Roles of supermolecule structure of melamine phosphomolybdate in intumescent flame retardant polypropylene composites

Abstract In this paper, supermolecular structure of melamine phosphomolybdate (MAPMo) was tailored by changing the ratio of MA/PMo. Effects of MAPMo on flame retardant efficiency of polypropylene/intumescent flame retardant (PP/IFR) system were investigated by using limiting oxygen index (LOI), UL-94 testing, microscale combustion calorimetry (MCC) etc. The thermal degradation behaviors of PP composites were tested by thermal gravimetric analysis (TGA). The results showed that the formation of supermolecular increases the thermal stability of MA and the ratio of MA/PMo has great effect on flame retardancy of PP/IFR. With the addition of 15.5 wt% IFR and 0.5 wt% MAPMo (MA/PMo ≤ 3), the PP composites can pass the UL-94 V-0 test without melt-dripping. In addition, more or less MAPMo are not suitable for improving flame retardancy of PP, the best content of MAPMo (3:1) is 0.3–0.8 wt%. The morphology of char residue reveals that the MAPMo promotes the reaction between APP and PER, accelerates the formation of perfect charring layer. Moreover, the MAPMo modifies the degradation of MA and tailors the surface morphology of the char residue. MAPMo doesn’t modify the bonds of the char compared to neat PP/IFR but improve the quality of char. It is the good char layers that protects the inside matrix from the erosion of heat and gas, resulting in good flame retardant properties.

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