High-barrier antibacterial food packaging film and method of preparation

Abstract

The application relates to the packaging technical field and discloses a high-barrier antibacterial food packaging film and a preparation method.The raw materials of the packaging film of the application include 100 parts by weight of polyvinyl alcohol, 2-8 parts by weight of modified polyvinyl alcohol, 5-30 parts by weight of carboxymethyl chitosan and 5-20 parts by weight of sodium-based montmorillonite;the modified polyvinyl alcohol contains quaternary ammonium salt as an antibacterial group, cooperatively plays an antibacterial role with the carboxymethyl chitosan and significantly improves the antibacterial performance of the packaging film.The modified polyvinyl alcohol introduces a quaternary ammonium salt cation structure with smaller steric hindrance at the side chain end, facilitates ion exchange of the montmorillonite, modifies the polyvinyl alcohol molecular chain on the surface of the montmorillonite, improves the compatibility and dispersibility of the montmorillonite in the polyvinyl alcohol packaging film and is beneficial to improving the mechanical strength and gas barrier performance of the packaging film.

Description

TECHNICAL FIELD

[0001] The present application relates to the packaging field, in particular to a high-barrier antibacterial food packaging film and a preparation method. BACKGROUND

[0002] Polyvinyl alcohol is cheap, non-toxic, environmentally friendly and biodegradable, and has a wide range of applications in packaging films, preservative films and other aspects. However, the antibacterial performance of polyvinyl alcohol film material is not good, and the oxygen gas permeability is large, which is not conducive to the preservation and preservation of food. Usually, chitosan, nano-silver, nano-titanium dioxide and other antibacterial agents are added to the polyvinyl alcohol film, among which chitosan has good biocompatibility, no toxicity and no pollution, and excellent antibacterial performance, and has important applications in packaging films and other aspects.

[0003] Montmorillonite is a natural silicate mineral, which is abundant in reserves, widely available, has a large specific surface area and excellent barrier properties. When added to the film material, it can improve the water vapor and gas barrier properties of the material. However, the compatibility of montmorillonite with polyvinyl alcohol is not good, which has a certain influence on the mechanical properties of polyvinyl alcohol film. The dispersibility of montmorillonite is poor, and it is not conducive to improving the barrier properties of the film material. Patent No. CN109897232B discloses a method for modifying degradable film material, which uses polyvinyl alcohol, chitosan, montmorillonite, carbon-hybrid modified expanded vermiculite and other raw materials to prepare a film material with the advantages of degradability. However, the patent does not solve the problem of poor barrier and antibacterial properties of polyvinyl alcohol film material. SUMMARY

[0004] The present application provides a high-barrier antibacterial food packaging film and a preparation method to solve the problem of poor barrier and antibacterial properties of polyvinyl alcohol film material.

[0005] The technical solution of the present application is a high-barrier antibacterial food packaging film, the raw materials of which include 100 parts by weight of polyvinyl alcohol, 2-8 parts by weight of modified polyvinyl alcohol, 5-30 parts by weight of carboxymethyl chitosan, and 5-20 parts by weight of sodium-based montmorillonite.

[0006] The preparation method of the modified polyvinyl alcohol is as follows:

[0007] (1) Add polyvinyl alcohol, 4-[4-(chloromethylbenzyl)oxy]-4-oxobutyric acid, and dibutyltin dilaurate to dimethyl sulfoxide, heat and react, add ethanol to the solution, precipitate the precipitate, wash the precipitate with ethanol after filtration, and dry to obtain a polyvinyl alcohol intermediate;

[0008] (2) Add the polyvinyl alcohol intermediate and tertiary amine monomer to N,N-dimethylformamide, heat and react, add ethanol to the solution, precipitate the precipitate, wash the precipitate with ethanol after filtration, and dry to obtain the modified polyvinyl alcohol. The preparation reaction formula is as follows:

[0009] .

[0010] Further, the amount of polyvinyl alcohol in (1) is 100 parts by weight, the amount of 4-[4-(chloromethylbenzyl)oxy]-4-oxobutanoic acid is 40-150 parts by weight, and the amount of dibutyltin dilaurate is 2-8 parts by weight.

[0011] Further, the reaction temperature in (1) is 120-130 DEG C, and the reaction time is 6-12 h.

