Low-odor polyvinyl alcohol as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polyvinyl alcohol preparation, and discloses low-odor polyvinyl alcohol as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) in the presence of an initiator, contacting a vinyl ester monomer with alcohol to carry out polymerization reaction, then contacting with alkali to carry out alcoholysis reaction, and then crushing to obtain initial polyvinyl alcohol particles; (2) mixing and contacting the initial polyvinyl alcohol particles with an alcoholic solution of acid to terminate the alcoholysis reaction to obtain polyvinyl alcohol; wherein the boiling point of the acid is greater than or equal to 150 DEG C. The polyvinyl alcohol prepared by the preparation method provided by the invention has low odor.

Description

Technical Field

[0001] The present invention relates to the technical field of polyvinyl alcohol preparation, and particularly relates to a low-odor polyvinyl alcohol, a preparation method thereof, and an application thereof. Background Art

[0002] Polyvinyl alcohol (PVA) is a water-soluble synthetic polymer material, which has higher strength and excellent film-forming property compared with other polymer materials, and is widely used in industries such as coatings, adhesives, stabilizers for emulsion polymerization, films, food packaging, cosmetics, and pharmaceuticals.

[0003] In recent years, a new type of cleaning product is becoming popular. This cleaning product is called a laundry bead or a laundry capsule, which is a unit packaging (unit package) of cleaning chemicals such as detergents, bleaches, and enzymes sealed with a water-soluble film. Polyvinyl alcohol has higher strength, toughness, and transparency, and is very suitable for manufacturing water-soluble films for unit packaging.

[0004] Polyvinyl alcohol hydrogel is a polymer material mainly composed of polyvinyl alcohol and water, and is prepared by physical cross-linking or chemical cross-linking of a polyvinyl alcohol solution. Polyvinyl alcohol hydrogel has good biocompatibility and biodegradability, and can be used to prepare medical dressings, artificial corneas, drug sustained-release systems and other medical devices. Polyvinyl alcohol hydrogel can also be used in cosmetics as a moisturizer and thickener, which can improve the consistency and viscosity of cosmetics, making them easier to apply and absorb. In addition, polyvinyl alcohol hydrogel can also be used in the agricultural field as a soil conditioner, which can improve the water retention and fertility of the soil and promote plant growth.

[0005] In addition to requiring polyvinyl alcohol to have low levels of harmful substances such as volatile matter and ash, the quantitative packaging film for cleaning products or the polyvinyl alcohol hydrogel for pharmaceuticals and cosmetics also requires that polyvinyl alcohol does not contain unpleasant odors. However, the preparation method of polyvinyl alcohol makes it contain some unpleasant odors. Although the unpleasant odors in polyvinyl alcohol do not in principle reduce its application performance, they will cause a decrease in consumer acceptance in daily necessities, cosmetics, and medical supplies.

[0006] Therefore, it is of great significance to research and develop a preparation method of low-odor polyvinyl alcohol. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defect that the polyvinyl alcohol prepared by the prior art has a strong odor, and to provide a low-odor polyvinyl alcohol, a preparation method thereof, and an application thereof. The polyvinyl alcohol prepared by the preparation method provided by the present invention has a lower odor.

[0008] To achieve the above object, a first aspect of the present invention provides a method for preparing polyvinyl alcohol, wherein the preparation method includes:

[0009] (1) In the presence of an initiator, contacting a vinyl ester monomer with an alcohol to carry out a polymerization reaction, then contacting with a base to carry out an alcoholysis reaction, and then performing a pulverization treatment to obtain initial polyvinyl alcohol particles;

[0010] (2) Mixing and contacting the initial polyvinyl alcohol particles with an alcoholic solution of an acid to terminate the alcoholysis reaction to obtain polyvinyl alcohol;

[0011] Wherein, the boiling point of the acid ≥ 150 °C.

[0012] A second aspect of the present invention provides a polyvinyl alcohol prepared by the preparation method described above.

[0013] A third aspect of the present invention provides an application of the above-mentioned polyvinyl alcohol in one or more of packaging films, cosmetics, and pharmaceuticals.

[0014] Through the above technical solution, the polyvinyl alcohol prepared by the preparation method of the present invention has a low unpleasant odor. Therefore, it is particularly suitable for use in packaging films, cosmetics, and pharmaceuticals where it is desired to reduce the odor. Detailed Embodiments

[0015] The endpoints and any values disclosed herein are not limited to the exact range or value. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0016] As described above, a first aspect of the present invention provides a method for preparing polyvinyl alcohol, wherein the preparation method includes:

[0017] (1) In the presence of an initiator, contacting a vinyl ester monomer with an alcohol to carry out a polymerization reaction, then contacting with a base to carry out an alcoholysis reaction, and then performing a pulverization treatment to obtain initial polyvinyl alcohol particles;

[0018] (2) Mixing and contacting the initial polyvinyl alcohol particles with an alcoholic solution of an acid to terminate the alcoholysis reaction to obtain polyvinyl alcohol;

[0019] Wherein, the boiling point of the acid ≥ 150 °C.

