Polyvinyl alcohol and preparation method thereof

Abstract

According to the polyvinyl alcohol and the preparation method thereof provided by the invention, the polyvinyl alcohol is prepared by taking 2-acrylamide-2-methylpropanesulfonic acid and dodecyl vinyl ether as reactive compound emulsifiers, and a hydrophilic sulfonic acid group and a soft-segment long-chain alkyl ether chain can be introduced into a polyvinyl alcohol molecular chain; on the basis of keeping the hydrophilicity, barrier property, biocompatibility and biodegradability of the polyvinyl alcohol, the flexibility and hydrolysis resistance of the polyvinyl alcohol are improved.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and particularly relates to polyvinyl alcohol and a preparation method thereof. Background Art

[0002] Polyvinyl alcohol (PVA) is a water-soluble functional polymer material with strong film-forming properties. The film it forms has the characteristics of transparency, good mechanical properties, and strong gas barrier capacity. It has excellent biocompatibility and biodegradability, and can be degraded into CO2 and H2O under the action of microorganisms. Therefore, it is widely used in daily necessities, papermaking, textiles, coatings, batteries, electronic components, biomedicine and other fields.

[0003] However, PVA has poor water resistance. This is because the side chains of PVA polymers contain a large number of hydrophilic hydroxyl groups, which are easy to form intramolecular and intermolecular hydrogen bonds. They are also prone to strong affinity for water in the dry and wet changes of the external environment, destroying the intramolecular and intermolecular hydrogen bonds of PVA molecules, causing PVA to swell and then lose its excellent performance in mechanical properties, barrier properties, etc., which greatly limits its further promotion and application.

[0004] At present, the improvement of PVA water resistance is mainly to modify PVA polymer to improve its water resistance, including physical modification and chemical modification. Physical modification is mainly to form hydrogen bonds and coordination bonds between PVA side chain hydroxyl groups and modifiers. For example, patent CN201510816800.5 adds tin tetrachloride to modify commercially available polyvinyl alcohol, and uses the strong coordination ability of tin ions to form a complex with the side chain hydroxyl groups of PVA. After film formation, it can exist stably in aqueous solution, and then significantly improve the water resistance of polyvinyl alcohol film; patent CN2018103209445 makes polyvinyl alcohol and chitosan or silicon dioxide simply physically blended, and prepares a composite modified film by forming hydrogen bonds between the side chain hydroxyl groups of PVA and chitosan or silicon dioxide to improve water resistance. Chemical modification mainly involves reacting the side chain hydroxyl groups of PVA with the modifier to form a stable chemical bond. For example, in Patent 201610289989.1, some hydroxyl groups in polyvinyl alcohol are partially oxidized to generate chemically active aldehyde groups. Under alkaline conditions, the resulting solution is reacted with amide substances to undergo a hydroxymethylation reaction to generate hydroxymethyl derivatives. During the coating and film-forming process, the hydroxyl groups are oxidized to form chemically active aldehyde groups. At 100°C, these hydroxymethyl derivatives undergo condensation reaction to form a partially self-crosslinked film, which significantly improves the water resistance and oxygen barrier properties of the PVA film. Patent 201510296306.0 causes the carboxyl group of maleic anhydride to undergo esterification reaction with the hydroxyl group of the PVA side chain to obtain maleic anhydride-grafted PVA, and reacts with a sodium silicate solution under the catalysis of concentrated sulfuric acid to obtain an inorganic silicon-maleic anhydride-grafted polyvinyl alcohol material. After the inorganic silicon-maleic anhydride-grafted polyvinyl alcohol material is formed into a film, it has good water resistance without heat treatment. No obvious swelling was found when the film-forming material was immersed in a boiling water bath for 4 hours, and there was no cracking or damage on the film surface.

[0005] However, existing physical and chemical modifications of PVA polymers require the preparation of PVA solutions first. PVA polymers are prone to swelling during the preparation of solutions dispersed in solvents, resulting in unsatisfactory modification effects. Physical modification has the defect of insufficient durability of the modification effect. In addition, during the chemical modification process, gelation is easily caused if the temperature is too high, the time is too long, and the content of modifier is too high. While, unsatisfactory modification effects are easily caused if the temperature is too low, the time is too short, and the content of modifier is insufficient. Summary of the invention

[0006] In order to overcome the problems existing in the prior art, the purpose of the present invention is to provide a polyvinyl alcohol and a method for preparing polyvinyl alcohol, wherein 2-acrylamide-2-methylpropane sulfonic acid and dodecyl vinyl ether are used as reactive compound emulsifiers to prepare polyvinyl alcohol, and hydrophilic sulfonic acid groups and soft segment long-chain alkyl ether chains can be introduced into the polyvinyl alcohol molecular chain, thereby improving the flexibility and hydrolysis resistance of polyvinyl alcohol while maintaining its hydrophilicity, barrier properties, biocompatibility and biodegradability.

