CN118108863A - Low-viscosity hydroxypropyl methyl cellulose and preparation method thereof - Google Patents
Low-viscosity hydroxypropyl methyl cellulose and preparation method thereof Download PDFInfo
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- 229920003088 hydroxypropyl methyl cellulose Polymers 0.000 title claims abstract description 48
- 235000010979 hydroxypropyl methyl cellulose Nutrition 0.000 title claims abstract description 48
- 239000001866 hydroxypropyl methyl cellulose Substances 0.000 title claims abstract description 47
- UFVKGYZPFZQRLF-UHFFFAOYSA-N hydroxypropyl methyl cellulose Chemical compound OC1C(O)C(OC)OC(CO)C1OC1C(O)C(O)C(OC2C(C(O)C(OC3C(C(O)C(O)C(CO)O3)O)C(CO)O2)O)C(CO)O1 UFVKGYZPFZQRLF-UHFFFAOYSA-N 0.000 title claims abstract description 47
- 238000002360 preparation method Methods 0.000 title abstract description 14
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims abstract description 63
- 229920002678 cellulose Polymers 0.000 claims abstract description 40
- 239000001913 cellulose Substances 0.000 claims abstract description 40
- 238000003756 stirring Methods 0.000 claims abstract description 24
- 238000010438 heat treatment Methods 0.000 claims abstract description 22
- 239000007800 oxidant agent Substances 0.000 claims abstract description 22
- NEHMKBQYUWJMIP-UHFFFAOYSA-N chloromethane Chemical compound ClC NEHMKBQYUWJMIP-UHFFFAOYSA-N 0.000 claims abstract description 18
- 238000000034 method Methods 0.000 claims abstract description 17
- 239000008234 soft water Substances 0.000 claims abstract description 17
- 230000001590 oxidative effect Effects 0.000 claims abstract description 16
- 238000005406 washing Methods 0.000 claims abstract description 15
- 238000006266 etherification reaction Methods 0.000 claims abstract description 14
- 239000002904 solvent Substances 0.000 claims abstract description 14
- GOOHAUXETOMSMM-UHFFFAOYSA-N Propylene oxide Chemical compound CC1CO1 GOOHAUXETOMSMM-UHFFFAOYSA-N 0.000 claims abstract description 10
- 238000001035 drying Methods 0.000 claims abstract description 9
- 230000003472 neutralizing effect Effects 0.000 claims abstract description 7
- 238000001816 cooling Methods 0.000 claims description 16
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 15
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical group OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 14
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 10
- 238000004519 manufacturing process Methods 0.000 claims description 10
- 229920000742 Cotton Polymers 0.000 claims description 9
- 239000000463 material Substances 0.000 claims description 9
- 239000005708 Sodium hypochlorite Substances 0.000 claims description 8
- 238000006243 chemical reaction Methods 0.000 claims description 8
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 claims description 8
- 230000003113 alkalizing effect Effects 0.000 claims description 6
- 239000012454 non-polar solvent Substances 0.000 claims description 6
- 239000002798 polar solvent Substances 0.000 claims description 6
- 238000006116 polymerization reaction Methods 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 238000003825 pressing Methods 0.000 claims description 5
- 238000006386 neutralization reaction Methods 0.000 claims description 4
- 229920001131 Pulp (paper) Polymers 0.000 claims description 3
- 238000005119 centrifugation Methods 0.000 claims description 2
- 229920003086 cellulose ether Polymers 0.000 abstract description 10
- 238000007613 slurry method Methods 0.000 abstract description 2
- 239000000047 product Substances 0.000 description 55
- 235000011121 sodium hydroxide Nutrition 0.000 description 16
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 15
- 230000000052 comparative effect Effects 0.000 description 12
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 8
- 239000002994 raw material Substances 0.000 description 8
- 239000012046 mixed solvent Substances 0.000 description 7
- 238000002834 transmittance Methods 0.000 description 6
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 4
- 230000002378 acidificating effect Effects 0.000 description 4
- 230000015556 catabolic process Effects 0.000 description 4
- 238000006731 degradation reaction Methods 0.000 description 4
- 125000000956 methoxy group Chemical group [H]C([H])([H])O* 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
- -1 hydroxypropyl group Chemical group 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 125000001165 hydrophobic group Chemical group 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 238000004806 packaging method and process Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000006722 reduction reaction Methods 0.000 description 2
