Method for dissolving cationic starch, papermaking agent and its use

Abstract

The invention relates to a method for dissolving cationic starch. In the method is obtained an aqueous polyelectrolyte solution comprising a synthetic cationic polymer, which has a charge density value of at least 0.1 meq/g, determined at pH3, the concentration of the cationic polymer in the polyelectrolyte solution being >2.5 weight-%, and the aqueous polyelectrolyte solution is brought together with cationic starch having a degree of substitution, DS, >0.1. The cationic starch is dissolved to the polyelectrolyte solution by heating and/or mixing. The invention relates also to a papermaking agent comprising 2-40 weight-% of synthetic cationic polymer which has a charge density value of at least 0.1 meq/g, determined at p H 3, and 2.5-25 weight-% cationic starch having degree of substitution, DS, >0.1. The papermaking agent is in slurry form and has a viscosity of 50-20 000 m Pas, measured at 25 C. with Brookfield DVI+ viscometer.

Claims

1. Method for dissolving cationic starch, which method comprises obtaining an aqueous polyelectrolyte solution comprising a synthetic cationic polymer, which has a charge density value of at least 0.1 meq/g, determined at pH 3, the concentration of the synthetic cationic polymer in the polyelectrolyte solution being >2.5 weight-%, bringing the aqueous polyelectrolyte solution together with cationic starch having a degree of substitution, DS, >0.1, the starch being in form of particulate material having dry solids content >60 weight-%, and dissolving the cationic starch in the polyelectrolyte solution by heating and/or mixing.

2. Method according to claim 1, characterised in that the aqueous polyelectrolyte solution comprising synthetic cationic polymer has a charge density value of 0.1 -23 meq/g, determined at pH 3.

3. Method according to claim 1, characterised in that the concentration of the synthetic cationic polymer in the polyelectrolyte solution, before the polyelectrolyte solution is brought together with cationic starch, is >2.5 weight-%.

4. Method according to claim 3, characterised in that the concentration of the cationic polymer, before the polyelectrolyte solution is brought together with cationic starch, is in the range of 2.5 -40 weight-%.

5. Method according to claim 1, characterised in that the synthetic cationic polymer has an average molecular weight in the range of 1 000-2 500 000 Dalton.

6. Method according to claim 1, characterised in selecting the synthetic cationic polymer from a group consisting of: copolymers of dialkylamine(s) and epichlorohydrin; polydiallylmethylammonium chloride (poly-DADMAC); poly(acrylamide-N-propyltrimethylammonium chloride (poly-APTAC); poly(methacrylamide-N-propyltrimethyl-ammonium chloride (poly-MAPTAC); polyamidoamine epichlorohydrin resin; polyethyleneimine; polyvinylformamide/polyvinylamine; cationic polyacrylamides a copolymer of acrylamide and DADMAC; a copolymer of acrylamide and APTAC; a copolymer of acrylamide and MAPTAC; and any of the mixtures of the said polymers.

7. Method according to claim 1, characterised in selecting the cationic starch from a group consisting of: potato starch, rice starch, corn starch, waxy corn starch, wheat starch, barley starch, sweet potato starch, tapioca starch and any of their mixtures.

8. Method according to claim 1, characterised in selecting a cationic starch which has an amylopectin content of >70%.

9. Method according to claim 1, characterised in using cationic starch, which has a degree of substitution, DS, in the range from 0.1 to 1.0.

10. Method according to claim 1, characterised in selecting a cationic starch which is non-degraded and/or free of cross-linkages.

11. Method according to claim 1, characterised in using cationic starch, where at least 75 weight-% of the starch material has an average molecular weight (MW) over 5 000 000 Dalton.

12. Method according to claim 1, characterised in using cationic starch having a charge density of 0.56-3.2 meq/g pure cationic starch.

13. Method according to claim 1, characterised in dispersing first the cationic starch into the polyelectrolyte solution in order to prevent formation of viscous gel lumps.

14. Method according to claim 1, characterised in adjusting the temperature of the polyelectrolyte solution to a temperature <40 C. before the addition of the cationic starch.

