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<record cy="WO" an="SE0001823" pn="WO012189020010329" dnum="0121890" kind="A1">

 <prs>

  <pr prn="SE19990922 9903418-3"/>

 </prs>

 <ipcs ed="7" mc="D21H01120">

  <ipc ic="D21H01725"></ipc>

 </ipcs>

 <ins>

  <in>LINDSTRM, Tom</in>

  <in>GLAD-NORDMARK, Gunborg</in>

  <in>RISINGER, Gunnel</in>

  <in>LAINE, Janne</in>

 </ins>

 <pas>

  <pa>STFI</pa>

 </pas>

 <tis>

  <ti xml:lang="EN">METHOD FOR MODIFYING CELLULOSE-BASED FIBER MATERIAL

  </ti>

 </tis>

 <abs>

  <ab xml:lang="EN">A method for modifying cellulose fibers; which are treated for at least

5 minutes with an aqueous solution of CMC or CMC-derivative containing

electrolyte at a temperature of at least approximately 100 C, and

the pH during the treatment is approximately 1.5-4.5, or higher than

11; or the concentration of electrolyte is approximately 0.001 -

0.5 M, if the electrolyte has monovalent cations, or approximately 0.0002

- 0.5 M, if the electrolyte has divalent cations, and cellulose fibers

that have been modified according to this method, and use of the modified

cellulose fibers for the manufacture of rayon fibers. A method for the

manufacture of paper with a high wet strength, whereby an aqueous suspension

of cellulose fibers is produced, and the cellulose fibers are modified

as described above, and wet-strength agent is added to the aqueous

suspension; and paper with a high wet strength manufactured according

to this method.

  </ab>

 </abs>

 <cls>

  <cl xml:lang="EN"> Claims

1. Method for modifying cellulose fibers, c h a r a c t e r i z e d in that the cellulose fibers

are treated for at least 5 minutes with an aqueous electrolyte-containing solution of CMC or a CMC

derivative, whereby

-the temperature during the treatment is at least 100 C, and

at least one of the following conditions apply:

A) the pH of the aqueous solution during the treatment lies in the interval of approximately 1.5-4.5,

preferably in the region 2-4; or

B) the pH of the aqueous solution during the treatment is higher than approximately 11; or

C) the concentration of the electrolyte in the aqueous solution lies in the interval of approximately

0.001-0.5 M, preferably 0.005-0.1 M, if the electrolyte has monovalent cations, or in the range of

approximately 0.0002-0.25 M, preferably 0.0005-0.1 M, if the electrolyte has divalent cations. 2. Method according to claim 1, c h a r a c t e r i z e d in that the pH of the aqueous

solution during the treatment lies in the interval of approximately 1.5-4.5 and the concentration of

the electrolyte in the aqueous solution lies within the interval of approximately 0.001-0.5 M if the

electrolyte has monovalent cations, or approximately 0.0002-0.25 M if the electrolyte has divalent

cations. 3. Method according to claim 1, c h a r a c t e r i z e d in that the pH of the aqueous

solution is higher than 11 and the concentration of the electrolyte in the aqueous solution lies within

the interval of approximately 0.001-0.5 [M] if the electrolyte has monovalent cations, or

approximately 0.0002-0.25 M if the electrolyte has divalent cations. 4. Method according to claim 1, c h a r a c t e r i z e d in that the cellulose fibers are

treated for approximately 5-180 minutes. 5. Method according to claim 1, c h a r a c t e r i z e d in that the temperature during the

treatment is at least approximately 120 C, and preferably up to approximately 150 C. 6. Method for manufacturing paper with a high wet strength, c h a r a c t e r i z e d in that

-an aqueous suspension of cellulose fibers is produced;

-the cellulose fibers are modified according to any one of the preceding claims; and

-wet-strength agent is added to the aqueous suspension of cellulose fibers. 7. Method according to claim 6, c h a r a c t e r i z e d in that a debonding agent is also

added to the aqueous suspension of cellulose fibers. 8. Cellulose fibers that have been modified according to the procedure according to any of

claims 1-5. 9. Paper with a high wet strength that can be manufactured according to either one of claims 6

or 7. 10. Use of modified cellulose fibers according to claim 8 for the manufacture of rayon fibers.

