Modified ethylene-vinyl alcohol-based copolymer, method for manufacturing the same, and molded article including the same

Abstract

This invention relates to modified ethylene-vinyl alcohol copolymers, methods for manufacturing them, and molded articles comprising them. Specifically, according to one embodiment of the invention, a modified ethylene-vinyl alcohol copolymer is provided, comprising a first repeating unit derived from ethylene; a second repeating unit derived from vinyl alcohol; and a third repeating unit derived from tetraethyl orthosilicate (TEOS).

Description

Technical Field

[0001] This invention relates to modified ethylene-vinyl alcohol copolymers, methods for manufacturing them, and molded articles comprising them. Cross-referencing (multiple) related applications

[0002] This application claims the benefits of Korean Patent Application No. 10-2020-0134426, filed with the Korean Intellectual Property Office on October 16, 2020, and Korean Patent Application No. 10-2021-0127979, filed on September 28, 2021, the disclosures of which are incorporated herein by reference in their entirety. Prior Technology

[0003] Ethylene-vinyl alcohol (EVOH) has excellent gas barrier properties, transparency, and mechanical properties, and is therefore widely used as a material for membranes, sheets, and household meal replacement containers.

[0004] However, due to the presence of hydroxyl (-OH) groups in the molecule, ethylene-vinyl alcohol exhibits high gas barrier properties in the dry state, but under humid conditions, water vapor is absorbed and the permeability increases rapidly.

[0005] To compensate for this moisture sensitivity, a method has been proposed for co-extruding ethylene-vinyl alcohol with polyolefin (PO) to manufacture multilayer molded articles, and a method for preparing ethylene-vinyl acetate (EVA) using a multifunctional initiator followed by saponification.

[0006] However, in the case of co-extruding polyolefins with a process window incompatible with ethylene-vinyl alcohol, gelation may occur, which may worsen processability, mechanical properties, etc., or fish eyes, streaks, etc. may form on the surface, thus reducing the appearance quality of the molded parts.

[0007] Meanwhile, when using multifunctional initiators, suitable comonomers and polymerization conditions should be found, and the process efficiency may be reduced when the polymerized EVA-based copolymer is saponified under unsuitable conditions. Summary of the Invention

[0008] [Technical Issues]

[0009] One objective of this invention is to improve molecular weight, complex viscosity, and viscoelasticity by controlling the structure of ethylene-vinyl alcohol copolymers, and to improve the processability and mechanical properties of molded parts. [Technical Solution]

[0010] Specifically, according to one embodiment of the present invention, a modified ethylene-vinyl alcohol copolymer is provided, comprising: a first repeating unit derived from ethylene; a second repeating unit derived from vinyl alcohol; and a third repeating unit derived from tetraethyl orthosilicate (TEOS).

[0011] According to another specific embodiment of the present invention, a method for manufacturing a modified ethylene-vinyl alcohol copolymer is provided, comprising the step of reacting the ethylene-vinyl alcohol copolymer with tetraethyl orthosilicate.

[0012] According to yet another specific example, a molded article comprising a modified ethylene-vinyl alcohol copolymer is provided. [Beneficial effects]

[0013] Compared to ethylene-vinyl alcohol copolymers that do not contain a third repeating unit, a specific example of a modified ethylene-vinyl alcohol copolymer can have a high molecular weight, complex viscosity and viscoelasticity, but also excellent flexibility, rigidity and melt strength.

[0014] Furthermore, a specific example of the manufacturing method corresponds to the post-modification of the ethylene-vinyl alcohol copolymer, without the need for the introduction of catalysts, solvents, etc., thus enabling low-cost, high-efficiency process operation, and diversifying the quality of the final product according to the quality of the ethylene-vinyl alcohol copolymer.

[0015] Furthermore, since a specific example of a molded part comprises a modified ethylene-vinyl alcohol copolymer with excellent flexibility, rigidity and melt strength, it can have excellent processability and mechanical properties. Simple Explanation of the Diagram

[0016] [Figure 1] shows the GPC analysis results of Comparative Example 1 and Example 1.

[0017] [Figure 2] shows the GPC analysis results of Comparative Example 1 and Example 2.

[0018] [Figure 3] shows the complex viscosity analysis results of Examples 1 and 2.

[0019] [Figure 4] shows the viscoelasticity analysis results of Examples 1 and 2. Implementation

[0020] The terminology used herein is for illustrative purposes only and is not intended to limit the invention. Singular expressions include their plural forms unless expressly stated or obvious from the context. As used herein, the terms “comprising,” “equipped with,” or “having,” etc., are intended to specify the presence of a feature, quantity, step, structural element, or combination thereof in a practice, and are not intended to exclude the presence or addition of one or more other features, quantities, steps, structural elements, or combinations thereof.

[0021] While various modifications and forms are possible to this invention, specific embodiments will be described and illustrated in detail below. However, it should be understood that this is not intended to limit the invention to the specific disclosure, and the invention includes all modifications, equivalents, or substitutions without departing from the spirit and scope of the invention.

[0022] Specific examples of the present invention will be described in detail below. [Modified Ethylene] [-] [Vinyl alcohol copolymer] [] []

[0023] According to one specific example of the present invention, a modified ethylene-vinyl alcohol copolymer is provided, comprising: a first repeating unit derived from ethylene; a second repeating unit derived from vinyl alcohol; and a third repeating unit derived from tetraethyl orthosilicate (TEOS).

[0024] Compared to ethylene-vinyl alcohol copolymers that do not contain a third repeating unit, this modified ethylene-vinyl alcohol copolymer can have high molecular weight, complex viscosity and viscoelasticity, but also has excellent flexibility, rigidity and melt strength.

[0025] Specifically, a modified ethylene-vinyl alcohol copolymer can be produced by reacting the ethylene-vinyl alcohol copolymer with tetraethyl orthosilicate.

