EP3137507A1

EP3137507A1 - Composition comprising cellulose fibres and crosslinking agents, water soluble crosslinked cellulose ethers, and the production thereof

Info

Publication number: EP3137507A1
Application number: EP15721122.8A
Authority: EP
Inventors: Ove Bartholsen; Hans Henrik ØVREBØ
Original assignee: Borregaard AS
Current assignee: Borregaard AS
Priority date: 2014-05-02
Filing date: 2015-04-29
Publication date: 2017-03-08
Also published as: WO2015165588A1

Abstract

The present invention relates to a composition comprising cellulose fibres and crosslinking agent(s) and process for the preparation thereof. The invention further relates to water soluble crosslinked cellulose ethers obtainable from a composition comprising cellulose fibres and one or more crosslinking agent(s) and the manufacture thereof.

Description

COMPOSITION COMPRISING CELLULOSE FIBRES AND CROSSLINKING AGENTS, WATER SOLUBLE CROSSLINKED CELLULOSE ETHERS, AND THE PRODUCTION

THEREOF

Field of the Invention The present invention relates to cellulosic fibrous products, and more particularly to a composition comprising cellulose fibres and one or more crosslinking agent(s), and a process for the preparation thereof. The cellulose fibrous products are useful in the production of various cellulose based products, and in particular in the production of cross- linked cellulose derivatives, specifically cellulose ethers. The present invention further relates to crosslinked cellulose derivatives and the production thereof from a composition of cellulose fibres and crosslinking agent(s).

Background and Objective of the Invention

The fundamental principles for manufacturing cellulose and cellulose derivatives, in particular cellulose ethers and cellulose esters, are known in the art. For example, in order to manufacture cellulose ethers, typically an alkali metal hydroxide solution is used to pre-treat and activate the cellulose before derivatization by etherification. The etherifica- tion is then typically performed with one or more alkyl halides and/or alkylene oxides and/or alkylating reagents having ionic functionalities, e.g. carboxylic residues such as halogen substituted carboxylic acids, e.g. chloroacetic acid or it's sodium salt.

For example, crosslinking of cellulose may be performed in the finishing process of cot- ton fabric with the objective to provide wrinkle resistance. Crosslinked cellulose fibres are also used in other consumer articles, such as disposable diapers, to improve the absorption capacity and in paper towels to improve the "wet strength". Crosslinked cellulose ethers are also used in pharmaceutical applications for controlled release of drugs. These examples of crosslinking of cellulose ethers frequently result in non- (or poorly) water soluble cellulose ethers, since the degree of crosslinking is high.

Exemplary cellulose ethers of particular commercial interest are: sodium carboxymethyl cellulose, methyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, ethyl cellulose, and mixtures of at least two components thereof. These cellulose ethers, and others, are useful in a wide range of household and industrial products such as construction materials, cosmetics, foods, coatings, paints, binders and controlled-release pharmaceuticals, e.g. for their properties as viscosity modifiers, water retention agents, film forming agents, foaming agents and/or binding agents. Although a wide range of cellulose raw materials can be used, two preferred raw materials for production of cellulose ethers are purified wood pulp (often denoted speciality cellulose) and cotton linters pulp. The properties of cellulose ethers are characterised by several parameters, wherein water retention capacity, viscosity and shear thinning of their solutions are particularly relevant parameters. Among others, specifically these pa- rameters may be advantageously affected by crosslinking the cellulose ether.

US 2,148,952 (E.I. du Pont de Nemours & Co.) discloses that soluble cellulose ethers of high viscosity may be prepared by reacting the cellulose with a monofunctional etherify- ing agent and a limited quantity of a Afunctional etherifying agent. Epichlorohydrin is used as bifunctional agent. The products produced are described as having extremely high viscosity with a tendency to form gels, and even to form a stiff paste. Hence, this publication demonstrates that achieving water soluble cellulose ethers with controlled and increased viscosity is challenging. US 4,321 ,367 (The Dow Chemical Company) describes preparation of crosslinked polysaccharide ethers such as cellulose ethers crosslinked with polyhalohydrocarbon entities such as 1 ,2-dichloroethane, 1 ,3-dibromopropane and 1 ,4-dichlorobutane. Tables I and II therein show that all products contain amounts of solid materials. US 6,958,393 (Wolff Cellulosics GmbH & Co. K.G.) describes cellulose derivatives such as cellulose ethers crosslinked with a crosslinking agent. The products are described as having gel-like rheological properties in aqueous solution. The crosslinker used by the inventors is epichlorohydrine, which is a reagent of high reactivity that forms rather short crosslinks and is known to lead to poorly soluble cellulose ether products.

JP 2004155806 (Shinetsu Chemical Co.) teaches crosslinked cellulose ethers where named crosslinkers used are e.g. ethylene glycol diglycidyl ether and propylene glycol diglycidyl ether. The crosslinked cellulose ethers are held to be excellent in salt re- sistance, have tackiness and biodegradability, and are feasible for use as additives to absorbent material to increase the absorption power and water holding capacity. The crosslinked products appear to contain solid material, since Table 1 (4^th and 7^th column) show that the viscosity decreases with the amount crosslinker added.

WO 2008/034176 (Ultraceuticals R&D PTY Ltd.) describes crosslinked gels of hyaluronic acid where the crosslinker is 1 ,4-butanediol diglycidyl ether and where a masking agent (e.g. glycidol) is preferably added. The objective is to produce hyaluronic acid gels for pharmaceuticals or cosmetic use, that are resistant to hyaluronidase degradation under physiological conditions.

WO 2009/127605 (Akzo Nobel N.V.) aims to produce cellulose ethers with an increased viscosity in aqueous solutions by the use of phosphate crosslinking agents. A disadvantage of using phosphate crosslinking agents is that the phosphonate ester linkages that are created between the cellulose backbones, are more labile to alkali and acidic environment than ether linkages.

US 2006/0142561 (Weyerhaeuser) discloses the manufacture of carboxyalkyl cellulose which may be crosslinked in a subsequent step. It is known from the art, in principle, that crosslinked cellulose derivatives such as cellulose ethers have useful rheological properties such as enhanced viscosity, improved water retention capacity and improved shear thinning properties. For example, the viscosity of a solution of cellulose ethers is mainly determined by the degree of polymerisation of the cellulose raw material. Other parameters affecting the viscosity of cellulose ether solutions are the manufacturing conditions of the cellulose ethers, as well as type and amount of the substituted ether groups. As of the application date, the raw material with the highest degree of polymerisation available appears to be cotton linters pulp. Use of wood pulp as raw material for cellulose derivatives is beneficial from several aspects, like cost, availability, and for avoiding the use of genetically modified raw material.

For many industrial applications, use of high molecular weight cellulose derivatives such as cellulose ethers with high solution viscosity is beneficial, e.g. in order to lower the amount of cellulose ethers needed in a given application, for example for special applications, such as paints and paper coating, and for control of the hydration rate. Therefore, for more than half a century, there have been efforts within this industry to find technical solutions to increase the viscosity of solutions of cellulose derivatives. These efforts include grafting of hydrophobic groups onto the cellulose ether backbones as well as various attempts to crosslink cellulose ether molecules with each other. It is, however, expensive to produce cellulose ethers with grafted hydrophobic groups as the reaction yield of the hydrophobic groups is low and high reaction temperatures are needed. Also, the cellulose ethers with grafted hydrophobic groups do not necessarily provide in- creased viscosity in solutions containing surface-active components.

Another approach to increase the viscosity in solution of cellulose ethers is to crosslink the cellulose ethers. However, the industrial scale production of crosslinked cellulose derivatives is challenging. One common problem is that crosslinked cellulosic ethers are not uniform and may contain non-homogenous areas and/or hard lumps, both when the product is in solid form or in soluble or gel form. Such lack of uniformity is generally unwanted.

The lack of uniformity is especially pronounced for crosslinked cellulose ethers produced by the so-called semidry process. In the industry, processes for making cellulose deriva- tives are typically performed using either slurry processes with an excess of diluting and dispersing organic solvents or semidry processes using a high solids content and low amount of liquid media. A particularly suitable kind of reactor for this "semidry" process is a Lodige® reactor as known in the art wherein the level of solvent is typically low. Such "semidry" processes are commonly used to produce cellulose ethers like methyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, hydroxypropyl cellulose and ethyl cellulose. Without wishing to be bound by theory, the lack of uniformity often encountered in these processes may be caused by concentration gradients of the crosslinker(s) in the cellulose matrix or in the cellulose pulp, which may occur when low amounts of crosslinker(s) are mixed with the cellulose. At industrial scale, it is challenging to avoid such a lack of uniformity, resulting in low quality crosslinked cellulose ether.

