Glyoxylated polyacrylamide polymer composition, its use and method for increasing the strength properties of paper, board or the like

Abstract

A cationic glyoxylated polyacrylamide polymer composition having improved storage stability for use in manufacture of paper, board or the like, which aqueous composition includes a glyoxylated polyacrylamide polymer having a cationic charge density in a range of 0.8-1.8 meq/g of dry polymer in dry content of 5-15% and a buffering acid. The aqueous composition has pH in a range of 2.2-4.0 and a viscosity of less than 80 mPas measured at 25° C. by using a Brookfield viscometer after 30 days storage at 35° C. or after 60 days storage at 23° C.

Claims

1. A cationic glyoxylated polyacrylamide polymer composition, comprising: a glyoxylated polyacrylamide polymer having a glyoxal to acrylamide unit molar ratio in a range of 0.50-0.65, a weight average molecular weight MW>250,000 g/mol, and a cationic charge density in a range of 0.8 meq/g-1.8 meq/g of dry polymer, in a dry content amount of 5%-15%; an aqueous medium; a buffering acid; an unreacted glyoxal in an amount of below 1 weight-% by a total weight of the composition; and the aqueous composition has a pH in a range of 2.2-4.0.

2. The composition according to claim 1, wherein the dry content of the glyoxylated polyacrylamide polymer is 9-11%.

3. The composition according to claim 1, wherein the composition has a viscosity of less than 80 mPas measured at 25° C. by using a Brookfield viscometer after 30 days.

4. The composition according to claim 1, wherein the composition has a viscosity of less than 50 mPas measured at 25° C. by using a Brookfield viscometer after 30 days storage at 35° C. or after 60 days storage at 23° C.

5. The composition according to claim 1, wherein the glyoxylated polyacrylamide polymer has a cationic charge density in a range of 1.0 meq/q-1.7 meq/g of dry polymer.

6. The composition according to claim 1, wherein the aqueous composition has a pH in a range of 2.8-3.5.

7. The composition according to claim 1, wherein the glyoxylated polyacrylamide polymer has a weight average molecular weight MW>300 000 g/mol.

8. The composition according to claim 1, wherein the composition comprises less than 50 weight-% of unreacted glyoxal based on total glyoxal.

9. The composition according to claim 1, wherein the buffering acid is an aqueous solution comprising formic acid in an amount of 10 mmol/l-200 mmol/l or citric acid in an amount of 5 mmol/l-100 mmol/l.

10. A method for producing an aqueous composition of a cationic glyoxylated polyacrylamide polymer according to claim 1, comprising: reacting glyoxal with a polyacrylamide base polymer in an alkaline aqueous solution, wherein the polyacrylamide base polymer having a weight average molecular weight MW in a range of 4000 g/mol-12,000 g/mol and comprising 9 mol-%-20 mol-% of cationic monomers is selected from diallyldimethylammonium chloride (DADMAC), 3-(acrylam idopropyl)trimethyl-ammonium chloride (APTAC), 3-(methacrylamidopropyl)trimethyl-ammonium chloride (MAPTAC) and combinations thereof, and wherein the polyacrylamide base polymer has a viscosity of 50 mPas-170 mPas measured at 25° C. by using a Brookfield viscometer at solids content of 40%, and terminating the glyoxylation reaction, when the aqueous solution has a viscosity of 17 mPas-27 mPas measured at 25° C. by using the Brookfield viscometer by adding a buffering acid, and optionally a mineral acid, to the aqueous composition of the glyoxylated polyacrylamide polymer for stabilizing the pH in a range of 2.2-4.0.

11. The method according to claim 10, wherein the polyacrylamide base polymer comprises 12 mol-%-20 mol-% of cationic monomers.

12. The method according to claim 10, wherein the polyacrylamide base polymer has a weight average molecular weight MW in a range of 6000 g/mol-10,000 g/mol.

13. A method for increasing the strength properties of paper, board or the like, comprising: obtaining a fibre stock, adding a cationic glyoxylated polyacrylamide polymer composition according to claim 1 to the fibre stock, and forming the fibre stock into paper, board or the like.

