Adding nonmetal compounds into polymer materials as fillers and flame retardant materials can not only reduce the production cost, but also reduce the combustion performance of polymer materials, killing two birds with one stone.

　　Magnesium hydroxide, as an inorganic flame retardant filler, has the characteristics of non-toxic, smokeless, halogen-free, non-corrosive, and good thermal stability.

　　Because of its safety and environmental protection characteristics, magnesium hydroxide is widely used in plastics, cables, rubber and other industries.

　　Preparation of magnesium hydroxide

　　There are two production methods of magnesium hydroxide flame retardant: one is through chemical synthesis, that is, through the use of magnesium chloride containing brine, halogen ore and other raw materials and caustic alkali in the water medium reaction, the generated magnesium hydroxide after filtration, washing, drying can be obtained;

　　The other is by grinding the natural mineral brucite to the required size.

　　Because the brucite contains a small amount of insoluble impurities such as sediment, the preparation of magnesium hydroxide must be carried out before the impurity removal pretreatment.

　　The method is to add hydrochlorite to a certain amount of deionized water, stir and dissolve it into saturated magnesium chloride solution at low temperature, and then remove suspended impurities by filtration.

　　Secondly, the preparation of magnesium hydroxide from fumei solid waste is a new way of environmental protection and economy.

　　Flame retardant principle of magnesium hydroxide

　　Under high temperature conditions, magnesium hydroxide is decomposed into magnesium oxide and water by heat, and the reaction equation is: Mg(OH)2→ (heating) →MgO+H20 is similar to aluminum hydroxide. Magnesium hydroxide flame retardant has a flame retardant effect by chemical decomposition and release of water when heated.

　　Therefore, it has the advantages of non-toxicity, low smoke and no secondary pollution, and the chemical properties of magnesium oxide formed by decomposition are stable.

　　Modification of magnesium hydroxide

　　Compared with halogenated organic flame retardants, it is usually necessary to fill more than 50% to achieve a comparable flame retardancy effect.

　　Due to the fact that magnesium hydroxide is an inorganic material, the compatibility between the surface and the polymer substrate is poor. Such a high filling amount, if the surface modification of magnesium hydroxide is not carried out, the mechanical properties of the composite will be reduced after it is filled into the polymer material.

　　Experiments show that the unmodified magnesium hydroxide exists in polymer materials in the form of most aggregates. Although the powder is very fine, there is a clear boundary and even a void between the aggregates and the matrix due to the incompatibility between the particle surface and the matrix.

　　Therefore, surface modification of magnesium hydroxide must be carried out to improve the compatibility with the polymer substrate, ensure the mechanical properties of the filling material, and even improve part of the mechanical properties of the material.

　　The modification technology of magnesium hydroxide can be divided into two types.

　　One is modified in the process of preparing magnesium hydroxide.

　　The daily modification of magnesium hydroxide can be divided into wet and dry processes.

　　The wet process has a good modification effect, but there are problems such as high cost and loss of modifier.

　　The cost of dry modification is low, but the modification effect is not satisfactory.

　　Titanate coupling agent, silane coupling agent, advanced fatty acid and its metal salt are the common modifiers of magnesium hydroxide.

　　At present, the amount of aluminum hydroxide in China is relatively large, but with the increase of polymer processing temperature, the easily decomposed aluminum hydroxide will reduce the flame retardant effect.

　　In comparison, magnesium hydroxide has the following advantages: the decomposition temperature of magnesium hydroxide reached 340℃, 100℃ higher than aluminum hydroxide, is conducive to improve the processing temperature of plastics, speed up the extrusion speed, improve the plasticizing effect, shorten the molding time, and the product surface gloss is high, will not produce surface defects.

　　At the same time, magnesium hydroxide can guarantee a high peel strength.

　　In addition, China is rich in magnesium minerals and fumei waste resources, so the application prospect of magnesium hydroxide flame retardant filler is very broad.