Homogeneous phase preparation method of hydroxy propyl cellulose

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a homogeneous phase preparation method of hydroxy propyl cellulose. The homogeneous preparation method comprises the following steps: mixing and dissolving cellulose, 1-ethyl-3-methylimidazole acetate and dimethyl sulfoxide (or toluene) to obtain a cellulose solution; mixing the cellulose solution with alkali for alkalization to obtain an alkalized cellulose solution; and mixing the alkalized cellulose solution with epoxypropane, carrying out etherification reaction, neutralizing the obtained reaction solution, and carrying out separation and purification to obtain the hydroxy propyl cellulose. According to the method, the cellulose is firstly dissolved and then reacts, under the condition that the same etherification reagent is consumed, the hydroxypropyl substitution degree of the prepared product is high, the problem of low substitution degree of a heterogeneous method product can be solved, and the homogeneous method is low in reagent consumption and higher in reaction efficiency. The preparation method disclosed by the invention is simple, rapid in reaction, high in etherification efficiency, small in etherifying agent dosage, recyclable in solvent, controllable in substitution degree and uniform in substitution degree distribution.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a homogeneous preparation method of hydroxypropyl cellulose. Background Art

[0002] Cellulose is a natural polymer compound with abundant reserves in the world and a wide range of sources. Currently, cellulose-based materials have been widely used in many fields such as petrochemicals, biomedicine, textiles, food, aerospace, etc. Compared with traditional petroleum-based materials, cellulose has the advantages of being cheap, easily available, renewable, and environmentally friendly. The development and use of cellulose and cellulose derivative materials is of great significance.

[0003] Chemical modification of cellulose can broaden the application field of cellulose materials. Hydroxypropyl cellulose is the product of hydroxypropylation of cellulose. It is a non-ionic cellulose ether with good biocompatibility, degradability, and edibility. It is often used in medicine, food, and chemical industries. According to the degree of substitution of hydroxypropyl in hydroxypropyl cellulose, it can be divided into high-substituted hydroxypropyl cellulose and low-substituted hydroxypropyl cellulose. Among them, high-substituted hydroxypropyl cellulose is a cellulose ether with excellent solubility. It is soluble in polar solvents, and the higher the degree of substitution, the better the solubility; while the hydroxypropyl content in low-substituted hydroxypropyl cellulose is generally less than 20%, with poor solubility, insoluble in water and general organic solvents, and generally used as a tablet disintegrant in medicine, and is also commonly used in food additives, building materials, cosmetics industry, etc.

[0004] Due to the presence of a large number of hydrogen bonds between cellulose molecular chains, cellulose is insoluble in water and common organic solvents at room temperature and has the characteristic of being insoluble. At present, the preparation of hydroxypropyl cellulose mostly adopts the heterogeneous method to derivatize cellulose. The main steps include: dispersing cellulose in a system such as water, isopropanol, etc., and reacting the etherification agent with the cellulose when the cellulose is not dissolved. The heterogeneous method is relatively simple to operate, but the degree of substitution of the hydroxypropyl cellulose obtained under normal pressure is low, and the amount of etherification agent used is large. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a homogeneous preparation method of hydroxypropyl cellulose. The homogeneous preparation method of the present invention can produce hydroxypropyl cellulose with a high degree of substitution under the same amount of etherification agent.

[0006] The present invention provides a homogeneous preparation method of hydroxypropyl cellulose, comprising the following steps:

[0007] Mixing and dissolving cellulose, 1-ethyl-3-methylimidazolium acetate and a diluent to obtain a cellulose solution; the diluent includes dimethyl sulfoxide or toluene;

[0008] The cellulose solution is mixed with alkali to obtain an alkalized cellulose solution;

[0009] The alkalized cellulose solution and propylene oxide are mixed to carry out etherification reaction, and the obtained reaction solution is neutralized, separated and purified to obtain hydroxypropyl cellulose.

[0010] Preferably, the usage ratio of the 1-ethyl 3-methylimidazole acetate to the diluent is 1 g: (2-8) mL.

[0011] Preferably, the concentration of cellulose in the cellulose solution is 1 wt% to 5 wt%.

[0012] Preferably, the amount of the alkali used is 1 to 20 times the molar amount of the glucose structural unit in the cellulose.

[0013] Preferably, the alkalization temperature is 25-50° C. and the time is 15 min-12 h.

