Improving the curing and flame retardancy of epoxy resin composites by multifunctional Si-containing cyclophosphazene derivatives

Novel star-like molecules containing P, N and Si with dual functions of flame retardance and curing promotion (abridged as HCCP–KH540) were successfully synthesized through the nucleophilic substitution reaction of hexachlorocyclotriphosphazene (HCCP) and 3-aminopropyltrimethoxysilane (KH540). HCCP–KH540 was incorporated with the matrix of epoxy resin (EP) to form a flame retardant composite abridged as E-HK. The activation energy of the curing reaction of the E-HK composite was reduced but the curing reaction rate was accelerated by HCCP–KH540. The E-HK composite with 30 phr content of HCCP–KH540 exhibited excellent flame retardancy with limiting oxygen index of 29.6% and V-1 rating in the vertical burning test as well as excellent thermal stability with a char yield of 23.77% at 700 °C, compared with only 8.64% for pure EP.