Dry strength composition, its use and method for making of paper, board or the like

Abstract

The invention relates to an aqueous dry strength composition suitable for use in manufacture of paper, board or the like. The composition includes a mixture of a synthetic polymer component, which is a copolymer of acrylamide and at least one anionic monomer, and a cationic starch component. The polymer component has an anionicity of 1-60 mol-%. The synthetic polymer component and cationic starch component provide the composition with a charge density in the range of 0.05-1 meq/g, when measured at pH 2.8, and 0.2-3 meq/g, when measured at pH 7.0. The invention also relates to a method for making of paper, board or the like, where the dry strength composition is diluted with water, and the solution of the dry strength composition is added to the fibre stock before or after the addition of a cationic strength agent.

Claims

1. An aqueous dry strength composition suitable for use in manufacture of paper, board or the like, which composition comprising a mixture of: a synthetic polymer component, which is a copolymer of acrylamide and at least one anionic monomer, the polymer component having an anionicity of 1-60 mol-%, and a cationic starch component, the synthetic polymer component and the cationic starch component providing the composition with a charge density in a range of: 0.05-1 meq/g, when measured at pH 2.8, and 0.2-3 meq/g, when measured at pH 7.0.

2. The composition according to claim 1, wherein the cationic starch component has an amylopectin content >80%.

3. The composition according to claim 1, wherein that the synthetic polymer component and cationic starch component provide a charge density in a range of: 0.1-0.5 meq/g, when measured at pH 2.8, and 0.4-2.0 meq/g, when measured at pH 7.0.

4. The composition according to claim 1, wherein the dry strength composition has anionic net charge already at pH 5.5.

5. The composition according to claim 1, wherein the dry strength composition comprises 10-90 weight-% of the synthetic polymeric component, and 10-90 weight-% of the cationic starch component.

6. The composition according to claim 1, wherein the cationic starch component has a substitution degree of 0.025-0.3.

7. The composition according to claim 1, wherein the cationic starch component is non-degraded starch.

8. The composition according to claim 1, wherein the synthetic polymer component is prepared by polymerization, of acrylamide and at least one anionic monomer, which is selected from unsaturated mono- or dicarboxylic acids.

9. The composition according to claim 1, wherein the synthetic polymer component has an anionicity of 3-40 mol-%.

10. The composition according to claim 1, wherein the synthetic polymer component has a weight average molecular weight MW in a range of 300 000-1 000 000 g/mol.

11. The composition according to claim 1, wherein the dry strength composition is free of cationic synthetic polymers.

12. The composition according to claim 1, wherein the dry strength composition has a Brookfield viscosity of <10 000 mPas, at solids content of 14 weight-% and at pH 3.0.

13. A method for making of paper, board or the like, comprising: obtaining a fibre stock having a pH value, adding a cationic strength agent to the fibre stock, diluting a dry strength composition according to claim 1 with water to obtain a solution of the dry strength composition having an end pH >3, and adding the solution of the dry strength composition to the fibre stock before or after the addition of the cationic strength agent.

14. The method according to claim 13, wherein the fibre stock comprises recycled fibres and/or chemical pulp, and/or the fibre stock has a conductivity of at least 2 mS/cm.

15. The method according to claim 13, wherein adding the dry strength composition is done in an amount of 0.5-4.0 kg/ton dry fibre stock.

16. The method according to claim 13, wherein adding the cationic strength agent and the dry strength composition is done, in such amount, that the number of excess anionic charges in the dry strength composition, at pH 7, is 20-200%, of the total number of cationic charges of the cationic strength agent.

17. The method according to claim 13, wherein the cationic strength agent is selected from a group of cationic starch, polyamidoamine-epichlorohydrin, cationic polymers of acrylamide, and polyvinylamines.

18. The method according to claim 13, wherein preparing the dry strength composition is done on-site.

19. The method according to claim 13, wherein the cationic strength agent is cationic starch, which is of identical botanic origin as the cationic starch component of the dry strength composition.

20. The method according to claim 13, wherein adding the dry strength composition is done after the cationic strength agent.

21. The method according to claim 13, wherein the fibre stock has a pH value at least 4.5, wherein the dry strength composition has an anionic net charge at the pH of the fibre stock.

Description

EXPERIMENTAL

(1) Synthetic Polymer Component: General Description of the Synthesis

(2) Anionic polyacrylamides used in dry strength compositions of the experimental section as synthetic polymer components were synthesised by radical polymerisation using the general procedure described in the following.

(3) Prior to the polymerisation all monomers used, water, Na-salt of EDTA and sodium hydroxide were mixed in a monomer tank. This mixture is hereafter called monomer mixture. Monomer mixture was purged with nitrogen gas for 15 min.

(4) A catalyst solution was prepared in a catalyst tank by mixing water and ammonium persulphate. The catalyst solution was made less than 30 min before its use.

(5) Water was added into a polymerisation reactor equipped with a mixer and a jacket for heating and cooling. The water was purged with nitrogen gas for 15 min. The water was heated to 100 C. Feeding of both the monomer mixture and the catalyst solution were started at the same time. Feed time for the monomer mixture was 90 min and feed time for the catalyst solution was 100 min. When the feed of catalyst solution was terminated, the mixing was continued for 45 min. The obtained aqueous polymer solution was cooled to 30 C. and removed from the polymerisation reactor.

(6) The following characteristics were analysed from the obtained aqueous polymer solution. Dry solids content was analysed by using Mettler Toledo HR73, at 150 C. Viscosity was analysed by using Brookfield DVI+, equipped with small sample adapter, at 25 C., using spindle S18 for solutions with viscosity <500 mPas and spindle S31 for solutions with viscosity 500 mPas or higher, and using the highest feasible rotation speed for the spindle. pH of the solution was analysed by using a calibrated pH-meter.

(7) Synthesis of Synthetic Polymer Component, AC13HM

(8) The production of one specific anionic polyacrylamide polymer, AC13HM, is explained in the following in detail as an example of the synthesis of an anionic polyacrylamide, suitable for use as synthetic polymer component in a dry strength composition.