[0014] Preferably, the mass of the propylene oxide is 0.3 to 10 times the mass of the cellulose.

[0015] Preferably, the temperature of the etherification reaction is 50-70° C., and the time is 2-12 hours.

[0016] Preferably, the separation and purification comprises dialysis, and the molecular weight cut-off of the dialysis is 7000 or 8000 to 14000.

[0017] Preferably, when the hydroxypropyl cellulose is low-substituted hydroxypropyl cellulose, the separation and purification comprises: mixing the neutralized reaction solution with an organic solvent to precipitate the hydroxypropyl cellulose, separating the solid from the liquid, and washing and drying the obtained solid; the organic solvent comprises acetone, ethanol or 1,4-dioxane.

[0018] Preferably, when the hydroxypropyl cellulose is a highly substituted hydroxypropyl cellulose, the separation and purification comprises: mixing the neutralized reaction solution with hot water to precipitate the hydroxypropyl cellulose, separating the solid from the liquid, and drying the obtained solid; the temperature of the hot water is 70-90°C.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The invention provides a homogeneous preparation method of hydroxypropyl cellulose, comprising the following steps: mixing and dissolving cellulose, 1-ethyl-3-methylimidazole acetate and a diluent to obtain a cellulose solution; the diluent comprises dimethyl sulfoxide or toluene; mixing the cellulose solution with an alkali to perform alkalization to obtain an alkalized cellulose solution; mixing the alkalized cellulose solution with propylene oxide to perform an etherification reaction, neutralizing the obtained reaction solution, and separating and purifying to obtain hydroxypropyl cellulose.

[0021] The homogeneous preparation method of the present invention comprises the following steps: firstly dissolving a cellulose raw material with 1-ethyl-3-methylimidazolium acetate and a diluent to obtain a cellulose solution, and then adding an alkali thereto for alkalization; after obtaining the alkalized cellulose solution, adding propylene oxide thereto for etherification reaction, and adjusting the pH of the reaction solution to neutral after the reaction, and performing separation and purification to obtain hydroxypropyl cellulose. Compared with the current heterogeneous synthesis method of hydroxypropyl cellulose, the present invention first dissolves the cellulose and then reacts, and the obtained product has a high degree of hydroxypropyl substitution under the condition of consuming the same etherification reagent, which can overcome the problem of low degree of substitution of the product of the heterogeneous method, and the homogeneous method consumes less etherification reagent and has higher reaction efficiency.

[0022] The preparation method of the invention is simple, has rapid reaction, high etherification efficiency, small amount of etherification agent, recoverable solvent, controllable substitution degree and uniform substitution degree distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 FT-IR comparison spectra of hydroxypropyl cellulose and microcrystalline cellulose prepared in Example 1;

[0025] Figure 2 The hydroxypropyl cellulose and microcrystalline cellulose prepared in Example 1 1 HNMR comparison spectra.

[0026] Figure 3 The hydroxypropyl number distribution diagram of the hydroxypropyl cellulose prepared in the homogeneous phase in Example 7;

[0027] Figure 4 The figure is a comparison chart of the hydroxypropyl number distribution of commercially available heterogeneously prepared hydroxypropyl cellulose. DETAILED DESCRIPTION

[0028] The present invention provides a homogeneous preparation method of hydroxypropyl cellulose, comprising the following steps:

[0029] Mixing and dissolving cellulose, 1-ethyl-3-methylimidazolium acetate and a diluent to obtain a cellulose solution; the diluent includes dimethyl sulfoxide or toluene;

[0030] The cellulose solution is mixed with alkali to obtain an alkalized cellulose solution;

[0031] The alkalized cellulose solution and propylene oxide are mixed to carry out etherification reaction, and the obtained reaction solution is neutralized, separated and purified to obtain hydroxypropyl cellulose.

[0032] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in the art.

[0033] The invention mixes and dissolves cellulose, 1-ethyl-3-methylimidazole acetate and a diluent to obtain a cellulose solution; the diluent comprises dimethyl sulfoxide (DMSO) or toluene.

[0034] In the present invention, the cellulose preferably includes microcrystalline cellulose or purified cotton, and the cellulose is preferably in a powder form.

