Low alcoholysis degree polyvinyl alcohol and preparation method thereof

Abstract

The application discloses a low-alcoholysis-degree polyvinyl alcohol and a preparation method thereof. First, a low-alcoholysis-degree polyvinyl alcohol alcoholysis solution is prepared, then, the low-alcoholysis-degree polyvinyl alcohol is precipitated in water containing a stabilizer, and finally, high-low-volatile-ingredient ultra-low-alcoholysis-degree polyvinyl alcohol is obtained. The preparation method is simple, and the ultra-low-alcoholysis-degree polyvinyl alcohol with uniform particle size and low volatile ingredients can be obtained.

Description

Technical Field

[0001] This invention relates to the field of polyvinyl alcohol technology, specifically to a low-volatile, low-hydrolysate polyvinyl alcohol and its preparation method. Background Technology

[0002] Polyvinyl alcohol (PVA) is a type of material with unique properties obtained by the polymerization and alcoholysis of vinyl acetate. It is widely used in textiles, construction, medicine, papermaking, and chemicals. The degree of polymerization and degree of alcoholysis of PVA significantly affect its performance. Currently, the most common products on the market are those with a high degree of alcoholysis (99%), partially alcoholyzed products (88%), and ultra-low degree of alcoholysis (less than 55%). Due to the wide range of variations in the degree of polymerization and degree of alcoholysis, PVA offers a broad range of performance characteristics, and its applications and usage are gradually increasing.

[0003] Currently, low-hydrolyzable polyvinyl alcohol (PVA) is increasingly used as a polymerization aid. However, due to its high solubility in methanol, the methanol embedded within it is difficult to remove during the drying process, thus affecting the quality of subsequent products. Currently, domestic manufacturers control the PVA content to 1.4-2.5%, which cannot meet the needs of specialized fields. Secondly, the current method of granulation in the PVA industry involves crushing. During the crushing process, the non-uniform molecular weight of PVA leads to excessive pulverization of some low-molecular-weight PVA, resulting in uneven particle size.

[0004] Reports suggest that by introducing a certain amount of steam into the dryer tail of pulverized low-hydrolysis polyvinyl alcohol (PVA) flakes to reduce the partial pressure of methanol, the methanol in the PVA can be more easily evaporated, thus reducing the methanol content in the product. However, due to the introduction of water vapor in the later stages of drying, the volatile matter content increases from 3.8% to 5.3%. CN113004443A proposes using non-polar solvents to accelerate the gelation process during PVA preparation, thereby producing low-hydrolysis PVA. However, for ultra-low-hydrolysis PVA (hydrolysis degree <55%) products that are soluble in methanol, there is some solubility in non-polar solvents, making complete gelation impossible. CN113024698B proposes adding a sodium borohydride protective solution during the drying process to accelerate the drying and removal of volatile matter, thereby improving whiteness, but does not mention the effectiveness of volatile matter removal. Summary of the Invention

[0005] The purpose of this invention is to provide an ultra-low degree of alcoholysis polyvinyl alcohol and its preparation method. The polyvinyl alcohol prepared using this method has the advantages of low volatile content (<1%) and ultra-low degree of alcoholysis (<55%). It can be used in fields requiring high purity of polymerization aids, such as biopharmaceuticals.

[0006] This invention is achieved through the following technical solution:

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

[0008] (1) Polymerization: Mix vinyl acetate, alcohols and initiators to carry out a polymerization reaction.

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

[0010] (3) Precipitation: Add the alcoholysis reaction solution to water to carry out precipitation.

[0011] (4) Washing: Washing 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 is 0.2-1 wt% of vinyl acetate.

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

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

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

[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℃ and the alcoholysis time is 5-60min.

[0021] Preferably, the alcoholysis reaction solution can be directly added to water for precipitation, or it can be mixed with a portion of water before being sprayed into the water, such as by spraying it into the water through a high-speed mixer. Premixing before spraying can help the product precipitate more quickly.

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

[0023] Preferably, in step (3), the mass of water mixed with the alcoholysis reaction solution is 2-6 times the mass of the alcoholysis reaction solution, more 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 or a combination of two or more of sodium dodecyltrimethyl chloride, sodium dodecylbenzenesulfonate, rhamnose ester, and sodium dodecyl sulfate.

