EP4638863A1

EP4638863A1 - Aqueous dispersion of alkyl ketene dimer and its use

Info

Publication number: EP4638863A1
Application number: EP23833173.0A
Authority: EP
Inventors: Eija KORTE; Nina SNEITZ; Elisabeth LACKINGER-CSARMANN; Jennifer RISER; Jaakko Hiltunen
Original assignee: Kemira Oyj
Current assignee: Kemira Oyj
Priority date: 2022-12-21
Filing date: 2023-12-20
Publication date: 2025-10-29
Also published as: KR20250125407A; CN120513331A; WO2024134029A1

Abstract

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

Description

AQUEOUS DISPERSION OF ALKYL KETENE DIMER AND ITS USE

The present invention relates to an aqueous dispersion of alkyl ketene dimer and its use according to the preambles of enclosed independent claims.

Sizing agents are used in manufacture of paper, board or the like for decreasing or preventing of the penetration of water, moisture and other liquids, such as printing inks, into the structure of the paper, board or the like. In internal sizing, the sizing agent is added into the fibre furnish, where it interacts with the fibres in order to increase the water repellency of the paper or board. In surface sizing, the sizing agent can be added on the surface of the partially or wholly dried web of paper, board or the like, for sealing off the surface of the web and thus achieving a decrease in the penetration of liquids, especially water, and moisture into the web.

Alkyl ketene dimer is a commonly used sizing agent in the manufacture of paper, board or the like. Alkyl ketene dimer is typically supplied in form of an aqueous dispersion, prepared by a chemical manufacturer and transported to the mill location. The dispersion should have appropriate stability to allow its transport from the manufacturing site to the location of use at the mill and also to allow a certain storage time at the mill, if needed. The alkyl ketene dispersions are usually stabilized by using starch or synthetic polymers as stabilizing agents. However, the traditional stabilizing agents are not optimal in view of the on-going need for increased sustainability. Synthetic polymers are usually manufactured from petroleum-based non-renewable sources. Starch, on the other hand, is obtained from renewable sources, but it is usually produced from plants that could be used for feeding humans and/or animals. Growing plants for starch production use valuable farming land that could be used for food production instead. Therefore, it would be beneficial to find new stabilizing agents, which would be bio-based, renewable and originate from natural sources that primarily cannot be used as food or feed production. Use of starch as a stabilizing agent in sizing dispersions may also cause an increased risk for bacterial growth and deposit problems in the manufacturing process of paper or board, as the starch provides nutrition for bacteria existing in the process.

In view of the above, there is a need for new effective stabilizing agent that can be used for stabilizing aqueous dispersions of alkyl ketene dimer. Under the present strive for sustainability the stabilizing agent should originate from renewable sources and should not be based on petrochemical products.

An object of the present invention is to minimise or even eliminate the disadvantages existing in the prior art.

An object of the present invention is also to provide an aqueous dispersion of alkyl ketene dimer with a sustainable stabilizing agent, which provides the dispersion with good stability as well as effective performance in sizing.

These objects are attained with the invention having the characteristics presented below in the characterising parts of the independent claims. Some preferred embodiments of the invention are presented in the dependent claims. The features recited in the dependent claims are freely combinable with each other unless otherwise explicitly stated. Furthermore, all features and advantages described in the specification and the claims apply for all aspects of the invention, unless otherwise explicitly stated.

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 as a stabilizing agent an anionic lignin- carbohydrate complex where lignin and carbohydrate are covalently bound with each other. A typical use according to the present invention of the aqueous dispersion according to the invention is for manufacture of cellulosic fibrous webs, such as paper, board, tissue or the like.

A typical method according to the present invention for manufacturing of a cellulosic fibrous web, such as paper, board, tissue or the like, comprises

- forming a fibre stock comprising cellulosic fibres,

- forming the fibre stock into a cellulosic fibrous web, and

- drying the cellulosic fibrous web, wherein an aqueous dispersion according to the invention is added to the fibre stock as an internal sizing agent and/or on the cellulosic fibrous web as a surface sizing agent.

The present invention also encompasses the use of lignin-carbohydrate complex where lignin and carbohydrate are covalently bound with each other, as defined in this text, as stabilizing agent for an aqueous dispersion of alkyl ketene dimer. A typical use according to the present invention of an anionic lignin-carbohydrate complex where lignin and carbohydrate are covalently bound with each other is thus as a stabilizing agent for an aqueous dispersion of alkyl ketene dimer.

