Strength agent composition

Abstract

A strength agent composition for a product, wherein the product is a paper, board, molded fiber, nonwoven and / or textile product comprising cellulose or other carbohydrate-based fibers is disclosed. The strength agent composition may comprise an amphoteric polyacrylamide and a cationic starch. The cationic starch may have a degree of substitution (DS) of at least 0.12.

Description

[0001] STRENGTH AGENT COMPOSITION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a strength agent composition for a product ; a method for preparing an aqueous solution of the strength agent composition; a method for manufacturing a product ; and use of the strength agent composition .

[0004] BACKGROUND

[0005] In the manufacture of paper, board, molded fiber, nonwoven and / or textile products from a fiber stock, various chemical agents and additives may be added to the fiber stock prior to forming a web therefrom . For example , strength agents such as starch or synthetic polymers may be added to the fiber stock to improve dry strength properties of the paper or board product .

[0006] Starch, however, may hinder dewatering of webs and cause microbiological issues . Further, there may be a need to improve sustainability in various ways , e . g . by reducing the dosage o f the strength agents added to the fiber stock .

[0007] SUMMARY

[0008] This Summary is provided to introduce a selection o f concepts in a simpli fied form that are further described below in the Detailed Description . This Summary is not intended to identi fy key features or essential features of the claimed subj ect matter, nor is it intended to be used to limit the scope of the claimed subj ect matter .

[0009] A strength agent composition for a product , wherein the product is a paper, board, molded fiber, nonwoven and / or textile product comprising cellulose or other carbohydrate-based fibers , is disclosed . The strength agent composition may comprise an amphoteric polyacrylamide and a cationic starch . The cationic starch may have a degree of substitution ( DS ) of at least 0 . 12 .

[0010] DETAILED DESCRIPTION

[0011] A strength agent composition for a product is disclosed .

[0012] The product may be a paper, board, molded fiber, nonwoven and / or textile product comprising cellulose or other carbohydrate-based fibers .

[0013] The strength agent composition may comprise an amphoteric polyacrylamide and a cationic starch .

[0014] The strength agent composition may be understood as referring to a composition that is suitable for use as a strength agent , for example as a dry strength agent .

[0015] The strength agent composition may improve dry strength when added to furnish, i . e . to fiber stock . The strength agent composition may improve e . g . tensile strength, burst strength, tear resistance , crushing resistance , and / or short span compression test ( SCT ) strength of the product . It may be added to various types of fiber stocks . It may however work particularly well in fiber stocks comprising chemi-thermomechanical pulp ( CTMP ) fibers . It may also work particularly well in fiber stocks comprising recycled fibers .

[0016] Not to be bound by theory, it may be that the amphoteric polyacrylamide and the cationic starch may interact together before entering the fiber materials and then with fibers in the fiber stock, forming a polymer network . The cationic starch and the amphoteric polyacrylamide are also relatively large polymers , and together they may form a relatively large polymer network . The strength agent composition may thus comprise or be capable of forming a polyelectrolyte complex ( PEC ) formed at least by the amphoteric polyacrylamide and the cationic starch . The PEC forms a polymer network that is not strongly linear, which allows for applying the strength agent composition to the fiber stock in an amount suf ficient to achieve desired dry strength . It may be understood that the PEC may be formed in an aqueous solution .

[0017] The strength agent composition according to one or more embodiments described in this speci fication may provide various benefits improving sustainability .

[0018] The strength agent composition may be provided in the form of a powder . In other words , it may be a dry particulate mixture , i . e . in the form of solid particles . Thus costs and emissions relating to transport and storage of the strength agent composition may be relatively low . Thus application costs calculated on the bas is of a desired dry strength may thus be relatively low .

[0019] The strength agent composition may have a dry solids content of at least about 80 % (w / w) , or preferably at least about 82 % (w / w) , or more preferably at least about 85 % (w / w) , or even more preferably about 85 - 95 % (w / w) , on the basis of the total weight of the strength agent composition .

[0020] Further, the strength agent composition may be microbiologically very stable , in particular in the form of a powder . Shel f li fe may be improved, as the risk of microbial growth or degradation during transportation and storage may be reduced .

[0021] The strength agent composition, e . g . in the form o f a powder, may be water soluble . In particular, it may be soluble in water at a temperature of 60 ° C or lower . The strength agent composition may be dissolved in water, such that an aqueous solution of the strength agent composition is obtained . Such a solution may be considered an aqueous strength agent composition . The strength agent composition may thus , in some embodiments , be in the form of an aqueous solution .

[0022] In the context of this speci fication, the term "aqueous solution" encompasses not only true solutions , but al so aqueous di spersions as wel l as solutions that may contain minor amounts of incompletely dissolved or partially dissolved material , or undissolved or incompletely dissolved residues . The aqueous solution may preferably contain less than 5 % (w / w) , more preferably less than 2 % (w / w) , even more preferably less than 1 % (w / w) of insoluble material , or it may be free from insoluble material . In the context of this speci fication, the term "water-soluble" may be understood such that the strength agent composition is fully miscible with water . When mixed with excess of water, the strength agent composition may be preferably fully dissolved and the obtained polymer solution may be preferably essentially free from discrete particles or granules .

[0023] The strength agent composition, e . g . in the form of a powder, may be dissolved in water at low temperatures ( e . g . at temperatures of 60 ° C or lower ) under stirring . The dissolution of the strength agent composition does not require cooking . Further, the dissolution of the strength agent composition does not require mechanical high speed dispersing and / or high shear dissolution . As no cooking is required, the stability of the amphoteric polyacrylamide in solution may be improved .

[0024] The strength agent composition is stable as an aqueous solution for at least 24 hours .

