A method for sizing a cellulose-based fibrous product, a sizing mixture, a method for manufacturing a cellulose-based fibrous product, and cellulose-based fibrous products obtainable by said methods

Abstract

According to an example aspect of the present invention, there is provided a method for sizing a cellulose-based fibrous product, comprising: - providing an aqueous sizing mixture comprising a lignin salt and a starch; - sizing the cellulose-based fibrous product with the aqueous sizing mixture; - heat treating the sized cellulose-based fibrous product at a temperature above 100 °C.

Description

A METHOD FOR SIZING A CELLULOSE-BASED FIBROUS PRODUCT, A SIZING MIXTURE, A METHOD FOR MANUFACTURING A CELLULOSE-BASED FIBROUS PRODUCT, AND CELLULOSE-BASED FIBROUS PRODUCTS OBTAINABLE BY SAID METHODSFIELD

[0001] The present invention relates to a method for sizing a cellulose-based fibrous product, as well as a sized cellulose-based fibrous product obtainable by this method.

[0002] The present invention further relates to an aqueous sizing mixture for use in this sizing method, as well as a method for preparing this aqueous sizing mixture.

[0003] The present invention further relates to a method for manufacturing a cellulose-based fibrous product, as well as a cellulose-based fibrous product obtainable by this method.BACKGROUND

[0004] Cellulose-based fibrous products, such as paper and paperboard products, are very used as packaging material. In many packaging cases it is important that the packaging material barrier properties are suitable for the item to be packed. For many products such as food stuffs it is important that the packaging material, or the packaging product, has proper mechanical and barrier properties, such as strength, stiffness (bending stiffness) and water repellence.

[0005] Conventionally, alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA) has been used as a water repellent in e.g. paper and paperboard packaging materials.

[0006] Strength and stiffness of e.g. paper and paperboard packaging materials has conventionally been improved by addition of starch.

[0007] Lignin is a promising raw-material for bio-based products. Significant quantities of lignin are available in the spent liquors from industrial Kraft pulping, i.e. in black liquor. Lignin concentration in black liquor is typically only 20-40 %-w on dry basis, with the rest of the dry matter comprising spent pulping chemicals and dissolved non-lignin wood components. High purity is important in lignin products. Finnish patent applicationFI20215920 discloses a cost-efficient separation and purification method that makes Kraft lignin utilization feasible at industrial scale.

[0008] EP2014829 discloses as one embodiment a method for treating a paper, wherein a paper product is treated by providing an aqueous lignin mixture having a lignin concentration and pH such that the lignin is present in both soluble and colloidal form, adding a crosslinking agent to the lignin mixture, treating the paper product with the mixture, and allowing the mixture to cure.

[0009] EP2014829 further discloses as another embodiment a method of treating a paper product, the method comprising: providing a mixture comprising lignin in an aqueous solution at a concentration and pH such that substantially all the lignin is solubilised, and treating the paper product with a cationic polymer followed by treating the paper product with the lignin mixture.

[0010] EP2014829 further discloses a composition for treating a paper product, comprising lignin mixed in an aqueous solution at a concentration and pH such that the lignin is present in both soluble and colloidal form and an amphiphilic polymer that is capable of temperature dependent self-assembly to the lignin mixture whereby the polymer becomes more hydrophobic upon drying.

[0011] In view of climate change there is an increased need for making products and manufacturing methods more sustainable.DEFINITIONS

[0012] In the present context, the term “cellulose-based fibrous product” comprises any product or material comprising or at least partly consisting of cellulose fibres. The cellulose fibres may have a fibre length in the range of 0.5-7.5 mm, a fibre diameter in the range of 5-60 pm and an aspect ratio (ratio of fibre length to fibre diameter or width) in the range of 8-1500. The cellulose fibres may originate from any natural sources of cellulose, including plants and trees. “Cellulose-based fibrous products” may include, but are not limited to, products such as paper, paperboard, corrugated paperboard, carton, and moulded fibre products containing cellulose fibres to at least some extent, such as egg cartons. In the present context, the terms “paperboard” and “cardboard” are considered as synonyms.

[0013] In the present context, the term “moulded fibre product” includes, but is notlimited to, cellulose-based fibrous products such as paper or paperboard that are moulded into desired three-dimensional shapes using a mould having a moulding cavity of desired shape. Examples of moulded fibre products are egg cartons, food containers, protective packaging for various products, single use medical products (bedpans, medical trays), horticultural products (planter pots, seedling trays) and lids for paper cups for beverages (e.g. coffee). Any conventionally used moulds for making conventional moulded fibre products may be used for making cellulose-based fibrous products in accordance with the present invention.

[0014] In the present context, a “lignin salt” is a chemical form of lignin, in which part of the acid groups in lignin are dissociated and the negative charge of the dissociated acid groups is counterbalanced by cations. The lignin salt may involve various cations, but typically there is one principal cation, which is the same as the cation of that alkaline pulping process, where the lignin salt originates from. In case of Kraft lignin salt, the primary cation is sodium (Na+). Kraft lignin salt may further contain minor amounts of potassium cation (K+) as an impurity.

[0015] In the present context, an alkali lignin agglomerate colloid is a union aggregate of alkali lignin macromolecules in a colloidal state, whereby the particle size of the aggregate is large enough (> 50 kDalton) to be filtered out (to remain on the membrane) in a large-pore membrane filtration. It is important to note that these agglomerate alkali lignin particles are at least ten times the size of the alkali lignin macromolecules in the original black liquor (typically about 5 kDalton) which flow through a large-pore membrane.

[0016] In the present context, curing means reaching the final level of product properties such as strength properties or water repellency. Curing can occur naturally over time, but it can be sped up by applying high temperature, i.e. heat treatment. In the current text the terms curing and heat treatment are used in parallel to describe these phenomena.SUMMARY OF THE INVENTION

[0017] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0018] According to a first aspect, in independent claim 1 there is provided a method for sizing a cellulose-based fibrous product, comprising:providing an aqueous sizing mixture comprising a lignin salt and a starch; sizing the cellulose-based fibrous product with the aqueous sizing mixture; heat treating the sized cellulose-based fibrous product at a temperature above 100 °C.

