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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Surface Chemical and Morphological Properties of Mechanical Pulps, Fibers and Fines

Heli Kangas

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 PUU 2 at Helsinki University of Technology (Espoo, Finland) on the 1st of December, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-22-9097-0)   [2596 KB]
Dissertation is also available in print

Abstract

The aim of this work was to study the surface chemical and morphological properties of different mechanical pulps with special focus on the effects of refining, bleaching and enzymatic modification on the surface properties of the isolated pulp fractions, namely fibers, fibrillar fines and flake-like fines. Special emphasis was placed on evaluating the suitability of time-of-flight secondary ion mass spectroscopy (ToF-SIMS) for studying the surface chemical properties of pulps and pulp fractions. Electron spectroscopy for chemical analysis/x-ray photoelectron spectroscopy (ESCA/XPS) was used to complement and/or verify the results given by ToF-SIMS. The morphological properties of pulps and pulp fractions were studied by atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM).

ToF-SIMS proved to be a valuable tool for studying the surface chemistry of mechanical pulps. For example, the content of guaiacyl units in the surface lignin could be determined and used to indicate which cell wall layer was exposed. The higher the intensity of peaks originating from guaiacyl lignin units, the higher the proportion of inner cell wall layers. ToF-SIMS can also identify several types of surface extractives based on their molecular masses and characteristic peaks in the spectra. However, ToF-SIMS cannot be considered to be a quantitative method for organics, and ESCA/XPS is therefore needed to complement the results.

The surface chemical and morphological properties of fibers differed from those of fines. The surfaces of fines contained more extractives and lignin, while the surfaces of fibers were richer in polysaccharides. Different types of fines also exhibited different surface properties, fibrils having more extractives on their surface and flakes more granular lignin. Refiner and groundwood pulps and pulp fractions differed in their surface chemical properties due to differences in the pulping processes.

Increased refining energy raised the intensity of peaks originating from guaiacyl lignin units on the surface of fibers, which together with FE-SEM images reflected the increased exposure of the secondary wall layer. The surface chemical properties of fines showed that at low specific energy consumption fibrils were formed from the outer fiber wall layers (P+S1), but the content of secondary wall material increased as a function of refining energy. At the start of refining, flakes originated from compound middle lamella (ML+P) but during later refining stages they were also released from the outer secondary wall (S1).

ToF-SIMS also indicated a decrease in the surface content of chromophores of coniferaldehyde origin during mechanical pulp bleaching. Bleaching was found to be effective in removing surface extractives, especially from the surface of fibrils. Lipase and laccase treatments combined with washing selectively removed extractives from the surface of mechanical pulps, especially from the surface of fibrils, and thus increased the hydrophilicity of the pulp.

This thesis consists of an overview and of the following 5 publications:

  1. Kleen, M., Kangas, H. and Laine, C. (2003). Chemical characterization of mechanical pulp fines and fiber surface layers. Nordic Pulp and Paper Research Journal 18 (4): 361-368. © 2003 by authors.
  2. Kangas, H. and Kleen, M. (2004). Surface chemical and morphological properties of mechanical pulp fines. Nordic Pulp and Paper Research Journal 19 (2): 191-199. © 2004 by authors.
  3. Kangas, H., Pöhler, T., Heikkurinen, A. and Kleen, M. (2004). Development of the mechanical pulp fibre surface as a function of refining energy. Journal of Pulp and Paper Science 30 (11): 298-306. © 2004 Pulp and Paper Technical Association of Canada (PAPTAC). By permission.
  4. Kangas, H. and Kleen, M. (2007). The effect of bleaching on the surface chemistry of mechanical pulps. Journal of Pulp and Paper Science, accepted for publication.
  5. Kangas, H., Suurnäkki, A. and Kleen, M. (2007). Modification of the surface chemistry of TMP with enzymes. Nordic Pulp and Paper Research Journal 22 (4): 415-423. © 2007 by authors.

Keywords: surface chemical properties, morphological properties, thermomechanical pulp, fiber, fines, fibril, flake, ESCA, XPS, ToF-SIMS, extractives, lignin, polysaccharides, surface chemistry, surface structure, mechanical pulp, TMP, CTMP, GW, PGW, Picea abies, refining, bleaching, peroxide, dithionite, enzymatic treatment

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© 2007 Helsinki University of Technology

Last update 2011-05-26