Ethylene-vinyl alcohol copolymer as well as processing method and application thereof

Abstract

The invention relates to the field of ethylene-vinyl alcohol copolymers, in particular to an ethylene-vinyl alcohol copolymer and a processing method and application thereof. The method comprises the following steps: carrying out heat treatment on an alcoholyzed ethylene-vinyl alcohol copolymer solution under a vacuum condition to obtain the ethylene-vinyl alcohol copolymer, wherein the conditions in the heat treatment process are controlled, so that the ethylene-vinyl alcohol copolymer meets the following characteristics: eta / T2 is more than or equal to 5 and less than or equal to 50; eta is the dynamic viscosity of the copolymer at T DEG C, cp; t is temperature, DEG C; the pH value of the ethylene-vinyl alcohol copolymer solution is 2-6. The ethylene-vinyl alcohol copolymer prepared by the invention is good in particle uniformity and low in yellow index after being braced and diced, the braced strip is not easy to break in the bracing process, the pore channel is not blocked, and the production stability of the ethylene-vinyl alcohol copolymer is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of ethylene-vinyl alcohol copolymers, and specifically to ethylene-vinyl alcohol copolymers, their processing methods and applications. Background Art

[0002] Ethylene-vinyl alcohol copolymer (abbreviated as EVOH) is a new type of polymer synthetic material that combines the processability of ethylene polymers and the gas barrier properties of vinyl alcohol polymers, and has excellent gas barrier properties, water resistance, oil resistance, ammonia resistance and other properties. EVOH, polyvinylidene chloride (PVDC) and polyamide (PA) are collectively referred to as the world's three major high-barrier resins. In the 1950s, DuPont of the United States first prepared EVOH resin by copolymerizing ethylene with vinyl acetate (VAc) and alcoholysis.

[0003] In the existing EVOH production process, EVOH is generally prepared by polymerizing ethylene and vinyl acetate by conventional methods such as emulsion polymerization, solution polymerization or suspension polymerization and then saponifying. In the solution polymerization process, an alcohol with no more than 4 carbons is usually used as the solvent, and methanol is preferably used. The ethylene-vinyl acetate copolymer solution obtained by polymerization contains solvent methanol and unreacted vinyl acetate monomer. By utilizing the property of methanol and vinyl acetate forming an azeotrope in the rectifying column, the unreacted vinyl acetate is removed by adding methanol solution or blowing in methanol vapor, and then it enters the alcoholysis device. The alcoholysis of ethylene-vinyl acetate copolymer can be carried out by kettle alcoholysis. CN103635526A discloses an ethylene-vinyl alcohol copolymer resin composition and its manufacturing method. Adding a compound of alkenediol makes the ethylene-vinyl alcohol copolymer have excellent appearance properties. In order to increase the washing effect, particles containing 70-150% by mass of water are prepared. In the presence of a large amount of water, it is more difficult to stably operate the product during strand pelletization. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problem that the product is not easy to stably operate during strand pelletization existing in the prior art, and to provide an ethylene-vinyl alcohol copolymer, its processing method and application.

[0005] To achieve the above purpose, the first aspect of the present invention provides a method for processing an ethylene-vinyl alcohol copolymer, the method comprising: under vacuum conditions, heat-treating the ethylene-vinyl alcohol copolymer solution after alcoholysis to obtain an ethylene-vinyl alcohol copolymer;

[0006] wherein, controlling the conditions during the heat treatment such that the ethylene-vinyl alcohol copolymer satisfies the following characteristics:

[0007] 5 ≤ η / T 2 ≤ 50;

[0008] η is the dynamic viscosity of the copolymer at T °C, cp; T is the temperature, °C;

[0009] The pH of the ethylene-vinyl alcohol copolymer solution is 2 - 6.

[0010] The second aspect of the present invention provides the ethylene-vinyl alcohol copolymer obtained by the above method.

[0011] The third aspect of the present invention provides the application of the above ethylene-vinyl alcohol copolymer in at least one of packaging materials, automobile fuel tanks, oxygen-barrier floor heating pipes, textile materials, and medical materials.