15. Method according to claim 1, characterised in dissolving the cationic starch in the polyelectrolyte solution by using steam cooking, at temperature of about 110 C. to about 180 C., or by using pot-cooking.

16. Method for dissolving cationic starch, which method comprises obtaining an aqueous polyelectrolyte solution comprising a synthetic cationic polymer, which has a charge density value of at least 0.1 meq/q, determined at pH 3, the concentration of the synthetic cationic polymer in the polyelectrolyte solution being >2.5 weight-%, bringing the aqueous polyelectrolyte solution together with cationic starch having a degree of substitution, DS, >0.1, and dissolving the cationic starch in the polyelectrolyte solution by using steam cooking, at the temperature of 110-180 C., or by using pot-cooking.

Description

EXPERIMENTAL

(1) The following non-limiting examples illustrate some embodiments of the present invention.

(2) In the following experiments the DS values of cationic starches is determined based on the bound nitrogen content, which is determined from purified starch samples.

(3) The purification of starch samples is performed as follows:

(4) 5 g of cationic starch sample is slurried with 250 ml solvent, comprising 70 weight-% of ethanol and 30 weight-% of deionised water. Obtained slurry is agitated with magnetic stirrer for 2 h. The slurry is filtered and the starch filter cake is collected. The slurrying, agitation and filtering stages are repeated twice. Then the purified starch is dried in an oven at 115 C. for 20 h. Nitrogen content of the purified sample is determined by Kjeldahl-method.

(5) In the following experiments the charge densities of synthetic cationic polymers are determined by Mtek PCD 03 pH particle charge detector, equipped with Mtek PCD T3 PDC Titrator three, and by using 0.001 N sodium poly-ethylenesulphonate as a titrant. Charge densities are calculated as meq/g dry product.

Experiment 1

(6) Making of aqueous mixture of cationic starch and polyelectrolyte solution comprising a co-polymer of dimethylamine and epichlorohydrin, cooking of the mixture

(7) The following materials are used in the Experiment 1:

(8) Starch, S1: cationic amylopectin potato starch powder, dry substance content 85.4%, N-content 1.45%, pH 6.6 (10% aq. sol), calculated charge density 1.0 meq/g.

(9) Synthetic cationic polymer, P1: aqueous solution of co-polymer of dimethylamine and epichlorohydrin, dry substance content 50.4%, viscosity 710 mPas, pH 4.8, determined charge density 7.3 meq/g dry product at pH 3, determined as described above.

(10) 59.5 g aqueous solution of synthetic cationic polymer P1 and 205 g deionized water is mixed in a reactor equipped with mechanical agitator and a water bath for heating in order to obtain a polyelectrolyte solution. The polyelectrolyte solution is agitated with anchor type agitator with rotation speed of 300 rpm. Temperature of the water bath and the solution is 25 C. Then 35.1 g starch powder S1 is mixed into the polyelectrolyte solution and low viscous mixture is formed. Water bath is then heated from 25 C. to 98 C., which takes about 15 min. Temperature of the mixture in the reactor increases from 25 C. to 95 C. in about 30 min. When temperature of the mixture increases, the viscosity also increases and the cloudy appearance starts to turn into transparent solution. When the temperature has reached 95 C., the mixture is agitated for 30 min. Evaporated water is replaced with hot deionized water. When the agitation time is completed, the resulting starch/polymer-mixture is dispersed 2 min with Kady LT 2000 rotor-stator high speed dispersion lab mill, using about 60% of the maximum speed at the temperature about 95-100 C. The evaporated water is replaced with deionized water. A yellowish transparent solution is obtained. Dry solids content is 19.4%, viscosity is 480 mPas at 25 C., measured with Brookfield DVI+ viscometer, equipped with SSA with spindle 18, rotation speed 6 rpm, and pH 5.6.

(11) According to Experiment 1 cationic starch can be mixed conveniently by using aqueous polyelectrolyte solution comprising a co-polymer of dimethylamine and epichlorohydrin and then dissolved easily by normal starch cooking procedure.

