Polymer composition and its uses

Abstract

A polymer composition includes a first host polymer, which is a copolymer of (meth)acrylamide and at least one cationic first monomer, and a second polymer, which is a copolymer of (meth)acrylamide and at least one cationic second monomer. The second polymer is polymerised in presence of the first host polymer, and the first host polymer has a higher cationicity than the second polymer, the difference in cationicity of the first host polymer and the second polymer being at least 3 mol-%, at least 5 mol-%, more preferably at least 7 mol-%. The polymer composition has a standard viscosity of >2.0 mPas, measured at 0.1 weight-% solids content in an aqueous NaCl solution (1 M), at 25 C., using Brookfield VII T viscometer with UL adapter. The invention relates also to uses of said polymer composition.

Claims

1. A polymer composition comprising: at most 10 weight-% of a first host polymer, calculated from a total polymeric material of the composition, as dry, which first host polymer is a copolymer of (meth)acrylamide and at least one cationic first monomer and has a weight average molecular weight <50,000 g/mol, a second polymer, which is a copolymer of (meth)acrylamide and at least one cationic second monomer, the second polymer being polymerized in presence of the first host polymer, wherein the first host polymer has a higher cationicity than the second polymer, the difference in cationicity of the first host polymer and the second polymer being at least 3 mol-%, and wherein the polymer composition has a charge density of at most 3 meq/q and a standard viscosity of >2.0 mPas, dissolved and measured at 0.1 weight-% solids content in an aqueous NaCl solution (1 M), at 25 C., using a Brookfield DVII T viscometer with a UL adapter.

2. The polymer composition according to claim 1, wherein the polymer composition is in form of a dry particulate product.

3. The polymer composition according to claim 2, wherein the polymer composition has a solids content of at least 80 weight-%.

4. The polymer composition according to claim 1, wherein the polymer composition has a charge density of at most 2.0 meq/g.

5. The polymer composition according to claim 1, wherein the first and/or second monomer is 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).

6. The polymer composition according to claim 1, wherein the cationic first monomer and the cationic second monomer are different from each other.

7. The polymer composition according to claim 1, wherein the second polymer has cationicity of at most 60 mol-%.

8. The polymer composition according to claim 1, wherein the first host polymer has cationicity of at most 80 mol-%.

9. The polymer composition according to claim 1, wherein the polymer composition has a standard viscosity of >3 mPas, measured at 0.1 weight-% solids content in an aqueous NaCl solution (1 M), at 25 C., using Brookfield DVII T viscometer with UL adapter.

10. A method for making paper or board, comprising: obtaining a fibre stock, adding a drainage agent to the fibre stock, forming the fibre stock into a fibre web, wherein the drainage agent comprises a polymer composition according to claim 1.

11. The method according to claim 10, further comprising allowing the fibre stock to pass a number of shearing stages and adding the drainage agent comprising the polymer composition to the fibre stock 3-60 seconds, before forming of the fibre web.

12. The method according to claim 10, wherein the dosage of the polymer composition is <20 kg/ton dry sludge.

13. The method according to claim 10, further comprising using the polymer composition as a draining agent in paper or board manufacture.

14. The method according to claim 10, further comprising using the polymer composition in a dosage of 0.05-1.0 kg/ton dry paper.

15. The polymer composition according to claim 1, wherein the difference in cationicity of the first host polymer and the second polymer is at least 5 mol-%.

16. The polymer composition according to claim 1, wherein the cationic first monomer is diallyldimethylammonium chloride and the cationic second monomer is [2-(acryloyloxy)ethyl] trimethylammonium chloride.

17. The polymer composition according to claim 1, wherein the second polymer has cationicity of at most 20 mol-%.

18. The polymer composition according to claim 1, wherein the first host polymer has cationicity of at most 40 mol-%.

Description

EXPERIMENTAL

(1) Some embodiments of the invention are described in the following non-limiting examples.

(2) General Procedure for Measurement of the Amount of Insolubles in a Polymer Composition

(3) Amount of insolubles in a polymer composition was measured as follows.

