WO2023118655A1

WO2023118655A1 - Polymer dispersion, its use and use of lignin-carbohydrate complex

Info

Publication number: WO2023118655A1
Application number: PCT/FI2022/050848
Authority: WO
Inventors: Anneli Lepo
Original assignee: Kemira Oyj
Priority date: 2021-12-21
Filing date: 2022-12-20
Publication date: 2023-06-29

Abstract

The invention relates to a polymer dispersion, which comprises polymer particles dispersed in an aqueous liquid phase and a stabilising agent which is an anionic lignin-carbohydrate complex, where lignin and carbohydrate are covalently bound to each other. The invention further relates to a use of an anionic lignin-carbohydrate complex as a stabilising agent.

Description

POLYMER DISPERSION, ITS USE AND USE OF LIGNIN-CARBOHYDRATE COMPLEX

The present invention relates to a use of an anionic lignin-carbohydrate complex, a polymer dispersion and its use according to preambles of the enclosed independent claims.

Various aqueous polymer dispersions are used in many industrial processes. For example, in pulp and paper industry polymer dispersions can be used as strength agents when they are added to the fibre stock, or as components in coating compositions as they are mixed with inorganic mineral particles and applied on the formed fibre web. Polymer dispersions are also used in many wastewater treatment processes, in manufacture of adhesives and/or paints as well as additives for various suspensions of inorganic particles in construction industry.

Polymer dispersions are usually stabilised. In practice this means that the polymer dispersion contains a stabilising agent that improves the stability of the dispersion and reduces or even eliminates the risk for particle aggregation and phase separation during the storage of the polymer dispersion. Stabilising agent can be either mixed into the liquid phase of the polymer dispersion together with the polymer, or the stabilising agent can be already present during the polymerisation of the dispersed polymer.

Usually polymer dispersions, especially polymer dispersions with small particle size, are stabilised by using other polymers or surfactants. Stabilising concepts based on synthetic polymeric compounds and surfactants made of petroleum-based raw materials have been traditionally considered preferable, at least in many pulp and paper applications, as they have good commercial availability. However, there is an increasing interest to increase the amount of renewable components, even in polymer dispersions. Starch has been used for stabilising some polymer dispersions, for example styrene acrylate dispersions. Starch is produced from plants that could be used for feeding humans and animals, and 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 stabilisers, which would be biobased, renewable and originate from natural sources that primarily cannot be used as food or feed production. Attempts have been made to use, for example, lignosulfonates or hemicelluloses as stabilising agents for polymer dispersions, but the results have not been promising in practical applications, particularly when water-based polymer dispersion having a small particle size and good storage stability is desired.

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

Another object of the present invention is to provide a polymer dispersion which comprises a more sustainable stabilising agent.

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.

All the described embodiments and advantages apply all aspects of the present invention, i.e. the use of the lignin-carbohydrate complex, the polymer dispersion and its use, when applicable, even if not always explicitly stated so.

A typical polymer dispersion according to the present invention comprises an aqueous liquid phase and polymer particles dispersed in the aqueous liquid phase, wherein the polymer dispersion comprises a stabilising agent which is an anionic lignin-carbohydrate complex, where lignin and carbohydrate are covalently bound to each other.

A typical use according to the present invention of an anionic lignin-carbohydrate complex, where lignin and carbohydrate are covalently bound to each other, is as a stabilising agent for a polymer dispersion comprising polymer particles dispersed in an aqueous liquid phase.

Now it has been surprisingly found out that a polymer dispersion can be effectively stabilised by using an anionic lignin-carbohydrate complex where lignin and carbohydrate are covalently bound with each other. The lignin-carbohydrate complex is able to stabilise the polymer dispersion and reduce or eliminate the agglomeration of polymer particles, thus providing at least as good or even better storage stability as the conventional stabilising agents based on synthetic polymeric compounds. Furthermore, it has been found that the use of lignin-carbohydrate complex, when used as stabilising agent during polymerisation, may provide the polymer dispersion with relatively even particle size distribution with relatively small average particle size, which is advantageous for practical applications, e.g. in coating of paper, board or the like. It is speculated, without wishing to be bound by a theory, that the amphiphilic nature of the lignin-carbohydrate complex attracts it effectively to the interface between polymer particles and the aqueous liquid phase, thus enabling an enhanced stabilising effect.

