Method for producing powdered silylated cellulose

Abstract

A method for preparing powdered silylated cellulose is disclosed, which method includes preparing a reaction product in a powder form that can be mixed and processed by conventional powder processing equipment.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 63 / 432,715, filed December 15, 2022. U.S. Provisional Patent Application No. 63 / 432,715 is incorporated herein by reference.

[0002] A method for producing powdered silylated cellulose is provided. More specifically, the method for producing powdered silylated cellulose is available on a commercial production scale.

[0003] Introduction Current technologies for producing silylated cellulose are based on low volume yield slurry or solution processes. Some of these processes use high pressure, where the cellulose is in a slurry of liquefied ammonia. Other methods utilize atmospheric pressure in large volumes of swelling solvent. These processes have the disadvantage of requiring very large amounts of swelling solvent and recrystallization solvent and generating large amounts of waste. Furthermore, the space-time yield of these processes is very low due to the volume requirements of the solvent. Therefore, these methods have not been commercially viable for large-scale use.

[0004] U.S. Patent No. 4,320,692 to Green discloses a method for preparing trimethylsilyl cellulose ethers, which comprises reacting cellulose with hexamethyldisilazane in the presence of a small amount of catalyst. In a preferred method for carrying out this process, the reaction temperature is maintained between about 100°C and about 135°C. At temperatures below 100°C, the reaction is found to be too slow to be practical, and at temperatures above 135°C, the reaction is found to be very unstable.

[0005] There is a need in the industry for a more volumetrically efficient process for preparing silylated cellulose, which preferably operates at ambient pressure and / or uses less solvent than existing processes. Summary of the Invention

[0006] Provided herein is a method for preparing silylated cellulose, the method comprising: 1) mixing starting materials including A) cellulose, B) a polar aprotic swelling solvent, C) a catalyst, and optionally D) a first portion of a silylating agent, thereby E) preparing a powdered intermediate; 2) E) adding D) a silylating agent continuously or intermittently to the powdered intermediate; Includes: DETAILED DESCRIPTION OF THE INVENTION

[0007] More specifically, the method for preparing the silylated cellulose introduced above comprises: 1) mixing starting materials, the starting materials being: A) cellulose comprising repeating monomer units having >2.5 hydroxyl groups per monomer unit; B) a polar aprotic swelling agent; C) a catalyst; Optionally, D) a silylating agent comprising a silylamine having a silicon-nitrogen moiety, D) a silylating agent is added in an amount sufficient to provide a quantity of silyl groups of 0 mol % to <50 mol % of the hydroxyl groups of A) cellulose, thereby forming E) a powdered intermediate; Including, Mixing and 2) E) adding to the powder intermediate an amount of D) a silylating agent continuously or intermittently for >2 hours; wherein the total amount of D) silylating agent added in steps 1) and 2) is >80 mol % to <200 mol %, or >80 mol % to <150 mol %, based on the amount of hydroxyl groups in the starting material A) cellulose, thereby forming a powdered reaction product containing silylated cellulose.

[0008] In step 1), the amount of D) silylating agent added in step 1) can be 0. Alternatively, in step 1), a first portion of D) silylating agent sufficient to provide silyl groups of >0 mol% to <50 mol%, alternatively 0.01 mol% to 49 mol%, or alternatively 30 mol% to 45 mol% of the hydroxyl groups of A) cellulose can be used. In this case, the powdered intermediate prepared in step 1) is a powdered reaction product containing partially silylated cellulose. Without wishing to be bound by theory, it is believed that if 50 mol% or more of the D) silylating agent is added at once in step 1), the reaction product containing the partially silylated cellulose becomes difficult to handle. However, it may be beneficial to add at least 30 mol% of D) silylating agent in step 1) to minimize the overall processing time. Alternatively, the amount of silylating agent added in step 1) can be at least 30 mol%, alternatively at least 34 mol%, alternatively at least 35 mol%; and at the same time, the amount of silylating agent can be less than 50 mol%, alternatively at most 45 mol%, alternatively at most 42 mol%, alternatively at most 40 mol%, relative to the hydroxyl groups of A) cellulose. (For example, the Si / COH ratio, which is the molar ratio of silyl groups in starting material D) to COH groups in starting material A), can be >0 to <0.50, alternatively 0.30 to 0.45, alternatively 0.34 to 0.42, alternatively 0.35 to 0.40.)