(4) A 1000 ml beaker was filled to 900 ml with tap water having temperature of 25 C. and stirred at maximum vortex ca. 450 rpm. 1 g0.001 g of dry polymer sample was weighed on an analytical balance and sprinkled into side of the water vortex. Stirring was continued for 60 minutes at same speed. The contents of the beaker were filtered through a stainless steel sieve with apertures of 300 microns. The beaker was washed thoroughly with tap water (25 C.), pouring the washings through the sieve. The sieve was washed under running tap water (25 C.) until the effluent was free from polymer (5-10 mins) and then allowed to drain. The amount of insolubles were detected by visual inspection and expressed as number of visible insoluble lumps (pieces) on the sieve.

(5) General Procedure for Measurement of the Standard Viscosity of a Polymer Composition

(6) Standard viscosity of a polymer composition was measured as follows.

(7) 200.0 g (0.1 g) of deionised water, conductivity <10 mS/cm, is weighed into a 600 ml tall form beaker. Water is stirred with a magnetic stirrer at maximum vortex. 0.33 g (0.001 g) polymer is tapped slowly into the vortex over a period of 15 seconds. The used weigh boat is flicked with a finger to knock off any remaining polymer particles into the solution. Stirring is continued at maximum vortex for a maximum of 5 minutes, until the polymer is dispersed. After that stirring is continued for a further 25 minutes on a setting of 350 rpm.

(8) 117.5 g (0.1 g) of NaCl solution, which is prepared by dissolving 700 g NaCl to 4000 g water, is added to the beaker and stirring is continued for an additional 5.0 min (15 sec). This time limit should not be exceeded.

(9) The solution is filtered through 250 micron stainless steel mesh sieve having diameter of 10 cm. A 16 ml aliquot of filtered solution is measured on a Brookfield viscometer using an UL adapter at 25 C. at the specified speed. Three readings are taken on the first aliquot, the first reading is ignored, and providing that the following two readings are within 0.05 cp, the average of the two readings is calculated. If the following two readings are greater than 0.05 cp apart, then the sample is disregarded and the process is repeated by using a second aliquot. Results are reported with 2 decimals.

Example of Preparation of the Polymer Compositions Used in the Experiments

(10) Inventive Compositions

(11) The first host polymer (HP1) was a copolymer of acrylamide and DADMAC, polymerised by using 80-90 mol-% of acrylamide monomers and 10-20 mol-% of DADMAC monomers. This means that the amount of DADMAC was 20-36 weight-%, calculated from the total weight of the monomers used for polymerisation of the first host polymer. The first host polymer had a weight average molecular weight of 10 000 Da, measured by GPC SEC with PEO as standard polymer, and a cationic charge of 1.2-2.2 meq/g.

(12) The second polymer was copolymer of acrylamide and [2-(acryloyloxy)ethyl] trimethylammonium chloride (ADAM-Cl). Before the polymerisation of the second polymer the used monomers, chain transfer agent, first host polymer and pH buffer in water were degassed with nitrogen at room temperature. Acrylamide monomers were added in amount of 90-98.5 mol-% and ADAM-Cl monomers were added in amount of 1.5-10 mol-%, as presented in Table 1 to a solution of the first host polymer. The difference in cationicity of the first host polymer and the second polymer are presented in Table 1, the first host polymer having a higher cationicity than the second polymer. The obtained reaction solution was cooled down at 3 C., an initiator added and polymerisation reaction started. The polymerisation was done in a batch reactor and it was adiabatic. After 30-40 min the polymerisation reaction was finished. The obtained polymer gel was processed by comminuting and drying. A polymer composition in form of a fine powder was obtained.

(13) The polymer compositions C1, C2, C3, C4m and C5m comprised 2-8 weight-% of the first host polymer and 92-98 weight-% of the second polymer.

(14) TABLE-US-00001 TABLE 1 Tested polymer compositions according to the invention. Cationicity Difference Standard Amount of 1.sup.st Host Polym. & Polym. Comp. Viscosity, Insolubles, ADAMCl 2.sup.nd Polym. charge Polym. Comp. Polym. Comp. Polymer [mol-%] [mol-%] [meq/g] [mPas] [pcs] C1 10 3-6 1.28 5.3 0 C2 5 7-10 0.71 4.8 0 C3 1.5 11-19 0.29 4.3 0 C4m 10 3-6 1.25 5.6 0 C5m 10 3-6 1.26 4.9 0
Reference Compositions R1, R2, R3, R7m:

(15) Reference compositions R1, R2, R3 and R7m were copolymers of acrylamide and [2-(acryloyloxy)ethyl] trimethylammonium chloride (ADAM-Cl). The charge density and standard viscosity of these reference compositions are given in Table 2.

