Nanoporous networks prepared by simple air drying of aqueous TEMPO-oxidized cellulose nanofibril dispersions.
Nanoporous networks prepared by simple air drying of aqueous TEMPO-oxidized cellulose nanofibril dispersions.
复制标题
DOI：
10.1021/bm300041k
复制
发表时间：
2012-02
影响因子：
6.2
通讯作者：
Junji Nemoto;T. Soyama;Tsuguyuki Saito;A. Isogai
中科院分区：
文献类型：
--
作者：
Junji Nemoto;T. Soyama;Tsuguyuki Saito;A. Isogai
具有纳米孔径的网状材料因其在医院和食品医疗洁净室的高效微粒空气（HEPA）过滤器、工业洁净室的超低渗透空气（ULPA）过滤器、复合增强框架、催化剂支撑和组织工程支架等方面的潜在应用而受到广泛关注。纤维素以结晶纳米原纤维的形式存在于植物细胞壁中，特别是木质纤维素纳米原纤维具有极小的宽度（约4 nm）、高长宽比和高弹性模量。6,7因此，从纤维素纳米原纤维中制备高性能的新型生物基环保多孔网络材料有望成为可能。木纤维素在水中的机械分解产生纤维化纤维素，纤维化纤维素由成束的纤维素纳米原纤维组成，宽度为25 - 100纳米。最近，许多预处理方法，如化学改性和酶水解纤维素纤维，在水中机械解体之前，已被证明对纤维素的纳米纤维是有效的。10−13在这些预处理中，2,2,6,6 -四甲基哌啶-1-氧（TEMPO）介导的木材纤维素纤维氧化使纤维素纳米原纤维在水中完全个体化，这在功能化和工业应用方面是有利的。当纤维素纳米原纤维或纳米纤维素的水分散体被直接干燥时，纤维素纳米原纤维在水分蒸发过程中紧密地聚集在一起，形成许多氢键。所获得的膜至少在干燥条件下具有低氧透性或高氧阻隔性。7,14对水性纳米纤维素分散体进行冷冻干燥或超临界干燥已被提出用于制备含有多孔纳米纤维网络的纤维素气凝胶。15−18这些气凝胶不仅具有高比表面积和低密度，而且具有比其他有机聚合物更好的机械性能。然而，由于冷冻干燥或超临界干燥需要特殊的设备和耗时的溶剂交换步骤，生产率极低。有机溶剂的使用限制了工业生产，需要溶剂回收系统。此外，在工业规模上建造和运行用于超临界干燥的高压灭菌器涉及重大成本。因此，更简单的过程，如热风干燥的水纳米纤维素分散体，将是理想的多孔纳米纤维素网络的形成。
Network materials with nanosized pores have attracted a great deal of attention because they have potential applications as high efficiency particulate air (HEPA) filters in hospitals and clean rooms for the food and medical fields, ultralow penetration air (ULPA) filters for industry clean rooms, composite-reinforcement frameworks, catalyst supports, and scaffolds for tissue engineering. 1− 5 Cellulose is present as crystalline nanofibrils in plant cell walls, and wood cellulose nanofibrils in particular have extremely small widths of∼ 4 nm, high aspect ratios, and high elastic moduli. 6, 7 Thus, new biobased and environmentally friendly porous network materials with high performances are expected to be able to be prepared from cellulose nanofibrils. Mechanical disintegration of wood celluloses in water produces fibrillated celluloses that consist of bundles of cellulose nanofibrils 25− 100 nm in width. 8, 9 Recently, a number of pretreatments such as chemical modification and enzymatic partial hydrolysis of cellulose fibers prior to mechanical disintegration in water have been shown to be effective in nanofibrillation of celluloses. 10− 13 Among these pretreatments, 2, 2, 6, 6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of wood cellulose fibers enables complete individualization of cellulose nanofibrils in water, which is advantageous in terms of functionalization and industrial applications.When aqueous dispersions of cellulose nanofibrils or nanocelluloses are directly dried, cellulose nanofibrils are tightly aggregated to one another during water evaporation, forming numerous hydrogen bonds. The obtained films have low oxygen permeabilities or high oxygen barrier properties at least under dry conditions. 7, 14 Freeze-drying or supercritical drying of aqueous nanocellulose dispersions has been proposed to prepare cellulose aerogels containing porous nanofibril networks. 15− 18 These aerogels not only have high specific surface areas and low densities, but also better mechanical properties than those of other organic polymers. However, because freeze-drying or supercritical drying require special equipment and time-consuming solventexchange steps, productivity is extremely low. The use of organic solvents limits industrial production, and a solvent recovery system is required. Furthermore, significant costs are involved in building and running an autoclave for supercritical drying at the industrial scale. Therefore, more simple processes, such as hot-air drying of the aqueous nanocellulose dispersions, would be desirable for the formation of porous nanocellulose networks.