Process for producing cross-linked cellulose ethers

Abstract

A process for producing a cross-linked cellulose ether comprising the steps of: (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; and (ii) contacting the activated cellulosic material of step (i) with at least one etherifying agent; wherein the at least one etherifying agent reacts with the activated cellulose material to form the crosslinked cellulose ether; and a crosslinked cellulose ether produced by the above process.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 202080028098.5 (filing date: April 17, 2020; invention title: Method for producing crosslinked cellulose ethers). Technical Field

[0002] The present invention relates to a method for producing crosslinked cellulose ethers and crosslinked cellulose ethers prepared by such methods. Background Art

[0003] Cellulose derivatives, such as cellulose ethers, are widely used as, for example, thickeners, binders, adhesives, and dispersants, water retention agents, protective colloids, stabilizers, and suspending, emulsifying, and film-forming agents due to their excellent properties and physiological safety. In addition, cellulose ethers are known to be used in dry-mixed mortars for various construction applications to improve the rheology of the mortar. In addition, cellulose ethers are used in mortars to impart water retention properties, thereby restricting the loss of water from the mortar to the absorbent substrate. This ensures that there is sufficient water available for the hydraulic binder (cement or gypsum) during the setting reaction, thereby resulting in a high mechanical strength of the final product. Lack of water will lead to incomplete setting, poor mechanical strength, crack formation, and low abrasion resistance.

[0004] To date, cellulose ethers have been produced by well-known conventional methods, which include subjecting a cellulose starting material, such as cellulose pulp, to two process operations (steps or stages): (1) an alkalization operation and (2) an etherification operation. For example, the well-known prior art conventional procedures for manufacturing cellulose ethers are described and illustrated in U.S. Patent No. 6,235,893 B1. The conventional method includes the following steps: (1) alkalizing the cellulose pulp; and (2) etherifying the alkalized cellulose pulp to form a cellulose ether. For example, in the conventional method, the cellulose pulp is alkalized with sodium hydroxide and etherified with chloromethane and an alkylene oxide (ethylene oxide or propylene oxide). Also, each of the above alkalization and etherification operations can be carried out stepwise, i.e., in one step or in two or more different separate steps, and each step can be carried out for a predetermined period of time under specified pressure and temperature process conditions. After manufacturing the cellulose ether, the cellulose ether can undergo additional desired process steps, such as: (3) washing the cellulose ether; (4) drying the cellulose ether; and (5) grinding the cellulose ether into a particulate form. Typically, the alkalization and etherification operations can be carried out in a single reactor or two or more reactors.

[0005] Recently, the conventional method of manufacturing cellulose ethers has been improved by using crosslinking technology to manufacture crosslinked cellulose ethers. Crosslinking technology involves cellulose ethers that can be chain-extended or crosslinked using bifunctional crosslinking agents such as dichloromethane, epichlorohydrin, or various diglycidyl ethers. For example, U.S. Patent No. 6,958,393 B2 (equivalent to EP1384727 B9) discloses a method of manufacturing crosslinked cellulose ethers containing polyether groups using crosslinking technology. Crosslinked cellulose ethers are produced by crosslinking cellulose ethers at a temperature of 90 degrees Celsius (°C) or lower, in an inert atmosphere such as nitrogen (N2), in the presence of a crosslinking agent containing polyether groups, and in the presence of a caustic or base. The crosslinking of the cellulose ethers is carried out in the reactor in which the cellulose ethers themselves are manufactured and in the presence of a caustic or base.

[0006] One advantage of using crosslinked cellulose ethers in, for example, dry-mix mortar formulations compared to pure non-crosslinked cellulose ethers is that by crosslinking the cellulose ether with a crosslinking agent, the viscosity of the aqueous solution of the cellulose ether can be increased and the resulting crosslinked cellulose ether having an increased or high viscosity can still remain water-soluble in the aqueous solution. Also, crosslinked cellulose ethers having an increased or high viscosity produced using crosslinking technology can be used at reduced dosage levels in, for example, mortar applications without compromising the product and application performance. Cellulose ethers are a relatively expensive component used in mortar formulations, and any reduction in the dosage of cellulose ether in the formulation can result in cost savings for the formulation.

[0007] In previously known methods, the dosage of the crosslinking agent used to crosslink cellulose ethers was kept very low to prevent "overcrosslinking", which in turn provided a crosslinked polymer product that remained water-insoluble and did not contribute to the viscosity of the aqueous solution. However, it was very difficult to achieve uniform distribution of the small amount of crosslinking agent added to the contents of a large reactor using previously known methods.

[0008] As used herein, "overcrosslinking" with reference to the crosslinking of cellulose ethers means that the reaction of the cellulose ether with the crosslinking agent is too extensive and results in a three-dimensional network of covalently linked cellulose ether chains; and such chains are insoluble in water and appear as gel particles in the aqueous phase. Overcrosslinking results in a decrease in the water solubility of the cellulose ether in the aqueous solution. When overcrosslinking occurs in the cellulose ether, the amount of the resulting crosslinked cellulose ether that is soluble in the aqueous solution decreases; and an appropriate viscosity of the crosslinked cellulose ether cannot be achieved in the aqueous solution. In other words, overcrosslinking results in an undesired decrease in viscosity. Compared to non-overcrosslinked cellulose ethers, overcrosslinked cellulose ethers exhibit a degree of crosslinking that results in a decrease in water solubility.

[0009] For example, the known method for crosslinking cellulose ethers described in U.S. Patent No. 6,958,393 B2 includes the following steps, such as: (1) alkalizing cellulose with an aqueous solution of an alkali metal hydroxide in the presence of a suspension medium; (2) reacting the alkalized cellulose with one or more alkylene oxides; (3) additionally reacting the alkalized cellulose with an alkyl halide present in the suspension medium; (4) subsequently or simultaneously, reacting the alkalized cellulose with a crosslinking agent using a specified amount of the crosslinking agent; (5) additionally adding an alkali metal hydroxide and / or an alkalizing agent to the reaction mixture of step (4); and (6) purifying and drying the resulting crosslinked cellulose ether.

[0010] The method described in U.S. Patent No. 6,958,393 B2 requires: (1) adding a crosslinking agent under high pressure during the etherification step of the method; (2) using epichlorohydrin (ECH) as a crosslinking agent in some cases; (3) adding a low level of the crosslinking agent in pure form or dispersed in an organic solvent; (4) the crosslinking agent being uniformly distributed at a limited low pure crosslinking agent level; and (5) the resulting product of the method exhibiting good performance. In addition to the above requirements, in some cases, using the above-known method results in poor distribution of the crosslinking agent in the reactor; and overcrosslinking of the crosslinked cellulose product and an undesired decrease in viscosity have developed. Also, the efficiency of the known method of U.S. Patent No. 6,958,393 B2 is not easily transferred from the laboratory scale to the pilot plant scale, and / or ultimately to the full-scale industrial plant scale. Therefore, a greater degree of expertise, knowledge, and technical effort is required to implement the above-known method on a plant scale; and to function under the conditions of the known method.

