Use of modified lignins as wet-end strength additives.

Abstract

A method for increasing paper strength is provided. The method includes adding a lignin-based compound to a pulp slurry and adding a cationic polymer to the pulp slurry. When added to the pulp slurry, the combination of the lignin-based compound and the cationic polymer provides an overall increase in paper strength.

Description

[Technical field]

[0001] The present disclosure relates generally to increasing paper strength. More particularly, the present disclosure relates to compositions containing modified lignin and methods of using the compositions to strengthen paper. [Background technology]

[0002] A typical papermaking process includes the steps of: 1) pulping wood or other papermaking fiber sources; 2) producing a paper mat from the pulp, which is an aqueous slurry of cellulosic fibers that may also contain additives such as inorganic mineral fillers or pigments; 3) depositing the slurry onto a moving papermaking wire or fabric; 4) forming a sheet from the solid components of the slurry by draining off the water; 5) pressing and drying the sheet to further remove water; and 6) potential rewetting by passing the dried sheet through a size press which further dries it to form a paper product.

[0003] When conducting a papermaking process, numerous concerns must be considered to ensure the quality of the final paper product. For example, when draining the water from the slurry, as many of the fibers and chemical additives as possible should be retained rather than being washed away with the water. Similarly, the final sheet should have adequate wet and dry strength. Dry strength of paper generally includes, for example, internal bonds, dry tensile strength, and burst strength.

[0004] Commonly used dry strength agents include natural polymers such as cationic starch, carboxymethyl cellulose (CMC), and guar gum, and synthetic polymers such as polyacrylamides (cationic, anionic, and amphoteric), glyoxalated polyacrylamide (GPAM), and polyvinylamine. In the dialdehyde-functionalized polyacrylamide category, glyoxalated polyacrylamide (GPAM), prepared from glyoxal and polyacrylamide backbones, is the most commonly used dry strength agent. Summary of the Invention

[0005] A method for increasing paper strength is provided that includes adding a lignin-based compound to a pulp slurry and adding a cationic polymer to the pulp slurry.

[0006] In some embodiments, the lignin-based compound is soluble in water at a pH of about 4 to about 14.

[0007] In some embodiments, the lignin-based compound has a weight average molecular weight of less than about 100,000 g / mol.

[0008] In some embodiments, the lignin-based compound has a negative zeta potential.

[0009] In certain embodiments, the cationic monomer comprises a monomer selected from the group consisting of acrylamide, methacrylamide, diallyldimethylammonium chloride (DADMAC), N-vinylamine, 2-dimethylaminoethyl acrylate (DMAEA), N,N,N-trimethylethanaminium chloride, diallylamine, poly(amidoamine), polyethyleneimine, and any combination thereof.

[0010] In some embodiments, the cationic polymer is crosslinked epichlorohydrin-dimethylamine, poly(amidoamine), or polyethyleneimine.

[0011] In some embodiments, the cationic polymer has a weight average molecular weight of about 50,000 Da to about 2,000,000 Da.

[0012] In some embodiments, the cationic polymer has a charge density of from about 0.1 meq / g to about 15 meq / g.

[0013] In some aspects, the lignin-based compound and the cationic polymer are added to the pulp slurry in the wet end of the papermaking process.

[0014] In some embodiments, the lignin-based compound and cationic polymer are added to the pulp slurry in the white water system, pulp stock storage chest, mixing chest, machine chest, headbox, save-all chest, or any combination thereof in the papermaking process.

[0015] In some embodiments, the lignin-based compound is added to the pulp slurry in an amount ranging from about 10 lbs / ton to about 100 lbs / ton.

[0016] In some embodiments, the cationic polymer is added to the pulp slurry in an amount ranging from about 1 lb / ton to about 30 lb / ton.

[0017] In some embodiments, the lignin-based compound is added to the pulp slurry before the cationic polymer is added.

[0018] In some embodiments, the lignin-based compound is added to the pulp slurry after the cationic polymer is added.

[0019] In some embodiments, the lignin-based compound and the cationic polymer are added to the pulp slurry at different locations in the wet end.

