US20050000666A1

US20050000666A1 - Use of hemicellulase composition in mechanical pulp production

Info

Publication number: US20050000666A1
Application number: US10/839,027
Authority: US
Inventors: James Taylor; Percy Jaquess; Henrik Lund; Hanne Pedersen; Hui Xu; Julie Clemmons
Original assignee: Novozymes AS; Buckman Laboratories International Inc; Novozymes North America Inc
Current assignee: Novozymes AS; Buckman Laboratories International Inc; Novozymes North America Inc
Priority date: 2003-05-06
Filing date: 2004-05-04
Publication date: 2005-01-06
Also published as: WO2004101889A3; WO2004101889A2; WO2004101889A8

Abstract

Methods for reducing energy required for a pulp refining processes by treating a mechanical pulp with a hemicellulase composition are presented. The enzymatic treatment can be carried out at a temperature of from about 10° C. to about 90° C., and/or at a pH of from about 2 to about 10. Paper made from the treated pulp has improved strength over paper made from untreated pulp.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119 of U.S. provisional application Ser. No. 60/468,219, filed on Nov. 15, 2002, the contents of which are fully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to methods for refining mechanical pulp, pulp made from such methods, and paper and paperboard products including the pulp.

BACKGROUND

Mechanical pulp is made from wood or wood chips, in which the wood fibers are separated by grinding or refining to obtain a desired freeness. Grinding and refining of wood or wood chips can have a high energy consumption. The use of heat and/or chemicals, as in thermomechanical pulp (TMP) production and chemithermomechanical pulp (CTMP) production, can lower the energy consumption. However, it is desirable to find means to further lower the energy consumption requirements for mechanical pulp production.
Wood includes cellulose, lignin, hemicellulose and extractives. Selective modification of one or more of these components during refining of the wood can improve features of the resultant pulp and paper products, or aid in the refining process. For example, during refining, the wood or pulp can be subjected to enzymatic treatment, including the use of cellulases or hemicellulases, as shown, for example, in Canadian Patent Application No. 2,030,836. The use of enzymes, for example, cellulases, has been reported to weaken the wood fibers due to the hydrolytic action on cellulose, resulting in a pulp material having impaired strength.
A number of enzymatic refining processes have been proposed to avoid the strength impairment resulting from the use of cellulases in mechanical refining process. U.S. Pat. No. 2,280,307, for example, describes a process that uses enzymes capable of hydrolyzing or dissolving hemicellulosic substances, but which reportedly have a minimum destructive effect on cellulose. U.S. Pat. No. 5,865,949 also describes a process for treating mechanical pulp which reportedly causes less impairment to the wood fibers, in particular, by treating mechanical pulp with a cellobiohydrolase, an endo-β-glucanase in an amount less than that which will significantly hydrolyze the cellulose, and a mannanase, and wherein the endo-β-glucanase activity is low compared to the cellobiohydrolase activity.
Certain types of enzymes also have been added to pulp at certain stages of the pulp and papermaking processes as, for example, bleaching agents, defibration agents, and dewatering agents. For example, during refining, the drainability and freeness value of the pulp can be significantly reduced. Accordingly, methods have been proposed to improve the drainage and freeness of the pulp following refining, for example, prior to loading on a paper making machine. U.S. Pat. No. 5,308,449, for example, is directed to a process for improving the drainage of pulp following completion of a refining process in which a cellulase and/or hemicellulase enzyme is used to treat a homogenous aqueous suspension of recycled paper pulp having a Schopper-Riegler (SR) degree of at least equal to 25 to produce a recycled paper pulp which has improved drainage. EP 0 351 655 is also directed to a process for improving the drainability and freeness value of pulp following completion of a refining process, and discloses the use of hemicellulose dissolving enzymes substantially free of cellulose dissolving enzymes.
A need exists for mechanical pulp production that requires less energy. A need also exists for a mechanical pulp production method that produces a stronger pulp and/or paper.
All patents, applications, and publications mentioned above and throughout the application are incorporated in their entirety by reference herein.

SUMMARY OF THE INVENTION

The present invention relates to methods for reducing energy required for refining pulp by treating a mechanical pulp with an enzymatic composition, for example a hemicellulase composition, including, for example, a mannanase, a xylanase, or a combination thereof. According to various embodiments, the mechanical pulp can be treated during refining with a hemicellulase composition that includes at least mannanase as the active ingredient. According to various embodiments, the mechanical pulp can be treated during refining with a hemicellulase composition that includes at least mannanase and xylanase as the active ingredients. The enzymatic treatment can be carried out at process temperatures of from about 10° C. to about 95° C., for example, from about 60° C. to about 90° C. The enzymatic treatment can be carried out at a pH of from about 2 to about 10. Other temperatures and/or pHs can be used.
A method of increasing strength of a refined pulp and resultant paper products including the pulp is provided, wherein the method includes treating the pulp with a hemicellulase composition during refining.
According to various embodiments, a hemicellulase composition can be substantially free of, or free of, a cellulase enzyme. According to various embodiments, a mannanase can be a thermostable mannanase and a xylanase can be a thermostable xylanase.
Methods of refining pulp which lower the energy required for refining are set forth herein. Methods for refining pulp wherein the refining process includes treatment of the pulp with a hemicellulase composition are presented, wherein the resultant pulp and/or paper products have improved strength as compared to untreated pulp or products made therewith.
Pulp and paper products made therefrom having increased strength are provided. Pulp and papers made therefrom which require less energy to produce are provided.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are only intended to provide a further explanation of the present invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are graphs showing C.S.F. vs. refining time for a fiber treated by the present invention and a control.