  </cl>

 </cls>

 <txts>

  <txt xml:lang="EN">

   Method for modifying cellulose-based fiber material

This invention concerns the technical field of paper manufacture, in particular chemical

additives during paper manufacture. The use of carboxymethyl cellulose, hereafter referred to as"CMC", as dry-strength agent or

as an additive during the grinding of paper pulp is described by, for example, B. T. Hofreiter in"Pulp

and Paper Chemistry and Chemical Technology", Chapter 14, Volume III, 3rd. edition, New York,1981; W. F. Reynolds in"Dry strength additives", Atlanta 1980; D. Eklund and T. Lindstrm in

"Paper Chemistry-an introduction", Grankulla, Finland 1991; J. C. Roberts in"Paper Chemistry" ;

Glasgow and London 1991. CMC is anionic and thus has a low affinity for cellulose fibers, since these are anionically

charged. Aluminium salts can be used to retain these additives, as has been described by, for example,

L. Laurell in"Svensk Papperstidning", 55th. annual edition, 1952, no. 10, page 366. J. W. Hensley and C. G. Inks (Text. Res. Journal, June 1959, page 505) have described the

failure of CMC to be adsorbed to cellulose fibers in electrolyte-free environments and the consequent

limitation of its use to what are known as"acidic"paper manufacturing methods in which aluminium

salts are used. Adsorption to the fiber material becomes extremely poor when CMC is used in systems

that are free of aluminium salts, something that is not compatible with modem paper manufacture.The reason for this is that the presence of anionic polymers, such as CMC, in the stock system

interferes with cationic additives of functional or process chemicals by forming what are known as

polyelectrolyte complexes. This is a well known phenomenon, and paper manufacturers often refer to

such substances as"anionic trash". Modem paper manufacturing processes in which extremely closed process water systems are

used are particularly sensitive for disturbing anionic substances, since a build-up of such substances

occurs in the system. These facts have resulted in the development of cationic additives that have a significantly

better affinity for the anionically charged cellulose fibers. Such additives currently have what is

essentially a monopoly in the market for dry-strength agents. In addition to its use as a dry-strength agent, the use of CMC together with wet-strength resin

has been described in US-A-3 058 873. This document specifies a synergistic action between the

addition of CMC and wet-strength resin when these additives are used at the same time during paper

manufacture. This depends on the fact that CMC can be precipitated on the fibers in the same way as

what is known as"anionic trash"can be retained on fibers with the aid of cationic chemical additives. The wet-strength agent is retained through colloidal precipitation. Optimal precipitation of CMC

occurs when a stochiometrically neutral complex of CMC and the wet-strength agent is obtained,

something that makes the process sensitive to disturbances in the chemistry of the stock. This leads to

an unstable process, since the retention of the wet-strength agent will depend on the variability in the

incoming raw material and the concentrations of dissolved and colloidal material in the process water. It would be desirable to be able to achieve a method by which adsorption of CMC to the

cellulose fibers could be significantly improved. In this way, the effect of CMC as dry-strength agent

during paper manufacture could be improved, among other things. Improved adsorption of CMC to

the cellulose fibers would also improve the retention of, and thus the effect of, wet-strength agents. One problem that is considered to be solved with the present invention is that of achieving

such a method. This problem is solved by the method according to claim 1 presented here. In more detail, the

present invention concerns a method whereby cellulose fibers are treated for at least 5 minutes with an

aqueous electrolyte-containing solution of CMC or a derivative of CMC, whereby the temperature

during the treatment is at least 100 C and at least one of the following conditions applies:

A) the pH of the aqueous solution during the treatment lies in the interval of approximately 1.5-4.5;

or

B) the pH of the aqueous solution during the treatment is higher than approximately 11; or

C) the concentration of the electrolyte in the aqueous solution lies in the interval of approximately

M if the electrolyte has monovalent cations, or in the range approximately 0.0002-0.25 M

if the electrolyte has divalent cations. It is preferable if condition C applies together with either condition A or condition B. A method for modifying cellulose fibers with a cellulose derivative such as CMC is described

in the published international patent application WO 99/57370. This method is performed at a pH of

