Improved methylcelluloses

Abstract

An exemplary process comprises synthesis of methylcellulose in the presence of methanol, leading to an improved methylcellulose having gel-like characteristics in solution.

Description

IMPROVED METHYLCELLULOSESField of the Invention

[0001] The field relates to the use of methylcellulose as stabilizer in food pharmaceuticals or other industrial areas.Background

[0002] Yield stress is a well-recognized physical and rheological property for liquid and solid materials. The yield stress is classically defined as the minimum shear stress that must be applied to the material to initiate flow. Such yield stress phenomena are often based on hydrogen bond networks, Coulomb or Van-der-Walls interactions between the polymers in solutions and such phenomena are often found for natural polymers like xanthan or low substituted CMC grades.

[0003] In certain polymers, yield stress phenomena is not present. For example, MC (methylcellulose) or HPMC (Hydroxypropyl methylcellulose) grades are known in the art as pure viscosity enhancing agents without the presence of yield stress phenomena in solutions.

[0004] It is known in the art that methanol is a by-product in the synthesis of methylcellulose, which is formed from the reaction of methyl chloride + sodium hydroxide.

[0005] In that regard, US20100298555A1 discloses a process for producing methylcellulose in an industrially convenient manner including the reaction of cellulose in a subcritical state at a temperature of 220 °C and pressure levels of 2 MPa.

[0006] However, yield stress phenomena are useful in many application fields like stabilization of foams, dispersion or suspension or other heterogenous liquid or semi-solid fluids. The yield stress delivers enhanced stability to keep these formulations stable over time whereas pure viscosity enhancing fluids would show separation over time.

[0007] There remains a need for improved methylcellulose compositions.Summary of the Invention

[0008] In one example, a methylcellulose having gel-like characteristics in solution, comprises anhydroglucose units joined by 1-4 linkages, wherein hydroxy groups of the anhydroglucose units are substituted with methyl groups such that a degree of substitution DS(methyl) is 1 .72 or less and a tan 5 (tan delta) value of less than 1.55 at a concentration of 2% of methylcellulose at an angular frequency of 1 rad / s and 20 °C, the tan delta value being indicative of the gel-like characteristics, wherein the tan delta value is derived from the ratio of loss modulus / storage modulus.

[0009] In one example, an exemplary process for preparing the foregoing methylcellulose comprises a step of treating cellulose pulp with an alkalization agent and a methylating agent in the presence of an alcohol.

[0010] An exemplary process comprises synthesis of methylcellulose in the presence of methanol, leading to synthesis of methylcellulose with high s231 s26 substitution pattern > 0.55 and having at a concentration of 2 % in pure aqueous solution and gel-like characteristics at a temperature of 20 - 25 °C, preferably at a temperature of 20 °C and having a tan delta value of < 1.55 at an angular frequency of 1 rad / s in the linear viscoelastic regime and further enhanced viscosity values.Brief Description of Figures

[0011] The above objects and other advantages of the invention will become more readily apparent upon reading the following description and drawings, in which:

[0012] FIG. 1 is a schematic describing one example of the claimed process.

[0013] FIG. 2 is a graph of storage modulus G' and loss modulus G” as a function of the angular frequency from 1 rad / s to 100 rad / s for the non-inventive Sample Number (No.) 211 vs the inventive Sample No. 215 at concentration of 2 % in water.

[0014] FIG. 3 is a graph of an exploded view (zoomed-in) of storage modulus G' and loss modulus G” as a function of the angular frequency from 1 rad / s to 10 rad / s for the non-inventive Sample No. 211 vs the inventive Sample No. 215 at concentration of 2 % in water.Detailed Description of the Invention

[0016] The examples provided in the detailed description are merely examples and should not be used to limit the scope of the claims in any claim construction or interpretation

[0017] A process for preparing a methylcellulose is disclosed. An exemplary process comprises:(a) treating cellulose pulp with an alkalization agent at a temperature below 55°C in the presence of methanol,(b) providing a methylating agent before, after or concurrently with the alkalization agent while increasing the reaction temperature to a temperature of 60°C or more,(c) reacting the alkalized cellulose with the methylating agent for at least 120 minutes or more at a final reaction temperature, and(d) washing the methylcellulose prepared in step (b).

[0018] Cellulose. As known in the art and as shown below, cellulose is a naturally occurring polysaccharide polymer composed of anhydroglucose units joined by 1-4 linkages.

[0019]

[0020] Each anhydroglucose unit contains hydroxyl groups at the 2, 3, and 6 positions. Partial or complete substitution of these hydroxyl groups creates cellulose derivatives. For example, treatment of cellulosic fibers with an alkaline solution, followed by a methylating agent, yields cellulose ethers substituted with one or more methoxy groups. If a cellulose derivative is not further substituted with other alkyls, such a cellulose ether is known as methylcellulose.

[0021] Many of the terms mentioned in the present specification are disclosed in US Patent No. 9,937,258, (hereinafter, the ‘258 patent), which discloses a methylcellulose, not part of the subject claimed invention. The disclosure of that patent is incorporated by reference.

[0022] Formula I below illustrates the numbering of the hydroxy groups in anhydroglucose units. Formula I is only used for illustrative purposes and does not represent the methylcellulose as disclosed in this specification.Formula I

[0023] Degree of substitution. This specification adopts the following definition for the degree of substitution. The degree of the methyl substitution, DS(methyl), of a cellulose ether is the average number of OH groups substituted with methyl groups per anhydroglucose unit. For determining the DS(methyl), the term "OH groups substituted with methyl groups" only includes the methylated OH groups at the polymer backbone, i.e. , that are directly a part of the anhydroglucose unit.