[0011] It has been found that, in order to carry out a successful crosslinking process, when a crosslinking agent is introduced into the process in a low amount, uniform distribution of the crosslinking agent must be achieved. Uniform distribution must be achieved to produce the desired branched polymer and to prevent local overdose that leads to overcrosslinking. Overcrosslinking (i.e., high-level crosslinking) results in an increase in the level of local crosslinking networks and local insoluble materials. It has also been found that overcrosslinking can depend on when and at which stage, step, or operation of the crosslinked cellulose ether production method the crosslinking agent is introduced into the process. For example, the crosslinking agent can be introduced or added before, during, or after the etherification operation. However, since the alkalization and etherification reactions are exothermic, there are many factors that can affect whether overcrosslinking occurs in the process. The factors can include, for example, reaction time, type of crosslinking agent introduced into the process, amount of crosslinking agent introduced into the process, how the crosslinking agent is introduced into the process, process conditions when the crosslinking agent is introduced into the process, and the time period over which the crosslinking agent is introduced into the process.

[0012] Accordingly, there is a desire to provide a new and improved process for producing crosslinked cellulose ethers, which process can be used on an industrial plant scale and is carried out with higher efficiency than known conventional processes; and at the same time, wherein the properties of the products obtained from such improved processes remain the same or better than those of the known products of conventional processes. SUMMARY OF THE INVENTION

[0013] The problems of the prior art processes can be solved by using the process of the present invention. The present invention relates to a novel process for preparing crosslinked cellulose ethers (referred to herein as "XCE") having a suitably increased viscosity.

[0014] The present invention relates to a novel low-pressure (e.g., at atmospheric pressure) process for preparing XCE having an enhanced aqueous solution viscosity. The present invention relates to providing a crosslinking agent dosage in a cellulose ether production process at atmospheric pressure, which enables the production of XCE, such as hydroxyethyl methylcellulose derivatives, which not only eliminates the cost-intensive high-pressure dosage step of known prior art processes, but also provides a product with an increased aqueous solution viscosity. Such a product can be used in a reduced dosage in, for example, dry-mix mortar formulations and still provide suitable performance characteristics.

[0015] In one embodiment, the crosslinking agent dosage occurs in a low-pressure step, which in the process of the present invention is, for example, the alkalization step of a process that is a step prior to a high-pressure etherification process step. In the present invention, controlling the dosage of the crosslinking agent provides an economical way to produce an XCE product with good rheological properties (higher viscosity level) with less technical effort. In addition, compared to known processes, the dosage concept of the present invention has the additional benefit of an enhanced process window for crosslinking agent addition.

[0016] In a preferred embodiment, the present invention relates to a process for producing XCE, which comprises the steps of: (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 at least one etherifying reagent reacts with the activated cellulose material to form XCE. The contacting step (i) can be carried out, for example, at a pressure less than or equal to (≤) 500 kilopascals (kPa); and at a temperature of ≤ 50 °C. The contacting step (ii) is carried out, for example, at a pressure greater than or equal to (≥) 1,500 kPa; and at a temperature of ≥ 70 °C. Optionally, the above process may include one or more additional steps of purifying, washing, drying, granulating, and grinding the XCE obtained from step (ii).

[0017] In another embodiment, the present invention relates to a method for producing a crosslinked cellulose ether, which comprises the following steps: (A) mixing (a) at least one crosslinking agent with (b) at least one alkalizing agent to form a crosslinking agent / alkalizing agent mixture; (B) bringing at least one cellulose material into contact with the mixture of step (A) to form an activated cellulose material; (C) bringing the activated cellulose material of step (B) into contact with at least one etherifying agent; wherein at least one etherifying agent reacts with the activated cellulose material to form a crosslinked cellulose ether; and (D) optionally, subjecting the crosslinked cellulose ether to one or more steps of purification, washing, drying, granulating and grinding.

[0018] In yet another preferred embodiment, the crosslinking agent is introduced or added into the process during the alkalization operation; and the crosslinking agent is added into the process in the form of a mixture of the crosslinking agent and the alkalizing agent.

[0019] In still another embodiment, the present invention relates to an XCE produced by the above method. When compared with non-crosslinked cellulose ethers, the XCE produced by the above method of the present invention advantageously has high water solubility, resulting in an increase in viscosity in an aqueous solution.

[0020] Yet another embodiment of the present invention relates to a composition for forming a dry-mixed mortar, which comprises the above XCE.

[0021] Surprisingly, it has been found that by using the method of the present invention and introducing a desired low dose of a uniformly distributed crosslinking agent compound under low-pressure process conditions (e.g., 100 kPa to 500 kPa), not only is the entire process of producing XCE advantageously simplified, but also an effective production method for manufacturing XCE is provided. For example, the dose of the crosslinking agent introduced in the method of the present invention is carried out in an earlier step of the method of the present invention, i.e., the dose of the crosslinking agent used in the present invention is introduced or added during the alkalization of the cellulose starting material operation of the method of the present invention; however, the dose of the crosslinking agent used in the known conventional method is introduced or added during the etherification operation. Therefore, compared with adding the crosslinking agent dose at the high-pressure point or step of the conventional method, the addition of the desired uniformly distributed crosslinking agent dose occurs at the low-pressure point or step of the method of the present invention. In a typical conventional method, an alkalizing agent such as sodium hydroxide (NaOH or caustic soda) is added to cellulose to perform the alkalization step. However, when the crosslinking agent is combined with an alkalizing agent as carried out according to the present invention, the alkalizing agent also acts as a diluent for the crosslinking agent so that the crosslinking agent can be uniformly distributed in the method. Advantageously, it may not be necessary to add a greater amount of the crosslinking agent in the alkalization step or in any other step following the process scheme of the present invention.

[0022] Some other benefits of the method of the present invention include, for example: (1) controlling the dosage of the crosslinking agent can produce XCE with a favorable and desired (and appropriate) increased viscosity level, thereby avoiding overcrosslinking, and especially for use in large-scale plant processes; (2) the crosslinking agent has low water solubility and forms a dispersion in an alkaline solution; (3) a small amount of crosslinking agent is required in the process, thus providing a higher viscosity with a small dosage of the crosslinking agent; (4) a small amount of crosslinking agent can be evenly distributed in a large-scale plant process; (5) the method does not require an additional spraying device in the reactor for carrying out the method of the present invention.

[0023] Furthermore, advantageously, the method of the present invention provides XCE products having the same or better performance characteristics as known products prepared by known methods. Additionally, advantageously, the method of the present invention can be carried out on a large-scale plant scale, the crosslinking agent dosage occurs in the alkalization step of the method of the present invention and there is no problem of overcrosslinking. Brief Description of the Drawings

[0024] Figure 1 To show a schematic flow chart of the method of the present invention. Detailed Description

[0025] "Evenly distributed" in the present disclosure, and with respect to bringing cellulose fibers into contact with different components, herein means 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 is a cube with a side length ten times the average particle size of the cellulose fibers in the given volume.