[0025] The strength agent composition may be applied as a relatively low dosage . For example , in a typical situation, 10 kg / 1 of wet end starch may be replaced with 2 kg / t of the strength agent composition according to one or more embodiments described in this speci fication . Further, with starch, increasing the dosage may slightly improve drainage time , but with increasing dosing levels , drainage may quickly start to deteriorate . This is a typical problem seen in paper or board machines . With the strength agent composition according to one or more embodiments described in this speci fication, drainage may be improved and may be significantly better with e . g . about 1 kg / 1 addition level than starch . Further, increasing the dosage of the strength agent composition according to one or more embodiments described in this speci fication may only slightly reduce drainage .

[0026] The strength agent composition may comprise a mixture of the amphoteric polyacrylamide and the cationic starch . In other words , the strength agent composition may comprise a mixture of the amphoteric polyacrylamide and the cationic starch in the form of a powder ( i . e . dry powder ) . In other words , the strength agent composition is a dry powder comprising the mixture of the amphoteric polyacrylamide and the cationic starch . In some embodiments , the strength agent composition may be understood as referring to a combination of the amphoteric polyacrylamide and the cationic starch, wherein the amphoteric polyacrylamide and the cationic starch may be provided e . g . as separate powders , for example in separate containers . Such separate powders could then be e . g . added to water separately and dissolved therein to form the aqueous solution of the strength agent composition .

[0027] The strength agent composition may comprise a mixture of solid particulate amphoteric polyacrylamide and solid particulate cationic starch . In other words , the strength agent composition may comprise or be a mixture of the amphoteric polyacrylamide and of the cationic starch, in which both the amphoteric polyacrylamide and the cationic starch are in dry, solid particulate form . Such a mixture in particulate form, in particular in dry particulate form, may be easy and economically advantageous to store and transport. The strength agent composition in the form of the dry (solid) particulate material may have a moisture content of at most 25 (w / w) , or at most 5 % (w / w) based on the total weight of the strength agent composition. The particle size of the dry (solid) particulate material may vary for example in the range of 5 to 2000 microns.

[0028] The strength agent composition may comprise at least at least 80 % (w / w) , or at least 90 % (w / w) , or at least 95 % (w / w) of the amphoteric polyacrylamide and the cationic starch, based on the total weight (or the total dry weight) of the strength agent composition. The strength agent composition may essentially consist of the amphoteric polyacrylamide and the cationic starch.

[0029] The cationic starch may have a degree of substitution (DS) of at least about 0.12, or preferably at least about 0.14, more preferably at least about 0.16, or a DS in the range of about 0.14 - 0.25, or preferably in the range of about 0.16 - 0.21. A higher DS may improve the solubility of the strength agent composition in water. Further, a higher DS may provide improved strength properties for the product, for example a paper, board and / or molded fiber products. The DS may be determined from the cationic starch after washing by calculating the DS from the nitrogen content of the cationic starch determined by the commonly known Kjeldahl method, e.g. according to ISO 1871:2009.

[0030] The amphoteric polyacrylamide and the cationic starch may form, or be capable of forming, a polyelectrolyte complex having a net charge density in the range of about 0.3 - 2.0 meq / g, or about 0.5 - 2.0 meq / g, preferably about 0.6 - 1.8 meq / g, more preferably about 0.7 - 1.5 meq / g, even more preferably about 0.75 - 1.2 meq / g, when measured in an aqueous solution at a pH of about 7. In other words, the amphoteric polyacrylamide and the cationic starch may provide the strength agent composition with a charge density in the range of about 0.5 - 2.0 meq / g when measured in an aqueous solution at a pH of about 7.

[0031] The cationic starch may have an intrinsic viscosity (IV) of at least about 1 dl / g, preferably in the range of about 1 - 2 dl / g.

[0032] The amphoteric polyacrylamide may have an intrinsic viscosity in the range of about 3 - 15 dl / g, preferably in the range of about 7 - 13 dl / g.

[0033] The intrinsic viscosities may be determined from the pure cationic starch or from the pure amphoteric polyacrylamide in a known manner, e.g. in a 1 N NaCl solution at 25 °C, at neutral pH by using an Ub- belohde capillary viscometer. The above IVs may be particularly well suited e.g. for improving the strength properties of the paper, board and / or molded fiber product. IV may in general depend on the molecular weight of a polymer.

[0034] The strength agent composition thus comprises both anionic groups mainly originating from the amphoteric polyacrylamide as well as cationic groups originating from the cationic starch and from the amphoteric polyacrylamide .

[0035] The charge density of the polymers can be influenced by the pH of the solution. For example, cationic polymers in which the cationic source is an amine, primary, secondary or tertiary, might be fully ionized at one pH and non-ionized at another pH. A cationic polymer, in which the cationic source is a quaternary ammonium salt, may be cationic in all relevant pH ranges. The optimal pH for PEC formation may be where both polymers are sufficiently charged.

[0036] The charge (density) may be determined at the target pH, adjusted with e.g. 10 weight! aqueous NaOH solution or 10 weight! H2SO4 solution, depending on the starting pH of the solution and the target pH, by charge titration. Mtitek Particle Charge Detector PCD03 may be used for end point detection.

[0037] The amphoteric polyacrylamide may have a (net) cationic charge density in the range of about 0.5 - 2.5 meq / g when measured in an aqueous solution at a pH of about 7.

[0038] The amphoteric polyacrylamide may have a (net) cationic charge density in the range of about 0.6 - 2.5 meq / g, or preferably in the range of about 0.7 - 2.2 meq / g, or more preferably in the range of about 0.8 1.8 meq / g, when measured in an aqueous solution at a pH of about 2.8.

[0039] The above charge densities may be suitable for providing an effective interaction between the amphoteric polyacrylamide and the cationic starch, as well as with fibers and fillers in a fiber stock to which the strength agent composition is added.

