Cellulose nanofibrils (CNFs) are top-down nanomaterials obtainable from abundant lignocelluloses. Despite recent advances in processing technologies, the effects of variations in the lignocellulose structure and composition on CNF isolation and properties are poorly understood. In this study, we compared the isolation of CNFs from tension wood (TW) and normal wood (NW) from Populus tremula (aspen). The TW has a higher cellulose content, native cellulose fibrils with a larger crystalline diameter, and less lignin than the NW, making it an interesting material for CNF isolation. The wood powders were oxidized directly by 2,2,6,6-tetramethylpiperidin-1-oxyl, and the morphology and mechanical behaviors of the nanofibril suspensions and networks were characterized. The TW was more difficult to fibrillate by both chemical and mechanical means. Larger nanofibrils (5–10 nm) composed of 1.2 nm structures were present in the TW CNFs, whereas the NW samples contained more of thin (1.6 nm) structures, which also comprised 77% of the solid yield compared to the 33% for TW. This difference was reflected in the TW CNF networks as decreased transmittance (15% vs. 50%), higher degree of crystallinity (85.9% vs. 78.0%), doubled toughness (11 MJ/m³) and higher elongation at break (12%) compared to NW. The difference was ascribed to greater preservation of the hierarchical, more crystalline microfibril structure, combined with a more cellulose-rich network (84% vs. 70%). This knowledge of the processing, structure, and properties of CNFs can facilitate the breeding and design of wood feedstocks to meet the increasing demand for nanoscale renewable materials.

Graphic abstract

中文翻译：

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张力木材和普通木材用于氧化纳米原纤化和网络特性的比较

纤维素纳米纤维（CNFs）是可以从丰富的木质纤维素中获得的自上而下的纳米材料。尽管加工技术方面有最新进展，但人们对木质纤维素结构和组成的变化对CNF分离和性能的影响知之甚少。在这项研究中，我们比较的CNF从拉木（TW）和正常的木材（NW）隔离欧洲山杨（阿斯彭）。TW比NW具有更高的纤维素含量，天然纤维素原纤维具有更大的晶体直径和更少的木质素，这使其成为用于CNF分离的有趣材料。木粉被2,2,6,6-四甲基哌啶-1-氧基直接氧化，表征了纳米原纤维悬浮液和网络的形态和力学行为。TW通过化学和机械方法均难以原纤化。TW CNF中存在由1.2 nm结构组成的较大的纳米原纤维（5-10 nm），而NW样品包含更多的薄（1.6 nm）结构，与TW的33％相比，其还占固体产率的77％ 。TW CNF网络反映了这种差异，如透射率降低（15％对50％），结晶度更高（85.9％对78.0％），韧性加倍（11 MJ / m）³）和更高的断裂伸长率（12％）。差异归因于更好地保留了分层的，更结晶的微纤维结构，并结合了纤维素含量更高的网络（84％比70％）。对CNF的加工，结构和特性的了解可以促进木材原料的育种和设计，以满足对纳米级可再生材料日益增长的需求。

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