Process for producing crosslinked cellulose ethers

Abstract

A process for producing a crosslinked cellulose ether, comprising: (i) contacting at least one cellulose material with a mixture comprising (ia) at least one crosslinking agent and (ib) at least one alkalizing reagent to form an activated cellulose material; and (ii) contacting the activated cellulose material of step (i) with at least one etherifying reagent, wherein the at least one etherifying reagent reacts with the activated cellulose material to form a crosslinked cellulose ether. The crosslinked cellulose ether produced by the process is also disclosed.

Description

[Technical field]

[0001] The present invention relates to a process for producing crosslinked cellulose ethers and to crosslinked cellulose ethers prepared by such a process. [Background technology]

[0002] Cellulose derivatives such as cellulose ethers are widely used, for example, as thickeners, adhesives, binders and dispersants, water retention agents, protective colloids, stabilizers, and suspensions, emulsifiers and film formers, due to their excellent properties and physiological safety. In addition, cellulose ethers are known to be used in dry-mix mortars in various construction applications to improve the rheology of the mortar. Cellulose ethers are also used in mortars to impart water retention, which limits the loss of water from the mortar to the absorbent substrate. This allows the hydraulic binder (cement or gypsum) to have sufficient water available during the setting reaction, resulting in high mechanical strength of the final product. Lack of water leads to incomplete setting, poor mechanical strength, crack formation, and reduced abrasion resistance.

[0003] Up to now, cellulose ethers have been produced by a well-known conventional process that includes subjecting a cellulose starting material, such as cellulose pulp, to two process operations (steps or stages): (1) an alkalizing operation and (2) an etherification operation. A well-known state-of-the-art conventional procedure for making cellulose ethers is illustrated and described, for example, in U.S. Pat. No. 6,235,893 B1. The conventional process includes (1) alkalizing cellulose pulp, and (2) etherifying the alkalized cellulose pulp to form a cellulose ether. For example, in a conventional process, cellulose pulp is alkalized with sodium hydroxide and etherified with methyl chloride and an alkylene oxide (ethylene oxide or propylene oxide). Also, each one of the above alkalization and etherification operations can be carried out stepwise, i.e., in one step or two or more different separate steps, and each step can be carried out for a given period of time at specific process conditions of pressure and temperature. After the cellulose ether is made, it can be subjected to further optional process steps, such as (3) washing the cellulose ether, (4) drying the cellulose ether, and (5) milling the cellulose ether into particles. Typically, the alkalinization and etherification operations can be carried out in a single reactor or in two or more reactors.

[0004] More recently, improvements have been made to the traditional process for making cellulose ethers by using crosslinking techniques to make crosslinked cellulose ethers. Crosslinking techniques involve cellulose ethers that can be chain extended or crosslinked using difunctional crosslinking agents such as methylene dichloride, epichlorohydrin, or various diglycidyl ethers. For example, U.S. Patent No. 6,958,393 B2 (equivalent to EP1384727B9) discloses a method for making polyether groups containing crosslinked cellulose ethers using crosslinking techniques. Crosslinked cellulose ethers are produced by crosslinking cellulose ethers at or below 90 degrees Celsius (°C) in the presence of an inert atmosphere, such as nitrogen (N2), a polyether group containing crosslinking agent, and in the presence of caustic or alkali. Crosslinking of cellulose ethers occurs in the reactor in which the cellulose ether itself is made, and in the presence of caustic or alkali.

[0005] One advantage of using crosslinked cellulose ethers, for example in dry mix mortar formulations, as opposed to pure non-crosslinked cellulose ethers, is that by crosslinking the cellulose ethers with a crosslinking agent, the viscosity of the aqueous solution of the cellulose ethers can be increased, and the resulting crosslinked cellulose ethers with increased or high viscosity can still remain water-soluble in aqueous solution. Also, the crosslinked cellulose ethers with increased or high viscosity produced using crosslinking techniques can be used at reduced dosage levels, for example, in mortar applications, without compromising product and application performance. Cellulose ethers are relatively expensive components used in mortar formulations, and reducing the amount of cellulose ether added in the formulation can save on the cost of the formulation.

[0006] In known processes, the loading of crosslinking agent used to crosslink the cellulose ether is kept very low to prevent "over-crosslinking", which in turn provides a polymer product that remains water-insoluble and does not contribute to the viscosity of the aqueous solution.However, uniform distribution of the small amount of crosslinking agent added to the contents of a larger reactor is very difficult to achieve using known processes.

[0007] "Over-crosslinking" in this specification means that the reaction between the cellulose ether and the crosslinking agent is too extensive in terms of crosslinking of the cellulose ether, resulting in a three-dimensional network of covalently bonded cellulose ether chains, and such chains are not water-soluble and appear as gel particles in the aqueous phase. Over-crosslinking leads to a decrease in the water solubility of the cellulose ether in aqueous solution. When over-crosslinking occurs in the cellulose ether, the amount of the resulting crosslinked cellulose ether is reduced and becomes soluble in aqueous solution, and the appropriate viscosity of the crosslinked cellulose ether cannot be achieved in aqueous solution. In other words, over-crosslinking leads to an undesirable decrease in viscosity. Over-crosslinked cellulose ether shows a degree of crosslinking that leads to a decrease in water solubility compared to non-over-crosslinked cellulose ether.

[0008] For example, the known process for crosslinking cellulose ethers described in U.S. Pat. No. 6,958,393 B2 includes several steps, such as (1) alkalizing cellulose with an aqueous alkali metal hydroxide solution in the presence of a suspending medium, (2) reacting the alkalized cellulose with one or more alkylene oxides, (3) further reacting the alkalized cellulose with an alkyl halide present in the suspending medium, (4) subsequently or simultaneously reacting the alkalized cellulose with a crosslinking agent using a specific amount of a crosslinking agent, (5) adding further alkali metal hydroxide and / or an alkalization agent to the reaction mixture of step (4), and (6) purifying and drying the resulting crosslinked cellulose ether.

[0009] The process described in US Pat. No. 6,958,393 B2 requires (1) the addition of a crosslinking agent during the etherification step of the process at high pressure, (2) the use of epichlorohydrin (ECH) as a crosslinking agent in some cases, (3) the addition of a low level of crosslinking agent either in a pure state or dispersed in an organic solvent, (4) uniform distribution of the crosslinking agent with limited low levels of pure crosslinking agent, and (5) the exhibit of good performance of the resulting product of the process. In addition to the above requirements, the use of the above known process sometimes resulted in poor distribution of the crosslinking agent in the reactor, leading to over-crosslinking and undesirable viscosity reduction of the crosslinked cellulose product. Also, the efficiency of the known process of US Pat. No. 6,958,393 B2 does not transfer easily from laboratory scale to pilot plant scale and / or ultimately to full-scale industrial plant scale. Therefore, the above known process requires a higher degree of expertise, knowledge and technical effort to function at plant scale and under the conditions of the known process.

