Surface Modification Of Magnesium Hydroxide Nano-particles And Its Application In Flame Retardant Polypropylene Composites

The surface modified nano-sized magnesium hydroxide was prepared with wet precipitation process using mixed surfactants, such as SDS with PA-Na, APG and MAP as modifiers. The yield could be above 97%. The mixture of surfactants, usage and dosage of surface modifiers were optimized by means of the measurements of suspension volume of the nano-particles in liquid paraffin.As a mass ratio of SDS to MAP was 2:1 and the total of 0.2 wt% of Mg(OH)₂ theoretical weight (4.35g) was used, the nano-Mg(OH)₂ with optimized dispersibility was obtained. The unmodified and modified samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), N₂ adsorption and tap density test, respectively. The experimental results show that the modified samples have good dispersion and crystal. Fourier transform infrared spectroscopy (FTIR) and suspension volume of the nano-Mg(OH)₂ in liquid paraffin results suggest mixed surfactants may be adsorbed onto the surface of magnesium hydroxide nano-particles changing the hydrophilic surface into hydrophobic and improving the dispersion stability in organic medium.Using the mixture of SDS and MAP as modifier, in which the a mass ratio of SDS and MAP was 1:1, the effect of modifier dosages on the as-prepared nano-Mg(OH)₂ were discussed by sample analysis with XRD, BET, TEM and suspension volume of the nano-particles in liquid paraffin. Optimized results were obtained with 0.2 wt% of modifier usage. The FTIR showed that in water, SDS/MAP could be absorbed onto the surface of as-prepared samples in the form of mono-layer or bi-laye depending on the dosage of SDS/MAP.The measurements of thermogravimetry-differential scanning calorimetry (TGA-DSC) indicated that the temperature of nano-Mg(OH)₂ decomposing decrease, but became widen, as a mass ratio of SDS to MAP was 2:1 and 0.2 wt% of modifier was used. When 50wt% of surface modified nano-Mg(OH)₂ was added in polypropylene (PP), the limiting oxygen index (LOI) value of the PP compound was about 35.0,tensile strength was about 27.01KPa,and elongation at break was about 12.01. In conclusion, surface modification of nano-Mg(OH)₂ could improve mechanical properties of PP/Mg(OH)₂.