Patent Application
20250223761
This disclosure relates to a method for repulping lignocellulosic fibers having at least one wet strength resin disposed thereon. More particularly, the disclosure relates to a method of repulping in which an enzymatic agent is present within an agitated aqueous slurry of the lignocellulosic fibers.
It is conventional during the manufacture of certain paper grades—in particular toweling, sanitary tissue, coffee filters and milk cartons—for wet strength resins to be added to the paper stock. Paper derives its strength from the hydrogen bonds between cellulosic fibers; without the addition of wet-strength resins, however, these interactions would easily be disrupted in the presence of water, causing the sheet to fall apart.
Paper fibers are ultimately a combination of cellulose, hemicellulose and lignin, with the ratio thereof being determined in part by the species of plant used and by the pulping process. The presence of these three components imparts an overall anionic charge to the fiber. As such, electrostatic attraction between the anionic fiber and a cationic polymer—as most wet strength resins are—can occur and this attraction associates the cationic polymer with the fiber. In the case of wet strength aids, once the cationic polymer is so-associated, it can then form covalent bonds with the fiber, creating a paper product that can be said to exhibit “permanent wet strength”. The covalent bonds are not easily disrupted by water.
Such wet strength resins—of which polyamide-epichlorohydrin resin, polyamine-epichlorohydrin resins, C6-diamine-epichlorohydrin resins, polyamine-epoxyalkyl organosulfonate resins, polyamide-epoxyalkyl organosulfonate resins, urea-formaldehyde resins and melamine-formaldehyde resins represent important examples—permit the paper products to retain from 10 to 50% of their dry strength when wet; in the absence of such resins, normally only from 3 to 5% of the dry strength would be retained after being wetted.
Problematically, the presence of wet strength resins in secondary fiber sources renders those sources difficult to re-pulp. Analogously, the re-pulping of paper “broke” is hindered by the presence of such wet-strength resins. Broke, which is not by convention considered secondary fiber, is continuously being produced in a paper mill and it is the function of the so-called “broke system” to collect this resource, process it and make it available for reuse. Given that broke can amount to well over 5 wt. % of a paper machine's total production, the broke system is thereby an essential part of the papermaking process, from both a financial and an operational perspective.
The re-pulping or disintegration of wet-strength containing fibers may be effected by the combined application of mechanical and thermal techniques over a significant duration of time. A supplementary “deflaker” unit may further be required to complement the main re-pulping unit to further separate any remaining flocs or bundles into individual fibers. Such methods tend to be slow and energy intensive and can thereby create a production bottle neck in repulping wet strength containing fiber.
Certain authors have sought to replace or to compliment thermomechanical repulping through the application of chemical treatments to the wet strength containing fiber. For example, U.S. Pat. No. 3,427,217 (Miller) describes the use of oxidizing salts—such as sodium hypochlorite and ammonium persulfate—to repulp broke containing wet-strength resins. Noting that hypochlorite salts can form environmentally undesirable organochloride-containing degradation products in effluents from this process, EP 0585955 A1 (Hercules Inc.) describes an alternative composition for repulping a cellulose fiber paper broke in an aqueous slurry: the disclosed composition comprises a non-chlorinating oxidizing agent and an alkali and is exemplified in that the alkali is a water-soluble buffering salt that is capable of maintaining the pH between 7 and 12 in the aqueous reaction mixture of the wet-strength broke and the oxidizing agent. It is postulated that ester linkages between the fiber and the wet-strength polymer can be hydrolyzed—albeit slowly—in an alkaline environment.
WO 2007/035507 A1 (Du Pont) discloses a repulping process for broke comprising a wet-strength resin and cellulosic fiber, said process comprising contacting an aqueous slurry of said broke with a mixture of: i) potassium monopersulfate as an oxidizing agent; and, ii) at least one of an active halogen agent, cyanuric acid, or a mixture thereof is disclosed.
Having regard to such chemical treatments, it is considered that the indiscriminate oxidizing of the wet strength containing fiber can reduce the quality of the fiber obtained and thereby negatively impact the properties of the paper produced therefrom. Further, the use of large amounts of inorganic oxidants can create safety issues and provide regulatory challenges for the safe disposal of effluents containing the oxidants. Moreover, inorganic oxidants can corrode piping, tanks and the paper machine itself, thereby diminishing machine runnability.
Accordingly, it is desirable to provide a method for repulping wet strength containing fibers which does not rely upon thermomechanical techniques or indiscriminate oxidizing agents. Furthermore, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with this background.
In accordance with a first aspect of the disclosure there is provided a method for repulping lignocellulosic fibers having at least one wet strength resin disposed thereon, the method comprising:
The prepared aqueous slurry may be exemplified by a consistency of from 1 to 20%, with from 1 to 10% being preferred herein. In an important embodiment of this method, the lignocellulosic fibers comprise or consist of secondary fibers. In another embodiment of this method, which is not mutually exclusive of the previous embodiment, the lignocellulosic fibers are provided from paper broke. Independently of, or additional to these embodiments, the lignocellulosic fibers may comprise lignocellulose fibers that are covalently bonded to the wet strength resin.
In certain embodiments, the step of preparing comprises: adding the lignocellulosic fiber to an aqueous liquid under agitation; and, dispersing the enzymatic agent into the agitated aqueous liquid to form the aqueous slurry. The aqueous slurry may further comprise a water-soluble buffering salt. Independently of, or additional to the presence of said salt, the aqueous slurry may be exemplified by a pH of from 6 to 8.
The method of the present disclosure may be further exemplified in that: the aqueous slurry is substantially free of oxidizing agents; and/or, the aqueous slurry is substantially free of hypochlorite salts.
In certain embodiments of the method, the aqueous slurry is maintained at a temperature of from 25 to 75° C., for example from 40 to 70° C. in agitation step b). Independently of, or additional to the preferred temperature condition, it is preferred that the agitation of step b) is performed for a duration of from 5 to 75 minutes, for example from 15 to 60 minutes.
In using a combination enzyme treatment of cellulase and hemicellulase in the recited method, the wet strength fiber is degraded in a targeted way; the hydrolysis of different chemical species within the fiber itself serves to weaken the points of covalent attachment to the polymer(s) present, thereby allowing mechanical shear forces to better disintegrate the wet strength fibers into individual fibers.