- VZGDMQKNWNREIO-UHFFFAOYSA-N tetrachloromethane Chemical compound ClC(Cl)(Cl)Cl VZGDMQKNWNREIO-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- NEHMKBQYUWJMIP-NJFSPNSNSA-N chloro(114C)methane Chemical compound [14CH3]Cl NEHMKBQYUWJMIP-NJFSPNSNSA-N 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- SZXQTJUDPRGNJN-UHFFFAOYSA-N dipropylene glycol Chemical compound OCCCOCCCO SZXQTJUDPRGNJN-UHFFFAOYSA-N 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229940050176 methyl chloride Drugs 0.000 description 1
- 230000033116 oxidation-reduction process Effects 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 description 1
- 239000008213 purified water Substances 0.000 description 1
- 238000006479 redox reaction Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000007873 sieving Methods 0.000 description 1
- 229910001415 sodium ion Inorganic materials 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Landscapes
- Polysaccharides And Polysaccharide Derivatives (AREA)
Abstract
The application discloses low-viscosity hydroxypropyl methyl cellulose and a preparation method thereof, and belongs to the technical field of cellulose preparation. The preparation method comprises the following steps: (1) alkalization: soft water and sodium hydroxide are added into a solvent, then the solvent is cooled to room temperature, a strong oxidant is added, and then crushed natural cellulose is added, stirred uniformly and alkalized to obtain an alkalized product; (2) etherification: adding propylene oxide and chloromethane, stirring uniformly, and heating to obtain an etherification product; (3) post-treatment: and after etherification, neutralizing and desolventizing, washing and drying the etherification product to obtain the low-viscosity hydroxypropyl methylcellulose. The method can produce the cellulose ether with low viscosity by a one-step slurry method, does not contain viscosity reducing medium, and the obtained hydroxypropyl methylcellulose product has higher uniformity and stability.
Description
Technical Field
The application relates to low-viscosity hydroxypropyl methyl cellulose and a preparation method thereof, and belongs to the technical field of cellulose preparation.
Background
Hydroxypropyl methyl cellulose (named hydroxypropyl methylcellulose, HPMC for short) is a nonionic mixed ether obtained by alkalizing, etherifying, neutralizing and washing natural cellulose, and the application range is extremely wide spread in a plurality of fields such as medicine, building, food, ceramics, electronics and the like. The application in different fields has different values of the required range of the product viscosity, for example, the required viscosity of building material grade is more than 1%10000 Pa.s, the required viscosity of medical food grade is generally less than 1%10000 Pa.s, and even less than 2%5 Pa.s.
In the current market, the production mode of the low-viscosity hydroxypropyl methyl cellulose ether adopts a method of viscosity reduction treatment of the formed medium-high-viscosity cellulose ether and acidic substances, strong oxidants or irradiation to obtain the required low-viscosity hydroxypropyl methyl cellulose ether. For example, the patent DE2016203A1 and the patent DE1543116a both adopt hydrogen peroxide to treat high-viscosity cellulose ether to obtain low-viscosity cellulose ether, which can make the viscosity-reducing medium carried in the product difficult to remove, and have the defects of uneven product viscosity, complicated operation steps, high cost and the like. CN113501971a describes a method for obtaining a low-polymerization-degree water-soluble cellulose ether having a low viscosity by dry depolymerizing a high-polymerization-degree water-soluble cellulose ether with a mixed gas of HCl-ClO 2, which also reduces the viscosity of a high-viscosity cellulose ether, and has the disadvantages of low utilization rate of raw materials, inconvenience in operation, easiness in corrosion of equipment and complicated post-treatment.
Disclosure of Invention
In order to solve the problems, the low-viscosity hydroxypropyl methylcellulose and the preparation method thereof are provided, the method can produce the cellulose ether with low viscosity by a one-step slurry method, and has the advantages of no viscosity reducing medium, simple operation, high safety, convenient post-treatment, no corrosion to equipment and the like, and the obtained hydroxypropyl methylcellulose has high uniformity and stability, and is suitable for industrialized mass production.
