MX2007004385A

MX2007004385A - Method of treating cellulose fibres.

Info

Publication number: MX2007004385A
Application number: MX2007004385A
Authority: MX
Inventors: Jan Nordin; Thomas Christopher Greschik; Baltsen Hans-Ake
Original assignee: Akzo Nobel Nv
Priority date: 2004-11-05
Filing date: 2005-09-28
Publication date: 2007-08-14
Also published as: BRPI0517695A; MY144586A; ZA200704416B; KR100915419B1; CA2585892A1; TWI342910B; AR054985A1; RU2341603C1; JP2008519176A; TW200628664A; EP1825053A1; CN101048545A; ES2398361T3; PL1825053T3; WO2006049542A1; AU2005301423B2; JP4684296B2; CA2585892C; NO20072359L; PT1825053E

Abstract

The present invention relates to a method of treating cellulose fibres. The invention further involves the production of paper from said treated fibres and the paper obtainable therefrom. The invention also relates to the use of a cellulose derivative as an additive to an acidic bleaching stage.

Description

METHOD FOR THE TREATMENT OF CELLULOSE FIBERS The present invention relates to a method for treating cellulose fibers. The present invention also relates to the production of paper from said treated fibers and to the paper that can be obtained therefrom. The invention also relates to the use of a cellulose derivative as an additive in an acid bleaching step BACKGROUND OF THE INVENTION In the field of papermaking, various methods are known to improve the strength of paper in the wet state by the retention of wet strength agents in the cellulose fibers in the pulp suspension while the paper is being formed. The wet strength of a paper refers to its ability to maintain its physical integrity and resist breakage, breakage, and tearing in use, especially in wet conditions. An additional important property of paper with greater resistance to moisture is softness, especially in the case of tissue paper or the like. Softness can be described as the tactile sensation perceived when a paper is held or rubbed against the skin. WO01 / 21890 discloses a method for modifying cellulose fibers in order to provide high wet strength to a paper. However this method includes the addition of electrolyte to the suspension of pulp and its treatment at a temperature of at least 100 ° C which restricts the flexibility and use of this process. The present invention has the purpose of offering a simple and efficient method as regards its use of energy to produce paper with a better wet strength and a better softness as well as other beneficial properties provided through the modification of the fibers. It is a further object of the present invention to provide a method that can be used with existing conventional equipment and machines. DISCLOSURE OF THE INVENTION The present invention relates to a method for modifying cellulose fibers, comprising the provision of a suspension of pulp or cellulose fibers, the addition of a cellulose derivative during the bleaching of said cellulose fibers at minus one acid bleaching stage. Preferably, electrolyte is not added in combination with the addition of cellulose derivative, except in the case of the optional addition of acid or base to adjust the pH. The addition of a base or an acid to regulate the pH can be effected in an amount of about 0.001 to about 0.5 M if the electrolyte is monovalent. For example, the addition of Ca2 + or another bivalent electrolyte could in some cases increase the risk of precipitation of calcium oxalate. The equipment used in the The bleaching process can then be capped due to the presence of these electrolyte-derived precipitates since the pulps can naturally contain oxalic acid. The electrolyte, however, does not significantly influence the modification of the fibers. The pH of the pulp suspension in the acid bleaching stage is suitably from about 1 to about 7, preferably from about 2 to about 6, and most especially from about 2 to about 4. The temperature during acid bleaching is appropriately about 30 to about 95 ° C, preferably about 60 to about 90 ° C. Preferably, the dry content of cellulose fiber in the pulp suspension is from about 1 to about 50% by weight, more preferably from about 15 to about about 30% by weight, and most especially from about 5 to about 15% by weight. The bleaching is carried out appropriately for a period of from about 0.1 to about 10 hours, preferably from about 1 hour to about 5 hours, and more preferably from about 1 hour to about 3 hours. The acid bleaching step in which the cellulose derivative is added can be during any of the stages in which the pulp is treated with chlorine dioxide, ozone, peracid, or other stages of Acid bleaching treatment, preferably during treatment with chlorine dioxide. In this context, acid steps integrated in the bleaching process or sequences of acid bleaching stages, such as for example washing steps, acidification, or acid chelation steps can also be included in the bleaching treatment during which time it can be added a cellulose derivative. It has been found that the adsorption of cellulose derivative onto cellulose fibers, particularly the adsorption of CMC into fibers results in a significantly increased surface charge compared to untreated CMC wood fibers. This may be the explanation why the wet strength of a paper produced from the CMC treated pulp where CMC was added in an acid bleaching step was significantly improved as well as the relative wet strength when subsequently a wet strength agent to the primary paper pulp in a papermaking process. The present method can therefore also provide improved softness properties of the paper produced. The softness of a sheet of paper can be estimated, at least indirectly, through the resistance value in relative wet state, which is defined as the ratio between the wet state tension index and the dry state stress index according to the formula RWS (in%) = (WS / DS) * 100, where RWS represents the relative wet strength, WS is the tension index in wet state and DS is the index of tension in dry state of a paper. RWS is often a good measurement of the softness of a paper; The higher the RWS, the higher the softness of the paper. The modification with cellulose derivative can also influence the effect of any subsequent addition of paper chemicals