It is proposed that the mechanical agitation distorts the cellulose and hemicellulose chains at or near the fiber surface, creating kinks and nodes in the fiber wall. These wall structures become more accessible in a water-swollen state, providing a point of attachment for hemicellulases and cellulases.
It is also observed that cellulase, when applied properly, can improve the tensile strength of the paper. The enzymatic action of the cellulase in concert with mechanical shear forces may act to re-fibrillate the fiber: the derived fibrils can contribute to hydrogen bonding between fibers and impart strength to paper derived therefrom.
In accordance with a second aspect of the present disclosure, there is provided an aqueous dispersion for use in repulping lignocellulosic fibers having at least one wet strength resin disposed thereon, the dispersion comprising:
The ratio by weight of hemicellulase to cellulase in the enzymatic agent may, for example, be from 10:1 to 1:10, in particular from 5:1 to 1:5 or from 2:1 to 1:2.
In preferred embodiments, the at least one hemicellulase is chosen from: xylanase; arabinofuranosidase; acetyl xylan esterase; α-d-glucuronidase; α-d-galactosidase; mannanase; endo-polygalacturonase; endoarabinase; exoarabinase; exo-β-1,3-galactanase; xyloglucan-specific exo-beta-1,4-glucanase ferulic acid esterase; galactomannanase; and, combinations thereof. It is particularly preferred that the at least one hemicellulase is chosen from: xylanase; acetyl xylan esterase; ferulic acid esterase; and, combinations thereof. And good results have been obtained where the at least one hemicellulase comprises or consists of at least one xylanase.
As the lignocellulosic fiber itself contains both cellulose and xylan, it is postulated that the wet strength polymer bonds to both species; the presence of at least one xylanase in combination with cellulase may thereby serve to target more than one anchor point between fiber and said polymer. Of the xylanase enzymes, a preference for one or more of endoxylanases, exoxylanases and β-xylosidases may be mentioned. A particular preference for the use of at least one endoxylanase is noted.
In preferred embodiments, the at least one cellulase is chosen from: cellobiohydrolase (CBH); endoglucanase (EG); beta-glucosidase (BG); and, combinations thereof. It is particularly preferred that the at least one cellulase comprises or consists of at least one endoglucanase.
In toto the sum of the i) at least one hemicellulase and ii) at least one cellulase should constitute from 30 to 100 wt. % of the enzymatic agent. For example, the enzymatic agent may comprise, based on the weight of the agent, from 40 to 100 wt. % or from 50 to 100 wt. % of the total of the i) at least one hemicellulase and ii) at least one cellulase. Each of these ranges encompasses an enzymatic agent which consists only of the hemicellulase(s) and cellulase(s) but, of course, the inclusion of further enzymes within the enzymatic agent is not precluded. As illustrative further enzymes, mention may be made of: lipases; pectinases; ligninolytic enzymes; proteolytic enzymes; esterases; and, amylases. Preferred further enzymes may be chosen from: proteolytic enzymes; esterases; amylases; and, combinations thereof.
In an important embodiment, the enzymatic agent comprises, based on the weight of the enzymatic agent:
In certain embodiments, the enzymatic agent comprises up to 30 wt. %, for example from 5 to 30 wt. % of at least one proteolytic enzyme, based on the weight of the enzymatic agent. In particular, the enzymatic agent may further comprise at least one protease chosen from: pronase; trypsin; chymotrypsin; bromelain; pepsin; collagenase; papain; and, combinations thereof.
In a further interesting embodiment, the enzymatic agent comprises up to 30 wt. %, for example from 5 to 30 wt. %, based on the weight of the enzymatic agent, of at least one esterase which does not have hemicellulase or cellulase activity.
In yet another interesting embodiment, the enzymatic agent comprises up to 30 wt. %, for example from 5 to 30 wt. %, based on the weight of the enzymatic agent, of at least one amylase chosen from α-amylase, β-amylase, γ-amylase and combinations thereof. For example, the enzymatic agent may further comprise at least one of α-amylase and β-amylase. Where an amylase is to be included in the enzymatic agent, it is particularly preferred for said amylase to comprise or consist of α-amylase.
The present disclosure also provides an enzymatic agent comprising: i) at least one hemicellulase; and, ii) at least one cellulase, wherein the ratio by weight of hemicellulase to cellulase in the enzymatic agent is from 10:1 to 1:10. In certain embodiments of the enzymatic agent, the ratio by weight of hemicellulase to cellulase in the enzymatic agent is from 5:1 to 1:5 or from 2:1 to 1:2. Moreover, the enzymatic agent may further comprise: at least one protease; at least one esterase which does not have hemicellulase or cellulase activity; and/or, at least one amylase chosen from α-amylase, β-amylase, γ-amylase and combinations thereof.
In an important embodiment of the aspects mentioned above: i) the at least one hemicellulase comprises or consists of at least one endoxylanase; and, ii) the at least one cellulase comprises or consists of at least one endoglucanase.
Where the aspects of the disclosure are described above as having certain embodiments, any one or more of those embodiments can be implemented in or combined with any one of the further embodiments, even if that combination is not explicitly described. Expressed differently, the described embodiments are not mutually exclusive, and permutations thereof remain within the scope of this disclosure.
The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
As used herein, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.
The terms “comprising”, “comprises” and “comprised of” as used herein are synonymous with “including”, “includes”, “containing” or “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. If used, the phrase “consisting of” is closed and excludes all additional elements. Further, the phrase “consisting essentially of” excludes additional material elements but allows the inclusion of non-material elements that do not substantially change the nature of the disclosure.
When amounts, concentrations, dimensions and other parameters are expressed in the form of a range, a preferable range, an upper limit value, a lower limit value or preferable upper and limit values, it should be understood that any ranges obtainable by combining any upper limit or preferable value with any lower limit or preferable value are also specifically disclosed, irrespective of whether the obtained ranges are clearly mentioned in the context.
Further, in accordance with standard understanding, a weight range represented as being “from 0 to x” specifically includes 0 wt. %: the ingredient defined by said range may be absent from the material or may be present in the material in an amount up to x wt. %.