According to one aspect of the present application, there is provided a method for preparing low viscosity hydroxypropyl methylcellulose, comprising the steps of:
(1) Alkalization: soft water and sodium hydroxide are added into a solvent in a reaction kettle, wherein the weight ratio of the soft water to the sodium hydroxide is 2: (2.7-3.4), heating to 70-80 ℃ to dissolve sodium hydroxide, cooling to room temperature, adding a strong oxidant, adding crushed natural cellulose, uniformly stirring, heating to 70-85 ℃ to treat for 10min, cooling to 20-30 ℃ and alkalizing for 120-180min to obtain an alkalized product, wherein the addition amount of the strong oxidant is 0.1-1% of the weight of the soft water, and the weight ratio of the natural cellulose to the sodium hydroxide is 1: (0.8-1.2);
(2) Etherification: vacuumizing to below-0.06 MPa after alkalization, adding propylene oxide and chloromethane, stirring uniformly, wherein the addition amount of the propylene oxide is 30-40% of the weight of the natural cellulose, the addition amount of the chloromethane is 1-1.3 times of the weight of the natural cellulose, heating to 40-60 ℃ for 3-4h after stirring uniformly, and heating to 80-95 ℃ for 2.5-3h to obtain an etherified product;
(3) Post-treatment: and after the etherification is finished, neutralizing, desolventizing, washing and drying the etherification product to obtain the low-viscosity cellulose ether.
According to the application, the strong oxidant is added in the alkalization process of the natural cellulose, so that the alkalization degradation speed and strength of a natural cellulose molecular chain can be accelerated, and the intermolecular acting force is reduced, so that the low-viscosity hydroxypropyl methyl cellulose suitable for market demands can be prepared in one step, the added strong oxidant forms soluble free ions in the oxidation-reduction reaction, the ions can be removed through the washing process, no impurities are introduced into the product, and the purity of the product is improved. Soft water is adopted for production, so that the content of free impurity ions in the product can be reduced, the purity of the product is further improved, and the product meets the requirements of medical food grade.
In the step (1), the temperature is raised to 70-80 ℃ to dissolve sodium hydroxide, so that the sodium hydroxide is uniformly dispersed in the whole medium system, and the reaction efficiency is improved; the addition amount of the strong oxidant is used for ensuring that the viscosity of the product is moderate, if the strong oxidant is too small, the low-viscosity product cannot be obtained, if the strong oxidant is too large, the product has no viscosity, the loss amount in the subsequent washing process is too large, the yield is reduced, and the production cost is increased.
Step (2) etherification is carried out on the epoxy propane at the temperature of 40-60 ℃, and a hydroxypropyl group is introduced, wherein the group is a hydrophilic group; methyl chloride is etherified at 80-95 ℃, methoxy is introduced, the group is a hydrophobic group, and the quantity of the hydrophobic group and the hydrophilic group in the product can be regulated and controlled through the quantity of the propylene oxide and the methyl chloride, so that the surface tension of the product in liquid is good, the gel performance is good, and the application of the product is facilitated.
Optionally, after adding the crushed natural cellulose, stirring at room temperature for 30-40 min to uniformly stir, wherein the operation is to uniformly disperse the natural cellulose into the whole system, uniformly mix and contact the natural cellulose with dissolved caustic soda flakes and a strong oxidant, so that the alkalization efficiency is improved, and the uniformity and yield of the product are further improved.
Optionally, the strong oxidant is hydrogen peroxide and/or sodium hypochlorite.
The strong oxidant forms soluble sodium ions, chloride ions, water and oxygen in the oxidation-reduction process, can be removed in the subsequent washing step, has easily available raw materials, and can reduce the production cost.
Optionally, the concentration of hydrogen peroxide in the hydrogen peroxide is 30%.
Optionally, the solvent comprises a non-polar solvent and a polar solvent.
Optionally, the weight ratio of the nonpolar solvent to the polar solvent is (7.5-9): (1-2.5), preferably 8.5:1.5.
