Ethylene-vinyl alcohol copolymer mixture, process for its preparation and use thereof

Abstract

The present application relates to the technical field of ethylene-vinyl alcohol copolymer, in particular to an ethylene-vinyl alcohol copolymer mixture, a preparation method and application thereof. The preparation method of the ethylene-vinyl alcohol copolymer mixture comprises the following steps: mixing an ethylene-vinyl alcohol copolymer solution obtained by alcoholysis of ethylene-vinyl acetate copolymer with a suspension solution containing inorganic matter, and then performing pressing and molding to obtain the ethylene-vinyl alcohol copolymer mixture; the amount of the inorganic matter is 160 ppm-5000 ppm based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution. The ethylene-vinyl alcohol copolymer mixture prepared by the method has a low rest angle, a low processing load and a low production energy consumption, and has stable processing performance.

Description

Technical Field

[0001] This invention relates to the field of ethylene-vinyl alcohol copolymer technology, and more specifically to an ethylene-vinyl alcohol copolymer mixture, its preparation method, and its application. Background Technology

[0002] Ethylene-vinyl alcohol copolymer (EVOH) resin is widely used in multilayers for preserving perishable goods. EVOH resin and multilayers play important roles in various industries, including food packaging, medical devices and consumables, pharmaceuticals, electronics, and agrochemicals. EVOH resin is often incorporated into multilayers as a unique layer to act as an oxygen barrier.

[0003] EVOH resin particles are granular solid materials. When these particles naturally accumulate, they form a cone. The angle between the generatrix of the cone and its base is called the angle of repose, which represents the frictional properties between the resin particles; it is also known as the angle of rest or angle of repose. The angle of repose can be used to evaluate the flowability of large particles such as resins and to assess the processing performance of polymer materials. A lower angle of repose results in smoother screw feeding, less friction between particles, lower processing torque, lower processing load, lower production energy consumption, and more stable production. Currently, it is known that EVOH particles formed from EVOH resin have a large surface roughness, a high angle of repose, and high friction between particles, leading to extremely high torque during EVOH processing. Although adding lubricants has been used to adjust the processability of EVOH, the effect is not ideal, and further improvement is still necessary.

[0004] Therefore, there is an urgent need to develop an ethylene-vinyl alcohol copolymer with a low angle of repose. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of high surface roughness and high torque during processing of ethylene-vinyl alcohol copolymer particles in existing technologies, and to provide an ethylene-vinyl alcohol copolymer mixture, its preparation method, and its applications. The ethylene-vinyl alcohol copolymer mixture prepared by this method has a lower angle of repose, lower friction between ethylene-vinyl alcohol copolymer particles, lower load during processing, lower production energy consumption, and stable processing performance.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing an ethylene-vinyl alcohol copolymer mixture, wherein an ethylene-vinyl alcohol copolymer solution obtained by alcoholysis of ethylene-vinyl acetate copolymer is mixed with a suspension containing inorganic matter, and the mixture is then pressed and shaped to obtain an ethylene-vinyl alcohol copolymer mixture.

[0007] The amount of inorganic material used is 160ppm-5000ppm, based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution.

[0008] A second aspect of the present invention provides an ethylene-vinyl alcohol copolymer mixture prepared by the method described in the first aspect above.

[0009] A third aspect of the present invention provides an 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.

[0010] Through the above technical solution, the present invention has the following beneficial effects:

[0011] The method for preparing an ethylene-vinyl alcohol copolymer mixture provided by this invention involves mixing an ethylene-vinyl alcohol copolymer solution obtained after alcoholysis with a suspension of inorganic substances, wherein the ethylene-vinyl alcohol copolymer and inorganic substances are used in a specific ratio. The inorganic particles adhere to the molecular chains of the ethylene-vinyl alcohol copolymer, and the suspended inorganic substances, due to the van der Waals forces and hydrogen bonds between water molecules and the ethylene-vinyl alcohol copolymer, promote the uniform distribution of inorganic particles in the ethylene-vinyl alcohol copolymer matrix. Compared with the prior art of adding lubricants, this method significantly reduces the coefficient of friction of the ethylene-vinyl alcohol copolymer mixture particles, resulting in a lower angle of repose for the ethylene-vinyl alcohol copolymer mixture particles. This improves the processing stability of the ethylene-vinyl alcohol copolymer, reduces processing load, and lowers noise, effectively reducing production energy consumption and making it suitable for industrial production. Detailed Implementation

[0012] 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.