DETAILED DESCRIPTION

The present invention relates to a method of refining pulp, wherein the method includes the use of a hemicellulase composition. Pulp, paper, and paperboard products made according to the method preferably exhibit excellent strength. Use of the hemicellulase composition during refining can preferably reduce refining energy requirements. As used herein, “hemicellulase” is meant to include all enzymes capable of hydrolyzing or dissolving hemicellulosic substances in wood. Hemicellulases can include, for example, mannanase, xylanase, galactanase, laccase, and the like and combinations thereof.
As used herein, a “mannanase” is preferably a hemicellulase classified as EC 3.2.1.78, and called endo-1,4-beta-mannosidase. Mannanase includes beta-mannanase, endo-1,4-mannanase, and galactomannanase. Mannanase is preferably capable of catalyzing the hydrolysis of 1,4-beta-D-mannosidic linkages in mannans, including glucomannans, galactomannans and galactoglucomannans. Mannans are polysaccharides primarily or entirely composed of D-mannose units.
As used herein, a “xylanase” is preferably a hemicellulase classified as EC 3.2.1.8, and called endo-1,4-beta-xylanase. Xylanase is preferably capable of catalyzing the hydrolysis of 1,4-beta-D-xylosidic linkages in xylans. Xylanase includes (1-4)-beta-xylan 4-xylanohydrolase, endo-1,4-xylanase, beta-1,4-xylanase, endo-1,4-xylanase, endo-beta-1,4-xylanase, endo-1,4-beta-D-xylanase, 1,4-beta-xylan xylanohydrolase, beta-xylanase, beta-1,4-xylan xylanohydrolase, endo-1,4-beta-xylanase, and beta-D-xylanase.
As used herein, “thermostable” as applied to an enzyme, such as a hemicellulase, means that the enzyme has sufficient activity in the conditions used for pulp refining and paper processing in the paper and pulp industry, including conditions used in thermomechanical and chemithermomechanical refining processes. Such conditions can include temperatures of from about 10° C. to about 95° C. Conditions can also include a pH range of from about 2 to about 10.
As used herein, “sufficient activity” means that the enzyme has at least 40% of its maximum activity within the temperature and/or pH ranges used in pulp refining processes. For example, the enzyme can have at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or 100% activity under refining conditions. According to various embodiments, the enzyme can have a sufficient activity at a temperature of at least about 70° C. and/or at a pH of about 4 or higher. “Sufficient activity” and “activity” refer to the capability of the enzyme to fibrillate cellulosic fibers so that each fiber is fibrillated in an amount of about 20% or more, for example, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, or 80% or more. According to various embodiments, sufficient activity can include fibrillation of one or more fiber in an amount of about 40% or more.
Mannanase activity can be measured by applying a solution to be tested to 4 mm diameter holes punched out in agar plates containing 0.2% AZCL galactomannan (available from Megazyme, Bray, Ireland). Mannanase activity can also be measured using the assay described in Example 2, or by other methods known to those skilled in the art. Xylanase activity can be measured by measuring the amount of reducing sugars released from birch xylan (available from Roth, Karlsruhe, Germany) or by measuring the amount of blue color released from AZCL-birch xylan (available from Megazyme), as described, for example, in U.S. Pat. No. 6,228,630.
Suitable hemicellulases for use in the present invention may be obtained or derived from any suitable source, including microorganisms, for example, fungi or bacteria, and plants.
The enzymes can be derived from genetically engineered bacteria and plants. For example, bacteria can be made to produce specific enzymes by homologous over-expression, heterologous over-expression, or a combination thereof, by methods known to those of ordinary skill in the art. Transgenic plants, such as transgenic trees, can also be made by known methods to express various enzymes described herein.
Commercially available mannanase can include GAMANASE®, available from Novozymes, Franklington, N.C. Mannanase can be produced by fungi or bacteria, for example, by microorganisms belonging to the following genera: Trichoderma (e.g. T. reesei), Aspergillus (e.g. A. Niger, A. Aculeatus, (see, e.g., U.S. Pat. No. 5,795,764)), Phanerochaete (e.g. P. chrysosporium), Penicillium (e.g. P. janthinelium, P. digitatum) and Bacillus. As a host organism for mannanase production, a white-rot fungi belonging to the genera Phlebia, Ceriporiopsis, or Trametes can be used. Mannanase can also be produced by strains that have been improved to produce mannanase, or by other genetically improved host organisms, where the genes coding for the mannanase have been transferred into a desired host organism. A host organism can be, for example, the fungus T. reesei, a yeast, another fungus or mold from genera such as Aspergillus, a bacterium, or any other microorganism whose genetic sequence is sufficiently known. Mannanase can be produced by homogeneous over-expression, heterogeneous over-expression, or a combination thereof. According to various embodiments, the mannanase can be produced by Trichoderma reesei, which can produce at least five mannanases.
Xylanase for use in the present invention can be obtained or derived from any suitable source, including fungal and bacterial organisms, for example, Aspergillus, Disporotrichum, Penicillium, Neurospora, Fusarium and Trichoderma. According to various embodiments, xylanase can be derived from a bacterial xylanase. For example, a Bacillus xylanase can be obtained from, for example, a strain of Bacillus, including, for example, Bacillus halodurans, Bacillus pumilus, Bacillus agaradhaerens, Bacillus circulans, Bacillus polymyxa, Bacillus stearothermophilus, and Bacillus subtilis. Xylanase can be derived from a fungal xylanase, for example, yeast or filamentous fungal polypeptides. Examples of fungal xylanases include those derived from the following fungal genera: Aspergillus, Aureobasidium, Emericella, Fusarium, Gaeumannomyces, Humicola, Lentinula, Magnaporthe, Neocallimastix, Nocardiopsis, Orpinomyces, Paecilomyces, Penicillium, Pichia, Schizophyllum, Talaromyces, Thermomyces, and Trichoderma.
According to various embodiments, a fungal xylanase derived from Aspergillus can be used, for example, SwissProt P48824, SwissProt P33557, SwissProt P55329, SwissProt P55330, SwissProt Q12557, SwissProt Q12550, SwissProt Q12549, SwissProt P55328, SwissProt Q12534, SwissProt P87037, SwissProt P55331, SwissProt Q12568, GenPept BAB20794.1, GenPept CAB69366.1; Trichoderma, such as SwissProt P48793, SwissProt P36218, SwissProt P36217, GenPept AAG01167.1, GenPept CAB60757.1; Thermomyces or Humicola, such as SwissProt Q43097; or a combination thereof. A xylanase can be the Thermomyces lanuginosus xylanase of SwissProt Q43097, as described in U.S. Pat. No. 5,817,500. Other xylanases suitable for use in the hemicellulase composition herein can be identified by those skilled in the art after reviewing the disclosure and claims, and can include those described in U.S. Pat. Nos. 6,080,567, 6,197,564, 6,228,630 and 6,083,733.
