An efficient halogen-free reactive flame-retardant active diluent for soy-castor oil-based fire safety UV-curable coatings

Soy-castor oil-based polyurethane acrylate prepolymer (SCPUA) was synthesized by using epoxidized soybean oil and ricinoleic acid as raw materials, and a cost-effective halogen-free flame retardant phosphorous silicon methacrylate monomer (PSMAM) was also synthesized and used as an efficient reactive diluent to mix with SCPUA to develop a novel vegetable oil-based UV-curable coating system. Benefited from the addition of PSMAM, the limiting oxygen index (LOI) of the coatings reaches up to 23%, and the coatings can self-extinguish instantly (within 1 s) after removing from flame, indicating that these coatings possess remarkable flame-retardant performance. Also, the flame-retardant mechanism is proposed, and it reveals that PSMAM promotes the formation of a dense and continuous char layer on the coating surface to serve as a heat and oxygen barrier, thus providing the coatings with remarkable flame retardancy. Besides, the use of PSMAM can improve the thermal stability of the coatings. More strikingly, these coatings exhibit excellent hardness (6H), flexibility (2 mm), adhesion (4B) and remarkable acid and alkali resistance as well as boiling water resistance. Therefore, excellent performances and cost-effective feature as well as the facile synthesis process make these newly-developed halogen-free flame-retardant vegetable-oil based UV-curable coatings more potential for practical applications.