Post-treatment method of ethylene-vinyl alcohol copolymer and ethylene-vinyl alcohol copolymer mixture and ethylene-vinyl alcohol film

Abstract

This invention relates to the field of post-processing technology for ethylene-vinyl alcohol copolymers, and discloses a post-processing method for ethylene-vinyl alcohol copolymers, as well as ethylene-vinyl alcohol copolymer mixtures and ethylene-vinyl alcohol films. The post-processing method for ethylene-vinyl alcohol copolymers includes: contacting ethylene-vinyl alcohol copolymer particles obtained after molding and granulation with silicone oil and polyethylene glycol monooctylphenyl ether to obtain an ethylene-vinyl alcohol copolymer mixture; based on the mass of the ethylene-vinyl alcohol copolymer particles, the total mass of the silicone oil and polyethylene glycol monooctylphenyl ether is 50-5000 ppm; the mass ratio of the silicone oil to the polyethylene glycol monooctylphenyl ether is 1:0.5-10. The ethylene-vinyl alcohol copolymer mixture prepared by this method has a low angle of repose, resulting in smaller torque and torque fluctuations during the preparation of ethylene-vinyl alcohol films, and a lower coefficient of dynamic friction of the ethylene-vinyl alcohol films.

Description

Technical Field

[0001] This invention relates to the field of post-processing technology for ethylene-vinyl alcohol copolymers, specifically to a post-processing method for ethylene-vinyl alcohol copolymers, as well as ethylene-vinyl alcohol copolymer mixtures and ethylene-vinyl alcohol films. Background Technology

[0002] Ethylene-vinyl alcohol copolymer (EVOH) possesses the excellent melt processability of polyethylene polymers while also exhibiting the superior gas barrier properties of vinyl alcohol polymerization. Its barrier properties are ten thousand times that of low-density polyethylene. EVOH also has excellent transparency, solvent resistance, and antistatic properties. Its molecular structure contains only three elements: carbon, hydrogen, and oxygen, making it environmentally friendly. It is widely used in food and pharmaceutical packaging, oxygen-barrier underfloor heating pipes, fuel tanks, textile materials, and medical materials.

[0003] Because EVOH is a crystalline polymer with a high softening temperature, it requires higher temperature and pressure conditions during downstream processing. This causes the screw extruder to bear extremely high torque loads during operation, and may result in large torque fluctuations, leading to high energy consumption in extrusion processing and fluctuations in the quality of molten products.

[0004] Therefore, there is an urgent need to develop an ethylene-vinyl alcohol copolymer with stable processing performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of high torque and large torque fluctuation in screw extruders during the processing of ethylene-vinyl alcohol copolymers in the prior art, and to provide a post-processing method for ethylene-vinyl alcohol copolymers, as well as ethylene-vinyl alcohol copolymer mixtures and ethylene-vinyl alcohol films. This post-processing method involves contacting the ethylene-vinyl alcohol copolymer particles obtained after molding and granulation with silicone oil and polyethylene glycol monooctylphenyl ether in a specific content and ratio. The resulting ethylene-vinyl alcohol copolymer mixture has a low angle of repose, resulting in smaller torque and torque fluctuations during the preparation of ethylene-vinyl alcohol films, and a lower coefficient of dynamic friction in the prepared ethylene-vinyl alcohol films.

[0006] To achieve the above objectives, the first aspect of the present invention provides a post-processing method for ethylene-vinyl alcohol copolymers, the method comprising: contacting ethylene-vinyl alcohol copolymer particles obtained after molding and granulation with silicone oil and polyethylene glycol monooctylphenyl ether to obtain an ethylene-vinyl alcohol copolymer mixture;

[0007] Based on the mass of the ethylene-vinyl alcohol copolymer particles, the total mass of the silicone oil and polyethylene glycol monooctylphenyl ether is 50-5000 ppm.

[0008] The mass ratio of the silicone oil to the polyethylene glycol monooctylphenyl ether is 1:0.5-10.

[0009] A second aspect of the present invention provides an ethylene-vinyl alcohol copolymer mixture prepared by the post-processing method described in the first aspect above.

[0010] A third aspect of the present invention provides the application of the ethylene-vinyl alcohol copolymer mixture described in the second aspect above in at least one of packaging materials, automotive fuel tanks, oxygen-barrier floor heating pipes, textile materials, and medical materials.

[0011] A fourth aspect of the present invention provides an ethylene-vinyl alcohol film, said film being prepared from the ethylene-vinyl alcohol copolymer mixture described in the second aspect above.

[0012] Through the above technical solution, the present invention has the following beneficial effects:

[0013] The post-processing method for ethylene-vinyl alcohol copolymers provided by this invention involves contacting the ethylene-vinyl alcohol copolymer particles obtained after molding and granulation with silicone oil and polyethylene glycol monooctylphenyl ether in specific contents and proportions. The silicone oil rapidly adheres to the surface of the ethylene-vinyl alcohol copolymer particles, while the polyethylene glycol monooctylphenyl ether enhances the distribution of silicone oil on the particle surface, forming a lubricating film. The silicone oil and polyethylene glycol monooctylphenyl ether, at a specific ratio, function better, effectively reducing the internal friction between ethylene-vinyl alcohol copolymer mixture particles and the friction and adhesion between the particles and processing equipment, preventing particle adhesion and preventing the ethylene-vinyl alcohol polymer from remaining in the processing equipment. The ethylene-vinyl alcohol copolymer mixture prepared by this post-processing method exhibits excellent processing stability and a low angle of repose, resulting in small torque and torque fluctuations during the preparation of ethylene-vinyl alcohol films, low production energy consumption, and a reduced dynamic friction coefficient in the prepared ethylene-vinyl alcohol films. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] The first aspect of the present invention provides a post-processing method for ethylene-vinyl alcohol copolymers, the method comprising: contacting ethylene-vinyl alcohol copolymer particles obtained after molding and granulation with silicone oil and polyethylene glycol monooctylphenyl ether to obtain an ethylene-vinyl alcohol copolymer mixture;

[0016] Based on the mass of the ethylene-vinyl alcohol copolymer particles, the total mass of the silicone oil and polyethylene glycol monooctylphenyl ether is 50-5000 ppm.

