Method for manufacturing a pulp suspension for paper or paperboard

Abstract

The present invention relates to a method for manufacturing a pulp suspension for paper or paperboard, the method comprising the steps: a) providing a pulp suspension comprising recycled pulp fibers; b) mixing a solubilized lignin or a lignin derivative with the pulp suspension; and c) adding a pH reducing agent to precipitate the solubilized lignin or lignin derivative in the pulp suspension to obtain a lignin enriched pulp suspension.

Description

[0001] METHOD FOR MANUFACTURING A PULP SUSPENSION FOR PAPER OR PAPERBOARD

[0002] Technical field

[0003] The present disclosure relates to methods for manufacturing pulp suspensions for paper or paperboard, particularly pulp suspensions comprising recycled pulp fibers.

[0004] Background

[0005] When using recycled pulp fibers in pulp suspensions for paper or paperboard, there is a need to ensure that the paper or paperboard substrates formed from the pulp suspensions have a good mechanical performance as well as acceptable and consistent optical properties, such as color and opacity. This issue is relevant for all paper or paperboard grades using recycled pulp fibers, but it is especially important for paper or paperboard grades, such as testliner, comprised mainly or entirely of recycled pulp fibers. Since the amount and quality of the recycled pulp fibers will almost inevitably vary, there is a need for methods to adjust the color or opacity of the pulp suspension and resulting paper or paperboard so that a consistent product can be obtained.

[0006] Adjusting the color or opacity is normally done by a) coating the paper or paperboard substrate or by b) adding various colorants, such as pigments or dyes to the to the pulp suspension. Coating is not always desired and adds cost and complexity to the process. The problem with adding colorants is that they typically require further addition of fixatives, which adds cost and may also lead to a range of problems, including impaired drainage, poor sheet formation, reduced mechanical performance, and compromised surface quality.

[0007] Therefore, there remains a need for improved and alternative techniques for manufacturing pulp suspensions for paper or paperboard, which can eliminate or ameliorate at least some of the drawbacks of the existing techniques. Specifically, there remains a need for improved and alternative methods for adjusting the color and opacity of the paper or paperboard substrates comprising recycled pulp fibers without negative impact on mechanical performance. The new methods should preferably be based on renewable materials.

[0008] Description of the invention

[0009] It is an object of the present disclosure to provide a method for manufacturing a pulp suspension for paper or paperboard, which alleviates at least some of the problems associated with prior art methods.

[0010] It is an object of the present disclosure to provide a method for manufacturing a pulp suspension for paper or paperboard, which allows for the color and opacity of the paper or paperboard substrates formed from the pulp suspension comprising recycled pulp fibers to be adjusted without negative impact on mechanical performance.

[0011] The above-mentioned objects, as well as other objects as will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

[0012] The present invention is based on the realization that mixing a solubilized lignin or a lignin derivative with a pulp suspension and then precipitating the solubilized lignin or lignin derivative in the pulp suspension by adding a pH reducing agent provides a convenient and bio-friendly way of adjusting the color and opacity of the paper or paperboard substrates formed from the pulp suspension. The mixing and precipitation can be performed as a batch treatment, before the pulp suspension is used in a method for manufacturing a paper or paperboard, or in-line in a method for manufacturing a paper or paperboard.

[0013] Dosing of lignin to pulp suspensions for paper or paperboard involves challenges including poor lignin retention, poor formation, uneven distribution and deposit formation. There is thus a need for improved methods enabling efficient incorporation of lignin in the pulp suspensions and resulting paper or paperboard. According to a first aspect illustrated herein, there is provided a method for manufacturing a pulp suspension for paper or paperboard, the method comprising the steps: a) providing a pulp suspension comprising recycled pulp fibers; b) mixing a solubilized lignin or a lignin derivative with the pulp suspension; and c) adding a pH reducing agent to precipitate the solubilized lignin or lignin derivative in the pulp suspension to obtain a lignin enriched pulp suspension.

[0014] A pulp suspension is an aqueous suspension comprising a water-suspended mixture of cellulose fibers and optionally other fibrous or non-fibrous materials, for example hemicellulose. The pulp suspension may also comprise some lignin nonsolubilized lignin as part of the cellulose fibers. This is mainly lignin bonded to cellulose in a so called lignocellulosic complex. The pulp can be mechanical, chemical or semi-chemical pulp, obtained from softwood or hardwood, bleached or unbleached, virgin or recycled, or a mixture thereof. In some embodiments, the pulp suspension is a kraft pulp suspension, preferably an unbleached kraft pulp suspension. Pulp suspensions are used for manufacturing paper and paperboard.

[0015] Paper generally refers to a material manufactured in thin sheets or webs from the pulp of wood or other fibrous substances comprising cellulose fibers, used for writing, drawing, or printing on, or as a construction or packaging material.