Now it has been surprisingly found out that an anionic lignin carbohydrate complex can be used as a stabilizing agent for an aqueous dispersion of alkyl ketene dimer, whereby it is possible to obtain a stable dispersion which has a good stability and which provides as good as, or even better, sizing efficiency as conventional alkyl ketene dispersions. The lignin-carbohydrate complex, when used as a stabilizing agent, allows the possibility to increase or maintain the content of the dispersion components originating from renewable sources while minimising the amount of components that could be used for food/feed production. Unexpectedly, a lignin-carbohydrate complex, originating e.g. from wood, can be used to replace conventional stabilizing agents, such as starch or synthetic polymers. Furthermore, it is speculated that use of lignin-carbohydrate complex might reduce microbiological problems and/or deposit formation in manufacture of cellulosic webs, as the said complex is probably less palatable for bacteria and the like, at least when compared to starch.

The anionic lignin-carbohydrate complex is present in the aqueous continuous phase, i.e. aqueous liquid phase, of the dispersion. It is assumed, without being bound by a theory, that the lignin-carbohydrate complex interacts with the surface of the alkyl ketene dimer particles and prevents the agglomeration of the particles.

The aqueous dispersion of the present invention comprises more alkyl ketene dimer than the anionic lignin-carbohydrate complex, given as weight-%, as active chemical. This means that the alkyl ketene dimer is the main component of the aqueous dispersion, and the anionic lignin-carbohydrate complex functions essentially as a stabilizing agent for the alkyl ketene dimer particles dispersed in the aqueous continuous phase. The aqueous dispersion may comprise 5 - 40 weight-%, preferably 7 - 35 weight-%, more preferably 10 - 30 weight-%, sometimes even 15 - 25 weight- %, of alkyl ketene dimer, calculated from total weight of the aqueous dispersion.

According to one embodiment the aqueous dispersion may comprise 0.1 - 20 weight- %, preferably 1 - 10 weight-%, more preferably 1 - 5 weight-%, sometimes even 1.5 - 5 weight-%, of the anionic lignin-carbohydrate complex, calculated from total weight of the aqueous dispersion. It is advantageous that a good stabilization effect may be obtained even with relatively low amount of the anionic lignin-carbohydrate complex. In this manner it may be possible to reduce the total amount of stabilizing agent, and still obtain desired dispersion stability without compromising other desired properties.

According to one embodiment of the present invention the aqueous dispersion may comprise the anionic lignin-carbohydrate complex and alkyl ketene dimer in a weight ratio of from 1 :2 to 1 :8, preferably from 1 :3 to 1 :7, more preferably from 1 :4 to 1 :6 (lignin- carbohydrate complex:alkyl ketene dimer). The anionic lignin-carbohydrate complex, which is used as a stabilizing agent in the present invention, is a natural polymeric complex that comprises lignin and carbohydrate(s), preferably hemicellulose(s), covalently bound with each other. The lignin-carbohydrate complex is thus a conjugate of lignin and carbohydrate(s), which are irreversibly bound which each other to a common structure. The anionic lignin- carbohydrate complex may have a branched structure. For example, the lignin or the carbohydrate may form a backbone structure for the complex and the other component, either carbohydrate or lignin, may form pendant groups, which are covalently bound to the backbone structure in order to form a branched structure.

The lignin-carbohydrate complex, suitable for use in the present invention, may be obtained from a side stream of a pulping process of softwood, hardwood or other cellulosic material comprising lignin. In one embodiment, a suitable lignin-carbohydrate complex may be obtained by enzymatic treatment of lignin-carbohydrate material originating from a wood pulping process. For example, the lignin-carbohydrate complex may be obtained by isolating lignin-carbohydrate material from side streams of wood pulping processes by filtration, such as membrane filtration, and by processing the said isolated lignin-carbohydrate material by enzymatic processing employing preferably laccase enzyme. Alternatively, lignin-carbohydrate complex may be isolated from lignocellulosic material, such as wood or pulp, by using separation and fractionation methods, known as such. For example, it is possible to isolate lignin-carbohydrate complexes by fractionating lignin from an industrial process, such as kraft pulping or sulphite pulping. Suitable lignin fractionating methods include, for example, solvent fractionation or precipitation fractionation. In solvent fractionation various organic solvents and their binary mixtures may be employed, such as acetone-hexane, acetone-water, ethanol-water, propyleneglycol monomethyl ether-water. Such fractionation method is described, inter alia, in Int. J. Biol. Macromolecules 106 (2018) 979-987.

