A chitosan-modified highly transparent antibacterial polylactic acid film and its preparation method and application

Abstract

The present invention discloses a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method and application thereof. The polylactic acid film comprises the following raw materials by weight: 10 to 16 parts of modified chitosan, 35 to 55 parts of polylactic acid, 5 to 15 parts of casein, 50 to 300 parts of solvent and 30 to 50 parts of gelatin, wherein the solvent comprises hexafluoroisopropanol and acetic acid solution. The antibacterial polylactic acid film provided by the present invention has good toughness, strength and transparency, is suitable for the field of food packaging, can extend the shelf life of food, and can reduce plastic waste pollution.

Description

Technical Field

[0001] The invention belongs to the field of bio-based degradable materials, and specifically relates to a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method and application thereof. Background Art

[0002] Food packaging is a key technology to ensure food safety, extend the shelf life of food, and avoid food waste. Petroleum-based plastics account for a large proportion of the materials used in food packaging in my country. Therefore, in response to the problem of waste plastic pollution, the development of green, new naturally degradable packaging materials is an important development direction for food packaging in the future. At present, while developing biodegradable packaging materials, researchers have also given food packaging films more new functions, such as anti-oxidation, antibacterial and intelligent monitoring.

[0003] In terms of antibacterial function, chitosan, as a cationic high molecular polymer widely found in crustaceans, has good biodegradability, biocompatibility and antibacterial properties. Its antibacterial property is reflected in the fact that it combines with negatively charged bacterial walls or cell membranes through electrostatic attraction, causing damage to the permeability and barrier properties of the bacterial membrane, and the bacterial contents leak out and cause death; on the other hand, it is reflected in the inhibition of the normal growth and reproduction of microorganisms by hindering DNA transcription and protein synthesis.

[0004] As a biodegradable material, polylactic acid is currently a hot topic in the development of active packaging. The raw materials of polylactic acid mostly come from agricultural production, and its processed product waste can be completely degraded into water and carbon dioxide in nature, without producing other waste, thus achieving a completely natural cycle. Although polylactic acid has the above advantages, its inherent brittleness and poor toughness limit its application in the packaging field.

[0005] Patent CN 113174702 B discloses a method for preparing a polylactic acid / chitosan / honeysuckle chlorogenic acid nanofiber membrane and its application. An antibacterial and antimicrobial nanofiber membrane with uniform distribution of honeysuckle chlorogenic acid is obtained by electrospinning. However, the disadvantage of the electrospinning method is that it requires high voltage, the mechanical properties of the produced fiber membrane are poor, and large-scale industrial production cannot be achieved at this stage. Patent CN108610502B discloses a method for preparing a transparent self-supporting packaging film based on visible light degradation of polylactic acid. With polylactic acid as the main material, chitosan as the modified material, and molybdenum disulfide as the modified material, a composite film with good transparency is obtained, and the film can be photocatalytically degraded under visible light irradiation, but the strength of the polylactic acid film in this method may be reduced. Summary of the invention

[0006] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method and application thereof. By modifying the chitosan which has its own antibacterial property, the toughness of the polylactic acid film is improved while the strength of the polylactic acid film is ensured, so that the antibacterial polylactic acid film has good toughness, strength and transparency, is suitable for the field of food packaging, can extend the shelf life of food, and can also reduce plastic waste pollution.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] The first aspect of the present invention provides a chitosan-modified highly transparent antibacterial polylactic acid film, which comprises the following raw materials in parts by weight: 10 to 16 parts of modified chitosan, 35 to 55 parts of polylactic acid, 5 to 15 parts of casein, 50 to 300 parts of solvent and 30 to 50 parts of gelatin; wherein the solvent comprises hexafluoroisopropanol and acetic acid solution.

[0009] In some embodiments, the volume fraction of the acetic acid solution is 2-5%.

[0010] In some embodiments, the mass ratio of hexafluoroisopropanol to acetic acid solution is (1.6-2.5):1.