[0024] Methoxyl content of the disclosed methylcellulose. The disclosed methylcellulose as taught in the present specification preferably has a content of methoxyl groups of from 28.7% or less. The determination of the methoxyl content in methylcellulose is carried out according to the United States Pharmacopeia (USP 34). The obtained values are % methoxyl (weight content) or are calculated to the degree of substitution.

[0025] The viscosity of the disclosed methylcellulose of the present specification is generally from 10mPa*s to 100,000 mPa*s when measured as a 2 wt. % aqueous solution at 20 °C at a shear rate of 2.51 s’1.

[0026] The methylcellulose as disclosed in the present specification is preferably in powder form.

[0027] General methods of making methylcellulose. Methods of making the methylcellulose as disclosed in the present specification are described in more detail in the Examples.

[0028] Alkalization agents used. Generally, cellulose pulp is treated with an alkalization agent, for example, alkali metal hydroxide (by a 50% by weight aqueous solution, i.e., w / w). In one example, the alkalization agent is NaOH. Preferably, about 3.0 to 10.0 mol NaOH per mol anhydroglucose units in the cellulose is used.

[0029] Uniform swelling and alkali distribution in the cellulose pulp is optionally controlled by mixing and agitation. During the exothermic alkalization reaction, the rate of addition of aqueous alkaline hydroxide is governed by the ability to cool a reactorcontaining the reactants. In one example, an organic solvent such as dimethyl ether as a diluent and coolant is added to the reactor.

[0030] Likewise, the headspace of the reactor is optionally purged with an inert gas (such as nitrogen) to minimize unwanted reactions with oxygen and molecular weight losses of the methylcellulose. In one example, the temperature during alkalization is maintained at or below 55°C, preferably below 50°C, more preferably below 45°C and most preferably below 40°C or can be at a lower temperature range of 15-20 °C. Thus, an exemplary temperature range during alkalization is from 15 to 55°C. For example, a solidification temperature of 50% NaOH is at approximately 12 °C.

[0031] Addition of a methylating agent and an alkalization agent. A methylating agent such as methyl chloride is also added to the cellulose pulp either (1) before or (2) after or (3) concurrently with the alkalization agent. Other methylating agents known in the art may be used. Exemplary methylating agents include methyl sulfate, methyl halogenide or dimethylcarbonate, for example.

[0032] In conventional methods, all reactants are added at the same time and there is no stage addition or additions in portions over long period of time.

[0033] An exemplary amount of 2.0 - 10.0 mol methylating agent per mol anhydroglucose units in the cellulose is added. Preferably, the methylating agent is added after the alkalization agent. Once the cellulose has been contacted with an alkalization agent and a methylating agent, the reaction temperature is increased to a final reaction temperature of 60°C or more, preferably from 65°C to 95°C, more preferably from 70°C to 90°C; and most preferably at temperatures of 70 - 85 °C Once the final reaction temperature has been reached, the alkalized cellulose is reacted with the methylating agent for at least 120 min.

[0034] Washing of methylcellulose product. The resulting methylcellulose is washed to remove salt and other reaction by-products. Any solvent in which salt is soluble may be employed, but hot water as a solvent is preferred, where the methylcellulose is not soluble, such as hot water at a temperature of 75 - 110 °C.

[0035] The methylcellulose may be washed in the reactor itself but is preferably washed in a separate washer located downstream of the reactor. Before or after washing, stripping may occur in which the methylcellulose can be stripped by exposure to steam to reduce residual organic content, in which by-products are removed.

[0036] Drying of methylcellulose product. The methylcellulose is preferably dried to a lower moisture content of 0.1 to 10.0% by weight of water (w / w) and more preferably 0.5 to 5.0% by weight of water and volatiles based on the weight of methylcellulose. The dried methylcellulose may generally be milled into particles and particles are separated througha sieve with about 300 m openings. If desired, drying and milling may be carried out simultaneously.

[0037] Some examples of the disclosed methylcellulose will now be described in detail in the following Examples. Unless otherwise mentioned, all parts and percentages are by weight. In the Examples, the following test procedures are used.Determination of s23 / s26 of Methylcellulose

[0038] The approach to measure the ether substituents in methylcellulose is generally known in the art. An exemplary reference for such measurement is described in Carbohydrate Research, 176 (1988) 137-144, Elsevier Science Publishers B.V., Amsterdam and DISTRIBUTION OF SUBSTITUENTS IN O-ETHYL-O-(2- HYDROXYETHYL)CELLULOSE by Bengt Lindberg, Ulf Lindquist, and Olle Stenberg, the disclosure of which is incorporated herein by reference.Determination of s23 / 26 as disclosed in the Examples

[0039] 10-12 mg of the methylcellulose were dissolved in 4.0 mL of dry analytical- grade dimethyl sulfoxide (DMSO) (Merck, Darmstadt, Germany, stored over 0.3 nm molecular sieve beads) at about 90 °C with stirring and then cooled to room temperature. The solution was stirred at room temperature over night to ensure complete solubilization / dissolution. The entire perethylation including the solubilization of the methylcellulose was performed using a dry nitrogen atmosphere in a 4 mL screw cap vial.