[0012] Through the above technical solution, the present invention performs heat treatment on the ethylene-vinyl alcohol copolymer solution under vacuum conditions, and by monitoring the dynamic viscosity at temperature T℃ as ηcp, making it satisfy the relationship: 5 ≤ η / T 2 ≤ 50, the obtained ethylene-vinyl alcohol copolymer product has good particle uniformity and low yellowness index after strand pelletization. During the strand process, it will neither break easily nor block the channels, significantly improving the production stability of the ethylene-vinyl alcohol copolymer. Description of the Drawings

[0013] Figure 1 is the production process flow of the present invention.

[0014] Description of the Reference Numerals

[0015] 01 is the motor; 02 is the mixing area; 03 is the first heating area; 04 is the second addition area; 5 is the extrusion area; 06 is the pressure controller; 101 is the material input pipeline; 102 and 103 are the gas output pipelines; 104 is the gas discharge pipeline; 105 is the extrusion pipeline Detailed Embodiments

[0016] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0017] The first aspect of the present invention provides a method for processing an ethylene-vinyl alcohol copolymer, the method comprising: performing heat treatment on the alcoholyzed ethylene-vinyl alcohol copolymer solution under vacuum conditions to obtain an ethylene-vinyl alcohol copolymer;

[0018] Wherein, controlling the conditions during the heat treatment such that the ethylene-vinyl alcohol copolymer satisfies the following characteristics:

[0019] 5 ≤ η / T 2 ≤ 50;

[0020] η is the dynamic viscosity of the copolymer at T °C, in cp; T is the temperature, in °C;

[0021] The pH of the ethylene-vinyl alcohol copolymer solution is 2 - 6, which can be 2, 3, 4, 5, 6 or any range formed by any two of the above values and the values within the range.

[0022] In the present invention, the ethylene-vinyl alcohol copolymer solution after alcoholysis is generally obtained by alcoholyzing ethylene-vinyl acetate and methanol under alkaline conditions. In order to obtain better product quality, acid addition for neutralization is required, which will cause moisture in the ethylene-vinyl alcohol copolymer solution and lead to problems such as unstable operation during product strip cutting and pelletizing.

[0023] The inventors of the present invention found that the ratio of η to T 2 is too small, it is difficult to form the product, and a large number of abnormal particles are easily generated. If the ratio is too large, the product is likely to block the forming channels, resulting in the product flowing out from local channels and generating a large number of long strip-shaped particles. Only when the ratio of η to T 2 meets the range defined in the present invention can an ethylene-vinyl alcohol copolymer with good particle uniformity and low yellowness index be obtained.

[0024] In the present invention, when actually detecting the dynamic viscosity and temperature, the detection should be carried out when the heat treatment has just ended or when extrusion is carried out just after the heat treatment has ended. When extrusion is carried out just after the heat treatment has ended, since the time is relatively short and the temperature change is small, when calculating η / T 2 the temperature at the end of the heat treatment is still used.

[0025] The inventors of the present invention found that when 5 ≤ η / T 2 ≤ 50, preferably 16 ≤ η / T 2 ≤ 30, the formed pellets of the obtained ethylene-vinyl alcohol copolymer are uniform and the production stability is good.

[0026] According to the present invention, the conditions of the heat treatment are not limited, as long as the dynamic viscosity and temperature satisfy the above relationship. In actual processing, the temperature can be controlled at 100 - 280 °C, which can be 100 °C, 120 °C, 140 °C, 160 °C, 180 °C, 200 °C, 220 °C, 240 °C, 260 °C, 280 °C or any range formed by any two of the above values and the values within the range, and the time is controlled at 10 - 60 minutes, which can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes or any range formed by any two of the above values and the values within the range, so that during the heat treatment process, the moisture and other impurities can be efficiently evaporated without damaging the product quality.