[0017] The mass ratio of the silicone oil to the polyethylene glycol monooctylphenyl ether is 1:0.5-10.

[0018] In this invention, the ethylene-vinyl alcohol copolymer particles obtained after molding and granulation are contacted with silicone oil and polyethylene glycol monooctylphenyl ether in a specific content and ratio. This effectively reduces the internal friction between the modified ethylene-vinyl alcohol copolymer particles and the friction and adhesion between the modified ethylene-vinyl alcohol copolymer particles and the processing equipment. The modified ethylene-vinyl alcohol copolymer particles have a lower angle of repose and prevent the particles from sticking together, thus reducing energy consumption.

[0019] In this invention, unless otherwise specified, the ethylene-vinyl alcohol copolymer mixture refers to a mixture of ethylene-vinyl alcohol copolymer / silicone oil / polyethylene glycol monooctylphenyl ether.

[0020] In some embodiments of the present invention, preferably, based on the mass of the ethylene-vinyl alcohol copolymer particles, the total mass of the silicone oil and polyethylene glycol monooctylphenyl ether is 50-5000 ppm, for example, it can be 50 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, and any range formed by any two of the above values ​​and values ​​within that range.

[0021] In this invention, controlling the total mass of the silicone oil and polyethylene glycol monooctylphenyl ether within the above-mentioned range is beneficial to reducing the angle of repose of the ethylene-vinyl alcohol copolymer mixture, reducing friction and resistance during processing, and thus helping to reduce the screw extruder torque and torque fluctuation of the ethylene-vinyl alcohol copolymer mixture during processing.

[0022] Preferably, based on the mass of the ethylene-vinyl alcohol copolymer particles, the total mass of the silicone oil and polyethylene glycol monooctylphenyl ether is 300-3000 ppm.

[0023] In some embodiments of the present invention, preferably, the mass ratio of the silicone oil to the polyethylene glycol monooctylphenyl ether is 1:0.5-10, for example, it can be 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, as well as any range of the above two values ​​and values ​​within that range.

[0024] In this invention, controlling the mass ratio of the silicone oil and the polyethylene glycol monooctylphenyl ether within the aforementioned range is beneficial for fully leveraging their synergistic effect, effectively reducing the angle of repose of the ethylene-vinyl alcohol copolymer mixture particles, resulting in more significant lubrication and anti-adhesion effects, thereby helping to reduce torque and torque fluctuations during processing. If the mass ratio of silicone oil to polyethylene glycol monooctylphenyl ether is greater than 1:0.5, the amount of silicone oil used is excessive, leading to uneven distribution of silicone oil on the polymer particle surface and a tendency for unstable transport during subsequent polymer melt processing; if the mass ratio of silicone oil to polyethylene glycol monooctylphenyl ether is less than 1:10, the amount of silicone oil used is insufficient, resulting in persistent problems such as large torque fluctuations and high torque during processing, which cannot be effectively resolved.

[0025] Preferably, the mass ratio of the silicone oil to the polyethylene glycol monooctylphenyl ether is 1:2-5.

[0026] In some embodiments of the present invention, preferably, the silicone oil has a dynamic viscosity of 500-3000 mPa·s at 25°C. In this invention, the viscosity of the silicone oil is tested according to the method specified in ASTM D7042.

[0027] In this invention, controlling the viscosity of the silicone oil within the above-mentioned range is beneficial for uniform mixing with polymer particles and ensuring uniform distribution on the particle surface.

[0028] Preferably, the silicone oil has a dynamic viscosity of 1000-2000 mPa·s at 25°C.

[0029] In some embodiments of the present invention, preferably, the silicone oil is selected from at least one of polydimethylsiloxane, ethyl silicone oil, methylethoxy silicone oil, methyl vinyl silicone oil, and phenyl silicone oil, and preferably polydimethylsiloxane. In the present invention, the silicone oil is more conducive to working in combination with polyethylene glycol monooctylphenyl ether, and is more conducive to playing a lubricating and anti-adhesion role.

[0030] In this invention, the method of contacting the ethylene-vinyl alcohol copolymer particles obtained after molding and granulation with silicone oil and polyethylene glycol monooctylphenyl ether is not particularly limited. The silicone oil and polyethylene glycol monooctylphenyl ether can be contacted first, and then the resulting mixture can be contacted with the ethylene-vinyl alcohol copolymer particles. Alternatively, the ethylene-vinyl alcohol copolymer particles, silicone oil, and polyethylene glycol monooctylphenyl ether can be directly mixed and contacted. Preferably, the silicone oil and polyethylene glycol monooctylphenyl ether are contacted first, and then the resulting mixture is contacted with the ethylene-vinyl alcohol copolymer particles.

[0031] In this invention, the contact conditions are not particularly limited, as long as sufficient contact between the ethylene-vinyl alcohol copolymer particles and the silicone oil and polyethylene glycol monooctylphenyl ether is ensured. Preferably, the contact conditions include: a contact temperature of 20-60°C and a contact time of 10-120 minutes.

[0032] In this invention, controlling the contact conditions within the above-mentioned range is beneficial for the rapid adhesion of silicone oil and polyethylene glycol monooctylphenyl ether to the surface of ethylene-vinyl alcohol copolymer particles, forming a thin lubricating film.

[0033] Preferably, the contact conditions include: a contact temperature of 25-40°C and a contact time of 30-90 minutes.

[0034] In this invention, the particle size of the ethylene-vinyl alcohol copolymer particles obtained after molding and granulation is not particularly limited, and can be the particle size of ethylene-vinyl alcohol copolymer particles obtained after molding and granulation in the art. Preferably, the average particle size of the ethylene-vinyl alcohol copolymer particles obtained after molding and granulation is 2-5 mm. In this invention, unless otherwise specified, the particle size of the ethylene-vinyl alcohol copolymer particles is determined by sieving.

[0035] In some embodiments of the present invention, preferably, the method for preparing the ethylene-vinyl alcohol copolymer particles includes:

[0036] S1. A polymerization reaction is carried out using a first solvent, an initiator, vinyl acetate, and ethylene as raw materials;

[0037] S2. The product obtained in step S1 is mixed sequentially with the second solvent and the terminator to obtain an ethylene-vinyl acetate copolymer solution.