[0040] After solubilization, the dissolved methylcellulose was transferred to a 22-mL screw-cap vial to begin the perethylation process. Powdered sodium hydroxide (freshly pestled, analytical grade, Merck, Darmstadt, Germany) and ethyl iodide (for synthesis, stabilized with silver, Merck-Schuchardt, Hohenbrunn, Germany) were introduced in a thirty-fold molar excess relative to the level of anhydroglucose units in the methylcellulose, and the mixture was vigorously stirred under nitrogen in the dark for three days at ambient temperature.

[0041] The perethylation was repeated with addition of the threefold amount of the reagents sodium hydroxide and ethyl iodide compared to the first reagent addition, and stirring at room temperature was continued for an additional two days. Optionally, the reaction mixture may be diluted with up to 1.5 mL dimethylsulfoxide (DMSO) to ensure good mixing during the course of the reaction. Next, five mL of 5 % aqueous sodium thiosulfate solution was poured into the reaction mixture, and the mixture was then extracted three times with 4 mL of dichloromethane. The combined extracts were washed three times with 2 mL of water. The organic phase was dried with anhydrous sodium sulfate (aboutl g). After filtration, the solvent was removed with a gentle stream of nitrogen, and the sample was stored at 4 °C until needed.

[0042] Hydrolysis of about 5 mg of the perethylated samples was performed under nitrogen in a 2-mL screw-cap vial with 1 mL of 90 % aqueous formic acid under stirring at 100 °C for 1 hour. The acid was removed in a stream of nitrogen at 35-40 °C and the hydrolysis was repeated with 1 mL of 2M aqueous trifluoroacetic acid for 3 hours at 120 °C in an inert nitrogen atmosphere with stirring. After completion, the acid was removed to dryness in a stream of nitrogen at ambient temperature using ca. 1 mL of toluene for co-distillation.

[0043] The residues of the hydrolysis were reduced with 0.5 mL of 0.5-M sodium borodeuteride (NaBD4 Deuterium reactant) in 2N aqueous ammonia solution (freshly prepared) for 3 hours at room temperature with stirring. The excess reagent was destroyed by dropwise addition of about 200 mL of concentrated acetic acid. The resulting solution is evaporated to dryness in a stream of nitrogen at about 35-40 °C and subsequently dried in vacuum for 15 min at room temperature. The viscous residue was dissolved in 0.5 mL of 15 % acetic acid in methanol and evaporated to dryness at room temperature. This was done five times and repeated four additional times with pure methanol. After the final evaporation, the sample was dried in vacuum overnight at room temperature.

[0044] The residue of the reduction was acetylated with 600 pL of acetic anhydride and 150 microliters of pyridine for 3 hrs at 90 °C. After cooling, the sample vial was filled with toluene and evaporated to dryness in a stream of nitrogen at room temperature. The residue was dissolved in 4 mL of dichloromethane and poured into 2 mL of water and extracted with 2 mL of dichloromethane. The extraction was repeated three times. The combined extracts were washed three times with 4 mL of water and dried with anhydrous sodium sulfate. The dried dichloromethane extract was subsequently submitted to GC analysis. Depending on the sensitivity of the GC system, a further dilution of the extract may be necessary.

[0045] Gas-liquid (GLC) chromatographic analyses. Gas-liquid (GLC) chromatographic analyses were performed using Agilent 6890N type of gas chromatographs (Agilent Technologies GmbH, 71034 Boeblingen, Germany) equipped with Agilent J&W capillary columns (30 m, 0.25-mm ID, 0.25-pm phase layer thickness) operated with 1 ,5-bar helium carrier gas. The gas chromatograph was programmed with a temperature profile that held constant at 60 °C for 1 min, heated up at a rate of 20 °C I min to 200 °C, heated further up with a rate of 4 °C / min to 250 °C, and heated further up with a rate of 20 °C I min to 310 °C where it was held constant for another 10 min. The injector temperature was set to 280 °C and the temperature of the flame ionization detector (FID) was set to 300 °C. Exactly 1 pL of each sample was injected in the splitlessmode at 0.5-min valve time. Data were acquired and processed with a LabSystems Atlas work station.

[0046] Quantitative monomer composition data. Quantitative monomer composition data were obtained from the peak areas measured by GLC with flame ionization (FID) detection. Molar responses of the monomers were calculated in line with the effective carbon number (ECN) concept but is modified as described in the table below. The effective carbon number (ECN) concept has been described by Ackman (R.G. Ackman, J. Gas Chromatogr., 2 (1964) 173-179 and R.F. Addison, R.G. Ackman, J. Gas Chromatogr., 6 (1968) 135-138) and applied to the quantitative analysis of partially alkylated alditol acetates by Sweet et. Al (D.P. Sweet, R.H. Shapiro, P. Albersheim, Carbohyd. Res., 40 (1975) 217-225).

[0047] ECN increments used for ECN calculations:

[0048] In order to correct for the different molar responses of the monomers, the peak areas were multiplied by molar response factors (MRF) monomer which is defined as the response relative to the 2,3,6-Me monomer.

[0049] The 2,3,6-Me monomer is chosen as a reference since it was present in all samples analyzed in the determination of s23 / s26.

[0050] MRF monomer = ECN 2,3,6-Me / ECN monomer

[0051] The mol fractions of the monomers were calculated by dividing the corrected peak areas by the total corrected peak area according to the following formulas:

[0052] (1) s23 is the sum of the molar fractions of anhydroglucose units which meet the following condition, / .e., the two hydroxy groups in the 2- and 3-positions of the anhydroglucose unit are the only positions substituted with methyl groups. However, the 6-position is not substituted with methyl groups (= 23-Me)]; and(2) s26 is the sum of the molar fractions of anhydroglucose units which meet the following condition [the two hydroxy groups in the 2- and 6-positions of the anhydroglucose unit are the only positions substituted with methyl groups. However, the 3-position is not substituted with methyl groups (= 26-Me).

