关键词: 废弃芳纶, 芳纶纳米纤维, 超薄气凝胶膜, 高透光性, 隔热性

Abstract: Aramid materials are extensively employed in the fields of aerospace, electronic devices, and intelligent wearables owning to their remarkable attributes of high strength, robust processability, commendable temperature resistance, and corrosion resistance. The widespread utilization of aramid unavoidably generates a substantial quantity of aramid wastes.
To maximize the utilization of aramid wastes, this study successfully produced ultra-thin aramid nanofiber (ANFs) aerogel films with high transparency and flexibility. This was achieved through the combination of immersion precipitation phase inversion and freeze-drying techniques, with waste aramid as the raw material. The morphologies, chemical structure, optical properties, thermal stability and insulation of the resulting ANFs aerogel films were characterized by using FESEM, FTIR, UV-Vis, TG-DTG and FILR. The results demonstrated the average diameter of ANFs is 18.32 nm. In comparison to aramid waste, the main chemical structures of the ANFs did not undergo significant changes, but there was noticeable improvement in the content of free amino groups. Additionally, to regulate the morphology of ANFs aerogel film, the film forming process parameters and coagulation bath temperature were optimized. These factors played a role in determining the morphologies of the fabricated films. The thickness of the fabricated ANFs aerogel film ranged from 0.5 to 2 μm, and such thickness could be controlled by manipulating the concentration of the ANFs solution and the coagulation bath temperature. The cross-sectional analysis of the ANFs films reveals the presence of intricate three-dimensional network structures. The as-fabricated samples exhibit notable characteristics of ANFs aerogel films, including a specific surface area of 52.73 m2 g-1, a porosity of 92.43% and a pore size of 7.92 nm. Additionally, the integrated performance of these aerogel films was evaluated, demonstrating their exceptional transparency. Within the visible range of 500-780 nm, the transmittance of these films exceeds 70%, with the highest transmittance reaching 90.70 %. Notably, the ANFs aerogel films exhibit an almost negligible UV transmittance rate, approaching 0%, indicating dramatic UV resistance. The ANFs aerogel films demonstrate remarkable thermal insulation capacities, as evidenced by a temperature difference of 28 ℃ between a heat source (120 ℃) and the surface of the four-layer ANFs aerogel films (with a single layer thickness of 1.36 μm). Furthermore, these films exhibit favorable thermal stability with a minimum decomposition temperature (Td) of 450℃. Additionally, the films exhibit exceptional flexibility and conformability. 
This paper presents the construction of aerogel films with integrated performance, utilizing exfoliated ANFs derived from aramid fiber wastes. This approach enables the efficient utilization of aramid waste resources. The research employs rigorous evaluation methods to provide valuable insights into the formation of aerogel films. The obtained results serve as reference for the design, development, continuous and batch production, and utilization of desirable ANFs aerogel films.

Key words: waste aramid, aramid nanofiber, ultra-thin aerogel film, high transparency, thermal insulation