Study On The Synthesis And Flame Retardancy Of Phenoxyphosphazenes In PC/ABS Alloy

Hexaphenoxycyclotriphosphazene (HPTCP) is a novel kind of flame retardants developed at home and abroad in recent years.It has not only a good retardant performance in PC and its alloys, but also little effect on the physical performance of PC and its alloys, thus payed closely attention at home and abroad. But the large amount of by-products such as octochlorocyclotetraphosphazene, decachlorocyclopentaphosphazene and other chlorophosphazene was produced during its synthesis process. If these chlorophosphazene can not exploited, they would become wastes, which would hampers the industrialization of HPTCP. As a result, this thesis has studied on the synthesis of phenoxyphosphazenes from these chlorophosphazene and their flame retardancy.In this paper, phenoxyphosphazenes were synthesized by the solid-liquid phase transfer catalytic process using chlorophosphazenes and phenol as raw materials. The results showed that the optimum conditions were as follows: n(phenol):n(KOH):n(phasetransfer catalyst):n(phosphazene)=6.0:6.8:0.19:1.0, dripping time for 0.5h, the reaction time of 0.5h under 50℃, 11h at 110-115℃. Under the above conditions, the yield and chlorine content of phenoxyphosphazenes are 93.51% and 1.16% respectively, and the degree of substitution of chlorine is 96.18%.The flame retardancy of HPTCP, HPTCP with little octophenoxy cyclotetraphosphazene (OPTCP) (about wt.8%, referred to as HOPTCP) and mixed phenoxyphosphazene (with HPTCP of about wt.52.3%, referred to as MPTCP) in PC/ABS was compared. The result showed that composition of phenoxyphosphazenes had a great influence on the flame retardancy. HPTCP has the best flame retardancy in PC/ABS, while MPTCP has the worst. The LOI of PC/ABS is 22.0%, no flame retarding class. When the loading of phenoxyphosphazenes was 15wt.% based on the total weight of composites,the LOI of the FR-PC/ABS with HPTCP could be up to 26.1% and the flame retarding class meet UL94V-0, the LOI of the FR-PC/ABS with HOPTCP could be up to 25.5% and the flame retarding class meet UL94V-1, while the LOI of FR-PC/ABS with MPTCP could be up to 22.7% and the flame retarding class only meet UL94V-2. In addition, compared with PC/ABS, HRR, THR, PHRR, MHRR and MEHC of the FR-PC/ABS reduced, and the mass reduced slowly, and the basic order of the above changes is HPTCP> HOPTCP> MPTCP.Thermal gravimetric analysis showed that the addition of phenoxyphosphazenes reduced the thermal stability of the material, but slightly for HPTCP and HOPTCP, while seriously for MPTCP.Phenoxyphosphazenes played flame retardancy by condensed phase. In the process of combustion, phenoxyphosphazenes could be pyrolyzed into phosphoric compounds such phosphoric acid, polyphosphoric acid, metaphosphoric acid and so on, which promoted the carbonization PC/ABS. The carbon becomes the intumescent layer under the foam action of CO2, N2, and NH3 from the decomposition of PC/ABS and phenoxyphosphazenes. The formed intumescent layer resulted in flame retardancy by the barrier effect on heat, air and decomposition products. OPTCP and other phosphazene in HPTCP make its carbonization poor, which reduced flame retardancy of HPTCP.