Use of a polymer product for deposit formation control in manufacture of paper or board

Abstract

The invention relates to a use of a water-soluble polymer product comprising amphoteric polyacrylamide, which has neutral or cationic net charge at pH 7, a weight-average molecular weight of 2 500 000-18 000 000 g/mol and a total ionicity of 4-28 mol-%. The polymer product is used for controlling deposit formation caused by hydrophobic substances in manufacture of paper or board, where a fibre web is formed from an aqueous suspension of fibres. The invention relates also to a method for controlling deposit formation caused by hydrophobic substances in manufacture of paper or board, where a fibre web is formed from an aqueous suspension of fibres, as well as to produced paper or board.

Claims

1.-18. (canceled)

19. A process for manufacture of paper or board, wherein a fibre web is formed from an aqueous suspension of fibres, the method comprising: providing the aqueous fibre suspension; optionally diluting the aqueous fibre suspension; delivering the aqueous fibre suspension to a headbox, and draining the aqueous fibre suspension on a wire screen to form a wet web of the paper or the paperboard; pressing and drying the wet web to obtain a web of the paper or the board; and adding a water-soluble polymer product comprising amphoteric polyacrylamide, which has a neutral or cationic net charge at pH 7, a weight-average molecular weight of 2 500 000-18 000 000 g/mol and a total ionicity of 4-28 mol-%, to the fibre suspension, for controlling deposit formation caused by hydrophobic substances.

20. A paper or board obtained by the process according to claim 19.

21. The process according to claim 19, wherein the amphoteric polyacrylamide has a weight-average molecular weight in a range of 3 000 000-18 000 000 g/mol, 3 500 000-11 000 000 g/mol, or 4 000 000-8 000 000 g/mol.

22. The process according to claim 19, wherein the total ionicity of the amphoteric polyacrylamide is in a range of 4-18 mol-%, 5-13 mol-%, 6-12 mol-%, or 6-10 mol-%.

23. The process according to claim 19, wherein the amphoteric polyacrylamide in the polymer product comprises 3-25 mol-%, 5-14 mol-%, or 5-9 mol-%, of structural units derived from cationic monomers, and 0.5-5 mol-%, 1-4 mol-%, or 1-2.5 mol-%, of structural units derived from anionic monomers.

24. The process according to claim 19, wherein 50-95%, 60-90%, or 70-85%, of the charged groups in the amphoteric polyacrylamide are cationic.

25. The process according to claim 19, wherein the amphoteric polyacrylamide has a net cationic charge as measured at pH 7.

26. The process according to claim 19, wherein the amphoteric polyacrylamide is a linear polyacrylamide.

27. The process according to claim 19, wherein the cationic groups of the amphoteric polyacrylamide originate from monomers selected from 2-(dimethylamino)ethyl acrylate (ADAM), [2-(acryloyloxy)ethyl] trimethylammonium chloride (ADAM-Cl), 2-(dimethylamino)ethyl acrylate benzylchloride, 2-(dimethylamino)ethyl acrylate dimethylsulphate, 2-dimethylaminoethyl methacrylate (MADAM), [2-(methacryloyloxy)ethyl] trimethylammonium chloride (MADAM-Cl), 2-dimethylaminoethyl methacrylate dimethylsulphate, [3-(acryloylamino)propyl] trimethylammonium chloride (APTAC), [3-(methacryloylamino)propyl] trimethylammonium chloride (MAPTAC) and diallyldimethylammonium chloride (DADMAC).

28. The process according to claim 19, wherein the anionic groups of the amphoteric polyacrylamide originate from monomers selected from unsaturated mono- or dicarboxylic acids, being acrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconic acid, crotonic acid, isocrotonic acid, angelic acid or tiglic acid.

29. The process according to claim 19, wherein the amphoteric polyacrylamide is obtained by gel polymerisation, where the content of non-aqueous solvent in the reaction mixture is less than 10 weight-%, less than 5 weight-%, or less than 3 weight-%.

