A method for producing an ethylene-vinyl alcohol copolymer resin composition

Abstract

The application discloses a preparation method of an ethylene-vinyl alcohol copolymer (EVOH) resin composition, which comprises multiple steps and is characterized in that: A. a polymerization reaction: after ethylene-vinyl acetate copolymer is generated, the temperature is first reduced, a terminating agent is added, and then pressure relief flash evaporation is performed; B. an alcoholysis reaction: an alcohol solution of the ethylene-vinyl acetate copolymer prepared in the step A is added with lye to perform alcoholysis, so that an EVOH alcohol solution is obtained; C. the EVOH alcohol solution prepared in the step B is added with an additive, cooling precipitation is performed, multiple washing is performed, and finally drying is performed to obtain the EVOH resin composition. The EVOH resin composition prepared by using the preparation method of the EVOH resin composition can be significantly improved in processability, can obviously reduce yellowing at high temperature, and can reduce the defect number after melt blown film, so that the prepared multilayer sheet, film and container and the like are free of crystal points, stripes and other defects.

Description

Technical Field

[0001] This invention relates to the field of ethylene-vinyl alcohol copolymers, specifically to a method for preparing an ethylene-vinyl alcohol copolymer resin composition. Background Technology

[0002] Ethylene-vinyl alcohol copolymer (EVOH), especially EVOH with an ethylene content of 20-50 mol%, has excellent gas barrier properties, approximately 10,000 times that of ordinary polyethylene. Combined with its transparency, processability, solvent resistance, and antistatic properties, it is widely used in packaging materials, automotive fuel tanks, oxygen-barrier underfloor heating pipes, textile materials, and medical materials.

[0003] Chinese patent document CN114426753A discloses an ethylene-vinyl alcohol copolymer composition and its preparation method: the composition includes an ethylene-vinyl alcohol copolymer, a carboxyl-containing substance, a potassium salt, and a sodium salt, wherein the carboxyl-containing substance includes acetic acid and a carboxylic acid containing a carbon-carbon double bond; the preparation method of the composition includes the following steps: the ethylene-vinyl acetate copolymer obtained by polymerization is alcoholyzed with sodium hydroxide, then granulated, and then washed, during which acetic acid and a carboxylic acid containing a carbon-carbon double bond are added for washing, and then potassium salt is added.

[0004] The existing technology has the following drawbacks: the multilayer sheets, films and containers made from the EVOH resin composition obtained by this process are prone to defects such as crystal points and streaks. Summary of the Invention

[0005] On one hand, the present invention provides a method for preparing EVOH resin compositions that do not produce defects such as crystal points or streaks in multilayer sheets, films, and containers, etc., made therefrom, comprising multiple steps, namely: A. Polymerization reaction: including generating ethylene-vinyl acetate copolymer, first lowering the temperature, adding a terminator, and then depressurizing and flash evaporating; B. Alcohololysis reaction: adding an alkaline solution to the alcohol solution of the ethylene-vinyl acetate copolymer obtained in step A for alcohololysis to obtain an EVOH alcohol solution; C. Washing and drying: adding an additive to the EVOH alcohol solution obtained in step B, cooling to precipitate, then washing multiple times, and finally drying to obtain the final product.

[0006] Furthermore, in step A, the temperature is reduced to 10-30°C; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0007] Furthermore, the terminator in step C is copper acetate; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0008] Furthermore, the additives mentioned in step C are heat stabilizers and / or antioxidants; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0009] Furthermore, the additive is one or more of carboxylic acids, alkali metal salts, alkaline earth metal salts, boric acid and its salts, and phosphoric acid and its salts; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0010] Furthermore, the multiple washing steps in step C include washing with water, washing with a mixed solution of water and alcohol, and washing with acetic acid; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0011] Furthermore, the alcohol is an alcohol with ≤4 carbon atoms; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0012] Furthermore, the alcohol with ≤4 carbon atoms is one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0013] Furthermore, the preparation method of the EVOH resin composition of the present invention includes the following steps: A. Polymerization reaction: including generating ethylene-vinyl acetate copolymer, first lowering the temperature to 10-30°C, adding a terminator with a content of 500-5000 ppm of ethylene-vinyl acetate copolymer, then depressurizing and flash evaporating, and adding alcohol solvent for distillation;