[0011] In some embodiments, the preparation steps of the modified chitosan are as follows:

[0012] S1, preparing a chitosan solution with a pH of 2.8 to 3.4 using chitosan, water and hydrochloric acid solution;

[0013] S2, dissolving chlorogenic acid and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride in a 60-80% by volume ethanol solution, then adding N-hydroxysuccinimide, stirring at -2°C to 2°C for 1 to 2 hours, to obtain a reaction solution 1;

[0014] S3, α-lipoic acid, anhydrous Na 2 SO 3 Dissolve in deionized water, then add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, and stir at room temperature for 40 to 60 minutes to obtain reaction solution 2;

[0015] S4. At -2°C to 2°C, drop the reaction solution 1 of step S2 into the chitosan solution of step S1, stir for 16 to 24 hours after the dropwise addition, then add the reaction solution 2 of step S3, heat to 25 to 28°C, adjust the pH to 6.0 to 6.6, stir for 3 to 5 hours, centrifuge and dry to obtain modified chitosan.

[0016] In some embodiments, the mass ratio of chlorogenic acid in step S2 to chitosan in step S1 is (0.22-0.28):1.

[0017] In some embodiments, the mass ratio of α-lipoic acid in step S3 to chitosan in step S1 is (0.18-0.22):1.

[0018] In some embodiments, in step S3, α-lipoic acid and anhydrous Na 2 SO 3 The mass ratio is 1:(0.8~1.2).

[0019] The present invention modifies chitosan which has antibacterial properties, improves the toughness of the polylactic acid film and ensures the tensile strength of the polylactic acid film. The principle is as follows:

[0020] (1) First, chlorogenic acid is grafted onto the hydroxyl groups in the chitosan structure. During this process, the phenolic hydroxyl groups of chlorogenic acid will also produce hydrogen bonds with the hydroxyl groups or amino groups in the chitosan molecules. The combination of the two enhances the cohesive force of the chitosan skeleton. Then, hydrogen bonds are formed between the hydroxyl groups contained in chitosan and the ester groups in polylactic acid, which enhances the intermolecular forces, strengthens the network stability of the membrane, reduces the free volume and molecular mobility of the membrane, and ensures the strength of the polylactic acid membrane.

[0021] (2) Furthermore, the activated carboxyl groups on α-lipoic acid react with the amino groups on chitosan to form a condensation reaction, so that the polylactic acid film molecules are not only bonded by hydrogen bonds, but also form a new network structure by disulfide bonds, thereby improving the toughness of the polylactic acid film. The new network structure improves the flexibility of the film layer by changing the original arrangement of molecules; secondly, the dynamic reversibility of disulfide bonds enables disconnection and reconstruction when stressed, thereby improving the tensile properties of the film layer; thirdly, the side chains of the modified chitosan and the molecular chains of polylactic acid are entangled with each other to form physical connection points, which enhance the physical entanglement between the molecular chains of the system, increase the elasticity of the system, and thus improve the elongation at break.

[0022] In some embodiments, the casein has a protein content of >92 wt %.

[0023] In some embodiments, the polylactic acid is compounded by L-polylactic acid and racemic polylactic acid.

[0024] In some embodiments, the mass ratio of the L-polylactic acid to the racemic polylactic acid is 1:(1.5-2.5).

[0025] The present invention compounded L-polylactic acid and racemic polylactic acid, utilized the strong plasticity of amorphous racemic polylactic acid and the high crystallinity and mechanical strength of L-polylactic acid, thereby improving the toughness and strength of the polylactic acid film and ensuring the physical and chemical stability of the polylactic acid film.

[0026] The second aspect of the present invention provides a method for preparing a chitosan-modified highly transparent antibacterial polylactic acid film, comprising the following steps:

[0027] (1) dissolving casein in hexafluoroisopropanol, then adding polylactic acid, and stirring at 33-40° C. for 3-5 hours to obtain a polylactic acid mixed solution;

[0028] (2) Dissolve the modified chitosan in acetic acid solution, add gelatin, and stir at 50-60° C. for 0.5-1.5 h, add the polylactic acid mixed solution in step (1) and stir for 2-3 h, then ultrasonicate for 5-15 min, pour the solution after ultrasonication on the film mold, dry it at room temperature for 20-30 h, and then peel it off to obtain the chitosan-modified highly transparent antibacterial polylactic acid film.