[0007] The objective of the present invention is achieved through the following technical solutions: A polyvinyl alcohol, whose raw materials include 20-60 parts of vinyl acetate, 0.5-1.5 parts of 2-acrylamide-2-methylpropane sulfonic acid, 0.5-1.5 parts of dodecyl vinyl ether, 0.05-0.1 parts of oxidant, 0.03-0.15 parts of reducing agent, 0.01-0.5 parts of sodium chloride and 100-300 parts of deionized water.

[0008] Preferably, the molar ratio of 2-acrylamide-2-methylpropanesulfonic acid to dodecyl vinyl ether is 1-2:1.

[0009] Preferably, the molar ratio of 2-acrylamide-2-methylpropanesulfonic acid to dodecyl vinyl ether is 1:1.

[0010] Preferably, a polyvinyl alcohol, whose raw materials include 40-50 parts of vinyl acetate, 0.8-1.2 parts of 2-acrylamide-2-methylpropane sulfonic acid, 0.8-1.2 parts of dodecyl vinyl ether, 0.08-0.1 parts of oxidant, 0.06-0.13 parts of reducing agent, 0.01-0.3 parts of sodium chloride, and 150-250 parts of deionized water.

[0011] Preferably, a polyvinyl alcohol, whose raw materials include 50 parts of vinyl acetate, 1 part of 2-acrylamide-2-methylpropane sulfonic acid, 1 part of dodecyl vinyl ether, 0.08 parts of oxidant, 0.12 parts of reducing agent, 0.09 parts of sodium chloride, and 200 parts of deionized water.

[0012] Preferably, the oxidant is one or more of potassium persulfate, sodium persulfate, ammonium persulfate, and hydrogen peroxide.

[0013] Preferably, the reducing agent is one or more of sodium bisulfite, ferrous chloride, tartaric acid, mercaptan, and VC.

[0014] A method for preparing polyvinyl alcohol comprises the following reaction steps: Step 1, adding vinyl acetate, 2-acrylamide-2-methylpropanesulfonic acid, dodecyl vinyl ether, a reducing agent, sodium chloride and deionized water into a reaction device, stirring at room temperature and passing nitrogen to prepare a solution A; Step 2, raising the temperature to 35°C, adding the oxidant dropwise, and completing the addition within 2 hours, continuing the reaction for 0.5-1 hour, lowering the temperature to room temperature, and ending the reaction to obtain a polymerization product B; Step 3, freezing at -10°C - 5°C for 5-12 hours, thawing at room temperature for 2-5 hours, filtering, and drying at 75°C -85°C to obtain 2-acrylamide-2-methylpropane sulfonic acid / dodecyl vinyl ether / vinyl acetate resin.

[0015] Step 4, dissolving the 2-acrylamide-2-methylpropane sulfonic acid / dodecyl vinyl ether / vinyl acetate resin obtained in step 3 in methanol to obtain a solution with a mass fraction of 10%-16%, adding sodium hydroxide methanol solution (solution mass fraction 30%) for alcoholysis to obtain the target polyvinyl alcohol resin.

[0016] Preferably, the molar ratio of 2-acrylamide-2-methylpropane sulfonic acid / dodecyl vinyl ether / vinyl acetate resin and sodium hydroxide is 1:0.015-0.025.

[0017] Preferably, the molar ratio of 2-acrylamide-2-methylpropane sulfonic acid / dodecyl vinyl ether / vinyl acetate resin and sodium hydroxide is 1:0.02.

[0018] Beneficial effects: 1. The polyvinyl alcohol resin of the present invention is prepared by emulsion polymerization, and reactive emulsifiers 2-acrylamide-2-methylpropane sulfonic acid and dodecyl vinyl ether are used as compound emulsifiers, which can not only exert the excellent emulsifying effect of the compound emulsifier, but also obtain 2-acrylamide-2-methylpropane sulfonic acid / dodecyl vinyl ether / polyvinyl alcohol resin by copolymerization, introduce functional groups into the molecular chain of the polyvinyl alcohol resin, and improve the performance of polyvinyl alcohol.