[0009] Steps 1) and 2) can be carried out in a reactor such as a batch vessel equipped with a jacket for heating and cooling and an agitator for mixing. The type of reactor is not critical and can be any reactor suitable for mixing liquids and powders. The temperature in steps 1) and 2) can be from 30°C to 150°C, alternatively from 50°C to 85°C, alternatively from 50°C to 80°C, alternatively from 55°C to 80°C. The pressure in steps 1) and 2) can be from 730 mmHg (97 kPa) to 790 mmHg (105 kPa), alternatively from 750 mmHg (100 kPa) to 770 mmHg (103 kPa).

[0010] In step 2), the feed rate of D) silylating agent can be defined as any aliquot or continuous flow control that is >0 to <20 mol% of the stoichiometry of the silylating agent added over a period of >24 to 500 minutes, based on a moving average of any two aliquots. Those skilled in the art will understand how to feed at this rate using aliquots or a continuous flow based on the description and examples below. Without wishing to be bound by theory, it is believed that by using this feed rate in step 2), the reaction product containing silylated cellulose can form a powder that can be handled with conventional solid processing equipment and that the formation of a paste or solid that cannot be mixed or removed from the reactor can be avoided. Without wishing to be bound by theory, it is believed that if the entire remaining D) silylating agent (e.g., ≥50 mol%) is added at once in step 2), the reaction product containing silylated cellulose would be difficult to handle. Therefore, in order to maintain the reaction product as a powder, the above continuous or intermittent feed rate is used in step 2). In step 2), the total amount of D) silylating agent added in steps 1) and 2) is >80 mol % to <200 mol % based on the amount of hydroxyl groups in the starting material A) cellulose.

[0011] The method may optionally further include one or more additional steps. For example, the method may further include A) drying the cellulose before step 1). Commercially available cellulose may contain absorbed water. To minimize the formation of by-products, the cellulose may be dried to remove at least some of the water. Drying may be carried out by any convenient means, such as exposing the cellulose to heat and / or reduced pressure or an inert gas stream.

[0012] The method may optionally further include, for example, adding an F) solvent different from the B) polar aprotic swelling agent during or before step 1). Alternatively, the method may further include an additional step before step 1), including dissolving a C) catalyst in one or both of the B) polar aprotic swelling agent and the F) solvent to form a catalyst solution. The resulting catalyst solution may be mixed with the A) cellulose before step 1) (e.g., before adding any silylating agent to the reactor). For example, the catalyst solution may be mixed with the A) cellulose for at least 10 minutes, or at least 15 minutes, while the catalyst solution may be mixed with the A) cellulose for up to 1 hour before adding the first portion of the D) silylating agent. If used, the F) solvent may be present in an amount >0 to 15 times the weight of the C) catalyst, or >0 to 12 times the weight of the catalyst. Alternatively, the method may be solvent-free, without using an F) solvent.

[0013] Alternatively, the method may further include an additional step of forming C) a catalyst by a process comprising reacting a portion of D) the silylating agent with an acid ex situ. Optionally, F) a solvent may be used to facilitate mixing of D) the silylating agent with the acid. When this step is added to the method, the silylating agent used to form the catalyst may be, but is not limited to, a silazane as described below for starting material D). The silazane selected to form the catalyst may be the same as or different from the starting material D) used in step 1) to carry out the silylation reaction. This step may be carried out by any convenient means, such as by mixing, at, for example, room temperature and ambient pressure.

[0014] The method may optionally further include an additional step of applying a vacuum to the powdered intermediate after step 1) and before step 2). The pressure may be, for example, ≦400 mmHg, alternatively ≦200 mmHg, or alternatively >0-100 mmHg. Alternatively, if D) a silylating agent is added in step 1), a vacuum may be applied to the powdered reaction product comprising the partially silylated cellulose, for example, to remove by-products.

[0015] The method may optionally further include step 4): washing the powdered silylated cellulose by mixing the powdered silylated cellulose with G) a washing solvent, thereby removing any remaining polar aprotic swelling agent, catalyst, and / or solvent, and / or any by-products that may be present. The washing solvent is not particularly limited; however, the washing solvent may be a low-boiling polar solvent that can dissolve any remaining starting materials and / or by-products without significantly solubilizing the silylated cellulose, and this can be used to facilitate evaporation from the silylated cellulose product. The washing in step 4) can be carried out by any convenient means, such as mixing the washing solvent with the powdered silylated cellulose produced as described above in the reactor used in step 1) or in an agitated slurry vessel, and then draining the solvent after a sufficient period of time. The washing step can be repeated as many times as necessary, for example, 1 to 10 times.