Production of crosslinked cellulose derivatives is also challenging when using a slurry process, which is often used to produce the cellulose derivatives sodium carboxymethyl cellulose and hydroxyethyl cellulose, wherein the cellulose fibres are dispersed in a relatively large volume of diluting solvent as reaction medium. The challenge is based on the fact that the added crosslinker will be dispersed or dissolved in a relatively large volume of solvent, which may result in unwanted side reactions and a significantly reduced level of crosslinks in the obtained cellulose ether.

Several attempts to solve the problem of producing uniformly crosslinked cellulose products have been proposed. Hamed et al. propose, in US 2003/0230391 , the addition of a surfactant to facilitate addition of a non-water soluble crosslinker to cellulose fibres. However, this solution is not feasible unless the end product is allowed to also contain surfactants as impurities, which is not the case for many applications.

As understood from the prior art discussion above, attempts have been made to crosslink cellulose or cellulose derivatives to provide cellulose products with desired properties. For cellulose ethers, crosslinking with the purpose of adjusting, e.g., the solution viscosity of cellulose has, however, resulted in products with undesired properties such as products with uneven/ non homogeneous appearance, products with too high viscosity, and products with poor water solubility. In particular in applications in solution, for example as viscosity modifiers, water retention agents, stabilisers and similar, non-water soluble ethers are usually undesirable. It is also important that the cellulose derivative products are stable, i.e. that the crosslinking entities are not broken during storage and during the respective use e.g. as viscosity modifiers.

Overall, there is a great demand in the market place for water soluble cellulose deriva- tives with improved rheological properties, and to obtain such cellulose derivatives from a variety of easily available cellulose raw material.

The cellulose starting materials in the form of cellulose fibres used to produce cellulose ethers are usually obtained from cellulose pulp manufacturers. The cellulose fibres are provided in the form of a web, sheet or roll, or in fluff form, in particular in the form of cellulose sheets.

Weyerhaeuser discloses in US2002/0031971 (WO 00/65146) that crosslinked cellulose fibres have a relatively low strength and cannot easily be transported in rolled form. Weyerhaeuser therefore proposes to avoid the transport problem by providing crosslink- able cellulosic fibrous product containing cellulose fibres and a crosslinking agent, which can be transported in rolled or sheet form. The crosslinkable fibrous product can then be converted to the crosslinked cellulosic product, e.g. by heating the cellulose with the applied crosslinker at the production site.

Cellulose to be etherified and optionally crosslinked is frequently provided in sheets or rolls to the manufacturer of cellulose derivatives such as cellulose ethers. It would be a benefit for the producers if the producers could use their standard production equipment for the production of cellulose ethers in the production of crosslinked cellulose ethers. However, as explained above, this may not be possible due to the challenge of achieving sufficient mixing of the added crosslinking agent in the cellulose fibrous product. Furthermore, it would be beneficial to avoid additional reaction steps in the etherification process, e.g. an additional step where the cellulose fibrous product is reacted with the crosslinking agent. Still further, it would simplify the production for the cellulose derivative producer to be provided with a cellulose product that can be processed according to the same established procedures, irrespective of whether the cellulose is to be crosslinked or not.

In particular, one objective is that the crosslinked ethers should be capable of being pro- cessed, at an industrial scale, in a similar or the same way as used when producing non- crosslinked product. Preferably, the equipment used for producing non-crosslinked cellulose ethers should also be used for production of the crosslinked ethers.

Another object of the present invention is to provide crosslinked cellulose derivatives such as ethers that are water soluble, and have increased viscosity and/or other desirable Theological properties compared to the corresponding non-crosslinked cellulose ethers, when the cellulose ethers are in solution, thus to provide crosslinkable cellulose products in the form of a composition of one or more crosslinking agent(s) and cellulose fibres, and method for its production, and to provide essentially water soluble crosslinked cellulose ethers that can be produced from a cellulose fibrous starting material in an easy, controllable and versatile manner.

Summary of the Invention

In accordance with the present invention, it has been surprisingly realized that by applying a comparatively low amount of crosslinking agent(s), in a uniform manner, to the cellulose material from the pulping process (i.e. prior to any derivatization, in particular etherification), improved and valuable starting materials are provided for the further processing to crosslinked cellulose ethers.

Accordingly, the present invention relates to cellulosic fibrous products, and more particular to a composition comprising cellulose fibres and one or more crosslinking agent(s), and a process for preparation thereof.

The cellulosic fibrous product is a crosslinkable cellulosic product, meaning that the product contains substantially no covalent bonds between the cellulose fibres and the crosslinking agent(s). The cellulose fibrous products according to the invention are useful in the production of various cellulose based products, and in particular in the production of crosslinked cellulose derivatives, specifically cellulose ethers.

Thus, the present invention further relates to crosslinked cellulose derivatives and the production thereof from a composition of cellulose fibres and crosslinking agent(s). More specifically, the crosslinked cellulose derivatives are crosslinked cellulose ethers and contain substantially no solid particles, or only a small amount of solid particles. The eel- lulose ethers are therefore predominantly, preferably essentially in water soluble form. The crosslinks in the crosslinked cellulose ethers are substantially covalent bonds formed between the hydroxyl groups of the anhydroglucose (AGU) of the backbones of the cellulose fibres, and a binding site of the crosslinking agent. Other bonds such as e.g. hydrogen bonds are usually also present to a certain extent in the crosslinked product according to the invention.

Cellulose ethers according to the invention relate to cellulose in which the hydroxyl (OH) groups of said cellulose AGU units have been partially or fully reacted with chemical rea- gents to substitute the proton of substantially all or of some of said hydroxyl groups.

In the present invention, cellulose fibres relate to cellulose that has been processed and dried in a device typically used in the cellulose pulp industry. Overall, the composition of cellulose fibres and crosslinking agent(s) according to the invention is a crosslinkable cellulosic fibre material. The cellulose fibres are in dried or partly dried form and may be in the form of a web, sheet or roll, or in fluff form. Crosslinking agent(s), also denoted "crosslinkers" or "linkers", are chemical entities which, in the context of the present invention, are capable of cellulose fibre crosslinking. Specifically, at least one of the objects addressed above is achieved with a composition comprising cellulose fibres and at least one crosslinking agent, and with crosslinked cellulose ethers being obtainable from a composition comprising cellulose fibres and at least one crosslinking agent. The manufacture of the composition and use of the composition in the manufacture of cellulose derivatives is also included, as well as a process for the production of crosslinked cellulose ethers.

According to a first aspect, the present invention relates to a composition comprising cellulose fibres and at least one crosslinking agent of Formula (I) below, wherein the composition has a solvent content of less than 20 weight%, and wherein substantially no covalent bonds are formed (including: have been formed) between the cellulose fibres and the crosslinking agents. Said composition is defined in independent claim 1 and claims 2 to 10 depending thereon. According to a second aspect, the present invention relates to a process for the manufacture of the composition according to the first aspect. Said process is defined in independent claim 1 1 and claims 12 to 14 depending thereon.

According to a third aspect, the present disclosure describes water soluble crosslinked cellulose ethers obtainable from a composition comprising cellulose fibres and one or more crosslinking agent(s), preferably a composition according to the first aspect of the invention.

According to a fourth aspect, the present invention relates to the use of a composition as defined in the first aspect in the manufacture of the water soluble crosslinked cellu- lose ethers as defined in the third aspect. Said use is defined in independent claim 15 and claim 16 depending thereon.

According to a fifth aspect, the present invention relates to a process for the manufacture of crosslinked cellulose ethers as defined in the third aspect. Said process is de- fined in independent claim 17 and claim 18 depending thereon.

Brief description of the Figures

Figures 1 to 3 show "flow curves" for crosslinked and non-crosslinked cellulose ethers in terms of viscosity η as a function of shear rate 7.

Detailed Description of the Invention First Aspect of the Invention

Composition comprising cellulose fibres and at least one crosslinking agent as defined in claims 1 to 10

The composition of the invention contains no or only a non-substantial amount of cova- lent bonds between the crosslinking agent(s) and the cellulose fibres and may therefore be denoted a "crosslinkable composition" . However, due to the nature of the cellulose fibres and the crosslinker, the crosslinker may form hydrogen bonds with the cellulose backbones, in the state as described in the composition according to the invention (crosslinker physically admixed with the cellulose fibers). In particular, said composition contains no or only limited amounts, in particular not more than 10 weight %, preferably not more than 5 weight %, more preferably not more than 2 weight %, in particular not more than 1 weight % of cellulose fibers in crosslinked form, based on the total amount of cellulose fibres. In a particularly preferred embodiment, said composition contains substantially no cellulose fibres in crosslinked form, i.e. the number of such covalent bonds is approaching 0%.

