Process for producing silylated cellulose

Abstract

A process for preparing silylated cellulose is disclosed. The method includes preparing a reaction product in the form of a paste and removing unreacted starting materials and / or by-products from the paste to form powdered silylated cellulose.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 432,713, filed Dec. 15, 2022, under 35 U.S.C. § 119(e). The U.S. Provisional Patent Application Serial No. 63 / 432,713 is hereby incorporated by reference. Technical Field

[0003] A method for producing methylsilylated cellulose is provided. More specifically, the method for producing methylsilylated cellulose can be utilized on a commercial production scale. Background Art

[0004] Current techniques for producing silylated cellulose are based on slurry or solution processes with low volumetric yields. Some of these processes utilize high pressure, where cellulose is suspended in a liquefied ammonia slurry. Others utilize an atmospheric pressure process, producing in a large - volume swelling solvent. These processes have significant drawbacks, not only requiring extremely large volumes of swelling and recrystallization solvents but also generating large amounts of waste liquid. Additionally, due to the large amount of solvent used, the space - time yield of these processes is extremely low. Therefore, these methods are not commercially viable for large - scale use.

[0005] U.S. Patent No. 4,320,692 to Green discloses a method for preparing trimethylsilyl cellulose ethers, which includes reacting cellulose with hexamethyldisilazane in the presence of a small amount of catalyst. In a preferred method of implementing this process, the reaction temperature is maintained between about 100 °C and about 135 °C. When the temperature is below 100 °C, the reaction is found to be too slow to be of practical use; when the temperature is above 135 °C, the reaction is found to become extremely unstable.

[0006] There is a long - standing need in the industry for a process with higher volumetric efficiency for preparing silylated cellulose. Ideally, the process should also operate at atmospheric pressure and / or consume less solvent than existing processes. Summary of the Invention

[0007] A method for preparing silylated cellulose is provided herein. The method includes:

[0008] 1) Mixing starting materials, which include

[0009] A) cellulose,

[0010] B) a polar aprotic swelling agent,

[0011] C) a catalyst, and

[0012] D) A silylating agent, including silylamine,

[0013] to form a reaction mixture; and

[0014] 2) Mixing the reaction mixture in a reactor equipped with a self-cleaning agitator paddle and heating the reaction mixture to form a reaction product comprising silylated cellulose. The starting materials used in this method include the starting materials A), B), C), D) introduced above, and the amounts of these starting materials are sufficient to prepare the reaction product as a paste. Detailed Description

[0015] More specifically, the method for preparing silylated cellulose introduced above includes:

[0016] 1) Mixing starting materials, which include

[0017] A) Cellulose, in which each monomer unit of the repeating monomer units contained therein has more than 2.5 hydroxyl groups,

[0018] B) A polar aprotic swelling agent,

[0019] C) A catalyst,

[0020] D) A silylating agent, including silylamine, which has a silicon-nitrogen (Si-N) moiety, and

[0021] optionally E) A solvent,

[0022] to form a reaction mixture; and

[0023] 2) Mixing the reaction mixture in a reactor equipped with a self-cleaning agitator paddle and heating the reaction mixture at a temperature of 30 °C to 150 °C to form a reaction product comprising silylated cellulose. The starting materials include A), B), C), D), and the amounts thereof are sufficient to prepare the reaction product as a paste.

[0024] This method may also optionally include one or more additional steps. For example, this method may also include drying A) cellulose before step 1). Commercially available cellulose may contain adsorbed water. To minimize the formation of by-products, the cellulose can be dried to remove at least part of the moisture. Drying can be carried out by any convenient means, such as heating the cellulose and / or placing it in a reduced-pressure environment, or exposing it to a stream of inert gas.

[0025] The method may optionally further comprise adding E) a solvent, which is different from B) the polar aprotic swelling agent, for example, added in step 1) or step 2). Alternatively, the method may further comprise an additional step, which includes: before step 1), dissolving C) the catalyst in one or both of B) the polar aprotic swelling agent and E) the solvent to form a catalyst solution. The resulting catalyst solution may be mixed with A) cellulose before step 1) (for example, before adding D) the silylating agent to the reactor). For example, the catalyst solution may be mixed with A) cellulose for at least 10 minutes, alternatively at least 15 minutes; meanwhile, before adding D) the silylating agent, the catalyst solution may be mixed with A) cellulose for up to 1 hour.