Experiment 2

(12) Making of aqueous mixture of cationic starch and polyelectrolyte solution comprising polyethyleneimine, cooking of the mixture

(13) The following materials are used in the Experiment 2:

(14) Starch, S1: as defined above.

(15) Synthetic cationic polymer, P2: aqueous solution of polyethyleneimine, dry substance content 25.1%, viscosity 420 mPas, pH 8.2, determined charge density 9.9 meq/g dry product at pH 3, determined as described above.

(16) The procedure is similar as in Experiment 1.120 g aqueous polymer solution polymer P2 and 145 g deionized water is mixed in a reactor equipped with an agitator in order to obtain a polyelectrolyte solution. 35.1 g starch powder S1 is mixed into the polyelectrolyte solution. Low viscous slurry is formed at first and starch is then dissolved using the same heating and agitation procedure as given in Experiment 1. When the dissolving is completed, a yellow transparent solution is obtained. Dry solids content is 19.5%, and viscosity is 800 mPas at 25 C., measured with Brookfield DVI+, spindle 31, rotation speed 30 rpm, and pH 7.8.

(17) According to Experiment 2 cationic starch can be mixed conveniently by using aqueous polyelectrolyte solution comprising polyethyleneimine and then dissolved easily by normal starch cooking procedure.

Experiment 3

(18) Making of aqueous mixture of cationic starch and polyelectrolyte solutions comprising different amounts of co-polymer of dimethylamine and epichlorohydrin

(19) The following materials are used in the Experiment 3:

(20) Starch, S1: as defined above.

(21) Synthetic cationic polymer, P1: as defined above.

(22) A series of cationic starch-polymer mixtures with different polymer concentrations are made, see Table 1. Aqueous polyelectrolyte solution comprising polymer P1 is diluted with water at about 25 C. Starch S1 is then dosed into the solution and mixed for 5 min. Viscosity of the resulting mixture is measured. Concentration of cationic starch in the final mixture is 10% in each mixture, except in the mixture 3-6, which does not contain any starch.

(23) TABLE-US-00001 TABLE 1 Compositions used in Experiment 3. P1 Conc of P1 before S1 Total Mixture dosage Water S1 dosage dosage mixture Viscosity Dry solids nb. (g) (g) (%) (g) (g) (mPas) (%) 3-1 59.5 205.3 11.3 35.1 300 500 19.9 3-2 44.6 220.2 8.5 35.1 300 2700 17.4 3-3 29.8 235.1 5.7 35.1 300 7500 14.9 3-4 14.9 250.0 2.8 35.1 300 31400 12.4 3-5 0.0 264.9 0.0 35.1 300 heterogenous gel not measured 3-6 59.5 240.5 10.0 0.0 300 37 10.0 S1 = starch, P1 = synthetic cationic polymer

(24) It can be seen from Table 1 that the amount of cationic polymer has an impact on the solubility of cationic starch. If polymer concentration is less than about 5 weight-%, the viscosity of the resulting mixture increases rapidly. However, even with a polymer concentration of 2.8 weight-% the mixture is homogenous and can be handled with normal pump equipment. The mixture 3-5, which does not contain any polymer, forms a heterogeneous gel, which contains lumps. Such gel is extremely difficult and impractical to handle in large volumes.

Experiment 4

(25) Effect of different cationic polymers in the polyelectrolyte solution on viscosity of the resulting mixture as the function of time

(26) The following materials are used in the experiment 4:

(27) Starch, S2: cationic potato starch powder, dry solids content: 87%, N-content 1.55, pH 5.5 (10% aq. solution) calculated charge density 1.1 meq/g.

(28) Synthetic cationic polymers:

(29) P1, P2: as defined above.

(30) P3: aqueous solution of poly-DADMAC, dry solids content 41.2%, viscosity 1800 mPas, pH 4.9, determined charge density 6.8 meq/g dry product at pH 3, determined as described above.

(31) P4: polyvinylamine product, aqueous solution with dry solids content 31.2%, viscosity 420 mPas, degree of hydrolysis 70%, MW average about 100 000 Dalton, pH 9.7, determined charge density 7.0 meq/g dry product at pH 3, determined as described above.