[0010] It has been found that for the crosslinking process to be successful, it is necessary to achieve a uniform distribution of the crosslinking agent when it is introduced into the process in small amounts. A uniform distribution must be achieved to create the desired branched polymer and prevent local overaddition leading to overcrosslinking. Overcrosslinking (i.e., high levels of crosslinking) leads to increased levels of local crosslinked networks and local insoluble materials. It has also been found that overcrosslinking can depend on when and at what stage, step or operation of the crosslinked cellulose ether manufacturing process the crosslinking agent is introduced into the process. For example, the crosslinking agent may be introduced or added before, during or after the etherification operation. However, since the alkalization and etherification reactions are exothermic reactions, there are many factors that can affect whether overcrosslinking occurs in the process. The factors can include, for example, the reaction time, the type of crosslinking agent introduced into the process, the amount of crosslinking agent introduced into the process, the manner in which the crosslinking agent is introduced into the process, the process conditions at the time the crosslinking agent is introduced, and over what period of time the crosslinking agent is introduced into the process. Summary of the Invention [Problem to be solved by the invention]

[0011] It is therefore desirable to provide new and improved processes for producing crosslinked cellulose ethers that are useful and can be implemented on an industrial plant scale with greater efficiency than known conventional processes, while at the same time the performance of the resulting products of such improved processes remains the same or better than the known products of the conventional processes.

[0012] The problems of the prior art processes can be solved using the process of the present invention.The present invention is directed to a novel process for preparing crosslinked cellulose ethers (herein referred to as "XCE") with appropriately increased viscosity.

[0013] The present invention is directed to a novel low pressure (e.g., at atmospheric pressure) process for preparing XCEs with increased aqueous solution viscosity. The present invention relates to providing a crosslinker addition in a cellulose ether manufacturing process at atmospheric pressure that allows for the production of XCEs, such as hydroxyethyl methylcellulose derivatives, which not only eliminates the costly high pressure addition step of known conventional processes, but also provides a product with increased aqueous solution viscosity. Such a product can be used in reduced amounts, for example in dry mix mortar formulations, and still provide suitable performance properties.

[0014] In one embodiment, the addition of the crosslinker is done at a low pressure step, which in the process of the present invention is, for example, the alkalization step of the process, which is a step before the high pressure etherification process step. In the present invention, the control of the crosslinker dosage provides an economical way to produce XCE products with good rheological performance (higher viscosity levels) but with less technical effort. Also, the dosage concept of the present invention has the additional advantage of an enhanced process window for the addition of the crosslinker compared to known processes.

[0015] In one preferred embodiment, the present invention is directed to a process for producing XCE, comprising: (i) contacting at least one cellulose material with a mixture comprising (ia) at least one crosslinking agent and (ib) at least one alkalizing agent to form an activated cellulose material; and (ii) contacting the activated cellulose material of step (i) with at least one etherification reagent, wherein the at least one etherification reagent reacts with the activated cellulose material to form XCE. The contacting step (i) can be carried out, for example, at a pressure of 500 kilopascals (kPa) or less (≦) and at a temperature of 50° C. or less (≦). The contacting step (ii) is carried out, for example, at a pressure of 1,500 kPa or more (≧) and at a temperature of up to 70° C. Optionally, the above process can include one or more additional steps of purifying, washing, drying, granulating, and milling the XCE obtained from step (ii).

[0016] In another embodiment, the present invention is directed to a process for producing a crosslinked cellulose ether, comprising the steps of: (A) mixing at least one crosslinking agent with (b) at least one alkalizing reagent to form a crosslinking agent / alkalizing reagent mixture; (B) contacting at least one cellulose material with the mixture of step (A) to form an activated cellulose material; (C) contacting the activated cellulose material of step (B) with at least one etherifying reagent, wherein the at least one etherifying reagent reacts with the activated cellulose material to form a crosslinked cellulose ether; and (D) optionally subjecting the crosslinked cellulose ether to one or more of the steps of refining, washing, drying, granulating, and milling.

[0017] In yet another preferred embodiment, the cross-linking agent is introduced or added to the process during the alkalinization operation, where the cross-linking agent is added to the process in the form of a mixture of the cross-linking agent and the alkalinization reagent.

[0018] In yet another embodiment, the present invention is directed to the XCE produced by the above process. The XCE produced by the above process of the present invention advantageously has high water solubility, leading to increased viscosity in aqueous solution when compared to non-crosslinked cellulose ethers.

[0019] Yet another embodiment of the present invention relates to a dry-mix mortar-forming composition comprising the XCE described above.

[0020] Surprisingly, it has been found that using the process of the present invention to introduce the desired low loading of uniformly distributed crosslinker compound under low pressure process conditions (e.g., 100 kPa to 500 kPa) not only advantageously simplifies the overall process for producing XCE, but also provides an efficient manufacturing process for making XCE. For example, the loading of crosslinker introduced in the process of the present invention is carried out at an earlier step of the process of the present invention, i.e., the loading of crosslinker used in the process of the present invention is introduced or added during the alkalinization of the cellulose starting material operation of the process of the present invention, whereas the loading of crosslinker used in known conventional processes is introduced or added during the etherification operation. Thus, the loading of the desired uniformly distributed crosslinker loading occurs at a low pressure point or step of the process of the present invention, as opposed to the loading of crosslinker at a high pressure point or step of the conventional process. In a typical conventional process, an alkalinizing agent, such as sodium hydroxide (NaOH or caustic soda), is added to the cellulose to carry out the alkalinization step. However, when the cross-linking agent is combined with an alkalizing reagent, as is done in accordance with the present invention, the alkalizing reagent also functions as a diluent for the cross-linking agent, allowing for uniform distribution of the cross-linking agent in the process. Advantageously, it may not be necessary to add additional amounts of cross-linking agent at the alkalizing step or any other step later in the process scheme of the present invention.

[0021] Some other advantages of the process of the present invention include, for example, (1) control of the crosslinker dosage results in XCE with a desired (and suitable) increased viscosity level that is advantageously avoided, especially in the use of large-scale plant processes; (2) the crosslinker has low water solubility and forms a dispersion in alkaline solutions; (3) small amounts of crosslinker are needed in the process to provide higher viscosity at low crosslinker dosages; (4) uniform distribution of small amounts of crosslinker is possible in large-scale plant-scale processes; and (5) the process does not require additional spraying devices in the reactor used to carry out the process of the present invention. Further, advantageously, the process of the present invention provides XCE products with the same or better performance characteristics than known products prepared by known processes. Additionally, advantageously, the process of the present invention can be carried out on a large plant scale with the crosslinker loadings performed in the alkalization step of the process of the present invention and without the problem of over-crosslinking. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic flow diagram illustrating the process of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] "Uniform distribution" in this disclosure, in reference to contacting cellulose fibers with different components, means herein that the cellulose fibers and other components have the same distribution in all the smallest volume elements of a given volume, the smallest volume element being a cube with an edge length 10 times the average particle size of the cellulose fibers in the given volume.

[0024] Generally, the process for producing XCE includes an alkalization step and an etherification step. A step of grinding the cellulosic starting material can be performed prior to the alkalization step, and is typically desired, and a washing (hot HO) / granulation step and / or drying / milling step of the XCE can be performed after the etherification step. During the alkalization operation of the process, a cross-linking agent is introduced or added to the alkalization operation to provide cross-linking of the cellulosic material later in the process, such as during the etherification operation.