[0013] The first aspect of the present invention provides a method for preparing an ethylene-vinyl alcohol copolymer mixture, wherein an ethylene-vinyl alcohol copolymer solution obtained by alcoholysis of ethylene-vinyl acetate copolymer is mixed with a suspension containing inorganic matter, and the mixture is then pressed and shaped to obtain an ethylene-vinyl alcohol copolymer mixture;

[0014] The amount of inorganic material used is 160ppm-5000ppm, based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution.

[0015] During their research, the inventors of this invention discovered that by mixing the ethylene-vinyl alcohol copolymer solution obtained after alcoholysis with a suspension of inorganic substances, and by using the ethylene-vinyl alcohol copolymer and inorganic substances in a specific ratio, the inorganic particles adhere to the molecular chains of the ethylene-vinyl alcohol copolymer. Furthermore, the water in the suspension interacts with the ethylene-vinyl alcohol copolymer through van der Waals and hydrogen bonding, which promotes the uniform distribution of inorganic particles within the ethylene-vinyl alcohol copolymer matrix. The inorganic particles partially disrupt the ordered structure within the ethylene-vinyl alcohol copolymer, making it easier to reach a molten state. Additionally, the nano-inorganic particles act as an external lubricant, reducing the processing load on the ethylene-vinyl alcohol copolymer mixture. The inorganic particles present on the surface of the ethylene-vinyl alcohol copolymer impart better slip properties, reducing the friction on the surface of the ethylene-vinyl alcohol copolymer mixture particles, thereby lowering its angle of repose.

[0016] In this invention, unless otherwise specified, the ethylene-vinyl alcohol copolymer mixture refers to a mixture of ethylene-vinyl alcohol copolymer and inorganic substances.

[0017] In some embodiments of the present invention, preferably, the amount of the inorganic substance is 160ppm-5000ppm based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution. For example, it can be 160ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, or any value within the range of the two values ​​mentioned above.

[0018] In this invention, controlling the amount of inorganic material within the aforementioned range is beneficial for improving the surface roughness of the ethylene-vinyl alcohol copolymer mixture particles and reducing the angle of repose, thereby reducing torque during subsequent processing and controlling costs. In this invention, based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution, the amount of inorganic material is less than 160 ppm. Insufficient inorganic material cannot effectively improve the surface roughness of the ethylene-vinyl alcohol copolymer mixture particles, nor can it provide molecular chain lubrication, failing to address the processing difficulties caused by high processing torque. Conversely, an excessive amount of inorganic material (greater than 5000 ppm) will occupy the space between ethylene-vinyl alcohol copolymer molecules, affecting the arrangement and interaction of molecular chains, making molding difficult, and leading to performance degradation.

[0019] Preferably, the amount of inorganic material used is 200ppm-5000ppm, more preferably 200ppm-2000ppm, based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution.

[0020] In some embodiments of the present invention, preferably, the inorganic material is selected from at least one of talc, titanium dioxide, mica powder, zinc oxide, boron nitride, silicon carbide, calcium carbonate, and silicon dioxide, and more preferably from at least one of talc, titanium dioxide, zinc oxide, boron nitride, silicon carbide, and silicon dioxide.

[0021] In some embodiments of the present invention, preferably, the average particle size of the inorganic material is 6.5 μm-75 μm, for example, it can be 6.5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, 38 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, or any value within the range of the two values ​​above.

[0022] In this invention, controlling the average particle size of inorganic materials within the above-mentioned range is beneficial for uniform adhesion to the ethylene-vinyl alcohol copolymer, reducing intermolecular friction and friction between polymer particles, thereby enhancing the long-term processing stability of the ethylene-vinyl alcohol copolymer mixture particles.

[0023] Preferably, the average particle size of the inorganic material is 6.5 μm-18 μm.

[0024] In some embodiments of the present invention, preferably, the content of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution is 10wt%-80wt%, for example, it can be 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, or any value within a range of any two values.

[0025] In this invention, controlling the content of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution within the above-mentioned range is beneficial to the full contact and mixing of ethylene-vinyl alcohol copolymer with inorganic substances, improving the uniformity of mixing with the inorganic suspension solution, and facilitating subsequent processing.

[0026] In some embodiments of the present invention, preferably, the mass ratio of solvent to inorganic matter in the suspension containing inorganic matter is 100:0.01-30, for example, it can be 100:0.01, 100:0.05, 100:0.1, 100:0.5, 100:1, 100:5, 100:10, 100:15, 100:20, 100:25, 100:30, or any value within any range of any two values.