Commercially available xylanases can include, for example, SHEARZYME®, BIOFEED WHEAT®, ULTRAFLO®, and VISCOZYME®, all from Novozymes, and SPEZYME® CP from Genencor Int., Rochester, N.Y.
A hemicellulase composition can include one or more hemicellulase, for example, mannanase, in an effective amount. An “effective amount” is a dosage of hemicellulase that is effective to fibrillate the fibers of the wood in the pulp. “Fibrillation,” as used herein, refers to separation of one or more fibril, or a portion of one or more fibril, from a fiber, such that the fiber has one or more fibrils, or one or more portions of fibrils, extending therefrom. The effective amount can vary based on the type of pulp being refined, for example, virgin hardwood kraft, virgin softwood kraft, recycled, groundwood, refiner groundwood, pressurized refiner groundwood, thermomechanical, chemithermomechanical, or a mixture thereof; the hemicellulase in the composition; and the reaction conditions, for example, temperature and pH. Other factors that can affect the amount of hemicellulase composition can be determined by those of ordinary skill in the art upon reading and understanding this disclosure and the appended claims.
The hemicellulase composition can include a neat hemicellulase, a neat mixture of hemicellulases, or a composition of one or more hemicellulases in combination with additives and/or fillers. Wherein the hemicellulase composition includes one or more neat hemicellulases, the composition can be added to a pulp for refining in an amount of from about 0.01 to about 0.1 pounds per ton of dry pulp, or from about 0.03 to about 0.05 pounds per ton of dry pulp.
Other amounts can be used. Wherein the hemicellulase composition includes one or more hemicellulases in combination with one or more additives and/or fillers, the composition can be added to a pulp for refining in an amount of from about 0.001 to about 20 pounds per ton dry pulp, for example, from about 0.01 to about 10 pounds per ton of dry pulp. Other amounts can be used. The hemicellulase composition can contain one or more hemicellulases to a total of up to 20% of the composition by weight, or from about 1% to about 10% of the composition by weight. According to various embodiments, the hemicellulase composition can include up to about 20% by weight, up to about 10% by weight, or up to about 5% by weight of the composition of hemicellulases. The composition can further include polyethylene glycol, hexylene glycol, polyvinylpyrrolidone, tetrahydrofuryl alcohol, glycerine, water, other conventional enzyme composition additives, as for example, described in U.S. Pat. No. 5,356,800, or a combination thereof.
According to various embodiments, the hemicellulase composition can include mannanase, for example, a thermostable mannanase. The hemicellulase composition can include mannanase and at least one other hemicellulase, for example, xylanase. Mannanase can be used as the only active ingredient in the hemicellulase composition. Also, mannanase and xylanase can be used as the only active ingredients in the hemicellulase composition. “Active ingredient” means a material that is effective to fibrillate one or more fibers of wood in the pulp. As an option, other active ingredients can be present.
According to various embodiments, the hemicellulase composition can be substantially free, or totally free, of non-hemicellulase enzymes, for example, cellulase enzymes including cellulases such as cellobiohydrolases and endoglucanases. The phrase “substantially free” means that only minimal amounts of other enzymes are present, for example, less than about 0.001 pounds per ton dry pulp, or less than about 0.0001 pounds per ton dry pulp. The term “totally free” means that no detectable enzyme activity is present other than the activity of the one or more active ingredients.
According to various embodiments, the hemicellulase composition can be used in combination with a surfactant. Any suitable surfactant known for use in pulp refining and paper production can be used. The surfactant can be a nonionic surfactant, for example, polyvinylpyrrolidone, Tween 20, or Triton X100. Of these surfactants, those with 6.5 moles of ethylene oxide to 7.5 moles of ethylene oxide are preferred with 7.0 moles of EO most preferred. The surfactant can be an alkyl ethoxylate, such as a linear alkyl ethoxylate. The alkyl group can be C8 to C16, e.g., laurel (C12). Other non-ionic surfactants include: Triton X-100 (polyethylene glycol tert-octylphenol ether), polyoxyethylene sorbitan monolaurate (Tween 20) and polyoxyethylene sorbitan monooleate (Tween 80), also polyoxyethylene 2-stearyl ether (Brij 72); N-(N-Dodecyl)-2-pyrrolidinone as the Surfadone series LP 100-300 by International Speciality Products, ethoxylated tetramethyl decynediol, nonyl phenols (e.g., in the present of polyvinyl pyrrolidone). Preferably, non-ionic surfactants that stabilize the enzyme under the conditions of high temperature at 50 centigrade are preferred. Of those surfactants which compliment the alkyl ethoxylate and also exhibit excellent compatibility with polyvinylpyrrolidone (PVP) and further demonstrating excellent temperature stabilization for the enzyme; the polyethylene glycol esters (PEG) series were selected. These esters express a unique series of hydrophilic and lipophilic properties over a wide range of operating conditions. When blended with PVP and alkyl ethoxylate in the presence of water; a clear, slightly viscous, non-precipitating matrix solution is produced which affords high temperature stability to the biological enzyme, e.g., beta-mannanase. The PEG series, e.g., PEG 200 through PEG 600 di and mono laurate, such as PEG 400 monolaurate, can be used.
Formula parameters should be selected for good liquid flowability, no haze, no precipitation of surfactants or the enzyme, excellent water compatibility and stability protection for the biological enzyme at high temperature. These parameters can be achieved by varying the ratios of the non-ionic surfactants. PVP in its own right improves the surfactancy of the other components without sacrificing its own dispersant properties. An enzyme formulation preferably has an alkyl ethoxylate, polyvinylpyrrolidone, polyethylene glycol ester, hemicellulase, and water.
Suitable formulas include, but are not limited to:

