Synthesis of melamine phenyl hypophosphite and its synergistic flame retardance with SiO2 on polypropylene

An organic compound melamine phenyl hypophosphite (MPHP), containing phosphorus and nitrogen, was synthesized and characterized. Its flame retardant properties and synergistic flame retardancy with silicon dioxide (SiO2) on polypropylene (PP) was investigated. The limiting oxygen index (LOI) value of PP/30%MPHP reached 31.3%, and UL 94V-0 rating was attained. The LOI value of PP/27%MPHP/3%SiO2 reached 28.7%, and the peak heat release rate (pk-HRR) of PP/27%MPHP/3%SiO2 was 42.3% lower than that of pure PP. In addition, the flame retardant mechanism was investigated using scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray, Fourier transform infrared spectroscopy and Pyrolysis–gas chromatography–mass spectrometry (PY–GC–MS). MPHP/SiO2 had synergistic flame retardant effect, and simultaneously exerted gas phase and condensed phase flame retardant effect. Adding a small amount of SiO2 to PP/MPHP, not only reduced the heat release rate, but also improved the mechanical properties.