[0027] In this invention, the mass ratio of solvent to inorganic matter in the suspension containing inorganic matter is controlled within the above-mentioned range to ensure the stability of the suspension, avoid sedimentation and agglomeration of inorganic particles, and facilitate the uniform distribution of inorganic particles in the ethylene-vinyl alcohol copolymer, thereby improving the performance of the ethylene-vinyl alcohol copolymer mixture.

[0028] Preferably, the mass ratio of solvent to inorganic matter in the suspension containing inorganic matter is 1:0.1-10.

[0029] In this invention, the type of solvent in the suspension containing inorganic matter is not particularly limited, as long as it can form a suspension containing inorganic matter with the aforementioned inorganic matter. Preferably, the solvent in the suspension containing inorganic matter is selected from C1-C4 alcohol solvents and / or water, more preferably selected from at least one of methanol, ethanol, ethylene glycol, n-propanol, propylene glycol and water.

[0030] In some embodiments of the present invention, preferably, the content of structural units from ethylene in the ethylene-vinyl acetate copolymer is 10 mol%-50 mol%, and the content of structural units from vinyl acetate is 50 mol%-90 mol%.

[0031] In this invention, controlling the content of structural units from ethylene and the content of structural units from vinyl acetate in the ethylene-vinyl acetate copolymer within the above-mentioned range is beneficial to giving the ethylene-vinyl acetate copolymer mixture better processability.

[0032] Preferably, the content of structural units derived from ethylene in the ethylene-vinyl acetate copolymer is 29 mol%-44 mol%, and the content of structural units derived from vinyl acetate is 56 mol%-71 mol%.

[0033] In this invention, the content of ethylene structural units and the content of vinyl acetate structural units in the ethylene-vinyl acetate copolymer are tested using an infrared spectrometer.

[0034] In this invention, the source of the ethylene-vinyl acetate copolymer is not particularly limited. It can be commercially available or prepared using existing technology, as long as the content of structural units from ethylene and the content of structural units from vinyl acetate in the ethylene-vinyl acetate copolymer meet the above-mentioned range.

[0035] In this invention, the mixing conditions for the ethylene-vinyl alcohol copolymer solution and the suspension containing inorganic substances are not particularly limited, as long as the ethylene-vinyl alcohol copolymer solution and the suspension containing inorganic substances are mixed evenly. Preferably, the mixing conditions include: under stirring conditions, the mixing temperature is 50℃-100℃, preferably 60℃-80℃; and the mixing time is 1h-20h, preferably 4h-10h.

[0036] In this invention, controlling the mixing conditions within the aforementioned range is beneficial for ensuring uniform dispersion of inorganic substances in the ethylene-vinyl alcohol copolymer solution, preventing agglomeration and precipitation, and optimizing the mixing process. Even better results are achieved within the preferred range.

[0037] In this invention, the stirring conditions are not particularly limited. Preferably, the stirring speed is 50 rpm to 200 rpm, and more preferably 60 rpm to 100 rpm.

[0038] In this invention, the method of alcoholysis is not particularly limited, and the alcoholysis method of ethylene-vinyl acetate copolymer conventionally used in the art can be employed. Preferably, the alcoholysis method includes contacting the ethylene-vinyl acetate copolymer with an alkaline solution.

[0039] In this invention, the molar ratio of the alkali in the alkaline solution 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 alkaline solution to vinyl acetate groups in the ethylene-vinyl acetate copolymer is 0.1-10:1.

[0040] In this invention, controlling the molar ratio of hydroxide ions in the alkaline solution to vinyl acetate groups in the ethylene-vinyl acetate copolymer within the above range is beneficial to improving reaction efficiency and reducing the generation of reaction byproducts.

[0041] Preferably, the molar ratio of hydroxide ions in the alkaline solution to vinyl acetate groups in the ethylene-vinyl acetate copolymer is 0.1-9:1.

[0042] In this invention, the conditions for alcoholysis are not particularly limited, and conventional alcoholysis conditions used in the art can be adopted, as long as complete alcoholysis is ensured.

[0043] In this invention, the type of solvent for 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 for the alkaline solution is an alcohol solvent, preferably an alcohol solvent with 1-4 carbon atoms, and more preferably at least one selected from methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol.

[0044] In this invention, the concentration of the alkaline solution is not particularly limited, as long as the molar ratio of hydroxide ions in the alkaline solution to vinyl acetate groups in the ethylene-vinyl acetate copolymer meets the above-mentioned range. Preferably, the concentration of the alkaline solution is 0.1 wt%-10 wt%. 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.

