Properties of magnesium hydroxide flame retardants

Plastics are commonly used materials in industrial production and daily life. Plastics are easy to burn and produce a large amount of toxic and harmful substances and smoke when burning. Effectively improving the flame retardancy of plastics is a problem that needs to be solved in practical applications. Magnesium hydroxide is an environmentally friendly green inorganic flame retardant with good flame retardant, smoke suppression and filling effects. It has a high decomposition temperature and does not produce toxic and harmful pollutants when decomposed. At the same time, magnesium hydroxide can be used in conjunction with other flame retardants to achieve a higher flame retardant effect.

When magnesium hydroxide is heated (340-490 degrees), it decomposes and absorbs the heat on the surface of the combustible material to achieve a flame retardant effect; at the same time, it releases a large amount of water to dilute the oxygen on the surface of the combustible material, and the active magnesium oxide generated by decomposition adheres to the surface of the combustible material and further prevents it. progress of burning. Magnesium hydroxide not only does not produce any harmful substances during the entire flame retardant process, but its decomposition products are also flame retardant and can absorb a large amount of harmful gases and smoke generated by the burning of rubber, plastics and other polymers. Active magnesium oxide continuously absorbs The melted residue of incomplete combustion can quickly stop combustion while eliminating smoke and preventing droplets. It is an emerging environmentally friendly inorganic flame retardant.

magnesium hydroxide flame retardant

Application of magnesium hydroxide flame retardant in PP

PP has low toxicity, low cost, good electrical insulation, good processability and chemical corrosion resistance, which meets the application requirements of automobiles, construction and other fields. However, PP is easy to burn, burns quickly, produces molten droplets during combustion, and releases a large amount of toxic smoke. Therefore, it is important to improve the heat resistance of PP. Chen Lingzhi et al. prepared activated carbon modified magnesium hydroxide flame retardant using magnesium sulfate, ammonia water and activated carbon as raw materials, and applied it to PP polymer. The results show that the application of modified magnesium hydroxide flame retardant to PP increases the limiting oxygen index (LOI) of PP from 19.6% to 28.9%, significantly improving its flame retardant properties.

Application of magnesium hydroxide flame retardant in polystyrene (PS)

PS has the characteristics of low price, easy processing, corrosion resistance, strong impact resistance and good durability, and is widely used in construction, decoration, electrical, transportation and other industries. PS has a low LOI value, is easy to burn, and can continue to burn after leaving the fire source. During the combustion process, it releases a lot of heat and toxic smoke, and produces serious molten droplets, which limits its wide application. The researchers added magnesium hydroxide to PS to study the changes in its flame retardant effect. The results show that with the increase in the amount of MH added, the CO2 generated during the thermal degradation of PS continues to decrease, the amount of residual carbon increases sharply, and the content of volatiles and semi-volatiles increases, indicating that the addition of magnesium hydroxide changes the flame retardancy of PS, increases its combustion temperature, and changes its combustion mechanism.

Application of magnesium hydroxide flame retardant in PVC

PVC is also a common thermoplastic general-purpose plastic, widely used in films, pipes, wallboards and electrical materials (especially cable insulation sheaths) and other fields, and can be divided into hard PVC and soft PVC. Hard PVC has a smaller amount of plasticizer added, and its flame retardant performance is better than soft PVC. However, PVC contains chlorine, which produces hydrogen chloride gas when it burns and decomposes, and also produces a large amount of toxic and harmful smoke. Therefore, while improving the flame retardancy of PVC, it is also necessary to pay attention to the large amount of smoke produced when PVC burns.

Magnesium hydroxide flame retardant can reduce the emission of toxic and harmful gases while improving the flame retardancy of PVC, and can be used in PVC composite materials. Wu Jianning et al. used different modifiers to modify the surface of MH, and studied the effect of modified magnesium hydroxide on the mechanical properties and flame retardant ability of PVC. The results show that the modification effect of zinc stearate as the modifier is the best, with an oil absorption value of 33.39%. The magnesium hydroxide particles obtained are more evenly dispersed, the agglomeration phenomenon is significantly improved, and the flame retardant ability of PVC is significantly improved, but the tensile strength of PVC has a certain impact.

Application of magnesium hydroxide flame retardant in PE

PE has excellent processability, electrical insulation, mechanical properties and high and low temperature resistance, and is widely used in construction, electrical, medical and other industries, but its LOI value is only about 17.4%, which is easy to burn, limiting its application range. Improving the flame retardancy of PE is also a hot topic of research. Common flame retardants for PE include halogen, phosphorus nitrogen, aluminum/magnesium inorganic flame retardants, etc., but magnesium hydroxide is favored for its low cost and environmental friendliness.

Tao Jun used three different particle sizes of magnesium hydroxide as flame retardants, mixed them with PE to make composite materials, and studied their mechanical properties, electrical properties, thermal stability and flame retardant properties. The results show that magnesium hydroxide can significantly improve the flame retardancy and thermal stability of PE. When the particle size of magnesium hydroxide is 3.1μm, the comprehensive performance of the composite material is the best, with a tensile strength of 16.1 MPa, an elongation at break of 400%, a LOI value of 22.3%, a peak heat release rate (PHRR) of 270 kW/m2, and a volume resistivity of 5.2×1013Ω·m.

Challenges and prospects of magnesium hydroxide flame retardants

Although magnesium hydroxide can be widely used in the plastics industry as a green, environmentally friendly, flame retardant material with excellent flame retardant effect and low cost, it is an additive flame retardant and needs to be added in large quantities to achieve higher flame retardant requirements; and magnesium hydroxide has strong polarity and strong hydrophilicity, is not easy to disperse in polymers, and is easy to agglomerate, which will lead to poor compatibility with plastics, reduced strength of the obtained composite plastics, poor processability and fluidity, and limit its large-scale application in the plastics industry.

In the future, we can strengthen the ultrafineness of magnesium hydroxide, develop new surface modifiers, compound with other flame retardants and conduct research on microencapsulation technology. While improving the flame retardancy of magnesium hydroxide, we can also improve its compatibility with plastics and reduce its impact on the mechanical properties of plastics, thereby expanding the application of magnesium hydroxide in the field of plastic flame retardancy.

Flame Retardant Magnesium Hydroxide
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