[0027] In the present invention, in order to control the evaporation rate such that the dynamic viscosity and temperature satisfy the above relationship, during actual processing, the vacuum degree of the vacuum condition can be controlled. Preferably, the vacuum degree of the vacuum condition is -5 to -80 KPa, which can be -5 KPa, -10 KPa, -15 KPa, -20 KPa, -25 KPa, -30 KPa, -35 KPa, -40 KPa, -45 KPa, -40 KPa, -55 KPa, -60 KPa, -65 KPa, -70 KPa, -75 KPa, -80 KPa or the range formed by any two of the above values and the values within the range. If the vacuum degree is too low, the gas is not easily evaporated; if the vacuum degree is too high, the gas easily entrains the resin, causing production fluctuations.

[0028] In the present invention, a higher pH will affect the quality of the product. Therefore, it is necessary to adjust the pH of the ethylene-vinyl alcohol copolymer solution after alcoholysis, and when the pH is controlled to be 3 - 5, the quality will be better.

[0029] In the present invention, the ethylene-vinyl alcohol copolymer solution includes an ethylene-vinyl alcohol copolymer, an alcohol solvent, and water. Among them, the water content is 4 wt% - 60 wt%, which can be 4 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt% or the range formed by any two of the above values and the values within the range.

[0030] In the present invention, the content of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution is 15 wt% - 90 wt%, which can be 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt% or the range formed by any two of the above values and the values within the range.

[0031] In the present invention, controlling the content of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution to satisfy the above range can control the viscosity of the product in the molding machine and ensure stable production.

[0032] Further, the content of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution is 30 wt% - 85 wt%.

[0033] In the present invention, the content of the alcohol solvent in the ethylene-vinyl alcohol copolymer solution is 1 wt% - 10 wt%, which can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt% or the range formed by any two of the above values and the values within the range.

[0034] In the present invention, controlling the content of the alcohol solvent in the ethylene-vinyl alcohol copolymer solution to meet the above range makes the product have good fluidity and controls stable production.

[0035] Further, the content of the alcohol solvent in the ethylene-vinyl alcohol copolymer solution is 2% to 8% by weight.

[0036] In the present invention, the alcohol solvent is not limited as long as it can enable the smooth alcoholysis of ethylene-vinyl acetate. Further preferably, the alcohol solvent is an alcohol solvent having 1 to 4 carbon atoms, preferably at least one of methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol, and more preferably methanol.

[0037] In the present invention, the heat treatment includes a first heat treatment and a second heat treatment.

[0038] In the present invention, dividing the heat treatment into a first heat treatment and a second heat treatment can achieve zone temperature control and further achieve precise control of the production process and product quality.

[0039] Further, the temperature of the first heat treatment is 100 - 190 °C, which can be 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C or any range formed by any two of the above values and the values within the range, and the time is 5 - 30 minutes, which can be 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes or any range formed by any two of the above values and the values within the range; more preferably, the temperature of the second heat treatment is 120 - 280 °C, which can be 120 °C, 140 °C, 160 °C, 180 °C, 200 °C, 220 °C, 240 °C, 260 °C, 280 °C or any range formed by any two of the above values and the values within the range, and the time is 5 - 30 minutes, which can be 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes or any range formed by any two of the above values and the values within the range.

[0040] In the present invention, the temperature of the second heat treatment is higher than that of the first heat treatment.

[0041] In the present invention, controlling the temperature of the second heat treatment to be higher than that of the first heat treatment can further achieve the control of the viscosity of the ethylene-vinyl alcohol copolymer and ensure stable and continuous production.

[0042] Further, the temperature of the second heat treatment is 10 - 100 °C higher than that of the first heat treatment, which can be 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C or any range formed by any two of the above values and the values within the range.

[0043] In the present invention, the first heat treatment is carried out first and then the second heat treatment is carried out.

[0044] In the present invention, there is no limitation on the instrument for performing the above heat treatment, as long as the temperature and the degree of vacuum can be regulated. Preferably, for continuous processing and suitable for industrial production, electric heating or oil bath heating is used. The above heat treatment can be carried out in an extruder, preferably a twin-screw extruder.