[0045] In this invention, preferably, the method further includes: mixing the ethylene-vinyl alcohol copolymer solution obtained after alcoholysis with an acid solution. In this invention, the amount of acid solution used is preferably 1-2000 ppm of the ethylene-vinyl alcohol copolymer. The concentration of the acid solution can be 0.05 wt%-5 wt%. 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 selected from acetic acid, propionic acid, citric acid, boric acid, and sodium dihydrogen phosphate. By mixing with the acid, the above-mentioned alkali is neutralized, thereby improving product quality.

[0046] In this invention, the pressing and molding methods can be methods conventionally used in the art, and will not be described in detail here.

[0047] In this invention, in order to obtain the final ethylene-vinyl alcohol copolymer mixture product, preferably, the method further includes: pressing and molding the product of the ethylene-vinyl alcohol copolymer solution and the suspension containing inorganic matter, followed by washing.

[0048] In this invention, the number of washing cycles is not particularly limited; the washing can be a single wash or multiple washes. The type of detergent used in this invention is not particularly limited; it can be alcohol, water, or a mixture of alcohol and water. 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. The weight ratio of water to alcohol in the alcohol-water mixture is preferably 1-20:99-80.

[0049] A second aspect of the present invention provides an ethylene-vinyl alcohol copolymer mixture prepared by the method described in the first aspect above.

[0050] In this invention, unless otherwise specified, the ethylene-vinyl alcohol copolymer mixture exists in the form of ethylene-vinyl alcohol copolymer / inorganic mixture particles.

[0051] In some embodiments of the present invention, preferably, the content of inorganic matter in the ethylene-vinyl alcohol copolymer mixture is 160ppm-5000ppm, more preferably 200ppm-5000ppm, and more preferably 200ppm-2000ppm. In the present invention, unless otherwise specified, the inorganic matter in the ethylene-vinyl alcohol copolymer mixture is tested using the evaporation residue test method.

[0052] In this invention, the shape of the ethylene-vinyl alcohol copolymer mixture particles is not particularly limited, and can be any shape of ethylene-vinyl alcohol copolymer mixture particles conventionally used in the art, for example, at least one of cylinder, sphere and ellipsoid.

[0053] In this invention, the particle size of the ethylene-vinyl alcohol copolymer mixture particles has a wide selection range. Preferably, the average particle size of the ethylene-vinyl alcohol copolymer mixture particles is 1 mm-20 mm, more preferably 1 mm-15 mm. In this invention, unless otherwise specified, the particle size of the ethylene-vinyl alcohol copolymer mixture particles refers to the maximum straight-line distance on the ethylene-vinyl alcohol copolymer mixture particles. The particle size of the ethylene-vinyl alcohol copolymer mixture particles in this invention is determined by a sieving method.

[0054] In this invention, preferably, the angle of repose of the ethylene-vinyl alcohol copolymer mixture particles is 10°-45°, more preferably 30°-40°. In this invention, the ethylene-vinyl alcohol copolymer mixture particles prepared by the above method have a low coefficient of friction, resulting in a low angle of repose, which is beneficial for improving the processing stability of the ethylene-vinyl alcohol copolymer mixture, reducing processing load, and lowering noise, thus effectively reducing production energy consumption.

[0055] In this invention, the method for testing the angle of repose of the ethylene-vinyl alcohol copolymer mixture particles follows the method described in patent CN108414397A, specifically including:

[0056] S1: Determine the particle size distribution of the sample and measure the geometric dimensions of the ethylene-vinyl alcohol copolymer mixture particles within the sample: The sample is sieved using a sieve to obtain the particle size distribution, and the number of ethylene-vinyl alcohol copolymer mixture particles at each level is determined; the geometric dimensions of the sieved ethylene-vinyl alcohol copolymer mixture particles at each level are measured, including length, width, and thickness, and the geometric dimensions satisfy a normal distribution; the sample mean of the geometric dimensions of the ethylene-vinyl alcohol copolymer mixture particles is statistically analyzed as the dimensional basis for establishing the particle model.

[0057] S2: Based on the sample mean of the geometric dimensions of the ethylene-vinyl alcohol copolymer mixture particles, establish particle models: Based on the sample mean of the geometric dimensions of the ethylene-vinyl alcohol copolymer mixture particles in the sample, establish multiple graded particle models; the particle models are set as cylindrical models, spherical models, or ellipsoidal models; the ratio of the number of particle models at each level is consistent with the ratio of the number of ethylene-vinyl alcohol copolymer mixture particles at each level in the sample sieving results.