[0016] Paperboard generally refers a to strong and / or stiff, thick paper. Paperboard is typically a multiply material comprised of two or more cellulose based plies. Paper can either be bleached or unbleached, coated or uncoated, and produced in a variety of thicknesses, depending on the end use requirements.

[0017] The pulp suspension of the present disclosure comprises recycled pulp fibers. The term recycled pulp fibers refers to fibers that are derived from previously used paper products. These fibers are reclaimed from waste paper through a recycling process, allowing them to be reused in the production of new paper products. The recycled pulp fibers may for example comprise fibers obtained from post consumer packaging waste such as waste from food packaging (e.g. food service board (FSB) or used beverage carton (UBC)). The recycled pulp fibers may also comprise fibers obtained from old corrugated containers (OCC). The process for obtaining recycled pulp fibers typically includes:

[0018] Collection: Waste paper is collected from households, businesses, and industries.

[0019] Sorting: The collected paper is sorted into different categories based on quality, type, and cleanliness.

[0020] Shredding and Pulping: The sorted paper is shredded into small pieces and mixed with water to create a pulp. This pulp is then cleaned to remove contaminants such as ink, adhesives, and other non-fiber materials.

[0021] De-inking: If necessary, the pulp undergoes a de-inking process to remove inks and dyes, especially for higher-quality paper grades.

[0022] Refining and Screening: The cleaned pulp is further refined and screened to improve fiber quality and remove any remaining impurities. Optionally, the cleaned pulp is further subjected to other treatments such as thermal treatment, bleaching, or microbial deactivation.

[0023] Paper or paperboard making: The recycled pulp fibers are then used to produce new paper products, either alone or blended with virgin pulp fibers for enhanced strength and quality.

[0024] In some embodiments, the pulp suspension provided in a) comprises 10-100 wt% recycled pulp fibers, based on the total fiber content of the pulp suspension. In some embodiments, the pulp suspension provided in a) comprises 30-100 wt%, 50-100 wt%, or 70-100 wt%, recycled pulp fibers, based on the total fiber content of the pulp suspension. The recycled fibers may comprise different types of pulp fibers. In some embodiments, the recycled fibers may comprise recycled kraft pulp fibers. In some embodiments, the pulp suspension provided in a) comprises 100 wt% recycled pulp fibers, based on the total fiber content of the pulp suspension.

[0025] In some embodiments, the pulp suspension provided in a) is a pulp suspension for testliner, for fluting with recycled fiber, or for Kraft paper or Kraft liner with recycled fiber. In some embodiments, the pulp suspension provided in a) is a pulp suspension for testliner. Testliner is a type of recycled paperboard used primarily for the production of corrugated board. Testliner is made from 100% recycled fibers, making it an eco-friendly option for packaging solutions. Examples of testliner include white top testliner, uncoated mottled testliner.

[0026] In some embodiments, the pulp suspension provided in a) comprises 50-100 wt% kraft pulp fibers, based on the total fiber content of the pulp suspension. In some embodiments, the pulp suspension provided in a) comprises 50-90 wt% or 50-70 wt% kraft pulp fibers, based on the total fiber content of the pulp suspension.

[0027] In some embodiments, the pH value of the pulp suspension provided in a) is at least 7, preferably at least 8, and more preferably at least 9. This pH helps to prevent premature precipitation of the solubilized lignin or lignin derivative before the pH reducing agent is added. This allows for the solubilized lignin or lignin derivative to be dispersed in the in the pulp suspension before it is precipitated.

[0028] The lignin or lignin derivative is mixed with the pulp suspension in solubilized form. In other words, lignin or lignin derivative is first solubilized and then mixed with the pulp suspension in solubilized form. The term “solubilized” describes a state where a substance has been made soluble through specific means, especially when it would not be soluble under normal conditions.

[0029] In some embodiments, the solubilized lignin or lignin derivative comprises lignin or lignin derivative in at least partially dissolved form. The term “partially dissolved” describes a state in the dissolution process where solubility limits or incomplete mixing results in both dissolved and undissolved solute coexisting. The term at “least partially dissolved” includes fully dissolved as well as partially dissolved. The solvent is preferably an aqueous solvent. The aqueous solvent may be water or water mixed with a small amount of an organic solvent. The aqueous solvent preferably comprises at least 90 wt% water. The aqueous solvent may further comprise up to 10 wt% of an organic solvent, preferably an alcohol. Thus, in some embodiments, the solubilized lignin or lignin derivative is solubilized in an aqueous solvent. The lignin or lignin derivative may thus be mixed with the pulp suspension in the form of an aqueous lignin solution or an aqueous lignin dispersion.

