The Preparation Of Superfine Magnesium Hydroxide By High-gravity Method Of Rotating Bed With Helix Channels

With the tightening of the current regulations,and the increase in the general a wareness about the risks related to materials flammability,because Organic flame retardants are harmful to the human body and the environment. So the inorganic flameretardants green and environmentally friendly are gradually popular. In the flame retardant market Ordinary Mg(OH)₂ with larger particle size,so high filler contents are required to obtain satisfactory fire properties.However,this high mineral loading resuits in a decrease of the mechanical performance of the materials.while the superfine Mg(OH)₂ added to the polymer,not only can reduce the amount of Mg(OH)₂ can also increase the rigidity of polymer.Traditional use of the inorganic flame retardant is aluminum hydroxide.Magnesium hydroxide in the thermally stable,suppressingfumes and neutralization ability are better than aluminum hydroxide(Al(OH)₃).as well as the advantage to replace traditional Al(OH)₃.So superfine Mg(OH)₂ become the trend. Therefore research and development of ultra-fine or nano magnesium hydroxide preparation technology is of great significance,also an urgent need.To prepared superfine Mg(OH)₂ by precipitation which with narrow particle size distribution and controlled shape,mixing process play an important role.Under ultragravity enviroment, the molecule diffuse and mass transfer is more quickly than normal gravity enviroment.which can generate an acceleration 1～3 orders of magnitude larger than the gravitational acceleration on the earth,and the improvement of throughout and the reinforce of process of microcosmic mixing and material transmission.The lamellar shaped and superfine Mg(OH)₂ was prepared using ammonia magnesium-decoposition in Rotating Bed With Helix Channels(RBHC).Several parameters were investigated such as addition method,the speed of RBHC,the plow,the influence of NH₃/Mg²⁺ molal ratio on yield and morphological strucrure.The optimizing condition is reversed precipitation,speed of 1000r/min,flow of 300m³/h and NH₃/Mg²⁺molal ratio was 6.Through the RBHC high gravity precipitation method with a combination of water treatment technology line,the superfine Mg(OH)₂ precipitate in RBHC high-gravity reactor,and the recrystallized is carried out by hydrothermal treatment. The sam ples is hexagonal plate with clear crystal boundaries and morphology rules.When theammonia concentration of 2mol/L and the hydrothermal treatment of 2h at 150℃. The ratio of raw materials and the reaction temperature unchanged, Compared with a particle size of Mg(OH)₂ of 1～100μm for 4h in three-necked flask,the Mg(OH)₂ preparedin RBHC is with a particle size of Mg(OH)₂ of 0～1μm for 0.5h. The resultsshow that the RBHC intensifys the mass transfer process,greatly reducing the micro-mixing time.Nucleation is controlled in the uniform micro-environment so the Mg(OH)₂ with narrow particle size distribution and controlled shape is prepared.In this paper ,on the study of the level and the kind of coating reagents appliesto magnesium hydroxide.prepared by RBHC.The experimental results showed thatthe toughness of the compositematerials and the dispersion of inorganic fillers reached the best when the level of stearic acid was 1%.And the mechanical propertiesshowed better.when amount of magnesium hydroxide of 20% polypropylene.The prepared product was characterized by scanning electron microscpoe(SEM), Laser granularity X-ray diffraction(XRD)and thermogravimetric analysis-differential scanningcalorimetry(TGA/DSC),Infra-red spectrum(IR),particle size distribution(PSD).