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Understanding the fiber development during co-refining of white birch and black spruce mixtures. Part 1. Chemithermomechanical pulping

Pulp & paper Canada, 2004-12, Vol.105 (12), p.83-87

2005 INIST-CNRS ;Copyright Southam Business Communications, Inc. Dec 2004 ;ISSN: 0316-4004 ;EISSN: 1923-3515 ;CODEN: PPCADD

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  • Title:
    Understanding the fiber development during co-refining of white birch and black spruce mixtures. Part 1. Chemithermomechanical pulping
  • Author: WU, M. R ; LANOUETTE, R ; VALADE, J. L
  • Subjects: Applied sciences ; Birch ; Brightness ; Chemicals ; Exact sciences and technology ; Paper, paperboard, non wovens ; Polymer industry, paints, wood ; Pulp & paper mills ; Pulp manufacturing ; Pulping ; Spruce ; Technology ; Wood. Paper. Non wovens
  • Is Part Of: Pulp & paper Canada, 2004-12, Vol.105 (12), p.83-87
  • Description: The morphological characteristics of wood are recognized to be the most important factors determining the mechanical pulp and paper quality [2]. The birch fibres have a much more rigid structure than spruce, such as higher density, shorter fibre length and a thicker cell wall. These characteristics could be the cause of low response to refining and give low strength properties of mechanical pulp but with a good opacity when chemicals are not used [3]. However, birch responds well to chemical and chemimechanical pulping, such as Kraft [4, 5] and NSSC [6]. In a mechanical pulping area, when handling birch wood, the greatest effects are achieved using sodium hydroxide treatment of the chips that reduces the energy consumption and more importantly improves the pulp strength properties [7, 8]. Unfortunately, the superior opacity of birch TMP is lost when chemicals are introduced. The reduction of brightness is not avoidable since relatively high alkali dosage is necessary to improve the strength properties of the mechanical pulp of birch and so the effectiveness of sulfite against alkaline darkening becomes limited. Co-refining with softwood is considered another alternative way to enlarge the utilization of birch in mechanical pulping. Several studies [8, 9, 10, 11, 12, 13] show that a partial substitution of softwood by dense hardwood had advantages in reducing the refining energy consumption and modifying the optical properties when chemicals were not used. But the strength properties were reduced largely when more than 20% of softwood was replaced by dense hardwood. Hence, the commercial utilization of birch in mechanical pulping is still on a relatively small scale although several studies have been carried out in this area during the last decade [7-13]. As expected, the CTMP-S had the highest long-fibre content while the CTMP-B had the lowest (Fig. 2). Inversely, CTMP-B had the highest short-fibre and fines content while the lowest for CTMP-S (Figs. 3 and 4). The use of white birch decreased the long-fibre content while increasing the short-fibre content and somewhat the fines content, regardless of the substitution degree. This suggested that using white birch reduced the longfibre content to a certain degree, and then neither the substitution ratio (30 to 60%) nor the chemical pre-treatment of white birch prior to mixing with black spruce affected the degree of fibre-cutting. In this case, all the pulps of chip mixtures had a similar average fibre length, which was located between CTMP-B and CTMP-S. It seems that the chemical treatment could maintain an average fibre length in co-refining probably due to the following reasons: one is that black spruce fibres protect white birch fibres from fibre-cutting; the other is that chemical treatment is much more efficient in swelling and sulfonating white birch, thus improving its fibre flexibility and decreasing the fibre-cutting in co-refining. The lower fibre flexibility and specific surface of the fines are the two important factors causing the poorer strength properties of the white birch CTMP compared to the black spruce CTMP. The use of white birch in blending with black spruce to produce CTMP showed little influence on the long fibre qualities, but decreased qualities of the short fibre and especially of the fines, according to the measurements of flexibility and hydrodynamic specific volume. These reductions were marginally affected by the substitution ratio. However, the substitution of untreated white birch with black spruce could produce CTMP pulps with comparable tensile strength and light scattering to the black spruce CTMP. The alkaline and alkaline sulfite pre-treatments of while birch before co-refining then with untreated black spruce is an alternative to maintain the tensile strength while increasing the light scattering and the brightness due to the absence of alkaline treatment on black spruce fibres compared to the reference CTMP. Furthermore, the problem of linting becomes less important when white birch is co-refined with black spruce to produce CTMP. The probable reason is that sulfonation increases somewhat the bonding ability of the ray cells and the vessels, besides the fact that a certain amount of vessel fragments and ray cells could be compensated by the introduction of high quality fibres and lines from black spruce.
  • Publisher: Don Mills, ON: Southam
  • Language: English
  • Identifier: ISSN: 0316-4004
    EISSN: 1923-3515
    CODEN: PPCADD
  • Source: ProQuest Central
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