Method for treating starch in pulp, paper and board making processes

Abstract

The invention relates to a method for treating starch in pulp, paper and board making processes, in which processes recycled fibre material is used as raw material wherein the recycled fibre material is pulped in a pulper and obtaining a pulp flow comprising an aqueous phase and at least recycled fibres and starch dispersed in the aqueous phase. The method comprising the following steps: adding amylase enzyme inhibitor and/or at least one biocide to pulp flow or to an aqueous process flow comprising starch for preventing starch degradation, andadding an amphoteric polymer obtained by copolymerisation of (meth)acrylamide with cationic and anionic monomers to pulp flow or to an aqueous process flow comprising starch for binding starch to the fibres.

Claims

1. A method for treating starch in pulp, paper and board making processes, in which processes recycled fibre material is used as raw material wherein the recycled fibre material, such as paper, board and/or broke, is pulped in a pulper and obtaining a pulp flow comprising an aqueous phase and at least recycled fibres and starch dispersed in the aqueous phase, wherein the method comprising the following steps: adding amylase enzyme inhibitor and/or at least one biocide to pulp flow or to an aqueous process flow comprising starch for preventing starch degradation, and adding an amphoteric polyacrylamide obtained by copolymerisation of (meth)acrylamide with cationic and anionic monomers, which amphoteric polyacrylamide has the mass average molecular weight over 1 500 000 g/mol and 10-90% of the charged groups are cationic, to pulp flow or to an aqueous process flow comprising starch for binding starch to the fibres.

2. The method according to claim 1, wherein the starch is a low molecular weight starch comprising an acid or enzyme modified surface size starch.

3. The method according to claim 1, wherein the mass average molecular weight of the amphoteric polyacrylamide is in the range of 1 500 000-6 000 000 g/mol.

4. The method according to claim 1, wherein the net charge of the amphoteric polyacrylamide is cationic.

5. The method according to claim 1, wherein 30-90%, of the charged groups in the amphoteric polyacrylamide are cationic.

6. The method according to claim 1, wherein the total ionicity of the amphoteric polyacrylamide is in the range of 2-70 mol-%.

7. The method according to claim 1, wherein the cationic groups in 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 diallyldimethyl-ammonium chloride (DADMAC).

8. The method according to claim 1, wherein the anionic groups in the amphoteric polyacrylamide originate from monomers selected from unsaturated mono- or dicarboxylic acids, such as acrylic acid, maleic acid, fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconic acid, crotonic acid, isocrotonic acid, angelic acid or tiglic acid.

9. The method according to claim 1, wherein amylase enzyme inhibitor comprises zinc ions.

10. The method according to claim 1, wherein at least one cationic coagulant is added to pulp flow or to an aqueous process flow comprising starch for improving starch retention.

11. The method according to claim 10, wherein the cationic coagulant is selected from the group comprising: bentonite, colloidal silica and conventional papermaking fixatives, such as polydiallyldimethylammonium chloride (poly-DADMAC) or polyamines, polyvinyl amine (PVAm), cationic polyacrylamide (C-PAM), polyethyleneimine (PEI), polyamidoamine-epichlorohydrin (PAAE), polyaluminum chloride, alum, methacrylamidopropyltrimethylammonium chloride (MAPTAC) or their mixtures.

12. The method according to claim 1, wherein biocide and/or amylase enzyme inhibitor are added simultaneously with the amphoteric polyacrylamide to pulp flow or process flow.

13. The method according to claim 1, wherein biocide and/or amylase enzyme inhibitor are added prior to the addition of said amphoteric polyacrylamide to pulp flow or process flow.

14. The method according to claim 1, wherein amphoteric polyacrylamide is added to the broke system, pulp, pulp storage tanks, to the water entering the pulper or into the pulper, water storage tanks or to pipe line before the broke or pulp storage tanks.

15. The method according to claim 1, wherein at least one coagulant is added simultaneously with the amphoteric polyacrylamide or after the addition of said amphoteric polyacrylamide to pulp flow or process flow.

16. The method according to claim 3, wherein the mass average molecular weight of the amphoteric polyacrylamide is in the range of 2 500 000-4 500 000 g/mol.

17. The method according to claim 16, wherein the mass average molecular weight of the amphoteric polyacrylamide is in the range of 2 700 000-4 300 000 g/mol.

18. The method according to claim 5, wherein 50-85%, of the charged groups in the amphoteric polyacrylamide are cationic.

19. The method according to claim 6, wherein the total ionicity of the amphoteric polyacrylamide is in the range of 2-50 mol-%.

