Ethylene-vinyl alcohol copolymer composition and preparation method thereof

Abstract

The present invention provides an ethylene-vinyl alcohol copolymer composition and a preparation method thereof, wherein the composition contains an ethylene-vinyl alcohol copolymer, a potassium element and a sodium element, wherein the mass ratio of the sodium element to the potassium element is 0.1:1-1:1, preferably 0.2:1-0.8:1, and more preferably 0.3:1-0.5:1. The present invention controls the contents of the sodium element and the potassium element in the EVOH resin composition within a specific ratio range, so that the heat resistance of the obtained EVOH resin composition is greatly improved, the initial decomposition temperature can be increased to 370-400°C, and the maximum decomposition temperature can be increased to 400-440°C, so that the EVOH resin can adapt to the process requirements of higher processing temperatures. Moreover, by further adding an acyl-containing carboxylic acid and a phosphorus-containing compound / boron-containing compound, the heat-resistant yellowing performance of the EVOH resin composition can be improved, and the increase in the yellowing index YI after heat treatment at 150°C for 5 hours can reach no more than 15.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Chinese patent applications CN202011103182.7 and CN202011104215.X filed on October 15, 2020, the contents of which are incorporated herein by reference. Technical Field

[0003] The invention relates to an ethylene-vinyl alcohol copolymer composition and a preparation method thereof. Background Art

[0004] EVOH resin has excellent odor barrier, transparency and gloss, and is resistant to grease, chemicals, UV rays and other rays, and has good mechanical properties, strength and tensile modulus. It is used as composite packaging film for meat, grease, industrial solvents, pesticides, foaming treatment, hollow containers and barrier layers. In addition, EVOH resin can also be compounded with other materials to form fire-resistant, antibacterial, antioxidant materials, etc.

[0005] However, EVOH resin has poor heat resistance. During processing (usually melt processing), it is easy to cause the product to turn yellow at high temperature and produce thermal decomposition products, which affects product quality.

[0006] At present, this problem is mainly solved by adding additives. For example, CN105623163A improves its thermal stability by adding 0.1-4.0% of component B (acid, selected from one or a mixture of inorganic acids or organic carboxylic acids, the organic carboxylic acid is selected from polycarboxylic acids with a carbon number of 2-20), 0.01-1.8% of component C (organic phenol or amine compound) and 0.1-4.0% of component D (alkali metal or alkaline earth metal salt) to the copolymer containing ethylene and vinyl alcohol structural units. It is claimed that the initial decomposition temperature (T0) of the prepared composition under nitrogen and air atmospheres is 264°C and 236°C, respectively, and the decomposition temperature (Td) is 326°C and 311°C, respectively. However, this solution has limited improvement in thermal stability and cannot meet the application requirements of higher processing temperatures.

[0007] WO0020211A1 improves the stability of the EVOH resin composition by adding boron compounds such as boric acid, boric esters, and boric acid salts, which can increase the initial decomposition temperature by 40-50° C. However, the EVOH composition obtained by this method has the problem of increased melt viscosity during melt processing, which leads to inconvenience in processing. Summary of the invention

[0008] The purpose of the present invention is to overcome the defect of poor thermal stability of the EVOH resin composition in the prior art, thereby providing an EVOH resin composition with higher thermal stability and a preparation method thereof.

[0009] The first aspect of the present invention provides an ethylene-vinyl alcohol copolymer composition, which contains an ethylene-vinyl alcohol copolymer, a potassium element and a sodium element, characterized in that the mass ratio of the sodium element to the potassium element is 0.1:1-1:1, preferably 0.2:1-0.8:1 and more preferably 0.3:1-0.5:1.

[0010] The second aspect of the present invention provides a method for preparing an ethylene-vinyl alcohol copolymer composition, characterized in that the method comprises the steps of alcoholyzing the ethylene-vinyl acetate copolymer obtained by the polymerization reaction, forming and granulating the copolymer, and then washing the copolymer to remove most of the sodium element, and then adding a potassium source, wherein the amount of the potassium source added is such that the mass ratio of the sodium element to the potassium element is 0.1:1-1:1, preferably 0.2:1-0.8:1, and more preferably 0.3:1-0.5:1.

