Method for manufacturing a fibrous web

Abstract

A method for manufacturing a fibrous web, such as web of paper, board, tissue or the like is disclosed. The method includes obtaining at least one fibre suspension of lignocellulosic and/or cellulosic fibres and feeding the fibre suspension into an intermediate residence entity. The fibre suspension including bacterial endospores, is discharged out of the intermediate residence entity via an outlet after a residence time of at least 2 hours in the intermediate residence entity and after a time delay the fibre suspension is formed into a fibrous web. Bacterial endospores are sensitized by adding a germinant surfactant including a primary or secondary ammonium head group and a linear unsubstituted C12-alkyl tail, to the fibre suspension at an addition point located at a lower part of the intermediate residence entity or after the outlet of the intermediate residence entity, but before the formation of the fibrous web.

Claims

1. A method for manufacturing a fibrous web, the method comprising: (a) obtaining at least one fibre suspension of lignocellulosic and/or cellulosic fibres, (b) feeding the fibre suspension into an intermediate residence entity, (c) discharging the fibre suspension, which comprises bacterial endospores, out of the intermediate residence entity via an outlet after a residence time of at least 2 hours in the intermediate residence entity, (d) forming after a time delay the fibre suspension into a fibrous web, wherein the bacterial endospores are sensitized by adding a germinant surfactant, which comprises a primary or a secondary ammonium head group and a linear unsubstituted C12-alkyl tail, to the fibre suspension at an addition point, which is located at a lower part of the intermediate residence entity or after the outlet of the intermediate residence entity, but before the formation of the fibrous web.

2. The method according to claim 1, further comprising diluting the fibre suspension from a first concentration to a second concentration with dilution water, whereby the germinant surfactant is added to the fibre suspension together with the dilution water.

3. The method according to claim 1, wherein the germinant surfactant is selected from n-dodecylamine or n-dodecylguanidine, dodecylamine salt or dodecylguanidine salt, or any of their mixture.

4. The method according to claim 3, wherein the dodecylguanidine salt is dodecylguanidine hydrochloride.

5. The method according to claim 1, wherein the time delay between the addition of the germinant surfactant and the formation of the fibrous web is less than 60 min.

6. The method according to claim 5, wherein the time delay between the addition of the germinant surfactant and the formation of the fibrous web is less than 45 min.

7. The method according to claim 5, wherein the time delay between the addition of the germinant surfactant and the formation of the fibrous web is less than 30 min.

8. The method according to claim 1, wherein the time delay between the addition of the germinant surfactant and the formation of the fibrous web is at least 15 min, and less than 8 hours, when there is at least one intermediate residence entity between the addition point and the fibrous web formation.

9. The method according to claim 8, wherein the time delay between the addition of the germinant surfactant and the formation of the fibrous web is at least 30 min.

10. The method according to claim 1, wherein adding the germinant surfactant is in an amount of >30 ppm, given as active surfactant.

11. The method according to claim 10, wherein adding the germinant surfactant is in an amount of 60-200 ppm, given as active surfactant.

12. The method according to claim 10, wherein adding the germinant surfactant is in an amount of 70-100 ppm, given as active surfactant.

13. The method according to claim 1, further comprising drying the formed fibrous web at a temperature of >90° C. and destroying the sensitized bacterial endospores.

14. The method according to claim 13, wherein the bacterial endospore content in the dried web is ≤1000 CFU/g.

15. The method according to claim 14, wherein the bacterial endospore content in the dried web is ≤500 CFU/g.

16. The method according to claim 14, wherein the bacterial endospore content in the dried web is ≤250 CFU/g.

17. The method according to claim 1, wherein the amount of bacterial endospores, given as CFU/ml, in the fibre suspension is reduced at least 20% between the outlet of the intermediate residence entity and the formation of the fibrous web.

18. The method according to claim 17, wherein the amount of bacterial endospores, given as CFU/ml, in the fibre suspension is reduced at least 40%.