[0040] The amphoteric polyacrylamide may have a ratio of anionic groups to cationic groups in the range of about 1:20 to 1:4.

[0041] The amphoteric polyacrylamide may be understood as referring to a copolymer of acrylamide comprising both anionic and cationic groups. The amphoteric polyacrylamide may be obtainable or obtained by polymerisation of acrylamide together with anionic and cationic monomers .

[0042] The amphoteric polyacrylamide may be linear, branched and / or crosslinked. The term "branched" may refer to a polymer, such as the amphoteric polyacrylamide, that has a main chain with one or more side chains (branches) connected to it. These branches may themselves have further branches, leading to a complex, tree-like structure. A linear polymer may refer to a polymer, such as the amphoteric polyacrylamide, which comprises or consists of a single continuous chain. The branches may be short-chain branches or long-chain branches . The amphoteric polyacrylamide may be a linear polyacrylamide . In other words , the amphoteric polyacrylamide may be unbranched and preferably not crosslinked . In the gel polymerisation the amount o f cros slinker may be less than 0 . 002 mol-% , preferably less than 0 . 0005 mol-% , more preferably less than 0 . 0001 mol-

[0043] In some embodiments , the gel polymerisation may be completely free of cross-linker . The linear amphoteric polyacrylamide may reduce ef fectively the possibility for insoluble polymer particles , which could reduce the quality of the produced product .

[0044] For example , 10 - 95 % , pre ferably 30 - 90 % , more preferably 50 - 85 % , even more preferably 60 - 80 % , of the charged groups in the amphoteric polyacrylamide structure may be cationic .

[0045] The amphoteric polyacrylamide in the polymer product may have a cationic net charge . This means that the net charge of the amphoteric polyacrylamide remains positive , even i f it contains anionic groups . Cationic net charge may improve the interaction of the amphoteric polyacrylamide with the fibers in the stock . The net charge of the amphoteric polyacrylamide is calculated as the sum of the charges of the cationic and anionic groups present .

[0046] The mass average molecular weight (MW) of the amphoteric polyacrylamide may be in the range of 1 500 000 - 9 000 000 g / mol , preferably 3 000 000 - 8 000 000 g / mol . Such an average molecular weight o f the amphoteric polyacrylamide may provide good attachment and bridging between the fibers in the stock . With such average molecular weights , the fibers may be more evenly spaced and the formation o f the web is not disturbed . The term "mass average molecular weight" is used to describe the magnitude of the polymer chain length . Mass average molecular weight values may be calculated from intrinsic viscosity results measured in a known manner in IN NaCl at 25 °C by using an Ubbelohde capillary viscometer. The capillary selected is appropriate, and in the measurements of this application an Ubbelohde capillary viscometer with constant K=0.005228 was used. The average molecular weight is then calculated from intrinsic viscosity result in a known manner using Mark- Houwink equation [r|]=K-Ma, where [q] is intrinsic viscosity, M molecular weight (g / mol) , and K and a are parameters given in Polymer Handbook, Fourth Edition, Volume 2, Editors: J. Brandrup, E.H. Immergut and E.A. Grulke, John Wiley & Sons, Inc., USA, 1999, p. VII / 11 for poly ( acrylamide ) . Accordingly, value of parameter K is 0.0191 ml / g and value of parameter "a" is 0.71. The average molecular weight range given for the parameters in the conditions used is 490 000 - 3 200 000 g / mol, but the same parameters are used to describe the magnitude of molecular weight also outside this range. pH of the polymer solutions for intrinsic viscosity determination may be adjusted to 2.7 by formic acid to avoid possible poly-ion complexation of amphoteric polyacrylamides.

[0047] The amphoteric polyacrylamide may comprise at least 80 mol-% structural units derived from acrylamide and / or methacrylamide monomers and 20 mol-% or less of structural units originating anionic and cationic monomers. The percentage values are calculated from the total dry weight of the polymer. The total ionicity of the amphoteric polyacrylamide may be in the range of about 4 - 20 mol-%, preferably about 5 - 16 mol-%, more preferably about 6 - 14 mol-%, even more preferably about 6 - 12 mol-%. Total ionicity includes all groups having ionic charge in the amphoteric polyacrylamide, most of the charged groups originating from the ionic monomers, but including also other charged groups originating from chain termination agents or the like. It has been observed that it may be beneficial when the total ionicity of the polymer for strength enhancing purposes is 15 mol-% or less. If the ionicity is higher, the polymer may have a tendency to flocculate anionic trash and other disturbing substances in the stock instead of providing a good attachment between the fibers. The ionicity may be selected in order to provide maximal strength for the final product and / or good formation of the web. Furthermore, the ionicity may be optimized in view of avoiding the zeta potential problems in the stock, i.e. positive zeta potential values.

[0048] 10 - 90 %, preferably 30 - 90 %, more preferably 50 - 85 %, even more preferably 60 - 80 %, of the charged groups in the amphoteric polyacrylamide may be cationic.

[0049] The cationic groups in the amphoteric polyacrylamide may originate from monomers selected from 2- (dimethylamino) ethyl acrylate (ADAM) , [2- (acryloyloxy) ethyl] trimethylammonium chloride (ADAM-CI) , 2- (dimethylamino) ethyl acrylate benzylchloride, 2- (dimethylamino ) ethyl acrylate dimethylsulphate, 2-dimethyl- aminoethyl methacrylate (MADAM) , [2- (methacryloyloxy) ethyl] trimethylammonium chloride (MADAM-CI) , 2- dimethylaminoethyl methacrylate dimethylsulphate, [3- ( acryloylamino ) propyl ] trimethylammonium chloride (AP- TAC) , [ 3- (methacryloylamino ) propyl ] trimethylammonium chloride (MAPTAC) , diallyldimethylammonium chloride (DADMAC) , and any mixtures or combinations thereof. Preferably the cationic groups in the amphoteric polyacrylamide may originate from monomers selected from [2- ( acryloyloxy ) ethyl ] trimethylammonium chloride (ADAM- CI) , [ 3- ( acryloylamino ) propyl ] trimethylammonium chloride (APTAC) , [ 3- (methacryloylamino ) propyl ] trimethylammonium chloride (MAPTAC) , and any mixtures or combinations thereof. More preferably the cationic monomer is [ 2- ( acryloyloxy) ethyl ] trimethylammonium chloride (ADAM-CI) .