6-13 and a temperature of up to 100 C, preferably in the approximate range of 20-80 C. It is

specified (on page 7, lines 29-30) that the temperature does not constitute a critical factor. There is

nothing specified or even implied that a temperature over 100 C would involve significant

advantages for the adsorption. In association with the present invention it has become apparent that CMC is not adsorbed

onto cellulose fibers unless an electrolyte is simultaneously present, and that a higher concentration of

electrolyte and high valencies of the counter-ious are advantageous for the adsorption. It has further

become apparent that it is necessary to resort to elevated temperatures in order to obtain a sufficiently

good adsorption. It has further become apparent not only that the adsorption is irreversible when the

concentration of CMC is reduced, but also that essentially ion-free conditions can be reached, with the

pulp in its Na-form, without CMC beingdesorbed to any significant degree. This is a very surprising

fact, since according to conventional techniques, essentially no CMC is adsorbed onto cellulose-based

fibers under such conditions. It is thus possible, according to the present invention, to achieve a pulp/paper process in

which the pulp is treated for a certain time at a high temperature under such electrolytic conditions

that promote the adsorption of CMC. The final pulp receives a higher number of carboxyl groups than

the original pulp, which gives a paper that is considerably stronger than paper made using pulp that

has been produced using conventional techniques. The cellulose fibers that are used with the present invention include all types of wood-based

fibers, such as bleached, half-bleached and unbleached sulfite, sulfate and soda pulps, together with

unbleached, half-bleached and bleached mechanical, thermomechanical, chemo-mechanical and

chemo-thermomechanical pulps, and mixtures of these. Both new fibers and recycled fibers can be

used with the present invention, as can mixtures of these. Pulps from both softwood and hardwood

trees can be used, as can mixtures of such pulps. Pulps that are not based on wood, such as cotton linters, regenerated cellulose, kenaf and

grass fibers can also be used with the present invention. The preferred concentration of CMC is approximately 0.02-4 % w/w, calculated on the dry

weight of the fiber material. A more preferred concentration is approximately 0.04-2 % w/w, and the

most preferred concentration of additive is approximately 0.08-1% w/w. The concept"CMC"is used here to include, in addition to carboxymethyl cellulose, various

derivatives thereof. The preferred molar degree of substitution is approximately 0.3-1.2 and the

preferred viscosity is approximately 25-8,000 mPa at a concentration of 4%. A higher viscosity is

preferred, since it has become clear that the irreversibility of the adsorption is higher for higher

molecular weights. A high concentration of pulp is particularly desirable if the adsorption is not quantitative,

since the loss of CMC can thus be reduced and CMC solution can easily be reintroduced into the

reaction vessel. Treatment of pulp preferably takes place as a separate treatment step at high pulp

concentration, but it can naturally also be carried out at the same time as, for example, digesting, or

during a bleaching step. As high a concentration of pulp as possible is thus desired, but this is

naturally limited by practical conditions during the conduct of the method. The preferred

concentration of pulp is approximately 3-50%, a more preferred concentration interval is

approximately 5-50%, and the most preferred concentration interval is approximately 10-30%. Such

high concentration mixes are known to one skilled in the arts within the relevant technical field, and

are suitable for use in association with the present invention. A preferred range of pH is approximately 2-4, in particular approximately 2.5-3.5. A higher concentration of electrolyte and a higher valence of the cation increase the affinity of

CMC for the pulp. The preferred concentration interval for salts with monovalent cations, such asNa, S04, is approximately 0.002-0.25 M, in particular within the range approximately 0.005-0.1 M. The preferred concentration interval for salts with divalent cations, such as CaCl,, is between

approximately 0.0005-0.1 M, in particular approximately 0.02-0.05 M. The preferred adsorption period is approximately 5-180 min, a more preferred adsorption

period is approximately 10-120 min and the most preferred adsorption period is approximately 1560 min. The preferred temperature is in excess of approximately 100 C, a more preferred temperature

is in excess of approximately 120 C and the most preferred adsorption temperature is up to

approximately 150 C. The method according to the invention is thus carried out at a pressure in

excess of atmospheric pressure. Suitable equipment and working conditions for this will be obvious

for one skilled in the arts. The pulp can be washed or diluted directly after the treatment, or it can be dried in the normal

manner. The present invention also concerns a method for production of paper with a high wet

strength, whereby

-an aqueous suspension of cellulose fibers is produced;

-the cellulose fibers are modified by treatment for at least 5 minutes with an aqueous solution of

CMC or a CMC derivative containing electrolyte, whereby

-the temperature during the treatment is at least approximately 100 C

and at least one of the following conditions apply:

A) the pH of the aqueous solution during the treatment lies in the interval of approximately 1.5-4.5;

or

B) the pH of the aqueous solution during the treatment is higher than approximately 11; or

C) the concentration of the electrolyte in the aqueous solution lies in the interval of approximately

