Flame Retardant and Self-Healing Coating containing Dynamic Disulfide Bonds for Polyurethane Rigid Foams via UV-Curing Technology

ABSTRAT Polyurethane rigid foam (RPUF) is widely used in building insulation materials, but the applications of which are limited by its high flammability. Although fireproof coatings have been proven to be effective at achieving fire-safe RPUF, the development of multi-functional fire-protective coatings still remain a huge challenge. Herein, a phosphorus-containing HEMA-HEDS-PPDC (HSP) prepolymer was successfully synthesized from hydroxyethyl methacrylate, bis (2-hydroxyethyl) disulfide and phenylphosphoryl dichloride, and then a crosslinked flame retardant coating was constructed on RPUF by UV-curable radical polymerization. Experimental results show that the HSP coating significantly improves the flame retardant performance of RPUF. Among them, HSP-2/RPUF reaches V-0 rating in the vertical combustion test, and the limiting oxygen index increases from 19.0% of pure RPUF to 26.8%. The mechanism study suggests that the flame retardant effect of the coating is due to the synergistic mechanism of physical barrier effect of dense carbon layer and chemical inhibition effect of phosphorus-containing free radicals. In addition, the highly crosslinked HSP network structure also endows the material with excellent water resistance and mechanical properties. It is particularly noteworthy that the disulfide bonds introduced into the system confer certain self-healing and recyclability properties to the coating. This study provides a new idea for developing multifunctional flame retardant coatings and has broad application prospects in the fire protection of flammable substrates.