[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℃ and the drying time is 1-8 hours. More preferably, the drying temperature is 100-110℃ and the drying time is 1-2 hours.

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

[0029] This application describes a process of precipitating polyvinyl alcohol (PVA) in water with the addition of a stabilizer. This process reduces the surface tension of the reaction droplets during precipitation, promotes the diffusion of methanol into the water, and removes methanol and other reagents from the PVA after alcoholysis. This effectively reduces the volatile content in the PVA product and ensures a high yield.

[0030] The polyvinyl alcohol prepared by this invention has low degree of alcoholysis and low volatile content, and the polyvinyl alcohol has uniform particle size. Detailed Implementation

[0031] Comparative Example 1

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

[0033] The properties of the obtained polyvinyl alcohol are as follows: yield >98%, degree of alcoholysis 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 (AIBN) and place them in a reaction vessel. The reaction temperature is 65℃, and the reaction time is 4 hours. Remove the polyvinyl acetate alcohol solution and add 0.5 times its mass of sodium hydroxide methanol solution (0.4wt%). React at 35℃ for 10 minutes. Neutralize the above reaction solution with 3 times its mass of deionized water and spray it through a high-speed mixer into deionized water containing 1wt% sodium dodecylbenzenesulfonate. The liquid flow rate at the nozzle outlet is 0.09 m / s to allow precipitation. After the solid precipitates, filter it and add 3 times its mass of 75℃ deionized water for washing and filtration to obtain polyvinyl alcohol solid. Dry the solid at 100℃ for 5 hours to obtain the polyvinyl alcohol product.

[0036] The properties of the obtained polyvinyl alcohol are as follows: yield >99.5%, degree of alcoholysis 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 (AIBN) and place them in a reaction vessel. The reaction temperature is 65℃, and the reaction time is 6 hours. Remove the polyvinyl acetate alcohol solution and add 0.1 times its mass of sodium hydroxide methanol solution (0.2wt%). React at 35℃ for 40 minutes. Neutralize the above reaction solution with 5 times its mass of deionized water and spray it through a high-speed mixer into deionized water containing 0.5wt% rhamnosyl ester. The liquid flow rate at the nozzle outlet is 0.45 m / s to allow precipitation. After the solid precipitates, filter it and add 2 times its mass of 75℃ deionized water for washing and filtration to obtain polyvinyl alcohol solid. Dry the solid at 120℃ for 4 hours to obtain the polyvinyl alcohol product.

[0039] The properties of the obtained polyvinyl alcohol are as follows: yield >99.2%, degree of alcoholysis 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 (AIBN) and place them in a reaction vessel. The reaction temperature is 65℃, and the reaction time is 6 hours. Remove the polyvinyl acetate alcohol solution and add 0.1 times its mass of sodium hydroxide methanol solution (0.2wt%). React at 35℃ for 40 minutes. Neutralize the above reaction solution with 3 times its mass of deionized water and spray it into the deionized water through a high-speed mixer at a liquid flow rate of 0.35 m / s at the nozzle outlet to induce precipitation. After the solid precipitates, filter it and add 2 times its mass of 75℃ deionized water for washing and filtration to obtain polyvinyl alcohol solid. Dry the solid at 120℃ for 4 hours to obtain the polyvinyl alcohol product.

[0042] The properties of the obtained polyvinyl alcohol are as follows: yield >99.2%, degree of alcoholysis 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 (AIBN) and place them in a reaction vessel. The reaction temperature is 65℃, and the reaction time is 6 hours. Remove the polyvinyl acetate alcohol solution and add 0.1 times its mass of sodium hydroxide methanol solution (0.2wt%). React at 35℃ for 60 minutes. Neutralize the above reaction solution with 5 times its mass of deionized water and spray it through a high-speed mixer into deionized water containing 0.5wt% rhamnosyl ester. The liquid flow rate at the nozzle outlet is 0.25 m / s to allow precipitation. After the solid precipitates, filter it and add 2 times its mass of 75℃ deionized water for washing and filtration to obtain polyvinyl alcohol solid. Dry the solid at 120℃ for 4 hours to obtain the polyvinyl alcohol product.