[0035] In the present invention, the dosage ratio of the 1-ethyl 3-methylimidazolium acetate and the diluent is preferably 1g:(2-8)mL, specifically 1g:3mL or 1g:6mL. The 1-ethyl 3-methylimidazolium acetate is an ionic liquid, which can destroy the hydrogen bonds between the cellulose molecular chains and dissolve the cellulose. The 1-ethyl 3-methylimidazolium acetate of the present invention has a strong dissolving ability for cellulose, low toxicity, and good chemical stability, and is a new type of green solvent. The present invention uses DMSO or toluene as a diluent, which can be miscible with cellulose and ionic liquids to form a homogeneous solution, and can dilute the reaction system at the same time; and the cost is low.

[0036] In the present invention, the dissolving method is preferably stirring, and the stirring is preferably heating and stirring at 90° C. for 10 min or stirring at room temperature for 30 min.

[0037] In the present invention, the mixed dissolution of cellulose, 1-ethyl-3-methylimidazolium acetate and a diluent preferably comprises: adding cellulose to a mixed solvent consisting of a diluent and 1-ethyl-3-methylimidazolium acetate, stirring and dissolving, and obtaining a cellulose solution;

[0038] Alternatively, cellulose is first heated and stirred in 1-ethyl-3-methylimidazole acetate to dissolve, and then a diluent is added to dilute the solution to obtain a cellulose solution; the heating and stirring temperature is preferably 90° C., and the time is preferably 10 minutes.

[0039] In the present invention, the concentration of cellulose in the cellulose solution is preferably 1 wt% to 5 wt%, specifically 1.7 wt%. The cellulose solution is a clear and transparent solution.

[0040] After obtaining the cellulose solution, the present invention mixes the cellulose solution with alkali to perform alkalization, thereby obtaining an alkalized cellulose solution.

[0041] In the present invention, the base preferably includes an alkali metal hydroxide, and the alkali metal hydroxide preferably includes one or more of lithium hydroxide, sodium hydroxide and potassium hydroxide, and more preferably sodium hydroxide.

[0042] In the present invention, the amount of the alkali used is preferably 1 to 20 times the molar amount of the glucose structural unit in the cellulose, and specifically can be 3 times (nNaOH / nAGU=3 / 1).

[0043] In the present invention, the alkalization temperature is preferably 25-50° C., specifically 30° C. or 40° C., and the alkalization time is preferably 15 min to 12 h, specifically 30 min or 8 h.

[0044] After obtaining the alkalized cellulose solution, the present invention mixes the alkalized cellulose solution with propylene oxide to carry out etherification reaction, neutralizes the obtained reaction solution, and separates and purifies it to obtain hydroxypropyl cellulose.

[0045] In the present invention, the mass of the propylene oxide is preferably 0.3 to 10 times the mass of the cellulose, and specifically can be 1 time, 3 times, 5.6 times or 7.16 times.

[0046] In the present invention, the temperature of the etherification reaction is preferably 50-70°C, specifically 60°C, and the time is preferably 2-12h, more preferably 5-7h, specifically 6h. The etherification reaction process undergoes the following reaction:

[0047]

[0048] Wherein, n is the number of sugar units, ranging from 40 to 400, and x is the number of hydroxypropyl groups.

[0049] In the present invention, the neutralization preferably uses an acid solution, and the acid solution preferably includes dilute hydrochloric acid or glacial acetic acid.

[0050] In the present invention, the separation and purification preferably includes dialysis, the molecular weight cutoff of the dialysis is preferably 7000 or 8000 to 14000, the dialysis time is preferably 48 to 96 hours, specifically 72 hours; the dialysis preferably uses a dialysis bag. The dialysis preferably also includes drying, and the drying is preferably freeze-drying. The present invention has no special requirements for the freeze-drying conditions. The dialysis method is applicable to the separation and purification of both high-substituted hydroxypropyl cellulose and low-substituted hydroxypropyl cellulose. The dialysis method is simple to operate and the product yield is high.

[0051] When the hydroxypropyl cellulose is low-substituted hydroxypropyl cellulose (L-HPC), the hydroxypropyl content in the low-substituted hydroxypropyl cellulose is 7wt% to 16wt%, which is converted into a molar substitution degree MS of 0.21 to 0.53, and the separation and purification preferably includes: mixing the neutralized reaction solution with an organic solvent to precipitate the hydroxypropyl cellulose, separating the solid from the liquid, and washing and drying the obtained solid. The organic solvent preferably includes acetone, ethanol or 1,4-dioxane; the solid-liquid separation method is preferably filtration; and the washing reagent is preferably an ethanol aqueous solution.

