Method for producing alpha-1,3-glucan fibrids based additive, alpha-1,3-glucan fibrids based additive and uses thereof

Abstract

Alpha-1,3-glucan fibrids based additive, which comprises a mixture of alpha-1,3-glucan fibrids and a cationic branched polymer. In a method for producing an alpha-1,3-glucan fibrids based additive, linear non-charged alpha-1,3-glucan is dissolved in an alkaline solvent to obtain an alpha-1,3- glucan solution, and alpha-1,3-glucan is precipitated under shear in acidic conditions and simultaneously mixing at least one cationic branched polymer with the alpha-1,3- glucan solution to producing a suspension of the alpha-1,3- glucan fibrid based additive comprising a mixture of alpha- 1,3-glucan fibrids and cationic branched polymer.

Description

[0001] METHOD FOR PRODUCING ALPHA-1 ,3-GLUCAN FIBRIDS BASED ADDITIVE, ALPHA-1 , 3-GLUCAN FIBRIDS BASED ADDITIVE AND USES THEREOF

[0002] Field of the invention

[0003] The present invention relates to a method for producing alpha-1 ,3-glucan fibrids based additive according to the claims presented below. Further, the invention relates to a novel alpha-1 ,3-glucan fibrids based additive and its use.

[0004] Background of the invention

[0005] In recent years, the demand for fiber-based packaging has been increasing worldwide due to ecologic motivations and an increase in online shopping. To meet the demand, the use of higher yield pulps combined with lower density products would be ideal. These changes can decrease both the demand of the raw materials and transportation costs through lighter products. However, the production of lighter fiber-based products requires the use of more effective dry strength additives to handle the requirements set for them. Furthermore, the higher yield pulp such as chemi-thermomechanical pulp (-90% yield) tend to form products with worse strength properties than those made up of chemical pulp such as kraft pulp (-40% yield).

[0006] Typically, dry strength additives used in paper or paperboard manufacturing are cationic high molecular weight polymers, that are able to adsorb onto the anionic fibers. The most commonly used additives are starches and polyacrylamides, both often modified to be cationic. In the past decade there has also been a lot of interest in the use of microfibrillated cellulose (MFC) to increase the dry strength. The downsides of using MFC as a strength additive are the increased density and water retention of the sheet, wherein it has negative impact on dewatering. Dewatering is however an important aspect in manufacture of paper or paperboard, since it is an energyconsuming part in the production of paper or board. Therefore, there is still a constant need to develop better additives for strength purposes in manufacturing of paper or paperboard in order to achieve both ecologic and economic benefits.

[0007] Alpha-1 ,3-glucan is a polysaccharide mostly found in fungal cell walls. Previously, it has not been utilized industrially due to its limited commercial availability. Recently, an enzymatically engineered production path has been found to produce alpha-1 ,3-glucan polymers from sucrose. The alpha-1 -3- glucan has advantages similar to those of cellulose (beta-1 ,4-glucan), such as renewability, biodegradability, insolubility in water, high hydrogen bonding potential, stiffness, etc., while being fully soluble in sodium hydroxide, unlike cellulose, which requires harsher and more expensive chemicals to be dissolved. Furthermore, alpha-1 ,3-glucan can be dissolved and subsequently precipitated under high shear force to produce a product termed fibrids. Fibrids can be produced from alpha-1 , 3-glucan e.g. by the method disclosed in the patent publication WO 2016 / 196022.

[0008] Summary of the Invention

[0009] It is an object of the present invention to reduce or even eliminate the above- mentioned problems appearing in prior art.

[0010] It is an object of the present invention to provide a method of producing alpha-1 ,3-glucan fibrids based additive. Especially, an object of the invention is to provide a method for producing alpha-1 , 3-glucan fibrids based additive for use in a manufacturing of paper or paperboard.

[0011] Further, an object of the present invention is to present a novel alpha-1 ,3- glucan fibrids based additive and its use. Especially, an object of the present invention is to provide an alpha-1 ,3-glucan fibrids based additive for use in manufacturing of paper or paperboard.

[0012] These objects are attained with the invention having the characteristics presented below in 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. The embodiments and advantages mentioned in this text relate, where applicable, both to the method, the alpha-1 ,3-glucan fibrids based additive as well as to the uses according to the invention, even though it is not always specifically mentioned.

[0013] Typical method according to the present invention for producing an alpha- 1 ,3-glucan fibrids based additive comprises

[0014] - dissolving linear alpha-1 ,3-glucan in an alkaline solvent to obtain an alpha- 1 ,3-glucan solution,

[0015] - obtaining at least one cationic branched polymer,

[0016] - precipitating alpha-1 ,3-glucan under shear in acidic conditions and simultaneously mixing the cationic branched polymer with the alpha-1 ,3- glucan solution to produce a suspension of the alpha-1 , 3-glucan fibrid based additive comprising a mixture of alpha-1 ,3-glucan fibrids and the cationic branched polymer.

[0017] Typical alpha-1 ,3-glucan fibrids based additive according to the present invention comprises a mixture of alpha-1 ,3-glucan fibrids and a cationic branched polymer. Typical alpha-1 ,3-glucan fibrids based additive of the present invention is produced by a method according to the present invention.