This composition of the cellulose fibres and the crosslinking agent(s), in accordance with the present invention, is useful as starting material for the production of crosslinked cellulose products, in particular in the production of crosslinked cellulose ethers, preferably water soluble cellulose ethers.

Throughout this disclosure, the terms shown in italics and in quotation marks are defined to be" in accordance" with the present invention.

The term "cellulose" encompasses any type of cellulose. No restrictions exist in regard to the type of cellulose that can be used in the composition and process according to the present invention.

As cellulose raw material for the present invention, main sources for cellulose ethers are cotton linters pulp and wood pulp. However, other sources like cellulose from fruit or vegetable origin, such as citrus, orange, lemon or tomato, cellulose from agricultural waste such as bagasse, and the like, cellulose from annual plants or energy crops, or cellulose with bacterial origin may also be used as the cellulose raw material. These types of cellulose are known in the art and any mixture of these or others may be used.

Preferred sources of cellulose are fibres derived from cotton linters pulp and either hard- wood or softwood pulps, or mixtures thereof. The pulping operation is preferably a sulphite or a Kraft process. Particularly preferred is cellulose derived from cotton linters pulp and from softwood pulp, in particular from spruce, from a sulphite pulping process. The cellulose from the cellulose pulping operation is further treated, preferably by washing and bleaching steps as required from a utility point of view, and may be partially de- watered and dried to the desired cellulose fibre and solvent content, and may be provided in the form of a web, sheet or roll, or in fluff form, the fluff form preferably being dried as loose fibres, more preferably delivered compressed into bales. In a preferred embodiment, the cellulose fibre and solvent content is provided in the form of a web or sheet.

To ensure stability, storability and ease of transportation, the composition comprising the cellulose fibres and one or more crosslinking agent(s) is dried to reach a suitable solvent content that should be below about 20 weight% based on the weight of the dried finished composition, preferably to less than 10 weight%, and particularly preferred from 6 to 8 weight.%, preferably wherein the solvent is water or comprises water.

The term "solvent means any solvent used in the process of producing the cellulose fi- bres as such, as well as any solvent that is used in the process of producing the claimed composition. Preferably, the solvent will consist predominantly of water.

The term "cellulose fibre" in accordance with the present invention relates to cellulose fibres that may also contain minor amounts of other substances, e.g. from the raw mate- rial such as lignin and hemicelluloses, and chemicals added and products formed during the pulping process such as lignosulfonates and sulfuric acid. Hence, the expression "cellulose fibre content' also includes cellulose fibres and minor amounts of other substances. The cellulose fibre content is frequently also denoted the "dry content of the cellulose fibre sheets. A suitable process is e.g. known from WO 2004/003290 A1 (EP 1 18 018 B1 ) and reference is made to this application, in this context, in particular in regard to cellulose fibers and dry content.

The cellulose fibres are preferably in the form of a web, sheet or roll, or in fluff form, more preferably in the form of cellulose sheets and are usually in a "dried" form such that the claimed composition formed from the cellulose fibres and the crosslinking agent has a solvent content of less than 20 weight%, as outlined above. In a further embodiment, the crosslinkable cellulosic fibrous product material comprising the composition of cellulose fibres in the form of a web, sheet or roll, or in fluff form, and the crosslinking agent(s), preferably has a cellulose fibre content of at least 80 weight%, and at least one crosslinking agent and a solvent.

The term "crosslinker(s)/crosslinking agent(s)" as used in accordance with the present invention relates to one or more crosslinking agent(s), unless specified otherwise. The expressions crosslinking agent(s) and crosslinker(s) are used interchangeably, herein. The crosslinking agent(s) are applied to the cellulose fibres to obtain the composition of cellulose fibres and crosslinking agent(s). Most preferably, one selected crosslinker is applied. The crosslinking agent(s) selected from the compounds of Formula (I) must be capable of forming covalent bonds between the carbohydrate polymer backbone of an- hydroglucose units (AGU) of cellulose, by reacting with the functional groups of the cellu- lose backbone (hydroxyl groups), when the cellulose fibres containing the crosslinking agent(s) are exposed to crosslinking reaction conditions (in subsequent step). However, substantially no such crosslinking should take place when the composition of cellulose fibres and crosslinking agent(s) according to the present invention is transported and stored under normal conditions, i.e. at temperatures typically from 0°C to 30°C and at moderate humidity (less than 60%, preferably less than 40%) as typically ensured in industry and transport operations settings. In particular, such "normal" conditions also imply the absence of reactive chemicals, in particular hydroxides.

In the present invention, where the process of forming the composition of the cellulose fibres and the crosslinking agent(s) is performed most conveniently in an aqueous solution, it is preferred that the at least one crosslinker is soluble or at least dispersible in water.

Furthermore, the crosslinking agent(s) should be stable and sufficiently reactive when exposed to the crosslinking conditions, e.g. when exposed to the strong alkali used to pre-treat the cellulose with the crosslinking agent(s) prior to the etherification reaction. The crosslinking agent(s) should also have acceptable toxicity both as reagent and in the final cellulose fibrous product. Crosslinking agent(s) that are suitable for performing the crosslinking reaction in the same stage as the derivatization reaction is/are preferred, since such compounds may render superfluous the need of a subsequent (separate) etherification step in the manufacture of the final cellulose product.

In principle, any crosslinking agent known in the art to be capable of crosslinking cellulose may be used within the ambit of the subject invention.

In one embodiment, the at least one crosslinking agent is selected from the group of compounds of Formula (I):

X-Y-X

Formula (I) wherein both X are the same and denote halogen atoms, alkene groups, epoxide groups or glycidyl ether groups, and Y denotes a C-i-C₁₄ straight or branched alkylene group, which may be interrupted by O, carbonyls, NH and/or S entities and/or may contain a C3- C₆ carbocyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl groups.

The composition comprising cellulose fibres and the at least one crosslinking agent, in accordance with the present invention, is produced by applying a solution or suspension of crosslinker(s) to the cellulose fibre and, if necessary, to adjust the solvent content of the composition to less than 20 weight%. These and further details of the product and process are specified in the claims and in the specification.

Compounds of Formula (I), wherein Y denotes a C₂ to C 0 straight or branched alkylene group, preferably a straight C₂ to C₆ alkylene group, which may be substituted by OH, and particularly a propylene group, and where X denotes a halogen atom, such as a chlorine atom, is a preferred group of crosslinking agent(s) of Formula (I).

The compounds 1 ,3-dichloropropane-2-ol (DCP) and 1 ,3-dichloropropane are particularly preferred as crosslinking agent. In one embodiment, the crosslinking agent(s) is/are selected from Formula (la)

Formula (la)

Wherein Y denotes a C-i-C-u straight or branched alkylene group, which may be interrupted by O, carbonyls, NH and/or S entities, and/or may contain a C₃-C₆ carbocyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl units.

In a further embodiment, the crosslinker agents are selected from the group of diglycidyl ethers of the formula (lb)

Formula (lb) wherein Y denotes a C₂ to Ci₀ straight or branched alkylene group, preferably C₂ to C₆ straight chain alkylene group and, more preferred, C₄ to C₆ straight chain alkylene group..

The compound 1 ,4-butandioldiglycidyl ether (BDE) is particularly preferably used as crosslinking agent..

The crosslinkers mentioned above are found to have properties that make them particularly suited to prepare the composition according to the present invention, including that they are sufficiently soluble or dispersible in water and that they can be spread along the cross-section of the cellulose fibres, and that they have a suitable reactivity, and therefore provide uniform crosslinked cellulose products, when (once) subjected to crosslinking conditions. The amount of crosslinking agent(s) is of particular relevance and should be carefully controlled. The amount of crosslinker(s) employed is dependent, among others, on the properties desired for the crosslinked cellulose end product. The amount is dependent on several factors such as the reactivity and selectivity of the crosslinker itself, and also on reactivity of additional reactants, e.g. the reactants used to form cellulose ethers.

Preferably, the amount of crosslinker(s) is from 0.0001 to 0.1 molar equivalents relative to the anhydroglucose units (AGU) of the cellulose fibres. More preferred, the crosslink- ing agent is applied in an amount of from 0.0005 to 0.05 molar equivalents, more preferred from 0.0007 to 0.03 molar equivalents relative to the anhydroglucose units (AGU) of the cellulose.

