Method for manufacture of paper, board or the like and use of the composition

Abstract

A method for manufacture of paper, board or the like, comprising the step of dissolving a composition into aqueous solution, whereby an aqueous treatment solution is obtained for adding the obtained treatment solution to the pulp. The composition comprising a copolymer of acrylamide and at least one cationic monomer, the copolymer comprising cationic monomers at least 15 mol-%, calculated from total amount of monomers, and an ionic crosslinker agent comprising at least two carboxyl groups, wherein the equivalent ratio of carboxyl groups:cationic monomer is between 1:20 and 1:0.5.

Claims

1. A method for making of paper, board or the like, comprising the steps of: providing a pulp, dissolving into an aqueous solution a composition comprising: (i) a copolymer of acrylamide and at least one cationic monomer, the copolymer comprising cationic monomers of at least 15 mol-%, calculated from the total amount of monomers, and (ii) an ionic crosslinker agent comprising at least two carboxyl groups, wherein the equivalent ratio of carboxyl groups:cationic monomer is between 1:20 and 1:0.5, whereby an aqueous treatment solution is obtained, adding the obtained treatment solution to the pulp, and forming the pulp into a fibrous web.

2. The method according to claim 1, wherein the pulp has a conductivity of at least 1 mS/cm in the head box stock.

3. The method according to claim 1, wherein the copolymer of acrylamide comprises cationic monomers of at least 20 mol-%.

4. The method according to claim 1, wherein the cationic monomer of the copolymer is selected from 2-(dimethylamino)ethyl acrylate (ADAM), [2-(acryloyloxy)ethyl] trimethylammonium chloride (ADAM-Cl), and any combination thereof.

5. The method according to claim 1, wherein the equivalent ratio of carboxyl groups:cationic monomer in the ionic crosslinker agent is between 1:15 and 0.8.

6. The method according to claim 1, wherein the copolymer of acrylamide further comprises anionic monomers, provided that the net charge of the copolymer is cationic at pH 7.

7. The method according to claim 1, wherein the composition is in the form of a dry powder.

8. The method according to claim 1, wherein the amount of ionic crosslinker agent is in a range of 2-20 weight-% of copolymer of acrylamide expressed as citric acid equivalent based on the molar weight of the citric acid.

9. The method according to claim 1, wherein the pulp comprises at least 50 weight-% of the dry fiber furnish recycled paper, or board or the like pulped in a pulper and/or unbleached kraft pulp and/or unbleached semichemical pulp.

10. The method according to claim 1, wherein the pulp comprises starch in an amount of at least 0.5 weight-%, based on dry total solids, as measured at a pulp storage or at a broke storage.

11. The method according to claim 1, wherein the composition is used in an amount of 50-1000 dry g/t dry pulp.

12. The method according to claim 1, wherein the obtained treatment solution is added after the last shear stage and prior to a head box of a paper or board machine.

13. The method according to claim 1, further comprising adding at least one amylase inhibitor and/or biocide to the pulp and/or a broke.

14. The method according to claim 1, wherein the pulp has a conductivity of at least 3.5 mS/cm in the head box stock.

15. The method according to claim 1, wherein the pulp has a conductivity of at least 3 mS/cm in the head box stock.

16. The method according to claim 1, wherein the copolymer of acrylamide comprises cationic monomers of at least at least 45 mol-%.

17. The method according to claim 1, wherein the equivalent ratio of carboxyl groups:cationic monomer in the ionic crosslinker agent is between 1:10 and 1:1.

18. The method according to claim 1, wherein the amount of ionic crosslinker agent is in a range of 5.5-20 weight-% of copolymer of acrylamide expressed as citric acid equivalent based on the molar weight of the citric acid.

19. The method according to claim 1, wherein the pulp comprises starch in an amount of at least 4 weight-%, based on dry total solids, as measured at a pulp storage or at a broke storage.

20. The method according to claim 1, wherein the composition is used in an amount of 300-800 dry g/t dry pulp.

Description

EXPERIMENTAL

(1) Unless otherwise stated, the data in percent is always percent by weight.

(2) Standard Viscosity was Determined by the Following Method:

(3) At first a salt solution is made by dissolving sodium chloride (525 g) in de-ionized water (3000 g) in a beaker equipped with a magnetic bar and magnetic stirred. The mixture is stirred with maximum speed of the magnetic stirred until sodium chloride was fully dissolved.