[0020] The present disclosure also provides a composition comprising a lignin-based compound and a cationic polymer.

[0021] Further disclosed herein is the use of lignin-based compounds and cationic polymers to strengthen paper.

[0022] The foregoing has outlined rather broadly the features and technical advantages of the present disclosure in order that the detailed description of the embodiments that follow may be better understood. Additional features and advantages of the present disclosure will be described hereinafter which form the subject of the claims of this application. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present disclosure. It should also be appreciated by those skilled in the art that such equivalent embodiments do not depart from the spirit and scope of the present disclosure as set forth in the appended claims. [Brief description of the drawings]

[0023] A detailed description of the invention is set forth herein below with specific reference to the following drawings.

[0024] [Figure 1] FIG. 1 shows tensile index values ​​measured for sheets treated in the wet end with poly(DADMAC) alone and a combination of poly(DADMAC) and a lignin-based compound added sequentially.

[0025] [Diagram 2] FIG. 1 shows SCT index values ​​measured for sheets treated in the wet end with poly(DADMAC) alone and with a combination of poly(DADMAC) and a lignin-based compound added sequentially.

[0026] [Diagram 3]FIG. 1 shows the average strength improvement values ​​of sheets made with lignin-based compounds and various dosages of poly(DADMAC) polymer and cross-linked epichlorohydrin-dimethylamine coagulant. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] A method for increasing paper strength is provided that includes adding a lignin-based compound to a pulp slurry and adding a cationic polymer to the pulp slurry.

[0028] As used herein, "lignin" refers to a structural component of cellulose fibers. Lignin is a high molecular weight cross-linked organic compound that is relatively hydrophobic. In the papermaking process, lignin is typically removed from the cellulose fiber mass and incinerated. The presence of lignin in paper can cause several undesirable effects, such as yellowing and reduced strength.

[0029] The lignin compound may be an enzyme-modified lignin. The enzyme-modified lignin may be a laccase-modified lignin. In some embodiments, the lignin compound is soluble in water at about 25° C., at a concentration of about 1% to about 20% by weight of the lignin compound, and at a pH of about 4 to about 14. In some embodiments, the lignin compound is soluble in water at about 25° C., at a concentration of about 1% to about 20% by weight of the lignin compound, and at a pH of about 6 to about 9. In some embodiments, the pH is about 6, about 7, about 8, or about 9 at a concentration of about 1% to about 20% by weight of the lignin compound at about 25° C. In some embodiments, the lignin compound is soluble in water at a concentration of about 10% to about 20% by weight of the lignin compound, and at a pH of about 4 to about 14.

[0030] In some embodiments, the lignin-based compound is soluble in water at about 25° C., at a concentration of about 10% to about 20% by weight of the lignin-based compound, and at a pH of about 6 to about 9. In some embodiments, the lignin-based compound is soluble in water at about 25° C., at a concentration of about 10% to about 20% by weight of the lignin-based compound, and at a pH of about 6, about 7, about 8, or about 9. In some embodiments, the lignin-based compound is soluble in water at about 25° C., at a concentration of about 20% by weight of the lignin-based compound, and at a pH of about 6, about 7, about 8, or about 9.

[0031] In some embodiments, the lignin compound has a negative zeta potential. The zeta potential of the lignin compound can be about -5 to about -100 mV, about -30 to about -100 mV, about -40 to about -80 mV, or about -50 to about -80 mV. In some embodiments, the zeta potential of the lignin compound can be about -60 to about -75 mV.

[0032] The lignin-based compound may have a particle size of less than about 10 μm. In some embodiments, the particle size of the lignin-based compound is less than about 500 nm. The particle size of the lignin-based compound may be measured, for example, using transmission electron microscopy (TEM).

[0033] In some embodiments, the lignin-based compound does not include pulp. In some embodiments, the lignin-based compound is not associated with pulp fibers prior to addition to the pulp slurry. In some embodiments, the lignin-based compound does not include cellulose. In some embodiments, the lignin-based compound is not associated with cellulose prior to addition to the pulp slurry. In some embodiments, adding the lignin-based compound to the pulp slurry does not include adding a lignin-containing pulp to the pulp slurry. In some embodiments, the lignin-based compound does not include lignosulfonates.