[0058] S3: Use the particle model to simulate particle flow and determine the geometric dimensions of the box: Use discrete element software to simulate particle flow, build a simulated box with a gate, test the angle of repose of the particle model, and gradually increase the geometric dimensions of the simulated box from small to large to conduct simulation tests until the change in the angle of repose measurement result is less than 5%, and use the final simulated box dimensions as the geometric dimensions for making the physical box. Specifically, the particle model is simulated using bonding particles in discrete element method (DEM) software. The bonding force parameters of the bonding particles include normal contact force and tangential contact force. The normal contact force is determined by the Mindlin model method in Hertz theory, and the tangential contact force is determined by the Thornton method, which combines the Savkoor-Briggs method and the Mindlin-Dereciewicz method. Angle of repose tests are performed on the particle model. First, the height of the simulated chamber is fixed at 30-50 times the average particle diameter of the particle model and kept constant. The initial length and width of the simulated chamber are both set to 10 times the average particle diameter of the particle model. Then, the length and width of the simulated chamber are gradually increased, each time by twice the average particle diameter of the particle model, until the change in the angle of repose test result is less than 5%, at which point the increase stops. The final simulated chamber dimensions are used as the basis for manufacturing the physical chamber.

[0059] S4: Construct a solid box according to the geometric dimensions of the box and measure the angle of repose: The solid box includes a transparent glass box, a scale, and a gate. The solid box is hexahedral in shape (with a smooth and flat internal surface). The top surface and one side are open, and the remaining sides are composed of baffles. The two side baffles adjacent to the open side are provided with grooves. The grooves are used to insert the gate, which serves as a baffle for the solid box on that side. There are two scales, which are respectively set on the left and right sides of the baffle perpendicular to the gate. The scales are arranged along the vertical boundary line of the solid box, and the direction of the scales is perpendicular to the ground. The readings are taken from the upper edge of the box as the origin and increase from top to bottom, in millimeters.

[0060] The process for measuring the angle of repose of ethylene-vinyl alcohol copolymer mixture particles is as follows: First, place the physical box on a flat and open ground. Pass the gate through the groove to make the transparent box completely closed. Then, load the ethylene-vinyl alcohol copolymer mixture particles to be tested into the box from above, filling or nearly filling the box, and leveling the upper surface of the material. Next, quickly pull the gate upwards, ensuring it is fully pulled up in one go, allowing the resin material to slide downwards naturally. Once the particles are completely still, measure and calculate. Observe the scales on both the left and right sides to obtain the left and right height values. Based on the left and right height values ​​and the length of the long side of the physical box, calculate the angle between the upper surface of the particles and the horizontal plane when they are still using trigonometric functions. The angle between the upper surface of the particles and the horizontal plane when they are still is the angle of repose.

[0061] A third aspect of the present invention provides an 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.

[0062] The present invention will be described in detail below through examples. All raw materials used in the following examples and comparative examples were commercially available.

[0063] Example 1

[0064] (1) Ethylene-vinyl acetate copolymer (containing 71 mol% of vinyl acetate structural units) was subjected to alcoholysis with a methanol solution of sodium hydroxide (concentration of 0.1 wt%), wherein the molar ratio of hydroxide ions in sodium hydroxide to vinyl acetate structural units in ethylene-vinyl acetate copolymer was 0.1:1, until alcoholysis was complete, and an ethylene-vinyl alcohol copolymer solution was obtained. The content of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution was 10 wt%.

[0065] (2) Add acetic acid solution (concentration of 1.5 wt%) to the ethylene-vinyl alcohol copolymer solution and stir until homogeneous, wherein the amount of acetic acid solution used is 1000 ppm relative to the weight of the ethylene-vinyl alcohol copolymer solids (based on 1 part by mass);

[0066] (3) Add an ethanol suspension of silica (average particle size of 18 μm) (mass ratio of ethanol to silica of 100:0.01) to the ethylene-vinyl alcohol copolymer solution obtained in step (2), and stir at 50 rpm for 1 h at 50 °C. The amount of silica used is 200 ppm based on the mass of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution, to obtain a mixed solution of ethylene-vinyl alcohol copolymer.

[0067] (4) The ethylene-vinyl alcohol copolymer mixture solution is pressed and shaped. The resulting ethylene-vinyl alcohol copolymer mixture particles are washed twice with water in a kettle with a stirring device, each time for 2 hours. Then, a mixture of water and ethanol (water and ethanol weight ratio of 1:99) is added to it and washed for 2 hours. After washing with water once more, acetic acid of 5 wt% relative to the ethylene-vinyl alcohol copolymer mixture particles (by mass 1 part) is added for acid washing. After acid washing, the mixture is centrifuged to dehydrate, dried and granulated, and then granulated to obtain cylindrical ethylene-vinyl alcohol copolymer mixture particles.

[0068] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 200 ppm.

