Magnesium hydroxide is not only a flame retardant.

Nowadays, with the rapid development of polymer synthesis technology, plastics, rubber, synthetic fibers and other materials are widely used in daily life. However, all high-molecular polymers have defects. Because they are composed of carbon and hydrogen atom chains, the compounds are flammable, which will lead to the rapid spread of fire. When a certain amount of flame retardant is added to the material, the flame retardant performance of the material will be improved correspondingly, but it will often affect the mechanical properties or other properties of the material, and sometimes bring inconvenience to processing. Therefore, in order to maintain the comprehensive properties of flame retardant composites, the comprehensive properties of flame retardants should be considered. Magnesium hydroxide, as a flame retardant material, has many advantages: (1) the decomposition temperature of magnesium hydroxide is high, and the ignition point is higher than that of aluminum hydroxide, so that the heating temperature of polymer materials is increased; (2) MgO produced after combustion and dehydration is a kind of refractory and an alkaline oxide, which can absorb acid gas; (3) strong heat absorption capacity and high flame retardant efficiency; (4) Low cost and easy processing in different polymer materials. In recent years, magnesium hydroxide, as a kind of green flame retardant, has been widely used. Preparation of magnesium hydroxide Two aspects that need to be controlled most in the preparation of magnesium hydroxide: (1) filtration performance. If the sedimentation performance of magnesium hydroxide slurry is poor, it will affect the washing and separation operation process, lead to the extension of magnesium hydroxide synthesis cycle, and affect the output of magnesium hydroxide; (2) Control the morphology, because the flame retardant effect of magnesium hydroxide with regular morphology is better, it is necessary to adopt appropriate production methods and technological conditions to meet the requirements. The main production processes of magnesium hydroxide include direct precipitation, grinding of magnesium-containing ore, hydration of magnesium oxide, etc. Direct precipitation method At present, there are many methods to synthesize magnesium hydroxide, among which precipitation is the most commonly used method. Because of its low price, simple operation and easy control of crystal morphology. In the precipitation method, salt solution is mainly used for precipitation, and strong alkali, such as ammonia water or sodium hydroxide, is usually used. Magnesium chloride, magnesium sulfate and magnesium nitrate are the most widely used magnesium salts, and magnesium acetate, an organic magnesium salt, is also occasionally used. The preparation of magnesium hydroxide by ammonia method in direct precipitation method is divided into one-step method and continuous precipitation method. The continuous precipitation method realizes the recycling of resources, reduces the production cost and ensures the product quality. Hydrothermal method Hydrothermal reaction can effectively control the morphology and size of magnesium hydroxide, and the properties of the product mainly depend on the type of precursor magnesium salt, the control of solvent and reaction temperature. The morphology of the product mainly depends on the pH of the solution and the reaction temperature. By adjusting the pH value, the morphology of magnesium hydroxide is nano-flower, needle, flake and sphere. The advantage of hydrothermal synthesis is that magnesium hydroxide with specific surface area greater than 100m2/g can be obtained. The disadvantage is that high temperature and high pressure are used in industry, and the cost is high. Acoustic chemical synthesis method The sonochemical method is to use ultrasonic waves with frequency ranging from 20kHz-10MHz to induce the formation and collapse of microcells, and generate active sites at high temperature and high pressure. Compared with the traditional method, this method takes place under the limit condition, which can greatly increase the reaction rate and generate small crystals with more uniform morphology. The characteristic of acoustic synthesis is that materials with different structures can be produced by changing the reaction medium. Sol-gel method Sol-gel method uses high-activity metal compounds as precursors, which are mixed in liquid phase, hydrolyzed and condensed to produce metal hydroxide. A stable transparent sol is formed, which slowly polymerizes after aging to form a network structure, and the solvent is lost in the reaction process to form a gel. The gel is dried and sintered to prepare nano-materials. The reaction process of this method is dispersion and dissolution of precursor, hydrolysis to generate monomer, polymerization to generate sol, drying and heat treatment to prepare nanometer magnesium hydroxide material. Use of magnesium hydroxide Magnesium hydroxide has a wide range of uses, and the flame retardant and environmental protection fields are the main application fields of magnesium hydroxide. In addition, because magnesium hydroxide slurry has high activity, good adsorption performance, convenient and controllable adjustment, magnesium hydroxide can also be used as a neutralizer to treat acidic waste liquid and sulfur-rich oxides, remove heavy metals and improve the acidity of soil, and can also be used as an antacid in pharmacy, fertilizer additives, etc. Application of flame retardant Magnesium hydroxide is an important halogen-free environment-friendly flame retardant. Its flame-retardant mechanism is to generate stable coating magnesium oxide and water vapor, so its flame-retardant efficiency is low. To achieve good flame-retardant effect, the addition amount of magnesium hydroxide is generally as high as 50%~60%. At this time, the mechanical properties and processability of flame-retardant composites are seriously reduced, and the usual methods are surface modification of magnesium hydroxide and synergistic flame retardant of magnesium hydroxide. Magnesium hydroxide flame retardant can be used not only alone, but also in combination with other synergistic agents, such as magnesium hydroxide/red phosphorus, magnesium hydroxide/zinc borate, magnesium hydroxide/carbon nanotubes and magnesium hydroxide/carbon black. Synergistic flame retardant of magnesium hydroxide can not only obtain better flame retardant effect, but also reduce the amount of flame retardant, thus reducing the cost. Application in the field of environmental protection (1) Treatment of acid-containing wastewater The neutralization reaction speed of magnesium hydroxide is slow, and the particles produced after the neutralization reaction have larger particle size and settle quickly. Magnesium hydroxide can simplify the operation procedures, reduce the operation time, have good controllability and reduce the treatment cost in the treatment of acid-containing wastewater. (2) heavy metal removal Due to its large specific surface area and strong adsorption capacity, magnesium hydroxide particles can remove heavy metal ions such as Ni2+, Cd2+ and Mn2+ which are harmful to the environment from industrial wastewater. Other heavy metal elements such as Mo, Co, Fe, W and V can also be removed by magnesium hydroxide, light burned magnesium oxide or aluminum magnesium carbonate. (3) flue gas desulfurization At present, there are nearly 20 kinds of mature desulfurization technologies, among which magnesium hydroxide desulfurization technology is economical and practical, and has a good development prospect in the future. The technological advantages of magnesium hydroxide desulfurization mainly include high desulfurization efficiency, low investment cost, low operation cost, high comprehensive benefit, reliable operation and no secondary pollution. tag Magnesium hydroxide, as a flame retardant, has excellent properties in various aspects, and its application scope will be more and more extensive. And magnesium hydroxide has the advantage of low price, which saves the cost for factory production. The preparation of magnesium hydroxide by lightly burning magnesium powder can improve the added value of products, realize the effective utilization of resources and effectively enhance the competitiveness of enterprises in the market economy.