[0019] According to a second aspect, in independent claim 11 there is provided a sized cellulose-based fibrous product obtainable by a method according to the first aspect of the invention.

[0020] According to a third aspect, in independent claim 13 there is provided an aqueous sizing mixture for use in a sizing method according to any one of the claims 1-10, wherein the aqueous sizing mixture comprises a lignin salt and a starch 13.

[0021] According to a fourth aspect, in independent claim 17 there is provided a method of preparing an aqueous sizing mixture according to any one of the claims 13-16, wherein a lignin salt, a starch and water are combined into an aqueous sizing mixture.

[0022] According to a fifth aspect, in independent claim 19 there is provided a method for manufacturing a cellulose-based fibrous product, comprising:- preparing an admixture of fibrous cellulosic material, a lignin salt, and a cationic fixative; - forming a cellulose-based fibrous pre-shaped intermediate product from said admixture; - drying said cellulose-based fibrous pre-shaped intermediate product;- subjecting the dried cellulose-based fibrous pre-shaped intermediate product to heat treatment at a temperature of 100 °C or above to obtain a cellulose-based fibrous product.

[0023] According to a sixth aspect, in independent claim 31 there is provided a cellulose-based fibrous product obtainable by a method according to any one of claims 19 to 30.

[0024] The benefits of the present invention are presented in conjunction with the description of the different embodiments of the invention in the section “Embodiments”.

[0025] Some of the preferred embodiments of the invention are presented in the dependent claims.EMBODIMENTS

[0026] According to a first aspect, there is provided a method for sizing a cellulose-based fibrous product, comprising:providing an aqueous sizing mixture comprising a lignin salt and a starch;sizing the cellulose-based fibrous product with the aqueous sizing mixture;heat treating the sized cellulose-based fibrous product at a temperature above 100 °C.

[0027] Preferable embodiments of first aspect may comprise any combination of the following features listed as bullet points below:• the lignin salt is derived from alkaline spent liquor from chemical cooking of lignocellulosic raw materials.• the lignin salt is provided in the form of an alkali lignin agglomerate colloid.• the heat treating is performed at a temperature in the range of from 105 to 240 °C, preferably from 120 to 200 °C, even more preferably 145 to 200 °C, and most preferably from 145 to 180 °C.• the proportion of the starch to the lignin salt is equal to or higher than 50 / 50, preferably 60 / 40 or higher, most preferably from 60 / 40 to 95 / 5. The proportion of the starch to the lignin salt is the proportion of the weight of the starch to the weight of the lignin salt, which is in the form of an alkali lignin agglomerate colloid.• said aqueous sizing mixture is prepared by combining the starch with the lignin salt at a pH of 8.5-11.5.• the pick-up of dry matter of the aqueous sizing mixture in the resulting sizing is 0.5 and 10 g / m2.• the lignin salt is an alkali lignin salt comprises sodium ion (Na+) as its alkali cation.• the cellulose-based fibrous product is pressed prior to, during or after the sizing with the aqueous sizing mixture.• the aqueous sizing mixture has a dry matter content in the range of 1-30 w-%, preferably 1-25 w-%, more preferably 1-20 w-%, most preferably 5-15 w-%. Thegiven w-% of dry matter content is in respect of the total weight of the aqueous sizing mixture.• the cellulose-based fibrous product is paper or paperboard.• the starch is a sizing starch, preferably a degraded starch such as oxidized potato starch• the heat treating is performed for a period of time in the range of 5-600 seconds (s), preferably 30-300 s.

[0028] The benefits achieved by the first aspect and its embodiments are that sizing a cellulose-based fibrous product, such as paper, with a combination of a lignin salt and a starch, including a curing treatment, i.e. a heat treating at a temperature above 100 °C, preferably of at least 145 °C and up to 240 °C, leads to improved material properties, such as, in particular, water repellency, strength and stiffness. Hereby better water repellency values are obtained with formulations having a higher part of starch than lignin salt. A further benefit is that at the production of brown liner material often a brown pigment is used to get such a material, but the first aspect of the present invention, which uses lignin salt already itself gives a colour to the product, which enables lower use of extra brown pigment.

[0029] According to a second aspect, there is provided a sized cellulose-based fibrous product obtainable by the above-described method.

[0030] Preferable embodiments of second aspect may comprise any combination of the following features listed as bullet points below:• the lignin salt is derived from alkaline spent liquor from chemical cooking of lignocellulosic raw materials.• the lignin salt is provided in the form of an alkali lignin agglomerate colloid.• the heat treating is performed at a temperature in the range of from 105 to 240 °C, preferably from 120 to 200 °C, even more preferably 145 to 200 °C, and most preferably from 145 to 180 °C.• the proportion of the starch to the lignin salt is equal to or higher than 50 / 50, preferably 60 / 40 or higher, most preferably from 60 / 40 to 95 / 5. The proportion ofthe starch to the lignin salt is the proportion of the weight of the starch to the weight of the lignin salt, which is in the form of an alkali lignin agglomerate colloid.• said aqueous sizing mixture is prepared by combining the starch with the lignin salt at a pH of 8.5-11.5.• the dry weight of the sizing obtained is 0.5 to 10 g / m2, preferably 2 to 6 g / m2, most preferably 4 to 6 g / m2.• the lignin salt is an alkali lignin salt comprising sodium ion (Na+) as its alkali cation.• the cellulose-based fibrous product is pressed prior to, during or after the sizing with the aqueous sizing mixture comprising the lignin salt and the starch.• the aqueous sizing mixture has a dry matter content in the range of 1-30 w-%, preferably 1-25 w-%, more preferably 1-20 w-%, and most preferably 5-15 w-%. The given w-% of dry matter content is in respect of the total weight of the aqueous sizing mixture.• the cellulose-based fibrous product is paper or paperboard.• the starch is a sizing starch, preferably a degraded starch such as oxidized potato starch

[0031] The benefits achieved by the second aspect and its embodiments are the same as above for the first aspect and its embodiments.