[0025] In one broad embodiment, the present invention relates to the addition of a crosslinking agent to a process for producing an XCE product, and the addition of a crosslinking agent. In one preferred embodiment, the crosslinking agent is added or added to an alkalizing step or process operation in combination with an alkalizing agent in the form of a mixture of the crosslinking agent and the alkalizing agent.

[0026] The small amount of crosslinker used in the present invention results in an ultra-high viscosity product with the same rheological performance (e.g., high viscosity measured in millipascal seconds [mPa.s]) as known products, but with a more efficient crosslinker. Advantageously, this results in a lower level of undesirable side reactions and minimizes the impact on wastewater treatment. The present invention also reduces the dosage of expensive crosslinker and prevents over-crosslinking.

[0027] The loading amount of crosslinking agent used in the present invention has the advantage of using alkali / water as the suspension medium (or diluent) of the crosslinking agent, so that the objective of providing uniform distribution of dispersion in the cellulose material during the loading step can be more easily achieved compared to the conventional process. In addition, the present invention using the suspension medium of alkali / water does not have the safety issues and environmental concerns in the XCE manufacturing plant, as the process known in the art using organic solvent as the diluent of the crosslinking agent.

[0028] Further advantages of the process of the present invention include, for example, (1) the process uses readily available crosslinkers based on diglycidyl ether chemistry, such as Epilox M 985 or Epilox P13-42, and (2) the crosslinker / alkali / water dispersion is non-toxic. In contrast, known processes use epichlorohydrin (ECH) as the crosslinker system, and such known processes have been known to be toxic, carcinogenic, and have low boiling point (116 °C) / low molecular weight (Mw) (92.53 g mol -1 ) Table I shows a comparison of the physical data of the Epilox product versus ECH. [Table 1]

[0029] The process of the present invention irreversibly provides XCE with beneficial rheological behavior and advantageous properties in various application fields. The present invention uses C10-C24 alkyl difunctional compounds (oxiranes and / or halides) and polypropylene glycol diglycidyl ether as crosslinking agents to prepare XCE. The process of the present invention introduces the crosslinking agent in the alkalinization step of the process using a crosslinking agent / alkali / water mixture or dispersion. Prior art processes using ECH as a crosslinking agent to prepare XCE often result in insoluble crosslinked products, and the crosslinking agents useful in the present invention pose less environmental concern than ECH.

[0030] Generally, the crosslinker / alkaline dispersion compositions useful in the present invention comprise a mixture of (i) a crosslinker, (ii) an alkalizing agent in water, and (iii) any other optional ingredients as desired.

[0031] The crosslinking agent used to prepare the cellulose ether of the present invention includes, for example, one or more crosslinking agents known in the art. Crosslinking agents that are water insoluble or have a solubility in water of less than (<) 10 percent (%) are typically used. For example, the water insoluble nature of the crosslinking agent optimizes the desired side reaction with the hydroxyl (-OH) group of the cellulose backbone and minimizes the undesired side reaction with the -OH group of the NaOH used in the alkalizing operation.

[0032] Suitable crosslinking agents for use in the present invention include, for example, polyoxyalkylene or polyalkylene glycol groups, and compounds having two or more, preferably two crosslinking groups, such as halogen, glycidyl or epoxy groups, or ethylenically unsaturated groups, such as vinyl groups, which form ether bonds with cellulose ethers when crosslinking the cellulose ethers. Suitable bifunctional compounds include, for example, 1,2-dichloro(poly)alkoxyethers, dichloropolyoxyethylenes, diglycidyl polyalkoxyethers, diglycidyl phosphonates, divinyl polyoxyalkylenes containing sulfone groups, and mixtures thereof. Compounds with two different functional groups can also be used. Examples of compounds containing two different functional groups include ECH, glycidyl(poly)oxyalkyl methacrylates, and mixtures thereof.

[0033] In one preferred embodiment, the crosslinking agent useful in the present invention can be based on diglycidyl ether chemistry. For example, the crosslinking agent can be a diglycidyl ether type crosslinking agent, as shown by the following chemical structure (I): [ka] In the above structure (I), "n" can be 3-25 in one embodiment, 7-20 in another embodiment, and 9-15 in yet another embodiment.

[0034] Examples of some commercially available crosslinkers useful in the present invention, such as crosslinkers based on diglycidyl ether chemistry, include Epilox P13-42 (the Epilox P13-42 product is structure (I) when n is equal to about 8), and Epilox M 985 (the Epilox M 985 product is structure (I) when n=≈13 (both of the above Epilox products are available from Leuna-Harze GmbH). Epilox M 985 crosslinker is a linear poly(propylene glycol) diglycidyl ether made from polypropylene glycol (PPG).

[0035] Crosslinkers such as Epilox M985 and Epilox P13-42 are examples of preferred embodiments because such crosslinkers are advantageously (1) non-toxic, and (2) have very high boiling points (e.g., greater than (>) 200° C.) / high Mw (e.g., greater than 600 grams / mole [g / mol]). This is in contrast to some of the known crosslinker systems used in the prior art, such as ECH, which (1) are toxic and / or carcinogenic, and (2) have low boiling points (e.g., 116° C.) and low Mw (e.g., 92.53 g / mol).

[0036] With a crosslinker such as Epilox M 985, actual covalent bond formation occurs with the cellulose material. This covalent bond formation advantageously increases the Mw of the cellulose ether. The cellulose ether with increased Mw of the present invention provides a means to reach beneficial properties, such as high viscosity levels (e.g., >20% higher than non-crosslinked cellulose ethers).

[0037] Some other examples of advantageous properties exhibited by the crosslinker include lower dosage levels in dry mix mortar applications without sacrificing performance properties.

[0038] In addition, when using the XCE of the present invention, for example when used in dry mix mortar formulations, the amount of XCE required to obtain the desired performance is reduced compared to non-crosslinked cellulose ethers. Such reduction in XCE loading, in turn, reduces the cost of use, which correlates with the reduced amount of cellulose ether required to obtain the desired performance, for example in cementitious tile adhesive applications.

[0039] In general, the amount of crosslinking agent used in the present invention can range from 0.0001 equivalents to 0.05 equivalents, with the unit "equivalent" representing the molar ratio of each crosslinking agent to the moles of anhydroglucose units (AGU) of the cellulose ether. The amount of crosslinking agent used in the process is generally 0.0005 equivalents to 0.03 equivalents in one embodiment, and 0.001 equivalents to 0.005 equivalents in another embodiment. If the amount of crosslinking agent used is more than 0.05 equivalents, over-crosslinking of XCE may occur, and thus the cellulose ether becomes insoluble. If the amount of crosslinking agent used is less than 0.0001 equivalents, the increase in viscosity of XCE, for example in a 1% solution, may not be detectable.

[0040] The alkalizing reagent (or alkalizing agent) used to mix with the crosslinker to dilute the crosslinker and also used during the alkalizing step of the process of the present invention includes, for example, one or more alkalizing reagents known in the art. For example, the alkalizing reagent includes a solution of an alkali metal hydroxide, such as NaOH, potassium hydroxide (KOH), lithium hydroxide (LiOH), and mixtures thereof. In some embodiments, an alkaline aqueous solution of KOH or LiOH is suitable for use as an alkalizing reagent, but for economic reasons, the alkali metal hydroxide used as an alkalizing reagent in the present invention is an aqueous NaOH solution. In a preferred embodiment, the alkali metal hydroxide used in the present invention is 50% caustic soda available from The Dow Chemical Company. The alkalizing reagent is used to alkalize native cellulose or cellulose hydrate when carrying out the process of the present invention, in one preferred embodiment.

