| Thermal insulation materials are widely used in aerospace,construction,clothing and other fields.For thermal insulation materials,while having good thermal insulation performance,they also need to have certain flexibility,so as to adapt to the surface of various objects.Aerogel is a common thermal insulation material.Although traditional inorganic aerogel has excellent thermal insulation performance,its flexibility is poor,and it is prone to brittle fracture under bending.However,due to the accumulation of nano-silicon networks in the composite flexible components,it is still impossible to develop composite aerogels with high flexibility and high thermal insulation.Nanocellulose aerogel has excellent flexibility and the characteristics of low density,high porosity,and environmental friendliness,but its thermal insulation performance is not as good as that of inorganic aerogels,and because the nanocellulose aerogel system contains a large number of hydroxyl groups,its thermal insulation performance will be greatly reduced in a humid environment.For this reason,without destroying the excellent flexibility of nanocellulose aerogel itself,it can improve its hydrophobicity and thermal insulation properties,and obtain nanocellulose-based aerogels with thermal insulation,hydrophobicity and mechanical properties,which has great research significance.In this paper,the mesoporous silicon network is generated in situ by introducing suitable organosilicon precursors into nanocellulose,and the cellulose-polysilane double network structure is constructed.A cellulose-polysilane double network aerogel with both thermal insulation,hydrophobic and mechanical properties was prepared by ambient pressure drying.After that,continue to optimize ambient pressure drying process,proportionally enlarge the process parameters,relying on the advantages of high efficiency,simple process flow and industrialization of ambient pressure drying,so as to prepare a large sample of cellulose-polysilane aerogel with both thermal insulation,hydrophobic and mechanical properties and realize its mass production.The specific research contents of this paper are as follows:1.Preparation of cellulose-polysilane aerogels with different ratios of“soft-hard”components and comparison of their performanceUsing bacterial cellulose（BC）as a template,methyltrimethoxysilane（MTMS）with low cross-linking degree was added to the BC system to ensure the overall flexibility of the system,in situ catalytic formation of cellulose-polysilane double network structure at high temperature.By adjusting the content of the"hard"component MTMS in the system（3,5,7,9 m L）,the proportion of the mesoporous silica network was adjusted,and finally cellulose-polysilane aerogels with different"soft-hard"component ratios were prepared.After characterization and comparison of cellulose-polysilane aerogels with different"soft-hard"component ratios,it is concluded that the BC-Si5 aerogel,which has content of MTMS is 5 m L,has the best comprehensive performance,with the low density of 0.12 g cm-3,the high porosity of 91.5%,the high specific surface area of691 m~2 g-1;the tensile strength reaches 1.9 MPa,which is equivalent to 50 times that of pure silica aerogel,and the elastic modulus is 10.7 MPa,the flexible mechanical properties are excellent;the water contact angle reaches 110.1°,which has excellent hydrophobic properties;the thermal conductivity is as low as 0.02061 W/（m·K）,which has excellent thermal insulation properties.Compared with other cellulose-polysilane aerogels with different"soft-hard"component ratios,BC-Si5 aerogel has the best comprehensive properties and the most potential for industrialization.2.Preparation of large samples of cellulose-polysilane aerogels with optimum“soft-hard”component and study of their performanceBased on the BC-Si5 aerogel with the best comprehensive performance,ambient pressure drying process was optimized,and the large samples of BC-Si5 aerogel with both thermal insulation,hydrophobicity and mechanical properties were prepared by proportionally enlarging the process parameters.The total area are 2×2 m~2,with sample thicknesses as low as 1.12 mm.The comprehensive performance characterization of the BC-Si5 aerogel large sample was carried out to explore the excellent performance and stability of the comprehensive performance after the process parameters were scaled up.The dimensional shrinkage rate is 9.2%,showing excellent anti-shrinkage performance;the air permeability under 200 Pa pressure reaches 35.1 mm/s,which is better than the commonly used thermal fabrics and has certain air permeability;the average moisture permeability reaches 3013.1 g/（m~2·24h）,which meets the basic requirements for moisture permeability of thermal clothing filling materials（>2200 g/（m~2·24h））,and has good moisture permeability;the average thermal conductivity is as low as 0.02077 W/（m·K）,the thermal insulation performance is better than that of lamb wool thermal clothing with a thickness of 15 times;the average contact angle reaches 110.3°,the hydrophobic performance is excellent and stable;the average burst fastness reaches 420.4 N,which meets the basic requirements for burst fastness of thermal clothing filling materials（>250 N）and has excellent mechanical properties.The characterization results show that in the process of scale-up production,the overall thermal insulation,hydrophobicity and mechanical properties of large samples of BC-Si5 aerogel are excellent and stable,and at the same time,it has good air and moisture permeability and shrinkage resistance,showing great application value and potential in the field of thermal insulation. |
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