[0026] Alternatively, the method may further comprise an additional step, which includes: forming C) the catalyst by a method including an ex-situ reaction of a part of D) the silylating agent with an acid. Optionally, E) the solvent may be used to facilitate the 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) the silazane described below as starting material D). The silazane selected for forming the catalyst may be the same as or different from the starting material D) used in step 1) for carrying out the silylation reaction. This step may be carried out via any convenient manner, such as by mixing at room temperature and atmospheric pressure.

[0027] In step 2), the reaction mixture is mixed for 15 minutes to ≥ 24 hours, alternatively 15 minutes to 24 hours, alternatively 30 minutes to 2 hours. The temperature in step 2) can be 30°C to 150°C, alternatively 50°C to 85°C, alternatively 50°C to 80°C, alternatively 55°C to 80°C. The pressure in step 2) can be 730 mmHg (97 kPa) to 790 mmHg (105 kPa), alternatively 750 mmHg (100 kPa) to 770 mmHg (103 kPa). The reaction mixture and / or reaction product produced in step 2) has a paste consistency, which cannot be mixed in a standard reaction vessel equipped with a single agitator paddle, nor can the reaction mixture be easily pumped. If cooled to room temperature, the paste may form a solid. If the paste forms in a reactor equipped with a single agitator paddle, at room temperature, the paste will solidify on the agitator paddle and will need to be removed manually from the reactor (i.e., the stubborn solid that will form cannot be pulverized inside the reactor nor discharged from the reactor by pumping, as illustrated in Comparative Example 5 below). Therefore, a reactor capable of mixing the reaction mixture and reaction product having this consistency is used. The reactor is equipped with a self-cleaning agitator paddle, which can be, for example, a kneading reactor or a sigma blade reactor. Without wishing to be bound by theory, we believe that the self-cleaning agitator paddle can prevent the formation of stubborn solids by continuously tearing fibrous, crystalline, and / or entangled components and maintaining the mixing state inside the reactor.

[0028] The method may further include step 3): heating the reaction product at a temperature of > 50°C to 105°C and a pressure of > 0 kPa to < 101 kPa to form a brittle solid or powder containing silylated cellulose. Alternatively, the temperature in step 3) can be 60°C to 105°C, alternatively 65°C to 90°C. Without wishing to be bound by theory, we believe that step 3) will remove most of the residual ammonia and the residual D) silylating agent, thereby converting the reaction product into a brittle solid, which can be easily pulverized to form powdered silylated cellulose, and the powdered silylated cellulose can be mixed and transported by gas or powder handling methods. The method may further include pulverizing the brittle solid (e.g., by any convenient means such as grinding) to form powdered silylated cellulose. Alternatively, the pulverization can be carried out during step 2) in a reactor equipped with a self-cleaning blade.

[0029] The method may optionally further include step 4): washing the powdered silylated cellulose by mixing it with F) a washing solvent to remove any residual polar aprotic swelling agent, catalyst, and / or solvent, and / or by-products that may be present. The choice of the washing solvent is not particularly limited; however, the washing solvent may be a low-boiling polar solvent that can dissolve the residual starting materials and / or by-products but does not significantly solubilize the silylated cellulose, and the washing solvent can be conveniently evaporated off from the silylated cellulose product. The washing in step 4) can be carried out in any convenient manner, such as by mixing the washing solvent with the powdered silylated cellulose produced as described above in the reactor used in step 1) or in a stirred slurry vessel, and then discharging the solvent after a sufficient length of time. The washing step can be repeated as many times as needed, such as from 1 to 10 times.

[0030] The method may optionally further include step 5): removing the washing solvent by any convenient means, such as filtration, heating, reduced pressure, and / or by purging with a gas (such as air or an inert gas (such as nitrogen)).