[0016] The method may optionally further comprise step 5): G) removing the wash solvent by any convenient means, such as filtration, heating, reduced pressure, etc., and / or by purging with a gas, such as air or an inert gas, such as nitrogen.

[0017] The resulting product is pure silylated cellulose produced with low waste and high volumetric efficiency. The silylated cellulose produced by this method alternatively has a DS of 2.0 to 3.0, alternatively 2.2 to 3.0, alternatively 2.5 to 3.0, alternatively 2.6 to 3.0, alternatively 2.8 to 3.0.

[0018] The starting materials used herein will be described in more detail below.

[0019] A) Cellulose The cellulose used in the above method, starting material A), has more than 2.5 to 3, or 3, hydroxyl groups per repeating monomer unit in the molecule. Cellulose is a polymer of β(1→4)-linked D-glucose repeating monomer units. Cellulose can have 200 or more repeating monomer units per molecule. Alternatively, cellulose can have at least 200, alternatively at least 300, alternatively at least 400, alternatively at least 500, alternatively at least 600, or alternatively at least 700 repeating monomer units, while cellulose can have up to 10,000, alternatively at most 9,000, alternatively at most 8,000, alternatively at most 7,000, alternatively at most 6,000, alternatively at most 5,000, or alternatively at most 4,000 repeating monomer units per molecule. Alternatively, the cellulose may have an Mn of 200 to 10,000, or alternatively, 400 to 8,000 repeating monomer units per molecule.

[0020] The type of cellulose can be, for example, microcrystalline cellulose or pulped cellulose. Sources of cellulose include, but are not limited to, cotton linters, pine, and tunisin (animal-derived cellulose). Cellulose is commercially available from a variety of sources.

[0021] B) Polar aprotic swelling agents The starting material B) used in the above process is a polar aprotic swelling agent. Examples of suitable polar aprotic swelling agents include N-methylpyrrolidone (NMP), N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), dimethyl sulfone, propylene carbonate, pyridazine, dimethylformamide (DMF), ethylene carbonate, sulfolane, tetrahydrothiophene-1-oxide, and hexamethylphosphoramide (HMPA).

[0022] The starting materials A) and B) are used in amounts such that the weight ratio of B) polar aprotic swelling agent to A) cellulose is <3:1, alternatively <1:1, alternatively <0.3:1 (B:A ratio). Alternatively, the B:A ratio may be at least 0.1:1, alternatively 0.11:1, alternatively 0.12:1, alternatively 0.13:1, alternatively 0.14:1, alternatively 0.15:1, while the B:A ratio may be up to <0.3:1, alternatively 0.29:1, alternatively 0.28:1, alternatively 0.27:1, alternatively 0.26:1.

[0023] C) catalyst The starting material C) in the above method is a catalyst capable of catalyzing the reaction between A) the hydroxyl groups of cellulose and D) the silicon-nitrogen (Si-N) moiety of the silylating agent. Examples of suitable catalysts include ammonium salts such as ammonium chloride, ammonium trifluoroacetate, or ammonium triflate; saccharin; sulfonic acids such as methanesulfonic acid, p-toluenesulfonic acid, or trifluoromethanesulfonic acid; trifluoroacetic acid; trimethylsilyl chloride; or combinations thereof. Alternatively, the catalyst can be selected from the group consisting of ammonium chloride, ammonium trifluoroacetate, or saccharin. Alternatively, the catalyst can be selected from the group consisting of ammonium chloride or ammonium trifluoroacetate. Alternatively, the catalyst can include (or be) ammonium trifluoroacetate.

[0024] The catalyst can be applied by several methods that will be understood by those skilled in the art. These can be C) adding the catalyst (e.g., ammonium trifluoroacetate, etc.) directly to the reactor, or C) dissolving the catalyst in B) a polar aprotic swelling agent or F) solvent, and then adding the resulting catalyst solution to the reactor. Alternatively, C) the catalyst can be formed by premixing certain silylating agents, such as silazanes or other silylamines (as described below for starting material D), with acids, such as trifluoroacetic acid or triflic acid, and then charging the resulting mixture containing the catalytic silylammonium salt to the reactor.

