| In recent years,with the improvement of people’s quality of life and the change of life concept,the traditional materials that enhance the thermal insulation performance by increasing the thickness of materials can no longer meet the needs of the public.Thermal insulation materials continue to develop in the direction of light weight,flexibility,high strength,high and low temperature resistance.The unique structural advantages of polyimide（PI）aerogel make it have high porosity,ultra-low density,low thermal conductivity and other properties,which are widely used in thermal insulation,adsorption purification,sound insulation and noise reduction,electromagnetic wave absorption and other fields.The common preparation method of PI aerogel is freeze-drying,which has the advantages of green environmental protection and low cost.However,a large number of ice crystals formed during the preparation process will seriously damage the aerogel structure,resulting in low mechanical strength and poor flexibility.Therefore,it is of great value to develop a PI composite aerogel material with strong mechanical properties,good flexibility and high thermal insulation performance.In view of the above problems,this paper combines electrospinning,freeze-drying and in-situ thermal crosslinking technology to prepare PI-based composite aerogels with interpenetrating network structure with high mechanical strength,good thermal insulation performance and suitable for various environmental applications at high and low temperatures.Based on PI-based composite aerogel,a composite aerogel material with electromagnetic wave absorption performance of nanofiber/lamellar coordinated structure with uniform filling of graphene oxide（GO）and silicon carbide（SIC）nanoparticles was constructed.The specific research contents are as follows:（1）In order to solve the problem of serious damage to the aerogel structure and poor mechanical properties during the freeze-drying process,the polyamide imide（PAI）nanofibers with similar structure to the PI matrix were selected as the reinforcing filler,and the crosslinking agent bismaleimide（BMI）was loaded in the nanofibers.The PI composite aerogel with nanofiber-reinforced semi-interpenetrating network structure was obtained by thermally initiated crosslinking polymerization.The relationship between the structure and properties of aerogels was optimized by adjusting the ratio of nanofibers to PI matrix.When the mass ratio is 1:1,the PI composite aerogel has the best performance,low density(26 mg cm-3),high pore structure（94.92%）,and most importantly,high tensile strength and good compression fatigue resistance.After 1000 cycles of compression,the plastic deformation of compression is only7%,and the thermal conductivity is extremely low(30.06 m W m-1 k-1),and in a wide temperature window,it shows excellent thermal insulation performance.（2）In order to make aerogels have higher value attributes to meet the application of more fields.On this basis,Ce3+doped lithium zinc ferrite/silica（CLZFO/Si O2）flexible inorganic nanofibers were prepared by sol-gel and high temperature calcination method,and they were used together with polyimide/silicon carbide（PAI/SIC）organic nanofibers as the reinforcing phase of aerogels,and mixed with GO and SIC into aerogels to construct nanofiber/lamellar coordinated structure high-performance electromagnetic wave absorbing aerogels uniformly filled with GO and SIC nanoparticles.The results show that the material exhibits high-efficiency electromagnetic wave absorption performance due to the good coordination between the components.The minimum reflection loss(RLmin)value at 5.4 GHz is-49 d B,and the effective absorption bandwidth is 4.3 GHz.At the same time,it exhibits excellent thermal insulation,and the thermal conductivity at room temperature is 31.12 m W m-1 k-1.Excellent mechanical properties,superhydrophobicity and fire resistance ensure the long-lasting and stable microwave absorption applications of aerogels in complex and extreme environments. |
