Abstract:

Objective This study aims to investigate the relationship between multi-scale structure and thermal insulation performance of bacterial cellulose （BC） composite aerogels. By addressing the microstructure control mechanisms during preparation， this work seeks to establish a green and efficient strategy for utilizing natural nanocellulose in high-performance insulation materials.

Method To achieve the efficient application of natural nanocellulose materials in the field of thermal insulation， this paper proposes a novel strategy for constructing multi-scale structured bacterial cellulose nano-aerogels. Using bacterial cellulose as a three-dimensional nanofiber skeleton， a multi-scale aerogel featuring a micrometer-scale framework and a nanoporous structure was fabricated via freeze-drying. The article systematically investigates the effects of different concentrations on the morphology， pore characteristics， and thermal conductivity of the aerogel materials， and comprehensively evaluates their thermal insulation performance.

Results Aerogels are a novel class of materials with unique properties， whose microstructure and macroscopic performance are influenced by multiple factors. This study reveals that precise control of bacterial cellulose concentration enables effective regulation of the micrometer-scale framework， allowing the construction of a multi-scale porous structure. Optimization of this structure is crucial for enhancing aerogel performance. BC-4， for example， exhibited a continuous structure with uniform pore distribution and a porosity as high as 94%. This highly porous structure enabled the aerogel to maintain low density while possessing excellent thermal insulation properties. Additionally， BC-4 demonstrated remarkable thermal stability， with its structure remaining virtually unchanged after heating at 180 ℃ for 360 min. Its thermal conductivity was as low as 0.021 65 W/（m·K）， significantly lower than that of many traditional insulation materials， endowing it with substantial application potential in the field of thermal insulation. A JK804 multi-channel temperature tester was employed to evaluate its thermal insulation performance. Under ambient temperatures of 60， 70， 80， 90， and 100 ℃， the temperature differences between the upper and lower surfaces of the BC aerogel reached 20-24℃， 25-32 ℃， 25.7-36.7 ℃， 35.7-46.1 ℃， 40.2-51.4 ℃， respectively. As the lower surface temperature increased， the temperature change on the upper surface gradually decreased， indicating stable insulation efficiency even at elevated temperatures. Compared with down materials， BC aerogels exhibited superior thermal insulation performance， and the good performance was maintained even after wetting treatment. Furthermore， the aerogel demonstrated excellent flexibility， recovering its original shape within five seconds after folding， suggesting broad application prospects in the field of high-temperature wearable materials.

Conclusion This study successfully utilized freeze-drying technology to achieve the one-step preparation of BC nano-aerogel. By precisely adjusting the concentration of BC， a multi-scale composite aerogel system that combines a micrometer-scale framework with a nano-porous structure was established， and the insulating performance of the aerogel under various temperature conditions was also explored to assess its potential and limitations in practical applications. The research demonstrated the potential of BC nano-aerogel as a high-performance insulating material but also provided new perspectives for further optimizing its performance and expanding its application fields. This innovative approach not only offers a new perspective for the green construction and structure-performance optimization of natural nanofiber composite insulating materials but also， due to the aerogel'

Key words: aerogel, bacterial cellulose, multi-scale structure, thermal conductivity, thermal insulation performance, freeze-drying