[0032] According to a third aspect, there is provided an aqueous sizing mixture for use in the above-mentioned sizing method, wherein the aqueous sizing mixture comprises a lignin salt and a starch.

[0033] Preferable embodiments of third aspect may comprise any combination of the following features listed as bullet points below:• the lignin salt is derived from alkaline spent liquor from chemical cooking of lignocellulosic raw materials.• the lignin salt is provided in the form of an alkali lignin agglomerate colloid.said alkali lignin salt is present in the aqueous sizing mixture in the form of an alkali lignin agglomerate colloid and the starch being present in the aqueous sizing mixture in the form of a cooked starch solution.• the proportion of the starch to the lignin salt is equal to or higher than 50 / 50, preferably 60 / 40 or higher, most preferably from 60 / 40 to 95 / 5. The proportion of the starch to the lignin salt is the proportion of the weight of the starch to the weight of the lignin salt, which is in the form of an alkali lignin agglomerate colloid.• the lignin salt is an alkali lignin salt comprising sodium ion (Na+) as its alkali cation.• the total amount of dry matter content of the lignin salt and the starch in the aqueous sizing mixture is 1-30 w-%, preferably 1-25 w-%, more preferably 1-20 w-%, and most preferably 5-15 w-%. The given w-% of dry matter content is in respect of the total weight of the aqueous sizing mixture.• the starch is a sizing starch, preferably a degraded starch such as oxidized potato starch.

[0034] The benefits achieved by the third aspect and its embodiments are the same as above for the first and second aspects and their embodiments.

[0035] According to a fourth aspect, there is provided a method of preparing the above-mentioned aqueous sizing mixture, wherein a lignin salt, a starch and water are combined into an aqueous sizing mixture.

[0036] Preferable embodiments of the fourth aspect may further comprise any combination of the following features listed as bullet points below:• the lignin salt is derived from alkaline spent liquor from chemical cooking of lignocellulosic raw materials, and the method comprises:- forming an alkali lignin agglomerate colloid from the lignin salt;- forming a cooked starch solution from the starch; and- combining the alkali lignin agglomerate colloid with the cooked starch solution into an aqueous sizing mixture.• the proportion of the starch to the lignin salt is equal to or higher than 50 / 50, preferably 60 / 40 or higher, most preferably from 60 / 40 to 95 / 5. The proportion ofthe starch to the lignin salt is the proportion of the weight of the starch to the weight of the lignin salt, which is in the form of an alkali lignin agglomerate colloid.• the aqueous sizing mixture is prepared by combining the starch with the lignin salt at apH of 8.5-11.5.• the lignin salt is an alkali lignin salt comprising sodium ion (Na+) as its alkali cation.• the total dry matter content of the lignin salt and the starch in the aqueous sizing mixture is 1-30 w-%, preferably 1-25 w-%, more preferably 1-20 w-%, and most preferably 5-15 w-%. The given w-% of dry matter content is in respect of the total weight of the aqueous sizing mixture.• the starch is a sizing starch, preferably a degraded starch such as oxidized potato starch.

[0037] The benefits achieved by the fourth aspect and its embodiments are the same as above for the first, second and third aspects and their embodiments.

[0038] According to a fifth aspect, there is provided a method for manufacturing a cellulose-based fibrous product, comprising:preparing an admixture of fibrous cellulosic material, a lignin salt, and a cationic fixative,forming a cellulose-based fibrous pre-shaped intermediate product from said admixture,drying said cellulose-based fibrous pre-shaped intermediate product,subjecting the dried cellulose-based fibrous pre-shaped intermediate product to heat treatment at a temperature of 100 °C or above to obtain a cellulose-based fibrous product.

[0039] Preferable embodiments of fifth aspect may further comprise any combination of the following features listed as bullet points below:• the lignin salt is derived from alkaline spent liquor from chemical cooking of lignocellulosic raw materials.• the lignin salt is provided as an alkali lignin agglomerate colloid.• the lignin salt is added to the admixture as an aqueous mixture of the lignin salt.the lignin salt is added in dry form to a water-based suspension of the fibrous cellulosic material.• the lignin salt is added in an amount sufficient of forming a pH 6.0-11.5 system when admixed with the water-based suspension of the fibrous cellulosic material.• the drying of the cellulose-based fibrous pre-shaped intermediate product is performed at a temperature in the range of in the range of 90-100 °C, preferably 94- 96 °C, most preferably at ca. 95 °C, optionally under vacuum such as at -0,9 bar pressure.• the drying of the cellulose-based fibrous pre-shaped intermediate product is performed by contacting it with heated air or by direct contact drying.• the heat treatment is performed at a temperature in the range of 100-170 °C, preferably 105-140 °C.• the cellulose-based fibrous pre-shaped intermediate product is in the form of a sheet and heat treatment is performed by passing the formed sheet of the cellulose-based fibrous product over heated rolls with a surface temperature of 100-200 °C, preferably 105-200 °C.• the heat treatment is performed at a temperature in the range of 100-240 °C, preferably 170-190 °C using a heat press.• the heat treatment is performed at a temperature in the range of 170-190 °C using a heat press, wherein the heat treatment is performed for a time period of 10 to 300 seconds, preferably for 30 to 300 seconds, more preferably for 60 to 300 seconds, and most preferably for 180 to 300 seconds.• a pressure of at least 0.8 bar is applied during heat treatment in the heatpress.• the dosage level of alkali lignin agglomerate colloid is in the range of 10 kg / t to 40 kg / t, preferably 15 kg / t to 35 kg / t, more preferably 25 kg / t to 35 kg / t, most preferably about 30 kg / t.• the cellulose-based fibrous product is paper, paperboard, or a moulded fibre product.• the lignin salt is an alkali lignin salt comprising sodium ion (Na+) as its alkali cation.the cationic fixative is preferably polyaluminium chloride (PAC)• a moulded fibre product (e.g. a paperboard cup) may be formed using a vacuum forming mould and a transfer mould. The thus formed preformed moulded fibre product (e.g. paperboard cup) may thereafter be dried in an oven or directly in the mould by heating the surfaces of the mould (e.g. the surfaces of a vacuum forming mould and a transfer mould).