[0038] S3. The ethylene-vinyl acetate copolymer solution is subjected to alcoholysis and granulation to obtain ethylene-vinyl alcohol copolymer particles.

[0039] In this invention, the ethylene-vinyl alcohol copolymer particles obtained by the above method have good processing stability, which is beneficial to improving the processing stability of the ethylene-vinyl alcohol copolymer mixture prepared subsequently. The angle of repose of the ethylene-vinyl alcohol copolymer mixture is reduced, the friction between the ethylene-vinyl alcohol copolymer mixtures is reduced, and the energy consumption is reduced, resulting in small torque and torque fluctuation during the preparation of ethylene-vinyl alcohol films, and a lower dynamic friction coefficient of the prepared ethylene-vinyl alcohol films.

[0040] In this invention, the amount of the initiator has a wide selection range. Preferably, based on the weight of the vinyl acetate, the amount of the initiator is 50-5000 ppm, more preferably 100-3000 ppm. In this invention, controlling the amount of the initiator within the above range is beneficial for controlling the weight-average molecular weight of the copolymer and improving the reaction efficiency. The preferred range has even better effects.

[0041] In this invention, the type of initiator is not particularly limited, as long as it can initiate the polymerization reaction between vinyl acetate and ethylene. Preferably, the initiator is selected from azo initiators and / or peroxide initiators. More preferably, the azo initiator is at least one of azobisisobutyronitrile, azobisisovalerate, azoisobutylcyanoformamide, azobiscyclohexylformitrile, and dimethyl azobisisobutyrate; the peroxide initiator is an organic peroxide and / or an inorganic peroxide; more preferably, the organic peroxide is selected from at least one of benzoyl peroxide, benzoyl tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, tert-pentyl peroxyneodecanate, bis(4-tert-butylcyclohexyl peroxydicarbonate), tert-pentyl peroxypentate, tert-butyl peroxyacetate, and dibutyl peroxydicarbonate; the inorganic peroxide is selected from at least one of hydrogen peroxide, ammonium persulfate, and potassium persulfate.

[0042] In this invention, the type of the first solvent is not particularly limited. Preferably, the first solvent is an alcohol solvent with 1-4 carbon atoms; more preferably, the first solvent is at least one selected from methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol; and even more preferably, the first solvent is methanol.

[0043] In this invention, the amount of the first solvent has a wide range of selection, as long as it can dissolve the initiator, vinyl acetate, and ethylene without affecting the polymerization reaction. Preferably, based on the weight of the vinyl acetate, the amount of the first solvent is 3-40% by weight, preferably 10-25% by weight.

[0044] In some embodiments of the present invention, preferably, the amount of ethylene used results in a polymerization pressure of 2-6 MPaG, more preferably 2.5-5.5 MPaG. In this invention, by controlling the amount of ethylene used to maintain the polymerization pressure within the above range, the content of ethylene-derived structural units in the ethylene-vinyl alcohol copolymer is controlled, resulting in a suitable content of ethylene structural units in the copolymer. The preferred range provides even better results.

[0045] In this invention, the conditions for the polymerization reaction are not particularly limited and can be those conventionally used in the art. Preferably, the polymerization reaction conditions include: a temperature of 30-90°C, more preferably 40-70°C; and a time of 2-15 hours, more preferably 4-10 hours. Controlling the polymerization conditions within the above ranges in this invention helps ensure that the ethylene-vinyl acetate copolymer has a suitable weight-average molecular weight and molecular weight distribution, facilitates monomer conversion, and simultaneously considers the reaction rate. The preferred range offers even better results.

[0046] In this invention, in step S2, the product obtained in step S1 is first mixed with a second solvent, and then mixed with a terminator. In this invention, the self-polymerization of vinyl acetate is initially terminated by using a second solvent, and the product obtained by mixing with the second solvent can be better mixed with the terminator, allowing the terminator to function more effectively.

[0047] In this invention, the amount of the second solvent has a wide selection range. Preferably, based on the weight of the vinyl acetate, the amount of the second solvent is 1-30% by weight, for example, it can be 1% by weight, 5% by weight, 10% by weight, 12% by weight, 14% by weight, 16% by weight, 18% by weight, 20% by weight, 22% by weight, 24% by weight, 26% by weight, 28% by weight, 30% by weight, and any two of the above values ​​within a range, preferably 15-25% by weight. In this invention, controlling the amount of the second solvent within the above range is beneficial to reducing the reaction rate and inhibiting the self-polymerization of vinyl acetate into polyvinyl acetate. The preferred range has even better effects.

[0048] In this invention, the type of the second solvent may be the same as or different from the first solvent. Preferably, the type of the second solvent is the same as the first solvent. Preferably, the second solvent is an alcohol solvent with 1-4 carbon atoms. More preferably, the second solvent is at least one selected from methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol. Even more preferably, the second solvent is methanol.

[0049] In this invention, preferably, the conditions for mixing the product obtained in step S1 with the second solvent include: a temperature of 40-70°C and a time of 1-5 hours. The pressure of the second contact is the same as that of the first contact. Controlling the contact conditions between the product obtained in step S1 and the second solvent within the above range has the characteristics of being consistent with the polymerization reaction conditions, eliminating the need to adjust process parameters, resulting in convenient operation and uniform mixing.

[0050] In some embodiments of the present invention, preferably, the amount of the terminator is 100-5000 ppm of the amount of vinyl acetate, more preferably 300-3000 ppm. In the present invention, controlling the amount of the terminator within the above range effectively reduces the content of polyvinyl acetate in the ethylene-vinyl acetate copolymer solution, preventing over-polymerization. The preferred range provides even better results.

[0051] In this invention, the type of terminating agent is not particularly limited. Preferably, the terminating agent is selected from at least one of 2,4-diphenyl-4-methyl-1-pentene, 2,2-diphenyl-1-trinitrophenylhydrazine, 1,1-diphenyl-2-trinitrophenylhydrazine, 2,4-diphenyl-4-methyl-1-pentene, copper acetate, cuprous chloride, and ferric chloride, and more preferably from at least one of 2,4-diphenyl-4-methyl-1-pentene, copper acetate, cuprous chloride, and ferric chloride.