- a) alkyl ethoxylate-from about 1% to about 5%
- b) polyvinylpyrrolidone-from about 20% to about 40%
- c) polyethylene glycol ester-from about 1% to about 20%
- d) water-from about 45% to about 60%

e) hemicellulase-from about 1% to about 20%, all % by weight of formulation;



	(a) alkyl ethoxylate (e.g., linear)	1-5%
	(b) tergitol XD	1-7%
	(c) PVP K-90	30-40%
	(d) water	48-58%; or
	(a) linear alkyl ethoxylate	1-3%
	(b) tergitol XD	1-3%
	(c) PVP K-90	35-40%
	(d) water	45-55%.

A most preferred formula is:



	(a) linear alkyl ethoxylate	1-2%
	(b) PEG 400	10-20%
	(c) PVP K-90	20-30%
	(d) water	45-50%

	**All above formulas may use 1-20% by weight hemicellulase, such as mannanase, e.g., beta-mannanase, once the stability solution has been composed.

Stability testing for all formulas involves being exposed to 50 centigrade (122 F) temperature for thirty (30) continuous days without losing more than 5% enzyme activity, and preferably without discoloration, without hazing, and without untoward precipitation of any components of the formulation solution. Enzyme activity is preferably defined as : One unit will liberate 1.0 micromole of mannose in 1 minute from locust bean gum substrate @ pH 5.3, 80 Centigrade with a 5-minute incubation time. The formulations mentioned above perform excellent liquid solutions stabilization for the Mannanase derived from all microorganisms (bacterial, fungal etc.). These formulations are superior to more common extract solutions of Alpha and Beta Mannanases and afford extended activity and utility at elevated temperature ranges.
According to various embodiments, a conventional papermaking polymer can be added to the pulp. The polymer can be a cationic polymer, a nonionic polymer, or an amphoteric polymer. If the polymer is an amphoteric polymer, it can be used under cationic conditions. The polymer can be, for example, a high molecular weight linear cationic polymer, a branched polyethylene oxide, a polyamidoamineglycol (PAAG) polymer, or the like. Exemplary high molecular weight linear cationic polymers suitable for use are described, for example, in U.S. Pat. Nos. 4,753,710 and 4,913,775, which are both incorporated herein in their entireties by reference. At least one other polymer can be used in addition to at least one of the polymers recited above, provided the other polymer does not substantially adversely affect the desirable properties achieved according to the present invention.
A cationic polymer composition can be added to the pulp before, after, or at the same time as addition of the hemicellulase composition. Examples of cationic polymers include, but are not limited to, cationic starches and cationic polyacrylamide polymers, for example, copolymers of an acrylamide with a cationic monomer, wherein the cationic monomer may be in a neutralized or quatemized form. Nitrogen-containing cationic polymers can be used. The cationic polymer can have a low molecular weight. Exemplary cationic monomers can be copolymerized with acrylamide to form cationic polymers useful according to the present teachings. The cationic monomers can include amino alkyl esters of acrylic or methacrylic acid, and diallylamines in either neutralized or quatemized form. Exemplary cationic monomers and cationic polyacrylamide polymers are described, for example, in U.S. Pat. No. 4,894,119, which is incorporated herein in its entirety by reference. The cationic polymer composition can be added in an amount effective to improve the drainage or retention of the pulp compared to the same pulp but having no cationic polymer present. In general, the cationic polymer can be added in an amount of at least about 0.05 pound per ton of pulp based on the dried solids weight of both the polymer and the pulp, and preferably in an amount of at least about 0.1 pound per ton of pulp. The cationic polymer can be added in an amount of from about 0.2 pound per ton of pulp to about 2.5 pounds per ton of pulp based on dried solids weights. Other amounts can be used.
A cationic polymer or an amphoteric polymer under cationic conditions can be added to the pulp in an amount of from about 5 grams to about 500 grams per ton of pulp based on the dried solids weight of both the polymer and the pulp. For example, the polymer can be added in an amount of from about 20 grams to about 200 grams, or from about 50 grams to about 100 grams per ton of pulp based on the dried solids weight of both the polymer and the pulp.
The polymer can be a polyacrylamide formed from comonomers that include, for example, 1-trimethylammonium-2-hydroxypropylmethacrylate methosulphate. Other examples of suitable polymers, include, but are not limited to, homopolymers of diallylamine monomers, homopolymers of aminoalkylesters of acrylic acids, and polyamines, as described, for example, in U.S. Pat. No. 4,894,119. Co-polymers, ter-polymers, or higher forms of polymers can also be used. A mixture of two or more polymers can be used. Regardless of charge, the polyacrylamide can have a molecular weight in excess of 100,000, for example, about 5,000,000 and 25,000,000. Suitable anionic polyacrylamides include those described in U.S. Pat. No. 4,798,653, which is incorporated herein in its entirety by reference.
When a cationic polymer is used and contains a cationic polyacrylamide, nonionic acrylamide units can be present in the copolymer in an amount of at least about 30 mol % and no greater than about 95 mol %. From about 5 mol % to about 70 mol % of the polymer can be formed from a cationic comonomer.
