WO2005080678A1

WO2005080678A1 - Modifying cellulose fibres by using amphoteric cellulose derivative

Info

Publication number: WO2005080678A1
Application number: PCT/SE2005/000136
Authority: WO
Inventors: Tom Lindström
Original assignee: Stfi, Skogsindustrins Teknisha Forskningsinstitut Ab
Priority date: 2004-02-20
Filing date: 2005-02-03
Publication date: 2005-09-01
Also published as: EP1716288B1; ES2525524T3; EP1716288A1; SE0400396D0

Abstract

The present invention provides a method for the modification of lignocellulosic materials. Cellulose fibres are treated with an aqueous electrolyte-containing solution of an amphoteric cellulose derivative for at least 5 minutes at a temperature of at least 50 °C. The pH during the treatment is approximately 1.5-4.5 or higher than 11; or the concentration of the electrolyte is approximately 0.0001-0.05 M if the electrolyte has monovalent cations, or approximately 0.0002-0.1 M if the electrolyte has divalent cations. Further the invention relates to products obtainable by the above mentioned method and uses of said products for manufacturing paper with a high wet strength and rayon fibres.

Description

Modifying cellulose fibres by using amphoteric cellulose derivative This invention relates to a method for the modification of lignocellulosic materials. Further the invention relates to products obtainable by the above mentioned method and uses of said products.

Background The use of carboxymethyl cellulose, hereafter referred to as "CMC", as dry-strength agent or as an additive during the beating 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. Lindstrόm 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 lignocellulosic 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. In WO 01/21890 a method for the modification of lignocellulosic fiber material is disclosed, which more specifically relates to a method whereby cellulose fibers are treated for at least 5 minutes with an aqueous electrolyte-containing solution (at acidic or basic conditions) of CMC (Carboxy methyl cellulose) or a derivative of CMC, whereby the temperature during the treatment is at least 100 °C (i.e. at relatively high temperatures) 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 0.001 - 0.5 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 further preferable if condition C applies together with either condition A or condition B. Further, results regarding the adsorption of CMC (adsorption conditions: different types of electrolytes, pH, pulp concentration, time, temperature, DS of CMC) are disclosed in Laine, J., Lindstrom, T., Glad Nordmark, G. and Risinger, G. (2000): Studies on Topochemical Modification of Cellulosic Fibres. Part 1. Chemical Conditions for the Attachment of Carboxymethyl Cellulose onto Fibres, Nordic Pulp Paper Res. J. 15(5), 520. The technical effects have also been disclosed in other publications (see Laine, J., Lindstrom, T., Glad Nordmark, G. and Risinger, G. (2002a): Studies on TopoChemical Modification of Cellulosic Fibres. Part 2. The Effect of Carboxymethyl Cellulose Attachment on Fibre Swelling and Paper Strength, Nordic Pulp Paper Res. J. 17(1), 50; Laine, J., Lindstrom, T., Glad Nordmark, G. and Risinger, G. (2002b): Studies on TopoChemical Modification of Cellulosic Fibres. Part 3. The Effect of Carboxymethyl Cellulose Attachment on Wet-strength Development by Alkaline-curing Polyamide-amine Epichlorohydrin Resins, Nordic Pulp Paper Res. J. 17(1), 57; and Laine, J. and Lindstrom, T. (2001): Topochemical Modification of Cellulosic Fibres with Bipolar Activators-An Overview of Some Technical Applications, Int. Papwirtsch. 1 , 40. However the above method, i.e. the one disclosed in WO 01/21890, has some short- comings. It is e.g. difficult to adsorb more than approximately 25 mg/g CMC and then a loading of approximately 40 mg/g CMC must be used (see e.g. a comparative example which is to be found in the example part of the present description). In order to use the above method it would be an obvious advantage if the adsorption is quantitative. It would also be an advantage if a less amount of electrolyte could be used during the pulp treatment as it is desirable in closed mills to minimize leakage of added chemicals. It would thus be desirable if larger addition amounts of CMC could be used, in particular if it is intended to eliminate the beating step during the paper manufacturing. Electric energy is consumed during the beating/refining and the fibers swell during the beating which is a huge disadvantage as the swelling water is not easily pressed away and thus it is necessary to spend more energy during the drying of the paper. Additionally, which is the economically most important factor for the paper manufacturer, the beating strongly limits the production on drying limited paper machines (the latter is the most common).