[0026] Generally, the method for producing XCE includes an alkalization step and an etherification step. The step of grinding the cellulose starting material can be carried out before the alkalization step and is typically desirable; and the washing (hot H2O) / granulation step and / or drying / grinding step of XCE can be carried out after the etherification step. During the alkalization operation of the method, a crosslinking agent is introduced or added to the alkalization operation to provide crosslinking of the cellulose material in subsequent downstream operations of the method, such as during the etherification operation.

[0027] In a broad embodiment, the present invention relates to the dosage of the crosslinking agent and the addition of the crosslinking agent to the method for producing XCE products. In a preferred embodiment, the crosslinking agent is added or dosed into the alkalization step or operation of the method in the form of a mixture of the crosslinking agent and an alkalization reagent combined with the alkalization reagent.

[0028] The small dosage of the crosslinking agent used in the present invention results in ultra-high viscosity products having the same rheological properties as known products (e.g., high viscosity measured in millipascal seconds [mPa.s]), but the crosslinking agent has higher efficiency. Advantageously, the result is a reduced level of undesired side reactions and a minimal impact on wastewater treatment. Additionally, in the present invention, the dosage of the expensive crosslinking agent can be reduced and overcrosslinking can be prevented.

[0029] The benefit of the crosslinker dosage used in the present invention is that alkali / water is used as the suspension medium (or diluent) of the crosslinker, so that the purpose of providing a uniform distribution of the dispersion in the cellulose material during the dosage step can be more easily achieved compared with the conventional method. In addition, the present invention using the alkali / water suspension medium has no safety problems and environmental problems in the XCE manufacturing plant, just like the methods known in the art using organic solvents as the diluent of the crosslinker.

[0030] Additional benefits of the method of the present invention include, for example, (1) the method uses crosslinkers based on diglycidyl ether chemistry that are easily obtainable, such as Epilox M 985 or Epilox P13-42; and (2); the crosslinker / alkali / water dispersion is non-toxic. In contrast, the known methods use epichlorohydrin (ECH) as the crosslinker system; and such known methods have several disadvantages, including, for example, that ECH is known to be toxic, carcinogenic and has a low boiling point (116 °C) / low molecular weight (Mw) (92.53 g·mol -1 ). Table I describes the comparison of the physical data of Epilox products with ECH.

[0031] Table I - Physical Data of Crosslinking Agents

[0032]

[0033] The method of the present invention provides an irreversible XCE that has beneficial rheological behavior and advantageous properties in various application fields. The present invention uses C10-C24 alkyl difunctional compounds (ethylene oxide and / or halide) and polypropylene glycol diglycidyl ether as crosslinkers to prepare XCE. The method of the present invention uses a crosslinker / alkali / water mixture or dispersion to introduce the crosslinker into the alkalization step of the method. The prior art methods using ECH as the crosslinker to prepare XCE usually produce insoluble crosslinked products, and, compared with ECH, the crosslinkers available for the present invention are less involved in environmental problems.

[0034] Generally, the crosslinker / alkali dispersion composition available for the present invention includes a mixture of the following: (i) a crosslinker and (ii) an alkalizing reagent in water; and (iii) any other optional components desired.

[0035] The crosslinkers used to prepare the cellulose ethers of the present invention include, for example, one or more crosslinkers known in the art. Crosslinkers having non-water-soluble properties or a solubility in water less than (<) 10 percent (%) are typically used. For example, the non-water-soluble properties of the crosslinker allow optimizing the occurrence of the desired side reactions with the hydroxyl (-OH) groups of the cellulose backbone and minimizing the undesired side reactions with the -OH groups of NaOH used in the alkalization operation.

[0036] Crosslinking agents suitable for the present invention include, for example, compounds having: polyalkylene oxide or polyalkylene glycol groups and two or more, preferably two crosslinking groups that form ether bonds with the cellulose ether when the cellulose ether is crosslinked, such as halogen groups, glycidyl groups or epoxy groups, or ethylenically unsaturated groups, such as vinyl groups. Suitable bifunctional compounds include, for example, 1,2-dichloro(poly)alkoxyethers, dichloropolyethylene oxide, diglycidyl polyalkoxyethers, diglycidyl phosphonate, divinyl polyalkylene oxide containing a sulfone group; and mixtures thereof. Compounds with two different functional groups can also be used. Examples of compounds with two different functional groups include ECH, glycidyl (poly)oxyalkyl methacrylate; and mixtures thereof.

[0037] In a preferred embodiment, the crosslinking agent that can be used 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 illustrated by the following chemical structure (I):

[0038]

[0039] Wherein, in the above structure (I), "n" can be 3 to 25 in one embodiment, 7 to 20 in another embodiment and 9 to 15 in yet another embodiment.

[0040] Examples of some of the commercial crosslinking agents that can be used in the present invention, for example, crosslinking agents based on diglycidyl ether chemistry, include Epilox P13-42, wherein when n is equal to (=) approximately (about) 8, the Epilox P13-42 product is of structure (I); and Epilox M 985, wherein when n = about 13, the Epilox M 985 product is of structure (I) (both of the above two Epilox products are available from Leuna-Harze GmbH). The Epilox M 985 crosslinking agent is a linear poly(propylene glycol) diglycidyl ether manufactured from polypropylene glycol (PPG).

[0041] Crosslinking agents such as Epilox M 985 and Epilox P13-42 are examples of preferred embodiments because advantageously, such crosslinking agents: (1) are non-toxic; and (2) have a very high boiling point (e.g., higher than (>) 200 °C) / high Mw (e.g., higher than 600 grams per mole [g / mol]). This is in contrast to some of the known crosslinking agent systems used in the prior art, such as ECH, which: (1) is toxic and / or carcinogenic; and (2) has a low boiling point (e.g., 116 °C) / low Mw (e.g., 92.53 g / mol).

[0042] Using a crosslinking agent such as Epilox M 985, true covalent bonds can be established with the cellulosic material. This establishment of covalent bonds advantageously increases the Mw of the cellulose ether. The cellulose ethers of the present invention with increased Mw provide a means of achieving beneficial properties, such as high viscosity levels (e.g., >20% higher compared to non-crosslinked cellulose ethers).

[0043] Examples of some other advantageous properties exhibited by the crosslinker may include lower dosage levels in dry mix mortar applications without sacrificing performance properties.

[0044] Furthermore, when using the XCE of the present invention, the amount of XCE required to obtain desired properties is reduced compared to non-crosslinked cellulose ethers, for example, when used in dry-mix mortar formulations. Such reductions in XCE dosage in turn reduce the cost of use, which is associated with the reduced amount of cellulose ether required to obtain desired properties, for example, in cement tile adhesive applications.

[0045] Typically, the amount of the crosslinking agent used in the present invention may be in the range of 0.0001 equivalent to 0.05 equivalent, where the unit "eq" represents the molar ratio of the number of moles of the corresponding crosslinking agent relative to the number of moles of anhydroglucose units (AGU) of the cellulose ether. The amount of the crosslinking agent used in the method is typically 0.0005 equivalent to 0.03 equivalent in one embodiment and 0.001 equivalent to 0.005 equivalent in another embodiment. When the amount of the crosslinking agent used is higher than 0.05 equivalent, excessive crosslinking of the XCE occurs; and thus the cellulose ether becomes insoluble. When the amount of the crosslinking agent used is lower than 0.0001 equivalent, for example, the viscosity increase of the XCE in a 1% solution is not detectable.

