Aqueous dispersions of alkyl ketene dimers and uses thereof

Abstract

The invention relates to an aqueous dispersion of an alkyl ketene dimer. The aqueous dispersion comprises alkyl ketene dimer particles dispersed in an aqueous continuous phase and an anionic lignin-carbohydrate complex as a stabilizer, wherein lignin and carbohydrate are covalently bound to each other.

Description

Technical Field

[0001] The present invention relates to aqueous dispersions of alkyl ketene dimers according to the preambles of the accompanying independent claims and to their use. Background Art

[0002] Sizing agents are used in the manufacture of paper, board, etc. to reduce or prevent the penetration of water, moisture, and other liquids (such as printing inks) into the structure of the paper, board, etc. In internal sizing, the sizing agent is added to the fiber furnish, where it interacts with the fibers to increase the water repellency of the paper or board. In surface sizing, the sizing agent can be added to the surface of a partially or completely dried web of paper, board, etc. to seal the surface of the web and thereby reduce the penetration of liquids, particularly water and moisture, into the web.

[0003] Alkyl ketene dimer is a commonly used sizing agent in the manufacture of paper, board, etc. Alkyl ketene dimer is usually supplied in the form of an aqueous dispersion, prepared by the chemical manufacturer and transported to the factory location. The dispersion should have appropriate stability to allow it to be transported from the manufacturing site to the use site of the factory, and if necessary, to allow a certain storage time at the factory. Alkyl ketene dispersions are usually stabilized by using starch or synthetic polymers as stabilizers. However, traditional stabilizers are not optimal in terms of the ongoing need to increase sustainability. Synthetic polymers are usually made from petroleum-based non-renewable resources. On the other hand, starch is obtained from renewable resources, but it is usually produced from plants that can be used to feed humans and / or animals. Planting plants for starch production takes up valuable arable land that can be used for food production. Therefore, it would be beneficial to find new stabilizers that would be bio-based, renewable and derived from natural sources that cannot be used primarily for food or feed production.

[0004] The use of starch as a stabilizer in the sizing dispersion may also lead to an increased risk of bacterial growth and deposition problems during the paper or board manufacturing process, as the starch provides nutrition for bacteria present in the process.

[0005] In view of the above, there is a need for new and effective stabilizers that can be used to stabilize aqueous dispersions of alkyl ketene dimers. In the current pursuit of sustainability, such stabilizers should be derived from renewable resources and should not be based on petrochemicals. Summary of the Invention

[0006] The object of the present invention is to minimize or even eliminate the disadvantages present in the prior art.

[0007] It was also an object of the present invention to provide an aqueous dispersion of alkyl ketene dimer with a sustainable stabilizer, which provides a dispersion with good stability and effective sizing properties.

[0008] These objects are achieved by the present invention having the following features presented in the characterizing sections of the independent claims. Preferred embodiments of the invention are presented in the dependent claims. Unless expressly stated otherwise, the features recited in the dependent claims may be freely combined with one another. Furthermore, unless expressly stated otherwise, all features and advantages described in the description and claims apply to all aspects of the present invention.

[0009] A typical aqueous dispersion of alkyl ketene dimer according to the present invention comprises alkyl ketene dimer particles dispersed in an aqueous continuous phase, wherein the aqueous dispersion comprises an anionic lignin-carbohydrate complex as a stabilizer, wherein the lignin and the carbohydrate are covalently bound to each other.

[0010] A typical use according to the invention of the aqueous dispersion according to the invention is for the production of cellulose fiber webs, such as paper, board, tissue or the like.

[0011] A typical method for producing a cellulosic fiber web (such as paper, board, tissue, etc.) according to the present invention comprises

[0012] - forming a fiber raw material comprising cellulose fibers,

[0013] - forming the fiber raw material into a cellulosic fiber web, and

[0014] - drying the cellulose fiber web, wherein the aqueous dispersion according to the invention is added as an internal size to the fiber raw material and / or as a surface size to the cellulose fiber web.

[0015] The present invention also includes the use of a lignin-carbohydrate complex as a stabilizer for aqueous dispersions of alkyl ketene dimers, wherein the lignin and the carbohydrate are covalently bound to each other as defined herein. Thus, a typical use of an anionic lignin-carbohydrate complex according to the present invention, wherein the lignin and the carbohydrate are covalently bound to each other, is as a stabilizer for aqueous dispersions of alkyl ketene dimers.

