| Magnesium hydroxide, one of inorganic additive flame retardants, is a kind of promising green flame retardant and has attracted much attention because of its good thermal stability, nontoxicity, fume suppression, char-forming promotion, and no formation of acid and corrosive gas product during burning process. However, its poor dispersibility in and compatibility with polymer matrices would decrease the mechanical properties of the filled polymer. In this paper, therefore, the preparation and surface modification of ultrafine and nanometer magnesium hydroxide were investigated aiming at the problems above-mentioned.Magnesium hydroxide nanoneedles and nanorods were synthesized by reverse precipitation in the presence of polyethylene glycol (PEG1000) at ambient temperature. The experimental results showed that the growth of magnesium hydroxide crystals and dispersivity of nanoparticles were greatly influenced by polymer dispersant. The mechanism of the formation of magnesium hydroxide nanorods and nanoneedles was also proposed.Well-dispersed magnesium hydroxide nanoplatelets were first synthesized by simple water-in-oil (w/o) microemulsion process, blowing gaseous ammonia (NH3) into the microemulsion zones solubilized by magnesium chloride solution (MgCl2). The typical quaternary microemulsions of Triton X-100/cyclohexane/n-hexanol/water were used as space-confining microreactors for the nucleation, growth and crystallization of magnesium hydroxide nanoparticles. The mole ratio of water to surfactant (ω0) played an important role in the sizes of micelles and nanoparticles, increasing with the increase ofω0. The compatibility and dispersibility of nanoparticles obtained from reverse micelles were improved in organic phase.The high-dispersed lamellar ultrafine magnesium hydroxide was obtained at relatively low hydrothermal temperature in the presence of cationic surfactant, cetyl trimethyl ammonium bromide (CTAB). The procedure described in this study is attractive since proper amount of CTAB could promote the dissolution and precipitation of magnesium hydroxide in hydrothermal system, resulting in the well-defined morphology, narrow size distribution and good crystallinity of ultrafine particles. The method led to the production of particles with mean size of 400 nm and a diameter of 60 nm. The optimal conditions of preparation were hydrothermal treatment at 150°C for 6 h at pH 11 with Mg2+/CTAB molar ratio of 80. The influence mechanism of CTAB on morphology of magnesium hydroxide was discussed.Hydrophobic magnesium hydroxide nanoparticles were obtained by means of grafting poly(methyl methacrylate) (PMMA) onto the surface of nanoparticles after oleic acid (OA) modification. The functional double bonds were firstly introduced on the surface of nanoparticles by OA modification, followed by dispersion polymerization on the particles surface in ethanol solution to graft PMMA on the surface of modified magnesium hydroxide. The results showed that the organic macromolecule PMMA could be successfully grafted on the surface of OA-modified magnesium hydroxide nanoparticles, with the dispersibility and the compatibility of nanoparticles greatly improved in organic phase.In order to solve the problems of dispersibility and flame retardant efficiency of magnesium hydroxide, the in-situ synthetic technique and flame retardant propertie of PMMA/Mg(OH)2/MMT were further researched on the basis of the synthesis and modification of magnesium hydroxide, employing montmorillonite (MMT) to improve the flame efficiency of magnesium hydroxide. The microemulsions and dispersion polymerization were first combined together to synthesize ternary nanocomposite. The magnesium hydroxide nanoparticles and layers of MMT were monodispersed in the PMMA matrix, basically ensuring the transparence of nanocomposite. And the flame retardant efficiency was greatly improved, with the obviouse decrease of heat release rate (HRR) and peak of heat release rate (PHRR). The flame retardant mechanism was discussed in detail. |
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