[0045] The properties of the obtained polyvinyl alcohol are as follows: yield >99.2%, degree of alcoholysis 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 (AIBN) and place them in a reaction vessel. The reaction temperature is 65℃, and the reaction time is 6 hours. Remove the polyvinyl acetate alcohol solution and add 0.1 times its mass of sodium hydroxide methanol solution (0.2wt%). React at 25℃ for 50 minutes. Neutralize the above reaction solution with 5 times its mass of deionized water and spray it through a high-speed mixer into deionized water containing 0.5wt% rhamnosyl ester. The liquid flow rate at the nozzle outlet is 0.3 m / s to allow precipitation. After the solid precipitates, filter it and add 2 times its mass of 75℃ deionized water for washing and filtration to obtain polyvinyl alcohol solid. Dry the solid at 120℃ for 4 hours to obtain the polyvinyl alcohol product.

[0048] The properties of the obtained polyvinyl alcohol are as follows: yield >99.2%, degree of alcoholysis 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, Includes the following steps: (1) Polymerization: Vinyl acetate, alcohols, and initiators are mixed and polymerized. (2) Alcohololysis: The polyvinyl acetate alcohol solution obtained after the above reaction is mixed with an alcohol solution of alkali to carry out the alcohololysis reaction; (3) Precipitation: Add the alcoholysis reaction solution to water to carry out precipitation; (4) Washing: Washing with water; (5) Drying: Filter and dry to obtain polyvinyl alcohol with low alcoholysis degree; In step (3), the water contains a stabilizer, which is any one or a combination of two or more of sodium dodecyltrimethyl chloride, sodium dodecylbenzenesulfonate, rhamnose ester, and sodium dodecyl sulfate.

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.

3. The preparation method according to claim 1, characterized in that, In step (1), the alcohol is one or more of methanol, ethanol, propanol, isopropanol, and tert-butanol.

4. The preparation method according to claim 1, characterized in that, The initiator is an azo initiator, and the initiator is 0.2-1 wt% of the mass of vinyl acetate.

5. The preparation method according to claim 1, characterized in that, In step (1), the reaction temperature is 60-70℃ and the reaction time is 5-8 hours.

6. The preparation method according to claim 1, characterized in that, The alcohol in the alkaline alcohol solution is one or more of methanol, ethanol, propanol, isopropanol, and tert-butanol.

7. The preparation method according to claim 1, characterized in that, The alkali in an alcoholic solution includes one or more of alkali metal hydroxides, alkaline earth metal hydroxides, and ammonia.

8. The preparation method according to claim 7, characterized in that, The alkali in an alcoholic solution is sodium hydroxide or potassium hydroxide.

9. The preparation method according to claim 1, characterized in that, The mass concentration of alkali in the alcoholic solution of alkali is 0.2wt%-1wt%.

10. The preparation method according to claim 1, characterized in that, The mass concentration of vinyl acetate in the polyvinyl acetate alcohol solution is 5-50 wt%.

11. The preparation method according to claim 1, characterized in that, The mass ratio of the alkali alcohol solution to the polyvinyl acetate alcohol solution is 1:1-10.

12. The preparation method according to claim 1, characterized in that, In step (2), the alcoholysis temperature is 25-65℃ and the alcoholysis time is 5-60min.

13. The preparation method according to claim 1, characterized in that, The alcoholysis reaction solution is either added directly to water for precipitation or mixed with some water first and then sprayed into the water.

14. The preparation method according to claim 1, characterized in that, In step (3), the mass of water mixed with the alcoholysis reaction solution is 2-6 times the mass of the alcoholysis reaction solution.

15. The preparation method according to claim 14, characterized in that, In step (3), the mass of water mixed with the alcoholysis reaction solution is 3-4 times the mass of the alcoholysis reaction solution.

16. The preparation method according to claim 1, characterized in that, The stabilizer has a mass fraction of 0.5-5%.

17. The preparation method according to claim 16, characterized in that, In step (3), the water contains a stabilizer, and the mass fraction of the stabilizer is 1-2%.

18. The preparation method according to claim 1, characterized in that, In step (4), the precipitated polyvinyl alcohol is washed with water at a temperature greater than 65°C.

19. The preparation method according to claim 1, characterized in that, In step (5), the drying temperature is 100-150℃ and the drying time is 1-8 hours.

20. The preparation method according to claim 19, characterized in that, In step (5), the drying temperature is 100-110℃ and the drying time is 1-2 hours.

21. Polyvinyl alcohol prepared by the preparation method according to any one of claims 1-20.