(4) De-ionized water (200.0 g) is dosed into a beaker. Magnetic stirrer bar is added into the beaker and stirred with maximum speed of magnetic stirrer. Cationic polyacrylamide polymer 0.330 g is dosed into the beaker in 15 seconds while stirring. The mixture is stirred with magnetic stirred for 5 min with maximum speed and then 25 min with 350 rpm. The salt solution (117.5 g, 15% (w/w) NaCl) is added into the beaker and the mixture is stirred for 5 min. The formed solution is filtered through 10 cm diameter, 250 micron stainless steel mesh sieve. Viscosity of the filtered solution (1.0% (w/w) sample in 5.5% (w/w) NaCl solution) is then determined with a Brookfield DV I+ viscometer, equipped with UL adapter ULA-35Z and YULA-15Z ULA spindle at 25 C. with maximum rotation speed. Sample size in viscosity determination is 16 ml.

(5) Solution Viscosity was Determined with the Following Method:

(6) Cationic polyacrylamide (2.50 g) was dissolved in water (497.5 g) to make 0.5% CPAM solutions. Viscosities were measured by Brookfield DV1, equipped with small sample adapter, at 25 C. with spindle S31 with maximum rotation speed.

Example 1. General Procedure for Exemplary Production of a Copolymer of Acrylamide and Cationic Monomers

(7) A reactor is charged with acrylamide solution (50 wt-%) and ADAM-Cl solution (80 wt-%) in a molar ratio given for each polymer product. pH is adjusted to about 2.5-4.5 by adding adipic acid 1 wt-% of total amount of monomers. Other chemicals, such as chain transfer agents, chelating agents, and thermal initiators are added to the monomer mixture. Then, the solution is purged with nitrogen gas. Polymerization is initiated by injecting a redox pair initiator system into the polymerization reactor. A cationic polyacrylamide gel is obtained as a result of the polymerization reaction. The gel is dried and finally powder or particles are obtained. The polymer compositions have dry content about 95-98 wt-%. Polymer properties are measured by using the obtained powder.

Example 2. Compositions of Ionically Crosslinked Copolymers of Acrylamide and Cationic Monomers

(8) Compositions of copolymers of acrylamide and cationic monomers, and citric acid or adipic acid added post-polymerization as ionic crosslinker agent are made by adding powder of cationic polyacrylamide in water and stirring with magnetic stirrer at 25 C. for 60 min and then adding acid to the polymer solution and stirring 15 min with magnetic stirrer. An example of polymer solution is presented in Table 1. CPAM in the solution is CPAM 49 mol-% ADAM-Cl, dry content 95%. Charge density of CPAM 49 mol-% is 3.7 meq/g polymer and total cationic charge in 0.5% solution is 18.5 meq/liter. MW of citric acid is 192.1 g/mol. Citric acid is tribasic acid and thus each mol of citric acid contains 3 equivalents of potential anions. Thus, for example 0.22 g citric acid may contain up to 3.4 meq anionic charges. Properties of the solutions and equivalent ratios of carboxyl groups:cationic monomers are in Table 2 The solutions are used in application example 1.

(9) TABLE-US-00001 TABLE 1 Preparation and properties of CPAM (49 mol-% ADAM-CI) non- crosslinked reference and ionically crosslinked composition sample (CS) solutions (2.6 g of CPAM with dry content 95% in 500 ml water, i.e. 0.5 w-% CPAM solution). Cationic charge of each sample was 18.5 meq/liter. For each sample the CPAM was polymerized in the presence of same amount of adipic acid, 1% (w/w) of CPAM, taken into account in equivalent ratios. Solution and standard viscosities were measured as defined earlier. Equivalent Post-polymerization Post-polymerization ratio Anionic added added of charge Solution Standard citric acid adipic acid carboxyl:cationic (meq/ Viscosity viscosity Sample (g/% of CPAM) (g/% of CPAM) monomer liter) pH mPas mPas Ref. 0 0 1:27 0.7 3.81 471 3.0 CS1 0.11/4.5 0 1:4.4 4.2 2.98 438 2.7 CS2 0.23/9.0 0 1:2.4 7.7 2.85 425 2.7 CS3 0.34/13.5 0 1:1.6 11.2 2.78 416 2.7 CS4 0 0.13/5.0 1:4.5 4.1 3.37 463 2.7 CS5 0 0.25/10 1:2.5 7.5 3.28 466 2.7 CS6 0.38/15 1:1.7 10.9 3.19 457 2.7

(10) From Table 1 it can be seen that the ionically crosslinked CPAM samples have decreased standard and solution viscosities compared to the non-crosslinked reference. Additionally, it can be seen that the solution viscosity decrease is more pronounced with higher relative crosslinker amount, and that higher viscosity decrease is obtained with tribasic crosslinker agent compared to divalent crosslinker agent, even for similar equivalent ratios.