[0020] The inventors of the present invention unexpectedly found that the unpleasant odor of polyvinyl alcohol (PVA) in the prior art is related to the acid of the neutralizing base catalyst used in the alcoholysis process for preparing polyvinyl alcohol. Acetic acid, propionic acid or methyl acetate are commonly used in the prior art. The inventors of the present invention believe that this odor is produced by the volatile derivatives of these acids or the oxidation products of these derivatives. It is further believed that these derivatives are formed by the reaction of acetic acid, propionic acid or methyl acetate with the thermal decomposition products of PVA, with the polyols used for plasticization, or with unknown by-products in the process of preparing PVA. Furthermore, when PVA is used to prepare products by means of a heat treatment step or a post-crosslinking step, the odor problem becomes particularly serious. Based on this, the inventors of the present invention preferably use one or more low-odor organic acids that are not volatile and are selected from 3-hydroxypropionic acid, 2-hydroxypropionic acid, citric acid, sodium hydrogen citrate, sodium dihydrogen citrate, tartaric acid, sodium hydrogen tartrate, sodium dihydrogen tartrate, malic acid, sodium malate, glutamic acid and aspartic acid to neutralize the base catalyst in the alcoholysis reaction to terminate the alcoholysis reaction, which can solve the defect problem of strong odor of polyvinyl alcohol.

[0021] According to the present invention, the boiling point of the acid is 175-550 °C; preferably, the acid is selected from one or more of 3-hydroxypropionic acid, 2-hydroxypropionic acid, citric acid, sodium hydrogen citrate, sodium dihydrogen citrate, tartaric acid, sodium hydrogen tartrate, sodium dihydrogen tartrate, malic acid, sodium hydrogen malate, glutamic acid and aspartic acid; more preferably, the acid is selected from one or more of 3-hydroxypropionic acid, citric acid, malic acid, glutamic acid, sodium hydrogen citrate and 2-hydroxypropionic acid.

[0022] According to the present invention, in step (1), a vinyl ester monomer is contacted with an alcohol to carry out a polymerization reaction to obtain an alcohol solution containing polyvinyl acetate; the alcohol solution containing polyvinyl acetate is contacted with a base to carry out an alcoholysis reaction and then subjected to a pulverization treatment to obtain initial polyvinyl alcohol particles; wherein, the molar ratio of the amount of the base to the molar amount of the vinyl acetate structural unit in the polyvinyl acetate is (0.004-0.045):1, preferably (0.006-0.02):1.

[0023] According to the present invention, the pH of the alcohol solution of the acid after being fully mixed with the initial polyvinyl alcohol particles is 6-7.

[0024] According to the present invention, the concentration of the alcohol solution of the polyvinyl acetate is 15-45%, preferably 25-36%.

[0025] According to the present invention, the alcoholysis reaction can be carried out by a known method; for example, it can be carried out in a state where the polymer of the present invention is dissolved in an alcohol or a solution containing water and alcohol. The conditions of the alcoholysis reaction include: the temperature is 30 - 50 °C, and the time is 5 - 60 min; preferably, the temperature is 45 - 50 °C, and the time is 20 - 50 min.

[0026] According to the present invention, in step (1), a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades is used. Vinyl ester monomer and alcohol are added, and while stirring, nitrogen replacement is carried out. The reactor is heated up, an initiator is added to start polymerization. After polymerization for a period of time, cooling is carried out and polymerization is stopped; then unreacted monomers are removed to obtain an alcohol solution of polyvinyl acetate (PVAc).

[0027] According to the present invention, the initiator used in the polymerization reaction can be a known initiator selected according to the polymerization method, generally an azo initiator, a peroxide initiator, or a redox initiator; among them, the azo initiator can be 2,2 - azobisisobutyronitrile; the peroxide initiator can be diisopropyl peroxydicarbonate; the redox initiator can be a composition of diisopropyl peroxydicarbonate and sodium bisulfite.

[0028] According to the present invention, the polymerization mode of the vinyl ester monomer can be any one of batch polymerization and continuous polymerization; among them, the polymerization method can be a known method such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc.

[0029] According to the present invention, when carrying out bulk polymerization or solution polymerization, alcohol is usually used as a solvent; among them, lower alcohols are more suitable for solution polymerization, and the lower alcohols are selected from one or more of methanol, ethanol, propanol, and butanol.

[0030] According to the present invention, the conditions of the polymerization reaction include: the temperature is 40 - 70 °C, preferably 55 - 65 °C.

[0031] According to the present invention, the base is sodium hydroxide and / or potassium hydroxide.

[0032] According to the present invention, the vinyl ester monomer is selected from one or more of vinyl acetate, acetic acid vinyl ester, propionic acid vinyl ester, butyric acid vinyl ester, isobutyric acid vinyl ester, trimethylacetic acid vinyl ester, hexanoic acid vinyl ester, octanoic acid vinyl ester, lauric acid vinyl ester, stearic acid vinyl ester, oleic acid vinyl ester, and benzoic acid vinyl ester, and preferably acetic acid vinyl ester.