[0016] It has now been surprisingly discovered that anionic lignin-carbohydrate complexes can be used as stabilizers for aqueous dispersions of ketene dimers, resulting in stable dispersions with good stability that provide sizing efficiencies as good as or even better than conventional alkyl ketene dispersions. When used as stabilizers, the lignin-carbohydrate complexes allow for increasing or maintaining the content of dispersion components derived from renewable resources while minimizing the amount of components available for food / feed production. Surprisingly, lignin-carbohydrate complexes derived from, for example, wood can be used to replace conventional stabilizers such as starch or synthetic polymers. Furthermore, it is speculated that the use of lignin-carbohydrate complexes may reduce microbial problems and / or deposit formation in the manufacture of cellulose webs, as the complexes may be less suitable for bacteria, etc., at least compared to starch.

[0017] The anionic lignin-carbohydrate complex is present in the water continuous phase (ie, aqueous liquid phase) of the dispersion. Without being bound by theory, it is hypothesized that the lignin-carbohydrate complex interacts with the surface of the ketene dimer particles and prevents agglomeration of the particles.

[0018] The aqueous dispersion of the present invention contains more alkyl ketene dimer than the anionic lignin-carbohydrate complex given in wt% as the active chemical. This means that the alkyl ketene dimer is the main component of the aqueous dispersion, and the anionic lignin-carbohydrate complex essentially acts as a stabilizer for the alkyl ketene dimer particles dispersed in the aqueous continuous phase. The aqueous dispersion may contain 5-40 wt% of alkyl ketene dimer, preferably 7-35 wt% of alkyl ketene dimer, more preferably 10-30 wt% of alkyl ketene dimer, and sometimes even 15-25 wt% of alkyl ketene dimer, calculated on the total weight of the aqueous dispersion.

[0019] According to one embodiment, the aqueous dispersion may contain 0.1-20 wt. %, preferably 1-10 wt. %, more preferably 1-5 wt. %, and sometimes even 1.5-5 wt. % of the anionic lignin-carbohydrate complex, calculated from the total weight of the aqueous dispersion. Advantageously, even with relatively low amounts of the anionic lignin-carbohydrate complex, a good stabilizing effect can be achieved. In this way, the total amount of stabilizer can be reduced while still achieving the desired dispersion stability without compromising other desired properties.

[0020] According to one embodiment of the present invention, the aqueous dispersion may contain the anionic lignin-carbohydrate complex and the alkyl ketene dimer in a weight ratio of 1:2 to 1:8, preferably 1:3 to 1:7, more preferably 1:4 to 1:6 (lignin-carbohydrate complex: alkyl ketene dimer).

[0021] The anionic lignin-carbohydrate complex used as a stabilizer in the present invention is a natural polymer complex comprising lignin and one or more carbohydrates (preferably one or more hemicelluloses) covalently bound to each other. Thus, the lignin-carbohydrate complex is a conjugate of lignin and one or more carbohydrates that are irreversibly bound to each other into a common structure. The anionic lignin-carbohydrate complex may have a branched structure. For example, the lignin or the carbohydrate may form the backbone structure of the complex, and another component (carbohydrate or lignin) may form a side group that is covalently bound to the backbone structure to form a branched structure.

[0022] Lignin-carbohydrate complexes suitable for the present invention can be obtained from the side stream of the pulping process of softwood, hardwood or other cellulosic materials containing lignin. In one embodiment, suitable lignin-carbohydrate complexes can be obtained by enzymatic treatment of the lignin-carbohydrate material derived from wood pulping process. For example, the lignin-carbohydrate complexes can be separated from the side stream of the wood pulping process by filtration (such as membrane filtration) and the separated lignin-carbohydrate material is obtained by enzymatic treatment preferably using laccase. Alternatively, the lignin-carbohydrate complexes can be separated from lignocellulosic materials (such as wood or paper pulp) by using known separation and classification methods. For example, lignin-carbohydrate complexes can be separated by classifying lignin from industrial processes (such as kraft pulping or sulfite pulping). Suitable lignin classification methods include, for example, solvent classification or precipitation classification. In solvent classification, various organic solvents and binary mixtures thereof can be used, such as acetone-hexane, acetone-water, ethanol-water, propylene glycol monomethyl ether-water. Such fractionation methods are described inter alia in Int. J. Biol. Macromolecules 106 (2018) 979-987.