to the primary pulp that can in turn influence both the necessary dosage of paper chemicals to the primary pulp and the quality of the paper product obtained. It has also been observed that the sizing, retention and removal of water can be improved as a result of the modified cellulose fibers in the papermaking process. Any additional paper chemical suitable for paper production can be added to the primary pulp pulp containing the bleached cellulose fibers modified. Such chemical agents may include, for example, dry strength agents, wet strength agents, retention agents, sizing agents, etc. Cellulose fibers can be derived from any type of material based on soft wood or based on hard wood, or non-wood based, for example in sulphite, sulphate or soda pulp, pre-milled, semi-milled, or unbleached, or else mechanical, thermomechanical, chemomechanical, chemothermomechanical, unbleached, semi-milled pulps or prebleached, and mixtures thereof. As examples of non-wood materials we can mention, for example, bagasse, kenaf, plant fibers, sisal or the like. The cellulose derivative, preferably an alkylcellulose derivative, and more preferably a carboxymethylcellulose derivative, and more preferably a carboxymethylcellulose derivative, is soluble in water, or at least partially soluble in water or dispersible in water, preferably soluble in water or at least partially soluble in water. Preferably, the cellulose derivative is ionic. The cellulose derivative can be anionic, cationic or amphoteric, preferably anionic or amphoteric. Examples of suitable cellulose derivatives include cellulose ethers, for example, cellulose, anionic, and amphoteric ethers, alkaline cellulose, cellulose-metal complexes, copolymer cellulose grafted preferably anionic cellulose ethers. The cellulose derivative preferably has ionic or charged groups, or substituents. Examples of suitable ionic groups include groups anionic and cationic. Examples of suitable anionic groups include carboxylate, for example, carboxyalkyl, sulfonate, for example sulfoalkyl, phosphate and phosphonate groups wherein the alkyl group can be methyl, ethylpropyl and mixtures thereof, preferably methyl; suitably, the cellulose derivative contains an anionic group comprising a carboxylate group to, for example, a carboxylalkyl group. The counter-ion of the anionic group is usually an alkali metal or an alkaline earth metal, suitably sodium. Examples of suitable cationic groups of cellulose derivatives according to the present invention include salts of amines, suitably salts of tertiary amines, and quaternary ammonium groups, preferably quaternary ammonium groups. Substituents fixed on the nitrogen atom of amines and quaternary ammonium groups can be the same or different and can be selected from alkyl, cycloalkyl, and alkoxyalkyl groups, and one, two or more of the substituents together with the nitrogen atom can form a ring heterocyclic The substituents, independently of one another, usually comprise from 1 to about 24 carbon atoms, preferably from 1 to about 8 carbon atoms. The nitrogen of the cationic group can be fixed on the cellulose or derivative thereof through a chain of atoms comprising preferably carbon and hydrogen atoms, and optionally 0 and / or N atoms. Typically, the chain of atoms is an alkylene group having 2 to 18 carbon atoms, preferably 2 to 8 carbon atoms, optionally interrupted or substituted by one or several heteroatoms, for example, 0 or N such as, for example, alkyleneoxy group or hydroxypropylene group. The cellulose derivatives containing cationic groups include those obtained by the reaction of cellulose or cellulose derivative with quaternization agent selected from 2,3-hydroxypropyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride and mixtures thereof. the same. The cellulose derivatives of this invention can contain nonionic groups such as for example alkyl or hydroxyalkyl groups for example, hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl and mixtures thereof, for example, hydroxyethylmethyl, hydroxypropylmethyl, hydroxybutylmethyl, hydroxyethylethyl, hydroxypropyl and the like. In a preferred embodiment of the invention, the cellulose derivative contains both ionic and nonionic groups. Examples of suitable cellulose derivatives according to the present invention include carboxyalkyl celloses, such as, for example, carboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl cellulose, sulfoethyl carboxymethyl cellulose, carboxymethyl hydroxyethyl cellulose ("CM-HEC"), carboxymethyl cellulose wherein the cellulose is substituted by one or more non-ionic substituents, preferably carboxymethyl cellulose ("CMC"). Examples of suitable cellulose derivatives and methods for their preparation include those disclosed in U.S. Patent No. 4,940,785, which is incorporated herein by reference. In the terms "degree of substitution" or "DS", as used herein, refer to the number of ring sites substituted for the beta-anhydroglucose rings of the cellulose derivative. Since there are three hydroxyl groups in each cellulose anhydrocide ring that are available for substitution, the maximum value of DS is 3.0. According to a preferred embodiment of the invention, the cellulose derivative has a degree of substitution of net ionic groups ("DSNI") of up to about 0.65, that is, the cellulose derivative has an average degree of net ionic substitution per unit. of glucose of up to about 0.65. The net ionic substitution can be net anionic, net cationic or net neutral. When the net ionic substitution is a net anionic substitution, there is a net excess of anionic groups (net anionic groups = the average number of anionic groups minus the average number of cationic groups, if any, per glucose unit) and DSNI is the same as the degree of substitution of net anionic groups ("DSNA"). When the net ionic substitution is a net cationic substitution, there is a net excess of cationic groups (net cationic groups = the average number of cationic groups minus the average number of anionic groups, if any, per unit of glucose) and DSN? it is the same as the degree of substitution of net cationic groups ("DSNC"). When the net ionic substitution is net neutral, the average number