Flame retardancy and toughness of epoxy resin induced by a star-shaped flame retardant containing P/Si/B

A star-shaped flame retardant containing Si/P/B (SiFAD) was synthesized and used to regulate the performance of epoxy (EP). The SiFAD modifies the flame retardancy, toughness and transparency of EP. The EP containing 6 wt% SiFAD displays a UL-94 V0 rating and a limiting oxygen index (LOI) of 34.7 vol%. The SiFAD promotes the early degradation of EP, increases the amount of char formed at high temperature, and improves the flame retardancy through the combined actions of gas phase and condensed phase. The tensile and impact strength of EP are both improved, especially the impact strength of EP containing 4 wt% SiFAD is 15.8 kJ/m2, which is 139% more than that of EP. The SiFAD in EP constructs high free volume through bridge effect, thus improves the impact strength of EP. In addition, microphase separation is produced in EP composites which is so small that the EP composites keep good transparency.