[0011] The present invention controls the contents of sodium and potassium in the EVOH resin composition within a specific ratio range, so that the heat resistance of the obtained EVOH resin composition is greatly improved, the initial decomposition temperature can be increased to 370-400°C, and the maximum decomposition temperature can be increased to 400-440°C, so that the EVOH resin can adapt to the process requirements of higher processing temperatures. Moreover, by further adding acyl-containing carboxylic acids and phosphorus-containing compounds / boron-containing compounds, the heat-resistant yellowing performance of the EVOH resin composition can be improved, and the increase value of the yellowing index YI after heat treatment at 150°C for 5 hours can reach no more than 15.

[0012] The EVOH resin composition method provided by the invention is simple and easy to operate, and is conducive to realizing industrialized production. DETAILED DESCRIPTION

[0013] In the ethylene-vinyl alcohol copolymer composition, the ethylene-vinyl alcohol copolymer is the main component, which is obtained by alcoholysis of ethylene-vinyl acetate copolymerization. The sodium element is a byproduct produced during the alcoholysis of the ethylene-vinyl acetate copolymer, and the content of the sodium element is usually reduced by subsequent washing. It is generally believed that the content of the sodium element needs to be controlled within a range as low as possible to obtain an ethylene-vinyl alcohol copolymer composition with better performance.

[0014] The inventors of the present invention unexpectedly discovered that by adding potassium after alcoholysis and washing, and controlling the mass ratio of sodium to potassium within a specific range of 0.1:1-1:1, preferably 0.2:1-0.8:1, and more preferably 0.3:1-0.5:1, the heat resistance of the resulting EVOH resin composition can be greatly improved.

[0015] Better effects can be obtained by controlling the content of sodium within a certain range. Preferably, the total amount of potassium and sodium is 100-3000 ppm, preferably 200-2000 ppm, more preferably 500-1000 ppm, relative to the mass of the ethylene-vinyl alcohol copolymer.

[0016] Preferably, the potassium element exists in the form of ions, more preferably in the form of potassium salts, and further preferably, the potassium salts are potassium carbonate and / or potassium bicarbonate. Potassium carbonate and potassium bicarbonate can achieve better results than inorganic potassium salts such as potassium nitrate, potassium phosphate, potassium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium sulfate, potassium chloride, and organic potassium salts such as potassium acetate and potassium formate.

[0017] In order to prevent the EVOH resin composition from being colored during melt molding, according to a preferred embodiment of the present invention, the EVOH resin composition further contains a monocarboxylic acid, which can be any carboxylic acid containing one COOH group and no acyl group that can achieve the above-mentioned effect. Preferably, the monocarboxylic acid has a structural formula of R 1 COOH, R 1 It is an alkyl group having 1-8 carbon atoms, more preferably 1-5 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, and further preferably one or more of formic acid, acetic acid, propionic acid, and butyric acid.

[0018] Preferably, the content of the monocarboxylic acid is 100-3000 ppm, preferably 150-2000 ppm, more preferably 300-1000 ppm, relative to the mass of the ethylene-vinyl alcohol copolymer.

[0019] The inventors of the present invention unexpectedly found that by making the EVOH resin composition contain a certain amount of acyl-containing carboxylic acid, the heat yellowing resistance of the resin composition can be further improved. Therefore, preferably, the composition also contains acyl-containing carboxylic acid. Preferably, the content of the acyl-containing carboxylic acid is 50-1000ppm, preferably 100-500ppm, and more preferably 200-350ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

[0020] When the composition of the present invention contains both monocarboxylic acid and acyl-containing carboxylic acid, preferably, relative to the mass of the ethylene-vinyl alcohol copolymer, the content of the acyl-containing carboxylic acid is 50-1000 ppm, preferably 100-500 ppm, and the content of the monocarboxylic acid is 100-3000 ppm, preferably 150-2000 ppm, more preferably 200-1500 ppm.