of anionic and cationic groups, if any, per glucose unit is the same, and DSN? as DSNA and DSNC are 0. According to another preferred embodiment of the invention, the cellulose derivative has a degree of substitution of carboxyalkyl groups ("DSCA") of up to about 0.65, ie, the cellulose derivative has an average degree of carboxyalkyl substitution per glucose unit of up to about 0.65. The carboxyalkyl groups are suitably carboxymethyl groups and, then, DSCA is the same as the degree of substitution of carboxymethyl groups ("DSCM") - According to these embodiments of the invention, DSN ?, DSNA, DSNC and DSCA, independently of each other, are usually up to about 0.60, suitably up to about 0.50, preferably up to about 0.45 and most preferably up to 0.40, while DSN ?, DSNA, DSNC and SCA, independently of each other, are usually at least 0.01, suitably at least about 0.05, preferably at least about 0.10, and more preferably at least about 0.15. The DSN ?, DSNA, DSNC and DSCA ranges, independently from about from about 0.01 to about 0.60, suitably from about 0.05 to about 0.50, preferably from about 0.10 to about 0.45, and more preferably from about 0.15 to about 0.40. Cellulose derivatives that are anionic or amphoteric usually have an anionic substitution degree ("DS") within a range of 0.01 to about 1.0, to the extent that DSN? and DSNA are in accordance with what is defined here; suitably about 0.5, preferably about 0.10, and more preferably about 0.15, and suitably up to about 0.75, preferably up to about 0.5, and most preferably up to about 0.4. Cellulose derivatives that are cationic or amphoteric may have a degree of cationic substitution ("DSC") within a range of 0.01 to about 1.0, to the extent that DSNI and DSNC are in accordance with the definition herein; suitably about 0.02, preferably about 0.03, and more preferably about 0.05, and suitably about 0.75, preferably about 0.5, and most preferably about 0.4. The cationic groups are adequately quaternary ammonium groups and then DSC is the same as the degree of substitution of quaternary ammonium groups ("DSQN"). For amphoteric cellulose derivatives of this invention, DSA or DSC can evidently be greater than 0.65 insofar as DSNñ and DSNC, respectively, are in accordance with what is defined herein. For example, if DSA is 0.75 and DSC is 0.15, then DSNA is 0.60 The water soluble cellulose derivatives suitably have a solubility of at least 85% by weight, based on the total weight of dry cellulose derivatives, in a aqueous solution, preferably at least 90% by weight, more preferably at least 95% by weight and more preferably at least 98% by weight. The cellulose derivative usually has an average molecular weight that is at least 20,000 Daltons, preferably at least 50000 Daltons, and up to about 1000000 Daltons, preferably up to about 50000 Daltons. The cellulose derivative is suitably added in an amount of from about 0.5 to about 50 kg / t, preferably from about 5 to about 20 kg / t, and more preferably from about 5 to about 10 kg / t of dry cellulose fibers. The invention also relates to a paper that can be obtained through a method comprising the removal of water in a mesh in a pulp primary of modified bleached cellulose fibers produced in accordance with a method described herein and forming a paper with said primary pulp with water removal. Having described the invention, it is evident that said invention can have numerous variations. Such variations should not be considered as departing from the essence and scope of the present invention and all modifications that would be apparent to a person skilled in the art are included within the scope of the claims. The following examples will further illustrate how the described invention can be effected without limiting its scope. If not stated otherwise, all parts and percentages refer to parts by weight and percentage by weight. EXAMPLES The purpose of the experiment was to adsorb CMC in fibers in a final acid bleaching stage, which in this case was in a chlorine dioxide stage. Even when it is not necessary, calcium chloride was used to improve adsorption. The pulp used was a five-stage, full-gloss elemental chlorine-free bleached softwood pulp having a final gloss of 90% ISO. A reference pulp was treated as pulp modified by CMC according to the present invention but without CMC loading. The final stage of chlorine dioxide was carried out at a temperature of 80 ° C for 180 minutes at a pulp consistency of 10% by weight. The chemical loads were: 10 kg / t of chlorine dioxide, as active chlorine 7 kg / t, kg / t of calcium chloride calculated as Ca2 + based on the weight of the dried pulp. The final pH of the chlorine dioxide stage was 2.8. The CMC used was Finnfix WRH from Noviant. The degree of substitution was 0.5 and the molecular weight 1 * 106. The wet strength agent Kenores de XO was added to a load of 15 kg / t dry pulp to the bleached pulp suspension. The resistance properties of the pulp treated with CMC were evaluated with different degrees of shake (° SR): The shake was carried out in a PFI blender at laboratory scale. The resistance properties of the pulp treated with whipped CMC were compared to the beaten reference pulp not treated with CMC and with a pulp to which CMC was added to the pulp suspension after bleaching. The analyzed pulp had a final gloss of 90% ISO and had been bleached with a final stage of chlorine dioxide (laboratory scale). Diagram 1 ° SR vs Resistance in the Humid State ßSR As can be seen from diagram 1, wet strength rises strongly when CMC has been adsorbed in a final stage of chlorine dioxide compared to the addition of CMC to the raw material or without the addition of CMC. Here, the increase in wet strength within the paper produced was up to 65%. Diagram 2 Relative Resistance in Wet State vs ° SR In diagram 2, RWS (relative strength in wet state) is plotted versus ° SR for adsorbed CMC in the final stage of chlorine acid dioxide and addition of CMC to the raw material in the papermaking process as well as a reference without addition of CMC. As is evident from diagram 2, the RWS is considerably increased in a paper obtained by the addition of CMC to the chlorine acid dioxide stage.