[0053] The ‘258 patent at Col. 4, Ins. 29-48 discloses the following:

[0054] In the ratio s23 / s26, s23 is the molar fraction of anhydroglucose units wherein only the two hydroxy groups in the 2- and 3-positions of the anhydroglucose unit aresubstituted with methyl groups and s26 is the molar fraction of anhydroglucose units wherein only the two hydroxy groups in the 2- and 6-positions of the anhydroglucose unit are substituted with methyl groups. For determining the s23, the term "the molar fraction of anhydroglucose units wherein only the two hydroxy groups in the 2- and 3-positions of the anhydroglucose unit are substituted with methyl groups" and the 6-positions are unsubstituted hydroxy groups. For determining the s26, the term “the molar fraction of anhydroglucose units wherein only the two hydroxy groups in the 2- and 6-positions of the anhydroglucose unit are substituted with methyl groups” means that the two hydroxy groups in the 2- and 6-positions are substituted with methyl groups and the 3-positions are unsubstituted hydroxy groups.Determination of the methoxyl content of a methylcellulose

[0055] The determination of the % methoxyl in methylcellulose was carried out according to the United States Pharmacopeia (USP34). The values obtained were 28.7 % methoxyl or less.Preparation of a 2 % pure aqueous solution of the methylcellulose

[0056] To obtain a 2 % aqueous solution of methylcellulose, 4 g of the cellulose ether powder (depending on the water content of the cellulose ether) was dissolved in 196 g water at 20 - 25 °C with overhead lab stirrer at 700 - 1500 rpm for 10 min. The resulting solution was then moved into a bath of 1.5 °C for further 1 h to complete the dissolution process. During this 1 h timeframe, this solution was than stirred with 500 - 1000 rpm and the water loss due to evaporation was balanced. The solution was than stored in a refrigerator overnight.Determination of the viscosity of methylcellulose

[0057] The steady-shear-flow viscosity q (20 °C, 2.51 and 10 s-1, 2 wt.% methylcellulose) of an aqueous 2-wt.% methylcellulose solution was measured at 20 °C with a Anton Paar MCR 501 rheometer with cone & plate geometry (CP50-1 / TG) over a shear rate regime from 0.1 - 1000 s-1with 21 data points. Based on this data, the viscosity at 2.51 and 10 s-1was assessed to describe these materials.As the following will show, a methylcellulose with yield stress phenomena has been synthesized based on the presence of methanol (MeOH) in the synthesis process. Surprisingly and unexpectedly, the exemplary methylcellulose has enhanced viscosity as evidenced by gel-like characteristics attributes at a medium degree of substitution (DS) (Me) of 1.16 to 1.72 based on the examples described in further detail below.

[0058] Commonly produced grades of methylcellulose in comparison have a higherDS of 1.64 to 1.92, as noted inthocel-a4m

[0059] As the following results show, Sample Numbers (Nos.) 115 and 116 surprisingly and unexpectedly have significantly enhanced viscosity as compared to reference Sample Nos. 112, 113 and 114. Samples Nos. 212 to 215 also demonstrate increased viscosity when compared with reference Sample No. 211.

[0060] The conventional prior art method synthesizes methylcellulose as follows:

[0061] Conventional synthesis of methylcellulose.

[0062] The conventional reaction synthesis can be described as follows:

[0063] Cellulose + NaOH solution + methyl chloride— > methylcellulose + methanol (side product) + sodium chloride (side product)

[0064] In such a conventional synthesis, the typical concentrations for a NaOH solutions are in the range of about 48 % to 52 %.

[0065] In the disclosed process, methanol was actively added to the synthesis of the methylcellulose based on cellulose + 50 % NaOH solution + methyl chloride.

[0066] A person of ordinary skill in the art would be dissuaded by using methanol for synthesizing methylcellulose, because one would expect a decrease in the DS (Me) based on increased side-reactions.

[0067] The reaction can be described as follows and differs from conventional methods in that methanol is added.Disclosed process of synthesis of methylcellulose.Cellulose + 50% NaOH solution + methyl chloride + methanol— > Methylcellulose + methanol (side product) + sodium chloride (side product)

[0068] 50% NaOH solution is an exemplary amount, but such concentrations can be readily adjusted by a person of ordinary skill in the art.

[0069] Figure 1 shows a flowchart of the general synthetic process for a methylcellulose with enhanced viscosity properties.

