Abstract

Directional freeze-drying is considered to regulate the structure of nanocellulose aerogels with special performances. In this work, TEMPO-oxidized cellulose nanofiber aerogels with high porosity (> 99.5%) and low density (~ 7 mg/cm³) were produced by different freeze-drying methods. The effects of temperature, freezing reagents and freezing methods on the structure and properties of aerogels were investigated. Among them, an anisotropic cellulose aerogel was obtained using a simple and flexible directional freezing in ethanol of − 30 °C by a self-made directional freezer. Our results demonstrated that it could present honeycomb-like pores in the transverse direction and regular directional tunnels in the longitudinal direction, and some attractive features, such as high water adsorption (120 g/g) and stability in water. Compared with other aerogels, this anisotropic structure also provided the aerogel with excellent compressive property (15.2 kPa) and faster liquid transport (4.95 mm/s) in the longitudinal direction than in other directions. The distinctive aerogels based on nanocellulose by directional freeze-drying are also expected to be combined with multifunctional materials to achieve directional applications to meet the requirements of different fields.

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摘要

定向冷冻干燥被认为可以调节具有特殊性能的纳米纤维素气凝胶的结构。在这项工作中，TEMPO氧化的纤维素纳米纤维气凝胶具有高孔隙率（> 99.5％）和低密度（〜7 mg / cm ^3））是通过不同的冷冻干燥方法生产的。研究了温度，冷冻剂和冷冻方法对气凝胶结构和性能的影响。其中，使用自制的定向冷冻机，在− 30°C的乙醇中进行简单灵活的定向冷冻，即可得到各向异性的纤维素气凝胶。我们的结果表明，它可以在横向出现蜂窝状的孔，在纵向出现规则的定向隧道，并具有吸引人的特征，例如高吸水率（120 g / g）和在水中的稳定性。与其他气凝胶相比，这种各向异性的结构还使气凝胶在纵向上的压缩特性（15.2 kPa）和液体传输速度更快（4.95 mm / s），而在其他方向上却更快。

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