ES2346634T3 - PROCEDURE FOR MODIFICATION OF A FIBER MATERIAL BASED ON CELLULOSE. - Google Patents

Abstract

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 DEG 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.

Description

Procedure for modifying a material cellulose based fiber.

This invention relates to the technical field of papermaking, particularly chemical additives during paper making

The use of carboxymethyl cellulose, hereinafter referred to as "CMC", as a dry strength agent or as an additive during milling of the paper pulp is described, for example, by BT Hofreiter in Pulp and Paper Chemistry and Chemical Technlogy , Chapter 14, Vol. III, 3rd edition, New York, (1981); WF Reynolds in Dry strength additives , Atlanta, (1980); D. Eklund and T. Lindstrom in Paper Chemistry - an introduction , Grankulla, Finland, (1991); JC Roberts in Paper Chemistry , Glasgow and London, (1991).

CMC is ionic and, consequently, has a low affinity for cellulose fibers, since these are anionically charged. Aluminum salts may be used to retain these additives, as described, for example, by L. Laurell in Svensk Papperstidning , 55th, annual edition, no. 10, p. 366, (1952).

JW Hensley and CG Inks Text. Res. Journal , p. 505, (June 1959), have described the failure of the CMC to be absorbed by cellulose fibers in electrolyte-free environments and the consequent limitation of its use for what is known as "acid" papermaking processes in the which aluminum salts are used. The adsorption of the fiber material becomes extremely poor when CMC is used in systems that are free of aluminum salts, something that is not compatible with modern papermaking. The reason for this is that the presence of anionic polymers, such as CMC, in the production system interferes with cationic additives of functional chemicals or the process by forming what is known as polyelectrolyte complexes. This is a well known phenomenon, and paper manufacturers often refer to such substances as "anionic waste."

The modern manufacturing procedures of paper, in which water treatment systems are used extremely closed, they are particularly sensitive to alteration by anionic substances, since an accumulation of these substances in the system.

These facts have resulted in development of cationic additives that have an affinity significantly better for cellulose fibers loaded anionically These additives currently possess what essentially it is a monopoly in the market of the agents of dry strength

In addition to its use as a resistance agent dry, the use of CMC in conjunction with resistance resin in wet has been described in the Document US-A-3 085 873. This document specifies a synergistic action between the addition of CMC and the resin wet strength when these additives are used at the same Time during papermaking. This depends on the fact that CMC can precipitate on the fibers in the same way as can be retained what is known as "anionic garbage" on the fibers with the help of cationic chemical additives. The agent wet strength is retained by precipitation colloidal Optimum CMC precipitation occurs when obtains a stoichiometrically neutral complex of CMC and agent wet strength, something that makes the procedure sensitive to alterations in the chemistry of the production material. This leads to an unstable procedure, since retention of the wet strength agent depend on the variability of raw material input and material concentrations dissolved and colloidal in the treatment water.

It would be desirable to be able to achieve a procedure whereby adsorption could be significantly improved of CMC for cellulose fibers. In this regard, among others things, the effect of CMC as an agent of dry strength during papermaking. Adsorption Improved CMC by cellulose fibers would also improve the retention, and therefore the effect, of the resistance agents wet

A problem that is considered solved with the The present invention is the one that has achieved a process of this kind.

This problem has been fixed by procedure according to claim 1 presented in the present memory In more detail, the present invention is refers to a process in which cellulose fibers are treat for at least 5 minutes with a solution that contains a aqueous CMC electrolyte or a CMC derivative, in which the temperature during treatment is at least 100 ° C and is applied at least one of the following conditions:

A) the pH of the aqueous solution during the treatment is within the range of 1.5-4.4; or

B) the pH of the aqueous solution during the treatment is greater than about 11; or

C) the concentration of the electrolyte in the aqueous solution is within the range of approximately 0.001-0.5 M if the electrolyte has monovalent cations, or within the range of approximately 0.0002-0.25 M if the electrolyte has cations divalent

It is preferable if condition C applies together with either condition A or condition B.

In the International Patent Application published WO 99/57370 describes a procedure for the modification of cellulose fibers with a cellulose derivative such as CMC. This procedure is carried out at a pH of 6-13 and at a temperature of up to 100 ° C, preferably within the approximate range of 20-80 ° C. It is specified (on page 7, lines 29-30) that temperature is not a factor critical. Nothing is specified or even understood as a temperature above 100 ° C would imply significant advantages for adsorption.