(16) TABLE-US-00002 TABLE 2 Used monomer amounts and polymer properties for reference compositions R1, R2, R3 and R7m. Charge Standard Viscosity Polymer [meq/g] [mPas] R1 1.2 5.1 (reference) R2 0.6 4.9 (reference) R3 0.2 4.0 (reference) R7m 1.2 3.4 (reference)
Reference Composition R4 and R4m:

(17) Reference composition R4 and R4m were prepared by mixing 2-8 weight-% of a copolymer of acrylamide and DADMAC together with 92-98 weight-% of a copolymer of acrylamide and ADAM-Cl. This means that the reference compositions R4 and R4m were blends of two different acrylamide copolymers. The properties of the copolymer of acrylamide and DADMAC correspond to the properties of the first host polymer given above. The cationicity difference between the copolymer of acrylamide and DADMAC and the copolymer of acrylamide and ADAM-Cl was 11-19 mol-% for reference composition R4, and 3-6 mol-% for reference composition R4m. The copolymer of acrylamide and DADMAC had a higher cationicity than the copolymer of acrylamide and ADAM-Cl. The charge density, as measured by Mtek charge titration, was 0.27 meq/g for the reference composition R4 and 1.24 meq/g for the reference composition R4m. It is intended that the individual components of the reference composition R4 corresponds to the first host polymer and second polymer of polymer composition C3, but reference composition R4 is prepared as a blend by mixing of two individual polymers. In the same manner individual components of the reference composition R4m corresponds to the first host polymer and second polymer of polymer compositions C4m and C5m, but reference composition R4m is prepared as a blend by mixing of two individual polymers.

(18) Reference Composition R5m:

(19) Reference composition R5m was prepared by polymerising 92-98 weight-% of a copolymer of acrylamide and ADAM-Cl in the presence of 2-8 weight-% of polyamine, which was a copolymer of epichlorohydrin and dimethylamine and had weight average molecular weight of 2000 g/mol, measured with GPC SEC, using PEO as standard polymer. 90 mol-% of acrylamide monomers and 10 mol-% of ADAM-Cl monomers were added to a solution of the copolymer of epichlorohydrin and dimethylamine and polymerised. The charge density of reference composition R5m, as measured by Mtek charge titration, was 0.3 meq/g, and standard viscosity 4.7 mPas. The reference composition R5m is similar to polymer compositions C1, C4m and C5m, but reference composition R5m is prepared by using different polymer as the first host polymer.

DRAINAGE EXAMPLES

Drainage Example 1

(20) Pulp Preparation

(21) Central European testliner board was used as raw-material. This testliner board comprised about 17% of ash and 5 weight-% (calculated to dry pulp) of surface size starch, which was enzymatically degraded native corn starch. Testliner board was cut to 22 cm squares. Dilution water was made from tap water by adjusting Ca.sup.2+ concentration to 520 mg/I by CaCl.sub.2) and by adjusting conductivity to 4 mS/cm by NaCl. 2.7 l of dilution water was heated to 85 C. The pieces of testliner board were wetted for 5 minutes in the heated dilution water at 2% concentration before disintegration of the pieces into a stock slurry. For disintegration a Britt jar disintegrator was used, with 30 000 rotations. After disintegration stock slurry was diluted to 0.69% by addition of dilution water.

(22) Dynamic Drainage Analyzer (DDA) Test

(23) A Dynamic Drainage Analyzer, DDA, (AB Akribi Kemikonsulter, Sweden) was used to measure drainage. DDA's vacuum and stirrer were calibrated and necessary adjustments to the settings were made. DDA was connected to a computer for measuring the time between vacuum application and the vacuum break point. A change of the vacuum expresses the forming time of a wet fibre web until air breaks through the thickening web indicating the drainage time. A drainage time limit was set to 30 seconds for the measurements.

(24) In drainage measurements, 500 ml of the stock sample was measured into the reaction jar. The drainage test was performed by mixing the sample stock with the stirrer at 1200 rpm for 40 seconds while the chemicals to be tested were added in predetermined order. Test chemical addition times are indicated in result tables as negative time before the start of the drainage. Drainage test was using a wire with 0.25 mm openings. 300 mbar vacuum for 30 s after drainage was used. Drainage time was recorded. Filtrate turbidity was measured immediately. Wet sheet was weighted to calculate dry content after forming. Wet pressing of the sheets was completed individually immediately after drainage tests in Lorenz & Wettre wet press for 1 min at 4 bar pressure, 2 blotting papers both sides of the sheet. Pressed sheet was weighted and weighted again after 5 min drying in Lorenz & Wettre hot plate dryer to calculate dry content after pressing.