[0026] In this respect, the first and second repeating units can be derived from ethylene-vinyl alcohol copolymers, respectively, and the third repeating unit can be derived from tetraethyl orthosilicate.

[0027] In this reaction, tetraethyl orthosilicate can act as a crosslinking agent. Specifically, tetraethyl orthosilicate mediates partial crosslinking within ethylene-vinyl alcohol copolymer molecules, as well as crosslinking between different ethylene-vinyl alcohol copolymer molecules, and may increase the molecular weight of the final product (i.e., the modified ethylene-vinyl alcohol copolymer).

[0028] In particular, long chain branches (LCBs) can be generated through cross-linking between molecules of different ethylene-vinyl alcohol copolymers, thereby improving the flexibility, rigidity and melt strength of the final product, and ultimately improving the processability and mechanical properties of the molded parts.

[0029] The following text will describe in detail a specific example of a modified ethylene-vinyl alcohol copolymer. [Repeating Unit] [] []

[0030] As described above, the first repeating unit and the second repeating unit can be derived from the reactant ethylene-vinyl alcohol copolymer.

[0031] In this respect, the first repeating unit can be represented by the following chemical formula 1, and the second repeating unit can be represented by the following chemical formula 2: [Chemical Formula 1] . [Chemical Formula 2] .

[0032] Meanwhile, the third repeating unit can be derived from the crosslinking agent tetraethyl orthosilicate, and can have an oxidation number of 1 to 4 depending on the degree of reaction with the ethylene-vinyl alcohol copolymer.

[0033] In this respect, the third repeating unit may contain one or more repeating units selected from the following chemical formulas 3-1 to 3-4: [Chemical Formula 3-1] [Chemical Formula 3-2] [Chemical Formula 3-3] [Chemical Formula 3-4] .

[0034] Furthermore, in modified EVOH containing alkyl polyether silicates with one or more alkyl substituents (rather than all alkoxy-substituted silicates (such as those of formulas 3 and 3-1 to 3-4)) as the third repeating unit, the free volume may increase due to the long alkyl polyether chain, potentially causing defects in crystal structure formation through plasticizing effects and interactions with vinyl alcohol groups. Additionally, when using additives containing thiol groups, alkyl polyether silicates with one or more alkyl substituents can form disulfide groups through thermal oxidation, potentially resulting in undesirable structural units. Moreover, because thiol groups have higher acidity than alcohol groups, thiolates may form instead of alkoxides in the presence of an alkaline catalyst (such as sodium hydroxide), thus potentially preventing the formation of the structural units desired to be derived herein. [Moles of repeating units] [] []

[0035] In a specific example of a modified ethylene-vinyl alcohol copolymer, the first repeating unit serves to increase mechanical properties and processability, while the second repeating unit serves to increase gas barrier properties.

[0036] Therefore, in a specific example of a modified ethylene-vinyl alcohol copolymer, if the molar amount of the first repeating unit is reduced, the processability may be reduced, and if the molar ratio of the second repeating unit is reduced, the gas barrier properties may be reduced.

[0037] Taking this trend into consideration, in a specific example, the molar ratio of the first repeating unit and the second repeating unit in a modified ethylene-vinyl alcohol copolymer can be controlled within the range of 20:80 to 40:60, specifically 25:75 to 35:65, for example, within the range of 30:70 to 33:67.

[0038] In a specific example, the molar ratio of the first repeating unit and the second repeating unit in the modified ethylene-vinyl alcohol copolymer can be the same as that in the reactant ethylene-vinyl alcohol copolymer. Therefore, the molar ratio of the first repeating unit and the second repeating unit in the final product modified ethylene-vinyl alcohol copolymer can be controlled by controlling the molar ratio of the first repeating unit and the second repeating unit in the reactant ethylene-vinyl alcohol copolymer.

[0039] In a specific example of a modified ethylene-vinyl alcohol copolymer, the role of the third repeating unit is to increase the molecular weight, the cross-linking structure and long chain branching in the molecule, as well as to improve the flexibility, rigidity and melt strength of the final product, and ultimately improve the processability and mechanical properties of the molded object.

[0040] Therefore, as the content of the third repeating unit in a specific example of a modified ethylene-vinyl alcohol copolymer decreases, the molecular weight, cross-linking structure, and long-chain branching may decrease. However, as the content of the third repeating unit increases, gel formation may occur and processability may deteriorate.

[0041] Taking into account this trend, in a specific example of a modified ethylene-vinyl alcohol copolymer, the content of the third repeating unit can be controlled within the range of 1 to 10 mol, specifically 1.5 to 7 mol (e.g., 2 to 4 mol), based on 100 mol of the second repeating unit.

[0042] In a specific example, the content of the third repeating unit in the modified ethylene-vinyl alcohol copolymer (based on 100 moles of the second repeating unit) can be the same as the amount of crosslinking agent introduced (based on 100 moles of the hydroxyl (-OH) groups in the reactant ethylene-vinyl alcohol copolymer). Therefore, the content of the third repeating unit in the final product modified ethylene-vinyl alcohol copolymer can be controlled by controlling the amount of crosslinking agent introduced (based on 100 moles of the hydroxyl (-OH) groups in the reactant ethylene-vinyl alcohol copolymer).

[0043] The total amount (100 mol%) of the modified ethylene-vinyl alcohol copolymer may include 25 to 35 mol% of a first repeating unit and 0.5 to 7 mol% of a third repeating unit, and the second repeating unit may be included in the remainder.

[0044] This takes into account the molar ratio of the first and second repeating units in the modified ethylene-vinyl alcohol copolymer, as well as the content of the third repeating unit (based on 100 moles of the second repeating unit).

