Enzyme-treated cellulosic webs

Abstract

A system and process for producing fibrous webs, such as tissue webs, is disclosed. The fibrous webs contain cellulosic fibers treated with one or more enzymes. In accordance with the present disclosure, the fibers are treated with the one or more enzymes while in an enclosed system for preventing human contact. The enzymes are then denatured prior to feeding the fibers to a web-forming process.

Description

[0001] 65131087PC01

[0002] ENZYME-TREATED CELLULOSIC WEBS

[0003] BACKGROUND

[0004] Absorbent tissue products such as paper towels, facial tissues, bath tissues and other similar products are designed to include several important properties. For example, the products should have good bulk, a soft feel and should be highly absorbent. The product should also have good strength and resist tearing, even while wet. Unfortunately, it is very difficult to produce a high strength tissue product that is also soft and highly absorbent.

[0005] In the past, for instance, various additives and methods have been used in order to increase the strength of tissue products. For example, various strength agents have been added to tissue products in the past including dry strength agents and wet strength agents. Some strength agents are considered temporary since they only maintain wet strength in the tissue for a specific length of time.

[0006] Various different enzymes have also been added during the production of tissue webs in the past in order to modify fiber properties, improve bonding, and enhance the overall quality of the tissue web. The enzymes are typically added during the preparation of pulp for papermaking. Such enzymes can include cellulases and hemicellulases. These enzymes, for instance, can partially hydrolyze cellulose fibers which softens them by weakening the outer layer of the fiber. Treating cellulose fibers with enzymes, for instance, reduces the amount of refining energy required to generate strength thereby improving drainage and reducing fines in the water system. Enzyme use may allow for the replacement of long northern softwood kraft fibers with shorter eucalyptus fibers. Tissue webs made from enzyme-treated fibers can also have better drainage and lower dust.

[0007] In the past, enzymes were combined with pulp fibers during the pulping process and then denatured during drying. For instance, the enzymes were denatured by being exposed to relatively high temperatures during the drying process.

[0008] Although enzymes can provide various benefits and advantages when incorporated into a tissue web, cellulolytic enzymes can be sensitizers for workers exposed to them. Sensitization refers to the development of an allergic reaction upon repeated exposure to a substance, even at low levels. For instance, cellulolytic enzymes are protein molecules and can act as allergens. Consequently, enzymes can only be used in controlled environments. Employees within the environment need to be tested prior to the introduction of enzymes into the environment to see it there is pre-sensitization. Subsequent required testing determines if employees have developed sensitization that could be linked to the environment. It is also necessary to verify that the enzymes in the finished product have been fully denatured. Also, the level of enzymes in the environment needs to be tested to ensure that it is at the lower limit. Testing of employees, the product and the environment requires a lot of65131087PC01

[0009] resources and continues while the enzymes are in use. These protocols have limited the ability of enzymes to be used in all facilities.

[0010] Sensitization is checked by using a single antigen in a skin prick or blood test. This limits the process to the use of a single enzyme instead of multiple enzymes at the same time reducing the opportunity to use an optimum blend of enzymes.

[0011] In addition to workers’ safety, enzymes are also incompatible with many chemical auxiliaries used during the production of tissue webs. For example, some enzymes are incompatible with many strength agents, debonders, and binders. For instance, carboxymethyl cellulose, a typical strength agent, can be degraded when contacted with various cellulolytic enzymes.

[0012] In view of the above, a need exists for a method and system for treating pulp fibers with enzymes while minimizing the exposure of workers or employees to the enzyme. A need also exists for a method for incorporating enzymes into tissue products in combination with other auxiliaries and components.

[0013] SUMMARY

[0014] In general, the present disclosure is directed to a process and system for treating pulp fibers with an enzyme and forming nonwoven webs from the resulting fibers. The present disclosure is also directed to tissue products made from the process. In accordance with the present disclosure, pulp fibers in an aqueous slurry are contacted with an enzyme. Before the aqueous slurry is used to form a nonwoven web, however, the enzyme is denatured. Consequently, nonwoven webs, such as tissue webs, can be formed in accordance with the present disclosure without any active enzymes being present during the process. By denaturing the enzyme prior to depositing the aqueous slurry on a forming surface, for instance, no active enzyme is present in the product and is not present in any mist produced during the process that may be contacted by bystanders. In accordance with the present disclosure, enzymes can be used to improve one or more properties of a tissue web while minimizing or eliminating exposure of the enzyme to workers or employees. In addition, improved tissue products are produced that only contain denatured enzymes.

[0015] In one embodiment, for instance, the present disclosure is directed to a method for the production of a fibrous cellulosic web. The method includes treating an aqueous slurry of cellulosic fibers with a cellulolytic enzyme to form enzyme-treated fibers. The cellulosic fibers can comprise pulp fibers. For instance, the pulp fibers can comprise wood pulp fibers, non-wood pulp fibers, or mixtures thereof. In one aspect, the pulp fibers comprise hardwood fibers, softwood fibers, or a mixture of hardwood fibers and softwood fibers.

[0016] In accordance with the present disclosure, the cellulolytic enzyme is denatured while the enzyme remains in a contained aqueous slurry of cellulosic fibers. After the cellulolytic enzyme has65131087PC01

[0017] been denatured, the aqueous slurry of cellulosic fibers is spread on a porous forming surface to form a cellulosic web, which is dried.