[0045] In the present invention, when using an extruder, the rotation speed of the extruder is controlled to be 30 - 200 revolutions per minute, which can be 30 revolutions per minute, 40 revolutions per minute, 60 revolutions per minute, 80 revolutions per minute, 100 revolutions per minute, 120 revolutions per minute, 140 revolutions per minute, 160 revolutions per minute, 180 revolutions per minute, 200 revolutions per minute or any value within the range formed by any two of the above values.

[0046] In the present invention, according to the actual production needs, the speed at which the ethylene - vinyl alcohol copolymer solution after alcoholysis enters the extruder is 80 - 1500 kg / h, which can be 80 kg / h, 90 kg / h, 100 kg / h, 110 kg / h, 120 kg / h, 130 kg / h, 140 kg / h, 150 kg / h, 200 kg / h, 300 kg / h, 400 kg / h, 500 kg / h, 600 kg / h, 700 kg / h, 800 kg / h, 900 kg / h, 1000 kg / h, 1100 kg / h, 1200 kg / h, 1300 kg / h, 1400 kg / h, 1500 kg / h or any value within the range formed by any two of the above values.

[0047] In the present invention, the method further includes: extruding, strand - forming, cooling, pelletizing, water - washing and drying the ethylene - vinyl alcohol copolymer.

[0048] Preferably, the temperature of the cooling is 10 - 25 °C, which can be 10 °C, 12 °C, 14 °C, 16 °C, 18 °C, 20 °C, 22 °C, 24 °C, 25 °C or any value within the range formed by any two of the above values, and the time is 10 - 30 minutes, which can be 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes or any value within the range formed by any two of the above values.

[0049] In the present invention, controlling the temperature and time of cooling to meet the above conditions can ensure that the product remains stable during the cooling process, prevent internal core - wrapping (the outside of the product particles is colorless and transparent, and the inside is white and uneven), and make the product particles uniform.

[0050] In the second aspect of the present invention, there is provided an ethylene - vinyl alcohol copolymer obtained by the above method.

[0051] According to the present invention, based on the total molar amount of the ethylene-vinyl alcohol copolymer, the content of the structural unit derived from ethylene is 20-60 mol%, which can be 20 mol%, 25 mol%, 30 mol%, 35 mol%, 40 mol%, 45 mol%, 50 mol%, 55 mol%, 60 mol% or any range formed by any two of the above values and the values within the range. Preferably, it is 25-50 mol%, which is consistent with the content of the ethylene structural unit in the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution before heat treatment.

[0052] According to the present invention, the weight-average molecular weight of the ethylene-vinyl alcohol copolymer is 20,000-250,000 g / mol, which can be 20,000 g / mol, 50,000 g / mol, 100,000 g / mol, 150,000 g / mol, 200,000 g / mol, 250,000 g / mol or any range formed by any two of the above values and the values within the range. Preferably, the weight-average molecular weight of the ethylene-vinyl acetate copolymer is 30,000-150,000 g / mol, and the molecular weight distribution is 1.1-3, which can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3 or any range formed by any two of the above values and the values within the range, which is consistent with the weight-average molecular weight and molecular weight distribution of the ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution before heat treatment.

[0053] According to the present invention, the degree of alcoholysis of the ethylene-vinyl alcohol copolymer is 99 mol% or more, which can be 99.1 mol%, 99.2 mol%, 99.3 mol%, 99.4 mol%, 99.5 mol%, 99.6 mol%, 99.7 mol%, 99.8 mol%, 99.9 mol%, 100 mol% or any range formed by any two of the above values and the values within the range.

[0054] According to the present invention, the yellowness index of the ethylene-vinyl alcohol copolymer is 6-16, which can be 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or any range formed by any two of the above values and the values within the range.

[0055] According to the present invention, the particles with the shortest cross-sectional diameter within 2-6 mm after strand pelletizing of the ethylene-vinyl alcohol copolymer through a 3 mm orifice plate are more than 95% by weight.

[0056] The third aspect of the present invention provides the application of the above-mentioned ethylene-vinyl alcohol copolymer in at least one of packaging materials, automobile fuel tanks, oxygen barrier floor heating pipes, textile materials and medical materials.