[0023] The lignin-carbohydrate complex used as a stabilizer in the present invention can be formed from lignin and one or more carbohydrates (such as hemicellulose). Preferably, the carbohydrate of the lignin-carbohydrate complex is hemicellulose. The one or more carbohydrates in the lignin-carbohydrate complex can preferably be formed from monosaccharides, such as mannose, galactose, glucose, xylose and / or arabinose, or fragments or residues thereof; or the one or more carbohydrates can be the one or more monosaccharides and / or fragments or residues thereof covalently bound to lignin. The exact amount of one or more monosaccharides in the lignin-carbohydrate complex and their relative ratios depend on the wood species (e.g. hardwood / softwood) that has been used in the pulping process and from which the lignin-carbohydrate complex is derived. Carbohydrates formed from monosaccharides can be present in the lignin-carbohydrate complex in the form of sugar residues, covalently bound to the lignin.

[0024] The anionic lignin-carbohydrate complex may contain various anionic functional groups, such as sulfonate, carboxyl and / or phenolic groups. The lignin-carbohydrate complex may contain, for example, >1300-1700 μmol / g, preferably 1400-1600 μmol / g of sulfonate; 300-500 μmol / g, preferably 350-450 μmol / g of carboxyl groups; and / or 125-250 μmol / g, preferably 150-225 μmol / g of phenolic groups.

[0025] According to a preferred embodiment of the present invention, the anionic lignin-carbohydrate complex is an anionic lignin sulfonate-carbohydrate complex. The anionic lignin sulfonate-carbohydrate complex can be obtained by enzymatic oxidation treatment. For example, it can be obtained by membrane filtration of a pre-hydrolysis mixture from a sulfite pulping process of wood and treated with an enzymatic oxidation treatment, preferably a laccase treatment. Preferably, the filtered pre-hydrolysis mixture is obtained from a sulfite pulping process of wood. The pre-hydrolysis mixture may contain wood-based components and pulping chemicals. Suitable anionic lignin sulfonate-carbohydrate complexes are disclosed in, for example, BioResources 13(4), 7606-7627, 2018, and they are commercially available from Ecohelix AB, Sweden.

[0026] The anionic lignin-carbohydrate complex has an anionic charge density of less than -0.2 meq / g, preferably less than -0.5 meq / g, more preferably less than -0.85 meq / g, measured at pH 7. The anionic charge density of the lignin-carbohydrate complex measured at pH 7 may be from -0.2 meq / g to -2.5 meq / g, preferably from -0.5 meq / g to -2.4 meq / g, more preferably from -0.85 meq / g to -2.3 meq / g. Sometimes, the anionic charge density of the complex measured at pH 7 may be from -0.5 meq / g to -1.75 meq / g, preferably from -0.85 to -1.5 meq / g. The anionic lignin-carbohydrate complex may even have an anionic charge density of -2.0 meq / g to -2.3 meq / g, preferably -2.1 meq / g to -2.2 meq / g or to -2.15 meq / g, measured at pH 7. All charge density values are given on a dry matter basis and were measured using a Mutek particle charge detector.

[0027] The weight average molecular weight MW of the lignin-carbohydrate complex may be >3500 g / mol, preferably >4000 g / mol, more preferably >5000 g / mol. For example, the weight average molecular weight MW of the anionic lignin-carbohydrate complex may be in the range of 3500-90000 g / mol, preferably 4000-80000 g / mol, more preferably 5000-70000 g / mol.