The words “preferred”, “preferably”, “desirably” and “particularly” are used herein to refer to embodiments of the disclosure that may afford particular benefits, under certain circumstances. However, the recitation of one or more preferable, preferred, desirable or particular embodiments does not imply that other embodiments are not useful and is not intended to exclude those other embodiments from the scope of the disclosure.
The words “exemplary” and “illustrative” are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” or “illustrative” is not to be construed as preferred or advantageous over other aspects or designs. Rather, use of the words exemplary and illustrative is intended to present concepts in a concrete fashion.
As used throughout this application, the word “may” is used in a permissive sense—that is meaning to have the potential to—rather than in the mandatory sense.
All percentages, ratios and proportions used herein are given on a weight basis unless otherwise specified.
As used herein, room temperature is 23° C. plus or minus 2° C.
As used herein the term “lignocellulosic fiber” references a fibrous structure comprising lignin, cellulose and hemicellulose. The fiber may, in addition, comprise starch and further non-starch polysaccharides.
As used herein, the term “enzyme” refers to a protein that catalyzes a chemical reaction. The catalytic function of an enzyme constitutes its “enzymatic activity” or “activity”. As used herein, the term “substrate” refers to a substance on which an enzyme performs its catalytic activity to generate a product.
Where an EC Number is provided herein, this reflects the Enzyme Commission numerical classification scheme for enzymes, which is based on the chemical reactions the enzymes catalyze and is in accord with the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (NC-IUBMB).
There are no limitations on the origin of the enzymes having utility in the present disclosure. Thus, for illustration, the term “cellulase” includes not only natural or wild-type cellulase, but also any mutants, variants and fragments thereof which exhibit cellulase activity, as well as synthetic cellulases such as shuffled cellulases and consensus cellulases. Such genetically engineered enzymes can be prepared by methods generally known in the art of which particular mentioned by be made of: Site-directed Mutagenesis; Polymerase Chain Reaction (PCR) using a PCR fragment containing the desired mutation as one of the primers in the PCR reactions; or, by Random Mutagenesis. The preparation of consensus proteins is described in inter alia EP 897985 B1 (DSM IP Assets BV).
The designation of an enzyme herein—such as cellulase—also encompasses operable analogues of that enzyme which possess the defined enzymatic activity. Such analogues include those formed by amino acid substitutions, alterations, modifications or other amino acid changes that either increase, decrease or do not alter the function of the enzyme protein sequence.
The designation of an enzyme herein also encompasses post-translational or post-synthetic modified forms of that enzyme which still possess the defined enzymatic activity. Modifications include but are not limited to: the incorporation of a non-naturally occurring amino acid into the molecule; phosphorylation; glycosylation; the addition of pendant groups to the molecules through, for instance, biotinylation; and, the addition of fluorophores, lumiphores, radioactive groups and antigens to the molecule.
The designation of an enzyme herein further encompasses zymogen forms. The term “zymogen” references an inactive precursor of an enzyme which requires a biochemical change—including by not limited to maturation cleavage and/or complex formation with other protein(s) and/or cofactor(s)—for it to become an active enzyme.
Each constituent enzyme of the enzymatic agent may, independently of one another, be in either a dissolved or immobilized form. As is known in the art, immobilization produces an enzyme that is physically or chemically confined or localized onto or within certain supports: the catalytic activity of the enzyme is retained, at least in part, after immobilization. Using immobilized enzymes may stabilize said enzymes, may enable the separation and re-use of the enzyme and enable the process of the disclosure to be operated continuously. Concomitantly, the disadvantages of using immobilized enzymes include: enzyme activity loss during immobilization; and, the actual, energetic and temporal costs of enzyme immobilization.
Enzyme immobilization techniques may be physical or chemical and include inter alia adsorption, encapsulation, entrapment, covalent binding and crosslinking. Instructive references in this context include: U.S. Pat. No. 5,998,183 (Le Fevre et al.); and, CA 2,421,829 A (Saville et al.).
As used herein, the terms “mediating compound” or “mediator” may be used interchangeably to refer to a chemical compound that functions as a redox mediator to shuttle electrons between an enzyme exhibiting oxidizing activity and a secondary substrate or electron donor. Such chemical mediating compounds may be referenced in the art as “enhancers” and “accelerators”.
As used herein, the term “secondary fiber” references lignocellulosic fibers which are not from a virgin fiber source: secondary fiber has previously been produced in a manufacturing process and has been reclaimed as raw material for another process. The term “virgin fiber” in turn references paper fibers which are used for the first time after harvesting of a source crop and which are processed to make a paper product. Included amongst secondary fibers are fibers used for a second, third or even further time in the production of a paper end-product. Sources of secondary fiber may be pre- and/or post-consumer and include, but are not limited to: tissue; fine paper; office paper; boxboard; linerboard; footboard; newsprint; publication scrap; book stock; sorted and manifold ledger; and, bag scrap. Each of these sources generally contains unique impurities, such as inks, dyes, pigments, fillers, wet-strength resins and coatings.
The term “wet strength lignocellulosic fiber” is used herein as a contraction of “lignocellulosic fibers having at least one wet strength resin disposed thereon”. It is thus noted that the present disclosure has particular applicability to “wet-strength secondary fiber”, which denotes secondary fiber which is associated with one or more wet-strength resin.
The terms “disposed on” and “disposed thereon” with respect to the lignocellulosic fibers encompasses the dispersion of the wet strength resin on the surface of the fibers as well as the absorption of the wet strength resins onto the fibrous substrate. Further, the terms encompass the bonding of the wet-strength resin to the fibers through: resin-fiber covalent bonds; hydrogen bonds; or, ionic bonds. The wet-strength resin may be interposed between fibers and, in certain circumstances, may be bonded to more than one fiber.
The term “broke” herein refers to partly or fully manufactured paper or paperboard that is discarded from paper or paperboard making, converting and/or finishing processes. The term also refers to the stock made by repulping these materials. The broke therefore represents a source of lignocellulosic fibers. The term “wet strength broke” is a contraction of “broke containing at least one wet strength resin”.
The term “slurry” as used herein means a suspension or mixture of insoluble particles in a liquid medium or vehicle.
The term “consistency” is defined as the percentage by weight of oven dry fiber to total weight of an aqueous slurry sample. Where applicable consistency is measured in accordance with TAPPI T240 Consistency (concentration) of Pulp Suspensions.