[0012] Further, the reaction temperature in (2) is 60-90 DEG C, and the reaction time is 24-48 h.

[0013] Further, the amount of polyvinyl alcohol intermediate in (2) is 100 parts by weight, and the amount of tertiary amine monomer is 15-80 parts by weight.

[0014] Further, the structure of the tertiary amine monomer in (2) is , R1 is methyl or ethyl, R2 is methyl or ethyl, and R3 is methyl or ethyl.

[0015] Further, the preparation method of 4-[4-(chloromethylbenzyl)oxy]-4-oxobutanoic acid is as follows: 4-(chloromethyl) benzyl alcohol, succinic anhydride and 4-dimethylaminopyridine are added into dichloromethane in a molar ratio of 1: (1-1.2): (0.4-0.5), and stirred at 20-30 DEG C for 18-24 h, then the crude product is washed with petroleum ether after distillation under reduced pressure, and then purified by recrystallization in ethyl acetate to obtain 4-[4-(chloromethylbenzyl)oxy]-4-oxobutanoic acid.

[0016] .

[0017] The application further provides a preparation method of the high-barrier antibacterial food packaging film, which comprises the following steps: adding sodium-based montmorillonite and modified polyvinyl alcohol into water, performing ultrasonic dispersion, then heating and stirring, finally adding polyvinyl alcohol, carboxymethyl chitosan and water, stirring and uniformly mixing, pouring into a mold for casting, vacuum defoaming, drying, and obtaining the high-barrier antibacterial food packaging film.

[0018] Further, the ultrasonic dispersion time is 20-40 min.

[0019] Further, the heating and stirring temperature is 60-70 DEG C, and the time is 7-12 h.

[0020] Further, the stirring and uniformly mixing temperature is 90-95 DEG C, and the time is 40-60 min.

[0021] The application has the beneficial technical effects that: the carboxyl of 4-[4-(chloromethylbenzyl)oxy]-4-oxobutanoic acid and the hydroxyl of polyvinyl alcohol are subjected to esterification reaction by taking dibutyl tin dilaurate as a catalyst, then the chloromethyl is subjected to quaternary ammonium reaction with a tertiary amine monomer to obtain modified polyvinyl alcohol, and finally the modified polyvinyl alcohol is blended with montmorillonite, carboxymethyl chitosan and polyvinyl alcohol to prepare a film, thereby obtaining a high-barrier antibacterial food packaging film.

[0022] The modified polyvinyl alcohol contains quaternary ammonium salt as an antibacterial group, alkyl ester and a benzene ring as a hydrophobic structure of an antibacterial agent, and cooperates with carboxymethyl chitosan to play a synergistic antibacterial effect, thereby significantly improving the antibacterial performance of the packaging film.

[0023] The modified polyvinyl alcohol of the application introduces a quaternary ammonium salt cation structure with smaller steric hindrance at the side chain end, facilitates ion exchange of montmorillonite, thereby modifying the polyvinyl alcohol molecular chain on the surface of the montmorillonite, improving the compatibility and dispersibility of the montmorillonite in the polyvinyl alcohol packaging film, and being beneficial to improving the mechanical strength of the packaging film, and meanwhile, the uniformly dispersed montmorillonite forms a continuous barrier phase, can inhibit the oxygen from penetrating through the packaging film, significantly reduces the oxygen transmission rate, and enhances the gas barrier performance.

[0024] The quaternary ammonium salt cation of the modified polyvinyl alcohol of the application forms electrostatic interaction with the carboxyl anion of chitosan, so that the modified polyvinyl alcohol plays a role of a compatibilizer, further improves the compatibility of polyvinyl alcohol and chitosan, and is beneficial to enhancing the tensile strength and other performances of the packaging film. DETAILED DESCRIPTION

[0025] For better illustrating the purpose, technical scheme and advantages of the application, the application will be further described below in combination with specific embodiments.

[0026] The polyvinyl alcohol is of type 1788 and is from Shandong Xiangzhao New Material Co., Ltd. The carboxymethyl chitosan is of type CMCS and is from Qingdao Yuekang Biotechnology Co., Ltd.