In a further preferred embodiment, the amount of crosslinker(s) is from 0.0001 to 0.005 molar equivalents, relative to the anhydroglucose units (AGU) of the cellulose fibres, more preferably from 0.0003 to 0.005 molar equivalents, more preferred from 0.0007 to 0.005 molar equivalents.

In a preferred embodiment of the composition, the crosslinking agent(s) is substantially uniformly distributed along or in the cellulose fibres and substantially not covalently bound to the cellulose fibres.

Second Aspect of the invention

Process comprising the Application of the crosslinker to the cellulose as defined in any one of claims 11 to 14

The crosslinking agent(s) should be applied to the cellulose fibres in a way that secures a most even and uniform distribution of the crosslinker in the resulting cellulose fibrous material, the composition of the present invention.

The term "even and uniform distribution" means that the distribution of the crosslinking agent(s) is substantially the same in two dimensions, i.e. on the surface, and/or in the depth of the material, i.e. in one further dimension, e.g. when the material is in the form of a web or a sheet. In one embodiment, the term "even and uniform distribution" encompasses a distribution, wherein preferably at least 90 weight% of the crosslinker(s), based on the total amount of crosslinker(s), preferably more than 95 %, more preferred 98 %, of the crosslinker show substantially the same concentration/amount in two dimensions, i.e. on the surface, and/or in the depth of the material, i.e. in one further dimension, e.g. when the material is in the form of a web or a sheet.

The term "even and uniform distribution" is synonymously used with the term "substantially uniformly distributed'.

The crosslinking agent(s) can be added to the cellulose material in any conceivable way, including addition of the crosslinking agent in aqueous solution or suspension to the cellulose material by spraying, dipping and/or soaking of the cellulose fibres. When the crosslinking agent is applied to a suspension of fibres in water, this is preferably done after the last bleaching step of the process of making the cellulose fibers ("pulping"), and even more preferred just before the drying step.

When added after the forming of a sheet or web, the crosslinker is preferably added "at the wire" or close to the drying machine press section, preferably close to the drying ma- chine press section. In such a case, a solution or suspension of the crosslinking agent in a suitable solvent, preferably water, is conveniently applied to the cellulose sheet by spraying and/or dipping the cellulose sheet with the crosslinker. The application may be performed on one side or both sides of the sheet. Alternatively, the crosslinker may also be applied to dried, commercial cellulose prior to the crosslinking reaction. Said addition or application of the crosslinker(s) to the cellulose material is carried out in a manner to make sure that substantially the same amount of crosslinker(s) is added or applied per unit² surface, preferably per mm² or cm² surface, and/or per unit depth, preferably per mm of depth. As noted above, the application of the crosslinking agent(s) will preferably be conducted during the drying process including the dewatering process of the cellulose pulp, i.e. after a sheet or web or similar of the cellulose fibres is formed. Typically, in this process, cellulose pulp with a low concentration of cellulose fibres is distributed over a pre-selected area, i.e. a continuously formed area, and the water is partially removed e.g. by applying pressure and/or vacuum and also by raising the temperature, if feasible, to above 100 °C, to remove the water by evaporation. When part of the water has been removed, the crosslinker is applied. After the crosslinking agent(s) has been applied to the cellulose, e.g. in the form of a sheet, the cellulose is preferably exposed to pressure, preferably to a pressure (slightly) above ambient pressure, in order to secure uniform distribution of the crosslinker throughout the entire amount of the cellulose. When the cellulose is in the form of a sheet or a web or the like, it is important to ensure that the crosslinker is spread over the entire cross section thereof. It is preferred to apply a pressure that helps achieving optimal distribution of the crosslinker in the cellulose sheet, without losing any at all or any significant amount of crosslinker during the pressing and the drying operations.

In one specific implementation of the invention, it is found that the crosslinking agent is applied to the cellulose material, preferably in web or sheet form, when the solvent, preferably usually predominantly water, content of the sheet is from about 70 to 35 weight% of solvent, preferably about 60 to 35 weight% of solvent.

In a preferred embodiment, the composition of the cellulose material with the crosslinking agent added is dried to reach a pre-selected dryness. The composition of cellulose fibres impregnated with crosslinking agent(s) should be stable to such an extent that the cross- linking agents will not, or only to a non-significant extent, covalently react with the cellu- lose during the drying stage of the cellulose, or during storage and transportation of the composition. The temperature employed during the drying process step should be high enough to provide for effective drying, preferably about or above 100 °C, to facilitate evaporation of water, but not so high that the crosslinker is affected, or reacts with the cellulose fibre, in any significant amount

To ensure stability, storability and ease of transportation, it is important that the composition of the cellulose fibres and crosslinking agent(s) is dried to a suitable water and/or solvent content, which solvent content should preferably be below about 20 weight% based on the total weight of the composition, preferably below 10 weight%, and more preferred from 6 to 8% of water and/or solvent or even below. The solvent will usually consist predominantly of water.

Third Aspect

Water soluble crosslinked cellulose ethers By using the composition of the present invention comprising cellulose fibres, e.g. in sheet or web form, with crosslinking agent(s) as the starting material for the production of cellulose derivatives, the producers of cellulose derivatives are able to obtain a uniform product and avoid the known production challenges outlined in the Background section. Specifically, producers of cellulose ethers do not need to implement any, or only very small changes, in their usual process for producing non-crosslinked cellulose ethers. In particular, they do not need to dose and add any crosslinking agent and also do not need to provide additional equipment to ensure sufficient mixing of the crosslinking agent(s) with the cellulose.

In the manufacturing of the cellulose ethers comprising the crosslinked carbohydrate polymers (cellulose backbones), the customer will use the composition of cellulose fibres containing the desired crosslinking agent(s) in the desired amount and treat the fibres with strong alkali, optionally after having performed a process, in which the cellulose sheets are grinded or milled to a desired degree. It is of particular relevance that the crosslinking agent tolerates the alkali treatment of cellulose performed prior to the conversion to crosslinked cellulose ethers, and will not decompose or lose its functionality. The formation of ether linkages between the cellulose backbones and the crosslinking agents entails that the crosslinks are stable over a large pH region and will not be easily destroyed in, e.g., alkaline environments.

The conversion of composition of cellulosic fibres and crosslinking agent(s) to cross- linked cellulose ethers is performed in processes known from the state of art, similar to the production of non-crosslinked cellulose ethers. Further, the preparation of crosslinked cellulose ethers from the said composition is also illustrated in the Example section. The etherification reactions are preferably performed by adding one or more etherification agent(s) directly to the alkalized composition of cellulose fibre and crosslinking agent, either simultaneously or in a sequential manner, and isolating and purifying the cross- linked cellulose ether from the reaction mixture.

Accordingly, in its broadest aspect, the present disclosure relates to water soluble cross- linked cellulose derivatives such as cellulose ethers that are obtainable by providing a composition comprising cellulose fibres and at least one crosslinking agent, and wherein the at least one crosslinking agent is substantially uniformly distributed in the cellulose fibres and substantially covalently unbound to the cellulose fibres, and to crosslink and etherify the cellulose fibres by reaction(s) with one or more suitable derivatization agents and with the at least one crosslinker. In further optional steps, the resulting crosslinked cellulose ethers may be purified and the concentration may be adjusted. The crosslinked cellulose ether may also be dried.

The term "cellulose derivatives" encompasses cellulose ethers, cellulose esters and cellulose containing nitro groups. The preferred cellulose derivatives according to the present invention are cellulose ethers. The term "substantially uniformly distributed' has the meaning as defined in the second aspect of the invention

The starting material in the form of the composition of cellulose fibres and one or more crosslinking agent(s) is manufactured by applying a solution or suspension of crosslink- ing agent(s) to cellulose fibres. The mode of application of the crosslinking agent(s) to the cellulose fibres can be by spraying, dipping and/or soaking the cellulose fibres, which are preferably in the form of a web, sheet or roll or in fluff form, with the crosslinking agent(s). Optionally, after the application of the crosslinking agent, the cellulose fibres are treated by pressing and/or drying. The crosslinking agents should be uniformly spread in the cellulose fibres.

The crosslinking and etherification reactions as such can be conducted using processes known from the state of the art. The manufacture of the water soluble, crosslinked cellulose ethers is usually initiated by treating the composition with one or more alkalizing agents, e.g. alkali or alkali earth metal hydroxides such as NaOH, KOH and/or Ca(OH)₂, to activate the cellulose fibres. Etherifying agent(s) are then added, either simultaneously or in a sequential manner. The temperature of the reaction may also be controlled, preferably at temperatures between 60 and 100 °C.