[0052] In this invention, the conditions for mixing the product obtained in step S1 with the terminator are not particularly limited. Preferably, the conditions for mixing the product obtained in step S1 with the terminator include: a temperature of 10-40°C and a time of 0.1-2 hours. The mixing of the product obtained in step S1 with the terminator is carried out under normal pressure. By controlling the mixing conditions of the product obtained in step S1 with the terminator within the above-mentioned range, it is ensured that the terminator can fully exert its terminating effect.

[0053] In some embodiments of the present invention, preferably, ethylene and vinyl acetate are removed sequentially from the product obtained in step S1 after mixing the terminator.

[0054] In this invention, the method for removing ethylene from the product is not particularly limited, as long as ethylene can be removed without introducing other impurities. Preferably, the method for removing ethylene is vacuum flash evaporation.

[0055] In this invention, preferably, the method for removing vinyl acetate includes: contacting the product obtained after mixing with the terminating agent in step S2 with a third solvent. The contact described in this invention is preferably a vapor contact.

[0056] In this invention, preferably, the third solvent vapor is introduced via countercurrent contact. For example, if the removal of vinyl acetate is carried out in a distillation column, the ethylene-vinyl acetate copolymer solution after the addition of the terminator is introduced into the top of the distillation column, and the third solvent vapor is introduced into the bottom of the distillation column to remove unreacted vinyl acetate monomers from the top of the column by distillation.

[0057] In this invention, the conditions for contacting the third solvent are not particularly limited. Preferably, the conditions for contacting the third solvent include: a temperature of 65-80°C, a pressure of 100-180 kPa, and a time of 0.5-3 h. In this invention, controlling the conditions for contacting the third solvent within the above ranges ensures sufficient gas-liquid exchange between the solvent vapor and the ethylene-vinyl acetate copolymer solution, thereby removing unreacted vinyl acetate.

[0058] In this invention, the third solvent may be the same as or different from the first and second solvents; preferably, it is the same as the first and second solvents. The type of the third solvent is not particularly limited, as long as it can remove vinyl acetate. Preferably, the third solvent is an alcohol solvent, preferably an alcohol solvent with 1-4 carbon atoms, more preferably at least one selected from methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol, and even more preferably methanol.

[0059] In this invention, the method of alcoholysis is not particularly limited. Preferably, the method of alcoholysis includes contacting the ethylene-vinyl acetate copolymer with an alkali.

[0060] In this invention, the molar ratio of the alkali to the vinyl acetate groups in the ethylene-vinyl acetate copolymer solution has a wide range of selection. Preferably, the molar ratio of hydroxide ions in the alkali to vinyl acetate groups in the ethylene-vinyl acetate copolymer is 0.005-0.5:1, more preferably 0.01-0.3:1.

[0061] In this invention, the content of ethylene-vinyl acetate copolymer in the ethylene-vinyl acetate copolymer solution has a wide range of selection. Preferably, the content of ethylene-vinyl acetate copolymer in the ethylene-vinyl acetate copolymer solution is 10-60% by weight, more preferably 20-50% by weight.

[0062] In this invention, the conditions for contacting the ethylene-vinyl acetate copolymer with an alkali are not particularly limited. Preferably, the conditions for contacting the alkali include: a temperature of 50-65°C, a time of 5-15 hours, and a contact pressure of atmospheric pressure. In this invention, controlling the contact conditions with the alkali within the above range and carrying out the reaction under atmospheric pressure is beneficial to ensuring that the prepared ethylene-vinyl alcohol copolymer has good processing stability.

[0063] In this invention, the alkali is an alkaline solution. The type of solvent in the alkaline solution is not particularly limited, as long as it can dissolve the alkali and does not affect the alcoholysis of ethylene-vinyl acetate. Preferably, the solvent of the alkaline solution is an alcohol solvent, preferably an alcohol solvent with 1-4 carbon atoms, more preferably at least one selected from methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol, and even more preferably methanol. The concentration of the alkaline solution is preferably 2%-30% by weight. The type of alkali in the alkaline solution is not limited, as long as it provides an alkaline environment. Preferably, the alkali is sodium hydroxide and / or potassium hydroxide.

[0064] In this invention, preferably, the method further includes: mixing the alcoholyzed ethylene-vinyl alcohol copolymer solution with an acid solution. In this invention, the acid solution contains H... + The preferred dosage is 1-2000 ppm of the ethylene-vinyl alcohol copolymer. The concentration of the acid solution can be 10-50% by weight. There are no particular limitations on the type of acid used in this invention, as long as it can provide cationic hydrogen. The acid is preferably at least one of acetic acid, propionic acid, boric acid, and sodium dihydrogen phosphate. By mixing with the acid, the above-mentioned alkali is neutralized, thereby improving product quality.

[0065] In this invention, preferably, the method further includes: molding and granulating the product of the ethylene-vinyl alcohol copolymer mixed with an acid solution. The molding and granulation method of this invention can employ extrusion methods conventionally used in the art, and will not be elaborated upon here.

[0066] In this invention, preferably, the method further includes washing the ethylene-vinyl alcohol copolymer particles obtained by molding and granulation. In this invention, there are no particular limitations on the number of washes or the type of detergent used. For example, the detergent can be a water-alcohol mixture, and the weight ratio of water to alcohol is preferably 1-20:99-80. Preferably, the alcohol is an alcohol solvent with 1-4 carbon atoms, preferably at least one selected from methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol.

[0067] In this invention, the weight-average molecular weight and molecular weight distribution of the ethylene-vinyl alcohol copolymer particles obtained after molding and granulation have a wide range of selectability. Preferably, the weight-average molecular weight of the copolymer is 30,000-150,000 g / mol, and the molecular weight distribution is 1.5-3.5. In this invention, controlling the weight-average molecular weight and molecular weight distribution of the copolymer within the above range gives the copolymer good mechanical properties and melt processability, which is beneficial for post-processing and results in ethylene-vinyl alcohol copolymer mixtures with superior performance after post-processing. In this invention, the weight-average molecular weight and molecular weight distribution of the ethylene-vinyl alcohol copolymer are measured by GPC method.

