Cellulose

, Volume 18, Issue 6, pp 1423–1432 | Cite as

Layer-like fatigue is induced during mechanical pulping

Article

Abstract

The question whether fatigue is induced during mechanical pulping was addressed experimentally. The grinding process was interrupted to image partly ground spruce samples. The grinding was performed at five different feed velocities using two different grindstones. This approach allowed creating an in situ snapshot of the developing grinding zone in the wood samples. The depth profiles of the stiffness modulus and nm-scale pores, close to and within, the grinding zone were quantified by ultrasonic pitch-catch measurements and thermoporosimetry. To perform these profiling measurements, wood material was iteratively removed layer-by-layer with a microtome from the sample surface after taking the snapshot. The grinding-induced changes in cell morphology inside the sample were imaged using microcomputed tomography, whereas the changes on the surface of the samples were imaged with optical microscopy and SEM. A layer that penetrated 0.5–1.5 mm into the sample exhibiting up to 80% decreased stiffness modulus—compared to the unaltered sample parts—was detected when the Wave-type grindstone was employed. The corresponding layer thickness was 0.3 mm with the conventional grindstone. The results match previously measured temperature profiles, and confirm the Atack-May hypothesis that grinding induces a fatigue layer. Confirming this old, widely used hypothesis is significant for the field of energy efficiency research related to mechanical pulping and may provide new opportunities for grinding research.

Keywords

Ultrasound Thermoporosimetry μ-CT Mechanical pulping Grinding Fatigue 

References

  1. Atack D (1955) The grinding process—a fundamental approach. Pulp Paper Mag 56:120–122Google Scholar
  2. Atack D (1971) Mechanical pulping at the institute, part III—mechanics of wood grinding. The Activities of the Pulp and Paper Research Institute of Canada, Trend Report 19, 6–11Google Scholar
  3. Björkqvist T (2002) A design method for an efficient fatigue process in wood grinding: an analytical approach. Tampere University of Technology, TampereGoogle Scholar
  4. Björkqvist T, Lautala P, Finell M, Lönnberg B, Saharinen E, Paulapuro H (1995) 19th international mechanical pulping conference, Ottawa, Canada, 12–15 June 1995, pp 65–70Google Scholar
  5. Björkqvist T, Tienari M, Lucander M (2007) Simulation of fatigue related variables in wood grinding. In: Proceedings of the IMPC, Minneapolis, Minnesota, USA, pp ISBN 1-59510-59145-59514Google Scholar
  6. Blechschmidt J, Engert P, Stephan M (1986) The glass transition of wood from the viewpoint of mechanical pulping. Wood Sci Technol 20:263–272Google Scholar
  7. Hamad W, Provan J (1995) Microstructural cumulative material degradation and fatigue-failure micromechanisms in wood-pulp fibres. Cellulose 2:159–177CrossRefGoogle Scholar
  8. Havimo M, Hari P (2010) Temperature gradient in wood during grinding. Appl Math Model 34:2872–2880CrossRefGoogle Scholar
  9. Lucander M, Björkqvist T (2005) New approach on the fundamental defibration mechanisms in wood grinding. Proceedings of the IMPC 2005, International Mechanical Pulping Conference, Oslo, Norway, 7–9 June 2005, pp 149–155 Google Scholar
  10. Maloney T, Paulapuro H (1999) The formation of pores in the cell wall. J Pulp Paper Sci 25:430–436Google Scholar
  11. May WD (1966) Mechanical pulping at the institute, part II—what happens in grinding? The Activities of the Pulp and Paper Research Institute of Canada, Trend Report 9, 7–13Google Scholar
  12. Panula-Ontto S, Lucander M, Pöhler T, Saharinen E, Björkqvist T (2007) Fatigue treatment of wood by high-frequency cyclic loading. In:Proceedings of the IMPC, Minneapolis, USA, pp ISBN 1-59510-59145-59514Google Scholar
  13. Salmén L (1987) The effect of the mechanical deformation on the fatigue of wood. J Pulp Paper Sci 13:J23–J28Google Scholar
  14. Salmi A, Salminen L, Hæggstrom E (2009) Quantifying fatigue generated in high strain rate cyclic loading of Norway spruce. J Appl Phys 106:104905CrossRefGoogle Scholar
  15. Salmi A, Salminen L, Engberg B, Björkqvist T, Haeggström E (2011) Unipolar cyclic compression causes localized plastic deformation in wood. J Appl Phys #JR11-3125 (submitted)Google Scholar
  16. Somboon P, Nieminen K, Paulapuro H (2008) Finite element analysis of the fatigue behavior of wood fiber cell walls. BioResources 3(4):983–994Google Scholar
  17. Sundholm J (ed) (1999) Mechanical pulping. Tappi. ISBN-10: 9525216055 ISBN-13: 978-9525216059. http://www.amazon.com/Mechanical-Pulping-Papermaking-Technology-0202FIN05/dp/9525216055

Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Ari Salmi
    • 1
    • 2
  • Erkki Saharinen
    • 1
  • Edward Hæggström
    • 2
  1. 1.VTT Technical Research Center FinlandEspooFinland
  2. 2.Electronics Research Laboratory, Department of Physics, Division of Materials PhysicsUniversity of HelsinkiHelsinkiFinland

Personalised recommendations