[0018] The aqueous slurry of cellulosic fibers can be treated with the enzyme at a pH of from about 5 to about 8.5, such as from about 5.5 to about 7.5, and at a temperature of from about 25°C to about 70°C. The cellulosic fibers can be treated for a period of time, referred to as residence time, of greater than about 30 minutes, such as greater than about 45 minutes, and less than about 5 hours, such as less than about 3 hours prior to denaturing the enzyme. In one aspect, the enzyme is added to the aqueous slurry of cellulosic fibers in an amount of greater than about 100 grams per ton of fibers, such as greater than about 200 grams per ton of fibers, such as greater than about 250 grams per ton of fibers, and less than about 500 grams per ton of fibers, such as less than about 450 grams per ton of fibers, such as less than about 400 grams per ton of fibers. The enzyme is contacted with the aqueous slurry of cellulosic fibers during mixing and while the slurry is at a consistency of greater than about 2%, such as greater than about 2.5%, such as greater than about 3%, and less than about 20%, such as less than about 15%.

[0019] In one embodiment, the cellulosic fibers can be refined, such as mechanically refined. In one aspect, the cellulosic fibers can be treated with the enzyme and then refined. Refining can occur before or after the cellulolytic enzyme is denatured. Treating the fibers with an enzyme prior to refining lessens the energy requirements needed to refine the fibers and produces less fines.

[0020] The enzyme can be denatured by being exposed to heat or by being exposed to an elevated pH. In one aspect, the enzyme is denatured by raising the pH of the aqueous slurry containing the enzyme-treated fibers to greater than about 8.5, such as greater than about 9, such as greater than about 9.5, such as greater than about 10, and less than about 13. In one aspect, the pH of the aqueous slurry is increased by adding a hypochlorite, such as sodium hypochlorite. The hypochlorite can be added at a concentration of greater than about 2 ppm, such as greater than about 2.5 ppm, and less than about 50 ppm, such as less than about 25 ppm, such as less than about 20 ppm, such as less than about 15 ppm, such as less than about 10 ppm. The pH of the aqueous slurry can be increased while in a mixing tank or can be added to piping exiting the mixing tank.

[0021] In one aspect, after the pH of the aqueous slurry has been increased and the enzyme has been denatured, free chlorine can be removed from the aqueous slurry. For instance, a chlorine scavenger can be added to the aqueous slurry of fibers. One example of a chlorine scavenger can comprise a bisulfite, such as sodium bisulfite. The sodium bisulfite can be added to the aqueous slurry at a stoichiometric ratio or at a greater than stoichiometric ratio in relation to the hypochlorite or in relation to the amount of chlorine contained in the aqueous slurry of fibers.

[0022] In one aspect, the aqueous slurry of fibers treated with the enzyme can be formed into a tissue65131087PC01

[0023] web. The tissue web can have a basis weight of from about 10 gsm to about 200 gsm, such as from about 12 gsm to about 130 gsm. The tissue web can have a bulk of greater than about 3 cc / g, such as greater than about 6 cc / g, such as greater than about 8 cc / g , and less than about 20 cc / g.

[0024] In one aspect, after the pH of the aqueous slurry has been increased to denature the enzyme and after a chlorine scavenger has been added to the aqueous slurry, various other auxiliaries can be contacted with the treated fibers. For instance, after the chlorine scavenger has been added, the pulp fibers can be treated with a dry strength agent, a wet strength agent, a debonder, or the like.

[0025] Other features and aspects of the present disclosure are discussed in greater detail below.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] A full and enabling disclosure of the present disclosure is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:

[0028] Figure 1 is a diagram illustrating one embodiment of a process and system in accordance with the present disclosure;

[0029] Figure 2 is an enlarged view of one embodiment of a papermaking process; and

[0030] Figure 3 is an enlarged view of another embodiment of a papermaking process that may be used in accordance with the present disclosure.

[0031] Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.

[0032] DEFINITIONS

[0033] The term "machine direction" as used herein refers to the direction of travel of the forming surface onto which fibers are deposited during formation of a nonwoven web.

[0034] The term "cross-machine direction" as used herein refers to the direction which is perpendicular to the machine direction defined above.

[0035] As used herein, the term "nonwoven web or material” refers to a web having a structure of individual fibers that are interlaid, but not in an identifiable manner as in a knitted or woven fabric. Nonwoven materials include, for example, carded webs, wet-laid webs, airlaid webs, foam-formed webs, and the like.

[0036] As used herein, the term "pulp” generally refers to a plurality of cellulose fibers that have undergone a pulping process such that the fibers have been individualized and wherein the fibers have an elongate shape in which the apparent length exceeds the apparent width. Pulp fibers can be fibrillated and can have a measurable freeness.

[0037] As used herein, the term "caliper” is the representative thickness of a pulp sheet and is generally measured as described in the Test Methods section below. Caliper commonly has units of millimeters or microns.65131087PC01

[0038] As used herein, the term “Freeness” refers to the Canadian Standard Freeness (CSF) determined in accordance with TAPPI Standard T 227 OM-94. Freeness commonly has units of milliliters (mL).

[0039] As used herein, the term “fiber length” generally refers to the length weighted average fiber length (LWAFL) of fibers measured using an OpTest Fiber Quality Analyzer, model FQA-360 (OpTest Equipment, Inc., Hawkesbury, ON) as described in the Test Methods section below. Fiber length commonly has units of millimeters.

[0040] DETAILED DESCRIPTION

[0041] It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present disclosure.

[0042] In general, the present disclosure is directed to a process and system for producing a nonwoven web, such as a tissue web, from enzyme-treated cellulosic fibers. Cellulosic fibers, which can comprise pulp fibers, are contacted with an enzyme in order to modify the fibers and alter at least one property of the resulting fibrous web being formed. In accordance with the present disclosure, the enzymes are contacted with the cellulosic fibers while being contained in one or more enclosed vessels (e.g. pulper, mixing chambers, piping, lines, tanks, etc.) that prevent any portion of the enzyme from becoming airborne and prevents contact of the enzyme with the operators running the process. After the one or more enzymes are contacted with the cellulosic fibers for a period of time, the one or more enzymes are then denatured while remaining in enclosed vessels. Only after all the enzymes have been denatured are the cellulosic fibers deposited onto a forming surface for forming a fibrous web. Consequently, fibrous webs or tissue webs made according to the present disclosure are devoid of active enzymes and thus completely safe for human contact.