As used herein, the term “dispersion” refers to a composition that contains discrete particles that are distributed throughout a continuous liquid medium.
The term “emulsion” as used herein refers to a stable mixture of two or more immiscible liquids held in liquid suspension: the mixture may be stabilized by the presence of emulsifiers or surfactants. More particularly, the term “aqueous emulsion” a mixture of water or an aqueous solution with an immiscible liquid—such as a liquid wax, oil or resin—held in liquid suspension. When the dispersed liquid is said wax, oil or resin and is in the discontinuous phase and the dispersion medium is in the continuous phase, this is referred to herein as an oil-in-water emulsion. Conversely, when either water or an aqueous solution is the dispersed phase and oil, wax or is the continuous phase, it is known as a water-in-oil emulsion.
The term “defoaming agent” is used herein to encompass materials which have one or more of an antifoaming efficacy, a defoaming efficacy or a de-aeration efficacy. Antifoaming references the inhibition or prevention of foam formation. Defoaming references the decrement or removal of foams which have already been formed. De-aeration refers to the escape of entrapped air.
Water, for use as a (co-)solvent or diluent herein, is intended to mean water of low solids content as would be understood by a person of ordinary skill in the art. The water may, for instance, be distilled water, demineralized water, deionized water, reverse osmosis water, boiler condensate water, or ultra-filtration water. Tap water may be tolerated in certain circumstances.
As used herein “solvents” are substances capable of dissolving another substance to form a uniform solution; during dissolution neither the solvent nor the dissolved substance undergoes a chemical change. Solvents may either be polar or non-polar. The term “alcoholic solvent” encompasses such solvents which are any water-soluble mono-alcohols, diols or polyols that are liquids at 25° C. at atmospheric pressure.
The present materials and compositions may be defined herein as being “substantially free” of certain compounds, elements, ions or other like components. The term “substantially free” is intended to mean that the compound, element, ion or other like component is not deliberately added to the material or composition and is present, at most, in only trace amounts which will have no (adverse) effect on the desired properties of the material or composition. Exemplary trace amounts are less than 1000 ppm, less than 500 ppm or even less than 100 ppm by weight of the material or composition. The term “substantially free” encompasses those embodiments where the specified compound, element, ion, or other like component is completely absent from the material or composition or is not present in any amount measurable by techniques generally used in the art.
The term “anhydrous” as used herein has equivalence to the term “substantially free of water”. Water is not deliberately added to a given composition and is present, at most, in only trace amounts which will have no (adverse) effect on the desired properties of the composition.
The present disclosure is directed to a method for repulping lignocellulosic fibers which are associated with at least one wet strength resin, in which method an enzymatic agent is present in an agitated aqueous slurry of that fiber. The disclosure further provides an aqueous dispersion of the enzymatic agent which is suitable for addition to such an aqueous slurry and also the enzymatic agent per se.
The enzymatic agent comprises:
The ratio by weight of hemicellulase to cellulase in the enzymatic agent may, for example, be from 10:1 to 1:10, in particular from 5:1 to 1:5 or from 2:1 to 1:2.
In toto the sum of the i) at least one hemicellulase and ii) at least one cellulase should constitute from 30 to 100 wt. % of the enzymatic agent. For example, the enzymatic agent may comprise, based on the weight of the agent, from 40 to 100 wt. % or from 50 to 100 wt. % of the total of the sum of i) at least one hemicellulase and ii) at least one cellulase. Each of these ranges encompasses an enzymatic agent which consists only of hemicellulase(s) and cellulase(s) but, of course, the inclusion of further enzymes within the enzymatic agent is not precluded. And as exemplary further enzymes mention may be made of: lipases; pectinases; ligninolytic enzymes; proteolytic enzymes; esterases; and, amylases. More particularly the further included enzymes may be chosen from: proteolytic enzymes; esterases; amylases; and, combinations thereof.
In an important embodiment, the enzymatic agent comprises, based on the weight of the enzymatic agent:
The enzymatic agent of the present disclosure comprises: i) at least one hemicellulase. Hemicellulases act to degrade hemicelluloses, such as xylans, xyloglucans, arabinoxylans, and glucomannans within the fiber.
The hemicellulose substrate is a complex carbohydrate structure consisting of different easy hydrolysable polymers based on: pentoses, such as xylose and arabinose; hexoses, such as mannose, glucose, and galactose; and, sugar acids. Hemicellulases commonly share similar activities with cellulases by virtue of the common β-1,4-glycosidic bonds in the backbone of hemicellulose substrates. As such, an important catalytic module found in certain hemicellulases is the glycoside hydrolase (GH) module that hydrolyze glycosidic bonds. A further main catalytic module found in certain hemicellulases is carbohydrate esterase, which hydrolyzes ester linkages of acetate or ferulic acid side groups.
Many hemicellulases are modular proteins which, in addition to their catalytic domains, include other functional modules. The most important modules are carbohydrate-binding modules, which facilitate the targeting of the enzymes to the insoluble polysaccharides and dockerin module that mediate the binding of the catalytic domains via cohesin-dockerin interactions, either to a microbial cell surface or to large enzymatic complexes, such as the cellulosome.
In an important embodiment of the present disclosure, the enzymatic agent comprises at least one hemicellulase chosen from: xylanase; α-L-arabinofuranosidase; acetyl xylan esterase; glucuronidase; endogalactanase; mannanase; pectinase; endoarabinase; exoarabinase; exo-galactanase; ferulic acid esterase; galactomannanase; xylogluconase; and, combinations thereof. More particularly, it is preferred that the at least one hemicellulase is chosen from: xylanase; acetyl xylan esterase; ferulic acid esterase; and, combinations thereof.
The term “acetyl xylan esterase” refers herein to enzymes classified under EC 3.1.1.72 which catalyze the deacetylation of xylans and xylo-oligosaccharides. The term “ferulic acid esterase” (FeA esterase, feruloyl esterase) refers herein to enzymes classified under EC 3.1.1.73: these enzymes are carbohydrate esterases which hydrolyze the ester linkage of FeA to 5-hydroxyl group of 1-arabinofuranosyl residues of the xylan backbone.
