Magnesium hydroxideBecause of the wide range of raw materials, good flame retardant performance, non-toxic, non-corrosive, etc., it is considered to be a kind of environmentally friendly green flame retardant with great development potential.

Magnesium hydroxide has a high decomposition energy, which is 140 ℃ higher than the thermal decomposition temperature of the commonly used inorganic flame retardant, which can make the polymer material withstand higher processing temperature, which is beneficial to accelerate the extrusion speed, shorten the molding time, and also help to improve the flame retardant efficiency.

The reason why magnesium hydroxide has flame retardant effect is closely related to its decomposition reaction at high temperature. When the ambient temperature reaches 340~490 ℃, Mg(OH)2 begins to decompose by heat, forming magnesium oxide and releasing crystalline H2O.

The decomposition reaction reaches its peak at 430 ℃, and the decomposition is completed at 490 ℃, leaving MgO. Crystalline H2O absorbs a large amount of heat, which will reduce the surface temperature of the material in the flame, and the released water vapor dilutes the oxygen on the surface, making combustion difficult, and has the effect of inhibiting combustible gas generated by polymer decomposition and cooling. In addition, magnesium oxide generated by decomposition is a good refractory material, forming a carbonized layer on the surface of the material, isolating the contact between combustible materials in the product and oxidation/high temperature environment, prevent the entry of oxygen and heat, so when the combustion source disappears, the fire is automatically extinguished, thus achieving the purpose of flame retardant.   

The polarity of magnesium hydroxide is very strong, the surface is positively charged, hydrophilic, and easy to reunite, and the compatibility of polymer materials is poor, so it is necessary to carry out surface treatment of magnesium hydroxide, commonly used methods include coupling agent method, anionic surfactant method, microencapsulation method and surface grafting method.

The ultrafine of magnesium hydroxide is to pulverize the magnesium hydroxide powder, adopt appropriate means to make the particle size as small as possible, even reach the nanometer level, increase the contact area between the flame retardant and the polymer matrix, enhance the affinity of magnesium hydroxide and the polymer, improve the compatibility between the two, and achieve the purpose of reducing the dosage and improving the flame retardant efficiency.

After magnesium hydroxide is ultra-fine, it has little wear on the equipment. It can be widely used in polypropylene, polyethylene, polyvinyl chloride, high impact polystyrene and ABS resin.

Based on the large specific surface area and strong adsorption force of magnesium hydroxide, it is reported in the literature that the specific surface area of solid powdered magnesium hydroxide is usually 10-14m 2/g, less than 20m 2/g, which is easy to adsorb and remove heavy metal ions such as Ni, Cd, Mn, Cr, etc., which are harmful to the environment, from various industrial waste liquids, so it is widely used to remove heavy metals in wastewater. It can be used alone or in combination with lime, bentonite, etc.