The lignin-carbohydrate complex, which is used as stabilizing agent in the present invention, may be formed of lignin and one or more carbohydrates, such as hemicelluloses. Preferably the carbohydrate of the lignin-carbohydrate complex is a hemicellulose. The carbohydrate(s) in the lignin-carbohydrate complex may preferably be formed from monosaccharides, such as mannose, galactose, glucose, xylose and/or arabinose, or their fragments or residues; or the carbohydrate(s) may be the said monosaccharide(s) and/or their fragments or residues, covalently bound to lignin. The exact amount of the monosaccharide(s) in the lignin-carbohydrate complex and their relative ratios depend on the wood species, e.g. hardwood/softwood, which has been used in the pulping process and from which the lignin-carbohydrate complex originates. The carbohydrates formed from monosaccharides may be present in the lignin- carbohydrate complex as sugar residues, covalently bound to the lignin.

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

According to one preferable embodiment of the invention the anionic lignin- carbohydrate complex is an anionic lignosulfonate-carbohydrate complex. The anionic lignosulfonate-carbohydrate complex may be obtained by an enzymatic oxidative treatment. It can be obtained, for example, by membrane filtration of a pre-hydrolysis mixture from a sulphite pulping process of wood, and treated by an enzymatic oxidative treatment, preferably by a laccase enzyme. Preferably the filtered pre-hydrolysis mixture is obtained from a sulphite pulping process of wood. The pre-hydrolysis mixture may contain wood-based components and pulping chemicals. Suitable anionic lignosulfonate-carbohydrate complexes are disclosed e.g. in BioResources 13(4), 7606 - 7627, 2018, and they are commercially available from Ecohelix AB, Sweden.

The anionic lignin-carbohydrate complex may have an anionic charge density 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 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, measured at pH 7. Sometimes the anionic charge density of the complex may be from -0.5 meq/g to -1 .75 meq/g, preferably from -0.85 to -1.5 meq/g, measured at pH 7. The anionic lignin-carbohydrate complex may even have an anionic charge density from -2.0 meq/g to -2.3 meq/g, preferably from - 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 as per dry substance and measured by using a Mutek Particle Charge Detector.

The lignin-carbohydrate complex may have a weight average molecular weight MW >3500 g/mol, preferably >4000 g/mol, more preferably > 5000 g/mol. For example, the anionic lignin-carbohydrate complex may have the weight average molecular weight MW in a range of 3500 - 90 000 g/mol, preferably 4 000 - 80 000 g/mol, more preferably 5000 - 70 000 g/mol.

According to one embodiment, the used lignin-carbohydrate complex may have relatively high molecular weight. The high molecular weight may have an impact on the behaviour and/or structural orientation of the lignin-carbohydrate complex at the boundary between the particles of alkyl ketene dimer and the aqueous continuous phase, which may have positive effect on dispersion stability. The lignin-carbohydrate complex may have a weight average molecular weight MW >8000 g/mol, preferably >10 000 g/mol, more preferably >12 000 g/mol or >15 000 g/mol, sometimes even >20 000 g/mol or >25 000 g/mol. The lignin-carbohydrate complex may have the weight average molecular weight MW in a range of 8 000 - 50 000 g/mol or 10 000 - 45 000 g/mol, preferably 12 000 - 40 000 g/mol or 15 000 - 37 000 g/mol. Sometimes the lignin-carbohydrate complex may have the weight average molecular weight MW in a 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. It is also possible that the lignin- carbohydrate complex may have the weight average molecular weight MW in a 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.

The anionic lignin-carbohydrate complex may comprise lignin and carbohydrate(s), preferably hemicellulose(s), in a ratio from 90:10 to 10:90, preferably from 80:20 to 20:80, more preferably from 75:25 to 25:75 (lignimcarbohydrate), i.e. have a lignin:carbohydrate ratio from 90:10 to 10:90, preferably from 80:20 to 20:80, more preferably from 75:25 to 25:75. According to one embodiment of the invention the anionic lignin-carbohydrate complex may comprise at least 10 weight-%, sometimes preferably at least 15 weight-%, of carbohydrate(s), preferably hemicellulose(s), calculated from total dry weight of the complex. The anionic lignin-carbohydrate complex may comprise carbohydrate(s) in a range of 10 - 40 weight-%, preferably 10 - 30 weight-% or 15 - 25 weight-%, calculated from total dry weight of the complex.