[0033] According to the present invention, in step (2), an alcohol solution of polyvinyl acetate from which vinyl ester monomers have been removed obtained through a polymerization process is subjected to alcoholysis reaction with an alkali (catalyst) to obtain a polyvinyl alcohol gel block, which is then pulverized to obtain initial polyvinyl alcohol particles. The degree of alcoholysis of the initial polyvinyl alcohol particles is 70 - 98.0 mol%, and the particle size is less than 10 mm. In the present invention, it should be noted that the particle size is the particle size dimension measured by the diameter of the sieve mesh.

[0034] According to the present invention, in step (3), after the alcoholysis is terminated, the alcoholysis solution and the solvent are filtered off, and after washing and drying treatments, polyvinyl alcohol particles are obtained.

[0035] According to the present invention, the washing and drying treatments include: washing the obtained polyvinyl alcohol particles with alcohol, centrifuging to remove the liquid, and then placing them in a vacuum dryer for drying to obtain polyvinyl alcohol.

[0036] According to the present invention, the drying conditions include: the temperature is 100 - 120 °C and the time is 3 - 5 h; preferably, the temperature is 105 - 115 °C and the time is 3 - 4 h.

[0037] The second aspect of the present invention provides a polyvinyl alcohol prepared by the preparation method described above.

[0038] According to the present invention, the odor grade of the polyvinyl alcohol is 1 - 2.

[0039] According to the present invention, the degree of alcoholysis of the polyvinyl alcohol is 70 - 98.0 mol%.

[0040] The third aspect of the present invention provides an application of the polyvinyl alcohol described above in one or more of packaging films, cosmetics, and pharmaceuticals.

[0041] The present invention will be described in detail below through examples.

[0042] In the following examples and comparative examples:

[0043] In the present invention, the degree of polymerization of polyvinyl alcohol is determined according to "GB / T 12010.9 - 1989 Determination Method for Average Degree of Polymerization of Polyvinyl Alcohol Resin";

[0044] In the present invention, the degree of alcoholysis of polyvinyl alcohol is determined according to "GB / T 12010.5 - 2010 Determination Method for Residual Acetic Acid (or Degree of Alcoholysis) of Polyvinyl Alcohol Resin";

[0045] In the present invention, the odor of polyvinyl alcohol is evaluated on a scale of 1-5, wherein 1 indicates no or almost imperceptible self-odor, 2 indicates slight self-odor, 3 indicates obvious self-odor, 4 indicates strong self-odor, and 5 indicates very strong self-odor.

[0046] Example 1

[0047] (1) Polymerization Using a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharge system, a thermometer, a nitrogen feeding system and a stirring blade, vinyl acetate (C 4 H 6 O 2 ) monomer, methanol, while stirring, replacing oxygen in the solution with nitrogen, raising the temperature of the reactor to 64°C, adding initiator azobisisobutyronitrile (AIBN) to start polymerization, and after a period of polymerization, cooling and stopping the polymerization; then removing the unreacted vinyl acetate monomer to obtain a methanol solution of polyvinyl acetate (PVAc), adjusting the concentration of the methanol solution of polyvinyl acetate to 31% by mass for later use;

[0048] (2) At 45°C, sodium hydroxide was added as an alcoholysis catalyst in a ratio of 0.01 molar ratio to the vinyl acetate unit in the polyvinyl acetate in a methanol solution having a concentration of 31% by mass, and an alcoholysis reaction was carried out for 20 minutes. After the alcoholysis, the obtained polyvinyl alcohol (alcoholysis degree of 88 mol%) was coarsely pulverized with a pulverizer to obtain a particle having a diameter of 1.04 mm. The initial PVA particles are formed on the sieve.

[0049] (3) After dissolving 3-hydroxypropionic acid in methanol, gradually add the solution to the polyvinyl alcohol particles and mix thoroughly until the pH value reaches 6.4, thereby terminating the alcoholysis reaction. After the alcoholysis is terminated, filter out the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry at 105° C. for 3 hours to obtain polyvinyl alcohol with an alcoholysis degree of 88 mol %.

[0050] Example 2

[0051] (1) Polymerization Using a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharge system, a thermometer, a nitrogen feeding system and a stirring blade, vinyl acetate (C 4 H 6 O 2(1) Vinyl acetate monomer and methanol were added. While stirring, the oxygen in the solution was replaced with nitrogen. The reactor was heated to 64 °C, and the initiator azobisisobutyronitrile (AIBN) was added to start the polymerization. After polymerization for a period of time, it was cooled and the polymerization was stopped. Then, the unreacted vinyl acetate monomer was removed to obtain a methanol solution of polyvinyl acetate (PVAc). The concentration of the polyvinyl acetate methanol solution was adjusted to 36% by mass for standby.

[0052] (2) At a temperature of 45 °C, in a methanol solution with a polyvinyl acetate concentration of 36% by mass, sodium hydroxide was added as an alcoholysis catalyst at a molar ratio of 0.008 relative to the vinyl acetate units in polyvinyl acetate, and an alcoholysis reaction was carried out for 20 min. After alcoholysis, the obtained polyvinyl alcohol (degree of alcoholysis: 81 mol%) was coarsely pulverized with a pulverizer to obtain initial polyvinyl alcohol particles that passed through a sieve with a diameter .