[0050] The anionic groups in the amphoteric polyacrylamide may originate from monomers selected from unsaturated mono- or dicarboxylic acids, such as acrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconic acid, crotonic acid, isocrotonic acid, angelic acid, tiglic acid, and any mixtures or combinations thereof . Preferably the anionic groups may originate from acrylic acid and / or itaconic acid .

[0051] The amphoteric polyacrylamide may be obtainable or obtained by gel polymerisation . According to an embodiment , this preparation process of the amphoteric polyacrylamide may use a reaction mixture comprising non-ionic monomers , such as acrylamide , and the charged anionic and cationic monomers . The monomers in the reaction mixture may be polymerised in presence of initiator ( s ) by using free radical polymerisation . The temperature in the beginning of the polymeri sation may be less than 40 ° C, optionally less than 30 ° C . In some embodiments , the temperature at the beginning of the polymerisation may be even less than 5 ° C . The free radical polymerisation of the reaction mixture produces amphoteric polyacrylamide , which i s in the form o f a gel or a highly viscous liquid . After the gel polymerisation, the obtained amphoteric polyacrylamide in gel form may be comminuted, such as shredded or chopped, and dried, whereby a particulate polymer product is obtained . Depending on the used reaction apparatus , shredding or chopping may be performed in the same reaction apparatus where the polymerisation takes place . For example , the polymerisation may be performed in a first zone of a screw mixer, and the shredding of the obtained polymer may be performed in a second zone of the said screw mixer . It is also possible that the shredding, chopping or other particle si ze adj ustment is performed in a treatment apparatus , which is separate from the reaction apparatus . For example , the obtained water soluble polymer may be trans ferred from the second end of a reaction apparatus , which is a belt conveyor, through a rotating hole screen or the like , where it is shredded or chopped into small particles . After shredding or chopping, the comminuted amphoteric polyacrylamide may be dried and milled to a desired particle size.

[0052] The amphoteric polyacrylamide may, in some embodiments, be obtainable or obtained by a gel polymerisation process, wherein a content of non-aqueous solvent in the reaction mixture is less than 10 % (w / w) , preferably less than 5 % (w / w) , more preferably less than 3 % (w / w) .

[0053] The amphoteric polyacrylamide may, in some embodiments, be obtainable or obtained by a gel polymerisation, wherein the content of monomers in the reaction mixture at the beginning of the polymerisation is at least 29 % (w / w) , preferably at least 30 % (w / w) , more preferably at least 32 % (w / w) .

[0054] A ratio of the amphoteric polyacrylamide to the cationic starch in the strength agent composition may be in the range of about 1:3 to 3:1, preferably in the range of about 1:2 to 2:1 by weight.

[0055] The cationic starch may have a cationic charge density in the range of about 0.6 - 1.5 meq / g when measured in an aqueous solution at a pH of about 7.

[0056] In particular, in embodiments in which the cationic starch has a DS of at least 0.16, the cationic starch may have a cationic charge density in the range of about 0.8 - 1.3 meq / g when measured in an aqueous solution at a pH of about 7.

[0057] The cationic starch may originate e.g. from potato, waxy potato, rice, waxy corn, sweet potato, arrowroot or tapioca starch, or any combination thereof. Preferably the cationic starch originates from waxy corn starch and / or waxy potato starch.

[0058] Cationic starch suitable for use in the strength agent composition may be obtained by cationising starch by any suitable method. The cationic starch may be obtained e.g. by using 3-chloro-2-hydroxypro- pyltrimethylammonium chloride or 2 , 3-epoxypropyltrime- thylammonium chloride. It is also possible to cationise starch by using cationic acrylamide derivatives , such as ( 3-acrylamidopropyl ) -trimethylammonium chloride . Various methods for cationisation of starch are known for a person skilled in the art .

[0059] According to an embodiment , the cationic starch may be obtainable or obtained by using cationisation as the sole chemical derivati zation of starch, and the cationic starch is thus non-cross-linked, non-grafted, or it has not been otherwise chemically modi fied .

[0060] The strength agent composition may comprise , at least in some embodiments , one or more further auxiliaries or additives , such as a preservative , a biocide , a stabili zer, an antioxidant , and / or a pH adj usting agent .

[0061] A method for preparing an aqueous solution of the strength agent composition according to one or more embodiments described in this speci fication is also disclosed .

[0062] The method may comprise dissolving the strength agent composition in water, thereby obtaining the aqueous solution of the strength agent composition .

[0063] The method may comprise dissolving the strength agent composition in water having a temperature of 60 ° C or lower, thereby obtaining the aqueous solution of the strength agent composition .

[0064] In some embodiments , the method may comprise dissolving an amphoteric polyacrylamide and a cationic starch in water, the water optionally having a temperature of 60 ° C or lower, thereby obtaining the aqueous solution of the strength agent composition . The amphoteric polyacrylamide and the cationic starch may be according to one or more embodiments described in this speci fication .

[0065] The strength agent composition may be dissolved in water having a temperature of e . g . about 28 - 60 °C . The water may have a pH of about 3 - 6 . The strength agent composition may be dissolved in the water at e . g . a concentration of 0 . 3 - 3 % (w / w) . The strength agent composition may be dissolved in the water with stirring, for example for about 10 - 120 minutes .