(25) Results of Drainage Example 1

(26) Drainage results of Example 1 are presented in Table 3.

(27) TABLE-US-00003 TABLE 3 Drainage results of Drainage Example 1. Dosage, at 10 s Drainage time Filtrate turbidity, # Polymer [kg/t] [s] NTU 1 0-test 0 6.9 482 2 R1 0.2 6.0 158 3 R1 0.4 5.5 97 4 R1 0.6 5.9 77 14 R7m 0.2 6.1 197 15 R7m 0.4 6.4 119 16 R7m 0.6 6.3 95 5 R5m 0.2 5.8 179 6 R5m 0.4 5.6 98 7 R5m 0.6 6.0 80 8 C4m 0.2 5.5 152 9 C4m 0.4 5.2 93 10 C4m 0.6 5.5 67 11 C5m 0.2 5.6 157 12 C5m 0.4 5.4 95 13 C5m 0.6 5.4 77

(28) Table 3 shows that a faster drainage time was achieved with the inventive polymer compositions C4m and C5m when compared to reference polymers R1, R5m, R7m. An improvement in drainage performance can be observed already with a low dosage of polymer C4m or C5m, which helps to reduce the amount of polymer needed in paper and board production. Especially, it can be observed that compositions C4m and C5m according to the present invention, where the first host polymer is a copolymer of acrylamide and DADMAC, have faster drainage in comparison to reference composition R5m, where the first host polymer is polyamine. Low filtrate turbidity, which indicates good retention of fines and fillers, as well as good retention of colloidal particles, have been achieved with the inventive compositions, especially with composition C4m, having a high standard viscosity value.

(29) Table 4 shows that dry content of the sheet was improved after forming and after pressing. Low dosage of the polymer was beneficial for the dry content of the sheet after pressing.

(30) TABLE-US-00004 TABLE 4 Dry content results. Dosage Dry content after Dry content after at 10 s forming pressing # Polymer [kg/t] [%] [%] 1 R1 0.4 24 49 2 C4m 0.2 25 51 3 C4m 0.4 25 50 4 C5m 0.4 25 50

Drainage Example 2

(31) Same test pulp, polymers and test methods were used in Drainage Example 2 than in Drainage Example 1.

(32) In Drainage Example 2 the test pulp was diluted to 0.50% consistency with the same conductivity adjusted dilution water that was used in Example 1. Retention was calculated as the weight of the dried DDA sheet to the dry weight of the pulp fed to the DDA.

(33) Results of Drainage Example 2

(34) Drainage results of Drainage Example 2 are presented in Table 5. Table 5 shows improvement in drainage and filtrate turbidity with the inventive polymer compositions C4m and C5m when compared to reference polymers.

(35) Microparticles (MP) such as bentonite, silica or cross-linked polymer particles can be used as a part of the retention and drainage system to improve drainage or retention further. Bentonite addition was tested to demonstrate the effect of microparticles together with inventive polymer compositions. Bentonite makes drainage faster and reduces turbidity further. It is seen that the polymer composition according to the invention provides improvements also when it is used together with microparticles.

(36) TABLE-US-00005 TABLE 5 Drainage results of Drainage Example 2. Polymer dosage Bentonite dosage Drainage Filtrate at 15 s at 10s time turbidity # Polymer [kg/t] [kg/t] [s] NTU 1 0-test 0 6.2 409 2 C4m 0.15 5.2 171 3 C4m 0.3 5.3 106 15 C4m 0.15 2 4.3 135 16 C4m 0.3 2 3.9 81 8 C5m 0.15 5.3 200 9 C5m 0.3 5.2 134 4 R4m 0.15 5.3 197 5 R4m 0.3 5.4 119 6 R1 0.15 5.3 192 7 R1 0.3 5.4 120 13 R1 0.15 2 4.4 147 14 R1 0.3 2 4.1 96 10 R7m 0.15 5.5 229 11 R7m 0.3 5.6 154 12 2 5.5 257

(37) Table 6 shows retention and dry content of the sheet after forming and after pressing when different polymers were used. It is seen that retention, dry content after forming and dry content after pressing were improved when a polymer composition according to the invention was used, compared to a blend of polymers as described above. The improvement was achieved already at relatively low dosage level of 0.15 kg/t of dry pulp.