[0030] In some embodiments, the pH value of the solubilized lignin or lignin derivative is at least 9, and preferably at least 10. In some embodiments, the lignin or lignin derivative is mixed with the pulp suspension in the form of an aqueous lignin dispersion. In some embodiments, the aqueous lignin dispersion has a solid content in the range of 5-50 wt%, and more preferably in the range of 10-40 wt%. The aqueous lignin dispersion is preferably prepared such that it is substantially free from large particles, such as particles having a diameter above 100 pm, preferably particles having a diameter above 50 pm, and more preferably particles having a diameter above 25 pm. Substantially free in this context means that less than 5 wt% of the total amount of lignin in the dispersion is present in the form of large particles. The particle size can for example be determined by fractionation using e.g. screens, wires or membranes.

[0031] In some embodiments, the solubilized lignin or lignin derivative comprises lignin or a lignin derivative in at least partially dissolved form obtained by at least partially dissolving the lignin or lignin derivative in an aqueous alkaline solvent, optionally combined with heating. The alkaline solvent may for example be an NaOH or KOH solution. The pH value of the alkaline solvent maybe at least 10, preferably at least 10.5. The heating may comprise heating to at least 50 °C, preferably to at least 60 °C.

[0032] In some embodiments, the solubilized lignin or lignin derivative comprises lignin or a lignin derivative in at least partially dissolved form obtained by high pressure homogenization or high pressure fluidization. High pressure homogenization comprises forcing an aqueous slurry comprising the lignin or lignin derivative through a narrow gap or orifice at extremely high pressures, typically ranging from 500 to 3000 Bar, such as in the range of 500-2000 Bar or 500-1500 Bar. As the slurry passes through the gap, it experiences intense shear forces and turbulence. The high pressure causes the lignin particles to collide with each other and with the homogenizer surfaces, further breaking them down. The rapid pressure drop after the orifice can also cause cavitation (formation and collapse of vapor bubbles), which contributes to further disintegration and solubilization of the lignin particles. High pressure fluidization comprises introducing an aqueous slurry comprising the lignin or lignin derivative into a chamber where it is subjected to high pressure, typically ranging from 500 to 3000 Bar, such as in the range of 500- 2000 Bar or 500-1500 Bar. A high-pressure fluid (usually water or a chemical solution) is pumped through the slurry, creating a fluidized state where the lignin particles are suspended and well-mixed in the fluid medium. The pressure and flow create intense mixing and agitation of the lignin particles, ensuring thorough contact between the particles and any added chemicals or treatments. The process can be precisely controlled in terms of pressure, flow rate, and treatment time to achieve the desired level of solubilization of the lignin particles.

[0033] In some embodiments, the solubilized lignin or lignin derivative comprises lignin or a lignin derivative in at least partially dissolved form obtained by a combination of i) at least partially dissolving the lignin or lignin derivative in an aqueous alkaline solvent, optionally combined with heating, and ii) at least partially dissolving the lignin or lignin derivative by high pressure homogenization or high pressure fluidization.

[0034] In some embodiments, the solubilized lignin or lignin derivative is mixed with the pulp suspension in an amount of 0.05-20 wt%, preferably 0.1-15 wt%, and more preferably 0.2-10 wt%, based on the total dry weight of the pulp suspension.

[0035] The present disclosure is concerned with adjusting the color and opacity of the paper or paperboard substrates formed from the pulp suspension. For this purpose, the particle size of the solubilized lignin or lignin derivative should preferably be small. The small particle size provides a high exposed surface area of the lignin per unit weight and facilitates uniform distribution of the lignin in the pulp suspension and formed paper, which is advantageous for adjusting color and opacity. In some embodiments the solubilized lignin or lignin derivative has an average hydrodynamic diameter determined by dynamic light scattering at pH >11 and detection at a wavelength of 658 nm of less than 1000 nm, preferably less than 800 nm, and more preferably less than 600 nm or less than 400 nm. An average hydrodynamic diameter of less than 600 nm or less than 400 nm is especially preferred for adjusting color and opacity. The average hydrodynamic diameter may typically be above 10 nm or above 20 nm. In some embodiments the solubilized lignin or lignin derivative has an average hydrodynamic diameter determined by dynamic light scattering at pH >11 and detection at a wavelength of 658 nm in the range of between 10-1000 nm, preferably in the range of between 10-800 nm, and more preferably in the range of between 10-600 nm or in the range of between 10-400 nm. In some embodiments the solubilized lignin or lignin derivative has an average hydrodynamic diameter determined by dynamic light scattering at pH >11 and detection at a wavelength of 658 nm in the range of between 20-1000 nm, preferably in the range of between 20-800 nm, and more preferably in the range of between 20-600 nm or in the range of between 20-400 nm. The average hydrodynamic diameter is preferably the Z-average hydrodynamic diameter. The average hydrodynamic diameter is preferably measured in an aqueous solvent, and more preferably in an aqueous NaOH solution.