[0031] The resulting product is a pure silylated cellulose with low waste emissions and high volume efficiency in the production process. The silylated cellulose produced by this method has a DS (degree of substitution) of 2.0 to 3.0, alternatively 2.2 to 3.0, alternatively 2.4 to 3.0, alternatively 2.6 to 3.0, alternatively 2.8 to 3.0.

[0032] The starting materials used herein will be described in further detail below.

[0033] A) Cellulose

[0034] Starting material A), namely the cellulose used in the above method, has >2.5 to 3 hydroxyl groups per repeating monomer unit in the molecule, alternatively 3 hydroxyl groups. Cellulose is a polymer of β(1→4)-linked D-glucose repeating monomer units. Each molecule of cellulose can have 200 or more repeating monomer units. Alternatively, cellulose can have at least 200, alternatively at least 300, alternatively at least 400, alternatively at least 500, alternatively at least 600, alternatively at least 700 repeating monomer units; at the same time, each molecule of cellulose can have at most 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, alternatively at most 4,000 repeating monomer units. Alternatively, each molecule of cellulose can have 200 to 10,000, alternatively 400 to 8,000 repeating monomer units.

[0035] The cellulose type can be, for example, microcrystalline cellulose or pulp cellulose. Sources of cellulose include, but are not limited to, cotton linter, pine wood, and tunicin (cellulose of animal origin). Cellulose is commercially available from various sources.

[0036] B) Polar aprotic swelling agent

[0037] The starting material B) used in the above method 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 hexamethylphosphoric triamide (HMPA).

[0038] The amounts of starting materials A) and B) are such that the weight ratio of the polar aprotic swelling agent B) to A) cellulose is < 3:1, alternatively < 1:1, alternatively < 0.3:1 (B:A ratio). Alternatively, the B:A ratio can 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 can be at most < 0.3:1, alternatively 0.29:1, alternatively 0.28:1, alternatively 0.27:1, alternatively 0.26:1.

[0039] C) Catalyst

[0040] The starting material C) in the above method is a catalyst that can catalyze the reaction between the hydroxyl groups of A) cellulose and the silicon-nitrogen (Si-N) moiety of D) a silylating agent. Examples of suitable catalysts include ammonium salts such as ammonium chloride, ammonium trifluoroacetate, or ammonium trifluoromethanesulfonate; saccharin; sulfonic acids such as methanesulfonic acid, p-toluenesulfonic acid, or trifluoromethanesulfonic acid (triflic acid); trifluoroacetic acid; trimethylchlorosilane; or combinations thereof. Alternatively, the catalyst can be selected from the group consisting of ammonium chloride, ammonium trifluoroacetate, or saccharin. Alternatively, the catalyst can comprise (or can be) ammonium trifluoroacetate.

[0041] Those skilled in the art should understand that the catalyst can be used by various methods. These methods can be directly adding the catalyst (such as ammonium trifluoroacetate) into the reactor, or first dissolving the catalyst in a polar aprotic swelling agent or a solvent, and then adding the obtained catalyst solution into the reactor. Alternatively, the catalyst can be formed by premixing a specific silylating agent (such as silazane or other silylamines (as described below for starting material D)) with an acid (such as trifluoroacetic acid or trifluoroboric acid), and then loading the obtained mixture containing the silylammonium salt catalyst into the reactor.

[0042] The amount of the catalyst depends on various factors, including the type of the catalyst and the selected temperature. However, based on the combined weight of starting materials A), B), C), and D) used in the method, the amount of the catalyst can be at least 0.01 wt%, alternatively at least 0.1 wt%, alternatively at least 0.3 wt%, while the amount of the catalyst can be at most 5 wt%, alternatively at most 4 wt%, alternatively at most 3 wt%, alternatively at most 2 wt%; alternatively, the amount of the catalyst can be 0.1 wt% to 5 wt%, alternatively 0.3 wt% to 2 wt%.

[0043] D) A silylating agent having an Si-N moiety

[0044] The starting material D) in the above method is a silylating agent having a silicon-nitrogen (Si-N) moiety, including silylamines. The Si-N moiety can react with the hydroxyl groups of cellulose. The silylating agent can be selected from silazanes, aminosilanes, or combinations thereof. For example, the silazane can be a disilazane of the following formula

[0045] where R 1 、R 2 、R 3 、R 4 、R 5 、R 6 and R 7Each is independently selected from the group consisting of H, an alkyl group having 1 to 18 carbon atoms, and an alkenyl group having 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-hydro-1,1,3,3-tetramethyldisilazane.