[0053] (3) 3-Hydroxypropionic acid was dissolved in methanol and then gradually added to the above polyvinyl alcohol particles and mixed well until the pH value reached 6.7 to terminate the alcoholysis reaction. After the alcoholysis was terminated, the alcoholysis solution and the solvent were filtered off, and then washed with methanol to obtain polyvinyl alcohol particles, which were dried at 105 °C for 3 h to obtain polyvinyl alcohol with a degree of alcoholysis of 81 mol%.

[0054] Example 3

[0055] (1) For polymerization, a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades was used. Vinyl acetate (C 4 H 6 O 2 ) monomer and methanol were added. While stirring, the oxygen in the solution was replaced with nitrogen. The reactor was heated to 64 °C, and the initiator azobisisobutyronitrile (AIBN) was added to start the polymerization. After polymerization for a period of time, it was cooled and the polymerization was stopped. Then, the unreacted vinyl acetate monomer was removed to obtain a methanol solution of polyvinyl acetate (PVAc). The concentration of the polyvinyl acetate methanol solution was adjusted to 15% by mass for standby.

[0056] (2) At a temperature of 45 °C, in a methanol solution with a polyvinyl acetate concentration of 15% by mass, sodium hydroxide was added as an alcoholysis catalyst at a molar ratio of 0.045 relative to the vinyl acetate units in polyvinyl acetate, and an alcoholysis reaction was carried out for 20 min. After alcoholysis, the obtained polyvinyl alcohol (degree of alcoholysis: 98 mol%) was coarsely pulverized with a pulverizer to obtain initial polyvinyl alcohol particles that passed through a sieve with a diameter .

[0057] (3) Dissolve 3-hydroxypropionic acid in methanol, and gradually add it to the above-mentioned polyvinyl alcohol particles and mix well until the pH value reaches 6.9 to terminate the alcoholysis reaction. After the alcoholysis is terminated, filter off the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry them at 105 °C for 3 h to obtain polyvinyl alcohol with an alcoholysis degree of 98 mol%.

[0058] Example 4

[0059] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2 ) monomer and methanol, displace the oxygen in the solution with nitrogen while stirring, heat the reactor to 64 °C, add the initiator azobisisobutyronitrile (AIBN) to start polymerization. After polymerization for a period of time, cool down and stop the polymerization; then remove the unreacted vinyl acetate monomer to obtain a methanol solution of polyvinyl acetate (PVAc), and adjust the concentration of the polyvinyl acetate methanol solution to 45% by mass for standby;

[0060] (2) At a temperature of 45 °C, add sodium hydroxide to a methanol solution with a polyvinyl acetate concentration of 45% by mass as an alcoholysis catalyst at a molar ratio of 0.004 relative to the vinyl acetate units in the polyvinyl acetate, and carry out an alcoholysis reaction for 20 min. After alcoholysis, coarsely crush the obtained polyvinyl alcohol (alcoholysis degree of 70 mol%) with a pulverizer to obtain initial polyvinyl alcohol particles that have passed through a sieve with a diameter of the sieve.

[0061] (3) Dissolve 3-hydroxypropionic acid in methanol, and gradually add it to the above-mentioned polyvinyl alcohol particles and mix well until the pH value reaches 6.1 to terminate the alcoholysis reaction. After the alcoholysis is terminated, filter off the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry them at 105 °C for 3 h to obtain polyvinyl alcohol with an alcoholysis degree of 70 mol%.

[0062] Example 5

[0063] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2The monomer, vinyl acetate, and methanol were used. While stirring, the oxygen in the solution was replaced with nitrogen. The reactor was heated to 64 °C, and the initiator azobisisobutyronitrile (AIBN) was added to start the polymerization. After polymerization for a certain period of time, it was cooled and the polymerization was stopped. Then, the unreacted vinyl acetate monomer was removed to obtain a methanol solution of polyvinyl acetate (PVAc). The concentration of the polyvinyl acetate methanol solution was adjusted to 25% by mass for standby.

[0064] (2) Under the condition of a temperature of 45 °C, in a methanol solution with a concentration of 25% by mass of polyvinyl acetate, sodium hydroxide was added as an alcoholysis catalyst at a molar ratio of 0.02 relative to the vinyl acetate units in the polyvinyl acetate, and an alcoholysis reaction was carried out for 20 min. After alcoholysis, the obtained polyvinyl alcohol (degree of alcoholysis: 75 mol%) was coarsely pulverized with a pulverizer to obtain the initial polyvinyl alcohol particles that passed through a sieve with a diameter specified.

[0065] (3) 3-Hydroxypropionic acid was dissolved in methanol and then gradually added to the above-mentioned polyvinyl alcohol particles and mixed well until the pH value reached 6.2 to terminate the alcoholysis reaction. After the alcoholysis was terminated, the alcoholysis solution and the solvent were filtered off, and then washed with methanol to obtain polyvinyl alcohol particles, which were dried at 105 °C for 3 h to obtain polyvinyl alcohol with a degree of alcoholysis of 75 mol%.