[0036] In some embodiments the solubilized lignin or lignin derivative has a molecular weight in the range of 500-4000 Da. The molecular weight may be determined by gel permeation chromatography coupled with UV.

[0037] In some embodiments the solubilized lignin or lignin derivative has an inorganic content in the range of 1-20 wt% as determined according to ISO 9795:2023. In some embodiments the solubilized lignin or lignin derivative has an inorganic content below 5 wt%, and more preferably below 3 wt%, as determined according to ISO 9795:2023.

[0038] In some embodiments the solubilized lignin or lignin derivative has a sulfur content in the range of 0.5-5 wt%, such as in the range of 0.75-5 wt%, as determined according to SCAN-CM 57:99.

[0039] In some embodiments, the solubilized lignin or lignin derivative is selected from the group consisting of kraft lignin, organosolv lignin, soda lignin, lignosulfonate, or a combination of two or more thereof, preferably kraft lignin. Kraft lignin can be precipitated from black liquor obtained from the kraft pulping process by for example adjusting pH. There are well known and commercially available methods for this, for example the LignoBoost method and the LignoForce method.

[0040] Organosolv lignin is obtained through the organosolv process, a method for separating lignin from cellulose and hemicellulose using an organic solvent or a mixture of solvents, often in combination with water.

[0041] Soda lignin is obtained through the soda pulping process, which uses an alkaline solution, typically sodium hydroxide (NaOH), as the pulping agent to dissolve lignin and some hemicellulose in biomass, leaving behind cellulose fibers.

[0042] Lignosulfonates are obtained through the sulfite pulping process, while separating lignin from cellulose fibers using sulfite salts.

[0043] The different processes for obtaining lignin may also be combined with acidic or alkaline hydrolysis, or enzymatic degradation or oxidation, to further improve the efficiency of the processes or the quality of the obtained lignin.

[0044] Examples of commercially available lignins that can be used with the inventive method include, but are not limited to, Lineo (Stora Enso), BioChoise (Domtar), BioPiva (UPM Kymmene), Amallin (West Fraser), and Ecolig or LigFlow (Suzano).

[0045] In some embodiments, the method further comprises mixing up to 10 wt% microfibri Hated cellulose (MFC) with the pulp suspension before adding the pH reducing agent.

[0046] MFC shall in the context of the patent application mean a cellulose particle, fiber or fibril having a width or diameter of from 20 nm to 1000 nm. Various methods exist to make MFC, such as single or multiple pass refining, pre-hydrolysis followed by refining or high shear disintegration or liberation of fibrils. One or several pretreatment steps is usually required in order to make MFC manufacturing both energy efficient and sustainable. The cellulose fibers of the pulp used when producing MFC may thus be native or pre-treated enzymatically or chemically, for example to reduce the quantity of hemicellulose or lignin. The cellulose fibers may be chemically modified before fibrillation, wherein the cellulose molecules contain functional groups other (or more) than found in the original cellulose. Such groups include, among others, carboxymethyl (CM), aldehyde and / or carboxyl groups (cellulose obtained by N-oxyl mediated oxidation, for example "TEMPO"), or quaternary ammonium (cationic cellulose). After being modified or oxidized in one of the above-described methods, it is easier to disintegrate the fibers into MFC.

[0047] The MFC helps to improve the retention of the solubilized lignin or lignin derivative in the pulp suspension. The MFC can be co-added with the solubilized lignin or lignin derivative. Optionally, the MFC can be mixed with the solubilized lignin or lignin derivative and the mixture added to the pulp suspension. Alternatively, the MFC can be mixed with the pulp suspension before the solubilized lignin or lignin derivative is mixed with the pulp suspension.

[0048] The solubilized lignin or lignin derivative will typically increase the pH value of the pulp suspension. In some embodiments, the pH value of the pulp suspension before adding the pH reducing agent is at least 8, preferably at least 9, and more preferably at least 10.

[0049] The method further comprises adding a pH reducing agent to precipitate the solubilized lignin or lignin derivative in the pulp suspension to obtain a lignin enriched pulp suspension. Upon precipitation, the lignin or lignin derivative will be deposited on the surfaces of the cellulose fibers of the pulp. The deposition may occur in the pulp suspension before or during forming of the base paper. The added lignin or lignin derivative will thus be present between the cellulose fibers of the pulp when the base paper is formed. This differs from the native lignin which may in some cases exist in the pulp, which will form part of the cellulose fibers.

[0050] The pH reducing agent is a chemical compound or capable of reducing the pH value of the pulp suspension comprising the solubilized lignin or lignin derivative. In some embodiments, the pH reducing agent is an acid. Examples of acids that may be used as pH reducing agents in the inventive method include, but are not limited to, sulfuric acid (H2SO4), hydrochloric acid (HCI), carbon dioxide (CO2), formic acid (HCOOH), and / or acetic acid (CH3COOH).

