Comparison of tension wood and normal wood for oxidative nanofibrillation and network characteristics

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ORIGINAL RESEARCH

Comparison of tension wood and normal wood for oxidative nanofibrillation and network characteristics Simon Jonasson . Anne Bu¨nder Kristiina Oksman

. Oisik Das

. Totte Niittyla¨

.

Received: 3 April 2020 / Accepted: 23 October 2020 Ó The Author(s) 2020

Abstract 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-1oxyl, and the morphology and mechanical behaviors of the nanofibril suspensions and networks were Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10570-020-03556-1) contains supplementary material, which is available to authorized users.

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.

S. Jonasson  O. Das  K. Oksman (&) Division of Materials Science, Lulea˚ University of Technology, Lulea˚, Sweden e-mail: [email protected] A. Bu¨nder  T. Niittyla¨ Department of Forest Genetics and Plant Physiology, Umea˚ Plant Science Centre, Swedish University of Agricultural Sciences, Umea˚, Sweden K. Oksman Mechanical and Industrial Engineering, University of Toronto, Toronto, Canada

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Cellulose

Graphic abstract

Keywords Cellulose nanofibril  Nanofibrillation  Fibril network  TEMPO oxidation  Tension wood  Wood properties

Introduction Cellulose nanofibrils (CNFs) are high-aspect-ratio fibers isolated from the native cellulose microfibrils that comprise the cell walls of all plants. Research and applications of CNFs have increased rapidly, as demonstrated by the large increase in CNF-related publications and patents in the last decade (Charreau