According to various embodiments, a retention aid such as an acidic aqueous alumina sol can be added in any amount sufficient to improve the retention of fines when the pulp is formed into a wet sheet or web. For example, acidic aqueous alumina sol can be added in an amount of at least about 0.05 pound per ton of pulp, at least about 0.2 pound per ton of pulp, an amount of from about 0.3 pound per ton of pulp to about 5.0 pounds per ton of pulp, wherein the weight in tons is based on the dried solids weight of both the sol and the pulp. Acidic aqueous alumina sol can be added in an amount of from about 0.01% by weight to about 0.5% by weight based on the dried solids weight of both the sol and the pulp.
The retention aid, for example, acidic aqueous alumina sol, can be added before or after significant shear steps in the papermaking process. For example, the retention aid can be added after the machine chest or stuff box if the papermaking system includes a machine chest and/or a stuff box. Good papermaking properties can be achieved even when the retention aid is added after the last significant shear step in the papermaking process. The retention aid can be added after a polymeric coagulant has been added to the pulp and after at least one significant shear step in the papermaking process.
According to various embodiments, a cationic starch can be added to the pulp to form a starch treated pulp. Starch can be added at one or more points along the flow of pulp through a papermaking apparatus. For example, cationic starch can be added to a pulp at about the same time that an acidic aqueous alumina sol is added to the pulp. A cationic starch can be added to the pulp or combined with the pulp prior to introducing the acidic aqueous alumina sol to the pulp. The cationic starch can alternatively or additionally be added to the pulp after the pulp is first treated with a hemicellulase composition, a coagulant, or both. Cationic starches can include, but are not limited to, potato starches, corn starches, and other wet-end starches, or combinations thereof. Conventional amounts of starch can be added to the pulp. An exemplary amount of starch is from about 5 to about 25 pounds per ton based on the dried solids weight of the pulp.
A biocide can be added to the pulp in accordance with conventional uses of biocides in papermaking processes. For example, a biocide can be added to the treated pulp after the pulp has been treated with a hemicellulase composition and, optionally, a cationic polymer. Biocides useful include those known to those skilled in the art, for example, biocides available from Buckman Laboratories International, Inc., Memphis, Tenn., including BUSANM™ biocides, such as, but not limited to, Busan 30WB, Busan 85, Busan 881, Busan 1009, and Busan 1030, and the like.
The pulp of the present invention can be treated with one or more other components, including polymers such as anionic and non-ionic polymers, clays, other fillers, dyes, pigments, defoamers, microbiocides, pH adjusting agents such as alum, other enzymes, and other conventional papermaking or processing additives. These additives can be added before, during, or after introduction of a hemicellulase composition. The hemicellulase composition can be added to the papermaking pulp before the addition of coagulants, flocculants, fillers, and other conventional and non-conventional papermaking additives, including additional enzymes.
The pulp can include a coagulant/flocculant retention system. Exemplary coagulant/flocculant systems that can be used can include, for example, an inorganic coagulant such as alum (alumina sulphate), a cationic starch, or a low molecular weight synthetic cationic polymer. The coagulant can reduce the negative surface charges present on particles in the pulp, for example, the surface charges of the cellulosic fines and mineral fillers, and thereby accomplishes some degree of agglomeration of such particles. A coagulant can be added to the pulp at any time. A flocculant can be added to the pulp, for example, after addition of the coagulant, and/or after one or more shear steps. The flocculant can include, for example, a synthetic anionic or cationic polymer, or other types of conventional flocculants.
The pulp can be any conventional softwood or hard wood species used in mechanical pulp production, such as spruce, fir, pine, hemlock, aspen, acacia, birch, beech, eucalyptus, oak, and other softwood and hardwood species. The pulp can contain cellulose fibers in an aqueous medium at a concentration of preferably at least about 50% by weight based on the total dried solids content of the pulp. The pulp can be, for example, virgin pulp (e.g., spruce, fir, pine, eucalyptus, and include virgin hardwood or virgin softwoods), hardwood kraft pulp, softwood kraft pulp, recycled pulp, groundwood, refiner groundwood, pressurized refiner groundwood, thermomechanical pulp, chemithermomechanical pulp, or mixtures thereof.
According to various embodiments, the papermaking system can include a primary refiner, a secondary refiner, a screen, a mixer, a latency and/or blend chest, and papermaking equipment, for example, screens. The papermaking system can also include metering devices for providing a suitable concentration of the hemicellulase composition or other additives to the flow of pulp. Valving, pumps, and metering equipment as known to those skilled in the art can also be used for introducing various additives described herein to the pulp.
According to one embodiment, a hemicellulase composition can be added to the pulp at anytime after the pulp leaves the first refiner (also known as the primary refiner) during the refining process. For example, the hemicellulase composition can be added before the second refiner (also known as the secondary refiner), after the second refiner, before the screen, after the screen, before the mixer, after the mixer, before the latency and/or blend chest, to the latency and/or blend chest. For example, the hemicellulase composition can be added after the second refiner, between the screen and the mixer, or after the mixer. A cationic polymer can be added before or simultaneously with the addition of the hemicellulase composition. Other additives as described can be added to the papermaking system as known to those skilled in the art.
