability of MCs is well maintained within 50 days at room temperature basing on the solvent extraction method. Concomitantly, self-healing ability is activated by the breakup of the MCs as cracks, then the healing agent (BPS) is released into the cracked regions to react with azide groups of the polymeric matrix. The BPS in the MCs is moved to cracked regions, which involves MCs diameter and weight fraction of PUF capsules. Moreover, the self-healing ability can reach high when BPS amounts (i.e., SHMs containing 5% and 10% of MCs) are available sufficiently to be outrightly filled into the cracked regions. Thereby, MCs' size and weight fraction can be reasonably selected to result in an optimal healing capacity for a pre-established size of cracks.