[0051] In some embodiments, the pH reducing agent is CO2. CO2 can be injected into and mixed with the pulp suspension by methods known to the skilled person. When CO2is mixed into the pulp suspension, it reacts with water to form carbonic acid (H2CO3), which partially dissociates into bicarbonate (HCO3“) and hydrogen ions (H+). This reaction lowers the pH of the pulp suspension.

[0052] In some embodiments, the pH reducing agent is alum (aluminum sulfate, AI2(SO4)3). Alum is not an acid in itself, but it hydrolyzes to form sulfuric acid and aluminum hydroxide, thereby effectively reducing the pH value of the pulp suspension.

[0053] The type and amount of pH reducing agent should preferably be sufficient to reduce the pH value of the pulp suspension by at least one pH unit, preferably by at least 2 pH units, and more preferably by at least 3 pH units. In some embodiments, the addition of the pH reducing agent reduces the pH value of the pulp suspension by at least one pH unit, preferably by at least 2 pH units, and more preferably by at least 3 pH units.

[0054] In some embodiments, the pH value of the lignin enriched pulp suspension after adding the pH reducing agent is below 7, preferably below 6, and more preferably below 5.

[0055] The addition of the pH reducing agent leads to precipitation of at least a part of the solubilized lignin or lignin derivative in the pulp suspension, whereby a lignin enriched pulp suspension is obtained.

[0056] The lignin enriched pulp suspension can be used directly as obtained for manufacturing paper or paperboard. Alternatively, the lignin enriched pulp suspension can be mixed with a second pulp suspension before being used for manufacturing paper or paperboard. The mixing and precipitation of the solubilized lignin or lignin derivative can also be performed only on a portion of a pulp suspension, and the obtained lignin enriched portion of the pulp suspension then mixed with the remaining untreated portion of the pulp suspension.

[0057] In some embodiments, the method further comprising the step: d) mixing the lignin enriched pulp suspension with a second pulp suspension.

[0058] In some embodiments, the lignin enriched pulp suspension is prepared from a pulp suspension comprising a high amount of recycled pulp fibers, such as at least 70 wt%, preferably at least 80 wt%, and more preferably at least 90 wt%, such as 100 wt%, of recycled pulp fibers, based on the total fiber content of the pulp suspension, and subsequently subjected to mixing with a second pulp suspension comprising a high amount of virgin pulp fibers, such as at least 70 wt%, preferably at least 80 wt%, and more preferably at least 90 wt%, such as 100 wt%, of virgin pulp fibers, based on the total fiber content of the second pulp suspension. This way, the lignin enrichment can be specifically focused on the pulp suspension comprising recycled pulp fibers. Thus, in some embodiments, the second pulp suspension comprises virgin pulp fibers. In some embodiments, the second pulp suspension comprises at least 70 wt%, preferably at least 80 wt%, and more preferably at least 90 wt%, of virgin pulp fibers, based on the total fiber content of the second pulp suspension.

[0059] In some embodiments, the lignin enriched pulp suspension is prepared from a pulp suspension originating from or containing broke, which lignin enriched pulp suspension may be subsequently subjected to mixing with a second pulp suspension.

[0060] In some embodiments, the method comprising the steps: a) providing a pulp suspension comprising recycled pulp fibers and dividing the pulp suspension into a first portion and a second portion; b) mixing a solubilized lignin or a lignin derivative with the first portion of the pulp suspension; c) adding a pH reducing agent to precipitate the solubilized lignin or lignin derivative in the first portion of the pulp suspension to obtain a lignin enriched pulp suspension; and d) mixing the lignin enriched pulp suspension with the second portion of the pulp suspension.

[0061] In some embodiments, the first portion comprises 10-90 wt%, preferably 10-70 wt%, and more preferably 10-50 wt%, of the pulp suspension provided in a).

[0062] In some embodiments, the pH value of the mixed pulp suspension obtained in d) is in the range of 6-9, and preferably at least in the range of 7-8.

[0063] The amount of lignin or a lignin derivative mixed with the pulp suspension may depend on the type lignin and the desired color or opacity adjustment. In some embodiments, the lignin enriched pulp suspension comprises 0.05-20 wt%, preferably 0.1-15 wt%, and more preferably 0.2-10 wt%, of lignin or a lignin derivative based on the total dry weight of the lignin enriched pulp suspension.

[0064] The pulp suspensions obtained by the inventive method preferably comprise less than 10 wt% of mineral filler, or even no mineral filler at all. In some embodiments, the obtained lignin enriched pulp suspension comprises less than 10 wt% of mineral filler based on the total dry weight of the lignin enriched pulp suspension. In embodiments, wherein the lignin enriched pulp suspension is mixed with a second pulp suspension or with the second portion of the pulp suspension, the obtained lignin enriched pulp suspension mixed with the second pulp suspension or with the second portion of the pulp suspension comprises less than 10 wt% of mineral filler based on the total dry weight of the obtained pulp suspension.