30. The process according to claim 19, wherein the polymer product has a polymer content of at least 25 weight-%, or at least 60 weight-%.

31. The process according to claim 19, wherein the water-soluble polymer product comprising amphoteric polyacrylamide is dissolved in water so as to obtain an aqueous treatment solution, which has a pH value of 2.5-5.

32. The process according to claim 19, further comprising adding inorganic microparticles, being bentonite microparticles, to the fibre suspension.

33. The process according to claim 19, wherein the fibre suspension comprises at least 50 weight-%, of recycled fibre material, being old corrugated containerboard or mixed waste, based on dry paper or paperboard.

34. The process according to claim 19, wherein the fibre suspension comprises recycled fibre material, which comprises more than 0.02 mg/g, or more than 0.2 mg/g, of hydrophobic substances having particle size in the range of 10-150 μm, calculated on basis of recycled fibre material as dry, of recycled fibre material as dry.

35. The process according to claim 19, wherein the fibre suspension comprises fibres obtained by kraft and/or mechanical pulping process(es).

36. The process according to claim 19, wherein the amphoteric polyacrylamide is added to the fibre suspension having consistency of above 14 g/l or stock component used to prepare the fibre suspension, before a machine chest, or before a mixing chest, of a paper or board machine.

37. The process according to claim 19, wherein the amphoteric polyacrylamide is used in amount of 100-2000 g/ton produced paper or board, in the range of 300-1500 g/ton produced paper or board, or in the range of 400-900 g/ton produced paper or board.

Description

EXPERIMENTAL

[0061] Some embodiments of the invention are described in the following non-limiting examples.

[0062] The following methods were used to in the experiments for analysis:

[0063] Extraction Measurement Method for Determining the Amount of Hydrophobic Substances, e.g. Stickies

[0064] Stickies are measured by taking a pulp sample and diluting it to 1% consistency. 500 ml of the pulp sample is screened in Dynamic Drainage Jar (DDJ) equipped with M80 wire in 25° C. temperature. DDJ is operated with 1200 rpm continuously. After 90% of the pulp sample is screened, 500 ml of washing water is added. Washing is repeated with additional 500 ml of water. DDJ is stopped, when 50 ml of pulp slurry is left on top of wire. Upper fraction remaining on wire and lower fraction screened through the wire are collected to filter paper by vacuum filtration with Bühner funnel. Munktell, Ahlström M00 drage 125 mm diameter filter papers are used. Filter papers with pulp are dried in oven, temperature 110° C., for 4 hours. Samples are weighted for dry weight determination. Filter papers are freeze dried and extracted with tetrahydrofurane. Gravimetric analysis followed by HPLC SEC measurement is conducted according to method presented at PhD Thesis of Tiina Sarja from Oulu University, Finland (Measurement, nature and removal of stickies in deinked pulp, Acta Universitatis Ouluensis, C Technica 275, Oulu University Press, 2007). Sticky extractives from the upper fraction is considered to represent macrostickies, having particle size >150 μm, and from the lower fraction microstickies, having particle size 10-150 μm. The results are calculated per total dry weight of fibre sample.

[0065] Flow Cytometry Method

[0066] 10 ml of pulp sample, where fixing chemical has been added, is mixed with 40 ml of distilled water. Sample is filtered to separate long fibres, which would otherwise disturb the measurement. Filtrate is diluted with distilled water and fluorescent colouring agent is added. Flow cytometric measurement is done with SL Blue device supplied by Partec GmbH. Colouring agent amount is tested so that the particles are distinguished based on fluorescence signal. Size of the particles is analysed by side scattering, which is calibrated by using standard size spherical polystyrene particles. 1 ml sample tube is used in flow cytometer of which 200 μl is analysed. Each particle is characterized by fluorescence intensity and by size. Hydrophobic population of stickies or pitch detected by higher fluorescence intensity is separated with gating from other particles including fines and pigments. Sample with at least 80% less stickies and pitch results in about 80% lower amount of particles in hydrophobic population gate. The separated hydrophobic population has size from 0.2 μm to 20 μm. The results from this hydrophobic population are calculated as number of particles, as average size of particles, as size distribution of particles or as area or volume of particles by assuming the shape as spherical.