[0041] Typically, the alkalizing reagent is in the form of a mixture of alkalizing reagent in water (e.g., 50% NaOH in water), and the concentration of the aqueous solution can vary. For example, the aqueous solution ranges from about 10 weight percent (wt%) to 90 wt%, in one embodiment, 25 wt% to 75 wt% in another embodiment, and 40 wt% to 60 wt% in yet another embodiment, based on the weight % of water. In a preferred embodiment, the aqueous solution is used as a 50% reagent in water.

[0042] The water used in the alkalinizing reagent can be obtained from any source. Different types of water include, for example, tap water, drinking water, and deionized water.

[0043] The alkalizing agent is formed by mixing the alkalizing agent with water by conventional mixing means either prior to or immediately prior to mixing the alkalizing agent with the crosslinking agent of the present invention.

[0044] In one general embodiment, the process for making a crosslinker / alkalinizing reagent dispersion or suspension useful in the present invention comprises (a) mixing at least one crosslinker with at least one alkalizing reagent to form a dispersion. Mixing the crosslinker and alkalizing reagent to form a dispersion can be performed by any conventional mixing means, such as any horizontal or vertical mixing device, or by pumping the crosslinker into the alkalizing reagent, or a combination of an alkalizing reagent supply line and a crosslinker supply line.

[0045] One example of the advantageous properties exhibited by the crosslinker / alkalinization reagent dispersion includes that the dispersion is easily and uniformly distributed over the cellulosic starting material during alkalinization.

[0046] In one broad embodiment, a process for producing XCE from a cellulosic starting material includes the steps of: (a) mixing at least one crosslinker with at least one alkalizing reagent to form a crosslinker / alkalizing reagent mixture; (b) contacting at least one cellulosic material with the crosslinker / alkalizing reagent mixture of step (a) to form an activated cellulosic material such that an activated cellulosic material is formed in the presence of the at least one crosslinker at a pressure of ≦500 kPa and a temperature of ≦50° C.; (c) contacting the activated cellulosic material of step (b) with at least one etherification reagent in the presence of the at least one crosslinker from step (b) to form an XCE; and (d) optionally performing one or more steps of purifying, washing, drying, granulating, and milling the XCE from step (c).

[0047] Referring to Figure 1, there is shown a process of the present invention, generally designated by reference numeral 10, illustrating various general process operations or steps for producing XCE, which has an enhanced viscosity in aqueous solution and is useful, for example, in dry mix mortars. As shown in Figure 1, the process includes a cellulosic starting material 11, such as pulp, and a dispersion or mixture of a crosslinker and an alkalizing reagent 12, which proceed to an alkalizing step 13, as indicated by arrows 11a and 12a, respectively.

[0048] The general process as shown in Figure 1 may include optional operations or steps, such as, for example, an optional grinding step 21, shown in dotted lines in Figure 1, which proceeds as shown by arrow 21a to form a cellulose starting material 11, which then proceeds to an alkalizing step 13, shown by arrow 11a. Although the grinding step 21 is optional, the grinding step 21 is typically used in preferred embodiments so that the cellulose starting material 11 (e.g., wood pulp) can be ground to form a ground floc of cellulose that can easily flow and mix in the reactor. The ground floc is also easily contacted with the crosslinker / alkalizing reagent mixture 12, such as by spraying the mixture onto the cellulose floc that is being mixed in the reactor using conventional spraying means. The ground floc of cellulose 11 can then proceed to an alkalizing step 13, shown by arrow 11a, which can then proceed.

[0049] In the alkalinization step 13, a crosslinker / alkalinization reagent dispersion mixture 12 comprising (i) an alkalinization reagent such as NaOH (50% in water) and (ii) a crosslinker as described above is mixed with the cellulosic material 11 to form activated cellulose 14, as indicated by arrow 13a, which then proceeds to an etherification step 15, as indicated by arrow 14a. In the alkalinization step 13 of the process 10, a combination or mixture 12 of crosslinker and alkalinization reagent (e.g., in the form of a dispersion or aqueous suspension 12) can be added to the alkalinization step 13, as indicated by arrow 12a. The alkalinization step 13 is a low pressure operation that advantageously serves to enable the addition of a desired predetermined loading of crosslinker present in the crosslinker / alkalinization reagent dispersion to the process.

[0050] Referring again to FIG. 1, after the alkalinization step 13, activated cellulose 14 is formed in the alkalinization step 13, and the activated cellulose is subjected to an etherification step 15, as shown by arrow 14a. In the etherification step 15, an etherification reagent 16 is introduced or added to the etherification step 17, as shown by arrow 16a, to contact the activated cellulose 14 and form a cellulose ether during the etherification step 15. Also in the etherification step 15, there is a crosslinker from the crosslinker / alkalinization reagent 12 mixture previously introduced in the alkalinization step 13, as shown by arrow 12a. The crosslinker together with the activated cellulose proceeds to the etherification step 15, as shown by arrow 14a. During the etherification step 15, the etherification reagent 16 is added to the etherification step 15, as shown by arrow 16a. And in the etherification step 15, the etherification reagent and the crosslinker contact the activated cellulose to form the XCE ether 17, which is formed in the presence of the crosslinker and in the etherification step 15, as shown by arrow 15a.

[0051] In another embodiment, the XCE 17 from the etherification step 15 can proceed to one or more additional optional operations or steps 22, shown in dotted lines in FIG. 1, as indicated by arrow 17a. Although step 22 is optional, one or more of steps 22 are typically desired and used in the process of the present invention. The optional step 22 can be selected from steps known to those skilled in the art, such as (1) a hot water (e.g., above 85° C.) (H2O) washing step to wash the XCE, (2) a granulation step to form XCE granules, (3) a drying step to dry the granulated XCE, and (4) a milling step to form the XCE into a powder product. Each of the above optional operations can be carried out in a single step operation, or two or more of the above optional steps can be combined into one operation, if desired.

[0052] For example, XCE 17 after etherification step 15 typically has unwanted volatile by-products and salts (NaCl) and therefore in a preferred embodiment, XCE 17 after etherification step 15 is processed through a washing step 22, as shown by arrow 15a, to wash away unwanted volatile by-products, salts, and other impurities from the XCE, followed by a drying step 22.

[0053] The starting material used to produce the cellulose ethers of the present invention and added to the alkalizing operation of the XCE production process is cellulose. Cellulose pulp is typically obtained from, for example, wood pulp or cotton linter pulp. The pulp is typically ground using conventional grinding means to provide cellulose in powder or floc form. In one preferred embodiment, suitable cellulose starting materials useful in the present invention include ground wood pulp, ground linter pulp, and mixtures thereof. In another preferred embodiment, wood pulp is used in the process, and the wood pulp is ground into ground flocs of cellulose as a means of making the cellulose feed more fluid when fed to the alkalizing process step. Generally, the pulp is ground to an optimal size of particles, for example, 1,000 microns (μm) to 10 μm in one embodiment, and 900 μm to 25 μm in another embodiment. Coarser particle sizes may reduce the efficiency of the alkalizing step, and finer particle sizes may take too long to grind. Prior to the alkalizing step, the reactor is typically filled with pulp flocs.