[0057] Combined with Figure 1, a specific embodiment of the present invention includes the following steps:

[0058] (1) The ethylene-vinyl alcohol copolymer solution after alcoholysis enters the extruder through 101 at a rate of 80 - 1500 kg / h. The rotation speed of the extruder is controlled by 01 to be 30 - 100 revolutions per minute. The ethylene-vinyl alcohol copolymer solution after alcoholysis undergoes a first heat treatment (temperature: 100 - 150 °C, time: 5 - 30 minutes) through 03 and a second heat treatment (temperature: 120 - 280 °C, time: 5 - 30 minutes) through 04;

[0059] (2) Control the gas generated by the first heat treatment to pass through 102 and the gas generated by the second heat treatment to pass through 103. The gases in 102 and 103 flow in parallel and are discharged from 104. Control 06 to make the vacuum degree -5 to -80 KPa;

[0060] (3) Extrude the product of step (2) through 05, monitor the dynamic viscosity at the end of the second heat treatment, and calculate whether the relationship between the dynamic viscosity and the temperature satisfies 5 ≤ η / T 2 ≤ 50, where η is the dynamic viscosity of the copolymer at T °C, cp; T is the temperature, °C;

[0061] (4) After the product of step (3) is discharged through 105, it is subjected to strand forming, cooling, pelletizing, water washing, and drying.

[0062] The present invention will be described in detail below through examples. In the following examples, the content of the structural unit derived from ethylene in the EVOH product is 32 mol%; the weight-average molecular weight is 75000 g / mol, and the molecular weight distribution is 1.6;

[0063] Product chromaticity analysis: Hunter Lab colorimeter, model: UltraScan VIS, mode type: RSIN including specular reflection, measurement method: general, observation area: 1 square inch, 3 holes, simulated light: natural light at 2 pm.

[0064] Dynamic viscosity test method: XH type high-temperature on-line viscometer.

[0065] The test method for the degree of alcoholysis is as follows: Crush the dried EVOH to 100 mesh, extract and purify it successively with deionized water, and dry it at 120 °C. The obtained ethylene-vinyl alcohol copolymer is subjected to NMR measurement under the following conditions, and the degree of alcoholysis is obtained by the following analysis method:

[0066] Analysis method: Obtain the integral value (I 1 ) of the peak at the chemical shift of 3.7 - 4 ppm and the integral value (I 2)。The integral value (I 3 ) of the peak with a chemical shift of 3.1 - 3.7 ppm was obtained from the spectrum measured at 95 °C, the integral value (I 4 ) of the peak with a chemical shift of 0.6 - 1.8 ppm, and the integral value (I 5 ) of the peak with a chemical shift of 1.9 - 2.1 ppm. Here, the peak with a chemical shift of 0.6 - 1.8 ppm mainly comes from methylene protons, and the peak with a chemical shift of 1.9 - 2.1 ppm comes from the protons of the methyl group in the unalcoholized vinyl acetate unit. The degree of alcoholysis is calculated using the following formula 1:

[0067] Formula 1:

[0068] Particle size distribution test method: Weigh 100 g of particle samples (elliptical), sieve them using a sample sieve (first through a 6 mm sieve hole, and then pass the sieved product through a 2 mm sieve hole), collect the particle samples with the shortest cross-sectional diameter of 2 - 6 mm, in g, and the formula is: weight of the shortest cross-sectional diameter of 2 - 6 mm / 100 × 100%.

[0069] The test method for weight-average molecular weight and molecular weight distribution is: Measured by the GPC method.

[0070] In the ethylene-vinyl alcohol copolymer solution, the degree of alcoholysis of the ethylene-vinyl alcohol copolymer is 99.5 mol%, the content of structural units from ethylene is 32 mol%, the weight-average molecular weight is 110000 g / mol, and the molecular weight distribution is 1.5.

[0071] Ethylene-vinyl alcohol copolymer solution: The content of ethylene-vinyl alcohol copolymer is 45 wt%, the content of methanol is 2 wt%, the content of water is 53 wt%; the pH is 3.8.

