A method for preparing high barrier polypropylene film

Abstract

The invention discloses a method for preparing a high barrier polypropylene film, and belongs to the technical field of polypropylene films. The method comprises the following raw materials in parts by weight: 80-100 parts of polypropylene resin, 18-30 parts of ethylene-vinyl alcohol copolymer, 5-15 parts of modifier, 0.1-0.3 parts of initiator, and 4-6 parts of lubricant. With polypropylene as the matrix, the film is endowed with excellent water barrier properties and mechanical properties; wherein the ethylene-vinyl alcohol copolymer can improve the gas barrier properties of the film, and is easy to process; the obtained film is a single-layer film, and the preparation process is simple; wherein the modifier can significantly enhance the film's antioxidant, antibacterial properties and a certain degree of hydrophobicity, and the performance is long-term and stable, and is not easy to fall off; therefore, the film prepared by the present invention has high mechanical properties, good barrier properties, simple process, and stable and efficient antioxidant, antibacterial properties and a certain degree of hydrophobicity, and has important application value in the technical field of polypropylene films.

Description

Technical Field

[0001] The invention belongs to the technical field of polypropylene films, and in particular relates to a method for preparing a high-barrier polypropylene film. Background Art

[0002] With the continuous development of science and technology and the improvement of the quality of life, people pay more and more attention to packaging materials. At present, high barrier packaging films are widely used in food, medicine, precision instruments and fine chemicals because of their effective function of blocking substances such as oxygen and water, extending the shelf life and basic performance of products. Common film materials include polyethylene, polypropylene, polyvinylidene chloride and polyvinyl alcohol. Among them, polypropylene film is a plastic product with light weight, environmental friendliness, low price, excellent performance, easy molding and wide application. It is a relatively high-quality barrier film material.

[0003] As people's needs continue to increase, traditional high-barrier packaging films are increasingly difficult to meet people's needs, so BOPP films with better performance have developed rapidly in recent years. However, BOPP films are made of multi-layer materials and then stretched in both the longitudinal and transverse directions, which undoubtedly increases the difficulty and conditions of preparation; not only that, for food or medicines that are stored for a long time, bacteria and mold will breed on the surface of the film in large quantities, which can easily cause the food to be eroded by mold and microorganisms. In addition, long-term storage of polypropylene films will cause certain aging, resulting in a decrease in the performance of the film. Therefore, it is urgent to invent a single-layer high-barrier polypropylene film that is antibacterial and aging-resistant to meet the higher demands in the field of polypropylene film technology. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide a method for preparing a high barrier polypropylene film.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for preparing a high barrier polypropylene film comprises the following steps:

[0007] The polypropylene resin and ethylene-vinyl alcohol copolymer are dried in an oven at 80°C, and then stirred and mixed evenly with a modifier, an initiator and a lubricant, added to a twin-screw extruder, melt blended, extruded, longitudinally stretched and transversely stretched into a film, and then corona treated, rolled up, and slit to form a high-barrier polypropylene film.

[0008] Furthermore, the raw materials are calculated in parts by weight as follows: 80-100 parts of polypropylene resin, 18-30 parts of ethylene-vinyl alcohol copolymer, 5-15 parts of modifier, 0.1-0.3 parts of initiator, and 4-6 parts of lubricant.

[0009] Furthermore, the initiator is one of benzoyl peroxide and lauroyl peroxide.

[0010] Furthermore, the lubricant is one of calcium stearate, zinc stearate and paraffin.

[0011] With polypropylene as the matrix, the film has excellent water barrier and mechanical properties; ethylene-vinyl alcohol copolymer has excellent barrier properties to gases such as oxygen, nitrogen, hydrogen and carbon dioxide. Not only that, ethylene-vinyl alcohol copolymer has a similar structure to polypropylene, has good compatibility and is easy to process; finally, the design of the single-layer film makes the preparation process simpler.

