The Synthesis Of Silica Areogel Via Atmospheric Pressure Drying And Its Application In Thermal Insulation Textile

Silica aerogels are gels with gas as dispersion medium. Silica aerogel is nanostructured material with high specific area, high porosity, low density, low dielectric constant and high thermal insulation value. Thus it has wide application prospect. Silica aerogel can be synthesisd by sol-gel method. Sol-gel precursors are mainly silicon alkoxides. There are mainly two drying methods, namely supercritical drying and ambient pressure drying. In supercritical drying, solvent reaches its critical point by the temperature and pressure control. Gel transforms into aerogel without damage of the network structure. But with high energy consumption, supercritical drying equipment is expensive and complicated. It is not suitable for continual and large-scale production. In order to prevent the shrinkage and collapse of the aerogel during ambient pressure drying, there are ways such as solvent exchange, surface modification to decrease the capillary forces and step drying is taken. Since silica aerogel has untra low thermal conductivity, it can be used to produce thermal insulation coating fabric, whicn can decrease the temperature inside the fabric covering. It has good application prospect because it is energy saving. The study of this paper is as followed:(1) Silica aerogel was synthesised using methyltrimethoxysilane(MTMS) as precursor by a two step (acid-base) sol-gel process followed by the ambient pressure drying. Flexible aerogel can be produced using MTMS precursor and the route is easy without the steps of solvent exchange and surface modification. So it can save time and reduce cost. The effects of sol-gel parameters (methanol/MTMS moral ratio, gelation temperature, ammonia concentration)on the thermal conductivity, density, surface area and pore size of the aerogels have been investigated. This paper synthesised silica aerogel with thermal conductivity0.03～0.04W/(m-K), surface aera450～650m2/g. The chemical structure of silica aerogel has been analysed by the FT-IR. Three-dimensional network struture with pores of silica aerogel can be showed by the FE-SEM. TG curve of silica aerogel indicates that it is stable under200℃and loses20%weight between200℃to800℃.(2) To study the preparation of silica aerogel coated fabric and heat insulation performance of SiO2-TiO2composite coating. Cotton fabric was coated with silica aerogel and TiO2as functional particles and PA as well as PU as adhesive agent. The influences of the amount of silica aerogel and the amount of adhesive agent on the insulation performance of coated fabric were studied. The coated fabric showed much better thermal insulation performance than the untreated fabric. The insulation performance of coated fabric was best as the mass ratio of the binder to deionized water is2:8and aerogel accounted for10%of the mass of the coating agent. SiO2-TiO2composite coating also displayed extraordinary thermal insulation behavior. Compared with the untreated fabric, the coated fabric manifested the same level of breaking strength, lower tearing strength, much better anti-ultraviolet capability with good abrasion fastness. Cotton fabric was coated with silica aerogel、TiO2as functional agents, the heat insulation performance of which improved a lot.