[0027] Example 1: a preparation method of a high-barrier antibacterial food packaging film, comprising the following steps:

[0028] (1) 40 mmol of 4-(chloromethyl)benzyl alcohol, 40 mmol of succinic anhydride and 20 mmol of 4-dimethylaminopyridine are added into 50 mL of dichloromethane, stirred at 30°C for 18 h, the crude product is washed with petroleum ether after distillation under reduced pressure, then purified by recrystallization in ethyl acetate to obtain 4-[4-(chloromethylbenzyl)oxy]-4-oxobutanoic acid;

[0029] (2) To 120 mL of dimethyl sulfoxide, 10 g of polyvinyl alcohol, 4 g (15.63 mmol) of 4-[4-(chloromethylbenzyl)oxy]-4-oxobutanoic acid, and 0.2 g of dibutyltin dilaurate were added, heated to 120°C, and stirred for 8 h. Ethanol was added to the solution, and precipitates were separated. The precipitates were washed with ethanol after filtration, and dried to obtain a polyvinyl alcohol intermediate;

[0030] (3) To 300 mL of N,N-dimethylformamide, 20 g of the polyvinyl alcohol intermediate, and 10 mL of an aqueous solution containing 3 g of trimethylamine were added, heated to 60°C, and stirred for 24 h under reflux. Ethanol was added to the solution, and precipitates were separated. The precipitates were washed with ethanol after filtration, and dried to obtain a modified polyvinyl alcohol;

[0031] (4) To 0.5 L of water, 25 g of sodium-based montmorillonite and 10 g of the modified polyvinyl alcohol were added, and ultrasonic dispersion was performed for 20 min. Then, ion exchange was performed by heating to 65°C and stirring for 7 h. Finally, 500 g of polyvinyl alcohol and 25 g of carboxymethyl chitosan were added, and 6 L of water was added. The mixture was stirred and uniformly mixed at 95°C for 40 min, and then cast into a mold, vacuum-deaerated, and dried to obtain a high-barrier antibacterial food packaging film.

[0032] Example 2: A method for preparing a high-barrier antibacterial food packaging film, comprising the following steps:

[0033] (1) To 60 mL of dichloromethane, 40 mmol of 4-(chloromethyl)benzyl alcohol, 48 mmol of succinic anhydride, and 16 mmol of 4-dimethylaminopyridine were added, and stirred at 20°C for 24 h. The crude product was washed with petroleum ether after distillation under reduced pressure, and then purified by recrystallization in ethyl acetate to obtain 4-[4-(chloromethylbenzyl)oxy]-4-oxobutanoic acid;

[0034] (2) To 150 mL of dimethyl sulfoxide, 10 g of polyvinyl alcohol, 10 g of 4-[4-(chloromethylbenzyl)oxy]-4-oxobutanoic acid, and 0.5 g of dibutyltin dilaurate were added, heated to 120°C, and stirred for 12 h. Ethanol was added to the solution, and precipitates were separated. The precipitates were washed with ethanol after filtration, and dried to obtain a polyvinyl alcohol intermediate;

[0035] (3) To 400 mL of N,N-dimethylformamide, 20 g of the polyvinyl alcohol intermediate and 11 g of triethylamine were added, heated to 60°C, and stirred for 48 h. Ethanol was added to the solution, and precipitates were separated. The precipitates were washed with ethanol after filtration, and dried to obtain a modified polyvinyl alcohol;

[0036] (4) To 1.2 L water, 60 g sodium-based montmorillonite and 25 g modified polyvinyl alcohol were added and ultrasonically dispersed for 40 min, then heated to 60 °C and stirred for 12 h for ion exchange, finally 500 g polyvinyl alcohol, 100 g carboxymethyl chitosan and 7 L water were added, heated to 95 °C, stirred and mixed for 40 min, cast into a mold, vacuum degassed, and dried to obtain a high-barrier antibacterial food packaging film.