[0052] When the hydroxypropyl cellulose is a highly substituted hydroxypropyl cellulose, the separation and purification preferably comprises: mixing the neutralized reaction solution with hot water to precipitate the hydroxypropyl cellulose, performing solid-liquid separation, and drying the obtained solid. The temperature of the hot water is preferably 70 to 90°C, specifically 80°C; the solid-liquid separation is preferably hot centrifugal separation or hot filtration; and before drying, the solid obtained by the solid-liquid separation is preferably washed, and the washing is preferably performed using hot water at 70 to 90°C, and the number of washings is preferably 2 to 3 times.

[0053] In order to further illustrate the present invention, the homogeneous preparation method of hydroxypropyl cellulose provided by the present invention is described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0054] Example 1

[0055] (1) 0.5 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to a mixed solvent consisting of 30 mL of DMSO and 5 g of 1-ethyl-3-methylimidazolium acetate, and heated and stirred at 90° C. for 10 min to completely dissolve the cellulose, thereby obtaining a uniform and transparent cellulose solution;

[0056] (2) adding 0.37 g of sodium hydroxide to the cellulose solution, stirring evenly, and alkalizing at 40° C. for 30 min to obtain an alkali cellulose solution;

[0057] (3) injecting 0.5 g of propylene oxide into the alkali cellulose solution for etherification at 60° C. for 6 h;

[0058] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0059] (5) The reaction solution was placed in a dialysis bag with a molecular weight cutoff of 8000 to 14000 for 72 hours, and then freeze-dried to obtain 0.426 g of low-substituted hydroxypropyl cellulose.

[0060] Structural characterization:

[0061] (1) Infrared spectroscopy characterization (FT-IR)

[0062] Take a small amount of microcrystalline cellulose / hydroxypropyl cellulose sample, add potassium bromide and mix and grind in an agate mortar, use a tablet press to press into transparent thin slices, and use an infrared spectrometer to perform infrared characterization on microcrystalline cellulose (MCC) and hydroxypropyl cellulose (HPC) samples, respectively, with a scanning range of 4000cm -1 ~400cm -1 , analyze the differences and main groups between the two, the results are as follows Figure 1 As shown. It can be seen that hydroxypropyl cellulose appears at 2974cm -1 The peak at 1465 cm is the stretching vibration absorption peak of the CH bond of the methyl group introduced into the hydroxypropyl group. -1 and 1380cm -1 The characteristic absorption peak at is the CH bending vibration absorption peak of the methyl group, indicating that the cellulose has been successfully grafted with hydroxypropyl groups and the resulting product is hydroxypropyl cellulose.

[0063] (2) Nuclear magnetic resonance characterization (NMR)

[0064] After the sample was hydrolyzed with acid for 20 hours, water and excess volatile acid were removed and then prepared into a sample for NMR testing. The purpose of hydrolysis is to destroy the β-1,4-glycosidic bond and reduce the molecular weight of hydroxypropyl cellulose, so that the signal-to-noise ratio can be improved to obtain a clearer and more accurate spectrum during NMR testing. The hydroxypropyl cellulose hydrolyzed sample in Example 1 was tested using a VARIAN II I 600MHz HD nuclear magnetic resonance spectrometer (NMR) from Bruker, Germany. 1 HNMR characterization, the results are as follows Figure 2 As shown. The chemical shift at 6ppm is the shift of the deuterated solvent, and compared with the raw material MCC, hydroxypropyl cellulose HPC has a new peak at 1ppm, which is the methyl proton peak of the introduced hydroxypropyl group, proving that the hydroxypropyl group was successfully introduced into the sugar unit of MCC to obtain the product HPC. At the same time, combined with the infrared spectrum, it is proved that the target product is successfully synthesized.

[0065] The waste liquid produced in Example 1 contains water, DMSO, imidazolyl cations, acetate, and sodium ions. The water is first removed by vacuum distillation to separate DMSO, and then the imidazolyl cations are separated by ion exchange resin, so that the ionic liquid (1-ethyl-3-methylimidazolium acetate) can be regenerated.