(32) The mixtures are prepared according to Table 2 in the following manner:

(33) Aqueous polyelectrolyte solution is prepared by diluting synthetic cationic polymer with water at about 25 C. Starch is then dosed into the polyelectrolyte solution, pH of the mixture is adjusted between 4.5-7, if necessary, with 25% sulphuric acid and mixed for 5 min, mixing speed 300 rpm. Viscosity of the resulting mixture is measured. The mixture is further mixed, mixing speed 100 rpm. Viscosity of the mixture is measured again after 30 min of mixing and 2 h of mixing. Measured viscosity values are shown in Table 3. Concentration of cationic starch and synthetic polymer is 15% in all mixtures, except in mixture 4-5, which does not contain any polymer.

(34) TABLE-US-00002 TABLE 2 Compositions in Experiment 4. Conc of P-product Dry solids of Mixture P-product P-product Water before S2 dosage S2-dosage Total mixture the mixture nb. (g) dosage (g) (%) (g) (g) (%) pH 4-1 P1 89.3 159 18.1 51.7 300 29.9 5.3 4-2 P3 109 139 18.1 51.7 300 30.0 4.6 4-3 P2 179 69.7 18.1 51.7 300 30.0 5.9 4-4 P4 144 104 18.1 51.7 300 29.9 5.3 4-5 0 248 0 51.7 300 15.1 4.5

(35) TABLE-US-00003 TABLE 3 Measured viscosity values for different mixture compositions of Table 2, as function of the agitation time Viscosity of the Viscosity after 30 Viscosity after Mixture mixture min mixing 120 min mixing nb. (mPas) (mPas) (mPas) 4-1 1380 3200 3860 4-2 4200 8400 14000 4-3 4170 6980 13800 4-4 6300 13700 68000 4-5 gel gel gel

(36) The results of Table 3 show that synthetic cationic polymers lower the viscosity values of mixtures comprising cationic starch. The effect achieved by using cationic polymer may last up to 2 h, which is long enough time in practice from handling point of view. Even in case where higher viscosity values are obtained, as seen for composition 4-4, the mixture itself is homogenous and can be transferred by suitable pumping equipment. Mixture 4-5, which does not contain any cationic polymer, forms immediately high viscous gel. Viscosity of the formed gel cannot be measured, and mixture 4-5 cannot be easily handled in practice in large quantities.

Experiment 5

(37) Effect of different cationic starches on viscosity of resulting starch-polyelectrolyte mixture as the function of time

(38) The following materials are used in the experiment 5:

(39) Starches:

(40) S1, S2: as defined above.

(41) S3: cationic potato starch, dry solids content 84.9%, N-content 1.2%, pH 5.3 (10% aq. solution), calculated charge density 0.86 meq/g.

(42) S4: cationic tapioca starch powder, dry solids content: 88.5%, N-content 1.4, pH 5.5 (10% aq. solution), calculated charge density 1.0 meq/g.

(43) S5: cationic amylopectin potato starch, dry solids 86.2%, N-content 2.0%, pH 6.4 (10% aq. solution), calculated charge density 1.4 meq/g.

(44) Synthetic cationic polymer, P1: as defined above.

(45) The mixtures are prepared according to Table 4 in the following manner:

(46) Aqueous polymer solution of P1 is diluted with water at about 25 C. Starch is then dosed into the obtained polyelectrolyte solution, pH of the solution is adjusted between 4.5-7, if necessary, with 25% sulphuric acid and mixed for 5 min, mixing speed 300 rpm. Viscosity of the mixture is measured. The mixture is further mixed, mixing speed 100 rpm. Viscosity of the mixture is measured again after 30 min of mixing and 2 h of mixing. Measured viscosity values are shown in Table 5.

