Preparation of microcapsules with IPDI monomer and isocyanate prepolymer as self-healing agent and their application in self-healing materials

Microcapsules were synthesized with the hybrid of Isophorone diisocyanate (IPDI) and terminal isocyanate prepolymer (CPU) as active healing agent, then the microcapsules were mixed with epoxy resin in order to form a metal anti-corrosion coating with excellent self-healing properties. Through process optimization and molecular design, the core material which was isocyanate hybrid (CPU-IPDI) with 17% Isocyanate group (-NCO) was synthesized by the reaction of IPDI and castor oil, and then the CPU-IPDI was encapsulated in the microcapsule with Diphenylmethane diisocyanate (MDI) as the shell by interface polymerization. Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric spectroscopy (TGA) confirmed the successful encapsulation of CPU-IPDI. The effect of the content of sodium lignosulfonate (NaLS) on the size and morphology of microcapsules were investigated. Optical microscopy (OM) and laser particle size analyzer show that the size of microcapsules decreases with the increase of the content of stabilizing agent. The microcapsules were prepared with 1% NaLS with a core content of 51.3%, an average particle size of 26.3 μm and a shell thickness of 1.44 ± 0.9 μm. In addition, the microcapsules loaded with CPU-IPDI were added to the epoxy coating, and the healing process of blank coating and self-healing coating was detected by SEM. The results show that the coating wound of containing 10% microcapsules has obvious healing. With saline infiltration and electrochemical impedance spectroscopy (EIS) test coating corrosion process, the results prove that after soaking in 3.5% NaCl solution for 7 days, the |Z| f = 0.01Hz value of the coating with 10 wt % microcapsules is about 1.9 × 106 Ω cm2, nearly three order higher than that of pure epoxy coating (3.1 × 103 Ω cm2), demonstrating the enhancement of protection ability.