The effect of residual fibres on the micro-topography of cellulose nanopaper

doi:10.1016/j.micron.2013.09.002

Micron

Volume 56, January 2014, Pages 80-84

https://doi.org/10.1016/j.micron.2013.09.002 Get rights and content

Highlights

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Residual fibres increase the roughness of cellulose nanopapers.
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Laser profilometry has adequate resolution to describe the micro-structure of nanopaper surfaces.
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Fractionation can be applied to reduce the fraction of coarse fibrous structures and thus increase smoothness of nanopapers.

Abstract

Nanopaper is a new material concept composed of nanocellulose, which has been proposed for a series of applications. Recently, the surface of nanopapers has also been emphasized as an important structure to control. This is due to the potential of nanopaper structures as a substrate for printing functionality, which could expand the applicability of nanopaper as a functionalized biomaterial. In this study, we demonstrate how the roughness of nanopaper is affected by the fraction of residual fibres that were not fibrillated into nanofibrils after a homogenization procedure. The topography and morphology were assessed with laser profilometry, atomic force microscopy and scanning (transmission) electron microscopy. The results show a linear correlation between the estimated fraction of residual fibres and the roughness of the assessed nanopapers. Furthermore, the fraction of residual fibres can be reduced by fractionating the nanocellulose, which is demonstrated in the present work. Such knowledge will be valuable for designing nanopaper surfaces with specific structural characteristics.

Introduction

Nanopaper is a new material concept composed of nanocellulose (Henriksson et al., 2008). Nanocellulose is a term, which may refer to various fibrillated materials such as microfibrillated cellulose (MFC). The diameter size distribution of the nanofibrils is broad in MFC materials produced without pre-treatment. MFC produced with pre-treatment, such as TEMPO mediated oxidation and carboxymethylation, contains nanofibrils with narrow diameter size distribution. Typical diameters of the nanofibrils produced with pre-treatments are less than roughly 20 nm (Saito et al., 2006, Wågberg et al., 2008, Chinga-Carrasco et al., 2012a). However, despite the nanofibrillation, the materials may also contain residual fibres (Chinga-Carrasco, 2011).

Moving forward the development of nanocellulose materials, nanopaper has been proposed as a substrate for printing functionality (Chinga-Carrasco et al., 2012b, Orelma et al., 2012). Nanopaper can be dense, with low oxygen transmission rate, high strength and transparent (Syverud and Stenius, 2009, Fukuzumi et al., 2009, Aulin et al., 2010, Siró et al., 2011, Chinga-Carrasco et al., 2012a). Such properties and the potential of nanopaper as substrate for printing functionality could potentially expand the utilization of nanocellulose as a biomaterial with chemical- and biosensor capabilities. Additionally, the concept of using nanopaper structures as substrates for fabricating organic field-effect transistors (OFET) was demonstrated by Chinga-Carrasco et al. (2012b) and by Huang et al. (2013).

Among various techniques for printing on flexible substrates, inkjet printing has gained a growing interest as a method for depositing functional materials (see e.g. Tekin et al., 2008, Tobjörk and Österbacka, 2011). Smooth surfaces with adequate surface energy are necessary for achieving good print resolution and low ink spreading during inkjet printing (Chinga-Carrasco et al., 2012b). This emphasizes the importance of controlling the surface roughness of a given nanopaper. Hence, the purpose of this study was to describe the surface structure of a variety of nanopapers and to provide evidence about the effect of residual fibres on the surface morphology. Such knowledge will widen our understanding of nanocellulose materials, and will shed more light on how to design nanopaper surfaces, with desired smoothness.

Section snippets

Pulp fibres and nanocellulose

Never dried Pinus radiata pulp fibres were used in this study. Additional details about the pulp fibres, including the carbohydrate composition are given by Chinga-Carrasco et al. (2012a). The pulp fibres were carboxymethylated according to Wågberg et al. (2008) for facilitating the homogenization process. The pulp fibres were then homogenized with a Rannie 15 type 12.56X homogenizer, operated at 1000 bar pressure. The pulp consistency during homogenizing was 0.5%. The fibrillated material was

Verification of the apparent residual fibre fraction

The quantified apparent fibre fraction of the 9 blend series (Table 1) was correlated with the true fibre fraction added to the BC3 material. The results indicate a linear correlation in the given range and with the series assessed in this study. The residual fibre fraction of the assessed nanocellulose materials was thus underestimated by a factor α = 2.27, given by the slope of the linear correlation in Fig. 1. This indicates that the true fraction of residual fibres is roughly twice as much as

Conclusion

This study provides evidence about the effect of residual fibres on the micro-structure of nanopaper surfaces. The residual fibres considerably affect the surface roughness at wavelengths larger than roughly 80 μm, which is in agreement with the lateral dimensions of cellulose fibres. Applying a simple fractionation step, the surface roughness was reduced from roughly 1 μm to less than 0.5 μm, which is a significant improvement. This indicates the importance of removing residual fibres when smooth

Acknowledgements

The authors thank Ingebjørg Leirset and Mirjana Filipovic (PFI) for good collaboration in the preparation of the nanocellulose samples. Gurvinder Singh, Vidar Fauske and Ida Noddeland at the NTNU NanoLab are thanked for valuable cooperation and assistance in the acquisition of the AFM and S(T)EM images. The Kazan National Research Technological University (KNRTU) and The Research Council of Norway (NanoHeal project, grant no. 219733) are acknowledged for funding part of this work.

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Short communicationThe effect of residual fibres on the micro-topography of cellulose nanopaper

Highlights

Abstract

Introduction

Section snippets

Pulp fibres and nanocellulose

Verification of the apparent residual fibre fraction

Conclusion

Acknowledgements

Micron

Model films from native cellulose nanofibrils. Preparation, swelling, and surface interactions

Biomacromolecules

Oxygen and oil barrier properties of microfibrillated cellulose films and coatings

Cellulose

Cellulose fibres, nanofibrils and microfibrils: the morphological sequence of MFC components from a plant physiology and fibre technology point of view

Nanoscale Res. Lett.

Computer-assisted quantification of the multiscale structure of films made of nanofibrillated cellulose

J. Nanoparticle Res.

Bleached and unbleached MFC nanobarriers – properties and hydrophobization with hexamethyldisilazane

J. Nanoparticle Res.

Inkjet-printed silver-nanoparticles on nano-engineered cellulose films for electrically conducting structures and organic transistors – concept and challenges

J. Nanoparticle Res.

Transparent and high gas barrier films of cellulose nanofibers prepared by TEMPO-mediated oxidation

Biomacromolecules

Cellulose nanopaper structures of high toughness

Biomacromolecules

A review of image analysis based methods to evaluate fiber properties

Lenzinger Berichte

Short communication
The effect of residual fibres on the micro-topography of cellulose nanopaper