19. The method according to claim 1, further comprising adding at least one biocidal agent to the fibre suspension.

20. The method according to claim 19, wherein the at least one biocidal agent is non-oxidizing biocide, which is selected from glutaraldehyde; 2,2-dibromo-3-nitrilopropionamide (DBNPA); 2-bromo-2-nitropropane-1,3-diol (Bronopol); quaternary ammonium compounds (quats); carbamates; 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT); 2-methyl-4-isothiazolin-3-one (MIT); 1,2-dibromo-2,4-dicyanobutane; bis(trichloromethyl)sulfone; 2-bromo-2-nitrostyrene; 4,5-dichloro-1,2-dithiol-3-one; 2-n-octyl-4-isothiazolin-3-one; 1,2-benzisothiazolin-3-one; ortho-phthaldehyde; other guanidines than dodecylguanidine salts, biguanidines, pyrithiones; 3-iodo-propynyl-N-butylcarbamate; phosphonium salts; dazomet; 2-(thiocyanomethylthio) benzothiazole; methylene bisthiocyanate (MBT); or any combination thereof.

21. Method according to claim 20, wherein the quaternary ammonium compound is selected from n-alkyl dimethyl benzyl ammonium chloride, didecyl dimethyl ammonium chloride (DDAC) or alkenyl dimethyl ammonium chloride.

22. The method according to claim 19, wherein the germinant surfactant and biocidal agent(s) are used sequentially.

23. The method according to claim 22, wherein the biocidal agent(s) is/are added before the germinant surfactant.

24. The method according to claim 19, wherein the at least one biocidal agent is an oxidizing biocide, which is selected from chlorine; alkali and alkaline earth hypochlorite salts; hypochlorous acid; chlorinated isocyanurates; bromine; alkali and alkaline earth hypobromite salts; hypobromous acid; bromine chloride; chlorine dioxide; ozone; hydrogen peroxide; peroxy compounds; halogenated hydantoins; monochloramines; monobromamines; dihaloamines; trihaloamines; urea reacted with an oxidant, ammonium salts, reacted with an oxidant; or any combination thereof.

25. Method according to claim 24, wherein the peroxy compound is selected from performic acid, peracetic acid, percarbonate or persulfate.

26. Method according to claim 24, wherein the halogenated hydantoin is selected from monohalodimethylhydantoins and dihalodimethylhydantoins.

27. Method according to claim 24, wherein the ammonium salt reacted with oxidant is selected from ammonium bromide or ammonium sulfate.

28. Method according to claim 24, wherein the oxidant is selected from alkali and alkaline earth hypochlorite salts or alkali and alkaline earth hypobromite salts.

29. The method according to claim 1, further comprising adding at least one active halogen containing biocidal agent to the fibre suspension in an amount of 1-10 ppm, given as active halogen.

30. The method according to claim 1, wherein the fibrous web is a web of paper, board or tissue and the intermediate residence entity is a pulper, a storage tower or a broke tower.

Description

EXPERIMENTAL

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

Example 1

(2) Objective of this laboratory test was to study bacterial killing and spore sensitisation effect of a germinant surfactant composition comprising 35 weight-% of dodecylguanidine hydrochloride (DGH) and dipropyleneglycol as solvent in paper machine process water, at variable pulp consistency.

(3) Authentic circulation water, with low fibre content, and authentic broke, with high fibre content, were collected from a paper machine, which produced food packaging board. Circulation water and broke samples were mixed together to obtain 6 samples in total, at 3 different pulp consistency levels.

(4) To obtain equal bacterial spore content in the samples at the start of the experiment, each sample was spiked with additional bacterial spores. Target spore level in the sample was set to ca. 10 000 CFU/ml. The spore solution for spiking was prepared as follows: authentic spore-forming bacteria that were isolated from a paper making process were pre-grown for 2 days at +37° C. in a modified nutrient broth, after which the mature spores were harvested, and washed by using centrifugation and cold water.

(5) Out of the 6 samples, 3 test samples were treated with germinant surfactant comprising dodecylguanidine hydrochloride (DGH) and 3 samples were left without any chemical addition as reference samples. After addition of germinant surfactant, the test samples as well as the reference samples (no addition) were stored at 45° C., mixing of 180 rpm, for 30 minutes, followed by quantification of total aerobic bacteria (non-pasteurized samples) and aerobic spores (plate count agar, +32° C., 2 days incubation). Prior to the aerobic spore determination, samples were pasteurized at +82° C. for 10 min. Weight of suspended solids per litre of liquid, i.e. pulp consistency, was determined at the end of the test (dry weight of sample per total weight of sample). Results of are shown in Table 1.