[0034] Examples of commercially available lignin-based compounds include, but are not limited to, METNIN™ SHIELD.

[0035] In some embodiments, the weight average molecular weight of the lignin-based compound is less than about 100,000 g / mol, hi some embodiments, the weight average molecular weight is in the range of about 1,000 g / mol to about 100,000 g / mol. For example, the weight average molecular weight may be about 10,000 g / mol to about 100,000 g / mol, about 20,000 g / mol to about 100,000 g / mol, about 30,000 g / mol to about 100,000 g / mol, about 40,000 g / mol to about 100,000 g / mol, about 50,000 g / mol to about 100,000 g / mol, about 60,000 g / mol to about 100,000 g / mol, about 70,000 g / mol to about 100,000 g / mol, about 80,000 g / mol to about 100,000 g / mol, or about 90,000 g / mol to about 100,000 g / mol.

[0036] The dosage of the lignin-based compound can be selected to achieve increased paper strength. For example, the lignin-based compound can be added to the pulp slurry in an amount ranging from about 10 lbs / ton to about 100 lbs / ton. In some embodiments, the amount of the lignin-based compound added to the pulp slurry is about 20 lbs / ton to about 80 lbs / ton. In some embodiments, the amount of the lignin-based compound added to the pulp slurry is about 20 lbs / ton, about 30 lbs / ton, about 40 lbs / ton, about 50 lbs / ton, about 60 lbs / ton, about 70 lbs / ton, or about 80 lbs / ton.

[0037] Cationic polymers may include other non-ionic comonomers such as acrylamide, methacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, N-vinylamine, N-vinylmethylacetamide, N-vinylpyrrolidone, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, Nt-butylacrylamide, N-methylolacrylamide, vinyl acetate, vinyl alcohol, similar monomers, and combinations thereof. In some embodiments, the non-ionic comonomer is acrylamide or methacrylamide.

[0038] Representative cationic comonomers include, for example, dialkylaminoalkyl acrylates and methacrylates and their quaternary or acid salts, such as, but not limited to, dimethylaminoethyl acrylate methyl chloride quaternary salt ("DMAEA-MCQ"), dimethylaminoethyl acrylate methyl sulfate quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl acrylate sulfate, dimethylaminoethyl acrylate hydrochloride, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl sulfate quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate sulfate, dimethylaminoethyl methacrylate hydrochloride, dialkylaminoalkyl acrylates and methacrylates, and their quaternary or acid salts, such as, but not limited to, dimethylaminoethyl acrylate methyl chloride quaternary salt ("DMAEA-MCQ"), dimethylaminoethyl acrylate methyl sulfate quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate sulfate, dimethylaminoethyl methacrylate hydrochloride, dialkylaminoalkyl acrylates and methacrylates, and their quaternary or acid salts, such as, but not limited to, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl sulfate quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate sulfate, dimethylaminoethyl methacrylate hydrochloride, dialkylaminoalkyl acrylates and methacrylates, and their quaternary or acid salts, such as, but not limited to, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate sulfate, dimethylaminoethyl methacrylate hydrochloride, dialkylaminoalkyl acrylates and methacrylates, and their quaternary or acid salts, Examples of suitable monomers include acrylamido or methacrylamide and their quaternary or acid salts, such as acrylamidopropyl trimethylammonium chloride, dimethylaminopropyl acrylamido methyl sulfate quaternary salt, dimethylaminopropyl acrylamide sulfate, dimethylaminopropyl acrylamide hydrochloride, methacrylamidepropyl trimethylammonium chloride, dimethylaminopropyl methacrylamide methyl sulfate quaternary salt, dimethylaminopropyl methacrylamide sulfate, dimethylaminopropyl methacrylamide hydrochloride, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, diallyl diethyl ammonium chloride, and diallyl dimethyl ammonium chloride ("DADMAC"), similar monomers, and combinations thereof. When present, the alkyl group is generally a substituted or unsubstituted C1-C4 alkyl.

