|Other Abstract||Aerogels are widely used in fields of special garments, aviation and military industry, petrochemical, energy saving building due to its low density, high specific surface area, high porosity and low thermal conductivity. Bio-based aerogels prepared from nature polymers not only possess the characteristics of traditional aerogels, but also integrate with their own excellent properties such as good flexibility, renewability, environmental friendliness. As one kind of bio-materials, cellulose is an abundant biopolymer in nature. As a new generation, cellulose aerogels combine the advantages of cellulose and traditional aerogels. However, pure cellulose aerogels have poor mechanical strength because of their own structure. Combining with inorganic nano-materials not only can improve their mechanical strength, but also endow them with characteristics of conduction, lyophobic, antiflaming and other interesting properties. In this thesis, cellulose and its derivatives were used as research object, combined with different inorganic nanomaterials to prepare cellulose-based composite aerogels, and their mechanical and heat insulation properties were investigated. The main contents and results are as follows:
(1) Cotton cellulose was used as raw material, cheaper sodium silicate was used as precursor and LiOH/urea/H2O system was used as solvent for dissolving cellulose. Then composite hydrogels were fabricated via in situ formation of silica in cellulose hydrogel. Finally, composite aerogels were obtained after drying with supercritical CO2. The effect of preparation conditions such as Na2SiO3 mass fraction, HCl concentration and cellulose concentration on structure and properties of composite aerogels were studied. The results show that the specific surface area of composite aerogels is increased by 65%, pore diameter is decreased 1 times, and compressive strength and Young’s modulus are increased by 3 times and 4 times, respectively.
(2) Composite aerogels with excellent mechanical property were prepared by using CMC as raw materials, 2D graphene oxide (GO) nano-sheet as reinforcement, boric acid (BA) as cross-linker. By controlling the heat transfer rate, composite aerogels with isotropy and anisotropy structure were prepared, and the mechanical property and heat insulating were studied. The results show that the composite aerogel with isotropy structure has compression strength of 110 kPa, which is 5 times the axial and 14 times the radial of anisotropy structure composite aerogels, and thermal conductivity is lower than those of two directions of anisotropy structure composite aerogels. And the effect of GO content in isotropy composite aerogels on their properties was also discussed. The results show that the mechanical property of composite aerogel increases with the increase of GO content. When GO content is up to 5 wt%, the compressive strength and Young’s modulus of composite aerogels reach 349 kPa and 1029 kPa, respectively, which are 1.6 and 4.5 times that of CMC aerogels, respectively. However, the increased content of graphene oxide in composite aerogels also increases their thermal conductivity.|