Application Examples

(11) Pulp Preparation

(12) European testliner board was used as raw-material. This testliner contains about 5% surface size starch, which was enzymatically degraded native corn starch. Dilution water was made from tap water by adjusting Ca.sup.2+ concentration to 520 mg/l by CaCl.sub.2 and by adjusting conductivity to 4 mS/cm by NaCl. Testliner board was cut to 2*2 cm squares. 2.7 l of dilution water was heated to 85 C. The pieces of testliner were wetted for 5 minutes in dilution water at 2% concentration before disintegration. Slurry was disintegrated in Britt jar disintegrator with 30 000 rotations. Pulp was diluted to 0.5% by adding dilution water.

(13) DDA Test

(14) DDA (dynamic drainage analyzer) from Akribi Kemi Konsulter, Sweden, was used to measure retention and drainage. 500 ml of pulp was used for each test point. Pulp was poured to DDA 30 s before drainage and DDA stirrer was adjusted to 1000 rpm. Polymer was added 10 s before drainage. Stirring was stopped 2 s before drainage. Vacuum was 300 mBar for 30 s after drainage started, wire opening was 0.25 mm.

(15) Drainage time was recorded, filtrate turbidity and PCD was measured immediately. DDA sheets were weighted and pressed in sheet press for 1 min at 4 bar having 2 plotter papers both sides. Sheets from the wire were dried in Lorenzt & Wettre hot plate dryer to abs dry for retention calculation. SCT measurements according to ISO 9895 were repeated 6 times from each DDA sheet. Result was indexed based on the basis weight (sheet dry weight/area) of the DDA-sheet.

(16) Determination of retention of the starch originating from the recycled pulp (in this case degraded nonionic starch originating from the coating of the testliner board) was made from DDA filtrate. This determination is also suitable for measuring starch amount in pulp. 25 ml of filtrate (or pulp) was added into 10 ml of 10%-w HCl. Mixture was stirred for 10 min with magnetic stirrer and filtrated by gravitation in a funnel with a black ribbon filter paper. 1 ml of filtrated mixture was added to 8.5 ml water. 0.5 ml iodine reagent, which consisted 7.5 g Kl/l+5 g/l I.sub.2 was added and absorbance value was measured at 610 nm by Hach Lange DR 900 spectrophotometer 1 min after iodine-solution was added. Zeroing of the spectrophotometer was done with the sample before iodine addition. C*film 07311 non-ionic degraded starch was used as reference to make calibration equation for starch content. Blank test for HCl-iodine solution absorbance was made to subtract baseline absorbance from the result. Starch retention was calculated as: (pulp starchfiltrate starch)/pulp starch*100%. Starch reduction was calculated as: (filtrate starch of zero testfiltrate starch)/filtrate starch*100%.

Application Example 1

(17) Test chemicals used in the example are presented in Table 2. The dosing and dosing times of the chemicals are presented in Table 3. Citric acid was added to CPAM at dissolving, the ionically crosslinked CPAM samples marked as CS1, CS2 and CS3 are same as in Table 1. The dosing times refer to time before drainage.

(18) TABLE-US-00002 TABLE 2 Test chemicals. Additive Description Parameters Concentration PAC Polyaluminium chloride 5.2% Al, 70% not diluted further silicate Basicity Silica FennoSil 442 (Kemira) dosing at 0.08% CPAM copolymer of ADAM-Cl and 49 mol-% cationic dissolving at 0.5%, acrylamide monomer, Mw ca. dosing at 0.08% 4 000 000 g/mol

(19) TABLE-US-00003 TABLE 3 Dosages and dosing times. time, s 600 15 10 PAC Silica CPAM Test no. kg/t prod kg/t dry kg/t dry 1 10 0.3 0 2 10 0.3 Ref 0.3 3 10 0.3 Ref 0.5 4 10 0.3 CS1 0.3 5 10 0.3 CS1 0.5 6 10 0.3 CS2 0.3 7 10 0.3 CS2 0.5 8 10 0.3 CS3 0.3 9 10 0.3 CS3 0.5 12 Ref 0.3 13 Ref 0.5 14 CS1 0.3 15 CS1 0.5

(20) TABLE-US-00004 TABLE 4 Test results for drainage (DDA), retention (DDA), starch retention and SCT index. Starch CPAM Equivalent Test Drainage Retention retention SCT ind (kg/ ratio no. time (s) (%) (%) (Nm/g) t dry) carbox:cat 1 10 92 21 36 0 2 6 93 23 33 Ref 0.3 1:27 3 5 94 33 35 Ref 0.5 1:27 4 6 93 27 35 CS1 0.3 1:4.4 5 5 94 34 36 CS1 0.5 1:4.4 6 6 94 31 36 CS2 0.3 1:2.4 7 5 95 31 37 CS2 0.5 1:2.4 8 6 94 30 36 CS3 0.3 1:1.6 9 5 94 35 36 CS3 0.5 1:1.6 12 6 93 14 35 Ref 0.3 1:27 13 6 93 20 36 Ref 0.5 1:27 14 6 94 20 35 CS1 0.3 1:4.4 15 6 94 27 37 CS1 0.5 1:4.4

