A novel phosphorous and silicon-containing benzoxazine: highly efficient multifunctional flame-retardant synergist for polyoxymethylene

The synergist of phosphorus and silicon-containing benzoxazine (p-BOZ) was prepared through three steps using phenylphosphonic dichloride, 3-aminopropyltriethoxysilane, and 4-methoxyphenol as raw materials. The structure of p-BOZ was demonstrated by 1H NMR. Ammonium polyphosphate (APP) and melamine (ME) were compounded to form an intumescent flame-retardant (IFR) system that can remarkably improve the flame retardancy of polyoxymethylene (POM). The performances of APP/ME/p-BOZ and the related mechanisms were studied by employing limited oxygen index (LOI), UL 94 rating, cone calorimeter test (CONE), thermogravimetric analysis (TGA), Raman spectral analysis, and scanning electron microscope (SEM). The results showed that the introduced p-BOZ can effectively enhance the char formation ability of the APP/ME/p-BOZ system in the condensed phase and improve the gas-phase performance simultaneously. The POM composites containing 2 wt% p-BOZ compounding with 20 wt% APP and 6 wt% ME reached UL94 V-0 rating and a LOI value of 42.8%. Meanwhile, average HRR, MLR, EHC, SEA, and TSP of the composite all exhibited significant reduction, further conforming that p-BOZ can act as an effective flame-retardant synergist and a smoke suppressant. The synergist of phosphorus and silicon-containing benzoxazine (p-BOZ) was prepared. The POM composites containing 2 wt% p-BOZ compounding with 20 wt% APP and 6 wt% ME reached UL94 V-0 rating and a LOI value of 42.8%.