[0037] Example 3: A method for preparing a high-barrier antibacterial food packaging film, comprising the following steps:

[0038] (1) To 150 mL dimethyl sulfoxide, 10 g polyvinyl alcohol, 15 g 4-[4- (chloromethylbenzyl) oxy] -4-oxobutanoic acid (prepared by the method of Example 1) and 0.8 g dibutyltin dilaurate were added and heated to 130 °C, stirred for 6 h, then ethanol was added to the solution to precipitate the sediment, which was filtered, washed with ethanol and dried to obtain a polyvinyl alcohol intermediate;

[0039] (2) To 400 mL N,N-dimethylformamide, 20 g polyvinyl alcohol intermediate and 53 mL aqueous solution containing 16 g trimethylamine were added and heated to 90 °C, stirred and condensed for reflux reaction for 36 h, then ethanol was added to the solution to precipitate the sediment, which was filtered, washed with ethanol and dried to obtain a modified polyvinyl alcohol;

[0040] (3) To 2 L water, 100 g sodium-based montmorillonite and 40 g modified polyvinyl alcohol were added and ultrasonically dispersed for 40 min, then heated to 70 °C and stirred for 8 h for ion exchange, finally 500 g polyvinyl alcohol, 200 g carboxymethyl chitosan and 8 L water were added, heated to 90 °C, stirred and mixed for 60 min, cast into a mold, vacuum degassed, and dried to obtain a high-barrier antibacterial food packaging film.

[0041] Comparative Example 1: To 0.5 L water, 25 g sodium-based montmorillonite and 10 g polyvinyl alcohol were added and ultrasonically dispersed for 20 min, then heated to 65 °C and stirred for 7 h, finally 500 g polyvinyl alcohol, 25 g carboxymethyl chitosan and 6 L water were added, heated to 95 °C, stirred and mixed for 40 min, cast into a mold, vacuum degassed, and dried to obtain a food packaging film.

[0042] Comparative Example 2: To 0.5 L water, 25 g sodium-based montmorillonite, 10 g cetyltrimethylammonium chloride were added and ultrasonically dispersed for 20 min, then heated to 65 °C and stirred for 7 h for ion exchange, finally 500 g polyvinyl alcohol, 25 g carboxymethyl chitosan and 6 L water were added, heated to 95 °C, stirred and mixed for 40 min, cast into a mold, vacuum degassed, and dried to obtain a food packaging film.

[0043] Comparative Example 3: (1) 10 g of polyvinyl alcohol was added to 120 mL of dimethyl sulfoxide, 2.34 g (15.63 mmol) of 6-chlorohexanoic acid, and 0.2 g of dibutyl tin dilaurate were added, heated to 120°C, and stirred for 8 h. Ethanol was added to the solution, and precipitates were separated. The precipitates were washed with ethanol after filtration, and dried to obtain a polyvinyl alcohol intermediate;

[0044] (2) 20 g of the polyvinyl alcohol intermediate was added to 300 mL of N,N-dimethylformamide, and 10 mL of an aqueous solution containing 3 g of trimethylamine was added. The solution was heated to 60°C, and stirred for 24 h under a condenser. Ethanol was added to the solution, and precipitates were separated. The precipitates were washed with ethanol after filtration, and dried to obtain a modified polyvinyl alcohol;

[0045] (3) 25 g of sodium-based montmorillonite and 10 g of the modified polyvinyl alcohol were added to 0.5 L of water, and ultrasonic dispersion was performed for 20 min. The solution was heated to 65°C, and ion exchange was performed for 7 h. Then, 500 g of polyvinyl alcohol and 25 g of carboxymethyl chitosan were added to 6 L of water, and stirred for 40 min. The solution was poured into a mold, and cast. The solution was vacuum degassed, and dried to obtain a food packaging film.

[0046] Comparative Example 4: (1) 10 g of polyvinyl alcohol was added to 120 mL of water, and heated to 95°C. After stirring, the solution was cooled to 50°C, and 2.36 g (15.63 mmol) of 2,3-epoxypropyl trimethylammonium chloride (having a structure of ) was added. Potassium hydroxide was added to adjust the pH to 10, and the solution was stirred for 5 h. Hydrochloric acid solution was added dropwise to adjust the pH to 7. The solution was dried to remove water, and the product was washed with ethanol, and dried to obtain a modified polyvinyl alcohol;

[0047] (2) 25 g of sodium-based montmorillonite and 10 g of the modified polyvinyl alcohol were added to 0.5 L of water, and ultrasonic dispersion was performed for 20 min. The solution was heated to 65°C, and ion exchange was performed for 7 h. Then, 500 g of polyvinyl alcohol and 25 g of carboxymethyl chitosan were added to 6 L of water, and stirred for 40 min. The solution was poured into a mold, and cast. The solution was vacuum degassed, and dried to obtain a food packaging film.