The polymer dispersion comprising an aqueous liquid phase and polymer particles dispersed in the aqueous liquid phase can be obtained or formed by using conventional techniques. For example, a polymer can be melted or brought into mouldable form, and thereafter formed into particles which are then dispersed into the aqueous liquid phase. The forming of particles may be performed, for example, by dispersing the melted or mouldable polymer in a reactor comprising the aqueous liquid phase by extrusion or other similar techniques. The forming of polymer particles may be performed either at an elevated pressure or at atmospheric pressure. Alternatively, the polymer dispersion may be formed by polymerising suitable monomers in an aqueous liquid phase, wherein the polymerisation leads to formation of polymer particles dispersed in the aqueous liquid phase. According to the present invention, the lignin-carbohydrate complex is present as a stabilising agent in the aqueous liquid phase irrespective how the polymer particles are formed into the aqueous liquid phase. According to one preferable embodiment, the lignin-carbohydrate complex is present in the aqueous liquid phase during the polymerisation of monomers into the polymer particles. The lignin-carbohydrate complex is added to the aqueous liquid phase, where the polymerisation is conducted, before or at the beginning of the polymerisation. In this manner polymer dispersions with advantageously small particle size are easily and effectively obtained. Preferably the lignin-carbohydrate complex is sole stabilising agent present during the radical polymerisation. According to one embodiment, the aqueous liquid phase is free of starch during polymerisation. The lignin-carbohydrate complex is effective as stabilising agent over a broad pH range, which gives more degrees of freedom in performing the polymerisation reactions. In one preferable embodiment, the pH during the polymerisation may be in a range of pH 5 - 6.

The polymer dispersion may comprise the stabilising agent in an amount of 8 - 45 weight-%, calculated from the total weight of polymer and stabilising agent, as dry. For example, when the lignin-carbohydrate complex is present as a stabilising agent in the aqueous liquid phase during the radical polymerisation, the polymer dispersion may comprise stabilising agent in an amount of 10 - 39 weight-%, preferably 16 - 34 weight-%, more preferably 20 - 30 weight-%, calculated from the total weight of polymer and stabilising agent, as dry.

The anionic lignin-carbohydrate complex, which is suitable for use as a stabilising 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.

The lignin-carbohydrate complex may be formed of lignin and one or more of carbohydrates, such as hemicelluloses. Preferably the carbohydrate of the lignin- carbohydrate complex is 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 said monosaccharide(s) and/or their fragments or residues. The exact amount of the monosaccharides 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 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.

The lignin-carbohydrate complex, suitable for use in the present invention, may be obtained from a side stream of a pulping process. In one embodiment, a suitable lignin-carbohydrate complex may be obtained by enzymatic treatment of lignin- carbohydrate material originating from a 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.

According to one preferable embodiment of the invention the anionic lignin- carbohydrate complex is an anionic lignosulfonate-carbohydrate complex. 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 >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 preferable embodiment, the lignin-carbohydrate complex may preferably have relatively high molecular weight. It is assumed, without wishing to be bound by a theory that the high molecular weight provides at least some of the surprising effects that have been observed. The high molecular weight may have an impact on the behaviour and/or structural orientation of the lignin-carbohydrate complex at the interface between the polymer particles and the aqueous liquid phase. 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 lignimcarbohydrate 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.

The lignin-carbohydrate complex, where lignin and carbohydrate are covalently bound to each other, can be used a stabilising agent for any polymer dispersion, where hydrophobic polymer particles are dispersed in an aqueous continuous liquid phase. The aqueous liquid phase may comprise also one or more additional solvents other than water, as long as the used additional solvent(s) is/are fully miscible with water and no phase separation occurs. For example, the aqueous liquid phase may comprise an additional solvent selected from carboxylic acids, such as acetic acid, and alcohols, such as ethanol or isopropanol. The amount of an additional solvent may be less than 35 weight-%, preferably less than 25 weight- %, more preferably less than 10 weight-%, even more preferably less than 5 weight- %, calculated from the total weight of the aqueous liquid phase. According to one embodiment the aqueous liquid phase consists of water.

According to one preferable embodiment of the present invention the lignin- carbohydrate complex may be used as stabilising agent in a polymer dispersion which comprises or consists of hydrophobic polymer particles obtained by radical polymerisation of one or more vinyl monomers comprising alkyl (meth)acrylates. The polymer dispersion may be obtained by a radical polymerisation of alkyl (meth)acrylate, for example C1 -C8 alkyl (meth)acrylate, preferably C1-C4 alkyl (meth)acrylate, and any of their mixtures, as described below. Alternatively, the polymer dispersion may be obtained by a radical polymerisation of several, such as two, three or more, different vinyl monomers, of which at least one is alkyl (meth)acrylate. Preferably the polymer dispersion is obtained by a radical polymerisation of two or three different vinyl monomers, of which at least one is alkyl (meth)acrylate.