[0046] Alternatively, the silylating agent can be an aminosilane, which can have the structural formula: R N x SiR 8 4-x , where each R N is an amino functional group bonded to silicon via a nitrogen atom; and each R 8 is independently selected from the group consisting of H, an alkyl group having 1 to 18 carbon atoms, and an alkenyl group having 2 to 18 carbon atoms, as described above for R 1 , where the subscript x is from 1 to 3. R N can have the structural formula -NR 9 2, where each R 9 is independently selected from the group consisting of H, an alkyl group having 1 to 18 carbon atoms, or an aryl group having 6 to 18 carbon atoms.

[0047] Examples of aminosilanes include tris(dimethylamino)silane, bis(diisopropylamino)silane, (N,N-dimethylamino)trimethylsilane, trimethyl(amino)silane {H2N-Si(CH3)3}, triethyl(amino)silane {H2N-Si(CH2-CH3)3}, tripropyl(amino)silane {H2N-Si(C3H7)3}, tributyl(amino)silane {H2N-Si(C4H9)3}, dimethylethyl(amino)silane, dimethylbutyl(amino)silane, trivinyl(amino)silane, dibutylethyl(amino)silane, tris(1-butenyl)(amino)silane, or triaryl(amino)silane. Suitable aminosilanes are known in the art and are commercially available from, for example, Sigma-Aldrich, Inc. (St. Louis, Missouri, USA) or Gelest Inc. (Morrisville, Pennsylvania, USA).

[0048] The amount of the starting material D), the silylating agent, is sufficient to maintain the molar ratio of the Si-N moiety of the D) silylating agent to the hydroxyl groups of the A) cellulose in the range of > 0.67:1 to 4:1 (D Si :A OH ratio). Alternatively, the D Si :A OH ratio can be 0.7:1 to 3.5:1, alternatively 0.8:1 to 3.0:1, alternatively 0.9:1 to 2.5:1, alternatively 1:1 to 2.0:1, alternatively 1.15:1 to 1.98:1, alternatively 1.3:1 to 1.4:1.

[0049] E) Solvent

[0050] The starting material E) used in the above method is an optional solvent, which is different from the B) polar aprotic swelling agent. The choice of the solvent is not particularly limited and can be any solvent capable of dissolving or dispersing the A) cellulose and / or the C) catalyst with one or more other starting materials. For example, the solvent can include aliphatic hydrocarbons (such as hexane), aromatic hydrocarbons (such as toluene or xylene), halogenated hydrocarbons (such as carbon tetrachloride), or ethers (such as tetrahydrofuran).

[0051] The amount of the solvent depends on various factors, including the type and amount of the selected catalyst. However, based on the combined weight of A), B), C), D), the amount of the solvent can be ≥ 0. Alternatively, the amount of the E) solvent can be 0 or > 0, while the amount of the solvent can be at most 15 times the weight of the catalyst, alternatively at most 12 times the weight of the catalyst. Without wishing to be bound by theory, we believe that in order to optimize the volume efficiency, it is desirable to completely eliminate the solvent or minimize its use.

[0052] F) Washing solvent

[0053] The starting material F) in the above method is an optional washing solvent, which can be used to remove the residual starting materials and / or by-products in the silylated cellulose produced by the method. The starting material F) can be different from the above starting materials B) and E). Examples of suitable washing solvents include water, ketones (such as acetone), monohydric alcohols (such as methanol or ethanol); alternatively acetone. Without wishing to be bound by theory, we believe that ketones (such as acetone) can effectively remove polar and non-polar residues and are at the same time easily removed from the silylated cellulose under reduced pressure.

[0054] Usage method

[0055] The silylated cellulose prepared as described herein can be used in a variety of end applications. For example, the silylated cellulose can replace the cellulose derivatives described in U.S. Patent No. 10,851,180 and be used in the optical films of image display devices. Alternatively, the silylated cellulose prepared as described above can be used as a thickening polymer in personal care applications (such as cosmetic formulations or sunscreen formulations), for example, as a supplement to or in place of the silylated cellulose polymer disclosed in PCT Patent Publication WO / 2022 / 066591.

