关键词: 气凝胶纤维, 细菌纤维素, 海藻酸钠, 湿法纺丝, 扭转性能

Abstract: "Throughout the history of human civilization, thermal insulation materials have always played a pivotal role. From early humans using animal furs to keep warm, to the emergence of hand-woven linen fabrics during the Neolithic Age, and later to the large-scale application of synthetic fibers after the Industrial Revolution, humanity's need for temperature regulation has driven the continuous innovation of textile materials. However, today, traditional thermal insulation materials can no longer meet the needs of workers in extreme environments such as polar regions and aerospace. The emergence of aerogel materials provides a new path to break through the bottleneck of thermal protection. Due to their unique nanoporous structure and ultra-high porosity, these materials exhibit astonishing insulation properties, showing immense potential for applications in extreme environmental protection. Nevertheless, the industrial application of aerogel fibers still faces critical technological bottlenecks. Their three-dimensional network structure is susceptible to mechanical stress during textile processing such as spinning and twisting, resulting in fiber breakage or pore collapse. Therefore, it is of great significance to develop aerogel fibers that possess both thermal insulation properties and adaptability to textile processing. Bacterial nanocellulose (BNC) is synthesized by microorganisms and has a unique network structure, endowing it with significantly higher strength compared to plant cellulose. Sodium alginate (SA), as a natural anionic polysaccharide, can crosslink with Ca²⁺ to form an ""egg-box"" structure, so as to enhance its mechanical properties. The combination of BNC and SA not only leverages the three-dimensional network structure of BNC to maintain high porosity, but also improves flexibility through the ionic crosslinking of SA. More importantly, both materials are bio-based and environmentally friendly. In this paper, bacterial cellulose and sodium alginate were mixed, and a CaCl2 aqueous solution was used as the coagulation bath to prepare hydrogel fibers via wet spinning. Subsequently, the hydrogel fibers were solvent-exchanged with tert-butanol and then freeze-dried to obtain aerogel fibers. Currently, studies on the mechanical properties of aerogel fibers mainly focus on tensile properties, while studies on their torsional properties are scarce. In this paper, a single-fiber torsion tester was used for the first time to investigate the torsional properties of aerogel fibers. The single torsion limit, twist angle, and torsional recovery rate of the samples were characterized, and changes in the fiber morphology, structure, and tensile strength before and after torsion were analyzed. The experimental results showed that the torsional resistance of bacterial cellulose/calcium alginate hybrid aerogel fibers gradually increased with the rising proportion of SA. The single torsion limits of the fibers were consistently above 15 r, with a maximum of (20.91.3) r, and the breaking twist angle could reach (62.31.4)°. Additionally, the porosity of the aerogel fibers before torsion was all above 90%. When twisted to 60% of their torsional limit, the porosity remained above 71%, and even after torsional fracture, the porosity was still entirely above 40%. These findings provide a theoretical basis for the subsequent spinning and processing of aerogel fibers."

Key words: "aerogel fiber, bacterial cellulose, sodium alginate, wet spinning, torsional property "