The polymer dispersion may comprise polymer particles, which are obtained by a radical polymerisation of vinyl monomers, such as alkyl (meth)acrylate, in the presence lignin-carbohydrate complex as a stabilising agent. According to one preferable embodiment, the polymer dispersion may be obtained by a radical polymerisation of at least one first monomer (a) which is selected from C1 -C8 alkyl (meth)acrylates and any of their mixtures; and optionally at least one second monomer (b) which is selected from styrene, substituted styrenes, such as a- methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any of their mixtures. According to one embodiment of the present invention the vinyl monomers may comprise at least one first monomer (a) which is selected from alkyl (meth)acrylates, such as C1 -C8 alkyl (meth)acrylates, preferably C1 -C4 alkyl (meth)acrylates, and any of their mixtures. Suitable first monomer (a) may be, for example, methyl acrylate; methyl methacrylate; ethyl acrylate; ethyl methacrylate; n-propyl or isopropyl acrylate and corresponding propyl methacrylates; n-butyl, iso-butyl, tert-butyl or 2-butyl acrylate and the corresponding butyl methacrylates; n-pentyl or neopentyl acrylate and the corresponding pentyl methacrylates; 2-hexyl or 2-ethylhexyl acrylate and corresponding methacrylates; n-octyl or isooctyl acrylate and corresponding methacrylates. According to one preferable embodiment the first monomer (a) is selected from C1 -C4-alkyl acrylates, C1 -C4-alkyl methacrylates or any of their mixtures, e.g. n-butyl, iso-butyl, tert-butyl or 2-butyl acrylate and the corresponding butyl methacrylates; methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate or propyl methacrylate. The first monomer (a) may be a mixture of at least two isomeric butyl acrylates. For example, the first monomer (a) may be a mixture of n-butyl acrylate and methyl methacrylate or a mixture of n-butyl acrylate and tert-butyl acrylate.

According to one embodiment of the present invention the vinyl monomers may comprise at least one second monomer (b) which may be selected from styrene, substituted styrenes, such as a-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any of their mixtures.

The polymer dispersion may be obtained by radical polymerisation of 25 - 99.9 weight-%, preferably 30 - 95 weight-%, more preferably 35 - 90 weight-%, of the first monomer (a), and 0.1 - 75 weight-%, preferably 5 - 60 weight-%, more preferably 10 - 55 weight-%, of the second monomer (b), calculated from the total dry solids content of the monomers (a) and (b).

According to one embodiment of the invention the polymer particles in the polymer dispersion may be obtained by radical copolymerisation of at least first monomers (a), second monomers (b) and at least one third monomer (c), which is ethylen ically unsaturated and different from first monomer (a) and second monomer (b) present simultaneously. Suitable ethylenically unsaturated third monomers (c) are ethylhexyl acrylate, stearyl acrylate, stearyl methacrylate, esters of acrylic and methacrylic acid with alcohols which have more than four C atoms, and further acrylonitrile, methacrylonitrile, acrylamide, vinyl acetate or anionic comonomers, such as acrylic acid, methacrylic acid, styrene sulphonic acid. Ethylhexyl acrylate and methacrylic acid may be preferred as third monomer (c). The amount of third monomer (c) may be 0 - 9 weight-%, preferably 0 - 7 weight-%, more preferably 0 - 5 weight-%, calculated from the total dry solids content of the monomers (a), (b) and (c).

It has been observed that the use of the lignin-carbohydrate complex as a stabilising agent may even positively influence the properties of the obtained polymer dispersion, especially when the lignin-carbohydrate complex is present during the polymerisation. For example, the glass transition temperature T_g of the polymer dispersion may be lower, especially when compared to similar prior art dispersions, where starch or sodium dodecyl sulphate has been used as stabilising agent. Low T_g indicates that possible films formed from the polymer dispersion may be less brittle and more ductile. This may enable use of monomers, such as methacrylates, which usually would result in higher T_g for the polymer dispersion. In this manner it may also be possible to reduce the amount of styrene and/or styrene monomers used in the polymerisation. For example, glass transition temperature T_g for a polymer dispersion, which is stabilised with an anionic lignin-carbohydrate complex, may be in a range from -10 °C to +95 °C, preferably from 0 °C to +80 °C, more preferably from +5 °C to +65 °C, and even more preferably from +10 °C to +40 °C. In this manner the anionic lignin-carbohydrate complex allows production of polymer dispersions with T_g values within wide limits.