[0040] The benefits achieved by the fifth aspect and its embodiments are that improved material properties using a dual chemistry system of polyaluminium chloride (PAC) and a lignin salt are observed on both recovered paper fibres and virgin paper fibres. Mainly these improved material properties are observed with recycled fibres. When applying pressure during the heat treatment with a heat press when using recycled fibres, it was found that contact drying was achieved instead of convection drying. Addition of the combination of PAC and a lignin salt to the wet-end and after curing these sheets shows besides good water repellency also increase in strength properties. The combination of PAC and a lignin salt constitutes a strength booster. The mechanism of this dual chemistry system, without binding to this theory, might be that the PAC brings the lignin salt, which preferably is in the form of an alkali lignin agglomerate colloid, very close to the paper fibres leading to these improved paper properties. This aspect might therefore enable to reduce the basis weight of paper or board. Only using PAC give less paper strength, but combined with a lignin salt, and cured at at least 145 °C or higher provides good water repellency properties.

[0041] During the heat treatment in the heatpress a pressure may be applied, which results in contact drying instead of convection drying. The applied pressure speeds up the process. For example, applying pressure for 50kN / 2 sheets results in a 0.8 bar pressure.

[0042] According to a sixth aspect, there is provided a cellulose-based fibrous product obtainable by the method as described directly hereinbefore as a fifth aspect.

[0043] Preferable embodiments of the sixth aspect may further comprise any combination of the following features listed as bullet points below:• the lignin salt is derived from alkaline spent liquor from chemical cooking of lignocellulosic raw materials.• the lignin salt is provided as an alkali lignin agglomerate colloid.the lignin salt is added to the admixture as an aqueous mixture of the lignin salt.the lignin salt is added in dry form to a water-based suspension of the fibrous cellulosic material.• the lignin salt is added in an amount sufficient of forming a pH 8.5-11.5 system when admixed with the water-based suspension of the fibrous cellulosic material.• the heat treatment is performed at a temperature in the range of 105-140 °C.• the cellulose-based fibrous pre-shaped intermediate product is in the form of a sheet and heat treatment is performed by passing the formed sheet of the cellulose-based fibrous product over heated rolls with a surface temperature of 105-200 °C.• the cellulose-based fibrous product is paper, paperboard, or moulded fibre products.• the lignin salt is an alkali lignin salt comprising sodium ion (Na+) as its alkali cation.• a moulded fibre product (e.g. a paperboard cup) may be formed using a vacuum forming mould and a transfer mould. The thus formed preformed moulded fibre product (e.g. paperboard cup) may thereafter be dried in an oven or directly in the mould by heating the surfaces of the mould (e.g. the surfaces of a vacuum forming mould and a transfer mould).

[0044] The benefits achieved by the sixth aspect and its embodiments are the same as above for the fifth aspect and its embodiments.

[0045] According to a seventh aspect, there is provided a sized cellulose-based fibrous product, preferably in the form of a paper, paperboard or a moulded fibre product, wherein the sizing comprises a lignin salt and a starch, the lignin salt preferably being in the form of an alkali lignin agglomerate colloid.

[0046] Preferable embodiments of the seventh aspect may comprise any combination of the following features listed as bullet points below:• the lignin salt is derived from alkaline spent liquor from chemical cooking of lignocellulosic raw materials.• the lignin salt is provided in the form of an alkali lignin agglomerate colloid.• the proportion of the starch to the lignin salt is equal to or higher than 50 / 50, preferably 60 / 40 or higher, most preferably from 60 / 40 to 95 / 5. The proportion ofthe starch to the lignin salt is the proportion of the weight of the starch to the weight of the lignin salt, which is in the form of an alkali lignin agglomerate colloid.• the pick-up of dry matter of the aqueous sizing mixture in the resulting sizing is 0.5 and 10 g / m2.• the lignin salt is an alkali lignin salt comprises sodium ion (Na+) as its alkali cation.• the aqueous sizing mixture has a dry matter content in the range of 1-30 w-%, preferably 1-25 w-%, more preferably 1-20 w-%, most preferably 5-15 w-%. The given w-% of dry matter content is in respect of the total weight of the aqueous sizing mixture.• the cellulose-based fibrous product is paper or paperboard.• the starch is a sizing starch, preferably a degraded starch such as oxidized potato starch

[0047] According to an eight aspect, there is provided a cellulose-based fibrous wte-end product, preferably in the form of a paper, paperboard or a moulded fibre product, comprising a lignin salt and a cationic fixative, the lignin salt preferably being in the form of an alkali lignin agglomerate colloid

[0048] Preferable embodiments of the eight aspect may comprise any combination of the following features listed as bullet points below:• the lignin salt is provided as an alkali lignin agglomerate colloid.• the dosage level of alkali lignin agglomerate colloid is in the range of 10 kg / t to 40 kg / t, preferably 15 kg / t to 35 kg / t, more preferably 25 kg / t to 35 kg / t, most preferably about 30 kg / t.• the lignin salt is an alkali lignin salt comprising sodium ion (Na+) as its alkali cation.• the cationic fixative is preferably polyaluminium chloride (PAC)

[0049] A degraded starch can be obtained amongst others by oxidation. Alternatively, a degraded starch can be obtained using a combination of native starch cooked in the presence of enzymes or using starch dextrins (acid treated starches). In all these treatments,the molecular structures of the starch polymers are degraded, resulting in a liquid with relatively higher content of solids (ca. 10 %) and low viscosity (below 150 mPas). Starch thus obtained can partly penetrate a paper sheet in the Z-direction.