[0054] As previously mentioned, the crosslinker is incorporated or introduced into the process during the alkalinization step of the process as a mixture with 50% NaOH in water.

[0055] The crosslinker / alkalinization reagent mixture composition is used in the process of the present invention to alkalize or "activate" a cellulose starting material to form an "activated cellulose material." At least one cellulose material is contacted with the crosslinker / alkalinization reagent mixture, and the cellulose in the alkalinization reagent mixture alkalizes the cellulose under process conditions to form the activated cellulose material. The step of contacting the cellulose material with the crosslinker / alkalinization reagent mixture is carried out by known means, such as, for example, by spraying and mixing the crosslinker / alkalinization reagent mixture onto the cellulose.

[0056] Typically, the crosslinker / alkali composition is added to the alkalinization step of the process in the form of a mixture of the crosslinker and alkalinization reagent, the mixture composition having a concentration ranging, for example, from 1 mol NaOH / mol AGU to 3.5 mol NaOH / mol AGU in one embodiment, from 1.5 mol NaOH / mol AGU to 3.3 mol NaOH / mol AGU in another embodiment, and from 1.8 mol NaOH / mol AGU to 3.1 mol NaOH / mol AGU in yet another embodiment.

[0057] The crosslinker / alkali dispersion added during the alkalinization step to contact the cellulose ether can be done by any known means of addition, such as by uniform spraying, and by any means that allows for uniform distribution of the NaOH to ensure sufficient activation of the cellulose pulp.

[0058] The alkalinization step of the process is carried out under low pressure and low temperature conditions. For example, the pressure of the alkalinization step ranges from 0 kilopascals (kPa) to 500 kPa in one embodiment, from 100 kPa to 400 kPa in another embodiment, and from 200 kPa to 300 kPa in yet another embodiment. The pressure ranges listed above are typical pressure level ranges in the reactor during the alkalinization step. Also, for example, the temperature of the alkalinization step of the process ranges from 10° C. to 50° C. in one embodiment, from 15° C. to 45° C. in another embodiment, and from 20° C. to 40° C. in yet another embodiment. The temperature ranges listed above are typical temperature ranges in the reactor during the alkalinization step. Higher temperatures used in the process of the present invention would result in undesirable pressure buildup.

[0059] To produce cellulose ethers according to the process of the present invention, an etherification reagent is mixed with the activated cellulose material prepared in the above alkalizing step. The etherification reagent used to prepare cellulose ethers includes, for example, one or more etherification reagents known in the art. For example, the etherification reagent can include ethylene oxide (EO), propylene oxide (PO), butylene oxide (BO), methyl chloride (MCl), ethyl chloride, chloroacetic acid, and mixtures thereof. In one preferred embodiment, the etherification reagent useful in the present invention is, for example, MCl, PO, EO, and mixtures thereof.

[0060] The amount of etherification reagent added to the etherification operation of the XCE manufacturing process includes, for example, 4 mol / AGU to 6 mol / AGU in one embodiment, 4.5 mol / AGU to 5.5 mol / AGU in another embodiment, and 4.7 mol / AGU to 5.3 mol / AGU in yet another embodiment. If the amount of etherification reagent used is <4 mol / AGU, the cellulose ether may be under-substituted and not completely water-soluble. If the amount of etherification reagent used is greater than 6 mol / AGU, this high addition of etherification reagent may cause the cellulose ether to become hydrophobic and less water-soluble.

[0061] The etherification reagent added to the etherification step to contact the activated cellulose can be carried out by any known means of addition, for example, by pumping the components into the reactor.

[0062] The etherification step of the process is carried out, for example, in a reaction vessel (reactor) under an inert atmosphere. Inert materials used in the process include, for example, N2, argon, and mixtures thereof. During the etherification step of the process, and as the reaction of the reactants occurs and proceeds to form the cellulose ether material, the pressure and temperature increase as a result of the exothermic reaction.

[0063] Since cellulose ether products are formed during the etherification step, the pressure of the etherification step of the process ranges, for example, from 1,500 kPa to 2,500 kPa in one embodiment, from 1,600 kPa to 2,400 kPa in another embodiment, and from 1,800 kPa to 2,200 kPa in yet another embodiment. At pressures below 1,500 kPa, the reaction rate is too slow, and at pressures above 2,500 kPa, special high pressure equipment is required.

[0064] The temperature of the etherification step of the process is, for example, 60° C. to 100° C. in one embodiment, 70° C. to 90° C. in another embodiment, and 75° C. to 85° C. in yet another embodiment. At temperatures below 60° C., the reaction rate will be unacceptably slow, and at temperatures above 100° C., unwanted side reactions may occur and pressure may increase. For example, if the pressure increases beyond 2,500 kPa, a different pressure reactor capable of handling the high pressure and more expensive would be required.

[0065] In general, the etherification reagent is added to the etherification step of the process and mixed with the activated cellulose material, so that the etherification reagent with the cellulose material forms a homogeneous reaction mixture, which then reacts under the process of etherification to form a cellulose ether. In the etherification step of the process, a crosslinking agent is also present in the reaction mixture, which originates from the alkalization step of the process and is carried over to the etherification step without the crosslinking agent reacting at the low temperature of the alkalization step. When the reaction mixture is heated in the etherification step at the above temperature range, the crosslinking agent reacts with the cellulose ether, and the XCE of the present invention is produced by the crosslinking action of the crosslinking agent with the cellulose ether. The crosslinking action of the cellulose ether to produce the XCE of the present invention can occur, for example, before, during, or after the etherification process step of the process. In a preferred embodiment, the crosslinking reaction of the present invention is produced during the etherification process step by adding a crosslinking agent to the etherification step. Crosslinking cellulose ether to produce XCE is a reaction well known in the prior art and is described, for example, in U.S. Patent No. 6,958,393 B2. Generally, the cellulose ether that is subjected to crosslinking with the crosslinking agent is typically a mixed cellulose ether that contains a hydroxyalkyl group and an alkyl ether group.For example, in one embodiment, the mixed cellulose ether that contains a hydroxyalkyl group and an alkyl ether group includes alkyl hydroxyethyl cellulose, such as hydroxyalkyl methyl cellulose.

[0066] In some embodiments, examples of cellulose ether compounds suitable for use in the present invention include methyl cellulose (MC), ethyl cellulose, propyl cellulose, butyl cellulose, hydroxyethyl methyl cellulose (HEMC), hydroxypropyl methyl cellulose (HPMC), hydroxyethyl cellulose (HEC), methyl hydroxyethyl hydroxypropyl cellulose (MHEHPC), ethyl hydroxyethyl cellulose (EHEC), methyl ethyl hydroxyethyl cellulose (MEHEC), hydrophobically modified ethyl hydroxyethyl cellulose (HMEHEC), hydrophobically modified hydroxyethyl cellulose (HMHEC), sulfoethyl methyl hydroxyethyl cellulose (SEMHEC), sulfoethyl methyl hydroxypropyl cellulose (SEMHPC), sulfoethyl hydroxyethyl cellulose (SEHEC), and mixtures thereof. In some preferred embodiments, the mixed cellulose ethers can include, for example, HEMC, HPMC, and mixtures thereof.