[0069] Example 2

[0070] (1) Ethylene-vinyl acetate copolymer (containing 62 mol% of the structural units from vinyl acetate) was subjected to alcoholysis with a methanol solution of sodium hydroxide (concentration of 10 wt%), wherein the molar ratio of hydroxide ions in sodium hydroxide to the vinyl acetate structural units in the ethylene-vinyl acetate copolymer was 10:1, until alcoholysis was complete, and an ethylene-vinyl alcohol copolymer solution was obtained. The content of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution was tested to be 80 wt%.

[0071] (2) Add propionic acid solution (concentration of 1.5 wt%) to the ethylene-vinyl alcohol copolymer solution and stir until homogeneous, wherein the amount of acetic acid used is 1000 ppm relative to the weight of the ethylene-vinyl alcohol copolymer solids (based on 1 part by mass);

[0072] (3) Add ethanol suspension of talc powder (average particle size of 6.5 μm) to the ethylene-vinyl alcohol copolymer solution obtained in step (2) (mass ratio of ethanol to talc powder is 100:30), stir at 200 rpm for 20 h at 80 °C, wherein the amount of talc powder used is 2000 ppm based on the mass of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution, to obtain a mixed solution of ethylene-vinyl alcohol copolymer;

[0073] (4) The ethylene-vinyl alcohol copolymer mixture solution is pressed and shaped. The resulting ethylene-vinyl alcohol copolymer mixture particles are washed twice with water in a kettle with a stirring device, each time for 2 hours. Then, a mixture of water and methanol (water and ethanol weight ratio of 20:80) is added to it for 2 hours. After washing with water once more, 5 wt% of propionic acid relative to the weight of the ethylene-vinyl alcohol copolymer mixture particles (based on 1 part by weight) is added for acid washing. After acid washing, the mixture is centrifuged to dehydrate, dried and granulated, and then granulated to obtain cylindrical ethylene-vinyl alcohol copolymer mixture particles.

[0074] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 2000 ppm.

[0075] Example 3

[0076] (1) Ethylene-vinyl acetate copolymer (containing 68 mol% of the structural units from vinyl acetate) was subjected to alcoholysis with a methanol solution of sodium hydroxide (concentration of 4 wt%), wherein the molar ratio of hydroxide ions in sodium hydroxide to the vinyl acetate structural units in the ethylene-vinyl acetate copolymer was 5:1, until alcoholysis was complete, and an ethylene-vinyl alcohol copolymer solution was obtained. The content of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution was 60 wt%.

[0077] (2) Add acetic acid solution (concentration of 1 wt%) to the ethylene-vinyl alcohol copolymer solution and stir until uniform, wherein the amount of citric acid used is 1000 ppm relative to the weight of the ethylene-vinyl alcohol copolymer solids (based on 1 part by mass);

[0078] (3) Add an ethanol suspension of titanium dioxide (average particle size of 10 μm) (mass ratio of ethanol to titanium dioxide of 100:15) to the ethylene-vinyl alcohol copolymer solution obtained in step (2), and stir at 100 rpm for 10 h at 65 °C. The amount of titanium dioxide used is 600 ppm, based on the mass of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution, to obtain a mixed solution of ethylene-vinyl alcohol copolymer.

[0079] (4) The ethylene-vinyl alcohol copolymer mixture solution is pressed and shaped. The resulting ethylene-vinyl alcohol copolymer mixture particles are washed twice with water in a kettle with a stirring device, each time for 2 hours. Then, a mixture of water and ethanol (water to ethanol weight ratio of 15:85) is added and washed for 2 hours. After washing with water once more, 0.8 wt% of citric acid relative to the ethylene-vinyl alcohol copolymer mixture particles (by mass of 1 part) is added for acid washing. After acid washing, the mixture is centrifuged to dehydrate, dried and granulated, and then granulated to obtain cylindrical ethylene-vinyl alcohol copolymer mixture particles.

[0080] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 600 ppm.

[0081] Example 4

[0082] The method is the same as in Example 1, except that in step (2), the average particle size of silica is increased from 18 μm to 75 μm.

[0083] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 200 ppm.

[0084] Example 5

[0085] The method is the same as in Example 1, except that in step (2), the average particle size of silica is reduced from 18 μm to 5 μm.

[0086] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 200 ppm.

[0087] Example 6

[0088] The method is the same as in Example 1, except that in step (2), the amount of silica used is 160 ppm, based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution.

[0089] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 160 ppm.

[0090] Example 7

[0091] The method is the same as in Example 1, except that in step (2), the amount of silica used is 5000 ppm, based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution.