(47) TABLE-US-00004 TABLE 4 Mixtures in Experiment 5. P-product Conc of P before S-product Mixture dosage Water S-product dosage dosage Total mixture nb. P-product (g) (g) (%) S-product (g) (g) 5-1 P1 89.3 157.7 18 S3 53.0 300 5-2 P1 89.3 159.9 18 S4 50.8 300 5-3 P1 89.3 159.0 18 S2 51.7 300 5-4 P1 89.3 158.0 18 S1 52.7 300 5-5 P1 89.3 158.5 18 S5 52.2 300 5-6 0 247.0 0 S3 53.0 300 5-7 0 249.2 0 S4 50.8 300 5-8 0 248.3 0 S2 51.7 300 5-9 0 247.3 0 S1 52.7 300 5-10 0 247.8 0 S5 52.2 300

(48) TABLE-US-00005 TABLE 5 Measured viscosity values for the different mixture compositions of Table 4, as function of the agitation time. Dry solids Viscosity Viscosity Viscosity of the of the after 30 after 120 Mixture mixture mixture min mixing min mixing nb. (%) pH (mPas) (mPas) (mPas) 5-1 30 4.9 73 72 72 5-2 30 5.4 106 138 215 5-3 30 5.3 1380 3200 3860 5-4 30 5.5 71 74 105 5-5 30 5.4 1130 1430 1760 5-6 15 4.8 ~1500 gel gel 5-7 15 5.9 gel gel gel 5-8 15 4.5 gel gel 37000 5-9 15 5.9 gel gel gel 5-10 15 5.7 gel gel gel

(49) The results show that cationic polymer significantly decrease the viscosity of mixtures comprising high cationic starches. Mixtures from 5-6 to 5-10, which do not contain any cationic polymer, form immediately high viscous gels. Viscosity of the formed gels cannot be measured, and compositions cannot be easily handled in practice in large quantities.

Experiment 6

(50) Effect of temperature to dissolution speed of starch in starch-polyelectrolyte mixtures

(51) The following materials are used in the experiment 6:

(52) Starches, S2, S3: as defined above.

(53) Synthetic cationic polymer, P1: as defined above.

(54) The mixtures are prepared according to Table 6 in the following manner:

(55) Aqueous polymer solution of P1 is diluted with water and heated to a target temperature at about 25 C. or at about 40 C., and kept at the chosen target temperature throughout the whole experiment. Starch is dosed into the obtained polyelectrolyte solution, pH of the mixture is adjusted between 4.5-7, if necessary, with 25% sulphuric acid and mixed for 5 min, mixing speed 300 rpm. Viscosity of the mixture is measured. The mixture is further mixed, mixing speed 100 rpm. Viscosity of the mixture is measured again after 30 min of mixing and 2 h of mixing. Measured viscosity values are shown in Table 7.

(56) TABLE-US-00006 TABLE 6 Mixtures in Experiment 6. Conc of P before P-product S-product S-product Mixture dosage Water dosage Temperature dosage Total mixture nb. P-product (g) (g) (%) ( C.) S-product (g) (g) 6-1 P1 89.3 157.7 18 25 S3 53.0 300 6-2 P1 89.3 157.7 18 40 S3 53.0 300 6-3 P1 89.3 159.0 18 25 S2 51.7 300 6-4 P1 89.3 159.0 18 40 S2 51.7 300 6-5 0 247.0 0 25 S3 53.0 300 6-6 0 247.0 0 40 S3 53.0 300 6-7 0 248.3 0 25 S2 51.7 300 6-8 0 248.3 0 40 S2 51.7 300 6-9 P1 149 99.5 30 40 S2 51.7 300

(57) TABLE-US-00007 TABLE 7 Measured viscosity values for the different mixture compositions of Table 6, as function of the agitation time Dry solids Viscosity Viscosity Viscosity of the of the after 30 min after 120 min Mixture mixture mixture mixing mixing nb. (%) pH (mPas) (mPas) (mPas) 6-1 30 4.8 73 72 72 6-2 30 4.7 91 140 139 6-3 30 5.3 1380 3200 3860 6-4 30 5.1 8300 13500 15800 6-5 15 4.8 ~1500 gel gel 6-6 15 4.8 gel gel gel 6-7 15 4.5 gel gel 37000 6-8 15 4.5 gel 63500 15200 6-9 40 5.3 960 1900 1960

(58) The results show that the viscosity of the starch/polyelectrolyte mixture increases, when temperature increases. Viscosity increase can be retarded by increasing the polymer concentration, as will be shown in Experiment 7. Mixtures from 6-5 to 6-8, which do not contain any cationic polymer, form immediately high viscous gels. Viscosity of the formed gels cannot be measured, and compositions cannot be easily handled in practice in large quantities.