According to one preferable embodiment of the present invention the polymer dispersion is obtained by radical polymerisation of vinyl monomers comprising alkyl (meth)acrylates in absence of styrene and substituted styrene monomers. The polymer dispersion may thus be obtained without a second monomer (b) selected from styrene, substituted styrenes, such as a-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any of their mixtures. The obtained polymer dispersion is thus preferably free of structural units originating from monomers selected from styrene, substituted styrenes, such as a-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any of their mixtures.

According to one embodiment of the present invention the lignin-carbohydrate complex may be used as stabilising agent in a radical polymerisation, where at least one polymerisation regulator is employed. The one or more polymerisation regulators, such as chain transfer agents, may be introduced to the polymerisation reaction simultaneously, but separately, with the monomer feed(s), or as mixed into at least one of the monomer feed(s). Suitable polymerisation regulators may be, for example, sulphur compounds, e.g. mercaptans.

The radical polymerisation, during which the lignin-carbohydrate complex is present as stabilising agent, may be carried out in the presence of a free radical initiator. Suitable free radical initiators may be, for example, peroxides such as hydrogen peroxide, sodium peroxo-disulfate, potassium peroxodisulfate, ammonium peroxodisulfate, or tert-butyl hydroperoxide. Peroxide initiator is usually used as part of a redox initiator system comprising also a reducing agent. Suitable combinations for the redox initiator systems comprising a peroxide may comprise, for example, ascorbic acid, and a heavy metal cation, such as iron, manganese, or cerium ions.

The radical polymerisation process may comprise also an additional postpolymerisation step, after termination of the monomer and initiator feed(s). During the post-polymerisation step the amount residual monomers in the obtained polymer dispersion is further reduced, for example, by addition of further initiator amount or a second initiator.

The radical polymerisation may be performed at a temperature in range of 50 - 100 °C, preferably 70 - 98 °C, more preferably 80 - 97 °C, to ensure the polymerisation of the monomers into small particle size polymer dispersion and low residual monomer level. The polymerisation pH may be 2.5 - 8.5, preferably 3.0 - 7.5, and even more preferably 4.5 - 6.9. When the anionic lignin-carbohydrate complex is present in the aqueous liquid phase during the polymerisation of the polymer particles, the polymer dispersion may comprise polymer particles having a particle size D50 <250 nm, preferably <180 nm, more preferably <150 nm, even more preferably <140 nm, sometimes even < 99 nm. The particle size D50 for the polymer particles of the dispersion may be, for example, in a range of 10 - 250 nm, preferably 15 - 180 nm, more preferably 20 - 150 nm, even more preferably 25 - 140 nm, sometimes even 25 - 99 nm. The polymer dispersion may comprise polymer particles, which have a particle size D90 <600 nm, preferably <500 nm, more preferably <350 nm, even more preferably <250 nm. The particle size D90 for the polymer particles of the dispersion may be, for example, in a range of 40 - 600 nm, preferably 50 - 500 nm, more preferably 70 - 350 nm, even more preferably 80 - 250 nm. The polymer dispersion may comprise polymer particles, which have a particle size D95 <700 nm, preferably <400 nm. The particle size D95 for the polymer particles of the dispersion may be, for example, in a range of 50 - 700 nm, preferably 80 - 400 nm, All particle sizes are measured by using Zetasizer Nano ZS, Malvern. In the present context the particle size D50 refers to the value for 50^th percentile of a volume-based distribution and the particle size D90 refers to the value for 90^th percentile of a volume-based distribution.

When the polymer dispersion is prepared from a melted or mouldable polymer and formed into particles, which are dispersed into the aqueous liquid phase comprising the lignin-carbohydrate complex, the polymer dispersion may comprise polymer particles having a particle size D50 <3000 nm, preferably <1500 nm. The particle size D50 for the polymer particles of this dispersion may be, for example, in a range of 200 - 3000 nm, preferably 300 - 1500 nm. Particle sizes D50 above 1000 nm are measured by using MasterSizer 2000, Malvern.