(6) TABLE-US-00001 TABLE 1 Results of Example 1 DGH content Aerobic spores, Total aerobic Pulp (mg/L cfu/ml (+82° C., 10 bacteria Bacterial consistency as min, +32° C., 2 d Spore (+32° C., 2 d killing (w/w-%) active) PCA) reduction (%) PCA) efficacy (%) 0.1  0 20 000 98 300 000 100 100    400     300 3  0  5 400 87  40 000  78 100    700  9 000 6  0  5 100 45 170 000  55 100  2 800  77 000

(7) Results in Table 1 show that germinant surfactant comprising DGH-biocide, at dosage 100 mg/I as active component, showed excellent bacterial killing (100%) and spore reduction (98%) effect in low 0.1% consistency sample. Similarly, good bacterial killing (78%) and spore reduction (87%) effects were obtained in 3 w-% consistency sample. In the sample having highest 6% consistency, the bacterial killing (55%) and spore reduction efficacy (45%) of the germinant surfactant were somewhat lower than in the other samples but still significant effect could be observed.

(8) Obtained results indicate that a germinant surfactant comprising DGH may effectively be used to hygienise spore contaminated process streams with different pulp consistencies. It thus provides a novel tool for reduction of bacterial spores in both low and thick pulp stock, such as dilute and thick broke towers. Such a hygienisation treatment, i.e. spore reduction of >45%, eventually helps the mills to meet strict hygiene limits set for food packaging board production.

Example 2

(9) Authentic broke and circulation water samples were collected from an alkaline paper mill producing food packaging board. 1 litre of broke was stored for 2 days, +45° C., with closed cap, without mixing, in order to induce anaerobism and thus bacterial sporulation. This stagnant sample was divided to four 100 ml samples, out of which two replicate samples were treated with a germinant surfactant comprising 35 weight-% dodecylguanidine hydrochloride (DGH) and dipropyleneglycol as solvent. The dosage was 70 mg/L as active DGH. Two replicates were left without any chemical additions as reference samples.

(10) After chemical contact time of 5 min, all samples were diluted three times with the circulation water and incubated for 30 minutes, at +45° C., mixing of 160 rpm. Total aerobes (PCA, +37° C.) and aerobic spores (PCA, +37° C.) were measured at start from reference samples and after the total contact time of 35 min from all samples. Results are shown in FIG. 1.

(11) In FIG. 1:

(12) A=fresh broke at start, no DGH

(13) B=Stagnant 2 d old broke, no DGH

(14) C=Stagnant 2 d old broke mixed with dilution water, no DGH

(15) D=Stagnant 2 d old broke treated with DGH ad 70 ppm (as active) for 5 min, and mixed with dilution water

(16) FIG. 1 shows for reference samples that fresh broke contained a large amount, 1.6×10.sup.7 CFU/ml, of total aerobic bacteria, but little, 14 CFU/ml, aerobic spores. After 2 days of “stagnant” storage at +45° C., the aerobic spore count of broke markedly increased from 14 CFU/ml to 500 CFU/ml, and total aerobes level remained at high level, 9.3×10.sup.6 CFU/ml. Due to addition of the dilution water, which was circulation water with 26 spores/ml, aerobic spore count decreased from 500 CFU/ml to 330 CFU/ml.

(17) When the stagnant and diluted broke was treated with germinant surfactant comprising DGH, at dosage of 70 mg/I active, the level of aerobic spores decreased from 330 CFU/ml to 120 CFU/ml, and total aerobic bacteria level decreased slightly from 9×10.sup.6 CFU/ml to 2×10.sup.6. Obtained results thus indicate that the germinant surfactant comprising DGH may be used at economically feasible treatment level for effective broke hygienisation, i.e. for spore reduction of >60%, which is a significant improvement for hygienic paper or board production, and killing of aerobic bacteria, in conditions that correspond to authentic processing of broke at food packaging board mills. Germinant surfactant comprising DGH thus provides a unique spore control solution for hygienic board production.

