Overview of the research on the application of magnesium hydroxide flame retardant in the field

Overview of the research on the application of magnesium hydroxide flame retardant in the field of plastics
Plastic is a commonly used material in industrial production and daily life. Plastics are easy to burn and produce a lot 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 (MH) is an environmentally friendly green inorganic flame retardant with good flame retardancy, smoke suppression and filling effect, its decomposition temperature is high and does not produce toxic and harmful pollutants during decomposition, while MH can be used synergistically with other flame retardants to achieve higher flame retardancy.

01.Application of magnesium hydroxide flame retardant in PP
PP has low toxicity, low cost, good electrical insulation, good processability and chemical resistance, to meet the requirements of automobile, construction and other fields of application. However, PP is easy to burn, burns quickly, produces molten droplets during combustion, and releases a large amount of toxic fumes, so it is important to improve the heat-resistant properties of PP. Chen Lingzhi et al. prepared activated carbon modified MH flame retardant with magnesium sulfate, ammonia and activated carbon as raw materials and applied it to PP polymer. The results show that by applying the modified MH flame retardant to PP, the limiting oxygen index (LOI) of PP is increased from 19.6% to 28.9%, which significantly improves its flame retardant properties.

02.Application of magnesium hydroxide flame retardant in polystyrene (PS)
PS is characterized by low price, easy processing, anti-corrosion, strong impact resistance, good durability, etc. It is widely used in construction, decoration, electrical, transportation, etc. The low LOI value of PS is easy to burn, and it can continue to burn after leaving the ignition source, which releases a large amount of heat, toxic fumes, and produces serious melt droplets during the combustion process, which restricts its wide application. Researchers added MH to PS to study the change of its flame retardant effect. The results show that: with the increase of MH addition, the CO2 produced in the thermal degradation process of PS decreases, the amount of residual charcoal rises sharply, and the content of volatiles and semi-volatiles increases, indicating that the addition of MH changes the flame retardancy of PS, improves its combustion temperature, and alters its combustion mechanism.
03.Application of magnesium hydroxide flame retardant in PVC
PVC is also a common thermoplastic general-purpose plastic, widely used in films, pipes, wall panels and electrical materials (especially cable insulation skin) and other fields, which can be divided into hard PVC and soft PVC. hard PVC adds less plasticizer, its flame retardant performance is better than soft PVC, but PVC contains chlorine, the decomposition of combustion produces hydrogen chloride gas, and at the same time produces a large number of poisonous and harmful smoke, so in order to improve the flame retardancy of PVC, it is necessary to add MH to improve the flame retardancy of PVC, which means that MH will change the combustion temperature of PS and increase its combustion mechanism. Therefore, it is necessary to pay attention to the large amount of smoke generated when PVC burns while improving the flame retardancy of PVC.

MH flame retardants can be used in PVC composites to reduce the emission of toxic and harmful gases while improving the flame retardancy of PVC. Wu et al. used different modifiers to modify the surface of MH and investigated the effect of modified MH 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, the oil absorption value is 33.39%, the MH particles obtained are more uniformly dispersed, the agglomeration phenomenon is obviously improved, and the flame retardant ability of PVC is obviously improved, but the tensile strength of PVC is affected to some extent.
04. Application of magnesium hydroxide flame retardant in PE
PE has excellent processability, electrical insulation, mechanical properties and high and low temperature resistance, is widely used in construction, electrical, medical and other industries, but its LOI value is only about 17.4%, easy to burn, limiting its application. Improving the flame retardancy of PE is also a hot research topic. Commonly used flame retardants for PE are halogenated, phosphorus and nitrogen, and aluminum/magnesium inorganic flame retardants, etc. However, MH is favored because of its low cost and environmentally friendly features.
Tao Jun used three kinds of MH with different particle sizes as flame retardants, mixed with PE to make composites, and studied its mechanical properties, electrical properties, thermal stability and flame retardant properties. The results show that MH can significantly enhance the flame retardancy and thermal stability of PE, and the composite material has the best comprehensive performance when the particle size of MH is 3.1 μm, 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.
05.Challenges and prospects of magnesium hydroxide flame retardants
Although magnesium hydroxide, as a kind of green, flame retardant effect, low cost flame retardant material, can be widely used in the plastics industry, but due to the MH is an additive flame retardant, need to add a large number of in order to achieve a high flame retardant requirements; and MH has a strong polarity, hydrophilicity, not easy to be dispersed in the macromolecule, prone to agglomeration, which will lead to poor compatibility with the plastics, resulting in the production of composite plastic This will lead to poor compatibility with plastics, and the resulting composite plastics will have reduced strength, poor processability and fluidity, limiting its large-scale application in the plastics industry.
In the future, by strengthening the ultrafine MH, developing new surface modifiers, compounding with other flame retardants and microencapsulation technology, we can improve the compatibility with plastics while improving the flame retardancy of MH and reduce its impact on the mechanical properties of plastics, so as to expand the application of MH in the field of flame retardancy of plastics.

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