[0043] The process of the present disclosure can offer various advantages and benefits in producing fibrous webs. The one or more enzymes, for instance, can be used to modify fiber properties for improving bonding and / or enhancing overall quality of the produced web. In one aspect, for instance, one or more enzymes can be used to increase the strength of webs made from the process by weakening the outer layer of the fiber. For example, enzyme treatment can be combined with refining for creating fibrules which cross and increase web strength. In this manner, less expensive and / or more sustainable fibers can be used to produce the fibrous web. In one aspect, for instance, fibrous webs can be made according to the present disclosure containing significant amounts of hardwood fibers, such as eucalyptus fibers, which can be a more sustainable source of cellulosic fibers than other pulp fibers used in the past. For example, fibrous webs made according to the present disclosure can contain hardwood fibers or eucalyptus fibers in an amount greater than about 20% by65131087PC01

[0044] weight, such as in an amount greater than about 30% by weight, such as in an amount greater than about 40% by weight, such as in an amount greater than about 50% by weight, such as in an amount greater than about 60% by weight, such as in an amount greater than about 70% by weight, such as in an amount up to about 100% by weight. The hardwood or eucalyptus fibers can be present in the fibrous web in an amount less than about 90% by weight, such as in an amount less than about 70% by weight, such as in an amount less than about 50% by weight, such as in an amount less than about 30% by weight.

[0045] In addition to controlling strength, one or more enzymes can be used according to the present disclosure in order to reduce energy requirements by reducing the amount of mechanical refining that may be needed on the fibers. In addition, the use of enzymes can reduce or eliminate the amount of auxiliary chemicals used to produce the product. One or more enzymes can also be used to produce fibrous webs that are softer, more absorbent, and brighter. In one aspect, the enzymes can break down small molecular components that retain water which enhances drainage of the pulp fibers when fed through a papermaking machine. This can also increase production efficiency and reduce energy consumption during drying. Overall, fibrous webs made according to the present disclosure may lower the environmental footprint of the product due to reduced chemical and energy use.

[0046] The use of enzymes according to the present disclosure can offer additional benefits related to fiber processing and process controls, especially when a mixture of enzymes is used. For instance, different enzymes can be selected for different purposes. In one aspect, in addition to an enzyme that breaks down the cellulosic fibers, an enzyme can be used for deinking, especially when processing recycled fibers. An enzyme can also be used to modify binder characteristics, such as starch characteristics. The enzymes can also be used for stickiness control and deposit control.

[0047] Referring to FIG. 1, one embodiment of a process and system in accordance with the present disclosure is shown. As illustrated, the process includes a mixing tank 10 that is designed to combine cellulosic fibers with water in order to form an aqueous suspension of fibers. In one aspect, the mixing tank 10 can comprise a pulping device. As shown, the mixing tank 10 is an enclosed vessel that includes a vent 11. Each mixing tank 10, for instance, can include a lid 19. Each lid 19 can seal each corresponding mixing tank 10 for preventing liquid or vapor release.

[0048] In accordance with the present disclosure, one or more enzymes are added to the aqueous suspension of fibers contained within the mixing tank 10. For instance, the process can include an enzyme supply 12 for feeding controlled amounts of one or more enzymes into the mixing tank 10. Various different enzymes can be used in accordance with the present disclosure including any suitable cellulolytic enzymes. Examples of enzymes include, for instance, cellulases, hemicellulases, and mixtures thereof.65131087PC01

[0049] Cellulases are enzymes that hydrolyze cellulose into smaller fragments by breaking down glycosidic bonds in cellulose chains. Examples of cellulases include endoglucanases which cleave internal bonds within cellulose chains, reduce the molecular weight of cellulose, and create new chain ends. Endoglucanases can enhance fiber flexibility and bonding and thereby increase the strength properties of fibrous webs made from the treated cellulose. Another cellulase that may be used in accordance with the present disclosure are exoglucanases. Exoglucanases remove cellobiose units from the ends of cellulose chains. Another example of a cellulase that may be used in accordance with the present disclosure are B-glucosidases. B-glucosidases hydrolyze cellobiose into glycose.

[0050] Hemicellulases that can be used in accordance with the present disclosure include xylanases. Xylanases break down xylan and can improve brightness in the resulting fibrous web. Another hemicellulase that may be used in accordance with the present disclosure are mannanases, which degrade mannan especially in softwood fibers. Mannanases can enhance pulp drainage and refining efficiency. Another hemicellulase that may be used are arabinofuranosidases which hydrolyze arabinose side chains from hemicellulose. Acetyl xylan esterases are still another class of hemicellulases that can used in accordance with the present disclosure. Acetyl xylan esterases remove acetyl groups from xylans, aiding in their degradation.

[0051] Other enzymes that can be used in accordance with the present disclosure include pectinases. Pectinases can actually reduce interfiber bonding strength for increasing the softness of the resulting fibrous product.

[0052] As shown in FIG. 1, one or more enzymes are combined with an aqueous slurry of cellulosic fibers. In general, any suitable cellulosic fiber capable of forming a nonwoven web can be used in accordance with the present disclosure. Fibers suitable for making nonwoven webs comprise any natural or synthetic cellulosic fibers including, but not limited to nonwoody fibers, such as cotton, abaca, kenaf, sabai grass, flax, esparto grass, straw, jute hemp, bagasse, milkweed floss fibers, and pineapple leaf fibers; and woody or pulp fibers such as those obtained from deciduous and coniferous trees, including softwood fibers, such as northern and southern softwood kraft fibers; hardwood fibers, such as eucalyptus, maple, birch, and aspen. Pulp fibers can be prepared in high-yield or low-yield forms and can be pulped in any known method, including kraft, sulfite, high-yield pulping methods and other known pulping methods. Fibers prepared from organosolv pulping methods can also be used, including the fibers and methods disclosed in U.S. Pat. No. 4,793,898, issued Dec. 27, 1988 to Laamanen et al.; U.S. Pat. No. 4,594,130, issued Jun. 10, 1986 to Chang et al.; and U.S. Pat. No. 3,585,104. Useful fibers can also be produced by anthraquinone pulping, exemplified by U.S. Pat. No.