[0018] The present invention relates to novel alpha-1 ,3-glucan fibrid based additives. It has been surprisingly found out that precipitating alpha-1 ,3- glucan fibrids in the presence of cationic branched polymer, the fibrid composite material comprising a mixture of alpha-1 ,3-glucan fibrids and the cationic branched polymer can be produced. It is observed that a cationic branched polymer, such as cationic glyoxylated polyacrylamide polymer or cationic branched water-soluble glucan polymer, can be precipitated to a part of the alpha-1 , 3-glucan fibrid structure, since alpha-1 ,3-glucan fibrid based additive produced by the method according to the present invention performed better than the reference points with same components dosed separately or just pre-mixed together.

[0019] Alpha-1 ,3-glucan fibrids based additive according to the present invention can be used in manufacturing of paper or paperboard. According to an embodiment of the present invention, alpha-1 , 3-glucan fibrids based additive can be used as a strength additive in manufacturing of paper or paperboard. The improved efficiency is observed in strength properties without affecting detrimental to dewatering properties. Especially, it has been observed an improved dry strength in manufacturing of paper or paperboard without affecting detrimental to dewatering properties. Alpha-1 ,3-glucan fibrid based additive produced by the method according to the present invention provides the synergistic effect of alpha-1 ,3 glucan fibrids and cationic branched polymer. Thus, an additive according to the present invention provides an improved strength efficiency in manufacturing of paper or paperboard.

[0020] According to an embodiment of the present invention, alpha-1 ,3-glucan fibrids based additive can be used as a strength additive in paper or paperboard manufacturing. Further, the use of the alpha-1 ,3-glucan fibrids based additive according to the present invention enables reduced use of raw materials and lighter products, leading to both economic and environmental benefits in paper or paperboard manufacturing. Use of the alpha-1 ,3-glucan fibrids based additives according to the present invention is not however limited only to this use.

[0021] Description of the drawings

[0022] In the following, some embodiments of the invention will be described in detail. The appended drawings are part of the description. In the drawings,

[0023] Figs. 1 and 2 shows the results of tensile strength and Z-directional strength tests of Example 1. Performance of alpha-1 ,3-glucan fibrids based additive according to the present invention (“composite”) is compared to separate addition of alpha-1 ,3-glucan fibrids and GPAM and to the premixture of alpha-1 ,3-glucan fibrids and GPAM.

[0024] Fig. 3 shows tensile index GM improvement (%) against the change (%) in the water retention value (WRV) for the results of Example 1.

[0025] Fig. 4 shows particle size distribution of Example 2.

[0026] Fig. 5 shows the results of tensile strength testing of Example 2. Fig. 6 shows the tensile index GM improvement (%) against the change (%) in the WRV for the results of Example 2.

[0027] Fig. 7 shows z-directional strength improvement (%) against tensile index GM improvement (%) for the results of Example 3.

[0028] Detailed description of the invention

[0029] In the present context the “alpha-1 ,3-glucan”, “a-1 ,3-glucan”, “alpha-1 ,3- glucan polymer” and “a-1 ,3-glucan polymer” denote a polymeric structure having a polysaccharide backbone which comprises D-glucose units linked together by glycosidic linkages. At least 70%, preferably at least 80%, more preferably at least 90% or 95%, sometimes even of 99% or 100%, of the glycosidic linkages are a-1 ,3-linkages. This means that in the polysaccharide backbone the a-D-glucose units are connected to each other through carbons 1 and 3 on adjacent a-D-glucose rings. The form of glycosidic linkages can be determined by a person skilled in the art by using methods known as such, for example1HNMR.

[0030] The alpha-1 ,3-glucan has advantages similar to those of cellulose (beta-1 ,4- glucan). However, unlike cellulose, which requires quite harsh and expensive chemistry to dissolve it, alpha-1 ,3-glucan can be easily dissolved into an alkaline solution, such as sodium hydroxide (NaOH) solution. This property is utilized in the method according to the present invention.

[0031] In a method according to the present invention for producing an alpha-1 ,3- glucan fibrids based additive, alpha-1 ,3-glucan polymer powder, typically microcrystalline alpha-1 ,3-glucan polymer powder, is first dissolved in an alkaline solvent, such as e.g. in NaOH solution to obtain an alpha-1 ,3-glucan solution, also called as a dope. As described above, alpha-1 ,3-glucan polymer to be dissolved in an alkaline solvent denotesa polymeric structure having a polysaccharide backbone which comprises D-glucose units linked together by glycosidic linkages. Types of an alkaline solvent for the alpha- 1 ,3-glucan may comprise an aqueous alkaline solution containing sodium hydroxide, potassium hydroxide, lithium hydroxide, lithium chloride / DMAC, DMSO / lithium chloride, etc. The alkaline solvent for the alpha-1 , 3-glucan should be miscible with the liquid used for the precipitation of the fibrids. After dissolving of alpha-1 ,3-glucan, the alpha-1 ,3-glucan fibrids can be precipitated in acidic conditions under shear forces. In a method according to the present invention, alpha-1 ,3-glucan fibrids are precipitated in the presence of cationic branched polymer. In an embodiment according to the present invention, alpha-1 ,3-glucan fibrids are precipitated in the presence of cationic glyoxylated polyacrylamide polymer (GPAM) and / or cationic branched glucan polymer. The cationic branched polymer is simultaneously mixed with the alpha-1 ,3-glucan solution (dope) when alpha-1 ,3-glucan is precipitated under shear in acidic conditions to produce a suspension of the alpha-1 ,3-glucan fibrid based additive comprising a mixture of alpha-1 ,3- glucan fibrids and cationic branched polymer. Precipitation under shear refers to an adequate mixing during precipitation to produce fibrillar structures. Any types of mixers can be used for mixing. The mixing speed and the duration of mixing can be adjusted as desired. The alpha-1 ,3-glucan fibrids precipitate when the alkaline alpha-1 ,3-glucan solution neutralizes in acid conditions. The method according to the present invention allows that the morphology of the alpha-1 ,3-glucan fibrids based additive can be controlled by controlling and / or altering the process parameters. At least one of the process parameters can be altered, which parameter may be selected e.g. from dope concentration (the amount of alpha-1 ,3-glucan mixed into the solvent), type of mixer, mixing speed, duration of mixing, pH during precipitation, rate of addition of solvent in which alpha-1 ,3-glucan is dissolved and the amount of cationic branched polymer. By altering the process parameters, it can be altered e.g. size of the alpha-1 ,3-glucan fibrids or shape of the fibrids.