[0066] Example 6

[0067] (1) For the polymerization, a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades was used. Vinyl acetate (C 4 H 6 O 2 ) monomer and methanol were added. While stirring, the oxygen in the solution was replaced with nitrogen. The reactor was heated to 64 °C, and the initiator azobisisobutyronitrile (AIBN) was added to start the polymerization. After polymerization for a certain period of time, it was cooled and the polymerization was stopped. Then, the unreacted vinyl acetate monomer was removed to obtain a methanol solution of polyvinyl acetate (PVAc). The concentration of the polyvinyl acetate methanol solution was adjusted to 31% by mass for standby.

[0068] (2) Under the condition of a temperature of 45 °C, in a methanol solution with a concentration of 31% by mass of polyvinyl acetate, sodium hydroxide was added as an alcoholysis catalyst at a molar ratio of 0.01 relative to the vinyl acetate units in the polyvinyl acetate, and an alcoholysis reaction was carried out for 20 min. After alcoholysis, the obtained polyvinyl alcohol (degree of alcoholysis: 90 mol%) was coarsely pulverized with a pulverizer to obtain the initial polyvinyl alcohol particles that passed through a sieve with a diameter specified.

[0069] (3) Dissolve citric acid in methanol, and gradually add it to the above-mentioned polyvinyl alcohol particles and mix well until the pH value reaches 6.4 to terminate the alcoholysis reaction. After the alcoholysis is terminated, filter off the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry them at 105 °C for 3 h to obtain polyvinyl alcohol with an alcoholysis degree of 90 mol%.

[0070] Example 7

[0071] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2 ) monomer and methanol, displace the oxygen in the solution with nitrogen while stirring, heat the reactor to 64 °C, add the initiator azobisisobutyronitrile (AIBN) to start polymerization. After polymerizing for a period of time, cool down and stop the polymerization; then remove the unreacted vinyl acetate monomer to obtain a methanol solution of polyvinyl acetate (PVAc), and adjust the concentration of the polyvinyl acetate methanol solution to 31% by mass for standby;

[0072] (2) At a temperature of 45 °C, add sodium hydroxide as an alcoholysis catalyst in a methanol solution with a polyvinyl acetate concentration of 31% by mass at a molar ratio of 0.01 relative to the vinyl acetate units in the polyvinyl acetate, and carry out an alcoholysis reaction for 20 min. After the alcoholysis, coarsely crush the obtained polyvinyl alcohol (with an alcoholysis degree of 85 mol%) with a pulverizer to obtain initial polyvinyl alcohol particles that have passed through a sieve with a diameter of the sieve.

[0073] (3) Dissolve malic acid in methanol, and gradually add it to the above-mentioned polyvinyl alcohol particles and mix well until the pH value reaches 6.4 to terminate the alcoholysis reaction. After the alcoholysis is terminated, filter off the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry them at 105 °C for 3 h to obtain polyvinyl alcohol with an alcoholysis degree of 85 mol%.

[0074] Example 8

[0075] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2(1) Add vinyl acetate monomer and methanol to a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. While stirring, displace the oxygen in the solution with nitrogen. Heat the reactor to 64 °C, add the initiator azobisisobutyronitrile (AIBN) to start polymerization. After polymerizing for a period of time, cool down and stop the polymerization. Then remove the unreacted vinyl acetate monomer to obtain a methanol solution of polyvinyl acetate (PVAc), and adjust the concentration of the polyvinyl acetate methanol solution to 31% by mass for standby.

[0076] (2) Under the temperature condition of 45 °C, add sodium hydroxide as an alcoholysis catalyst to a methanol solution with a polyvinyl acetate concentration of 31% by mass at a molar ratio of 0.01 relative to the vinyl acetate units in the polyvinyl acetate, and carry out an alcoholysis reaction for 20 min. After alcoholysis, coarsely crush the obtained polyvinyl alcohol (degree of alcoholysis: 86 mol%) with a pulverizer to obtain initial polyvinyl alcohol particles that have passed through a sieve with a diameter of .

[0077] (3) Dissolve glutamic acid in methanol, and gradually add it to the above polyvinyl alcohol particles and mix well until the pH value reaches 6.3 to terminate the alcoholysis reaction. After the alcoholysis is terminated, filter out the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry them at 105 °C for 3 h to obtain polyvinyl alcohol with a degree of alcoholysis of 86 mol%.

[0078] Example 9

[0079] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2 ) monomer and methanol. While stirring, displace the oxygen in the solution with nitrogen. Heat the reactor to 64 °C, add the initiator azobisisobutyronitrile (AIBN) to start polymerization. After polymerizing for a period of time, cool down and stop the polymerization. Then remove the unreacted vinyl acetate monomer to obtain a methanol solution of polyvinyl acetate (PVAc), and adjust the concentration of the polyvinyl acetate methanol solution to 31% by mass for standby.