[0028] According to one embodiment, the lignin-carbohydrate complex used may have a relatively high molecular weight. The high molecular weight may affect the behavior and / or structural orientation of the lignin-carbohydrate complex at the boundary between the alkyl ketene dimer particles and the water continuous phase, which may have a positive effect on the dispersion stability. The weight average molecular weight MW of the lignin-carbohydrate complex may be >8000 g / mol, preferably >10000 g / mol, more preferably >12000 g / mol or >15000 g / mol, sometimes even >20000 g / mol or >25000 g / mol. The weight average molecular weight MW of the lignin-saccharide complex may be in the range of 8000-50000 g / mol or 10000-45000 g / mol, preferably 12000-40000 g / mol or 15000-37000 g / mol. Sometimes the weight average molecular weight MW of the lignin-carbohydrate complex may be in the range of 20,000-45,000 g / mol, preferably 25,000-40,000 g / mol, more preferably 25,000-35,000 g / mol or 25,000-27,000 g / mol. The weight average molecular weight MW of the lignin-carbohydrate complex may also be in the range of 15,000-120,000 g / mol or 20,000-90,000 g / mol, preferably 25,000-80,000 g / mol, more preferably 30,000-70,000 g / mol.

[0029] The anionic lignin-carbohydrate complex may comprise lignin and one or more carbohydrates (preferably one or more hemicelluloses) in a ratio of 90:10 to 10:90, preferably 80:20 to 20:80, more preferably 75:25 to 25:75 (lignin carbohydrates), i.e. a lignin: carbohydrate ratio of 90:10 to 10:90, preferably 80:20 to 20:80, more preferably 75:25 to 25:75. According to one embodiment of the present invention, the anionic lignin-carbohydrate complex may comprise at least 10% by weight, sometimes preferably at least 15% by weight, of one or more carbohydrates, preferably one or more hemicelluloses, calculated from the total dry weight of the complex. The anionic lignin-carbohydrate complex may comprise 10-40% by weight, preferably 10-30% by weight or 15-25% by weight of one or more carbohydrates, calculated from the total dry weight of the complex.

[0030] According to one embodiment of the present invention, the aqueous dispersion may contain 1-25 wt. %, preferably 5-20 wt. %, and more preferably 8-18 wt. % of alkyl ketene dimer, calculated from the total dry weight of the aqueous dispersion. The alkyl ketene dimer particles dispersed in the aqueous continuous phase of the dispersion have a particle size D95 ≤ 5 μm, preferably in the range of 0.5-5 μm, and more preferably 1-4.5 μm. The particle size D95 indicates that 95% of the total particles are smaller than a given value. Therefore, when used as a stabilizer, the lignin-carbohydrate complex provides a stable dispersion with a high alkyl ketene dimer content and a particle size similar to that of dispersions using conventional stabilizers.

[0031] The alkyl ketene dimer used in the dispersion may be a C14-C22 alkyl ketene dimer, preferably a C16-C18 alkyl ketene dimer, or a mixture thereof.

[0032] The aqueous dispersion of alkyl ketene dimer may further comprise a surfactant, a biocide and / or alum.

[0033] According to one embodiment, the aqueous dispersion may contain a surfactant, which may be selected from the group consisting of: condensation products of phenolsulfonic acid and formaldehyde; condensation products of naphthalenesulfonic acid and formaldehyde; and condensation products of naphthalenesulfonic acid, phenol, formaldehyde and urea, wherein the sulfonic acid groups of the condensation products may be protonated or deprotonated. Calculated from the gross weight of the aqueous dispersion, the aqueous dispersion may contain 0.01-1% by weight, preferably 0.05-0.7% by weight, more preferably 0.1-0.5% by weight of a surfactant. In the case where the dispersion contains two or more surfactants, the given value represents the total amount of all surfactants present.

[0034] The aqueous dispersion may also contain a biocide. The biocide may be selected from 5-chloro-2-methyl-2H-isothiazolin-3-one, 2-methyl-2H-isothiazolin-3-one, 2-bromo-2-nitropropane-1,3-diol, or any mixture thereof. According to one embodiment of the present invention, the aqueous dispersion may contain 0.001-0.015 wt. %, preferably 0.001-0.01 wt. %, of biocide, calculated based on the total weight of the aqueous dispersion. In the case where the aqueous dispersion contains two or more biocides, the given value represents the total amount of all biocides present.

[0035] The aqueous dispersion may contain alum. According to one embodiment, the aqueous dispersion may contain 0.1-5% by weight, preferably 0.2-4% by weight, more preferably 0.5-3% by weight of alum, calculated from the total weight of the aqueous dispersion. However, the presence of alum or other aluminum compounds is not mandatory, and according to one embodiment, the aqueous dispersion does not contain aluminum compounds such as alum.

