Preparation and characterization of nano-Fe3O4/paraffin encapsulated isocyanate microcapsule by electromagnetic controlled rupture for self-healing cementitious materials

Abstract In this paper, a novel electromagnetic controlled rupture microcapsule (ECRM) with ultrahigh self-healing capability was prepared by melt condensation method, whose shell was constructed by nano-Fe3O4 and paraffin, and whose core was toluene-di-isocyanate (TDI). Effect of paraffin/TDI mass ratio on core fraction of ECRM was investigated. The morphology, particle size distribution and component identification of ECRM were characterized by cold field emission scanning electron microscope (CFE-SEM), laser particle analyzer and Fourier transform infrared spectrometer (FTIR), respectively. Subsequently, the effects of ECRM on mechanical propertyand self-healing ability of mortars were evaluated. The results showed that the paraffin/TDI mass ratio delivered a major impact on core fraction of ECRM. The core fraction of ECRM was 65.3% when the mass ratio of paraffin/TDI was 1:2. The particle size distribution of ECRM mainly ranged from 60 μm to 1258 μm with 600 rpm agitation rate. The ECRM exhibited ellipsoidal with a rough surface. FTIR confirmed the successfully encapsulation of TDI in the shell of paraffin and nano-Fe3O4. In addition, ECRM containing 10 wt% nano-Fe3O4 can be heated to higher than 60 ℃ under electromagnetic field (output voltage: 600 V, field frequency: 124 kHz) for 500 s. Compared to the control mortar, the compressive strength and the flexural strength of mortar showed positive correlation with the ECRM dosage increasing (0 to 4 wt%). The reserved ratio of compressive strength of damaged mortar containing 6% ECRM with 60% compressive strength preload was 91.4% after self-healing for 30 min under electromagnetic field and curing for 24 h at room temperature. This work is anticipated to afford new insights for solving rupture problems of microcapsules in self-healing cementitious materials.