14. The method according to claim 13, wherein the fibre stock has a zeta potential in a range of −25 mV-+10 mV before addition of the cationic glyoxylated polyacrylamide polymer composition.

15. The method according to claim 14, wherein zeta potential of the fibre stock is negative.

16. The method according to claim 13, wherein the glyoxylated polyacrylamide polymer composition is added in an amount of 0.5 kg-4 kg as dry composition/ton dry stock.

17. The method according to claim 13, wherein the polymer composition is added to the fibre stock comprising at least 50 weight-% of unbleached kraft pulp, bleached kraft pulp or recycled pulp.

Description

EXPERIMENTAL

(1) Analysis Methods: Dry content was determined by Mettler Toldedo HR73 IR dryer, at 150° C. Viscosity was determined by Brookfield DV1 viscometer, equipped with small sample adapter, spindle was SC4-S18, maximum rotation speed, temperature was 25° C. pH was determined with calibrated pH meter. The weight average molecular weight (MW) was determined by size-exclusion chromatography (SEC) using Agilent 1100 SE chromatography equipment with integrated pump, autosampler and degasser. Eluent is a buffer solution (0.3125 M CH.sub.3COOH+0.3125 M CH.sub.3COONa) with a flow rate of 0.5 ml/min at 35° C. Typical sample concentration is 2-4 mg/ml, with an injection volume of 50 μl. Ethylene glycol (1 mg/ml) is used as a flow marker. Column set consists of three columns (a TSKgel PWXL guard column and two TSKgel GMPWXL columns). Refractive index detector by Agilent is used for detection (T=35° C.). Molecular weights are determined using conventional (column) calibration with poly(ethylene oxide)/poly(ethylene glycol) narrow molecular weight distribution standards (Polymer Standards Service). Unreacted glyoxal was determined using the method described in the article of Zhu et al. “HPLC determination of glyoxal in aldehyde solution with 3-methyl-2-benzothiazolinone hydrazone” (Front. Chem. Sci. Eng. 2011, 5(1): 117-121) using UPLC. 1.2 ml of aqueous dilution of sample or glyoxal standard is diluted to 20 ml with freshly prepared MBTH solution, and kept in water bath of 70° C. for 110 min to form yellow diazine. Analysis by Acquity UPLC BEH C18 1.7 μm, 2.1 mm×50 mm, 2 μl injection, 0.4 ml/min; UV-detection at 410 nm. Residual acrylamide was determined by HPLC.

Example 1

(2) Polyacrylamide Base Polymer (BP-1) for GPAM Series 1 (DADMAC Content 12.5 Mol-% of Monomers (24.5 wt-% of Monomers))

(3) Water (140 g), diallyldimethylammonium chloride (DADMAC) 65 wt-% aqueous solution (31.0 g), diethylenetriaminepenta-acetic acid (DTPA) 40 wt-% aqueous solution (0.52 g), and citric acid (0.84 g) are fed into the 1 liter glass reactor, equipped with mechanical mixer and a jacket for heating and cooling. pH is adjusted to 4.5-5.0 with sodium hydroxide solution (20 wt-%). The mixture is heated to 100° C. Small nitrogen flow is put on. Acrylamide (AMD) 50 wt-% aqueous solution (459 g) and DADMAC 65 wt-% aqueous solution (84.2 g) are fed into monomer tank and mixed for 5 min. Ammonium persulfate (APS) solution is made into catalyst 1 tank by dissolving APS (4.76 g) in water (35.0 g). Sodium metabisulfite (MBS) solution is made into catalyst 2 tank by dissolving MBS (9.59 g) in water (34.2 g). Catalyst 1 (APS), catalyst 2 (MBS), and monomer mixture (AMD/DADMAC) feeds are started simultaneously, when water is boiling/refluxing clearly and temperature is 100° C. Reaction time starts. Feed time for catalyst 1 (APS) is 130 min. Feed time for catalyst 2 (MBS) is 120 min. Feed time for monomer mixture (AMD/DADMAC) is 105 min. Temperature of the reaction mixture is kept at 100° C. and the mixture must be refluxed during catalyst and monomer feed. Reaction mixture is kept at 100° C. for 45 min, when catalyst 1 feed has been ended. Product (BP-1) is cooled below 25° C.

