Magnesium hydroxide flame retardant material

With the continuous development and progress of economy, polymer materials are used more and more widely. In recent years, fire accidents caused by polymers have attracted great attention from all walks of life, and the research and development of flame retardant polymers has become a hot spot. At present, the organic flame retardants used in the market, such as large smoke and toxic smoke, are restricted by laws in Europe, the United States, Japan and China. Therefore, inorganic flame retardants have received great attention. The decomposition temperature of magnesium hydroxide flame retardant is high (340 ℃~450 ℃), the thermal decomposition products are MgO and H2O, which do not release any toxic and harmful substances, and have no harm to the environment and human health. Therefore, magnesium hydroxide flame retardant is one of the most concerned inorganic flame retardants at present, and has broad application prospects.
At present, magnesium hydroxide flame retardants produced in the market are basically of micron grade (d>5 μ m) , the particle size distribution is wide, which requires a lot of filling in the application; In addition, the prepared magnesium hydroxide product is easy to agglomerate, has strong hydrophobicity, and is incompatible with high polymer. In practical application, magnesium hydroxide has caused serious damage to the mechanical properties of polymer materials, greatly limiting the application of magnesium hydroxide flame retardant. It has become a research hotspot for current scientific and technological workers to obtain magnesium hydroxide flame retardant with low surface polarity, strong hydrophilicity, small particle size, narrow distribution, and good compatibility with polymer through certain physical and chemical methods.
On the one hand, the surface modification of magnesium hydroxide with organic functional groups can reduce the surface polarity of magnesium hydroxide and improve its compatibility with polymer; The micro - and nano - sized superfine magnesium hydroxide has low filling amount, and the composite prepared by using it has good performance. On the other hand, the flame retardancy of micro nano magnesium hydroxide with the same quality is several times higher than that of micro micro magnesium hydroxide, and has a low impact on the performance of polymer polymer materials. The micro nano magnesium hydroxide with low polarity can be uniformly dispersed in the polymer material, which makes the flame retardancy and mechanical properties of the whole material consistent. Therefore, the surface modification and superfine of magnesium hydroxide flame retardant can solve the shortcomings in the application of magnesium hydroxide flame retardant.
Scientific and technological workers at home and abroad have mainly carried out the following three aspects of work on the modification of magnesium hydroxide: (1) Research on the surface modification of magnesium hydroxide by organic compounds to reduce the surface polarity of magnesium hydroxide, reduce the hydrophobicity of magnesium hydroxide, and solve the problem of its incompatibility with high molecular polymers; (2) The research on modification and preparation of superfine magnesium hydroxide solves the shortcomings of easy agglomeration, poor dispersion and large filling amount of magnesium hydroxide; (3) Study on the formation mechanism of superfine magnesium hydroxide with additives.
Application requirements of magnesium hydroxide flame retardant materials
Magnesium hydroxide as a flame retardant has the following requirements:
(1) It must have extremely high purity (Mg (OH) 2>93%). High purity magnesium hydroxide not only has high flame retardancy, but also can reduce its addition in the material;
(2) The particle size is small, and the composite prepared by micro nano magnesium hydroxide is far superior to the micro magnesium hydroxide in all aspects of performance (including flame retardancy, smoke suppression and mechanical properties);
(3) The surface polarity is low. When the surface polarity of magnesium hydroxide decreases, the degree of agglomeration will decrease, and the dispersion and compatibility will increase. Only when it is added to the polymer as a flame retardant material can it have good compatibility with the polymer and reduce the impact on the mechanical properties of the material.
Reasons for Modification of Magnesium Hydroxide Flame Retardant Materials
At present, magnesium hydroxide produced in the market has a large particle size ratio, and some products have a particle size up to tens of microns. They are directly added as flame retardants, which has poor dispersion and has a great impact on the mechanical properties of materials. In industry, physical methods are usually used for grinding to reduce the particle size to several microns. The magnesium hydroxide prepared by physical methods has high surface polarity and is easy to agglomerate. As a flame retardant material, it is incompatible with the polymer matrix, which not only reduces its flame retardant performance, but also causes serious damage to the mechanical properties of the material. Compared with organic flame retardants, inorganic flame retardants have larger filling amount, which leads to the reduction of the efficiency of inorganic flame retardants. In order to achieve better flame retardancy of magnesium hydroxide flame retardant in practical application, a large number of magnesium hydroxide must be used in the polymer matrix, and a large amount of magnesium hydroxide will reduce the mechanical properties of the composite. By preparing industrial magnesium hydroxide into micro nano magnesium hydroxide with orderly microstructure, the amount of magnesium hydroxide added in the polymer matrix can be greatly reduced. The micro nano magnesium hydroxide material has many anion and cation vacancies exposed on its surface, strong polarity, high surface free energy, easy aggregation and poor dispersion. As a flame retardant material, it is difficult to be well compatible with the polymer matrix. The "free" sites or regions on the surface of materials can have different structures by using the functionality of specific compounds. At the same time, these regions are the attachment points of modified molecules and metal atoms, which are widely used in the material field. By using specific compounds to modify the surface of magnesium hydroxide, the shortcomings of high surface free energy, strong polarity and easy agglomeration can be solved. The modified magnesium hydroxide has excellent compatibility with the polymer matrix. Therefore, the surface modification and superfine preparation of magnesium hydroxide have received extensive attention from domestic and foreign scientific and technological workers.
As a flame retardant of high polymer, magnesium hydroxide is most important to be compatible with high polymer, achieve uniform dispersion, and finally achieve the purpose of flame retardant. The surface modification of magnesium hydroxide with specific compounds can reduce the surface polarity of magnesium hydroxide, make its surface hydrophobic, and improve the compatibility of magnesium hydroxide with polymers. Surface chemical modification of magnesium hydroxide is to use chemical methods to selectively adsorb or specifically adsorb or react with functional groups in organic molecules or inorganic gel molecules on the surface of magnesium hydroxide powder, so as to coat the particle surface, organicize the particle surface or change the polarity, and finally achieve surface modification. Common surface modifiers mainly include coupling agents silane coupling agents, titanate, aluminate coupling agents, higher fatty acids and their derivatives. The modification of magnesium hydroxide can also achieve other functions, such as changing the particle morphology of magnesium hydroxide and expanding its application range.