[0053] 5,595,628 issued Jan. 21, 1997, to Gordon et al.

[0054] In one embodiment, all or a portion of the fiber furnish may comprise synthetic fibers, such as65131087PC01

[0055] regenerated cellulose fibers. For instance, regenerated cellulose fibers, such as rayon fibers, lyocell fibers, or viscose fibers can be present in the fiber furnish in an amount from about 3% by weight to about 30% by weight.

[0056] Chemically treated natural cellulosic fibers can be used such as mercerized pulps, chemically stiffened or crosslinked fibers, or sulfonated fibers. While recycled fibers can be used, virgin fibers are generally useful for their mechanical properties and lack of contaminants. Mercerized fibers, cellulose produced by microbes, and other cellulosic material or cellulosic derivatives can be used. Suitable papermaking fibers can also include recycled fibers, virgin fibers, or mixes thereof. In certain embodiments capable of high bulk and good compressive properties, the fibers can have a Canadian Standard Freeness of at least 200, more specifically at least 300, more specifically still at least 400, and most specifically at least 500.

[0057] Other papermaking fibers that can be used in the present disclosure include paper broke or recycled fibers and high yield fibers. High yield pulp fibers are those papermaking fibers produced by pulping processes providing a yield of about 65% or greater, more specifically about 75% or greater, and still more specifically about 75% to about 95%. Yield is the resulting amount of processed fibers expressed as a percentage of the initial wood mass. Such pulping processes include bleached chemithermomechanical pulp (BCTMP), chemithermomechanical pulp (CTMP), pressure / pressure thermomechanical pulp (PTMP), thermomechanical pulp (TMP), thermomechanical chemical pulp (TMCP), high yield sulfite pulps, and high yield Kraft pulps, all of which leave the resulting fibers with high levels of lignin. High yield fibers are well known for their stiffness in both dry and wet states relative to typical chemically pulped fibers.

[0058] In one embodiment, the fiber furnish can contain crosslinked fibers, such as crosslinked pulp fibers.

[0059] In still another aspect, the pulp fibers can comprise non-wood pulp fibers. Non-wood pulp fibers include bast fibers. Examples of bast fibers include flax fibers, hemp fibers, jute fibers, kenaf fibers, ramie fibers, abaca fibers, sunn fibers, and mixtures thereof.

[0060] The amount of one or more enzymes combined with the cellulosic fibers can depend upon various factors including the type of enzyme being used and the type of cellulosic fibers contained in the aqueous slurry. In one aspect, one or more enzymes can be added to the fibrous slurry in an amount of greater than about 100 grams of enzyme per ton of fiber, such as greater than about 150 grams of enzyme per ton of fiber, such as greater than about 200 grams of enzyme per ton of fiber, such as greater than about 250 grams of enzyme per ton of fiber, such as greater than about 300 grams of enzyme per ton of fiber, such as greater than about 350 grams of enzyme per ton of fiber, and less than about 1 ,000 grams of enzyme per ton of fiber, such as less than about 800 grams of65131087PC01

[0061] enzyme per ton of fiber, such as less than about 500 grams of enzyme per ton of fiber, such as less than about 450 grams of enzyme per ton of fiber, such as less than about 400 grams of enzyme per ton of fiber.

[0062] The consistency of the fibrous slurry during mixing with the one or more enzymes can also vary. In general, the consistency of the fibrous slurry is from about 2% to about 30%. For instance, the consistency of the fibrous slurry can be greater than about 2.5%, such as greater than about 3%, such as greater than about 3.5%, such as greater than about 4%, and less than about 25%, such as less than about 20%, such as less than about 15%, such as less than about 10%, such as less than about 8%, such as less than about 6%.

[0063] During contact between the one or more enzymes and the cellulosic fibers, the aqueous slurry should have a pH that is compatible with the one or more enzymes. In one aspect, for instance, the pH of the aqueous slurry can be from about 5 to about 8.5. For instance, the pH of the aqueous slurry can be greater than about 5.5, such as greater than about 6, such as greater than about 6.5, and less than about 8, such as less than about 7.5. The temperature of the aqueous slurry should also be compatible with the one or more enzymes. In general, the temperature of the aqueous slurry can be from about 20°C to about 80°C. For instance, the temperature of the aqueous slurry can be greater than about 25°C, such as greater than about 30°C, and less than about 70°C, such as less than about 50°C, such as less than about 40°C.

[0064] The amount of time the one or more enzymes contact the cellulosic fibers prior to denaturing the enzymes can also vary depending upon process conditions and the different components that are present. In one aspect, at least one enzyme and cellulosic fibers are contacted for a period of time of at least about 15 minutes, such as at least about 30 minutes, such as at least about 45 minutes, such as at least about 1 hour. The contact time is generally less than about 5 hours, such as less than about 3 hours, such as less than about 2 hours, such as less than about 1 hour, such as less than about 45 minutes.

