Polyvinyl alcohol with low alcoholysis degree and preparation method thereof

Abstract

The preparation method comprises the following steps: firstly, preparing a low-alcoholysis-degree polyvinyl alcohol alcoholysis solution, and then, carrying out precipitation in water containing a stabilizer, so as to obtain the low-volatile-matter ultralow-alcoholysis-degree polyvinyl alcohol. The preparation method is simple, and the polyvinyl alcohol with the ultralow alcoholysis degree, which is uniform in particle size and low in volatile matter, can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of polyvinyl alcohol, and in particular to a polyvinyl alcohol with low volatility and low alcoholysis degree and a preparation method thereof. Background Art

[0002] Polyvinyl alcohol (PVA) is a kind of material with special properties obtained by polymerization and alcoholysis of vinyl acetate. It is widely used in textile, construction, medicine, papermaking, chemical industry and other fields. The degree of polymerization and alcoholysis of polyvinyl alcohol have a great influence on its performance. Currently, the common products on the market are 99% high alcoholysis products, 88% partial alcoholysis products, and ultra-low alcoholysis products with less than 55%. Due to the wide range of variation of the degree of polymerization and alcoholysis of polyvinyl alcohol, its performance can cover a wide range, and its application field and usage are gradually increasing.

[0003] At present, low alcoholysis degree polyvinyl alcohol is increasingly used in polymerization aids. However, due to its high solubility in methanol, the methanol embedded in it is difficult to remove during the drying process, thus affecting the quality of other subsequent products. At present, domestic manufacturers control the content of polyvinyl alcohol to 1.4-2.5%, which cannot meet the needs of special fields. Secondly, the polyvinyl alcohol industry currently granulates it by crushing. During the crushing process, due to the uneven molecular weight of polyvinyl alcohol, some low molecular weight polyvinyl alcohol will be over-powdered and the particle fineness will be uneven.

[0004] It has been reported that the low alcoholysis degree polyvinyl alcohol flakes after crushing are introduced into a certain amount of steam at the end of the dryer to reduce the partial pressure of methanol, thereby making the methanol in the polyvinyl alcohol easy to evaporate and reducing the methanol content in the product. However, due to the introduction of water vapor in the later stage of drying, its volatile matter increases from 3.8% to 5.3%. CN113004443A proposes to use non-polar solvents to accelerate the gelation process in the preparation process of polyvinyl alcohol, thereby preparing low alcoholysis degree polyvinyl alcohol, but for ultra-low alcoholysis degree polyvinyl alcohol (alcoholysis degree <55%) products that can be dissolved in methanol, they have a certain solubility in non-polar solvents and cannot completely precipitate gel. CN113024698B proposes to add sodium borohydride protective solution during the drying process to accelerate the drying of materials to remove volatiles and improve whiteness, but does not mention the effect of removing volatiles. Summary of the invention

[0005] The purpose of the present invention is to provide a polyvinyl alcohol with ultra-low alcoholysis degree and a preparation method thereof. The polyvinyl alcohol prepared by the preparation method of the present invention has the advantages of low volatility (<1%) and ultra-low alcoholysis degree (<55%). It can be used in fields requiring high purity of polymerization aids, such as biomedicine.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing polyvinyl alcohol with a low alcoholysis degree comprises the following steps:

[0008] (1) Polymerization: Vinyl acetate, alcohols, and initiators are mixed to carry out polymerization reaction.

[0009] (2) Alcoholysis: The polyvinyl acetate alcohol solution obtained after the above reaction is mixed with an alcohol solution of an alkali to carry out an alcoholysis reaction.

[0010] (3) Precipitation: Add the alcoholysis reaction solution into water for precipitation.

[0011] (4) Washing: Washing is performed with water.

[0012] (5) Drying: Filter and dry to obtain polyvinyl alcohol with low alcoholysis degree.

[0013] Preferably, in step (1), the mass ratio of vinyl acetate to alcohol is 100:20-200.

[0014] Preferably, in step (1), the alcohol is one or more of methanol, ethanol, propanol, isopropanol, tert-butanol, etc.