[0067] For the cellulose ethers useful in the present invention, alkyl substitution is described in cellulose ether chemistry by the term "degree of substitution DS" determined by the Zeisel method. DS is the average number of substituted OH groups per anhydroglucose unit. Methyl substitution can be reported, for example, as DS(methyl) or DS(M). Hydroxyalkyl substitution is described by the term "molar substitution MS" determined by the Zeisel method. MS is the average number of moles of etherification reagent bound as ether per mole of anhydroglucose unit. Etherification with the etherification reagent EO is reported, for example, as MS(hydroxyethyl) or MS(HE). Etherification with the etherification reagent PO is correspondingly reported as MS(hydroxypropyl) or MS(HP). Side groups are determined using the Zeisel method (see G. Bartelmus and R. Ketterer, Z. Anal. Chem. 286 (1977), 161-190).

[0068] XCE produced by the process of the invention includes, for example, any of the cellulose ethers mentioned above having some degree of alkyl substitution. For example, crosslinked HEC has a degree of substitution MS(HE) of 1.5 to 4.5 in one embodiment, and MS(HE) of 2.0 to 3.0 in another embodiment. In yet another embodiment, mixed ethers of methylcellulose that are crosslinked can be used in the process of the invention. For example, for HEMC, the DS(M) value ranges from 1.2 to 2.1 in one embodiment, from 1.3 to 1.7 in another embodiment, and from 1.35 to 1.6 in yet another embodiment, and the MS(HE) value ranges from 0.05 to 0.75 in one embodiment, from 0.15 to 0.45 in another embodiment, and from 0.20 to 0.40 in yet another embodiment. For HPMC, the DS(M) value ranges from 1.2 to 2.1 in one embodiment, and from 1.3 to 2.0 in another embodiment, and the MS(HP) value ranges from 0.1 to 1.5 in one embodiment, and from 0.2 to 1.2 in another embodiment.

[0069] After the etherification step described above, the XCE product produced can be treated with various additional optional processing steps. For example, the obtained XCE can be washed or purified, granulated, dried, and / or ground into powder form using conventional methods typically used to produce cellulose derivative products and powders therefrom. For example, before or after washing, volatile organic components present in the XCE can be reduced or removed from the XCE product by distillation or steam stripping. Optional steps are well known to those skilled in the art, and any of the above methods can be used in the process of the present invention. For example, after the etherification step described above, the XCE is typically washed and filtered to produce a filter cake. The filter cake has a very short shelf life and can be cumbersome to handle. Therefore, of the various optional steps described above, in one preferred embodiment, it is desirable to carry out at least washing, drying, and milling steps of the XCE product to form a dry powder product for ease of handling, packaging, and storage purposes.

[0070] Some of the advantageous properties exhibited by the XCE produced by the above-described process of the present invention include, for example, (1) very high viscosity aqueous solutions are obtained, allowing for reduced dosage in, for example, mortar formulation applications.

[0071] For example, the increase in viscosity of the aqueous XCE solution produced by the process of the present invention comprises an increase in viscosity of greater than 15% in one embodiment, greater than 20% in another embodiment, greater than 30% in yet another embodiment, and greater than 50% in yet another embodiment, when compared to the aqueous solution of non-crosslinked cellulose ether.

[0072] In one broad embodiment, the XCE of the present invention can be used as an additive for dry-mix mortar formulations, such as rendering, cementitious tile bonding, cement extrusion, etc. For example, in the process of making a dry-mix mortar formulation, the process includes mixing (I) the above-mentioned XCE used as a water retention agent with (II) the desired conventional dry-mix mortar formulation components, such as hydrolyzed binders including cement or gypsum.

[0073] In a preferred embodiment, the dry mix mortar formulation can be prepared by mixing components (I) and (II) (e.g., physical blends of solid powders) by conventional mixing means as known in the art. Some advantageous properties exhibited by dry mix mortar formulations include, for example, the ability to use lower loadings of XCE (>10%), which can result in lower formulation costs. To prepare the dry mix mortar formulation, the amount of XCE generally used as water retention agent component (I) can be, for example, 0.01% to 1.0% by weight (based on the total amount of dry mix mortar) in one embodiment, 0.05% to 0.8% by weight in another embodiment, and 0.1% to 0.5% by weight in yet another embodiment. Below these levels, the water retention of the dry mix mortar becomes insufficient, and above these limits, the formulation becomes too costly.

[0074] Conventional dry mix mortar formulation ingredients, component (II), may include, for example, ingredients such as hydrolyzed binders such as cement, gypsum, fly ash, furnace slag, and the like, as well as aggregates (sand), fine fillers (calcium carbonate, fumed silica, dolomite, and the like), air entraining agents, defoamers, redispersible polymer powders, hydrophobic agents, and mixtures thereof. EXAMPLES

[0075] The following examples are presented to further illustrate the invention, but should not be construed as limiting the scope of the claims. All parts and percentages are by weight unless otherwise indicated.

[0076] Various terms and designations used in the inventive examples (Inv. Ex.) and comparative examples (Comp. Ex.) are explained as follows: "HEMC" stands for hydroxyethyl methylcellulose. "HPMC" is an abbreviation for hydroxyethyl methylcellulose. "AGU" stands for anhydroglucose unit.

[0077] "LVN" stands for limiting viscosity number of the pulp, measured according to the procedure described in ISO 5351 (2010).

[0078] The various raw materials or components used in the examples are described as follows: Epilox M 985 is a poly(propylene glycol) diglycidyl ether available from Leuna Harze.

[0079] Examples of crosslinking compounds based on diglycidyl ethers which can be used in the process of the present invention are described in Eugene W. Jones, Crosslinking of Cotton Cellulose with Diglycidyl Ether, Journal of Applied polymer science, Vol. V, issue no 18, 714-720 (1961).

[0080] Generally, the following examples are prepared according to the principles of Williamson ether synthesis, as described in the reference "Non-Ionic cellulose Ethers" by R. Donges, British Polymer Journal Vol. 23, pp 315-326 (1990), in which "activated" or alkalized cellulose is produced by treating ground cellulose in contact with 50% caustic soda. This activation or alkalization step is then followed by an etherification operation using MCl and EO.

[0081] The following examples in Table II use HEMC: Additionally, the following examples in Table II use the same pulp material.

[0082] Comparative Example A - Cellulose Ether Synthesized Without Crosslinker (Baseline) Milled cellulose flocs (1.5 moles [mol]) were added to a 5 liter (L) autoclave (reactor). The limiting viscosity number (LVN) of the pulp was measured according to the procedure described in ISO 5351 (2010). Milled cellulose flocs (LVN ≥ 1,450 milliliters per gram [mL / g]) were added to the autoclave.