[0080] (2) Under the temperature condition of 45 °C, add sodium hydroxide as an alcoholysis catalyst to a methanol solution with a polyvinyl acetate concentration of 31% by mass at a molar ratio of 0.01 relative to the vinyl acetate units in the polyvinyl acetate, and carry out an alcoholysis reaction for 20 min. After alcoholysis, coarsely crush the obtained polyvinyl alcohol (degree of alcoholysis: 89 mol%) with a pulverizer to obtain initial polyvinyl alcohol particles that have passed through a sieve with a diameter of .

[0081] (3) Dissolve 2-hydroxypropanoic acid in methanol, and gradually add it to the above-mentioned polyvinyl alcohol particles and mix well until the pH value reaches 6.1 to terminate the alcoholysis reaction. After the alcoholysis is terminated, filter out the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry them at 105 °C for 3 h to obtain polyvinyl alcohol with an alcoholysis degree of 89 mol%.

[0082] Example 10

[0083] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2 ) monomer and methanol. While stirring, displace the oxygen in the solution with nitrogen. Heat the reactor to 64 °C, add the initiator azobisisobutyronitrile (AIBN) to start polymerization. After polymerizing for a period of time, cool down and stop the polymerization; then remove the unreacted vinyl acetate monomer to obtain a methanol solution of polyvinyl acetate (PVAc), and adjust the concentration of the polyvinyl acetate methanol solution to 31% by mass for standby;

[0084] (2) Under the temperature condition of 45 °C, add sodium hydroxide to the methanol solution with a polyvinyl acetate concentration of 31% by mass as an alcoholysis catalyst at a molar ratio of 0.01 relative to the vinyl acetate units in polyvinyl acetate, and carry out an alcoholysis reaction for 20 min. After the alcoholysis, coarsely crush the obtained polyvinyl alcohol (with an alcoholysis degree of 88 mol%) with a crusher to obtain initial polyvinyl alcohol particles that have passed through a sieve with a diameter .

[0085] (3) Dissolve tartaric acid in methanol, and gradually add it to the above-mentioned polyvinyl alcohol particles and mix well until the pH value reaches 6.3 to terminate the alcoholysis reaction. After the alcoholysis is terminated, filter out the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry them at 105 °C for 3 h to obtain polyvinyl alcohol with an alcoholysis degree of 88 mol%.

[0086] Example 11

[0087] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2The monomer and methanol were used. While stirring, the oxygen in the solution was replaced with nitrogen. The reactor was heated to 64 °C, and the initiator azobisisobutyronitrile (AIBN) was added to start the polymerization. After polymerization for a certain period of time, it was cooled and the polymerization was stopped. Then, the unreacted vinyl acetate monomer was removed to obtain a methanol solution of polyvinyl acetate (PVAc), and the concentration of the polyvinyl acetate methanol solution was adjusted to 31% by mass for standby.

[0088] (2) Under the temperature condition of 45 °C, in a methanol solution with a polyvinyl acetate concentration of 31% by mass, sodium hydroxide was added as an alcoholysis catalyst at a molar ratio of 0.01 relative to the vinyl acetate units in the polyvinyl acetate, and an alcoholysis reaction was carried out for 20 min. After alcoholysis, the obtained polyvinyl alcohol (degree of alcoholysis: 88 mol%) was coarsely pulverized with a pulverizer to obtain the initial polyvinyl alcohol particles that passed through a sieve with a diameter .

[0089] (3) Aspartic acid was dissolved in methanol and then gradually added to the above polyvinyl alcohol particles and mixed well until the pH value reached 6.4 to terminate the alcoholysis reaction. After the alcoholysis was terminated, the alcoholysis solution and the solvent were filtered off, and then washed with methanol to obtain polyvinyl alcohol particles, which were dried at 105 °C for 3 h to obtain polyvinyl alcohol with a degree of alcoholysis of 88 mol%.

[0090] Example 12

[0091] (1) For polymerization, a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades was used. Vinyl acetate (C 4 H 6 O 2 ) monomer and methanol were added. While stirring, the oxygen in the solution was replaced with nitrogen. The reactor was heated to 64 °C, and the initiator azobisisobutyronitrile (AIBN) was added to start the polymerization. After polymerization for a certain period of time, it was cooled and the polymerization was stopped. Then, the unreacted vinyl acetate monomer was removed to obtain a methanol solution of polyvinyl acetate (PVAc), and the concentration of the polyvinyl acetate methanol solution was adjusted to 31% by mass for standby.

[0092] (2) Under the temperature condition of 45 °C, in a methanol solution with a polyvinyl acetate concentration of 31% by mass, sodium hydroxide was added as an alcoholysis catalyst at a molar ratio of 0.01 relative to the vinyl acetate units in the polyvinyl acetate, and an alcoholysis reaction was carried out for 20 min. After alcoholysis, the obtained polyvinyl alcohol (degree of alcoholysis: 87 mol%) was coarsely pulverized with a pulverizer to obtain the initial polyvinyl alcohol particles that passed through a sieve with a diameter .