[0014] B. Alcohololysis reaction: The alcohol solution of ethylene-vinyl acetate copolymer obtained in step A is prepared into a solution with a mass fraction of 15-40%, and an alkaline solution is added for alcohololysis to obtain EVOH alcohol solution;

[0015] C. Add 0.01-1 parts of additive relative to the weight of EVOH solid to the EVOH alcohol solution obtained in step B, then put it into an aqueous solution at 0-10℃, cut it into particles, wash it with water first, then wash it with a mixed solution of water and alcohol with a weight ratio of 1-50:50-99, and finally add acetic acid for washing with water, centrifuge to dehydrate, and dry to obtain the product.

[0016] This further ensures that the multilayer sheets, films, and containers made from the prepared EVOH resin composition will not have defects such as crystal points and streaks.

[0017] The present invention also provides the application of the EVOH resin composition prepared by the method described herein in membranes, multilayer sheets and containers.

[0018] Unless otherwise specified, all parts mentioned in this invention are parts by weight.

[0019] The present invention has the following beneficial effects:

[0020] The preparation method of the EVOH resin composition of this invention can eliminate active free radicals in the polymerization system, reduce the self-polymerization of vinyl acetate to polyvinyl acetate during the subsequent depressurization and removal of ethylene monomer and the process before the removal of vinyl acetate monomer, thereby reducing the amount of polyvinyl alcohol (PVA) generated during the subsequent alcoholysis process, so that the content of PVA in the polyvinyl acetate homopolymer is less than 5000 ppm; at the same time, the content of EVOH with ethylene content <15 mol% is less than 3 wt%, which can significantly improve its processing performance, significantly reduce yellowing at high temperature, and reduce the number of defects after melt blown film; thus, the multilayer sheets, films and containers produced will not have defects such as crystal points and streaks. Detailed Implementation

[0021] 1. Definition

[0022] (1) Depressurization flash evaporation: The process of evaporating and vaporizing low-boiling-point substances by rapidly releasing pressure.

[0023] (2) Polymerization reaction: The process of converting low molecular weight monomers into high molecular weight polymers.

[0024] (3) Distillation: is a thermodynamic separation process that utilizes the different boiling points of the components in a mixed liquid or liquid-solid system to evaporate the low-boiling-point components and then condense them to separate the entire component. It is a unit operation process that combines evaporation and condensation.

[0025] (4) Alcohololysis: the reaction in which acyl halides, acid anhydrides, esters, etc. are decomposed by alcohols to generate esters and other compounds.

[0026] (5) Washing: Cleaning.

[0027] (6) Cooling: refers to the process of lowering the temperature of a hot object without causing a phase change.

[0028] (7) Precipitation: The solute is separated from the solution.

[0029] 2. Various preferred solutions involving the scope

[0030] (1) The weight ratio of alcohol to water is 1-40:60-99.

[0031] (2) The weight ratio of alcohol to water is 10-25:75-90.

[0032] (3) Methanol is preferred.