[0039] Further, in certain embodiments, the cationic monomer is one or more selected from the group consisting of diallyldimethylammonium chloride (DADMAC), N-vinylamine, 2-dimethylaminoethyl acrylate (DMAEA), N,N,N-trimethylethanaminium chloride, diallylamine, poly(amidoamine), and polyethyleneimine.

[0040] Generally, the amine-containing polymers used in accordance with the present disclosure may take the form of a water-in-oil emulsion, a dry powder, a dispersion, or an aqueous solution. In certain embodiments, the amine-containing polymers may be prepared via free radical polymerization techniques in water using free radical initiation.

[0041] In some embodiments, the amine-containing polymer is a copolymer formed by diallylamine / substituted diallylamine and (meth)acrylamide, such as diallylamine-(meth)acrylamide copolymer ("DAA / AcAm"). Moreover, it is also possible to use a mixture of one or more copolymers formed by diallylamine / substituted diallylamine and (meth)acrylamide as the amine-containing polymer.

[0042] In certain aspects, the molar percentage of cationic monomer (e.g., diallylamine) in a cationic polymer, such as a diallylamine-(meth)acrylamide copolymer, can be in the range of about 1 to about 99%. The amine-containing polymer can be composed primarily of amine-based monomers, i.e., can contain more amine-based monomer units than other comonomer units, such as (meth)acrylamide. In those embodiments, where cost is a determining factor with respect to the composition of the oil-in-water emulsion, the molar percentage of amine-based monomer in the amine-containing polymer can be from about 10% to about 80%, from about 15% to about 60%, or from about 18% to about 40%. In certain embodiments, the amine-containing polymers of the present disclosure are not derived from Hoffman degradation and do not contain polyethyleneamine units.

[0043] In some embodiments, the cationic polymer is crosslinked epichlorohydrin-dimethylamine, poly(amidoamine), or polyethyleneimine.

[0044] The weight average molecular weight of the cationic polymer may be in the range of about 50,000 Da to about 2,000,000 Da. In some embodiments, the weight average molecular weight is in the range of about 50,000 Da to about 1,000,000 Da. For example, the weight average molecular weight is about 50,000 Da to about 900,000 Da, about 50,000 Da to about 800,000 Da, about 50,000 Da to about 700,000 Da, about 50,000 Da to about 600,000 Da, about 50,000 Da to about 500,000 Da, about 100,000 Da to about 1,000,000 Da, or the like. The weight average molecular weight may range from about 0,000 Da, about 200,000 Da to about 1,000,000 Da, about 300,000 Da to about 1,000,000 Da, about 400,000 Da to about 1,000,000 Da, about 500,000 Da to about 1,000,000 Da, or about 500,000 Da to about 700,000 Da. In some embodiments, the weight average molecular weight is about 1,000,000 Da.

[0045] The charge density of the cationic polymer, measured in milliequivalents (meq) per gram (g), can range from about 0.1 meq / g to about 15 meq / g. In some embodiments, the charge density of the cationic polymer can range from about 0.5 meq / g to about 10 meq / g. In some embodiments, the charge density of the cationic polymer can range from about 1.0 meq / g to about 10 meq / g. In some embodiments, the charge density of the cationic polymer is about 1.0 meq / g, about 2.0 meq / g, about 3.0 meq / g, about 4.0 meq / g, about 4.5 meq / g, about 5.0 meq / g, about 6.0 meq / g, about 7.0 meq / g, about 8.0 meq / g, or about 9.0 meq / g.

[0046] The dosage of the cationic polymer can be selected to achieve increased paper strength. For example, the cationic polymer can be added to the pulp slurry in an amount ranging from about 1 lb / ton to about 30 lb / ton. In some embodiments, the cationic polymer can be added to the pulp slurry in an amount ranging from about 1 lb / ton to about 20 lb / ton. In some embodiments, the cationic polymer can be added to the pulp slurry in an amount ranging from about 5 lb / ton to about 20 lb / ton. In some embodiments, the cationic polymer can be added to the pulp slurry in an amount ranging from about 6 lb / ton to about 18 lb / ton. In some embodiments, the cationic polymer can be added to the pulp slurry in an amount ranging from about 8 lb / ton to about 18 lb / ton.