[0050] EXAMPLES

[0051] In the following at least some embodiments of the present invention were tested and the results are presented in the form of the below Examples 1 to 5. For the purposes of performing the tests in the Examples 1 to 5, a lignin salt in the form of an alkali lignin agglomerate colloid was prepared according to the process described in Examples 1 and 2 as published in the Finnish patent application FI20215920.

[0052] In examples 1 and 2 of FI20215920, a Kraft lignin salt is derived from softwood kraft black liquor from a paper pulp mill. In this known process, the pH of softwood kraft black liquor is decreased to 10.0 using CO2 at 60 °C. A lignin precipitate suspension is then filtered to obtain a kraft lignin filter cake (with 57 % dry matter content). The lignin filter cake is mixed with deionized water to form a lignin agglomerate colloid at 10 % dry solids content. The lignin agglomerate colloid thus obtained is pre-filtered and subjected to large pore membrane filtration using a 50 kDa cut-off membrane (Alfa Laval -GR51PP). This large pore membrane filtration produces a concentrate recovering lignin (82 % dry matter content) as well as a permeate containing main inorganic anions (carbonate, sulphate). The concentrate volume (from Example 1 of FI20215920) is mixed with deionized water to achieve 10 % dry solids content and subjected to another large-pore membrane filtration using a 50 kDa cut-off membrane (Alfa Laval-GR51PP). The resulting oven dry solids concentrations in the concentrate and permeate volumes are 21 % and 1.3 %. The concentrate having an oven dry lignin salt solids concentration of 21 %, i.e. a lignin agglomerate colloid, was used as such in the below Examples 1-5 of the present invention. Since the main (most abundant) anion of the lignin salt is sodium (Na+), which is an alkali metal, the lignin agglomerate colloid may in this context also be referred to as an “alkali lignin agglomerate colloid”.

[0053] Example 1. Benefits of an alkali lignin agglomerate colloid in a wet-end

[0054] The effect of the addition of an alkali lignin agglomerate colloid in a wet-end application was tested by adding alkali lignin agglomerate colloid into a wood pulp material formulation together with a cationic fixative (FA 18, polyaluminum chloride product). The alkali lignin agglomerate colloid used in the tests was prepared from industrial softwood kraft black liquor. The impact of adding the alkali lignin agglomerate colloid in a wet-end application was tested with recycled paper pulp and virgin bleached kraft pulp. The recycled paper pulp used was an industrially relevant mix of waste paper comprising 1.01 : 1.02 mixed paper to unsorted board (% OCC, % maganizes and % mixed office waste). Cf. www.paperonweb.com / EN-643-154434A.pdf. Cationic starch of type cationic maize starch modified with a quaternary ammonium salt (degree of substitution (DS) of 0.04) was used as a reference for stiffness booster and AKD as a reference for a water repellency booster. The additions made were 10 or 30 kg of additive per dry metric ton of pulp material (kg / t).

[0055] The hand sheets were prepared using a Rapid Kothen former. Hand sheets with two different basis weights were produced: hand sheets with ca. 100 g / m2for testing strength, thickness, porosity, and water repellency, and hand sheets with ca. 500 g / m2for testing stiffness. The hand sheets were first dried for at least 5 minutes at 95 °C in a Rapid Kothen former under vacuum and then heat-treated at 170 °C for 1 hour. Subsequently, the papers were conditioned at room temperature under normal conditions for at least 24 hours before the mechanical properties of the papers were analyzed. The heat-treated hand sheets were subjected to standard paper technical tests (Tappi T494) that represent the product strength (breaking length), stiffness (bending stiffness) and water repellency (Cobb60). The bending stiffness measurement was performed using a Testometric x350-10 device according to the ISO 178 standard. The measurement of the Cobb60 value was performed in accordance with Tappi T441 om-09 (2013).

[0056] The test results are shown in Table 1. It is seen that applying 30 kg / t of the alkali lignin agglomerate colloid on recycled fibers resulted in significant improvement in strength, stiffness and water repellency (over blank). The advantages in stiffness and water repellency are comparable to that achieved with a commercially used boosters, cationic starch (stiffness) and AKD (water repellency). It is seen that the cationic fixative (FA 18) alone gives improved properties, but applying the alkali lignin agglomerate colloid togetherwith FA18 gives the best results, especially in water repellency. FA18 is a commercial product name for aluminum-chloride, basic / Poly aluminium chloride (CAS 1327-41-9) having a concentration of 35-45 %. The abbreviation PAC is used for poly aluminium chloride elsewhere in this document.

[0057] Significant improvement in strength, stiffness and water repellency is seen also, when applying the alkali lignin agglomerate colloid on bleached pulp (lower part of Table 1). Strength and stiffness improvement is seen already when applying 10 kg / t of the alkali lignin agglomerate colloid. Increasing the charge to 30 kg / t provides the advantage in water repellency.

[0058] Table 1. Wet-end application test results using alkali lignin agglomerate colloid.

[0059] Example 2, Effects of curing time on wet-end application of an alkali lignin agglomerate colloid

[0060] Handsheets were made applying the alkali lignin agglomerate colloid for a wetend paper or board application including the curing of these sheets using a heat press.

[0061] In the examination of the wet-end paper and board application, critical part is the binding of the alkali lignin agglomerate colloid onto the fibres using a cationic fixative. Hereby, poly aluminum chloride - PAC (a typical fixative used in paper chemistry), (FA 18, same as in example 1) was used, and the dosage levels were monitored by analyzing the different pulp samples made.

