Preparation of melamine borate coated red phosphorus microcapsules and use of zinc borate as synergistic flame retardant in polyethylene

Abstract Microcapsules (Mic‐MBP) based on the melamine borate coated red phosphorus (RP) were prepared, and its synergistic flame retardant with zinc borate (ZB) on polyethylene (PE) was investigated. The flame retardant properties of the PE/20% Mic‐MBP/10%ZB were superior to that of PE/20%RP/10%ZB. Furthermore, the limiting oxygen index of PE/20%Mic‐MBP/10%ZB was 25.2%, and PE/20%Mic‐MBP/10%ZB reached the UL‐94V‐0 rating. Compared with PE, the peak heat release rate (pk‐HRR), total heat release (THR) and average effective heat of combustion (av‐EHC) of PE/20%Mic‐MBP/10%ZB had decreased. In addition, the flame retardant mechanism was investigated by scanning electron microscopy (SEM), X‐ray diffraction (XRD), pyrolysis‐gas chromatography–mass spectrometry (PY‐GC–MS) and Fourier transform infrared spectroscopy (FT‐IR). The results showed that the residual char of PE/20%Mic‐MBP/10%ZB had thermal stability, and the formation of phosphorus free radicals and nonflammable gases effectively reduced the burning intensity of the gas phase. It indicated that Mic‐MBP/ZB showed a condensed and gas phase flame retardant effect.