[0048] Comparative Example 5: (1) 10 g of polyvinyl alcohol was added to 120 mL of water, and heated to 95°C. After stirring, the solution was cooled to 50°C, and 4.77 g (15.63 mmol) of dodecyldimethyl epoxypropyl ammonium chloride (having a structure of ) was added. Potassium hydroxide was added to adjust the pH to 10, and the solution was stirred for 5 h. Hydrochloric acid solution was added dropwise to adjust the pH to 7. The solution was dried to remove water, and the product was washed with ethanol, and dried to obtain a modified polyvinyl alcohol;

[0049] (2) 25 g of sodium-based montmorillonite and 10 g of modified polyvinyl alcohol were added to 0.5 L of water, ultrasonically dispersed for 20 min, then heated to 65°C, stirred for 7 h, and finally 500 g of polyvinyl alcohol, 25 g of carboxymethyl chitosan, and 6 L of water were added, heated to 95°C, stirred for 40 min, cast into a mold, vacuum degassed, and dried to obtain a food packaging film.

[0050] Staphylococcus aureus and Escherichia coli were respectively cultured in a constant temperature incubator at 37°C for 24 h, then diluted to a concentration of 1×10 7 cfu / mL of bacterial solution, 0.2 mL of bacterial solution was taken and uniformly coated on the surface of beef extract peptone culture medium, then a 8 mm diameter packaging film patch was attached to the surface of the culture medium, and the culture was incubated in a constant temperature incubator at 37°C for 24 h, then the diameter of the inhibition zone was measured, each group of samples was tested 5 times, and the average value was taken.

[0051] The tensile strength was tested according to standard GB / T 1040.3-2006. The oxygen transmission rate was tested according to standard GB / T 19789-2021. Table 1 is shown as follows:

[0052] Table 1: Performance test results of each example and comparative example

[0053]

[0054] Compared with Comparative Example 1, the polyvinyl alcohol packaging film of Examples 1-3 has a larger inhibition zone diameter for Escherichia coli and Staphylococcus aureus, high tensile strength, low oxygen transmission rate, and excellent antibacterial, strength, and gas barrier properties. This is mainly because the modified polyvinyl alcohol contains quaternary ammonium salt as an antibacterial group, alkyl ester and benzene ring as a hydrophobic structure of the antibacterial agent, and cooperates with carboxymethyl chitosan to significantly improve the antibacterial performance of the packaging film. The modified polyvinyl alcohol introduces a quaternary ammonium salt cation structure with smaller steric hindrance at the side chain end, which facilitates ion exchange with montmorillonite, thereby modifying the polyvinyl alcohol molecular chain on the surface of montmorillonite, improving the compatibility and dispersibility of montmorillonite in the polyvinyl alcohol packaging film, and facilitating the improvement of the mechanical strength of the packaging film. Meanwhile, the uniformly dispersed montmorillonite forms a continuous barrier phase, which can inhibit the transmission of oxygen through the packaging film, significantly reduce the oxygen transmission rate, and enhance the gas barrier performance. The quaternary ammonium salt cation of the modified polyvinyl alcohol forms electrostatic interaction with the carboxyl group of chitosan, making the modified polyvinyl alcohol act as a compatibilizer, further improving the compatibility of polyvinyl alcohol and chitosan, and facilitating the enhancement of the tensile strength of the packaging film.

[0055] The ion exchange of the montmorillonite in Comparative Example 2 is carried out by using hexadecyl trimethyl ammonium chloride, which is difficult to effectively improve the compatibility and dispersibility between the montmorillonite and the polyvinyl alcohol, resulting in low tensile strength, high oxygen permeability, poor mechanical strength and gas barrier property of the packaging film.

[0056] The 6-chlorohexanoic acid and the prepared modified polyvinyl alcohol in Comparative Example 3 do not contain hydrophobic structures such as benzene rings, which is not conducive to improving the antibacterial property of the modified polyvinyl alcohol, resulting in low antibacterial circle diameter and poor antibacterial property of the packaging film.

