Synthesis and Characterization of a Multifunctional Sustained-Release Organic–Inorganic Hybrid Microcapsule with Self-Healing and Flame-Retardancy Properties

As their service life increases, cement-based materials inevitably undergo microcracking and local damage. In response to this problem, this study used phacoemulsification-solvent volatilization to prepare a multifunctional sustained-release microcapsule (SFRM) with self-healing and flame-retardant characteristics. The synthesis of SFRM is based on the modification of ethyl cellulose with nano-SiO2 particles and cross-linking with a silane coupling agent to form an organic–inorganic hybrid wall material. The epoxy resin is blended with hexaphenoxy cyclotriphosphazene (HPCTP) to form a composite core emulsion. The surface morphology, particle size distribution, core–shell composition, and thermal stability of SFRM were analyzed via scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), Malvern, Fourier-transform infrared (FT-IR), and TD-DSC-DTG. It is concluded that SFRM was successfully synthesized with superior particle size distribution and thermal stability. When the ratio of SiO2 solution and EC alcohol solution reached 1:2, the particle size distribution of the microcapsules was 30–190 μm, and the D50 decreased to 70 μm. The core material content, slow-release performance, and flame retardancy of SFRM were measured using a UV-1800 spectrophotometer and Hartmann tubes, and the compressive and repair properties of SFRM were evaluated by uniaxial compression tests. The results demonstrate that SFRM has satisfactory slow-release and flame-retardancy properties, the LC is 67%, and the first-order kinetic model shows the best fit and conforms to the non-Fickian diffusion mechanism. The SFRM repair rate can reach approximately 61%. This is of substantial significance to the field of self-repairing cement-based materials.