[0083] The autoclave reactor was purged three times with N2, after which the autoclave reactor was heated to 40°C. Dimethyl ether (DME, 4.7 mol / mol AGU), and a first charge of methyl chloride ("MCl 1", 3.2 mol / mol AGU) were then added to the autoclave. A first charge of caustic soda ("NaOH 1", 50%, 1.9 mol NaOH / mol AGU) was added to the autoclave in three portions over a period of two minutes (min) at a temperature of 40°C. The resulting reaction mixture was then held at 40°C for 30 minutes. EO (0.45 mol / mol AGU) was then added to the reaction mixture, and the reaction mixture was held at 40°C for 10 minutes.

[0084] The resulting mass was heated to 80° C. in 45 minutes. At 80° C., the second MCl charge ("MCl 2", 1.3 mol / mol AGU) was quickly injected into the mass. Then, the second caustic soda charge ("NaOH 2", 0.67 mol / mol AGU) was added in seven portions over 30 minutes, followed by a cook-off period of 70 minutes at 80° C. After the 70 minutes cook-off period, the resulting XCE product was formed. The resulting XCE product was then subjected to the following process steps using conventional procedures known in the art: hot water washing, neutralization with formic acid, granulation using a lab granulator (Bosch Mum), drying, and milling.

[0085] Comparative Example B - Crosslinked Cellulose Ether Synthesized with Epilox M 985 The same procedure as described in Comparative Example A was used in this example, except that EO was added to the reaction mixture and the reaction mixture was held at 40° C. for 10 minutes before the crosslinker Epilox M 985 (0.0030 mol / mol) was added to the autoclave.

[0086] Comparative Example C - Crosslinked Cellulose Ethers Synthesized with Epichlorohydrin The same procedure as described in Comparative Example A was used in this example, except that ECH was used as the crosslinker (0.0030 mol / mol premixed with 4 grams [g] of isopropyl alcohol) and the ECH was added to the autoclave after EO was added to the reaction mixture and the reaction mixture was held at 40° C. for 10 minutes.

[0087] Inventive Example 1 - Crosslinked Cellulose Ether Synthesized with Epilox M985 The crushed cellulose flocs (1.5 mol) were added to a 5 L autoclave. After purging the autoclave with N2 three times, the reactor was heated to 40 °C. Then, DME (4.7 mol / mol AGU) and MCl 1 (3.2 mol / mol AGU) were injected into the autoclave. NaOH 1 (50% strength, 1.9 mol NaOH / mol AGU) was added to the autoclave in three portions: (1) 50% (0.95 mol NaOH / mol AGU) in three portions for 2 min at a temperature of 40 °C, (2) 25% as an emulsion with 0.003 mol / mol crosslinker through a separate dosing device (bypass), and (3) 25% as a washing step through the dosing device. The mixture was then held at 40 °C for 30 min. EO (0.45 mol / mol AGU) was added to the reaction mixture and the reaction mixture was held at 40 °C for 10 min.

[0088] The resulting mass was heated to 80°C in 45 minutes. At 80°C, MCl2 (1.3 mol / mol AGU) was quickly injected into the mass. A second caustic soda charge ("NaOH2", 0.67 mol / mol AGU) was then added to the autoclave in seven portions over 30 minutes, followed by a cook-off period of 70 minutes at 80°C. After the 70 minutes cook-off period, the resulting XCE product was formed. The resulting XCE product was then subjected to the following process steps using conventional procedures known in the art: hot water washing, neutralization with formic acid, granulation using a lab granulator (Bosch Mum), drying, and milling. [Table 2]

[0089] The results of carrying out the above Comparative Examples A-C and the inventive Example 1 are listed in Table II. The use of a 50% NaOH solution in water (or "50% caustic soda") was found to be beneficial as a diluent for the crosslinker used in the inventive process for producing XCE. The crosslinker in combination with 50% caustic soda was easily sprayed onto the pulp. The stability of the crosslinker in a high pH environment such as 50% caustic soda was checked by measuring the epoxy equivalent weight (EEW) of the 50% caustic soda containing crosslinker according to DIN 16946 before and after storage in 50% NaOH for 30 minutes at room temperature (RT; approximately 25°C). During this time, the EEW does not change significantly.

[0090] From the results in Table II, the cellulose ether without crosslinker (Comparative Example A) shows a viscosity of 5,160 mPa.s as a 1% aqueous solution. Addition of Epilox M 985 (0.003 mol / mol) during the etherification step increases the viscosity to 5,720 mPa.s (Comparative Example B). However, replacement of Epilox M 985 with epichlorohydrin (Comparative Example C) results in a significant decrease in viscosity (2,120 mPa.s) due to the formation of water insolubles on the crosslinked gel particles. In the process of the present invention, when Epilox M 985 crosslinker was added to the process during the alkalization step (Inventive Example 1), a more uniform distribution of the crosslinker and an optimized viscosity (6,090 mPa.s) of the resulting XCE was produced.

[0091] The following examples, listed in Table III, use HPMC. The examples were produced in a laboratory reactor (5 L autoclave). All examples were carried out using the same pulp material.

[0092] Comparative Example D - Cellulose Ether Synthesized Without Crosslinker (Baseline) Milled cellulose floc (1.5 mol) was added to a 5 L autoclave. The autoclave was purged with N2 three times and then the reactor was heated to 40°C. DME (4.7 mol / mol AGU) and MCI 1 (3.2 mol / mol AGU) were then added to the autoclave. NaOH 1 (50% strength, 1.9 mol NaOH / mol AGU) was added to the autoclave in three portions for 2 minutes at a temperature of 40°C. The reaction mixture was then held at 40°C for 30 minutes. PO (0.45 mol / mol AGU) was then added to the reaction mixture and the reaction mixture was held at 40°C for 10 minutes.

[0093] The resulting mass was heated to 80°C in 45 minutes. At 80°C, MCl2 (1.3 mol / mol AGU) was quickly injected into the mass. A second caustic soda charge ("NaOH2", 0.67 mol / mol AGU) was then added to the autoclave in seven portions over 30 minutes, followed by a cook-off period of 70 minutes at 80°C. After the 70 minutes cook-off period, the resulting XCE product was formed. The resulting XCE product was then subjected to the following process steps using conventional procedures known in the art: hot water washing, neutralization with formic acid, granulation using a lab granulator (Bosch Mum), drying, and milling.

[0094] Comparative Example E - Crosslinked cellulose ether synthesized with Epilox M 985 The same procedure was used in this example as described in Comparative Example D, except that the crosslinker Epilox M 985 (0.0030 mol / mol) was added to the autoclave reactor after the PO was added to the reaction mixture and the reaction mixture was held at 40° C. for 10 minutes.

[0095] Inventive Example 2 - Crosslinked Cellulose Ether Synthesized with Epilox M 985 The ground cellulose floc (1.5 mol) was added to a 5 L autoclave. After purging the autoclave with N2 three times, the reactor was heated to 40°C. Then, DME (4.7 mol / mol AGU) and MCI 1 (3.2 mol / mol AGU) were added to the autoclave. NaOH 1 (50% strength by weight, 1.9 mol NaOH / mol AGU) was added to the autoclave in three portions: (1) 50% (0.95 mol NaOH / mol AGU) in three portions for 2 minutes at a temperature of 40°C, (2) 25% as an emulsion with 0.003 mol / mol crosslinker through a separate dosing device (bypass), (3) 25% as a washing step through the dosing device. The mixture was then held at 40°C for 30 minutes. PO (0.45 mol / mol AGU) was then added to the reaction mixture, and the reaction mixture was held at 40°C for 10 minutes.