[0066] Example 2

[0067] (1) 0.5 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to a mixed solvent consisting of 30 mL of DMSO and 5 g of 1-ethyl-3-methylimidazolium acetate, and stirred at room temperature for 30 min to completely dissolve the cellulose, thereby obtaining a uniform and transparent cellulose solution;

[0068] (2) adding 0.37 g of sodium hydroxide to the cellulose solution, stirring evenly, and alkalizing at 40° C. for 30 min to obtain an alkali cellulose solution;

[0069] (3) injecting 0.5 g of propylene oxide into the alkali cellulose solution for etherification at 60° C. for 6 h;

[0070] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0071] (5) The reaction solution was placed in a dialysis bag with a molecular weight cutoff of 8000 to 14000 for 72 hours, and then freeze-dried to obtain 0.435 g of low-substituted hydroxypropyl cellulose.

[0072] The hydroxypropyl cellulose prepared in Example 2 was subjected to FT-IR and 1 H NMR characterization showed that the results were similar to those in Example 1.

[0073] Example 3

[0074] (1) 0.5 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to a mixed solvent consisting of 30 mL of DMSO and 10 g of 1-ethyl-3-methylimidazolium acetate, and stirred at room temperature for 30 min to completely dissolve the cellulose, thereby obtaining a uniform and transparent cellulose solution;

[0075] (2) adding 0.37 g of sodium hydroxide to the cellulose solution, stirring evenly, and alkalizing at 40° C. for 30 min to obtain an alkali cellulose solution;

[0076] (3) injecting 1.5 g of propylene oxide into the alkali cellulose solution for etherification at 60° C. for 6 h;

[0077] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0078] (5) The reaction solution was placed in a dialysis bag with a molecular weight cutoff of 8000 to 14000 for 72 hours, and then freeze-dried to obtain 0.492 g of medium-substituted hydroxypropyl cellulose.

[0079] The hydroxypropyl cellulose prepared in Example 3 was subjected to FT-IR and 1 H NMR characterization, the results are similar to those in Example 1

[0080] Example 4

[0081] (1) 1 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to a mixed solvent consisting of 60 mL of DMSO and 10 g of 1-ethyl-3-methylimidazolium acetate, and stirred at room temperature for 30 min to completely dissolve the cellulose, thereby obtaining a uniform and transparent cellulose solution;

[0082] (2) adding 0.74 g of sodium hydroxide to the cellulose solution, stirring evenly, and alkalizing at 40° C. for 30 min to obtain an alkali cellulose solution;

[0083] (3) injecting 5.6 g of propylene oxide into the alkali cellulose solution for etherification at 60° C. for 6 h;

[0084] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0085] (5) The reaction solution was placed in a dialysis bag with a molecular weight cutoff of 7000 and dialyzed for 72 hours, followed by freeze-drying to obtain 1.454 g of highly substituted hydroxypropyl cellulose.

[0086] The hydroxypropyl cellulose prepared in Example 4 was subjected to FT-IR and 1 H NMR characterization showed that the results were similar to those in Example 1.

[0087] Example 5

[0088] (1) 1 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to a mixed solvent consisting of 60 mL of DMSO and 10 g of 1-ethyl-3-methylimidazolium acetate, and stirred at room temperature for 30 min to completely dissolve the cellulose, thereby obtaining a uniform and transparent cellulose solution;

[0089] (2) adding 0.74 g of sodium hydroxide to the cellulose solution, stirring evenly, and alkalizing at 40° C. for 30 min to obtain an alkali cellulose solution;

[0090] (3) injecting 5.6 g of propylene oxide into the alkali cellulose solution for etherification at 60° C. for 6 h;

[0091] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0092] (5) The reaction solution was added to hot water at 80° C. and stirred until the hydroxypropyl cellulose was fully precipitated. The precipitate was then centrifuged while hot to obtain the lower layer, which was then dried to obtain 1.128 g of highly substituted hydroxypropyl cellulose.

[0093] The hydroxypropyl cellulose prepared in Example 5 was subjected to FT-IR and 1 H NMR characterization showed that the results were similar to those in Example 1.

[0094] Example 6

[0095] (1) 1 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to 10 g of 1-ethyl-3-methylimidazolium acetate, stirred at 90° C. for 10 min to completely dissolve the cellulose, and 30 mL of toluene was added for dilution to obtain a uniform and transparent cellulose solution;

[0096] (2) adding 0.74 g of sodium hydroxide to the cellulose solution, stirring evenly, and alkalizing at 40° C. for 30 min to obtain an alkali cellulose solution;

[0097] (3) injecting 5.6 g of propylene oxide into the alkali cellulose solution for etherification at 60° C. for 6 h;

[0098] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0099] (5) The reaction solution was placed in a dialysis bag with a molecular weight cutoff of 7000 and dialyzed for 72 h, followed by freeze-drying to obtain 1.477 g of highly substituted hydroxypropyl cellulose.