[0056] Example

[0057] These examples are provided to illustrate the invention to those skilled in the art and should not be construed as limiting the scope of the invention described in the claims. The starting materials used in these examples are summarized in Table 1 below.

[0058] Table 1 - Starting materials

[0059] Starting materials Description Source A1 Microcrystalline cellulose Avicel PH - 101 from IFF A2 Pulped cellulose Ground E60 from Georgia Pacific B1 DMSO Dimethyl sulfoxide Sigma - Aldrich <![CDATA[C1 NH4Cl]]> Ammonium chloride Sigma - Aldrich D1 HMDZ Hexamethyldisilazane Dow F1 Acetone Oakwood Chemicals

[0060] Reaction with stripping

[0061] In this Example 1, the cellulose was silylated in a Sigma paddle stirrer (reactor): First, 243 grams of microcrystalline cellulose was loaded, and then a pre-dissolved mixed solution of 68.25 grams of DMSO and 6.07 grams of NH4Cl was loaded, and stirring was continued for 10 minutes. 483.25 grams of HMDZ was loaded into the reactor, and the hot oil supply for heating the reactor was set to 90 °C. When the temperature of the reaction mixture stabilized, the reactor was maintained at this temperature for 1 hour. After the reaction was completed, the resulting reaction product was a paste, with a texture viscous like toffee. After the heat preservation ended, the vacuum was pumped to <200 Torr and maintained for 1 hour to ensure that no liquid dripped from the vacuum flask. While maintaining the vacuum, the reaction product changed from a paste to a brittle flaky powder. A total of 547.2 grams of the resulting crude product was recovered. The DS of the resulting silylated cellulose was 3.0.

[0062] In Example 2, the silylation of cellulose was carried out in a Sigma paddle stirrer (reactor): First, 304 g of pulped cellulose was loaded, and then a mixed solution of 86.4 g of DMSO and 6.07 g of NH4Cl, which had been pre-dissolved, was loaded, and stirring was continued for 25 minutes. 604.1 g of HMDZ was loaded into the reactor, and the hot oil supply for the reactor was set to 90 °C. When the temperature of the reaction mixture was stable, the reactor was maintained at this temperature for 1 hour. After the reaction was completed, the material was a paste, with a texture as viscous as toffee. After the heat preservation was over, the vacuum was pumped down to <200 Torr and maintained for 1 hour to ensure that no liquid dripped from the vacuum flask. While maintaining the vacuum, the reaction product changed from a paste to a brittle flaky powder. A total of 678.35 g of crude product was recovered. The DS of the obtained silylated cellulose was 2.4.

[0063] Stripping after reaction, followed by washing and filtering using a plate - and - frame filter press

[0064] In Example 3, the silylation of cellulose was carried out in a Sigma paddle stirrer: First, 242 g of pulped cellulose was loaded, and then a mixed solution of 68.4 g of DMSO and 6.0 g of NH4Cl, which had been pre-dissolved, was loaded, and stirring was continued for 10 minutes. 484 g of HMDZ was loaded into the reactor, and then it was heated to 73 °C and maintained for 1 hour. After the reaction was completed, the reaction product was a paste, with a texture as viscous as toffee. After the heat preservation at about 73 °C was over, the vacuum was pumped down to <200 mmHg, and the pressure was maintained for 1 hour after the dripping stopped. While maintaining the vacuum, the reaction product changed from a paste to a brittle flaky powder. A total of 540.9 g of the obtained crude product was recovered.

[0065] After the crude product was loaded into the filter press, acetone was filled until the liquid level was slightly higher than the solid. The obtained material was manually mixed and then allowed to stand for about 15 minutes, and then the liquid was drained. Acetone was added again until the liquid level was slightly higher than the solid, manually mixed and allowed to stand for about 15 minutes, and the liquid was drained again. The final acetone washing solution was loaded until the acetone liquid level was slightly higher than the solid, manually mixed and allowed to stand for about 15 minutes, and then the liquid was drained. Subsequently, the filter press was sealed, purged with low-pressure nitrogen, and allowed to stand overnight. In the morning of the next day, the obtained silylated cellulose was taken out. The silylated cellulose had a total silicon DS of 3.0.

