The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Studies on the Ultrastructure of Natural Fibres and its Effects on the Fibre Utilization

Tuomas Hänninen

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the School of Chemical Technology for public examination and debate in Auditorium Puu2 at the Aalto University School of Chemical Technology (Espoo, Finland) on the 11th of November 2011 at 12 noon.

Overview in PDF format (ISBN 978-952-60-4359-3)   [4216 KB]
Dissertation is also available in print (ISBN 978-952-60-4358-6)

Abstract

The ultrastructure of plant fibers has a significant effect on the properties of plants as well as on the behavior of the plant material undergoing various processing conditions, which logically affects the the final applications of plant-based materials. In this thesis, the ultrastructure of natural fibres was analysed using several complementary techniques to gain new insights into the ultrastructure of both wood and non-wood fibres.

The hierarchical structure of the natural fibre cell wall was found to play a vital role in cell wall reactivity and the material properties of fibres. Fibre defects, disruptions in the cell wall hierarchy, were found to have significantly increased susceptibility to chemical reactions when compared to intact fibre sections. An increase in the amount of defects was also found to slightly decrease the fibre strength properties. Another hierarchical feature, the microfibril angle was found to govern several properties of fibres and wood material. High strain to failure could be seen in both paper handsheets and samples of juniper wood, a species with a high microfibril angle. The effect of microfibril angle overrides the effects of chemistry and fibre dimensions when explaining the fibre properties.

The distribution of the cell wall components were, in fact, found to be similar in all of the wood species analysed. However, differences could be found in the distribution of lignin functional groups between spruce and pine. Differences in coniferyl aldehyde group distributions were seen also in size exclusion chromatography measurements of isolated lignin samples. Such deviation between pine and spruce was used to explain the differences in their behaviour during thermomechanical pulping.

Size exclusion chromatography also revealed differences in the ultrastructures of similarly processed eucalyptus and birch pulps. Eucalyptus pulp was found to have considerable amounts of lignin associated with the cellulose fraction of the pulp, whilst in birch most of the lignin was associated with hemicelluloses. Such differences can be of use when optimizing bleaching processes to decrease the consumption of chemicals.

This thesis consists of an overview and of the following 6 publications:

  1. T. Hänninen, A. Michud, and M. Hughes. 2011. Kink bands in bast fibres and their effects on mechanical properties. Plastics, Rubber and Composites, volume 40, numbers 6-7, pages 307-310.
  2. Tuomas Hänninen, Anders Thygesen, Shahid Mehmood, Bo Madsen, and Mark Hughes. 2012. Mechanical processing of bast fibres: The occurrence of damage and its effect on fibre structure. Industrial Crops and Products, volume 39, pages 7-11. © 2012 by authors and © 2012 Elsevier. By permission.
  3. Tuomas Hänninen, Pekka Tukiainen, Kirsi Svedström, Ritva Serimaa, Pekka Saranpää, Eero Kontturi, Mark Hughes, and Tapani Vuorinen. 2012. Ultrastructural evaluation of compression wood-like properties of common juniper (Juniperus communis L.). Holzforschung, volume 66, number 3, pages 389-395.
  4. Tuomas Hänninen, Eero Kontturi, Kirsi Leppänen, Ritva Serimaa, and Tapani Vuorinen. 2011. Kraft pulping of Juniperus communis results in paper with unusually high elasticity. BioResources, volume 6, number 4, pages 3824-3835. © 2011 by authors.
  5. Tuomas Hänninen, Eero Kontturi, and Tapani Vuorinen. 2011. Distribution of lignin and its coniferyl alcohol and coniferyl aldehyde groups in Picea abies and Pinus sylvestris as observed by Raman imaging. Phytochemistry, volume 72, numbers 14-15, pages 1889-1895.
  6. Tuomas A. Hänninen, Eero Kontturi, Akira Isogai, and Tapani Vuorinen. 2008. Differences in residual lignin properties between Betula verrucosa and Eucalyptus urograndis kraft pulps. Biopolymers, volume 89, number 10, pages 889-893.

Keywords: ultrastructure, natural fibres, wood, bast fibres, defects, Raman imaging

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© 2011 Aalto University

Last update 2012-07-24