[0046] The alkalizing agent (or alkalizing agent) used for mixing with the cross-linking agent to dilute the cross-linking agent and also used during the alkalization step of the method of the present invention includes, for example, one or more alkalizing agents known in the art. For example, the alkalizing agent includes a solution of an alkali metal hydroxide such as NaOH, potassium hydroxide (KOH), lithium hydroxide (LiOH), and a mixture thereof. Although in some embodiments, an alkaline aqueous solution of KOH or LiOH is suitable for use as an alkalizing agent, for economic reasons, the alkali metal hydroxide used as an alkalizing agent 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, which can be purchased from The Dow Chemical Company. In a preferred embodiment, when carrying out the method of the present invention, the alkalizing agent is used to alkalize natural cellulose or cellulose hydrate,

[0047] Typically, the alkalizing reagent is in the form of a mixture of the alkalizing reagent in water (e.g., 50% NaOH in water); and the concentration of the aqueous solution can vary. For example, by weight % of water, the aqueous solution ranges from 10 weight percent (wt%) to 90 wt% in one embodiment, from 25 wt% to 75 wt% in another embodiment, and from 40 wt% to 60 wt% in yet another embodiment. In a preferred embodiment, the aqueous solution is used as a 50% reagent in water.

[0048] The water used in the alkalizing reagent is obtained from any source. Different types of water include, for example, tap water, drinking water, and deionized water.

[0049] The alkalizing reagent is formed by mixing the alkalizing reagent and water by conventional mixing means before or just prior to mixing the alkalizing reagent with the crosslinking agent of the present invention.

[0050] In a general embodiment, a method for producing a crosslinking agent / alkalizing reagent dispersion or suspension useful in the present invention comprises: (a) mixing at least one crosslinking agent with at least one alkalizing reagent to form a dispersion. Mixing the crosslinking agent and the alkalizing reagent to form a dispersion is carried out by any conventional mixing means such as any horizontal or vertical mixing device; or it can be carried out by pumping the crosslinking agent into the alkalizing reagent; or by a combination of the feed lines of the alkalizing agent and the crosslinking agent for mixing.

[0051] An example of one of the advantageous properties exhibited by the crosslinking agent / alkalizing reagent dispersion includes that the dispersion is easily and uniformly distributed on the cellulose starting material during alkalization.

[0052] A broad embodiment, a method for producing XCE from a cellulose starting material comprises the steps of: (a) mixing at least one crosslinking agent with at least one alkalizing reagent to form a crosslinking agent / alkalizing reagent mixture; (b) contacting at least one cellulose material with the crosslinking agent / alkalizing reagent mixture of step (a) to form an activated cellulose material such that the activated cellulose material is formed in the presence of at least one crosslinking agent and at a pressure of ≤500 kPa; and at a temperature of ≤50 °C; (c) contacting the activated cellulose material of step (b) with at least one etherifying reagent in the presence of at least one crosslinking agent from step (b) to form XCE; and (d) optionally, subjecting the XCE from step (c) to one or more steps of purification, washing, drying, granulating, and grinding.

[0053] Reference Figure 1 , shows the method of the present invention, which is generally indicated by reference numeral 10, having various general process operations or steps for producing an XCE with enhanced viscosity of an aqueous solution and useful, for example, in dry-mix mortar formulations. As Figure 1As shown, the method includes, for example: a cellulose starting material 11, such as pulp, and a dispersion or mixture 12 of a crosslinking agent and an alkalizing agent, which travel to an alkalizing step 13 as indicated by arrows 11a and 12a, respectively.

[0054] Such as Figure 1 The general process as described in may include optional operations or steps, for example, Figure 1 The optional grinding step 21 shown by the dashed line in, which travels as indicated by arrow 21a to form the cellulose starting material 11, and then travels to the alkalizing step 13 as indicated by arrow 11a. Although the grinding step 21 is optional, the grinding step 21 is typically used in the preferred embodiment so that the cellulose starting material 11 (e.g., wood pulp) can be ground to form ground cellulose fluff, which can easily flow and mix in the reactor. The ground fluff is also easily contacted with the crosslinking agent / alkalizing agent mixture 12, such as by spraying the mixture onto the ground cellulose fluff mixed in the reactor using conventional spraying means. The ground fluff of cellulose 11 then travels and then travels to the alkalizing step 13 as indicated by arrow 11a.

[0055] In the alkalizing step 13, a crosslinking agent / alkalizing agent dispersion mixture 12 containing (i) an alkalizing agent such as NaOH (50% in water) and (ii) a crosslinking agent as described above is mixed with the cellulose material 11 to form activated cellulose 14 as indicated by arrow 13a, which then travels to an etherification step 15 as indicated by arrow 14a. In the alkalizing step 13 of the method 10, as indicated by arrow 12a, a combination or mixture 12 of a crosslinking agent and an alkalizing agent, for example in the form of a dispersion or an aqueous suspension 12, can be added to the alkalizing step 13. The alkalizing step 13 is a low-pressure operation, which advantageously helps to add a desired predetermined dose of the crosslinking agent present in the crosslinking agent / alkalizing agent dispersion to the process.

[0056] Referring again to Figure 1, after the alkalization step 13, activated cellulose 14 is formed in the alkalization step 13, and the activated cellulose undergoes an etherification step 15 as indicated by arrow 14a. In the etherification step 15, an etherification reagent 16 is introduced or added to the etherification step 17 as indicated by arrow 16a to contact the activated cellulose 14 and form a cellulose ether during the etherification step 15. Further, present in the etherification step 15 is a crosslinking agent from the mixture of crosslinking agent / alkalization reagent 12, which has been previously introduced into the alkalization step 13 as indicated by arrow 12a. As indicated by arrow 14a, the crosslinking agent proceeds with the activated cellulose to the etherification step 15. In the etherification step 15, the etherification reagent 16 is added to the etherification step 15 as indicated by arrow 16a. And in the etherification step 15, the etherification reagent and the crosslinking agent contact the activated cellulose to form an XCE ether 17 formed in the presence of the crosslinking agent and in the etherification step 15 as indicated by arrow 15a.

[0057] In another embodiment, the XCE 17 from the etherification step 15 may proceed as indicated by arrow 17a to Figure 1 one or more additional optional operations or steps 22 as shown by the dashed line in. Although the step 22 is optional, one or more of the steps 22 are typically desired and used in the method of the present invention. The optional step 22 may be selected from steps known to those skilled in the art, such as: (1) a hot (e.g., above 85 °C) water (H2O) washing step for washing the XCE; (2) a granulation step for forming XCE granules; (3) a drying step for drying the granulated XCE; and (4) a grinding step for forming the XCE into a powdery product. Each of the above optional operations may be carried out in a single-step operation; or, if desired, two or more of the above optional steps may be combined in one operation.

[0058] For example, the XCE 17 after the etherification step 15 typically has unwanted volatile by-products and salts (NaCl); and thus, in a preferred embodiment, the XCE 17 after the etherification step 15 is processed through a washing step 22 as indicated by arrow 15a to wash out the unwanted volatile by-products, salts, and other impurities from the XCE, and then a drying step 22 is carried out.