(38) TABLE-US-00006 TABLE 6 Retention and dry content of the sheet after forming and pressing Polymer dosage Dry content Dry content at 15 s after forming after pressing Retention # Polymer [kg/t] [%] [%] [%] 1 0-test 0 N/A N/A 86 2 C4m 0.15 26 52 88 3 R4m 0.15 26 51 88 4 R1 0.15 25 50 86 5 C5m 0.15 27 52 90

SLUDGE DEWATERING EXAMPLES

(39) The apparatuses and methods used in sludge dewatering examples are given in Table 7.

(40) TABLE-US-00007 TABLE 7 Characterization of apparatuses and methods used in sludge dewatering examples. Property Apparatus/Standard pH Knick Portamess 911 pH Charge density Mtek Conductivity Knick Portamess 911 Cond Dry solids SFS 3008 Suspended solids SFS 3008 Ash (525 C.) ISO 1762 Turbidity HACH 2100AN IS Turbidimeter//ISO 7027

(41) Usable fibre content was determined by measuring 100 g of sludge to a 150 m wire, where the distance between the wire threads is 150 m, i.e. 100 mesh screen. The sludge was washed with running water until all other material except the fibres was washed off. After this the fibres were collected from the wire and dried in oven at 105 C. overnight. The dry fibres were weighed. Usable fibre content (150 m wire) was calculated by using equation (1):

(42) $\begin{array}{cc}\mathrm{Usable}\mathrm{fibers}\left(150\mathrm{.Math.m}\mathrm{wire}\right)=\frac{\mathrm{mass}\mathrm{of}\mathrm{dry}\mathrm{fiber}}{\mathrm{sludge}\mathrm{dry}\mathrm{solids}*\mathrm{mass}\mathrm{of}\mathrm{sludge}\mathrm{sample}}& \left(1\right)\end{array}$

(43) Gravity dewaterability of sludge was tested with Polytest. The sludge samples were filtered with Polytest cylinder of 10 cm diameter using in bottom a wire cloth having air permeability of 5400 m.sup.3/m.sup.2h. Treads/cm was 13.0/5.9. The sludge sample amount was 200-400 g, but always identical between samples compared. Mixing of the polymer composition was done with motor stirrer in baffled mixing vessel. Mixing speed was 600 rpm and mixing time was 10 seconds.

Sludge Dewatering Example 1

(44) This example simulates dewatering process of combined waste sludges from pulp or paper mill. Measured sludge properties are presented in Table 8.

(45) TABLE-US-00008 TABLE 8 Properties of combined waste sludge in Sludge Dewatering Example 1. Property Value pH 6.57 Charge density 363 eq/l Conductivity 3.41 mS/cm Dry solids 4.11% Suspended solids 3.53% Usable fibres (150 m wire) 9.25% Ash (525 C.) 63.7%

(46) Polymer compositions were diluted to 0.1% concentration before dosing to the sludge. Dewatering rate was tested with Polytest as described above. Polymer doses were 0.84 kg/ton dry sludge. Sludge sample was 400 g. Amount of drained water was measured after 10, 25 and 55 seconds. Suspended solids content was measured from the drained reject water. Results from these experiments are presented in Table 9.

(47) TABLE-US-00009 TABLE 9 Results for drainage and reject water suspended solids. Drainage 10 s Drainage 25 s Drainage 55 s Reject water SS Polymer [g] [g] [g] [mg/l] R1 144.1 192.3 281.0 567 C1 160.6 212.4 295.0 515

(48) Polymer composition C1 according to the invention had better performance than the reference composition R1. Polymer composition C1 had a faster dewatering and better reject water quality than the reference composition R1. All of these factors are important for economical sludge dewatering.

Sludge Dewatering Example 2

(49) This example simulates dewatering process of newsprint deinking pulp (DIP) sludge. DIP sludge refers to sludge that is generated in processing and repulping recycled paper or board. Measured sludge properties are presented in Table 10.

