关键词: 莱赛尔纤维, 2,2,6,6-四甲基哌啶氧化物, 聚乙烯醇, 纤维素气凝胶, 隔热性能, 压缩性能

Abstract: Thermal insulation is one of the crucial needs for the development of human society. Fibers such as cotton and linen were among the earliest thermal insulation materials used and are widely found in nature. It is necessary to increase the thicknes to achieve excellent thermal insulation effects. However, enhancing the thermal resistance of clothing by adding thickness typically exhibits diminishing marginal returns, where the thermal resistance per unit thickness decreases as the overall thickness increases. Meanwhile, clothing weight increases linearly with thickness, which contradicts the development trend of lightweight and warm cold-weather apparel. Therefore, it is necessary to develop materials that combine lightweight properties with superior thermal insulation performance. Cellulose aerogel materials, characterized by their unique three-dimensional nanoscale porous structures, exhibit outstanding thermal insulation properties. Their pore sizes, typically ranging from 2 nm to 50 nm, are smaller than the mean free path of air molecules (approximately 70 nm), effectively suppressing convective heat transfer. Additionally, their highly porous structure also significantly reduces solid thermal conduction. Nevertheless, cellulose aerogel materials have certain limitations. Cellulose is insoluble in water and tends to settle easily in aqueous solutions, and the dispersion of cellulose in water greatly impacts the final properties of the aerogel. Furthermore, the preparation process for cellulose aerogels is complex and costly, and the materials often exhibit poor mechanical properties, which restrict their application scope. Consequently, there is a need to find a simple and feasible method for producing aerogels with good mechanical properties and low thermal conductivity. To address the issue of cellulose being prone to sedimentation in water and to improve the compressive mechanical properties and pore structure of cellulose aerogels, easily fibrillatable Lyocell fibers were employed as the raw material. The process involved mechanical treatment and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation of the Lyocell fibers, followed by steps such as pressure filtration, drying, and redispersion to prepare a uniform cellulose dispersion. Subsequently, cellulose aerogels were fabricated via freeze-drying. Additionally, cellulose composite aerogels were prepared by adding 0.5% (by concentration) polyvinyl alcohol (PVA) to the cellulose dispersion, followed by freeze-drying. The effects of cellulose concentration and the addition of PVA on the structure and properties of aerogels were studied. The results indicated that the cellulose underwent significant fibrillation after mechanical treatment and TEMPO oxidation, and the oxidized cellulose could be uniformly dispersed in water. As the cellulose concentration increased, both the thermal conductivity of cellulose aerogel and cellulose composite aerogel exhibited a trend of initially decreasing and then increasing. When the cellulose concentration was 0.75%, the thermal conductivity of both types of aerogels reached their lowest values, with the cellulose aerogel showing a thermal conductivity of 0.02462 W/(m·K) and the cellulose composite aerogel showing 0.02496 W/(m·K). The addition of PVA increased the specific surface area and pore wall thickness of cellulose composite aerogel, while also enhancing its compressive elastic recovery performance.

Key words: Lyocell fiber, TEMPO, polyvinyl alcohol, cellulose aerogel, thermal insulation performance, compressive performance