Freezing-Extraction/Vacuum-Drying Method for Robust and Fatigue-Resistant Polyimide Fibrous Aerogels and Their Composites with Enhanced Fire Retardancy

Abstract

In the rapid development of modern materials, there is a great need for novel energy-saving, time-saving, cost-saving, and facile approaches to fabricate light, low-density, and high-porosity aerogels with excellent mechanical and thermal performance. In this work, a freeze-extraction method combined with normal vacuum-drying (VD), using short electrospun polyimide (PI) fibers as a supporting skeleton, was developed to prepare high-performance PI fibrous aerogels (PIFAs) without the need for a special drying process. The resulting PIFAs exhibit low density (≤ 52.8 mg·cm−3) and high porosity (> 96%). The PIFAs are highly fatigue resistant, with cycling compression for at least 20 000 cycles and a low energy-loss coefficient. A thermal conductivity of 40.4 mW·m−1·K−1 was obtained for a PIFA with a density of 39.1 mg·cm−3. Further modification of the PIFAs with polysilazane led to enhanced fire resistance and a high residue (> 70%) in a nitrogen atmosphere. These excellent properties make PIFAs and their composites promising candidates for lightweight construction, thermal insulating, and fireproof layers for the construction industry, aviation, and aerospace industries, as well as for high-temperature reaction catalyst carriers. In addition, the proposed freezing-extraction/VD approach can be extended to other material systems to provide savings in energy, time, and costs.