| Colemanite (2CaO·3B2O3·5H2O) is a kind of calcium borate mineral, which is mainly used in the manufacture of boric acid in industry. High whiteness, high quality, low arsenic colemanite can be used to make alkali-free fiberglass, heat resistant and flame retardant materials. Based on our previous work:First, colemanite with a high iron content and a lower whiteness was bleached by a chemical method; Next, modification and coupling agents were selected to modify colemanite powder, which can improve the affinity and compatibility between the mineral filler and organic polymer; Finally, composite flame retardant was obtained by means of grafting amine-polyphosphate onto the surface of colemanite using PPA and laurylamine as raw materials in order to improve the flame retardant performance and reduce the adding amount of inorganic powders. The research results are as follows:(1) Colemanite was bleached by using oxalic acid and citric acid as extraction solvents, and the bleached product was characterized by whiteness meter and XRD analysis. The optimized bleaching process conditions were:the concentration of oxalic acid is0.4mol/L, extraction temperature is75℃, extraction time is90min, pulp density is600g/L. Under these conditions, the whiteness of the bleached product rose from49.5%to59.5%, which was increased by10%.(2) Based on our previous work, for improving the compatibility of colemanite with the polymer, titanate coupling agent and silane coupling agent were selected as modifiers to modify colemanite powder. The modified product was characterized by XRD. FT-IR, suspension performance and activation index test. The activation indexes are98.86%and98.02%with1%addition of the titanate or silane coupling agents, respectively.The modified colemanite/EVA composites were prepared and the effects of coupling agent addition and inorganic powder addition on the mechanical properties and flame retardancy of EVA composites were investigated. The EVA composites were characterized by mechanics performance testing, oxygen index, TG-DTG and SEM. The EVA composites doped with40%of modified colemanite (1%NDZ-311or1%KH-570coupling agents) exhibit average tensile strengths of9.80MPa and8.65MPa, average breaking elongations of696.5%and697.22%, and limit oxygen indexes of29.6%and30.5%. respectively. TG-DTG results show that composites matrix residual rate can increase to30%, maximum weight loss rate is reduced by introducing modified colemanite. Colemanite can replace zinc borate by comparing with the mechanical properties and flame retardancy of zinc borate composites.(3) For further improving flame retardancy, organic-inorganic composite was obtained by the reaction of polyphosphoric acid with lauryl amine on colemanite surface, which made ammonium polyphosphate coat on colemanite and the product was characteried by XRD, FT-IR, suspension performance, and activation index test. Composite product’s activation index was more than80%and was coated with ammonium polyphosphate. Then the composite flame retardant/EVA composite was prepared and the effects of ammonium polyphosphate addition and inorganic powder addition on the mechanical properties and flame retardancy of EVA composites were investigated, respectively. Using SEM, FT-IR, XRD, the oxygen index test and tensile strength test method, we can conclude that the composite with40%(3%of ammonium polyphosphate) addition of organic-inorganic flame retardant exhibits a tensile strength of8.57MPa, the average breaking elongation of671.3%, limiting oxygen index of up to32.6%. The addition of organic-inorganic flame retardant improved flame retardant properties of the composite and reduced the addition amount of inorganic powder by doping with ammonium polyphosphate. |
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