(9) Prior to the start of the polymerisation the monomer mixture was prepared in a monomer tank by mixing 45.2 g of water; 200.5 g of acrylamide, 50% aqueous solution; 14.5 g of acrylic acid; 0.59 g of Na salt of EDTA, 39% aqueous solution; 8.1 g of sodium hydroxide, 50% aqueous solution. The monomer mixture was purged with nitrogen gas for 15 min. A catalyst solution was prepared in a catalyst tank by mixing 27 g of water and 0.088 g of ammonium persulphate. 440 g of water was added into a polymerisation reactor and purged with nitrogen gas for 15 min. The water was heated to 100 C. Feeding of both the monomer mixture and the catalyst solution to the polymerisation reactor was started at the same time. Feed time for the monomer mixture was 90 min and for the catalyst solution 100 min. When the feed of the catalyst solution was terminated, the mixing was continued for 45 min. The obtained polymer was cooled to 30 C. and then removed from the polymerisation reactor. The synthetic anionic polyacrylamide polymer had dry solids content of 15.1 weight-%, viscosity of 7030 mPas, weight average molecular weight MW ca. 0.7 Mg/mol and pH 5.2.

(10) Preparation of Cationic Starch Component, Starch-A

(11) 97.6 g cationic waxy potato starch, Starch-A, dry content 82 weight-% (for other properties see Table 7), was sludged in 436 g of water in a reactor equipped with a jacket for heating, a condenser and agitator. Slurry was heated to 99 C. while agitating by 500 rpm and kept at that temperature for 45 min with agitation on. The formed starch solution, when cooled, had concentration of 15.8 weight-% and viscosity of 1400 mPas.

(12) Preparation of Dry Strength Composition

(13) A series of aqueous dry strength compositions were prepared using the following general procedure. Synthetic APAM polymer solution, e.g. AC13HM, as described above, and starch solution of cationic starch, e.g. Starch-A, as described above, were mixed for 60 min at 25 C. by 1000 rpm. For example, dry strength composition SP1 (see Table 1) was prepared by mixing 66.0 g of polymer solution AC13HM as described above and 63 g of Starch-A solution as described above.

(14) Dry strength compositions with different proportions of synthetic polymer component and cationic starch component, different dry content and different pH value were prepared. Dry strength compositions with lower dry content were prepared by dilution with de-ionized water. Dry strength compositions with low pH were prepared by adjusting their pH to the desired target value by adding sulphuric acid 25 weight-%.

(15) Dry strength compositions prepared and their properties are given in Table 1. The synthetic polymer component was AC13HM and the cationic starch component was Starch-A in the dry strength compositions of Table 1, except for dry strength composition SPmix88, where the synthetic polymer component was AC13HM and cationic starch component was Starch-1; and for dry strength compositions SP4, and SP5, where the synthetic polymer component was AC11HM and the cationic starch component was Starch-A; and for dry strength composition SP6, where the synthetic polymer was AC11LM and the cationic starch component was Starch-A. For details of chemicals, see Table 7. Viscosity values in Table 1 were measured by using Brookfield LV, DV1 SSA with maximum rpm and spindle instructed by equipment.

(16) It can be seen from the results of Table 1 that when the pH of the dry strength composition is 3.7, the viscosity of the dry strength composition is lower than when the pH of the dry strength composition is 5.2. This indicates that the synthetic polymer component in the dry strength composition is complexed more strongly at pH 5.2, where the polymer component is more anionic. Higher proportion of the synthetic polymer component increases the viscosity of the dry strength composition. Viscosity of the dry strength compositions can be decreased by dilution with water.

(17) TABLE-US-00001 TABLE 1 Dry strength compositions prepared. Dry Strength Vis- Charge Charge Dry Compo- cosity at pH 7 at pH 2.8 solids Starch APAM sition (mPas) pH (meq/g) (meq/g) (%) (w-%) (w-%) SP1 7700 3.7 0.67 0.20 15.5 50 50 SP2 11700 3.7 1.04 0.13 15.3 33 67 SP3 9650 3.6 0.57 0.20 14.8 50 50 SP1a 28000 5.2 0.67 0.20 15.5 50 50 SP1b 13900 5.2 0.67 0.20 13.0 50 50 SP1c 4000 3.7 0.67 0.20 13.0 50 50 SP2a 35200 5.2 1.04 0.13 15.3 33 67 SP2b 11700 3.7 1.04 0.13 15.3 33 67 SP2c NA 5.5 1.04 0.13 15.3 33 67 SPmix88 NA 5.0 0.71 0.11 1.0 50 50 SP4 4700 3.0 0.64 0.28 14.0 50 50 SP5 3170 3.0 0.20 0.28 14.7 69 31 SP6 3470 3.0 0.64 0.28 15.2 50 50

(18) Impact of the charge density to characteristics of dry strength composition was studied by preparing a dry strength composition as follows. Synthetic polymer component AC11HM, see Table 7, and cooked cationic Starch-A, as described above, were dissolved each separately in deionized water. The obtained solutions were combined with equal dry weight-% of synthetic polymer component and cationic starch component. After mixing for 60 mins at room temperature a clear solution having solids content of 14.3 weight-% was obtained. pH of the solution was adjusted by 32 weight-% sulphuric acid or sodium hydroxide solution to a desired target value. Viscosities of the solutions were measured with Brookfield DV1+viscometer at different pH values. Viscosity results are given in Table 2.

(19) Results of Table 2 show that viscosity increased as the function of pH. Viscosity increase is moderate between pH 2.8 and 3.5 as well as between pH 4.5 and 7. Viscosity increased significantly when pH increased from 3.5 to 4.5.