[0032] In the present context, the term “fibrids” means nongranular, fibrous, or filmlike particles with at least one of their three dimensions being of minor magnitude relative to the largest dimension. The formation of the alpha-1 ,3- glucan fibrids in the presence of cationic branched polymer produces a fibrid composite product with better qualities than the sum of its parts. When the alpha-1 ,3-glucan fibrids are formed in the presence of cationic branched polymer, the branched cationic polymer will retain on the fibrids better than when alpha-1 , 3-glucan and cationic branched polymer are just mixed together. Cationic branched polymer could even possibly be encapsulated inside the alpha-1 , 3-glucan fibrids, as the precipitation happens in the presence of cationic branched polymer. The method according to the present invention enables the inclusion of cationic branched polymer in the fibrids formation. In the method according to the present invention alpha-1 , 3-glucan polymer and cationic branched polymer forms a composite structure, which is herein called as an alpha-1 , 3-glucan fibrids based additive comprising a mixture of alpha-1 , 3-glucan fibrids and cationic branched polymer.

[0033] In an embodiment according to the present invention, the alpha-1 , 3-glucan solution may comprise 5 - 14 weight-%, preferably 10 - 14 weight-%, and more preferably 11 - 13 weight-%, of the alpha-1 , 3-glucan, calculated from the total weight of the solution.

[0034] According to the present invention, alpha-1 , 3-glucan, which is dissolved in an alkaline solution to produce a dope and for use to build up the fibrids, is linear non-charged alpha-1 , 3-glucan polymer. According to an embodiment of the present invention, alpha-1 , 3-glucan used in the method comprises the alpha- 1 , 3-glucan having a neutral charge. This means that the alpha-1 , 3-glucan polymer does not comprise any charged substitution groups substituted to the hydroxyl groups of the polysaccharide backbone of the polymer. The polysaccharide backbone of the alpha-1 , 3-glucan polymer is linear, i.e. it is unbranched. According to an embodiment of the present invention, the alpha- 1 , 3-glucan has a molecular weight of 100 000 - 250 000 Da.

[0035] In an embodiment according to the method of the present invention, the alpha-1 , 3-glucan and the cationic branched polymer are mixed in a weight ratio of between 10:1 and 40:1 , preferably in a weight ratio of between 10:1 and 25:1 , and more preferably in a weight ratio of between 15:1 and 25:1 .

[0036] In a method according to the present invention, cationic branched polymer is mixed to the alpha-1 , 3-glucan simultaneously when alpha-1 , 3-glucan is precipitated under shear in an acid condition. Acidic condition refers to an acidic solution. Any suitable acid can be used. According to an embodiment of the present invention, an acidic solution comprises sulphuric acid. According to an embodiment of the present invention, the alpha-1 , 3-glucan and cationic branched polymer can be added to an acidic solution using any methods known by a skilled person. For example direct injection to an acidic solution can be used. In an embodiment according to the present invention, at least a part of cationic branched polymer is mixed to the alpha-1 , 3-glucan solution prior to supplying in contact with an acidic solution or prior to an injection into an acidic solution, preferably cationic branched polymer is mixed to the alpha-1 ,3-glucan solution prior to supplying in contact with an acidic solution or prior to an injection into an acidic solution. Alternatively, the alpha- 1 ,3-glucan solution and the cationic branched polymer are simultaneously supplied in contact with an acidic solution, or simultaneously injected into an acidic solution. In an exemplary embodiment according to the present invention, a method is carried out as continuous mixing using flow-through reactor. In the flow-through reactor, alpha-1 ,3-glucan, cationic branched polymer and an acidic solution are continuously supplied into the reactor and the obtained alpha-1 ,3-glucan fibrid based additive is continuously collected at the outlet. During the addition of the alpha-1 ,3-glucan and cationic branched polymer in contact with the acidic solution, the mixture of them is subjected to shear forces and turbulence allowing for the alpha-1 ,3- glucan fibrids to form via precipitation.

[0037] According to an embodiment of the present invention, the suspension of the alpha-1 ,3-glucan fibrid based additive comprising a mixture of alpha-1 ,3- glucan fibrids and cationic branched polymer has a pH in the range of 1 - 6, preferably 2 - 6 or 3 - 6.

[0038] According to the present invention a cationic branched polymer may be any kind of cationic branched water-soluble polymer. In the present disclosure, the branched polymers refer to the polymers that have a branched structure. Branched polymers have side chains that are attached to the backbone of polymer. Hence, branching of the polymer materials occurs via replacement of some atoms from the polymer chain with substituents. The substituent group can be either short side chain or long side chain attached to the backbone of the polymer. There are different types of branched polymers such as graft polymers and comb polymers.