[0015] Preferably, the initiator is an azo initiator, and the initiator accounts for 0.2-1 wt% of the mass of vinyl acetate.

[0016] Preferably, in step (1), the reaction temperature is 60-70° C. and the reaction time is 5-8 hours.

[0017] Preferably, the alcohol in the alcoholic alkali solution is one or more of methanol, ethanol, propanol, isopropanol, and tert-butanol, the alkali in the alcoholic alkali solution includes one or more of alkali metal hydroxides, alkaline earth metal hydroxides, ammonia, etc., preferably sodium hydroxide or potassium hydroxide, and the mass concentration of the alkali in the alcoholic alkali solution is 0.2wt%-1wt%.

[0018] Preferably, the mass concentration of vinyl acetate in the polyvinyl acetate alcohol solution is 5-50wt%.

[0019] Preferably, the mass ratio of the alkali alcohol solution to the polyvinyl acetate alcohol solution is 1:1-10.

[0020] Preferably, in step (2), the alcoholysis temperature is 25-65° C., and the alcoholysis time is 5-60 min.

[0021] Preferably, the alcoholysis reaction liquid can be directly added to water for precipitation, or it can be mixed with part of the water before being sprayed into the water, such as by a high-speed mixer. The method of premixing before spraying can help the product precipitate faster.

[0022] In the present invention, the injection velocity can be selected according to the needs of those skilled in the art, and is preferably 0.05-0.5 m / s.

[0023] Preferably, in step (3), the mass of the water first mixed with the alcoholysis reaction liquid is 2-6 times the mass of the alcoholysis reaction liquid, preferably 3-4 times.

[0024] Preferably, in step (3), the water contains a stabilizer, and the mass fraction of the stabilizer is 0.5-5%, preferably 1-2%.

[0025] Preferably, the stabilizer is any one of dodecyltrimethyl sodium chloride, sodium dodecylbenzene sulfonate, rhamnose ester, sodium dodecyl sulfate, or a combination of two or more thereof.

[0026] Preferably, the water used for washing in step (4) is water with a temperature greater than 65° C., and the precipitated polyvinyl alcohol is washed with water.

[0027] Preferably, in step (5), the drying temperature is 100-150°C, and the drying time is 1-8 hours. Preferably, the drying temperature is 100-110°C, and the drying time is 1-2 hours.

[0028] The invention also provides polyvinyl alcohol prepared by the preparation method.

[0029] The present application precipitates polyvinyl alcohol with water and adds a stabilizer to the water. During the precipitation, the surface tension of the reaction droplets is reduced, the diffusion of methanol into the water is promoted, and the methanol and other reagents in the polyvinyl alcohol after alcoholysis are removed. The volatile matter in the polyvinyl alcohol product can be effectively reduced, and a high yield of the product can be ensured.

[0030] The polyvinyl alcohol prepared by the invention has low alcoholysis degree and low volatile matter, and the particle size of the polyvinyl alcohol is uniform. DETAILED DESCRIPTION

[0031] Comparative Example 1

[0032] Weigh 100g of vinyl acetate, 200g of methanol / isopropanol (mass ratio 1:1), and 0.8g of azobisisobutyronitrile and put them into a reaction tank. The reaction temperature is 65°C and the reaction time is 4 hours. Take out the polyvinyl acetate alcohol solution, add 0.5 times the mass of sodium hydroxide methanol solution (0.4wt%), and react at 35°C for 10 minutes. Add 3 times the mass of deionized water to the above reaction solution and spray it into the deionized water through a high-speed mixer. The liquid flow rate at the nozzle outlet is 0.3m / s for precipitation. After the solid is precipitated, filter it, and add 3 times the mass of 75°C deionized water for washing and filtration to obtain polyvinyl alcohol solid. Dry the above solid at 100°C for 5h to obtain a polyvinyl alcohol product.

[0033] The properties of the obtained polyvinyl alcohol are as follows: yield>98%, alcoholysis degree 35%, volatile matter 1.2%, and particle size distribution coefficient 1.28.

