In extreme industrial or urban environments, lightweight thermal insulation textiles for personal heat management are crucial for reducing the risk of heat illness or hypothermia. Natural polymers such as cellulose and chitin, with their excellent environmental friendliness and renewability, have become highly attractive bio-based raw materials. Meanwhile, aerogels are widely recognized as exceptional insulating materials due to their high porosity and low thermal conductivity. To overcome the dependence of traditional aerogels on molds and achieve mass production, mature wet spinning technology was introduced to continuously process aerogel precursors into fibers, laying the foundation for continuous production of geometrically diverse textiles.

However, existing textile fillings and coatings still face bottlenecks such as heaviness, fossil-derived materials, and insufficient biocompatibility. Although natural polymers are sustainable, they lack adequate insulation when lightweighted, while heavier structures compromise breathability and comfort. The most critical challenge lies in the fact that aerogel fiber preparation often heavily relies on tedious solvent exchange and high-pressure supercritical drying techniques. This significantly increases process complexity, production costs, and safety constraints, and is extremely difficult to integrate with continuous spinning processes, thereby severely hindering the scalable industrial application of efficient bio-based thermal insulation textiles.

To address the above challenges, a team led by Wuhan University of Technology and others conducted systematic research using ZEPTOOLS' ZEM series scanning electron microscope. Drawing inspiration from the structure of down feathers, the team developed bio-based cellulose/chitin coaxial cryogel fibers with triple thermal insulation barriers via coaxial wet spinning combined with freeze-drying technology, achieving a core innovation in the continuous scalable preparation of high-performance thermal insulation textile fibers without the need for supercritical drying.

Title: Down-Feather-Inspired Cellulose/Chitin Coaxial Cryogel Fibers with Triple Barriers for Thermal Insulation Textiles
Journal: Biomacromolecules
URL: https://doi.org/10.1021/acs.biomac.6c00864

Inspired by the dual-pore thermal insulation structure of natural down, the research team developed a novel continuous preparation strategy for bio-based cellulose/chitin coaxial cryogel fibers. The study cleverly employed coaxial wet spinning technology, extruding the outer cellulose solution and inner chitin solution simultaneously into a dilute sulfur acid coagulation bath. Through the significantly different solidification speed differences of the two polysaccharide components, a stable core-shell hierarchical coaxial structure was formed directly in a single spinning step. In the subsequent drying stage, this process directly utilized conventional freeze-drying to replace the traditionally mandatory, high-cost, and cumbersome supercritical drying required in conventional aerogel manufacturing. This preparation pathway not only greatly reduced process complexity and safety risks but also achieved efficient compatibility with existing industrialized continuous fiber processing lines, opening a brand-new direction for large-scale continuous production of bio-based thermal insulation textiles.

To elucidate the fine correlation between the internal micro-morphology of the coaxial aerogel fibers and their thermal insulation mechanism, the research team conducted an in-depth analysis of the core-shell hierarchical pore structure of the fibers. During this process, researchers utilized ZEPTOOLS' ZEM series desktop scanning electron microscope to perform high-resolution imaging observations of the material's micro-morphology at an accelerating voltage of 15 kV. Electron microscopy results conclusively confirmed that the freeze-dried aerogel fibers successfully constructed a unique microscopic triple thermal insulation barrier: the outermost layer consists of a porous shell of regenerated cellulose micrometer-scale pores, the core region is a nanometer-scale pore network composed of chitin, and between the shell and core lies a micrometer-scale interfacial air interlayer. Revealed clearly by the ZEM series desktop scanning electron microscope, this biomimetic three-layer architecture suppresses heat transfer through solid conduction, gas conduction, and interfacial heat transfer on a microscopic scale by shortening the mean free path of gas molecules, breaking solid thermal bridges, and increasing infrared radiation scattering.

Excellent mechanical properties are the core prerequisite for cryogel fibers to enter practical textile applications. Therefore, the research team systematically regulated the tensile properties of fibers at different polysaccharide concentrations. Experimental results showed that when both the cellulose shell layer and chitin core layer used spinning solutions with a mass fraction of 4%, the cryogel fibers exhibited the most ideal tensile strength and denseness of internal structure, effectively avoiding phase separation unevenness and microscopic defects caused by excessively high concentrations. In mechanical testing, a single coaxial cryogel fiber with optimized components demonstrated remarkable load-bearing capacity, successfully suspending a 500-gram weight. Meanwhile, these fibers possessed excellent bending flexibility and could be easily knotted. Throughout manual weaving and repeated winding/unwinding around fingers, the entire core-shell microstructure and interfacial air layer remained undistorted, undamaged, and free of fiber detachment, fully validating the feasibility of large-scale weaving.

Based on the superior physical properties of the fibers, the research team wove them into bulk textiles and comprehensively evaluated their personal heat management efficacy from two dimensions: static thermal conductivity and dynamic environmental simulation. Test data showed that the coaxial aerogel fiber textiles exhibited an extremely low thermal conductivity of only 0.033 W/(m·K), significantly lower than most reported similar bio-based textile materials. In harsh environment simulation tests on hot and cold dual-stage temperature fields, the textile maintained a relatively lower surface temperature on an 80°C high-temperature hotplate, significantly extending the time to reach steady state, while on a -20°C cold plate it exhibited an extremely slow cooling rate, with surface temperatures after stabilization markedly higher than those of traditional commercial cotton, polyester, and wool textiles. This series of significant advantages manifested in macroscopic thermodynamics strongly demonstrated that the bio-based coaxial fibers achieved a perfect balance of lightweight and efficient bidirectional thermal insulation without relying on high-density materials.

ZEPTOOLS' ZEM series scanning electron microscope is a highly integrated, portable, and cost-effective scientific instrument. It features rapid pump-down, high imaging speed, diverse detector options, suitable for morphology observation and compositional analysis, and can accommodate various in-situ experimental needs. The equipment has low installation environment requirements, is not floor-restricted, and is easy to operate, allowing even non-professionals to get started quickly. It can be more broadly applied in new materials research, life sciences, failure analysis, industrial quality inspection, and many other fields, providing a powerful and cost-effective microscopic characterization solution for a wide range of research institutions and enterprises.