[0068] In this invention, the content of ethylene-derived structural units in the ethylene-vinyl alcohol copolymer particles obtained after molding and granulation has a wide range of selectability. Preferably, the content of ethylene-derived structural units in the ethylene-vinyl alcohol copolymer is 20-50 mol%. The above content of ethylene-derived structural units is based on the total molar content of the copolymer. In this invention, controlling the content of ethylene-derived structural units in the copolymer within the above range is beneficial to giving the copolymer better melt processability, thereby facilitating post-processing and resulting in ethylene-vinyl alcohol copolymer mixtures with superior performance after post-processing. In this invention, the content of ethylene structural units in the ethylene-vinyl alcohol copolymer is tested using the method specified in GB / T 41877.2-2022.

[0069] In this invention, unless otherwise specified, the raw materials can be commercially available or prepared using existing technologies.

[0070] A second aspect of the present invention provides an ethylene-vinyl alcohol copolymer mixture prepared by the post-processing method described in the first aspect above.

[0071] In some embodiments of the present invention, preferably, the angle of repose of the ethylene-vinyl alcohol copolymer mixture is 18-35°, more preferably 20-30°. In the present invention, the ethylene-vinyl alcohol copolymer mixture prepared by the method exhibits excellent processing stability and a low angle of repose, resulting in minimal torque and torque fluctuations during the preparation of ethylene-vinyl alcohol films.

[0072] In this invention, unless otherwise specified, the angle of repose refers to the angle between the generatrix of the cone formed by the natural accumulation of ethylene-vinyl alcohol copolymer particles and the bottom surface. In this invention, the angle of repose of the ethylene-vinyl alcohol copolymer mixture is tested using an injection method, specifically: ethylene-vinyl alcohol copolymer mixture particles are injected under gravity through a funnel into the center of a 10cm diameter disk until the material on the inclined side of the particle accumulation layer automatically rolls out along the edge of the disk. The injection is then stopped, and the angle between the inclined surface of the material and the bottom surface is measured using a protractor, thus obtaining the angle of repose.

[0073] A third aspect of the present invention provides the application of the ethylene-vinyl alcohol copolymer mixture described in the second aspect above in at least one of packaging materials, automotive fuel tanks, oxygen-barrier floor heating pipes, textile materials, and medical materials.

[0074] A fourth aspect of the present invention provides an ethylene-vinyl alcohol film, said film being prepared from the ethylene-vinyl alcohol copolymer mixture described in the second aspect above.

[0075] In this invention, there are no limitations on the method for preparing ethylene-vinyl alcohol films from ethylene-vinyl alcohol copolymer mixtures. Conventional testing methods in the art can be used, for example, a blown film machine or a cast film machine can be used.

[0076] In this invention, preferably, the torque during the preparation of the ethylene-vinyl alcohol film is ≤30 Nm, and the torque fluctuation range is ≤1 Nm. In this invention, the ethylene-vinyl alcohol copolymer mixture has a low angle of repose, resulting in small torque and torque fluctuation during the preparation of the ethylene-vinyl alcohol film, and low production energy consumption.

[0077] In this invention, an internal mixer (model Rheomix 600OS) is used to mix the ethylene-vinyl alcohol copolymer at 200°C and a rotor speed of 30 rpm. The mixed ethylene-vinyl alcohol copolymer is then extruded through a single screw (L / D≥25) to produce an ethylene-vinyl alcohol copolymer film. The screw model is Pheomix 19 / 25OS Screw 3:1L / D 25, with a maximum speed of 250 rpm, a maximum stress of 160 Nm, and the screw temperature is set in three zones: 190 / 220 / 220°C. The screw speed is 60-80 rpm, the stretching speed is 2.5-3 m / s, the film width is controlled at 20-30 mm, and the film thickness is controlled at 20-30 μm.

[0078] In some embodiments of the present invention, preferably, the coefficient of kinetic friction of the ethylene-vinyl alcohol film is ≤0.6. In the present invention, the angle of repose of the ethylene-vinyl alcohol copolymer mixture is low, the internal friction between the particles of the ethylene-vinyl alcohol copolymer mixture and the friction between the particles and the processing equipment are low, resulting in a lower coefficient of kinetic friction for the prepared ethylene-vinyl alcohol film.

[0079] In this invention, unless otherwise specified, the coefficient of dynamic friction of the ethylene-vinyl alcohol film is tested according to the GB / T10006-2021 standard, with test conditions of 100mm stroke, 100mm / min speed, and 200g load.

[0080] The present invention will be described in detail below through embodiments.

[0081] All raw materials used in the following examples and comparative examples were commercially available.

[0082] The weight-average molecular weight and molecular weight distribution of the ethylene-vinyl alcohol copolymer were determined by the GPC method; the ethylene structural unit content in the ethylene-vinyl alcohol copolymer was tested according to the method specified in GB / T 41877.2-2022.

[0083] Example 1

[0084] (1) Add 100 parts by weight of vinyl acetate, 18 parts by weight of methanol, and 0.11 parts by weight of azobisisobutyronitrile to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. Raise the temperature to 60°C, maintain the ethylene pressure at 3.8 MPaG, and react for 6 hours with stirring.

[0085] (2) Add 15 parts by weight of methanol to the product obtained in step (1) (keeping the temperature and pressure constant for 3 hours), add 800 ppm (based on the amount of vinyl acetate) of 2,4-diphenyl-4-methyl-1-pentene (for 0.5 hours at 25°C), stir evenly, and then remove unreacted ethylene by flash evaporation under normal pressure. Then, introduce methanol vapor (for 2 hours at 70°C at 140 kPa) and distill to remove unreacted vinyl acetate to obtain an ethylene-vinyl acetate copolymer solution.

[0086] (3) Adjust the ethylene-vinyl acetate copolymer solution to a mass fraction of 35%, and then add a methanol solution of sodium hydroxide (concentration of 10wt%) at 65°C for alcoholysis (time of 5h, pressure of atmospheric pressure). The molar ratio of hydroxide ions in sodium hydroxide to vinyl acetate groups in ethylene-vinyl acetate copolymer is 0.14:1. After alcoholysis, an ethylene-vinyl alcohol copolymer solution is obtained.