[0039] According to the present invention, a cationic branched polymer comprises at least one cationic branched polymer. According to an embodiment of the present invention, a cationic branched polymer comprises cationic glyoxalated polyacrylamide polymer (GPAM) and / or cationic branched glucan polymer. It is assumed, without being bound by any theory, that the branched polymers have three-dimensional structure that flocs the fibrids to form larger complexes that can retain in fibers better.

[0040] In an embodiment according to the present invention, a cationic branched polymer may comprise cationic glyoxalated polyacrylamide polymer (GPAM). A cationic glyoxalated polyacrylamide polymer refers to cationic polyacrylamide polymer having a pendant glyoxalated group. In glyoxalation, basepolymer is reacted with glyoxal. The cationic polyacrylamide basepolymer may be a copolymer of acrylamide and at least one cationic monomer. According to an embodiment of the invention the polyacrylamide basepolymer is prepared by polymerizing of acrylamide and at least one cationic monomer. The acrylamide may be acrylamide or another primary amine-containing monomer, such as methacrylamide, ethylacrylamide, N- ethyl methacrylamide, N-butyl methacrylamide, or N-ethyl methacrylamide, or combinations thereof. The cationic monomer may be any suitable cationic monomer generally used in such cationic GPAMs. According to one embodiment of the invention the cationic polyacrylamide basepolymer may be prepared by polymerisation of acrylamide and at least one cationic monomer, which is selected from diallyl dimethyl ammonium chloride (DADMAC), [3- (acrylamide)propyl]trimethyl-ammonium chloride (APTAC), and [3- (methacrylamido)propyl]trimethyl-ammonium chloride (MAPTAC) and combinations thereof. The cationic glyoxalated polyacrylamide may comprise only one type of cationic monomers, or it may comprise more than one type of cationic monomers. In an embodiment according to the present invention, a cationic glyoxalated polyacrylamide polymer comprises at least 5 mol-% of cationic monomers, preferably at least 10 mol-% of cationic monomers, and more preferably at least 20 mol-% of cationic monomers, based on the total moles of polymerizable monomers. According to an embodiment of the invention cationic glyoxalated polyacrylamide polymer comprises 5 - 40 mol- % of cationic monomers, preferably 5 - 25 mol-% of cationic monomers, based on the total moles of polymerizable monomers.

[0041] The molecular weight of the cationic polyacrylamide basepolymer before glyoxalation has a major contribution to the molecular weight of the final GPAM. A weight average molecular weight of the cationic polyacrylamide basepolymer of the cationic glyoxalated polyacrylamide polymer may vary.

[0042] According to an embodiment of the present invention, a weight average molecular weight of a polyacrylamide basepolymer is in the range of 10 000 - 200 000 Da, preferably in the range of 100 000 - 200 000 Da. A basepolymer of the cationic glyoxalated polyacrylamide polymer refers in this disclosure to the main chain of the acrylamide polymer which is a result of the polymerisation reaction of acrylamide and cationic monomers. The main chain is substantially linear chain to which all other chains may be regarded as pendant. Methods for measuring the weight-average molecular weight are well known by a skilled person, for example gel-permeation chromatography (GPC) or size-exclusion chromatography (SEC), may be used.

[0043] A cationic glyoxalated polyacrylamide polymer is water-soluble, which means that the polymer is miscible with water. When mixed with an excess of water, the polymer is preferably fully dissolved and the obtained polymer solution is preferably essentially free from discrete polymer particles or granules. Excess of water means that the obtained polymer solution is not a saturated solution. According to the method of the present invention, an aqueous solution of GPAM is used. In an embodiment according to the present invention, the aqueous solution of GPAM comprises 2-5 weight-% or 2-3 weight-% of GPAM, calculated from total weight of the solution.

[0044] In another exemplary embodiment according to the present invention, a cationic branched polymer may comprise cationic branched glucan polymer(s). Cationic branched glucan polymer may comprise cationic crosslinked alpha-1 ,3-glucan polymers, cationic graft copolymers of dextran and alpha-1 ,3-glucan and any mixtures thereof.

[0045] Cationic crosslinked alpha-1 ,3-glucan polymer comprises cationic substitution groups substituted to the hydroxyl groups of the polysaccharide backbone of the polymer. The cationic substitution group of cationic alpha- 1 ,3-glucan polymer may be a substituted ammonium group, preferably a quaternary ammonium group, more preferably a trialkyl ammonium group. Alkyl group in the trialkyl ammonium group may be, for example a methyl group, a hydroxymethyl group, a hydroxyethyl group or a hydroxypropyl group. The substituted ammonium group may be, for example, trimethylammonium group. According to one preferable embodiment of the invention the cationic apha-1 ,3-glucan polymer may have a charge density value in a range of 0.1 - 50 peq / g, preferably 0.5 - 30 peq / g, more preferably 1 - 10 peq / g. According to one embodiment of the invention the cationic alpha-1 ,3-glucan polymer comprising cationic substitution groups attached to its structure may have a substitution degree (DS) in a range of 0.05 - 1 , preferably 0.05 - 0,75, more preferably 0.1 - 0.75, even more preferably 0.15 - 0.5. The substitution degree refers to the average number of hydroxyl groups substituted in each D-glucose unit in the polysaccharide backbone of alpha-1 ,3-glucan polymer. Since there are three hydroxyl groups in each D- glucose unit, the substitution degree can be no higher than 3.

