The hydrothermal treatment of magnesium hydroxide is a method in which water is used as a solvent to carry out a chemical reaction between a boiling point of water and a supercritical temperature at a constant pressure and time. In the high temperature and high pressure aqueous solution, the increase of molecular motion will lead to an increase in the reaction rate, increase the solubility of the magnesium hydroxide solid synthesized under normal temperature conditions, and achieve some reactions that are difficult to carry out at normal temperature and pressure.
The size, morphology, nucleation, growth rate, etc. of the magnesium hydroxide particles are controlled by controlling the pressure and temperature of the hydrothermal reaction. The higher the temperature, the faster the diffusion rate of ions, the dissolution of small crystals, the acceleration of ions in the process of migration to large crystals, the faster growth of crystals, and the formation of crystalline products with large particle size and low water content. . At the same time, the specific surface area and pressure of magnesium hydroxide have a great relationship. The greater the pressure, the smaller the specific surface area of the magnesium hydroxide. Therefore, under certain pressure and temperature conditions, a suitable specific surface area can be obtained.
Although it is still in its infancy in the development of crystalline flame retardant magnesium hydroxide, it can be found by scanning electron microscopy that the particles of magnesium hydroxide after hydrothermal reaction show a regular sheet and the average particle size increases. It has good dispersibility and can be used as a flame retardant additive for organic polymers.
Due to the increasing application of high molecular polymer materials, the requirements for flame retardant properties of flame retardant materials are also increasing. Because inorganic flame retardant magnesium hydroxide has multiple flame retardant, non-toxic, low smoke and other characteristics, it is receiving more and more attention. However, magnesium hydroxide synthesized under normal temperature and normal pressure conditions generally exhibits irregular structure, large specific surface area, wide particle size distribution, and strong agglomeration between particles, which not only limits the polymerization of magnesium hydroxide in the polymer. Dispersion in the material, and compatibility is not ideal, and is not suitable as a flame retardant material.
Secondly, magnesium hydroxide can be used as a flame retardant material after being modified by a surface modifier. After the modification of the magnesium hydroxide, a flame retardant magnesium hydroxide flame retardant additive having a small specific surface area, a large average particle diameter, a regular sheet structure, and good dispersibility and compatibility can be obtained.