Controlled synthesis of magnesium hydroxide nanoparticles with different morphological structures and related properties in flame retardant ethylene–vinyl acetate blends

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Abstract
Magnesium hydroxide nanoparticles with different morphological structures of needle-, lamellar- and rod-like nanocrystals have been synthesized by solution precipitation reactions of alkaline with magnesium chloride in the presence of complex dispersants and characterized in terms of morphology, particle size, crystal habits and thermal behaviour by transmission electron microscopy, x-ray diffraction and thermogravimetric analysis. The sizes and morphologies of magnesium hydroxide nanocrystals can be controlled mainly by the reaction conditions of temperature, alkaline-injection rate and the concentrations of reactants. The data show that the needle-like morphology is of size 10 × 100 nm2, the lamellar shape 50 nm in diameter and estimated 10 nm in thickness, and the rod-like nanoparticles 4 µm in length and 95 nm in diameter, respectively. All three kinds of nanoparticles are of hexagonal structures. The needle- and lamellar-like nanoparticles can be obtained by the reactions of alkaline injected into magnesium chloride solution at about 2 and 20 °C, respectively, while the rod-like nanoparticles can be prepared by a slower alkaline-injection rate and lower aqueous ammonia concentration at about 10 °C. The results obtained from the ethylene–vinyl acetate nanocomposites blended with the lamellar-like nanoparticles show that magnesium hydroxide nanocrystals possess higher flame retardant efficiency and mechanical reinforcing effect by comparison with common micrometre grade magnesium hydroxide particles.