[0046] The cationic crosslinked alpha-1 , 3-glucan polymer may be obtained by contacting the cationic alpha-1 ,3-glucan polymer with a crosslinker and a solvent, e.g. water. The amount of used crosslinker may be 20 - 5000 ppm, preferably 100 - 5000 ppm, calculated of polymer dry weight. According to one embodiment it is possible to use a crosslinker selected from a group comprising epihalohydrins, such as epichlorohydrin; epoxy compounds; diglycidyl ethers, such as diglycidyl ether or ethylene glycol diglycidyl ether; polyvalent metals, such as zirconium carbonate or cyanuric chloride; glyoxal; and polycarboxylic acids, such as citric acid, glutaric acid, adipic acid.

[0047] Alternatively, the cationic branched glucan polymer suitable for use in the present invention may be a cationic ester- or ether-derivative of a graft copolymer of dextran and a-1 , 3-glucan. Suitable graft copolymer derivatives, methods for their preparation and determination of their glycosidic linkage profile are described, for example, in WO 2021 / 247810. The degree of polymerization of the alpha-1 ,3-glucan may be in a range of 20 - 3000, preferably 500 - 2000. For example, the degree of polymerisation may be in a range of 20 - 2000 or 55 - 1000. Degree of polymerization refers here to the number of glucose units comprised within an individual side chain.

[0048] In the present context the term “dextran” denotes an a-glucan where at least 50%, preferably at least 60 %, more preferably at least 70 %, or even at least 80 % or at least 90 %, of the glycosidic linkages are a-1 ,6-glycosidic linkages, wherein the balance to 100 % is typically a-1 ,3-glycosidic linkages. Dextran has substantially linear structure, which means that is has 0 - 5 % of branches before formation of graft copolymer with a-1 , 3-glucan. Possible branches in dextran itself are usually short, one to three glucose monomers in length. According to one embodiment of the invention, the cationic graft copolymer may comprise 10 - 70 weight-%, preferably 20 - 60 weight-%, more preferably 30 - 50 weight-%, of dextran, calculated from the dry weight of the graft copolymer before ester or ether derivatization. The cationic graft copolymer may comprise, for example 30 - 90 weight-%, preferably 40 - 80 weight-%, more preferably 50 - 70 weight-%, of a-1 ,3-glucan, e.g. a-1 , 3- glucan side chains, calculated from the dry weight of the graft copolymer before ester or ether derivatization.

[0049] According to one embodiment, the cationic graft copolymer may be cationic graft copolymer of dextran and alpha-1 ,3-glucan comprising dextran backbone and a-1 ,3-glucan side chains, where preferably the said side chains are linked to the dextran backbone via a-1 ,2 and / or a-1 ,3 and / or a-1 ,4 branches. The a-1 ,3-glucan side chains may comprise at least 70%, preferably at least 80%, more preferably at least 90% or at least 95%, sometimes even of 99% or 100%, of a-1 ,3-glycosidic linkages.

[0050] The graft copolymer derivatives comprise one or more cationic groups linked to the graft copolymer via an ester- or ether-l inkage. The cationic group may comprise a substituted ammonium group, such as primary, secondary, tertiary or quaternary ammonium group, preferably a quaternary ammonium group, more preferably a trialkyl ammonium group. An ammonium group may be substituted with alkyl and / or aryl group(s), for example with C1 - C4 alkyl or C6 - C24 alkyl groups. One of the groups of the substituted ammonium group comprises one carbon or a carbon chain in ether- or ester-linkage to the graft copolymer.

[0051] According to one embodiment of the invention the composition may comprise a cationic graft copolymer of dextran and alpha-1 ,3-glucan which is crosslinked. Crosslinking of the branched structure of the graft copolymer further modifies the three-dimensionality of the cationic biopolymer.

[0052] In one preferred embodiment of the present invention, method for producing alpha-1 ,3-glucan fibrids based additive comprises

[0053] - dissolving linear, non-charged alpha-1 ,3-glucan in an alkaline solvent to obtain an alpha-1 ,3-glucan solution, - obtaining at least one cationic branched polymer selected from glyoxalated polyacrylamide polymer (GPAM) and / or cationic branched glucan polymer, and

[0054] - precipitating alpha-1 ,3-glucan under shear in acidic conditions and simultaneously mixing the cationic branched polymer with the alpha-1 ,3- glucan solution to produce a suspension of the alpha-1 , 3-glucan fibrid based additive comprising a mixture of alpha-1 ,3-glucan fibrids and the cationic branched polymer.

[0055] Alpha-1 ,3-glucan fibrids based additive according to the present invention comprises a mixture of alpha-1 ,3-glucan fibrids and a cationic branched polymer. In one preferred embodiment according to the present invention, alpha-1 ,3-glucan fibrids based additive according to the present invention comprises a mxture of alpha-1 , 3-glucan fibrids and a cationic GPAM and / or cationic branched glucan polymer. The fibrids have a fibrous shape with an average length of between 10 pm and 1 mm and width of between 200 nm and 200 pm.

[0056] According to an embodiment of the present invention alpha-1 ,3-glucan fibrids based additive is produced by a method according to the present invention.

[0057] According to an embodiment of the present invention, the alpha-1 ,3-glucan fibrids based additive is a suspension, which comprises 1 - 4 weight-%, preferably 2 - 3 weight-% of the additive comprising a mixture of alpha-1 , 3- glucan fibrids and a cationic branched polymer, such as cationic glyoxylated polyacrylamide polymer and / or cationic branched glucan polymer.