[0093] (3) Dissolve sodium hydrogen malate in methanol and gradually add it to the above-mentioned polyvinyl alcohol particles for thorough mixing until the pH value reaches 6.2 to terminate the alcoholysis reaction. After the alcoholysis is terminated, filter off the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry them at 105 °C for 3 h to obtain polyvinyl alcohol with an alcoholysis degree of 87 mol%.

[0094] Comparative Example 1

[0095] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2 ) monomer and methanol. While stirring, displace the oxygen in the solution with nitrogen. Heat the reactor to 64 °C, add the initiator azobisisobutyronitrile (AIBN) to start polymerization. After polymerization for a period of time, cool down and stop the polymerization; then remove the unreacted vinyl acetate monomer to obtain a methanol solution of polyvinyl acetate (PVAc), and adjust the concentration of the polyvinyl acetate methanol solution to 31% by mass for standby;

[0096] (2) At a temperature of 45 °C, add sodium hydroxide to a methanol solution with a polyvinyl acetate concentration of 31% by mass at a molar ratio of 0.01 relative to the vinyl acetate units in the polyvinyl acetate as an alcoholysis catalyst, and carry out an alcoholysis reaction for 20 min. After alcoholysis, coarsely crush the obtained polyvinyl alcohol (alcoholysis degree of 88 mol%) with a pulverizer to obtain the initial polyvinyl alcohol particles that have passed through a sieve with a diameter of the sieve.

[0097] (3) Dissolve acetic acid in methanol and gradually add it to the above-mentioned polyvinyl alcohol particles for thorough mixing until the pH value reaches 6.4 to terminate the alcoholysis reaction. After the alcoholysis is terminated, filter off the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry them at 105 °C for 3 h to obtain polyvinyl alcohol with an alcoholysis degree of 88 mol%.

[0098] Comparative Example 2

[0099] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2(1) Add vinyl acetate monomer and methanol, and while stirring, displace the oxygen in the solution with nitrogen. Heat the reactor to 64 °C, add the initiator azobisisobutyronitrile (AIBN) to start polymerization. After polymerizing for a period of time, cool down and stop the polymerization. Then remove the unreacted vinyl acetate monomer to obtain a methanol solution of polyvinyl acetate (PVAc), and adjust the concentration of the polyvinyl acetate methanol solution to 31% by mass for standby.

[0100] (2) At a temperature of 45 °C, in a methanol solution with a polyvinyl acetate concentration of 31% by mass, add sodium hydroxide as an alcoholysis catalyst at a molar ratio of 0.01 relative to the vinyl acetate units in polyvinyl acetate, and carry out an alcoholysis reaction for 20 min. After alcoholysis, coarsely crush the obtained polyvinyl alcohol (degree of alcoholysis: 87 mol%) with a pulverizer to obtain initial polyvinyl alcohol particles that have passed through a sieve with a diameter of .

[0101] (3) Dissolve propionic acid in methanol, and gradually add it to the above polyvinyl alcohol particles and mix well until the pH value reaches 6.4 to terminate the alcoholysis reaction. After terminating the alcoholysis, filter out the alcoholysis solution and the solvent, then wash with methanol to obtain polyvinyl alcohol particles, and dry them at 105 °C for 3 h to obtain polyvinyl alcohol with a degree of alcoholysis of 87 mol%.

[0102] Comparative Example 3

[0103] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2 ) monomer and methanol, and while stirring, displace the oxygen in the solution with nitrogen. Heat the reactor to 64 °C, add the initiator azobisisobutyronitrile (AIBN) to start polymerization. After polymerizing for a period of time, cool down and stop the polymerization. Then remove the unreacted vinyl acetate monomer to obtain a methanol solution of polyvinyl acetate (PVAc), and adjust the concentration of the polyvinyl acetate methanol solution to 31% by mass for standby.

[0104] (2) At a temperature of 45 °C, in a methanol solution with a polyvinyl acetate concentration of 31% by mass, add sodium hydroxide as an alcoholysis catalyst at a molar ratio of 0.01 relative to the vinyl acetate units in polyvinyl acetate, and carry out an alcoholysis reaction for 20 min. After alcoholysis, coarsely crush the obtained polyvinyl alcohol (degree of alcoholysis: 86 mol%) with a pulverizer to obtain initial polyvinyl alcohol particles that have passed through a sieve with a diameter of .

[0105] (3) After dissolving methyl acetate in methanol, gradually add it to the above-mentioned polyvinyl alcohol particles and mix well until the pH value reaches 6.5, then terminate the alcoholysis reaction. After the alcoholysis is terminated, filter out the alcoholysis solution and the solvent, and then wash with methanol to obtain polyvinyl alcohol particles. Dry them at 105 °C for 3 h to obtain polyvinyl alcohol with an alcoholysis degree of 86 mol%.