In a particularly preferred embodiment, crosslinking and etherification is performed at least partially simultaneously, preferably completely simultaneously. This embodiment excludes that the cellulose fibres are crosslinked in a first step and then etherified in a second, subsequent step, or are etherified in a first step and are crosslinked in a second, subsequent step. The inventors of the present invention have surprisingly discovered that the at least partially simultaneous, preferably completely simultaneous, crosslinking and etherification results in more or essentially completely water-soluble crosslinked cellulose ethers, which have beneficial properties in terms of viscosity and homogeneity. This renders these products particularly advantageous for uses that are addressed in the" Background and Objectives" section.

The etherifying agent(s) can be chosen among those known from the art. No limitations exist in regard to which chemical reagents are used for the etherification. Common etherification agents are alkyl halides and alkylene oxides and alkylating reagents having ionic functionalities. Preferably, the alkyl and alkylene moieties have from 1 to 6 carbon atoms, more preferred from 1 to 3 carbon atoms.

Particularly preferred alkyl halides for etherification are methyl chloride and ethyl chloride. Particularly preferred alkylene oxides for etherification are ethylene oxide and pro- pylene oxide. Particularly preferred alkylating reagent for etherification having ionic functionalities is monochloroacetic acid.

The crosslinking agent(s) may be any crosslinker that provide crosslinked cellulose ethers being water soluble and provided that the crosslinking agent(s) are sufficiently water soluble or water dispersible to be applied to the cellulose fibrous material and distributed in the cellulose material in a uniform manner. Preferably, the crosslinker(s) is/are the crosslinking agents as defined in the first aspect of the invention.

More specifically, the present disclosure includes crosslinked cellulose ethers being wa- ter soluble and being obtainable by a process comprising at least the following steps (a) and (b) and optionally step (c):

(a) providing a composition comprising cellulose fibres and at least one crosslinking agent of Formula (I)

X-Y-X

Formula (I) wherein both X are the same and denote halogen atoms, alkene groups, epoxide groups or glycidyl ether groups, and Y denotes a Ci-C₁₄ straight or branched al- kylene group which may be interrupted by O, carbonyls, NH and/or S entities and/or may contain a C₃-C₆ carbocyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl groups,

and wherein the crosslinking agent(s) are substantially uniformly distributed in the cellulose fibres and substantially covalently unbound to the cellulose fibres,

(b) crosslinking and etherifying the cellulose fibres, and

(c) optionally purifying and/or optionally regulating the concentration and/or optionally drying the resulting product.

As noted above, the crosslinking agent(s) may be any crosslinker that provides cross- linked cellulose derivatives being water soluble.

In the present invention, where the process of forming the composition of the cellulose fibres and the crosslinking agent(s) is performed most conveniently in an aqueous solution, the crosslinking agent(s) should be sufficiently water soluble or water dispersible to be applied to the cellulose material and distributed in the cellulose material in a uniform manner.

Preferably, the amount of crosslinkers is from 0.0001 to 0.1 molar equivalents relative to the anhydroglucose units (AGU) of the cellulose, further preferably as described above in the first aspect.

The composition comprising cellulose fibres and at least one crosslinking agent should contain substantially no covalent bonds between the cellulose fibres and the crosslinkers before the composition is subjected to the ether manufacturing process. The crosslinked cellulose ethers formed should also be sufficiently stable for the intended use, and have desired properties such as rheological properties.

In a preferred embodiment, a class of suitable crosslinking agents are those of Formula (la):

Formula (la) wherein Y denotes a Ci-C ₄ straight or branched alkylene group which may be interrupt- ed by O, carbonyls, NH and/or S entities and/or may contain a C₃-C₆ carbocyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl units.

More preferred are crosslinkers of Formula (I) or Formula (la), wherein Y denotes the entity -CH₂-0-Y'-0- CH₂-, wherein Y' denotes a C₂-C₆ straight alkylene group or branched alkylene group, or a straight alkylene group interrupted by oxygen, or denotes a cyclohexyl entity, and/or may be substituted by OH, methyl, and/or glycidyl ether units.

Even more preferred are crosslinkers of Formula (I) or Formula (la), wherein Y denotes - CH₂-0-Y'-0- CH₂-, and wherein Y' denotes an entity selected from C₂-C₆ straight al- kylene, and preferably C -C₆ straight alkylene groups.

The preferred crosslinkers are illustrated by the following formula:

wherein Y denotes a C₂-C₆ straight alkylene group or branched alkylene group, or a straight alkylene group interrupted by oxygen, or denotes a cyclohexyl entity, and/or may be substituted by OH, methyl, and/or glycidyl ether units.

Particularly preferred crosslinkers are 1 ,4-butanediol diglycidyl ether (BDE) and 1 ,6- hexanediol diglycidyl ether, in particular BDE. The amount of crosslinkers selected from diepoxy compounds of Formula (I) are preferably from 0.0001 to 0.1 molar equivalents relative to the anhydroglucose units (AGU) of the cellulose. More preferred, the crosslinking agent(s) are applied in an amount of from 0.0005 to 0.05 molar equivalents, and even more preferred from 0.0007 to 0.03 molar equivalents relative to the anhydroglucose units (AGU) of the cellulose.

The crosslinked cellulose ethers of the invention are essentially water soluble and contain only a small, preferably an insignificant amount of solid material, e.g. solid particles. The crosslinked cellulose ether products, in accordance with the present invention, have good water solubility, as evidenced by an essentially transparent liquid product, which displays a comparatively high optical transmittance. The method of measuring the optical transmittance is described below in the Experimental Section. In a preferred embodiment, the water-soluble crosslinked cellulose ether has an optical transmittance, as measured with a UVA IS spectrometer at 457 nm and in a solution of 1 % of crosslinked cellulose ether in water, of at least 50%, preferably at least 70%, further preferably at least 90% of the transmittance of the corresponding non-crosslinked cellulose ether, as measured under the same conditions.

Preferred crosslinked cellulose ethers are those as discussed above, i.e. cellulose ethers where the cellulose ether entity is chosen from the group of sodium carboxymethyl cellulose, methyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and ethyl cellulose.

By using the composition comprising cellulose fibres, e.g. in sheet form, with crosslinking agent(s) as the starting material for the production of cellulose ethers, the producers of cellulose ethers can obtain a uniform product and avoid the known production challenges outlined above in the "Background and Objectives" section. Specifically, producers of cellulose ethers for example, do not need to implement any, or only small changes to their usual process for producing non crosslinked cellulose ethers. In particular they do not need to dose and add the crosslinking agent and also do not need to provide additional equipment to ensure sufficient mixing of the crosslinking agent(s) with the cellulose. Hence, in the manufacture of the crosslinked cellulose ethers, well known procedures from the state of art are easily adapted.

In the manufacturing of the cellulose ethers comprising crosslinked carbohydrate poly- mers (cellulose backbones), the customer will use the cellulose fibres containing the desired crosslinking agent(s) in the desired amounts and treat the fibres with strong alkali, optionally after having performed a process where the cellulose material, e.g. the cellulose sheets, are grinded or milled to a desired degree. It is of relevance that the cross- linking agent tolerates the alkali treatment of cellulose performed prior to the conversion to cellulose derivative, and will not decompose or lose its functionality. The covalent crosslinks, e.g. ether bonds, formed between the cellulose backbones and the crosslinking agent(s) should not be easily destroyed in e.g. alkali environments.

In the conversion of cellulosic fibrous composition to cellulose derivatives, the etherifica- tion reactions are preferably performed by adding the one or more etherification agents directly to the alkalized cellulose, either simultaneously or in a sequential manner, and isolating and purifying the cellulose ether from the reaction mixture. The etherification and crosslinking reactions may then take place concurrently or in a sequential manner, dependent on the reactivity of the reagents and the reaction conditions employed, pref- erably at least partially simultaneously.

In one embodiment, the manufacture of the crosslinked cellulose ethers is performed using a semidry process, preferably being performed using a Lodige® reactor. In another embodiment, the manufacture of the crosslinked cellulose ethers is performed using a slurry process.

In manufacture of the cellulose ethers, the etherifying agent(s) can be chosen among those known from the state of the art. No limitations exist in regard to which chemical reagents are used for the etherification. Common etherification agents are alkyl halides and alkylene oxides and alkylating reagents having ionic functionalities. Preferably, the alkyl and alkylene moieties have 1 to 6 carbon atoms, more preferred have 1 to 3 carbon atoms. Particularly preferred alkyl halides are methyl chloride and ethyl chloride. Particularly preferred alkylene oxides are ethylene oxide and propylene oxide. Particularly preferred alkylating reagent having ionic functionalities is monochloroacetic acid. In a further embodiment, additional etherification agents may be added in one or more further reaction steps. In such steps, the etherification agents can be the same or different from the etherification agents initially used.