[0034] Example 1

[0035] Weigh 100g of vinyl acetate, 200g of methanol / isopropanol (mass ratio 1:1), and 0.8g of azobisisobutyronitrile and put them into a reaction tank. The reaction temperature is 65°C and the reaction time is 4 hours. Take out the polyvinyl acetate alcohol solution, add 0.5 times the mass of sodium hydroxide methanol solution (0.4wt%), and react at 35°C for 10 minutes. Neutralize the above reaction solution with 3 times the mass of deionized water and spray it into deionized water containing 1wt% sodium dodecylbenzene sulfonate through a high-speed mixer. The liquid flow rate at the nozzle outlet is 0.09m / s, and precipitate. After the solid is precipitated, filter it, and add 3 times the mass of 75°C deionized water to wash and filter to obtain polyvinyl alcohol solid. Dry the above solid at 100°C for 5h to obtain a polyvinyl alcohol product.

[0036] The properties of the obtained polyvinyl alcohol are as follows: yield>99.5%, alcoholysis degree 35%, volatile matter 0.35%, and particle size distribution coefficient 0.5.

[0037] Example 2

[0038] Weigh 100g of vinyl acetate, 200g of methanol / ethanol (mass ratio 2:1), and 0.2g of azobisisobutyronitrile and put them into a reaction tank. The reaction temperature is 65°C and the reaction time is 6 hours. Take out the polyvinyl acetate alcohol solution, add 0.1 times the mass of sodium hydroxide methanol solution (0.2wt%), and react at 35°C for 40 minutes. Neutralize the above reaction solution with 5 times the mass of deionized water and spray it into deionized water containing 0.5wt% rhamnosyl ester through a high-speed mixer. The liquid flow rate at the nozzle outlet is 0.45m / s, and precipitate. After the solid is precipitated, filter it, and add 2 times the mass of 75°C deionized water for washing and filtration to obtain polyvinyl alcohol solid. Dry the above solid at 120°C for 4h to obtain a polyvinyl alcohol product.

[0039] The properties of the obtained polyvinyl alcohol are as follows: yield>99.2%, alcoholysis degree 45%, volatile matter 0.32%, and particle size distribution coefficient 0.38.

[0040] Example 3

[0041] Weigh 100g of vinyl acetate, 200g of methanol / ethanol (mass ratio 2:1), and 0.2g of azobisisobutyronitrile and put them into a reaction tank. The reaction temperature is 65°C and the reaction time is 6 hours. Take out the polyvinyl acetate alcohol solution, add 0.1 times the mass of sodium hydroxide methanol solution (0.2wt%), and react at 35°C for 40 minutes. Neutralize the above reaction solution with 3 times the mass of deionized water and spray it into deionized water through a high-speed mixer. The liquid flow rate at the nozzle outlet is 0.35m / s, and precipitate. After the solid is precipitated, filter it, and add 2 times the mass of 75°C deionized water for washing and filtration to obtain polyvinyl alcohol solid. Dry the above solid at 120°C for 4h to obtain a polyvinyl alcohol product.

[0042] The properties of the obtained polyvinyl alcohol are as follows: yield>99.2%, alcoholysis degree 45%, volatile matter 0.38%, and particle size distribution coefficient 0.4.

[0043] Example 4

[0044] Weigh 100g of vinyl acetate, 200g of methanol / ethanol (mass ratio 2:1), and 0.2g of azobisisobutyronitrile and put them into a reaction tank. The reaction temperature is 65°C and the reaction time is 6 hours. Take out the polyvinyl acetate alcohol solution, add 0.1 times the mass of sodium hydroxide methanol solution (0.2wt%), and react at 35°C for 60 minutes. Neutralize the above reaction solution with 5 times the mass of deionized water and spray it into deionized water containing 0.5wt% rhamnosyl ester through a high-speed mixer. The liquid flow rate at the nozzle outlet is 0.25m / s, and precipitate. After the solid is precipitated, filter it, and add 2 times the mass of 75°C deionized water for washing and filtration to obtain polyvinyl alcohol solid. Dry the above solid at 120°C for 4h to obtain a polyvinyl alcohol product.

[0045] The properties of the obtained polyvinyl alcohol are as follows: yield>99.2%, alcoholysis degree 55%, volatile matter 0.26%, and particle size distribution coefficient 0.3.

