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

Abstract

The invention relates to the technical field of preparation of ethylene-vinyl alcohol copolymers, and discloses an ethylene-vinyl alcohol copolymer as well as a preparation method and application thereof. The preparation method comprises the following steps: contacting first vinyl acetate, a first initiator, monohydric alcohol and ethylene in a closed container for constant-temperature and constant-pressure reaction to obtain an ethylene-vinyl alcohol copolymer; wherein the second vinyl acetate and the second initiator are supplemented in the constant-temperature and constant-pressure reaction process. The yellow index of the ethylene-vinyl alcohol copolymer (EVOH) prepared by the method provided by the invention is 4-8, the molecular weight distribution index is 1-1.6, and the EVOH with excellent hue can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of ethylene-vinyl alcohol copolymers, and particularly relates to an ethylene-vinyl alcohol copolymer, a preparation method thereof, and applications. Background Art

[0002] Ethylene-vinyl alcohol copolymer (EVOH) is a crystalline polymer with a chain structure, integrating the good processability of ethylene polymers and the extremely high gas barrier property of vinyl alcohol polymers. It is known as one of the three major barrier resins in the world together with polyvinylidene chloride (PVDC) and polyamide (PA). Its gas barrier property is 100 times higher than that of PA (polyamide), 10,000 times higher than that of PE and PP, and dozens of times higher than that of the commonly used high-barrier material PVDC. EVOH is also one of the important fine chemical products in the downstream of VAc. Due to its excellent barrier property, it is widely used in fields such as food packaging, pharmaceutical packaging, cosmetic packaging, and automobile fuel tanks.

[0003] Due to the continuous expansion of the uses of EVOH, the quality requirements for EVOH are getting higher and higher. For example, in the packaging industry, there are relatively high requirements for the hue. EVOH is obtained by copolymerizing vinyl acetate (VAC) and ethylene and then saponifying, and generally solution polymerization is selected. In the later stage of the solution polymerization reaction, due to the consumption of VAC, the ratio changes, and the molecular weight of the generated EVOH becomes smaller and smaller, resulting in an increasingly wide molecular weight distribution (PDI). And when the molecular weight distribution is too wide and there are too many low molecular weights, EVOH is more likely to turn yellow. At the same time, impurities such as acetaldehyde and sodium acetate in the production process of EVOH are also the main culprits causing yellowing.

[0004] Therefore, it is of great significance to research and develop an ethylene-vinyl alcohol copolymer and a preparation method thereof. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defect problem that the ethylene-vinyl alcohol copolymer (EVOH) prepared by the prior art is prone to yellowing, resulting in a relatively poor hue of EVOH, and to provide an ethylene-vinyl alcohol copolymer, a preparation method thereof, and applications. The yellow index of the ethylene-vinyl alcohol copolymer (EVOH) prepared by the method provided by the present invention is 4 - 8, and the molecular weight distribution index is 1 - 1.6, and an EVOH with excellent hue can be obtained.

[0006] In order to achieve the above purpose, the first aspect of the present invention provides a preparation method of an ethylene-vinyl alcohol copolymer, wherein the preparation method includes the following steps:

[0007] Contacting first vinyl acetate, a first initiator, a monohydric alcohol with ethylene in a closed container for an isothermal and isobaric reaction to obtain an ethylene-vinyl alcohol copolymer;

[0008] Among them, during the constant temperature and pressure reaction process, second vinyl acetate and a second initiator are supplemented.

[0009] The second aspect of the present invention provides an ethylene-vinyl alcohol copolymer prepared by the preparation method described above.

[0010] The third aspect of the present invention provides an application of the above-mentioned ethylene-vinyl alcohol copolymer in the packaging industry.

[0011] Through the above technical solutions, by adopting the preparation method of the ethylene-vinyl alcohol copolymer of the present invention, by strictly controlling various factors affecting the hue, the yellowness index of the prepared ethylene-vinyl alcohol copolymer (EVOH) is 4-8, and the molecular weight distribution index is 1-1.6. The prepared EVOH has excellent hue and is very suitable for use in the packaging industry, especially can be widely applied to fields such as food packaging, pharmaceutical packaging, cosmetic packaging, and automobile fuel tanks. Detailed Embodiments

[0012] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. 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.

[0013] As described above, the first aspect of the present invention provides a preparation method of an ethylene-vinyl alcohol copolymer, wherein the preparation method includes the following steps:

[0014] Contact first vinyl acetate, a first initiator, a monohydric alcohol and ethylene in a closed container for a constant temperature and pressure reaction to obtain an ethylene-vinyl alcohol copolymer;

[0015] Among them, during the constant temperature and pressure reaction process, second vinyl acetate and a second initiator are supplemented.