(21) From Table 4 it can be seen that a CPAM flocculant is essential for obtaining improved drainage performance, and that ionic crosslinking does not disturb the drainage performance of the CPAM. When a 3-component program of PAC, silica and CPAM is used, a significant improvement of starch retention can be seen over CPAM alone, especially when using 3-component program with the ionically crosslinked CPAM of the present invention. As use of CPAM increases overall retention and flocculation, it is natural that SCT strength decreases. While the ionically crosslinked CPAM of the present invention achieves in both programs the same improvement of overall retention and drainage as the non-crosslinked CPAM, there is no decrease in SCT strength, even a slight increase in SCT can be seen in test no. 7. Further, it can be seen that the starch retention increases as the amount of ionic crosslinker agent increases. It is believed that the more structured, ionically crosslinked CPAM is better option for trapping of the degraded nonionic starch originating from the surface size of the testliner board.

Application Example 2

(22) Compositions of ionically crosslinked copolymers used in this example were manufactured as disclosed in Example 2, with properties presented in Table 5. Dosing times before drainage, dosages and test results are presented in Table 6.

(23) TABLE-US-00005 TABLE 5 Compositions of ionically crosslinked copolymers of acrylamide and varying amounts of ADAM-Cl/cationic charge cationic Post-polymerization Cationic Anionic monomers added citric Eq.ratio of charge charge MWr, Std. in CPAM acid carboxyl:cationic (meq/ (meq/ about viscosity Sample (mol-%) (% of CPAM) monomer liter) liter) (g/mol) mPas Comp 1 5 3.3 1:1.3 3.2 2.6 6M 3.1 Comp 2 10 3.3 1:2.3 6.0 2.6 6M 3.5 CS7 20 10 1:1.3 10.5 7.8 4M 2.7 CS8 33 10 1:1.9 14.8 7.8 4M 2.7 CS9 49 10 1:2.4 18.5 7.8 4M 2.7

(24) TABLE-US-00006 TABLE 6 Dosing times, dosages and test results. time, s 10 10 10 10 Cationic SCT Starch Test Comp 2. CS7 CS8 CS9 monomers index reduction no. kg/t dry kg/t dry kg/t dry kg/t dry (mol-%) Eq.ratio (Nm/g) (%) 16* 0 14.9 17 0.3 10 1:2.3 13.4 14 18 0.5 10 1:2.3 14.0 19 19 0.5 20 1:1.3 14.4 21 20 0.5 33 1:1.9 14.3 21 21 0.3 49 1:2.4 14.5 16 22 0.5 49 1:2.4 14.8 25 *zero test

(25) From Table 6 it can be seen that ionically crosslinked CPAMs having higher cationicity provided higher SCT strengths and starch reductions, compared to CPAM having cationicity of 10 mol-%.

Application Example 3

(26) Same samples were used as in the previous example, presented in Table 5. Dosing times before drainage and dosages are presented in Table 7 and test results in Table 8.

(27) TABLE-US-00007 TABLE 7 Dosing times and dosages. 600 PAC 15 10 10 10 10 time, s kg/t Silica Comp1 CS7 CS8 CS9 test no. prod kg/t dry kg/t dry kg/t dry kg/t dry kg/t dry 23 10 24 10 0.45 25 10 0.45 0.4 26 10 0.45 0.8 27 10 0.45 0.4 28 10 0.45 0.8 29 10 0.45 0.4 30 10 0.45 0.8 31 10 0.45 0.4 32 10 0.45 0.8

(28) TABLE-US-00008 TABLE 8 Cationic Equivalent ratio monomers carboxyl:cationic test no. (mol-%) monomers DDA drainage time, s Retention, % Turbidity, NTU Starch reduction, % 23* 7.3 90 557 0 24 15.2 91 538 4 25 5 1:1.3 7.2 93 105 9 26 5 1:1.3 6.9 93 101 12 27 20 1:1.3 7.0 95 75 13 28 20 1:1.3 5.9 93 77 15 29 33 1:1.9 7.8 95 83 14 30 33 1:1.9 6.4 94 86 19 31 49 1:2.4 8.1 94 83 16 32 49 1:2.4 6.0 94 87 19 *zero test

(29) From Table 8 it can be seen that ionically crosslinked CPAMs having cationicity above 15 mol-% (test no. 27-32) provided higher starch reductions and lower turbidities, compared to CPAM having cationicity of just 5 mol-%. Additionally, ionically crosslinked CPAMs having higher cationicity provided improved drainage and retention even at lower dosage. Further it can be seen that when the relative amount of carboxyl to cationic monomers was higher, shorter drainage times were obtained, as well as lower turbidities suggesting improved colloids retention.