(4) Dry content of BP-1 was 40.0 wt-%, viscosity of the solution was 159 mPas and pH was 3.8. Molecular weight average (MW) was 8400 g/mol by SEC analysis. Unreacted acrylamide was not detected in the polymer solution and the amount was below detection limit 5 mg/kg solution. Unreacted acrylamide corresponds to value below 12.5 mg/kg of dry material.

(5) Cationic Glyoxylated Polyacrylamide Polymer Composition Series 1, Glyoxylation of Base Polymer BP-1

(6) GPAM products are produced by the following procedure. BP-1 and water are dosed into a reactor. The mixture is mixed for 5 min. pH is adjusted to 7-8 with NaOH 10 wt-%-solution (about 1.2 g). Glyoxal is added to the reactor. The mixture is mixed for 5 min. Temperature is adjusted to 23-26° C. pH is adjusted to 8.7-9.2 with NaOH 32 wt-% solution. Viscosity is monitored in the function of reaction time. If pH decreases below 8.7, it is then re-adjusted to about 9.0 with NaOH 32 wt-% solution. Total amount of NaOH 32% solution is about 4 g. Temperature is kept at 23-26° C. during glyoxylation reaction. When viscosity is increased to target value, then reaction is stopped by immediately adding either sulphuric acid solution (20 wt-%) and/or formic acid and pH is decreased to about 3.0. Dry content, viscosity, pH and unreacted glyoxal and MWr were determined.

(7) Material amounts, molar ratio of glyoxal to amide in base polymer and glyoxal concentration at the start are presented in the table 1. Determined values are in the table 2. The GPAM products 1-A and 1-B are unbuffered references.

(8) TABLE-US-00001 TABLE 1 GPAM series 1. Product GPAM 1-A GPAM 1-B GPAM 1-C GPAM 1-D GPAM 1-E GPAM 1-F Substance Amount, g Amount, g Amount, g Amount, g Amount, g Amount, g BP-1 (40.0 wt-%) 177.1 179.6 182.9 180.6 181.9 177.1 Water 734.4 734.4 734.4 737.7 737 735.7 Glyoxal (40.0 wt-%) 66.52 64.06 64.1 63.0 61.9 66.5 Formic acid (25 wt-%) 0.0 0.0 3.7 3.7 4.2 5.6 Molar ratio, 0.64 0.61 0.61 0.60 0.58 0.64 Glyoxal/Amide Glyoxal start, wt-% 2.66 2.56 2.56 2.52 2.47 2.66

(9) TABLE-US-00002 TABLE 2 Determined values of GPAM series 1. Unreacted Unreacted Dry Charge glyoxal in glyoxal of total Formic acid content Viscosity density composition glyoxal Product (mmol/liter) (%) (mPas) pH (meq/g, dry) (%) (%) GPAM 1-A 0 10.0 22 3.1 ~0.95 0.99 37 GPAM 1-B 0 10.1 18 3.1 ~0.95 0.99 39 GPAM 1-C 20 9.9 26 3.0 ~0.95 0.98 38 GPAM 1-D 20 9.7 26 3.0 ~0.95 0.93 37 GPAM 1-E 23 9.7 24 3.0 ~0.95 0.90 36 GPAM 1-F 31 10.0 24 3.0 ~0.95 0.98 37

(10) The weight average molecular weight MW of GPAM 1-A was 464 200 g/mol and GPAM 1-B was 460 250 g/mol. Based on the similar dry contents and viscosities of all samples in Table 2, also the magnitude of the weight average molecular weight Mw of the samples may be expected to be similar.

(11) Cationic glyoxylated polyacrylamide polymer compositions at dry content of about 10% and the amount of unreacted glyoxal of total glyoxal below 40% had unreacted glyoxal below 1 weight-% by the total weight of the composition.