[0019] 2. The polyvinyl alcohol resin of the present invention uses 2-acrylamide-2-methylpropane sulfonic acid and dodecyl vinyl ether as reactive compound emulsifiers to prepare polyvinyl alcohol, and obtains 2-acrylamide-2-methylpropane sulfonic acid / dodecyl vinyl ether / polyvinyl alcohol resin by copolymerization, which can introduce hydrophilic sulfonic acid groups and soft segment long-chain alkyl ether chains into the polyvinyl alcohol molecular chain, thereby improving the flexibility and hydrolysis resistance of polyvinyl alcohol while maintaining its hydrophilicity, barrier properties, biocompatibility and biodegradability. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] The present invention is further explained below in conjunction with specific implementation modes.

[0022] Example 1 A polyvinyl alcohol, the preparation method of which comprises the following reaction steps: Step 1, 50 parts of vinyl acetate, 1 part of 2-acrylamide-2-methylpropanesulfonic acid, 1 part of dodecyl vinyl ether, 0.12 parts of reducing agent VC, 0.09 parts of sodium chloride and 200 parts of deionized water are added into a reaction device, stirred at room temperature and purged with nitrogen to prepare a solution A; Step 2, raising the temperature to 35°C, adding oxidant potassium persulfate dropwise (adding 0.08 parts of potassium persulfate to water to prepare a 30% by mass potassium persulfate aqueous solution), the dripping is completed within 2 hours, and the reaction is continued for 0.5-1 hour, and the temperature is lowered to room temperature to terminate the reaction to obtain a polymerization product B; Step 3, freezing at -10°C to -5°C for 10 hours, thawing at room temperature for 5 hours, filtering, and drying at 80°C to obtain 2-acrylamide-2-methylpropane sulfonic acid / dodecyl vinyl ether / vinyl acetate resin.

[0023] Step 4: dissolve the 2-acrylamide-2-methylpropanesulfonic acid / dodecyl vinyl ether / vinyl acetate resin obtained in step 3 in methanol to obtain a solution with a mass fraction of 15%, and add a sodium hydroxide methanol solution (solution mass fraction 30%) for alcoholysis to obtain the target polyvinyl alcohol resin. The molar ratio of 2-acrylamide-2-methylpropanesulfonic acid / dodecyl vinyl ether / vinyl acetate resin to sodium hydroxide is 1:0.02.

[0024] Comparative Example 1 A polyvinyl alcohol, the preparation method of which comprises the following reaction steps: Step 1, 50 parts of vinyl acetate, 1 part of 2-acrylamide-2-methylpropanesulfonic acid, 1 part of Tween 20, 0.12 parts of reducing agent VC, 0.09 parts of sodium chloride and 200 parts of deionized water are added into a reaction device, stirred at room temperature and purged with nitrogen to prepare a solution A; Step 2, raising the temperature to 35°C, adding oxidant potassium persulfate dropwise (adding 0.08 parts of potassium persulfate to water to prepare a 30% by mass potassium persulfate aqueous solution), the dripping is completed within 2 hours, and the reaction is continued for 0.5-1 hour, and the temperature is lowered to room temperature to terminate the reaction to obtain a polymerization product B; Step 3, freezing at -10°C to -5°C for 10 hours, thawing at room temperature for 5 hours, filtering, and drying at 80°C to obtain 2-acrylamide-2-methylpropanesulfonic acid / vinyl acetate resin.

[0025] Step 4: dissolve the 2-acrylamide-2-methylpropanesulfonic acid / vinyl acetate resin obtained in step 3 in methanol to obtain a solution with a mass fraction of 15%, and add a sodium hydroxide methanol solution (solution mass fraction 30%) for alcoholysis to obtain the target polyvinyl alcohol resin. The molar ratio of 2-acrylamide-2-methylpropanesulfonic acid / vinyl acetate resin to sodium hydroxide is 1:0.02.

[0026] Comparative Example 2 A polyvinyl alcohol, the preparation method of which comprises the following reaction steps: Step 1, 50 parts of vinyl acetate, 1 part of sodium dodecyl sulfonate, 1 part of dodecyl vinyl ether, 0.12 parts of reducing agent VC, 0.09 parts of sodium chloride and 200 parts of deionized water are added into a reaction device, stirred at room temperature and purged with nitrogen to prepare a solution A; Step 2, raising the temperature to 35°C, adding oxidant potassium persulfate dropwise (adding 0.08 parts of potassium persulfate to water to prepare a 30% by mass potassium persulfate aqueous solution), the dripping is completed within 2 hours, and the reaction is continued for 0.5-1 hour, and the temperature is lowered to room temperature to terminate the reaction to obtain a polymerization product B; Step 3: Freeze at -10°C to -5°C for 10 hours, thaw at room temperature for 5 hours, filter, and dry at 80°C to obtain dodecyl vinyl ether / vinyl acetate resin.

