Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
  • D21D5/02—Straining or screening the pulp
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/001—Modification of pulp properties
  • D21C9/007—Modification of pulp properties by mechanical or physical means
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/12—Pulp from non-woody plants or crops, e.g. cotton, flax, straw, bagasse

Definitions

• the invention relates to improving the characteristics of pulp, particularly no ⁇ wood pulp, by selectively removing part of the fines from the pulp.
• the fines of pulp generally refer to a fraction that passes through a
• the fines of chemical wood memep are mainly generated as a result of refining and are called secondary fines.
• the fines positively affect the strength characteristics of the memep, the tensile strength, for example.
• Chemical nonwood pulps in contrast, are mainly utilized unrefined because of their good bonding characteristics and because the iarge quantity of fines restricts their dewatering characteristics, which further deteriorate in refining.
• the content of fines is intrinsically extremely high particularly in straw fibres, and straw fibre pulps also possess poor dewatering characteristics.
• the fines of nonwood pulp are mainiy primary fines, and they are found to have a positive effect both on the tensile strength and on the opacity (Rousu & Niini- maki 2007).
• pre-processing the raw material wheat straw, for example, enables the removal of fines, and that pre-processing enables a reduction in the content of inorganic components, such as silicon, in the memep, the achievement of a higher content of holocellulose in the pulp and an increase in fibre length (Ma et al. 1992, Papatheofanous et al. 1995, Peter- sen 1988, Paav ⁇ ainen & Tulppala 1996).
• pulp is typicaiiy pre-processed as multi-step pre-processing, often first comprising dry processing followed by wet processing, in addition, a drawback of multi-step preprocessing is that, in dry processing, much desirabie materia! and fibre are a!so removed along with the fines, and, furthermore, wet processing results in much waste water. Stili further, wet processing is not suitable for all pulp pro- duction processes because of the extra water introduced into the process. In addition, these process steps require special investments,
• the fines to be removed are mainiy composed of epidermal cells, small parenchyma cells, silicate and cork cells, and different fragments of vessel cells and corresponding non-fibrous cell types. These particles are characterized by their small size and their small ratio of width to length, and their flake-like nature.
• nonwood pulp refers to memep produced from the fibres of grass-stemmed plants (grass fibres), bast fibres, leaf fibres or fruit fibres.
• grass-stemmed plants grass fibres
• useful fibres based on grass-stemmed plants include straw, e.g. cereai straw (wheat, rye, oat, barley, rice), reeds, e.g.
• reed canary grass common reed, papyrus, sugar cane, or bagasse, bamboo, and grasses, e.g. esparto, sabai and lemon grass.
• bast fibres include flax, such as stems of common fiax and sterns of oil flax, hemp, East Indian hemp, kenaf, jute, ramie, paper mulberry, gampi fibre and mitsumata fibre.
• leaf fibres include abaca and sisai, for example.
• fruit fibres include cottonseed hairs, cotton linter fibres, kapok, and coir fibre.
• grass-stemmed plants useful in the present invention and grow- ing in Finland may be mentioned: common reed, reed canary grass, timothy, cocksfoot, yeilow sweet ciover, smooth brome, red fescue, white sweet clover, red clover, goat's rue and alfalfa.
• pulp produced from grass- stemmed plants such as straw pulp
• pulp produced from annual grass-stemmed plants is used.
• pulp produced from perennial non-arboreal plants is used.
• agricultural waste materia! including the above-mentioned cereal straw, for example, may also be used.
• the pulp may be any nonwood pulp produced by any conventional pulp production processes, such as pulp produced by the sulphate, sulphite or soda process.
• the pulp may also be pulp produced by solvent-based proc- esses, such as formic acid-based and/or acetic acid-based, alcohol-based or ionic processes.
• the pulp may be bleached or unbleached pulp.
• fines particles of a size having a length of at most 0.18 mm and a width of at most 0.05 mm are removed from nonwood pulp.
• the average length of the particles is at most 0.10 mm, their width being at most 0.04 mm.
• the definition of particle size, 'a size having a length of at most 0.18 rnm or 0.10 mm 1 means that the average length (the average iargest dimension) in the particie size distribution of the particles to be removed is at most 0.18 rnm or at most 0.10 mm, respectively.
• the width thereof (the average smallest dimension) is at most 0.05 mm and 0.04 mm, respectively.
• the shape of the particles to be removed is preferably flake-like, in a particularly preferred embodiment, the ratio of the width of the particles to the length thereof is equal to or more than 1:10, still more preferably equal to or more than 1 :5 and particularly equal to or more than 1 :2, up to the value 1 :1.
• the fines particles to be removed are mainly composed of epidermal ce ⁇ s, parenchyma cells, silicate ceils, fragments of vessel cells, cork cells and/or corresponding non-fibrous ceils and/or parts of these cells or combinations of these cells and/or ceil parts of said nonwood plants.
• paren- chyma cells refer to small parenchyma cells having a length (largest dimension) of at most 0.18 mm in accordance with the above-presented definition.
