Preparation Of Aramid Nanofibers Aerogels And Study On Its Properties

Aerogel is a kind of porous material with three-dimensional spatial structure filled with gas medium.The characteristics of ultra-low thermal conductivity,ultra-low density,ultra-high porosity and ultra-high specific surface area made aerogels have excellent properties in optical,thermal,acoustical,electrical and mechanical fields,and have a wide range of applications in environmental protection,aerospace,catalysis,energy storage,thermal insulation and other fields.Compared with other aerogels,the aramid nanofibers(ANFs)aerogels prepared by the aramid fiber precursor system have become one of the most advanced thermal insulation materials in the world due to its higher thermal decomposition temperature,stronger mechanical properties and lower thermal conductivity.The up-bottom strategy is commonly used for the preparation of ANFs aerogels,which has the advantages of simple process and low cost.The drawback is the long preparation time(around 10 days),with the preparation of ANFs dispersions taking around 7 days and the preparation of high concentration ANFs dispersions taking longer(40 days).Therefore,it is of great practical significance to find a simple and quick synthesis route.In this paper,ANFs aerogels were prepared by a completely top-down method.Adding proton additives in the aramid fiber/DMSO/KOH system was adopted to accelerate the deprotonation of aramid fiber to form ANFs dispersion to shorten the preparation time of ANFs aerogel and overcome the problem of the long preparation cycle of traditional process.(1)The effects of the types of proton auxiliaries(water,methanol and ethanol)and the amount of proton auxiliaries on preparation time of ANFs aerogels were investigated.The results show that:5%deionized water,4%methanol and 6%ethanol as proton auxiliary respectively in the system can shorten the preparation time of 0.5%ANFs dispersions from 7 days to 4 h,1.5 h and 1 h without proton additives,and shorten the preparation time of 2.0%ANFs dispersions from 40 days to 12 h,8 h and 8 h.(2)The effect of ethanol solution concentration on the preparation of ANFs aerogel was investigated.The results showed that the aerogels with uniform thickness can be obtained when the concentration of ethanol solution is 30%,and the aerogels prepared have the smallest apparent density and the largest porosity.(3)The effects of atmospheric drying,vacuum drying and vacuum freeze drying on the preparation of ANFs aerogels were investigated.The results showed that only the aerogels prepared by vacuum freeze-drying process have a clear three-dimensional network porous structure.(4)SEM,apparent density and porosity of ANFs aerogels prepared by different proton auxilaries were tested.The results showed that the mesh size and fiber diameter of aerogel prepared by methanol are the most uniform.Compared with water and ethanol,the ANFs aerogels prepared with methanol proton additives have the lowest apparent density(0.0665 g/cm~3)and the highest porosity(95.45%).(5)The ANFs aerogels prepared by three proton auxiliaries were characterized by Raman spectroscopy,XRD and FT-IR.The results showed that the structure of ANFs aerogel and aramid fiber is basically the same and proved that ANFs aerogel still keeps the structural integrity of the original aramid fiber after preparation.(6)The transmittance of ANFs aerogel in visible and ultraviolet light region was investigated.The results showed that the aerogel has a very high transmittance(80%)in the visible light region and a low transmittance(15%)in the ultraviolet light region.(7)The thermal insulation performance and mechanical strength of ANFs aerogel were tested.The results showed that the ANFs aerogel prepared in this paper has good mechanical properties(12.68 MPa)and the thermal conductivity is as low as 0.037 W/m·K.(8)The adsorption properties of ANFs aerogel for dyes were investigated.Using rhodamine B and methylene blue as the target pollutants,the results showed that the adsorption efficiency of ANFs aerobel on rhodamine B dye solution can reach 90%in 5 h,whileas enven as high as 98%for methylene blue dye.