According to one embodiment of the present invention the aqueous dispersion may comprise 1 - 25 weight-%, preferably 5 - 20 weight-%, more preferably 8 - 18 weight- %, of alkyl ketene dimer, calculated from total weight of the aqueous dispersion. The alkyl ketene dimer particles, which are dispersed in the aqueous continuous phase of the dispersion, may have a particle size D95 <5 pm, preferably in a range of 0.5 - 5 pm, more preferably 1 - 4.5 pm. Particle size D95 indicates that 95% of the total particles are smaller than the given value. The lignin-carbohydrate complex, when used as stabilizing agent, thus provides stable dispersions with high alkyl ketene dimer content, and with particle size which is similar to the dispersions employing conventional stabilizing agents.

The alkyl ketene dimer used in the dispersion may be C14-C22 alkyl ketene dimer, preferably C16-C18 alkyl ketene dimer, or their mixture.

The aqueous dispersion of alkyl ketene dimer may further comprise surfactant(s), biocide(s) and/or alum. According to one embodiment, the aqueous dispersion may comprise one or more surfactants, which may be selected from a group comprising condensation products of phenol sulphonic acid and formaldehyde; condensation products of naphthalene sulphonic acid and formaldehyde; and condensation products of naphthalene sulphonic acid, phenol, formaldehyde and urea, wherein sulphonic acid groups of the condensation products may be protonated or deprotonated. The aqueous dispersion may comprise 0.01 - 1 weight-%, preferably 0.05 - 0.7 weight-%, more preferably 0.1

- 0.5 weight-%, of surfactant(s), calculated from the total weight of the dispersion. In case the dispersion comprises two or more surfactants, the given values indicate the total amount of all surfactants present.

The aqueous dispersion may further comprise one or more biocides. The biocides may be selected from 5-chloro-2-methyl-2H-isothiazolin-3-one, 2-methyl-2-H-isothiazolin-3- one, 2-bromo-2-nitropropane-1 ,3-diol, or any of their mixtures. According to one embodiment of the invention, the aqueous dispersion may comprise 0.001 - 0.015 weight-%, preferably 0.001 - 0.01 weight-%, of biocide(s) calculated from the total weight of the aqueous dispersion. In case the aqueous dispersion comprises two or more biocides, the given values indicate the total amount of all biocides present.

The aqueous dispersion may comprise alum. According to one embodiment the aqueous dispersion may comprise alum in amount of 0.1 - 5 weight-%, preferably 0.2

- 4 weight-%, more preferably 0.5 - 3 weight-%, of alum, calculated from the total weight of the aqueous dispersion. However, the presence of alum or other aluminium compounds is not mandatory, and according to one embodiment, the aqueous dispersion is free of aluminium compounds, such as alum.

According to one preferable embodiment the aqueous dispersion of alkyl ketene dimer is free of starch and/or of synthetic polymers other than the alkyl ketene dimer. The aqueous continuous phase of the dispersion preferably does not contain other solvents than water, i.e. the solvent forming the continuous phase of the dispersion is preferably solely water. The aqueous dispersion of alkyl ketene dimer may have a pH value <5, preferably <4. The pH of the dispersion may be, for example, in a range from 2 to 5, preferably from 3 to 4. The pH of the dispersion may be adjusted to desired level by using conventionally accepted methods, e.g. by addition of a suitable strong acid, such as sulphuric acid, and/or buffering agents.

The aqueous dispersion of alkyl ketene dimer may have a stability of at least one week, preferably at least two weeks, more preferably at least three weeks, measured as a change of dispersion viscosity, as a function of time. The viscosity of the aqueous dispersion preferably changes less than 10%, more preferably less than 7.5%, within the defined time period. This means that the viscosity of the aqueous dispersion is measured directly after the preparation of the aqueous dispersion and a first viscosity value is obtained. After the aqueous dispersion is allowed to stand a defined time period, e.g. 1 week, 2 weeks or 3 weeks, the viscosity of the dispersion is measured anew, and a second viscosity value is obtained. The aqueous dispersion is considered stable, when the difference between the first viscosity value and the second viscosity value is less than 10%, preferably less than 7.5%, more preferably less than 5% of the first viscosity value.

