Phosphorus-containing epoxy resins for flame retardancy V: Synergistic effect of phosphorus-silicon on flame retardancy

Epoxy resins containing phosphorus and/or silicon are prepared from phosphorus/silicon-containing epoxides and diamine curing agents. The flame-retardant properties of the phosphorus/silicon-containing epoxy were studied. Furthermore, the phosphorus–silicon synergistic effect on LOI enhancement and increasing flame retardancy of the epoxy materials were demonstrated. While under flame, phosphorus provides the tendency of char formation, and silicon provides the enhancement on thermal stability of the char, to show their individual benefit on flame retardancy. Introducing both phosphorus and silicon together in the epoxy resin composition brings the success of combining these two factors in a flame retardation mechanism. An LOI enhancement from 26 to 36 is observed for epoxy resins containing both phosphorus and silicon. Moreover, the synergistic effect of phosphorus–silicon on fire resistance can be further leveled up by using siloxane reagents to replace silanes. Epoxy resins with a composition of phosphorus epoxides and siloxane diamines exhibit a high LOI value of 41, to demonstrate the high synergistic efficiency of phosphorus and silicon on flame retardation.