[0033] (4) A method for preparing an EVOH resin composition, comprising the following steps:

[0034] The first step of the polymerization reaction employs methods such as solution polymerization, emulsion polymerization, or suspension polymerization, with free radical solution polymerization being preferred. 100 parts of vinyl acetate and 5-50 parts of an alcohol solvent, particularly alcohols with 1-4 carbon atoms, such as methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol, are added. A mixture of two of the above alcohols can also be used, or the above alcohols can be the main component with other minor components. 0.01-0.5 parts of an initiator are used, which can be an azo initiator or a peroxide initiator. The azo initiator can be an oil-soluble initiator such as azobisisobutyronitrile, azobisisovalerate, azoisobutylcyanoformamide, azobiscyclohexylformitrile, or dimethyl azobisisobutyrate. The peroxide initiator can be an organic peroxide such as benzoyl peroxide. The initiator can be tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, tert-amyl peroxynedecanoate, bis(4-tert-butylcyclohexyl peroxydicarbonate), tert-amyl peroxypentanoate, tert-butyl peroxyacetate, bis-butyl peroxydicarbonate, etc., or inorganic peroxides such as hydrogen peroxide, ammonium persulfate, potassium persulfate, etc. One or more initiators are preferred in combination. The temperature is raised to 40-70℃, the ethylene pressure is maintained at 3-6MPa, and the reaction is carried out under stirring for 2-15 hours. The pressure is kept constant, the temperature is lowered to 0-30℃, and copper acetate (containing 500-5000 ppm of the ethylene-vinyl acetate copolymer) is added as a terminator. After stirring, the pressure is released and the mixture is flash-evaporated. An alcohol solvent is then added for distillation to obtain an alcohol solution of the ethylene-vinyl acetate copolymer.

[0035] The second step is alcoholysis. The obtained alcohol solution of ethylene-vinyl acetate copolymer is prepared into a solution with a mass fraction of 15-40% in methanol. Then, an alcohol solution of sodium hydroxide with a molar ratio of 0.05-0.5:1 to ethylene-vinyl acetate copolymer is added for alcoholysis. After alcoholysis, an alcohol solution of EVOH is obtained.

[0036] Add 0.01-1 parts (by weight of EVOH solids) of additive solution to the obtained EVOH methanol solution and stir until homogeneous. Extrude the EVOH solution obtained from alcoholysis into an aqueous solution at 0-10℃ using an extrusion device with a perforated plate. After precipitating into strips, cut them into granules using a common cutting method. Wash the EVOH granules with water in a stirred tank, washing for 2 hours each time, repeating the washing process twice. After two washes, add a mixed solution of water and alcohol to the stirred tank and wash at 60-90℃ for 2 hours, then wash again with water. During the water washing process, add 0.005-0.1 parts (by weight of EVOH) of acetic acid for acid washing, followed by centrifugation and dehydration. Dry the EVOH granules to obtain the final product.

[0037] The examples provided are for illustrative purposes only and are not intended to limit the scope of the invention. Therefore, non-essential modifications and adjustments made to the embodiments by those skilled in the art based on the above description are still within the protection scope of this invention.

[0038] 3. Detection Method

[0039] Test method for EVOH content of ethylene content <15mol% in granules: Accurately weigh 1g of sample and place it in an Erlenmeyer flask. Add 100g of a mixed solvent of water and ethanol (10g ethanol + 90g water), reflux in a water bath at 100℃ for 4 hours, filter, save the filtrate, add another 100g of water and reflux for 4 hours, filter again, evaporate the filtrates from both filtrations, and weigh the amount of residue. The ratio of the amount of residue to the amount of sample is the EVOH content of ethylene content <15mol% in the granules.

[0040] Test method for PVA content in granules: Accurately weigh 10g of EVOH sample into a 500mL beaker, add 300-400mL of distilled water, heat to boiling with a glass rod on an electric stove until about 100mL of water evaporates from the beaker, filter into a 500mL volumetric flask. Repeat the operation at least 3 times, then dilute the 500mL volumetric flask to volume. Take 10.00mL of the sample from the volumetric flask and place it in a 20mL graduated test tube, add 4.00mL of boric acid solution and 1mL of iodine-potassium iodide solution, dilute to the mark with water, shake well, and measure the absorbance at 640nm using a 1cm cuvette, with a reagent blank as a reference.

