Fabrication Characterization And Performance Of Aramid Aerogel Fibers

Aerogel materials have high specific surface area,high porosity,low thermal conductivity and other characteristics,which are widely used in high-energy physics,aerospace and civil fields.However,the morphology of aerogel materials has been mainly in the form of blocks or powders for a long time,which is due to the characteristics of the mesoporous-based multi-level pore structure that limits the mechanical properties and thus the morphology of aerogel materials.In this paper,the main research objective is to prepare aerogel fibers that can be practically applied,and the preparation technology and characterization method of aramid aerogel fibers are studied and their application prospects are explored.1.Fabrication and spinnability of aramid nanofibers(ANFs)dispersions:Different concentrations of aramid nanofibers were fabricated by deprotonation and exfoliation methods,and the morphology and structure of aramid nanofibers were characterized.The liquid crystal transition points were calculated according to their morphological characteristics,and the aramid nanofiber liquid crystal dispersions were obtained by upgrading the concentrations.The particle size analysis and rheological analysis of the nanofiber structure inside the aramid nanofiber liquid crystal dispersion showed that the nanofiber network structure was formed inside the dispersion and its structural stability increased with the increase of concentration,and the theoretical basis for the aramid nanofiber dispersion to withstand the draft deformation was discussed.Further characterization of the sol-gel transition of aramid nanofibers and the trial-production of aramid hydrogel fibers by wet spinning demonstrated the spinnability of aramid nanofiber dispersions.2.Study on fabrication of wet spinning aramid aerogel fiber:This chapter prepares ANFs gel fiber by wet spinning technique with aramid nanofiber dispersion as spinning solution,and then uses solvent replacement and supercritical drying technology to make the solvent inside the gel fiber removed to fabricate aramid aerogel fiber.The aerogel fibers have a mechanical strength of 7 MPa,a break elongation of 14%,and can be bent,knotted and woven into cloth on a loom without damaging the mechanical properties.In addition,the thermal conductivity of aramid aerogel fiber is 0.037 W/mK,which exceeds the performance of existing commercial thermal insulation fibers and is comparable to the thermal insulation performance of superfine fibers.In addition,the prepared aramid aerogel fibers can be dyed and hydrophobically modified,which can meet the practical use requirements and be endowed with various functions.3.Study on the fabrication of aramid liquid crystal aerogel fiber:In order to further improve the strength of aramid aerogel fiber and expand its application,based on the above-mentioned wet spinning technology of aramid aerogel fiber,highly oriented hydrogel fiber was prepared with high concentration of ANFs liquid crystal dispersion as spinning solution,followed by the removal of solvent by supercritical drying to obtain highly oriented aerogel fiber.The fibers exhibited excellent mechanical properties with a fracture strength of 50 MPa and elongation at break of 23%while maintaining a high specific surface area(240 m2/g).In addition,due to its rich internal mesoporous structure,the thermal conductivity of the resulting aramid aerogel fiber is 0.038 W/mK,which can be used for thermal insulation after weaving.Finally,the highly oriented aerogel fibers are low-transparency fibers in the aerogel fiber state and transform into high-transparency gel fibers after absorbing solvents,and with the change of orientation,the fibers show significant color changes under polarized light microscopy,exhibiting peculiar optical properties.Based on this,information digited textile is designed,which can be used in the fields of information storage and secrecy.4.Study on blow spinning of aramid aerogel fibers:Aramid nanofibers were used as raw materials to prepare aramid aerogel fiber flocs by blow spinning technology.The feasibility of air spinning of aramid nanofiber dispersion is investigated,and the effects of different spinning gel methods and spinning parameters on blow spinning aerogel fiber are studied to finally determine the reliable preparation parameters of blow spinning aerogel fiber.The blow spinning aerogel fibers are composed of micron-sized aramid aerogel fibers and the surface densities ranging from 1 g/m2 to 6 g/m2.The blow spinning aerogel fibers are macroscopically a three-dimensional network structure formed by the lap fusion of micron fibers,which exhibits good mechanical properties and can suspend a weight 2500 times its own mass with a strength of 1 MPa.The thermal conductivity of the floc is lower than that of the aerogel and microfiber flocs obtained by wet spinning.The specific surface area is 160 m2/g,and the filtration capacity of 3 g/m2 air-spun aramid aerogel fiber is over 95%for PM2.5 particles and over 85%for VOCs adsorption.In summary,this work realizes the preparation of aramid aerogel fibers by wet spinning technique,the internal morphology control of aramid aerogel fibers,the preparation of aramid aerogel fibers by airflow spinning technique and the characterization of the properties of aramid aerogel fibers.This work validates the theory of dynamic sol-gel transition by preparing aramid aerogel fibers from aramid nanofibers,realizes the regulation of gel skeleton structure during dynamic sol-gel process,develops dynamic sol-gel transition strategy into draft gel synchronization strategy and draft gel step-by-step strategy,and realizes dynamic sol-gel transition outside of wet spinning process.This work has developed new methods for the preparation of aerogel fibers,prepared new polymer aerogel fibers,enriched and extended the theory of dynamic sol-gel transition during the preparation of aerogel fibers,and laid the foundation for the subsequent research work on aerogel fibers.