Summary of the invention

The present invention solves one or more of the above problems and/or limitations by providing according to a first aspect a method for modifying cellulose fibers wherein the cellulose fibers are treated for at least 5 minutes with an aqueous electrolyte-containing solution of an amphoteric cellulose derivative whereby the temperature during the treatment is at least about 50 ^CC, 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 0.0001-0.05 M, preferably approximately 0.001-0.04 M, if the electrolyte has monovalent cations (such as Na₂S0₄) , or in the range of approximately 0.0002-0.1 M, preferably approximately 0.0005-0.02 M, if the electrolyte has divalent cations (such as CaCI₂). It is preferable if condition C applies together of either condition A or condition B. The present invention also provides according to a second aspect a modified lignocellulosic material obtainable by the method according to the first aspect. The present invention also provides according to a third aspect use of the lignocellulosic material of the second aspect.

Detailed description of the invention It is intended throughout the present description that the expression "amphoteric cellulose derivative" embraces any cellulose derivative comprising simultaneously both cationic and anionic moieties. Further said amphoteric cellulose derivative is preferably an amphoteric cellulose derivative which still is net, negatively charged, but comprises a less amount of cationicly active groups. Still further preferred said cellulose derivative is an amphoteric CMC derivative, especially preferred an amphoteric CMC derivative with a preferred molar substitution degree between 0.3 and 1.2, i.e. D.S = 0.3 - 1.2. This CMC derivative may further have been cationized in a, for the skilled person, well known manner to a substitution degree between 0-1.0, preferably 0-0.4. The cationization is preferably performed by the introduction of at least one ammonium function ; most preferred a secondary, tertiary or quaternary ammonium function (or a mixture thereof) into the derivative. The cellulose fibers that may be 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, thermo mechanical, chemo-mechanical and chemo-thermo mechanical 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 amphoteric cellulose derivative 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 viscosity may be approximately 25 -8,000 mPa at a concentration of 4%. The preferred concentration of pulp is approximately 1 - 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. According to a preferred embodiment of the first aspect of the present invention the cellulose fibers are treated for approximately 5 - 180 minutes, a more preferred adsorption period is approximately 10 - 120 min and the most preferred adsorption period is approximately 15 - 60 min. According to a preferred embodiment of the first aspect of the present invention the temperature during the treatment is in excess of approximately 100 °C, preferably at least approximately 120 °C, and most preferred 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 provides according to a preferred embodiment of the first aspect of the present invention a method for manufacturing paper with a high wet strength, wherein -an aqueous suspension of cellulose fibers is produced; -the cellulose fibers are modified according to the first aspect of the present invention; and -wet-strength agent is added to the aqueous suspension of cellulose fibers. A debonding agent may also preferably be added to the aqueous suspension of cellulose fibers. 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" as set out earlier. 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.O2 - 1.5 % and the most preferred concentration is 0.05 - 0.8 %. Wet-strength agents that can be used include all cationic polymeric wet-strength 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 glyoxal polyacrylamide resins. The above method provided for making paper with a high wet strength but low dry strength, can be used, for example, for producing paper structures that are strong when wet and absorbent. What are known as "debonding agents" may be 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. The present invention also provides according to a preferred embodiment of the second aspect of the present invention a paper with a high wet strength obtainable by the preferred embodiment of the method according to the first aspect as set out above i.e. the method for manufacturing paper with a high wet strength. The present invention also provides according to a preferred embodiment of the third aspect of the present invention use of modified cellulose fibers according to the second aspect for the manufacture of rayon fibers. The modified cellulose fibers demonstrate a higher reactivity during subsequent chemical treatments, for example, when manufacturing rayon fibers Preferred features of each aspect of the invention are as for each of the other aspects mutatis mutandis. The prior art documents mentioned herein are incorporated to the fullest extent permitted by law. The invention is further described in the following examples in conjunction with the appended figures, which do not limit the scope of the invention in any way. Embodiments of the present invention are described in more detail with the aid of examples of embodiments and figures, the only purpose of which is to illustrate the invention and are in no way intended to limit its extent.

