Magnesium Hydroxide – A Green Inorganic Flame Retardant

Magnesium hydroxide is a flame-retardant filler. When decomposed by heat, it releases bonded water and absorbs a large amount of latent heat to reduce the surface temperature of the synthetic material. It has the property of inhibiting the decomposition of the polymer and cooling the combustible gases generated.

Magnesium hydroxide is recognized as an excellent flame retardant with the triple function of flame retardant, smoke suppression, and filling in the rubber and plastic industry. It is widely used in rubber, chemical, building materials, plastics, electronics, unsaturated polyester, paints and coatings, and other polymer materials. It especially has excellent flame retardant and smoke suppressing effect on mining duct coating cloth, PVC whole-core transportation belt, flame retardant aluminum plastic board, flame retardant tarp, PVC wire and cable material, mining cable sheath, cable accessories, etc.

Principle of Flame Retardant

Magnesium hydroxide decomposes when heated (340-490 degrees) to absorb heat from the surface of the combustion material. It also releases a large amount of water to dilute the oxygen on the surface of the combustible material. The generated active magnesium oxide attached to the surface of combustible materials further prevents the burning. Magnesium hydroxide in the flame retardant process does not produce any harmful substances, and its decomposition products can also absorb a large number of harmful gases and smoke generated in burning. Activated magnesium oxide constantly absorbs the molten residue of incomplete combustion, eliminating the smoke and molten drops, so that the combustion will soon stop.

Magnesium Hydroxide Flame Retardant 1

Types of Flame Retardants

According to chemical composition, flame retardants can be divided into organic flame retardants and inorganic flame retardants. Organic flame retardants are divided into two systems – phosphorus and halogen. As organic flame retardants generate toxic decomposition products and smoke, they are gradually replaced by inorganic flame retardants.

Inorganic flame retardants mainly include magnesium hydroxide, aluminum hydroxide, red phosphorus, antimony oxide, tin oxide, molybdenum oxide, ammonium molybdate, zinc borate, etc. Among them, magnesium hydroxide and aluminum hydroxide decompose and absorb heat and produce H2O to isolate the air. Its decomposition of the oxide are high-temperature resistant substance. These two flame retardants not only can be flame retardant but also filler, with features such as no corrosive halogen and harmful gases, non-volatile, long-lasting effect, non-toxic, smokeless, and non-drip.

Advantages of Magnesium Hydroxide

At present, aluminum hydroxide is used more frequently than magnesium hydroxide. With the increase of polymer processing temperature, however, aluminum hydroxide is easy to decompose and reduces the flame retardant effect. Compared with aluminum hydroxide, magnesium hydroxide has the following advantages:

  1. The thermal decomposition temperature of magnesium hydroxide reaches 340℃, which is 100℃ higher than aluminum hydroxide. This is conducive to the increase of plastic processing temperature and can speed up the extrusion speed, improve the plasticizing effect and shorten the molding time. The surface gloss of the products is high and no surface defects will be produced. At the same time, it can ensure a super strong peel strength.
  2. It has uniform particle size distribution, good compatibility with the substrate, and has a small impact on the mechanical properties of the product.
  3. The magnesium oxide generated by magnesium hydroxide burning and dehydration is a high-strength, high-heat-resistant material that can be used as a protective layer to isolate fire and harmful gases. Magnesium hydroxide has a strong ability to neutralize with acid.  It can quickly neutralize acidic gases produced in the burning process like SO2, NOx, CO2, etc.
  4. Magnesium hydroxide has a strong decomposition ability, high efficiency of flame retardant, strong smoke suppression ability, and small friction on the equipment.
  5. It has lower price, large filling capacity, and can greatly reduce the cost.

    Magnesium Hydroxide Flame Retardant 2

Surface Modifying of Magnesium Hydroxide

Magnesium hydroxide is an ideal inorganic flame retardant filler that has a good application prospect for polymer-based composite. However, to achieve the flame retardant effect close to halogen-containing organic flame retardants, the filling amount should generally reach more than 50%. As magnesium hydroxide is inorganic, its surface is less compatible with the polymer matrix. Filing into the composite material, it may affect its mechanical properties without surface modification treatment. Therefore, magnesium hydroxide must be surface-modified to improve its compatibility with the polymer matrix, and even to improve some of the mechanical properties of the material.

Experimentally, it is proved that unmodified magnesium hydroxide exists as agglomerates in PP. Although the powder itself is extremely small, there are obvious boundaries and even voids between the particle agglomerates and the PP matrix due to the incompatibility between the particle surface and the PP matrix. The formation of cavities after the escape of magnesium hydroxide particles during brittle breakage indicates that the unmodified magnesium hydroxide only plays the role of filling and flame retardant in PP without chemical bonding with PP. Surface-modified magnesium hydroxide disperses more uniformly in PP, and its particles disperse in the material mostly in the form of original grade particles or small agglomerated particles.

Hoyonn Magnesium Hydroxide Filler

Hoyonn Magnesium Hydroxide is processed from natural brucite powder. It is an ideal flame retardant filler for engineering plastics, epoxy resin, rubber, wire and cable, mining cable filler, etc. We have three types of different purities and particle sizes. Learn more about the product or contact us for any problem.

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