[0065] In one aspect, one or more enzymes can be combined with the aqueous slurry of fibers in the mixing tank 10 for a period of time and then denatured prior to being fed to a papermaking process 13 as shown in FIG. 1. For example, the mixing tank 10 can be in direct fluid communication with a headbox 34 that is configured to deposit the aqueous suspension of fibers onto a porous forming surface for forming a nonwoven web. Alternatively, as shown in FIG. 1 , various other tanks can optionally be placed in between the headbox 34 and the mixing tank 10. In addition, one or more mechanical refiners 15, 17 can be installed in the system for refining the cellulosic fibers after the fibers have been contacted with the enzyme.65131087PC01

[0066] For example, in the embodiment illustrated in FIG. 1, the process includes a first stock chest 14 in communication with a first mechanical refiner 15 and a second stock chest 16 in fluid communication with a second mechanical refiner 17. The first fiber refiner 15 and the second fiber refiner 17 are in fluid communication with a machine chest 18 that then delivers the aqueous suspension of fibers to the headbox 34. In one embodiment as shown in FIG. 1, for instance, the aqueous suspension of fibers in the mixing tank 10 can be combined with one or more enzymes and fed to the first stock chest 14 and the second stock chest 16. In one aspect, a portion of the aqueous suspension of fibers is fed to the first stock chest 14 while the remainder of the aqueous slurry of fibers is fed to the second stock chest 16. Alternatively, the entire aqueous suspension of fibers can be fed to the first stock chest 14 and then sequentially fed to the second stock chest 16.

[0067] The stock chests 14 and 16 act as an intermediate storage tank for the aqueous slurry of fibers after they have been contacted with the one or more enzymes and allows for additional residence time between the fiber and the enzyme. The stock chests 14 and 16, for instance, can be used to adjust fiber concentration in the aqueous slurry, allow for deaeration, and / or permit continued mixing the aqueous slurry of fibers. In the embodiment illustrated in FIG. 1, the stock chests 14 and 16 can also be used to adjust the flow rate of the aqueous suspension of fibers that are fed to the mechanical refiners 15 and 17.

[0068] The mechanical refiners 15 and 17 are for further refining the cellulosic fibers after they have been treated with the one or more enzymes. Refining the fibers, for instance, can cause fibrillation and create fibrils which cross and increase sheet strength when the nonwoven web is formed and / or increase softness.

[0069] In the embodiment illustrated in FIG. 1 , the cellulosic fibers are refined after contact with the one or more enzymes but prior to denaturing the enzymes. Alternatively, cellulosic fibers can be contacted with one or more enzymes and the enzymes can be denatured prior to feeding the cellulosic fibers to the mechanical refiners 15 and 17.

[0070] In one aspect, the enzyme-treated fibers are only lightly refined in the refiners 15 and 17 due to the action of the enzymes on the fibers. Thus, throughput through the refiners can be relatively high at reduced energy requirements.

[0071] From the refiners 15 and 17, the aqueous slurry of cellulosic fibers is fed to the machine chest 18. The machine chest holds and conditions the fibrous stock immediately before it is pumped to the papermaking process 13 and particularly to the headbox 34. Although optional, the machine chest 18 can fine-tune fiber stock consistency by adding or removing water from the tank. The machine chest 18 can also maintain constant flow to the headbox 34 even if there are upstream process interruptions.65131087PC01

[0072] Various different additives and auxiliaries can also be added to the machine chest 18. Such additives can include, for instance, dyes, retention aids, or other chemical treatments.

[0073] As shown in FIG. 1 , the stock chests 14 and 16 and the machine chest 18 all comprise enclosed vessels that include a vent 11. As shown, the ventilation system can all feed into the same vent tube for enzyme capture or controlled release.

[0074] Prior to being fed to the papermaking process 13, in accordance with the present disclosure, the one or more enzymes are denatured. The enzymes can be denatured using various different methods and techniques. In one aspect, for instance, the aqueous suspension of fibers can be heated to a temperature sufficient to denature the enzymes. Heating the aqueous suspension of fibers, however, may have relatively high energy demands.

[0075] Alternatively, the pH of the aqueous suspension of cellulosic fibers can be increased causing the one or more enzymes to denature. For example, the pH of the aqueous suspension of fibers can be increased to greater than about 8.5, such as greater than about 9, such as greater than about 9.5, such as greater than about 10, and less than about 13. Any suitable pH adjusting agent can be added to the aqueous suspension of fibers that does not interfere with web formation and does not negatively impact the fibers or the nonwoven web being formed. pH adjusting agents that can be used to increase the pH include any suitable base or alkaline compound. Examples of bases include hydroxides, such as sodium hydroxide or the like. In one aspect, the pH adjusting agent can be a hypochlorite, such as sodium hypochlorite.

[0076] The pH adjusting agent can be added at any time in the process after the one or more enzymes and the cellulosic fibers have been in contact with each other for a sufficient period of time depending upon the desired result. In the embodiment illustrated in FIG. 1, for instance, the process includes a pH adjusting agent supply 20 that increases the pH of the aqueous suspension of fibers after the machine chest 18 and in the piping or line leading to the headbox 34. It should be understood, however, that the pH adjusting supply 20 can be fed to the mixing tank 10, the stock chests 14 and / or 16, or to the machine chest 18. The pH adjusting agent can also be fed to the refiners 15 and 17 or can be fed to any of the lines connecting the different components.

[0077] In one aspect, after the one or more enzymes are denatured, the aqueous suspension of fibers can be fed directly to the papermaking process 13 and to the headbox 34. The increase in pH and / or the presence of the pH adjusting agent, however, may interfere, in some applications, with various chemicals, components, or auxiliaries that are being combined with the cellulosic fibers in forming the nonwoven web. Thus, in one embodiment, the pH of the aqueous suspension of fibers is decreased and / or the pH adjusting agent is neutralized prior to feeding the aqueous suspension of fibers to the papermaking process 13.65131087PC01

[0078] For instance, as shown in FIG. 1, the process and system can further include a pH adjusting agent neutralizer supply 22 which, in one embodiment, can feed a chlorine scavenger to the aqueous suspension of fibers. For example, in one embodiment, the chlorine scavenger can comprise a bisulfite, such as sodium bisulfite. The chlorine scavenger can also comprise any suitable acid. The acid can be sulfuric acid, hydrochloric acid, citric acid, or the like. The chlorine scavenger can be added to the aqueous suspension of fibers at a stoichiometric ratio or at a greater than stoichiometric ratio in relation to the pH adjusting agent such as the sodium hypochlorite. In one aspect, the chlorine scavenger can be added in an amount sufficient to remove all free chlorine from the aqueous suspension of fibers and / or lower the pH to less than about 85.