[0047] The lignin-based compound and the cationic polymer can be added to the pulp slurry separately or simultaneously. When added simultaneously, the lignin-based compound and the cationic polymer can be added independently or as part of a single composition. The feeding techniques for the lignin-based compound and the cationic polymer include, but are not limited to, adding the components to the pulp slurry separately in any order, or premixing the components and then adding them to the pulp slurry, or feeding the components simultaneously to the pulp slurry. In some aspects, the lignin-based compound is added to the pulp slurry before the cationic polymer is added. In some aspects, the lignin-based compound is added to the pulp slurry after the cationic polymer is added. In some aspects, the lignin-based compound and the cationic polymer are added to the pulp slurry at different locations in the wet end.

[0048] As used herein, the "wet end" of the papermaking process refers to the portion that contains the slurry of fibers. The wet end does not include the portion of the papermaking process commonly called the "dry end" where the pulp is formed into a paper sheet and dried.

[0049] The lignin-based compound and cationic polymer are added to the pulp slurry at the wet end of the papermaking process. Particular locations or unit operations in the wet end include, but are not limited to, the white water system, the pulp stock receiving chest, the mixing chest, the machine chest, and the headbox.

[0050] In some aspects, a composition is provided that includes a lignin-based compound as described herein and a cationic polymer as described herein. In some aspects, the composition may consist essentially of the lignin-based compound and the cationic polymer.

[0051] The transitional phrase "consisting essentially of" limits the scope of the claim to the particular elements, ingredients, raw materials and / or steps, and those that do not materially affect the basic and novel characteristics of the claimed invention. A basic and novel feature of the combination of a lignin-based compound and a cationic polymer is the unexpected increase in paper strength observed when the compound is added to a paper slurry at the wet end. An example of how paper strength can be measured is provided in the Examples.

[0052] In some aspects, the composition comprises a lignin-based compound and a cationic polymer. In some aspects, the composition comprises a lignin-based compound, a cationic polymer, and a solvent. The solvent can be, for example, water. EXAMPLES

[0053] Working Example

[0054] Example 1

[0055] The lignin-based compound was dosed at about 20, about 40, and about 80 lbs / ton active, and the polyDADMAC polymer (about 5.1 meq / g; weight average MW about 5000 to about 500000 g / mol) was dosed at about 4.5, about 8.5, and about 17 lbs / ton active. Sufficient polyDADMAC polymer was added to achieve a net cationic charge. The polyDADMAC polymer was added first, followed by the lignin-based compound, to a 0.9 wt% aqueous solution of fiber (recycled board). After mixing each component in the fiber slurry for about 10 seconds, mixing was stopped and handsheets were made. The handsheets were conditioned at about 23°C and about 50% relative humidity, and the strength of the resulting handsheets was measured. Specifically, the sheet tensile and short span compression (SCT) were measured, and the results are shown in Figures 1 and 2. From this data, it can be seen that the lignin-based compound was retained on the fiber surface, resulting in a significant increase in strength. Table 1 shows the cationic polymers that were tested.

[0056] The lignin-based compound tested in these examples had a zeta potential of about -66.6 mV at a pH of about 7.6, a zeta potential of about -66.8 mV at a pH of about 9.6, a particle size of about 9.9 nm as measured by dynamic light scattering, and a pH of about 9.2 in undiluted form. [Table 1]

[0057] Example 2

[0058] Further studies were conducted to evaluate the impact of other cationic polymers. An EPI-DMA polymer (about 4.3 meq / g; weight average MW about 500,000 to about 700,000 Da; Cationic Polymer 2) was compared to a polyDADMAC polymer (Cationic Polymer 1). In this study, the dosage of the lignin-based compound was fixed at about 80 lbs / ton active. The dosages of Cationic Polymer 1 ranged from about 6.25, about 12.50, about 18.75, and about 25.00 lbs / ton active, and the dosages of Cationic Polymer 2 were set at about 7.48, about 14.95, about 22.43, and about 29.90 lbs / ton active. Although the dosages of the two polymers were different, these particular dosages were chosen so that the total system charge was the same (Cationic Polymers 1 and 2 have slightly different charge densities). The cationic polymer and lignin-based compound were added sequentially as described above and handsheets were made and tested for tensile, burst, SCT and ring crush strength. The results are shown in Table 2 and the average strength improvement is shown in Figure 3. The percentages reported for tensile, burst, SCT, RCT and average are the percent change compared to the blank. [Table 2]