[0071] Terms used in experimental examplesDS = degree of substitutionMeOH = MethanolMe = Methyl-groupsDME (Dimethyl ether), a slurry agent, which is typically used during the synthesis of methylcellulose derivativesFC = flow curve which is a rheological shear flow experiment to analyze the viscosity as function of the shear rate at constant temperature mPa s = unit of viscosityViscosity @ 2.51 s-1[mPas] = Viscosity at a shear rate of 2.51 s-1Viscosity @ 10 s-1[mPas] = Viscosity at a shear rate of 10 s-1The following protocols apply to the three examples described below.Dissolution procedure

[0072] To achieve a homogenous solution, 4 g of the cellulose ether powder (depending on the water content of the cellulose ether) was dissolved in 196 g water at 20 - 25 °C with overhead lab stirrer at 700 - 1500 rpm for 10 min. The resulting solution was then moved into a bath of 1.5 °C for further 1 h to complete the dissolution process. During this 1 h timeframe, this solution was than stirred with 500 - 1000 rpm and the water loss due to evaporation was balanced. The solution was than stored in a refrigerator overnight. The gel-like characteristics of the inventive methylcelluloses are observed after dissolution in water and the viscosities as well as storage modulus G' and loss modulus G” are subsequently measured.Determination of the viscosity of methylcellulose

[0073] The steady-shear-flow viscosity q (20 °C, 2.51 and 10 s’1, 2 wt.% methylcellulose) of an aqueous 2-wt.% methylcellulose solution was measured at 20 °C with an Anton Paar MCR 501 rheometer with cone & plate geometry (CP50-1 / TG) over a shear rate regime from 0.1 - 1000 s-1with 21 data points. Based on this data, the viscosity at 2.51 and 10 s-1was assessed to describe these materials.Oscillation experiment

[0074] The 2% solution was further analyzed according to an oscillation experiment at constant temperature of 20 °C in the linear visco-elastic regime. Therefore, an Anton Paar Rheometer MCR 501 with cone and plate geometry CP-50 / 10was used. The oscillation experiments were performed over an angular frequency regime from 0.1 - 100 rad I s. with a constant deformation of 0.5 %.

[0075] As the following shows, Example 1 and Example 2 (i.e., Sample Nos. 212-215) describe two examples of inclusion of methanol in the synthesis of methylcellulose. In Example 2, Sample No. 211 is not part of the claimed inventions as no methanol was used.

[0076] In this exemplary methylcellulose of Example 2, the presence of yield stress in the exemplary methylcellulose is accompanied by a more gel-like structure in solution. The gel-like properties are shown by oscillation sweep data at constant temperature of 20 °C and further enhanced viscosities in the shear flow. Furthermore, the feature of the presence of a gel-like solution structure is accompanied with a special substitution, i.e., distribution of the methyl-substituents of s23 I s26 > 0.55 and a tan delta value of less than 1.55. The concept of tan delta will be explained later in the specification.Example 1- Inclusion of methanol during synthesis using a first specific type of cellulose raw materials (pulp)

[0077] Cellulose pulp. The following details the steps of preparation. 1.5 mol of cellulose pulp (Biofloc 96) was used. Biofloc 96 is cellulose raw material produced by Tembec / Rayonier with an intrinsic viscosity of 750 mg 1 1 according to ISO 5351.Production of Methylcellulose

[0078] Methylcellulose was produced according to the following procedure. Finely ground wood cellulose pulp was loaded into a jacketed, agitated reactor. The reactor was evacuated and purged with nitrogen to remove oxygen, and then evacuated again.

[0079] The reaction is carried out in two stages. In the first stage, a 50% by weight aqueous solution of sodium hydroxide was sprayed onto the cellulose pulp until 4 mols of sodium hydroxide per mol of anhydroglucose units of the cellulose are added to the reactor as shown in the following Table 1 ; this process has been performed at a constant temperature of 40 °C. After stirring, the mixture of aqueous sodium hydroxide solution and cellulose for about 30 minutes at 40 °C, either (1) no dimethyl ether was added to Sample No. 112 or (2) 1.5 moles of dimethyl ether were added to Sample No. 113 or (3) 3 moles of dimethyl ether were added to Sample No. 114; (4) 1.5 moles of dimethyl ether were added to Sample No. 115, (5) 1.5 moles of dimethyl ether were added to sample 116 and for each respective sample. For Sample Nos. 115 and 116, an amountof 50 g / 100 g methanol was sprayed on the cellulose pulp after the removal of oxygen and prior to the addition of the NaOH.

[0080] 5 moles of methyl chloride per mol of anhydroglucose units were added to the reactor, as shown in the following Table 1 , an exemplary example.Table 1 describes the synthesis conditions for synthesis of methylcellulose for Sample Nos. 112-116.Table 1

[0081] The contents of the reactor were then heated to 75° C as shown in Table 1 respectively, for Sample Nos. 112-116. After reaching the desired reaction temperature, the reaction was allowed to proceed as shown in Table 1.

[0082] At the end of the reaction, the pressure was released, and the reactor was purged with nitrogen for two times. Afterwards the temperature was decreased to 20 - 25 °C.

[0083] The contents of the reactor were removed and transferred to a tank containing hot water.

[0084] The resulting crude methylcellulose was then neutralized with formic acid and washed chloride free with hot water (assessed by AgNCh flocculation test), cooled to room temperature and dried at 55 °C in an air-swept drier, and the material is then ground using e.g. , an Alpine UPZ mill using a 0.3-mm screen.

[0085] The AgNCh test is used to identify residual NaCI is the crude MC, and hot water washing step is continued until AgNCh test is negative and no turbidity is observed.

[0086] Alpine mill is a common way to reduce the particle size of the methylcellulose and performed after washing and drying. Prior to Alpine mill, particles are relatively coarse and based on milling, particle size is reduced in average to a smaller 300 pm size, for example, after alpine mill.

[0087] The following Table 2 mentions values for the degree of substitution and the flow curve values of the viscosity of the samples of Table 1 and repeats the values of methanol with respect to weight and mol / mol from Table 1. Table 2 specifies the experimental results of the samples of Table 1.Table 2

[0088] As Table 2 shows, Sample Nos. 115 and 116 have significantly enhanced viscosities as 2 % concentration water-based solutions, when comparing with Sample Nos. 112-114 as shown by the FC viscosity values.Surprising and unexpected results.