[0046] Example 5

[0047] Weigh 100g of vinyl acetate, 200g of methanol / ethanol (mass ratio 2:1), and 0.5g of azobisisobutyronitrile and put them into a reaction tank. The reaction temperature is 65°C and the reaction time is 6 hours. Take out the polyvinyl acetate alcohol solution, add 0.1 times the mass of sodium hydroxide methanol solution (0.2wt%), and react at 25°C for 50 minutes. Neutralize the above reaction solution with 5 times the mass of deionized water and spray it into deionized water containing 0.5wt% rhamnose ester through a high-speed mixer. The liquid flow rate at the nozzle outlet is 0.3m / s, and precipitate. After the solid is precipitated, filter it, and add 2 times the mass of 75°C deionized water for washing and filtration to obtain polyvinyl alcohol solid. Dry the above solid at 120°C for 4h to obtain a polyvinyl alcohol product.

[0048] The properties of the obtained polyvinyl alcohol are as follows: yield>99.2%, alcoholysis degree 40%, volatile matter 0.30%, and particle size distribution coefficient 0.35.

Claims

1. A method for preparing polyvinyl alcohol with low alcoholysis degree, characterized in that: The following steps are involved: (1) Polymerization: vinyl acetate, alcohols, and initiators are mixed to carry out polymerization reaction; (2) alcoholysis: mixing the polyvinyl acetate alcohol solution obtained after the above reaction with an alcohol solution of an alkali to carry out an alcoholysis reaction; (3) precipitation: adding the alcoholysis reaction liquid into water for precipitation; (4) Washing: washing with water; (5) Drying: Filter and dry to obtain polyvinyl alcohol with low alcoholysis degree.

2. The preparation method according to claim 1, characterized in that: In step (1), the mass ratio of vinyl acetate to alcohol is 100:20-200; Preferably, in step (1), the alcohol is one or more of methanol, ethanol, propanol, isopropanol, tert-butanol, etc.; Preferably, the initiator is an azo initiator, and the initiator is 0.2-1wt% of the mass of vinyl acetate; Preferably, in step (1), the reaction temperature is 60-70° C. and the reaction time is 5-8 hours.

3. The preparation method according to claim 1 or 2, characterized in that: The alcohol in the alcohol solution of the base is one or more of methanol, ethanol, propanol, isopropanol, and tert-butanol; Preferably, the alkali in the alkali alcohol solution comprises one or more of alkali metal hydroxides, alkaline earth metal hydroxides, ammonia, etc., preferably sodium hydroxide or potassium hydroxide; Preferably, the mass concentration of the alkali in the alcoholic alkali solution is 0.2 wt%-1 wt%.

4. The preparation method according to any one of claims 1 to 3, characterized in that The mass concentration of vinyl acetate in the polyvinyl acetate alcohol solution is 5-50wt%; Preferably, the mass ratio of the alkali alcohol solution to the polyvinyl acetate alcohol solution is 1:1-10; Preferably, in step (2), the alcoholysis temperature is 25-65° C., and the alcoholysis time is 5-60 min.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The alcoholysis reaction liquid is directly added into water for precipitation or first mixed with part of water and then sprayed into water; Preferably, in step (3), the mass of the water first mixed with the alcoholysis reaction liquid is 2-6 times the mass of the alcoholysis reaction liquid, preferably 3-4 times.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In the step (3), the water contains a stabilizer, and the mass fraction of the stabilizer is 0.5-5%, preferably 1-2%; Preferably, the stabilizer is any one of dodecyltrimethyl sodium chloride, sodium dodecylbenzene sulfonate, rhamnose ester, sodium dodecyl sulfate, or a combination of two or more thereof.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The water used for washing in the step (4) is water with a temperature greater than 65° C., and the precipitated polyvinyl alcohol is washed with water.

8. The preparation method according to any one of claims 1 to 7, characterized in that: In the step (5), the drying temperature is 100-150° C. and the drying time is 1-8 hours; Preferably, the drying temperature is 100-110° C. and the drying time is 1-2 hours.

9. Polyvinyl alcohol prepared according to the preparation method according to any one of claims 1 to 8.