[0066] The dissolving may be performed as a batch proces s or as a continuous process . The dissolving may be performed, for example , by continuous dissolution at a temperature of about 40 ° C, at a pH o f about 3 . 5 , at a concentration of about 1 . 4 % (w / w) and for about a 40 min dissolving time . Thereby about 10 insoluble particles may be obtained on a 200 pm wire in a 200 ml sample with 3 min washing . The dissolving may be assisted by stirring . High-shear dissolution may not be necessary .

[0067] When the strength agent composition is dissolved in water, thereby obtaining the aqueous solution of the strength agent composition, the amphoteric polyacrylamide and the cationic starch may form the polyelectrolyte complex . The amphoteric polyacrylamide and the cationic starch may therefore be in the form of the polyelectrolyte complex in the aqueous solution .

[0068] The obtained aqueous strength agent composition may then be optionally di luted . The aqueous strength agent composition may be introduced, after the optional dilution, to the fibre stock at a selected application location .

[0069] In some embodiments , the strength agent composition may be mixed on-site at a paper or board mill . This means that the amphoteric polyacrylamide and the cationic starch may be transported separately, for example as dry products , to the site of use , such as paper mi ll or board mill . At the site of use , the amphoteric polyacrylamide and the cationic starch may be optionally dissolved and / or diluted and prepared into the aqueous solution of the strength agent composition by mixing .

[0070] Any features disclosed in the context of the strength agent composition, including any features relating to the amphoteric polyacrylamide and the cationic starch, may be understood as also being disclosed in the context of the methods and uses disclosed in this speci fication .

[0071] A method for manufacturing a product is further disclosed . The product may be a paper, board, molded fiber, nonwoven and / or textile product comprising cellulose or other carbohydrate-based fibers .

[0072] The method may comprise adding an aqueous solution of the strength agent composition according to one or more embodiments described in this speci fication to a fiber stock, and forming a fibrous web of the fiber stock comprising the strength agent composition .

[0073] The method may further comprise dissolving the strength agent composition in water, thereby obtaining the aqueous solution of the strength agent composition .

[0074] The method may further comprise dissolving the strength agent composition in water having a temperature of 60 ° C or lower, thereby obtaining the aqueous solution o f the strength agent composition . I t may be dissolved e . g . as described above .

[0075] When the strength agent composition is dissolved in water, thereby obtaining the aqueous solution of the strength agent composition, the amphoteric polyacrylamide and the cationic starch may form the polyelectrolyte complex . The amphoteric polyacrylamide and the cationic starch may therefore be in the form of the polyelectrolyte complex in the aqueous solution . The amphoteric polyacrylamide and the cationic starch may thus be in the form of the polyelectrolyte complex prior to and when adding the aqueous solution of the strength agent composition to the fiber stock .

[0076] The aqueous solution of the strength agent composition may be added to the f iber stock as a wet end chemical .

[0077] The term " fiber stock" may be understood as referring to an aqueous suspension, which comprises fibers and optionally a filler . The fiber stock, i . e . furnish, is not particularly limited, as the strength agent composition may be suitable for various different fiber sources and end uses. The fiber stock may comprise recycled fibres and / or virgin fibres.

[0078] The fiber stock may comprise e.g. chemi-ther- momechanical pulp fibers and / or recycled fibers.

[0079] The fiber stock may comprise e.g. at least about 20 % , or at least about 50 % , or at least about 60 %, of the chemi-thermomechanical pulp fibers based on the total dry weight of the fibers in the fiber stock.

[0080] The fiber stock may comprise e.g. at least about 50 % of the recycled fibers based on the total dry weight of the fibers in the fiber stock.

[0081] However, the proportions of the CTMP fibers and / or of the recycled fibers are not particularly limited .

[0082] The solids content of the aqueous solution of the strength agent composition may be e.g. in the range of 0.3 - 3 weight-%, preferably 0.5 - 2 weight-%. This may provide easy mixing of the strength agent composition and avoiding an excess addition of water to the fiber stock. Optionally the strength agent composition may be further diluted before introduction to the fiber stock. Preferably the viscosity of the aqueous solution of the dry strength composition, e.g. at the said solids content range, is less than 5000 mPas, preferably less than 1000 mPas, more preferably less than 500 mPas, as measured at 25 °C by using Brookfield LV DV1, to ensure good mixing to the fiber stock.

[0083] The strength agent composition may be introduced to thick stock and / or to thin stock. Preferably the strength agent composition is introduced at least to the thick stock. Thick stock is here understood as fibre stock having consistency >2 weight-%, preferably >2.5 weight-%. By introducing the strength agent composition to the thick stock i.e. to higher consistency, an improvement in strength effect may be attained, allowing the strength agent composition to interact with fibers before dilution of the thick stock with white water that may bring fines, fillers, anionic trash, etc., which might otherwise consume the ionic and / or hydrogen bonding capacity of the composition.

[0084] The strength agent composition may be applied also on a fiber web and / or between wet plies of a multiply construct before joining, for improving one or more strength properties, or as an adhesive in the manufacture of corrugated board from fluting and liner. Alternatively, the strength agent composition may be used in sizing emulsions, such as ASA, AKD or rosin emulsions, as stabilizing polymer, and / or for improving retention of internal sizing agent.

[0085] It is also possible to add one or more other additives, such as a retention aid, to the fiber stock. Suitable retention aids may include, for example, anionic and cationic polyacrylamides having a weight-average molecular weight more than 3 000 000 g / mol, and / or inorganic microparticles such as silica, bentonite, etc.

[0086] The method may further comprise forming the product from the fibrous web.

[0087] The product may comprise cellulose fibers.