The aqueous dispersion may be obtained by homogenizing the molten alkyl ketene dimer wax in the aqueous continuous phase in a presence of the stabilizing agent. The use of lignin-carbohydrate complex as stabilizing agent allows the use of conventional methods for manufacturing dispersions of alkyl ketene dimer, which is advantageous in view of large-scale production.

The aqueous dispersion of the present invention may be used in manufacture of cellulosic fibrous webs, such as paper, board, tissue or the like. Especially, the aqueous dispersion may be used as an internal sizing agent or for surface sizing for cellulosic fibrous webs, such as paper or board. When used as an internal sizing agent for manufacture of paper, board or the like, the aqueous dispersion may be added to a fibre suspension comprising cellulosic fibres in an amount that results alkyl ketene dimer addition in a range of 0.25 - 5 kg/metric ton or 1 - 5 kg/metric ton, given as active agent per produced fibrous web, as dry.

DESCRIPTION OF THE DRAWINGS

Fig. 1 shows the sizing performance of Dispersion A which is an aqueous dispersion of alkyl ketene dimer, stabilized with lignin-carbohydrate complex; Dispersion B which is a dispersion of alkyl ketene dimer, stabilized with starch; and Dispersion C which is a dispersion of alkyl ketene dimer, stabilized with polyamidoamine epichlorohydrin (PAE).

EXPERIMENTAL

Some embodiments of the present invention are described in the following non-limiting examples.

Example 1 : Preparation of stabilized alkyl ketene dispersion

Lignin-carbohydrate complex obtained as 20 weight-% solution from Ecohelix AB, Sweden, was used as a stabilizing agent for Dispersion A (see Table 1 ). 2 weight-% solution of the lignin-carbohydrate complex had pH 5.5, viscosity 1.2 mPas and charge density -45 peq/g.

Dispersion A was prepared by diluting the lignin-carbohydrate complex solution (20 weight-%) to the desired concentration with 39.7 g of water. After that the surfactant was added to the lignin-carbohydrate complex solution and pH of the solution was adjusted to 4.5 with sulphuric acid. Solution was heated to a temperature of 90 °C and melted alkyl ketene dimer wax added, followed by pre-dispersing step with Ultra- Turrax® T50 homogenizer and homogenization in a laboratory homogenizer. If any signs of wax precipitation were observed on the surface, a mechanical blender was used to avoid the layering effect. After that the dispersion was cooled to a temperature ca 25 -27 °C, and a biocide and alum was added to the dispersion. pH of the dispersion was adjusted to 3.3 - 3.8 and diluted to about 15 weight-% concentration with water. The compositions of alkyl ketene dimer dispersion are given in Table 1. Dispersion B was a commercial alkyl ketene dimer dispersion stabilized with starch, and Dispersion C was a commercial alkyl ketene dimer dispersion stabilized with polyamidoamine epichlorohydrin (PAE). Dispersions B and C were used as a reference.

Table 1 Compositions of alkyl ketene dimer dispersions

During one week storage in room temperature the stability of Dispersion A was similar to the stability of Dispersion B and Dispersion C. The stability of Dispersion A was deemed acceptable by visual observation and confirmed by viscosity measurements. The viscosity of Dispersion A changed only 6.7% within the defined time period of one week. The viscosity of the dispersion at day 0 was 3 mPas and 3.3 mPas after one week storage at room temperature.

Example 2 Evaluation of the Sizing Effect of Stabilized Alkyl Ketene Dimer Dispersions

Alkyl ketene dispersions of Example 1 were used in manufacture of handsheets in laboratory.

Handsheets, about 98 g/m², were made on a KCL type paper machine former. The used furnish was a 50:50 blend of pinewood pulp and birch pulp. Furnish pH was 7.2. Cationic cooked starch, 5 kg/ton dry, and cationic polyacrylamide 0.1 kg/ton dry, were added as retention agents. Alkyl ketene dispersion was dosed in amount of 0.25 kg/ton dry, 0.75 kg/ton dry and 1.2 kg/ton dry.

Handsheets were dried in a drying cabinet and cured after drying at 105 °C. Cobb60 values were determined according to standard ISO 535, T441 .

