Study On Preparation And Properties Of Silica Nanofiber/Nanoparticle Composites

In recent years,fire accidents occur frequently all over the world.The public safety,emergency rescue industry and industrial economic development caused by fire accidents have been widely concerned by all countries,and emergency rescue equipment is the most important one involved.High-performance heat-protective clothing can effectively prevent the thermal damage caused by the complex scene of fire.The thermal barrier in its composite structure can effectively block heat conduction and lower heat transmission efficiency,thereby improving its durability.The performance of the thermal barrier is directly related to the whole thermal protective performance of heat-protective clothing.At present,the heat insulation material used in emergency rescue products is usually high-performance organic fiber,such as aramid fiber,polyimide and so on,which has low temperature resistance and is used generally below 600℃.Inorganic fiber can withstand temperature up to 1000℃.However,due to its high brittleness and low strength,the traditional inorganic fiber material has limited its further application in the field of clothing.The fiber diameter and grain size of the ceramic fiber membrane prepared by electrostatic spinning technology are reduced to the order of nanometer,thus the fiber membrane is flexible to a certain extent.However,the internal continuous through-hole structure affects its thermal insulation effect to a certain extent.Therefore,this paper aims to improve the thermal insulation performance of electrostatic spinning ceramic nanofiber membrane.By introducing insulation material--SiO₂aerogel nanoparticles into the material,the construction of multistage pore structure is realized,which effectively extends the heat transfer path and reduces the heat conduction effect of gas molecules.Finally,a lightweight,high temperature resistant fibrous nanoporous composite is developed for the heat insulation layer of thermal protective clothing.In this paper,the silica aerogel particles are refined to 200 nm without damaging the mesoporous structure by means of grinding and ultrasound.Next,the flexible self-supporting SiO₂nanofiber membranes are prepared based on sol-gel electrostatic spinning technology and high temperature calcination process.Then,the refined aerogel powder is evenly mixed in the silica sol binder,and the SiO₂nanofiber membrane is impregnated in it.After a series of processes such as freeze drying and calcining,the aerogel particles are attached to the pores of SiO₂nanofiber,so as to realize the introduction of nano-porous structure in the fiber membrane.In order to obtain the SiO₂nanofiber/nanoparticle composite material with both mechanical properties and thermal insulation performance,the paper change the load of aerogel particles on the SiO₂nanofiber membrane by regulating different concentrations of aerogel powder in silica sol.Composite insulation materials with loading rates of aerogel particles of 20%,30%,40%,50%,55%and 65%are prepared.Finally the microstructure,mechanical properties and thermal insulation properties of the composite are tested and characterized.The results indicate that the introduction of aerogel particles will cause the decrease of the flexibility and tensile fracture strength of the materials to a certain extent.However,the compressive strength and structural stability of the material will be significantly improved.When the loading rate of aerogel particles is controlled at 50%,the composite material has good comprehensive mechanical properties.At this time,the fracture strength of the material is 63 KPa,and the maximum compressive strength can reach 21.5 KPa under60%strain.According to experiments of thermal conductivity at room temperature and high temperature hot stage,on the one hand,the introduction of the nanoporous structure can increase the heat transfer path and tortuosity.On the other hand,the nanoporous pores largely limit the gas heat conduction.Hence,the heat insulation performance of the composite material is effectively improved,whose thermal conductivity at room temperature is 0.0301W/（m·K）,and its surface temperature at 400℃lower nearly 20℃than that of SiO₂nanofiber film.However,excessive load will lead to the acceleration of the solid phase heat conduction and the decline of the heat insulation performance.In conclusion,the nanoporous inorganic fiber insulation material prepared in the paper with 50%aerogel particles loading rate has excellent comprehensive performance and has great application potential and economic benefits in the fields of fire prevention,heat insulation and fire fighting.