College of Chemistry and Molecular Sciences , Wuhan University , Wuhan 430072 , China.
School of Textile Materials and Engineering , Wuyi University , Jiangmen 529020 , China.
ACS Nano. 2019 Apr 23;13(4):4843-4853. doi: 10.1021/acsnano.9b02081. Epub 2019 Apr 8.
While tremendous efforts have been dedicated to developing environmentally friendly films made from natural polymers and renewable resources, in particular, multifunctional films featuring extraordinary mechanical properties, optical performance, and ordered nanostructure, challenges still remain in achieving all these characteristics in a single material via a scalable process. Here, we designed a green route to fabricating strong, super tough, regenerated cellulose films featuring tightly stacked and long-range aligned cellulose nanofibers self-assembled from cellulose solution in alkali/urea aqueous systems. The well-aligned nanofibers were generated by directionally controlling the aggregation of cellulose chains in the hydrogel state using a preorientation-assisted dual cross-linking approach; i.e., a physical cross-linking was rapidly introduced to permanently reserve the temporarily aligned nanostructure generated by preorienting the covalent cross-linked gels. After a structural densification in air-drying of hydrogel, high strength was achieved, and more importantly, a record-high toughness (41.1 MJ m) in anisotropic nanofibers-structured cellulose films (ACFs) was reached. Moreover, the densely packed and well-aligned cellulose nanofibers significantly decreased the interstices in the films to avoid light scattering, granting ACFs with high optical clarity (91%), low haze (<3%), and birefringence behaviors. This facile and high-efficiency strategy might be very scalable in fabricating high-strength, super tough, and clear cellulose films for emerging biodegradable next-generation packaging, flexible electronic, and optoelectronic applications.
虽然人们已经付出了巨大的努力来开发由天然聚合物和可再生资源制成的环保薄膜，特别是具有非凡机械性能、光学性能和有序纳米结构的多功能薄膜，但在通过可扩展的工艺在单一材料中实现所有这些特性方面仍然存在挑战。在这里，我们设计了一种绿色途径来制造强韧的、可再生纤维素薄膜，其特点是在碱/尿素水溶液体系中，纤维素溶液自组装形成紧密堆积和长程取向的纤维素纳米纤维。通过使用预定向辅助双交联方法，定向控制水凝胶状态下纤维素链的聚集，从而产生良好取向的纳米纤维；即快速引入物理交联，以永久保留通过预定向共价交联凝胶产生的暂时取向的纳米结构。在水凝胶的空气干燥过程中进行结构致密化后，实现了高强度，更重要的是，在各向异性纳米纤维结构纤维素薄膜（ACF）中达到了创纪录的高韧性（41.1MJ m）。此外，致密且取向良好的纤维素纳米纤维显著减小了薄膜中的间隙，以避免光散射，使 ACF 具有高光学清晰度（91%）、低雾度（<3%）和双折射行为。这种简单高效的策略在制造高强度、超韧性和透明纤维素薄膜方面具有很大的可扩展性，可用于新兴的可生物降解的下一代包装、柔性电子和光电应用。