[0021] The acyl-containing carboxylic acid may be any substance containing both an acyl group -C(=O)- and a carboxyl group -COOH in the molecule. The number of the acyl group and the carboxyl group may be one or more, and the acyl group and the carboxyl group may be separated by one or more carbon atoms. The acyl group is preferably an acetyl group CH 3 -C(=O)-. The acyl-containing carboxylic acid may contain one or more aromatic rings. The number of carbon atoms in the acyl-containing carboxylic acid may be 3-10. Preferably, the acyl-containing carboxylic acid is one or more of acetoacetic acid, levulinic acid, acetobutyric acid, acetylsalicylic acid, levulinic acid, acetylsuccinic acid and acetylbenzoic acid.

[0022] The structural formula of the acyl-containing carboxylic acid is preferably R 2 COR 3 COOH, where R 2 is an alkyl group having 1 to 5 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl, and more preferably methyl, that is, the acyl-containing carboxylic acid is an acetyl-containing carboxylic acid, R 3 is a straight chain or branched chain alkylene group having 1 to 5 carbon atoms, such as methylene, ethylene, propylene, etc., and R 3 With R 1 The inventors of the present invention have found that by making the acyl-containing carboxylic acid satisfy R 3 With R 1 The number of carbon atoms is the same, and the heat stability and heat yellowing resistance of the obtained EVOH composition can be greatly improved.

[0023] The composition of the present invention may also contain boron and / or phosphorus. Preferably, the mass of the ethylene-vinyl alcohol copolymer is 100% by weight of boric acid H 3 BO 3 The content of boron is 50-1000ppm, preferably 50-500ppm, in terms of H 3 PO 4 The content of phosphorus is 50-1000ppm, preferably 100-500ppm. Boron can exist in the form of various boron-containing compounds, and the boron-containing compounds can be boric acid, boric esters or borates, etc. The phosphorus-containing compound can be phosphoric acid and its salts, and there is no particular limitation as phosphate, preferably an alkali metal salt of phosphoric acid. Specifically, it can be one or more of potassium phosphate, sodium phosphate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, etc. It should be noted that when the phosphorus compound is various potassium salts of phosphoric acid, the amount of potassium therein is included in the potassium content in the composition.

[0024] In the present invention, the contents of potassium and sodium are measured by ICP-OES. The contents of monocarboxylic acids, acyl-containing carboxylic acids and phosphorus compounds are measured by ion chromatography. The content of boron compounds is measured by atomic emission spectroscopy after sample ashing.

[0025] In the present invention, the ethylene-vinyl acetate copolymer can be an EVOH copolymer obtained by various specifications and methods. Preferably, the melt index (190° C., 2160 g) of the ethylene-vinyl acetate copolymer is 0.5-10 g / 10 min.

[0026] According to a preferred embodiment of the present invention, the EVOH resin composition contains ethylene-vinyl alcohol copolymer, acetic acid, potassium salt and sodium salt, the content of acetic acid is 100-3000ppm relative to the mass of the ethylene-vinyl alcohol copolymer, the amount of potassium salt and sodium salt is 100-3000ppm of the total amount of sodium ions contained in the sodium salt and potassium ions contained in the potassium salt relative to the mass of the ethylene-vinyl alcohol copolymer, and the mass ratio of sodium ions contained in the sodium salt to potassium ions contained in the potassium salt is 0.1:1-1:1.

[0027] It can be any ethylene-vinyl acetate copolymer prepared by existing methods, for example, it can be prepared by polymerization reaction. The solvent used in the polymerization reaction is preferably an alcohol solvent, and the initiator used in the polymerization reaction is preferably an azo initiator or a peroxide initiator.

[0028] The second aspect of the present invention provides a method for preparing an ethylene-vinyl alcohol copolymer composition, which comprises the steps of alcoholyzing the ethylene-vinyl acetate copolymer obtained by the polymerization reaction, forming and granulating the copolymer, and then washing the copolymer to remove most of the sodium element, and then adding a potassium source, wherein the amount of the potassium source added is such that the mass ratio of the sodium element to the potassium element is 0.1:1-1:1, preferably 0.2:1-0.8:1, and more preferably 0.3:1-0.5:1.

