As the global environment has become increasingly threatened, nanocellulose-based lightweight porous materials have attracted more and more attention in the field of thermal insulation due to their sustainability and biocompatibility. However, nanocellulose-based lightweight porous materials have poor elasticity and the porous structure is prone to irreversible collapse during compression. In order to give nanocellulose-based lightweight porous materials wider application scenarios in thermal insulation, herein, we selected blocked waterborne polyurethane (BWPU) to enhance the flexibility of nanocellulose cryogel, and successfully prepared anisotropic, elastic cellulose nanofibril-waterborne polyurethane (CNF-WPU) cryogel by directional freeze-casting and freeze-drying combined with high temperature post-treatment. The obtained anisotropic CNF-WPU cryogel has good elasticity, demonstrated by a high reversible compression of 60%. Moreover, the anisotropic structure also leads to anisotropic thermal conductivity, an extremely low thermal conductivity of 0.02755 W m⁻¹ K⁻¹ in the radial direction (perpendicular to the lamella structure) and a thermal conductivity of 0.03924 W m⁻¹ K⁻¹ in the axial direction (parallel to the lamella structure) can be achieved. And the CNF-WPU cryogel still retain its outstanding thermal insulation performance (thermal conductivity of 0.02755 W m⁻¹ K⁻¹) after a reversible compression of 60%.

Graphical abstract

中文翻译：

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水性聚氨酯交联的各向异性、弹性纤维素纳米纤维冷冻凝胶，具有优异的隔热性能

随着全球环境日益受到威胁，纳米纤维素基轻质多孔材料以其可持续性和生物相容性在保温隔热领域越来越受到关注。然而，基于纳米纤维素的轻质多孔材料弹性较差，多孔结构在压缩过程中容易发生不可逆的塌陷。为了让纳米纤维素基轻质多孔材料在保温隔热方面有更广泛的应用场景，我们选择封闭水性聚氨酯（BWPU）来增强纳米纤维素冷冻凝胶的柔韧性，并成功制备了各向异性、弹性纤维素纳米纤维-水性聚氨酯（CNF-WPU）。 ) 冷冻凝胶通过定向冷冻浇注和冷冻干燥结合高温后处理。获得的各向异性 CNF-WPU 冷冻凝胶具有良好的弹性，可通过 60% 的高可逆压缩来证明。此外，各向异性结构还导致各向异性导热系数，0.02755 W m 的极低导热系数可以实现径向(垂直于薄片结构)的-1 K -1 和轴向(平行于薄片结构)的0.03924 W m ^-1  K ^-1的^热 导^率。并且CNF-WPU冷冻凝胶在经过60%的可逆压缩后仍保持其出色的隔热性能（导热系数为0.02755 W m ^-1  K ^{-1 ）。}

图形概要