[0092] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 5000 ppm.

[0093] Example 8

[0094] The method is the same as in Example 1, except that in step (2), the mass ratio of ethanol to silicon dioxide is 100:30.

[0095] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 200 ppm.

[0096] Example 9

[0097] The method is the same as in Example 1, except that in step (1), the content of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution obtained after alcoholysis is 80 wt%.

[0098] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 200 ppm.

[0099] Example 10

[0100] The method of Example 1 is the same, except that in step (1), the average particle size of silica is reduced from 18 μm to 5 μm.

[0101] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 200 ppm.

[0102] Example 11

[0103] The method is the same as in Example 1, except that in step (2), silicon dioxide is replaced by an equal amount of calcium carbonate (with an average particle size of 18 μm).

[0104] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 200 ppm.

[0105] Comparative Example 1

[0106] The method is the same as in Example 1, except that in step (2), the amount of silica used is 50 ppm, based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution.

[0107] Tests showed that the inorganic content in the ethylene-vinyl alcohol copolymer mixture particles was 50 ppm.

[0108] Comparative Example 2

[0109] The method described in Example 1 is different except that step (3) is omitted, and cylindrical ethylene-vinyl alcohol copolymer particles are obtained. The prepared ethylene-vinyl alcohol copolymer particles are dry-mixed with silica (particle size of 900 μm) at 120°C and 10 rpm for 1 h, wherein the mass ratio of ethylene-vinyl acetate copolymer to silica is 100:0.01; and cylindrical ethylene-vinyl alcohol copolymer mixture particles are obtained.

[0110] Comparative Example 3

[0111] Resin composite particles containing ethylene-vinyl alcohol copolymer (ethylene-vinyl alcohol copolymer mixture particles) were prepared according to the method of Example 1 of JP202393037A.

[0112] Test Example 1

[0113] The ethylene-vinyl alcohol copolymer mixture particles prepared in the examples and comparative examples were subjected to angle of repose tests. The solid box was determined and the angle of repose test was performed according to the method described in patent CN108414397A. The test results are shown in Table 1. The specific method includes:

[0114] S1. Determine the particle size distribution of the ethylene-vinyl alcohol copolymer mixture. Prepare at least 100 ethylene-vinyl alcohol copolymer mixture particles. Based on the sample size of the ethylene-vinyl alcohol copolymer mixture particles, sieve them using a sieve machine to determine the quantity of ethylene-vinyl alcohol copolymer mixture particles at each grade. Use vernier calipers to measure the length, width, and thickness of the ethylene-vinyl alcohol copolymer mixture particles respectively. The length, width, and thickness values ​​of the sample particle size should meet a normal distribution. Then, statistically analyze the sample mean as the basis for establishing the particle model.

[0115] S2. Establish a particle model. The particle shape model should be selected as a cylindrical model as needed. The particle shape model is equal to the sample mean of the particle size of the ethylene-vinyl alcohol copolymer mixture measured in step S1.

[0116] S3. Perform particle flow simulation to determine the geometric dimensions of the box. This step is performed in the discrete element method (DEM) software. The normal contact force is determined based on the Mindlin model method based on Hertz theory, and the tangential contact force increment is determined based on the Thornton method, which combines the Savkoor-Briggs method and the Mindlin-Dereciewicz method. A model box is built in the software, and simulation experiments are conducted by gradually increasing the box dimensions. The specific method is as follows: First, the height of the box is fixed at 30-50 times the average particle size of the ethylene-vinyl alcohol copolymer mixture and kept constant. The initial length and width of the box are both set to 10 times the average particle size of the ethylene-vinyl alcohol copolymer mixture. Then, the length and width are gradually increased, each time by twice the particle size, until the change in the angle of repose test results of the numerical simulation is less than 5%, at which point the increase stops. The final simulated box dimensions are used as the basis for manufacturing the physical box.

[0117] S4. Construct a solid box and measure the angle of repose. The solid box is constructed using a transparent glass plate and includes: a transparent box, a scale, and a gate. The solid box is hexahedral in shape, with the top surface and one side open. The remaining sides are composed of baffles. The two side baffles adjacent to the open side have grooves for inserting the gate, which serves as a baffle on that side of the solid box. Two scales are provided, one on each side of the baffle perpendicular to the gate. The scales are arranged along the vertical boundary line of the solid box, perpendicular to the ground. The readings increase from top to bottom, with the upper edge of the box as the origin, and are in millimeters.