[0058] According to an embodiment of the present invention alpha-1 ,3-glucan fibrids based additive is used as an additive in a paper or paperboard manufacturing. In an embodiment of the present invention alpha-1 ,3-glucan fibrids based additive is used as a strength additive in paper or board manufacturing, preferably a dry strength additive in paper or board manufacturing.

[0059] Method according to an embodiment of the present invention for increasing strength, preferably dry strength, in a manufacture of a fibrous web comprising cellulosic fibres, such as in manufacture of paper or paperboard, the method comprising

[0060] - obtaining a fibre suspension comprising cellulosic fibres,

[0061] - adding to the fibre suspension alpha-1 ,3-glucan fibrids based additive according to the present invention, and

[0062] - forming a fibrous web from the fibre suspension and removing water from the fibre web.

[0063] EXPERIMENTAL

[0064] Materials

[0065] Enzymatically engineered alpha-1 ,3-glucan polymer powder was provided by IFF (DuPont Nutrition and Biosciences). The alpha-1 ,3-glucan polymer was acquired as a dried powder at 90 weight-% dry matter content.

[0066] Bleached chemi-thermomechanical pulp, BCTMP, (dry matter content 87 weight-%) and broke (dry matter content 92 weight-%) was acquired from a Nordic pulp and paperboard producer.

[0067] Glyoxalated polyacrylamides with varying cationicity: GPAM-LOW, GPAM- MED and GPAM-high provided by Kemira Oyj were used in the Examples. The different GPAMs are described in Table 1 .

[0068] Table 1. GPAM products that were used. Production of alpha-1 ,3-qlucan fibrids and alpha-1 -3-qlucan fibrids based additive comprising alpha-1 ,3-qlucan fibrids and cationic branched polymer

[0069] The alpha-1 ,3-glucan fibrids were fabricated by first dissolving alpha-1 ,3- glucan polymer powder into 4-5% NaOH to obtain 11 wt-% alpha-1 ,3-glucan solution. The obtained alpha-1 ,3-glucan solution, called dope, was mixed with a mixer (Heidolph, RZR 2102 control) for up to 15 minutes to ensure complete dissolution. A reaction vessel was filled with around 100 g of 1 .5 %- wt sulfuric acid solution. IKA T 25 digital Ultra-Turrax was placed into the reaction vessel, and it was set to 25 000 rpm to mix a content of the reaction vessel. The dope (20 g) was injected into the reaction vessel during 20 to 30 seconds, precipitating the dissolved alpha-1 , 3-glucan polymer into fibrids. Laboratory made alpha-1 ,3-glucan fibrid is used as reference in the Examples, referred as “neutral fibrid” or “Ref neutral fibrid”.

[0070] The alpha-1 , 3-glucan fibrids based additives according to the present invention were produced in similar fashion, but cationic branched polymer, such as cationic glyoxalated polyacrylamide polymer or cationic branched alpha-1 ,3-glucan polymer, being injected simultaneously with dope into the reaction vessel.

[0071] Preparation of the pulp

[0072] BTCMP was hot disintegrated with laboratory pulper (Novifibre, 45I) at 3.5% solids content in 80°C tap water for 5 minutes at 500rpm, followed by 25min at OOrpm. The broke was first torn into approximately 25mm*25mm squares and soaked in room temperature tap water overnight. It was then beaten at 1.57% solids with Valley Hollander beater for 30min until the Schopper-Riegler value was 25.

[0073] Sheet forming

[0074] The laboratory sheets were prepared using DSF (Dynamic Sheet Former, Techpap). The BCTMP and broke were diluted to 0.5% dry matter content, and the furnish, containing 75% BCTMP and 25% broke, was mixed. In addition to the alpha-1 ,3-glucan fibrids and alpha-1 -3-glucan fibrids based additive according to the present invention, silica and polyacrylamide-based retention and drainage aids and cationic starch were used to simulate the process more realistically. The target grammage for the sheets was 100 g / m2and it was adjusted trough changing the amount of furnish used for each test run. The pumping speed for the furnish was 950 rds / min and the speed of the drum was 1250 rpm. The drainage time was set to 40 s. The sheets were pressed twice between felts and blotting papers with nip press at 5 bars of pressure, and subsequently dried with a lab sheet drier oven (STFI) for 10 minutes at 130°C. The dried sheets were taken to controlled climate room for conditioning before testing. The samples were conditioned according to ISO 187 standard (23°C, 50% humidity) in a standard climate room for at least 4 hours.

[0075] Measurements

[0076] The tensile strengths of the paper samples were measured using Lorentzen & Wettre Tensile Tester code 066. The samples were prepared by stamping them to 20 x 15 mm strips per sample, 10 in the machine direction and 10 in the cross direction. The samples were measured using method based on ISO 1924-3 standard but using 12mm / min test speed.

[0077] The z-directional strength of the paper samples was measured using Lorentzen & Wettre ZD Tensile Tester, utilizing 3M Type ST-415 tape. The method was based on the ISO 15754:2009 standard.