The obtained polymer dispersion may have a solids content of at least 10 weight- %, preferably at least 20 weight-%, sometimes even at least 25 weight-%. According to one embodiment the solids content of the polymer dispersion may be in a range of 10 - 60 weight-%, preferably 15 - 50 weight-%, more preferably 20 - 40 weight- %. The obtained polymer dispersion may have a viscosity of <500 mPas, preferably <200 mPas, more preferably <50 mPas. The viscosity may be in a range of 1 - 500 mPas, preferably 1 - 200 mPas, more preferably 2 - 50 mPas. All the viscosity values are measured at 25 °C, with Brookfield LVDV viscometer, in a small sample adapter with spindle 18, measured at solids content of 25 weight-%. pH of the obtained polymer dispersion may be 3.0 - 8.0, preferably 4.0 - 7.0, measured at 25 °C. Zeta potential of the polymer dispersion may be 20 - 80 mV, preferably 30 - 60 mV, most preferably 35 - 55 mV measured with Malvern Zetasizer Nano at pH 5 at 22 °C.

The polymer dispersion may contain in addition to the stabilising agent also other additives, such as defoamers, co-surfactants plasticizers, and/or pH adjustment chemicals.

The polymer dispersion stabilised with the lignin-carbohydrate complex is especially suitable for use in a manufacture of a fibrous web, such as paper, board, tissue, non-woven or the like. The polymer dispersion may be used in surface sizing or as a component in a surface sizing composition or a coating composition for paper or board. Especially in coating compositions the polymer dispersion of the present invention may improve the barrier properties, such as water resistance, of the formed coating. It has been observed that the use of lignin-carbohydrate complex provides the polymer dispersion with hydrophobic properties.

The polymer dispersion stabilised with the lignin-carbohydrate complex is further suitable for use in paints, adhesives and/or various suspensions comprising inorganic mineral particles, such as concrete.

According to one preferable embodiment, the anionic lignin-carbohydrate complex is used as a stabilising agent for a polymer dispersion comprising polymer particles dispersed in an aqueous liquid phase, wherein the lignin and the carbohydrate(s) are covalently bound to each other. Some aspects of this embodiment are described in the following numbered clauses. 1. Use of an anionic lignin-carbohydrate complex, where lignin and carbohydrate are covalently bound to each other, as a stabilising agent for a polymer dispersion comprising polymer particles dispersed in an aqueous liquid phase.

2. Use according to clause 1 , wherein the carbohydrate of the lignin-carbohydrate complex is hemicellulose.

3. Use according to clause 1 or 2, wherein the carbohydrate is formed from monosaccharides, such as mannose, galactose, glucose, xylose and/or arabinose.

4. Use according to clause 1 or 2, wherein the carbohydrate is monosaccharide, such as mannose, galactose, glucose, xylose and/or arabinose.

5. Use according to any of preceding clauses 1 -4, wherein the lignin-carbohydrate complex is used as stabilising agent in an amount of 8 - 45 weight-%, calculated from the total weight of polymer and stabilising agent, as dry.

6. Use according to any of preceding clauses 1 - 5, wherein the lignin-carbohydrate complex comprises anionic functional groups selected from sulfonate groups, carboxyl groups and/or phenolic groups.

7. Use according to any of preceding clauses 1 - 6, wherein the lignin-carbohydrate complex has a lignimcarbohydrate ratio from 90:10 to 10:90, preferably from 80:20 to 20:80, more preferably from 75:25 to 25:75.

8. Use according to any of preceding clauses 1 - 8, wherein 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.

10. Use according to any of preceding clauses 1 - 8, wherein the 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.

11. Use according to any of preceding clauses 1 - 10, wherein the lignin- carbohydrate complex comprises at least 10 weight-%, preferably at least 15 weight- % of carbohydrates, calculated from total dry weight of the complex.

12. Use according to any of preceding clauses 1 - 11 , wherein the lignin- carbohydrate complex is present in the aqueous liquid phase during the polymerisation of the polymer particles.

13. Use according to clause 1 - 12, wherein the polymer particles are obtained by a radical polymerisation of vinyl monomers comprising alkyl (meth)acrylate in the presence lignin-carbohydrate complex as the stabilising agent.

14. Use according to clause 12 or 13, wherein the polymer particles have a particle size D50 in a range of 10 - 250 nm, preferably 15 - 180 nm, more preferably 20 - 150 nm.

15. Use according to clause 12, 13 or 14, wherein the lignin-carbohydrate complex is used as stabilising agent in the amount of 10 - 39 weight-%, preferably 16 - 34 weight-%, more preferably 20 - 30 weight-%, calculated from the total weight of polymer particles and stabilising agent, as dry.

16. Use according to clause 13, 14 or 15, wherein the vinyl monomers comprise at least one first monomer (a) which is selected from C1-C8 alkyl (meth)acrylates and any of their mixtures.

