Reactive organophosphorus retardant-enhanced sorbitol epoxy resins with highly thermal and flame-retardant performance

As a low-cost sugar-based chemical, sorbitol has been less reported in recent years in the field of epoxy resins. In view of the low viscosity characteristics of its epoxy monomer, it is of great significance to prepare the advanced resin system via a solvent-free green curing process. As known, most of the existing flame-retardant networks contain organophosphorus flame retardants. To achieve excellent flame- retardant effect, a large amount of phosphorus was added to the resin matrices. As a result, apart from exacerbating the migration of organophosphorus, their thermal stability and phase transition temperature are further reduced, thus weakening the thermal properties of the material to a certain extent. In order to overcome those problems, we introduced ultra-low amounts of phosphorus to achieve efficient flame retardant into the sorbitol -based epoxy resin. It was found that the introduction of EP-DOPO in 0.55 P wt% amount could achieve a UL94-V0 grade flame retardant effect. Different from other phosphorus-containing flame retardants, reactive EP-DOPO favored an improvement in both thermal stability and phase transition temperature, meanwhile, it effectively avoids the phosphorus migration as well.