[0041] Method for determining the number of surface defects in membrane products: A 30cm*24cm membrane sample was prepared using an SG-45 blown film machine, and the surface defects in the membrane were analyzed using a surface defect analyzer MVT-SIS. The number of defects larger than 0.5mm*0.5mm in the sample was counted.

[0042] Example 1

[0043] 100 parts of vinyl acetate, 12 parts of methanol, and 0.1 parts of azobisisobutyronitrile (AIOBR) were added to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. The temperature was raised to 60°C, and the ethylene pressure was maintained at 3.8 MPaG. After reacting for 4 hours with stirring, the pressure was kept constant, and the temperature was lowered to 28°C. Then, 800 ppm of copper acetate, a terminator relative to the generated ethylene-vinyl acetate copolymer, was added. After stirring for 1 hour, the pressure was released and the ethylene was flash-evaporated to remove it. Unreacted vinyl acetate was removed by distillation with methanol. The ethylene content in the obtained copolymer was tested to be 32 mol%.

[0044] The methanol solution of the obtained ethylene-vinyl acetate copolymer was prepared into a 28% (w / w) solution with methanol, and then an alkaline solution was added for alcoholysis. The alkaline solution was a methanol solution of NaOH, and the molar ratio of the alkaline solution to the ethylene-vinyl acetate copolymer was controlled at 0.5:1. After alcoholysis, an EVOH methanol solution was obtained.

[0045] Add 0.3 parts by weight of the additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 200 ppm propionic acid, 300 ppm boric acid and 400 ppm sodium dihydrogen phosphate relative to the weight of the EVOH solid.

[0046] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extrusion device with a perforated plate. After precipitating into strips, the strips were cut into granules using a standard cutting method. The EVOH granules were then washed with water in a stirred tank for 2 hours each time, repeated twice. After two washes, a mixed solution of water and methanol (water:methanol = 15:85) was added to the stirred tank and washed at 60°C for 2 hours. This was followed by a second water wash, during which 0.01 parts by weight of acetic acid relative to the EVOH solids were added for acid washing. The granules were then centrifuged, dehydrated, and dried to obtain the final EVOH granules.

[0047] The EVOH particles obtained after drying were tested and found to contain 3600 ppm of homopolymer PVA and 2.1 wt% of EVOH with ethylene content <15 mol%. After heat treatment at 150℃ for 5 hours, the yellowness index increased by ΔYI = 16.

[0048] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects in the EVOH film was found to be 17, and the change in screw current ΔA = 1A.

[0049] Example 2

[0050] 100 parts of vinyl acetate, 12 parts of methanol, and 0.1 parts of tert-pentyl peroxide were added to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. The temperature was raised to 60°C, and the ethylene pressure was maintained at 4.3 MPaG. After reacting for 4 hours with stirring, the pressure was kept constant, and the temperature was lowered to 20°C. Then, 2000 ppm of copper acetate as a terminator relative to the generated ethylene-vinyl acetate copolymer was added. After stirring for 1 hour, the pressure was released and the ethylene was flash-evaporated to remove it. Unreacted vinyl acetate was removed by distillation with methanol. The ethylene content of the obtained copolymer was tested to be 38 mol%.

[0051] The methanol solution of the obtained ethylene-vinyl acetate copolymer was prepared into a 38% (w / w) solution with methanol, and then an alkaline solution was added for alcoholysis. The alkaline solution was a methanol solution of NaOH, and the molar ratio of the alkaline solution to the ethylene-vinyl acetate copolymer was controlled at 0.12:1. After alcoholysis, an EVOH methanol solution was obtained.

[0052] Add 0.6 parts by weight of additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 300 ppm acetic acid, 200 ppm boric acid or 600 ppm sodium dihydrogen phosphate relative to the weight of EVOH solid.