(20) TABLE-US-00002 TABLE 2 Viscosity of the dry strength composition at 14 weight-% concentration as the function of pH. Viscosity pH (mPas) 2.8 5 239 3.5 6 670 3.9 9 100 4.5 14 600 5.0 16 850 7.0 17 050

(21) Samples were diluted with deionized water for suitable concentration for measurements of indicative charge densities by titration with Mtek PCD 03, using polyethylenesulphonate solution or poly-DADMAC solution as titrant. Results are given in Table 3.

(22) TABLE-US-00003 TABLE 3 Indicative charge density values of the dry strength composition at 14% concentration as the function of pH. Charge density Appearance of dry pH (meq/g dry) strength composition 2.8 0.32 Clear transparent 3.5 0.13 Slightly cloudy 3.8 0.02 Cloudy 4.5 0.20 Cloudy 5.0 0.34 Slightly cloudy 7.0 0.69 Clear transparent

(23) Charge density results in Table 3 show that the net charge of the dry strength composition comprising a synthetic polymer component and a cationic starch component turns from cationic to anionic at pH about 3.7. This means that polyion complex is formed in great degree already at pH about 3.5, at which pH determined cationic charge has decreased by about 60%. At pH over 4.5 a large amount of the cationic charges are complexed by the anionic groups of the synthetic polymer component. Charge density results support the observations of viscosity results in Table 2 that polyion complex formation occurs between pH 3.5 and 5.

Application Examples 1-9

(24) Technical performance of dry strength compositions and comparative reference products was tested with various pulp and sheet studies.

(25) Pulps used in the application examples and their properties are given in Table 4.

(26) Properties of pulps were characterized using devices and/or standard methods listed in Table 5. pH, turbidity, conductivity and charge were measured from the filtrate of gravity filtration through black ribbon filter paper.

(27) The properties of produced paper sheets were measured by using sheet testing devices and standard methods listed in Table 6.

(28) Chemicals used in the application examples are given in Table 7.

(29) TABLE-US-00004 TABLE 4 Pulps used in the application examples. White OCC White Pulp, Pulp, CTMP, Broke, Water, Pulp, Water, Property Ex. 1 Ex. 2 Ex. 3 Ex. 3 Ex. 3 Ex. 4 Ex. 4 pH 6.9 6.7 6.6 7.1 6.7 6.3 5.6 Turbidity, NTU 2 2 100 104 35.8 549 80 Conductivity of filtrate, 1.1 1.1 1.9 2.4 2.0 4.7 4.1 mS/cm Cationic demand, eqv/l 20.7 9.6 185 48 33 0.0 0.0 Zeta potential, mV 26.3 20.7 19.2 11.7 4.4 Consistency, g/l 4.7 4.8 40.7 37.0 1.0 39 0.3

(30) TABLE-US-00005 TABLE 5 Pulp characterization methods Property Device/Standard pH Knick Portamess 911 Turbidity (NTU) WTW Turb 555IR Conductivity (mS/cm) Knick Portamess 911 Charge (ekv/l) Mtek PCD 03 Zeta potential (mV) Mtek SZP-06 Consistency (g/l) ISO 4119

(31) TABLE-US-00006 TABLE 6 Sheet testing devices and standard methods used for produced paper sheets. Measurement Device Standard Basis weight Mettler Toledo ISO 536 Ash content, 525 C. ISO 1762 Scott bond Huygen Tappi T 569 Z-directional tensile Lorentzen & Wettre ISO 15754 Taber, bending stiffness Lorentzen & Wettre Tappi T 489 om-08 Tensile strength, Elastic Lorentzen & Wettre ISO 1924-3 modulus

(32) TABLE-US-00007 TABLE 7 Chemicals used in the application examples. Name Composition/Product, Manufacturer Description APAM-1 Copolymer of acrylamide and 8 mol-% acrylic acid MW ca. 0.5 Mg/mol AC13HM Copolymer of acrylamide and 12.5 mol-% acrylic MW ca. 0.7 Mg/mol acid AC11HM Copolymer of acrylamide and 11 mol-% acrylic MW ca. 0.7 Mg/mol acid AC11LM Copolymer of acrylamide and 11 mol-% acrylic MW ca. 0.5 Mg/mol acid APAM-E Anionic polyacrylamide Emulsion polymer dissolved at 0.8% concentration Starch-A Cationic amylopectin starch 0.4 meq/g (DS 0.07) cationic, >95% amylopectin, cooked Starch-1 Cationic potato starch: Raisamyl 50021, 0.2 meq/g (DS 0.035), 80% Chemigate amylopectin, cooked Starch-2 Cationic starch: C*Bond HR 35844, Cargill cooked SCPAM Copolymer of acrylamide and 10 mol-% ADAM-Cl Solution polymer, MW ca. 0.8 Mg/mol CPAM Copolymer of acrylamide and 10 mol-% ADAM-Cl MW ca. 7 Mg/mol, dry polymer dissolved at 0.5% concentration CPAM-2 Copolymer of acrylamide and 10 mol-% ADAM-Cl MW ca. 12 Mg/mol, dry polymer dissolved at 0.5% concentration GPAM Glyoxylated cationic polyacrylamide: FennoBond Water solution 3150, Kemira Oyj, Finland CMC Carboxymethyl cellulose: Finnfix 300, CP Kelco dissolved at 80 C. pDADMAC polyDADMAC MW ca. 0.2 Mg/mol Alum Aluminium sulphate: ALG, Kemira Oyj, Finland GCC Ground calcium carbonate: Hydrocarb 60, Omya particle size distribution: 60% of particles < 2 m Silica Colloidal silica: FennoSil 495, Kemira Oyj, Finland Silica-2 Colloidal silica: FennoSil 442, Kemira Oyj, Finland c-PVOH Polyvinylalcohol having 12 mol-% vinylamine MW ca. 0.1 Mg/mol groups and 88 mol-% vinylalcohol groups

Application Example 1

(33) This example simulates preparation of tissue paper, fine paper, kraft paper or surface layer for multi-ply board.