20. The method according to claim 19, wherein the total ionicity of the amphoteric polyacrylamide is in the range of 6-10 mol-%.

Description

EXPERIMENTAL

(1) A better understanding of the present invention may be obtained through the following examples which are set worth to illustrate, but are not to be construed as the limit of the present invention.

Example 1: Inhibition of Starch Degradation

(2) Starch degradation was studied in paper machine conditions. Board from a machine using recycled fiber was re-pulpered into adjusted water (pH 7, Ca.sup.2+ 520 mg/l, conductivity 4 mS/cm) to simulate condition in paper machine broke system. The consistency of the pulp slurry was 1%. 1 l of amylase enzyme solution (Alpha-Amylase, A6948, AppliChem) was added into 300 ml pulp slurry. It was divided into three 100 ml portions and 0, 20 or 50 ppm zinc was added into the portions. Reference bottle was pulp slurry with no amylase enzyme added. After 20 h contact time starch concentration was measured as absorbance value using conventional iodine staining at 610 nm. The results are shown in Table 1.

(3) TABLE-US-00001 TABLE 1 Inhibition of starch degradation in recycled pulp. Starch amount, A610 Control, No amylase 0.282 Amylase, 0 ppm zinc 0.011 Amylase, 20 ppm zinc 0.151 Amylase, 50 ppm zinc 0.181

(4) It can be seen from Table 1 that in the bottle with no added zinc, amylase had degraded almost all of the starch. The additions of 20 and 50 ppm zinc had preserved most of the starch in the experiment.

Example 2: Starch Retention Study

(5) Test slurry was prepared from European testliner board, which comprises 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. Firstly, 2.7 l of dilution water was heated to 85 C. and 100 ppm of Zn.sup.2+ was added to dilution water, which corresponds 50 ppm at pulp diluted to 1% consistency. Testliner board was cutted to 2*2 cm squares and cutted testliner was wetted for 5 minutes in dilution water at 2 concentration before disintegration. Then, slurry was disintegrated in Britt jar disintegrator with 30 000 rotations and 50 ml of white water from paper mill was added to contaminate pulp slurry by microbes in order to start degradation of starch. Finally, the obtained pulp was diluted to consistency 1% by adding dilution water and then pulp was cooled to 25 C. and stored for 20 hours in low speed stirring (Heidolph 100 rpm) before the sheet preparation.

(6) DDA (dynamic drainage analyzer from Akribi Kemi Konsulter, Sweden) was used to measure the retention degree of starch to paper and drainage. The used test chemicals are listed below and test chemical addition times to the pulp slurry are indicated as negative time before the drainage starts in Table 3. The volume of pulp slurry in DDA was 500 ml for each test point and stirrer speed of DDA was 1000 rpm. The stirring was stopped 2 s before drainage. Vacuum was 300 mbar for 30 s after drainage started and wire opening was 0.25 mm.

(7) Used test chemicals were: PAC: coagulant, polyaluminum chloride, basicity 40% and Al content 7.5 weight-%. PA: coagulant, commercial polyamine type cationic polymer Fennofix 50 (Kemira Oyj). AMF-A: amphoteric polymer, a copolymer of MAPTAC, acrylicacid and acrylamide. AMF-C: amphoteric polymer, a copolymer of ADAM-Cl, acrylicacid and acrylamide. AMF-N: amphoteric polymer, a copolymer of MAPTAC, acrylicacid and acrylamide.

(8) Properties of amphoteric polymers are presented in Table 2. Polymers were dissolved in water to 0.5% concentration and further diluted to 0.17% before addition to the test slurry.

(9) TABLE-US-00002 TABLE 2 Amphoteric acrylamide copolymers. Cationic Anionic Non-ionic Molecular monomers monomers monomers weight [mol-%] [mol-%] [mol-%] [g/mol] AMF-A 2 7 91 4 000 000 AMF-C 7 2 91 4 000 000 AMF-N 5 5 90 4 000 000

(10) Determination of soluble starch was made from DDA filtrate sample. 25 ml of filtrate was added to 10 ml of 10%-w HCl and the mixture was stirred for 10 min in 50 ml breaker with magnetic stirrer and then mixture was filtrated by gravitation in a funnel with black ribbon filter paper. 1 ml of filtrated mixture was added to 0.5 ml iodine reagent, which consisted 7.5 g/l KI+5 g/l I.sub.2. Absorbance value was measured at 610 nm by Hach Lange DR 900 spectrophotometer 2 min after iodine-solution was added. Zeroing of the spectrophotometer was done with the sample before iodine addition. Calibration curve for measurement is prepared by using C*film 07311 non-ionic degraded starch.