[0059] From this data it appears that both cationic polymers 1 and 2 can be used to retain lignin-based compounds and improve strength, however the optimal cationic polymer dosage differs slightly between the two products.

[0060] Further studies were conducted to evaluate the use of different cationic polymers as retention aids for lignin-based compounds. In this case, a high charge low molecular weight polyvinylamine (PVAM) was used (cationic polymer 3). The properties of this polymer are shown in Table 3. The PVAM polymer dosage was set at approximately 18 lbs / ton active to maintain a total system charge of approximately +0.25 meq. Strength performance results are shown in Table 4. These data show that the PVAM / lignin-based compound combination can improve strength by over approximately 30% from baseline. This is a significant result in that typical strength aids can usually provide a strength increase of 10-15%. [Table 3] [Table 4]

[0061] Example 3

[0062] Another study was conducted to evaluate the ability of two commercially available strength products, Cationic Polymers 4 and 5, to retain lignin-based compounds and increase strength. A second goal of this study was to vary the amount of Cationic Polymer 3 to evaluate the optimal PVAM dosage. Cationic Polymers 4 and 5 were dosed at about 8 lbs / ton active, respectively, and the PVAM dosages were set at about 6, about 12, and about 18 lbs / ton active. The dosage of the lignin-based compound was fixed at about 60 lbs / ton active. The results of this study are shown in Table 5 below. Although strength can be improved using Cationic Polymer 4 or Cationic Polymer 5, the strength improvement is much lower than that provided by PVAM (Cationic Polymer 3). The PVAM dosage also significantly impacts strength, with noticeable changes in performance observed at each PVAM dosage. Again, the average strength increase obtained using a high dosage of PVAM with the lignin-based compound was about 30%, consistent with previous studies. [Table 5]

[0063] These results show that lignin-based compounds can be retained on fiber surfaces using an appropriate retention system that employs polymers with lower cationic charge density and molecular weight than the average of commercially available strength aids. In the method of the present invention, lignin, typically considered a waste component of cellulose, can be used in the wet end of the paper machine to produce significant levels of strength, twice as high as typical wet end strength aids.

[0064] All of the compositions and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. The present invention may be embodied in many different forms, and certain preferred embodiments of the present invention are described in detail herein. The present disclosure is an exemplification of the principles of the present invention, and is not intended to limit the invention to the specific embodiments illustrated. It should be noted that, unless expressly stated otherwise, the term "a" is intended to include "at least one" or "one or more." For example, "a polymer" is intended to include "at least one polymer" or "one or more polymers."

[0065] Any ranges expressed in either absolute or approximate terms are intended to encompass both, and any definitions used herein are intended to be illustrative, not limiting. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein should be understood to encompass any and all subranges subsumed therein, including all fractional and whole values.

[0066] Any composition disclosed herein can comprise, consist of, or consist essentially of any element, component, and / or ingredient disclosed herein, or any combination of two or more of the elements, components, or ingredients disclosed herein.

[0067] Any method disclosed herein may comprise, consist of, or consist essentially of any method steps disclosed herein, or any combination of two or more of the method steps disclosed herein.

[0068] The transitional phrase "comprising," which is synonymous with "including," "containing," or "characterized by," is inclusive or open-ended and does not exclude additional, unrecited elements, components, ingredients, and / or method steps.

[0069] The transitional phrase "consisting of" excludes any element, component, ingredient, and / or method step not specified in the claim.

[0070] Unless otherwise specified, all molecular weights referred to herein are weight average molecular weights and all viscosities were measured at 25° C. using neat (undiluted) polymer.