The pulp can be treated with a hemicellulase composition when the pulp is at a temperature of from about 10° C. to about 95° C. , from about 35° C. to about 95° C. , from about 60° C. to about 90° C., or from about 80° C. to about 90° C. The pulp can be at a pH of from about 2 to about 10, from about 4 to about 7, or from about 4 to about 5.5. A treatment time can be from about 5 minutes to about 4 hours, from about 5 minutes to about 2 hours, or from about 15 minutes to about 1 hour.
The enzyme treatment is carried out during the refining process, but before completion of the refining process. The enzyme treatment is preferably carried out on “coarse pulp.” A “coarse pulp” refers to lignocellulosic material used as the raw material of the mechanical pulp, which has been subjected to at least one mechanical refining process step. The term coarse pulp therefore encompasses, e.g., once refined or ground pulp, twice refined or ground pulp, the reject pulp and long fiber fractions, and combinations thereof. Preferably, the enzyme treatment, i.e., mannanase treatment, is carried out on once refined or ground pulp or the reject pulp. More preferably, the mannanase is treatment is carried out on both once refined pulp and the reject pulp.
In another embodiment, the hemicellulase composition can be added after the latency chest in a refining operation. As an example, the hemicellulase composition can be added after the screening that occurs after the latency chest. As a further example, the hemicellulase composition can be added after the screening that occurs in the latency chest and in the feedline which contains the rejected material from the screening process that occurs after the latency chest. In this embodiment, the rejected refined pulp is typically passed into a feed tank and then subsequently subjected to a reject refiner in order to meet necessary specifications for further processing into paper. In this particular embodiment, the hemicellulase composition can be added during the screening operation or added after the screening step, or added into the reject flow prior to its introduction into the tank. As another option, the hemicellulase composition can be added anywhere between the latency chest and the reject refiner. As another option, the hemicellulase composition can be added anywhere between the latency chest and where the pulp that has been subjected to refining in the reject refiner is reintroduced into the process stream prior to being bleached and entering the leveling chest.
As another option, the hemicellulase composition can be added any time after the latency chest and prior to the leveling chest. As an example, the hemicellulase composition can be added prior to the leveling chest which is immediately prior to the blending chest and any optional de-inking operation. Furthermore, the hemicellulase composition can be added any time between the latency chest and the bleaching step. Thus, any possibilities with respect to the introduction of the hemicellulase composition can be used in the present invention. It has been discovered that when the hemicellulase composition is introduced after the latency chest and in the manner, for example, described above, various positive properties can be achieved such as the pulp obtaining improved strength. One interesting point of the present invention is in one or several embodiments, the present invention achieves improved strength of the pulp without increasing the freeness of the pulp which can be beneficial in certain embodiments.
According to various embodiments, the enzyme composition or enzyme treatment, as described herein, may further comprise with one or more additional enzymes. In a preferred embodiment, the enzyme composition or enzyme treatment may comprise an esterase, such as, a lipase. Examples of commercial lipases are Resinase HT and Resinase ATX (available from Novozymes, North America, Inc.) In another preferred embodiment, the enzyme composition or enzyme treatment may comprise a pectin degrading enzymes, such as, a pectinase. Examples of commercial pectinases are Novozym 863, Pectinex 3XL, Pectinex Smash, and Pectinex Smash XXL(available from Novozymes, North America, Inc.).
The introduction of the hemicellulase can be achieved at one or more points and the introduction can be continuous, semi-continuous, batch, or combinations thereof.
According to various embodiments, the consistency of the pulp can be less than 10%, from about 1% to about 7%, or from about 3% to about 5%.
A pulp processed as described herein can exhibit improved strength. Paper products made from the pulp also exhibit improved strength. The addition of a hemicellulase composition increases the amount of fibrillation of the wood fibers, increasing the number of bonding sites available on each fiber, and therefore allowing more binding between the fibers, increasing the strength of the fiber mat, and paper products made with the fibers or fiber mat. The increased fibrillation does not significantly reduce the length of the fibers. Further, the freeness and drainability of the pulp can remain the same, or decrease, due to increased retention of fiber fines and filler. The addition of the hemicellulase composition to pulp during processing can reduce the amount of refining energy needed.
A pulp produced by the methods described herein can be used in the production of paper products, including, for example, cardboard, paper towels, newspaper, and hygiene products. The methods described herein can also be suitable for textile manufacturing.