[0087] (4) Add acetic acid solution (35 wt%) and boric acid solution (2 wt%) to the ethylene-vinyl alcohol copolymer solution, and stir until homogeneous. The acetic acid and boric acid contain H+. + The dosages were 800 ppm and 300 ppm, respectively, relative to the weight of the ethylene-vinyl alcohol copolymer solids.

[0088] (5) The ethylene-vinyl alcohol copolymer solution obtained in step (4) is extruded into an aqueous solution at 5°C through an extrusion device with a perforated plate. After precipitating into strips, it is cut into particles using a common cutting method. Then, water is added to a kettle with a stirring device to wash the ethylene-vinyl alcohol copolymer particles. Each wash lasts for 2 hours and is repeated twice. Then, a mixed solution of water and ethanol is added to a kettle with a stirring device. After washing at 75°C for 2 hours, it is washed with water once more. During the water washing process, acetic acid with a mass of 0.01 parts relative to the mass of the ethylene-vinyl alcohol copolymer particles (based on a mass of 100 parts) is added for acid washing and centrifugal dehydration.

[0089] (6) Add 2000 ppm of polydimethylsiloxane (with a dynamic viscosity of 1500 mPa·s at 25°C) and a mixture of polyethylene glycol monooctylphenyl ether (polydimethylsiloxane: polyethylene glycol monooctylphenyl ether = 1:3.5) relative to the mass of the ethylene-vinyl alcohol copolymer particles (average particle size of 3.2 mm) to the ethylene-vinyl alcohol copolymer particles obtained by dehydration. Mix for 60 min at 30°C and dry to obtain the ethylene-vinyl alcohol copolymer mixture.

[0090] According to the test results, the weight-average molecular weight of the ethylene-vinyl alcohol copolymer particles in this embodiment is 106,700 g / mol, the molecular weight distribution is 2.1, and the ethylene structural unit content is 32 mol%.

[0091] Example 2

[0092] (1) Add 100 parts by weight of vinyl acetate, 10 parts by weight of methanol, and 0.03 parts by weight of pentyl peroxide to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. Raise the temperature to 65°C, maintain the ethylene pressure at 3.2 MPaG, and react for 5 hours with stirring.

[0093] (2) Add 10 parts by weight of methanol to the product obtained in step (1) (keep the temperature and pressure constant for 2 hours), add 500 ppm of copper acetate (based on the amount of vinyl acetate used) (for 2 hours at 40°C), stir evenly, then release the pressure and flash evaporate to remove unreacted ethylene at atmospheric pressure, then introduce methanol vapor (for 0.5 hours at 80°C and 180 kPa), and distill to remove unreacted vinyl acetate to obtain an ethylene-vinyl acetate copolymer solution.

[0094] (3) Adjust the ethylene-vinyl acetate copolymer solution to a mass fraction of 45%, and then add a methanol solution of sodium hydroxide (concentration of 30wt%) at 60°C for alcoholysis (time of 8h, pressure of atmospheric pressure). The molar ratio of hydroxide ions in sodium hydroxide to vinyl acetate groups in ethylene-vinyl acetate copolymer is 0.09:1. After alcoholysis, an ethylene-vinyl alcohol copolymer solution is obtained.

[0095] (4) Add acetic acid solution (20 wt%) and boric acid solution (2 wt%) to the ethylene-vinyl alcohol copolymer solution, and stir until homogeneous. The acetic acid and boric acid contain H+. + The dosages were 500 ppm and 100 ppm, respectively, relative to the weight of the ethylene-vinyl alcohol copolymer solids.

[0096] (5) The ethylene-vinyl alcohol copolymer solution obtained in step (4) is extruded into an aqueous solution at 5°C through an extrusion device with a perforated plate. After precipitating into strips, it is cut into particles using a common cutting method. Then, water is added to a kettle with a stirring device to wash the ethylene-vinyl alcohol copolymer particles. Each wash lasts for 2 hours and is repeated twice. Then, a mixed solution of water and ethanol is added to a kettle with a stirring device. After washing at 75°C for 2 hours, it is washed with water once more. During the water washing process, acetic acid with a mass of 0.01 parts relative to the mass of the ethylene-vinyl alcohol copolymer particles (based on a mass of 100 parts) is added for acid washing and centrifugal dehydration.

[0097] (6) Add 300 ppm of polydimethylsiloxane (viscosity of 1000 mPa·s at 25°C) and a mixture of polyethylene glycol monooctylphenyl ether (polydimethylsiloxane: polyethylene glycol monooctylphenyl ether ratio of 1:2) relative to the mass of the ethylene-vinyl alcohol copolymer particles (average particle size of 2.8 mm) to the ethylene-vinyl alcohol copolymer particles obtained by dehydration. Mix for 90 min at 25°C and dry to obtain the ethylene-vinyl alcohol copolymer mixture.

[0098] According to the test results, the weight-average molecular weight of the ethylene-vinyl alcohol copolymer particles in this embodiment is 130960 g / mol, the molecular weight distribution is 2.3, and the ethylene structural unit content is 28 mol%.

[0099] Example 3

[0100] (1) Add 100 parts by weight of vinyl acetate, 25 parts by weight of methanol, and 0.1 parts by weight of azobisisobutyronitrile to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. Raise the temperature to 60°C, maintain the ethylene pressure at 5.0 MPaG, and react for 6.5 hours with stirring.

[0101] (2) Add 25 parts by weight of methanol to the product obtained in step (1) (keeping the temperature and pressure constant for 4 hours), add 1000 ppm (based on the amount of vinyl acetate) of cuprous chloride (for 0.1 hours at 35°C), stir evenly, then release the pressure and flash evaporate to remove unreacted ethylene at atmospheric pressure, then introduce methanol vapor (for 2 hours at 70°C at 140 kPa), and distill to remove unreacted vinyl acetate to obtain an ethylene-vinyl acetate copolymer solution.

[0102] (3) Adjust the ethylene-vinyl acetate copolymer solution to a mass fraction of 25%, and then add a methanol solution of sodium hydroxide (concentration of 10wt%) at 55°C for alcoholysis (time of 10h, pressure of atmospheric pressure). The molar ratio of hydroxide ions in sodium hydroxide to vinyl acetate groups in ethylene-vinyl acetate copolymer is 0.2:1. After alcoholysis, an ethylene-vinyl alcohol copolymer solution is obtained.

