Preparation Of Hexagonal Magnesium Hydroxide Using Ammonia Process And Study Of Such Magnesium Hydroxide In EVA Compounds

MH has attracted extensive attention as a raw material for production of environment-friendly flame retardant that simultaneously acts as a smoke suppressant, with no evolution of hazardous substance. In this paper, the study of synthesizing magnesium hydroxide with ammonia gas was discussed. The key results are as follows:(1)Magnesium hydroxide of high concentration slurry was directly synthesized using bischofite and ammonia as the raw materials. This study showed that optimal process parameters were stirring speed of 350 r/min, ammonia to magnesium ratio of 2:1, ammonia addition rate of 320 m L/min, aging time of 90 min, reaction temperature of 60 ℃ and magnesium chloride concentration of 4.30 mol/L. The products were characterized by scanning electron microscope, X-ray diffraction and laser particle size analyzer. The magnesium hydroxide obtained using the optimal reaction conditions have D50 of 1.43 μm, D90 of 2.40 μm, purity of 99.60% and whiteness of 99.34. The reaction yield reached 69.41% with a magnesium hydroxide slurry content of 12.26%.(2)Magnesium hydroxide was synthesized using magnesium sulfate and ammonia as the raw materials. This study showed that optimal process parameters were stirring speed of 450 r/min, ammonia to magnesium ratio of 2.4:1, ammonia addition rate of 500 m L/min, aging time of 60 min, reaction temperature of 60 ℃ and magnesium sulfate concentration of 2.50 mol/L. The products were characterized by scanning electron microscope, X-ray diffraction and laser particle size analyzer. The magnesium hydroxide obtained using the optimal reaction conditions have D50 of 12.06 μm, D90 of 18.99 μm, purity of 96.75%. The reaction yield reached 68.02% with a magnesium hydroxide slurry content of 7.37%.(3)Regular hexagonal plates of magnesium hydroxide with high slurry concentration were prepared by hydrothermal modification of the synthesized MH slurry in the optimum processing conditions using bischofite and ammonia as raw materials. The effects of hydrothermal temperature, stirring speed, hydrothermal duration, and dilution multiple on the preparation of MH flame retardant were investigated. Scanning electron microscopy, X-ray diffraction, and laser particle analysis were performed to characterize the product morphologies, structures, and size distributions. Results indicated that the growth direction of MH crystal changed, and the regular hexagonal plates of MH with uniform particle size and high dispersion characteristic formed after hydrothermal modification treatment. A mass fraction of 15.50% MH of magnesium hydroxide slurry was obtained by high-concentration(4.30 mol/L) magnesium chloride and ammonia as the raw materials.(4) The magnesium hydroxide(MH) flame retardants made from ammonia under various hydrothermal conditions were studied by comparing mechanical properties of the EVA compounds containing such MH at 30 and 50%, respectively. Comparisons were made between these experimental MH and other commercial Chinese MH products and an Albemarle MH called H-5, in such aspects as tensile property, TGA thermogram and cross-section characteristics of fractured tensile bars. The results show that, compared to other four MH, the MH obtained by 160 ℃ hydrothermal treatment has low surface polarity, best dispersion and best compatibility with EVA. The MH/EVA composite materials are characterized by elevated initial decomposition temperature, thus difficult to be ignited. Such materials show finite resilience, thus able to withstand elevated forces. When fracture occurs, the fractured section of tensile bars show some distinct “wire extension”, thus resulting in increased mechanical property. It is concluded that the experimental MH prepare.