[0016] The inventors of the present invention found that during the process of preparing an ethylene-vinyl alcohol copolymer, during the process of contacting first vinyl acetate, a first initiator, a monohydric alcohol and ethylene in a closed container for a constant temperature and pressure reaction, second vinyl acetate and a second initiator are supplemented to ensure that during the constant temperature and pressure reaction process, the ratio of vinyl acetate and initiator to dissolved ethylene (that is, the ethylene that can participate in the reaction) to the solvent ratio remains unchanged, thereby narrowing the molecular weight distribution index and obtaining an EVOH with excellent hue.

[0017] According to the present invention, during the constant temperature and constant pressure reaction process, second vinyl acetate and a second initiator are supplemented. In the present invention, the rates of supplementing the second vinyl acetate and the second initiator are constant. In the present invention, there is no particular limitation on the rates of supplementing the second vinyl acetate and the second initiator, and they can be determined according to the amounts of the supplemented second vinyl acetate and second initiator and the time of the constant temperature and constant pressure reaction.

[0018] According to the present invention, relative to 100 parts by weight of the first vinyl acetate, the amount of the first initiator is 0.01 - 0.1 part by weight, the amount of the monohydric alcohol is 5 - 50 parts by weight, the amount of the second vinyl acetate is 40 - 80 parts by weight, and the amount of the second initiator is 0.005 - 0.08 part by weight; preferably, relative to 100 parts by weight of the first vinyl acetate, the amount of the first initiator is 0.022 - 0.091 part by weight, the amount of the monohydric alcohol is 5 - 20 parts by weight, the amount of the second vinyl acetate is 45 - 78 parts by weight, and the amount of the second initiator is 0.013 - 0.045 part by weight. In the present invention, by controlling the amounts of each reaction material within the foregoing ranges, an EVOH with excellent hue can be obtained.

[0019] According to the present invention, the conditions of the constant temperature and constant pressure reaction include: the pressure is 10 - 60 bar, the polymerization temperature is 40 - 70 °C, and the reaction time is 2 - 10 h; preferably, the conditions of the constant temperature and constant pressure reaction include: the pressure is 30 - 58 bar, the polymerization temperature is 53 - 62 °C, and the reaction time is 3 - 8.2 h; more preferably, the conditions of the constant temperature and constant pressure reaction include: the pressure is 32 - 55 bar, the polymerization temperature is 54 - 60 °C, and the reaction time is 3 - 8.2 h. In the present invention, if the pressure is too low or too high, the ethylene content in the prepared ethylene - vinyl alcohol copolymer will exceed 20 - 50 mol%, thus the processability and barrier property cannot be balanced. If the temperature is too low, the reaction rate will be too slow, affecting the preparation efficiency; if the temperature is too high, the regularity of the molecular chain segments will be affected, and side reactions will increase. If the reaction time is too short, the yield will be too low; if the reaction time is too long, the viscosity will be too high, resulting in a self - accelerating effect and the reaction becoming uncontrollable.

[0020] In the present invention, for EVOH with the same ethylene content, the lower the molecular weight, the lower the melting temperature and the thermal decomposition temperature. If the molecular weight distribution is relatively wide, when the EVOH with a larger molecular weight melts, the EVOH with an extremely small molecular weight has already started to decompose upon heating, forming coloring groups and affecting the hue of the EVOH. The polymerization reaction of EVOH is a free - radical polymerization, and its molecular weight is closely related to the ratio of the two monomers and the solvent. As the reaction progresses, the monomers will gradually decrease, and the solvent ratio will increase, resulting in a decrease in the molecular weight of the subsequently polymerized EVOH.

[0021] According to the present invention, the first vinyl acetate and the second vinyl acetate are the same and are both self-produced products of Chongqing Chuanwei Chemical Co., Ltd. (CWHG) of Sinopec Group.

[0022] According to the present invention, the first initiator and the second initiator are the same or different, and each is selected from one or more of azo initiators, peroxide initiators, and organic peroxides.

[0023] According to the present invention, the azo initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, and azobis(2-methylbutyronitrile); preferably, the azo initiator is one or more of azobisisobutyronitrile, azobisisoheptonitrile, and dimethyl azobisisobutyrate.

[0024] According to the present invention, the peroxide initiator is selected from one or more of hydrogen peroxide, ammonium persulfate, and potassium persulfate.