[0045] For example, the total amount (100 mol%) of the modified ethylene-vinyl alcohol copolymer may include 29 to 32 mol% of the first repeating unit and 1 to 3 mol% of the third repeating unit, and the second repeating unit may be included in the remainder.

[0046] The “remaining amount” of the content of the second repeating unit refers to [the total amount of the modified ethylene-vinyl alcohol copolymer (100 mol%) - (the sum of repeating units excluding the second repeating unit)].

[0047] Specifically, when the modified ethylene-vinyl alcohol copolymer contains only the first to third repeating units, the content of the second repeating unit can be [total amount of modified ethylene-vinyl alcohol copolymer (100 mol%) - (content of the first repeating unit + content of the third repeating unit)].

[0048] Furthermore, in the case where the modified ethylene-vinyl alcohol copolymer includes other repeating units (e.g., a fourth repeating unit) in addition to the first to third repeating units, the content of the second repeating unit can be [total amount of modified ethylene-vinyl alcohol copolymer (100 mol%) - (content of the first repeating unit + content of the third repeating unit + content of the fourth repeating unit)].

[0049] In EVOH, as the ethylene content corresponding to the first repeating unit decreases, it may exhibit properties similar to poly(vinyl alcohol) (PVA), and the relatively flexible ethylene structure may be reduced, thus worsening processability. Conversely, as the number of vinyl alcohol structural units increases, Tg and Tm may increase, and when the ethylene content is reduced to very low levels, Tm may become above the decomposition temperature, thus making processing difficult.

[0050] In addition to the first repeating unit, the second repeating unit, and the third repeating unit, the modified ethylene-vinyl alcohol copolymer may further include heterogeneous repeating units.

[0051] The heterogeneous repeating unit can be derived from the reactant ethylene-vinyl alcohol copolymer. Specifically, when a monomer mixture comprising ethylene monomers, ethylene carboxylate monomer ethyl, and heterogeneous monomers is polymerized to prepare an ethylene-vinyl acetate (EVA) copolymer, and then saponified to prepare an ethylene-vinyl alcohol copolymer, the heterogeneous repeating unit may be further included together with the first and second repeating units. If such an ethylene-vinyl alcohol copolymer is reacted with a crosslinking agent, a modified ethylene-vinyl alcohol copolymer comprising, in addition to the first and second repeating units, a heterogeneous repeating unit can be further obtained.

[0052] Depending on the type and content of the heterogeneous repeating units, modified ethylene-vinyl alcohol copolymers with various qualities can be provided. The type and content of the heterogeneous repeating units can be determined according to well-known technical knowledge in the relevant field. [Weight-average molecular weight and molecular weight distribution] [] []

[0053] Compared with unmodified ethylene-vinyl alcohol copolymers, modified ethylene-vinyl alcohol copolymers can have higher molecular weights.

[0054] Specifically, the modified ethylene-vinyl alcohol copolymer can have a weight average molecular weight of 100,000 to 200,000 g / mol and a molecular weight distribution (MWD; Mw / Mn) of 1.0 to 3.0.

[0055] However, if the molecular weight of the modified ethylene-vinyl alcohol copolymer is too low, membrane manufacturing may be problematic; if it is too high, processability issues may arise. Furthermore, as the weight-average molecular weight of the modified ethylene-vinyl alcohol copolymer increases, the molecular weight distribution tends to broaden; if the molecular weight distribution broadens, processability problems may occur.

[0056] Considering this trend, the weight average molecular weight of the modified ethylene-vinyl alcohol copolymer can be controlled at 100,000 g / mol or higher, 110,000 g / mol or higher, or 120,000 g / mol or higher, and 200,000 g / mol or lower, 190,000 g / mol or lower, or 180,000 g / mol or lower. Furthermore, the molecular weight distribution of the modified ethylene-vinyl alcohol copolymer can be controlled at 1.0 or higher, 1.3 or higher, or 1.5 or higher, and 3.0 or lower, 2.5 or lower, or 2.0 or lower.

[0057] The weight average molecular weight and molecular weight distribution of the final product, the modified ethylene-vinyl alcohol copolymer, can be controlled by adjusting the molecular weight of the reactant, the amount of crosslinking agent introduced, and the reaction time. [Modified Ethylene] [-] [Manufacturing method of vinyl alcohol copolymers] [] []

[0058] According to another specific example of the present invention, a method for manufacturing modified ethylene-vinyl alcohol copolymers is provided, comprising the step of reacting the ethylene-vinyl alcohol copolymer with tetraethyl orthosilicate (TEOS) in a temperature range of 50 to 100°C.

[0059] By reacting ethylene-vinyl alcohol copolymers with tetraethyl orthosilicate within a reaction temperature range, partial crosslinking within the ethylene-vinyl alcohol copolymer molecules and crosslinking between different ethylene-vinyl alcohol copolymer molecules can be formed, and a modified ethylene-vinyl alcohol copolymer as described above can ultimately be obtained.

[0060] One specific example of the manufacturing method corresponds to the preparation of an ethylene-vinyl alcohol copolymer followed by subsequent modification, without the need for the introduction of catalysts, solvents, etc., thus enabling low-cost operation and a high-efficiency process.

[0061] Furthermore, the quality of the final product can vary depending on the quality of the reactant ethylene-vinyl alcohol copolymer. Specifically, the quality of the reactant ethylene-vinyl alcohol copolymer can be determined by factors such as the molar ratio of the first and second repeating units, and the type and content of any additional repeating units.

[0062] The following text will describe in detail the characteristics of a specific manufacturing method, but will omit any descriptions that are repeated in the specific example described above. [Reaction Conditions] [] []

[0063] In a specific example, the reaction can be carried out in a temperature range in which the ethylene-vinyl alcohol copolymer and tetraethyl orthosilicate can react, specifically 50 to 100°C, more specifically 60 to 90°C, for example 70 to 80°C.