[0059] The starting material for making the cellulose ethers of the present invention and added to the alkalization 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 the form of powder or fluff. In a preferred embodiment, suitable cellulose starting materials for use in the present invention include ground wood pulp, ground cotton linter pulp, and mixtures thereof. In another preferred embodiment, wood pulp is used in the process; and the wood pulp is ground into ground fluff of cellulose as a means to make the cellulose feed more flowable when fed into the alkalization process step. Generally, the pulp is ground into particles of an optimum size, for example, in one embodiment from 1,000 micrometers (μm) to 10 μm, and in another embodiment from 900 μm to 25 μm. Coarser particle sizes can reduce the efficiency of the alkalization step, while finer particle sizes can take too much time to grind. Prior to the alkalization step, the reactor is typically filled with pulp.

[0060] As described above, the crosslinking agent is incorporated or introduced into the process as a mixture with 50% NaOH in water during the alkalization step of the method.

[0061] In the method of the present invention, a crosslinking agent / alkalization reagent mixture composition is used to alkalize or "activate" the cellulose starting material and form an "activated cellulose material". At least one cellulose material is contacted with the crosslinking agent / alkalization reagent mixture, wherein the alkalization reagent in the mixture alkalizes the cellulose under process conditions to form the activated cellulose material. The step of contacting the cellulose material with the crosslinking agent / alkalization reagent mixture is carried out, for example, by known means, such as by spraying and mixing the crosslinking agent / alkalization reagent mixture into the cellulose.

[0062] Generally, the crosslinking agent / alkali composition is added to the alkalization step of the method in the form of a mixture of the crosslinking agent and the alkalization reagent, wherein the concentration of the mixture composition is, in one embodiment, in the range of, for example, 1 mol NaOH / mol AGU to 3.5 mol NaOH / mol AGU; in another embodiment, in the range of 1.5 mol NaOH / mol AGU to 3.3 mol NaOH / mol AGU; and in yet another embodiment, in the range of 1.8 mol NaOH / mol AGU to 3.1 mol NaOH / mol AGU.

[0063] The crosslinking agent / alkali dispersion contacted with the cellulose ether during the alkalization step can be carried out by any known addition means, such as by uniform spraying and any means capable of uniformly distributing NaOH, to ensure sufficient activation of the cellulose pulp.

[0064] The alkalization step of the method is carried out under low pressure and low temperature conditions. For example, the pressure of the alkalization step ranges from 0 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 above pressure ranges are typical pressure level ranges in the reactor during the alkalization step. And, for example, the temperature of the alkalization step of the method 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 above temperature ranges are typical temperature ranges in the reactor during the alkalization step. A higher temperature used in the method of the present invention will result in an undesired increase in pressure.

[0065] To produce a cellulose ether according to the method of the present invention, an etherifying reagent is mixed with the activated cellulose material prepared in the above alkalization step. The etherifying reagents used for preparing the cellulose ether include, for example, one or more etherifying reagents known in the art. For example, the etherifying reagent may include ethylene oxide (EO), propylene oxide (PO), butylene oxide (BO), methyl chloride (MCl), chloroethane, chloroacetic acid, and mixtures thereof. In a preferred embodiment, the etherifying reagents usable in the present invention are, for example, MCl, PO, EO, and mixtures thereof.

[0066] The amount of the etherifying reagent added to the etherification operation of the XCE production method 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 the etherifying reagent used is <4 mol / AGU, then the cellulose ether may be under-substituted and not completely soluble in water. If the amount of the etherifying reagent used is greater than 6 mol / AGU, then this higher dose of the etherifying reagent may cause the cellulose ether to become hydrophobic and its water solubility to decrease.

[0067] The etherifying reagent added to the etherification step to contact the activated cellulose can be carried out by any known addition means, such as by pumping the components into the reactor.

[0068] The etherification step of the method is carried out, for example, in a reaction vessel (reactor) under an inert atmosphere. The inert materials used in the method include, for example, N2, argon, and mixtures thereof. During the etherification step of the method and as the reaction of the reactants occurs and proceeds to form the cellulose ether material, the pressure and temperature increase due to the exothermic reaction.

[0069] As the cellulose ether is formed during the etherification step, the pressure of the etherification step of the method is in the range of, for example, 1,500 kPa to 2,500 kPa in one embodiment, in the range of 1,600 kPa to 2,400 kPa in another embodiment, and in the range of 1,800 kPa to 2,200 kPa in yet another embodiment. At pressures <1,500 kPa, the reaction rate is too slow; and at pressures >2,500 kPa, special high-pressure equipment is required.

[0070] The etherification step of the method also includes a temperature of, 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 <60 °C, the reaction rate becomes unacceptably slow; and at temperatures >100 °C, unwanted side reactions can occur and the pressure increases. If the pressure increases beyond, for example, 2,500 kPa, then a different pressure reactor capable of handling high pressure and more expensive will be required.

[0071] Typically, an etherification reagent is added to the etherification step of the method and mixed with the activated cellulose material; such that the etherification reagent and the cellulose material form a homogeneous reaction mixture, which in turn reacts in the etherification process to form a cellulose ether. In the etherification step of the method, a crosslinking agent is also present in the reaction mixture, which is derived from the alkalization step of the method and proceeds to the etherification step without reacting at the low temperature of the alkalization step. When the reaction mixture is heated in the etherification step within the temperature range discussed above, the crosslinking agent reacts with the cellulose ether and the crosslinking of the crosslinking agent and the cellulose ether produces the XCE of the present invention. The crosslinking 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 method. In a preferred embodiment, the crosslinking reaction in the present invention is produced by adding a crosslinking agent to the etherification step during the etherification process step. Crosslinking the 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. Typically, the cellulose ether crosslinked with the crosslinking agent is typically a mixed cellulose ether containing hydroxyalkyl groups and alkyl ether groups. For example, in one embodiment of a mixed cellulose ether containing hydroxyalkyl groups and alkyl ether groups, it includes alkyl hydroxyethyl cellulose, such as hydroxyalkyl methyl cellulose.

[0072] In some embodiments, examples of the cellulose ether compounds suitable for the present invention include methylcellulose (MC), ethylcellulose, propylcellulose, butylcellulose, hydroxyethyl methylcellulose (HEMC), hydroxypropyl methylcellulose (HPMC), hydroxyethylcellulose (HEC), methylhydroxyethyl hydroxypropylcellulose (MHEHPC), ethylhydroxyethylcellulose (EHEC), methylethylhydroxyethylcellulose (MEHEC), hydrophobically modified ethylhydroxyethylcellulose (HMEHEC), hydrophobically modified hydroxyethylcellulose (HMHEC), sulfoethyl methylhydroxyethylcellulose (SEMHEC), sulfoethyl methyl-hydroxypropylcellulose (SEMHPC), sulfoethyl hydroxyethylcellulose (SEHEC), and mixtures thereof. In some preferred embodiments, the mixed cellulose ether may include, for example, HEMC, HPMC, and mixtures thereof.