[0053] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extruder equipped with a perforated plate. After precipitating into strips, the strips were cut into granules using a standard cutting method. The EVOH granules were then washed with water in a stirred tank, with each wash lasting 2 hours, repeated twice. After two washes, a mixed solution of water and ethanol (water:ethanol = 20:80) was added to the stirred tank and washed at 60°C for 2 hours. This was followed by a second water wash, during which 0.05 parts by weight of acetic acid relative to the EVOH solids were added for acid washing. The granules were then centrifuged, dehydrated, and dried to obtain the final EVOH granules.

[0054] The EVOH particles obtained after drying were tested and found to contain 3100 ppm of homopolymer PVA and 1.9 wt% of EVOH with ethylene content <15 mol%. The yellowness index of the particles increased by ΔYI = 9 after heat treatment at 150℃ for 5 hours.

[0055] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects on the EVOH film was found to be 13, and the change in screw current ΔA = 1A.

[0056] Example 3

[0057] 100 parts of vinyl acetate, 12 parts of methanol, and 0.1 parts of tert-pentyl peroxide were added to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. The temperature was raised to 60°C, and the ethylene pressure was maintained at 3.6 MPaG. After reacting for 4 hours with stirring, the pressure was kept constant and the temperature was lowered to 28°C. Then, 600 ppm of copper acetate as a terminator relative to the generated ethylene-vinyl acetate copolymer was added. After stirring for 1 hour, the pressure was released and the ethylene was flash-evaporated to remove it. Unreacted vinyl acetate was removed by distillation with methanol. The ethylene content in the obtained copolymer was tested to be 32 mol%.

[0058] The methanol solution of the obtained ethylene-vinyl acetate copolymer was prepared into a 35% (w / w) solution with methanol, and then an alkaline solution was added for alcoholysis. The alkaline solution was a methanol solution of NaOH, and the molar ratio of the alkaline solution to the ethylene-vinyl acetate copolymer was controlled at 0.08:1. After alcoholysis, an EVOH methanol solution was obtained.

[0059] Add 0.8 parts by weight of the additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 300 ppm of acetic acid, 300 ppm of boric acid or 600 ppm of potassium dihydrogen phosphate relative to the weight of the EVOH solid.

[0060] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extruder equipped with a perforated plate. After precipitating into strips, the strips were cut into granules using a standard cutting method. The EVOH granules were then washed with water in a stirred tank, with each wash lasting 2 hours, repeated twice. After two washes, a mixed solution of water and ethanol (water:ethanol = 20:80) was added to the stirred tank and washed at 60°C for 2 hours. This was followed by a second water wash, during which 0.05 parts by weight of acetic acid relative to the EVOH solids were added for acid washing. The granules were then centrifuged, dehydrated, and dried to obtain the final EVOH granules.

[0061] The EVOH particles obtained after drying were tested and found to contain 2800 ppm of homopolymer PVA and 1.8 wt% of EVOH with ethylene content <15 mol%. The yellowness index of the particles increased by ΔYI = 7 after heat treatment at 150℃ for 5 hours.

[0062] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects on the EVOH film was found to be 10, and the change in screw current ΔA = 1A.

[0063] Comparative Example 1

[0064] 100 parts of vinyl acetate, 12 parts of methanol, and 0.1 parts of tert-pentyl peroxide were added to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. The temperature was raised to 60°C, and the ethylene pressure was maintained at 4.3 MPaG. After reacting for 4 hours with stirring, the pressure was kept constant, and the temperature was lowered to 45°C. Then, 2000 ppm of copper acetate as a terminator relative to the generated ethylene-vinyl acetate copolymer was added. After stirring for 1 hour, the pressure was released and the ethylene was flash-evaporated to remove it. Unreacted vinyl acetate was removed by distillation with methanol. The ethylene content of the obtained copolymer was tested to be 38 mol%.