[0062] The pulp samples generated with and without alkali lignin agglomerate colloid present were used to make handsheets using a Rapid Kothen hand sheet former to determine the paper properties obtained using the combination of the cationic fixative with dosage levels of alkali lignin agglomerate colloid of 15 kg / t and 30 kg / t making handsheets with a basis weight of 100 g / m2. To make at least 50 handsheets each having a dosage level of alkali lignin agglomerate colloid of 15 kg / t or 30 kg / t, 181 of pulp batches (1 % consistency) were made per dosage level of alkali lignin agglomerate colloid, at which first ca. 13 ml of PAC (FA 18, same as used in example 1) was dosed to the pulp, to get positively charged pulp fibers. This was checked by measuring the Zeta Potential of the fiber furnish. Subsequently, the alkali lignin agglomerate colloid material was dosed at 15 kg / t (13 ml of alkali lignin agglomerate colloid product) and at 30 kg / t (26 ml of alkali lignin agglomerate colloid product. Also blank handsheets were made as well, with and without FA18 cationic fixative.

[0063] After the handsheets were made, curing experiments were performed using a heat press. Using the heat press, the handsheets are in direct contact with the heat generated which may speed up the curing of the alkali lignin agglomerate colloid -containing product. The following settings of temperature and time were tested:- Temperature of 120 °C at t= 60, 180, 300, and 600 seconds- Temperature of 145 °C at t= 60, 180, 300, and 600 seconds- Temperature of 170 °C at t= 30, 60, 180, and 300 seconds- Temperature of 190 °C at t= 10, 30, 60, 180, and 300 seconds

[0064] Blanks with and without FA-18 were tested at 120 °C and 170 °C cured for 10 and 600 seconds.

[0065] After conditioning of the handsheets, water repellency (Cobb60), strength (breaking length), and elongation have been analyzed. Curing results regarding strength and water repellency obtained are summarized in Table 2.

[0066] Table 2: Strength and water repellency results of the cured handsheets made.* Dosage of alkali lignin agglomerate colloid in kg / ton.

[0067] Table 2 shows that the curing times surprisingly can be tremendously reduced (going from at least 1 hour in a drying table to 180-300 seconds with contact heating) obtaining improved mechanically paper properties (improved strength and water repellency properties). However, this still requires temperatures of 170 - 190 °C. Looking at the Cobb60-value, very low water repellency values can be obtained in case handsheets are made by adding 30 kg / t alkali lignin agglomerate colloid cured at 190 °C for 180 or 300 seconds; similar Cobb60 value is obtained when 10 kg / t AKD is dosed to the recycled fiber furnish. Curing at lower temperatures still results in poor water repellency values. Significant increase in breaking length (strength) values are obtained also when using higher temperatures (170 or 190 °C).

[0068] Curing of wet-end treated paper sheets with contact heat, using a heat press, showed that the curing time can be reduced, significantly and tremendously. In this screening study, it was shown that curing can be performed at 190 °C for 180-300 seconds instead of the previous used 1 h at 145 or 170 °C. By doing so, water repellency values of 20-25 g / m2(comparable with a dosage level of 10 kg / t AKD) were obtained together with a tensile strength value of about 3400 m breaking length (improvement of 28% compared to no addition of an additive).

[0069] Example 3, Alkali lignin agglomerate colloid application benefits in sizing

[0070] The benefits of using an alkali lignin agglomerate colloid as a sizing agent were tested by treating unbleached Kraft like paper sheets in a size press applicator. Size press sizing starch (degraded starch) was used as a reference. The alkali lignin agglomerate colloid was applied as a blend with a cooked sizing starch solution in 50 / 50 and 20 / 80 w / w ratios (given as dry matter content of alkali lignin agglomerate colloid / dry sizing starch). The cooked sizing starch solution used had a dry matter content of ca. 9 % and was made from oxidized potato starch. The alkali lignin agglomerate colloid used had a dry matter content of ca. 10 %. The concentrations of the alkali lignin agglomerate colloid and the cooked sizing starch solution were selected so that the amount of dry material applied onto the paper sheets was ~ 6 g / m2. The material was applied onto the sheet by treating 3-4 times with the size press and drying the sheets after each sizing treatment at a drying table at ca 105 °C for at least 5 minutes.

[0071] The sizing was carried out using a pressure of 2 bar and a roll speed of 3 rpm. The rolls of the applicator were heated with warm water to keep the sizing solution at atemperature of 50-60 °C. The dry sized paper samples were heat treated at 170 °C for 1 h. Subsequently, the papers were conditioned at room temperature under normal conditions for at least 24 hours before the mechanical properties of the papers were analyzed. The following analyzes were performed on the obtained treated paper samples: thickness, breaking length, stiffness, porosity, and water repellency (Cobb60).

[0072] The results are gathered in Table 3. It is seen that lignin containing samples show strength (breaking length) and stiffness properties superior to the blank sample and at similar level as the reference starch sized sample. Furthermore, the lignin containing samples exhibit a greatly improved water repellency (lower Cobb60 result) over both the blank and the starch reference samples.

[0073] Table 3. Sizing test results using an alkali lignin agglomerate colloid.* Processing means sizing the sheet with the alkali lignin agglomerate colloid followed by consecutive drying of the sized sheet. This step is repeated to obtain a certain sizing weight not for the sake of applying multiple layers.** 50 / 50 blend means 50 w-% (w / w) alkali lignin agglomerate colloid and 50 w-% starch (oxidized potato starch) blend.*** 20 / 80 blend means a 20 w-% (w / w) alkali lignin agglomerate colloid and 80 w-% starch (oxidized potato starch) blend.

[0074] Example 4, Comparison of the performance of a powder form alkali lignin salt product and an alkali lignin agglomerate colloid in sizing.

[0075] The performance of a powder form alkali lignin salt product and the performance of an alkali lignin agglomerate colloid was compared in sizing application tests. The powder form alkali lignin salt product was first dissolved in water to achieve a 20 % solids liquid sample. This liquid sample was then used together with sizing starch to size unbleached Kraft like paper sheets in a similar way as presented in Example 3 : material was applied ontothe sheets by treating paper 3-4 times with the size press with the sheets dried after each sizing treatment, however, this time the sized paper samples were only dried at 105 °C, but not heat treated at 170 °C. The dried samples were analyzed for thickness, breaking length, stiffness, porosity, and water repellency (Cobb60). Table Table 3 results show practically identical properties for paper samples sized using the dissolved powder (dry) form alkali lignin salt product and an alkali lignin agglomerate colloid (not prepared by dissolving a dry powder of the alkali lignin salt).