[0065] The pulp suspensions obtained by the inventive method preferably comprise less than 5 kg / tn, preferably less than 3 kg / tn, and more preferably less than 1 kg / tn, of dyes and pigments, or even no dyes and pigments at all. In some embodiments, the obtained lignin enriched pulp suspension comprises less than 5 kg / tn, preferably less than 3 kg / tn, and more preferably less than 1 kg / tn, of dyes and pigments based on the total dry weight of the lignin enriched pulp suspension. In embodiments, wherein the lignin enriched pulp suspension is mixed with a second pulp suspension or with the second portion of the pulp suspension, the obtained lignin enriched pulp suspension mixed with the second pulp suspension or with the second portion of the pulp suspension comprises less than In some embodiments, the obtained lignin enriched pulp suspension comprises less than 5 kg / tn, preferably less than 3 kg / tn, and more preferably less than 1 kg / tn, of dyes and pigments based on the total dry weight of the obtained pulp suspension.

[0066] According to a second aspect illustrated herein, there is provided a method for manufacturing a paper or paperboard comprising 10-100 wt% recycled pulp fibers, based on the total fiber content of the paper or paperboard, the method comprising the steps of: a) manufacturing a lignin enriched pulp suspension according to the first aspect; b) forming a wet web comprising the lignin enriched pulp suspension; c) dewatering and drying the wet web to obtain a paper or paperboard substrate; and optionally d) calendering the obtained paper or paperboard substrate.

[0067] The manufacturing of the lignin enriched pulp suspension in step a) of the second aspect may be further defined as set out above with reference to the first aspect.

[0068] The forming of the wet web in b) may be done using conventional paper or paperboard forming techniques known in the art. Although different arrangements for performing the steps of the inventive method could be contemplated by the skilled person, the inventive method may advantageously be performed in a paper machine, more preferably in a Fourdrinier type paper machine, i.e. a paper machine based on based on the principles of the Fourdrinier Machine. The Fourdrinier type paper machine uses a moving dewatering fabric or woven mesh, commonly referred to as a “wire”, to create a continuous web by filtering out the fibers held in the cellulose pulp composition and producing a continuously moving wet web of fiber. This wet web is subsequently dried in the machine to produce paper or paperboard. The lignin enriched pulp suspension can be used directly as obtained for forming the wet web. Alternatively, the lignin enriched pulp suspension can be mixed with a second pulp suspension before being used for forming the wet web. The mixing and precipitation of the solubilized lignin or lignin derivative can also be performed only on a portion of a pulp suspension, and the obtained lignin enriched portion of the pulp suspension then mixed with the remaining untreated portion of the pulp suspension. The obtained mixture of the lignin enriched pulp suspension with the second portion of the pulp suspension may then be used for forming the wet web.

[0069] A multiply paper or paperboard substrate may be prepared using methods known in the art using one or more headboxes, and one or more wires, respectively. In one example, a multiply paper or paperboard substrate may be formed using two or more headboxes or a multilayer headbox on a single wire. In another example, the plies of a multiply paper or paperboard substrate may be formed separately on two or more separate wires with associated headboxes, and then laminated to form the multiply paper or paperboard substrate.

[0070] In embodiments, wherein the paper or paperboard is a multiply paper or paperboard, the lignin enriched pulp suspension may be used in any or all plies of the multiply paper or paperboard. However, the lignin enriched pulp suspension may be especially useful in the outermost plies of the multiply paper or paperboard since the effect of the lignin enriched pulp on the optical properties of the paper or paperboard will be greater. In some embodiments, the paper or paperboard is a multiply paper or paperboard, wherein the lignin enriched pulp suspension is used for forming at least an outermost ply of the multiply paper or paperboard.

[0071] In some embodiments, the wet web formed in b) comprises 10-100 wt% recycled pulp fibers, based on the total fiber content of the wet web. In some embodiments, the wet web formed in b) comprises 30-100 wt%, 50-100 wt%, or 70-100 wt%, recycled pulp fibers, based on the total fiber content of the pulp suspension. In some embodiments, the wet web formed in b) is a pulp suspension for testliner. Testliner is a type of recycled paperboard used primarily for the production of corrugated board. Testliner is made from 100% recycled fibers, making it an eco- friendly option for packaging solutions. In some embodiments, the obtained paper or paperboard substrate is a testliner.

[0072] The mechanical properties of the obtained paper or paperboard substrate can be improved if the paper or paperboard substrate is subjected to calendering at a temperature of 80 °C or more, preferably 90 °C or more or 100 °C or more. This hot calendering plasticizes the precipitated lignin and produces a more homogenous product with better wet strength, higher moisture resistance and less creep than the uncalendered paper or paperboard substrate. Unless otherwise specified the calendering temperatures herein refer to the calender roll surface temperature.