[0073] For the cellulose ethers useful in the present invention, alkyl substitution is described in cellulose ether chemistry by the term "degree of substitution DS", as determined by the Zeisel method. DS is the average number of substituted OH groups per anhydroglucose unit. Methyl substitution may be reported, for example, as DS(methyl) or DS(M). Hydroxyalkyl substitution is described by the term "molar substitution MS", as determined by the Zeisel method. MS is the average number of moles of etherifying reagent bonded as an ether per mol of anhydroglucose units. Etherification with the etherifying reagent EO is reported, for example, as MS(hydroxyethyl) or MS(HE). Etherification with the etherifying reagent PO is correspondingly reported as MS(hydroxypropyl) or MS(HP). Side groups are determined using the Zeisel method (reference: G. Bartelmus and R. Ketterer, Z. Anal. Chem. 286 (1977), pp. 161 - 190).

[0074] The XCE produced by the method of the present invention includes, for example, any of the above-mentioned cellulose ethers having an alkyl substitution degree. For example, crosslinked HEC has a degree of substitution MS(HE) of 1.5 to 4.5 in one embodiment and a degree of substitution MS(HE) of 2.0 to 3.0 in another embodiment. In yet another embodiment, a mixed ether of methylcellulose to be crosslinked can be used in the method of the present invention. For example, in the case of 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. In the case of 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.

[0075] After the above etherification step, the produced XCE product can be processed through various additional optional processing steps. For example, the obtained XCE can be washed or purified, granulated, dried, and / or ground into a powder form using conventional methods commonly used for producing cellulose derivative products and the resulting powders. 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. The optional steps are well known to those skilled in the art, and any of the above methods can be used in the method of the present invention. For example, after the above etherification step, the XCE is typically washed and filtered to produce a filter cake. The shelf life of the filter cake can be very short and it can be troublesome to handle. Therefore, among the above various optional steps, in a preferred embodiment, it is desirable to perform at least a washing step, a drying step, and a grinding step on the XCE product to form a dry powder product for easy handling, packaging, and storage purposes.

[0076] Some of the advantageous properties exhibited by the XCE produced by the above method of the present invention include, for example, (1) obtaining a very high aqueous solution viscosity, such that the dosage in, for example, mortar formulation applications can be reduced.

[0077] For example, when compared with an aqueous solution of a non-crosslinked cellulose ether, the viscosity increase of the aqueous solution of XCE produced by the method of the present invention includes a viscosity increase of more than 15% in one embodiment, more than 20% in another embodiment, more than 30% in yet another embodiment, and more than 50% in still another embodiment.

[0078] In a broad embodiment, the XCE of the present invention can be used as an additive in dry-mixed mortar formulations, such as plastering or cement tile adhesives or cement extrusion, etc. For example, in a method of manufacturing a dry-mixed mortar formulation, the method includes the step of mixing: (I) the above-mentioned XCE used as a water retention agent; and (II) desired conventional dry-mixed mortar formulation components, such as hydrolyzed binders, including, for example, cement or gypsum.

[0079] In a preferred embodiment, the dry-mixed mortar formulation can be prepared by mixing components (I) and (II) by conventional mixing means known in the art (e.g., physical blends of solid powders). Some of the advantageous properties exhibited by the dry-mixed mortar formulation can include, for example, the ability to use a lower dose of XCE (>10%) thereby causing a reduction in the formulation cost. Generally, in order to prepare a dry-mixed mortar formulation, the amount of XCE used as the water retention agent component (I) can be, for example, 0.01 wt% to 1.0 wt% (based on the total dry-mixed mortar) in one embodiment, 0.05 wt% to 0.8 wt% in another embodiment, and 0.1 wt% to 0.5 wt% in yet another embodiment. Below these levels, the water retention of the dry-mixed mortar is insufficient, and above these limits, the cost of the formulation becomes too high.

[0080] Conventional dry-mixed mortar formulation components, i.e., component (II), can include components such as hydrolyzed binders such as cement, gypsum, fly ash, slag, etc., and aggregates (sand), fine fillers (calcium carbonate, fumed silica, dolomite, etc.), air-entraining agents, defoaming agents, redispersible polymer powders, water repellents; and mixtures thereof.

[0081] Examples

[0082] The following examples are provided to illustrate the present invention in further detail, but should not be construed as limiting the scope of the claims. Unless otherwise indicated, all parts and percentages are by weight.

[0083] The various terms and nomenclatures used in the inventive examples (Inv.Ex.) and comparative examples (Comp.Ex.) are explained as follows:

[0084] "HEMC" represents hydroxyethyl methylcellulose.

[0085] "HPMC" represents hydroxypropyl methylcellulose.

[0086] "AGU" represents anhydroglucose unit.

[0087] "LVN" represents the limiting viscosity number of pulp measured according to the procedure described in ISO 5351 (2010).

[0088] The various raw materials or components used in the examples are explained as follows:

[0089] Epilox M 985 is a poly(propylene glycol) diglycidyl ether available from Leuna Harze.

[0090] Examples of diglycidyl ether-based crosslinking compounds useful in the methods of the present invention are described in Eugene W. Jones, "Crosslinking of Cotton Cellulose with Diglycidyl Ether," Journal of Applied Polymer Science, Vol. V, No. 18, 714 - 720 (1961).

[0091] Generally, the following examples are produced according to the principles of Williamson ether synthesis, as described in R. Donges, "Non-Ionic cellulose Ethers," British Polymer Journal, Vol. 23, pp. 315 - 326 (1990); wherein "activated" or alkalized cellulose is produced by contacting and treating ground cellulose with 50% caustic soda. This activation or alkalization step is then followed by an etherification operation using MCl and EO.

[0092] The examples described below and in Table II use HEMC. Additionally, the examples described below and in Table II use the same pulp material.

[0093] Comparative Example A - Cellulose Ether Synthesized without Using a Crosslinking Agent (Baseline)

[0094] Ground cellulose fluff (1.5 moles [mol]) is added to a 5-liter (L) autoclave (reactor). The limiting viscosity number (LVN) of the pulp is measured according to the procedure described in ISO 5351 (2010). Ground cellulose fluff (LVN ≥ 1,450 milliliters / gram [mL / g]) is added to the autoclave.

[0095] After purging the autoclave reactor three times with N2, the autoclave reactor was heated to 40 °C. Then, dimethyl ether (DME, 4.7 mol / mol AGU) and the first batch of methyl chloride (“MCl 1”; 3.2 mol / mol AGU) were added to the autoclave. During 2 minutes (min) at a temperature of 40 °C, the first batch of caustic soda (“NaOH 1”; 50%, 1.9 mol NaOH / mol AGU) was added to the autoclave in 3 portions. The resulting reaction mixture was maintained at 40 °C for 30 minutes. Then EO (0.45 mol / mol AGU) was added to the reaction mixture; and the reaction mixture was maintained at 40 °C for 10 minutes.