17. Use according to clause 16, wherein the vinyl monomers comprise at least one second monomer (b) which is selected from styrene, substituted styrenes, such as a-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any of their mixtures. 18. Use according to clause 17, wherein the vinyl monomers comprise 25 - 99.9 weight-%, preferably 30 - 95 weight-%, more preferably 35 - 90 weight-%, of the first monomer (a), and 0.1 - 75 weight-%, preferably 5 - 60 weight-%, more preferably 10 - 55 weight-%, of the second monomer (b), calculated from the total dry solids content of the monomers (a) and (b).

19. Use according to clause 17 or 18, wherein the polymer particles are obtained by radical polymerisation of at least the first monomers (a), the second monomers (b) and at least one third monomer (c), which is ethylenically unsaturated and different from the first monomers (a) and the second monomers (b).

EXPERIMENTAL

Some embodiments of the invention are described more closely in the following nonlimiting examples.

Used Methods

The following measurement methods and conditions have been used in the examples:

The viscosity values are measured at 25 °C, with Brookfield LVDV viscometer, in a small sample adapter with spindle 18 and 60 rpm. pH values are measured at 25 °C by using standard laboratory pH meter.

The solids content values are measured using a Mettler Toledo Halogen moisture analyser.

The particle size measurements are done by using Malvern Zetasizer Nano.

The glass transition temperatures are measured from freeze dried samples using a differential scanning calorimeter Mettler Toledo DSC 3+.

In Examples 1 - 9 an anionic lignin-carbohydrate complex, where lignin and carbohydrate are covalently bound to each other, is used as a dispersant. The lignin- carbohydrate complex was obtained from Ecohelix AB, Sweden, and had a solids content of 17 %. Example 1

102 g of the lignin-carbohydrate complex is mixed under stirring into 98 g of water under a nitrogen atmosphere in a glass reactor with a cooling/heating jacket. To the reactor is added 0.07 g of ferrous(ll)sulphate heptahydrate This starting mixture is heated to 85 °C under one hour’s time. pH of the starting mixture is adjusted to pH 6.0 with 30% sodium hydroxide. A sample from a string mixture is taken, and the pH adjustment of the starting mixture is controlled by measuring the pH of the sample at 25 °C.

Three minutes before a monomer feed is started, a feed of 3.5% hydrogen peroxide solution is started to the reactor on a feed rate 0.15 g/min and continued for 135 minutes. The monomer mixture including 15 g of n-butyl acrylate, 30 g of styrene, and 15 g of tert-butyl acrylate is fed to the reactor during 120 minutes at constant feed rate. The reactor temperature is kept at 85 °C during these feeds and for 45 minutes after the feeds have been discontinued. After that the obtained polymer dispersion is cooled to a room temperature, followed by pH adjustment to pH 4.5 - 5.0 with 30% sulfuric acid solution. The obtained polymer dispersion is filtrated by using a 100 pm filter cloth.

A finely divided polymer dispersion with a solids content of 26 weight-%, pH 4.7, and viscosity of 11 mPas is obtained. Glass transition temperature of the polymer is +13 °C. Characteristic glass transition temperature of the similar polymer polymerised in Example 1 would be expected to be in the range from +40 °C to +50°C, when stabilised, for example with conventionally used sodium dodecyl sulphate. The advantageous impact of the used anionic lignin-hemicellulose complex to the glass transition temperature of the obtained polymer dispersion is clearly observable.

Example 2

Example 2 is done following the same procedure as in Example 1 with the following exceptions. The amount of the lignin-carbohydrate complex is 121 g and the amount of water is 117 g. The starting mixture is heated up 93 °C, and its pH is adjusted to pH 5.0 with 30% sulfuric acid before the polymerisation at 93 °C. The feed time of 3.5% hydrogen peroxide solution is 120 minutes.

A finely divided polymer dispersion with a solids content of 23 weight-%, pH 4.5, and viscosity of 14 mPas is obtained.

Example 3

Example 3 is done following the same procedure as in Example 1 with the following exceptions. The amount of the lignin-carbohydrate complex is 121 g and the amount of water is 117 g. The pH of the starting mixture is adjusted to pH 5.0 with 30% sulfuric acid before the polymerisation. The feed time of 3.5% hydrogen peroxide solution is 155 minutes.

A finely divided polymer dispersion with a solids content of 26 weight-%, pH 4.4, and viscosity of 15 mPas is obtained.

