Methods to improve the performance of magnesium hydroxide flame retardant
Magnesium hydroxide is currently the most researched and fastest-growing green flame retardant. It does not produce secondary pollution, has good thermal stability, does not volatilize, does not precipitate, does not produce toxic gases, does not corrode processing equipment, and has significant smoke elimination effects. It has many advantages such as strong and efficient substrate carbonization, and is rich in magnesium ore resources. However, magnesium hydroxide prepared by conventional methods has strong polarity and hydrophilicity. The crystal grains tend to agglomerate twice, have poor dispersion, and have extremely poor compatibility with non-polar polymer materials, making it difficult to form an interface. Good bonding and adhesion, so as the magnesium hydroxide content in polymer materials increases, its processing performance and mechanical properties also decrease sharply, so that its application is limited. In order to make magnesium hydroxide better used for flame retardant polymer materials, there are mainly the following methods:
(1) Ultra-fine particle size. At the processing temperature of polymer materials, magnesium hydroxide exists in the form of granules in the system. Generally speaking, when the filling amount is the same, the finer the granularity of magnesium hydroxide, the more uniform its dispersion, and the more obvious the flame retardant effect. , the smaller the negative impact on the physical and mechanical properties of the material, and it may even have the effect of plasticizing and reinforcing rigid particles.
(2) Change the crystal structure of magnesium hydroxide to prepare a special morphology (hexagonal flake). Usually, magnesium hydroxide mixed at room temperature is subjected to hydrothermal modification. In a specific high-temperature and high-pressure aqueous solution, magnesium hydroxide undergoes crystallization and reorganization, and the structure and morphology of the crystal are changed through the process of dissolution-recondensation-crystallization growth. Hexagonal flaky magnesium hydroxide has low surface polarity and surface energy, and has good miscibility with polymer materials. It has unique advantages as a flame retardant. In addition, hexagonal plate-shaped magnesium hydroxide is easy to be mixed with resin and has reinforcing properties, so it has good mixing and processing properties.
(3) Surface modification treatment of magnesium hydroxide. Magnesium hydroxide is a highly polar inorganic compound that is hydrophilic. Even if the magnesium hydroxide is very dry, there is still a non-negligible amount of moisture in the crystal. Therefore, magnesium hydroxide is very difficult to mix with polymer materials. It is easy to agglomerate and has poor compatibility with polymer materials, making the surface of the matrix defective, rough and dull. After modification by magnesium hydroxide, the surface polarity of the crystal grains is eliminated, which improves the dispersion, compatibility and affinity in polymer materials, has better flame retardant properties, and also acts as a reinforcing agent. Function, improve the mechanical strength of polymer materials.
(4) Develop a composite flame retardant of magnesium hydroxide. Choose other flame retardants to compound with magnesium hydroxide to take advantage of the flame retardant synergy to effectively improve the flame retardant performance. In flame retardant technology, the synergistic effect can not only produce more effective flame retardant systems, but also make it possible to reduce the use of chemical reagents in other flame retardants and improve the flame retardant efficiency of flame retardants.