In relation to the present invention, considers it obvious that CMC is not adsorbed on the fibers of cellulose unless an electrolyte is present simultaneously, and that a higher concentration of electrolyte and high valences of the counterions are advantageous for adsorption. Is considered it is also obvious that it is necessary to resort to high temperatures with in order to obtain a sufficiently good adsorption. Is considered equally obvious not only that adsorption is irreversible when CMC concentration is reduced, they can also essentially ion-free conditions are reached, with the pulp in its Na form, without the CMC being desorbed to a degree significant. This is a very surprising fact, since According to conventional techniques, there is essentially no CMC adsorbed on the cellulose-based fibers under said terms.

Accordingly, in accordance with this invention, it is possible to achieve a pulp / paper process in the which pulp is treated for a certain time at a high temperature under such electrolytic conditions that promote CMC adsorption. The final pulp receives a higher number of groups carboxyl than the original pulp, which results in a paper that is considerably stronger than paper made using pulp that It has been produced using conventional techniques.

The cellulose fibers that have been used in the The present invention includes all types of fiber based on wood, such as bleached sulphite, sulfate and soda pulps, semi-bleached and unbleached, together with mechanical, thermomechanical pulps, chemical-mechanical and non-bleached chemical-thermomechanics, semi-bleached and bleached, and mixtures of same. Both new and new fibers may be used herein. Recycled fibers, as well as mixtures thereof. Pulps from both softwood trees can be used as hardwood, as well as mixtures of these pulps

Likewise, they can be used herein invention non-wood based pulps, such as cotton, regenerated cellulose, hemp of India and fibers of grass.

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 of about 0.04-2% w / w, and the concentration the most preferred additive is approximately 0.08-1% w / w

The concept of "CMC" is used herein. memory to include, in addition to carboxymethyl cellulose, various derivatives thereof. The preferred molar degree of substitution is about 0.3-1.2 and the preferred viscosity is about 25-8,000 mPa at a 4% concentration. A higher concentration is preferred, since that it is evident that the irreversibility of adsorption is greater for higher molecular weights.

A high concentration of the pulp is particularly desirable if adsorption is not quantitative, given that the loss of CMC can, in this way, be reduced and the solution CMC can easily be reintroduced into the container of reaction. Preferably, the pulp treatment takes place as a separate treatment stage at high concentration of the pulp, but naturally it can be carried out equally time that, for example, digestion, or during a stage of Whitening. Accordingly, a concentration of pulp as high as possible, but naturally this is limited by practical conditions during the completion of the process. The preferred pulp concentration is approximately 3-50%, a range of most preferred concentration is about 5-50%, and the concentration range the most Preferred is about 10-30%. These High concentration mixtures are known to an expert in techniques within the appropriate technical field, and are suitable for use in relation to the present invention.

A preferred pH range is approximately from 2-4, in particular approximately from 2.5-3.5.

A higher concentration of electrolyte and a higher valence of the cation increase the affinity of the CMC for the pulp. The preferred concentration range for salts with monovalent cations, such as Na 2 SO 4, is about 0.002-0.25 M, in particular within the range of about 0.005-0.1 M. The concentration range Preferred for salts with divalent cations, such as CaCl2, is between about
0.0005-0.1 M, in particular approximately 0.02-0.05 M.

The preferred adsorption period is approximately 5-180 minutes, a period of most preferred adsorption is about 10-120 minutes and the most preferred period is approximately 15-60 minutes

The preferred temperature is higher than approximately 100 ° C, a more preferred temperature is greater than approximately 120 ° C and the most preferred adsorption temperature It is up to about 150 ° C. Consequently, the procedure according to the invention it is carried out at a pressure greater than atmospheric pressure The equipment and working conditions suitable for this will be obvious to an expert in techniques

The pulp can be washed or diluted directly after treatment, or it can be dried in the normal way.

The present invention also relates to a procedure for the production of paper with high strength wet, in which

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be produces an aqueous suspension of cellulose fibers;

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the Cellulose fibers are modified by treatment during minus 5 minutes with an aqueous solution of CMC or a derivative of CMC which contains electrolyte, in which

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the temperature during treatment is at least about 100 ° C,

and at least one of the terms following:

TO)

the pH of the aqueous solution during treatment is found within the range of about 1.5-4.4; or

B)

the pH of the aqueous solution during treatment is greater than about 11; or

C)

the concentration of the electrolyte in the aqueous solution is found within the range of approximately 0.001-0.5 M if the electrolyte has cations monovalent, or within the range of approximately 0.0002-0.25 M if the electrolyte has cations divalent; Y

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he wet strength agent is added to the fiber suspension of cellulose.

