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Aalto

On the Beating of Reinforcement Pulp

Eero Hiltunen

Dissertation for the degree of Doctor of Science in Technology 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 24th of January 2003 at 12 noon.

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Abstract

The aim of this work was to gain a better understanding of the effect of reinforcement pulp beating on the strength of mechanical pulp-dominated paper. The main purpose of reinforcement pulp beating is to improve the runnability of paper. The first objective of this study was to maximize the runnability related strength properties by beating. It was assumed that the flaw-resisting ability of paper correlates with the runnability of the dry paper web. In-plane fracture properties were assumed to describe the flaw-resisting ability. The second objective was to understand the mechanism how beating affects paper strength and structure (e.g. the size of the fracture process zone).

It was found that the reinforcement pulp ranking and optimisation of beating depend on the criteria used. The selection of critical strength properties affects the pulp ranking - sometimes different methods give opposite results (e.g. neutral sulphite vs. kraft). It was found that beating does not increase the in-plane fracture energy of mechanical pulp-dominated paper. Fracture toughness and elastic breaking strain increase only a little. However, tensile strength, elastic modulus and z-directional strength properties increase. It was concluded that beating does not significantly improve the flaw-resisting ability of mechanical pulp-dominated paper, while the strength of unflawed paper does increase.

It was found that the fracture properties of mixture sheets cannot be estimated based only on fracture properties of pure components. The additivity behaviour of fracture properties was strongly non-linear. The fracture energy of pulp mixtures seems to correlate mainly with the average fibre length (and not with the beating level). Beating increases the fracture energy per fracture zone area in the pure chemical pulp sheets but not in the mixture sheets. Evidently beating does not increase the energy needed to open interfibre bonds in mechanical pulp-dominated paper.

The results can be explained by the beating induced increase in both interfibre bonding and fibre segment activation. It was also found necessary to divide bonding into in-plane and out-of-plane components. The results largely support the activation theory originally presented in the 1960's. However, no direct measurement of activation was used in this study. Low-freeness mechanical pulp seems to have as high (in-plane) interfibre bonding as but lower activation than beaten reinforcement pulp. Therefore reinforcement pulp beating improves bonding-related properties such as elastic breaking strain or in-plane fracture energy only marginally. On the other hand, properties strongly dependent on activation, such as elastic modulus and tensile strength, are increased by reinforcement pulp beating.

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

  1. Hiltunen, E., Laine, J. E. and Zhang, G., The effect of refining chemical softwood pulp on the strength properties of a sheet made from a mixture of mechanical and chemical pulp. 52nd Appita Annual General Conference Proceedings. Brisbane, Australia, May 11-14, 1998. Appita, Carlton, 1998. Vol. 1, pp. 239-245.
  2. Hiltunen, E., Kettunen, H., Laine, J. E. and Paulapuro, H., 2000. Effect of softwood kraft refining on a mechanical-chemical mixture sheet. Tappi Journal 83, No. 10, p. 67, full text version in http://www.tappi.org, 9 pages.
  3. Hiltunen, E., Kettunen, H., Laine, J. E. and Paulapuro, H., 2002. Effects of softwood kraft pulp refining on fracture behaviour of TMP-Based paper. Paper Technology 43, No. 7, pp. 35-39.
  4. Hiltunen, E., Kettunen, H., Laine, J. E. and Paulapuro, H., 2002. Behaviour of Reinforcement Fibres in TMP-Based Paper. Paperi ja Puu 84, No. 4, pp. 269-273.
  5. Zhang, G., Hiltunen, E., Laine, J. E., Paulapuro, H., Kettunen, H. and Niskanen, K., 2002. Comparison of the effects of wet straining and refining on the fracture properties of paper. Nordic Pulp and Paper Research Journal 17, No. 1, pp. 45-49.
  6. Tanaka, A., Hiltunen, E., Kettunen, H. and Niskanen, K., Fracture properties in Filled Papers. The Science of Papermaking, Transactions of the 12th Fundamental Research Symposium. Oxford, England, 17-21 September 2001. FRS, Frecheville Court, 2001. Vol. 2, pp. 1403-1421.
  7. Yu, Y., Kettunen, H., Hiltunen, E. and Niskanen, K., 2000. Comparison of abaca and spruce as reinforcement fibre. Appita Journal 53, No. 4, pp. 287-291.
  8. Hiltunen, E., Laine, J. E. and Paulapuro, H., Effect of fibre charge on refining of softwood kraft pulp. PTS-Symposium 1999 PAPIERFASERSTOFF-TECHNIK: Brachliegende Potentiale beim Einsatz von Faser- und Hilfstoffen. Dresden, Germany, April 14-15, 1999. PTS, München, 1999. Pages 19, 19E and 19-1 to 19-10.

Keywords: beating, refining, reinforcement pulp, runnability, strength, fracture toughness, bonding, activation

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© 2003 Helsinki University of Technology

Last update 2011-05-26