Magnesium hydroxide has the characteristics of flame retardant, smoke abatement, drip resistance, safety, etc. It has good thermal stability, decomposition temperature as high as 340~490 ℃, small particle size, which is able to meet the mixing and processing molding of many plastics, and it is a kind of environmentally friendly and green flame retardant emerging in recent years.
Nano magnesium hydroxide is in thermodynamic instability due to small particle size and high surface energy, and it is easy to produce aggregation and agglomeration in the process of preparation and application. At the same time, the surface of magnesium hydroxide is hydrophilic and oleophobic, while the polymer material matrix shows lipophilic and hydrophobic, the two are incompatible with each other, which will result in poor dispersion of magnesium hydroxide in the material. The uneven dispersion will lead to premature combustion in the region of small magnesium hydroxide loading, reducing the efficiency of flame retardant; add too much magnesium hydroxide in the region, the inorganic particles are difficult to be uniformly dispersed into the polymer matrix, which will seriously reduce the mechanical properties of polymer materials. Therefore, the nanosizing and modification research of magnesium hydroxide becomes the key to overcome these problems, to improve its compatibility in polymer materials while reducing the filling amount of flame retardant, and then to achieve the effect of improving the mechanical properties and flame retardant properties of materials.
The traditional modification methods mainly include surfactant method, coupling agent method and microencapsulation method. According to the difference of its stability in water, the modification methods are further divided into dry and wet methods. Magnesium hydroxide has poor compatibility in polymers, and its surface modification treatment by different modifiers can improve its dispersion in the polymer matrix and enhance the performance of composites.
Messi Biology conducted a surface modification study of nano magnesium hydroxide using a novel nano polyacrylate emulsion as a modifier. Activation index test, contact angle test, infrared spectral analysis and thermogravimetric analysis were used to study the structure and properties of modified nano-magnesium hydroxide, and the results showed that:
(1) The results of activation index characterization showed that the best modification effect was achieved with the new nano-polyacrylate emulsion as the modifier with an addition amount of 0.6;
(2) The results of infrared spectral analysis showed that polyacrylate has been adsorbed on the surface of magnesium hydroxide nanoparticles by the modification of the novel nano-polyacrylate emulsion;
(3) The results of contact angle test showed that the surface property of nano-magnesium hydroxide modified by novel nano-polyacrylate emulsion changed from hydrophilic-oleophobic to oleophilic-hydrophobic, which enabled it to be better dispersed in non-polar medium;
(4) The results of thermogravimetric analysis showed that the modified nanomagnesium hydroxide did not affect its thermal stability, and its onset thermal decomposition temperature was rather higher than that of the unmodified nanomagnesium hydroxide, and the residual mass ratio indicated that the modified polyacrylate had been adsorbed on the surface of the nanomagnesium hydroxide particles, which was consistent with the results of the infrared spectroscopic characterization.
(5) The modification effect of other traditional silane coupling agents on nano-magnesium hydroxide was compared, and the results showed that the dispersibility and hydrophobicity and lipophilicity of nano-magnesium hydroxide modified with the new polyacrylate microemulsion were better than those of traditional silane coupling agents.