Actually, it has also become obvious that cellulose fibers treated in accordance with the present invention, when treated with wet strength agent, they provide a wet strength far superior to the resistance that can explained by the greater adsorption of resistance agent in wet to the fibers.

This may be due to the fact that it is more advantageous to retain the distributed wet strength agent evenly over fiber surfaces, as is the case according to the present invention, that having it as a colloidal precipitate, as occurs according to the Document US-A-3 085 873.

A role can be defined as resistance in wet in this context, when the geometric mean value of the wet strength divided by dry strength exceeds 0.15.

Compatible mixtures of agents wet strength and other chemicals used in the paper production can be used within the scope of this invention, such as those known as "agents of taken off".

The preferred concentration of the agent wet strength used as an additive to the production material is up to about 2% w / w, calculated on (the weight of) the dry fibers, a more preferred concentration is about 0.02-1.5% and the most preferred concentration is 0.05-0.8%.

Wet strength agents that can used include all cationic polymer resins. These include, for example, wet strength agents that provide permanent wet strength: resins of urea-formaldehyde resins melanin-formaldehyde and resins of polyamide-amide. Examples of agents from wet strength that provide wet strength Temporary are polyethylene imine resins, dialdehyde starch, polyvinyl amine and glyoxal polyacrylamide.

In accordance with an embodiment of the present invention, a method is also provided for the papermaking with high wet strength but with low dry strength, a procedure that can be used, by example, for the production of paper structures that are strong when they are wet and adsorbent. In this embodiment, the known as "peeling agents", and the agents of Preferred detached are quaternary ammonium salts with chains of fatty acid that can be retained by attraction electrostatic to negatively charged groups on the fiber surface The result is a role with a relationship wet strength / dry strength than preferably exceeds 0.1, a more preferred value exceeds 0.2 and the value more preferred exceeds 0.3.

It has also been obvious that if the fibers treated in accordance with the present invention are dried, produced a pulp that when re-pulp gives fibers with a superior water retention capacity. In other words, the treatment of this nature has resulted in a fiber that has been Keratinized to a lesser extent during drying. Such fibers also demonstrate superior reactivity during treatments later chemicals, for example, when manufacturing fibers of rayon

Other embodiments of the present invention are describe in greater detail with the help of examples of realizations, whose sole purpose is to illustrate the invention and not limit its scope in any way.

Examples

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Example 1

This example, according to the technology known, demonstrates the way in which environmental conditions chemical affect the amounts of different types of CMC that are irreversibly adsorbed. The CMC preparations that have been used were commercially available preparations from Metsä-Serla: Finnix 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 4% concentration. The pulp used was wood sulfate pulp soft, not dried, long fiber, bleached, from Metsä-Serla / Husum factories. Adsorption tests were performed at a pulp concentration of 2%. The pulp was washed with 0.01 M HCl after treatment and then transferred to its form Na in deionized water. The pulp was washed after 2 hours with water deionized The amount of CMC adsorbed was determined by conductometric assessment. The amount of CMC that was added was 40 mg / g The abbreviation "DS" is used to indicate the degree of molar substitution for the CMC used.

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one

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Table 1 shows that the presence of Electrolyte is necessary to obtain adsorption. It is also Obviously, the adsorption is higher at higher temperatures. Likewise, high alkalinity is advantageous for adsorption. He degree of molar substitution or the molecular weight of the CMC is not critical, but adsorption increases when the degree of substitution decreases

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Example 2

This example shows that you can join in a way irreversible a relatively very high amount of CMC to a pulp sulfate in a soft way without drying, bleached (factories Metsä-Serla / Husum) by selecting a high temperature and a high concentration of electrolyte. The experiment was performed. treating the pulp at 120 ° C or 150 ° C for 2 hours in CaCl2 0.05 M buffered with NaHCO 3 0.001 M. The amounts of CMC adsorbed (Finnix WRH and Cekol FF2) were measured both after wash the pulp with deionized water (Ca form) as after washing the pulp with 0.01 M HCl, deionized water, adjusting its pH value using NaOH at pH 8 and balancing it with a NaHCO 3 buffer 0.001 M for 2 hours (Na form). As the table shows, it desorbed a smaller amount of CMC when the pulp had transferred to its Na form. "WRV" is an abbreviation for "Water retention value" and is a measure of the capacity of the pulp to retain water (in this case, the Na form was measured at 3,000 g and 15 minutes in deionized water).