The term “α-L-arabinofuranosidase” refers herein to enzymes classified under EC 3.2.1.55 and which are accessory enzymes that cleave α-L-arabinofuranosidic linkages. The term “α-d-glucuronidase” refers herein to enzymes classified under EC 3.2.1.139 that catalyze the hydrolysis of α-D-glucuronoside to D-glucuronate. The term “α-d-galactosidase” refers herein to enzymes classified under EC 3.2.1.22 which catalyze the hydrolysis of terminal, non-reducing α-D-galactose residues in α-D-galactosides, including galactose oligosaccharides, galactomannans and galactolipids.
The term “mannanase” (β-Mannosidase) refers herein to enzymes classified under EC 3.2.1.25 and which catalyze the hydrolysis of terminal, non-reducing β-D-mannose residues in β-D-mannosides. The term “galactomannase” as used herein refers to the enzyme identified by CAS No. 50812-17-4. The term “exo-D-1,3-galactanase” refers herein to enzymes which act to hydrolyse the β-1,3-galactosyl linkage. The term “xyloglucan-specific exo-beta-1,4-glucanase” refers herein to enzymes classified under EC 3.2.1.155 which catalyze the hydrolysis of (D-1,4)-D-glucosidic linkages in xyloglucans so as to successively remove oligosaccharides from the chain end.
The term “endo-polygalacturonase” refers herein to enzymes classified under 3.2.1.15 which catalyse the random hydrolysis of (1,4)-α-D-galactosiduronic linkages in pectate and other galacturonans. The term “endoarabinase” (endo-1,5-α-1-arabinanase) refers herein to enzymes classified under 3.2.1.99 which catalyse the endo-hydrolysis of (1,5)-α-arabinofuranose linkages which are present within side chains of pectin. “Exoarabinase” (exo-1,5-α-1-arabinanase) catalyses the exo-hydrolysis of (1,5)-α-arabinofuranose linkages.
The term “xylanase” herein refers to a family of multicomponent enzymes that comprise a glycoside hydrolase (GH) module that hydrolyzes the glycosidic bonds (β-1,4) of xylans, such as arabinoxylans and glucuronoxylans, into xylose. Good results have been obtained where the at least one hemicellulase comprises or consists of at least one xylanase. The or each xylanase may desirably be chosen from: endo-1,4-D-xylanases (EC3.2.1.8); exoxylanases (EC 3.2.1.37); and, β-xylosidases (EC 3.2.1.37).
The enzymatic agent of the present disclosure comprises: ii) at least one cellulase. It will be typical for the ratio by weight of hemicellulase (part i)) to cellulase (part ii)) in the enzymatic agent to be from 10:1 to 1:10. For example, the ratio by weight of hemicellulase (part i)) to cellulase (part ii)) in the enzymatic agent may be from 5:1 to 1:5 or from 2:1 to 1:2. Each of these stated ranges encompass a ratio by weight of 1:1, which ratio may have utility in certain circumstances.
Most cellulases comprise modular multidomain proteins containing at least three separate structural elements of different functions, specifically a catalytic domain (CD), a cellulose binding domain (CBD), and an interdomain linker. In the present process, good results have been obtained where part ii) of the enzymatic agent comprises at least one cellulase chosen from: cellobiohydrolase (CBH); endoglucanase (EG); beta-glucosidase (BG); and, combinations thereof. In an exemplary embodiment, part ii) of the enzymatic agent comprises or consists of at least one endoglucanase.
Cellobiohydrolase (CBH) as used herein refers to exocellulase enzymes classified under EC 3.2.1.91 that hydrolyze the 1,4-β-D-glucosidic linkages from the reducing or non-reducing ends of a polymer containing said linkages, such as cellulose, whereby cellobiose is released. The enzymes are also called 1,4-D-D-glucan cellobiohydrolases or cellulose 1,4-D-cellobiosidases. Two different cellobiohydrolases have been isolated from Trichoderma reesei (CBHI; CBHII) which possess a modular structure consisting of a catalytic domain linked to a cellulose-binding domain (CBD): CBHI cleaves progressively from the reducing end of cellulose while CBHII cleaves progressively from the non-reducing end of cellulose. It is noted that some naturally occurring cellobiohydrolases lack a cellulose-binding domain.
Endoglucanase (EG) refers herein to enzymes classified under EC 3.2.1.4. The enzymes are 1,4-D-D-glucan 4-glucanohydrolases and catalyze the endohydrolysis of 1,4-D-D-glycosidic linkages in polymers of glucose, included but not limited to cellulose. Some naturally occurring endoglucanases have a cellulose binding domain, while others do not.
D-glucosidase (BG) refers herein to enzymes classified under EC 3.2.1.21 which catalyze the hydrolysis of the β-1,4 linkage between two glucose molecules in a cellulose polymer and further the hydrolysis of cellobiose into two molecules of glucose (Glc).
iii) Proteolytic Enzymes
The enzymatic agent may comprise, based on the weight of the enzymatic agent, from 0 to 30 wt. % of iii) at least one proteolytic enzyme. For instance, the enzymatic agent may comprise up to 25 wt. % or up to 20 wt. % of iii) said at least one proteolytic enzyme, based on the weight of the enzymatic agent.
The term “proteolytic enzyme” refers to any enzyme that possesses proteolytic activity and can thereby catalyze the hydrolysis of a protein, preferably the hydrolysis of a peptide bond. The proteolytic enzymes having utility in the present disclosure are those enzymes classified under EC 3.4.
In a particular embodiment, the enzymatic agent comprises at least one protease, said protease being an enzyme that has protease activity and hydrolyzes peptide bonds. The enzymatic agent may, for example, comprise at least one protease chosen from aspartic proteases, serine proteases, cysteine proteases, metalloproteases and combinations thereof. In certain embodiments the enzymatic agent may comprise at least one protease chosen from: pronase (3.4.24.4); trypsin (EC 3.4.21.4); chymotrypsin (EC 3.4.21.1); pepsin A (3.4.23.1); collagenase (3.4.24.3); bromelain (EC 3.4.22); papain (EC 3.4.22.2); and, combinations thereof.
The enzymatic agent may comprise, based on the weight of the enzymatic agent, from 0 to 30 wt. % of iv) at least one esterase which does not have hemicellulase or cellulase activity. For instance, the enzymatic agent may comprise up to 25 wt. % or up to 20 wt. % of iii) said at least one esterase, based on the weight of the enzymatic agent.