• the fines particles to be removed comprise at least 50%, preferably at least 75% of said ceil types.
• the quantity of fines particles to be removed is typically less than 8%, preferably less than 5% of the total pulp, calculated from the dry pulp.
• suitable industrial devices include filters, screens, classifiers (pressure classifier, for example) and hydrocycSones (vortex cleaners), for example.
• screening is used, the sieve opening being within the range 180 to 40 ⁇ m, preferably 100 to 40 ⁇ m, particularly 60 to 40 ⁇ m.
• the fines may be removed before pulp production from the raw material of the pulp, in connection with pulp production or after pulp production from the finished pulp.
• fines particles are removed after pulp production directly from the finished pulp, the consistency thereof being reduced to 0.1 to 5%.
• the separation may be performed from filtrates of pulp washers, a paper machine and a dryer, from a disc filter, from the accept of a pressure screen when a mesh of 0.05 to 0.2 mm, for example, is used as the slot screen or a holey screen or a vortex cleaner with suitable pressure differences or different combinations thereof.
• the following examples are intended as illustrative, not restrictive examples of the invention.
• Wheat straw pulp produced with a formic and acetic acid-based mixed acid and bleached by an EPP sequence was used as the starting material.
• the pulp was fractioned with a screen having a sieve opening of 40 ⁇ m by removing the fines part that had passed through the screen.
• the fines quantity removed corresponded to 2.34% of the total pulp.
• drainability time was measured with a Shopper Riegler device, and free dewatering time in a sheet mould at 13 0 C 1 and paper sheets were prepared, from which the tensile strength of the pulp was tested. The measurements were performed both from the un-processed starting pulp and from the fines-removed pulp (with the portion passed through the 40- ⁇ m screen removed).
• the fines separated were analyzed microscopically. It was found that the fines consisted mainly of epidermal ceils, small parenchyma cells, silicate cells, fragments of vessel cells, cork cells and corresponding non-fibrous particles and parts thereof.
• the shape of the particles was flake-like, the ratio of their width to their length being typically more than 1 :5.
• the wheat straw pulp of Example 1 was fractioned with a screen having a sieve opening of 50 ⁇ m by removing the fines part that had passed through the screen.
• the fines quantity removed corresponded to 3.87% of the total pulp.
• drainabllity time was measured with a Shopper Riegier device and free dewatering time in a sheet mould at 13 0 C. The measurements were performed both from the un-processed starting pulp (reference) and from the fines-removed pulp. In addition to the reference, pulp from which different percentages of fines having passed through a 200-mesh standard screen (sieve opening 74 ⁇ m) had been removed was used as comparison.
• Example 3 For the fines separated, the average length of particles as determined with optical analyzers was 0.18 mm. In a microscopic analysis, the same particle types as in Example 1 were detected. The shape of the particles was flake-like too, but the ratio of width to length was typically more than 1:10. Example 3.
• Wheat straw pulp was fractioned by fractioning the fines thereof (obtained by fractioning with a 200 ⁇ mesh standard screen having a sieve opening of 74 ⁇ m and by collecting the portion having passed through the screen) into three parts as follows: (1 ) fines having passed through a 50- ⁇ r ⁇ screen were removed from the fines, (2), fines having passed through a 40- ⁇ m screen were removed from the fines having passed through the 50- ⁇ m screen, and (3) fines having passed through the 40- ⁇ m screen were collected.
• Wheat straw pulp was fractioned by removing the fines portion having passed through a 40- ⁇ m screen and the portion having passed through a 50- ⁇ m screen.
• the fines quantities removed corresponded to 2.34% and 3.87%, respectively, of the entire530p.
• Sheets were prepared from the original pot and from the puips from which the above-mentioned fines fractions had been removed, and the light absorption coefficients, opacities and brightness of the sheets were determined.
• the light absorption coefficient was found to have improved by 9.4% when the fines portion having passed through the 40- ⁇ m screen was removed from the pulp, and, correspondingly, by 17.6% when the fines portion having passed through the 50- ⁇ m screen was removed from the putp.
• the opacity decreased only by 0.6% and 1.1%, but the brightness of the puips improved by 1.0 brightness units and 1.9 brightness units.
• Paaviiainen L., Tulppaia, J., Finell, M. & Rehnberg, Q., Reed ca- nary grass pulp produced on mill scale. Proc. Pulping Conference, Orlando, Florida, 1 : 335-341 , 1999.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

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• 2007
  • 2007-10-18 FI FI20075735A patent/FI121545B/fi not_active IP Right Cessation
• 2008
  • 2008-10-16 WO PCT/FI2008/050580 patent/WO2009050338A1/en not_active Ceased
  • 2008-10-16 JP JP2010529419A patent/JP2011500984A/ja active Pending
  • 2008-10-16 CN CN2008801120662A patent/CN101827973B/zh not_active Expired - Fee Related
  • 2008-10-16 EP EP08839495.2A patent/EP2201171A4/de not_active Withdrawn

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