[0064] Conversely, at temperatures below 50°C, for example, at room temperature of 20 to 30°C, ethylene-vinyl alcohol copolymers and tetraethyl orthosilicate can be simply mixed without reacting.

[0065] In a specific example, the reaction can proceed for a period of time during which the ethylene-vinyl alcohol copolymer and tetraethyl orthosilicate can react, specifically 2 to 30 hours, more specifically 3 to 27 hours, for example 4 to 24 hours.

[0066] When other conditions (such as reaction temperature) are constant, as the reaction time is extended within the above range, some cross-linking and long-chain branching in the molecule may increase. However, if the reaction time is too long, gel formation may occur and processability may deteriorate.

[0067] Meanwhile, a specific reaction can be carried out by stirring at a speed of 50 to 400 rpm, specifically 100 to 300 rpm, for example, 150 to 250 rpm.

[0068] All other things being equal, as the stirring speed increases within the above range, some cross-linking and long-chain branching in the molecules may increase. However, if the stirring speed is increased excessively, gel formation may occur and processability may deteriorate. [Post-processing] [] []

[0069] Impurities may remain in the reaction products, such as the catalyst used to prepare the ethylene-vinyl alcohol copolymer. To remove these, the reaction products can be further washed after the reaction is complete, and the washed reaction products can be dried.

[0070] In the raw material ethylene-vinyl alcohol copolymer, the catalyst used in the preparation process may remain as an impurity. Even after reaction with tetraethyl orthosilicate, the impurity catalyst may remain and may not be removed until the washing process.

[0071] Specifically, the reaction product can be soaked in distilled water for a sufficient time, and then the solid / liquid can be separated using a filter. The separated solid can be left at room temperature or dried by heating in an oven.

[0072] More specific washing and drying conditions can be determined in accordance with well-known technical knowledge in the field to which this invention pertains. [Reactants] [] []

[0073] As explained above, the molar ratio of the first repeating unit and the second repeating unit in the final product modified ethylene-vinyl alcohol copolymer can be controlled by controlling the molar ratio of the first repeating unit and the second repeating unit in the reactant ethylene-vinyl alcohol copolymer.

[0074] In this respect, the molar ratio of the first repeating unit and the second repeating unit in the reactant ethylene-vinyl alcohol copolymer can be controlled within the range of 20:80 to 40:60, specifically 25:75 to 35:65, for example, within the range of 30:70 to 33:67.

[0075] Furthermore, the content of the third repeating unit in the final product modified ethylene-vinyl alcohol copolymer can be controlled by controlling the amount of crosslinking agent introduced (based on 100 moles of hydroxyl (-OH groups) in the reactant ethylene-vinyl alcohol copolymer).

[0076] In this regard, based on 100 moles of hydroxyl (-OH) groups in the reactant ethylene-vinyl alcohol copolymer, the amount of crosslinking agent introduced can be controlled within 1 to 10 moles, specifically 1.5 to 7 moles, for example, within the range of 2 to 4 moles.

[0077] Alternatively, commercially available products can be used as reactants, such as ethylene-vinyl alcohol copolymers, or they can be prepared in-house.

[0078] In the latter case, prior to the reaction in a specific example, the process may further include the steps of polymerizing a monomer mixture comprising ethylene monomers and ethylene carboxylate monomers to prepare an ethylene-vinyl acetate (EVA) copolymer; and saponifying the ethylene-vinyl acetate to prepare an ethylene-vinyl alcohol copolymer.

[0079] The preparation and saponification procedures for ethylene-vinyl acetate can be carried out in accordance with well-known technical knowledge in the field to which this invention pertains. The procedures known in the field will be described in part below.

[0080] The preparation of ethylene-vinyl acetate can be carried out by common polymerization methods, specifically, by using a free radical initiator in a solvent.

[0081] During polymerization, the amounts of ethylene-based monomers and vinyl acetate-based monomers introduced can be determined by considering the content of repeating units derived from each compound in the final copolymer. Specifically, the molar ratio can be from 20:80 to 40:60, more specifically from 25:75 to 35:65, for example, from 30:70 to 33:67. Furthermore, when reacting at the above molar ratios, the content of ethylene-derived repeating units in the prepared ethylene-vinyl acetate copolymer can be optimized, thereby reducing the hygroscopicity of the polymer and preventing deterioration of its gas barrier properties in high humidity environments.

[0082] The monomer mixture may further include heterogeneous monomers. In this case, the prepared ethylene-vinyl acetate and the final modified ethylene-vinyl alcohol copolymer may further include heterogeneous repeating units. The type and amount of heterogeneous repeating units can be determined in accordance with technical knowledge known in the art to which this invention pertains.

[0083] Regarding initiators and free radical initiators, examples include azo compounds such as 2,2'-azobis-(2,4-dimethylpentanonitrile), 2,2'-azobisisobutanonitrile, 2,2'-azobis-(4-methoxy-2,4-dimethylpentanonitrile), 2,2'-azobis-(2-methylisobutyrate), etc.; peroxide dicarbonates such as bis-(4-tert-butylcyclohexyl peroxide), dicyclohexyl peroxide, bis(2-ethylhexyl)di-second butyl peroxide, diisopropyl peroxide, etc.; peroxides such as acetyl peroxide, lauryl peroxide, dilauryl peroxide, didecyl peroxide, dioctyl peroxide, etc.; and mixtures of two or more of these may be used.

[0084] Based on 100 mol of a total monomer mixture comprising ethylene monomers and ethylene carbonate monomers, the initiator can be introduced at a content of 0.001 to 1 mol, more specifically 0.001 mol or more, or 0.01 mol or more, and 1 mol or less, or 0.1 mol or less. When introduced within the above content range, polymers can be prepared with excellent efficiency.