Experiment 7

(59) Effect of polymer concentration to the viscosity of starch/polyelectrolyte mixtures

(60) The following materials are used in the experiment 7:

(61) Starch, S1: as described above.

(62) Synthetic cationic polymers:

(63) P1, P2, P3, P4: as defined above.

(64) P5: aqueous solution of co-polymer of adipic acid and diethylenetriamine, dry solids content 40.2%, viscosity 55 mPas, determined charge density 4.3 meq/g dry product at pH 3, determined as described above.

(65) P6: aqueous solution of cationic polyacrylamide, copolymer of acrylamide and DADMAC, dry solids content 26.1%, pH 3.6, viscosity 10 mPas, determined charge density 0.32 meq/g dry product at pH 3, determined as described above.

(66) The mixtures are prepared according to Table 8 in the following manner:

(67) Aqueous polymer solution is diluted with water at about 25 C. Starch is then dosed into the obtained polyelectrolyte solution, pH of the mixture is adjusted between 4.5-7, if necessary, with 25% sulphuric acid and mixed for 5 min, mixing speed 300 rpm. Viscosity of the mixture is measured. The mixture is further mixed, mixing speed 100 rpm. Viscosity of the mixture is measured again after 30 min of mixing and 2 h of mixing. Measured viscosity values are shown in Table 3. Concentration of cationic starch and synthetic polymer is 15% in all the mixtures, except in mixture 7-11, which does not contain any polymer. Measured viscosity values are shown in Table 9.

(68) The results show that cationic polymer decreases effectively dissolution of cationic starch, even low cationic polyacrylamide is effective as a dispersing agent. Mixture 7-11, which does not contain any cationic polymer, forms immediately high viscous gel. Viscosity of the formed gel cannot be measured, and composition cannot be easily handled in practice in large quantities.

(69) TABLE-US-00008 TABLE 8 Mixtures in Experiment 7. Conc of P before S- Dry solids P-product product S-product Total of the Mixture dosage Water dosage dosage mixture mixture nb. P-product (g) (g) (%) S-product (g) (g) (%) pH 7-1 P1 89.3 158.0 18.2 S1 52.7 300 30 5.5 7-2 P3 109.2 138.1 18.2 S1 52.7 300 30 5.1 7-3 P2 179.3 68.0 18.2 S1 52.7 300 30 5.8 7-4 P4 144.2 103.1 18.2 S1 52.7 300 30 5.6 7-5 P1 74.4 199.2 13.7 S1 26.3 300 20 5.3 7-6 P3 91.0 182.6 13.7 S1 26.3 300 20 5.1 7-7 P2 149.4 124.3 13.7 S1 26.3 300 20 5.6 7-8 P4 120.2 153.5 13.7 S1 26.3 300 20 5.3 7-9 P5 145.9 127.7 13.7 S1 26.3 300 20 4.5 7-10 P6 143.7 130.0 13.7 S1 26.3 300 20 4.5 7-11 0 247.3 0 S1 52.7 300 15 6.3

(70) TABLE-US-00009 TABLE 9 Measured viscosity values for the different mixture compositions of Table 7, as function of the agitation time Dry solids Viscosity Viscosity of the Viscosity of after 30 min after 120 Mixture mixture the mixture mixing min mixing nb. (%) pH (mPas) (mPas) (mPas) 7-1 30 5.5 71 74 105 7-2 30 5.1 216 218 256 7-3 30 5.8 315 328 384 7-4 30 5.6 235 197 215 7-5 20 5.3 27 30 41 7-6 20 5.1 152 154 177 7-7 20 5.6 290 296 329 7-8 20 5.3 120 121 125 7-9 20 4.5 93 157 289 7-10 20 4.5 10 12 16 7-11 15 6.3 gel gel gel

(71) 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.