[0025] According to the present invention, the organic peroxide is selected from one or more of benzoyl peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, tert-amyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, tert-amyl peroxypivalate, tert-butyl peroxyacetate, and dibutyl peroxydicarbonate; preferably, the organic peroxide is selected from one or more of tert-amyl peroxyneodecanoate, tert-amyl peroxypivalate, and tert-butyl peroxyneodecanoate.

[0026] According to the present invention, the monohydric alcohol is a C 1 -C 4 monohydric alcohol; preferably, the monohydric alcohol is selected from one or more of methanol, ethanol, propanol, n-butanol, isobutanol, tert-butanol, dimethyl methanol, and 3-methyl-2-butanol; more preferably, the monohydric alcohol is selected from one or more of methanol, ethanol, propanol, n-butanol, and tert-butanol.

[0027] According to the present invention, the preparation method further includes: after carrying out the constant temperature and constant pressure reaction, removing residual monomers, alcoholysis saponification, washing, and drying treatments.

[0028] In the present invention, residual monomers can be removed by rotary evaporation drying or by solvent displacement. After removing the residual monomers, the total content of the first vinyl acetate and the second vinyl acetate is 2-100 ppm.

[0029] According to the present invention, the alcoholysis saponification is carried out in two steps: in the first step, an alkali solution is added for alcoholysis, and first, the obtained EVAc solution is added to a methanol solution of NaOH for alcoholysis; in the second step, saponification is carried out by adding a certain amount of aqueous NaOH solution for saponification.

[0030] In the present invention, the saponification can be any one of homogeneous saponification method, solvent dispersion saponification method and melting saponification method, preferably homogeneous saponification method or solvent dispersion saponification method.

[0031] According to the present invention, during the alcoholysis saponification treatment process, the degree of alcoholysis is 99-99.9 mol%, preferably, the degree of alcoholysis is 99.18-99.81 mol%.

[0032] According to the present invention, the washing includes pickling and water washing. Preferably, pickling is carried out with an aqueous acetic acid solution, and the concentration of the aqueous acetic acid solution is 50-1000 ppm. In the present invention, the water washing is preferably carried out 3-6 times.

[0033] According to the present invention, for the drying, it is dried at 75-120 °C for 5-24 hours until its volatile matter reaches 0.1-0.5%, preferably 0.11-0.43%.

[0034] According to a preferred specific embodiment of the present invention, a method for preparing an ethylene-vinyl alcohol copolymer comprises the following steps:

[0035] 100 parts of the first VAC, 5-50 parts of a monohydric alcohol and 0.01-0.1 part of the first initiator are added to a closed container, and the container is purged with 7 bar of ethylene gas three times, and then ethylene gas is introduced to keep the pressure at 10-60 bar, and stirred, heated to 40-70 °C, and the reaction starts under constant temperature and pressure. At the same time, 40-80 parts of the second VAC and 0.005-0.08 part of the second initiator are continuously added at a constant rate and the reaction ends after 2-10 hours. Then the residual monomers are removed, followed by alcoholysis saponification, washing and drying to obtain EVOH.

[0036] The second aspect of the present invention provides an ethylene-vinyl alcohol copolymer prepared by the aforementioned preparation method.

[0037] According to the present invention, the yellowness index of the ethylene-vinyl alcohol copolymer is 4-8, and the molecular weight distribution index is 1-1.6; preferably, the yellowness index of the ethylene-vinyl alcohol is 4.2-7.6, and the molecular weight distribution index is 1.11-1.52.

[0038] The third aspect of the present invention provides an application of the aforementioned ethylene-vinyl alcohol copolymer in the packaging industry.

[0039] According to the present invention, the packaging industry can be a field with high barrier requirements. Preferably, the packaging industry includes one or more of food films, red wine films, beverage bottles and cosmetic bottles.

[0040] The present invention will be described in detail below through examples.

[0041] In the following examples and comparative examples:

[0042] The yellow index parameter was measured by a Hunter Lab colorimeter, model: UltraScan VIS, mode type: RSIN including specular reflection, measurement method: general, observation area: 1.000 inch, 3 holes, simulated light: natural light at 2:00 pm;

[0043] The number-average molecular weight and molecular weight distribution parameters were measured by high-temperature gel permeation chromatography (GPC, PL-GPC220, Aglient Co., USA) for the molecular weight and molecular weight distribution of the EVOH sample. The solvent was dimethyl sulfoxide, the test temperature was 70 °C, the sample concentration was 0.1 mg / ml, and the flow rate was 100.0 μl;

[0044] The volatile matter and alcoholysis degree parameters were measured according to the internal control standard of Chongqing Chuanwei Chemical Co., Ltd. (CWHG) of Sinopec Group;

[0045] The ethylene content was determined according to GB / T41877.2.

