Synthesis And Surface Modification Of Magnesium Hydroxide Nanorads And Its Application Performance

Nowadays, the supplies of magnesium hydroxide on market are almost the products with morphology of hexagonal flake, little products with rod-like magnesium hydroxide are provided. The main reason is that the production technologies of magnesium hydroxide nanorods is still immature. The preparation methods of magnesium hydroxide nanorods mainly incrudes precipitation conversion method, hydrothermal method and solid arc discharge method. The precipitation conversion method has the advantage of simple production process, but the major problem is low yield; the hydrothermal method and solid arc discharge method have the shortcomings of complex process and high production cost. In order to overcome the defects of existing technology, we first present a new method to synthesize magnesium hydroxide nanorods in this work, the magnesium hydroxide nanorods is synthesized via ion-exchange conversion method by using basic magnesium chloride nanorod as precursor. In the processing, the basic magnesium chloride nanorod was previously prepared by reacting magnesium oxide with hexahydrate magnesium chloride, and filled with in ion exchange column, and then passing NaOH-ethanol aqueous solution to the column, meanwhile the basic magnesium chloride nanorod was converted to magnesium hydroxide nanorod through ion exchange reaction. The surface modification of prepared products was carried out, the flame retardance, flow ability and mechanical properties of PE/nano Mg(OH)2were also investigated. The product was characterized by scanning electron-microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and thermo-gravimetric (TG). The main experimental content and experimental results are as follows:1. Based on the preparation of basic magnesium chloride nanorods, the influence of Ethanol/water volume ratio, concentration of sodium hydroxide, reaction time on the conversion of basic magnesium chloride nanorods into magnesium hydroxide nanorods was studied. Results show that the basic magnesium chloride nanorods can be transformed into magnesium hydroxide nanorods by ion-exchange conversion method, and the yield of magnesium hydroxide nanorods is sharply higher than precipitation process(the yield of precipitation method was about15%, the yield of this work was about45%); larger proportion of water to ethanol, higher sodium hydroxide concentration and longer reaction time might take negative effect on magnesium hydroxide nanorods growth. The optimal prepared condition is that the volume ratio of ethanol to water is4:1,the NaOH concentration is2mol/L and the reaction time is1hour. Under this conditions, the prepared magnesium hydroxide nanorods is about20～30nm in length,50-200nm in diameter, and the length to diameter ratio is of150to400. 2.The surface modification of magnesium hydroxide nanorods was treated by stearic acid, silane coupling agent and ester titanate coupling agent DNZ311through wet method, the activation index and surface contact Angle were used to value modifying efficiency. Results show that the sample modified by stearic acid has the highest activation index and the largest contact angle, means that stearic acid is the best one among three kinds of modifier, which in accordance with the following sequence:stearic acid>titanate coupling agent>silane coupling agent.3.The preparation of magnesium hydroxide nanorods using basic magnesium chloride as precursors and reacted with sodium hydroxide, urea, six methyl tetramine respectively via solid phase reaction method was studied. Results show that the length of magnesium hydroxide nanorods decreased with the grinding time, but the uniformity becomes better; When heating time elongated, the morphology will transformed from long bar into flake shape; SEM shows that adding sodium chloride, a fluxing agent, in the reaction mixture of basic magnesium hydroxide nanorods and sodium hydroxide helps to the generation of product with rods shape. The length of magnesium hydroxide nanorods synthesized by solid phase reaction is less than that of ion exchange process, which with around3～5μm in length, and the yield is about45%, which is the same as the ion exchange process, and much higher than the precipitation conversion method.4. The magnesium hydroxide was filling in high density polyethylene (HDPE) to prepare samples of inorganic/organic [PE/Mg(OH)2] composite, which were used to test the oxygen index and the tensile strength, in order to evaluate the flame retardant performance. Results showed that:Compared with commercial magnesium hydroxide, the performances such as flame retardancy, tensile strength and modulus of elasticity of HDPE filled with flake or rod-like nanometer magnesium hydroxide increased. The performance of modified magnesium hydroxide is better than the unmodified. Tensile strength of HDPE filled with rod-like nanometer magnesium hydroxide modified by stearic acid reach27.8MPa, which larger more than the value(13.2MPa) of tensile strength of HDPE.