[0103] (4) Add acetic acid solution (45 wt%) and boric acid solution (2 wt%) to the ethylene-vinyl alcohol copolymer solution, and stir until homogeneous. The acetic acid and boric acid contain H... + The dosages were 1000 ppm and 300 ppm, respectively, relative to the weight of the ethylene-vinyl alcohol copolymer solids.

[0104] (5) The ethylene-vinyl alcohol copolymer solution obtained in step (4) is extruded into an aqueous solution at 5°C through an extrusion device with a perforated plate. After precipitating into strips, it is cut into particles using a common cutting method. Then, water is added to a kettle with a stirring device to wash the ethylene-vinyl alcohol copolymer particles. Each wash lasts for 2 hours and is repeated twice. Then, a mixed solution of water and ethanol is added to a kettle with a stirring device. After washing at 75°C for 2 hours, it is washed with water once more. During the water washing process, acetic acid with a mass of 0.01 parts relative to the mass of the ethylene-vinyl alcohol copolymer particles (based on a mass of 100 parts) is added for acid washing and centrifugal dehydration.

[0105] (6) Add 3000 ppm of polydimethylsiloxane (viscosity of 1800 mPa·s at 25°C) and a mixture of polyethylene glycol monooctylphenyl ether (polydimethylsiloxane: polyethylene glycol monooctylphenyl ether ratio of 1:5) relative to the mass of the ethylene-vinyl alcohol copolymer particles (average particle size of 4 mm) to the ethylene-vinyl alcohol copolymer particles obtained by dehydration. Mix for 35 min at 40°C and dry to obtain the ethylene-vinyl alcohol copolymer mixture.

[0106] According to the test results, the weight-average molecular weight of the ethylene-vinyl alcohol copolymer particles in this embodiment is 630-120 g / mol, the molecular weight distribution is 2.5, and the ethylene structural unit content is 42 mol%.

[0107] Example 4

[0108] The method described in Example 1 differs in that, in step (6), a mixture of polydimethylsiloxane and polyethylene glycol monooctylphenyl ether (polydimethylsiloxane: polyethylene glycol monooctylphenyl ether = 1:3.5) is added to the ethylene-vinyl alcohol copolymer particles obtained by dehydration at a ratio of 50 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

[0109] Example 5

[0110] The method described in Example 1 differs in that, in step (6), a mixture of polydimethylsiloxane and polyethylene glycol monooctylphenyl ether (polydimethylsiloxane: polyethylene glycol monooctylphenyl ether = 1:3.5) is added to the ethylene-vinyl alcohol copolymer particles obtained by dehydration at a ratio of 5000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

[0111] Example 6

[0112] The method described in Example 1 differs in that, in step (6), a mixture of polydimethylsiloxane and polyethylene glycol monooctylphenyl ether (polydimethylsiloxane: polyethylene glycol monooctylphenyl ether = 1:0.5) is added to the ethylene-vinyl alcohol copolymer particles obtained by dehydration.

[0113] Example 7

[0114] The method described in Example 1 differs in that, in step (6), a mixture of polydimethylsiloxane and polyethylene glycol monooctylphenyl ether (polydimethylsiloxane: polyethylene glycol monooctylphenyl ether = 1:10) is added to the ethylene-vinyl alcohol copolymer particles obtained by dehydration.

[0115] Example 8

[0116] The method described in Example 1 differs in that, in step (6), a mixture of polydimethylsiloxane and polyethylene glycol monooctylphenyl ether (polydimethylsiloxane: polyethylene glycol monooctylphenyl ether = 1:10) is added to the ethylene-vinyl alcohol copolymer particles obtained by dehydration.

[0117] Example 9

[0118] The method described in Example 1 is different except that in step (6), polydimethylsiloxane is replaced by an equal amount of ethyl silicone oil (viscosity of 1100 mPa·s at 25°C).

[0119] Example 10

[0120] The method described in Example 1 is different except that in step (6), polydimethylsiloxane is replaced by an equal amount of phenyl silicone oil (viscosity of 1600 mPa·s at 25°C).

[0121] Example 11

[0122] The method described in Example 1 is different except that in step (6), the polydimethylsiloxane is replaced in equal amounts with polydimethylsiloxane with a viscosity of 700 mPa·s at 25°C.

[0123] Comparative Example 1

[0124] The method is the same as in Example 1, except that polydimethylsiloxane is not added in step (6).

[0125] Comparative Example 2

[0126] The method is the same as in Example 1, except that polyethylene glycol monooctylphenyl ether is not added in step (6).

[0127] Comparative Example 3

[0128] The method is the same as in Example 1, except that in step (6), the mass ratio of polydimethylsiloxane to polyethylene glycol monooctylphenyl ether is 1:0.1.

[0129] Comparative Example 4

[0130] The method is the same as in Example 1, except that in step (6), the amount of the mixture of polydimethylsiloxane and polyethylene glycol monooctylphenyl ether is 7000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

[0131] Comparative Example 5

[0132] The method is the same as in Example 1, except that in step (6), polyethylene glycol monooctylphenyl ether is replaced with sodium dodecyl sulfate in equal amounts.

[0133] Test Example 1

[0134] The ethylene-vinyl alcohol copolymer mixtures prepared in the examples and comparative examples were subjected to an angle of repose test. The test method included: injecting the ethylene-vinyl alcohol copolymer mixture particles into the center of a 10 cm diameter disk through a funnel under gravity until the material on the inclined side of the particle accumulation layer automatically rolled out along the edge of the disk, at which point the sample addition was stopped, and then measuring the angle between the inclined surface of the material and the bottom surface with a protractor to obtain the angle of repose. The test results of the angle of repose are shown in Table 1.