[0079] Components or chemical auxiliaries that may be impacted by the pH adjusting agent can include various strength enhancing agents or binders including cellulose derivatives such as carboxymethyl cellulose. pH adjusting agents can also affect debonders and wet strength agents. Consequently, in one aspect, debonders, dry strength agents, and wet strength agents can be added to the aqueous suspension of fibers or to the fibrous web as it is formed after the aqueous suspension of fibers has been treated with a chlorine scavenger. In one aspect, for instance, these components and auxiliaries can be added directly to the headbox 34.

[0080] For example, such auxiliary chemicals can include debonding agents, wet strength agents, and dry strength agents. Suitable debonding agents that may be used in the present disclosure include cationic debonding agents such as fatty dialkyl quaternary amine salts, mono fatty alkyl tertiary amine salts, primary amine salts, imidazoline quaternary salts, silicone quaternary salt and unsaturated fatty alkyl amine salts. Other suitable debonding agents are disclosed in U.S. Pat. No.

[0081] 5,529,665 to Kaun which is incorporated herein by reference. In particular, Kaun discloses the use of cationic silicone compositions as debonding agents.

[0082] In one embodiment, the debonding agent used in the process of the present disclosure is an organic quaternary ammonium chloride and, particularly, a silicone-based amine salt of a quaternary ammonium chloride. For example, the debonding agent can be PROSOFT® TQ1003, marketed by the Hercules Corporation. The debonding agent can be added to the fiber slurry in an amount of from about 1 kg per metric tonne to about 10 kg per metric tonne of fibers present within the slurry.

[0083] In an alternative embodiment, the debonding agent can be an imidazoline-based agent. The imidazoline-based debonding agent can be obtained, for instance, from the Witco Corporation. The imidazoline-based debonding agent can be added in an amount of between 2.0 to about 15 kg per metric tonne.

[0084] In one embodiment, the debonding agent can be added to the fiber furnish according to a process as disclosed in PCT Application having an International Publication No. WO 99 / 34057 filed on65131087PC01

[0085] Dec. 17, 1998 or in PCT Published Application having an International Publication No. WO 00 / 66835 filed on Apr. 28, 2000, which are both incorporated herein by reference. In the above publications, a process is disclosed in which a chemical additive, such as a debonding agent, is adsorbed onto cellulosic papermaking fibers at high levels. The process includes the steps of treating a fiber slurry with an excess of the chemical additive, allowing sufficient residence time for adsorption to occur, filtering the slurry to remove unadsorbed chemical additives, and redispersing the filtered pulp with fresh water prior to forming a web.

[0086] Wet strength agents that can be added to the cellulosic fibers include polyamideepichlorohydrin resins, urea-formaldehyde resins, melamine-formaldehyde resins, polyvinylamines, and mixtures thereof. Dry strength agents that can be incorporated into the nonwoven web include cationic starches, polyacrylamides, cellulose derivatives such as carboxymethyl cellulose, guar gum derivatives, and the like.

[0087] After the cellulosic fibers have been treated in accordance with the present disclosure, the fibers can be used to make all different types of products, including tissue webs. The papermaking process 13, as shown in FIG. 1, can utilize creping, wet creping, double creping, embossing, wet pressing, air pressing, through-air drying, creped through-air drying, uncreped through-air drying, hydroentangling, and the like.

[0088] For example, referring to FIG. 2, shown is a method for making throughdried tissue sheets. (For simplicity, the various tensioning rolls schematically used to define the several fabric runs are shown, but not numbered. It will be appreciated that variations from the apparatus and method illustrated in FIG. 2 can be made without departing from the general process). Shown is a twin wire former having a papermaking headbox 34, such as a layered headbox, which injects or deposits a stream 36 of an aqueous suspension of papermaking fibers onto the forming fabric 38 positioned on a forming roll 39. The forming fabric serves to support and carry the newly-formed wet web downstream in the process as the web is partially dewatered to a consistency of about 10 dry weight percent. Additional dewatering of the wet web can be carried out, such as by vacuum suction, while the wet web is supported by the forming fabric.

[0089] The wet web is then transferred from the forming fabric to a transfer fabric 40. In one embodiment, the transfer fabric can be traveling at a slower speed than the forming fabric in order to impart increased stretch into the web. This is commonly referred to as a “rush” transfer. Preferably the transfer fabric can have a void volume that is equal to or less than that of the forming fabric. The relative speed difference between the two fabrics can be from 0-60 percent, more specifically from about 15-45 percent. Transfer is preferably carried out with the assistance of a vacuum shoe 42 such65131087PC01

[0090] that the forming fabric and the transfer fabric simultaneously converge and diverge at the leading edge of the vacuum slot.

[0091] The web is then transferred from the transfer fabric to the throughdrying fabric 44 with the aid of a vacuum transfer roll 46 or a vacuum transfer shoe, optionally again using a fixed gap transfer as previously described. The throughdrying fabric can be traveling at about the same speed or a different speed relative to the transfer fabric. If desired, the throughdrying fabric can be run at a slower speed to further enhance stretch. Transfer can be carried out with vacuum assistance to ensure deformation of the sheet to conform to the throughdrying fabric, thus yielding desired bulk and appearance if desired Suitable throughdrying fabrics are described in U.S. Pat No. 5,429,686 issued to Kai F. Chiu et al. and U.S. Pat. No. 5,672,248 to Wendt, et al. which are incorporated by reference.