[0085] As for the solvent, those with high solubility for the monomeric compound can be used. Specifically, alcohols such as methanol, ethanol, propanol, isopropanol, tert-butanol, and n-pentanol can be mentioned; ketones such as methyl ethyl ketone and acetone; or sulfides such as dimethyl sulfide; and mixtures of two or more of these can be used. Among these, alcohols exhibiting superior solubility can be used, and more specifically, tert-butanol can be used.

[0086] Based on 100 parts by weight of a total monomer mixture comprising ethylene monomers and ethylene carboxylate monomers, the solvent can be introduced in amounts of 30 to 60 parts by weight, more specifically 30 parts by weight or more, or 40 parts by weight or more, and 60 parts by weight or less, or 50 parts by weight or less. When introduced within the above ranges, the monomers can be completely dissolved, and polymers can be prepared with excellent polymerization efficiency.

[0087] Polymerization reactions involving mixtures of vinyl monomers and vinyl carboxylate monomers can be carried out at temperatures ranging from 50 to 80°C, more specifically at 50°C or higher, or 60°C or higher, and 80°C or lower, or 70°C or lower. When the reaction is carried out within the above temperature range, there is no need to worry about a deterioration in polymerization efficiency due to unreacted or overreacted reactions.

[0088] Ethylene-vinyl acetate copolymers are prepared by polymerization reaction process, and by controlling the monomer content and preparation conditions in the preparation process, the prepared copolymers can exhibit optimized weight average molecular weight, molecular weight distribution, and content of structural units derived from ethylene.

[0089] Specifically, the ethylene-vinyl acetate copolymer may have a weight average molecular weight of 90,000 to 350,000 g / mol, more specifically 100,000 g / mol or higher, or 110,000 g / mol or higher, and 150,000 g / mol or lower, 140,000 g / mol or lower, or 130,000 g / mol or lower. Furthermore, the molecular weight distribution (MWD) may be 1.0 to 3.0, more specifically 1.0 or higher, 1.3 or higher, or 1.5 or higher, and 3.0 or lower, 2.5 or lower, or 2.0 or lower. Furthermore, based on the total repeating units in 100 mol% of an ethylene-vinyl acetate copolymer, the content of repeating units derived from ethylene can be 20 mol% or higher, 25 mol% or higher, or 30 mol% or higher, and 40 mol% or lower, 35 mol% or lower, or 33 mol% or lower. Because this copolymer has a high weight-average molecular weight, a narrow molecular weight distribution, and an optimized content of repeating units derived from olefins, it can maintain excellent mechanical properties during film fabrication while exhibiting superior gas barrier properties.

[0090] More specifically, copolymers of olefins and vinyl carboxylic acid ester compounds can be ethylene-vinyl acetate copolymers that satisfy the above properties.

[0091] Ethylene-vinyl acetate copolymers can be hydrolyzed through saponification and converted into ethylene-vinyl alcohol copolymers.

[0092] Hydrolysis can be carried out by introducing an alkaline material or alkali (such as caustic soda). Through saponification caused by the introduction of an alkaline substance, copolymers of olefins and vinyl carboxylate compounds are hydrolyzed, and the repeating units in the copolymer derived from vinyl carboxylate compounds can be partially or completely converted into repeating units containing hydroxyl groups.

[0093] Based on 100 moles of ethylene-vinyl acetate copolymer, the alkaline material can be introduced in amounts of 5 to 15 moles, more specifically 5 moles or more, or 7 moles or more, and 15 moles or less, or 12 moles or less. If the alkaline content is less than 5 moles, hydrolysis may not occur sufficiently, and if the alkaline content is greater than 15 moles, excessive wastewater may be generated during the catalyst removal process, and insufficient catalyst removal may lead to membrane discoloration or unevenness.

[0094] Basic substances can be dissolved in alcohol solvents (such as methanol) and introduced as solutions, thereby increasing reaction efficiency.

[0095] Furthermore, hydrolysis can be carried out at temperatures between 50 and 70°C, more specifically at 50°C or higher, or 60°C or higher, and 70°C or lower, or 65°C or lower. When carried out within the above temperature range, hydrolysis can occur sufficiently at an appropriate reaction rate. [Molded objects] [] []

[0096] According to yet another specific example of the present invention, a molded article comprising a modified ethylene-vinyl alcohol copolymer of one specific example is provided.

[0097] A specific example of a molded article exhibits the characteristic gas barrier properties of ethylene-vinyl alcohol copolymers, and therefore can be used in a variety of applications, such as membranes, sheets, containers, fibers, etc., that require gas barrier properties.

[0098] In particular, because a specific example of a molded article comprises a modified ethylene-vinyl alcohol copolymer with excellent flexibility, rigidity and melt strength, it can have excellent processability and mechanical properties.

[0099] Specifically, according to ASTM 412, molded parts may have tensile strengths of 50 to 100 MPa, specifically 55 to 95 MPa, for example 60 to 90 MPa, and tensile stresses of 2,000 to 3,000 MPa, specifically 2,030 to 2,700 MPa, for example 2,050 to 2,500 MPa at 300% elongation.

[0100] Molded parts with excellent processability and mechanical properties can be used in packaging materials, such as food packaging films, sheets, cosmetic containers, and gasoline tank containers.

[0101] Molded products can be manufactured using common molding methods, such as injection molding, compression molding, and extrusion molding. Among these, extrusion molding includes T-die molding, blow molding, pipe extrusion, wire extrusion, release die extrusion, and blow molding. It can also be used for co-extrusion molding of vinyl alcohol copolymers with other thermoplastic resin layers.

[0102] When manufacturing molded objects, well-known additives may be added if necessary, such as reinforcing materials (e.g., glass fiber, carbon fiber, etc.), colorants, stabilizers (e.g., hydrotalcite), foaming agents, desiccants, thermoplastic resins, etc.

