Preparation and thermal insulation properties of encapsulated polyacrylonitrile/SiO2 aerogel composite nanofibers
Objective Aerogel is a novel class of three-dimensional network solid materials,which are porous,high in thermal resistance,and low in volume density,and can be prepared by sol-gel method under the action of gaseous dispersion medium.Aerogels therefore have enormous application potential in the area of thermal insulators,energy conservation because they can effectively delay and block heat flow and reduce heat loss.However,low mechanical strength,high brittleness and easy breakage would hinder the actual aerogel applications.One-step forming of aerogel composite fiber can be achieved by using polymer solution and aerogel powder,and the synergistic improvement of thermal insulation/warmth retention performance can be further achieved by regulating the microstructure of monomer fiber and the macro structure of fiber assembly.However,there are few reports on this aspect.Method In order to effectively integrate the functional and structural advantages of nano-aerogel and nanofiber,a new production technology was designed and developed to prepare polyacrylonitrile(PAN)/SiO2 aerogel composite nanofibers by one-step method using coaxially solution blowing process.In spinning process,the SiO2 aerogel and the PAN were served as core layer and skin layer respectively,at the speed of 2 mL/h and 12 mL/h.The influences of SiO2 aerogel content in composite fibers on fiber morphology,structure,stability,mechanical properties,and thermal insulation properties were specifically studied.Results The PAN/SiO2 aerogel composite nanofibers prepared by coaxially solution blown spinning were continuous,uniform and loosely arranged,and the fiber diameter was distributed primarily in the range of 100-400 nm.Furthermore,three-dimensional crimps were shown in morphology and structure due to the disordered shearing effect of high-speed airflow during the fiber forming process.The introduction of SiO2 aerogel significantly affected the surface morphology of the fibers,forming a porous fold structure.PAN/SiO2 aerogel composite nanofibers were heated up in an oven at 180 ℃ for 240 min to evaluate their thermal stability.After heating,the fibers still retained their porous fold structure,showing good thermal stability.Moreover,the contents of micropores and mesoporous pores on the fiber surface were gradually increased with the increase of SiO2 aerogel content.The obtained PAN/SiO2 aerogel composite nanofibers demonstrated excellent thermal insulation,and the thermal conductivity of the sample with SiO2 aerogel mass concentration of 6 mg/mL was as low as 0.037 38 W/(m·K)at 40 ℃.Under the condition of 50 ℃,the surface temperature of the fiber tested by thermal infrared was 32.5 ℃,and under the condition of 65 ℃,the surface temperature of the fiber tested by thermal infrared was 37.5 ℃.In addition,the weighed PAN/SiO2 aerogel composite nanofibers had a low gram weight(about 70 g/m2),and felt soft and fluffy.Owing to its excellent thermal insulation and convenient and stable production process,PAN/SiO2 aerogel composite nanofibers indicate a broad future market in aspects of thermal insulation,field survival and industrial thermal insulation.Conclusion This paper reported a new route of macro quantization preparation of aerogel composite nanofibers by"one-step method".Specifically,PAN/SiO2 aerogel composite nanofibers were prepared by solution blowing coaxial spinning technology using PAN and SiO2 aerogel particles.In conclusion,the prepared solution blown aerogel fiber has the advantages of low weight and flexible manufacture process,and the spinning efficiency can reach 8-12 times that of electrospinning.It can play a broad application prospect in the aspects of thermal insulation,industrial thermal insulation,and military thermal infrared shielding.In the future,an important development direction of aerogel fibers and their products is to utilize simple fiber processing technology to realize one-step integrated processing.
polyacrylonitrilenanofibercoaxially solution blowing processaerogel composite fiberSiO2aerogelthermal insulation material
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