[0067] Other Measurement Methods for Pulp Samples

[0068] For turbidity test 30 ml of pulp sample was filtered through black-ribbon filter paper in gravity filtration funnel and the filtrate was saved for measurements. Turbidity was measured immediately from the filtrate.

[0069] Measurement devices and/or standards used in characterisation of pulp/filtrate properties are given in Table 1.

TABLE-US-00001 TABLE 1 Measurement devices and/or standards used in Example 1. Property 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

[0070] General Description of the Polymer Product Preparation

[0071] Preparation of Monomer Solution for the Amphoteric Polyacrylamide

[0072] Monomer solution is prepared by mixing 248.3 g of 50% acrylamide solution, 0.01 g of 40% DTPA Na-salt solution, 2.9 g of sodium gluconate, 4.4 g of dipropylene glycol, 1.9 g of adipic acid, and 7.2 g of citric acid in a temperature controlled laboratory glass reactor at 20-25° C. The mixture is stirred until solid substances are dissolved. To the solution is added 32.6 g of 80% ADAM-Cl. pH of the solution is adjusted to 3.0 with citric acid, and 2.8 g of acrylic acid is added to the solution. pH is adjusted to be 2.5-3.0.

[0073] Preparation of Dry Polymer Product

[0074] After the monomer solution is prepared according to the description, the monomer solution is purged with nitrogen flow in order to remove oxygen. An initiator is added to the monomer solution. The initiator solution is 4 ml of 6% 2-hydroxy-2-methylpropiophenone in polyethylene glycol-water (1:1 by weight) solution. The monomer solution is placed on a tray to form a layer of about 1 cm under UV-light. UV-light is mainly on the range 350-400 nm, for example light tubes Philips Actinic BL TL 40W can be used. Intensity of the light is increased as the polymerisation proceeds to complete the polymerisation. The first 10 minutes the light intensity is 550 μW/cm.sup.2, and following 30 minutes it is 2000 μW/cm.sup.2. The obtained gel is run through an extruder and dried to moisture content less than 10% at temperature of 60° C. The dried polymer is ground and sieved to particle size 0.5-1.0 mm.

[0075] Intrinsic viscosity of the polymer product was determined by Ubbelohde capillary viscometer in 1 M NaCl at 25° C. Polymer product was dissolved in 1 M NaCl and a series of dilutions at suitable concentrations ranging from 0.01 to 0.5 g/dl for viscosity determinations. pH of the polymer solution for capillary viscosity determination was adjusted to 2.7 by formic acid to avoid impact of probable poly-ion complexation for viscosity. Molecular weights were calculated using “K” and “a” parameters of polyacrylamide. The value of parameter “K” is 0.0191 ml/g and the value of parameter “a” is 0.71. Determined intrinsic viscosity was 9.9 dl/g and calculated molecular weight 4 400 000 g/mol.

Chemicals Used in the Examples

[0076] Chemicals used in the examples are given in Table 2.