[0027] Step 4: dissolving the dodecyl vinyl ether / vinyl acetate resin obtained in step 3 in methanol to obtain a solution with a mass fraction of 15%, and adding a sodium hydroxide methanol solution (solution mass fraction of 30%) for alcoholysis to obtain the target polyvinyl alcohol resin. The molar ratio of dodecyl vinyl ether / vinyl acetate resin to sodium hydroxide is 1:0.02.

[0028] Comparative Example 3 A polyvinyl alcohol, the preparation method of which comprises the following reaction steps: Step 1, 50 parts of vinyl acetate, 1 part of sodium dodecyl sulfate, 1 part of Tween 20, 0.12 parts of reducing agent VC, 0.09 parts of sodium chloride and 200 parts of deionized water are added into a reaction device, stirred at room temperature and purged with nitrogen to prepare a solution A; Step 2, raising the temperature to 35°C, adding oxidant potassium persulfate dropwise (adding 0.08 parts of potassium persulfate to water to prepare a 30% by mass potassium persulfate aqueous solution), the dripping is completed within 2 hours, and the reaction is continued for 0.5-1 hour, and the temperature is lowered to room temperature to terminate the reaction to obtain a polymerization product B; Step 3, freezing at -10°C to -5°C for 10 hours, thawing at room temperature for 5 hours, filtering, and drying at 80°C to obtain vinyl acetate resin.

[0029] Step 4: dissolve the vinyl acetate resin obtained in step 3 in methanol to obtain a solution with a mass fraction of 15%, and add a sodium hydroxide methanol solution (solution mass fraction of 30%) for alcoholysis to obtain the target polyvinyl alcohol resin, wherein the molar ratio of the vinyl acetate resin to the sodium hydroxide is 1:0.02.

[0030] Performance Testing Weigh 100 parts of water and 15 parts of the polyvinyl alcohol resin prepared in the example or comparative example, heat to 90°C and stir to dissolve for 1 hour, then cool to 80°C and continue stirring for 3 hours. After static degassing, form a film by salivation. The water resistance temperature, swelling rate and tensile strength of the coating are measured, as shown in the following table.

[0031] Test method for water resistance and temperature: Cut the drooling film into multiple samples, put them into deionized water for water absorption and swelling, heat them up, start stirring when the water temperature reaches 90°C, stir for 10 seconds, let it stand for 60 seconds, dry and weigh it, test the mass of a sample every time the temperature drops by 5°C until the mass of the film remains unchanged, and record the water temperature at this time.

[0032] Swelling rate test method: Cut the film formed by drooling, dry it at 80℃ until the mass remains unchanged, soak it in distilled water at room temperature for 24 hours, then take out the film and quickly absorb the water on the surface of the film with absorbent paper, and weigh it. 0 ) / m 0 100% to calculate the swelling rate, where: S is the swelling rate (%); m is the swelling mass after immersion (g); m 0 is the initial mass of the dried film (g). For each sample, 5 sets of parallel samples were measured and the average value was taken.

[0033] Test method for tensile strength and elongation at break: The tensile strength and elongation at break of the polyvinyl alcohol film are tested according to the national standard GB / T 1040.3-2006.

[0034] Table 1 Polyvinyl alcohol film properties From the comparison between Example 1 and Comparative Example 1, and between Comparative Example 2 and Comparative Example 3, it can be seen that the polyamide resin curing agent polyvinyl alcohol prepared in Example 1 of the present application has significantly higher water resistance temperature, higher swelling rate, higher tensile strength and elongation at break. This is because the emulsion polymerization method is adopted for preparation, and the reactive emulsifiers 2-acrylamide-2-methylpropane sulfonic acid and dodecyl vinyl ether are used as compound emulsifiers, which can not only exert the excellent emulsifying effect of the compound emulsifier, but also obtain 2-acrylamide-2-methylpropane sulfonic acid / dodecyl vinyl ether / polyvinyl alcohol resin by copolymerization, and introduce hydrophilic sulfonic acid groups and soft segment long-chain alkyl ether chains into the polyvinyl alcohol molecular chain. The hydrophilic sulfonic acid groups can maintain the hydrophilicity of polyvinyl alcohol, and at the same time have the effect of improving hydrolysis resistance and high temperature resistance. The ether bonds in the soft segment long-chain alkyl ether chains are hydrophilic, and the soft segment long-chain alkyl can improve the flexibility and hydrolysis resistance of polyvinyl alcohol. Comparative Example 1 only introduced hydrophilic sulfonic acid groups, Comparative Example 2 only introduced soft segment long-chain alkyl ether chains, and Comparative Example 3 introduced neither hydrophilic sulfonic acid groups nor soft segment long-chain alkyl ether chains. Therefore, the performance in terms of water resistance temperature, swelling rate, tensile strength and elongation at break are not as good as Example 1.

