Synthesis Of Magnesium Hydroxide Whiskers And Its Application In Polymer Materials

In recent decades, polymer industry is flourishing. Common materials such as plastic, fiber, rubber, and various functional polymer materials have been widely used in industry, agriculture, military, aerospace and other areas of national economies, which are gradually replacing the traditional steel, cement, metal, wood, cotton and other natural materials. However, most polymers are flammable, combustible, fast combustion heat releasing, high heat value, fast rate of flame spread and difficult to extinguish. And sometimes the combustion of polymers produces toxic gases and smoke, which is not only harming the environment, but also threating the lives and property of the people. Therefore, study on the flame-retardant of the polymer materials to improve the flame retardancy of polymeric materials is an urgent problem.Magnesium hydroxide has been used as flame retardant for polymer materials. It has low toxicity, excellent flame retardancy and smoke suppression properties. However, the addation of ordinary magnesium hydroxide usually decrease the mechanical properties of polymer materials. Magnesium hydroxide whiskers with peculiar crystal can significantly improve the mechanical properties and fire-proof properties of these resins.This thesis explores the optimal conditions of preparing magnesium hydroxide whiskers and basic magnesium sulfate whiskers. The reaction mechanism has been discussed. The main contents of this thesis are shown as follows:1.Employed magnesium chloride, sodium hydroxide and magnesium sulfate as raw materials, basic magnesium sulfate whiskers was prepared under hydrothermal conditions. The structure, morphology, and thermodynamics decomposition behavior of the products were characterized with XRD, SEM, EDS, and TGA-DTA. SEM and XRD results show good crystalline whiskers with diameters of about 1~2μm, length of about 200~350μm, aspect ratio more than 100 was obtained; its surface is smooth, delicate appearance, which can be used as a high-quality flame retardant and reinforced material; EDS and TGA-DTA results show that the products formula is 5Mg(OH)2·MgSO4·2H2O. The influences of reaction conditions on the morphology and structure of basic magnesium sulfate whiskers were discussed.2.Using magnesium sulfate whiskers as precursor, sodium hydroxide as the precipitation transformation agent, magnesium hydroxide whiskers was prepared with hydrothermal reaction. The influence of the reaction temperature, reaction time and concentration of precipitation transformation agent was considered. SEM and XRD show that the crystal structure of the product has a diameter of 1.0~1.5μm, the length is about 150~250μm, and the aspect ratio is about 100. Meanwhile, the growth mechanism of magnesium hydroxide whiskers and the optimum reaction conditions were discussed .3. The surface modification process of magnesium hydroxide whiskers using stearic acid and sodium oleate was studied. The optimum processof stearic acid modification was determined to be that the weight of stearic acid was 8%, the modification temperature was 60℃and the reaction time was 60 min by analyzing the active exponent. The modification method with sodium oleate was that the weight of sodium oleate was 6%, the modification temperature was 60℃and the reaction time was 60 min. The results of IR indicated that the surface modification agent was attached to magnesium hydroxide whiskers by chemical bound. The contact angle study showed that the property of the whiskers surface changed from hydrophilic into hydrophobic.4. The influence of modified magnesium hydroxide whiskers on fire-proof and mechanical properties of PP and ABS system was investigated by testing the tensile stress, strain at break, oxygen index etc.