(34) Test fibre stock was a mixture of chemical hardwood pulp and softwood pulp. Chemical pulps were prepared in Valley Hollander. Hardwood (HW) pulp was bleached birch kraft pulp refined to 25 SR and softwood (SW) pulp was bleached pine kraft pulp refined to 25 SR. Pulps were mixed together in 75%/25% HW/SW ratio, diluted with deionized water containing NaCl addition to 1.5 mS/cm level. Properties of the obtained test fibre stock are given in Table 4.

(35) In hand sheet preparation chemicals were added to the test fibre stock in a dynamic drainage jar under mixing with 1000 rpm. Cationic strength chemicals were diluted before dosing to 0.2% concentration. Anionic chemicals and retention chemicals were diluted to 0.05% concentration before dosing. The chemicals added and their addition times are given in Table 8. All chemical amounts are given as kg dry chemical per ton dry fibre stock.

(36) Hand sheets having basis weight of 80 g/m.sup.2 were formed by using Rapid Kothen sheet former with circulation water in accordance with ISO 5269-2:2012. The sheets were dried in vacuum dryers for 6 minutes at 92 C. and at 1000 mbar. Before testing the laboratory sheets were pre-conditioned for 24 h at 23 C. in 50% relative humidity, according to ISO 187. The measured tensile index and Scott bond values for the prepared hand sheets are given in Table 8.

(37) It can be seen from Table 8 that Test 1-4, where the dry strength composition SP1 was used, produced improvement in tensile and Scott bond values compared to Test 1-2, where only cationic strength agents were used. Test 1-4 provided improvement also to Test 1-3, where a system with separate additions of cationic strength agents and anionic polymer APAM-1 was used. The dry strength composition SP1 thus produces favourable strength properties for this kind of use.

(38) TABLE-US-00008 TABLE 8 Hand sheet tests of application example 1: chemical additions and measured results. Tensile Scott - 60 s - 60 s - 30 s - 30 s - 30 s - 10 s index Bond Time SCPAM Starch-A APAM-1 SP1 SP2 CPAM2 (Nm/g) (J/m.sup.2) Test 1-1 0 0 0.05 34 146 (ref.) Test 1-2 1 1 0.05 40 211 (ref.) Test 1-3 1 1 1.5 0.05 42 212 (ref.) Test 1-4 1 1 1.5 0.05 43 227

(39) For zeta-potential measurement a 500 ml of test fibre stock was taken to beaker. Cationic chemicals were diluted to 0.2% concentration and anionic chemicals to 0.05% concentration. After addition of cationic chemical(s), if any, fibre stock was mixed for 1 min with spoon before measurement or addition of an anionic chemical. If anionic chemical was added, the fibre stock was mixed for further 1 min with spoon before the measurement. Results of zeta potential measurements are given in Table 9.

(40) TABLE-US-00009 TABLE 9 Results of zeta potential measurements. Added Chemical SCPAM Starch-A APAM-1 SP1 SP2 Zeta potential # (kg/t dry) (kg/t dry) (kg/t dry) (kg/t dry) (kg/t dry) (mV) 1 28 2 1 1 10 3 1 1 0.15 10 4 1 1 0.3 17 5 1 1 0.5 23 6 1 1 1 24 7 1 1 1.5 25 8 1 1 0.15 15 9 1 1 0.3 20 10 1 1 0.5 25 11 1 1 1 25 12 1 1 1.5 27 13 1 1 0.15 14 14 1 1 0.3 15 15 1 1 0.5 22 16 1 1 1 23 17 1 1 1.5 25

(41) The results of zeta potential measurements shown in Table 9 indicate that the dry strength composition SP1 is able to shift very effectively surface charge of fibres towards anionic direction even when the anionicity of the dry strength composition is low.

Application Example 2

(42) This example simulates preparation of printing and writing paper.

(43) Test fibre stock was a mixture of chemical hardwood pulp and softwood pulp. Chemical pulps, which are typical for fine paper, were prepared in Valley Hollander. Hardwood (HW) pulp was bleached birch kraft pulp refined to 25 SR and softwood (SW) pulp was bleached pine kraft pulp refined to 25 SR. Pulps were mixed together in 75%/25% HW/SW ratio, diluted with deionized water containing NaCl addition to 1.5 mS/cm level. Properties of the obtained test fibre stock are given in Table 4.

(44) In hand sheet preparation chemicals were added to the test fibre stock in a dynamic drainage jar under mixing with 1000 rpm. Cationic strength chemicals were diluted before dosing to 0.2% concentration. Anionic chemicals and retention chemicals CPAM and APAM-E were diluted to 0.05% concentration before dosing. The chemicals added and their addition times are given in Table 10. All chemical amounts are given as kg dry chemical per ton dry fibre stock, except APAM-E, which is given as kg emulsion per ton dry fibre stock.

(45) GCC was added to the fibre stock at 25 s from drainage time. Required GCC addition was made to obtain 25% ash content for the produced paper sheets.

(46) Hand sheets having basis weight of 80 g/m.sup.2 were formed by using Rapid Kothen sheet former with circulation water in accordance with ISO 5269-2:2012. The sheets were dried in vacuum dryers for 6 minutes at 92 C. and at 1000 mbar. Before testing the laboratory sheets were pre-conditioned for 24 h at 23 C. in 50% relative humidity, according to ISO 187. The measured tensile index and Scott bond values for the prepared hand sheets are given in Table 10.

(47) It can be seen from Table 10 that dry strength composition SP1 is able to generate higher tensile and Scott bond values than conventional anionic strength polymers APAM-1 and APAM-2. Tensile strength is needed, for example, for good runnability of the web in paper machine, as well as for good behaviour in printing and copying processes. Good Scott bond values may be required for offset printing applications.

(48) High Scott bond value can be also used as an indication of reduced dusting tendency of the paper. Typically papermakers wish to maximize the ash content by addition of more filler, but drawback is lowered strength and increased dusting. The obtained Scott bond values indicate that dry strength composition according to the present invention, such as SP1, may be used to allow increase in ash content, i.e. increase in amount of added filler to the fibre stock.