[0076] Table 4. Comparison of test results, when using a dissolved dry powder form alkali lignin salt product and an alkali lignin agglomerate colloid in Kraft like paper sizing application.* Processing means sizing the sheet followed by consecutive drying of the sized sheet. This step is repeated to obtain a certain sizing weight not for the sake of applying multiple layers. Heat treatment of 105 °C for Ih.** 50 / 50 blend means 50 w-% (w / w) alkali lignin agglomerate colloid and 50 w-% (w / w) starch (oxidized potato starch) blend.

[0077] Example 5, Impact of heat treatment temperature on strength, stiffness, and water repellency properties of alkali lignin agglomerate colloid treated paper samples in sizing application.

[0078] Unbleached kraft like paper was sized with a size press applicator using a 50 / 50 w-% (w / w) blend of the alkali lignin agglomerate colloid (as obtained above according to examples 1 and 2 of FI20215920) and a solution of cooked sizing starch. The blend applied was achieved by mixing cooked sizing starch solution with ca. 7 % solids and alkali lignin agglomerate colloid with a concentration of ca. 10 % solids. The resulting mixture contained ca. 9 % dry matter and had a viscosity of 8 mPas at 60°C. The lignin / starch blend was appliedon the paper samples to achieve ca. 5 g / m2dry sizing layer (at least 4 repeated applications).

[0079] After sizing, the sheets were either naturally cured during 14 days at room temperature or heat treated at 105, 125, 145 or 170 °C for Ih. Subsequently, the papers were conditioned at room temperature under normal conditions for at least 24 hours before the mechanical properties of the papers were analyzed. The following analyses were performed on the paper samples: thickness, breaking length, stiffness, porosity, and water repellency (Cobb60).

[0080] The results obtained are summarized in Table 5. It is seen that the strength (breaking length) improvement is achieved already without heat treatment; no further improvement in strength is seen via heat treatment. However, stiffness is improved notably after heat treatment at 125 °C or higher. Applying the blend of the alkali lignin salt in the form of the alkali lignin agglomerate colloid and starch blend improves the water repellency significantly already without heat treatment, but the best water repellency results (Cobb60 < 20 g / m2) are obtained only after heat treatment at 145 °C or higher.

[0081] Table 5. Test results showing the impact of heat treatment temperature on sized kraft like paper.* The 50 / 50 blend sizing used in this table is a 50 / 50 w-% (w / w) blend of the alkali lignin agglomerate colloid and a solution of cooked sizing starch.

[0082] Moulded Fibre Products

[0083] Curing of wet-end treated paper sheets with contact heat, using a heat press, in the above-described examples 1 and 2, clearly show that the curing time can be reduced, significantly and tremendously. In example 2, it was shown that curing can be performed at 190 °C for 180-300 seconds instead of the previous used 1 h at 145 or 170 °C in example 1. By doing so, water repellency values of 20-25 g / m2were obtained (comparable with a dosage level of 10 kg / t AKD), together with tensile strength value of about 3400 m breaking length (improvement of 28 % compared to no addition of an additive).

[0084] As regards production of moulded fibre products, there are two routes, namely, a rough for moulded fibre products such as egg cartons (also called egg trays) in combination with air tunnel drying, and a smooth for high added value packing materials (e.g. lids for drinking cups, luxury product packaging, high end electronics packaging) with drying under pressure in a mould. Hereby, temperature ranges are used in practice (depending on product and machine) for rough moulded products in the area of 200-280 °C (air, 1-2 minutes) and 180-230 °C for smooth moulded products (30 sec).

[0085] In the present invention moulded fibre products include cellulose-based fibrous products such as paper or paperboard that are moulded into desired three-dimensional shapes using a mould having a moulding cavity of desired shape. Examples of moulded fibre products are egg cartons and lids for paper cups for beverages (e.g. coffee). Any conventionally used moulds for making conventional moulded fibre products may be used for making cellulose-based fibrous products in accordance with the present invention.

[0086] A moulded fibre product may made as a further preferred embodiment of the method for manufacturing a cellulose-based fibrous product. In such a case, the moulding occurs in a mould in conjunction with the steps of drying, heat-treating and / or curing the cellulose-based fibrous pre-shaped intermediate product. For example, a moulded fibre product (e.g. a paperboard cup) may be formed using a vacuum forming mould and a transfer mould. The thus formed preformed moulded fibre product (e.g. paperboard cup) may thereafter be dried in an oven or directly in the mould by heating the surfaces of the mould (e.g. the surfaces of a vacuum forming mould and a transfer mould).

[0087] A moulded fibre product may alternatively be made as a further preferred embodiment of a sized cellulose-based fibrous product obtainable by a method according to the first aspect of the present invention. In such as case, the moulding occurs in a mould in conjunction with the heat-treating of the sized cellulose-based fibrous product.

[0088] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0089] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0090] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0091] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0092] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0093] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singularform, throughout this document does not exclude a plurality.ACRONYMS LIST

[0094] AKD Alkyl ketene dimerVCF virgin cellulose fibreRF recycled fiberPAC polyaluminium chlorideCITATION LISTPatent Literature FI20215920EP2014829

Claims

CLAIMS:

1. A method for sizing a cellulose-based fibrous product, comprising:providing an aqueous sizing mixture comprising a lignin salt provided in the form of an alkali lignin agglomerate colloid and a starch;sizing the cellulose-based fibrous product with the aqueous sizing mixture; heat treating the sized cellulose-based fibrous product at a temperature above 100 °C.

2. A method according to claim 1, wherein the lignin salt provided in the form of an alkali lignin agglomerate colloid is derived from alkaline spent liquor from chemical cooking of lignocellulosic raw materials.

3. A method according to claim 1 or 2, wherein the heat treating is performed at a temperature in the range of from 105 to 240 °C, preferably from 120 to 200 °C, even more preferably 145 to 200 °C, and most preferably from 145 to 180 °C.

