Preparation of efficiently intumescent-flame-retarded polypropylene composite: synergistic effect of novel phosphorus-containing polyhedral oligomeric silsesquioxane

In this paper, the laboratory-synthesized single-component intumescent flame retardant (IFR) and the phosphorus-containing polyhedral oligomeric silsesquioxane (P-POSS) as a novel synergist were combined to be applied in preparation of the halogen-free flame-retarded (FR) polypropylene (PP) composite. The involved structure, property and flame-retarding mechanism were systematically investigated. The experimental results show that incorporation of only 1.0 wt-% loading of P-POSS remarkably enhances the flame-retarding property and mechanical performance of FR PP composite, exhibiting the efficiently synergistic effect. The synergistic effect of P-POSS is explained by the reinforcing effect of its decomposition products SiO2 and phosphoric acid-based compounds on the condensed-phase char layers. Also, the incorporated 1.0 wt-% P-POSS particles significantly improve the dispersion of IFR fillers and the interfacial compatibility. The prepared FR PP composite possesses excellent comprehensive properties including a comparable mechanical performance of pure PP and flame retardancy (1.6 mm UL94 V-0 rating), and exhibits a good application prospect.