TABLE-US-00002 TABLE 2 Chemicals used in the examples. Dissolving Dosing Chemical conc. % conc. % Description CPAM 0.5 0.02 cationic copolymer of 10 mol-% ADAM-CI and 90 mol-% acrylamide Molecular weight 6 Mg/mol AMF 0.5 (at 0.02 amphoteric copolymer of 7 mol-% ADAM-CI, 2 pH 3.5) mol-% acrylic acid and 91 mol-% acrylamide, manufactured as described above Molecular weight 4.4 Mg/mol PA 0.5 0.02 Polyamine Molecular weight 250 000 g/mol PVOH 4 0.2 Copolymer of 88 mol-% vinylalcohol and 12 mol-% vinyl acetate Brookfield viscosity 50 mPas at 4% concentration. BENT 2 0.2 bentonite, Altonite SF, Kemira Oyj DISP 1 0.05 anionic dispersing agent, FennoDispo 320, Kemira Oyj PAC N/A 1 (used polyaluminiumchloride, FennoFloc A100, in 15 s) Kemira Oyj

Example 1: Fixation Test

[0077] Used Pulps

[0078] Recycled fibre pulp containing European old corrugated containerboard, OCC, diluted to 2% consistency with board machine clear filtrate.

[0079] Kraft pulp was unbleached spruce pulp, diluted to 2% consistency with board machine clear filtrate.

[0080] Measured properties for pulps and filtrate are given in Table 3.

TABLE-US-00003 TABLE 3 Results from measurements of pulp properties. Recycled Kraft Clear Property Pulp Pulp Filtrate pH 7.8 8.16 6.24 Turbidity, NTU 346 72 14 Conductivity, mS/cm 2.29 1.11 0.94 Charge, μekv/l −139 −684 −99 Consistency, g/l 83.0 73.8 0 Ash content, % 8.21 Macrostickies, 0.30 size >150 μm, mg/g Microstickies, 0.47 size 10-150 μm, mg/g

[0081] In measurements pulp samples were heated to temperature of 50° C. Pulp sample and added chemical were mixed in 500 ml beaker by blade stirrer with 200 rpm for 2 min after chemical addition. When a dispersing agent was used it was first added to the sample and the sample then mixed for 15 min before following chemical addition.

[0082] Flow cytometry sample was taken after mixing from the pulp sample.

[0083] In Table 4 are presented the fixation test results measured by using flow cytometry method described above for recycled fibre pulp samples. It can be seen from the results that polymer product comprising amphoteric polyacrylamide (AMF) is most efficient in fixing colloidal particles, which cause turbidity, as well as hydrophobic particles in separate ranges of 0.2-3.0 μm and 3.0-20 μm. The obtained effect is excellent in both size categories simultaneously, whereas other fixation and passivation agents are effective only for low or high size range. Also total area and volume of hydrophopic material is reduced, which indicates reduced deposit formation risk in a paper machine. Particle size distributions of hydrophobic particles measured by flow cytometry for test #1 and test #6 are presented in FIG. 1. Results indicate that the fixation efficiency is good in wide particle size range. Hydrophobicity distributions for the same tests #1 and #6 are shown in FIG. 2. This illustrates that use of the polymer product comprising amphoteric polymer is efficient for particles with different hydrophobicity levels. This is beneficial for fixation of stickies, as the stickies may originate from various chemical substances and have widely variable hydrophobicity.

TABLE-US-00004 TABLE 4 Fixation and flow cytometry test results for recycled fibre pulp sample. Hydrophobic particles by flow cytometry Added Dosage, Turbidity Count, Count Total area, Total volume, # Chemical g/t NTU 0.2-3.0 μm 3.0-20 μm m.sup.2/m.sup.3 cm.sup.3/m.sup.3 1 — 0 680 41847500 3047500 68.5 42.8 2 CPAM 150 238 16302500 3680000 73.4 60.8 3 CPAM 300 131 11812500 3483750 69.9 61.0 4 AMF 150 226 17816250 3997500 78.7 63.2 5 AMF 300 85 7053750 3007500 58.5 52.0 6 AMF 500 56 3548750 1657500 33.3 30.5 7 PA 125 360 27585000 2736250 57.6 37.2 8 PA 250 308 30453750 3726250 77.9 52.6 9 PA 500 87 22798750 4581250 87.6 62.3 10 PVOH 40 675 32902500 2781250 61.8 40.9 11 PVOH 80 697 34767500 2683750 60.8 39.9 12 PVOH 160 740 18983750 1716250 36.8 24.0 13 BENT 2000 315 37240000 4643750 96.0 62.8 14 BENT 4000 139 19156250 4681250 85.1 59.8 15 DISP + 300 391 33978750 3212500 68.7 43.6 PA 500 16 DISP + 300 111 3615000 1286250 26.9 24.4 AMF 500