Optionally, the nonpolar solvent is selected from at least one of toluene, benzene, and carbon tetrachloride; the polar solvent is at least one selected from ethanol, propanol, isopropanol and methanol.
The solvent is used for dissolving the raw materials and uniformly dispersing the raw materials, and when a binary mixed solvent consisting of a nonpolar solvent and a polar solvent is adopted, the medium effect is better, and the strong oxidant is uniformly dispersed into the whole medium system, so that the product obtained by the reaction has higher uniformity of various indexes such as viscosity and the like and better performance.
Optionally, the natural cellulose has a bulk density of 120-190g/L.
The fluffy density is beneficial to improving the contact area of the natural cellulose, so that the reaction efficiency of the natural cellulose is improved.
Optionally, the natural cellulose is refined cotton and/or wood pulp, and the polymerization degree of the refined cotton is M30-M60.
The application can adopt refined cotton with various polymerization degrees as raw materials, can obtain the ultra-low viscosity high-substituted hydroxypropyl methyl cellulose, has low requirement on the selectivity of the raw materials, and the product is white and clean and is easy to crush, the hydroxypropyl oxide content of the prepared hydroxypropyl methyl cellulose is 6-8.5%, the methoxy content is 26-30%, the viscosity is below 10mps, and the light transmittance (2% aqueous solution) is above 90%. The polymerization degree of the refined cotton is M30-M60, so that the viscosity of the hydroxypropyl methylcellulose is ensured to be proper, and if the polymerization degree is too high, the viscosity of the product is easily increased.
Optionally, the neutralization and desolventizing steps are specifically as follows: cooling the etherified product to below 76 ℃, then introducing nitrogen to raise the pressure of the kettle to 0.2MPa, pressing the kettle to a desolventizing kettle, adding acetic acid to neutralize to neutrality, and then distilling to remove the solvent.
Optionally, the washing specifically comprises: soft water at 80-100 ℃ is added into the neutralization and desolventizing product, and the product is obtained after washing for 1.5-2h and centrifugation.
The product is insoluble in hot soft water, so that the above washing process can remove salt, further improving the purity of the product.
Optionally, the drying is performed until the moisture of the material is less than or equal to 5.0%.
Optionally, crushing the dried raw materials to a sieving rate of more than 99.5% by 100 meshes, then putting the materials into a mixer for mixing for 4-6h, and packaging and warehousing in a packaging room after the mixing is finished. The raw materials are crushed and mixed for a certain time, so that the uniformity of the manufactured products is further improved, and the consistency of the manufactured products in batches is improved.
According to another aspect of the present application, there is provided a low-viscosity hydroxypropyl methylcellulose prepared by the method for preparing a low-viscosity hydroxypropyl methylcellulose of any of the above.
The beneficial effects of the application include, but are not limited to:
1. According to the preparation method of the low-viscosity hydroxypropyl methyl cellulose, the strong oxidant is added in the alkalization process of the natural cellulose, so that the alkalization degradation speed and strength of a molecular chain of the natural cellulose can be accelerated, and the intermolecular acting force is reduced, and the low-viscosity cellulose ether suitable for market demands is obtained.
2. The preparation method of the low-viscosity hydroxypropyl methylcellulose provided by the application has the advantages that the low-viscosity hydroxypropyl methylcellulose is directly in place in one step, the subsequent viscosity reduction operation is not needed, the operation is simple, the production cost can be greatly reduced, and the preparation method is suitable for industrial mass production.
3. The low-viscosity hydroxypropyl methylcellulose disclosed by the application has the characteristics of no viscosity reducing medium, uniform viscosity, high stability, white and clean product, easiness in crushing and more than 90% of light transmittance, and the application range of the low-viscosity hydroxypropyl methylcellulose is widened.
Detailed Description
The present application is described in detail below with reference to examples, but the present application is not limited to these examples.
Unless otherwise indicated, the starting materials in the examples and comparative examples of the present application were purchased commercially.
Unless otherwise specified, the methods employed in the examples and comparative examples of the present application are conventional methods in the prior art, and the parts employed in the following examples and comparative examples are parts by weight.