[0118] The method for measuring the angle of repose includes: First, place the chamber on a flat, open surface. Before measurement, pass the gate through the groove to create a closed structure on all sides of the transparent chamber. Then, load the ethylene-vinyl alcohol copolymer mixture particles to be tested into the chamber from the top, filling or nearly filling it completely, and leveling the upper surface of the material. Next, quickly pull the gate upwards in one continuous motion without stopping or hesitating. The particles will slide downwards naturally. Once the particles are completely still, the measurement can be taken. Observe the height values ​​on the left and right sides respectively. Using the pre-designed length of the chamber's long side, the angle between the upper surface of the particles and the horizontal plane when they are still can be obtained through trigonometric functions; this is the angle of repose. Due to particle size variations, errors are inevitable in the readings. Repeat the above operation three times and take the average of the results to reduce the impact of errors.

[0119] Test Example 2

[0120] The ethylene-vinyl alcohol copolymer mixtures prepared in the examples and comparative examples were processed to prepare ethylene-vinyl alcohol films. The preparation method included: adding the ethylene-vinyl alcohol copolymer mixture into a casting film machine (ME20-MFA-FSA100V2), with a single screw having an L / D ≥ 25, and obtaining a film at a screw temperature of 200℃, a rotation speed of 15 rpm, and a stretching speed of 5 m / min. The width of the cast film was controlled at 15 mm, and the film thickness was controlled at 20 μm. The load and noise conditions during the preparation of the ethylene-vinyl alcohol film are shown in Table 1.

[0121] Table 1

[0122]

[0123] As can be seen from the results in Table 1, the method provided by this invention, which mixes the ethylene-vinyl alcohol copolymer solution obtained after alcoholysis with a suspension of inorganic substances, and the ethylene-vinyl alcohol copolymer and inorganic substances have a specific ratio, results in an ethylene-vinyl alcohol copolymer mixture with a low angle of repose, low processing load, and no noise, effectively reducing production energy consumption and making it suitable for industrial production.

[0124] 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 method for preparing an ethylene-vinyl alcohol copolymer mixture, characterized in that, The ethylene-vinyl alcohol copolymer solution obtained by alcoholysis of ethylene-vinyl acetate copolymer is mixed with a suspension containing inorganic matter, and then pressed and shaped to obtain an ethylene-vinyl alcohol copolymer mixture. The amount of inorganic material used is 160ppm-5000ppm, based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution.

2. The method according to claim 1, wherein, The inorganic material is selected from at least one of talc, titanium dioxide, mica powder, zinc oxide, boron nitride, silicon carbide, calcium carbonate, and silicon dioxide, and is preferably selected from at least one of talc, titanium dioxide, zinc oxide, boron nitride, silicon carbide, and silicon dioxide. Preferably, the average particle size of the inorganic material is 6.5μm-75μm, and more preferably 6.5μm-18μm.

3. The method according to claim 1 or 2, wherein, Based on the mass of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution, the amount of the inorganic substance is 200ppm-5000ppm, more preferably 200ppm-2000ppm; Preferably, the content of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution is 10-80 wt%.

4. The method according to claim 1, wherein, The mass ratio of solvent to inorganic matter in the suspension containing inorganic matter is 100:0.01-30, preferably 100:0.1-10; Preferably, the solvent in the suspension containing inorganic matter is selected from C1-C4 alcohol solvents and / or water, more preferably from at least one of methanol, ethanol, ethylene glycol, n-propanol, propylene glycol and water.

5. The method according to claim 1, wherein, The content of structural units derived from ethylene in the ethylene-vinyl acetate copolymer is 10 mol%-50 mol%, preferably 29 mol%-44 mol%; the content of structural units derived from vinyl acetate in the ethylene-vinyl acetate copolymer is 50 mol%-90 mol%, preferably 56 mol%-71 mol%.

6. The method according to claim 1, wherein, The mixing conditions include: under stirring conditions, the mixing temperature is 50-100℃, preferably 60-80℃; the mixing residence time is 1h-20h, preferably 4h-10h. Preferably, the stirring speed is 50 rpm to 200 rpm, and more preferably 60 rpm to 100 rpm.

7. The method according to claim 1, wherein, The alcoholysis method includes contacting the ethylene-vinyl acetate copolymer with an alkaline solution; Preferably, the molar ratio of hydroxide ions in the alkaline solution to vinyl acetate groups in the ethylene-vinyl acetate copolymer is 0.1-10:

1.

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

9. The ethylene-vinyl alcohol copolymer mixture according to claim 8, wherein, The inorganic content in the ethylene-vinyl alcohol copolymer mixture is 160ppm-5000ppm, preferably 200ppm-5000ppm, and more preferably 200ppm-2000ppm.

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

Images