[0025] The amount of catalyst depends on various factors such as the type of catalyst and the temperature selected, but may be at least 0.01 wt.%, alternatively at least 0.1 wt.%, alternatively at least 0.3 wt.%, while the amount of catalyst may be at most 5 wt.%, alternatively at most 4 wt.%, alternatively at most 3 wt.%, alternatively at most 2 wt.%; alternatively, the amount of catalyst may be 0.1 wt.% to 5 wt.%, alternatively at most 0.3 wt.% to 2 wt.%, based on the total weight of the starting materials A), B), C), and D) used in the process.

[0026] D) Silylation Agents with Si-N Moieties The starting material D) in the above process is a silylating agent comprising a silylamine having a silicon-nitrogen (Si—N) moiety. The Si—N moiety is reactive with the hydroxyl groups of A) cellulose. The silylating agent can be selected from a silazane, an aminosilane, or a combination thereof. For example, a silazane can be represented by the formula

[0027] [ka] [In the formula, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , and R 7are each independently selected from the group consisting of H, an alkyl group of 1 to 18 carbon atoms, and an alkenyl group of 2 to 18 carbon atoms. Suitable alkyl groups include methyl, ethyl, propyl, and butyl; alternatively, methyl, ethyl, and propyl. Suitable alkenyl groups include vinyl, allyl, and hexenyl. Examples of suitable disilazanes include 1,1,1,3,3,3-hexamethyldisilazane (HMDZ), 1,3-ethyl-1,1,3,3-tetramethyldisilazane, 1,3-dipropyl-1,1,3,3-tetramethyldisilazane, 1,3-dibutyl-1,1,3,3-tetramethyldisilazane, 1,3-divinyl-1,1,3,3-tetramethyldisilazane, 1,3-diallyl-1,1,3,3-tetramethyldisilazane, 1,3-dibutenyl-1,1,3,3-tetramethyldisilazane, and 1,3-hydrido-1,1,3,3-tetramethyldisilazane.

[0028] Alternatively, the silylating agent may be a compound of the formula: N x SiR 8 4-x [In the formula, each R N is an amino functional group bonded to silicon through a nitrogen atom, and each R 8 is R 1 As described above for R, R may be an aminosilane that may have R independently selected from the group consisting of H, alkyl groups of 1 to 18 carbon atoms, and alkenyl groups of 2 to 18 carbon atoms, where subscript x is 1 to 3. N is the formula -NR 9 2[In the formula, each R 9 are independently selected from the group consisting of H, an alkyl group of 1 to 18 carbon atoms, or an aryl group of 6 to 18 carbon atoms.

[0029] Aminosilanes are exemplified by tris(dimethylamino)silane, bis(diisopropylamino)silane, (N,N-dimethylamino)trimethylsilane, trimethyl(amino)silane {HN—Si(CH)}, triethyl(amino)silane {HN—Si(CH—CH)}, tripropyl(amino)silane {HN—Si(CH)}, tributyl(amino)silane {HN—Si(CH)}, dimethylethyl(amino)silane, dimethylbutyl(amino)silane, trivinyl(amino)silane, dibutylethyl(amino)silane, tri(1-butenyl)(amino)silane, or triaryl(amino)silane. Suitable aminosilanes are known in the art and commercially available, for example, from Sigma-Aldrich, Inc. (St. Louis, Missouri, USA) or Gelest Inc. (Morrisville, Pennsylvania, USA).

[0030] The silylating agent for starting material D) can be any one of the silazanes and / or aminosilanes described above. Alternatively, the D) silylating agent can be a combination of two or more silazanes, two or more aminosilanes, or a combination of a silazane and an aminosilane. The silylating agent for starting material D) can be a silylating agent having a molar ratio of >0.67:1 to 4:1 (D Si :A OH The molar ratio of D) Si-N moieties of the silylating agent to A) hydroxyl groups of the cellulose is used in an amount sufficient to provide a molar ratio of D) Si-N moieties of the silylating agent to A) hydroxyl groups of the cellulose. Si :A OH The ratio may be from 0.7:1 to 3.5:1, alternatively from 0.8:1 to 3.0:1, alternatively from 0.9:2.5:1, alternatively from 1:1 to 2.0:1, alternatively from 1.15:1 to 1.98:1, alternatively from 1.3:1 to 1.4:1.

[0031] F) Solvent The starting material F) used in the above method is an optional solvent different from B) the polar aprotic swelling agent. The solvent is not particularly limited and can be any solvent that can dissolve or disperse C) the catalyst together with one or more other starting materials. For example, the solvent can include an aliphatic hydrocarbon such as hexane, an aromatic hydrocarbon such as toluene or xylene, a halogenated hydrocarbon such as carbon tetrachloride, or an ether such as tetrahydrofuran.