Example 1
The embodiment relates to a preparation method of low-viscosity hydroxypropyl methylcellulose, which comprises the following steps:
(1) Alkalization: 6600 parts of mixed solvent, 480 parts of soft water and 648 parts of sodium hydroxide are added into a reaction kettle, wherein the weight ratio of toluene to isopropanol in the mixed solvent is 9:1, heating to 70 ℃, timing for 30min to dissolve sodium hydroxide, cooling to room temperature, adding 0.48 part of sodium hypochlorite, stirring for 40min, adding 518.4 parts of crushed natural cellulose, stirring for 30min at room temperature to be uniformly stirred, heating to 70 ℃ for 10min, cooling to 20 ℃, alkalizing for 180min to obtain an alkalized product, wherein the natural cellulose is wood pulp, and the bulk is 120g/L;
(2) Etherification: after alkalization, vacuumizing to-0.06 Mpa, adding 155.5 parts of propylene oxide and 777.6 parts of chloromethane, stirring for 60min to be uniform, heating to 40 ℃ for treatment 4h, and heating to 80 ℃ for treatment 3h to obtain an etherified product;
(3) Post-treatment: cooling the etherified product to below 76 ℃, then introducing nitrogen to enable the kettle pressure to rise to 0.2MPa, pressing the material to a desolventizing kettle, adding acetic acid, neutralizing to neutrality, distilling to remove the solvent to obtain a neutralized desolventized product, adding soft water at 80 ℃ into the neutralized desolventized product, washing for 2 hours, centrifuging to obtain an undried product, then sending the undried product to a flash dryer, and drying the material to moisture of less than or equal to 5.0% through the flash dryer to obtain the low-viscosity hydroxypropyl methyl cellulose.
Example 2
The embodiment relates to a preparation method of low-viscosity hydroxypropyl methylcellulose, which comprises the following steps:
(1) Alkalization: 6600 parts of mixed solvent, 480 parts of soft water and 700 parts of sodium hydroxide are added into a reaction kettle, wherein the weight ratio of toluene to isopropanol in the mixed solvent is 8.5:1.5, heating to 80 ℃, timing for 30min to dissolve sodium hydroxide, cooling to room temperature, adding 4 parts of sodium hypochlorite, stirring for 30min, adding 700 parts of crushed natural cellulose, stirring for 30min at room temperature to be uniform, heating to 80 ℃ for 10min, cooling to 20 ℃, alkalizing for 150min to obtain an alkalized product, wherein the natural cellulose is M30 purified cotton, and the bulk is 150g/L;
(2) Etherification: after alkalization, vacuumizing to-0.06 Mpa, adding 300 parts of propylene oxide and 1000 parts of chloromethane, stirring for 60min until uniform, heating to 55 ℃ for 3h, and heating to 85 ℃ for 2.5h to obtain an etherified product;
(3) Post-treatment: cooling the etherified product to below 76 ℃, then introducing nitrogen to enable the kettle pressure to rise to 0.2MPa, pressing the material to a desolventizing kettle, adding acetic acid, neutralizing to neutrality, distilling to remove the solvent to obtain a neutralized desolventized product, adding soft water at 95 ℃ into the neutralized desolventized product, washing for 1.5h, centrifuging to obtain an undried product, then sending the undried product to a flash dryer, and drying the material to moisture of less than or equal to 5.0% through the flash dryer to obtain the low-viscosity hydroxypropyl methylcellulose.