[0100] The hydroxypropyl cellulose prepared in Example 6 was subjected to FT-IR and 1 H NMR characterization showed that the results were similar to those in Example 1.

[0101] Example 7

[0102] (1) 1 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to 10 g of 1-ethyl-3-methylimidazolium acetate, stirred at 90° C. for 10 min to completely dissolve the cellulose, and 30 mL of toluene was added for dilution to obtain a uniform and transparent cellulose solution;

[0103] (2) adding 0.74 g of sodium hydroxide to the cellulose solution, stirring evenly, and alkalizing at 40° C. for 8 h to obtain an alkali cellulose solution;

[0104] (3) injecting 5.6 g of propylene oxide into the alkali cellulose solution for etherification at 60° C. for 6 h;

[0105] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0106] (5) The reaction solution was placed in a dialysis bag with a molecular weight cutoff of 7000 and dialyzed for 72 h, followed by freeze-drying to obtain 1.483 g of highly substituted hydroxypropyl cellulose.

[0107] The hydroxypropyl cellulose prepared in Example 7 was subjected to FT-IR and 1 H NMR characterization showed that the results were similar to those in Example 1.

[0108] Example 8

[0109] (1) 1 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to 10 g of 1-ethyl-3-methylimidazolium acetate, stirred at 90° C. for 10 min to completely dissolve the cellulose, and 30 mL of toluene was added for dilution to obtain a uniform and transparent cellulose solution;

[0110] (2) adding 0.74 g of sodium hydroxide to the cellulose solution, stirring evenly, and alkalizing at 40° C. for 8 h to obtain an alkali cellulose solution;

[0111] (3) injecting 7.16 g of propylene oxide into the alkali cellulose solution for etherification at 60° C. for 6 h;

[0112] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0113] (5) The reaction solution was placed in a dialysis bag with a molecular weight cutoff of 7000 and dialyzed for 72 h, followed by freeze-drying to obtain 1.598 g of highly substituted hydroxypropyl cellulose.

[0114] The hydroxypropyl cellulose prepared in Example 8 was subjected to FT-IR and 1 H NMR characterization showed that the results were similar to those in Example 1.

[0115] Comparative Example 1

[0116] (1) 1 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to 20 mL of 90% by volume isopropanol aqueous solution and stirred to disperse;

[0117] (2) adding 0.74 g of sodium hydroxide to the reaction solution, stirring evenly, and alkalizing at room temperature for 60 min to obtain alkali cellulose;

[0118] (3) injecting 7.16 g of propylene oxide into the alkali cellulose for etherification at 60° C. for 6 h;

[0119] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0120] (5) The reaction solution was added to hot water at 80° C. and stirred until the hydroxypropyl cellulose was fully precipitated. The solid was then filtered while hot and dried to obtain 0.927 g of low-substituted hydroxypropyl cellulose.

[0121] The hydroxypropyl cellulose prepared in Comparative Example 1 was subjected to FT-IR and 1 H NMR characterization showed that the results were similar to those in Example 1.

[0122] Comparative Example 2

[0123] (1) 1 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to 20 mL of 90% by volume isopropanol aqueous solution and stirred to disperse;

[0124] (2) adding 0.74 g of sodium hydroxide to the reaction solution, stirring evenly, and alkalizing at 30° C. for 2 h to obtain alkali cellulose;

[0125] (3) injecting 7.16 g of propylene oxide into the alkali cellulose for etherification at 60° C. for 6 h;

[0126] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0127] (5) The reaction solution was added to hot water at 80° C. and stirred until the hydroxypropyl cellulose was fully precipitated. The solid was then filtered while hot and dried to obtain 0.879 g of low-substituted hydroxypropyl cellulose.

[0128] The hydroxypropyl cellulose prepared in Comparative Example 2 was subjected to FT-IR and 1 H NMR characterization showed that the results were similar to those in Example 1.