[0088] The product may be a paper product. The product may be a board product. The product may be a molded fiber product. The product may be a nonwoven and / or textile product, the nonwoven and / or textile product comprising cellulose or other carbohydrate-based fibers .

[0089] Thus the method steps required for forming the product from the fibrous web may depend on the type of the product .

[0090] The product may be e.g. a folding boxboard (FBB) optionally comprising chemi-thermomechanical pulp (CTMP) fibers, such as a folding boxboard comprising a mid-ply comprising chemi-thermomechanical pulp fibers, or a fluting comprising recycled fibers. The pH of the fibre stock may be e.g. in the range of about 4 to 9, or in the range of about 6.5 to 7.5.

[0091] The strength agent composition may be added to the fiber stock e.g. in an amount of about 0.5 - 3 kg / t .

[0092] Use of the strength agent composition according to one or more embodiments described in this specification for improving one or more strength properties of a product is disclosed. The product may be a paper, board, molded fiber, nonwoven and / or textile product comprising cellulose or other carbohydrate-based fibers.

[0093] The one or more strength properties may comprise e.g. one or more of tensile strength, burst strength, tear resistance, crushing resistance, and / or short span compression test (SCT) strength.

[0094] EXAMPLES

[0095] Reference will now be made in detail to various embodiments, an example of which is illustrated in the accompanying drawings .

[0096] The description below discloses some embodiments in such a detail that a person skilled in the art is able to utilize the embodiments based on the disclosure. Not all steps or features of the embodiments are discussed in detail, as many of the steps or features will be obvious for the person skilled in the art based on this specification.

[0097] EXAMPLE 1

[0098] The strength agent composition of an amphoteric polyacrylamide and a cationic starch on the z- directional tensile strength (ZDT) was studied with folding box board furnish containing CTMP pulp (70%) and coated broke (30%) acquired from European mill. 150 g / m2sheets were formed with dynamic sheet former (DSF) (Techpap) as follows: Test fibre stock was diluted to 0.6 % consistency with deionized water, pH was adjusted to 7 and conductivity to 1.5 mS / cm. The obtained pulp mixture was added to DSF. Chemical additions were made to mixing tank of DSF. Water was drained out after all the pulp was sprayed. Drum was operated with 1250 rpm, mixer for pulp 450 rpm, pulp pump 950 rpm / min, number of sweeps 100 and scoop time was 60 s. Sheet was removed from drum between wire and 1 blotting paper on the other side of the sheet. Wetted blotting paper and wire were removed. Sheets were wet pressed at Techpap nip press with 5 bar pressure with 2 passes having new blotting paper each side of the sheet before each pass. Sheets were dried in restrained condition in drum dryer. Drum temperature was adjusted to 92 °C and passing time to 1 min. Four passes were made. First two passes with between blotting papers and 2 passes without. Before testing in the laboratory sheets were pre-conditioned for 24 h at 23 °C in 50 % relative humidity, according to the standard ISO 187 .

[0099] Reference strength additive used in the experiments was cationic potato starch (DS 0.045) (5 and 10 kg / t) , a typically used strength aid in this type of furnish. With new strength additive (composition of amphoteric polyacrylamide and cationic starch) addition levels were 1 and 2 kg / t. All chemical amounts were kg dry chemical per ton dry fibre stock. All points included retention aids (CPAM 200 g / t and silica 200 g / t) .

[0100] Table 1. Sheet testing devices and standard methods used for produced paper sheets. Results showed (Table 2) that composition of amphoteric polyacrylamide and cationic starch increased substantially Z-directional strength. To get same strength levels compared to traditional cationic wetend starch dosage levels were significantly lower with this new composition.

[0101] Table 2. Effect different strength systems on board properties

[0102] EXAMPLE 2

[0103] The strength agent composition of an amphoteric polyacrylamide and a cationic starch on the z- directional tensile strength (ZDT) was studied with folding box board furnish containing chemi-thermomechanical pulp (CTMP) (20%) groundwood pulp (GW) (50%) and coated broke (30%) acquired from European mill. 120 g / m2sheets were formed with dynamic sheet former (DSF) (Techpap) as follows: Test fibre stock was diluted to 0.6 % consistency with deionized water, pH was adjusted to 7 and conductivity to 1 mS / cm. The obtained pulp mixture was added to DSF. Chemical additions were made to mixing tank of DSF. Water was drained out after all the pulp was sprayed. Drum was operated with 1250 rpm, mixer for pulp 450 rpm, pulp pump 950 rpm / min, number of sweeps 100 and scoop time was 60 s. Sheet was removed from drum between wire and 1 blotting paper on the other side of the sheet. Wetted blotting paper and wire were removed. Sheets were wet pressed at Techpap nip press with 5 bar pressure with 2 passes having new blotting paper each side of the sheet before each pass. Sheets were dried in restrained condition in drum dryer. Drum temperature was adjusted to 92 °C and passing time to 1 min. Four passes were made. First two passes with between blotting papers and 2 passes without. Before testing in the laboratory sheets were pre-conditioned for 24 h at 23 °C in 50 % relative humidity, according to the standard ISO 187 .

[0104] Reference strength additive used in the experiments was cationic corn starch (DS0.027) (2.5, 5 and 10 kg / t) , a typically used strength aid in this type of furnish. With new strength additive (composition of amphoteric polyacrylamide and cationic starch) addition levels were 0.5, 1 and 2 kg / t. All chemical amounts were kg dry chemical per ton dry fibre stock. All points included retention aids (CPAM 200 g / 1 and anionic micropolymer 200 g / t) .

[0105] Table 3. Sheet testing devices and standard methods used for produced paper sheets.

[0106] Results showed (Table 4) that composition of amphoteric polyacrylamide and cationic starch increased substantially Z-directional strength. To get same strength levels compared to traditional cationic wetend starch dosage levels were significantly lower with the new strength additive.