[0012] Furthermore, the modifier is prepared by the following steps:

[0013] S1. Add methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, thiodiethanol, lithium diisopropylamide (catalyst, LAD) and N,N-dimethylformamide (DMF) into a three-necked flask equipped with a stirring device, stir and mix evenly, pass nitrogen to remove air, heat to 70°C, react for 6 hours, and after the reaction is completed, remove the solvent by vacuum distillation, wash with anhydrous ethanol 2-3 times, and obtain intermediate 1; the ratio of methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, thiodiethanol, lithium diisopropylamide and N,N-dimethylformamide is 29.2g:13.3g:0.2g:100mL;

[0014] Under the catalysis of lithium diisopropylamide, methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and thiodiethanol undergo an ester exchange reaction. By controlling the molar ratio of the two to be close to 1:1 and the thiodiethanol to be slightly excessive, only one hydroxyl group on the thiodiethanol participates in the reaction to obtain intermediate 1. The specific reaction process is as follows:

[0015]

[0016] S2. In a three-necked flask equipped with a stirring device, the intermediate 1, allylmalonic acid and N,N-dimethylformamide were stirred and mixed uniformly, and dibutyltin oxide (catalyst) and dicyclohexylcarbodiimide (DCC, dehydrating agent) were added, and the reaction temperature was controlled to 75° C. The reaction was kept warm for 6 hours, and stirring was continued during the reaction. After the reaction was completed, the reaction was filtered, the solvent was removed by rotary evaporation, and vacuum drying was performed to obtain intermediate 2; the ratio of the amount of intermediate 1, allylmalonic acid, N,N-dimethylformamide, dibutyltin oxide, and dicyclohexylcarbodiimide was 38.2 g:15.3 g:150 mL:0.2 g:20.6 g;

[0017] Under the catalysis of dibutyltin oxide and DCC, the carboxyl group on allylmalonic acid and the hydroxyl group on intermediate 1 undergo esterification reaction. By controlling the molar ratio of the two to be close to 1:1 and the allylmalonic acid to be slightly excessive, only one carboxyl group on the allylmalonic acid participates in the reaction to obtain intermediate 2. The specific reaction process is as follows:

[0018]

[0019] S3, in a three-necked flask equipped with a stirring device, triphenylphosphine (PPh3) was dissolved in toluene, 3-chloro-1-propanol was slowly added dropwise, and the temperature was raised to 50°C, and the reaction was stirred for 6 hours. After the reaction was completed, the solvent was removed by distillation under reduced pressure to obtain intermediate 3; the ratio of triphenylphosphine, toluene and 3-chloro-1-propanol was 26.2g:100mL:9.4g;

[0020] Triphenylphosphine reacts with the chlorine group of 3-chloro-1-propanol to obtain the quaternary phosphonium product intermediate 3; the specific reaction process is as follows:

[0021]

[0022] S4. In a three-necked flask equipped with a stirring reflux device, the intermediate 2, the intermediate 3 and N, N-dimethylformamide were mixed and stirred uniformly, and then dicyclohexylcarbodiimide and 4-dimethylaminopyridine were added in sequence, and the reaction temperature was controlled to 80°C. The reaction was kept warm for 8 hours. After the reaction was completed, it was filtered, and part of the solvent was removed by rotary evaporation. Then, it was purified by column chromatography (the eluent was a mixed solvent of benzene / ethyl acetate, and the volume ratio of the two was 2:3), and the eluent was removed by rotary evaporation to obtain a modifier; the ratio of the amount of intermediate 2, intermediate 3, N, N-dimethylformamide, dicyclohexylcarbodiimide and 4-dimethylaminopyridine was 50.8g:32.7g:200mL:20.6g:0.3g;

[0023] Under the action of dicyclohexylcarbodiimide and 4-dimethylaminopyridine, intermediate 2 and intermediate 3 undergo esterification reaction to obtain a modifier; the specific reaction process is as follows:

[0024]