(12) GPAM series 1 product were stored at 23° C. and 35° C. pH and viscosities were determined during storage. pH and viscosities were determined at 25° C. The results are presented in Tables 3 and 4.

(13) TABLE-US-00003 TABLE 3 pH stability of unbuffered GPAM of series 1 during storage at 23° C. and 35° C. Product GPAM 1-A GPAM 1-A GPAM 1-B GPAM 1-B Time/days 23° C. 35° C. 23° C. 35° C. 0 3.1 3.1 3.1 3.1 6 3.6 4.2 3.6 4.2 19 3.9 4.6 3.8 4.6 30 — — 4.1 —

(14) TABLE-US-00004 TABLE 4 pH stability of buffered GPAM of series 1 during storage at 35° C. Product GPAM 1-C GPAM 1-D GPAM 1-E GPAM 1-F Glyoxal/AMD 0.61 0.60 0.58 0.64 Dry solids % 9.9 9.7 9.7 10.0 Formic acid, mM 20 20 23 31 Time/days pH pH pH pH  0 3.0 3.0 3.0 3.0  8 3.3 3.2 3.2 3.0 20 3.3 3.2 3.1 3.0 33 3.3 3.2 3.1 3.0 49 — — 3.3 3.1 60 — — 3.3 3.1

(15) pH of unbuffered cationic glyoxylated polyacrylamide polymer compositions drifts upwards during storage. Drifting speed speeds up at higher temperature. Buffering facilitates keeping pH below 4 for 60 days at 35° C.

(16) Buffering improves storage stability of the GPAM products as presented in Table 5.

(17) TABLE-US-00005 TABLE 5 Viscosity stability of GPAM series 1 during storage at 35° C. Product GPAM 1-A GPAM 1-B GPAM 1-C GPAM 1-D GPAM 1-E GPAM 1-F Glyoxal/AMD 0.64 0.61 0.61 0.60 0.58 0.64 Dry solids % 10.0 10.1 9.9 9.7 9.7 10.0 Formic acid, mM 0 0 20 20 23 31 Days at 35° C. mPas mPas mPas mPas mPas mPas  0 22 18 26 26 24 24  6 23 18 — — — —  8 — — 28 25 22 23 19 gel 27 — — — — 20 — 36 28 24 25 30 gel — — — — 33 75 35 27 27 49 gel gel 39 35 60 71 44

Example 2

(18) Polyacrylamide Base Polymer (BP-2) for GPAM Series 2 (DADMAC Content 14.3 Mol-% of Monomers (27.5 wt-% of Monomers))

(19) Water (148 g), diallyldimethylammonium chloride (DADMAC) 65 wt-% aqueous solution (32.1 g), diethylenetriaminepenta-acetic acid (DTPA) 40 wt-% aqueous solution (0.50 g), and citric acid (0.81 g) are fed into the reactor. pH is adjusted to 4.5-5.0 with sodium hydroxide solution (20 wt-%). The mixture is heated to 100° C. Small nitrogen flow is put on. Acrylamide (AMD) 50 wt-% aqueous solution (444 g) and DADMAC 65 wt-% aqueous solution (97.4 g) are fed into monomer tank and mixed for 5 min. Ammonium persulfate (APS) solution is made into catalyst 1 tank by dissolving APS (5.4 g) in water (35.0 g). Sodium metabisulfite (MBS) solution is made into catalyst 2 tank by dissolving MBS (10.9 g) in water (34.2 g). Catalyst 1 (APS), catalyst 2 (MBS), and monomer mixture (AMD/DADMAC) feeds are started simultaneously, when water is boiling/refluxing clearly and temperature is 100° C. Reaction time starts. Feed time for catalyst 1 (APS) is 130 min. Feed time for catalyst 2 (MBS) is 120 min. Feed time for monomer mixture (AMD/DADMAC) is 105 min. Temperature of the reaction mixture is kept at 100° C. and the mixture must be refluxed during catalyst and monomer dosings. Reaction mixture is kept at 100° C. for 45 min, when catalyst 1 feed has been ended. Product is cooled below 25° C. and then analysed.