The results are shown in Figure 1 . Figure 1 shows the sizing performance of Dispersion A which was an alkyl ketene dimer dispersion stabilized with lignin-carbohydrate complex (filled circles, broken line), of Dispersion B which was a commercial alkyl ketene dimer dispersion stabilized with starch (filled diamonds, dot line), and of Dispersion C which was a commercial alkyl ketene dimer dispersion stabilized with polyamidoamine epichlorohydrin (unfilled circles, solid line)

It is seen that Dispersion A, stabilized with lignin-carbohydrate complex provided as good as, or even better, sizing performance (Cobb60 value) in comparison to commercial Dispersions B and C, where starch or synthetic polymer is used as stabilizing agent. It is highly unexpected that sizing performance of Dispersion A was comparable to the sizing performance of the Dispersion C, stabilized with a synthetic polymer.

The project leading to this application has received funding from the Bio Based Industries Joint Undertaking (JU) under grant agreement No 837866. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and the Bio Based Industries Consortium.

Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.

Claims

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

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

3. The aqueous dispersion according to claim 1 or 2, characterised in that the aqueous dispersion comprises 5 - 40 weight-%, preferably 7 - 35 weight-%, more preferably 10

- 30 weight-%, sometimes even 15 - 25 weight-%, of alkyl ketene dimer, calculated from total weight of the aqueous dispersion.

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

5. The aqueous dispersion according to any of preceding claims 1 - 4, characterised in that the lignin-carbohydrate complex has a weight average molecular weight MW in a range of 3500 - 90 000 g/mol, preferably 4 000 - 80 000 g/mol, more preferably 5000

- 70 000 g/mol.

6. The aqueous dispersion according to any of preceding claims 1 - 5, characterised in that the anionic lignin-carbohydrate complex has an anionic charge density 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.

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

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

9. The aqueous dispersion according to any of preceding claims 1 - 8, characterised in that the carbohydrate of the lignin-carbohydrate complex is a hemicellulose.

10. The aqueous dispersion according to any of preceding claims 1 - 9, characterised in that the carbohydrate is formed from a monosaccharide, such as galactose, glucose, mannose, arabinose, covalently bound to a lignin.

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

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

13. The aqueous dispersion according to any of preceding claims 1 - 12, characterised in that the aqueous dispersion further comprises surfactant(s), biocide(s) and/or alum.

14. The aqueous dispersion according to claim 13, characterised in that the aqueous dispersion comprises - 0.01 - 1 weight-%, preferably 0.05 - 0.7 weight-%, more preferably 0.1 - 0.5 weight- %, of surfactant(s),

- 0.001 - 0.015 weight-%, preferably 0.001 - 0.01 weight-%, of biocide(s), and/or - 0.1 - 5 weight-%, preferably 0.2 - 4 weight-%, more preferably 0.5 - 3 weight-%, of alum, calculated from the total weight of the aqueous dispersion.

15. The aqueous dispersion according to any of preceding claims 1 - 14, characterised in that alkyl ketene dimer particles have a particle size D95 <5 pm, preferably in a range of 0.5 - 5 pm, preferably 1 - 4.5 pm.

16. The aqueous dispersion according to any of preceding claims 1 - 15, characterised in that the aqueous dispersion is obtained by homogenizing the alkyl ketene dimer in the aqueous phase in a presence of the stabilizing agent.

17. Use of an aqueous dispersion according to any of claims 1 - 16 for manufacture of a cellulosic fibrous web, such as paper, board, tissue or the like, preferably as an internal sizing agent or for surface sizing.

18. Use of an anionic lignin-carbohydrate complex where lignin and carbohydrate are covalently bound with each other as a stabilizing agent for an aqueous dispersion of alkyl ketene dimer.

19. Use according to claim 18, characterised in that the anionic lignin-carbohydrate complex comprises anionic functional groups selected from sulfonate groups, carboxyl groups and/or phenolic groups; and/or has an anionic charge density 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.

20. Use according to claim 18 or 19, characterised in that the carbohydrate of the anionic lignin-carbohydrate complex is formed from a monosaccharide, such as galactose, glucose, mannose, arabinose, or their fragments or residues.

21 . Method for manufacturing of a cellulosic fibrous web, such as paper, board, tissue or the like, comprising

- forming a fibre stock comprising cellulosic fibres,

- forming the fibre stock into a cellulosic fibrous web, and

- drying the cellulosic fibrous web, wherein an aqueous dispersion according to any of claims 1 - 16 is added to the fibre stock as an internal sizing agent and/or on the cellulosic fibrous web as a surface sizing agent.