Study Of Mtms-based Hydrophobic Silica Aerogels Prepared Via Ambient Pressure Drying And Its Reinforcing Modification

Silica aerogel has many unique properties owing to its special structure, such as low density, high porosity, high specific surface area and low thermal conductivity. Various applications, for instance, super thermal insulation materials, acoustic impedance coupling materials, catalysis and catalysis carriers, gas-filtering materials have already been investigated and reported.This paper uses methyltrimethoxysilane (MTMS) as the procedure for sol-gel process, which has methyl groups as hydrophobic groups, to prepare hydrophobic silica aerogel via ambient pressure drying. The method avoids the after-hydrophobic process when use the usual procedure such as tetraethyl orthosilicate. And also plenty of solutions are not needed for exchange or washing the gel to strength the structure of the aerogel. So it is considered to be a faster and more environmental method.The proportion to prepare silica aerogel is studied by orthogonal experimental design, and the influences of different factors during the sol-gel process were studied, such as the concentration of the catalysis, the content of the solution and the content of the water. The structure and the properties of silica aerogels are studied when each factor changed. The results show that when the molar ratio of MTMS: MeOH: H2O is 1:35:8, the concentration of the ammonia is 5.4 mol/L, the properties of the silica aerogel are best, which the density of the aerogel is 0.16 g/cm3, the shrinkage of the aerogel is 29%. It is found that silica aerogel prepared by this method has unique hydrophobic properties, which contact angle could be as high as 130°or even higher, water could rolling on the aerogel easily. The density of the silica aerogels is in the range of 0.16～0.33 g/cm3, the anvarage pore size is 9.51nm.The effects of BD-3077 as polyether type silicone surface modifier, in which chemical structure, density, shrinkage rate and thermal stability are studied. The results show that the shrinkage rate of the silica aerogel is reduced when adding BD-3077. When the weight percent of BD-3077 is 5%, the shrinkage rate of the silica aerogel is the smallest at 22%. Glycerol is adding as a drying control chemical additives to prevent the cracks during the drying process. The best weight percent of the glycerol is 0.05%.Silane coupling agent KH550, isocyanate polycondensate and one-component polyurethane are used to reinforce the structure of silica aerogel. The aerogels reinforced by isocyanate polycondensate or one-component polyurethane have higher strength compared to KH550, but the density are higher and the thermal stability are lower. The experiments show that the weight percent of the KH550 and isocyanate polycondensate is 2%, silica aerogels with less cracks are easier to get. And when adding one-component polyurethane the strengh of silica aerogel is higher, but the density and the shrinkage rate are larger, which are between 0.62 g/cm3~0.95 g/cm3,46%~53%, respectively. A further study is expected in the effects of isocyanate polycondensate and one-component polyurethane on the silica aerogels.