(20) Dry content was 40.0 wt-%, viscosity of the solution was 117 mPas and pH 3.5. Unreacted acrylamide was not detected in the polymer solution and the amount was below detection limit 5 mg/kg solution. Unreacted acrylamide corresponds to value below 12.5 mg/kg of dry material.

(21) Cationic Glyoxylated Polyacrylamide Polymer Composition Series 2, Glyoxylation of Base Polymer BP-2

(22) GPAM products are produced by the following procedure. BP-2 and water are dosed into a reactor. The mixture is mixed for 5 min. pH is adjusted to 7-8 with NaOH 10 wt-%-solution (about 1.2 g). Glyoxal is added to the reactor. The mixture is mixed for 5 min. Temperature is adjusted to 23-26° C. pH is adjusted to 8.7-9.2 with NaOH 32 wt-%-solution. Viscosity is monitored in the function of reaction time. If pH decreases below 8.7, it is then re-adjusted to about 9.0 with NaOH 32 wt-% solution. Total amount of NaOH 32% solution is about 4 g. Temperature is kept at 23-26° C. during glyoxylation reaction. When viscosity is increased to target value, then reaction is stopped by immediately adding formic acid (99%). Dry content, viscosity, pH and free glyoxal (unreacted glyoxal) was determined.

(23) Material amounts, molar ratio of glyoxal to amide in base polymer and glyoxal concentration at the start are presented in the Table 6. Determined values are presented in the Table 7. Storage stability of the GPAM products is presented in Tables 8 and 9.

(24) TABLE-US-00006 TABLE 6 GPAM series 2. Product GPAM 2-A GPAM 2-B GPAM 2-C Substance Amount, g Amount, g Amount, g BP-2 (40 wt-%), g 184.6 186.2 187.9 Water, g 744.2 744.2 744.0 Glyoxal (40 wt-%), g 62.1 60.5 59.0 Formic acid (99%), g 4.2 4.2 4.2 Molar ratio glyoxal/Amide 0.60 0.58 0.56 Glyoxal at start, wt-% 2.48 2.42 2.36

(25) TABLE-US-00007 TABLE 7 Determined values of GPAM series 2. Product GPAM 2-A GPAM 2-B GPAM 2-C Molar ratio glyoxal/AMD 0.60 0.58 0.56 Formic acid, mM 90 90 90 Dry solids, % 9.91 10.1 10.2 Viscosity, mPas 24.2 23.5 23 pH 3.0 3.0 3.0 Charge density, meq/g, dry ~1.2 ~1.2 ~1.2 Unreacted glyoxal in 0.80 0.77 0.81 composition, % Unreacted glyoxal of total 32.0 31.8 34.1 glyoxal, %

(26) TABLE-US-00008 TABLE 8 Viscosity and pH stability of GPAM of series 2 during storage at 35° C. Storage GPAM 2-A GPAM 2-B GPAM 2-C time Viscosity, GPAM 2-A Viscosity, GPAM 2-B Viscosity, GPAM 2-C Days mPas pH mPas pH mPas pH 0 24.2 3.0 23.5 3.00 23.0 3.00 23 22.2 3.16 21.0 3.21 22.3 3.17 57 24.4 3.29 23.7 3.30 26.4 3.26 86 24.9 3.25 24.5 3.27 28.9 3.28 104 25.1 3.26 23.5 3.28 23.9 3.27

(27) GPAM with unreacted glyoxal content less than 1.0 wt-% and storage stability at 35° C. over 100 days can be maintained when viscosity of polyacrylamide base polymer is below 120 mPas at 40% concentration and unreacted glyoxal is below 35 wt-% of the total glyoxal and the GPAM is buffered.

