| With the gradual improvement of the global flame retardant laws, regulations and the industry standards, the traditional flame retardants show a technical bottleneck insurmountable to face the design of flame retardant agents and flame retardant polymer materials needs to consider their environmental stability and the latest requirements of sustainable development, and to solve the problem of that the use of flame retardants finds itself in a dilemma in reducing the incidence rate of fire and its negative impact on the ecological environment. The catalytic carbonization flame retardant technology has its advantage in solving the above problems and meeting the needs of development, has become one of the most active and development potential research direction in the field of flame retardancy. This technology plays out its flame retardant effect by using a small amount of catalytic carbonization agent to change the thermal degradation model of polymer, and to promote carbonization.In this thesis, three different solid acids boron phosphate(BP) containing Br?nsted and Lewis acid sites, and with controllable acidity and ceramic properties, had been prepared by calcining at high temperature using boric acid and phosphoric acid as precursors. BP was used as catalytic carbonization agent to incorporate into epoxy resins(EP). And its effects on the curing, thermal behavior, mechanical and flame retardant properties of EP were studied by various methods. In addition, its catalytic carbonization flame retardant mechanism on EP was also studied in detail by thermal degradation analysis in nitrogen and air.(1) Three different BP all were white solid nano-powders with high thermal stability,and their atomic mole ratios between boron and phosphorus were 1.27(BP1.25), 1.06(BP1)and 0.84(BP0.8) respectively. The sequence of acid strength and the amount of Br?nsted acid sites all were BP1.25 > BP0.8 > BP1, and that of the amount of Lewis acid sites was BP0.8 > BP1.25 > BP1. Moreover, the relative amounts between Br?nsted and Lewis acid sites were 1.27(BP1.25), 0.40(BP1) and 0.35(BP0.8) respectively.(2) Curing behavior study indicated that the comprehensive effect between the catalytic chain growth of BP and its steric hindrance effect resulted in the reduction ofcrosslinking density, which leading to the reduction of glass transition temperature and storage modulus.(3) Combustion property study showed that in comparison with pure EP, the EP/BP composites had a higher LOI value, and passed a V-1 rate in UL 94 vertical burning test(3.2 mm). Further more, the incorporation of BP into EP led to the reduction of the flame retardant parameters, such as heat release potential, peak of heat release rate, total heat release and the average specific extinction area, and so on. The dramatic expansion in the process of carbonization and the formation of a uniform, closed and complete carbonaceous protective coating with the honeycomb structure brought out the EP/BP composites to have a better anti flame penetration performance. Compared with the three different phosphorus containing flame retardants(DOPO, APP and Trimer), the prepared BP shown a better flame retardancy property. In addition, the acid strength and its distribution strongly affected the catalytic carbonization flame retardant efficiency of BP. The more acidic and the more Br?nsted acid sites of BP, the catalytic carbonization flame retardant efficiency was higher.(4) The thermal degradation behavior in nitrogen indicated that BP catalyzed the thermal degradation, dehydration and carbonization of EP at a lower temperature, and reduced the release of gaseous products, especially the low molecular weight flammable compounds such as acetone and hydrocarbons, and thus leading to the formation of the carbonaceous residues with higher carbon and nitrogen atomic concentration and graphitization degree. There was a relationship between the catalytic effect of BP and its acid strength and distribution. The more acidic and the more Br?nsted acid sites of BP, the effect of catalytic degradation and carbonization was even more pronounced.(5) Based on the thermal degradation results obtained in nitrogen, the catalytic thermal degradation and carbonization mechanism of BP on EP was proposed. Under heating,Br?nsted acid sites of the BP surface catalyzed dehydration of the secondary hydroxyl on the skeleton of EP and produced unsaturated structural units; Lewis acid sites of the BP surface catalyzed the dehydrogenation of the secondary carbon atoms to produce keton carbonyl; Subsequently, under the catalytic activity of Br?nsted and Lewis acid sites of BP,the aromatic thermal degradation compounds can couple or crosslink with another ring or unsaturated species by Friedel-Crafts chemistry to produce sticky carbonaceous residues.(6) The thermal oxidative degradation behavior in air demonstrated that BP was not only catalyzed the thermal degradation and carbonization process of EP, reduced the release of the low molecular weight flammable compounds and increased the yield of carbonaceous residues, but also improved the regularity of the turbostratic graphite carbon layers and enhanced the anti thermal oxidative properties of carbonaceous residues. The enhancement of anti thermal oxidative properties can attribute to the fact that the zig-zag sites of(101) crystal face on the edge of graphite like carbon crystal were poisoned to lose activity by BP using B—O—C and P—O—C bonds, and the arm-chair sites of(112)crystal face on the edge of graphite like carbon crystal were poisoned to lose activity by BP using P—C bonds.(7) Based on the obtained results in flame retardancy and thermal degradation behavior tests, a mode of catalytic carbonization flame retardant mechanism of EP/BP composites was proposed. Because of the catalytic effect of BP, the EP was thermal degraded and carbonized at a lower temperature to form an intumescent carbonaceous protective coating with the honeycomb structure and better insulation effect. Also, the graphitization degree and anti thermal oxidative properties of carbonaceous residues all were enhanced. In this way, the flame retardant property of EP was improved. |
PDF Full Text Request