[0089] As shown in the analytical data of the samples in Table 2 above, the addition of the methanol surprisingly and unexpectedly showed increased viscosities in Sample Nos. 115 and 116 at concentration of 2 % in water. Without being bound by theory, it is believed that since methanol is a primary alcohol, side reactions are faster with the primary alcohol of the methanol, methanol chloride is consumed and there are less reactions with the cellulose, thereby leading to a lower degree of substitution for Sample Nos. 115 and 116.

[0090] Methylcellulose solutions are known to have often have a shear ratedependent viscosity. Based on this known aspect, the viscosity values of the solutions are given at two different shear rates to reflect this non-Newtonian viscosity behavior of these methylcellulose. Accordingly, two FC values are shown in Table 2.

[0091] As the Table 2 shows, Sample Nos. 115 and 116 have significantly enhanced viscosities for 2 % concentrated solutions when compared with Sample Nos. 112-114.

[0092] In Example 1 , methanol had been sprayed onto the cellulose pulp after the oxygen removal and prior to the addition of NaOH.

[0093] Example 2-lnclusion of methanol during synthesis using a specific second type of cellulose raw material (cellulose pulp)

[0094] In this series of synthesis, the cellulose pulp Biofloc 96V has been used. Biofloc 96V is a well-known cellulose raw material (pulp) produced by Tembec / Rayonier. with an intrinsic viscosity of 900 mg / l according to ISO 5351.

[0095] The same synthetic process used for production synthesis of methycellulose as described in Example 1 applies to Example 2, except for variation in the amounts applied.

[0096] For the Sample Nos. 212 to 214 the cellulose pulp was immersed for 18 hours in methanol, For Sample No. 215, Biofloc 96V (Cellulose pulp) was immersed in methanol for 66 hours.

[0097] Biofloc 96V has a slightly higher molar mass and intrinsic viscosity than Biofloc 96; therefore, the viscosity of the samples in water based on Biofloc 96V is enhanced.

[0098] Since Biofloc 96V has different characteristics than Biofloc 96, the results of the water based viscosity in the samples in Example 2 cannot be directly compared to the samples in Example 1.

[0099] In this example, the amounts of reactant methyl chloride were increased to compensate the reduction in the DS (Me) based on the methanol addition. Additionally, the amount of dimethyl ether (DME) in the synthesis process was reduced to zero from an initial starting value of 3.0 mol I mol but no significant effect was seen by the change in the amounts of dimethyl ether.

[0100] The following table shows the synthesis conditions with a variation of the amount of Methanol (MeOH) and the contact time of the MeOH with the cellulose pulp.

[0101] For the samples of Example 2, Sample Nos. 212-215, the cellulose pulp had been stored for different times in methanol and the immersed cellulose was added to the reactor.Table 3

[0102] The following Table 4 also includes a duplicate set of information from Table 3 relating to methanol amount and DS (ME).Table 4

[0103] Before discussing the results of T able 4, an explanation of tan delta is provided below.Tan Delta Definition

[0104] Tan delta mentioned in Table 4 is the ratio of loss modulus (G”) divided by storage modulus (G'), i.e., G” / G ' .

[0105] The loss modulus, G” represents the viscous properties of the solution. The storage modulus G' represents the elastic properties of the solution.

[0106] There are at least two separate, independent factors that correlate with an increase of the water-based -viscosity: (1) increase of molecular mass of the cellulose pulp or (2) a more gel-like characteristics as explained below.

[0107] Enhanced viscosity. Polymers that enhance the viscosity of water or hydrated polymers without the presence of gel-like characteristics in solution are the agents that have significantly higher loss modulus G” as compared to G' , esp. at medium to low angular frequencies like 1 rad I s. An exemplary polymer as such without the addition of methanol during synthesis is Sample No. 211.

[0108] Examples of tan delta values with high viscosity and without the presence of a gel-like structure in solution would include values of greater than 1.55 up to 2.0 or even higher, for example.

[0109] The type of cellulose pulp is also indicative of increased water-based viscosities. For comparing Samples Nos. 112-114 and Sample No. 211 , different cellulose pulp were used. Sample No. 211 , which used higher viscous cellulose pulp had higher viscosities at 2 % in water than Sample Nos. 112-114.

[0110] Sample Nos. 112-114 and Sample 211 are considered to be pure water-based viscosity enhancing polymers without the presence of methanol during synthesis and therefore exhibit no gel-like structure in solution. For example, Sample No. 211 has dominant G” over G' especially at low frequencies, as shown in Figure 2 as well as in Figure 3 showing an exploded view of Figure 2 regarding low angular frequencies.

[0111] Enhanced gel-like characteristics indicative of greater viscosity than pure viscosity enhancing polymers. With the addition of methanol in the synthesis process, the viscosities in water of the disclosed inventive polymers are greater than the viscosities of pure viscosity enhancing polymers. These further increased viscosities are caused by the presence of a gel-like characteristics in water-based solution. This gel-like solution structure is seen by presence of enhanced storage modulus G'; whereas the loss modulus remained constant

[0112] . Based on these characteristics the tan delta values (based on G” / G') of the2 % solutions are decreased for the inventive samples, where methanol has been added during the synthesis process.