[0035] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A polyvinyl alcohol, the raw materials of which include 20-60 parts of vinyl acetate, 0.5-1.5 parts of 2-acrylamide-2-methylpropane sulfonic acid, 0.5-1.5 parts of dodecyl vinyl ether, 0.05-0.1 parts of oxidant, 0.03-0.15 parts of reducing agent, 0.01-0.5 parts of sodium chloride, and 100-300 parts of deionized water, wherein: The molar ratio of 2-acrylamide-2-methylpropanesulfonic acid to dodecyl vinyl ether is 1-2:

1.

2. The polyvinyl alcohol according to claim 1, characterized in that The molar ratio of the 2-acrylamide-2-methylpropane sulfonic acid to dodecyl vinyl ether is 1:

1.

3. The polyvinyl alcohol according to claim 1, characterized in that 40-50 parts of vinyl acetate, 0.8-1.2 parts of 2-acrylamide-2-methylpropane sulfonic acid, 0.8-1.2 parts of dodecyl vinyl ether, 0.08-0.1 parts of oxidant, 0.06-0.13 parts of reducing agent, 0.01-0.3 parts of sodium chloride, and 150-250 parts of deionized water.

4. The polyvinyl alcohol according to claim 1, characterized in that 50 parts of vinyl acetate, 1 part of 2-acrylamide-2-methylpropanesulfonic acid, 1 part of dodecyl vinyl ether, 0.08 parts of oxidizing agent, 0.12 parts of reducing agent, 0.09 parts of sodium chloride, and 200 parts of deionized water.

5. The polyvinyl alcohol according to claim 1, characterized in that The oxidant is one or more of potassium persulfate, sodium persulfate, ammonium persulfate, and hydrogen peroxide, and the reducing agent is one or more of sodium bisulfite, ferrous chloride, tartaric acid, mercaptan, and VC.

6. A method for preparing polyvinyl alcohol according to any one of claims 1 to 5, characterized in that: The process comprises the following reaction steps: Step 1, adding vinyl acetate, 2-acrylamide-2-methylpropanesulfonic acid, dodecyl vinyl ether, a reducing agent, sodium chloride and deionized water into a reaction device, stirring at room temperature and passing nitrogen to prepare a solution A; Step 2, raising the temperature to 35°C, adding the oxidant dropwise, and completing the addition within 2 hours, continuing the reaction for 0.5-1 hour, lowering the temperature to room temperature, and ending the reaction to obtain a polymerization product B; Step 3, freezing the polymerization product B obtained in step 2 at -10°C--5°C for 5-12 hours, thawing it at room temperature for 2-5 hours, filtering it, and drying it at 75°C-85°C to obtain 2-acrylamide-2-methylpropanesulfonic acid / dodecyl vinyl ether / vinyl acetate resin; Step 4, dissolving the 2-acrylamide-2-methylpropane sulfonic acid / dodecyl vinyl ether / vinyl acetate resin obtained in step 3 in methanol to obtain a solution with a mass fraction of 10%-16%, adding sodium hydroxide methanol solution for alcoholysis to obtain polyvinyl alcohol resin.

7. The method for preparing polyvinyl alcohol according to claim 6, characterized in that: The molar ratio of 2-acrylamide-2-methylpropanesulfonic acid / dodecyl vinyl ether / vinyl acetate resin and sodium hydroxide is 1:0.015-0.

025.

8. The method for preparing polyvinyl alcohol according to claim 6, characterized in that: The molar ratio of 2-acrylamide-2-methylpropanesulfonic acid / dodecyl vinyl ether / vinyl acetate resin and sodium hydroxide is 1:0.02; the polyamine is one or more of p-xylene diamine, tetramethylene diamine, and hexamethylene diamine.

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