[0092] In one embodiment, the throughdrying fabric contains high and long impression knuckles. For example, the throughdrying fabric can have about from about 5 to about 300 impression knuckles per square inch which are raised at least about 0.005 inches above the plane of the fabric. During drying, the web can be macroscopically arranged to conform to the surface of the throughdrying fabric and form a three-dimensional surface. Flat surfaces, however, can also be used in the present disclosure.

[0093] The side of the web contacting the throughdrying fabric is typically referred to as the “fabric side” of the paper web. The fabric side of the paper web, as described above, may have a shape that conforms to the surface of the throughdrying fabric after the fabric is dried in the throughdryer. The opposite side of the paper web, on the other hand, is typically referred to as the “air side”. The air side of the web is typically smoother than the fabric side during normal throughdrying processes.

[0094] The level of vacuum used for the web transfers can be from about 3 to about 15 inches of mercury (75 to about 380 millimeters of mercury), preferably about 5 inches (125 millimeters) of mercury. The vacuum shoe (negative pressure) can be supplemented or replaced by the use of positive pressure from the opposite side of the web to blow the web onto the next fabric in addition to or as a replacement for sucking it onto the next fabric with vacuum. Also, a vacuum roll or rolls can be used to replace the vacuum shoe(s).

[0095] While supported by the throughdrying fabric, the web is finally dried to a consistency of about 94 percent or greater by the throughdryer 48 and thereafter transferred to a carrier fabric 50. The dried basesheet 52 is transported to the reel 54 using carrier fabric 50 and an optional carrier fabric 56.

[0096] An optional pressurized turning roll 58 can be used to facilitate transfer of the web from carrier fabric 50 to fabric 56. Suitable carrier fabrics for this purpose are Albany International 84M or 94M and Asten 959 or 937, all of which are relatively smooth fabrics having a fine pattern. Although not shown, reel calendering or subsequent off-line calendering can be used to improve the smoothness and softness of the basesheet.65131087PC01

[0097] In one embodiment, the paper web 52 is a textured web which has been dried in a three-dimensional state such that the hydrogen bonds joining fibers were substantially formed while the web was not in a flat, planar state. For instance, the web can be formed while the web is on a highly textured throughdrying fabric or other three-dimensional substrate. Processes for producing uncreped throughdried fabrics are, for instance, disclosed in U.S. Pat. No. 5,672,248 to Wendt, et al.; U.S. Pat. No. 5,656,132 to Farrington, et al.; U.S. Pat. No. 6,120,642 to Lindsay and Burazin; U.S. Pat. No. 6,096,169 to Hermans, et al.; U.S. Pat. No. 6,197,154 to Chen, et al.; and U.S. Pat. No. 6,143,135 to Hada, et al., all of which are herein incorporated by reference in their entireties.

[0098] Alternatively, a creping process can be used to produce the fibrous web. For example, referring to FIG. 3, one embodiment of a process for forming wet or dry creped tissue webs is shown. In this embodiment, a headbox 80 emits an aqueous suspension of fibers onto forming fabric 82 which is supported and driven by a plurality of guide rolls 84. A vacuum box 86 is disposed beneath forming fabric 82 and is adapted to remove water from the fiber furnish to assist in forming a web. From forming fabric 82, a formed web 88 is transferred to a second fabric 90, which may be either a wire or a felt. Fabric 90 is supported for movement around a continuous path by a plurality of guide rolls 92.

[0099] Also included is a pick up roll 94 designed to facilitate transfer of web 88 from fabric 82 to fabric 90.

[0100] From fabric 90, web 88, in this embodiment, is transferred to the surface of a rotatable heated dryer drum 96, such as a Yankee dryer with the assistance of a press roll 93. A bonding agent can be used to adhere the web 88 to the dryer drum 96. The bonding agent may be applied topically to the tissue web 88 while the web is traveling on the fabric 90 or may be applied to the surface of the dryer drum 96 for transfer onto one side of the tissue web 88. In this embodiment, as web 88 is carried through a portion of the rotational path of the dryer surface, heat is imparted to the web causing most of the moisture contained within the web to be evaporated. Web 88 is then removed from dryer drum 96 by a creping blade 98. Creping web 88 as it is formed further reduces internal bonding within the web and increases softness.

[0101] Fibrous webs, or tissue products made according to the present disclosure, can generally have a basis weight of from about 10 gsm to about 200 gsm. For instance, the basis weight can be greater than about 12 gsm, such as greater than about 15 gsm, such as greater than about 20 gsm, such as greater than about 25 gsm, such as greater than about 30 gsm, and less than about 130 gsm, such as less than about 120 gsm, such as less than about 100 gsm, such as less than about 80 gsm, such as less than about 60 gsm, such as less than about 50 gsm, such as less than about 40 gsm.

[0102] The tissue web bulk may also vary from about 3 cc / g to 20 cc / g, such as from about 5 cc / g to 15 cc / g. The sheet “bulk” is calculated as the quotient of the caliper of a dry tissue sheet, expressed in microns, divided by the dry basis weight, expressed in grams per square meter. The resulting sheet65131087PC01

[0103] bulk is expressed in cubic centimeters per gram. More specifically, the caliper is measured as the total thickness of a stack of ten representative sheets and dividing the total thickness of the stack by ten, where each sheet within the stack is placed with the same side up. Caliper is measured in accordance with TAPPI test method T411 om-89 “Thickness (caliper) of Paper, Paperboard, and Combined Board” with Note 3 for stacked sheets. The micrometer used for carrying out T411 om-89 is an Emveco 200-A Tissue Caliper Tester available from Emveco, Inc., Newberg, Oreg. The micrometer has a load of 2.00 kilo-Pascals (132 grams per square inch), a pressure foot area of 2500 square millimeters, a pressure foot diameter of 56.42 millimeters, a dwell time of 3 seconds and a lowering rate of 0.8 millimeters per second. In various embodiments, the bulk can be greater than about 6 cc / g, such as greater than about 8 cc / g.