Example 4

Example 4 is done following the same procedure as in Example 1 with the following exceptions. The amount of the lignin-carbohydrate complex is 121 g and the amount of water 117 g. The pH of the starting mixture is adjusted to pH 6.3 with 30% sodium hydroxide before the polymerisation. The feed time of 3.5% hydrogen peroxide solution is 150 minutes.

A finely divided polymer dispersion with a solids content of 27 weight-%, pH 4.5, and viscosity of 13 mPas is obtained.

Example 5

Example 5 is done following the same procedure as in Example 1 with the following exceptions. The amount of the lignin-carbohydrate complex is 140 g and the amount of water 135 g. The pH of the starting mixture is adjusted to pH 5.0 with 30% sulfuric acid before the polymerisation. The feed time of 3.5% hydrogen peroxide solution is 195 minutes. A finely divided polymer dispersion with a solids content of 24 weight-%, pH 4.5, and viscosity of 8 mPas is obtained.

Example 6

Example 6 is done following the same procedure as in Example 1 with the following exceptions. The pH of the starting mixture is adjusted to pH 7.0 with 30% sodium hydroxide before the polymerisation. The feed time of 3.5% hydrogen peroxide solution was 150 minutes.

A finely divided polymer dispersion with a solids content of 27 weight-%, pH 5.0, and viscosity of 20 mPas is obtained.

Example 7

Example 7 is done following the same procedure as in Example 1 with the following exceptions. The pH of the starting mixture is adjusted to pH 3.2 with 30% sulfuric acid before the polymerisation. The feed time of 3.5% hydrogen peroxide solution is 195 minutes.

A finely divided polymer dispersion with a solids content of 26 weight-%, pH 4.6, and viscosity of 6 mPas is obtained.

Example 8

Example 8 is done following the same procedure as in Example 1 with the following exceptions. The pH of the starting mixture is adjusted to pH 2.3 with 30% sulfuric acid before the polymerisation. The feed time of 3.5% hydrogen peroxide solution is 220 minutes.

A finely divided polymer dispersion with a solids content of 26 weight-%, pH 4.5, and viscosity of 20 mPas is obtained.

Example 9

Example 9 is done following the same procedure as in Example 1 with the following exceptions. The starting mixture is heated up 75 °C and its pH is adjusted to pH 5.0 with 30% sulfuric acid before the polymerisation which is done at 75 °C. The feed time of 3.5% hydrogen peroxide solution is 210 minutes.

A finely divided polymer dispersion with a solids content of 29 weight-%, pH 4.5, and viscosity of 368 mPas is obtained.

Example 10 (Comparative)

18 g of lignosulfonate (Ufoxane 2, Borregaard, solid content 93 %) is mixed with stirring into 182 g of water under a nitrogen atmosphere in a glass reactor with a cooling/heating jacket. To the reactor is added 0.07 g of ferrous(ll)sulphate heptahydrate. This starting mixture is heated to 85°C. pH of the starting mixture is adjusted to pH 5.0 with 30% sulfuric acid. pH is measured at 25 °C. Three minutes before a monomer feed is started, a feed of 3.5% hydrogen peroxide solution is started to the reactor on a feed rate of 0.15 g/min and continued for 225 minutes. The monomer mixture including 15 g of n-butyl acrylate, 30 g of styrene, and 15 g of tert-butyl acrylate is fed to the reactor during 120 minutes at constant feed rate. The reactor temperature is kept at 85 °C during these feeds and for 45 minutes after the feeds have been discontinued. After that the obtained polymer dispersion is cooled to a room temperature, followed by pH adjustment to pH 4.5 - 5.0 with 30% sulfuric acid solution. The obtained polymer dispersion is filtrated by using a 100 pm filter cloth.

A polymer dispersion with a solids content of 23 weight-%, pH 4.8, and viscosity of 36 mPas is obtained. The polymer dispersion was unstable and phase separation occurred within hours.

The particle size distributions for polymer dispersions obtained in Examples 1 - 10 are shown in Table 1. It can be seen from Table 1 that when anionic lignin- carbohydrate complex where lignin and carbohydrate are covalently bound to each other is used as stabilising agent in the polymerisation, the obtained polymer dispersions have relatively narrow particle size distributions. The difference to the polymer dispersion which has been obtained by using lignosulfonate as stabilising agent is significant and wholly unexpected. Table 1 Particle size distributions for polymer dispersions obtained in Examples

1 - 10

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

22 CLAIMS

1. A polymer dispersion, which comprises an aqueous liquid phase and polymer particles dispersed in the aqueous liquid phase, the polymer dispersion comprising a stabilising agent which is an anionic lignin-carbohydrate complex, where lignin and carbohydrate are covalently bound to each other.

