Schiele Carina, Ruiz-Caldas Maria-Ximena, Wu Tingting, Nocerino Elisabetta, Åhl Agnes, Mathew Aji P, Nyström Gustav, Bergström Lennart, Apostolopoulou-Kalkavoura Varvara
Department of Materials and Environmental Chemistry, Stockholm University, SE-10691 Stockholm, Sweden.
Cellulose & Wood Materials Laboratory, Empa, Überlandstrasse 129, CH-8600, Dübendorf, Switzerland.
Nanoscale. 2024 Aug 7;16(30):14275-14286. doi: 10.1039/d4nr01720j.
Biopolymer-based functional materials are essential for reducing the carbon footprint and providing high-quality lightweight materials suitable for packaging and thermal insulation. Here, cellulose nanocrystals (CNCs) were efficiently upcycled from post-consumer cotton clothing by TEMPO-mediated oxidation and HCl hydrolysis with a yield of 62% and combined with wood cellulose nanofibrils (CNFs) to produce anisotropic foams by unidirectional freeze-casting followed by freeze drying (FD) or supercritical-drying (SCD). Unidirectional freeze-casting resulted in foams with aligned macropores irrespective of the drying method, but the particle packing in the foam wall was significantly affected by how the ice was removed. The FD foams showed tightly packed and aligned CNC and CNF particles while the SCD foams displayed a more network-like structure in the foam walls. The SCD compared to FD foams had more pores smaller than 300 nm and higher specific surface area but they were more susceptible to moisture-induced shrinkage, especially at relative humidities (RH) > 50%. The FD and SCD foams displayed low radial thermal conductivity, and the FD foams displayed a higher mechanical strength and stiffness in compression in the direction of the aligned particles. Better understanding how drying influences the structural, thermal, mechanical and moisture-related properties of foams based on repurposed cotton is important for the development of sustainable nanostructured materials for various applications.
基于生物聚合物的功能材料对于减少碳足迹以及提供适用于包装和隔热的高质量轻质材料至关重要。在此，通过TEMPO介导的氧化和HCl水解从消费后的棉质衣物中高效回收纤维素纳米晶体（CNC），产率为62%，并将其与木质纤维素纳米纤维（CNF）结合，通过单向冷冻铸造，然后冷冻干燥（FD）或超临界干燥（SCD）来制备各向异性泡沫。无论干燥方法如何，单向冷冻铸造都会产生具有排列整齐大孔的泡沫，但泡沫壁中的颗粒堆积情况会受到除冰方式的显著影响。FD泡沫显示出紧密堆积且排列整齐的CNC和CNF颗粒，而SCD泡沫在泡沫壁中呈现出更类似网络的结构。与FD泡沫相比，SCD泡沫具有更多小于300 nm的孔隙和更高的比表面积，但它们更容易受到水分引起的收缩影响，尤其是在相对湿度（RH）> 50%时。FD和SCD泡沫均显示出较低的径向热导率，并且FD泡沫在排列颗粒方向上的压缩中表现出更高的机械强度和刚度。更好地理解干燥如何影响基于再生棉的泡沫的结构、热、机械和与水分相关的性能，对于开发适用于各种应用的可持续纳米结构材料至关重要。