(49) TABLE-US-00010 TABLE 10 Hand sheet tests of application example 2: chemical additions and measured results. Tensile Scott - 60 s - 60 s - 40 s - 40 s - 40 s -15 s - 10 s index Bond Time GPAM Starch APAM-1 SP1 APAM-2 CPAM APAM-E (Nm/g) (J/m.sup.2) Test 2-1 0.1 0.05 20.2 54 (ref.) Test 2-2 2.5 0.1 0.05 20.0 79 (ref.) Test 2-3 2.5 0.8 0.1 0.05 23.5 111 (ref.) Test 2-4 2.5 1.6 0.1 0.05 22.5 99 (ref.) Test 2-5 2.5 0.8 0.1 0.05 24.7 128 Test 2-6 2.5 1.6 0.1 0.05 28.1 157 Test 2-7 2.5 0.8 0.1 0.05 23.7 118 (ref.) Test 2-8 2.5 1.6 0.1 0.05 24.5 109 (ref.) Test 2-9 12 0.1 0.05 32.3 230 (ref.) Test 2-10 12 1.6 0.1 0.05 35.3 254 (ref.) Test 2-11 12 1.6 0.1 0.05 35.9 273 Test 2-12 12 1.6 0.1 0.05 33.2 251 (ref.)

(50) For zeta potential measurement a 500 ml test fibre stock was taken to a beaker. Anionic chemicals were diluted to 0.05% concentration. Fibre stock was mixed for 1 min with spoon before zeta potential measurement (0-Test) or before the addition of an anionic chemical. When anionic chemical was added, the fibre stock was mixed for further 1 min with spoon before the zeta potential measurement. The used chemicals and their amounts are given in Table 11. All chemical amounts are given as kg dry chemical per ton dry fibre stock. Results of zeta potential measurements are also given in Table 11.

(51) The results of zeta potential measurements shown in Table 11 indicate that the dry strength composition SP1 is able to shift very effectively surface charge of fibres towards anionic direction.

(52) TABLE-US-00011 TABLE 11 Results of zeta potential measurements in application example 2. Zeta potential Chemical Dosage (mV) 0-test 30 APAM-1 0.4 30 APAM-1 0.8 30 APAM-1 1.6 31 SP1 0.4 33 SP1 0.8 34 SP1 1.6 35

Application Example 3

(53) Test fibre stock was a mixture of chemithermo mechanical pulp CTMP and broke. CTMP and broke were mixed in 60% CTMP/40% broke dry ratio. Pulp mixture was diluted to 0.5%. Half of the dilution water volume was white water and half was deionized water with 2 mS/cm conductivity adjusted by NaCl. Properties of the used CTMP, broke and white water are given in Table 4.

(54) In hand sheet preparation chemicals were added to the prepared test fibre stock in a dynamic drainage jar under mixing with 1000 rpm. Cationic strength chemicals were diluted before dosing to 0.2% concentration. Anionic chemicals and retention chemicals were diluted to 0.05% concentration before dosing. The chemicals added and their addition times are given in Table 12. All chemical amounts are given as kg dry chemical per ton dry fibre stock.

(55) Hand sheets having basis weight of 100 g/m.sup.2 were formed by using Rapid Kothen sheet former with circulation water in accordance with ISO 5269-2:2012. Handsheet machine dilution water conductivity was adjusted to 2 mS/cm with NaCl. Sheets were wet pressed individually by adding 2 blotting papers on top side and 2 blotting papers on back side. Wet pressing was performed with Lorenz & Wettre sheet press for 1 min with 4 bar pressure adjustment. The sheets were dried in vacuum dryers for 5 minutes at 92 C. and at 1000 mbar. Before testing the laboratory sheets were pre-conditioned for 24 h at 23 C. in 50 relative humidity, according to ISO 187. The measured z-directional tensile and Scott bond values for the prepared hand sheets are given in Table 12.

(56) It can be seen from Table 12 that increased addition of starch together with dry strength composition SP3 provides higher Z-directional tensile strength and Scott bond value for the produced paper. The results obtained with the dry strength composition are also better than the results obtained with conventional two component strength system, which comprises separately added cationic starch and CMC. The strength properties improved with the dry strength composition are beneficial, for example, for middle ply of folding box board. Furthermore, too low Scott bond value leads to problems in printing due to sheet structure splitting.

(57) TABLE-US-00012 TABLE 12 Hand sheet test of application example 3: chemical additions and measured results. - 55 s - 50 s - 40 s - 35 s - 30 s - 20 s - 10 s Z-dir. Scott Alum pDADMAC Starch-2 CMC SP3 CPAM Silica Tensile Bond Time (kg/t) (kg/t) (kg/t) (kg/t) (kg/t) (kg/t) (kg/t) (kPa) J/m.sup.2) Test 3-1 1 0.2 5 0 0 0.2 0.075 373 159 (ref.) Test 3-2 1 0.2 20 2 0 0.2 0.075 415 181 (ref.) Test 3-3 1 0.2 20 0 0.3 0.2 0.075 440 192

Application Example 4

(58) This example simulates recycled fibre based paper or board manufacturing.

(59) Test fibre stock was made from OCC recycled fibre pulp (OCC=old corrugated cardboard). The OCC pulp was diluted to 1.0%. Half of the dilution water volume was white water and half was deionized water with 4 mS/cm conductivity adjusted by NaCl. The properties of the used OCC pulp and white water are given in Table 4.

(60) In hand sheet preparation chemicals were added to the test fibre stock in a dynamic drainage jar under mixing with 1000 rpm. Cationic strength chemicals were diluted before dosing to 0.2% concentration. Anionic chemicals and retention chemicals were diluted to 0.05% concentration before dosing. The chemicals added and their addition times are given in Table 13. All chemical amounts are given as kg dry chemical per ton dry fibre stock.

