Cellulose nanofibril foams are cellulose-based porous materials with outstanding mechanical properties, resulting from the high strength-to-weight ratio of nanofibrils. Here we report the development of an optimized fabrication process for highly porous cellulose foams, based on a well-controlled freeze-thawing-drying (FTD) process at ambient pressure. This process enables the fabrication of foams with ultra-high porosity, up to 99.4%, density of 10 mg/cm3, and liquid (such as oil) absorption capacity of 100 L/kg. The proposed approach is based on the ice-templating of nanocellulose suspension in water, followed by thawing in ethanol and drying at environmental pressures. As such, the proposed fabrication route overcomes one of the major bottle-necks of the classical freeze-drying approach, by eliminating the energy-demanding vacuum drying step required to avoid wet foam collapse upon drying. As a result, the process is simple, environmentally friendly, and easily scalable. Details of the foam development fabrication process and functionalization are thoroughly discussed, highlighting the main parameters affecting the process, e.g., the concentration of nanocellulose and additives used to control the ice nucleation. The foams are also characterized by mechanical tests and oil absorption measurements, which are used to assess the foam absorption capability as well as the foam porosity. Compound water-in-oil drop impact experiments are used to demonstrate the potential of immiscible liquid separation using cellulose foams.
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机译:纤维素纳米原纤维泡沫是基于纤维素的多孔材料,由于纳米原纤维的高强度重量比,因此具有出色的机械性能。在这里,我们报告了一种在环境压力下基于良好控制的冻融干燥(FTD)工艺的高度多孔纤维素泡沫的优化制造工艺的开发。该工艺能够制造出具有高达99.4%的超高孔隙率,密度为10 mg / cm 3 sup>和100 L / kg的液体(例如油)吸收能力的泡沫。所提出的方法是基于将纳米纤维素悬浮液在水中进行冰模板化,然后在乙醇中解冻并在环境压力下干燥。这样,通过消除为避免湿泡沫在干燥时倒塌所需的耗能的真空干燥步骤,提出的制造路线克服了传统冷冻干燥方法的主要瓶颈之一。结果,该过程简单,环保并且易于扩展。深入讨论了泡沫开发制造过程和功能化的细节,重点介绍了影响该过程的主要参数,例如,纳米纤维素的浓度和用于控制冰核形成的添加剂。泡沫还通过机械测试和吸油率测量来表征,这些测试用于评估泡沫吸收能力以及泡沫孔隙率。复合油包水跌落冲击试验用于证明使用纤维素泡沫进行不混溶液体分离的潜力。
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