[0032] The amount of solvent depends on various factors, such as the type and amount of catalyst selected. However, the amount of solvent can be ≥ 0 to 15 times the weight of the C) catalyst, or up to 12 times the weight of the catalyst. Without wishing to be bound by theory, it is believed that it is desirable to minimize the amount of solvent for volumetric efficiency.

[0033] G) Washing solvent Starting material G) in the method described herein is an optional wash solvent that can be used to remove residual starting materials and / or by-products from the silylated cellulose produced by this method. The wash solvent can be different from the starting materials B) and F) described above. Examples of suitable wash solvents include water, ketones such as acetone, monohydric alcohols such as methanol or ethanol, or acetone. Without wishing to be bound by theory, it is believed that ketones such as acetone can effectively remove both polar and non-polar residues, and at the same time, are easy to remove from the silylated cellulose by reduced pressure.

[0034] How to use The silylated cellulose prepared as described herein can be used in a variety of end uses. For example, the silylated cellulose can be used in place of the cellulose derivatives described in U.S. Pat. No. 10,851,180 in optical films for image display devices. Alternatively, the silylated cellulose prepared as described above can be used as a thickening polymer in personal care applications (e.g., cosmetic or sun care formulations) in addition to or instead of the silylated cellulose polymers disclosed in, for example, PCT Patent Publication WO 2022 / 066591. [Example]

[0035] These examples are provided to illustrate the invention to one of ordinary skill in the art and should not be construed as limiting the scope of the invention as set forth in the claims. The starting materials used in the examples are summarized in Table 1 below.

[0036] [Table 1]

[0037] Example 1 In this Example 1, 236.2 grams of microcrystalline cellulose was charged to a Sigma Blade mixer (reactor), followed by a pre-dissolved solution of 65.4 grams of DMSO and 5.7 grams of NH4Cl, and the cellulose was silylated by mixing for 30 minutes. 130.3 grams of HMDZ (0.37 moles of Si:COH) was charged to the reactor at ambient temperature, heated to 53°C, and then maintained at that temperature for 1 hour. Up to this point, the mixture maintained the consistency of a wet powder. The reactor was then evacuated to <200 mmHg for 15 minutes, so that the condensate remained in the dry ice vacuum trap. The vacuum was then released with nitrogen, and aliquots of HMDZ were added over time to continue the reaction. 182.7 grams of HMDZ (0.52 moles of Si:COH) was added in approximately 60 gram aliquots every 30 minutes. The material in the reactor maintained a free-flowing consistency as a wet powder throughout this time. The reactor was then evacuated to <200 mmHg for 30 minutes. The vacuum was then released with nitrogen, and aliquots of HMDZ were charged sequentially to continue the reaction. An additional 135.1 g of HMDZ (0.38 moles Si:COH) was charged in four approximately equal aliquots every 40 minutes to bring the total molar Si:COH ratio to 1.27. With each addition, the material assumed the consistency of a free-flowing wet powder and slowly converted to a free-flowing dry powder over approximately 20 minutes. After the final addition, the reactor was held at temperature for 1 hour. The reactor was then evacuated to <200 mmHg and held for approximately 45 minutes. The reactor was cooled, and the resulting crude product (527.2 grams) was recovered. The resulting silylated cellulose powder had a DS of 3.0.

[0038] Example 2. In this Example 2, 235 grams of pulped cellulose was charged to a Sigma Blade mixer, followed by a pre-dissolved solution of 64.7 grams of DMSO and 5.68 grams of NH4Cl, and the cellulose was silylated by mixing for 30 minutes. 140 grams of HMDZ (0.4 moles Si:COH) was charged to the reactor, which was then heated to 50°C and maintained for 1 hour, at which point a vacuum of <200 mmHg was applied to remove the liquid from the reactor. An additional 217 grams of HMDZ (0.62 moles Si:COH) was then charged in seven equal increments, each 15 minutes apart, at which point a vacuum of <200 mmHg was applied to remove the liquid from the reactor. An additional 85 grams of HMDZ (0.24 moles Si:Si(COH)) was then charged in six equal increments, each 20 minutes apart, to bring the total molar Si:COH ratio to 1.26. The reactor was then held at 50°C for 1 hour. The material in the reactor was a free-flowing powder throughout the feed and vacuum strip. After maintaining the temperature, the reactor was evacuated to <200 mmHg. After achieving vacuum, the reactor was heated at 90°C for 30 minutes to ensure that no liquid dripped into the vacuum flask. 513.27 grams of crude product were recovered. The crude product was washed with acetone in a Buchner funnel and then dried in a pan overnight. The resulting silylated cellulose powder had a DS of 2.0.