[0029] Preferably, the potassium source is a potassium salt, and more preferably, the potassium salt is potassium carbonate and / or potassium bicarbonate.

[0030] Preferably, the cleaning reduces the content of sodium to 50-2000 ppm, and then potassium salt is added to control the total amount of sodium ions and potassium ions contained in the potassium salt to be within a desired range.

[0031] The cleaning generally includes water washing and acid washing.

[0032] In the present invention, it is preferred to use a monocarboxylic acid or an acyl group-containing carboxylic acid for the acid washing.

[0033] Preferably, the mass ratio of the monocarboxylic acid to the ethylene-vinyl alcohol copolymer may be 0.0001:1-0.1:1, preferably 0.001:1-0.05:1, more preferably 0.015:1-0.05:1.

[0034] In a further preferred case, the mass ratio of the acyl-containing carboxylic acid to the monocarboxylic acid is 0.1:1-1:1, preferably 0.2:1-0.8:1, and more preferably 0.2:1-0.5:1.

[0035] The types of the monocarboxylic acid and the acyl group-containing carboxylic acid are as described above.

[0036] Further preferably, the method further comprises adding a phosphorus-containing compound and / or a boron-containing compound to the acid-washed ethylene-vinyl acetate copolymer.

[0037] Preferably, the phosphorus-containing compound is added in an amount of 0.0002-0.001 parts by weight relative to 1 part by weight of ethylene-vinyl acetate copolymer.

[0038] Preferably, the boron-containing compound is added in an amount of 0.0001-0.001 parts by weight relative to 1 part by weight of ethylene-vinyl acetate copolymer.

[0039] The boron-containing compound and the phosphorus-containing compound may be added when the potassium salt is added, or they may be added separately.

[0040] There is no particular restriction on the manner of adding potassium salt, boron-containing compound and phosphorus-containing compound. It is preferred that the above compounds are dissolved in water, and then the solution is added to the ethylene-vinyl alcohol copolymer and mixed evenly. The concentration of the solution is not particularly limited, and can be various concentrations, as long as the potassium salt, boron-containing compound and phosphorus-containing compound can be loaded into the ethylene-vinyl alcohol copolymer. Since the ethylene-vinyl alcohol copolymer has a certain pore structure, the potassium salt, boron-containing compound and phosphorus-containing compound can be loaded into the ethylene-vinyl alcohol copolymer by a saturated impregnation method, and then the solvent is removed by drying to obtain an ethylene-vinyl alcohol copolymer composition.

[0041] The polymerization reaction for preparing ethylene-vinyl acetate copolymer can adopt various existing methods, such as solution polymerization, emulsion polymerization or suspension polymerization. Solution polymerization is preferred, and the solvent used in the polymerization reaction is preferably an alcohol solvent. The alcohol solvent can include alcohols with 1-4 carbon atoms, such as methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol, etc., or a mixed solvent of the above two alcohols, or a solvent with the above alcohols as the main component and other small components.

[0042] The initiator used in the polymerization reaction can be an azo initiator or a peroxide initiator.

[0043] Further, the azo initiator includes oil-soluble initiators such as azobisisobutyronitrile, azobisisovaleronitrile, azoisobutylcyanoformamide, azobiscyclohexylcarbonitrile, dimethyl azobisisobutyrate, and the like.

[0044] Further, the peroxide initiator includes organic peroxides (such as benzoyl peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, t-pentyl peroxyneodecanoate, bis(4-t-butylcyclohexyl)peroxydicarbonate, t-pentyl peroxypivalate, t-butyl peroxyacetate, dibutyl peroxydicarbonate, etc.) or inorganic peroxides (such as hydrogen peroxide, ammonium persulfate, potassium persulfate, etc.)

[0045] Furthermore, the initiator includes an organic peroxide initiator.

