Understanding nanocellulose chirality and structure-properties relationship at the single fibril level.

Ivan Usov,Jozef Adamcik,Gustav Nyström,Andreas Fall,Raffaele Mezzenga,Lennart Bergström,Stephan Handschin,Christina Schütz

doi:10.1038/ncomms8564

Ivan Usov, Jozef Adamcik + Show 6 more

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https://doi.org/10.1038/ncomms8564

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Abstract

Nanocellulose fibrils are ubiquitous in nature and nanotechnologies but their mesoscopic structural assembly is not yet fully understood. Here we study the structural features of rod-like cellulose nanoparticles on a single particle level, by applying statistical polymer physics concepts on electron and atomic force microscopy images, and we assess their physical properties via quantitative nanomechanical mapping. We show evidence of right-handed chirality, observed on both bundles and on single fibrils. Statistical analysis of contours from microscopy images shows a non-Gaussian kink angle distribution. This is inconsistent with a structure consisting of alternating amorphous and crystalline domains along the contour and supports process-induced kink formation. The intrinsic mechanical properties of nanocellulose are extracted from nanoindentation and persistence length method for transversal and longitudinal directions, respectively. The structural analysis is pushed to the level of single cellulose polymer chains, and their smallest associated unit with a proposed 2 × 2 chain-packing arrangement.

Highlights

Nanocellulose fibrils are ubiquitous in nature and nanotechnologies but their mesoscopic structural assembly is not yet fully understood
In the present work we provide a comprehensive and consistent structural description over multiple length scales of nanocellulose of different origin and pretreatment: TEMPO-mediated oxidized W-cellulose nanofibrils (CNF), W-cellulose nanocrystals (CNCs) and bacterial cellulose nanocrystals (B-CNC)
We find that all types of nanocellulose fibrils and crystals with an observable twisting along the contour possess a right-handed chirality

Summary

Introduction

Nanocellulose fibrils are ubiquitous in nature and nanotechnologies but their mesoscopic structural assembly is not yet fully understood. Over the last decades, elongated rod-like cellulose nanoparticles, shorter cellulose nanocrystals (CNCs) and longer cellulose nanofibrils (CNF), have been used to form chiral nematic liquid crystals[5], aerogels[6], photonic[7] and inorganic hybrid materials[8] Even though these materials have impressive properties and show great potential for a broad range of applications, the fine structure of their nanocellulose components has not yet been fully elucidated[9]. How CNC arrange in chiral nematic liquid crystalline phases[11,12,13] and how CNF arrange in films[14], aerogels[15] or foams[16] is well characterized In between these two length scales, a gap remains, where the structure and assembly of nanocellulose fibrils are not yet fully understood. With the rapid development of experimental techniques, new and more detailed structural information becomes available, allowing these outstanding fundamental questions to be revisited and conclusively assessed

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