Study On Synthesis Of Polyaminocyclotriphosphazene Modified With Melamine And Its Flame Retardance In Epoxy Resin

Hexaamidocyclotriphosphazene is one of a few commercialized phosphazene flame retardants. However, it is not used as a flame-retardants additive of plastics due to its high water solubility, strong alkaline, and the difficulty to separate from by-product-ammonium chloride. Hexaamidocyclotriphosphazene can be translated to water-insoluble polyaminocyclotriphosphazene (PHACTPA) by polymerization, but hygroscopicity of PHACTPA is strong, water-soluble still is bigger and thermal stability is poor. So, in this paper, hexaamidocyclotriphosphazene modified with melamine (MPHACTPA) was studied.With melamine (MA), hexachlorocyclotriphosphazene (TCP) and liquid ammonia as raw materials, MPHACTPA was synthesized by the condensation of TCP and MA, then ammoniation with ammonia, final polycondensation. The optimum conditions of condensation were as follows:temperature is 80℃, time is 18h. The optimum conditions of polycondensation were as follows:temperature is 180℃, time is 20 minutes. The yield and P recovery and thermal stability of the product were improved significantly, and the moisture absorption and solubility were reduced by melamine modification.When the ratio of MA and TCP is 1:1,1:1.5 and 1:2, three kinds of MPHACTPA (MPHACTPA-1, MPHACTPA-2, MPHACTPA-3) were prepared, their flame retardancy in E-44/DG731 were compared with PHACTPA. The experimental results show that with 30wt.% dosage, the limited oxygen index (LOI) of the FR-E-44/DG731 with MPHACTPA-1, MPHACTPA-2, MPHACTPA-3 and PHACTPA respectively are 28.6%,30.1%,28.3% and 29.6%, the flame retardant level are FV-0, FV-0, FV-0 and FV-1 respectively, where the flame retardant effect of MPHACTPA-2 is best. Compared with E-44/DG731, the total heat release (THR), the highest average heat release rate (MHRR) and total heat release of the FR-E-44/DG731 is decreased obviously. TGA results indicated PHACTPA and MPHACTPA can reduce thermal stability of the E-44/DG731, but influence of MPHACTPA-1 was smaller. Residues analysis revealed PHACTPA and MPHACTPA played a flame retardancy mainly by condensed phase mechanism, where PHACTPA or MPHACTPA was decomposed into non-volatile phosphoric acid compounds, which promoted charing of E-44/DG731, and CO2, NH3 and N2 released from the decomposition of PHACTPA or MPHACTPA foamed the residues, the formed intumescent layer resulted in the barrier effect on heat, air and decomposition products. TGA-IR and the residual rate of P show that some phosphorus compounds were vaporized to gaseous phase, which may cause flame retardant effect in the gas phase.