Macroscopic-Scale Preparation of Aramid Nanofiber Aerogel by Modified Freezing- Drying Method

Aerogel has been widely known as a low-density and highly porous material and is closely connected with the complex processing methods, such as freeze-drying or supercritical drying. In this work, using the polymerization-induced aramid nanofiber (PANF) as a building block, we put forward a modified freezing-drying method for the high-efficiency preparation of all-para-aromatic-amide aerogels. In the preparation process, PANF hydrogel is first frozen at -18 degrees C and then dried at 20-150 degrees C for the formation of PANF aerogel. The PANF framework formed during the freezing process is crucial for the formation of the PANF aerogel. Moreover, the space-occupying effect of ice crystals is also helpful for the formation of the macroscopic pore structure in the aerogel. Aerogels with large size or well-controlled shape could be successfully obtained by this method. Through the variation of PANF concentration in the hydrogel and drying temperature, aerogels with different densities (20-185 mg/cm(3)) could be achieved, and the lowest density is reached at 150 degrees C, with the PANF concentration of 0.7%. The low-density PANF aerogels show high specific compressive strengths and low thermal conductivities, which are comparable to those resulting from the freeze-drying or supercritical drying method. Furthermore, the shrinkage phenomenon in the drying process could be skillfully utilized for the preparation of PANF aerogel-coated objects. The PANF aerogels could be applied as a thermal insulating material or shock absorption material in practical applications.

Automated summary

Aerogel is a low-density, highly porous material closely connected to complex processing methods. By using a modified freezing-drying method with polymerization-induced aramid nanofibers as building blocks, all-para-aromatic-amide aerogels with high efficiency can be prepared. The aerogels have high compressive strengths and low thermal conductivities, making them suitable for applications as thermal insulating or shock absorption materials.