[0039] Example 3 - Commercial scale run In this Example 3, 1735 grams of microcrystalline cellulose was charged to a Littleford Plow mixer, followed by a pre-dissolved solution of 467.5 grams of DMSO and 41.3 grams of NH4Cl, and the cellulose was silylated by mixing for 30 minutes. 870 grams of HMDZ (0.34 moles of Si:COH) was continuously fed through a spray nozzle using a pressure pot and needle valve over a period of 34 minutes while the reactor was maintained at 65°C. The mixture was then mixed for 1 hour while maintaining the temperature. At this time, a vacuum of <50 mmHg was applied and maintained for 15 minutes. An additional 894.6 grams of HMDZ (0.34 moles of Si:COH) was then continuously fed through a spray nozzle using a pressure pot and needle valve over a period of 126 minutes while the reactor was maintained at 65°C. The HMDZ feed rate was then slowed and an additional 1,490 grams of HMDZ (0.58 moles Si:COH) was continuously fed through the atomizing nozzle using a pressure pot and needle valve over 317 minutes while maintaining the reactor at 65°C to achieve a total molar Si:COH ratio of 1.26. The reactor was then held at 65°C for 29 minutes. The material in the reactor was a fine, free-flowing powder throughout the reaction and feeds. After maintaining the temperature, the reactor was evacuated to <50 mmHg. After achieving vacuum, the reactor was heated to 90°C for 60 minutes to ensure that no liquid dripped into the vacuum flask.

[0040] After vacuum stripping the crude product, a portion of the resulting material (1055 grams) was removed from the reactor. 8000 grams of cold acetone (3°C) was then charged to the reactor along with the remaining crude silylated cellulose, and the slurry was mixed occasionally (at 60 RPM for three 2-5 minute periods over a 33 minute period) while maintaining the slurry temperature at 25°C. The bottom port was then opened, and the material was drained through a bag filter to capture the solids. The solids were returned to the reactor and washed twice. 6000 grams of acetone was charged to the reactor and mixed with a plow at 60 RPM and at 25°C for 31 minutes. The bottom port was then opened, and the material was drained through a bag filter to capture the solids. 1350 grams of silylated cellulose was removed during this process and set aside. The remaining solids were returned to the reactor. 4000 grams of acetone was charged to the reactor and mixed with a plow at 60 RPM for 31 minutes. The bottom port was then opened and the material was discharged through a filter. The collected solids were finally returned to the reactor. The reactor was then heated to 90°C and the remaining powder was mixed at 120 RPM while a vacuum of -22 inHg was applied. The vacuum drying process was held for 72 minutes. The product was then cooled and discharged from the plow mixer as a fine, dry powder. The final dried product collected was 1300 grams of powdered silylated cellulose with a DS of 2.5.

[0041] Example 4 - Silylated Cellulose Using TFAA.NH3 Catalyst In this Example 4, 249 grams of microcrystalline cellulose was charged to a Sigma Blade mixer, followed by a pre-dissolved solution of 68 grams of DMSO and 10.43 grams of ammonium trifluoroacetate, and the cellulose was silylated by mixing for 15 minutes. 157 grams of HMDZ (0.42 moles Si:COH) was charged to the reactor, which was then heated to 65°C and held for 1 hour. At this time, a vacuum was pulled to <200 torr to remove liquid from the reactor. The vacuum was then released with nitrogen. An additional 188 grams of HMDZ (0.51 moles Si:COH) was then charged in six equal increments, each 10 minutes apart. The material in the reactor remained a fine, dry powder throughout. An additional 140.5 grams of HMDZ (0.38 moles Si:Si(COH)) was then charged in seven equal increments, each 20 minutes apart, to bring the total molar Si:COH ratio to 1.31. The material in the reactor remained a fine, dry powder throughout. The reactor was then held at 65°C for 1 hour. After maintaining the temperature, the reactor was evacuated to <200 torr. After achieving vacuum, the reactor was heated to 90°C for 30 minutes to ensure that no liquid dripped into the vacuum flask. 579.02 grams of crude product were recovered. This material was washed three times with acetone in a pressure filter and then dried overnight by purging with nitrogen. The resulting silylated cellulose powder had a DS of 2.6.