4. A method according to any one of the claims 1 to 3, wherein the proportion of the starch to the lignin salt provided in the form of an alkali lignin agglomerate colloid is equal to or higher than 50 / 50, preferably 60 / 40 or higher, most preferably from 60 / 40 to 95 / 5.

5. A method according to any one of claims 1 to 4, wherein said aqueous sizing mixture is prepared by combining the starch with the lignin salt provided in the form of an alkali lignin agglomerate colloid at a pH of 8.5-11.5.

6. A method according to any one of claims 1 to 5, wherein the lignin salt provided in the form of an alkali lignin agglomerate colloid comprises sodium ion (Na+) as its alkali cation.

7. A method according to any one of claims 1 to 6, wherein the cellulose-based fibrous product is pressed prior to, during or after the sizing with the aqueous sizing mixture.

8. A method according to any one of claims 1 to 7, wherein the aqueous sizing mixture has a dry matter content in the range of 1-30 w-%, preferably 1-25 w-%, more preferably 1- 20 w-%, most preferably 5-15 w-%.

9. A method according to any one of claims 1-8, wherein the cellulose-based fibrous product is paper, paperboard, or a moulded fibre product.

10. A sized cellulose-based fibrous product obtainable by a method according to any one of claims 1 to 9.

11. A sized cellulose-based fibrous product according to claim 10, wherein the dry weight of the sizing achieved is 0.5-10 g / m2, preferably 2 to 6 g / m2, most preferably 4 to 6 g / m2.

12. An aqueous sizing mixture for use in a sizing method according to any one of the claims 1-9, wherein the aqueous sizing mixture comprises a lignin salt provided in the form of an alkali lignin agglomerate colloid and a starch.

13. An aqueous sizing mixture according to claim 12, the starch being present in the aqueous sizing mixture in the form of a cooked starch solution.

14. An aqueous sizing mixture according to claim 12 or 13, wherein the proportion of the starch to the lignin salt provided in the form of an alkali lignin agglomerate colloid is equal to or higher than 50 / 50, preferably 60 / 40 or higher, most preferably from 60 / 40 to 95 / 5.

15. An aqueous sizing mixture according to any one of claims 12 to 14, wherein the dry matter content of the lignin salt provided in the form of an alkali lignin agglomerate colloid and the starch in the aqueous sizing mixture is 1-30 w-%, preferably 1-25 w-%, more preferably 1-20 w-%, and most preferably 5-15 w-%.

16. A method of preparing an aqueous sizing mixture according to any one of the claims 12- 14, wherein a lignin salt provided in the form of an alkali lignin agglomerate colloid, a starch and water are combined into an aqueous sizing mixture.

17. A method according to claim 16, wherein the lignin salt provided in the form of an alkali lignin agglomerate colloid is derived from alkaline spent liquor from chemical cooking of lignocellulosic raw materials, comprising:- forming an alkali lignin agglomerate colloid from the lignin salt;- forming a cooked starch solution from the starch; and- combining the alkali lignin agglomerate colloid with the cooked starch solution into an aqueous sizing mixture.

18. A method for manufacturing a cellulose-based fibrous product, comprising:- preparing an admixture of fibrous cellulosic material, a lignin salt provided in the form of an alkali lignin agglomerate colloid, and a cationic fixative;- forming a cellulose-based fibrous pre-shaped intermediate product from said admixture;- drying said cellulose-based fibrous pre-shaped intermediate product;- subjecting the dried cellulose-based fibrous pre-shaped intermediate product to heat treatment at a temperature of 100 °C or above to obtain a cellulose-based fibrous product.

19. A method according to claim 18, wherein the lignin salt provided in the form of an alkali lignin agglomerate colloid is derived from alkaline spent liquor from chemical cooking of lignocellulosic raw materials.

20. A method according to claim 18 or 19, wherein the lignin salt provided in the form of an alkali lignin agglomerate colloid is added to the admixture as an aqueous mixture of the lignin salt provided in the form of an alkali lignin agglomerate colloid.

21. A method according to any one of claims 18 to 19, wherein the lignin salt provided in the form of an alkali lignin agglomerate colloid is added in dry form to a water-based suspension of the fibrous cellulosic material.

22. A method according to any one of the claims 18 to 21, wherein the lignin salt provided in the form of an alkali lignin agglomerate colloid is added in an amount sufficient of forming a pH 6.0-11.5 system when admixed with the water-based suspension of the fibrous cellulosic material.

23. A method according to any one of the claims 18 to 22, wherein the heat treatment is performed at a temperature in the range of 100-170 °C, preferably 105-140 °C.

24. A method according to any one of the claims 18 to 22, wherein the cellulose-based fibrous pre-shaped intermediate product is in the form of a sheet and heat treatment is performed by passing the sheet of the cellulose-based fibrous product over heated rolls with a surface temperature of 100-200 °C, preferably 105-200 °C.

25. A method according to any one of the claims 18 or 24, wherein the heat treatment is performed at a temperature in the range of 100-240 °C, preferably 170-190 °C using a heat press.

26. A method according to claim 25, wherein the heat treatment is performed for 180 to 300 seconds at a temperature of 170-190 °C.

27. A method according to any one of the claims 18 to 26, wherein the cellulose-based fibrous product is paper, paperboard, or moulded fibre product.

28. A method according to any one of claims 16 to 27, wherein the lignin salt provided in the form of an alkali lignin agglomerate colloid comprises sodium ion (Na+) as its alkali cation.

29. A cellulose-based fibrous product obtainable by a method according to any one of claims 18 to 28.

30. A sized cellulose-based fibrous product, preferably in the form of a paper, paperboard or a moulded fibre product, wherein the sizing comprises a lignin salt provided in the form of an alkali lignin agglomerate colloid and a starch.

31. A cellulose-based fibrous wet-end product comprising a lignin salt provided in the form of an alkali lignin agglomerate colloid and a cationic fixative.

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