EXAMPLES

Example 1

Freeness

Mannanase was added in an amount of 0.171 pounds/ton dry pulp to TMP at a temperature of 85° C. The treated consistency was 3%. The treated pulp was placed in a Valley beater at a temperature of 20° C., a pH of 5.13, and the resulting pulp had a consistency of 1.57%. The treated TMP was measured for freeness at various time intervals during beating. A control sample was also measured. As the results in the table and FIG. 1 demonstrate, the freeness significantly affected by the treatment with mannanase.

Canada Standard Freeness (C.S.F.) Results of

Mannanase Treated Fiber Modification

Time Control Mannanase Treated

(minutes) Freeness Value Freeness Value

0 485 470

5 425 425

20 360 370

35 285 300

65 200 180

95 100 100

Example 2

Mannanase Activity Assay at Elevated Temperatures

Mannanase activity was determined using a 0.5% solution of locust bean gum galactomannan (available from Sigma-Aldrich, St. Louis, Mo., as Sigma G-0753) as the substrate. Diluted mannanase and the substrate were incubated at a targeted temperature and pH 5.0 for 5 min. Released reducing sugars were assayed by adding 3,5-dinitrosalicylic acid (DNS) solution. The mixture was boiled in a water bath for 5 min. After cooling, the absorbency was measured at 540 nm. The optimal temperature for this enzyme is about 80° C., as shown in the table below.