(28) TABLE-US-00009 TABLE 9 Viscosity and pH stability of GPAM of series 2 during storage at 23° C. Storage GPAM 2-A GPAM 2-B GPAM 2-C time Viscosity, GPAM 2-A Viscosity, GPAM 2-B Viscosity, GPAM 2-C Days mPas pH mPas pH mPas pH 0 24.2 3.0 23.5 3.0 23.0 3.0 23 22.9 3.15 21.6 3.14 21.5 3.12 63 24.2 3.31 22.8 3.32 23.1 3.27 86 24.7 3.27 23.3 3.29 23.2 3.27 104 25.1 3.28 24.6 3.31 33.3 3.28

Example 3

(29) Polyacrylamide Base Polymer (BP-3) for GPAM Series 3 (DADMAC Content 24.2 Mol-% of Monomers (42.0 wt-% of Monomers))

(30) Water (168 g), diallyldimethylammonium chloride (DADMAC) 65 wt-% aqueous solution (53.2 g), diethylenetriaminepenta-acetic acid (DTPA) 40 wt-% aqueous solution (0.62 g), and citric acid (0.81 g) are fed into the reactor. pH is adjusted to 4.5-5.0 with sodium hydroxide solution (20 wt-%). The mixture is heated to 100° C. Small nitrogen flow is put on. Acrylamide (AMD) 50 wt-% aqueous solution (356.6 g) and DADMAC 65 wt-% aqueous solution (144.7 g) are fed into monomer tank and mixed for 5 min. Ammonium persulfate (APS) solution is made into catalyst 1 tank by dissolving APS (4.4 g) in water (32.3 g). Sodium metabisulfite (MBS) solution is made into catalyst 2 tank by dissolving MBS (8.8 g) in water (31.5 g). Catalyst 1 (APS), catalyst 2 (MBS), and monomer mixture (AMD/DADMAC) feeds are started simultaneously, when water is boiling/refluxing clearly and temperature is 100° C. Reaction time starts. Feed time for catalyst 1 (APS) is 130 min. Feed time for catalyst 2 (MBS) is 120 min. Feed time for monomer mixture (AMD/DADMAC) is 105 min. Temperature of the reaction mixture is kept at 100° C. and the mixture must be refluxed during catalyst and monomer dosings. Reaction mixture is kept at 100° C. for 45 min, when catalyst 1 feed has been ended. Product is cooled below 25° C. and then analysed.

(31) Dry content was 40.0 wt-%, viscosity of the solution was 99 mPas and pH was 3.9. Unreacted acrylamide was not detected in the polymer solution and the amount was below detection limit 5 mg/kg solution. Unreacted acrylamide corresponds to value below 12.5 mg/kg of dry material.

(32) Cationic Glyoxylated Polyacrylamide Polymer Composition Series 3, Glyoxylation of Base Polymer BP-3

(33) GPAM products are produced using the procedure described in example 2. Material amounts, molar ratio of glyoxal to amide in polyacrylamide base polymer and glyoxal concentration at the start are presented in the Table 10. Determined values are presented in the Table 11. Storage stability of the GPAM products is presented in Table 12.

(34) TABLE-US-00010 TABLE 10 GPAM series 3. Product GPAM 3-A GPAM 3-B Substance Amount, g Amount, g BP-3 (40 wt-%) 189.0 191.4 Water 746.3 746.3 Glyoxal (40 wt-%) 57.8 55.5 Formic acid (99%) 1.86 1.86 Molar ratio glyoxal/Amide 0.68 0.64 Glyoxal at start, wt-% 2.31 2.22

(35) TABLE-US-00011 TABLE 11 Determined values of GPAM series 3. Product GPAM 3-A GPAM 3-B Molar ratio glyoxal/AMD 0.68 0.64 Formic acid, mM 40 40 Dry solids, % 9.97 9.90 Viscosity, mPas 24.3 23.4 pH 2.99 3.00 Charge density, meq/g, dry ~1.8 ~1.8 Unreacted glyoxal in 0.87 0.81 composition, % Unreacted glyoxal of total 37.7 36.5 glyoxal, %

(36) TABLE-US-00012 TABLE 12 Viscosity and pH stability of GPAM of series 3 during storage at 23° C. Storage time GPAM 3-A GPAM 3-A GPAM 3-B GPAM 3-B Days Viscosity, mPas pH Viscosity, mPas pH 0 24.3 2.99 23.4 3.00 37 22.4 3.22 22.2 3.22 120 22.8 3.31 21.8 3.31

(37) GPAM solution with unreacted glyoxal level below 1.0 wt-% and storage stability at 23° C. more than 120 days is achieved when the amount of unreacted glyoxal is less than 40% of the total glyoxal.