(11) Test pulp starch content was determined by same method than DDA filtrate starch content. Starch retention was calculated by using the equation: (pulp starchfiltrate starch)/pulp starch*100%.

(12) In addition, filtrate turbidity was measured immediately by HACH 2100 AN IS turbidimeter by using ISO 7027 method.

(13) The results are presented at Table 3. From Table 3 it can be seen that the addition of amphoteric polymer and zinc are reducing filtrate turbidity and increasing starch retention. Further improvement is achieved by adding coagulant like PAC or PA with zinc and amphoteric polymer. PAC coagulant improves drainage time, turbidity and starch retention.

(14) TABLE-US-00003 TABLE 3 Starch retention tests with DDA. Zn.sup.2+ ppm PAC PA AMF-A AMF-C AMF-N Filtrate vol. kg/t Al kg/t dry kg/t dry kg/t dry kg/t dry Drain turbidity Starch in pulp 600 s 600 s 10 s 10 s 10 s times NTU retention % Retention % 0 10.3 908 6 95 50 10.4 882 5 95 50 0.7 12.4 390 15 96 50 0.75 10.2 653 11 94 50 0.75 0.7 6.6 128 22 97 50 0.75 0.7 6.1 108 14 100 50 0.75 0.7 7.3 154 19 98 50 0.5 0.7 10.9 236 16 97 0 0.5 0.7 10.7 255 9 97

Example 3: Starch Retention Study

(15) Test pulp was thick stock from core board mill, which uses cationic granular starch, in this example to study starch retention. Glutaraldehyde (GL) was used as biocide and Zn ions were used as amylase enzyme inhibitor. Coagulant was commercial polyamine type cationic polymer Fennofix 50 (Kemira Oyj) and it was used in amount 1.4 kg/t. Amphoteric dry polymer product used was AMF-C, which is a copolymer of ADAM-Cl, acrylicacid and acrylamide. The added amounts of the chemicals are presented in Table 4. Reference sample does not contain any chemical additions.

(16) The fibre stock was firstly treated with biocide and amylase enzyme inhibitor. Then after 4 h contact time the stock was diluted with process water from the same mill 60 s before drainage to 1% consistency. DDA (dynamic drainage analyzer from Akribi Kemi Konsulter, Sweden) was used to measure the retention degree of starch to paper and drainage.

(17) The volume of stock sample in DDA was 500 ml for each test point and stirring was adjusted to 1000 rpm before drainage. Coagulant was added 60 s before drainage and amphoteric polymer AMF-C 30 s before drainage. Stirring was sopped 2 s before drainage. Vacuum was 300 mbar for 30 s after drainage started and wire opening was 0.25 mm.

(18) Soluble starch content of DDA filtrate was determined as follows:

(19) 25 ml of filtrate was added to 10 ml of 10%-w HCl and mixture was stirred for 10 min in 50 ml breaker with magnetic stirrer. Then, mixture was filtrated by gravitation in a funnel with black ribbon filter paper. 1 ml of filtrated mixture was added to 0.5 ml iodine reagent, which consisted 7.5 g/l KI+5 g/l I.sub.2. Absorbancy value was measured at 610 nm by Hach Lange DR 900 spectrophotometer 2 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. Starch concentration correlates linearly to the absorbance measure, i.e. increasing absorbance indicate higher starch concentration. The results are given in Table 4.

(20) TABLE-US-00004 TABLE 4 Results for Performance Example 3 Sample Starch, mg/l Drain time, s Reference 435 20.5 GL 25 ppm + Zn 50 ppm 422 20.1 GL 50 ppm + Zn 100 ppm 446 20.1 GL 25 ppm + Zn 50 ppm + coagulant 362 16.3 1.4 kg/t + AMF-C 0.7 kg/t GL 50 ppm + Zn 100 ppm + coagulant 375 15.5 1.4 kg/t + AMF-C 0.7 kg/t GL 25 ppm + Zn 50 ppm + coagulant 345 13.7 1.4 kg/t + AMF-C 1.4 kg/t

(21) The results in Table 4 show that amphoteric polymer product have a positive impact on starch retention when used with coagulant since the amount of starch clearly decreased in filtrate.

(22) The invention is not restricted to the examples of the above description, but it can be modified within the scope of the inventive idea presented in the claims.