Short description of the figures Fig 1 shows a comparison between the adsorption of an amphoteric cellulose derivative (CMC A) and pure carboxy methyl cellulose (CMC B) to a bleached, decrilied soft wood sulphate pulp. Figure 2 shows a comparison between adsorption (at different pH-values) of an amphoteric (CMC A) cellulose derivative and pure carboxy methyl cellulose (CMC B) to a bleached, decrilied soft wood sulphate pulp. Figure 3 shows a comparison between adsorption (at different temperatures) of an amphoteric (CMC A) cellulose derivative and pure carboxy methyl cellulose (CMC B) to a bleached, decrilied soft wood sulphate pulp. Figure 4 (comprising Figure 4a and 4b, respectively) shows a comparison between adsorption (at different pH values) of an amphoteric (CMC A) cellulose derivative and pure carboxy methyl cellulose (CMC B) to a bleached, decrilied soft wood sulphate pulp. Examples Example 1 This example shows how the chemical conditions (electrolyte concentration) influence the adsorbed amount of two types of CMC. The used CMC-preparations were on one hand a commercially available preparation Finnfix WRH (Preparation B) with a DS = 0.56 and on the other hand an experimental cellulose preparation A, the origin of both were Noviant, Finland. The experimental cellulose preparation A (CMC A) hade been made through a method comprising the addition of 2,3-epoxi-trimethyl ammonium propane chloride to CMC at slightly elevated temperature and under basic conditions, pH 7-12. This method gives rise to a product which can be summarized as follows:

CMC-O-CH2-CHOH-CH₂-N-(CH₃)3 ⁺ Cl ^" (counter ion)

Thus an amphoteric CMC derivative is obtained by introducing into the CMC a quaternary ammonium function, through the hydroxyl groups of the CMC. The preparation had a substitution degree, with respect to carboxy methyl groups of DS = 0.65 and with respect to cationic nitrogen groups a DS = 0.052. Obviously it is possible to use, instead of said tri- methyl ammonium chloride, a secondary (such as di-methyl amine) or a tertiary amine (or mixtures thereof which also may comprise substances comprising quaternary ammonium functions). By using either of said amines it is possible to obtain a cationic polymer, and as CMC comprises anionic moieties it is thus possible to obtain an amphoteric CMC derivative as set out earlier. The pulp was a bleached long-fibred never-dried soft wood pulp from M-Real/Husum mills. The fine material in the pulp was removed through screening the pulp on a Celleco- filter with the hole diameters of 100 μm. The adsorption experiments were performed at 2% pulp concentration. The totally adsorbed amount of cellulose derivative was determined either through the use of conductometric titration (FinnFix WRH) or through N-determination on the pulp (Antek 7000). The adsorption time was 120 min. and the temperature 120 °C. During a series of experiment the amount of electrolyte was varied (CaCI₂), pH=8.0. The dosage of the cellulose derivative was 40 mg/g. Figure 1 shows how an increased concentration of electrolyte increases the adsorption of the amphoteric cellulose derivative. The adsorption is quantitative at high concentrations of the electrolyte. If pure carboxy methyl cellulose is used then the adsorption becomes weaker to the pulp. It is difficult to adsorb more than 25 mg/g CMC/g fiber at an addition of 40 mg/g. The role of the electrolyte addition is to decrease the repulsion between the negatively charged cellulose and the negatively charged cellulose derivatives. Example 2 This example shows how the chemical conditions (pH) influence the adsorbed amount of two types of CMC. In the experiments the same cellulose derivatives, pulp, pulp cone, and temperature as in example 1 were used. No addition of electrolyte concentration was done in this example but pH was varied between 2.5 and 4.2, the interval where the dissociation degree of the pulps and the cellulose derivatives carboxyl groups is varied. Figure 2 shows how a lower pH increases the adsorption of the amphoteric cellulose derivative. The adsorption is quantitative at lower pH-values than 3.3. If pure carboxy methyl cellulose is used then the adsorption becomes lower to the pulp. It is very difficult to adsorb more than 20 mg/g CMC/g fiber through varying pH at an addition of 40 mg/g of the pure CMC-derivative.