[0036] According to a preferred embodiment, the aqueous dispersion of alkyl ketene dimer does not contain starch and / or synthetic polymers other than the alkyl ketene dimer. The aqueous continuous phase of the dispersion preferably does not contain any solvent other than water, that is, the solvent forming the continuous phase of the dispersion is preferably only water.

[0037] The pH value of the aqueous dispersion of the alkyl ketene dimer may be ≤ 5, preferably ≤ 4. The pH value of the dispersion may be, for example, in the range of 2 to 5, preferably 3 to 4. The pH of the dispersion may be adjusted to the desired level using conventionally accepted methods, for example, by adding a suitable strong acid such as sulfuric acid and / or a buffer.

[0038] The aqueous dispersion of the alkyl ketene dimer can have a stability of at least one week, preferably at least two weeks, and more preferably at least three weeks, as measured by the change in dispersion viscosity over time. The viscosity of the aqueous dispersion preferably changes by less than 10%, more preferably by less than 7.5%, over a specified time period. This means that the viscosity of the aqueous dispersion is measured directly after preparation, and a first viscosity value is obtained. After allowing the aqueous dispersion to stand for a specified period of time, such as one, two, or three weeks, the viscosity of the dispersion is remeasured, and a second viscosity value is obtained. The aqueous dispersion is considered stable when the difference between the first and second viscosity values is less than 10%, preferably less than 7.5%, and more preferably less than 5% of the first viscosity value.

[0039] The aqueous dispersion can be obtained by homogenizing molten alkyl ketene dimer wax in the aqueous continuous phase in the presence of the stabilizer. Using the lignin-carbohydrate complex as a stabilizer allows conventional methods to be used to produce dispersions of alkyl ketene dimer, which is advantageous in terms of large-scale production.

[0040] The aqueous dispersion of the present invention can be used to produce cellulose fiber webs such as paper, board, tissue, and the like. In particular, the aqueous dispersion can be used as an internal sizing agent or surface sizing agent for cellulose fiber webs such as paper or board. When used as an internal sizing agent for producing paper, board, and the like, the aqueous dispersion can be added to a fiber suspension containing an amount of cellulose fibers such that the amount of alkyl ketene dimer added is in the range of 0.25-5 kg / metric ton or 1-5 kg / metric ton, given as active agent per dry weight of the fiber web produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Shown are the sizing properties of Dispersion A, an aqueous dispersion of alkyl ketene dimer stabilized with a lignin-carbohydrate complex; Dispersion B, a dispersion of alkyl ketene dimer stabilized with starch; and Dispersion C, a dispersion of alkyl ketene dimer stabilized with polyamidoamine epichlorohydrin (PAE). DETAILED DESCRIPTION

[0042] experiment

[0043] Some embodiments of the invention are described in the following non-limiting examples.

[0044] Example 1: Preparation of a stable alkyl ketene dispersion

[0045] A lignin-carbohydrate complex obtained as a 20 wt% solution from Ecohelix AB, Sweden, was used as a stabilizer for dispersion A (see Table 1). The 2 wt% solution of the lignin-carbohydrate complex had a pH of 5.5, a viscosity of 1.2 mPas and a charge density of -45 μeq / g.

[0046] Dispersion A was prepared by diluting the lignin-carbohydrate complex solution (20 wt%) with 39.7 g of water to the desired concentration. Subsequently, a surfactant was added to the lignin-carbohydrate complex solution and the pH of the solution was adjusted to 4.5 with sulfuric acid. The solution was heated to a temperature of 90° C. and molten alkyl ketene dimer wax was added, followed by filtration. A T50 homogenizer was used for the pre-dispersion step and homogenization was performed in a laboratory homogenizer. If any signs of wax precipitation were observed on the surface, a mechanical stirrer was used to prevent stratification. The dispersion was then cooled to a temperature of approximately 25-27°C, and a biocide and alum were added to the dispersion. The pH of the dispersion was adjusted to 3.3-3.8 and diluted with water to a concentration of approximately 15% by weight.