[0071] As used herein, the term "about" refers to a cited value that is within error resulting from the standard deviation found in their respective testing measurements; where such error cannot be determined, "about" may refer, for example, to within 5% of the cited value.

[0072] Moreover, the present invention encompasses all possible combinations of any or all of the various embodiments described herein. It should also be understood that various changes and modifications to the preferred embodiments of the present invention 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 invention and without diminishing its intended advantages. Accordingly, such changes and modifications are intended to be covered by the appended claims.

Claims

1. 1. A method for increasing paper strength, comprising: adding a lignin-based compound to the pulp slurry; adding a cationic polymer to said pulp slurry.

2. 10. The method of claim 1, wherein the lignin-based compound is soluble in water at about 25°C, a concentration of the lignin-based compound of about 1% to about 20% by weight, and a pH of about 4 to about 14.

3. 3. The method of claim 1 or 2, wherein the lignin-based compound has a weight average molecular weight of less than about 100,000 g / mol.

4. 3. The method of claim 1 or 2, wherein the lignin-based compound has a negative zeta potential.

5. The method of claim 1 or 2, wherein the lignin-based compound does not contain pulp.

6. 3. The method of claim 1 or 2, wherein the cationic polymer comprises a monomer selected from the group consisting of acrylamide, methacrylamide, diallyldimethylammonium chloride (DADMAC), N-vinylamine, 2-dimethylaminoethyl acrylate (DMAEA), N,N,N-trimethylethanaminium chloride, diallylamine, poly(amidoamine), polyethyleneimine, and any combination thereof.

7. 3. The method of claim 1 or 2, wherein the cationic polymer is crosslinked epichlorohydrin-dimethylamine, poly(amidoamine), or polyethyleneimine.

8. 3. The method of claim 1, wherein the cationic polymer has a weight average molecular weight of about 50,000 Da to about 2,000,000 Da.

9. The method of claim 1 or 2, wherein the cationic polymer has a charge density of from about 0.1 meq / g to about 15 meq / g.

10. 3. The method of claim 1 or 2, wherein the lignin-based compound and the cationic polymer are added to the pulp slurry in the wet end of the papermaking process.

11. 3. The method of claim 1 or 2, wherein the lignin-based compound and the cationic polymer are added to the pulp slurry in a white water system, a pulp stock storage chest, a mixing chest, a machine chest, a headbox, a save-all chest, or any combination thereof in the papermaking process.

12. 3. The method of claim 1 or 2, wherein the lignin-based compound is added to the pulp slurry in an amount ranging from about 10 lbs / ton to about 100 lbs / ton.

13. 3. The method of claim 1 or 2, wherein the cationic polymer is added to the pulp slurry in an amount ranging from about 1 lb / ton to about 30 lb / ton.

14. 3. The method of claim 1 or 2, wherein the lignin-based compound is added to the pulp slurry before the cationic polymer is added.

15. 3. The method of claim 1 or 2, wherein the lignin-based compound is added to the pulp slurry after the cationic polymer has been added.

16. The method of claim 1 or 2, wherein the lignin-based compound and the cationic polymer are added to the pulp slurry at different locations within the wet end.

17. 1. A composition comprising: Lignin-based compounds, and A composition comprising a cationic polymer.

18. 20. The composition of claim 17, wherein the lignin-based compound has a weight average molecular weight of less than about 100,000 g / mol and a negative zeta potential.

19. 19. The composition of claim 17 or 18, wherein the cationic polymer comprises a monomer selected from the group consisting of acrylamide, methacrylamide, diallyldimethylammonium chloride (DADMAC), N-vinylamine, 2-dimethylaminoethyl acrylate (DMAEA), N,N,N-trimethylethanaminium chloride, diallylamine, poly(amidoamine), polyethyleneimine, and any combination thereof.

20. 19. The composition of claim 17 or 18, wherein the cationic polymer is crosslinked epichlorohydrin-dimethylamine, poly(amidoamine), or polyethyleneimine.

21. 19. The composition of claim 17 or 18, wherein the composition is pulp-free.

22. Use of lignin-based compounds and cationic polymers to strengthen paper.

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