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

Abstract

Magnesium hydroxide nanoparticles with different morphological structures of needle-,lamellar- and rod-like nanocrystals have been synthesized by solution precipitation reactionsof alkaline with magnesium chloride in the presence of complex dispersants andcharacterized in terms of morphology, particle size, crystal habits and thermal behaviour bytransmission electron microscopy, x-ray diffraction and thermogravimetric analysis. Thesizes and morphologies of magnesium hydroxide nanocrystals can be controlledmainly by the reaction conditions of temperature, alkaline-injection rate and theconcentrations of reactants. The data show that the needle-like morphology is of size10 × 100 nm2,the lamellar shape 50 nm in diameter and estimated 10 nm in thickness, and the rod-like nanoparticles4 µm in length and 95 nm in diameter, respectively. All three kinds of nanoparticles are ofhexagonal structures. The needle- and lamellar-like nanoparticles can be obtained by thereactions of alkaline injected into magnesium chloride solution at about 2 and20 °C, respectively, while the rod-like nanoparticles can be prepared by a sloweralkaline-injection rate and lower aqueous ammonia concentration at about10 °C. The results obtained from the ethylene–vinyl acetate nanocomposites blended with thelamellar-like nanoparticles show that magnesium hydroxide nanocrystals possess higherflame retardant efficiency and mechanical reinforcing effect by comparison with commonmicrometre grade magnesium hydroxide particles.