[0073] In some embodiments, the calendering in step d) is performed at a temperature in the range of 80-250 °C, preferably in the range of 90-250 °C, and more preferably in the range of 100-200 °C.

[0074] The calendering in step d) is preferably performed at a moisture content of the obtained paper or paperboard in the range of 6-20 wt%, and more preferably in the range of 6-15 wt%.

[0075] In some embodiments, the calendering in step d) is performed with a nip load of 30 kN / m or more.

[0076] The calendering in step d) may be performed in one or more nips. Each nip of the calendering in step d) may be a soft-soft nip, a soft-hard nip, or a hard-hard nip.

[0077] In some embodiments, the grammage of the paper substrate based on dry weight is in the range of 50-400 g / m2, preferably in the range of 100-400 g / m2, and more preferably in the range of 150-400 g / m2.

[0078] In some embodiments, the obtained paper or paperboard substrate has a density in the range of 400-950 kg / m3, preferably in the range of 500-900 kg / m3, and more preferably in the range of 600-900 kg / m3. In some embodiments, the obtained paper or paperboard substrate has a wet strength in the machine direction (MD) of at least 0.35 kN / m preferably at least 0.5 kN / m, and more preferably at least 0.6 kN / m, as determined according to SCAN-P 20:95.

[0079] In some embodiments, the obtained paper or paperboard substrate has an opacity of at least 60 %, preferably at least 85 %, and more preferably at least 98 %, according to standard ISO 2471.

[0080] In some embodiments, the obtained paper or paperboard substrate has a brightness (R457 C / 2° + UV) of less than 70 %, preferably less than 50 %, and more preferably less than 40 %, according to standard ISO 2470-1.

[0081] In some embodiments, the obtained paper or paperboard substrate has a burst index of at least 2.0 kPa*m2 / g, and preferably at least 2.5 kPa*m2 / g, according to SCAN-P 25.

[0082] In some embodiments, the obtained paper or paperboard substrate has an SCT index, GM (Geometric mean), of at least 18 Nm / g, and preferably at least 20 Nm / g, according to ISO 9895.

[0083] In some embodiments, the obtained paper or paperboard substrate has a Bendtsen roughness of at least 600 ml / min, preferably at least 700 ml / min, according to standard ISO 8791-2.

[0084] In some embodiments, the paper substrate has a Gurley porosity below 50 s / 100 ml measured according to standard SCAN-P19:78.

[0085] In some embodiments, the obtained paper or paperboard substrate has a specific formation below 1.6 gA0.5 / m, preferably below 1.5 gA0.5 / m, more preferably below 1.0 gA0.5 / m, and more preferably below 0.7 gA0.5 / m, as determined according to SCAN-P 92:09. According to a third aspect illustrated herein, there is provided the use of a lignin enriched pulp suspension manufactured according to the first aspect in the manufacture of a paper or paperboard comprising 10-100 wt% recycled pulp fibers.

[0086] The manufacturing of the lignin enriched pulp suspension in the third aspect may be further defined as set out above with reference to the first aspect.

[0087] The use of the lignin enriched pulp suspension in the manufacture of a paper or paperboard comprising 10-100 wt% recycled pulp fibers in the third aspect may be further defined as set out above with reference to the second aspect.

[0088] Generally, while the products, materials, plies, layers and processes are described in terms of “comprising” various components or steps, the products, materials, plies, layers and processes can also “consist essentially of” or “consist of” the various components and steps.

[0089] It is further noted that the disclosure relates to all possible combinations of features, unless explicitly stated otherwise.

[0090] While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. EXAMPLES

[0091] 3 trials were run on a pilot papermaking machine with a softwood kraft pulp suspension. Targeted grammage of the formed paper substrates was 100 g / m2.

[0092] To the softwood kraft pulp suspension 2 kg / tn of sodium dodecyl sulfate (SDS) was added as a debonder and / or wetting agent. A paper substrate was prepared from the mixture on the pilot papermaking machine. The results are presented in Table 1. substrate from lignin enriched

[0093] Lignin was partially dissolved in a NaOH solution at pH 10 at a temperature of 50 °C. To the softwood kraft pulp suspension the partially dissolved kraft lignin was added in an amount corresponding to 5 wt% of kraft lignin based on the total dry weight of the pulp suspension. The lignin was then precipitated onto the fibers of the pulp by reducing the pH of the pulp suspension to pH 3. A paper substrate was prepared from the mixture in the same manner as in Example 1. The results are presented in Table 1 . The properties of the obtained paper substrate were on same level as in Example 1.

[0094] Example 3 - Preparation of paper substrate from lignin enriched pulp suspension Example 3 was carried out in the same manner as Example 2, with the difference that the partially dissolved kraft lignin was added in an amount corresponding to 20 wt% of kraft lignin based on the total dry weight of the pulp suspension. The results are presented in Table 1. The results were roughly the same as the results for Example 2, except for a clear change in the optical properties of the paper substrate. Table 1.