2. Polymer dispersion according to claim 1 , characterised in that the carbohydrate of the lignin-carbohydrate complex is hemicellulose.

3. Polymer dispersion according to claim 1 or 2, characterised in that the carbohydrate is formed from monosaccharides, such as mannose, galactose, glucose, xylose and/or arabinose.

4. Polymer dispersion according to claim 1 or 2, characterised in that the carbohydrate is monosaccharide, such as mannose, galactose, glucose, xylose and/or arabinose.

5. Polymer dispersion according to any of preceding claims 1 - 4, characterised in that the polymer dispersion comprises the stabilising agent in an amount of 8 - 45 weight-%, calculated from the total weight of polymer and stabilising agent, as dry.

6. Polymer dispersion according to any of preceding claims 1 - 5, characterised in that the anionic lignin-carbohydrate complex comprises anionic functional groups selected from sulfonate groups, carboxyl groups and/or phenolic groups.

7. Polymer dispersion according to any of preceding claims 1 - 6, characterised in that the anionic lignin-carbohydrate complex has a lignimcarbohydrate ratio from 90:10 to 10:90, preferably from 80:20 to 20:80, more preferably from 75:25 to 25:75.

8. Polymer dispersion according to any of preceding claims 1 - 7, characterised in that the anionic 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.

9. Polymer dispersion according to any of preceding claims 1 - 8, 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.

10. Polymer dispersion according to any of preceding claims 1 - 9, characterised in that the anionic lignin-carbohydrate complex comprises at least 10 weight-%, preferably at least 15 weight-%, of carbohydrate, calculated from total dry weight of the complex.

11 . Polymer dispersion according to any of preceding claims 1 - 10, characterised in that the polymer dispersion comprises polymer particles, which are obtained by a radical polymerisation of vinyl monomers comprising alkyl (meth)acrylate, in the presence lignin-carbohydrate complex as a stabilising agent.

12. Polymer dispersion according to claim 11 , characterised in that the polymer dispersion comprises polymer particles having a particle size D50 in a range of 10 - 250 nm, preferably 15 - 180 nm, more preferably 20 - 150 nm.

13. Polymer dispersion according to claim 11 or 12, characterised in that the polymer dispersion comprises stabilising agent in an amount of 10 - 39 weight-%, preferably 16 - 34 weight-%, more preferably 20 - 30 weight-%, calculated from the total weight of polymer particles and stabilising agent, as dry.

14. Polymer dispersion according to claim 11 , 12 or 13, characterised in that the vinyl monomers comprise at least one first monomer (a) which is selected from C1- C8 alkyl (meth)acrylates and any of their mixtures.

15. Polymer dispersion according to claim 14, characterised in that the vinyl monomers comprise at least one second monomer (b) which is selected from styrene, substituted styrenes, such as a-methylstyrene, vinyltoluene, ethylvinyltoluene, chloromethylstyrene, and any of their mixtures.

16. Polymer dispersion according to claim 15, characterised in that the vinyl monomers comprise 25 - 99.9 weight-%, preferably 30 - 95 weight-%, more preferably 35 - 90 weight-%, of the first monomer (a), and 0.1 - 75 weight-%, preferably 5 - 60 weight-%, more preferably 10 - 55 weight-%, of the second monomer (b), calculated from the total dry solids content of the monomers (a) and (b).

17. Polymer dispersion according to claim 15 or 16, characterised in that the polymer particles are obtained by radical polymerisation of at least the first monomers (a), the second monomers (b) and at least one third monomer (c), which is ethylen ically unsaturated and different from the first monomers (a) and the second monomers (b).

18. Use of a polymer dispersion according to any of claims 1 - 17 in a manufacture of a fibrous web, such as paper, board, tissue or the like.

19. Use according to claim 18, characterised in that the polymer dispersion is used as a component in a surface sizing composition or a coating composition.

20. Use of polymer dispersion according to any of claims 1 -17 in a manufacture of paints or adhesives.

21. Use of an anionic lignin-carbohydrate complex, where the lignin and the carbohydrate(s) are covalently bound to each other, as a stabilising agent for a polymer dispersion comprising polymer particles dispersed in an aqueous liquid phase.

22. Use according to claim 21 , characterised in that the lignin-carbohydrate complex is present in the aqueous liquid phase during the polymerisation of the polymer particles. 25

23. Use according to claims 21 or 22, characterised in that the polymer particles are obtained by a radical polymerisation of one or more vinyl monomers comprising alkyl (meth)acrylates.