M if the electrolyte has monovalent cations, or in the range of approximately

0.0002-0.25 M if the electrolyte has divalent cations; and

-wet-strength agent is added to the aqueous suspension of cellulose fibers. It has actually also become clear that cellulose fibers treated according to the present

invention, when treated with wet-strength agent, provide a much higher wet strength than the strength

that can be explained by the higher adsorption of wet-strength agent to the fibers. This may be due to the fact that it is more advantageous to retain the wet-strength agent

evenly distributed over the fiber surfaces, as occurs according to the present invention, than it is to

have it as a colloidal precipitation, as occurs according to US-A 3 058 873. A paper can be defined as wet-strengthened in this context when the geometric mean value of

the wet strength divided by the dry strength exceeds 0.15. Mixtures of compatible wet-strength agents and other chemicals used in paper production can

be used within the scope of the present invention, as can what are known as"debonding agents."

The preferred concentration of wet-strength agent used as additive to the stock is up to

approximately 2% w/w, calculated on the [weight of] dry fibers, a more preferred concentration is

approximately 0.02-1.5 % and the most preferred concentration is 0.05-0.8 %. Wet-strength agents that can be used include all cationic polymeric resins. These include, for

example, those wet-strength agents that give permanent wet strength: urea-formaldehyde resins,

melamine-formaldehyde resins and polyamide-amine resins. Examples of wet-strength agents that

give temporary wet strength are polyethylene imine, dialdehyde starch, polyvinyl amine and glyoxalpolyacrylamide resins. According to one embodiment of the present invention, a method is also provided for making

paper with a high wet strength but low dry strength, a method that can be used, for example, for

producing paper structures that are strong when wet and absorbent. What are known as"debondingagents"are used in this embodiment, and preferred debonding agents are quaternary ammonium salts

with fatty acid chains that can be retained by electrostatic attraction to the negatively charged groups

on the surfaces of the fibers. The result is a paper with a wet strength/dry strength ratio that

preferably exceeds 0.1, a more preferred value exceeds 0.2 and the most preferred value exceeds 0.3. It has also become clear that if fibers treated according to the present invention are dried, a

pulp is produced that when repulped gives fibers with a higher water retention ability. In other words,

the treatment of this nature has given a fiber that has been keratinized to a lesser degree during drying. Such fibers demonstrate also a higher reactivity during subsequent chemical treatments, for example,

when manufacturing rayon fibers. Other embodiments of the present invention are described in more detail with the aid of

examples of embodiments, the only purpose of which are to illustrate the invention and are in no way

intended to limit its scope. Examples

Example 1: This example according to known technology demonstrates how the conditions in

the chemical environment affect the amounts of different types of CMC that are irreversibly adsorbed. The CMC preparations that were used were commercially available preparations from Metsa-Serla:

Finnfix WRH with a DS of 0.56 and a viscosity of 530 mPa at a concentration of 2%, and Cekol FF2

with a DS of 0.7-0.85 and a viscosity of 25 mPa at a concentration of 4%. The pulp was a bleached,long-fibered, undried softwood sulfate pulp from Metsa-Serla/Husum's factories. The adsorption trials

were conducted at a pulp concentration of 2%. The pulp was washed with 0.01 M HCl after the

treatment and then transferred to its Na-form in de-ionise water. The pulp was washed after 2 hours

with de-ionise water. The amount of CMC adsorbed was determined by conductometric titration. The amount of CMC that was added was 40 mg/g."DS"is used to denote the degree of molar

substitution for the CMC used.Table 1

ChemicalTemp(C)AdsorptiontimeAmountofAmountofCekol

conditions(hours)FinnfixWRHFF2adsorbed

adsorbed(mg/g)(mg/g)

De-ionisewater80 2 0

0.1 MNaCl 23 4. 8

0.1 M NaOH 80 16. 1

0.1 M NaCI

0.1 M NaCl 80 8. 9 2. 9

0.1 M NaCI 80 72 11. 4

0.05MCaC12 80 2 17. 4

Table 1 shows that the presence of electrolyte is necessary to obtain adsorption. It is also clear that the

adsorption is higher at higher temperatures. Higher alkalinity is also advantageous for the adsorption.The degree of molar substitution or the molecular weight of CMC is not critical, but the adsorption

increases when the degree of substitution decreases. Example 2: This example shows that a very high relative amount of CMC can be irreversibly