[0103] Membrane-made objects can be used alone, for example, in the form of a membrane, or as a coating on a substrate, or in a multilayer structure with other membranes.

[0104] The effects and benefits of the present invention will be described in more detail below through specific embodiments. However, these embodiments are provided merely as illustrative of the invention and are not intended to limit the scope of the invention. [] [Example] [1(] [Modified] [EVOH)] []

[0105] An ethylene vinyl alcohol (EVOH) solution was prepared. This EVOH solution contained 5 wt% EVOH and the remainder methanol. Furthermore, the EVOH had a weight average molecular weight (Mw) of 120,000 g / mol, a molecular weight distribution (MWD) of 1.7, a copolymer content of 32 mol% of ethylene-derived repeating units, and a hydroxyl (-OH) content of 68 mol%.

[0106] In a 500 mL autoclave, 365 g of EVOH solution and 3.3 g of tetraethyl orthosilicate (TEOS) crosslinking agent were introduced. The amount of crosslinking agent introduced corresponds to 4 moles, based on 100 moles of hydroxyl (-OH) groups in the EVOH solution.

[0107] After the reactants were introduced, the reaction was carried out at 75°C with stirring at 200 rpm for 24 hours.

[0108] After the reaction was complete, the product, cooled to room temperature, was placed in 2 L of distilled water and washed for 2 hours, followed by solid / liquid separation using a vacuum filter.

[0109] The solid material separated by solid / liquid separation was dried in a vacuum oven at 50°C for 24 hours, thus finally obtaining the modified EVOH of Example 1. [Example] [2(] [Change reaction time] [)]

[0110] Modified EVOH was prepared using the same method as in Example 1, but the reaction time was changed to 4 hours. [Example] [3(] [Change the crosslinking agent] [TEOS] [Content] [)] []

[0111] Modified EVOH was prepared by the same method as in Example 1, but TEOS was introduced at a content of 0.83 g corresponding to 1 mole, based on the hydroxyl (-OH group) content of 100 moles of EVOH in the EVOH solution. [, , ] [Example] [4(] [Change the crosslinking agent] [TEOS] [Content] [) , , ] [, , ]

[0112] Modified EVOH was prepared by the same method as in Example 1, but TEOS was introduced at a content of 1.65 g corresponding to 2 moles based on 100 moles of hydroxyl groups (-OH groups) of EVOH in the EVOH solution. [] [Comparative Example] [1(EVOH)]

[0113] In Comparative Example 1, EVOH itself was used without crosslinking agent treatment.

[0114] The EVOH used was the same as that used in Example 1 (Mw: 120,000 g / mol, MWD: 1.7, content of repeating units derived from ethylene: 32 mol%, content of -OH groups: 68 mol%). [Comparative Example] [2(] [use] [1,2-] [Butane crosslinking agent] [)]

[0115] Modified EVOH was prepared by the same method as in Example 1, but 1.14 g corresponded to 4 moles of hydroxyl (-OH group) in 100 moles of EVOH in the EVOH solution, and 1,2-epoxybutane was introduced instead of TEOS as a crosslinking agent.

[0116] For reference, the ethylene content, the amount of crosslinking agent introduced (based on 100 moles of hydroxyl (-OH group) of EVOH before reaction), the reaction time and the reaction temperature in Examples 1 to 4, Comparative Examples 1 and 2 are summarized in Table 1 below. [] Table 1 Ethylene content in EVOH before reaction Crosslinking agent reaction time reaction temperature type Import volume Example 1 32 mol% TEOS 4 moles 24 hours 75℃ Example 2 32 mol% TEOS 4 moles 4 hours 75℃ Example 3 32 mol% TEOS 1 mole 24 hours 75℃ Example 4 32 mol% TEOS 2 moles 24 hours 75℃ Comparative Example 1 32 mol% - - - - Comparative Example 2 32 mol% 1,2-Epoxybutane 4 moles 24 hours 75℃ [Experimental Example] [1] []

[0117] For the EVOH of Comparative Example 1 and the modified EVOH of Examples 1 to 4 and Comparative Example 2, the content of repeating units derived from ethylene, weight average molecular weight (Mw), molecular weight distribution (MWD; Mw / Mn), melt complex viscosity, and viscoelasticity were evaluated.

[0118] The specific evaluation methods are as follows. [(1)] [Content of repeating units derived from ethylene] [] []

[0119] Using a 1H NMR spectrometer (Bruker Avance III HD 700 MHz), the sample was dissolved in tetrahydrofuran (THF-d8), and the 1H-NMR spectrum was then measured at room temperature. Peaks with four protons in the ethylene monomer and five protons in the vinyl acetate (VA) monomer appeared in the range of 0.74 to 2.1 ppm, while a single proton in the VA monomer appeared at 4.78 ppm. The content (mol%) of ethylene-derived repeating units in the copolymer was calculated using the following mathematical formula: [Mathematical Expression 1] The content of repeating units derived from ethylene (mol%) = [r / (r+1)] × 100 In mathematical formula 1, r = , n(ethylene) is the mole of the repeating unit derived from ethylene, n(VAc) is the mole of the repeating unit derived from ethyl acetate, I 0.74-2.1ppm is the integral value of the peak area appearing at 0.74 to 2.1 ppm, and I 4.78ppm is the integral value of the peak area appearing at 4.78 ppm. [(2)] [Weight-average molecular weight] [(Mw)] [and molecular weight distribution] (MWD) [;] [Mw / Mn)] []