[0113] Accordingly, when the storage modulus is higher than the loss modulus, tan delta values < 1 are obtained. Thus, a tan delta for these solutions of 1.0 or lower is indicative of significant gel-like structure. Sample Nos. 214 and 215 have tan delta values of less than 1.55, i.e., 0.92 and 0.90 respectively.

[0114] As shown in T able 4, these increased viscosities of these solution in exemplary Sample No. 215 are caused by a significant increased gel - like characteristics of this solution as shown by the tan delta (G” I G') values in the Table 4 and are exemplary based on the comparison of the storage & loss modulus as a function of the angular frequencies for Sample No. 211 vs. Sample No, 215.

[0115] There are differences in gel-like characteristics of these solutions between Sample No. 211 and sample 215, as shown in Figure 2 as well as Figure 3 with an exploded (zoomed-in) view on low angular frequencies. Sample No. 211 shows a clear differentiation of G' and G” especially at low angular frequencies with dominant G” values. For the Sample No. 215, G” values (loss modulus values) were similar to those G” values of Sample No. 211. However, the G' values (storage modulus values) at low angular frequencies at 1-10 rad / s are significantly enhanced in Sample No. 215, which indicates an increase of a more gel like solution structure. The differences are further noted based on the data of this frequency sweep for 2 % concentrated solutions of sample No. 211 given in Table 5 as well as this data for sample No. 215 given in Table 6.Table 5Frequency - Sweep data for Sample No. 211Table 6Frequency - Sweep data for Sample No. 215

[0116] Flow curve viscosity values at two shear rates. Methylcellulose solutions are known to often have a shear rate -dependent viscosity. Based on this known aspect, the viscosity values are given for two different shear rates to reflect this non-Newtonian viscosity behavior of these methylcelluloses. Accordingly, two FC viscosity values are shown in Table 4.

[0117] As seen from the above table, the degree of substitution decreases based on the presence of methanol during the alkalization and synthesis. Sample Nos. 212 to 215 showed enhanced viscosities as shown by lowered tan delta values as well as high s23 / s26 values of greater than 0.55 when comparing with the same values for Sample No. 211.

[0118] As can be observed from Table 4, Sample No. 215 has enhanced gel-like characteristics in solution when compared to Sample No. 211 as the tan delta ratio decreased.

[0119] The presence of a gel like solution structure correlates to a special substitution distribution as shown by the s23 / s26 > 0.55 value in Table 4 above. Sample No. 215 had enhanced gel-like characteristics and a s23 / s26 value of greater than 0.55.

[0120] The increased amounts of methanol during the alkalization step leads to a significantly increased viscosity of the solution as shown by the results in Table 4.

[0121] The following compares the differences in viscosities between Sample No. 211 and Sample Nos. 112-114 for 2 % concentrated solutions, for example.

[0122] As mentioned previously, the type of cellulose pulp is also indicative of increased viscosities for the hydrated samples. As observed from Table 4, non-inventive Sample No. 211 , by contrast, showed enhanced viscosities and no presence of a gel-like solution structure as evidenced by a high tan delta of 2.06 and had s23 I s26 values < 0.55, when comparing with the values for non-inventive Sample Nos. 112-114 in Example 1 , which utilized a different cellulose pulp. Sample Nos. 112-114 also had no presence of a gel-like solution structure.

[0123] The increased amounts of methanol during the alkalization step for inventive Sample Nos. 212-215 leads to a significantly increased viscosity of the solution as shown by the results in Table 4.

[0124] Example 3 describes an example of the synthesis of methylcellulose in the absence of methanol. Example 3 referring to Sample Nos. 248-250 serves a control, while Examples 1 and 2 relating to Sample Nos. 115, 116, 212, 213, 214 and 215 are examples of the claimed methylcellulose with increased gel-like characteristics in solution.Example 3- Absence of methanol addition during synthesis (Control)

[0125] To validate that the increased gel-like characteristics for a 2% solution of methylcellulose at temperature of 20 °C (low tan delta values) and high s23 I s26 values is caused by the methanol addition and not due to the effect of the decreased DS(Me) values of the samples, a series of methylcellulose was produced without the addition of methanol and decreasing DS(Me) values.

[0126] In this series of synthesis shown in Table 7, the cellulose pulp Biofloc 96V was used for Example 3 as in Example 2.

[0127] The Sample Nos. 248 to 250 were made without the addition of MeOH. Based on the absence I presence of Dimethyl ether (DME) and the variation of the NaOH and methyl chloride amounts during the synthesis, methylcelluloses with a variation of the degree of substitution DS (Me) were obtained.

[0128] When adding methyl chloride, the amount of methyl chloride for sample 250 was significantly reduced ( / .e., 3 mol / mol), for example as shown in the following Table 7 when comparing the methyl chloride addition with the methyl chloride additions for the inventive Sample Nos. 212-215 in Table 3 (i.e., 7-9 mol / mol).Table 7

[0129] The water-based viscosities at a concentration of 2 % of all of these samples in Table 7 were very similar and no trend of an increase of the viscosity with decreasing DS (Me) was observed.

[0130] Furthermore, there was no trend of increased gel-like characteristics in solution based on decreasing tan delta values with decreasing DS (Me) and the samples all had s23 / s26 below 0.55, by contrast with the inventive samples.

[0131] As can be seen from Table 7, the viscosity data in water-based solutions of these samples of Table 7 show no trend towards significant increased viscosity values with decreasing DS(Me). Thus, Sample No. 248 and Sample No. 250 had no significant differences in viscosity values as noted by the FC values.