[0046] Furthermore, the ratio is as follows, by mass: 10-40 parts of solvent, 60-200 parts of vinyl acetate monomer, 0.01-0.3 parts of initiator and 5-60 parts of ethylene monomer.

[0047] Furthermore, the ratio is as follows, based on mass: 10-35 parts of solvent, 80-150 parts of vinyl acetate monomer, 0.03-0.2 parts of initiator and 20-40 parts of ethylene monomer.

[0048] The methods of alcoholysis and molding granulation are well known to those skilled in the art and will not be described in detail here.

[0049] In the present invention, unless otherwise specified, the parts are parts by mass or parts by weight.

[0050] The present invention will be further described below by way of examples. In the examples, the initial decomposition temperature and the maximum decomposition temperature are detected by using a thermogravimetric analyzer, in a nitrogen atmosphere, at a heating rate of 10°C / min, the temperature is raised from room temperature to 800°C, and the temperature at which the sample decomposes 5% (w) is the initial decomposition temperature T 0 (℃), the temperature when the sample decomposes 50% (w) is the highest decomposition temperature T 1 (℃).

[0051] The method for testing the yellowness index YI is as follows: weigh 10-15g of sample and use a colorimeter to test the initial yellowness index YI of the sample and the yellowness index YI after heat treatment at 150℃ for 5 hours. The smaller the YI value, the lower the coloration.

[0052] The method for detecting the sodium and potassium ion content is as follows: crush the EVOH sample through a 100-mesh sieve, weigh 10g of the sample and 50ml of ion exchange water, stir and reflux in a 95°C water bath for 10 hours. Dilute the extract 5 times with ion exchange water and test it using an inductively coupled plasma atomic emission spectrometer (ICP-0ES).

[0053] The method for detecting the content of monocarboxylic acid, phosphoric acid and acyl carboxylic acid is as follows: crush and sieve the EVOH sample, weigh 10g of the sample and 50ml of deionized water, stir and reflux in a 95℃ water bath for 10 hours. Dilute the extract 5 times (volume) with deionized water and test it by ion chromatography, the chromatographic column is Metrosep A Supp / 250,4, and the mobile phase is Na 2 CO 3 and NaHCO 3 Mixed solution, calibration solution is sodium acetate aqueous solution.

[0054] The boric acid test method is to weigh 100 grams of the sample, ash it in a muffle furnace, dissolve the ash in 200 ml of a 0.01 equivalent nitric acid aqueous solution, analyze the boron content by atomic absorption spectroscopy, and then convert it to the weight of boric acid to obtain the content of the boron compound.

[0055] Example 1

[0056] A. Polymerization: 25 parts of methanol, 190 parts of vinyl acetate and 0.05 parts of t-pentyl peroxyneodecanoate were added to a polymerization kettle equipped with a stirrer, ethylene was introduced to maintain the pressure in the polymerization kettle at 3.7 MPa and the temperature at 60°C, and the reaction was carried out for 5 hours to obtain an ethylene-vinyl acetate copolymer solution, and ethylene and vinyl acetate monomers were removed by decompression and rectification to obtain an ethylene-vinyl acetate copolymer solution;

[0057] B. Alcoholysis: The mass fraction of the ethylene-vinyl acetate copolymer solution obtained in step A is adjusted to 40%, and then a sodium hydroxide-methanol solution (sodium hydroxide is a solute) with a concentration of 40 g / L is added for alcoholysis, and the amount of the sodium hydroxide-methanol solution is such that the molar ratio of the sodium hydroxide in the sodium hydroxide-methanol solution to the vinyl acetate group contained in the ethylene-vinyl acetate copolymer is 0.05:1, and the reaction is carried out for 4 hours until the alcoholysis is complete;

[0058] C. Granulation: After alcoholysis of ethylene-vinyl acetate copolymer, the ethylene-vinyl alcohol copolymer solution obtained by alcoholysis is extruded into a 5°C aqueous solution through an extrusion device with a perforated plate, and after being precipitated into strips, it is cut into particles by a common cutting method;