[0025] The prepared modifier molecules contain thioester, hindered phenol, quaternary phosphonium salt, ester group and carbon-carbon double bond structure. Thioester, as an antioxidant, can improve the antioxidant performance of polypropylene matrix to a certain extent. In addition, the introduced hindered phenol can provide active hydrogen atoms to capture peroxyl free radicals, and can synergize with thioester to greatly improve the antioxidant performance of the matrix. In addition, the thioether group can also improve the mechanical properties of the matrix. The introduced quaternary phosphonium salt functional group, in which the positively charged phosphonium ion is adsorbed on the bacterial surface, can interact with the negatively charged cell membrane of the bacteria, and penetrate the bacterial membrane. It penetrates the cell wall, combines with the cell membrane, destroys the surface structure of the cell, causes the intracellular substances to flow out, stops the respiratory function of the bacteria and leads to cell death, which not only enhances the antibacterial properties of the matrix, but also has better antibacterial activity than quaternary ammonium salts; in addition, the introduced ester group is a hydrophobic group, which can enhance the hydrophobicity of the matrix to a certain extent; finally, the carbon-carbon double bond in the modifier molecule can produce chemical bonding with the matrix, which not only improves the compatibility of the modifier and the matrix, so that the performance of the modifier can be fully exerted, but also prevents the migration and seepage of the modifier, thereby improving the stability of the modifier.

[0026] Beneficial effects of the present invention:

[0027] 1. The film prepared by the present invention uses polypropylene as a matrix, which gives the film excellent water-blocking and mechanical properties;

[0028] 2. Adding ethylene-vinyl alcohol copolymer can improve the gas barrier properties of the film and make it easy to process;

[0029] 3. The obtained film is a single-layer film, and the preparation process is simple;

[0030] 4. The various groups in the prepared modifier molecules work synergistically, significantly enhancing the film's antioxidant and antibacterial properties and a certain degree of hydrophobicity, and the performance is long-lasting and stable, and not easy to fall off;

[0031] Therefore, the film prepared by the present invention has high mechanical properties, good barrier properties, simple process, stable and efficient antioxidant and antibacterial properties and a certain degree of hydrophobicity, and has important application value in the field of polypropylene film technology. DETAILED DESCRIPTION

[0032] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Embodiment 1

[0034] Preparation of modifier:

[0035] S1. Add 29.2 g of methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 13.3 g of thiodiethanol, 0.2 g of lithium diisopropylamide and 100 mL of N,N-dimethylformamide into a three-necked flask equipped with a stirring device, stir and mix evenly, pass nitrogen to remove air, heat to 70° C., react for 6 h, and after the reaction is completed, remove the solvent by distillation under reduced pressure, wash twice with anhydrous ethanol to obtain intermediate 1;

[0036] S2. In a three-necked flask equipped with a stirring device, 38.2 g of intermediate 1, 15.3 g of allylmalonic acid and 150 mL of N,N-dimethylformamide were stirred and mixed uniformly, 0.2 g of dibutyltin oxide and 20.6 g of dicyclohexylcarbodiimide were added, the reaction temperature was controlled to 75°C, and the reaction was kept warm for 6 hours with continuous stirring during the reaction. After the reaction was completed, the reaction was filtered, the solvent was removed by rotary evaporation, and vacuum dried to obtain intermediate 2;

[0037] S3. In a three-necked flask equipped with a stirring device, 26.2 g of triphenylphosphine was dissolved in 100 mL of toluene, 9.4 g of 3-chloro-1-propanol was slowly added dropwise, and the temperature was raised to 50° C. The reaction was stirred for 6 h. After the reaction was completed, the solvent was removed by distillation under reduced pressure to obtain intermediate 3;

[0038] S4. In a three-necked flask equipped with a stirring reflux device, 50.8 g of intermediate 2, 32.7 g of intermediate 3 and 200 mL of N, N-dimethylformamide were mixed and stirred evenly, and then 20.6 g of dicyclohexylcarbodiimide and 0.3 g of 4-dimethylaminopyridine were added in sequence. The reaction temperature was controlled to 80°C and the reaction was kept warm for 8 hours. After the reaction was completed, it was filtered and part of the solvent was removed by rotary evaporation. Then, it was purified by column chromatography (the eluent was a mixed solvent of benzene / ethyl acetate in a volume ratio of 2:3), and the eluent was removed by rotary evaporation to obtain a modifier.

