| Maintaining body temperature is very important for endotherms like humans.However,common clothes made from nature fibers or synthetic fibers have moderate performance and restricted improvement,which suffer from the disadvantage of relative high thermal conductivity.To achieve excellent warmth,the clothes are generally required to increase their thickness and weight,which is not consistent with the development trend of lightweight,simple and convenient clothing and market demand.Aerogels are nanoporous solid materials with low thermal conductivity,high porosity,and low density.Therefore,they are very useful as lightweight thermal insulation materials.However,from the perspective of application,traditional aerogel has disadvantages such as water absorption,fragility,poor wearability and poor shape adaptability,so commercial aerogel products for daily clothing are very limited.Therefore,it is of great scientific significance and commercial value to select a kind of raw material from a wide range of sources and easy to process,and use a simple,feasible and mass-produced method to prepare the thermal aerogel with good mechanical properties,low thermal conductivity,waterproof and breathable.In this paper,the preparation of flexible and good thermal insulating properties of aerogels as the goal,choose low cost,good biodegradability and non-toxic cellulose acetate as raw materials,combined with the electrostatic spinning technology and fibre frozen molding process,a one-dimensional nanometer fiber dispersion can be converted to a three-dimensional network structure of aerogels without any solvent exchange.Cellulose acetate based aerogel with good thermal insulation performance was developed and prepared.On this basis,the aqueous blocked isocyanate crosslinker(BIC)/cellulose acetate(CA)composite nanofibers were further prepared,and the superelastic aerogel with"honeycomb"structure was constructed by in-situ crosslinking with this framework,which significantly improved the mechanical properties of aerogel.The research results are as follows:The cellulose acetate nanofibers were prepared by electrospinning method.When the concentration of the spinning solution was 15%,the surface of the fiber was smooth without beads,and the average diameter was 247 nm.By adjusting the content of nanofibers in the dispersion,pure cellulose acetate nanofiber aerogels with different densities can be prepared.As the density of pure cellulose acetate nanofiber aerogel increases from 5.5 mg·cm-3 to 10.2 mg·cm-3,the compressive stress at 60%strain increased from 0.63 k Pa to 2.78 k Pa,and the thermal conductivity from 25.26m W·m-1·K-1 increased to 31.57 m W·m-1·K-1.The mechanical stability and low thermal conductivity of cellulose acetate nanofibers make it promising to be used in thermal clothing and other fields.On the basis of the above research,to improve the mechanical properties without increasing the density,porosity and thermal conductivity of the nanofiber aerogel,BIC/CA composite nanofibers were prepared by electrospinning method.After freezing forming and in situ crosslinking,superelastic composite aerogel with"honeycomb"structure was finally constructed.The composite nanofiber membranes with smooth surface and no bead at different BIC/CA mass ratios were prepared by electrospinning method.As the proportion of BIC increases,the average diameter of nanofibers increases from 391 nm to 876 nm.Furthermore,a uniform and stable BIC/CA composite nanofiber dispersion can be obtained,and the BIC/CA composite nanofiber aerogel(HNFA)can be obtained by freeze-drying the uniform BIC/CA composite nanofiber dispersion and then thermal crosslinking.Through uniaxial quasi-static compressive stress and strain test,it is found that at similar density,the compressive strength of the composite nanofiber aerogel with BIC/CA ratio of0.75(HNFA-0.75)is almost twice that of pure CA nanofiber aerogel.HNFA-0.75 can be fully recovered after 10 compression cycles,while the pure CA nanofiber aerogel showed obvious plastic deformation.It proves that we have successfully realized that the compressive strength and elastic properties of nanofiber aerogels can be significantly improved without affecting the density of nanofiber aerogels.When the BIC/CA ratio is less than 0.75,the compressive strength of HNFA increases continuously with the increase of BIC/CA ratio.When BIC/CA ratio exceeds 1,the compressive stress begins to decrease,and then decreases with the increase of BIC/CA ratio,which corresponds to the change of aerogel microstructure.HNFA-0.75 has good elastic compressibility at a density of7.5 mg·cm-3 and can quickly recover 90%of large compression deformation.It has strong fatigue resistance at more than 20000 bending times,and it still has good elasticity at ultra-low temperature(-196?).Moreover,HNFA has excellent thermal insulation performance,with very low thermal conductivity(27.2?28.4 m W·m-1·K-1).It can increase the temperature of artificial skin from 31?to 42.8?,which is better than commercial cotton clothing and down jacket.Moreover,it has good breathability and superhydrophobic properties.The static contact angle is 162°,proving that it has a wide application prospect in light thermal insulation thermal clothing. |
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