[0059] D. Water washing: Then, water 5 times the mass of the particles is added to wash the ethylene-vinyl alcohol copolymer particles in a kettle container equipped with a stirring device, and each washing takes 2 hours, and the washing is repeated 2 times;

[0060] E. Pickling: Add 5 times the mass of water to the ethylene-vinyl alcohol copolymer particles in a kettle container with a stirring device to wash the particles, add 0.015 parts of acetic acid and 0.007 parts of acetoacetic acid relative to 1 part of EVOH (by mass) to the washing liquid, and pickle for 2 hours. After the pickling is completed, centrifuge and dehydrate;

[0061] F. Tempering: Add 0.0013 parts of potassium carbonate, 0.0001 parts of boric acid and 0.0006 parts of sodium dihydrogen phosphate aqueous solution relative to the mass of EVOH (1 part by mass) to the EVOH particles after centrifugal dehydration, mix well and perform saturated impregnation, and then dry at 115°C for 24 hours to obtain an EVOH resin composition.

[0062] Example 2-Example 12

[0063] An EVOH resin composition was prepared according to the method of Example 1, except that the types and amounts of the monocarboxylic acid, acyl-containing carboxylic acid and potassium source in step E were as shown in Table 1. The properties of the obtained EVOH resin composition are shown in Table 2.

[0064] Comparative Example 1

[0065] An EVOH resin composition was prepared according to the method of Example 1, except that the types and amounts of the monocarboxylic acid, the acyl-containing carboxylic acid in step E and the potassium source in step F were as shown in Table 1. The properties of the obtained EVOH resin composition are shown in Table 2.

[0066] Table 1

[0067]

[0068]

[0069] Table 2

[0070]

[0071]

[0072] It can be seen from the data in Table 2 above that the method provided by the present invention can obtain an EVOH resin composition with improved heat resistance and heat yellowing resistance.

[0073] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. An ethylene-vinyl alcohol copolymer composition, comprising an ethylene-vinyl alcohol copolymer, a potassium element and a sodium element, characterized in that: The mass ratio of sodium element to potassium element is 0.1:1-1:

1. The composition also contains a monocarboxylic acid R1COOH, R1 is an alkyl group with 1 to 5 carbon atoms, and the composition also contains an acyl-containing carboxylic acid, wherein the acyl-containing carboxylic acid is one or more of acetoacetic acid, acetylsalicylic acid, levulinic acid, acetobutyric acid, acetylsuccinic acid and acetylbenzoic acid; relative to the mass of the ethylene-vinyl alcohol copolymer, the total amount of potassium element and sodium element is 100-3000ppm; relative to the mass of the ethylene-vinyl alcohol copolymer, the content of the monocarboxylic acid is 100-3000ppm; relative to the mass of the ethylene-vinyl alcohol copolymer, the content of the acyl-containing carboxylic acid is 50-1000ppm.

2. The composition according to claim 1, wherein The mass ratio of sodium to potassium is 0.2:1-0.8:

1.

3. The composition according to claim 2, wherein The mass ratio of sodium to potassium is 0.3:1-0.5:

1.

4. The composition according to claim 1, wherein The total amount of potassium and sodium elements is 200-2000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

5. The composition according to claim 4, wherein The total amount of potassium and sodium elements is 500-1000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

6. The composition according to any one of claims 1 to 3, wherein The potassium element exists in the form of ions.

7. The composition according to claim 6, wherein The potassium element exists in the form of potassium salt.

8. The composition according to claim 7, wherein The potassium salt is potassium carbonate and / or potassium bicarbonate.

9. A composition according to any one of claims 1 to 3, wherein The monocarboxylic acid is selected from one or more of formic acid, acetic acid, propionic acid and butyric acid.

