Classifications

• • 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
  • D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
  • D21C5/005—Treatment of cellulose-containing material with microorganisms or enzymes

Definitions

• the invention relates to a method for im­proving the drainability of mechanical pulp, such as a thermomechanical or deinked pulp, by treating the pulp by a hemicellulose-hydrolyzing enzyme.
• the drainability of pulp is usually described by the freeness value. It is known that mechanical treatment and deinking deteriorate the drainability of pulp. The use of deinked pulp in particular is re­stricted due to its poor drainability.
• mechani­cal treatment a fibre is exposed to stresses, which results in an abundant formation of fine-grained ma­terial. For this reason, the drainage properties of finished pulp are not at optimum, which appears as a decreased freeness value. In many cases, the drainage properties, i.e. the practical value of a pulp would be substantially increased if the freeness value could be improved by 10 to 20 units.
• fibres are separated from wood mechanically by means of heat only without any addition of chemicals.
• the fibre is thereby subjected to stresses so that the lignin bind­ing the fibres together is softened. Under continued mechanical stress, the elasticity of lignin fails and the fibres are detached from each other.
• Mechanical pulps include groundwood pulp, re­finer mechanical pulp, pressure groundwood pulp and thermomechanical pulp.
• the required tempera­ture rises in the above order, being at its lowest in the production of groundwood pulp and at its highest in the production of thermomechanical pulp.
• thermomechanical pulp With groundwood pulp, the negative and positive properties of fine-grained material are substantially balanced, whereas the potential strength properties of thermomechanical pulp in particular are clearly super­ior to the drainage properties. However, the strength properties of groundwood pulp are relatively poor as compared with the properties of thermomechanical pulp.
• Recycled pulp is manufactured of waste paper, whereby wood fibre utilized at least once in the form of paper is reused.
• the main function of a recycled pulp process is to remove impurities contained in waste paper. Methods used for this pur­pose can be divided into three groups:
• Recycled pulps can be deinked, if desired.
• the basic idea of deinking is to separate ink from the fibre chemically and mechanically and to bring the separated ink to a hydrophilic state in a fibre-water slush.
• the separated ink can be removed from the slush by flotation and/or by washing.
• a deinking plant uses as raw material two kinds of waste paper: home waste paper and newsprint waste.
• Home waste paper is unsorted and its composition varies. It typically contains 60 to 70% of newsprint, 20 to 30% of magazine paper and less than 10% of various kinds of paperboard and cardboard.
• French Patent Specification 2,557,894 discloses a method in which chemical pulp is subjected to treatment with xylanase enzyme with the purpose of re­ducing the beating time.
• Canadian Patent Specification 758,488 relates to a method in which the beatability of pulp is improved by a cellulase/pectinase/lipase enzyme treatment.
• French Patent Specification 2,571,738 in turn discloses a method in which pulp is provided with special properties by cellulase treat­ ment.
• Japanese Patent Specification 60,126,395 dis­closes a method for improving the beating process by enzyme addition.
• Japanese Patent Specification 59,009,299 dis­closes a method in which alkaline cellulase and a surface-active agent are added to a deinking process for making the removal of ink more efficient.
• Japanese Patent Application 63,059,494 dis­closes a method for improving the whiteness of re­cycled pulp by means of alkaline cellulase.
• French Patent Application 8,613,208 discloses a method for improving the properties of previously beaten pulp, such as recycled pulp having a Schopper-­Riegler (SR) number exceeding 25, by means of a cellu­lase/hemicellulase treatment.
• SR Schopper-­Riegler
• the SR number can be decreased without affect­ing adversely the other properties of the pulp.
• the SR number describes the drainability of pulp; the lower the SR value, the better the rate of dewatering is.
• Said application describes mainly the treatment of recycled pulps containing plenty of chemical pulp.
• the enzyme treatment according to said ap­plication to recycled pulps containing mainly mech­anical pulp, it has been found that treatment with en­zyme mixtures containing substantial amounts of cel­lulase deteriorates the strength properties of the pulp; this appears from the examples set forth below.