Example 3
The embodiment relates to a preparation method of low-viscosity hydroxypropyl methylcellulose, which comprises the following steps:
(1) Alkalization: 6600 parts of mixed solvent, 480 parts of soft water and 816 parts of sodium hydroxide are added into a reaction kettle, wherein the weight ratio of toluene to isopropanol in the mixed solvent is 7.5:2.5, heating to 80 ℃, timing for 30min to dissolve sodium hydroxide, cooling to room temperature, adding 4.8 parts of hydrogen peroxide, wherein the concentration of hydrogen peroxide is 30%, stirring for 20min, adding 979.2 parts of crushed natural cellulose, stirring for 30min at room temperature until stirring uniformly, heating to 85 ℃ for 10min, cooling to 30 ℃, alkalizing for 120min to obtain an alkalized product, wherein the natural cellulose is M60 refined cotton, and the bulk is 190g/L;
(2) Etherification: after alkalization, vacuumizing to-0.06 Mpa, adding 391.7 parts of propylene oxide and 979.2 parts of chloromethane, stirring for 60min to be uniform, heating to 60 ℃ for treatment for 3 hours, and heating to 95 ℃ for treatment for 2.5 hours to obtain an etherified product;
(3) Post-treatment: cooling the etherified product to below 76 ℃, then introducing nitrogen to enable the kettle pressure to rise to 0.2MPa, pressing the material to a desolventizing kettle, adding acetic acid, neutralizing to neutrality, distilling to remove the solvent to obtain a neutralized desolventized product, adding soft water at 100 ℃ into the neutralized desolventized product, washing for 1.5h, centrifuging to obtain an undried product, then sending the undried product to a flash dryer, and drying the material to moisture of less than or equal to 5.0% through the flash dryer to obtain the low-viscosity hydroxypropyl methylcellulose.
Example 4
This example differs from example 2 in that a single toluene was used as the solvent, and the remainder was the same as example 2.
Example 5
This example differs from example 2 in that the natural cellulose has a bulk of 100g/L, the remainder being the same as example 2.
Example 6
This example differs from example 2 in that the natural cellulose is M80 purified cotton, and the remainder is the same as in example 2.
Comparative example 1
This comparative example differs from example 2 in that in step (1) sodium hydroxide is dissolved and then natural cellulose is added directly, sodium hypochlorite, a strong oxidizer, is not added, and the remainder is the same as example 2.
Comparative example 2
The difference between this comparative example and example 2 is that in step (1), sodium hydroxide is dissolved and cooled to room temperature, and then sodium hypochlorite 2 parts are added, followed by stirring for 20 minutes, then 700 parts of crushed natural cellulose are added, followed by stirring for 20 minutes, and then sodium hypochlorite 2 parts are added, and stirring is carried out at room temperature for 30 minutes until stirring is uniform, and then heating treatment is carried out, and the rest is the same as in example 2.
Comparative example 3
This comparative example is different from example 2 in that 700 parts of crushed natural cellulose is added after the sodium hydroxide is dissolved in step (1), stirred for 20 minutes, then 4 parts of sodium hypochlorite is added, stirred at room temperature for 30 minutes until the mixture is stirred uniformly, and then the temperature is raised again, and the rest is the same as example 2.
Test example 1
The products prepared in the above examples and comparative examples and low viscosity hydroxypropyl methylcellulose samples obtained by acidic degradation were subjected to viscosity, loss on drying, hot residue, whiteness, light transmittance, bulk density, hydroxypropoxy group and methoxy group detection, the detection methods are shown in table 1, and the detection results are shown in table 2. The acidic degraded low-viscosity hydroxypropyl methylcellulose is a sample provided by Shandong light technologies development limited company.
TABLE 1
TABLE 2
The viscosity in Table 2 means that 2.0g of hydroxypropyl methylcellulose sample dried to constant weight is added into a beaker, purified water at 80-90 ℃ is added to prepare a 2% solution, the solution is fully stirred for 10min, then the solution is cooled in an ice bath for 40min, air bubbles are removed by stirring in the cooling process, the solution is placed into a constant temperature tank, the temperature is 20+/-1 ℃, and the viscosity is measured by an NDJ-1 rotary viscometer.
According to the data in the table, the low-viscosity hydroxypropyl methylcellulose can be prepared by a one-step method, the product is white and clean, the light transmittance is good, and various quality indexes are better than those of an acidic degradation sample. As can be seen from the comparison of the examples 2 and 4, the adoption of a single solvent can lead to uneven dispersion of the strong oxidant, so that the light transmittance of the product is reduced, the bulk density is reduced, the hot residues are more, and the performance is reduced; as is clear from comparison of examples 5, 6 and example 2, the natural cellulose has a smaller bulk value, and the contact area of the natural cellulose is smaller, so that the viscosity of the product is slightly higher, the light transmittance is lower, the bulk density is lower, the substitution degree of hydroxypropyl and methoxy groups is lower, the performance is lowered, and the polymerization degree of the natural cellulose is larger, so that the viscosity of the final product is increased.