[0078] The water retention value (WRV) was used as a test method to approximate the effect of the alpha-1 ,3-glucan based additive according to the present invention on the wet press solids on paper. The after-press dry matter content, i.e., the amount of water can be mechanically removed from the paper is an important characteristic. The mechanical removal of water from the sheet is much more energy efficient than drying with heat. The method used was a modified version of the traditional WRV measurement, where 90% of bleached kraft pulp was used in combination with 10% of the alpha- 1 ,3-glucan based additive according to the present invention / alpha-1 ,3- glucan fibrids / reference (no fibrids). First, 9.67 g of 30.7%-wt pulp was mixed well with 16.5 grams of 2% the alpha-1 ,3-glucan based additive according to the present invention / alpha-1 ,3-glucan fibrids / reference in a plastic bag. The bag was submerged in 50°C water bath for 5 minutes before dividing the contents in to 4 cylinders. Next, the cylinders were centrifuged for 15 minutes at 23°C in 3000 G. The cakes were then removed from the cylinders and weighed immediately. Finally, the cakes were dried at 105°C for at least 4 h before the final dried cakes were weighed.

[0079] The particle size distributions of different samples were measured using Malvern Mastersizer 2000. The samples were diluted in deionized water, and measured using dispersant refractive index 1.33, sample refractive index 1 .59, and absorption factor 0.01 . Mie theory was used to describe the results.

[0080] Example 1 : Performance of alpha-1 ,3-glucan fibrids based additive according to the present invention against separate addition of alpha-1 ,3- glucan fibrids and GPAM and against premixture of alpha-1 ,3-glucan fibrids and GPAM

[0081] The performance of the alpha-1 , 3-glucan fibrids based additive according to the present invention comprising alpha-1 ,3-glucan fibrids and cationic glyoxalated polyacrylamide (GPAM) were tested against separate addition of alpha-1 ,3-glucan fibrids and GPAM and against a premixture of them. In the premixture, the formed alpha-1 ,3-glucan fibrids and GPAM were premixed together in a IKA T25 digital Ultra-Turrax for 30 s at 10 000 rpm before the addition to the pulp.

[0082] The water retention was tested by a modified WRV method. Further, strength performance was evaluated by preparation and testing of handsheets, where premixed or separately dosed alpha-1 ,3-glucan fibrids and GPAM test points were used as reference.

[0083] The samples that were used for sheet forming are introduced in Table 2. Composite refers to the alpha-1 ,3-glucan fibrids based additive according to the present invention. Table 2. The descriptions of samples used.

[0084] The sheet forming was performed with 30 kg / ton addition of fibrids in every test point. It corresponded to 3kg / ton, 1.5kg / ton and 0.75kg / ton additions of GPAM-MED based on the different fibrid to GPAM ratios. Figures 1 and 2 show that the alpha-1 ,3-glucan fibrids based additive according to the present invention (referred as composite in Figs. 1 and 2) performed the best in both in- and out-of-plane strength.

[0085] In addition to performing the best regarding strength, the composites according to the present invention also thrived in WRV tests as they did not substantially increase the water retention in comparison to neutral fibrid, (“Ref’). Figure 3 shows that the composites according to the present invention improves tensile strength in comparison to reference material (neutral fibrids as such) and to separate addition of GPAM and fibrids and the pre-mixture of them, and do not affect detrimentally to the drainage properties.

[0086] Example 2: Performance of GPAMs with different cationicity in alpha-1 , 3- qlucan fibrids based additive against separate addition of alpha-1 ,3-glucan fibrids and GPAM The effect of the cationicity of the glyoxalated polyacrylamide on the strength development of the alpha-1 ,3-glucan fibrids based additive according to the present invention was studied. The results were compared to reference points where the fibrids and GPAM were applied separately to the furnish. The samples are described in the Table 3. Composite refers to the alpha-1 ,3- glucan fibrids based additive according to the present invention.

[0087] Table 3. Descriptions of the samples

[0088] The particle size distributions of the fibrids prepared from different GPAMs, were studied using a premixed fibrid / GPAM-HIGH mixture and neutral fibrid without GPAM as references. The particle size distributions (Figure 4) show that the alpha-1 ,3-glucan fibrids based additives were very similar in their size distributions. Thus, the cationicity of GPAM does not affect the precipitation significantly. However, there are clear differences in the size distributions between the neutral fibrid, pre-mixed fibrid / GPAM, and the alpha-1 ,3-glucan fibrids based additives according to the present invention. The alpha-1 , 3-glucan fibrids based additives according to the present invention contain more particles at higher sizes compared to the references. This could possibly indicate crosslinking of the fibrids to larger flocs.

[0089] In tensile strength testing, the highest tensile strength was obtained by GP- HIGH with the highest cationicity, as can be seen in Figure 5. The tensile strength in the separate addition test points trended down with the increase of the cationicity of the GPAM. The trend in composites seemed to be inverse.

[0090] While some of the separately added references were competitive in the strength results, their water retention results were significantly worse than those of the composites. Composite refers to the alpha-1 , 3-glucan fibrids based additive according to the present invention. In Figure 6 the tensile strengths are graphed against WRV, to highlight the performance of GP- HIGH. Reference (0-ref) was without any addition of fibrids or composites.

[0091] Example 3: Performance of different cationic polymers in alpha-1 ,3-qlucan fibrids based additive

[0092] In this experiment, it was studied use of different cationic polymers, both linear and branched polymers, in alpha-1 ,3-glucan fibrids based additive. Test series comprises seven different cationic polymers. The polymers and their key properties are introduced in Table 4 below.

[0093] Table 4. Description of polymers. DS of B-glucan was 0.03 and it comprises 30% dextran and 70% alpha-1 ,3- glucan.