• the strength values are decreased even by minor amounts of cellulase especially if the pulp containing enzymes has to be stored for longer periods of time on account of process disturbances, for instance.
• the enzyme used in the treatment does not affect adversely the strength properties of pulp, not even during a long time of ac­tion (several hours).
• the object of the present invention is to im­prove the drainability of mechanical pulp, particu­larly thermomechanical and/or deinked pulp, by means of enzyme treatment while maintaining the strength properties of the pulp.
• the invention is characterized by adding to mechanical pulp or to pulp mainly containing mech­anical pulp, such as thermomechanical or deinking pulp, at least one hemicellulose-dissolving enzyme or an enzyme preparation containing at least one hemicel­lulose-dissolving enzyme and being substantially free from cellulose-dissolving enzymes.
• mech­anical pulp such as thermomechanical or deinking pulp
• at least one hemicellulose-dissolving enzyme or an enzyme preparation containing at least one hemicel­lulose-dissolving enzyme and being substantially free from cellulose-dissolving enzymes The addition of en­zymes can be carried out in connection with the acidi­fication of the pulp or thereafter.
• Hemicellulose-dissolving enzymes include xylan­ases, beta xylosidase, acetyl esterase, alpha arabin­osidase, alpha glucuronidase, arabinases and manna­nases.
• Particularly preferred enzymes are xylanases and mannanases.
• Enzymes suited for the application according to the invention include hemicellulases and hemicellulase preparations, especially xylanases and mannanases, which are substantially free from cellulases.
• the term "cellulases” refers to enzymes which are able to dissolve crystalline cellulose and to li­berate therefrom remarkable amounts of sugars or oligosaccharides.
• enzymes referred to in the invention are produced e.g. by actinomycetes (such as Streptomyces olivochromogenes) , bacteria (such as Ba­cillus sp.) and fungi (such as Penicillium steckii) .
• a suitable enzyme dosing is about 30 to 200,000 units/kg on the dry content of the pulp, preferably about 100 to 50,000 units/kg.
• the treatment can be carried out within the pH range from about 2 to about 10, preferably from about 4 to about 8, depending e.g. on the origin and properties of the used hemicellulase enzyme.
• the treating time depends on the enzyme dosage and the treatment conditions, ranging from 10 minutes to one day, preferably from half an hour to 8 hours.
• the temperature during the enzyme treatment may vary from about 10 to about 90 o C, preferably from about 25 to 70 o .
• the xylanase activity of the enzyme prepara­tions was determined as follows:
• xylan solution 1%, Sigma No: X-­0376, prepared in 50 mM Na citrate buffer, pH 5.3
• an enzyme suitably diluted in the same buffer was added.
• the solution was incubated at +50 o C in a water bath for 30 minutes.
• the reaction was stopped by adding 3 ml of DNS reagent (3,5-dinitrosalicylate re­agent), and the colour was developed by cooking the sample for 5 minutes.
• the absorbance was measured at a wave length of 540 nm.
• One enzyme unit liberates one micromole of reducing sugars calculated as xylose per one minute under the assay conditions.
• the mannanase activity of the enzyme prepara­tions was determined as follows:
• locust bean gum solution (0.5%, Sigma No: G-0753, prepared in 50 mM Na-citrate buffer, pH 5.3) 1 ml of an enzyme suitably diluted in the same buffer was added. The solution was incubated at +50 o C in a water bath for 10 minutes. The reaction was stopped by adding 3 ml of DNS reagent, and the colour was developed by cooking for 5 minutes. The absorbance was measured at a wave length of 540 nm. One enzyme unit liberates one micromole of reducing sugars calcu­lated as mannose per one minute under the assay con­ditions.
• the cellulase activity of the enzyme prepara­ tions was determined as filter paper activity (Ghose T.K. et al., Symposium of Enzymatic Hydrolysis of Cel­lulose, Bailey M., Enari T.M., Linko M., Eds. (SITRA, Aulanko, Finland, 1975), p. 111 to 136):
• a piece of filter paper (Whatman 1, 50 mg) was added to 1 ml of acetate buffer (0.05 M NaAc, pH 4.8). 1 ml of a suitably diluted enzyme solution was added. The solution was incubated for one hour at 50 o C. The reaction was stopped by adding 3 ml of DNS reagent, and the colour was developed and measured as in the xylanase determination. One activity unit liberates 1 micromole of reducing sugars calculated as glucose per one minute.