[0107] Table 4. Effect different strength systems on board properties .

[0108] EXAMPLE 3

[0109] In this study, the strength agent composition of an amphoteric polyacrylamide and a cationic starch on SCT ( short span compression strength) , burst strength and crushing resistance ( Corrugating Medium Test ( CMT30 ) was tested .

[0110] Tested furnish was prepared from recycled board (RCF) obtained from German mill . 110 g / m2 sheets were formed with Rapid Koethen sheet former (RK) as follows : RCF was wet disintegrated in 3% consistency at 70 ° C with Noviprofibre -pulper for 30sec at 500rpm and 25min at 1000 rpm without soaking . Wet disintegrated pulp was further diluted to 1% with tap water and pH and conductivity adj usted to 6 . 8 and 3 . 0 mS / cm. Chemical additions were made to mixing vessel (mixing speed 1000 rpm) and after chemical additions pulp was poured to RK sheet former and water was drained out through wire with suction . Sheets were made with recirculation mode : first six sheets were thrown away and after that 4 sheets were made for testing . Sheet was removed from wire and vacuum dried at 92 ° C in restrain . Before testing in the laboratory, sheets were pre-conditioned for 24 h at 23 °C in 50 % relative humidity, according to the standard ISO 187 . Chemical amounts were kg dry chemical per ton dry RCF fibre stock. In the reference point no strength additives were used. All the test points included retention aids (CPAM 400 g / t and Silica 400 g / t) .

[0111] Table 5. Sheet testing devices and standard methods used for produced paper sheets.

[0112] Results showed (Table 6) that the new strength additive improved significantly all the strength properties .

[0113] Table 6. Effect different strength systems on board properties .

[0114] EXAMPLE 4

[0115] In this study effect of the strength agent composition of an amphoteric polyacrylamide and a cationic starch was tested on strength properties of unbleached kraft pulp furnish acquired from northern European mill. 110 g / m2sheet were made with Dynamic Sheet Former (DSF) (Techpap) as follows: Pulp was added to mixing tank of DSF where all the chemical additions were also made. Water was drained out after all the pulp was sprayed. Drum was operated with 1250 rpm, mixer for pulp 450 rpm, pulp pump 950 rpm / min, number of sweeps 100 and scoop time was 60 s. Sheet was removed from drum between wire and 1 blotting paper on the other side of the sheet. Wetted blotting paper and wire were removed. Sheets were wet pressed at Techpap nip press with 5 bar pressure with 2 passes having new blotting paper each side of the sheet before each pass. Sheets were dried in restrained condition in drum dryer. Drum temperature was adjusted to 92 °C and passing time to 1 min. Four passes were made. First two passes with between blotting papers and 2 passes without. Before testing in the laboratory sheets were pre-conditioned for 24 h at 23 °C in 50 % relative humidity, according to the standard ISO 187.

[0116] Reference strength additive used in the experiments was cationic corn starch (DS0.027) (5 and 10 kg / t) , a typically used strength aid in this type of furnish. With new strength additive (composition of amphoteric polyacrylamide and cationic starch) addition levels were 0.5, 1 and 2 kg / t. All chemical amounts were kg dry chemical per ton dry fibre stock. All points included retention aids (CPAM 200 g / 1 and silica 200 g / t) .

[0117] Table 7. Sheet testing devices and standard methods used for produced paper sheets.

[0118] Strength results are presented in Table 8. Results show that similar strength performance can be achieved with significantly lower dosing levels with new strength agent compared to traditional wet-end starch.

[0119] Table 8. Effect of different strength systems on board properties .

[0120] EXAMPLE 5

[0121] This example shows how the new strength agent which is a composition of an amphoteric polyacrylamide and a cationic starch affect drainage of the pulp compared to traditional wet-end starch (DS 0.035, potato) , when dosed to a thick stock of pulp.

[0122] The furnish used in test contained CTMP pulp (80%) and coated broke (20%) acquired from a European mill. The drainage was measured by using DDA (Dynamic Drainage Analyzer) equipment. The strength agents were dosed to 500 ml of pulp, which was at 1.2 % consistency, 60 s before start of filtering. Retention aids were used in every test point and they were cationic polyacrylamide (200g / t as dry) and silica (400g / t as dry) and they were added 15s and 10s before filtering respectively. In addition, following parameters were used in DDA:

[0123] Mixing speed 1000 rpm Wire with 0.25 mm openings Vacuum 300 bar Follow-up time 20 s

[0124] Dosing levels of reference strength additive (cationic potato starch, a typically used strength aid in this type of furnish) were 1, 5 and 10 kg / 1. To achieve same strength performance than starch with new strength additive (composition of amphoteric polyacrylamide and cationic starch) dosing levels are considerably lower (examples 1, 2 and 4) . Thus, addition levels tested for drainage were also lower (1, 2 and 3kg / t) .

[0125] Drainage results are presented in Table 9. With starch, Ikg / t addition level slightly improves drainage time but with increasing dosing level (5 and 10 kg / t) drainage quickly starts to deteriorate. This is a typical problem seen in paper or board machines. With new strength agent results show that drainage is improved and is significantly better with Ikg / t addition level than starch and it only slightly deteriorates with increasing dosage. Even with addition level of 3 kg / t drainage is better than with starch at Ikg / t.

[0126] Table 9. Effect different strength systems on drainage.

[0127] EXAMPLE 6

[0128] Cationic starches have a tendency for retrogradation. In this example, stability of the new strength agent which is a composition of an amphoteric polyacrylamide and cationic starch was studied when it is dissolved in water. The test was done as follows: First the strength agent was dissolved to 1.0% consistency in a beaker equipped with magnetic stirrer (at temperature of 50 °C for 1 hour) . After cooling to room temperature (RT) biocide (500ppm, isothiazolin) was added to the solution. Then conductivity and pH were measured 7 times within 14 days period and viscosity in the beginning and in the end of same period (Table 10) . Visual observation of the solution was also conducted. In the measured values there were no changes and also visually sample remained the same during 14 day period. Thus, it can be concluded that sample stayed stable for 14 days.

