Trigger efficiency enhancement of polymeric microcapsules for self-healing cementitious materials

In this work, silane coupling agent, [3-(2-Aminoethylamino)propyl]trimethoxysilane (KH792), was applied to improve the trigger efficiency of poly(phenol-formaldehyde) (PPF) microcapsules in the cementitious materials. Two schemes of reaction procedure were proposed based on different chemical reaction mechanism. The chemical structure of surface modified microcapsules was investigated by attenuated total reflection-Fourier transformation infrared spectrometry (ATR-FTIR) and then further proofed by X-ray photoelectron spectroscopy (XPS). The thermal properties and the decomposition temperature of the modified microcapsules were characterized by thermal gravimetric analysis (TGA). The morphology of the surface modified microcapsules and the crack surface of microcapsule-embedded cement paste were observed by environmental scanning electron microscope (ESEM). Finally, the influence of microcapsules incorporation and surface modification on the compressive strength of the self-healing cementitious system was evaluated. It was found that the microcapsules modified with reaction scheme 1 possess significantly higher trigger efficiency in cement matrix (41% for S1-10 sample and 63% for S1-30 sample) than the plain microcapsule (22%) and microcapsules modified with reaction scheme 2 (less than 10%). Although the incorporation of PPF microcapsules has an overall negative effect on the mechanical property of cement matrix, longer reaction time of surface modification could slightly mitigate this impact.