(61) Hand sheets having basis weight of 110 g/m.sup.2 were formed by using Rapid Kothen sheet former with circulation water in accordance with ISO 5269-2:2012. Hand sheet machine dilution water conductivity was adjusted to 4 mS/cm with 1.76 g/I CaCl.sub.2*2H.sub.2O and with NaCl. Ash content of the sheets was adjusted to 8% by controlling retention with CPAM dosage. Required dosage was 0.15 kg/t as average. The sheets were dried in vacuum dryers for 6 minutes at 92 C. and at 1000 mbar. Before testing the laboratory sheets were pre-conditioned for 24 h at 23 C. in 50% relative humidity, according to ISO 187. The measured SCT index and burst index values for the prepared hand sheets are given in Table 13.

(62) It can be seen from Table 13 that SCT index and burst index values can be improved with dry strength composition SP1. Improved SCT index and burst index values are beneficial for liner, fluting and core board grades. Furthermore it can be seen that strength properties obtained with a combination of cationic additive and dry strength composition SP1 are better than strength properties achieved with addition of cationic additive alone.

(63) It should be noted that many OCC based recycled fibre pulps may have a cationic demand and zeta potential close to zero and at the same time high conductivity. This causes a special challenge to the ionic dry strength additives used in the wet end, since the additives are not retained well and/or attached to the fibres. Dry strength composition according to the invention overcomes this problem due to its unique structure and due to high amount of ionic groups.

(64) TABLE-US-00013 TABLE 13 Hand sheet tests of application example 4: chemical additions and measured results. - 120 s - 120 s - 120 s - 60 s - 10 s SCT index Burst index Time Starch-A SCPAM GPAM SP1 CPAM (Nm/g) (kpam.sup.2/g) Test 4-1 0.15 21.4 1.64 (ref.) Test 4-2 1 1 0.15 23.1 1.97 (ref.) Test 4-3 1 1 1.5 0.15 23.8 1.95 Test 4-4 1.5 0.15 21.7 1.76 (ref.) Test 4-5 1.5 1.5 0.15 22.2 1.96

Application Example 5

(65) In this example manufacturing of folding boxboard and liquid packaging board was simulated with 3-layer sheets made with Formette-dynamic hand sheet former manufactured by Techpap.

(66) A mixture of bleached pine kraft pulp and bleached birch kraft pulp was used in top and back ply furnish. Amount of pine kraft pulp was 35% and bleached birch kraft pulp 65%. Middle ply furnish was bleached CTMP with 440 ml Canadian standard Freeness refining degree. Pulps were disintegrated according to ISO 5263:1995. Kraft pulps were disintegrated at room temperature and CTMP at 85 C. Pulps were diluted to 0.5% consistency with deionized water. Pulps were added to Formette layer-by-layer in order: top, middle, back. Chemical additions were made to mixing tank of Formette according to Table 14. All chemical amounts are given as kg dry chemical per ton dry fibre stock. Water was drained out after all the pulp was sprayed to form a 3-layer web. Drum was operated with 1400 rpm, mixer for pulp 400 rpm, pulp pump 1100 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. Sheet was cut to 15 cm*20 cm size and 3 blotting papers were placed on top side and 3 blotting papers on back side of the sheet before wet pressing in Lorenz & Wettre laboratory wet press. Wet pressing was at 5 bar for 4 min. Sheets were dried 1 blotting paper in top and 1 blotting paper in back of the sheet in restrained condition in a felted steam heated cast iron drum dryer at 92 C. for 3 min. Before testing the laboratory sheets were pre-conditioned for 24 h at 23 C. in 50 relative humidity, according to ISO 187.

(67) TABLE-US-00014 TABLE 14 Dynamic hand sheet test program for application example 5. Top/Back layer weight: 35 g/m.sup.2/35 g/m.sup.2 Middle Layer - 50 s - 40 s - 20 s - 10 s Weight - 60 s - 50 s - 40 s - 10 s Time Starch SP3 CPAM Silica-2 (g/m.sup.2) pDADMAC Starch SP3 Silica-2 Test 5-1 5 0.1 0.3 264 0.24 5 0.3 (ref.) Test 5-2 12 10 0.1 0.3 247 0.24 20 10 0.3 Test 5-3 12 10 0.1 0.3 264 0.24 20 20 0.3 Test 5-4 12 10 0.1 0.3 228 0.24 20 10 0.3 Test 5-5 12 10 0.1 0.3 232 0.24 20 20 0.3

(68) The measured results for the prepared dynamic hand sheets are given in Table 15. Typically only 5 kg/t of starch has been used for folding boxboard, because high amounts of starch reduce bulk and bending stiffness. It can be seen from Table 15 that higher tensile strength values and bending stiffness can be obtained at same basis weight by addition of dry strength composition SP3 with increased amount of starch, see test 5-1 and test 5-3.

(69) Further it can be seen from Table 15 that the dry strength composition according to the invention increases bending stiffness. Same or higher bending stiffness was obtained with lower basis weight in tests 5-2, 5-4 and 5-5 compared to reference test 5-1. This achievement decreases significantly amount of middle ply furnish and board making costs. Lighter packages can be manufactured for the same end use, which reduces transportation costs and emissions in the life cycle of packaging product.

(70) Furthermore, it can be observed from Table 15 that z-directional tensile and Scott bond values are improved when dry strength composition according to the invention is used. Z-directional tensile and Scott bond are critical for offset-printability of the board. Improvement of these properties can be used to make middle ply furnish even bulkier, as typically higher bulk leads to lower Scott bond or lower z-directional tensile. Increased bulk is beneficial for bending stiffness.

(71) TABLE-US-00015 TABLE 15 Dynamic hand sheet test results for application example 5. Tensile Bending Basis Tensile Tensile stiffness Z-dir. Scott stiffness, weight index MD index CD index MD Tensile Bond Taber 15 MD (g/m.sup.2) (Nm/g) (Nm/g) (mNm/kg) (kPa) (J/m.sup.2) (mNm) Test 5-1 271 23 10 4.3 62 40 25 (ref.) Test 5-2 254 29 17 5.4 82 82 43 Test 5-3 271 28 15 4.6 97 52 42 Test 5-4 235 34 16 5.6 129 72 34 Test 5-5 239 37 17 5.7 120 75 36

Application Example 6

(72) This example simulates preparation of multi-ply board, such as folding box board or liquid packaging board. Test sheets were made with Formette-dynamic hand sheet former manufactured by Techpap.