[0132] Applications of the inventive methylcellulose with gel-like characteristics in solution. The obtained methylcellulose products with gel-like characteristics in solution can stabilize a dispersion, suspension or an emulsion. Furthermore, these inventive methylcelluloses can stabilize heterogeneous fluids or semi-solid fluids; For example, the inventive methylcellulose may be used as a binder for battery slurries or for use in 3D printing. The inventive methylcelluloses may be used for consumer applications such as consumer products such as cremes, toothpastes, for example, and for topical applications including ointments and pain-relieving medications, for example.

[0133] The inventive methylcelluloses can also be used for any other applications where there is a need for a polymer to exhibit yield stress phenomena accompanied by a gel-like solution structure.

[0134] The foregoing inventive methylcellulose can help avoid separation of a two- phase system over time.

[0135] The range of recited numerical values disclosed in the specification includes values , e.g., + / — 5-10% of the recited value, that a person of ordinary skill in the art would consider equivalent to the recited value, e.g., having the same function or result.

[0136] The claims are not limited by the preferred embodiments and examples but will cover many modifications and equivalents consistent with the written description as a whole.

Claims

What is claimed is:

1. A methylcellulose having gel-like characteristics in solution, comprising anhydroglucose units joined by 1-4 linkages, wherein hydroxy groups of the anhydroglucose units are substituted with methyl groups such that a degree of substitution DS(methyl) is 1.72 or less and a tan delta value of less than 1.55 at a concentration of 2% of methylcellulose at an angular frequency of 1 rad / s and 20 °C, the tan delta value being indicative of the gel-like characteristics in solution, wherein the tan delta value is derived from the ratio of loss modulus I storage modulus.

2. The methylcellulose according to claim 1 , wherein the hydroxy groups of the anhydroglucose units are substituted with methyl groups such that the s23 / s26 is 0.55 or more, wherein s23 is the molar fraction of anhydroglucose units wherein only the two hydroxy groups in the 2- and 3-positions of the anhydroglucose unit are substituted with methyl groups and wherein s26 is the molar fraction of anhydroglucose units wherein only the two hydroxy groups in the 2- and 6-positions of the anhydroglucose unit are substituted with methyl groups.

3. The methylcellulose according to any one of claims 1-2, wherein a 2% aqueous solution of the methylcellulose at 20 °C at a shear rate of 2.51 s-1 has a viscosity of 10 to 100,000 mPa-s or more, more preferably a viscosity of 100 mPa s to 90,000 mPa s, and most preferably has a viscosity of 500 mPa s or more.

4. The methylcellulose according to any one of claims 1-3, wherein the tan 5 (G” / G') value is 1.55 or less, preferably 1.5 or less, more preferably 1.4 or less, most preferably 1.3 or less, most preferably 1.2 or less, most preferably 1.1 or less or 1.00 or less at 1 rad / s measured 24 hours after dissolution of the methylcellulose at a concentration of 2 % at 20°C.

5. The methylcellulose according to any one of claims 1-4, wherein the hydroxy groups of anhydroglucose units are substituted with methyl groups such that the s23 / s26 of the methylcellulose is from 0.55 or higher .

6. A process for preparing a methylcellulose according to any one of claims 1-5, the process comprising the step of treating cellulose pulp with an alkalization agent and amethylating agent in the presence of an alcohol.

7. The process according to claim 6, wherein the alcohol is added in an amount of 0.5- 12 mol / mol per anhydroglucose unit, preferably from 2 to 10 mol / mol per anhydroglucose unit, and most preferably from 4 to 8 mol / mol per anhydroglucose unit.

8. The process according to any one of claims 6-7, wherein the alcohol is methanol.

9. The process according to any one of claims 6-8, wherein the temperature during alkalization is below 45°C.

10. The process according to any one of claims 6-9, wherein the alkalization agent is sodium hydroxide, and the sodium hydroxide is added in an amount of 3.0 to 10 mol / mol per anhydroglucose unit, preferably 3.2 to 9 mol / mol anhydroglucose unit and most preferably 3.5 to 8.5 mol / mol per anhydroglucose unit.

11. The process according to any one of claims 6-10, wherein the methylating agent is added in an amount of 3 to 12 mol / mol per anhydroglucose unit, preferably 3.5 to 11 mol / mol per anhydroglucose unit, and most preferably 4 to 10 mol / mol per anhydroglucose unit, before, after or concurrently with the alkalization agent and the alcohol.

12. The process according to any one of claims 6-11 , wherein the methylating agent is methyl chloride.

13. The process according to any one of claims 6-12, wherein the reaction temperature is increased to between 50-80 °C over 20-90 minutes.

14. The process according to any one of claims 6-13, wherein the alkalized cellulose is reacted with the methylating agent for 90-300 minutes to obtain the methylcellulose.

15. The process according to claim 14, wherein the obtained methylcellulose is washed.

16. The process according to claim 15, wherein the washed methylcellulose is dried and milled to a powder.

17. A product as defined in any one of claims 1-5 obtainable by the process as defined inany one of claims 6-16.

18. A method of using the methylcellulose of Claim 1 for stabilizing a dispersion, a suspension or an emulsion.

19. The method of Claim 18, wherein the dispersion, a suspension or an emulsion is a food composition, a pharmaceutical dosage form or a detergent.

20. The method of Claim 18, wherein the methylcellulose used for stabilizing is for use as a binder or for use in 3D printing.

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