bound to a bleached undried softwood sulfate pulp (Metsa-Serla/Husum factories) by the selection of

a high temperature and a high electrolyte concentration. The experiment was performed by treating

the pulp at 120 C or at 150C for 2 hours in 0.05 M CaCl, buffered with 0.001 M NaHCO3. The

amounts of CMC adsorbed (FinnFix WRH and Cekol FF2) were measured both after washing the

pulp with de-ionise water (Ca-form) and after washing the pulp with 0.01 M HCI, de-ionise water,

adjusting its pH value using NaOH to a pH of 8 and equilibrating it with an 0.001 M NaHC03 buffer

for 2 hours (Na-form). As the table shows, a smaller amount of CMC is desorbed when the pulp has

been transferred into its Na-form."WRV"is an abbreviation for"Water Retention Value"and is a

measure of the ability of the pulp to retain water (here the Na-form was measured at 3,000 g and 15

minutes in de-ionise water).Table 2

TypeofCMCTreatment Dosage (mg/g) Ionic formAmountWRV (%)

temperature (C) adsorbed (mg/g)

120 0 Na 0135

Finnfix WRH 120 20 Ca 17. 7

Finnfix WRH 120 20 Na 14. 8 173

Finnfix WRX 120 40 Ca 27. 3

Finnfix WRH 120 40 Na 23. 4 195

Finnfix WRH 150 40 Ca 26. 3

FinnfixWRH 150 40 Na 23. 1 182

Cekol FF2 120 20 Ca 15. 5

Cekol FF2 120 20 Na 11. 5 146

Cekol FF2 120 40 Ca 22. 4

Cekol FF2 120 40 Na 18. 5 156

Cekol FF2 150 40 Ca 19. 1

Example 3: CMC (Finnfix WRH) was adsorbed onto a bleached undried softwood sulfate

pulp (Metsa-Serla/Husum factories) at different pH values in de-ionised water at 120 C. The pulp had

been transferred to its Na-form before the pH was adjusted. The amount of CMC added was 20 mg/g.The results in Table 3 show that a certain amount is adsorbed at 120 C, but better adsorption is

achieved if electrolyte is present during the treatment (compare with Table 2).Table 3

TypeofCMCpHduringtreatmentAmountadsorbed WRV (Na-form)

(mg/g)pH = 8.0

WRH 3 8. 6 136

WRH 8 5. 2 141

WRH _ 8. 9 151

Example 4: This example shows that the adsorbed amount of CMC is adsorbed to the

cellulose fibers so strongly that it remains on the fibers even after a prolonged period of leaching. The

bleached sulfate pulp from Example 2 was treated with 40 mg/g Finnfix WRH for 2 hours at 120 C

in 0.1 M NaCl. The amount adsorbed after this treatment was 7.7 mg/g. After leaching the pulp in de-ionised water for 19 hours, the adsorbed amount was 7.4 mg/g. Example 5: This example shows that selecting a high temperature and a high concentration of

electrolyte at the adsorption step gives a pulp that has a lower water retention ability than that

obtained if the CMC is adsorbed onto the pulp at a lower temperature. The experiment was performed by treating an undried softwood sulfate pulp (Metsa-Serla/Husum factories) at 23 C, 80 C and 120 C for 12 hours in 0.05 M CaC12 buffered by 0.001 MNaHCO3. The amount of adsorbed CMC (Finnfix WRH; 20 mg/g) was measured after washing the

pulp with 0.01 M HC1, de-ionised water, adjusting its pH with NaOH to a pH of 8 and equilibrating it

with 0.001 M NaHCO3 buffer for 2 hours (Na-form). WRV is an abbreviation for"Water Retention

Value"according to the definition given earlier. Table 10 shows that the increase in WRV per mg/g of adsorbed CMC is considerably lower if

the CMC has been adsorbed at a higher temperature (120 C) than if it has been adsorbed at a lower

temperature. This is particularly advantageous if it is to be easy to de-water the pulp on the paper

machine. The ability of the pulp to retain water, however, does not reflect the strength of the paper

that is manufactured from the pulp under consideration. Table 10

Temperatureduring WRV(%)AmountFinnfix WRH (WRW-WRW ref) per

treatment(C)adsorbed(mg/g)mg/gadsorbedCMC

Reference 129-23 200 4. 8 14. 8

80 204 8. 3 9. 0

120 173 14. 8 3. 0

  </txt>

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