(73) Test fibre stock was made from 80% of bleached dried CTMP having Canadian standard Freeness of 580 ml and 20% of dry base paper broke from manufacture of folding box board. Test pulp was disintegrated according to ISO 5263:1995, at 80 C. Test fibre stock was diluted to 0.6% consistency with deionized water, pH was adjusted to 7, and NaCl salt was added to obtain conductivity of 1.5 mS/cm.

(74) Dry strength composition SP4 was made by mixing 50 weight-% of Starch-A and 50 weight-% of AC11HM. For properties, see Table 1. Reference dry strength composition SPC with cationic net charge was made by mixing 50 weight-% of Starch-A and 50 weight-% of SCPAM, and it had viscosity of 4500 mPas, pH 4.0, charge of 0.78 meq/g at pH 7, charge of 0.28 meq/g at pH 2.8, and dry solids content of 14 weight-%.

(75) In the test the dry strength composition, either SP4 or SPC, was added after a cationic strength agent, which was cationic starch (Starch-1). Retention polymer used was CPAM-2.

(76) Pulp mixture was added to Formette. Chemical additions were made to mixing tank of Formette according to Table 16. All chemical amounts are given as kg dry chemical per ton dry fibre stock. Water was drained out after all the pulp was sprayed. Drum was operated with 1400 rpm, mixer for pulp 400 rpm, pulp pump 1100 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 cut to 15 cm*20 cm size. Sheets were dried in restrained condition in STFI restrained dryers. Before testing in the laboratory sheets were pre-conditioned for 24 h at 23 C. in 50% relative humidity, according to ISO 187.

(77) TABLE-US-00016 TABLE 16 Dynamic hand sheet test program for application example 6. Time - 60 s - 30 s - 30 s - 15 s Starch-1 SP4 SPC CPAM-2 Test (kg/t) (kg/t) (kg/t) (kg/t) Test 6-1 (ref.) 0.15 Test 6-2 (ref.) 15 0.15 Test 6-3 15 1.2 0.15 Test 6-4 15 2.4 0.15 Test 6-5 (ref.) 15 1.2 0.15 Test 6-6 (ref.) 15 2.4 0.15

(78) Z-directional tensile and elastic modulus in machine direction (MD) and in cross direction (CD) analysed with tensile strength test were measured according to methods in table 6.

(79) Table 17 presents the measurement results. Addition of cationic starch only reduced press solids, whereas the addition of dry anionic strength composition SP4 improved press solids. Z-directional tensile and elastic modulus are important strength properties for folding box board and liquid packaging board manufacturing. Tests 6-3 and 6-4 with strength composition SP4 showed higher Z-directional tensile and higher elastic modulus values than tests 6-5 and 6-6 where cationic dry strength composition SPC was used.

(80) TABLE-US-00017 TABLE 17 Measurement results of solids after wet pressing, Z-directional tensile (ZDT) and Elastic modulus (E-mod) for application example 6. Press solids ZDT E-mod CD E-mod MD (%) (kPa) (GPa) (GPa) Test 6-1 (ref.) 37 101 0.19 214 Test 6-2 (ref.) 35 225 0.23 2.39 Test 6-3 40 240 0.23 2.38 Test 6-4 38 260 0.24 2.44 Test 6-5 (ref.) 239 0.22 2.37 Test 6-6 (ref.) 233 0.22 2.34

Application Example 7

(81) This example simulates preparation of multi-ply board containing recycled fibres.

(82) Dry strength composition SP4 was same as in Example 6 and dry strength composition SP5 was made by mixing 69 weight-% of Starch-A and 31 weight-% of AC11HM. For properties, see Table 1. Cationic dry strength composition SPC was the same as in Example 6.

(83) Test pulp was thick stock from board machine consisting 70% DIP made from old magazines and 30% BCTMP long fibre bale pulp slushed in pulper. Pulp was diluted with board mill clear filtrate to 1% consistency. Conductivity of the diluted test pulp was 2.2 mS/cm.

(84) In hand sheet preparation chemicals were added to the prepared test fibre stock in a dynamic drainage jar under mixing with 1000 rpm. Cationic strength chemicals were diluted before dosing to 0.2% concentration. Anionic chemicals and retention chemicals were diluted to 0.05% concentration before dosing. The chemicals added and their addition times are given in Table 18. All chemical amounts are given as kg dry chemical per ton dry fibre stock. Retention polymer dosage was adjusted to keep retention and basis weight constant in the hand sheets.

(85) Hand sheets having basis weight of 100 g/m.sup.2 were formed by using Rapid Kothen sheet former in accordance with ISO 5269-2:2012. Handsheet machine dilution water conductivity was adjusted to 2.2 mS/cm with NaCl. Sheets were wet pressed individually by adding 2 blotting papers on top side and 2 blotting papers on back side. Wet pressing was performed with Lorenz & Wettre sheet press for 1 min with 4 bar pressure adjustment. The sheets were dried in vacuum dryers for 5 minutes at 92 C. and at 1000 mbar. Before testing the laboratory sheets were pre-conditioned for 24 h at 23 C. in 50% relative humidity, according to ISO 187. The measured changes in tensile index, burst index and Z-directional tensile are given in Table 18. The change is given as increase in percentage values, calculated between each individual test point and 0-test (test 7-1). All test points contained 6 ash in the sheet.

(86) It is seen from Table 18 that anionic dry strength composition SP4 improved tensile, burst and Z-directional tensile when used together with cationic dry strength composition SPC. Strength composition SP5 with low anionicity, tests 7-5 & 7-6, improved strength properties in comparison to 0-test 7-1 without any addition of dry strength compositions. Burst strength improvement, which is achieved with SP4 and SP5, is comparable with the result achieved with a cationic dry strength composition SPC in test 7-2. Tests 7-3 and 7-4 indicate that the dry strength composition according to the invention provides improved tensile properties especially when it is used together with a cationic strength agent.