[0039] Embodiment 2

[0040] Preparation of modifier:

[0041] S1. Add 58.4 g of methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 26.6 g of thiodiethanol, 0.4 g of lithium diisopropylamide and 200 mL of N,N-dimethylformamide into a three-necked flask equipped with a stirring device, stir and mix evenly, pass nitrogen to remove air, heat to 70° C., react for 6 h, and after the reaction is completed, remove the solvent by distillation under reduced pressure, wash twice with anhydrous ethanol to obtain intermediate 1;

[0042] S2. In a three-necked flask equipped with a stirring device, 76.4 g of intermediate 1, 30.6 g of allylmalonic acid and 300 mL of N,N-dimethylformamide were stirred and mixed uniformly, and 0.4 g of dibutyltin oxide and 41.2 g of dicyclohexylcarbodiimide were added. The reaction temperature was controlled to 75° C. and the reaction was kept warm for 6 h. Stirring was continued during the reaction. After the reaction was completed, the reaction was filtered, the solvent was removed by rotary evaporation, and vacuum drying was performed to obtain intermediate 2.

[0043] S3. In a three-necked flask equipped with a stirring device, 52.4 g of triphenylphosphine was dissolved in 200 mL of toluene, 18.8 g of 3-chloro-1-propanol was slowly added dropwise, and the temperature was raised to 50° C. The reaction was stirred for 6 h. After the reaction was completed, the solvent was removed by reduced pressure distillation to obtain intermediate 3;

[0044] S4. In a three-necked flask equipped with a stirring reflux device, 101.6 g of intermediate 2, 65.4 g of intermediate 3 and 400 mL of N,N-dimethylformamide were mixed and stirred evenly, and then 41.2 g of dicyclohexylcarbodiimide and 0.6 g of 4-dimethylaminopyridine were added in sequence. The reaction temperature was controlled to 80°C and the reaction was kept warm for 8 hours. After the reaction was completed, it was filtered and part of the solvent was removed by rotary evaporation. Then, it was purified by column chromatography (the eluent was a mixed solvent of benzene / ethyl acetate in a volume ratio of 2:3), and the eluent was removed by rotary evaporation to obtain a modifier.

[0045] Embodiment 3

[0046] 80g of polypropylene resin and 18g of ethylene-vinyl alcohol copolymer were dried in an oven at 80°C, and then mixed evenly with 5g of the modifier prepared in Example 1, 0.1g of benzoyl peroxide and 4g of calcium stearate, added to a twin-screw extruder, melt blended, extruded, longitudinally stretched and transversely stretched into a film, and then corona treated, rolled, and slit to form a high barrier polypropylene film.

[0047] Embodiment 4

[0048] 90g of polypropylene resin and 24g of ethylene-vinyl alcohol copolymer were dried in an oven at 80°C, and then stirred and mixed with 10g of the modifier prepared in Example 2, 0.2g of lauroyl peroxide and 5g of zinc stearate, added to a twin-screw extruder, melt blended, extruded, longitudinally stretched and transversely stretched into a film, and then corona treated, rolled, and slit to form a high barrier polypropylene film.

[0049] Embodiment 5

[0050] 100 g of polypropylene resin and 30 g of ethylene-vinyl alcohol copolymer were dried in an oven at 80° C., and then mixed evenly with 15 g of the modifier prepared in Example 2, 0.3 g of lauroyl peroxide and 6 g of paraffin wax, added to a twin-screw extruder, melt blended, extruded, longitudinally stretched and transversely stretched into a film, and then corona treated, rolled, and slit to form a high barrier polypropylene film.

[0051] Comparative Example 1

[0052] The modifier in Example 5 was replaced by a commercially available antioxidant of equal mass, and the remaining steps were the same as those in Example 5 to obtain a film.

[0053] Comparative Example 2

[0054] A commercially available high barrier polypropylene film was used.