The term “esterase” refers herein to the subgroup of α,β-hydrolase-fold enzymes which are classified under EC 3.1.1.1 and which catalyze the hydrolysis of an ester bond to form a carboxylic acid and an alcohol.
The enzymatic agent may comprise, based on the weight of the enzymatic agent, from 0 to 30 wt. % of v) at least one amylase chosen from α-amylase, β-amylase, γ-amylase and combinations thereof. For instance, the enzymatic agent may comprise up to 25 wt. % or up to 20 wt. % of v) said at least one amylase, based on the weight of the enzymatic agent.
The term “amylase” as used herein refers to an enzyme that catalyzes the hydrolysis of starch into sugars. The “α-amylase” refers herein to enzymes classified under EC 3.2.1.1, which enzymes are calcium metalloenzymes. A-amylase acts at random points along the starch chain, breaking down long-chain saccharides to ultimately yield either: maltotriose and maltose from amylose; or, maltose, glucose and (alpha) limit dextrin (short chained branched remnant) from amylopectin.
The term “β-amylase” refers to enzymes classified under EC 3.2.1.2 and which are part of the glycoside hydrolase (GH) family 14. These enzymes work from the non-reducing end of the amylose and amylopectin, and catalyze the hydrolysis of the second α-1,4 glycosidic bond, cleaving off two glucose units (maltose) at a time.
The term “γ-Amylase” refers to enzymes classified under EC 3.2.1.3. These enzymes will cleave α(1-6) glycosidic linkages, as well as the last α-1,4 glycosidic bond at the non-reducing end of amylose and amylopectin, yielding glucose.
In an embodiment, the enzymatic agent comprises at least one amylase chosen from α-amylase, β-amylase and combinations thereof. These stated amylase enzymes have activities for which the optimum pH is more proximate to the desired pH range of the methods of the present disclosure. For this reason, when amylase is included in the enzymatic agent, it is most preferred that said amylase comprises or consists of α-amylase.
The present method may be performed in the presence of adjunct ingredients. These are ingredients which are deliberately added either to the aqueous dispersion of the enzymatic agent or to the aqueous slurry. A distinction is thereby made between such adjuncts and those compounds—including inks and other contaminants—which are present in the aqueous slurry by virtue of the dispersion of wet-strength lignocellulosic fiber therein.
For surety, the present disclosure encompasses both of: an aqueous dispersion for use in repulping lignocellulosic fibers containing at least one wet strength resin, which aqueous dispersion comprises water and enzymatic agent as described hereinabove and which further comprises the adjuncts; and, a process of preparing an aqueous slurry of the wet strength lignocellulosic fibers, wherein the aqueous slurry comprises the enzymatic agent as described hereinabove and further comprises the adjuncts. Where the aqueous slurry has an operable or preferable level of such adjuncts, the compounds may be added to the slurry directly, via the aqueous dispersion of the enzymatic agent or by both modes of addition.
Exemplary adjunct ingredients include but are not limited to: mediating compounds; pH regulators, such as acidulants and water-soluble buffers; co-solvents, in particular C1-C12 alcoholic co-solvents; defoaming agents; non-oxidizing repulping additives, including polymeric additives; de-inking additives, including de-inking enzymes such as lipases, pectinases and ligninolytic enzymes; and, surfactants.
It certain embodiments, at least one mediating compound which enhances the activity of an enzyme being used will be present in the aqueous slurry. The at least one mediating compound should desirably be present in the aqueous slurry in an amount of from 1 to 1000 ppm by weight or from 1 to 500 ppm by weight, based on the total weight of the aqueous slurry.
Commonly such a mediating compound will selectively bind to the compound to be hydrolyzed. The degree of binding of the mediating compound (A) to the compound to be hydrolyzed (B) may be quantified by the chemical equilibrium constant (Kd) resulting from the following binding reaction:
The chemical equilibrium constant (Kd) is then given by:
It is preferred herein that the mediating compound will have a chemical equilibrium constant (Kd) for the compound to be hydrolyzed of less that 1×104 and preferably less than 1×10−6.
Without intention to limit the present disclosure, suitable classes of mediating compounds include: cofactors; antibodies and fragments thereof which retain their binding properties; peptides; and, pepidomimics, wherein peptides are modified by the incorporation of non-natural amino acids and/or non-natural chemical linkages between the amino acids.
The aqueous slurry may, in certain circumstances, contain a water-soluble buffer which serves to maintain the slurry within a desired pH range, which range will be determined by the operative pH of the enzymes present. For example, the following water-soluble buffers may have utility herein: for the maintenance of a pH of from 4 to 5.5, an acetate buffer; for the maintenance of a pH of from 6 to 8, a phosphate buffer; and, for the maintenance of a pH of 9, a glycine-sodium hydroxide buffer. With regard to the preferred operating pH of from 6 to 8 for the present process, suitable phosphate buffers include, but are not limited to: sodium phosphate; potassium phosphate; orthophosphoric acid (H3PO4); ammonium phosphate (NH4H2PO4); and, ammonium phosphate, dibasic ((NH4)2HPO4).
The amount of water-soluble buffer added to the aqueous slurry should be effective to maintain the pH in the desired pH range. For instance, the water-soluble buffer may be added to the slurry in an amount of from 1 to 1000 ppm by weight or from 1 to 500 ppm by weight, based on the total weight of the aqueous slurry.
The aqueous dispersion or aqueous slurry may optionally comprise at least one surfactant chosen from: anionic surfactants; cationic surfactants; zwitterionic surfactants; non-ionic surfactants; and, mixtures thereof. For instance, surfactant may in toto be added to the aqueous slurry in an amount of from 1 to 1000 ppm by weight or from 1 to 500 ppm by weight, based on the total weight of the aqueous slurry. In certain embodiments, the aqueous slurry or aqueous dispersion further comprises at least one non-ionic surfactant.