[0057] The modified polyvinyl alcohol obtained by the ring-opening reaction of the epoxy group of 2,3-epoxypropyl trimethyl ammonium chloride with the hydroxyl group of polyvinyl alcohol in Comparative Example 4 does not contain alkyl ester and benzene ring hydrophobic structures, which is not conducive to improving the antibacterial property of the modified polyvinyl alcohol, resulting in low antibacterial circle diameter and poor antibacterial property of the packaging film.

[0058] In Comparative Example 5, the polyvinyl alcohol is modified by using dodecyldimethyl epoxypropyl ammonium chloride, and the introduced quaternary ammonium salt group is sandwiched between the polyvinyl alcohol molecular chain and the dodecyl long carbon chain, which has large steric hindrance and cannot be ion exchanged with the montmorillonite, resulting in that the polyvinyl alcohol molecular chain is difficult to be modified on the surface of the montmorillonite, the compatibility and dispersibility between the montmorillonite and the polyvinyl alcohol are poor, the tensile strength of the packaging film is low, the oxygen permeability is high, and the mechanical strength and gas barrier property are poor.

[0059] The specific embodiments are only an explanation of the present application, which is not a limitation of the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the present specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A high-barrier antibacterial food packaging film, characterized in that, The raw materials include 100 parts by weight of polyvinyl alcohol, 2-8 parts by weight of modified polyvinyl alcohol, 5-30 parts by weight of carboxymethyl chitosan, and 5-20 parts by weight of sodium montmorillonite. The method for preparing the modified polyvinyl alcohol is as follows: (1) Add polyvinyl alcohol, 4-[4-(chloromethylbenzyl)oxy]-4-oxobutyric acid and dibutyltin dilaurate to dimethyl sulfoxide, heat to react, add ethanol to the solution, precipitate, filter, wash the precipitate, dry, and obtain polyvinyl alcohol intermediate. (2) Add polyvinyl alcohol intermediate and tertiary amine monomer to N,N-dimethylformamide, heat to react, add ethanol to the solution, precipitate, filter, wash the precipitate, dry, and obtain modified polyvinyl alcohol. In (1), the amount of polyvinyl alcohol is 100 parts by weight, the amount of 4-[4-(chloromethylbenzyl)oxy]-4-oxobutyric acid is 40-150 parts by weight, and the amount of dibutyltin dilaurate is 2-8 parts by weight. The amount of polyvinyl alcohol intermediate used in (2) is 100 parts by weight, and the amount of tertiary amine monomer used is 15-80 parts by weight. The structural formula of the tertiary amine monomer in (2) is as follows: R1 is methyl or ethyl, R2 is methyl or ethyl, and R3 is methyl or ethyl; The preparation method of 4-[4-(chloromethylbenzyl)oxy]-4-oxobutyric acid is as follows: 4-(chloromethyl)benzyl alcohol, succinic anhydride, and 4-dimethylaminopyridine are added to dichloromethane in a molar ratio of 1:(1-1.2):(0.4-0.5), and the mixture is stirred at 20-30℃ for 18-24 h. After vacuum distillation, the crude product is washed, recrystallized and purified to obtain 4-[4-(chloromethylbenzyl)oxy]-4-oxobutyric acid.

2. The high-barrier antibacterial food packaging film according to claim 1, characterized in that, The reaction temperature in (1) is 120-130℃ and the reaction time is 6-12h.

3. The high-barrier antibacterial food packaging film according to claim 1, characterized in that, The reaction temperature in (2) is 60-90℃ and the reaction time is 24-48h.

4. The method for preparing the high-barrier antibacterial food packaging film according to any one of claims 1-3, characterized in that, Includes the following steps: Sodium montmorillonite and modified polyvinyl alcohol are added to water and ultrasonically dispersed. Then, the mixture is heated and stirred. Finally, polyvinyl alcohol, carboxymethyl chitosan, and water are added and stirred until well mixed. The mixture is then poured into a mold for casting, vacuum degassing, and drying to obtain a high-barrier antibacterial food packaging film.

5. The method for preparing the high-barrier antibacterial food packaging film according to claim 4, characterized in that, The temperature during heating and stirring is 60-70℃, and the time is 7-12 hours.

6. The method for preparing the high-barrier antibacterial food packaging film according to claim 4, characterized in that, The temperature during the stirring and mixing process is 90-95℃, and the time is 40-60 minutes.

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