[0096] The resulting material was heated to 80 °C within 45 minutes. At 80 °C, the second batch of MCl (“MCl 2”; 1.3 mol / mol AGU) was rapidly injected into the material. Then, the second batch of caustic soda (“NaOH 2”; 0.67 mol / mol AGU) was added to the autoclave in 7 portions over 30 minutes, followed by a cooking time of 70 minutes at 80 °C. After the 70 - minute cooking time, the resulting XCE product was formed. Then the following process steps were carried out on the resulting XCE product using conventional procedures known in the art: hot water washing, neutralization with formic acid, granulation using a laboratory granulator (Bosch Mum), drying, and grinding.

[0097] Comparative Example B - Crosslinked Cellulose Ether Synthesized Using Epilox M 985

[0098] In this example, the same procedure as described in Comparative Example A was used, except that after adding EO to the reaction mixture and maintaining the reaction mixture at 40 °C for 10 minutes, the cross - linker Epilox M 985 (0.0030 mol / mol) was added to the autoclave.

[0099] Comparative Example C - Crosslinked Cellulose Ether Synthesized Using Epichlorohydrin

[0100] In this example, the same procedure as described in Comparative Example A was used, except that after adding EO to the reaction mixture and maintaining the reaction mixture at 40 °C for 10 minutes, ECH was used as the cross - linker (pre - mixed with 4 grams [g] of isopropanol to 0.0030 mol / mol) and ECH was added to the autoclave.

[0101] Inventive Example 1 - Crosslinked Cellulose Ether Synthesized Using Epilox M 985

[0102] The ground cellulose fluff (1.5 mol) was added to a 5 L autoclave. After purging the autoclave three times with N2, 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 (strength 50%, 1.9 mol NaOH / mol AGU) was added to the autoclave in the following 3 parts: (1) 50% (0.95 mol NaOH / mol AGU) was added in 3 portions over a period of 2 minutes at a temperature of 40 °C; (2) 25% as an emulsion using a separate dosing device (bypass) which had 0.003 mol / mol crosslinking agent; and (3) 25% as a cleaning step using the dosing device. Then, the resulting reaction mixture was held at 40 °C for 30 minutes. EO (0.45 mol / mol AGU) was added to the reaction mixture; and the reaction mixture was held at 40 °C for 10 minutes.

[0103] The resulting material was heated to 80 °C within 45 minutes. At 80 °C, MCl 2 (1.3 mol / mol AGU) was rapidly injected into the material. Then, NaOH 2 (0.67 mol / mol AGU) was added to the autoclave in 7 portions over 30 minutes, followed by a cooking time of 70 minutes at 80 °C. After the 70 - minute cooking time, the resulting XCE product was formed. Then the resulting XCE product was subjected to the following process steps using conventional procedures known in the art: hot water washing, neutralization with formic acid, granulation using a laboratory granulator (Bosch Mum), drying, and grinding.

[0104] Table II

[0105]

[0106] The results of the above Comparative Examples A - C and Invention Example 1 are described in Table II. It was found that using 50% aqueous NaOH (or "50% caustic soda") as a diluent for the crosslinking agent in the process for producing XCE according to the present invention was beneficial. The combination of the crosslinking agent with 50% caustic soda was easily sprayed onto the pulp. The stability of the crosslinking agent in a high - pH environment such as 50% caustic soda was checked by measuring the epoxy equivalent weight (EEW) of 50% caustic soda containing the crosslinking agent before and after storage in 50% NaOH at room temperature (RT; about 25 °C) for 30 minutes according to DIN16946. The EEW did not change significantly during this time period.

[0107] Based on the results described in Table II, the cellulose ether without using any crosslinking agent (Comparative Example A) showed a viscosity of 5,160 mPa·s as a 1% aqueous solution. Adding Epilox M 985 (0.003 mol / mol) during the etherification step increased the viscosity to 5,720 mPa·s (Comparative Example B). However, replacing Epilox M 985 with epichlorohydrin (Comparative Example C) resulted in a significant loss of viscosity (2,120 mPa·s) due to the formation of water-insoluble over-crosslinked gel particles. In the method of the present invention, when the Epilox M 985 crosslinking agent was added to the process during the alkalization step (Inventive Example 1), a more uniform crosslinking agent distribution and an optimized viscosity of the resulting XCE (6,090 mPa·s) were produced.

[0108] The examples described below and 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.

[0109] Comparative Example D - Cellulose Ether Synthesized without Using a Crosslinking Agent (Baseline)

[0110] The ground cellulose fluff (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 (strength 50%, 1.9 mol NaOH / mol AGU) was added to the autoclave in 3 portions over 2 minutes at a temperature of 40 °C. The reaction mixture was maintained at 40 °C for 30 minutes. Then, PO (0.45 mol / mol AGU) was added to the reaction mixture; and the reaction mixture was maintained at 40 °C for 10 minutes.

[0111] The resulting material was heated to 80 °C within 45 minutes. At 80 °C, MCI 2 (1.3 mol / mol AGU) was rapidly injected into the material. Then, NaOH 2 (0.67 mol / mol AGU) was added to the autoclave in 7 portions over 30 minutes, followed by a cooking time of 70 minutes at 80 °C. After the 70-minute cooking time, the resulting XCE product was formed. Then, the following process steps were carried out on the resulting XCE product using conventional procedures known in the art: hot water washing, neutralization with formic acid, granulation using a laboratory granulator (Bosch Mum), drying, and grinding.

[0112] Comparative Example E - Crosslinked Cellulose Ether Synthesized Using Epilox M 985

[0113] In this example, the same procedure as described in Comparative Example D was used, except that after adding PO to the reaction mixture and maintaining the reaction mixture at 40 °C for 10 minutes, the crosslinking agent Epilox M 985 (0.0030 mol / mol) was added to the autoclave reactor.

[0114] Inventive Example 2 - Crosslinked Cellulose Ether Synthesized Using Epilox M 985

[0115] The ground cellulose fluff (1.5 mol) was added to a 5 L autoclave. After purging the autoclave three times with N2, 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 (strength 50 wt%, 1.9 mol NaOH / mol AGU) was added to the autoclave in the following 3 parts: (1) 50% (0.95 mol NaOH / mol AGU) was added in 3 portions over a period of 2 minutes at a temperature of 40 °C; (2) 25% as an emulsion using a separate dosing device (bypass) which had 0.003 mol / mol crosslinking agent; and (3) 25% as a cleaning step using the dosing device. Then, the resulting reaction mixture was maintained at 40 °C for 30 minutes. Then, PO (0.45 mol / mol AGU) was added to the reaction mixture; and the reaction mixture was maintained at 40 °C for 10 minutes.

[0116] The resulting material was heated to 80 °C within 45 minutes. At 80 °C, MCI 2 (1.3 mol / mol AGU) was rapidly injected into the material. Then, NaOH 2 (0.67 mol / mol AGU) was added in 7 portions over 30 minutes, followed by a cooking time of 70 minutes at 80 °C. After the 70-minute cooking time, the resulting XCE product was formed. Then, the following process steps were carried out on the resulting XCE product using conventional procedures known in the art: hot water washing, neutralization with formic acid, granulation using a laboratory granulator (Bosch Mum), drying, and grinding.