[0055] Embodiments 3, 4, 5, and comparative examples 1 and 2 were made into corresponding shapes according to different test standards, and the following performance tests were performed:

[0056] The tensile strength was determined using the national standard GB / T 1040.3-2006 "Determination of tensile properties of plastics Part 3: Test conditions for films and sheets";

[0057] The oxygen permeability is measured using the national standard GB / T 1038-2022 "Plastic film and sheeting gas permeability test method pressure difference method";

[0058] The water vapor permeability is measured using the national standard GB / T 1037-2010 "Plastic film and sheeting water vapor permeability determination cup weight gain and weight loss method";

[0059] The induction time of the sample was determined using the national standard GB / T 19466.6-2009 "Plastics Differential Scanning Calorimetry (DSC) Part 6: Determination of Oxidation Induction Time (Isothermal OIT) and Oxidation Induction Temperature (Dynamic OIT)";

[0060] The national standard GB / T 31402-2015 "Test method for antibacterial performance of plastic surfaces" was adopted, and the film method was used to detect the inhibitory effect on Escherichia coli and Staphylococcus aureus; the method is as follows: Escherichia coli or Staphylococcus aureus bacteria were inoculated on the plate culture medium, covered with a film and preserved for 24 hours, and then live bacteria were cultured; the parallel experimental results of the blank samples were compared to obtain the antibacterial rate of the sample;

[0061] After the samples were placed at room temperature for 180 days, the antibacterial properties of the samples were measured using the same standard;

[0062] The measured results are shown in the following table:

[0063]

[0064] It can be seen from the above table that the film prepared in the embodiment of the present invention has better barrier properties, antioxidant properties and antibacterial properties than the comparative example, and has stable performance, and has important application value in the field of polypropylene film technology.

[0065] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0066] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high barrier polypropylene film, characterized in that: The following steps are involved: The polypropylene resin and ethylene-vinyl alcohol copolymer are dried, and then mixed with a modifier, an initiator and a lubricant to be uniformly stirred, added into a twin-screw extruder, melt blended, extruded, longitudinally stretched and transversely stretched into a film, and then corona treated, rolled, and slit to form a high-barrier polypropylene film; Wherein, the modifier is prepared by the following steps: S1. After methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, thiodiethanol, lithium diisopropylamide and N,N-dimethylformamide were stirred and mixed evenly, nitrogen was passed to remove air, the temperature was raised to 70°C, the reaction was carried out for 6 hours, the reaction was completed, and the mixture was distilled under reduced pressure and washed to obtain intermediate 1; the ratio of methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, thiodiethanol, lithium diisopropylamide and N,N-dimethylformamide was 29.2g:13.3g:0.2g:100mL; S2. Stir and mix the intermediate 1, allylmalonic acid and N,N-dimethylformamide, add dibutyltin oxide and dicyclohexylcarbodiimide, react at 75°C for 6h, stir continuously during the reaction, filter, rotary evaporate and dry to obtain intermediate 2; the ratio of the amount of intermediate 1, allylmalonic acid, N,N-dimethylformamide, dibutyltin oxide and dicyclohexylcarbodiimide is 38.2g:15.3g:150mL:0.2g:20.6g; S3, dissolving triphenylphosphine in toluene, adding 3-chloro-1-propanol dropwise, raising the temperature to 50°C, stirring and reacting for 6 hours, and after the reaction is completed, distilling under reduced pressure to obtain intermediate 3; the ratio of triphenylphosphine, toluene and 3-chloro-1-propanol is 26.2g:100mL:9.4g; S4. After mixing and stirring intermediate 2, intermediate 3 and N,N-dimethylformamide evenly, add dicyclohexylcarbodiimide and 4-dimethylaminopyridine in turn, react at 80°C for 8 hours, and after the reaction is completed, filter, rotary evaporate, purify by column chromatography, and rotary evaporate to obtain a modifier; the usage ratio of intermediate 2, intermediate 3, N,N-dimethylformamide, dicyclohexylcarbodiimide and 4-dimethylaminopyridine is 50.8g:32.7g:200mL:20.6g:0.3g.

2. The method for preparing a high barrier polypropylene film according to claim 1, characterized in that: The raw materials are calculated in parts by weight as follows: 80-100 parts of polypropylene resin, 18-30 parts of ethylene-vinyl alcohol copolymer, 5-15 parts of modifier, 0.1-0.3 parts of initiator, and 4-6 parts of lubricant.

3. The method for preparing a high barrier polypropylene film according to claim 1, characterized in that: The initiator is one of benzoyl peroxide and lauroyl peroxide.

4. The method for preparing a high barrier polypropylene film according to claim 1, characterized in that: The lubricant is one of calcium stearate, zinc stearate and paraffin.

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