[0129] Comparative Example 3

[0130] (1) 1 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to a mixed solvent consisting of 40 mL of DMSO and 3.3 g of tetrabutylammonium fluoride trihydrate, and the mixture was stirred and heated to 60° C. to completely dissolve the microcrystalline cellulose, thereby obtaining a clear and transparent cellulose solution;

[0131] (2) adding 0.74 g of sodium hydroxide to the reaction solution, stirring evenly, and alkalizing at 40° C. for 8 h to obtain alkali cellulose;

[0132] (3) injecting 5.6 g of propylene oxide into the alkali cellulose for etherification at 60° C. for 6 h;

[0133] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0134] (5) The reaction solution was placed in a dialysis bag with a molecular weight cutoff of 7000 and dialyzed for 72 h, followed by freeze-drying to obtain 1.375 g of highly substituted hydroxypropyl cellulose.

[0135] The hydroxypropyl cellulose prepared in Comparative Example 3 was subjected to FT-IR and 1 H NMR characterization showed that the results were similar to those in Example 1.

[0136] Comparative Example 4

[0137] (1) 1 g of microcrystalline cellulose (Chengdu Kelong Chemical) was added to a mixed solvent consisting of 40 mL of DMSO and 3.3 g of tetrabutylammonium fluoride trihydrate, and the mixture was stirred and heated to 60° C. to completely dissolve the microcrystalline cellulose, thereby obtaining a clear and transparent cellulose solution;

[0138] (2) adding 0.74 g of sodium hydroxide to the reaction solution, stirring evenly, and alkalizing at 40° C. for 8 h to obtain alkali cellulose;

[0139] (3) injecting 7.16 g of propylene oxide into the alkali cellulose for etherification at 60° C. for 6 h;

[0140] (4) adjusting the pH of the reaction solution after the etherification to neutral using glacial acetic acid;

[0141] (5) The reaction solution was placed in a dialysis bag with a molecular weight cutoff of 7000 and dialyzed for 72 h, followed by freeze-drying to obtain 1.461 g of highly substituted hydroxypropyl cellulose.

[0142] The hydroxypropyl cellulose prepared in Comparative Example 4 was subjected to FT-IR and 1 H NMR characterization showed that the results were similar to those in Example 1.

[0143] The hydroxypropyl cellulose prepared in the examples and comparative examples was tested for yield, molar substitution (MS), hydroxypropyl content (HC) and solubility. The test results are shown in Table 1:

[0144] Table 1 Yield, molar substitution (MS), hydroxypropyl content (HC) and solubility test results of hydroxypropyl cellulose of Examples 1 to 8 and Comparative Examples 1 to 4

[0145]

[0146]

[0147] Note: 1) Yield calculation formula: Yield = (actual mass / theoretical mass) * 100%, that is

[0148]

[0149] Where m is the mass of the product and m0 is the mass of the raw material MCC.

[0150] 2) Molar substitution MS is determined by 1 H NMR was measured using a 10% DCl solution in D2O.

[0151] 3) Calculation formula of hydroxypropyl content HC:

[0152] From the results in Table 1, we can see that:

[0153] Examples 1 and 2 illustrate that the method used in dissolving cellulose has little effect on the results.

[0154] Examples 2, 3 and 4, as well as 7 and 8 illustrate that hydroxypropyl cellulose products with different molar substitution degrees MS can be obtained by controlling the amounts of cellulose raw material and etherifying agent propylene oxide.

[0155] By comparing Example 4 and Example 5, it was found that different purification methods had a greater impact on the yield, and a higher yield could be obtained by dialysis purification of high-substituted hydroxypropyl cellulose.

[0156] In Example 6, the diluent solvent is replaced with toluene. Compared with DMSO as the diluent (compared with Example 4), under the same other conditions, the MS does not change much.

[0157] Comparative Examples 1 and 2 use a heterogeneous method. It can be seen that compared with the method of synthesizing HPC in a homogeneous phase, under similar conditions for etherification reaction, the MS value of HPC synthesized by the heterogeneous method is lower, and the MS value of HPC synthesized by the homogeneous method is significantly higher, and the efficiency is higher.

[0158] Examples 6, 7 and 8 illustrate that by appropriately extending the alkalization time and appropriately increasing the amount of the etherifying agent PO, the hydroxyl activity of cellulose is fully released and the etherification efficiency is further improved.