Claims

CLAIMS 1. A method for modifying cellulose fibers, said method comprises the supply of a pulp suspension of cellulose fibers, the addition of a cellulose derivative during the bleaching of said cellulose fibers in at least one acid bleaching stage.
2. The method according to claim 1, wherein the cellulose derivative is added in a final stage of acid bleaching.
3. The method according to any of claims 1-2, wherein the cellulose derivative is a carboxyalkyl cellulose.
4. The method according to any of claims 1-3, wherein the cellulose derivative is carboxymethyl cellulose.
5. The method according to any of claims 1-4, wherein the final stage of acid bleaching is a chlorine dioxide stage.
6. The method according to any of claims 1-5, wherein the cellulose derivative is added in an amount of about 0.5 to about 50 kg / t of dry cellulose fibers.
The method according to any of claims 1-6, wherein the dry content of the cellulose fibers in the suspension is about 1 to about 50% by weight.
8. The method according to any of claims 1-7, wherein a wet strength agent is subsequently added to a suspension of bleached pulp.
The method according to any of claims 1-8, wherein a dry strength agent is subsequently added to a suspension of bleached pulp.
10. The method according to any of claims 1-9, wherein the final bleaching step is carried out at a pH of about 2 to about 4.
11. A paper production method comprising supplying a suspension of bleached pulp according to any of claims 1-10, removal of water in said pulp suspension in a mesh and formation of a paper in said pulp suspension with removal of water.
12. A paper that can be obtained by the method according to claim 11.
13. The use of a cellulose derivative as an additive to a suspension of cellulose fibers treated in an acid bleaching stage.
14. The use of a cellulose derivative according to claim 13, wherein the bleaching step is a step of chlorine acid dioxide.