[0072] Example 1

[0073] 120 kg / h of ethylene-vinyl alcohol copolymer solution enters the extruder through pipeline 101. The rotation speed of the extruder is controlled at 40 revolutions per minute through 01. The temperature of the first heating zone 03 is controlled at 120 °C, and the residence time of the material is 12 minutes. After passing through the first heating zone 03, the gas phase is discharged through the natural exhaust port pipeline 103, and then enters the second heating zone 04. The temperature of the second heating zone 04 is controlled at 140 °C, and the residence time of the material is 16 minutes. After passing through the second heating zone, the gas phase is discharged through the second exhaust port 104. Then, it is extruded through the extrusion zone 05. At this time, the viscosity of the ethylene-vinyl alcohol copolymer is detected to be 500,000 cp (130 °C), and the evaporation rate of the gas phase in the extruder is stably controlled (the vacuum degree is -15 KPa). It is formed into strips through a 12-hole perforated plate with a diameter of φ3 mm, and then passes through a cooling water tank. The temperature of the cooling water tank is controlled at 20 °C (the time is 12 minutes). Then, EVOH particles are obtained through a pelletizer, and then the EVOH product is obtained through water washing and drying. The analysis of the EVOH product is shown in Table 1.

[0074] Example 2

[0075] 120 kg / h of ethylene-vinyl alcohol copolymer solution enters the extruder through pipeline 101. The rotation speed of the extruder is controlled at 80 revolutions per minute through 01. The temperature of the first heating zone 03 is controlled at 180 °C, and the residence time of the material is 18 minutes. After passing through the first heating zone 03, the gas phase is discharged through the natural exhaust port pipeline 103, and then enters the second heating zone 04. The temperature of the second heating zone 04 is controlled at 210 °C, and the residence time of the material is 20 minutes. After passing through the second heating zone, the gas phase is discharged through the second exhaust port 104. Then, it is extruded through the extrusion zone 05. At this time, the viscosity of the ethylene-vinyl alcohol copolymer is detected to be 1,000,000 cp (210 °C), and the evaporation rate of the gas phase in the molding machine is stably controlled (the vacuum degree is -15 KPa). It is formed into strips through a 12-hole perforated plate with a diameter of φ3 mm, and then passes through a cooling water tank. The temperature of the cooling water tank is controlled at 20 °C, and the cooling time is 12 minutes. Then, EVOH particles are obtained through a pelletizer, and then the EVOH product is obtained through water washing and drying. The analysis of the EVOH product is shown in Table 1.

[0076] Example 3

[0077] According to the method of Example 1, the difference is that the temperatures of the first heating zone and the second heating zone are exchanged. The analysis of the EVOH product is shown in Table 1.

[0078] Example 4

[0079] According to the method of Example 1, the difference is that the temperature of the second heating zone is 180 °C. The analysis of the EVOH product is shown in Table 1.

[0080] Example 5

[0081] According to the method of Example 1, except that the rotation speed is changed to 80 revolutions per minute. Analyze the EVOH products as shown in Table 1.

[0082] Example 6

[0083] According to the method of Example 1, except that the temperature of the first heating zone is 180 °C. Analyze the EVOH products as shown in Table 2.

[0084] Example 7

[0085] According to the method of Example 1, except that according to the dynamic viscosity of the ethylene-vinyl alcohol copolymer of 60000 cp, the temperature of the first heating zone is adjusted to 105 °C and the temperature of the second heating zone is adjusted to 135 °C. Analyze the EVOH products as shown in Table 2.

[0086] Example 8

[0087] According to the method of Example 1, except that according to the dynamic viscosity of the ethylene-vinyl alcohol copolymer of 2000000 cp, the temperature of the first heating zone is adjusted to 205 °C and the temperature of the second heating zone is adjusted to 225 °C. Analyze the EVOH products as shown in Table 2.

[0088] Comparative Example 1

[0089] According to the method of Example 1, except that the vacuum degree is controlled at -5 KPa. Analyze the EVOH products in Table 2.

[0090] Comparative Example 2

[0091] According to the method of Example 1, except that the vacuum degree is controlled at -50 KPa. Analyze the EVOH products as shown in Table 2.