[0129] Table 10. pH, conductivity and viscosity of new strength agent during a 14 days period.

[0130] While there have been shown and described and pointed out fundamental novel features as applied to preferred embodiments thereof , it will be understood that various omissions and substitutions and changes in the form and details of the devices and methods described may be made by those skilled in the art without departing from the spirit of the disclosure . For example , it is expressly intended that all combinations of those elements and / or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the disclosure . Moreover, it should be recogni zed that structures and / or elements and / or method steps shown and / or described in connection with any disclosed form or embodiments may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice .

[0131] The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features , to the extent that such features or combinations are capable of being carried out based on the present speci fication as a whole , in the light of the common general knowledge of a person skilled in the art , irrespective of whether such features or combinations o f features solve any problems disclosed herein, and without limitation to the scope of the claims . The applicant indicates that the disclosed aspects / embodiments may consist of any such individual feature or combination of features . In view of the foregoing description it will be evident to a person skilled in the art that various modi fications may be made within the scope of the disclosure . It is obvious to a person skilled in the art that with the advancement of technology, the basic idea may be implemented in various ways . The embodiments are thus not limited to the examples described above ; instead they may vary within the scope of the claims .

[0132] The embodiments described hereinbefore may be used in any combination with each other . Several of the embodiments may be combined together to form a further embodiment . A method, a product , an arrangement , or a use , disclosed herein, may comprise at least one of the embodiments described hereinbefore . It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments . The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all o f the stated benefits and advantages . It will further be understood that reference to ' an ' item refers to one or more of those items . The term "comprising" or " including" is used in this speci fication to mean including the feature ( s ) or act ( s ) followed thereafter, without excluding the presence of one or more additional features or acts .

Claims

CLAIMS1. A strength agent composition for a product, wherein the product is a paper, board, molded fiber, nonwoven and / or textile product comprising cellulose or other carbohydrate-based fibers, wherein the strength agent composition comprises an amphoteric polyacrylamide and a cationic starch, wherein the cationic starch has a degree of substitution (DS) of at least 0.12, and wherein the strength agent composition is in the form of a powder.

2. The strength agent composition according to claim 1, wherein the strength agent composition has a dry solids content of at least about 80 % (w / w) , or preferably at least about 82 % (w / w) , or more preferably at least about 85 % (w / w) , on the basis of the total weight of the strength agent composition.

3. The strength agent composition according to claim 1 or 2, wherein the cationic starch has a DS of at least 0.14, preferably at least 0.16, or a DS in the range of 0.14 - 0.25, preferably in the range of 0.16 - 0.21.

4. The strength agent composition according to any one of claims 1 - 3, wherein the amphoteric polyacrylamide and the cationic starch are capable of forming a polyelectrolyte complex having a net charge density in the range of about 0.3 - 2.0 meq / g, preferably about 0.6 - 1.8 meq / g, more preferably about 0.7 - 1.5 meq / g, even more preferably about 0.75 - 1.2 meq / g, when measured in an aqueous solution at a pH of about 7.

5. The strength agent composition according to any one of claims 1 - 4, wherein the cationic starch has an intrinsic viscosity (IV) of at least about 1 dl / g, preferably in the range of about 1 - 2 dl / g.

6. The strength agent composition according to any one of claims 1 - 5, wherein the amphoteric polyacrylamide has an intrinsic viscosity in the range ofabout 3 - 15 dl / g, preferably in the range of about 7 - 13 dl / g.

7. The strength agent composition according to any one of claims 1 - 6, wherein the amphoteric polyacrylamide has a ratio of anionic groups to cationic groups in the range of about 1:20 to 1:4.

8. The strength agent composition according to any one of claims 1 - 7, wherein a ratio of the amphoteric polyacrylamide to the cationic starch is in the range of about 1:3 to 3:1, preferably in the range of about 1:2 to 2:1 by weight.

9. The strength agent composition according to any one of claims 1 - 8, wherein the cationic starch has a cationic charge density in the range of about 0.6 - 1.5 meq / g, preferably about 0.8 - 1.3 meq / g, when measured in an aqueous solution at a pH of about 7.

10. The strength agent composition according to any one of claims 1 - 9, wherein the strength agent composition comprises a mixture of the amphoteric polyacrylamide and the cationic starch in the form of a powder .

11. A method for preparing an aqueous solution of the strength agent composition according to any one of claims 1 - 10, wherein the method comprises dissolving the strength agent composition in water having a temperature of 60 °C or lower, thereby obtaining the aqueous solution of the strength agent composition.

12. A method for manufacturing a product, wherein the product is a paper product, board product, molded fiber product, nonwoven and / or textile product comprising cellulose or other carbohydrate-based fibers, wherein the method comprises adding an aqueous solution of the strength agent composition according to any one of claims 1 - 10 to a fiber stock, and forming a fibrous web of the fiber stock comprising the strength agent composition.13 . The method according to claim 12 , wherein the fiber stock comprises chemi-thermomechanical pulp fibers and / or recycled fibers .14 . The method according to claim 12 or 13 , wherein the product is a folding boxboard optionally comprising chemi-thermomechanical pulp fibers , such as a folding boxboard comprising a mid-ply comprising chemi-thermomechanical pulp fibers , or a fluting comprising recycled fibers . 15 . Use of the strength agent composition according to any one of claims 1 - 10 for improving one or more strength properties of a product , wherein the product is a paper, board, molded fiber, nonwoven and / or textile product comprising cellulose or other carbohy- drate-based fibers .

Images