Example 3 This example shows how the temperature influences the adsorbed amount of two types of CMC. In the experiments the same cellulose derivatives, pulp, pulp cone, and adsorption time as in example 1 were used. The experiments were performed at a pH=8 and in an electrolyte of 0.05 M CaCI₂. Figure 3 shows how an increased temperature increases the adsorption. The adsorption becomes quantitative at the highest temperature, 120 °C. The adsorption of the pure CMC is lower than for the amphoteric preparation.

Example 4 The method in the previously known WO 01/21890 is particularly characterized by that a great part of the adsorbed derivative was irreversibly adsorbed to the fibers. This is a distinguishing feature in the above method, which means that you are not only adsorbing a derivative to the fibers but also that you in fact has modified the fibers. The modification also becomes toposelective, depending on the molecular weight of the cellulose derivative. In the referred cases in the above application the toposelectivitity was over 70 %, i.e. more than 70 % of the adsorbed negative (and positive charges for the amphoteric derivative) charges is located on the fiber surface. The toposelectivitity is defined as surface charge determined with high molecular poly-DADMAC, Mw over 1.000.000/total charge determined by conductometric titration. These series of experiments was performed exactly like in example 1 , but in order to determine the irreversibly adsorbed amount of cellulose derivative the pulp was washed after the adsorption with 0.01 M HCI and was transferred to its Na-form in deionized water. After 2 hours of leaching in deionized water, the pulp was washed on a filter with a surplus of deionized water. The amount of irreversibly (not away-washable according to the method) adsorbed CMC was then determined by using conductometric titration. Added amount of cellulose derivative was 20 and 40 mg/g respectively. The results are depicted in Figure 4, showing 4a and 4b respectively. The results show that practically the entire cellulose derivative has been irreversibly adsorbed to the pulp. Various embodiments of the present invention have been described above but a person skilled in the art realizes further minor alterations, which would fall into the scope of the present invention. The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. For example, any of the above- noted methods can be combined with other known methods. Other aspects, advantages and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.

Claims

Claims 1. Method for modifying cellulose fibers, characterized in that the cellulose fibers are treated for at least 5 minutes with an aqueous electrolyte-containing solution of an amphoteric cellulose derivative, whereby the temperature during the treatment is at least 50° 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 0.0001 - 0.05 M, preferably approximately 0.001 - 0.04 M, if the electrolyte has monovalent cations, or in the range of approximately 0.0002 - 0.1 M, preferably approximately 0.0005-O.02 M, if the electrolyte has divalent cations.

2. Method according to claim ^characterized in that condition C applies together of either condition A or condition B. 3. Method according to claim ^characterized in that the amphoteric cellulose derivative is a CMC derivative, preferably with a molar substitution degree between 0.

3 and 1.2. 4. Method according to claim 3, characterized in that the CMC derivative have been cationized to a substitution degree between 0 and 1.0, preferably 0 and 0.

4.

5. Method according to claim 4, characterized in that the cationization has been performed by the introduction of at least one ammonium function, preferably a secondary, tertiary or quaternary ammonium function, into the derivative.

6. Method according to claim 1, characterized in that the cellulose fibers are treated for approximately 5 -180 minutes.

7. Method according to claim ^characterized in that the temperature during the treatment is in excess of approximately 100 °C, preferably at least approximately 120 °C, and most preferred up to approximately 150 ^CC.

8. Method for manufacturing paper with a high wet strength, characterized 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.

9. Method according to claim 8, characterized in that a debonding agent is also added to the aqueous suspension of cellulose fibers.

10. Cellulose fibers obtainable by the method according to any one of claims 1-7.

11. Paper with a high wet strength obtainable by the method according to either one of claims 8 or 9.

12. Use of modified cellulose fibers according to claim 10 for the manufacture of rayon fibers.