Example 4: Application Example

(38) Test pulp was consisted 70% eucalyptus bleached hardwood kraft pulp refining degree SR 23 and 30% pine bleached kraft pulp refining degree SR 20. Pulp mixture properties are presented at Table 13.

(39) TABLE-US-00013 TABLE 13 Properties of pulp mixture. pH 6.81 Turbidity, NTU 0.8 Conductivity, μS/cm 1099 Cationic demand, μekv/l 18.28 Zeta potential, mV −18.0 Consistency, g/l 4.9

(40) For the preparation of laboratory sheets the stock was diluted to 0.5 consistency with conductivity controlled water and for the test pulp of Zeta-potential the stock was diluted to 2.0% consistency with conductivity controlled water. Conductivity controlled water was made from tap water by adding NaCl until water reached conductivity of 1500 ρS/cm. pH of diluted pulps was adjusted to 7.0 by NaOH. Strength composition was added 60 s before sheet forming. Hand sheets having basis weight of 80 g/m.sup.2 were formed by using Rapid Köthen sheet former with tap water dilution in accordance with ISO 5269-2:2012. The basis weight of the sheets was adjusted by the volume of the thin stock and the amount of stock portion was kept constant. 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. Used pulp and sheet testing devices and standards are given in Table 14. The indexed strength value is the strength divided by basis weight of the paper/board.

(41) TABLE-US-00014 TABLE 14 Pulp and sheet testing devices and standards. Property/Measurement Device/Standard pH Knick Portamess 911 Turbidity (NTU) WTW Turb 555IR Conductivity (mS/cm) Knick Portamess 911 Charge (μekv/l) Mütek PCD 03 Zeta potential (mV) Mütek SZP-06 Consistency (g/l) ISO 4119 Basis weight Mettler Toledo/ISO 536 Ash content, 525° C. ISO 1762 Wet immediate tensile Lorentzen & Wettre Tensile tester/ISO 3781: strength 2011, 1 min immerse time Tensile strength Lorentzen & Wettre Tensile tester/ISO 1924-3

(42) Tested strength chemical compositions are presented at Table 15. GPAM ref has charge density 1.8 meq/g dry and unreacted glyoxal content of 1.2 wt-%. Test points and results are presented at Table 16. Test points 1-4 are reference points. In Table 16 Zeta-potential of test point 4 is positive and indicates overdosage that would cause difficulties like foaming, deposits or sheet release problems in paper making process. GPAM compositions according to the invention give higher dry tensile strength values at 2-4 kg/t dry dosages. Also immediate wet tensile at 2-4 kg/t dry dosages are similar or better.

(43) TABLE-US-00015 TABLE 15 Tested compositions. Composition GPAM ref GPAM 1-C GPAM 1-E GPAM 1-F Dry material, % 12.5 9.9 9.7 10.0 Viscosity, mPas 23 26 24 24 pH 3.4 3.0 3.0 3.0

(44) TABLE-US-00016 TABLE 16 Test points and results. Zeta Ten- wet imm. GPAM GPAM GPAM GPAM poten- sile tensile Test ref. 1-3 1-6 1-7 tial index index No. kg/t dry kg/t dry kg/t dry kg/t dry mV Nm/g Nm/g 1 0 −90 45.4 0.9 2 1 −74 50.4 3.4 3 2 −38 53.0 5.0 4 4 11 57.5 6.7 5 1 −81 51.2 3.2 6 2 −67 55.0 5.0 7 4 −34 56.7 6.9 8 1 −82 48.9 3.3 9 2 −62 55.2 5.2 10 4 −25 57.0 7.5 11 1 −78 49.3 3.5 12 2 −61 54.9 5.2 13 4 −29 59.2 7.6