Preparation, Structure, Performance And Hydrophobic Modification Of Cellulose Aerogel And Cellulose-SiO₂Composite Aerogel

Aerogel materials which prepared by cellulose have a number of merits such as biodegradability, biocompativility, and pollution-free. In this paper, cellulose hydrogel was prepared by using linter cellulose as main body, NaOH/thiourea/H2O system as the solvent and the frozen-thaw method. Cellulose aerogels were obtained by the freeze-drying technology. This method of preparation avoided complicated and non-controllable chemical cross-linking process. It had mild reactive conditions and was easy to control the formation of hydrogel. The improvement involved to add60℃ethanol. Cellulose aerogels which had the fastest reaction rate and the best heat insulation performance were obtained by controlling the ratio of solvent. Meanwhile, the impacts of cellulose concentration on the density, porosity, volume shrinkage, compression strength and thermal conductivity of the aerogels were investigated. In order to reduce the influence of hydrophilicity on heat insulation performance of polysaccharide aerogel, cold plasma technology was adopted with CCI4as plasma to conduct hydrophobic modification.The results showed that the mechanical strength of hydrogel reinforced2.3%and gelation time reduced63%with60℃ethanol. The optimal ratio of NaOH/thiourea/H2O solvent system for cellulose was NaOH9.5wt%, thiourea4.5wt%. Under this condition, the obtained cellulose aerogel had the density low to0.233g/cm3, and the porosity up to84.88%. Cellulose aerogel had good heat insulation performance, while the main factors affecting thermal conductivity were density and porosity. Thermal conductivity reduced with the increase of porosity and the decrease of density. It could be as low as0.029W/(m-K). Cellulose aerogel was easy to adsorb moisture. The moisture adsorption had a significant influence on the heat insulation performance of aerogel. After conducting hydrophobic modification using CCI4as plasma, the surface of cellulose aerogel was changed from hydrophilic to hydrophobic and water contact angle was as high as102°. Hydrophobic modification was not affected the heat insulation performance of aerogel.On the basis of mentioned cellulose hydrogel, cellulose-SiO2composite hydrogel was prepared by the immersion method with controlling the hydrolysis-fasculation rate of tetraethyl orthosilicate (TEOS). The composite aerogels were obtained through the freeze-drying technology. The effects of cellulose concentration and SiO2content on the structure and heat insulation performance of composite aerogel were studied. In order to reduce the influence of hydrophilicity on heat insulation performance of composite aerogel, cold plasma technology was adopted with CCl4as plasma to conduct hydrophobic modification. The effects of charge power and during time on water contact angle were observed.The results showed that when hydrolysis pH was3and the amount of ammonia was8ml in fasculation reaction, SiO2had the best composite efficiency. Under this condition, obtained composite cellulose aerogel had the density low to0.1064g/cm3, the porosity up to75.79%and the compressive strength received to6.4MPa. Cellulose-SiO2composite aerogel had good heat insulation performance. The composition of SiO2could obviously reduce the thermal conductivity of cellulose aerogel. The main factors affecting thermal conductivity were density and porosity, the thermal conductivity could be as low as0.026W/(m-K). Heat insulation mechanic was discussed. The composition of SiO2reduced hydrophilicity of cellulose aerogel, but the humidity of environment had a significant influence on heat insulation performance. After hydrophobic modification using CCl4as plasma was conducted, the surface of composite aerogel was changed from hydrophilic to hydrophobic and water contact angle was as high as132°. The modified composite aerogel still kept good heat insulation performance.