• MULTIFECT L 250 (commercial preparation, Finn­sugar Ltd, prepared by the mold Trichoderma longi- brachiatum activity: xyl­anase 250 units/g, cellu­lase about 100 units/g)
• MULTIFECT K (commercial preparation), Finnsugar Ltd, prepared by the fungus Trichoderma longi­brachiatum; activity: xyl­anase 6,000 units /g, cel­lulase 30 units/g)
• preparation 3 represents a useful enzyme preparation containing hemicellulose-dissolving enzyme (xylanase) and being substantially free from cellulose-dissolving enzymes.
• Preparations 1 and 2 are reference prepara­tions, which in addition to the hemicellulose activity contain varying amounts of cellulose-dissolving enzyme activities.
• aqueous slurry having a dry matter content of 10% was prepared from dried deinked pulp (Keräys­kuitu Oy, export grade) and allowed to stand overnight at room temperature. The slurry was then diluted with water to a dry content of 5% and defibered in a lab­oratory mixer (3,000 rpm, 15 min). The pH of the slur­ry was adjusted from the initial pH of about 7 to 5.4 by means of 1 M sulphuric acid.
• the hemicellulase treatment clearly improved the drainability of the pulp.
• Unbleached, unacidified deinked pulp (Keräys­kuitu Oy) having a dry matter content of about 7.5 % was allowed to stand overnight, whereafter it was di­luted to a concentration of 20 g/l and was defibered and beaten in a hollander to a freeness value of 130. After the beating, the pH was adjusted to 5.5 by 1 M H2SO4.
• Xylanase enzyme preparation (enzyme preparation 3) was added to the pulp in amounts that appear from Table 4. The pulp was heated by means of a steam coil to 50 o C and it was incubated at 50 o C in a water bath. The freeness was determined after the pulp had been incubated one hour and four hours. The results are shown in Table 4. Table 4 Results from the enzyme treatment Sample Enzyme 3 Enzyme 3 Control Xylanase content (units/kg) 500 1250 - Cellulase content(units/kg) - - - Freeness (ml) 0 h 142 142 142 1 h 154 158 141 4 h 153 163 141
• Bleached, acidified (pH 7.7) deinked pulp (Keräyskuitu Oy, normal grade) having a dry matter content of about 10% was allowed to stand overnight, whereafter it was diluted to a concentration of 20 g/l and defibered by a hollander. After defibering the pH was adjusted to 5.5 by 1 M H2SO4, whereafter beating was carried out. The freeness of the pulp before beat­ing was 199 and after a beating time of 5 minutes 131.
• Xylanase enzyme preparation (enzyme preparation 3) was added to the pulp in amounts that appear from Table 5. The pulp was heated by means of a steam coil to 50 o C and it was incubated at 50 o C in a water bath. The freeness value was determined after the pulp had been incubated for one hour and four hours, re­spectively. The results are shown in Table 5. Table 5 Results from the enzyme treatment Sample Enzyme 3 Enzyme 3 Control Xylanase content (units/kg) 500 1250 - Cellulase content(units/kg) - - - Freeness (ml) 0 h 131 131 1 h 142 145 131 4 h 149 144 133
• the enzyme When the enzyme is applied in an integrated plant, i.e. in a plant in which either a plant produc­ing mechanical pulp or a deinking plant is connected to a paper mill, the enzyme addition can be carried out before the pulp is transferred to a paper machine. If the above-mentioned deinking plant is not inte­grated with a paper mill, the enzymes can be added to the slurry of the pulp and then allowed to act a suit­able period of time, whereafter the pulp is dried and after-treated as desired. Enzymes can be alternatively added to the pulp slurry at the paper mill and then allowed to act, if the pulp has been purchased from elsewhere.
• Enzyme treatment is also suitable for chemi­mechanical pulp, in which the separating of fibres is mainly carried out mechanically while using a weak chemical dosage as an aid for softening the lignin.
• a typical example of such pulp is CTMP pulp (chemical thermomechanical pulp).

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Citations (2)

• 1988
  • 1988-07-22 FI FI883491A patent/FI81394C/fi not_active IP Right Cessation
• 1989
  • 1989-07-04 NZ NZ229811A patent/NZ229811A/en unknown
  • 1989-07-06 ES ES198989112331T patent/ES2037341T3/es not_active Expired - Lifetime
  • 1989-07-06 DE DE8989112331T patent/DE68903608T2/de not_active Expired - Fee Related
  • 1989-07-06 AT AT89112331T patent/ATE82781T1/de not_active IP Right Cessation
  • 1989-07-06 EP EP89112331A patent/EP0351655B1/fr not_active Expired - Lifetime
  • 1989-07-21 CA CA000606351A patent/CA1339605C/fr not_active Expired - Fee Related
  • 1989-07-24 BR BR898903649A patent/BR8903649A/pt not_active IP Right Cessation
• 1992
  • 1992-12-07 GR GR920402824T patent/GR3006466T3/el unknown

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