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.
Aalto

Oxidative Activation of Wood Fibers for the Manufacture of Medium-Density Fiberboard (MDF)

Petri Widsten

Dissertation for the degree of Doctor of Philosophy to be presented with due permission of the Department of Forest Products Technology, for public examination and debate in Auditorium E at Helsinki University of Technology (Espoo, Finland) on the 29th of November 2002 at 12 noon.

Overview in PDF format (ISBN 951-22-6192-8)   [1086 KB]
Dissertation is also available in print (ISBN 951-22-6191-X)

Abstract

The aim of this thesis work was to study the possibilities of radical formation in wood fiber surfaces to enable direct fiber-to-fiber adhesion by radical-based reactions in the manufacture of fibreboard, particularly medium-density fiberboard (MDF). The fibers were produced by defibration at high temperatures. Radical formation was achieved by treatment with laccase, treatment with Fenton's reagent, or gamma-irradiation.

High-temperature defibration was found to cause cleavage of interunit beta-aryl ether linkages of lignin, resulting in formation of mechanoradicals and phenolic hydroxyl groups. The proportion of water-extractable low-molecular weight lignin and hemicelluloses present in the fibers increased with an increase in defibration temperature.

In the laccase treatment of fibers in water suspension, much more radicals were formed in hardwood than in softwood fibers for fibers produced at equal temperature. Radical formation increased with increasing defibration temperature. The treatment of fibers with Fenton's reagent in water suspension resulted in the formation of similar numbers of radicals in hardwood and softwood fibers. Radical formation increased with increasing defibration temperature but not so drastically as with laccase treatments. Also the gamma-irradiated fibers contained large numbers of radicals. Their content increased as a function of increasing defibration temperature and was higher for hardwood than for softwood fibers.

The internal bond strength (IB) of fiberboards made from fibers treated with laccase or Fenton's reagent in the defibrator blowline improved with increasing defibration temperature. The IB of boards made from laccase-treated fibers correlated with the number of radicals formed in the fibers on laccase treatment in water suspension, indicating that adhesion in the boards was largely due to reactions of radicals on the fiber surfaces. The IB of boards made from fibers treated with Fenton's reagent also correlated with the radical content of the fibers, but this relationship was not as strong as with the laccase treatments. This suggests that bonding mechanisms other than radical coupling may have contributed significantly to adhesion. Gamma-irradiation of fibers before their fabrication into boards resulted in a marked increase in board IB, indicating that radicals play a significant role in the adhesion of boards made from gamma-irradiated fibers.

This thesis consists of an overview and of the following 8 publications:

  1. Widsten, P., Laine, J.E., Qvintus-Leino, P. and Tuominen, S. Effect of high-temperature fiberization on the chemical structure of softwood. Journal of Wood Chemistry and Technology 21(3), 227-245 (2001). © 2001 Marcel Dekker Inc. By permission.
  2. Widsten, P., Laine, J.E., Qvintus-Leino, P. and Tuominen, S. Effect of high-temperature defibration on the chemical structure of hardwood. Holzforschung 56(1), 51-59, 2002. © 2002 Walter de Gruyter. By permission.
  3. Widsten, P., Laine, J.E. and Tuominen, S. Radical formation on laccase treatment of wood defibrated at high temperatures. Part 1. Studies with hardwood fibers. Nordic Pulp and Paper Research Journal 17(2), 139-146, 2002. © 2002 NPPRJ. By permission.
  4. Widsten, P., Laine, J.E. and Tuominen, S. Radical formation on laccase treatment of wood defibrated at high temperatures. Part 2. Studies with softwood fibers. Cellulose Chemistry and Technology 36(1-2), 2002.
  5. Widsten, P., Laine, J.E., Qvintus-Leino, P. and Tuominen, S. Effect of high defibration temperature on the properties of medium-density fiberboard (MDF) made from laccase-treated hardwood fibers. Accepted for publication in Journal of Adhesion Science and Technology.
  6. Widsten, P., Laine, J.E., Qvintus-Leino, P. and Tuominen, S. The influence of high defibration temperature on the properties of fiberboard made from laccase-treated softwood fibers. Submitted to Wood Science and Technology.
  7. Widsten, P., Laine, J.E., Qvintus-Leino, P. and Tuominen, S. Manufacture of fiberboard from wood fibers treated with Fenton's reagent (H2O2/FeSO4). Accepted for publication in Holzforschung.
  8. Widsten, P., Qvintus-Leino, P., Tuominen, S. and Laine, J.E. Studies on the use of Fenton's reagent (H2O2-FeSO4) and gamma-irradiation to produce radicals in wood fibers to be used for fiberboard. Submitted to Paperi ja Puu.

Keywords: defibration, laccase, Fenton's reagent, gamma-irradiation

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© 2002 Helsinki University of Technology


Last update 2011-05-26