Preparation Of Thermal Protection Para-aramid Aerogel And It’s Performance Study

As a new type of high porosity three-dimensional network structure material,aerogel gel has excellent properties such as low density,low thermal conductivity,high specific surface area and high porosity.Its light weight and excellent heat insulation performance can be used as the heat insulation layer material of firefighting clothing.Inorganic aerogels based on silica dioxide and organic aerogels based on cellulose are common in aerogels.However,the former has poor mechanical properties and easy collapse of the skeleton,while the latter has poor high temperature resistance,which limits the development of aerogels in the field of thermal insulation.Para-aramid fiber is concerned by researchers because of its excellent properties such as ultra-high strength,high modulus,and high temperature resistance.Using aramid fiber to prepare aerogel gel and explore its application in the field of heat insulation is the current research hotspot.In the preparation of para-aramid aerogel,there are many problems,such as long dissolution period,easy collapse of freeze-drying skeleton.This paper takes contrapuntal aramid fiber（Kevlar 29）as raw material,by using ionic liquid/cosolvent system to dissolve the fiber,adding tert-butanol as the freezing medium to adjust the pore structure in pure water replacement solution,and adds nano-titanium dioxide（TiO₂）as precursor,so as to achieve preparation of para-aramid aerogel with stable skeleton,excellent thermal insulation performance and low thermal radiation.The analysis of its microstructure,specific surface area and thermal insulation performance can provide certain reference value for the application of para-aramid aerogel in the thermal insulation layer of firefighting clothing.The specific research content is as follows:Firstly,taking para-aramid fiber（Kevlar 29）as raw material,tetrabutylammonium fluoride hydrate（TBAF）,tetrabutylammonium fluoride trihydrate（TBAF·3H₂O）,1-butyl-3-methylimidazolium chloride（[BMIM]Cl）ionic liquid as solvent,dimethyl sulfoxide（DMSO）,N,N-dimethylformamide（DMF）as cosolvent,the solvent and cosolvent are combined to form a dissolution system,and different types of ionic liquids are explored Effect of cosolvent dissolution system on the solubility of Kevlar 29 fiber.The results showed that Kevlar 29 fiber could not be dissolved effectively by ionic liquid or cosolvent alone.When DMSO and DMF are used as cosolvents,only DMSO can effectively dissolve Kevlar 29 fibers in coordination with ionic liquids.In the dissolution system composed of ionic liquid and DMSO,TBAF/DMSO has the strongest solubility,and the order of solubility is:TBAF/DMSO>TBAF·3H₂O/DMSO>[BMIM]Cl/DMSO.The solubility of TBAF/DMSO ionic liquid and cosolvent system increases with the increase of temperature.When the dissolution temperature is 60℃,the dissolution time is the longest.When the dissolution temperature is 80℃,the dissolution time is the shortest.At the same time,it was found that 1 wt%Kevlar 29 could not be completely dissolved when the concentration of TBAF was lower than 6 wt%.When m（TBAF）:m（DMSO）=1:11,1 wt%Kevlar 29 fiber can be dissolved rapidly within 2 h.In order to solve the problem that the aerogel framework is easy to collapse under freeze-drying conditions,the para-aramid aerogel gel precursor was prepared with Kevlar 29 fiber as raw material and TBAF/DMSO as dissolution system.The para-aramid aerogel was obtained by tertiary butyl alcohol（TBA）replacement and freeze-drying.The results show that the addition of TBA to the displacement fluid can improve the collapse of aerogel gel skeleton and reduce the shrinkage of aerogel gel,because the addition of TBA will form needle like ice crystals,which will form a stable three-dimensional network structure after sublimation.The aramid aerogel prepared by 50%TBA displacement drying has the lowest shrinkage,density of0.021 g/cm³,specific surface area of 208.05 m²/g,and thermal conductivity of0.028 W/（m·K）.After the PS sheet is placed in the aerogel gel and baked at 215℃for45 minutes,there is no shrinkage change between the PS sheet and the aerogel gel,and the temperature difference of the aerogel quilt surface is stable at 145℃.It shows that the aramid aerogel regulated by TBA can not only solve the problem of skeleton collapse,but also has good heat insulation effect.In order to reduce the use of organic solvents and accelerate the replacement efficiency,based on the volume fraction of 50%TBA.Change the replacement path,initially replace it with pure water,and then soak it in 50%TBA solution and freeze dry it.It is found that the replacement time can be effectively reduced,and the prepared aerogel gel also has low thermal conductivity and good thermal stability.In order to reduce the effect of thermal radiation on aerogel gel,nanometer TiO₂with certain absorption and reflection infrared wavelength was selected to be added to the precursor,and the effects of adding nanometer TiO₂with different mass ratio on the structure,heat insulation and thermal radiation of aramid aerogel were explored.The results show that the aramid composite aerogel with nanometer TiO₂has relatively good apparent morphology and low shrinkage.Nanometer TiO₂is physically coated in the aerogel gel framework to form a stable nano porous network material.XRD and bet analysis showed that the performance of aramid aerogel was stable after adding nanometer TiO₂,and the loading effect was good.The pore diameter of aerogel gel was between 10 and 15 nm,which belonged to mesoporous.According to the near-infrared light heat insulation test,under the joint action of TiO₂and the pore structure of aerogel gel,the thermal insulation performance of aramid aerogel becomes stronger,which effectively reduces the influence of thermal radiation on aerogel.The above study,based on the freeze-drying technology,the use of ionic liquid/cosolvent solution system,tert-butyl alcohol replacement system and TiO₂load,obtained the qualitative light,excellent heat insulation performance of aramid aerogel,to solve the aerogel skeleton under the condition of freeze drying is easy to collapse and reduce the thermal radiation problems provide train of thought.The prepared aerogel is expected to be used as thermal insulation material for fire suits.