(87) TABLE-US-00018 TABLE 18 Hand sheet tests of application example 7: chemical additions and measured results. Tensile Burst Z-dir. - 60 s - 30 s - 30 s - 10 s index index tensile Time SPC SP4 SP5 CPAM-2 (%) (%) (%) Test 7-1 0.2 0 0 0 (ref.) Test 7-2 3 0.1 7 10 18 (ref.) Test 7-3 3 1 0.1 9 11 20 Test 7-4 3 2 0.1 21 12 19 Test 7-5 2 0.1 2 7 10 Test 7-6 3.5 0.1 2 10 13

Application Example 8

(88) This example simulates preparation of multi-ply board such as folding box board or liquid packaging board with Formette-dynamic hand sheet former manufactured by Techpap. Dry strength compositions SP4 and SP6 are used.

(89) Test fibre stock was made from bleached dried chemithermomechanical pulp CTMP having Canadian standard Freeness of 580 ml and dry base paper broke from manufacture of folding box board. CTMP and broke were mixed in 80% CTMP/20% broke dry ratio. Pulps were disintegrated according to ISO 5263:1995, at 80 C. Pulp mixture was diluted to 0.6% consistency with deionized water, its pH was adjusted to 7 and NaCl was added to obtain conductivity level of 1.5 mS/cm.

(90) Pulp mixture was added to Formette and the sheets were prepared, pressed and cut in the same manner than in Application Example 6. Chemical additions were made to the mixing tank of Formette according to Table 19. Retention polymer was CPAM-2. All chemical amounts are given as kg dry chemical per ton dry fibre stock. Sheets were dried in restrained condition in a drum dryer at 92 C. first pass with blotting paper and second pass without. Drying time was 1 min/pass. Before testing in the laboratory the sheets were pre-conditioned for 24 h at 23 C. in 50% relative humidity, according to ISO 187.

(91) Z-directional tensile and tensile strength (MD) were measured according to methods in table 6.

(92) TABLE-US-00019 TABLE 19 Hand sheet tests of application example 8: chemical additions and measured results. Press Z-dir. Tensile - 60 s - 30 s - 30 s - 10 s solids Tensile index MD Time Starch-1 SP4 SP6 CPAM-2 (%) (kPa) (Nm/g) Test 8-1 0.05 37 104 28 Test 8-2 15 0.05 40 175 35 Test 8-3 15 1.2 0.05 43 223 38 Test 8-4 15 2.4 0.05 43 203 40 Test 8-5 15 1.2 0.05 38 183 38 Test 8-6 15 2.4 0.05 38 186 38

(93) The results of Application Example 8 are shown also in Table 19. The obtained results indicate that the molecular weight of the anionic synthetic polymer component has an impact on the performance of the dry strength composition. When the polymer component had a higher molecular weight (test 8-3, 8-4) an improvement in press solids, Z-directional tensile and in tensile strength could be observed. The obtained effect is greater than in tests 8-5 & 8-6 where the synthetic polymer component ha a lower molecular weight of about 500 000 g/mol. This behaviour indicates that molecular weight of anionic synthetic polymer component may affect the charge distribution on the surface of the formed complex with the cationic starch component.

Application Example 9

(94) This example simulates preparation of multi-ply board, such as folding box board or liquid packaging board, with Formette-dynamic hand sheet former manufactured by Techpap.

(95) In Application Example 9 dry strength composition SP4 was used with cationic strength agent polyvinylalcohol c-PVOH.

(96) Test fibre stock was made from bleached dried chemithermomechanical pulp CTMP having Canadian standard Freeness of 580 ml and dry base paper broke of folding box board. CTMP and broke were mixed in 80% CTMP/20% broke dry ratio. Pulps were disintegrated according to ISO 5263:1995, at 80 C. Pulp mixture was diluted to 0.6% consistency with deionized water, its pH was adjusted to 7 and NaCl was added to obtain conductivity level of 1.5 mS/cm.

(97) Pulp mixture was added to Formette and the sheets were prepared, pressed and cut in the same manner than in Application Example 6, except the drum was operated with 800 rpm. Chemical additions were made to the mixing tank of Formette according to Table 20. Retention polymer was CPAM-2. All chemical amounts are given as kg dry chemical per ton dry fibre stock. Sheets were dried in restrained condition in a drum dryer at 92 C. first pass with blotting paper and second pass without. Drying time was 1 min/pass. Before testing in the laboratory the sheets were pre-conditioned for 24 h at 23 C. in 50% relative humidity, according to ISO 187.

(98) TABLE-US-00020 TABLE 20 Dynamic hand sheet test program for application example 9. Z-dir. Tensile - 60 s - 30 s - 20 s - 10 s Tensile index MD Time c-PVOH SP4 c-PVOH CPAM-2 (kPa) (Nm/g) Test 9-1 0.05 97 17 Test 9-2 0.5 0.05 140 24 Test 9-3 0.5 2.4 0.05 154 27 Test 9-4 2.4 0.5 0.05 145 29

(99) The results in Table 20 show surprisingly that irrespective of the addition order of the dry strength composition SP4 and cationic strength agent c-PVOH, the strength properties of the final sheet were improved. Addition of the cationic strength agent c-PVOH first provided an improvement in Z-directional tensile value, whereas addition of anionic dry strength composition SP4 first provided an improvement in tensile index. This creates valuable opportunities in the manufacture of different paper and board grades, since the strength requirements vary between the various grades. Sometimes good strength properties are desired in MD direction and sometimes in Z-direction. The dry strength composition SP4 according to the present invention also provided the surprising effect that the strength performance was good even with a low dosage of cationic strength agent c-PVOH. Typically cationic strength agents are dosed relatively larger amounts, more than 1 kg/t.

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