[0042] Example 5 In this Example 5, 1440 grams of microcrystalline cellulose was charged to a Littleford Plow mixer, followed by a pre-dissolved solution of 404 grams of DMSO and 35.6 grams of NH4Cl, and the cellulose was silylated by mixing for 35 minutes. 955 grams of HMDZ (0.44 moles of Si:COH) was continuously fed through a spray nozzle using a pressure pot and needle valve over 50 minutes while the reactor was maintained at 70°C. The mixture was then maintained at temperature and mixed for 20 minutes, at which point a vacuum was drawn to <50 mmHg and held for 20 minutes. An additional 870 grams of HMDZ (0.40 moles of Si:COH) was then continuously fed through a spray nozzle using a pressure pot and needle valve over 147 minutes while the reactor was maintained at 70°C. A vacuum was drawn to <50 mmHg and held for 10 minutes. An additional 910 grams of HMDZ (0.42 moles Si:COH) was then continuously fed through a spray nozzle using a pressure pot and needle valve over 127 minutes while maintaining the reactor at 70°C to achieve a total molar Si:COH ratio of 1.27. The reactor was then held at 65°C for 30 minutes. The material in the reactor was a dry powder throughout the reaction and feeds. After maintaining the temperature, the reactor was evacuated to <50 mmHg. After achieving vacuum, the reactor was heated to 80°C for 13 minutes, ensuring that no liquid dripped into the vacuum flask.

[0043] A 1.6 kg sample was divided into two equal portions. Both fractions were washed with acetone (1 L) on a coarse glass frit. For both fractions, the solids were ground into powder using a laboratory blender, washed twice more with 1 L of acetone on a glass frit, and filtered. The sample was left to dry in a fume hood for 24 hours. The solids from both fractions were combined, washed twice more with 1 L of acetone on a glass frit, and filtered. The sample was left to dry in a fume hood for 72 hours. The resulting silylated cellulose powder had a DS of 2.7.

[0044] Comparative Example 6 - Bulk HMDZ initially charged without step 2) In this Comparative Example 6, 2.64 kg of pulped cellulose was charged to a horizontal plow-type mixer, followed by a pre-dissolved solution of 740 g of DMSO and 65.4 g of NH4Cl, followed by mixing for 30 minutes to silylate the cellulose. The mixer was heated to 90°C. When the internal temperature reached 68°C, 5.25 kg of HMDZ (1.33 moles Si:COH) was charged over 10 minutes. When the internal temperature reached 90°C, the temperature of the hot oil system was reduced to prevent the internal temperature from exceeding 90°C. The reactor was maintained at this temperature for 1.5 hours; however, high amperage was observed. When a vacuum was applied to the system, the agitator failed and could not be restarted. Upon opening the mixer, it was observed that the entire volume of the mixer was filled with a hardened foam that had to be manually trimmed from the mixer. This example demonstrates that powdered silylated cellulose is not formed when the silylating agent (HMDZ) is added all at once, rather than following the method of the present invention. The hardened solid formed is impractical to handle, and the method of silylation of cellulose in this comparative example is not suitable for commercial-scale production of silylated cellulose.

[0045] DS, or degree of substitution, is defined as the average number of hydroxyl groups per monomer unit of the silylated cellulose. DS is determined by ATR-FTIR as follows: The degree of substitution of -SiR3 in the silylated cellulose prepared by the method described herein, DS, was determined using a technique known in the art based on attenuated total reflectance-Fourier transform infrared spectroscopy, which analyzes the spectral peak areas calculated in MATLAB using the spectral parameters provided in Table 2, with the DS values ​​determined as reported in Table 3.

[0046] [Table 2]

[0047] [Table 3] [Industrial Applicability]

[0048] Without wishing to be bound by theory, it is believed that the method described herein can provide silylated cellulose having a DS of ≥ 2, alternatively ≥ 2.5, alternatively ≥ 2.6, or alternatively ≥ 2-3.0. Examples 1-4 demonstrated that the method of the present invention can prepare silylated cellulose with a degree of substitution of up to 3.0. Examples 1-4 and Comparative Example 5 demonstrated that the method of the present invention offers the advantage of providing silylated cellulose in a powder form that is easy to transport, in a volume-efficient manner that does not require the use of solvents during the silylation reaction. Furthermore, the method of the present invention is suitable for commercial-scale production of silylated cellulose. The above examples demonstrated that the method can produce batches of silylated cellulose of ≥ 500 g, alternatively ≥ 600 g, alternatively ≥ 1 kg, or alternatively ≥ 3 kg.