[0095] Gurley porosity was measured according to standard ISO 5636-5. SCT Index (machine direction (MD), cross direction (CD), and geometric mean (GM)) was measured according to ISO 9895.

[0096] Brightness R457 0 / 2° + UV was measured according to ISO 2470-1. Opacity was measured according to ISO 2471.

[0097] Burst index (kPa*m2 / g) was measured according to SCAN-P 25.

Claims

CLAIMS1 . A method for manufacturing a pulp suspension for paper or paperboard, the method comprising the steps: a) providing a pulp suspension comprising recycled pulp fibers; b) mixing a solubilized lignin or a lignin derivative with the pulp suspension; and c) adding a pH reducing agent to precipitate the solubilized lignin or lignin derivative in the pulp suspension to obtain a lignin enriched pulp suspension.

2. The method according to claim 1 , wherein the pulp suspension provided in a) comprises 10-100 wt% recycled pulp fibers, based on the total fiber content of the pulp suspension.

3. The method according to any one of the preceding claims, wherein the pulp suspension provided in a) comprises 50-100 wt% kraft pulp fibers, based on the total fiber content of the pulp suspension.

4. The method according to any one of the preceding claims, wherein the pH value of the pulp suspension provided in a) is at least 7, preferably at least 8, and more preferably at least 9.

5. The method according to any one of the preceding claims, wherein the pH value of the solubilized lignin or lignin derivative is at least 9, and preferably at least 10.

6. The method according to any one of the preceding claims, wherein the solubilized lignin or lignin derivative is mixed with the pulp suspension in an amount of 0.05-20 wt%, preferably 0.1-15 wt%, and more preferably 0.2-10 wt%, based on the total dry weight of the pulp suspension.

7. The method according to any one of the preceding claims, wherein the lignin or lignin derivative is selected from the group consisting of kraft lignin, organosolv lignin, soda lignin, lignosulfonate, or a combination of two or more thereof, preferably kraft lignin.

8. The method according to any one of the preceding claims, wherein the pH value of the pulp suspension before adding the pH reducing agent is at least 8, preferably at least 9, and more preferably at least 10.

9. The method according to any one of the preceding claims, wherein the pH reducing agent is CO2.

10. The method according to any one of the preceding claims, wherein the pH value of the lignin enriched pulp suspension after adding the pH reducing agent is below 7, preferably below 6, and more preferably below 5.11 . The method according to any one of the preceding claims, the method further comprising the step: d) mixing the lignin enriched pulp suspension with a second pulp suspension.

12. The method according to any one of the preceding claims, wherein the lignin enriched pulp suspension comprises 0.05-20 wt%, preferably 0.1-15 wt%, and more preferably 0.2-10 wt%, of lignin or a lignin derivative based on the total dry weight of the lignin enriched pulp suspension.

13. The method according to any one of the preceding claims, wherein the obtained lignin enriched pulp suspension comprises less than 10 wt% of mineral filler based on the total dry weight of the lignin enriched pulp suspension.

14. The method according to any one of the preceding claims, wherein the obtained lignin enriched pulp suspension comprises less than 5 kg / tn, preferably less than 3 kg / tn, and more preferably less than 1 kg / tn, of dyes and pigments based on the total dry weight of the lignin enriched pulp suspension.

15. The method according to any one of the preceding claims, wherein the solubilized lignin or lignin derivative has an average hydrodynamic diameter determined by dynamic light scattering at pH >11 and detection at a wavelength of 658 nm of less than 600 nm, and more preferably less than 400 nm.

16. A method for manufacturing a paper or paperboard comprising 10-100 wt% recycled pulp fibers, based on the total fiber content of the paper or paperboard, the method comprising the steps of: a) manufacturing a lignin enriched pulp suspension according to any one of claims 1-15; b) forming a wet web comprising the lignin enriched pulp suspension; c) dewatering and drying the wet web to obtain a paper or paperboard substrate; and optionally d) calendering the obtained paper or paperboard substrate.

17. The method according to claim 16, wherein the paper or paperboard is a multiply paper or paperboard, and wherein the lignin enriched pulp suspension is used for forming at least an outermost ply of the multiply paper or paperboard.

18. The method according to any one of claims 16-17, wherein the paper or paperboard is a testliner.

19. The method according to any one of claims 16-18, wherein the calendering in step d) is performed at a temperature in the range of 80-250 °C, preferably in the range of 90-250 °C, and more preferably in the range of 100-200 °C.

20. Use of a lignin enriched pulp suspension manufactured according to any one of claims 1-15 in the manufacture of a paper or paperboard comprising 10-100 wt% recycled pulp fibers.

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