[0120] The weight-average molecular weight (Mw) and molecular weight distribution (MWD; Mw / Mn) measured using gel permeation chromatography (GPC) under the following conditions are shown in Table 2. <Measurement Conditions> Measurement equipment: Agilent GPC (Agilent 1200 series, USA) Column: Connection of PL Mixed B Solvent: DMF / 0.05M LiBr (filtered through 0.45 μm filter) Sample concentration: ~1 mg / mL (100 μl injection) Flow rate: 1.0 ml / min Column temperature: 65℃ Detector: Waters refractive index detector (Waters 2414 RID) Standard: Polystyrene (PS) (calibrated using a cubic function)

[0121] As for polystyrene standards, six types with molecular weights (g / mol) of 9,600 / 31,420 / 113,300 / 327,300 / 1,270,000 / 4,230,000 were used. -Data processing:

[0122] 1) The copolymer sample was dissolved in dimethyl sulfoxide (DMSO) at a concentration of 2.0 mg / ml and filtered through a 0.45 μm syringe filter. 2) The sample solution was injected to obtain a GPC chromatogram. 3) The standard solution was injected to obtain a GPC chromatogram. 4) The calibration curve and formula were obtained from the chromatogram of the standard solution, and the residence time of the sample solution was substituted into the formula to obtain the weight-average molecular weight and number-average molecular weight of the sample. The molecular weight distribution (Mw / Mn) was calculated from the measured weight-average molecular weight (Mw) and number-average molecular weight (Mn). The results are shown in Table 2 and Figures 1 and 2 below. [(3)] [Complex viscosity and viscoelasticity of melt] [] []

[0123] The sample was placed in the sample container of a rheometer (AR2000EX Peltier plate, TA Instruments Corp.), heated to 190°C and melted, and then the complex viscosity and viscoelasticity were measured by gradually increasing the angular shear. The results are shown in Figures 3 and 4. Table 2 ethylene content Mw MWD Example 1 32mol% 176,000 g / mol 1.98 Example 2 32mol% 128,000 g / mol 1.56 Example 3 32mol% 126,000 g / mol 1.60 Example 4 32mol% 142,000 g / mol 1.78 Comparative Example 1 32mol% 121,000 g / mol 1.66 Comparative Example 2 32mol% 149,000 g / mol 1.85

[0124] In Table 2, “ethylene content” refers to the ethylene content in each final product of Comparative Examples 1, 2, and Examples 1 to 4 (i.e., EVOH of Comparative Example 1, and modified EVOH of Examples 1 to 4 and Comparative Example 2).

[0125] As can be seen from Table 2, the EVOH of Examples 1 to 4 have a higher weight average molecular weight compared with the EVOH of Comparative Example 1.

[0126] Furthermore, as can be seen from Figures 1 and 2, compared with unmodified EVOH (Comparative Example 1), EVOH modified by TEOS (Examples 1 and 2) has high melt complex viscosity and viscoelasticity.

[0127] Therefore, the high melt complex viscosity and viscoelasticity in Examples 1 and 2 are generated by the reaction of EVOH with the crosslinking agent (TEOS), resulting from partial crosslinking of EVOH molecules and crosslinking between different EVOH molecules, and the resulting molecular weight increases.

[0128] In particular, the high-gradient melt complex viscosity in Examples 1 and 4 is generated by long chain branching (LCB) through cross-linking between different EVOH molecules.

[0129] Meanwhile, in Examples 1 and 2, where the amount of crosslinking agent introduced is the same, the modified EVOH of Example 1, which has a longer reaction time, has a higher molecular weight and a wider molecular weight distribution, as well as higher melt complex viscosity and viscoelasticity.

[0130] Therefore, it can be seen that when the amount of crosslinking agent introduced is the same, as the reaction time increases, the partial crosslinking of EVOH molecules and the crosslinking between different EVOH molecules increase, and in particular, long chain branching (LCB) is further increased through the crosslinking between different EVOH molecules.

[0131] Furthermore, it has been demonstrated that in Examples 1, 3, and 4, where the amount of crosslinking agent introduced varies, Example 1, with a higher TEOS content, exhibits a higher molecular weight and a wider molecular weight distribution. Similarly, under the same reaction conditions, as the amount of crosslinking agent introduced increases, the partial crosslinking within the EVOH molecules and the crosslinking between different EVOH molecules increase, and in particular, long-chain branching (LCB) is further increased through crosslinking between different EVOH molecules. [Experimental Example] [2] []

[0132] For the EVOH of Comparative Example 1 and the modified EVOH of Examples 1 and 2, the mechanical properties were evaluated according to ASTM 412, and the results are described in Table 3 below.

[0133] Specifically, a hot press testing machine is used to press the sample at 180°C for 5 minutes with 20 tons of pressure to create a mold.

[0134] Using an air-operated film cutter (product name: Air-Cut, MJC-150-S30-10, manufacturer: Myung Ji Tech), the extruded film is cut to obtain a dog-bone-shaped sample in which UTM measurements can be performed.

[0135] Specify three points on the specimen and measure its average thickness, then input this data into the Universal Test Machine 4204 (Instron) according to ASTM 412. Set the grip-to-grip distance to 70 mm and measure the tensile strength when cutting the specimen at a speed of 100 mm / min and the tensile stress at 300% elongation (300% modulus). Table 3 Tensile strength Modulus (300%) Example 1 69.3 MPa 2,340 MPa Example 2 62.9 MPa 2,070 MPa Example 3 58.3 MPa 2,010 MPa Example 4 64.7 MPa 2,130 MPa Comparative Example 1 56.9 MPa 1,940 MPa Comparative Example 2 46.4 MPa 927 MPa

[0136] According to Table 3, compared with the EVOH of Comparative Example 1 and the modified EVOH of Comparative Example 2, the membrane samples containing the modified EVOH of Examples 1 to 4 have high tensile strength and modulus.

[0137] The molecular weight of EVOH is increased by reacting with a crosslinking agent (TEOS), especially by increasing the branching of long chains. This improves the flexibility, rigidity and melt strength of the modified EVOH, as well as the processability and mechanical properties of the film sample containing it.