[0135] Test Example 2

[0136] The ethylene-vinyl alcohol copolymer mixtures prepared in the examples and comparative examples were used to prepare ethylene-vinyl alcohol films. The preparation method included: mixing the ethylene-vinyl alcohol copolymer mixtures in a Banbury mixer (model Rheomix 600OS) at 200°C and a rotor speed of 30 rpm; extruding the mixed ethylene-vinyl alcohol copolymer mixtures into ethylene-vinyl alcohol films through a single screw (L / D≥25); wherein the screw model was Pheomex 19 / 25OS Screw 3:1L / D25, the maximum speed was 250 rpm, the maximum stress was 160 Nm, the screw temperature was set in three zones, namely 190 / 220 / 220°C, the screw speed was 60 rpm, the stretching speed was 3 m / s, the film width was controlled at 20 mm, and the film thickness was controlled at 20 μm. The torque and torque fluctuation range during the preparation of ethylene-vinyl alcohol films are shown in Table 1.

[0137] The dynamic friction coefficient of the ethylene-vinyl alcohol film was tested according to GB / T 10006-2021 standard. The test conditions were 100 mm stroke, 100 mm / min speed, and 200 g load. The test results are shown in Table 1.

[0138] Table 1

[0139] serial number Angle of repose (°) Torque (Nm) Torque fluctuation range (Nm) coefficient of kinetic friction Example 1 23.5 21 0.4 0.32 Example 2 29.3 24 0.7 0.48 Example 3 18.9 19 0.8 0.34 Example 4 33.7 26 0.7 0.50 Example 5 25.3 21 0.5 0.37 Example 6 32 24 0.8 0.41 Example 7 31.6 23 0.7 0.39 Example 8 34.5 28 0.8 0.43 Example 9 28.5 23 0.5 0.38 Example 10 29 24 0.5 0.40 Example 11 28.9 25 0.7 0.44 Comparative Example 1 38.8 33 1.9 0.81 Comparative Example 2 37.2 31 1.6 0.77 Comparative Example 3 36.5 31 1.2 0.70 Comparative Example 4 16.7 17 1.2 0.72 Comparative Example 5 36.7 32 1.3 0.80

[0140] As can be seen from the results in Table 1, the ethylene-vinyl alcohol copolymer mixture prepared by the method provided in this invention has good processing stability and a low angle of repose. During the processing of ethylene-vinyl alcohol films prepared from this ethylene-vinyl alcohol copolymer mixture, the torque is ≤30 Nm, the torque fluctuation range is ≤1 Nm, and the dynamic friction coefficient of the obtained ethylene-vinyl alcohol film is ≤0.6.

[0141] 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 inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A post-processing method for ethylene-vinyl alcohol copolymers, characterized in that, The method includes: contacting the ethylene-vinyl alcohol copolymer particles obtained after molding and granulation with silicone oil and polyethylene glycol monooctylphenyl ether to obtain an ethylene-vinyl alcohol copolymer mixture; Based on the mass of the ethylene-vinyl alcohol copolymer particles, the total mass of the silicone oil and polyethylene glycol monooctylphenyl ether is 50-5000 ppm. The mass ratio of the silicone oil to the polyethylene glycol monooctylphenyl ether is 1:0.5-10.

2. The post-processing method according to claim 1, wherein, Based on the mass of the ethylene-vinyl alcohol copolymer particles, the total mass of the silicone oil and polyethylene glycol monooctylphenyl ether is 300-3000 ppm; Preferably, the mass ratio of the silicone oil to the polyethylene glycol monooctylphenyl ether is 1:2-5.

3. The post-processing method according to claim 1 or 2, wherein, The silicone oil has a dynamic viscosity of 500-3000 mPa·s at 25°C, preferably 1000-2000 mPa·s; Preferably, the silicone oil is selected from at least one of polydimethylsiloxane, ethyl silicone oil, methylethoxy silicone oil, methyl vinyl silicone oil and phenyl silicone oil, and is preferably polydimethylsiloxane.

4. The post-processing method according to claim 1, wherein, The contact conditions include: a contact temperature of 20-60℃, preferably 25-40℃; and a contact time of 10-120 min, preferably 30-90 min.

5. The post-processing method according to claim 1, wherein, The method for preparing the ethylene-vinyl alcohol copolymer particles includes: S1. A polymerization reaction is carried out using a first solvent, an initiator, vinyl acetate, and ethylene as raw materials; S2. The product obtained in step S1 is mixed sequentially with the second solvent and the terminator to obtain an ethylene-vinyl acetate copolymer solution. S3. The ethylene-vinyl acetate copolymer solution is subjected to alcoholysis and granulation to obtain the ethylene-vinyl alcohol copolymer particles.

6. The post-processing method according to claim 5, wherein, Based on the weight of the vinyl acetate, the amount of the second solvent is 1% to 30% by weight; Preferably, the amount of the terminating agent is 100-5000 ppm of the amount of vinyl acetate used; Preferably, the terminating agent is selected from at least one of 2,4-diphenyl-4-methyl-1-pentene, 2,2-diphenyl-1-trinitrophenylhydrazine, 1,1-diphenyl-2-trinitrophenylhydrazine, 2,4-diphenyl-4-methyl-1-pentene, copper acetate, cuprous chloride, and ferric chloride, and more preferably from at least one of 2,4-diphenyl-4-methyl-1-pentene, copper acetate, cuprous chloride, and ferric chloride; Preferably, the conditions for mixing the product obtained in step S1 with the second solvent include: a temperature of 40-70°C and a time of 1-5 hours; Preferably, the conditions for mixing the product obtained in step S1 with the terminator include: a temperature of 10-40°C and a time of 0.1-2 h; Preferably, the method further includes: sequentially removing ethylene and vinyl acetate from the product obtained in step S1 after mixing the terminator.

7. An ethylene-vinyl alcohol copolymer mixture prepared by the post-processing method according to any one of claims 1-6.

8. The ethylene-vinyl alcohol copolymer mixture according to claim 7, wherein, The angle of repose of the ethylene-vinyl alcohol copolymer mixture is 18-35°, preferably 20-30°.

9. The use of the ethylene-vinyl alcohol copolymer mixture of claim 7 or 8 in at least one of packaging materials, automotive fuel tanks, oxygen-barrier floor heating pipes, textile materials, and medical materials.

10. An ethylene-vinyl alcohol film, characterized in that, The film is prepared from the ethylene-vinyl alcohol copolymer mixture according to claim 7 or 8; Preferably, the coefficient of dynamic friction of the ethylene-vinyl alcohol film is ≤0.6.