[0047] The compositions of the alkyl ketene dimer dispersions are shown in Table 1. Dispersion B is a commercial alkyl ketene dimer dispersion stabilized with starch, and dispersion C is a commercial alkyl ketene dimer dispersion stabilized with polyamidoamine epichlorohydrin (PAE). Dispersions B and C serve as references.

[0048] Table 1 Composition of alkyl ketene dimer dispersion

[0049]

[0050] During storage at room temperature for one week, the stability of Dispersion A was similar to that of Dispersions B and C. The stability of Dispersion A was deemed acceptable by visual observation and confirmed by viscosity measurement. Over the specified period of one week, the viscosity of Dispersion A changed by only 6.7%. After storage at room temperature for one week, the viscosity of the dispersions on Day 0 was 3 mPas and 3.3 mPas.

[0051] Example 2 Evaluation of the Sizing Effect of Stable Alkyl Ketene Dimer Dispersions

[0052] In the laboratory, the alkyl ketene dispersion of Example 1 was used to make handsheets.

[0053] About 98g / m 2 The handsheets were made on a KCL paper machine. The furnish used was a 50:50 blend of pine and birch pulp. The furnish pH was 7.2.

[0054] Cationic cooked starch (5 kg / ton dry matter) and cationic polyacrylamide (0.1 kg / ton dry matter) were added as retention aids. Alkyl ketene dispersions were added in amounts of 0.25 kg / ton dry matter, 0.75 kg / ton dry matter, and 1.2 kg / ton dry matter.

[0055] The handsheets were dried in a drying oven and cured after drying at 105° C. The Cobb 60 value was determined according to standard ISO 535, T441.

[0056] The results are as follows Figure 1 shown. Figure 1 The following sizing properties are shown: Dispersion A, which is an alkyl ketene dimer dispersion stabilized with a lignin-carbohydrate complex (solid circles, dashed line); Dispersion B, which is a commercial alkyl ketene dimer dispersion stabilized with starch (open diamonds, dotted line); and Dispersion C, which is a commercial alkyl ketene dimer dispersion stabilized with polyamidoamine epichlorohydrin (open circles, solid line).

[0057] It can be seen that the sizing performance (Cobb60 value) of dispersion A stabilized with lignin-carbohydrate complex is as good as or better than that of commercial dispersions B and C using starch or synthetic polymers as stabilizers. Quite unexpectedly, the sizing performance of dispersion A is comparable to that of dispersion C stabilized with a synthetic polymer.

[0058] The proposed project has received funding from the Biobased Industries Consortium (JU) under grant agreement No. 837866. JU is supported by the European Union’s Horizon 2020 research and innovation programme and the Biobased Industries Consortium.

[0059] Even though the present invention has been described with reference to what are currently the most practical and preferred embodiments, it should be understood that the present invention should not be limited to the above-described embodiments, but the present invention is intended to cover different modifications and equivalent technical solutions within the scope of the appended claims.

Claims

1. An aqueous dispersion of an alkyl ketene dimer, comprising alkyl ketene dimer particles dispersed in an aqueous continuous phase, wherein the aqueous dispersion comprises an anionic lignin-carbohydrate complex as a stabilizer, wherein the lignin and the carbohydrate are covalently bound to each other.

2. The aqueous dispersion according to claim 1, characterized in that The aqueous dispersion comprises 0.1-20 wt. %, preferably 1-10 wt. %, more preferably 1-5 wt. % of the anionic lignin-carbohydrate complex, calculated on the total weight of the aqueous dispersion.

3. The aqueous dispersion according to claim 1 or 2, characterized in that The aqueous dispersion comprises 5-40% by weight, preferably 7-35% by weight, more preferably 10-30% by weight, sometimes even 15-25% by weight, of alkyl ketene dimer, calculated on the total weight of the aqueous dispersion.

4. The aqueous dispersion according to claim 1, 2 or 3, characterized in that The anionic lignin-carbohydrate complex comprises anionic functional groups selected from sulfonate, carboxyl and / or phenolic groups.

5. The aqueous dispersion according to any one of the preceding claims 1 to 4, characterized in that The lignin-carbohydrate complex has a weight average molecular weight MW in the range of 3500-90000 g / mol, preferably 4000-80000 g / mol, more preferably 5000-70000 g / mol.