10. The composition according to claim 1, wherein The content of the monocarboxylic acid is 150-2000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

11. The composition according to claim 10, wherein The content of the monocarboxylic acid is 300-1000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

12. The composition according to claim 1, wherein The content of the acyl group-containing carboxylic acid is 100-500 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

13. The composition according to claim 12, wherein The content of the acyl group-containing carboxylic acid is 200-350 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

14. The composition according to any one of claims 1 to 3, wherein The composition also contains boron and / or phosphorus. Relative to the mass of the ethylene-vinyl alcohol copolymer, the content of the boron is 50-1000 ppm in terms of boric acid H3BO3, and the content of the phosphorus is 50-1000 ppm in terms of H3PO4.

15. The composition according to claim 14, wherein Calculated in boric acid H3BO3, the content of boron is 50-500ppm, and calculated in H3PO4, the content of phosphorus is 100-500ppm.

16. A method for preparing an ethylene-vinyl alcohol copolymer composition, characterized in that: The method comprises the following steps: alcoholyzing the ethylene-vinyl acetate copolymer obtained by the polymerization reaction, molding and granulating the copolymer, and then washing the copolymer to remove most of the sodium element, and then adding a potassium source, wherein the amount of the potassium source added is such that the mass ratio of the sodium element to the potassium element is 0.1:1-1:

1. The washing comprises water washing and acid washing, and the acid washing is performed using a monocarboxylic acid R1COOH and an acyl-containing carboxylic acid, wherein R1 is an alkyl group having 1-5 carbon atoms, and the acyl-containing carboxylic acid is one or more of acetoacetic acid, acetylsalicylic acid, levulinic acid, acetylsuccinic acid and acetylbenzoic acid. The washing is such that the total amount of potassium element and sodium element is 100-3000ppm relative to the mass of the ethylene-vinyl alcohol copolymer. The mass ratio of the monocarboxylic acid to the ethylene-vinyl alcohol copolymer is 0.0001:1-0.1:

1. The mass ratio of the acyl-containing carboxylic acid to the monocarboxylic acid is 0.1:1-1:

1.

17. The preparation method according to claim 16, wherein: The amount of potassium source added is such that the mass ratio of sodium element to potassium element is 0.2:1-0.8:

1.

18. The preparation method according to claim 17, wherein: The amount of potassium source added is such that the mass ratio of sodium element to potassium element is 0.3:1-0.5:

1.

19. The preparation method according to any one of claims 16 to 18, wherein: The potassium source is potassium salt.

20. The preparation method according to claim 19, wherein: The potassium salt is potassium carbonate and / or potassium bicarbonate.

21. The preparation method according to any one of claims 16 to 18, wherein: The cleaning is performed so that the total amount of potassium and sodium elements is 200-2000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

22. The preparation method according to claim 21, wherein The cleaning is performed so that the total amount of potassium and sodium elements is 1000-2000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer.

23. The preparation method according to any one of claims 16 to 18, wherein: The mass ratio of the monocarboxylic acid to the ethylene-vinyl alcohol copolymer is 0.001:1-0.05:1; the mass ratio of the acyl-containing carboxylic acid to the monocarboxylic acid is 0.2:1-0.8:

1.

24. The preparation method according to claim 23, wherein: The mass ratio of the monocarboxylic acid to the ethylene-vinyl alcohol copolymer is 0.015:1-0.05:1; the mass ratio of the acyl-containing carboxylic acid to the monocarboxylic acid is 0.2:1-0.5:

1.

25. The preparation method according to any one of claims 16 to 18, wherein: The monocarboxylic acid is one or more of formic acid, acetic acid and propionic acid.

26. The preparation method according to any one of claims 16 to 18, wherein: The method further comprises adding a phosphorus-containing compound and / or a boron-containing compound to the acid-washed ethylene-vinyl alcohol copolymer.

27. The preparation method according to claim 26, wherein: Relative to 1 part by weight of ethylene-vinyl alcohol copolymer, the added amount of the phosphorus-containing compound is 0.0002-0.001 part by weight, and the added amount of the boron-containing compound is 0.0001-0.001 part by weight.

28. The preparation method according to any one of claims 16 to 18, wherein: The solvent used in the polymerization reaction is an alcohol solvent, and the initiator used in the polymerization reaction is an azo initiator or a peroxide initiator.

Images