[0066] Stripping after reaction, followed by washing and filtering using a Buchner funnel

[0067] In Example 4 herein, the silylation of cellulose was carried out in a Sigma paddle stirrer: First, 234.7 g of pulped cellulose was loaded, and then a mixed solution of 68.2 g of DMSO and 6.0 g of NH4Cl dissolved in advance was loaded, and stirring was continued for 10 minutes. 484 g of HMDZ was loaded into the reactor, and then the reaction mixture was heated to 73 °C and maintained for 1 hour. After the reaction was completed, the resulting reaction product was a paste, with a viscous texture similar to toffee. After insulation at about 73 °C was completed, the vacuum was pumped down to <200 mmHg, and the pressure was maintained for 1 hour after the dripping stopped. While maintaining the vacuum, the reaction product changed from a paste to a brittle flaky powder. A total of 571.52 g of the obtained crude product was recovered.

[0068] 22.77 g of the crude product was taken and loaded into a Buchner funnel in a fume hood. 79 g of acetone was loaded into the funnel containing the crude product, and it was manually mixed for 1 minute. Subsequently, while manually stirring the crude product and acetone, the receiving flask was evacuated to discharge the acetone. 109 g of acetone was loaded again, and mixing and liquid drainage were completed in the same manner. Then 100 g of additional acetone was added, mixed, and discharged similarly. The residual sample was thinly spread on a tray in a fume hood and left to stand overnight to allow the residual acetone to evaporate. In the morning of the next day, 19.37 g of dry powdered silylated cellulose was recovered. The silylated cellulose contained 3.0 of total silicon DS.

[0069] Comparative example – Non - self - cleaning blade (single agitator shaft structure)

[0070] In Example 5 herein, the silylation of cellulose was carried out in a horizontal plowshare mixer: First, 2.64 kg of pulped cellulose was loaded, and then a mixed solution of 740 g of DMSO and 65.4 g of NH4Cl dissolved in advance was loaded, and stirring was continued for 30 minutes. The stirrer was heated to 90 °C. When the internal temperature reached 68 °C, 5.25 kg of HMDZ was loaded within 10 minutes. The reactor was maintained at 90 °C for 1.5 hours; however, a too-high current was observed during this period. When the system was evacuated, the stirrer malfunctioned and could not be restarted. When the stirrer was turned on, it was observed that the entire internal space was completely filled with hardened foamy material, which needed to be manually cut and removed.

[0071] Industrial applicability

[0072] Without wishing to be bound by theory, we believe that the methods described herein can provide silylated celluloses having DS > 2, alternatively DS > 2.3, alternatively DS in the range of ≥ 2.4 to 3.0. Examples 1 to 4 show that, by the method of the present invention, silylated celluloses having a degree of substitution ≥ 2.8 are prepared in a reactor with self-cleaning blades. Examples 1 to 4 and 5 show that the method of the present invention, which includes a stripping step after the reaction, has significant advantages: not only can silylated celluloses in powder form, which are easy to transport, be obtained, but also no solvent needs to be used during the silylation reaction, and it has excellent volume efficiency. In addition, the method of the present invention is applicable to the production of silylated celluloses, such as silylated celluloses, on a commercial scale. The above examples show that the present method can produce silylated celluloses in batches of ≥ 500 g, alternatively ≥ 600 g, alternatively ≥ 1 kg, alternatively ≥ 3 kg.

[0073] Without wishing to be bound by theory, we believe that the method of the present invention can provide additional advantages: by controlling the temperature at ≤ 85 °C during the silylation reaction in step 2), the yellowing of the produced silylated cellulose can be minimized or even completely avoided.

