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By improving the existing preparation methods, a piperazine polypyrophosphat (PAPP) with high thermal stability was synthesized. It was compounded with halloysite nanotube (HNTs) and melamine cyanurate (MCA) to form P-N-Si intumescent flame retardant, and was used in synergistic flame retardant epoxy resin (EP). The effect of intumescent flame retardant on the flame retardancy of EP was investigated by means of limiting oxygen index, vertical combustion, cone calorimeter and SEM etc. The results show that the introduction of the compound flame retardant forms a dense and continuous intumescent carbon layer, which improves the flame retardant efficiency of the epoxy resin in the condensed phase and the gas phase. It reduces the heat release and heat release rate of epoxy resin and the toxic gases release effectively. When the PAPP/HNTs/MCA ratio is 7∶1∶2, the limiting oxygen index of flame retardant resin reaches 34.3%, the UL-94 vertical combustion test reaches V-0 level. Compared with pure EP, the amount of residual carbon is increased significantly, the peak heat release rate (HRR) is decreased by 60.56%, and the total heat release (THR) and toxic gas emissions are reduced significantly for modified EP. In addition, the thermogravimetric analysis results suggest that the initial decomposition temperature of flame retardant modified EP is decreased by 4.4% (ΔT), and the modified EP still has high thermal stability.

Propylene glycol methyl ether was directly synthesized from propylene and hydrogen peroxide under mild conditions via aluminum modified titanium silicalite-1 as a bifunctional catalyst. It has both active sites capable of epoxidation and active sites capable of ring opening reactions, thus realizing the one-pot preparation of propylene glycol methyl ether by propylene. The synergistic effect of Ti–Al on the catalytic performance and the distribution of propylene glycol methyl ether isomer were investigated in detail, and the synergistic catalysis between the two active sites was characterized. The gradual introduction of aluminum reduced the activation ability for hydrogen peroxide, but gradually increased the selectivity for propylene glycol methyl ether. Under the optimum conditions, the selectivity for propylene glycol methyl ether reached 91.53%. Combined with Density Functional Theory (DFT) calculations, the synergistic catalytic effect of doped Al and framework Ti in titanium silicalite-1 is discussed in detail from a microscopic perspective. Al increases the Lewis acid strength of Ti active sites and promotes the conversion of propylene to propylene oxide (PO), and simultaneously Ti increases the Brønsted acid strength of Al active sites and promotes the conversion of propylene oxide to propylene glycol ether. [ABSTRACT FROM AUTHOR]