As can be seen from the comparison of example 2 and comparative example 1, the viscosity of the product prepared without the addition of the strong oxidizing agent reached 178mpa.s, which is far higher than that of example 2, i.e., the ideal low viscosity hydroxypropyl methylcellulose could not be obtained in the absence of the strong oxidizing agent; as can be seen from a comparison of example 2 and comparative examples 2-3, the low viscosity hydroxypropyl methylcellulose was obtained by adding the strong oxidizer first and then adding the natural cellulose, which better meets the low viscosity standard.
The above description is only an example of the present application, and the scope of the present application is not limited to the specific examples, but is defined by the claims of the present application. Various modifications and variations of the present application will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application should be included in the protection scope of the present application.
Claims (10)
1. A method for preparing low-viscosity hydroxypropyl methylcellulose, which is characterized by comprising the following steps:
(1) Alkalization: soft water and sodium hydroxide are added into a solvent in a reaction kettle, wherein the weight ratio of the soft water to the sodium hydroxide is 2: (2.7-3.4), heating to 70-80 ℃ to dissolve sodium hydroxide, cooling to room temperature, adding a strong oxidant, adding crushed natural cellulose, uniformly stirring, heating to 70-85 ℃ to treat for 10min, cooling to 20-30 ℃ and alkalizing for 120-180min to obtain an alkalized product, wherein the addition amount of the strong oxidant is 0.1-1% of the weight of the soft water, and the weight ratio of the natural cellulose to the sodium hydroxide is 1: (0.8-1.2);
(2) Etherification: vacuumizing to below-0.06 MPa after alkalization, adding propylene oxide and chloromethane, stirring uniformly, wherein the addition amount of the propylene oxide is 30-40% of the weight of the natural cellulose, the addition amount of the chloromethane is 1-1.5 times of the weight of the natural cellulose, heating to 40-60 ℃ for 3-4h after stirring uniformly, and heating to 80-95 ℃ for 2.5-3h to obtain an etherified product;
(3) Post-treatment: and after etherification, neutralizing and desolventizing, washing and drying the etherification product to obtain the low-viscosity hydroxypropyl methylcellulose.
2. The method for preparing low-viscosity hydroxypropyl methylcellulose according to claim 1, wherein the strong oxidizer is hydrogen peroxide and/or sodium hypochlorite.
3. The method for producing a low-viscosity hydroxypropyl methylcellulose according to claim 1, wherein the solvent comprises a nonpolar solvent and a polar solvent.
4. The method for producing a low-viscosity hydroxypropylmethyl cellulose according to claim 3, wherein the weight ratio of the nonpolar solvent to the polar solvent is (7.5-9): (1-2.5).
5. The method for preparing low viscosity hydroxypropyl methylcellulose according to claim 1, wherein the natural cellulose has a bulk density of 120-190g/L.
6. The method for producing a low-viscosity hydroxypropyl methylcellulose according to claim 1, wherein the natural cellulose is purified cotton and/or wood pulp, and the purified cotton has a degree of polymerization of M30 to M60.
7. The method for preparing low-viscosity hydroxypropyl methylcellulose according to claim 1, wherein the neutralization and desolventizing steps are as follows: cooling the etherified product to below 76 ℃, then introducing nitrogen to raise the pressure of the kettle to 0.2MPa, pressing the kettle to a desolventizing kettle, adding acetic acid to neutralize to neutrality, and then distilling to remove the solvent.
8. The method for preparing low-viscosity hydroxypropyl methylcellulose according to claim 1, wherein the washing is specifically: soft water at 80-100 ℃ is added into the neutralization and desolventizing product, and the product is obtained after washing for 1.5-2h and centrifugation.
9. The method for preparing low viscosity hydroxypropyl methylcellulose of claim 1, wherein said drying is to a moisture content of the material of 5.0% or less.
10. The low-viscosity hydroxypropyl methylcellulose of any one of claims 1 to 9.
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