[0092] Comparative Example 3

[0093] According to the method of Example 1, except that the pH of the ethylene-vinyl alcohol copolymer solution is 7. Analyze the EVOH products as shown in Table 2.

[0094] Table 1

[0095]

[0096]

[0097] Table 2

[0098]

[0099] As can be seen from the results in Table 1, the ethylene-vinyl alcohol copolymer processed by the present invention has uniform particle size and a lower yellowness index after being granulated by a pelletizer after strand forming and cooling. During the strand forming process, the strands are neither easily broken nor blocked. However, in the comparative example, the particle sizes are not uniform, and there are many abnormal particles that are too small or too large, which may also result in a higher yellowness index of the product, thus making the product yellowish, and the strands are also easily broken and the channels are blocked during the strand forming process.

[0100] 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 technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for processing ethylene-vinyl alcohol copolymer, characterized in that, the method includes: under vacuum conditions, performing heat treatment on the ethylene-vinyl alcohol copolymer solution after alcoholysis to obtain ethylene-vinyl alcohol copolymer; wherein, controlling the conditions during the heat treatment such that the ethylene-vinyl alcohol copolymer satisfies the following characteristics: 5 ≤ η / T 2 ≤ 50; η is the dynamic viscosity of the copolymer at T °C, cp; T is the temperature, °C; the pH of the ethylene-vinyl alcohol copolymer solution is 2 - 6.

2. The method according to claim 1, wherein, 16 ≤ η / T 2 ≤ 30; and / or, the pH of the ethylene-vinyl alcohol copolymer solution is 3 - 5.

3. The method according to claim 1 or 2, wherein, the ethylene-vinyl alcohol copolymer solution includes ethylene-vinyl alcohol copolymer, alcohol solvent and water, wherein the content of water is 4 wt% - 60 wt%.

4. The method according to claim 3, wherein, the content of ethylene-vinyl alcohol copolymer in the ethylene-vinyl alcohol copolymer solution is 15 wt% - 95 wt%; and / or, the content of alcohol solvent in the ethylene-vinyl alcohol copolymer solution is 1 wt% - 10 wt%; and / or, the alcohol solvent is an alcohol solvent with 1 - 4 carbon atoms, preferably at least one of methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol, more preferably methanol.

5. The method according to claim 1 or 2, wherein, the heat treatment includes a first heat treatment and a second heat treatment.

6. The method according to claim 5, wherein, the temperature of the first heat treatment is 100 - 190 °C, and the time is 5 - 30 minutes; and / or, the temperature of the second heat treatment is 120 - 280 °C, and the time is 5 - 30 minutes; and / or, the temperature of the second heat treatment is higher than that of the first heat treatment; and / or, the temperature of the second heat treatment is 10 - 100 °C higher than that of the first heat treatment.

7. The method according to claim 1 or 2, the heat treatment is carried out in an extruder; preferably carried out in a twin-screw extruder; preferably, the rotation speed of the extruder is 30 - 200 revolutions per minute; preferably, the speed at which the ethylene-vinyl alcohol copolymer solution after alcoholysis enters the extruder is 80 - 1500 kg / h.

8. The ethylene-vinyl alcohol copolymer obtained by the method according to any one of claims 1 - 7.

9. The ethylene-vinyl alcohol copolymer according to claim 8, wherein, based on the total molar amount of the ethylene-vinyl alcohol copolymer, the content of structural units from ethylene is 20 - 60 mol%, preferably 25 - 50 mol%; and / or, the weight-average molecular weight of the ethylene-vinyl alcohol copolymer is 20,000 - 250,000 g / mol, and the molecular weight distribution is 1.1 - 3; and / or, the degree of alcoholysis of the ethylene-vinyl alcohol copolymer is above 99 mol%; and / or, the yellow index of the ethylene-vinyl alcohol copolymer is 6 - 16; and / or, the particles with a shortest cross-sectional diameter within 2 - 6 mm after the ethylene-vinyl alcohol copolymer is granulated by pulling and cutting through a 3 mm orifice plate account for more than 95 wt%.

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

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