Preparation And Surface Modification Of Silica Nanoparticle

There is abundant and cheap resource of kaolin in China. Therefore, aiming to increase economic efficiency and added value of kaolin products, even to promote the higher level products, deeper processing must be applied to kaolin. In this research, the high-quality nano-silica is prepared from Suzhou kaolin by chemical precipitation and modified for applying in silicon rubber. Consequently, the economic value and useful value of Kaolin have been improved in industry.Firstly, the nano-silica is prepared from kaolin by chemical precipitation. Influence of the calcinatory temperature, calcinatory holding time, and acid treatment time, acid concentration, reaction temperature on output capacity of nano-silica powder are analyzed. The optimal process is acquired: first calcinatory temperature is 700℃and holding time is 1.5 h, the concentration of first acid treatment is 20%, the temperature of first acid treatment is 95℃and the reaction time is 120 min, the pH value of second acid treatment is 5-7, the concentration of second acid treatment is 10%, the second calcinatory temperature is 400℃and the holding time is 1 h. The purity of nano-silica powder could reach to 97.24%;the average particle size is about 10-20 nm;the whiteness is 98; specific surface area of them is 320 m²/g.Secondly, in order to improve compatibility between silica nanoparticles and silicone rubber, the nano-silica should be modified for hydrophobicity. The silane coupling agent ofγ-aminopropyl triethoxy (JH-A110) and stearic acid as modifier are used for complex-modification of nano-silica. Influence of the different polar of solvents, reaction temperature of complex-modification, the mass fraction of JH-A110 and stearic acid, and the reaction time of complex-modification on modified effect of nano-silica are analyzed. The optimal conditions are as follows: the mass fraction of silane coupling agent is 12%, the temperature of the first modification is 110℃for 3 h, the solvent of complex-modification is toluene, the mass fraction of stearic acid is 10%,the reaction temperature of complex-modification is 45℃and the reaction time is 90 min. After complex-modification, the nano-silica obtains strong hydrophobic, the maximum contact angle could reach 140°, and hydrophobic index is close to 100%. The modified silica is characterized by FTIR, XPS, and Sedimentation tests. The results show that amino group (-NH2) is grafted successfully onto the surface of nano-silica particles by modification with silane coupling agent; after the complex-modification with stearic acid, amido bond (-CONH-) is formed by amino group (-NH₂) and carboxyl group (-COOH) of stearic acid; the CH₃ (CH₂)₁₆COHN-(CH₂)₃ group forms on the surface of nano-silica.Finally, in order to investigate the reinforcement effect of nano-silica, the modified and unmodified nano-silica is filled in methyl vinyl silicone rubber, respectively. Their tensile strength and elongation at break are tested. The results show that compared silicone rubber filled with unmodified nano-silica, the mechanical property of the silicone rubber filled with modified silica is better. The tensile strength increases from 3.25 Mpa to 12.8 Mpa, and the elongation at break increases from 650% to 1008 %. As can be seen from SEM figure, the compatibility between modified silica and silicone rubber could be improved significantly, and better reinforcement effect could be obtained.