Non-ionic surfactants having utility herein should preferably be exemplified by a number average molecular weight (Mn) of from 2000 to 20000 daltons, for example from 2000 to 10000 daltons or from 2000 to 8000 daltons. And exemplary non-ionic surfactants include: polyethylene oxides, such as PEG 300 or PEG 400; fatty alcohols; primary alcohol (C2-C4)alkoxylates; secondary alcohol (C2-C4)alkoxylates; alkylphenol (C2-C4)alkoxylates; alkylamino (C2-C4)alkoxylates; amine polyglycol condensates, such as Triton® CF-32 available from Union Carbide; polyoxy(C2-C3)alkylene fatty acid esters; polysorbates; sodium lauryl sulfate; sorbitan monolaurate; sorbitan monooleate; sorbitan monopalmitate; sorbitan trioleate; and, silicone surfactants, such as silicone polyether copolymers.
The aqueous slurry may, in certain circumstances, comprise at least one oxidizing agent. Any such oxidizing agent should desirably be a non-chlorinating oxidizing agent and it is certainly preferred that the aqueous slurry be substantially free of hypochlorite salts. Examples of non-chlorinating oxidizing agents include but are not limited to: organic hydroperoxides, such as t-butyl hydroperoxide and cumene hydroperoxide; organic peracids, such as peracetic acid and perbenzoic acid; ammonium, alkali metal and alkaline earth metal salts of persulfuric acid; and, ammonium, alkali metal and alkaline earth metal salts of mono-persulfuric acid.
When used, the total amount of oxidizing agent added to the slurry should be less than 1000 ppm by weight, based on the total weight of the aqueous slurry. For example, oxidizing agent(s) may be added in toto in an amount of less than 500 ppm by weight or less than 200 ppm by weight, based on the total weight of the aqueous slurry. However, as noted above, it is preferred for the aqueous slurry to be substantially free of oxidizing agents.
In accordance with a first illustrative embodiment of the present disclosure, there is provided a method for repulping lignocellulosic fibers having at least one wet strength resin disposed thereon, the method comprising:
In accordance with a second illustrative embodiment of the present disclosure there is provided a method for repulping lignocellulosic fibers having at least one wet strength resin disposed thereon, the method comprising:
In both these illustrative embodiments, it is preferred that the aqueous slurry is further exemplified by being substantially free of oxidizing agents; and/or, the aqueous slurry is substantially free of hypochlorite salts. Independently or, of additional to this statement of preference, it is desirable for the ratio by weight of hemicellulase to cellulase in the enzymatic agent to be from 5:1 to 1:5 or even from 2:1 to 1:2.
To form the defined aqueous slurry, the wet-strength lignocellulosic fiber, the enzymatic agent and any adjunct ingredients are brought together and mixed. It is important that the mixing homogenously distributes the ingredients throughout the slurry: thorough and effective mixing can be determinative of a homogeneous distribution of any constituent particulate materials. Whilst the order in which the wet-strength lignocellulosic fiber, water, enzymatic agent and, where applicable, adjunct ingredients are mixed may not typically be germane, it may of course be varied to ensure the homogeneity of the mixture. It may, for instance, be judicious to adjust the pH and temperature of the water, and to dissolve any water-soluble ingredients prior to adding the wet-strength lignocellulosic fiber.
The wet-strength lignocellulosic fiber which is to be contacted with the enzymatic agent may have been subjected to one or more pre-treatment steps prior to being included in the aqueous slurry. For example, wet-strength secondary fiber may have been subjected to one or more of: comminution; chemical de-inking; mechanical de-inking; de-contamination; and, washing. In those pre-treatment processes wherein inks or contaminants are extracted from the secondary fiber, that fiber may be separated from the extractant liquid medium by, for instance, centrifugation, decanting, filtering or screening. The separation step can be preceded by a concentration step or a dilution step and can be followed by supplementary dilution and separation steps.
If necessary, the treatment dispersion may be prepared well in advance of its application. However, in an interesting alternative embodiment, a concentrated treatment dispersion may first be obtained by mixing the enzymatic components with only a fraction of the water that would be present in the treatment dispersion as utilized: the concentrated treatment composition may then be diluted with the remaining water shortly before its contacting the secondary fiber or a process stream containing the secondary fiber. It is considered that such concentrated compositions may be prepared and stored as either single-package concentrates—that can be converted by dilution with water only—or as multi-part concentrates, two or more of which must be combined and diluted to form a complete working dispersion according to the disclosure. Any dilution can be effected simply by the addition of water, in particular deionized and/or demineralized water, under mixing. The dispersion might equally be prepared within a rinse stream whereby one or more streams of the concentrate(s) is injected into a continuous stream of water.
For a given grade of wet-strength lignocellulosic fiber or wet-strength secondary fiber, the optimum amount of enzymatic agent to be added can be determined using preliminary tests. It will however be conventional for the treatment dispersion according to the present disclosure to added to the aqueous slurry such that the enzymatic agent is present in an amount of from 10 to 5000 ppm by weight, based on the total weight of the aqueous slurry. For example, the treatment dispersion may be added such that the enzymatic agent is present in an amount of from 100 to 5000 ppm by weight or from 1000 to 5000 ppm by weight, based on the total weight of the aqueous slurry. In an alternative expression, which is not intended to mutually exclusive of that given before, the treatment dispersion may be added such that the enzymatic agent is present in an amount of from 1 to 500 μl or from 100 to 500 μl per litre of the aqueous slurry.
The temperature of the aqueous slurry should not be such that the enzymes become inactive or become denatured. Whilst the optimum temperature of an enzymatic agent containing at least two enzymes may be determined through experimentation and may be utilized in the present method, it is preferred herein that the aqueous slurry is maintained at a temperature of from 25 to 75° C. during the step of mechanical agitation (step b). The maintenance of the aqueous slurry at a temperature of from 30 to 70° C. or from 40 to 70° C. in agitating step b) may be mentioned as exemplary conditions.
The purpose of the agitation step b) of the present method is to create a homogeneous suspension of fibers in water from the disintegration of the (secondary) fiber. For this step, the aqueous slurry is typically retained in a chamber, which chamber will be disposed in a so-called re-pulper of which there are two major variants in the art; the use of both re-pulper variants is envisaged in the present method. Hydrapulpers have bottom or side mounted rotors which are responsible for the transport and mixing of material in a repulper vat, as well as for the disintegration of secondary fiber. Horizontal drum type repulpers provide for the repulping of secondary fiber through being tossed by the internal baffles of the rotating drum. For completeness, it is noted that hydrapulpers may also be provided with baffles to combat solid body rotation but such rotation might equally also be inhibited through the selection of a particular shape of vat, of which non-round or D-shaped vats may be mentioned as examples.