[0094] The samples were prepared similar manner as alpha-1 ,3-glucan fibrids based additives comprising alpha-1 ,3-glucan fibrids and cationic branched polymer, as described above. The polymer is injected simultaneously with dope into the reaction vessel. The doses for the polymers were chosen to be similar as their normal dosing in papermaking. The polyacrylamide based retention chemicals were added at 1 :52 ratio, which corresponds to 0.6 kg / ton addition to pulp, when using fibrid dose of 30 kg / ton. The cationic starch, GPAM, and alpha-1 ,3-glucans were dosed at 1 :20 ratio to the fibrid composite, which corresponds to 1.5 kg / ton addition to pulp. The strength performance of the composites was evaluated by preparing laboratory handsheets with the method introduced above. The results are shown in Figure 7. Neutral fibrid is also presented in Figure 7 as a reference.

[0095] The alpha-1 ,3-glucan fibrids based additives with branched cationic polymer additives, such as GPAM and B-glucan, performed the better than linear counterparts in in- and out-of-plane strength.

[0096] Summary of the results

[0097] Alpha-1 ,3-glucan fibrids based additive produced according to the present invention performed better than their reference counterparts. The better performance was found in both in- and out-of-plane strength and in water retention. Alpha-1 , 3-glucan fibrids based additive is produced in the presence ofa cationic branched polymer, such as GPAM and / or cationic branched glucan polymer.

[0098] According to the present invention, alpha-1 ,3-glucan fibrids based additive prepared with highest cationicity GPAM was found to produce highest strength handsheets. Also, the medium cationicity products performed better than the reference points with same components dosed separately or premixed. The furnish with the alpha-1 ,3-glucan based additive according to the present invention had also the lowest water retention values, another desirable quality for the product, considering machine speeds and drying costs. Further, it has been observed that cationic branched polymers act desirable in the alpha-1 ,3-glucan fibrids based additive of the present invention compared to the linear polymers. Overall, based on the Examples the method according to the present invention can be used to produce effective dry strength additives.

Claims

Claims1. A method for producing an alpha-1 ,3-glucan fibrids based additive, characterized in that the method comprises - dissolving linear alpha-1 ,3-glucan in an alkaline solvent to obtain an alpha-1 ,3-glucan solution,- obtaining at least one cationic branched polymer,- precipitating alpha-1 ,3-glucan under shear in acidic conditions and simultaneously mixing the cationic branched polymer with the alpha-1 ,3- glucan solution to produce a suspension of the alpha-1 , 3-glucan fibrid based additive comprising a mixture of alpha-1 ,3-glucan fibrids and the cationic branched polymer.

2. The method according to claim 1 , characterized in that the alpha-1 ,3- glucan solution comprises 5 - 14 weight-%, preferably 10 - 14 weight-%, and more preferably 11 - 13 weight-%, of the linear alpha-1 , 3-glucan, calculated from the total weight of the solution.

3. The method according to claim 1 or 2, characterized in that the alpha-1 ,3- glucan comprises the alpha-1 ,3-glucan having a neutral charge.

4. The method according to any of the preceding claims, characterized in that the alpha-1 ,3-glucan and the cationic branched polymer are mixed in a weight ratio of between 10:1 and 40:1 , preferably in a weight ratio of between 10:1 and 25:1 , and more preferably in a weight ratio of between 15:1 and 25:1.

5. The method according to any of the preceding claims, characterized in that at least a part of the cationic branched polymer is mixed to the alpha-1 ,3- glucan solution prior to supplying in contact with an acidic solution.

6. The method according to any of the preceding claims, characterized in that the alpha-1 ,3-glucan solution and the cationic branched polymer are simultaneously supplying in contact with an acidic solution.

7. The method according to any of the preceding claims, characterized in that the suspension of the alpha-1 ,3-glucan fibrid based additive comprisinga mixture of alpha-1 ,3-glucan fibrids and the cationic branched polymer has a pH in the range of 1 - 6, preferably 2 - 6 or 3 - 6.

8. The method according to any of the preceding claims, characterized in that the cationic branched polymer comprises cationic glyoxalated polyacrylamide polymer and / or cationic branched glucan polymer.

9. The method according to claim 8, characterized in that the cationic glyoxalated polyacrylamide polymer comprises at least 5 mol-% of cationic monomers, preferably at least 10 mol-% of cationic monomers, and more preferably at least 20 mol-% of cationic monomers, based on the total moles of polymerizable monomers.

10. The method according to claim 8 or 9, characterized in that the cationic glyoxalated polyacrylamide polymer comprises 5 - 40 mol-% of cationic monomers, based on the total moles of polymerizable monomers.

11. The method according to any of the preceding claims, characterized in that cationic branched glucan polymer comprises cationic crosslinked alpha- 1 ,3-glucan polymers, graft copolymers of dextran and alpha-1 ,3-glucan and any mixtures thereof.

12. Alpha-1 ,3-glucan fibrids based additive comprising a mixture alpha-1 ,3- glucan fibrids and a cationic branched polymer.

13. The additive according to claim 12, characterized in that the fibrids have a fibrous shape with an average length of between 10 pm and 1 mm and width of between 200 nm and 200 pm.

14. The additive according to claim 12 or 13, characterized in that the alpha- 1 ,3-glucan based additive is produced by a method according to any of the preceding claims 1 - 11.

15. Use of the alpha-1 ,3-glucan based additive according to any of the preceding claims 12 - 14 as a strength additive in paper or board manufacturing.

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