[0046] The raw materials VAC and methanol were all produced by Chongqing Chuanwei Chemical Co., Ltd. (CWHG) of Sinopec Group. Ethylene was cylinder ethylene with a purity of 99.9%, a commercial product of Dalian Dete Gas Co., Ltd.

[0047] Unless otherwise specified, the following are all in parts by weight and weight percentages.

[0048] "Parts" all refer to "parts by weight".

[0049] Example 1

[0050] This example is to illustrate the ethylene-vinyl alcohol copolymer prepared by the method of the present invention.

[0051] (1) Add 100 parts by weight of the first VAC, 10 parts by weight of methanol and 0.022 parts by weight of the first initiator tert-amyl peroxyneodecanoate to a 3-liter high-pressure reactor;

[0052] (2) Replace with 7 bar of ethylene gas 3 times, then introduce ethylene gas to keep the pressure at 50 bar, stir, heat up to 55 °C, and start the reaction at constant temperature and pressure. At the same time, supplement 62 parts of the second VAC and 0.014 parts of the second initiator tert-amyl peroxyneodecanoate at a constant rate during the reaction period and end the reaction after 8.2 hours to obtain an EVAc methanol solution containing VAC;

[0053] (3) Then, the method of adding methanol in multiple batches and heating to displace VAC was adopted to remove the residual monomers. After removal, the VAC content was 47 ppm. The obtained EVAc methanol solution was then added with 20 parts by weight of NaOH methanol solution for saponification. After alcoholysis saponification, the degree of alcoholysis was as shown in Table 1, washed once with 1 part by weight of acetic acid and washed three times with 500 parts by weight of water, and dried at 100 °C for 8 hours to obtain EVOH.

[0054] Examples 2 - 8

[0055] This example is to illustrate the ethylene - vinyl alcohol copolymer prepared by the method of the present invention.

[0056] Examples 2 - 8 were prepared for ethylene - vinyl alcohol copolymer according to the same method as in Example 1, except that the reaction materials, the amounts of reaction materials, and the process conditions were different, as specifically shown in Table 1.

[0057] Comparative Example 1

[0058] Ethylene - vinyl alcohol copolymer was prepared according to the same method as in Example 1, except that in step (2), the second vinyl acetate and the second initiator were not supplemented, that is, "62 parts of the second VAC and 0.014 parts of the second initiator" were not supplemented.

[0059] As a result, the ethylene - vinyl alcohol copolymer was prepared.

[0060] Comparative Example 2

[0061] Ethylene - vinyl alcohol copolymer was prepared according to the same method as in Example 1, except that in step (2), the second initiator was not supplemented, that is, "0.014 parts of the second initiator" were not supplemented.

[0062] As a result, the ethylene - vinyl alcohol copolymer was prepared.

[0063] Comparative Example 3

[0064] Ethylene - vinyl alcohol copolymer was prepared according to the same method as in Example 1, except that in step (2), "reacting for 8.2 hours" was modified to "reacting for 15 hours".

[0065] As a result, the ethylene - vinyl alcohol copolymer was obtained.

[0066] Comparative Example 4

[0067] Ethylene - vinyl alcohol copolymer was prepared according to the same method as in Example 1, except that in step (2), "heating to 55 °C" was modified to "heating to 75 °C".

[0068] As a result, the ethylene - vinyl alcohol copolymer was obtained.

[0069] Comparative Example 5

[0070] The ethylene-vinyl alcohol copolymer was prepared in the same manner as in Example 1, except that: in step (2), instead of adding the second VAC and the second initiator, the "62 parts by weight of the second VAC and 0.014 parts by weight of the second initiator" added in step (2) were added to the 3 L high-pressure reactor together with "100 parts by weight of the first VAC, 10 parts by weight of methanol, and 0.022 parts by weight of the first initiator, tert-amyl peroxyneodecanoate" in step (1).

[0071] Specifically:

[0072] (1) 162 parts by weight of the first VAC, 10 parts by weight of methanol, and 0.036 parts by weight of the first initiator, tert-amyl peroxyneodecanoate, were added to a 3 L high-pressure reactor;

[0073] (2) The reactor was purged with ethylene gas at 7 bar three times, and then ethylene gas was introduced to maintain the pressure at 50 bar. The mixture was stirred and heated to 55 °C, and the reaction was started under constant temperature and pressure;

[0074] (3) The residual VAC was removed by the method of adding methanol in multiple batches to displace VAC. After removal, the VAC content was 47 ppm. The obtained EVAc methanol solution was then saponified by adding 20 parts by weight of a NaOH methanol solution. After alcoholysis and saponification, the degree of alcoholysis was as shown in Table 1, washed once with 1 part by weight of acetic acid and washed three times with 500 parts by weight of water, and dried at 100 °C for 8 hours to obtain EVOH.