2

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Example 3

CMC (Finnix WRH) was adsorbed on a pulp at softwood sulfate, not dried, bleached (factories Metsä-Serla / Husum) at different pH values in deionized water at 120 ° C. The pulp had been transferred to its Na form before adjust the pH. The amount of CMC added was 20 mg / g. The Results from Table 3 show that a certain adsorbed amount at 120 ° C, but better adsorption was achieved if there is present electrolyte during treatment (compare Table 2).

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3

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Example 4

This example shows that the amount adsorbed of CMC was adsorbed by cellulose cells so strongly that it stays on the fibers even after a period prolonged leaching. Pulp bleached sulfate from of 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 deionized water for 19 hours, the amount adsorbed was 7.4 mg / g

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Example 5

This example shows that the selection of a high temperature and a high concentration of electrolyte in the stage adsorption provide a pulp that has a lower capacity to retention than that obtained if the CMC is adsorbed on the pulp a lower temperature

The experiment was performed by treating a pulp at soft wood sulfate without drying (Metä-Serla / Husum factories) a 23 ° C, 80 ° C and 120 ° C for 12 hours in 0.05M CaCl2 buffered with NaHCO 3 0.001 M. The amount of CMC adsorbed (Finnfix WRH; 20 mg / g) was measured after washing the pulp with 0.01 M HCl, water deionized, adjusting its pH with NaOH to a pH of 8 and balancing it with 0.001M NaHCO3 buffer for 2 hours (Na form). WRV is An abbreviation for "Water Retention Value" according with the definition given above.

Table 10 shows that the increase in WRV by mg / g of adsorbed CMC is considerably lower if the CMC has adsorbed at a higher temperature (120 ° C) than if it has been absorbed at a lower temperature. This is particularly advantageous if it is Easy to remove the water from the pulp on the paper machine. Without However, the pulp's ability to retain water does not reflect the resistance of the paper that has been manufactured from the pulp in consideration.

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TABLE 10

4

Claims (7)

1. Method of modifying cellulose fibers, characterized in that the cellulose fibers are treated for at least 5 minutes with an aqueous solution containing a CMC electrolyte or a CMC derivative, in which - the temperature during treatment is at less than 100 ° C and at least one of the conditions applies following:

TO)

the pH of the aqueous solution during treatment is found within the range of approximately 1.5-4.5, preferably within the region of 2-4; or

B)

the pH of the aqueous solution during treatment is greater than about 11; or

C)

the concentration of the electrolyte in the aqueous solution is found within the range of approximately 0.001-0.5 M, preferably 0.005-0.1 M, if the electrolyte has cations monovalent, or within the range of approximately 0.0002-0.25 M, preferably 0.0005-0.1 M, if the electrolyte has cations divalent

2. Method according to claim 1, characterized in that the pH of the aqueous solution during the treatment is within the range of about 1.5-4.5 and the concentration of the electrolyte in the aqueous solution is within the range range of about 0.001-0.5 M if the electrolyte has monovalent cations, or about 0.0002-0.25 M if the electrolyte has divalent cations. 3. Method according to claim 1, characterized in that the pH of the aqueous solution is greater than 11 and the concentration of the electrolyte in the aqueous solution is within the range of about 0.001-0.5 M if the electrolyte has cations monovalent, or approximately 0.0002-0.25 M if the electrolyte has divalent cations. 4. Method according to claim 1, characterized in that the cellulose fibers are treated for approximately 5-180 minutes. 5. Method according to claim 1, characterized in that the temperature during the treatment is at least about 120 ° C, and preferably up to about 150 ° C. 6. Procedure for the manufacture of paper with a high wet strength, characterized in that - an aqueous suspension of fibers of cellulose; - cellulose fibers are modified accordingly with any one of the preceding claims; Y - wet strength agent is added to the aqueous suspension of cellulose fibers. 7. Method according to claim 6, characterized in that a release agent is also added to the aqueous suspension of cellulose fibers.