Swelling of individual cellulose nanofibrils in water, role of crystallinity: an AFM study
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ORIGINAL RESEARCH
Swelling of individual cellulose nanofibrils in water, role of crystallinity: an AFM study Vegar Ottesen
. Kristin Syverud
Received: 26 March 2020 / Accepted: 6 October 2020 The Author(s) 2020
Abstract Atomic force microscopy (AFM) can be used to quantitatively study nanomaterials in different media, e.g. vacuum, air, or submerged in a liquid. A technique was developed to study swelling of individual cellulose nanofibrils (CNFs) using AFM. As a case study, CNFs with different degrees of crystallinity (DoC) were examined for swellability going from dry to wet (submerged in de-ionized water). Swelling was found to depend on DoC, but no
significant correlation between fibril diameter and swellability was seen. Upon introduction of de-ionized water high DoC samples (65 2%) were found to have a diameter increase of 34% on average, whereas low DoC (44 2%) were found to have a diameter increase of 44% on average. A tested control, consisting of platinum nanowires on silisium, did not swell.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10570-020-03517-8) contains supplementary material, which is available to authorized users. V. Ottesen (&) K. Syverud Department of Chemical Engineering, NTNU, Trondheim, Norway e-mail: [email protected] K. Syverud e-mail: [email protected] K. Syverud RISE PFI, Trondheim, Norway
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Cellulose
Graphic abstract
Keywords
Cellulose nanofibrils Swelling AFM
Introduction Swelling of wood, plant fibers and fiber networks (such as paper or textiles) is of immense importance for mechanical properties of the material in question (Benselfelt and Wagberg 2019; Mantanis et al. 1994). Swelling and deswelling of cellulose-based materials is a longstanding part of production of e.g. textiles, paper, etc. Swelling of cotton fibers has been reported in the literature as far back as the early 1900s, where the swelling of cotton in water was reported as 27.5% (Von Hohnel 1905). Later work frequently shows similar values (Moore et al. 1950). Radial swelling of cotton fibers is typically reported as around 20% in literature today (Carr 1995). While whole fiber swelling and fiber product swelling is well discussed, little attention has been afforded the smaller constituents of the plant fiber. As increased attention is afforded cellulose nanomaterials, the properties of these, including how such properties change in different materials, becomes an increasingly important subject both for industry and academia. Swelling of cellulose nanomaterials is, however, not at this point well discussed in the literature. Swelling of nanocellulose and derivatives is a subject on which researchers early on provided some early theoretical work (Stone and Scallan 1968). Experimentally work has focused on films, gels and fiber networks rather than the nanofibrils themselves (Kontturi et al. 2013, 2011; Xu et al. 2016; Torstensen et al. 2018a; Benselfelt and Wagberg 2019). To our k
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