Temperature, ° C. Relative Activity, %

40 30

50 37

60 56

70 82

80 100

90 61

Example 3

Enzymatic Hydrolysis of Southern Pine TMP Reject Pulp

Southern pine TMP reject pulp with a consistency of 2.5% was treated with mannanase in an amount of 1 mg/g of pulp at 80° C. and pH 5.0 for 30 minutes. The control experiment was run at exactly the same conditions except mannanase was not added. The amount of reducing sugar released was determined by DNS method. The control did not release any detectable amount of reducing sugar, while the mannose-treated pulp released about 1 mg/g of pulp. This demonstrates that mannanase can hydrolyze the mannan component in TMP pulp in a relatively short time and at a high temperature similar to the conditions of a TMP mill process.

Example 4

Mannanase Aided Refining

Southern pine TMP reject pulp having a 2.5% consistency was treated with mannanase in an amount of 1 mg/g of pulp at 80° C. and pH 5.0for 30 minutes. After the enzymatic treatment, the pulp was transferred to a Cool-Base Waring Blender and refined on a medium setting for the designated time. The results are shown in the FIG. 2. As can be seen from FIG. 2, the mannanase-treated pulp takes less time to refine in order to reach a targeted freeness. The mannanase-treated pulp also required less refining energy for a given freeness.

Example 5

Combined Mannanase and Xylanase Treatment of TMP Reject Pulp

Southern pine TMP reject pulp having a 2.5% consistency was treated with a mixture of mannanase and xylanase at 80° C. and pH 5.0 for 30 minutes. The enzyme dosage for both mannanase and xylanase was 1 mg/g of pulp. Refining was done with a Cool-Base Waring Blender for 10 min. The results are set forth in the table below.

Treatment CSF Freeness, mL

Control 380

Mannanase 345

Mannanase + Xylanase 320
As shown in the table, both the use of mannanase alone and in combination with xylanase can also reduce the freeness over the value of the control. The combination of mannanase and xylanase can be used in some embodiments to reduce the pulp freeness even further than mannanase alone. Use of mannanase, or mannanase with xylanase, provides a reduction in refining energy.

Example 6

Effect of Mannanase Treatment on Strength Properties

Handsheets made from the pulp of Example 4 after 10 minutes of refining were evaluated for their strength properties. The results are shown in the table below. Treatment with mannanase resulted in a denser handsheet and improved the paper properties under the same refining conditions as the control.

Treatment Bulk, cm³/g TEA, J/m² Tensile Index, Nm/g

Control 4.14 9.67 20.9

Mannanase 3.95 11.49 21.5
It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments of the present invention without departing from the spirit or scope of the present invention. Thus, it is intended that the present invention covers other modifications and variations of this invention within the scope of the appended claims and their equivalents.

Claims

1. A method for preparing a mechanical pulp, comprising mechanically refining a pulp, wherein during the mechanical refining process the pulp is treated with an enzyme composition comprising a thermostable mannanase.

2. The method of claim 1, wherein the mannanase treatment is carried out at a temperature of 65-95° C.

3. The method of claim 1, wherein the mannanase treatment is carried out at a temperature of 80-90° C.

4. The method of claim 1, wherein the pulp is treated with the combination of a thermostable mannanase and a surfactant.

5. The method of claim 4, wherein the surfactant is a non-ionic surfactant.

6. The method of claim 1, wherein the enzyme composition is substantially free of or free of other enzymes.

7. The method of claim 1, wherein the enzyme composition is substantially free of or free of cellulase enzymes.

8. The method of claim 1, wherein the enzyme composition comprises a thermostable xylanase.

9. The method of claim 1, wherein the enzyme composition consists of a thermostable mannanase.

10. The method of claim 1, wherein the enzyme composition consists essentially of a thermostable mannanase.

11. The method of claim 8, wherein the enzyme composition consists of a thermostable mannanase and a thermostable xylanase.

12. The method of claim 8, wherein the enzyme composition consists essentially of a thermostable mannanase and a thermostable xylanase.

13. The method of claim 1, wherein the mannanase is used in an amount 0.001 mg/g to 10 mg/g of pulp.

14. The method of claim 1, wherein the mechanical refining process is a thermomechanical refining process or chemithermomechanical refining process.

15. The method of claim 1, wherein the pulp is coarse pulp.

16. The method of claim 15, wherein the coarse pulp is once refined or ground pulp, twice refined or ground pulp, reject pulp, long fiber fractions, and combinations thereof.

17. The method of claim 15, wherein the coarse pulp is once refined pulp and/or reject pulp.

18. The method of claim 1, wherein the method further comprises preparing a paper product from the mechanical pulp.

19-20. (Cancelled)

21. A method for preparing pulp, comprising:

providing a pulp source;

converting the pulp source to a pulp;

refining the pulp; and

treating the pulp with a hemicellulase composition,

wherein treating the pulp with the hemicellulase composition occurs during refining of at least a portion of the pulp.

22. The method of claim 21, wherein said refining includes use of at least one refiner, a latency chest, at least one screen, and at least one mixer, and further includes:

processing the pulp in the at least one refiner;

holding the processed pulp in the latency chest for a period of time;

screening the processed pulp; and

mixing the processed pulp,

wherein treating the pulp with the hemicellulase composition occurs after processing the pulp.

23-65. (Cancelled)