The product obtained may be purified by methods well known from the art, e.g. by wash- ing. In the final preparation of the crosslinked cellulose ethers for further use e.g. as viscosity enhancing agent, the concentration may be optionally regulated and/or the product may be optionally dried.

Fourth Aspect of the Invention

Use of a composition in the manufacture of cellulose ethers according to the third aspect as defined in claims 15 and 16

In a further aspect, the present invention reads on the use, or a method of use, of the composition comprising the cellulose fibres and one or more crosslinking agent(s) as defined in the first aspect in the manufacture of water soluble crosslinked cellulose ethers.

Thus, the present invention also relates to the use of a composition comprising cellulose fibres and one or more crosslinking agent(s) of formula (I)

X-Y-X

Formula (I) where X and Y have the meaning as defined above, in the manufacture of the water- soluble crosslinked cellulose ethers defined in the third aspect, and to a process for the manufacture of the composition comprising cellulose fibres and at least one crosslinking agent. In one embodiment, the one or more crosslinking agent(s) is of Formula (la)

Formula (la) wherein Y denotes a Ci-C ₄ straight or branched alkylene group which may be interrupted by O, carbonyls, NH and/or S entities and/or may contain a C₃-C₆ carbocyclic group, and/or may be substituted by OH, NH_2> SH, epoxide and/or glycidyl units.

Fifth Aspect of the Invention

Process for the manufacture of crosslinked cellulose ethers according to the third as- pect as defined in claims 17 and 18

Still further, the present invention provides a process for the manufacture of water soluble, crosslinked cellulose ethers defined above, where the process at least comprises the following steps (a) and (b) and optionally step (c):

(a) providing a composition comprising cellulose fibres and one or more crosslinking agent(s) of Formula (I)

X-Y-X

and wherein the crosslinking agent(s) is/are substantially uniformly distributed in the cellulose fibres and substantially covalently unbound to the cellulose fibres, (b) crosslinking and etherifying the cellulose fibres, and

(c) optionally purifying and/or optionally adjusting the concentration and/or optionally drying the resulting product. In one embodiment, the one or more crosslinking agent(s) is/are of Formula (la)

Formula (la) wherein Y denotes a C_rC ₄ straight or branched alkylene group, which may be interrupted by O, carbonyls, NH and/or S entities and/or may contain a C₃-C₆ carbocyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl units.

The application of the crosslinker to the cellulose is performed in the manner as defined in the second aspect of the invention, and steps (a) and (b) and optionally step (c) are performed in a manner as disclosed in the third aspect of the invention. Examples

In the examples, abbreviations having the following meaning are used:

AGU - anhydroglucose unit of the cellulose

ADMT - Air Dry Metric Tonne (90% dry weight)

BDE - 1 ,4-butanediol diglycidyl ether

CLP - Cotton linters pulp

CMC - Carboxymethyl cellulose

DCP - 1 ,3-dichloropropane-2-ol

DME - dimethyl ether

MCA - mono-chloroacetic acid

MHPC - methyl hydroxypropyl cellulose

PO - propylene oxide % denotes weight% if not specified otherwise.

Example 1 - Cellulose material from spruce pulp with 1,4-butandiol diglycidyl ether crosslinker Cellulose pulp was produced from spruce in a conventional sulphite process. The pulping process includes e.g. the process steps of cooking, bleaching and drying of the cellulose pulp. BDE was added to the cellulose pulp at the drying machine by spraying BDE, diluted in water, onto the cellulose pulp. The amount of added BDE was 2 kg / ADMT cellulose. This results in a composition in accordance with claim 1. The cellulose sheets were milled in a conventional way, using a sieve with the mesh size of 0.315 mm. The intrinsic viscosity of the cellulose powder in cupriethylenediamine was 1640 ml/g.

Example 2 - Cellulose from spruce pulp with 1, 4-butanediol diglycidyl ether cross/inker

Example 1 was repeated with an amount of added BDE of 3,5 kg / ADMT cellulose. The cellulose pulp was milled in a conventional way as in example 1.

The intrinsic viscosity of the cellulose powder in cupriethylenediamine was 1640 ml/g.

Example 3 - Comparative Example - Cellulose from spruce pulp without crosslinker Example 1 was repeated but without the addition of crosslinker. The cellulose pulp was milled in a conventional way as in example 1 . The intrinsic viscosity of the cellulose powder in cupriethylenediamine was 1640 ml/g., i.e. the same as for the corresponding composition of Examples 1 and 2 (with crosslinker added) Example 4 - Cotton /inters pulp with 1,4-butandiol diglycidyl ether crosslinker

BDE was added to a sample of CLP. The addition of BDE was done in laboratory scale by spraying BDE, diluted in water, onto a wetted sample of the CLP. The amount of added BDE was 2,3 kg / ADMT CLP.

The CLP sheets were milled in a conventional way, using a sieve with the mesh size of 0.25 mm, before conversion to carboxymethyl cellulose was performed. The intrinsic viscosity of the cellulose powder in cupriethylenediamine was 1770 ml/g. Example 5 - Comparative Example - Cotton /inters pulp without crosslinker

Example 4 was repeated but without the addition of crosslinker. The cellulose pulp was milled in a conventional way as in example 4. The intrinsic viscosity of the cellulose powder in cupriethylenediamine was 1770 ml/g. This composition is in accordance with claim 1. Example 6 - Conversion of the cellulose material to methyl hydroxypropyl cellulose ether

Methyl hydroxypropyl cellulose ether was produced using the cellulose material de- scribed in Examples 1 and 3.

7.0 kg of cellulose (moisture content of ca. 7 % by weight) was put into a pilot reactor used to prepare cellulose ethers. The reactor was closed and evacuation of the air followed. The reactor was then filled with nitrogen gas. 8.30 kg of 50 % NaOH was added in three portions to the reactor (during stirring) with 5 min between each portion.

After the addition of NaOH was completed, first 3.65 kg of dimethyl ether (DME), then 1.80 kg of propylene oxide (PO) and finally 6.20 kg of methyl chloride were added. Each of these additions occurred at room temperature. After these additions, the temperature in the reactor was raised according to the following sequence: increase of temperature up to 65°C during 50 min, holding the temperature at 65°C during 30 min, increasing the temperature up to 90°C during 50 min, and holding the temperature at 90°C during 50 min. The reaction was stopped by reducing the temperature and the pressure to ambient conditions.

After completion of the derivatization reaction, the resulting methyl hydroxypropyl cellulose was washed with hot deionised water, filtered and dried.

Example 7 - Conversion of the cellulose material to a carboxymethyl cellulose ether

The cellulose ether carboxymethyl cellulose was produced using the cellulose material described in Examples 1 to 5.

9.00 g cellulose powder was added to a glass reactor and N₂(g) was flushed through the system for 15 min. 131.5 mL isopropanol (100%, degassed) and 10.2 ml_ H₂O (ion exchanged, degassed) was added followed by a dropwise addition of 5.5 g NaOH in 5.1 mL H₂O. The mixture was stirred for 60 min at 20 °C under a N_2(g) atmosphere. Then 12.8 g MCA in 24.5 mL isopropanol (87%, degassed) was added as slurry. The reaction mixture was heated to 60 °C over 30 min and then stirred at 60 °C for 60 min. ~1 ml_ Phenolphthalein was added giving a pink reaction mixture. The reaction was quenched by dropwise addition of acetic acid in isopropanol (one part acetic acid in two parts isopropanol) until the pink colour disappeared. The reaction mixture was filtered and washed with 87% isopropanol, 5 x 70% MeOH and 100% MeOH. The product was dried under vacuum at 60 °C overnight.

Example 8 - Addition of cross/inker during the process of converting the cellulose material to carboxymethyl cellulose ether Cellulose ether carboxymethyl cellulose was produced using cellulose pulp produced from spruce wood in a conventional sulphite process. The cellulose sheets were milled in a conventional way, using a sieve with the mesh size of 0.250 mm. The intrinsic viscosity of the cellulose powder, as measured in cupriethylenediamine, was 1520 ml/g. The carboxymethyl cellulose was produced according to the process decribed in example 7, but with BDE added to the solution of caustic soda before the mixed solution was added to the pulp. The amount of added BDE was 0.8 kg / ADMT cellulose.

Example 9 - Addition of cross/inker during the process of converting the cellulose mate- rial to carboxymethyl cellulose ether

Example 8 was repeated with an amount of added BDE of 2.4 kg / ADMT cellulose.