Example 3

(18) Objective of this laboratory test was to study effect of biocidal pre-treatment on bacterial killing and spore sensitisation efficacy of a germinant surfactant comprising 35 weight-% of dodecylguanidine hydrochloride (DGH) and dipropyleneglycol as solvent in paper machine process water.

(19) Authentic circulation water (1 litre) was collected from a paper machine producing food packaging board and divided into 4 samples with volume of 50 ml. To obtain equal bacterial spore content in the samples at start of the experiment, each sample was spiked with additional bacterial spores. The target level for spores was c.a. 10 000 CFU/ml. The spore solution for spiking was prepared as follows: authentic spore-forming bacteria that were isolated from a paper making process were pre-grown for 2 days at +37° C. in modified nutrient broth, after which the mature spores were harvested, and washed by using centrifugation and cold water. Out of the 4 samples, the first sample was left without any chemical addition as a reference sample. the second sample was treated with sodium hypochlorite, at dosage of 5 mg/I, given as active chlorine; the third sample was treated with a germinant surfactant comprising dodecylguanidine hydrochloride (DGH), at dosage level of 100 mg/I, given as active compound; and the fourth sample was treated with sodium hypochlorite, at dosage of 5 mg/I, given as active chlorine) for 1 minute, after which the third sample was treated with a germinant surfactant comprising dodecylguanidine hydrochloride (DGH), at dosage level of 100 mg/I, given as active compound;

(20) Samples were stored at 45° C., under mixing of 180 rpm, for 30 minutes except samples 2 and 4, which were in addition pre-treated with sodium hypochlorite for 1 minute. After the treatment the amount of total aerobic bacteria (non-pasteurized samples) and aerobic spores were quantified (plate count agar, +32° C., 2 days incubation). Prior to the aerobic spore determination, samples were pasteurized at +82° C. for 10 min. Results of are shown in Table 2

(21) TABLE-US-00002 TABLE 2 Results of Example 3. Total aerobic bacteria Aerobic spores PCA +32, 30 min PCA +32 Sample @45° C. 30 min @45° C. pH Redox 1. Process water, no biocides 7 000 000 13 000 7.6 165 2. Process water with sodium   320 000 17 000 7.7 154 hypochlorite as 5 ppm (as active Chlorine) 3. Process water with DGH as 100   10 000  3 000 7.6 166 ppm (as active) 4. Process water, with sodium    4 700   900 7.7 147 hypochlorite as 5 ppm (as act Cl) pre-treatment (1 min), followed by DGH treatment as 100 ppm (as active)

(22) Results in Table 3 show that sodium hypochlorite showed good killing effect against total aerobic bacteria, whereby the level decreased from 7 000 000 CFU/ml to 32 000 CFU/ml, but it did not have any effect on bacterial spores, as the spore counts were at 17 000 CFU/ml level despite the chlorine treatment.

(23) Germinant surfactant comprising DGH showed alone an excellent bacterial killing effect, as the total aerobic bacteria level decreased from 7 000 000 CFU/ml to 10 000 CFU/ml, and also good spore sensitisation effect, as the aerobic spore count decreased from 13 000 to 3000 CFU/ml, i.e. spore reduction of >70%, which is a significant improvement for hygienic paper or board production. The most effective killing and spore reduction effect was obtained with sodium hypochlorite as pre-treatment, followed by treatment with germinant surfactant comprising DGH. This dual biocide treatment, which did not change process pH nor ORP, caused a drastic drop in total aerobic bacteria level from 7 000 000 CFU/ml to 4 700 CFU/ml and in bacterial spore count from 13 000 CFU/ml to 900 CFU/ml, i.e. spore reduction of >90%, which is a significant improvement in hygienic paper or board production. Obtained results indicate clearly that fast acting biocides, such as sodium hypochlorite, may preferably be used as a pre-treatment before dosage of germinant surfactant comprising DGH for spore reduction purposes. Germinant surfactant comprising DGH together with sodium hypochlorite pre-treatment provides a novel tool for easy and quick reduction of bacterial spores, such as spore reduction>90%, in pulp and paper process streams which eventually helps food packaging board mills to meet strict hygiene limits of final board.

(24) 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.