[0104] Various different tissue products can be made in accordance with the present disclosure. The tissue products can comprise single ply products or multiple ply products. For instance, the products can comprise two plies, three plies, or four plies. Tissue products that can be made in accordance with the present disclosure include bath tissue, facial tissue, paper towels, industrial wipers, and the like.

[0105] These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.

Claims

65131087PC01What Is Claimed:

1. A method for the production of a fibrous cellulose web comprising:treating an aqueous slurry of cellulosic fibers with a cellulolytic enzyme to form enzyme-treated fibers;denaturing the cellulolytic enzyme while the enzyme remains in the aqueous slurry of cellulosic fibers; andafter denaturing the cellulolytic enzyme, spreading the cellulosic fibers on a forming surface to form a cellulosic web.2 A method as defined in claim 1 , wherein the aqueous slurry of cellulosic fibers are treated with the enzyme at a pH of from about 5 to about 8.5, such as from about 5.5 to about 7.5, and at a temperature of from about 25°C to about 70°C.

3. A method as defined in claim 1 , wherein the cellulosic fibers are treated with the enzyme for a period of time of greater than about 30 minutes, such as greater than about 45 minutes, and less than about 5 hours, such as less than about 3 hours.

4. A method as defined in claim 1 , wherein the enzyme is added to the slurry of cellulosic fibers in an amount of greater than about 100 grams of enzyme per ton of fibers, such as greater than about 200 grams of enzyme per ton of fibers, such as greater than about 250 grams of enzyme per ton of fibers, and less than about 500 grams of enzyme per ton of fibers, such as less than about 450 grams of enzyme per ton of fibers, such as less than about 400 grams of enzyme per ton of fibers.

5. A method as defined in claim 1 , wherein the slurry of cellulosic fibers is treated with the enzyme at a consistency of greater than about 2%, such as greater than about 3%, and less than about 20%, such as less than about 15%, such as less than about 10%.

6. A method as defined in claim 1 , further comprising the step of refining the cellulosic fibers prior to forming the cellulosic web.

7. A method as defined in claim 6, wherein the cellulosic fibers are refined after being treated with the enzyme but prior to denaturing the enzyme.8 A method as defined in claim 6, wherein the cellulosic fibers are refined after the enzyme has been denatured but prior to forming the cellulosic web.

9. A method as defined in claim 1 , wherein the enzyme is denatured by raising the pH of the aqueous slurry containing the enzyme-treated fibers to greater than about 8.5, such as greater than about 9, such as greater than about 9.5, such as greater than about 10, and less than about 13.

10. A method as defined in claim 9, wherein the pH of the aqueous slurry is increased by adding a hypochlorite.

11. A method as defined in claim 9, wherein the pH of the aqueous slurry is increased by65131087PC01adding sodium hypochlorite.

12. A method as defined in claim 10, wherein the hypochlorite is added to the aqueous slurry of fibers at a concentration of greater than about 2 ppm, such as greater than about 2.5 ppm, and less than about 5 ppm, such as less than about 4 ppm.

13. A method as defined in claim 9, wherein the cellulosic fibers are treated with the enzyme in a mixing tank, and wherein the enzyme is denatured in a pipe exiting the mixing tank.

14. A method as defined in claim 10, further comprising the step of removing or neutralizing the hypochlorite in the aqueous slurry after denaturing the enzyme.

15. A method as defined in claim 14, wherein the hypochlorite is removed or neutralized by adding a free chlorine scavenger to the aqueous slurry of fibers.

16. A method as defined in claim 15, wherein the chlorine scavenger comprises a bisulfite, such as sodium bisulfite.

17. A method as defined in claim 15, wherein the chlorine scavenger is added at a stoichiometric ratio or at a greater than stoichiometric ratio in relation to free chlorine contained in the slurry of cellulosic fibers.

18. A method as defined in claim 1, wherein the slurry of cellulosic fibers comprises hardwood fibers.

19. A method as defined in claim 1, wherein the slurry of cellulosic fibers comprises softwood fibers.

20. A method as defined in claim 1 , wherein the slurry of cellulosic fibers comprises a mixture of hardwood fibers and softwood fibers.

21. A method as defined in claim 1 , wherein the slurry of cellulosic fibers is treated with the cellulolytic enzyme while being held is one or more enclosed vessels until at least the cellulolytic enzyme is denatured.

22. A method as defined in claim 21, wherein the one or more enclosed vessels are vented for collecting vapors being released by the slurry of cellulosic fibers.

23. A method as defined in claim 1 , wherein the slurry of cellulosic fibers is treated with a mixture of enzymes.

24. A method as defined in claim 23, wherein an enzyme is included in the mixture that deinks the slurry of cellulosic fibers.

25. A method as defined in claim 1 , wherein the cellulosic web comprises a tissue web.

26. A method as defined in claim 1 , wherein the cellulosic web formed during the process after drying has a basis weight of from about 10 gsm to about 200 gsm, such as from about 12 gsm to about 130 gsm, and displays a bulk of greater than about 3 cc / g, such as greater than about 6 cc / g,65131087PC01such as greater than about 8 cc / g, and less than about 20 cc / g.

27. A method as defined in claim 15, wherein the cellulosic fibers are combined with a dry strength agent after the chlorine scavenger has been added to the aqueous slurry of fibers and prior to forming the cellulosic web.

28. A method as defined in claim 15, wherein the cellulosic fibers are combined with a wet strength agent after the chlorine scavenger has been added to the aqueous slurry of fibers and prior to forming the cellulosic web.

29. A method as defined in claim 15, wherein the cellulosic fibers are combined with a debonder or a cellulose derivative after the chlorine scavenger has been added to the aqueous slurry of fibers and prior to forming the cellulosic web.

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