Example 10 - Comparative Example - Addition of crosslinker during the process of converting the cellulose material to carboxymethyl cellulose ether

Example 8 was repeated without the addition of BDE, as a reference example.

Example 11 - Addition of crosslinker during the process of converting the cellulose material to carboxymethyl cellulose ether

Cellulose ether carboxymethyl cellulose was produced using cellulose pulp produced from spruce in a conventional sulphite process. The cellulose sheets were milled in a conventional way, using a sieve with the mesh size of 0.250 mm. The intrinsic viscosity of the cellulose powder in cupriethylenediamine was 1620 ml/g.

The carboxymethyl cellulose was produced according to the process described in exam- pie 7, but after the addition of NaOH and the following stirring for 60 minutes, BDE was added and mixed with the alkalised cellulose for 2 hours at 60 °C before the procedure followed with addition of MCA. The amount of added BDE was 4.0 kg / ADMT cellulose.

Example 12 - Comparative Example - Addition of crosslinker during the process of con- verting the cellulose material to carboxymethyl cellulose ether

Example 1 1 was repeated without the addition of BDE, as a reference example.

Example 13 - Cellulose material from spruce pulp with 1 ,3-dichloropropane-2-ol cross- linker

Cellulose pulp was produced from spruce in a conventional sulphite process. The pulping process includes e.g. the process steps of cooking, bleaching and drying of the cellulose pulp. DCP was added to the pulp sample. The addition of DCP was done in laboratory scale by soaking the sheets into a bath of DCP in water. The amount of added DCP was 2,5 kg / ADMT pulp

The cellulose sheets were milled in a conventional way, using a sieve with the mesh size of 0.25 mm. The intrinsic viscosity of the cellulose powder in cupriethylenediamine was 1640 ml/g

Example 14 - Addition of crosslinker during the process of converting the cellulose material to carboxymethyl cellulose ether

The carboxymethyl cellulose was produced according to the process decribed in exam- pie 7, but after the addition of NaOH and the following stirring for 15 minutes, DCP was added and mixed with the alkalised cellulose for 10 min before the procedure followed with addition of MCA. The amount of added DCP was 2.5 kg / ADMT cellulose.

Example 15 - Pulp with 1 ,3-chloropropane-2-ol crosslinker

Example 4 was repeated, but with the addition on DCP as crosslinker

The amount of added DCP was 2.5 kg / ADMT cellulose.

The sheets were milled in a conventional way, using a sieve with the mesh size of 0.25 mm, before conversion to carboxymethyl cellulose was performed. Example 16 - Comparative Example - Addition of crosslinker during the process of converting the cellulose material to carboxymethyl cellulose ether

Example 14 was repeated without the addition of DCP, as a reference example. Performance Characteristics

The rheological characterisations of the aqueous solutions of methyl hydroxypropyl cellulose and carboxymethyl cellulose prepared in Examples 6 to 16 were performed on a rheometer (Anton Paar Physica MCR 301 ). The temperature for the measurements was 20°C and a cone-plate geometry was used (diameter: 75 mm, angle: 2°). The type of rheological measurement performed was rotational viscosity measurements, where the viscosity was measured as a function of the shear rate. The reported viscosity was determined at shear rates of 0.01 , 1 .0 and 2.5 s^~1.

The transmittance measurements were performed on a Perkin-Elmer UV VIS spectrome- ter. Reported transmittance readings were obtained at 457 nm and in a 1 % solution of the cellulose ether, with water as the solvent. A high transmittance value indicates that the amount of insoluble material in the solution is low.

Brief description of the Figures:

Figure 1 presents flow curves of MHPC samples prepared from Examples 1 and 3 [- downward pointing triangle- Example 1 ; -open circles- Example 3 ( comparative)]

Figure 2 presents flow curves of CMC samples prepared from Examples 1 , 2 and 3 [- downward pointing triangle- Example 2; -open square- Example 1 ; - open circles- Example 3 ( comparative)]

Figure 3 presents flow curves of CMC samples prepared from Examples 4 and 5 [-open circles- Example 4; -downward pointing triangles- Example 5 (comparative)]

Results

The results of the viscosity and turbidity measurements of the prepared samples of me- thyl hydroxypropyl cellulose ether (MHPC) are given in Table 1 . These results clearly show that the MHPC produced from the composition of cellulose fibres with crosslinker (Example 1 ) has a significantly higher viscosity than the one prepared from cellulose not impregnated with crosslinker (Example 3), at low shear rates (0.01 s^"1). The crosslinked MHPC sample prepared from the composition of Example 1 displays more shear thinning than that of the reference sample prepared from Example 3. Therefore, at the higher shear rate of 2.5 s^~1, the viscosity of the crosslinked ether prepared from the composition of Example 1 and the ether prepared from the composition from Example 3 are nearly the same, with the crosslinked ether prepared from the mate- rial from Example 1 having slightly lower viscosity than the ether prepared from the material of example 3. The flow curves obtained from these samples are displayed in Figure 1.

The crosslinked MHPC sample prepared from composition of cellulose fibres with cross- linker of Example 1 displays good solubility in water. As shown in Table 1 there is little difference in transparency measured by transmittance between the crosslinked ether from the material of Example 1 and the reference ether from the material of Example 3.

Table 1: Viscosity and transmittance of aqueous solutions of methyl hydroxypropyl cellu- lose (MHPC) made from softwood sulphite pulp

Cellulose Experiment BDE / Viscosity Viscosity Transmittance material ADMT cel(Pa s) at 0.01 (Pa s) at 2.5 of 1.0 %

lulose s^" of 0.5 % s^" of 0.5% MHPC (%)

MHPC MHPC

Example 1 Example 6 2,0 kg 30.7 1.37 77

Example 3 Example 6 5.3 1.67 82

(comparative)

The results of viscosity and turbidity measurements of the CMC type ethers prepared from the cellulose from Example 1 , 2 and 3 are given in Table 2. These results show clearly that a significant increase in viscosity is obtained in the CMC ethers prepared from cellulose impregnated with crosslinker (Examples 1 and 2) compared to the reference cellulose sample that does not contain crosslinker (Example 3). Again, the viscosity increase in viscosity of the ethers by means of crosslinking is more pronounced at lower shear rates than in the more shear thinning area. The flow curves obtained from these samples are shown in Figure 2. This Figure also shows that the viscosity of the cross- linked samples increases with increasing dosage of the crosslinker. Both crosslinked ethers (Example 1 and 2) display good solubility in water as indicated by the transmit- tance measurements shown in Table 2.

Table 2: Viscosity and transmittance of aqueous solutions of carboxymethyl cellulose (CMC) made from softwood sulphite pulp

Table 3 shows the viscosity and turbidity measurements of CMC ethers prepared from the cellulose of examples 4 and 5. These measurements show that a very large increase in viscosity is observed in the CMC ether prepared from cellulose impregnated with crosslinker, and a good solubility in water is observed. The flow curves obtained from these samples are displayed in Figure 3. Table 3: Viscosity and transmittance of aqueous solutions of carboxymethyl cellulose (CMC) made from cotton /inters pulp

Table 4 shows the viscosity of CMC ethers prepared according to examples 8 to 12, where the crosslinker was added at two different stages during the process to convert the cellulose to carboxymethyl cellulose. In particular, adding BDE mixed with the caustic soda (Examples 8 to 10), shows no increase in measured CMC viscosity by means of adding a cross-linker at this stage. The same lack of effect was found when dosing BDE after the mercerication step but before addition of MCA, see Examples 1 1 and 12.

Table 4: Viscosity of aqueous solutions of carboxymethyl cellulose (CMC) made from softwood sulphite pulp

Cellulose Experiment BDE per Viscosity (mPa s)

material ADMT celluat 1 .0 s^"1 of 0.25

lose % CMC

Example 8 Example 8 0.8 kg 38

Example 8 Example 9 2.4 kg 36

Example 8 Example 10 no cross-linker 41

(comparative) added

Example 11 Example 11 4.0 66

Example 1 1 Example 12 no cross-linker 68

(comparative) added

Table 5: Viscosity of aqueous solutions of carboxymethyl cellulose (CMC) made from softwood sulphite pulp

Examples 1 to 7 described above demonstrate that the ethers produced from the compositions of cellulose fibres and crosslinking agent have higher solution viscosity than the corresponding cellulose ethers prepared from cellulose fibres without crosslinking agent. The dosing of crosslinker in the cellulose fibres allows for adjusting the viscosity of the resulting cellulose derivatives. The composition containing cellulose and crosslinking agent results in cellulose ethers with good water solubility, wherein no significant difference in water solubility is detected compared to the reference cellulose ethers.