In both re-pulper variants, the (secondary) fibers are broken down by inter alia: turbulence; attrition through inter-particle contact or rubbing; and, direct impact of particles with the rotor or baffles. In hydrapulpers, the fiber is further broken done through being sheared between the rotor and an extraction plate.
The time required for the complete defibering of the wet-strength lignocellulosic fiber under mechanical agitation depends inter alia on: the consistency of the aqueous slurry; the kind of lignocellulosic fiber or secondary fiber; the type and amount of wet-strength resin; the wet strength of the lignocellulosic fiber or secondary fiber; the aging and/or heat curing history of the lignocellulosic fiber or secondary fiber; and, the power of the re-pulper. Defibering may be considered complete when the provided fiber has disintegrated to a suspension of individual fibers in water, free of knots or bundles of fibers.
Without intention to limit the present disclosure, where the aqueous slurry has a consistency of from 1 to 10%, the re-pulper should provide a power input of from 5 to 500 kilowatt hours per 1000 kg of aqueous slurry. A power input of from 10 to 330 kW-h/1000 kg or from 10 to 250 kW-h/1000 kg may be sufficient at that consistency to effect defibering within an appropriate time frame.
It is preferred that the operating conditions of the re-pulper are selected such that the agitation of step b) is performed for a duration of from 5 to 75 minutes, preferably from 15 to 60 minutes.
The present method does not preclude a period of soaking prior to the application of mechanical agitation to the aqueous slurry, particularly where this may be of benefit to the pulp yield. In this soaking period, the enzymatic agent acts upon the wet strength lignocellulosic fiber in the absence of mechanical shear forces. Exemplary soaking periods of from 5 to 120 minutes or from 5 to 60 minutes may be mentioned. The soaking temperature may be the same or different from the performance temperature of agitation step b) of the process but should not be such that the enzymes become inactive or denatured. Thus, whilst the optimum temperature of an enzymatic agent containing at least two enzymes may be determined through experimentation and may be utilized in the soaking step, it is preferred herein that the aqueous slurry is maintained at a temperature of from 25 to 75° C. in that step.
The following examples are illustrative of the present disclosure and are not intended to limit the scope of the disclosure in any way.
The following materials were employed in the Examples:
Enzymatic Agents: The compositions of two enzymatic agents (A, B) utilized for dosage to the wet-strength secondary fiber are provided in Table 1 herein below.
The following experimental and testing procedures were followed in the Examples:
Consistency: All consistency measures detailed below are based on oven dry weight. Where applicable consistency is measured in accordance with TAPPI T240 Consistency (concentration) of Pulp Suspensions. A known weight of pulp suspension is filtered in a Büchner funnel. Fibers and other suspended matter are retained on an oven dried, pre-weighed filter paper. After drying to a constant weight at 105±3° C., the oven-dry weight of the retained matter is determined and calculated as the percentage of original pulp suspension weight.
Repulping Procedure: Repulping tests were carried out according to TAPPI Method T205 OM-88. The apparatus used consisted of a cylindrical reaction vessel (diameter: 15.2 cm; height: 19.2 cm) having spiral baffles on the walls and furnished with a three-bladed propeller agitator. A 300 g oven-dried sample of wet-strengthened paper towels (Irving Macon) was cut into square pieces (6.45 cm2), sealed in a Ziplock® bag and stored for 12 hours. The moisture content of the cut paper was measured before it was suspended—in a Adironadack Hydropulper—in heated water (40° C.) containing 5 mM buffer (pH 7.0) to form a pulp having a consistency of 10%. Where applicable the enzymatic agents (A, B) detailed in Table 1 above were added and the mixture was agitated at 500 rpm whilst maintaining the temperature at either 45° C. or 60° C. (Table 2). Small samples (12 g) of the slurry were withdrawn after 15, 30, 40, 50 and 60 minutes and used to form a handsheet for purposes of qualitative visual observation on a backlit scanner.
After 60 minutes, 150 g of pulp was first diluted with deionized water to a consistency of 1.2% for the purposes of freeness testing and then further diluted with deionized water to a consistency of 0.3%. The final pulp was used to make handsheets having a grammage (basis weight) of 60 g/m2, which handsheets were utilized for the measurement of tensile properties.
Freeness (CSF): The freeness of the pulp was measured in accordance with the Canadian Standard, TAPPI Method T227 OM-21 using a 1000 ml pulp sample.
Tensile Strength: This measures the maximum tensile force developed in a test specimen before rupture on a tensile test carried to rupture under prescribed conditions. Tensile strength herein is the force per unit width of test specimen (Nm−1). The tensile strength was measured in accordance with TAPPI Method T494 OM-22 Tensile properties of paper and paperboard (using constant rate of elongation apparatus).
Tensile Index: This parameter is the above defined tensile strength (Nm−1) divided by grammage.
Tensile Energy Absorption (TEA): This measures the work done when a specimen is stressed to rupture in tension under prescribed conditions as measured by the integral of the tensile strength over the range of tensile strain from zero to maximum strain. The TEA is expressed as energy per unit area (test span x width) of test specimen (Jm−2). The Tensile Energy Absorption was measured herein in accordance with TAPPI Method T494 OM-22 Tensile properties of paper and paperboard (using constant rate of elongation apparatus).
The results of the above-described tests are detailed in Table 2 hereinbelow.
In all instances where an enzymatic treatment was utilized, the enzymatic agent provided a positive impact on fiber dispersion after 15 minutes of repulping, relative to the Reference Examples, which effect became more obvious after 30 minutes.
Further, compared to the relevant Reference Examples performed under equivalent repulping conditions, the enzymatic agent contributed to improved handsheet formation and increased tensile strength thereof.
It should be understood that various changes and modifications to the exemplary embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims. Also, it should be appreciated that the features of the dependent claims may be embodied in the compositions and methods of each of the independent claims.
Many modifications to and other embodiments of the disclosure set forth herein will come to mind to one skilled in the art to which these disclosures pertain, once having the benefit of the teachings in the foregoing descriptions. Therefore, it is understood that the disclosures are not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Application No. 63/619,328, filed Jan. 10, 2024.
| Number | Date | Country | |
|---|---|---|---|
| 63619328 | Jan 2024 | US |