[0117] Table III

[0118]

[0119]

[0120] The results of Comparative Examples D and E and Inventive Example 2 described above are presented in Table III. Similar to Comparative Examples A - C and Inventive Example 1 described above using HEMC, the results summarized in Table III show the same observations in Comparative Examples D and E using HPMC and Inventive Example 2. Since the pulp materials used in the examples described in Table III are different from those used in the examples described in Table II, the non - crosslinked HPMC (Comparative Example D) has a 1% aqueous solution viscosity of 8,350 mPa·s. When Epilox M 985 is added to the process during the etherification step, the viscosity of XCE (Comparative Example E) increases slightly. However, when the Epilox M 985 crosslinking agent is added to the method of the present invention during the alkalization step, the viscosity of the XCE of the present invention (Inventive Example 2) (10,700 mPa·s) increases more significantly than the other Comparative Examples D and E.

[0121] In summary, the present invention includes, but is not limited to, the following items:

[0122] 1. A method for producing a cross - linked cellulose ether, comprising the steps of:

[0123] (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

[0124] (ii) contacting the activated cellulose material of step (i) with at least one etherifying reagent; wherein

[0125] the at least one etherifying reagent reacts with the activated cellulose material to form the cross - linked cellulose ether.

[0126] 2. A method for producing a cross - linked cellulose ether, comprising the steps of:

[0127] (A) mixing (a) at least one crosslinking agent with (b) at least one alkalizing reagent to form a crosslinking agent / alkalizing reagent mixture;

[0128] (B) contacting at least one cellulose material with the mixture of step (A) to form an activated cellulose material; and

[0129] (C) contacting the activated cellulose material of step (B) with at least one etherifying reagent; wherein

[0130] the at least one etherifying reagent reacts with the activated cellulose material to form the cross - linked cellulose ether.

[0131] 3. The method according to claim 1 or claim 2, further comprising the step of subjecting the crosslinked cellulose ether to one or more steps of purification, washing, drying, granulation, and grinding.

[0132] 4. The method according to claim 1, wherein the activated cellulose material is formed at a pressure of less than or equal to 500 kPa and a temperature of less than or equal to 50 °C.

[0133] 5. The method according to claim 1, wherein the crosslinked cellulose ether is formed at a pressure of greater than or equal to 1,000 kPa and a temperature of higher than 70 °C.

[0134] 6. The method according to claim 1, wherein the at least one crosslinking agent is a diglycidyl ether type crosslinking agent having the following chemical structure (I):

[0135]

[0136] wherein n is from 3 to 25; and wherein the at least one alkalizing reagent is selected from the group consisting of solutions of sodium hydroxide, potassium hydroxide, lithium hydroxide, and mixtures thereof.

[0137] 7. The method according to claim 1, wherein the at least one cellulose material is selected from the group consisting of wood pulp, cotton linters, and mixtures thereof; and wherein 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.

[0138] 8. The method according to claim 1, wherein steps (i) and (ii) are carried out in an inert atmosphere.

[0139] 9. The method according to claim 1, wherein the at least one crosslinking agent is present in the mixture of step (i) at a concentration of from 0.0001 mole of the crosslinking agent per mole of anhydroglucose units of the cellulose ether to 0.05 mole of the crosslinking agent per mole of anhydroglucose units of the cellulose ether; and 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.

[0140] 10. The method according to claim 1, further comprising the step of grinding the at least one cellulose material to form a ground cellulose fluff material; and wherein the grinding step is carried out before contacting the at least one cellulose material with the dispersion mixture of step (a).

[0141] 11. A crosslinked cellulose ether produced by the method according to claim 1.

[0142] 12. A dry-mixed mortar formulation comprising:

[0143] (I) The crosslinked cellulose ether according to claim 11; and

[0144] (II) A hydrolyzed binder; and wherein the hydrolyzed binder is a cement or gypsum material.

Claims

1. A method for producing a crosslinked cellulose ether, comprising the following steps: (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, wherein the at least one crosslinking agent is present in the mixture at a concentration of from 0.0001 moles of the crosslinking agent per mole of anhydroglucose units of the cellulose ether to 0.05 moles of the crosslinking agent per mole of anhydroglucose units of the cellulose ether; and (ii) contacting the activated cellulose material of step (i) with at least one etherifying agent; wherein the at least one etherifying agent reacts with the activated cellulose material to form the crosslinked cellulose ether; wherein the at least one crosslinking agent is a polyalkylene oxide or a polyalkylene diglycidyl ether in emulsion form; wherein the at least one etherifying agent is selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, methyl chloride, ethyl chloride, and mixtures thereof; wherein the activated cellulose material is formed at a pressure of less than or equal to 500 kPa and a temperature of less than or equal to 50 °C, and the crosslinked cellulose ether is formed at a pressure of greater than or equal to 1,000 kPa and a temperature of greater than 70 °C.

2. A method for producing a crosslinked cellulose ether, comprising the following steps: (A) mixing (a) at least one crosslinking agent with (b) at least one alkalizing agent to form a crosslinking agent / alkalizing agent mixture, wherein the at least one crosslinking agent is present in the mixture at a concentration of from 0.0001 moles of the crosslinking agent per mole of anhydroglucose units of the cellulose ether to 0.05 moles of the crosslinking agent per mole of anhydroglucose units of the cellulose ether; (B) contacting at least one cellulose material with the mixture of step (A) to form an activated cellulose material; and (C) contacting the activated cellulose material of step (B) with at least one etherifying agent; wherein the at least one etherifying agent reacts with the activated cellulose material to form the crosslinked cellulose ether; wherein the at least one crosslinking agent is a polyalkylene oxide or a polyalkylene diglycidyl ether in emulsion form; wherein the at least one etherifying agent is selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, methyl chloride, ethyl chloride, and mixtures thereof; wherein the activated cellulose material is formed at a pressure of less than or equal to 500 kPa and a temperature of less than or equal to 50 °C, and the crosslinked cellulose ether is formed at a pressure of greater than or equal to 1,000 kPa and a temperature of greater than 70 °C.

3. The method according to claim 1 or claim 2, further comprising the step of subjecting the crosslinked cellulose ether to one or more of the steps of purification, washing, drying, granulation, and grinding.

4. The method according to claim 1, wherein the at least one alkalizing agent is selected from the group consisting of solutions of sodium hydroxide, potassium hydroxide, lithium hydroxide, and mixtures thereof.

5. The method according to claim 1, wherein the at least one cellulose material is selected from the group consisting of wood pulp, cotton linters, and mixtures thereof.

6. The method according to claim 1, wherein steps (i) and (ii) are carried out in an inert atmosphere.

7. The method according to claim 1, wherein the at least one basifying agent is present in the mixture of step (i) at a concentration of from 1 mole of basifying agent per mole of anhydroglucose units of the cellulose material to 3.5 moles of basifying agent per mole of anhydroglucose units of the cellulose material to form the activated cellulose material.

8. The method according to claim 1, further comprising the step of grinding the at least one cellulose material to form a ground cellulose fluff material; and wherein the grinding step is carried out before bringing the at least one cellulose material into contact with the dispersion mixture of step (a).

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