[0049] Without wishing to be bound by theory, it is believed that the method of the present invention may provide the additional advantage of minimizing or eliminating yellowing of the silylated cellulose produced by conducting the silylation reaction at a temperature of ≦85° C.

[0050] Definitions and Use of Terms All amounts, ratios, and percentages herein are by weight unless otherwise specified. The articles "a," "an," and "the" each mean one or more unless otherwise specified. The singular includes the plural unless otherwise specified. The "Summary" and "Abstract" are incorporated herein by reference. The transitional phrases "comprising," "consisting essentially of," and "consisting of" are used as set forth in Sections §2111.03 I, II, and III of the Manual of Patent Examining Procedure, Ninth Edition, Revision 08.2017, Last Revised January 2018.

[0051] Abbreviations used herein have the definitions in Table 4.

[0052] [Table 4]

Claims

1. 1. A method for making powdered silylated cellulose, said method comprising: 1) mixing starting materials, the starting materials comprising: A) a cellulose comprising repeating monomer units having >2.5 to 3 hydroxyl groups per monomer unit; B) a polar aprotic swelling agent; C) a catalyst; and optionally D) a silylating agent comprising a silylamine having a silicon-nitrogen moiety, D) the silylating agent is added in step 1) in an amount sufficient to provide A) a quantity of silyl groups of 0 mol % to <50 mol % of the hydroxyl groups of the cellulose, thereby forming E) a powdered product; and mixing the 2) E) adding to the powdered product an amount of D) the silylating agent continuously or intermittently for >2 hours; wherein the total amount of D) said silylating agent added in steps 1) and 2) is >80 mol % to <200 mol % based on the amount of hydroxyl groups of starting material A) said cellulose, thereby forming a powdered reaction product comprising silylated cellulose.

2. 2. The method of claim 1, wherein in step 1), D) the amount of the silylating agent is sufficient to provide A) 30 mol % to 45 mol % of the hydroxyl groups of the cellulose, and the reaction product prepared in step 1) comprises partially silylated cellulose.

3. 3. The method of claim 2, further comprising reducing the pressure on the reaction product comprising powdered partially silylated cellulose prior to step 2).

4. The method of any one of claims 1 to 3, further comprising A) drying the cellulose before step 1).

5. 5. The method of any one of claims 1 to 4, wherein B) the polar aprotic swelling agent and A) the cellulose are used in amounts such that the weight ratio of B) the polar aprotic swelling agent:A) the cellulose is <3:1 (B:A ratio).

6. C) The method according to any one of claims 1 to 5, wherein the catalyst is selected from saccharin, ammonium trifluoroacetate, and ammonium chloride.

7. C) The method of claim 6, wherein the catalyst is ammonium trifluoroacetate.

8. 6. The method of any one of claims 1 to 5, further comprising C) forming the catalyst by a process comprising reacting a silazane with an acid ex-situ.

9. 9. The method of any one of claims 1 to 8, wherein steps 1) and 2) are carried out at a pressure of from 730 mmHg (97 kPa) to 790 mmHg (105 kPa).

10. 10. The method according to any one of claims 1 to 9, wherein steps 1) and 2) are carried out with heating at a temperature of from 50°C to 85°C.

11. Step 3): The method of any one of claims 1 to 10, further comprising heating the reaction product at a temperature of >50°C to 90°C at a pressure of >0 kPa to <101 kPa and pulverizing the reaction product, thereby forming a powdered silylated cellulose.

12. Step 4): The powdered silylation 12. The method of claim 11, further comprising washing the powdered silylated cellulose 1 to 10 times by mixing the cellulose with G) a washing solvent.

13. 13. The method of claim 12, wherein G) the washing solvent is removed by heating, vacuum, and / or purging with gas.

14. 14. The method of any one of claims 1 to 13, wherein the powdered silylated cellulose is produced in an amount of at least 500 g.

15. 15. The method according to any one of claims 1 to 14, wherein in step 2), D) the feed rate of the silylating agent is any aliquot or continuous flow control that is >0 to <20 mol % of the stoichiometry of the silylating agent charged over a period of >24 minutes to 500 minutes based on a running average over any two aliquots.

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