[0106] Comparative Example 4

[0107] (1) For polymerization, use a polymerization kettle equipped with a reflux condenser, a raw material feeding system, a reaction liquid discharging system, a thermometer, a nitrogen adding system, and stirring blades. Add vinyl acetate (C 4 H 6 O 2 ) monomer and methanol. While stirring, displace the oxygen in the solution with nitrogen. Heat the reactor to 64 °C, add the initiator azobisisobutyronitrile (AIBN) to start the polymerization. After polymerizing for a period of time, cool down and stop the polymerization. Then remove the unreacted vinyl acetate monomer to obtain a methanol solution of polyvinyl acetate (PVAc), and adjust the concentration of the polyvinyl acetate methanol solution to 31% by mass for standby;

[0108] (2) At a temperature of 45 °C, add sodium hydroxide to a methanol solution with a polyvinyl acetate concentration of 31% by mass as an alcoholysis catalyst in a molar ratio of 0.01 relative to the vinyl acetate units in the polyvinyl acetate, and carry out an alcoholysis reaction for 20 min. After the alcoholysis, coarsely crush the obtained polyvinyl alcohol (alcoholysis degree of 88 mol%) with a pulverizer to obtain initial polyvinyl alcohol particles that have passed through a sieve with a diameter of .

[0109] (3) After dissolving acetic acid in methanol, gradually add it to the above-mentioned polyvinyl alcohol particles and mix well until the pH value reaches 6.7, then terminate the alcoholysis reaction. After the alcoholysis is terminated, filter out the alcoholysis solution and the solvent, and then wash with methanol to obtain polyvinyl alcohol particles. Dry them at 105 °C for 3 h to obtain polyvinyl alcohol with an alcoholysis degree of 88 mol%.

[0110] In addition, specifically, the conditions in the methods for preparing polyvinyl alcohol in Examples 1-12 and Comparative Examples 1-4 are shown in Table 1.

[0111] Test Example

[0112] Evaluate the odor of the polyvinyl alcohol prepared in Examples 1-12 and Comparative Examples 1-4. Specifically, heat 5 samples of 20 g each of the polyvinyl alcohol in a hermetically sealed sample container at 40 °C for 5 h, and then rate them on a scale of 1-5. The results are shown in Table 2.

[0113] Table 1

[0114]

[0115]

[0116] Table 2

[0117]

[0118]

[0119] As can be seen from the results in Table 2, the polyvinyl alcohol prepared by the preparation method of the present invention has a low unpleasant odor and can be used in packaging films, cosmetics or pharmaceuticals.

[0120] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing polyvinyl alcohol, characterized in that, the preparation method includes: (1) In the presence of an initiator, contacting a vinyl ester monomer with an alcohol for a polymerization reaction, then contacting with a base for an alcoholysis reaction and then subjecting to a pulverization treatment to obtain initial polyvinyl alcohol particles; (2) Mixing and contacting the initial polyvinyl alcohol particles with an alcoholic solution of an acid to terminate the alcoholysis reaction to obtain polyvinyl alcohol; wherein, the boiling point of the acid ≥ 150 °C.

2. The preparation method according to claim 1, wherein, the boiling point of the acid is 175 - 550 °C; Preferably, the acid is selected from one or more of 3-hydroxypropionic acid, 2-hydroxypropionic acid, citric acid, sodium hydrogen citrate, sodium dihydrogen citrate, tartaric acid, sodium hydrogen tartrate, sodium dihydrogen tartrate, malic acid, sodium hydrogen malate, glutamic acid and aspartic acid; More preferably, the acid is selected from one or more of 3-hydroxypropionic acid, citric acid, malic acid, glutamic acid, sodium hydrogen citrate and 2-hydroxypropionic acid.

3. The preparation method according to claim 1 or 2, wherein, In step (1), contacting a vinyl ester monomer with an alcohol for a polymerization reaction to obtain an alcoholic solution containing polyvinyl acetate; Preferably, the molar ratio of the amount of the base to the molar amount of the vinyl acetate structural unit in the polyvinyl acetate is (0.004 - 0.045):

1.

4. The preparation method according to any one of claims 1 - 3, wherein, The pH after the alcoholic solution of the acid is sufficiently mixed with the initial polyvinyl alcohol particles is 6 - 7.

5. The preparation method according to claim 1, wherein, The vinyl ester monomer is selected from one or more of vinyl acetate, vinyl acetate, vinyl propionate, vinyl butyrate, isobutyl vinyl acetate, trimethylacetic acid vinyl ester, vinyl hexanoate, vinyl octanoate, vinyl laurate, vinyl stearate, vinyl oleate and vinyl benzoate, preferably vinyl acetate.

6. The preparation method according to claim 1, wherein, The particle size of the initial polyvinyl alcohol particles is less than 10 mm.

7. A polyvinyl alcohol prepared by the preparation method according to any one of claims 1 - 6.

8. The polyvinyl alcohol according to claim 7, wherein, The odor grade of the polyvinyl alcohol is 1 - 2.

9. The polyvinyl alcohol according to claim 7 or 8, wherein, The alcoholysis degree of the polyvinyl alcohol is 70 - 98 mol%.

10. An application of the polyvinyl alcohol according to any one of claims 7 - 9 in one or more of packaging films, cosmetics and pharmaceuticals.

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