6. Aqueous dispersion according to any one of the preceding claims 1 to 5, characterized in that The anionic lignin-carbohydrate complex has an anionic charge density measured at pH 7 of less than -0.2 meq / g, preferably less than -0.5 meq / g, more preferably less than -0.85 meq / g.

7. Aqueous dispersion according to any one of the preceding claims 1 to 6, characterized in that The lignin-carbohydrate complex comprises at least 10 wt. %, preferably at least 15 wt. % carbohydrates, calculated on the total dry weight of the complex.

8. Aqueous dispersion according to any one of the preceding claims 1 to 7, characterized in that The lignin-carbohydrate complex has a lignin:carbohydrate ratio of 90:10 to 10:90, preferably 80:20 to 20:80, more preferably 75:25 to 25:

75.

9. Aqueous dispersion according to any one of the preceding claims 1 to 8, characterized in that The carbohydrate of the lignin-carbohydrate complex is hemicellulose.

10. Aqueous dispersion according to any one of the preceding claims 1 to 9, characterized in that The carbohydrates are formed by monosaccharides such as galactose, glucose, mannose, arabinose, which are covalently bound to lignin.

11. Aqueous dispersion according to any one of the preceding claims 1 to 10, characterized in that The aqueous dispersion comprises the anionic lignin-carbohydrate complex and the alkyl ketene dimer in a weight ratio of 1:2 to 1:8, preferably 1:3 to 1:7, more preferably 1:4 to 1:6 (lignin-carbohydrate complex:alkyl ketene dimer).

12. Aqueous dispersion according to any one of the preceding claims 1 to 11, characterized in that The alkyl ketene dimer is a C14-C22 alkyl ketene dimer, preferably a C16-C18 alkyl ketene dimer.

13. Aqueous dispersion according to any one of the preceding claims 1 to 12, characterized in that The aqueous dispersion also contains a surfactant, a biocide and / or alum.

14. The aqueous dispersion according to claim 13, characterized in that The aqueous dispersion comprises 0.01-1 wt. %, preferably 0.05-0.7 wt. %, more preferably 0.1-0.5 wt. % of a surfactant, calculated on the total weight of the aqueous dispersion, - 0.001-0.015% by weight, preferably 0.001-0.01% by weight, of a biocide, and / or - 0.1-5% by weight, preferably 0.2-4% by weight, more preferably 0.5-3% by weight of alum.

15. Aqueous dispersion according to any one of the preceding claims 1 to 14, characterized in that The alkyl ketene dimer particles have a particle size D95 of ≤5 μm, preferably in the range of 0.5-5 μm, preferably 1-4.5 μm.

16. Aqueous dispersion according to any one of the preceding claims 1 to 15, characterized in that The aqueous dispersion is obtained by homogenizing the alkyl ketene dimer in an aqueous phase in the presence of a stabilizer.

17. Use of the aqueous dispersion according to any one of claims 1 to 16 for the production of cellulose fiber webs such as paper, board, tissue, etc., preferably as internal sizing agent or for surface sizing.

18. Use of anionic lignin-carbohydrate complexes as stabilizers for aqueous dispersions of alkyl ketene dimers, wherein the lignin and the carbohydrate are covalently bound to one another.

19. The use according to claim 18, characterized in that The anionic lignin-carbohydrate complex comprises anionic functional groups selected from sulfonate, carboxyl and / or phenolic groups; and / or has an anionic charge density measured at pH 7 of less than -0.2 meq / g, preferably less than -0.5 meq / g, more preferably less than -0.85 meq / g.

20. The use according to claim 18 or 19, characterized in that The carbohydrates of the anionic lignin-carbohydrate complex are formed from monosaccharides such as galactose, glucose, mannose, arabinose, or fragments or residues thereof.

21. A method for producing a cellulosic fiber web such as paper, board, tissue, etc., the method comprising - forming a fiber raw material comprising cellulose fibers, - forming the fiber raw material into a cellulosic fiber web, and - drying the cellulose fiber web, The aqueous dispersion according to any one of claims 1 to 16 is added as an internal sizing agent to the fiber raw material and / or as a surface sizing agent to the cellulose fiber web.

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