Examples 8 to 12 show, surprisingly, that the addition of the crosslinker directly to the slurry meant to be etherified in a slurry-based cellulose ether process (i.e. not adding the crosslinker earlier to the cellulose fibers, as is the case for the compositions and pro- cesses and uses according to the present invention) results in no significant increase of the viscosity of the resulting cellulose ether, at the claimed dosage levels. Without wishing to be bound by theory, it is believed that in this case, the crosslinker essentially stays in the solvent (interacts with the solvent) in this case, and therefore does not affect the cellulose ether viscosity. On the other hand, in the composition, process and use according to the present invention, the crosslinker effectively "sticks" to the cellulose fibers and can exert the viscosity increasing crosslinking effect in the subsequent etherification and crosslinking reaction, even in a slurry process. Examples 13 to 16 show that the effect of adding crosslinker to the sheets, compared to addition to the reactor, also applies when DCP is used as crosslinker.

This proves that the claimed invention has a superior effect with regard to obtaining in- creased cellulose ether viscosity, in particular for cellulose ethers produced by means of using a solvent based slurry process, which is the process of choice for the production of carboxymethyl cellulose and hydroxyethyl cellulose, among others. Furthermore, the effect is present for an array of different crosslinkers.

Claims

Composition comprising cellulose fibres and at least one crosslinking agent of Formula (I)

X-Y-X

Formula (I) wherein both X are the same and denote halogen atoms, alkene groups, epoxide groups or glycidyl ether groups, and Y denotes a C_rCu straight or branched al- kylene group which may be interrupted by O, carbonyls, NH and/or S entities and/or may contain a C₃-C₆ carbocyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl groups, preferably wherein the composition has a solvent content of less than 20 weight%;

wherein substantially no covalent bonds are formed between the cellulose fibres and the crosslinking agents; and

wherein the amount of crosslinking agent of Formula (I) is from 0.0001 to 0.1 molar equivalents relative to the anhydroglucose units of the cellulose fibres.

Composition of claim 1 wherein the amount of crosslinking agent is from 0.0005 to 0.05 molar equivalents, preferably from 0.0007 to 0.03 molar equivalents.

Composition of claims 1 or 2 being in the form of a web, sheet or roll, or in fluff form, the fluff form preferably being dried as loose fibres, more preferably delivered compressed into bales.

Composition of any of the preceding claims, wherein the crosslinking agent(s) are substantially uniformly distributed in the cellulose fibres.

Composition of any of the preceding claims, wherein in Formula (I) Y denotes a C₂ to C₁₀ straight or branched alkylene group, preferably a straight C₂ to C₆ alkylene group and particularly preferred a straight propylene group, and where X denote halogen, particularly preferred chlorine atoms. Composition of any one of claims 1 to 5, wherein the crosslinking agent(s) is/are selected from Formula (la)

Formula (la) wherein Y denotes a C1-C14 straight or branched alkylene group which may be interrupted by O, carbonyls, NH and/or S entities and/or may contain a C₃-C₆ carbo- cyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl units.

Composition of any one of the preceding claims, wherein the crosslinking agent(s) is/are selected from Formula (lb)

Formula (lb) wherein Y denotes a C₂ to C₁₀ straight or branched alkylene group, preferably C₂ C₆ straight chain alkylene group and more preferred a C₄ to C₆ straight chain kylene group.

Composition of any one of the preceding claims, wherein the crosslinking agent is selected from 1 ,4-butanediol diglycidyl ether and 1 ,6_rhexanediol diglycidyl ether, and preferably is 1 ,4-butanediol diglycidyl ether.

Composition of any of the preceding claims, wherein the solvent content is less than 10 weight%, and particularly preferred from 6 to 8 weight%, based on the total weight of the composition. Composition of any of the preceding claims, wherein the cellulose fibres are obtained from cotton linters and wood material, preferably from softwood pulp and cotton linters pulp, specifically from spruce from a sulphite pulping process.

Process for the manufacture of the composition as defined in any one of preceding claims, wherein a solution or suspension of the crosslinking agent(s) as defined in any of claims 1 or 5 to 8 is applied to the cellulose fibres in a uniform manner by spraying, dipping and/or soaking of the cellulose fibres, preferably in the form of a web, sheet or roll, or in fluff form, optionally followed by a pressing and/or drying process.

12. Process of claim 1 1 , wherein the crosslinking agent(s) are substantially uniformly distributed in the cellulose fibres.

13. Process of claim 1 1 or 12, wherein the one or more crosslinking agent(s) is/are of Formula (la) or of Formula (lb) as defined in claim 6 or 7.

14. Process of any one of claims 1 1 to 13, wherein the cellulose fibres are in the form of cellulose fibre web, sheet or roll, or in fluff form, preferably from cotton linters pulp or spruce cellulose pulp, preferably having a cellulose fibre content of at least 80 weight%.

15. Use of a composition as defined in any one of claims 1 to 10 in the manufacture of a water soluble crosslinked cellulose ether, which is characterized in being obtainable by a process comprising at least the following steps (a) and (b) and optionally step (c):

X-Y-X

Formula (I) wherein both X are the same and denote halogen atoms, alkene groups, epoxide groups or glycidyl ether groups, and Y denotes a Ci~Ci₄ straight or branched alkylene group which may be interrupted by O, carbonyls, NH and/or S entities and/or may contain a C₃-C₆ carbocyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl groups, wherein the crosslinking agent(s) is/are substantially uniformly distributed in the cellulose fibres and substantially covalently unbound to the cellulose fibres, and wherein the amount of crosslinking agent of Formula (I) is from 0.0001 to 0.1 molar equivalents relative to the anhydroglucose units of the cellulose fibres,

(b) crosslinking and etherifying the cellulose fibres, and

(c) optionally purifying and/or optionally regulating the concentration and/or optionally drying the resulting product, preferably wherein the water-soluble crosslinked cellulose ether, in solution, has an optical transmittance, as measured with a UVA IS spectrometer at 457 nm and in a solution of 1 % of crosslinked cellulose ether in water, of at least 50%, preferably at least 70%, further preferably at least 90% of the transmittance of the corresponding non-crosslinked cellulose ether, as measured under the same conditions.

Use of claim 15, wherein the one or more crosslinking agent(s) of Formula (I) is of Formula (la)

Formula (la) wherein Y denotes a C C₁₄ straight or branched alkylene group which may be interrupted by O, carbonyls, NH and/or S entities and/or may contain a C₃-C₆ carbocyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl units, and wherein the crosslinking agent(s) are substantially uniformly distributed in the cellulose fibres and substantially covalently unbound to the cellulose fibres.

Process for the manufacture of a water soluble crosslinked cellulose ether, comprising at least the following steps (a) and (b) and optionally step (c):

X-Y-X

Formula (I) wherein both X are the same and denote halogen atoms, alkene groups, epoxide groups or glycidyl ether groups, and Y denotes a Ci-C₁₄ straight or branched alkylene group which may be interrupted by O, carbonyls, NH and/or S entities and/or may contain a C₃-C₆ carbocyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl groups, wherein the crosslinking agent(s) is/are substantially uniformly distributed in the cellulose fibres and substantially covalently unbound to the cellulose fibres, and wherein the amount of crosslinking agent of Formula (I) is from 0.0001 to 0.1 molar equivalents relative to the anhydroglucose units of the cellulose fibres,

(b) crosslinking and etherifying the cellulose fibres, and

(c) optionally purifying and/or optionally adjusting the concentration and/or optionally drying the resulting product, preferably wherein the water-soluble crosslinked cellulose ether, in solution, has an optical transmittance, as measured with a UV/VIS spectrometer at 457 nm and in a solution of 1 % of crosslinked cellulose ether in water, of at least 50%, preferably at least 70%, further preferably at least 90% of the transmittance of the corresponding non-crosslinked cellulose ether, as measured under the same conditions.

Process of claim 17 wherein the one or more crosslinking agent(s) is/are of Formula (la)

Formula (la) wherein Y denotes a CrC₁₄ straight or branched alkylene group which may be interrupted by O, carbonyls, NH and/or S entities and/or may contain a C₃-C₆ carbo- cyclic group, and/or may be substituted by OH, NH₂, SH, epoxide and/or glycidyl units.

Process of one of claims 17 or 18, wherein step (b) is performed using a semidry process, or:

wherein step (b) is performed using a slurry process.

Crosslinked cellulose ethers obtainable by a process as described in any one of claims 17 to 19.