[0074] Definition and usage of terms

[0075] Unless otherwise indicated, all amounts, ratios, and percentages herein are by weight. Unless otherwise indicated, each of the articles "a", "an", and "the" refers to one or more. Unless otherwise indicated, the singular includes the plural meaning. The description of the invention and the abstract of the specification are hereby incorporated by reference. The transitional phrases "comprising", "consisting essentially of", and "consisting of" are used as described in Chapters §2111.03I., II., and III of the Ninth Edition of the Manual of Patent Examining Procedure, Revision 08.2017, last revised in January 2018.

[0076] DS or degree of substitution is defined as the average number of hydroxyl groups silylated in each monomer unit of cellulose. DS is determined by ATR-FTIR as follows. The degree of substitution (DS) of -SiR3 in the silylated cellulose prepared by the method described herein is determined using techniques known in the art: based on attenuated total reflection - Fourier transform infrared spectroscopy, using the spectral parameters provided in Table 2, analyzing the peak areas calculated by MATLAB, and the measured DS values are reported in Table 3.

[0077] Table 2 .

[0078]

[0079] Table 3. DS values of the above examples 。

[0080]

[0081] The abbreviations used herein have the definitions in Table 4.

[0082] Table 4 - Abbreviations

[0083] Abbreviations Definition ATR - FTIR Attenuated total reflection - Fourier transform infrared ℃ Degree Celsius DS Degree of substitution g Gram h Hour Kg or kg Kilogram min Minute RT Room temperature of 23°C ± 3°C

Claims

1. A method for preparing silylated cellulose, wherein the method comprises: 1) Mixing starting materials, the starting materials comprising A) cellulose, the cellulose comprising repeating monomer units and each monomer unit having more than 2.5 to 3 hydroxyl groups, B) a polar aprotic swelling agent, C) a catalyst, and D) a silylating agent, including a silylamine having a silicon-nitrogen moiety, thereby forming a reaction mixture; and 2) Mixing the reaction mixture in a reactor equipped with a self-cleaning agitator paddle and heating the reaction mixture at a temperature of 30 °C to 150 °C, thereby forming a reaction product comprising the silylated cellulose with a degree of substitution > 2, and wherein the amounts of the starting materials are such that the reaction mixture or the reaction product is a paste.

2. The method according to claim 1, further comprising drying A) the cellulose before step 1).

3. The method according to claim 1 or claim 2 further comprises: Before step 1), dissolve C) the catalyst in B) the polar aprotic swelling agent, E) a solvent, or a combination thereof.

4. The method according to any one of claims 1 to 3, wherein the amounts of B) the polar aprotic swelling agent and A) the cellulose are such that the weight ratio of B) the polar aprotic swelling agent to A) the cellulose is in the range of 0.1:1 to < 3:1 (B:A ratio).

5. The method according to any one of claims 1 to 4, wherein the amounts of the silylating agent in D) and the cellulose in A) are such that the molar ratio of the silicon-nitrogen moiety to the hydroxyl group is in the range of > 0.5:1 to 4:1 (D Si :A OH ratio).

6. The method according to any one of claims 1 to 5, wherein the catalyst comprises ammonium chloride or ammonium trifluoroacetate.

7. The method according to any one of claims 1 to 6, wherein the method further comprises: Form C) the catalyst by a method comprising an ex-situ reaction of a silazane with an acid.

8. The method according to any one of claims 1 to 7, wherein step 2) is carried out at a pressure of 730 mmHg (97 kPa) to 790 mmHg (105 kPa).

9. The method according to any one of claims 1 to 8, wherein step 2) is carried out at a temperature of 50 °C to 85 °C.

10. The method according to claim 1, wherein the method further comprises step 3): heating the reaction product at a temperature of > 50 °C to 90 °C and at a pressure of > 0 kPa to < 101 kPa, and comminuting the reaction product, thereby forming powdered silylated cellulose.

11. The method according to claim 10, further comprising step 4): washing the powdered silylated cellulose 1 to 10 times by mixing the powdered silylated cellulose and F) a washing solvent.

12. The method according to claim 11, wherein E) the washing solvent is removed by heating, reducing the pressure, and / or by purging with a gas.

13. The method according to any one of claims 1 to 12, wherein the reactor is a kneading reactor or a sigma blade agitator.

14. The method according to any one of claims 1 to 12, wherein the silylated cellulose is produced in an amount of at least 500 grams.

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