(50) TABLE-US-00010 TABLE 10 Properties of DIP sludge in Sludge Dewatering Example 2. Property Value pH 7.53 Charge density 270 eq/l Conductivity 3.69 mS/cm Dry solids 2.52% Usable fibres (150 m wire) 9.47% Ash (525 C.) 65.63%

(51) Polymer compositions were diluted to 0.1% concentration before dosing to the sludge. Dewatering rate was tested with Polytest as described above. Polymer doses were 0.9 kg/ton dry sludge. Sludge samples were 400 g. Amount of drained water was measured after 10 and 25 seconds. Suspended solids content was measured from the drained reject water. Results from these experiments are presented in Table 11.

(52) TABLE-US-00011 TABLE 11 Results for drainage and reject water suspended solids. Drainage 10 s Drainage 25 s Reject water SS Polymer [g] [g] [mg/l] R2 270.2 324.6 784.28 C2 298.0 329.5 689.57

(53) Polymer composition C2 according to the invention had better performance than the reference composition R2. Polymer composition C2 had faster dewatering and better reject water quality than the industrial reference composition R2. All of these factors are important for economical sludge dewatering.

Sludge Dewatering Example 3

(54) This example simulates dewatering process of newsprint deinking pulp sludge. Measured sludge properties are presented in Table 12.

(55) TABLE-US-00012 TABLE 12 Properties of DIP sludge in sludge dewatering example 3. Property value pH 7.51 Charge density 1385 eg/l Conductivity 3.20 mS/cm Dry solids 2.74% Suspended solids 2.23% Usable fibres (150 m wire) 9.89% Ash (525 C.) 61.55%

(56) Polymer compositions were diluted to 0.1% concentration before dosing to the sludge. Dewatering rate was tested with Polytest as described above. Polymer doses were 0.75 kg/ton dry sludge and 1.0 kg/ton dry sludge. Size of sludge samples was 400 g. Amount of drained water was measured after 10 and 25 seconds. Suspended solids content was measured from the drained reject water. After Polytest the sludge sample was pressed with Afmitec Friesland B.V. minipress for 60 seconds with 5 bar pressure. Dry solids content of the sludge sample was measured after the pressing. Results from these experiments are presented in Table 13.

(57) TABLE-US-00013 TABLE 13 Drainage, reject water SS and DS after pressing results Drainage Drainage Reject DS after Dose 10 s 25 s water SS pressing Polymer [kg/t DS] [g] [g] [mg/l] [%] R3 0.75 221 298 1183 56.7 C3 0.75 257 323 1174 58.0 R3 1.0 259 324 952 56.6 C3 1.0 275 330 749 57.8

(58) Polymer composition C3 according to the invention had better performance than the reference composition R3. Polymer composition C3 had faster dewatering, better reject water quality and higher dry solids after pressing than the industrial reference composition R3. All of these factors are important for economical sludge dewatering.

Sludge Dewatering Example 4

(59) This example simulates dewatering process of newsprint deinking pulp sludge. Measured sludge properties are presented in Table 14.

(60) TABLE-US-00014 TABLE 14 Properties of DIP sludge in sludge dewatering example 4. Property Value pH 7.4 Charge density, eq/l 1562 Conductivity, mS/cm 3.22 Dry solids, % 2.58 Suspended solids, % 2.01 Usable fibres (150 m wire) 12.82 Ash (525 C.), % 58.67

(61) Polymer compositions were diluted to 0.1% concentration before dosing to the sludge. Dewatering rate was tested with Polytest as described above. Polymer doses were 0.75 kg/ton dry sludge and 1.0 kg/ton dry sludge. Size of sludge samples was 200 g. Amount of drained water was measured after 5 seconds. Turbidity and suspended solids content was measured from the drained reject water. Results from these experiments are presented in Table 15.

(62) The results show the difference between polymer composition according to the present invention and blend of similar polymer components.

(63) TABLE-US-00015 TABLE 15 Results for drainage, reject water suspended solids and turbidity. Drainage Reject water Reject Dose 5 s turbidity, water SS Polymer [kg/t DS] [g] NTU [mg/l] R4 0.75 129 6094 2188 C3 0.75 133 4475 1635 R4 1.0 143 3247 1277 C3 1.0 149 2337 1085

(64) Polymer composition C3 according to the invention has better performance than the reference composition R4 comprising a blend of corresponding individual polymers. Polymer composition C3 had faster dewatering and better filtrate quality. Both of these factors are important for economical sludge dewatering. This demonstrates that a polymer composition according to the present invention is beneficial compared to a blend of corresponding individual polymers.

(65) 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.