[0159] The yield is directly calculated based on the mass of the product hydroxypropyl cellulose. The yield of Example 7 is 148.3%, the yield of Example 8 is 159.8%, and the molar substitution MS is 2.8 and 3.6, respectively. Under the conditions of Examples 7 and 8, the yield of hydroxypropyl cellulose is high and the molar substitution is high. In Comparative Examples 3 and 4, the solvent system of 1-ethyl-3-methylimidazolium acetate in Examples 7 and 8 is replaced by a mixture solvent system of tetrabutylammonium fluoride trihydrate and dimethyl sulfoxide, respectively, and the yield and molar substitution are reduced; and the products of Comparative Examples 3 and 4 are difficult to purify cleanly, and there are also some yellow-brown byproducts that are insoluble in water in a short time.

[0160] Figure 3 is the hydroxypropyl number distribution diagram of the hydroxypropyl cellulose of Example 7; Figure 4 This is a comparison chart of the hydroxypropyl number distribution of commercially available heterogeneously prepared hydroxypropyl cellulose (highly substituted low viscosity 75-150mpas, MS=3.4, source leaf biotechnology). Through mass spectrometry detection, it was found that the hydroxypropyl number distribution of HPC synthesized by homogeneous method is more concentrated than that of HPC synthesized by heterogeneous method, indicating that its distribution is more uniform. Figure 3 It can be seen that the number of hydroxypropyl cellulose prepared by the homogeneous method is concentrated around 3, and the hydroxypropyl substitution distribution is more uniform; Figure 4This indicates that the number of hydroxypropyl groups in the hydroxypropyl cellulose sample prepared by the heterogeneous method is distributed between 1 and 5, and the peak intensities of 1 to 5 are close, indicating that its distribution uniformity is poor.

[0161] The invention provides a homogeneous preparation method of hydroxypropyl cellulose. The preparation method has simple process, rapid reaction, small consumption of etherification reagent and good product substitution uniformity.

[0162] Although the above-mentioned embodiments have made a detailed description of the present invention, they are only some embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on the embodiments of the present invention without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A homogeneous preparation method of hydroxypropyl cellulose, characterized in that: The following steps are involved: Mixing and dissolving cellulose, 1-ethyl-3-methylimidazolium acetate and a diluent to obtain a cellulose solution; the diluent includes dimethyl sulfoxide or toluene; The cellulose solution is mixed with alkali to obtain an alkalized cellulose solution; The alkalized cellulose solution and propylene oxide are mixed to carry out etherification reaction, and the obtained reaction solution is neutralized, separated and purified to obtain hydroxypropyl cellulose.

2. The homogeneous preparation method according to claim 1, characterized in that: The dosage ratio of the 1-ethyl 3-methyl imidazole acetate to the diluent is 1 g: (2-8) mL.

3. The homogeneous preparation method according to claim 1 or 2, characterized in that: The concentration of cellulose in the cellulose solution is 1 wt% to 5 wt%.

4. The homogeneous preparation method according to claim 1, characterized in that: The amount of the alkali used is 1 to 20 times the molar amount of the glucose structural unit in the cellulose.

5. The homogeneous preparation method according to claim 1 or 4, characterized in that: The alkalization temperature is 25-50°C and the time is 15 minutes to 12 hours.

6. The homogeneous preparation method according to claim 1, characterized in that: The mass of the propylene oxide is 0.3 to 10 times the mass of the cellulose.

7. The homogeneous preparation method according to claim 1 or 6, characterized in that: The temperature of the etherification reaction is 50-70° C. and the time is 2-12 hours.

8. The homogeneous preparation method according to claim 1, characterized in that: The separation and purification comprises dialysis, and the molecular weight cut-off of the dialysis is 7000 or 8000-14000.

9. The homogeneous preparation method according to claim 1, characterized in that: When the hydroxypropyl cellulose is low-substituted hydroxypropyl cellulose, the separation and purification comprises: mixing the neutralized reaction solution with an organic solvent to precipitate the hydroxypropyl cellulose, separating the solid from the liquid, and washing and drying the obtained solid; the organic solvent comprises acetone, ethanol or 1,4-dioxane.

10. The homogeneous preparation method according to claim 1, characterized in that: When the hydroxypropyl cellulose is a highly substituted hydroxypropyl cellulose, the separation and purification comprises: mixing the neutralized reaction solution with hot water to precipitate the hydroxypropyl cellulose, separating the solid from the liquid, and drying the obtained solid; the temperature of the hot water is 70-90°C.

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