[0096] The resulting mass was heated to 80°C in 45 minutes. At 80°C, MCl2 (1.3 mol / mol AGU) was quickly injected into the mass. A second caustic soda charge ("NaOH2", 0.67 mol / mol AGU) was then added in seven portions over 30 minutes, followed by a cook-off period of 70 minutes at 80°C. After the 70 minutes cook-off period, the resulting XCE product was formed. The resulting XCE product was then subjected to the following process steps using conventional procedures known in the art: hot water washing, neutralization with formic acid, granulation using a lab granulator (Bosch Mum), drying, and milling. [Table 3]

[0097] The results of carrying out Comparative Examples D and E and Inventive Example 2 above are listed in Table III. As with Comparative Examples A-C and Inventive Example 1 above using HEMC, the results summarized in Table III show the same observations as Comparative Examples D and E and Inventive Example 2 using HPMC. Because the pulp material used in the examples listed in Table III is different from the pulp material used in the examples listed in Table II, the 1% aqueous viscosity of the non-crosslinked HPMC (Comparative Example D) is 8,350 mPa.s. The addition of Epilox M 985 to the process during the etherification step slightly increased the viscosity of XCE (Comparative Example E). However, when Epilox M 985 crosslinker was added to the inventive step during the alkalization step, the viscosity of XCE of the inventive (Inventive Example 2) (10,700 mPa.s) increased significantly more than the other Comparative Examples D and E. The invention as originally claimed in the present application is set forth below. [1] A process for producing crosslinked cellulose ethers, comprising: (i) contacting at least one cellulosic material with a mixture comprising (ia) at least one cross-linking agent and (ib) at least one alkalizing agent to form an activated cellulosic material; (ii) contacting the activated cellulose material of step (i) with at least one etherification reagent, wherein the at least one etherification reagent reacts with the activated cellulose material to form the crosslinked cellulose ether. [2] A process for producing a crosslinked cellulose ether, comprising: (A) mixing (a) at least one crosslinker with (b) at least one alkalizing reagent to form a crosslinker / alkalinizing reagent mixture; (B) contacting at least one cellulosic material with the mixture of step (A) to form an activated cellulosic material; and (C) contacting the activated cellulose material of step (B) with at least one etherification reagent, wherein the at least one etherification reagent reacts with the activated cellulose material to form a crosslinked cellulose ether. [3] The process of [1] or [2], further comprising subjecting the crosslinked cellulose ether to one or more of the steps of refining, washing, drying, granulating, and milling. [4] The process of [1], wherein the activated cellulose material is formed at a pressure of 500 kilopascals or less and a temperature of 50°C or less. [5] The process of [1], wherein the crosslinked cellulose ether is formed at a pressure of 1,000 kilopascals or more and a temperature above 70°C. [6] The at least one crosslinking agent is a diglycidyl ether type crosslinking agent having the following chemical structure (I): [ka] [1], wherein n is 3 to 25, and the at least one alkalizing reagent is selected from the group consisting of solutions of sodium hydroxide, potassium hydroxide, lithium hydroxide, and mixtures thereof. [7] The process of [1], wherein the at least one cellulosic material is selected from the group consisting of wood pulp, cotton linters, and mixtures thereof, and the at least one etherifying reagent is selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, methyl chloride, ethyl chloride, and mixtures thereof. [8] The process of [1], wherein steps (i) and (ii) are carried out in an inert atmosphere. [9] The process of [1], wherein the at least one crosslinking agent is present in the mixture of step (i) at a concentration of from 0.0001 moles of crosslinking agent per mole of anhydroglucose units of the cellulose ether to 0.05 moles of crosslinking agent per mole of anhydroglucose units of the cellulose ether, and the at least one alkalizing reagent is present in the mixture of step (i) at a concentration of from 1 mole of alkalizing reagent per mole of anhydroglucose units of the cellulosic material to 3.5 moles of alkalizing reagent per mole of anhydroglucose units of the cellulosic material, to form the activated cellulose material.

[10] The process of [1], further comprising the step of grinding the at least one cellulose material to form a comminuted cellulose floc material, wherein the grinding step is performed prior to contacting the at least one cellulose material with the dispersion mixture of step (a).

[11] A crosslinked cellulose ether produced by the process described in [1].

[12] A dry mix mortar composition comprising: (I) a crosslinked cellulose ether according to

[11] , (II) a hydrolyzable binder, wherein the hydrolyzable binder is a cement or gypsum material.

Claims

1. 1. A process for producing a crosslinked cellulose ether, comprising: (i) contacting at least one cellulosic material with a mixture comprising (ia) at least one cross-linking agent and (ib) at least one alkalizing reagent to form an activated cellulosic material; (ii) contacting the activated cellulose material of step (i) with at least one etherification reagent, wherein the at least one etherification reagent reacts with the activated cellulose material to form the crosslinked cellulose ether. Including, the at least one etherification reagent is selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, methyl chloride, ethyl chloride, and mixtures thereof; The at least one crosslinking agent is a diglycidyl ether type crosslinking agent having the following chemical structure (I): 【Chemistry 1】 wherein n is 3 to 25, and said at least one alkalizing reagent is selected from the group consisting of solutions of sodium hydroxide, potassium hydroxide, lithium hydroxide, and mixtures thereof. process.

2. 1. A process for producing a crosslinked cellulose ether, comprising: (A) mixing (a) at least one crosslinking agent with (b) at least one alkalizing reagent to form a crosslinking agent / alkalinizing reagent mixture; (B) contacting at least one cellulosic material with the mixture of step (A) to form an activated cellulosic material; and (C) contacting the activated cellulose material of step (B) with at least one etherification reagent, wherein the at least one etherification reagent reacts with the activated cellulose material to form a crosslinked cellulose ether. Including, the at least one etherification reagent is selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, methyl chloride, ethyl chloride, and mixtures thereof; process.

3. 3. The process of claim 1 or claim 2, further comprising subjecting the crosslinked cellulose ether to one or more of the steps of refining, washing, drying, granulating, and milling.

4. 10. The process of claim 1, wherein the activated cellulose material is formed at a pressure of 500 kilopascals or less and a temperature of 50°C or less.

5. 2. The process of claim 1, wherein the crosslinked cellulose ether is formed at a pressure of 1,000 kilopascals or more and a temperature above 70°C.

6. 2. The process of claim 1, wherein the at least one cellulosic material is selected from the group consisting of wood pulp, cotton linters, and mixtures thereof.

7. 2. The process of claim 1, wherein steps (i) and (ii) are carried out in an inert atmosphere.

8. The process of claim 1, wherein the at least one alkalizing reagent is present in the mixture of step (i) at a concentration of from 1 mole of alkalizing reagent per mole of anhydroglucose units of the cellulose material to 3.5 moles of alkalizing reagent per mole of anhydroglucose units of the cellulose material to form the activated cellulose material.

9. 2. The process of claim 1, further comprising the step of grinding the at least one cellulose material to form a ground cellulose flock material, the grinding step being performed prior to contacting the at least one cellulose material with a mixture comprising (ia) at least one cross-linking agent and (ib) at least one alkalizing reagent.

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