[0084] In Table 5 are presented the fixation test results measured by using flow cytometry method described above for various test pulp samples, comprising kraft pulp or a mixture of kraft pulp and recycled pulp. Chemicals were added to pulps before or after mixing pulps together. Results in Table 5 show that addition of polyaluminium chloride and the polymer product comprising amphoteric polyacrylamide was fixing hydrophobic particles having size of 0.2-20 μm in kraft pulp. The results show also efficiency of the polymer product comprising amphoteric polyacrylamide when it was added to the recycled fibre pulp or to kraft pulp together with polyaluminum chloride before components were mixed together. This demonstrates the addition of the polymer product to stock components before the mixing chest. Clear benefit was observed in hydrophobic particles of 0.2-20 μm, in volume of these particles and in turbidity.

[0085] All chemical additions in Table 5 are given as kg active/ton dry pulp. Pulp samples were mixed for 5 min after a PAC addition and for 1 min after an AMF addition.

TABLE-US-00005 TABLE 5 Fixation test for various pulp samples Additions to Hydrophobic particles Additions to recycled fibre by flow cytometry kraft pulp pulp Count, Volume, Turbidity, # Test pulp component component 0.2-20 μm cm.sup.3/m.sup.3 NTU 1 Kraft 100% 1567500 0.85266789 51 2 Kraft 100% 0.5 PAC 0.5 + 1203750 1.1005207 43 0.2 AMF 3 Kraft 70% + 21065000 21.9402782 525 RCF 30% 4 Kraft 70% + 0.5 PAC + 0.5 AMF 4410000 15.2084352 95 RCF 30% 0.2 AMF

Example 2

[0086] Used Pulp

[0087] Dried bleached birch pulp, wet disintegrated to 1.5% consistency.

[0088] Measured properties for pulps and filtrate are given in Table 6.

TABLE-US-00006 TABLE 6 Results from measurements of pulp properties. Measurement Bleached kraft pulp pH 7.30 Turbidity, NTU 4 Conductivity, μS/cm 132.1 Charge, μekv/l −15 Consistency, g/l 15.1

[0089] Pulp was heated to 45° C. A 100 ml sample taken from pulp, chemical was added and mixed by shaking half-filled vessel for 15 s after chemical addition. When dispersing agent was used it was added first and then mixed for 15 min before following chemical addition. Flow cytometry sample was taken after mixing from the test sample. For turbidity test 30 ml of sample was filtered through black-ribbon filter paper in gravity filtration funnel.

[0090] Table 7 shows that polymer product comprising amphoteric polyacrylamide improves the fixation of hydrophobic particles both in 1-3 μm and in 3-20 μm size category, where polyamine (PA) is effective only at high dosage in 1-3 μm size category. Also total area and total volume of hydrophobic particles was reduced with use of the polymer product comprising amphoteric polyacrylamide.

TABLE-US-00007 TABLE 7 Fixation and flow cytometry test results for bleached kraft pulp. Hydrophobic particles by flow cytometry Count, Count, Dosage, 1.0-3.0 3.0-20 Area, Volume, # Polymer g/t μm μm m.sup.2/m.sup.3 cm.sup.3/m.sup.3 1 — 0 11500 550 0.015 0.012 2 PA 50 14250 650 0.016 0.010 3 PA 100 13300 750 0.016 0.011 4 PA 250 8000 800 0.019 0.016 5 AMF 100 6600 450 0.008 0.005 6 AMF 200 6400 250 0.007 0.004

[0091] 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.