[0138] Furthermore, it can be confirmed that when modified EVOH is used as a crosslinking agent, those containing repeating units derived from orthosilicone esters (such as TEO) are not used. However, for example, when 1,2-epoxybutane is used, the tensile strength and modulus are worse than those of unmodified EVOH.

[0139] In the case of 1,2-epoxybutane, the ethyl chain structural unit is inserted into the vinyl alcohol structural unit, and while the vinyl alcohol structural unit forms a crystal structure by intermolecular forces (such as hydrogen bonding), the ethyl chain structure may cause defects, and the increased free volume of the ethyl chain may lead to a plasticizing effect. Due to these properties, Tg and Tm may decrease, resulting in suppressed interactions, and thus potentially reduced modulus and tensile strength. Although a crosslinking agent is used in this disclosure to induce the increase of intermolecular bonds, 1,2-epoxybutane is not a crosslinking mediator. Furthermore, an acid catalyst should be used in the reaction of 1,2-epoxybutane, which differs from the description herein.

[0140] In other words, it can be confirmed that, compared with EVOH, all modified EVOH do not have improved processability and mechanical properties.

[0141] Meanwhile, in Examples 1 and 2, which have the same amount of crosslinking agent introduced, the membrane sample of the modified EVOH of Example 1, which has a longer reaction time, has higher tensile strength and modulus.

[0142] Therefore, it can be seen that when the amount of crosslinking agent introduced is the same, with a longer reaction time, the partial crosslinking of EVOH molecules and the crosslinking between different EVOH molecules increase, and in particular, long chain branching (LCB) is increased by crosslinking between different EVOH molecules, which further improves the processability and properties of this film sample.

[0143] Furthermore, in Examples 1, 3, and 4, which have the same reaction time, the membrane sample containing modified EVOH from Example 1, which has a higher TEOS crosslinking agent content, exhibits higher tensile strength and modulus. This is because with the increase of TEOS content, more long chain branches (LCBs) are generated through crosslinking between EVOH molecules, further improving the processability and properties of the membrane sample. [in conclusion] [] []

[0144] Combining the results of Experiments 1 and 2, it can be seen that the polymer structure can be controlled by inducing partial cross-linking and generating long chain branches (LCBs) in the molecule through the reaction of EVOH and cross-linking agent (TEOS).

[0145] These modified EVOHs provide flexibility and rigidity to the membranes, resulting in increased melt strength, thereby improving the processability and properties of the membranes.

[0146] Meanwhile, although commercially available EVOH was used in the experiments in this paper, the reaction of EVOH with the crosslinking agent (TEOS) corresponds to the modification after the preparation of EVOH.

[0147] Therefore, modified EVOH with various qualities can be easily developed by changing the EVA preparation conditions, EVOH preparation conditions (such as the conditions for preparing EVOH by EVA saponification), and post-treatment conditions.

[0148] Furthermore, after preparing EVOH by saponification of EVA, a subsequent process is carried out using the same cleaning agent and without introducing additional catalysts or solvents to recover the solvent. This reduces the overall cost of the process and allows for efficient operation.

Claims

1. A modified ethylene-vinyl alcohol copolymer comprising: a first repeating unit derived from ethylene; a second repeating unit derived from vinyl alcohol; and a third repeating unit derived from tetraethyl orthosilicate (TEOS), wherein, based on 100 mol% of the modified ethylene-vinyl alcohol copolymer, the first repeating unit comprises 25 to 35 mol%, the third repeating unit comprises 2 to 4 mol%, and the second repeating unit is the remainder; and the modified ethylene-vinyl alcohol copolymer has a weight average molecular weight of 100,000 to 200,000 g / mol, wherein the modified ethylene-vinyl alcohol copolymer has a molecular weight distribution (MWD; Mw / Mn) of 1.78 to 1.98, and the molar ratio of the first repeating unit to the second repeating unit in the modified ethylene-vinyl alcohol copolymer is 30:70 to 33:67, wherein the first repeating unit is represented by the following chemical formula 1: [Chemical Formula 1] The second repeating unit is represented by the following chemical formula 2: [chemical formula 2], and the third repeating unit comprises one or more repeating units selected from the following chemical formulas 3-1 to 3-4: [chemical formula 3-1] [chemical formula 3-2] [chemical formula 3-3] [chemical formula 3-4].

2. The modified ethylene-vinyl alcohol copolymer of claim 1, wherein the molar ratio of the first repeating unit to the second repeating unit is 20:80 to 40:

60.

3. A method for manufacturing the modified ethylene-vinyl alcohol copolymer as claimed in claim 1, comprising: reacting the ethylene-vinyl alcohol copolymer with tetraethyl orthosilicate (TEOS) at a temperature range of 50 to 100°C and a stirring speed of 50 to 400 rpm for 20 to 24 hours; and reacting 2 to 4 moles of tetraethyl orthosilicate based on 100 moles of hydroxyl (-OH) groups in the ethylene-vinyl alcohol copolymer.

4. The method of claim 3, wherein the reaction is carried out in a temperature range of 60 to 90°C.

5. The method of claim 3, wherein the ethylene-vinyl alcohol copolymer comprises a first repeating unit derived from ethylene and a second repeating unit derived from vinyl alcohol in a molar ratio of 20:80 to 40:

60.

6. The method of claim 3 further includes the following steps after the reaction: washing the reaction product; and drying the washed reaction product.

7. A molded article comprising a modified ethylene-vinyl alcohol copolymer as claimed in claim 1.

8. A molded article as claimed in item 7, wherein the molded article has a tensile strength of 50 to 100 MPa according to ASTM 412.

9. A molded article as claimed in claim 7, wherein the molded article has a tensile stress of 2,000 to 3,000 MPa at 300% elongation according to ASTM 412.

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