[0075] As a result, an ethylene-vinyl alcohol copolymer was obtained.

[0076] Table 1

[0077]

[0078]

[0079] Test Example

[0080] The ethylene-vinyl alcohol copolymers prepared in Examples 1-8 and Comparative Examples 1-5 were subjected to various preparation tests, and the results are shown in Table 2.

[0081] Table 2

[0082]

[0083]

[0084] As can be seen from the results in Table 2, the yellowness index of the ethylene-vinyl alcohol copolymer prepared by the preparation method of the present invention is 4.2-7.6, the molecular weight distribution index is 1.11-1.52, the volatile content is 0.11-0.43%, and the degree of alcoholysis is 99.18-99.81 mol%. It is possible to prepare EVOH with excellent hue, which is very suitable for use in the packaging industry, especially widely applicable to fields such as food packaging, pharmaceutical packaging, cosmetic packaging, and automobile fuel tanks.

[0085] 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 preparing ethylene-vinyl alcohol copolymer, characterized in that, the preparation method comprises the following steps: contacting vinyl acetate, a first initiator, a monohydric alcohol and ethylene in a closed container for a constant temperature and pressure reaction to obtain an ethylene-vinyl alcohol copolymer; wherein, during the constant temperature and pressure reaction, a second vinyl acetate and a second initiator are supplemented.

2. The preparation method according to claim 1, wherein, relative to 100 parts by weight of the first vinyl acetate, the dosage of the first initiator is 0.01-0.1 part by weight, the dosage of the monohydric alcohol is 5-50 parts by weight, the dosage of the second vinyl acetate is 40-80 parts by weight, and the dosage of the second initiator is 0.005-0.08 part by weight; preferably, relative to 100 parts by weight of the first vinyl acetate, the dosage of the first initiator is 0.022-0.091 part by weight, the dosage of the monohydric alcohol is 5-20 parts by weight, the dosage of the second vinyl acetate is 45-78 parts by weight, and the dosage of the second initiator is 0.013-0.045 part by weight.

3. The preparation method according to claim 1, wherein, the conditions of the constant temperature and pressure reaction include: the pressure is 10-60 bar, the polymerization temperature is 40-70 °C, and the reaction time is 2-10 h; preferably, the conditions of the constant temperature and pressure reaction include: the pressure is 30-58 bar, the polymerization temperature is 53-62 °C, and the reaction time is 3-8.2 h.

4. The preparation method according to any one of claims 1-3, wherein, the preparation method further comprises: after the constant temperature and pressure reaction, removing residual monomers, alcoholysis saponification, washing and drying treatments are carried out.

5. The preparation method according to claim 4, wherein, after removing the residual monomers, the total content of the first vinyl acetate and the second vinyl acetate is 2-50 ppm; and / or, during the alcoholysis saponification treatment, the degree of alcoholysis is 99.0-99.9 mol%; and / or, the washing includes pickling and water washing, preferably, pickling is carried out with an acetic acid aqueous solution, and the concentration of the acetic acid aqueous solution is 50-1000 ppm.

6. The preparation method according to claim 1 or 2, wherein, the first initiator and the second initiator are the same or different, and each is selected from one or more of azo initiators, peroxide initiators and organic peroxides; preferably, the azo initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate and azobis(2-methylbutyronitrile); preferably, the peroxide initiator is selected from one or more of hydrogen peroxide, ammonium persulfate and potassium persulfate; preferably, the organic peroxide is selected from one or more of benzoyl peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, tert-amyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, tert-amyl peroxy pivalate, tert-butyl peroxyacetate and dibutyl peroxydicarbonate.

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

8. The ethylene-vinyl alcohol copolymer according to claim 7, wherein, the yellowness index of the ethylene-vinyl alcohol copolymer is 4-8, and the molecular weight distribution index is 1-1.

6.

9. The ethylene-vinyl alcohol copolymer according to claim 8, wherein, the yellowness index of the ethylene-vinyl alcohol is 4.2-7.6, and the molecular weight distribution index is 1.11-1.

52.

10. Use of the ethylene-vinyl alcohol copolymer according to any one of claims 7-9 in the packaging industry.

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