[0065] The methanol solution of the obtained ethylene-vinyl acetate copolymer was prepared into a 38% (w / w) solution with methanol, and then an alkaline solution was added for alcoholysis. The alkaline solution was a methanol solution of NaOH, and the molar ratio of the alkaline solution to the ethylene-vinyl acetate copolymer was controlled at 0.12:1. After alcoholysis, an EVOH methanol solution was obtained.

[0066] Add 0.6 parts by weight of additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 300 ppm acetic acid, 200 ppm boric acid or 600 ppm sodium dihydrogen phosphate relative to the EVOH solid.

[0067] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extruder equipped with a perforated plate. The precipitated strips were then cut into granules using a standard cutting method. The EVOH granules were washed with water in a stirred tank for 2 hours each time, repeated twice. After centrifugation and dehydration, the EVOH granules were dried to obtain the final EVOH granules.

[0068] The EVOH particles obtained after drying were tested and found to contain 7800 ppm of homopolymer PVA and 4.8 wt% of EVOH with ethylene content <15 mol%. The yellowness index of the particles increased by ΔYI = 18 after heat treatment at 150℃ for 5 hours.

[0069] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects on the EVOH film was examined, and the change in screw current ΔA = 2A was observed.

[0070] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing an ethylene-vinyl alcohol copolymer (EVOH) resin composition, comprising multiple steps, characterized in that: The steps are: A. Polymerization reaction: after generating ethylene-vinyl acetate copolymer, the temperature is lowered, a terminator is added, and then the pressure is released and flash evaporated; B. Alcohololysis reaction: the alcohol solution of ethylene-vinyl acetate copolymer obtained in step A is added to an alkaline solution for alcohololysis to obtain EVOH alcohol solution; C. Add additives to the EVOH alcohol solution obtained in step B, cool to precipitate, wash several times, and finally dry to obtain the final product; In step A, lower the temperature to 10-30℃.

2. The method for preparing the EVOH resin composition according to claim 1, characterized in that: The terminating agent mentioned in step A is copper acetate.

3. The method for preparing the EVOH resin composition according to claim 1 or 2, characterized in that: The additives mentioned in step C are heat stabilizers and / or antioxidants.

4. The method for preparing the EVOH resin composition according to claim 3, characterized in that: The additive is one or more of the following: carboxylic acid, alkali metal salt, alkaline earth metal salt, boric acid and its salt, and phosphoric acid and its salt.

5. The method for preparing the EVOH resin composition according to claim 1 or 2, characterized in that: The multiple washing steps described in step C include washing with water, washing with a mixed solution of water and alcohol, and washing with acetic acid.

6. The method for preparing the EVOH resin composition according to claim 5, characterized in that: The alcohol is an alcohol with ≤4 carbon atoms.

7. The method for preparing the EVOH resin composition according to claim 6, characterized in that: The alcohols with ≤4 carbon atoms are one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol.

8. The method for preparing the EVOH resin composition according to claim 1 or 2, characterized in that: Includes the following steps: A. Polymerization reaction: After generating ethylene-vinyl acetate copolymer, the temperature is first lowered to 10-30℃, a terminator with a content of 500-5000ppm of ethylene-vinyl acetate copolymer is added, then pressure is released and flash evaporation is carried out, and alcohol solvent is added for distillation. B. Alcohololysis reaction: Prepare an alcohol solution of ethylene-vinyl acetate copolymer obtained in step A with a mass fraction of 15-40%, add alkaline solution for alcohololysis, and obtain EVOH alcohol solution; C. Add 0.01-1 parts of additive relative to the weight of EVOH solid to the EVOH alcohol solution obtained in step B, then put it into an aqueous solution at 0-10℃, cut it into particles, wash it with water first, then wash it with a mixed solution of water and alcohol with a weight ratio of 1-50:50-99, and finally add acetic acid for washing with water, centrifuge to dehydrate, and dry to obtain the final product.

9. The use of the EVOH resin composition prepared by any one of the preparation methods according to claims 1-8 in membranes, multilayer sheets and containers.