[0029] For food packaging films, high transparency makes it easy to observe the state of food. Although the modified chitosan of the present invention can improve the toughness of the polylactic acid film and ensure the strength of the polylactic acid film, it cannot further improve the transparency of the polylactic acid film.

[0030] The present invention improves the transparency of the polylactic acid film by mixing casein with compound polylactic acid. The possible reason is that the addition of casein firstly breaks the regular and orderly structure inside the polylactic acid and changes the distribution of molecular weight, thereby improving the transparency of the polymer; secondly, it may reduce the crystal size of the polylactic acid film, reduce the scattering of light, increase the pass rate, and thus improve the transparency. The present invention also achieves the above effects while avoiding hindering the subsequent film formation by specifically selecting the protein content of casein.

[0031] The third aspect of the present invention provides the use of chitosan-modified highly transparent antibacterial polylactic acid film in food packaging.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention provides an antibacterial polylactic acid film with good toughness, strength and transparency, which is suitable for the field of food packaging, can extend the shelf life of food, and can reduce plastic waste pollution.

[0034] 2. The present invention improves the toughness of the polylactic acid film while ensuring the strength of the polylactic acid film by modifying the chitosan which has its own antibacterial property.

[0035] 3. The present invention improves the toughness and flexibility of the polylactic acid film by compounding L-polylactic acid and racemic polylactic acid, and also ensures the physical and chemical stability of the polylactic acid film.

[0036] 4. The present invention improves the molecular weight distribution and crystal size of the polylactic acid film by mixing casein with the compound polylactic acid, thereby improving the transparency of the polylactic acid film. DETAILED DESCRIPTION

[0037] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0038] In order to facilitate those skilled in the art to implement the present invention, some raw materials and manufacturers of the embodiments and comparative examples are described as follows:

[0039] Chitosan was purchased from Shandong Haiyihua Biotechnology Co., Ltd.;

[0040] Casein was purchased from Guangzhou Jingfu Bioengineering Co., Ltd.;

[0041] L-polylactic acid was purchased from Dongguan Chuangnuo Plastic Chemical Co., Ltd.;

[0042] Racemic polylactic acid was purchased from Shandong Zengyi Biotechnology Co., Ltd., model number PDLLA-07;

[0043] Gelatin was purchased from Baotou Dongbao Biotechnology Co., Ltd.

[0044] Preparation Example 1

[0045] The preparation steps of modified chitosan-A are as follows:

[0046] S1. Prepare a chitosan solution with a pH of 3 using 100 g chitosan, 500 g water and 1 mol / L hydrochloric acid solution;

[0047] S2, dissolving 25 g of chlorogenic acid and 12.4 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride in 800 mL of 70% ethanol solution, then adding 8.8 g of N-hydroxysuccinimide, and stirring at 0° C. for 1 h to obtain reaction solution 1;

[0048] S3, 20g α-lipoic acid, 20g anhydrous Na 2 SO 3 Dissolve in 300 mL of deionized water, then add 9.6 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, and stir at room temperature for 50 min to obtain reaction solution 2;

[0049] S4. At -1°C, drop the reaction solution 1 of step S2 into the chitosan solution of step S1, stir for 20 hours after the dropwise addition, then add the reaction solution 2 of step S3, raise the temperature to 27°C, adjust the pH to 6.3, stir for 4 hours, centrifuge at 10000 rpm for 20 minutes, and freeze-dry the supernatant to obtain modified chitosan-A.

[0050] Preparation Example 2

[0051] The preparation steps of modified chitosan-B are as follows:

[0052] The difference between this preparation example and preparation example 1 is that 20 g of chlorogenic acid was used in step S2.

[0053] Preparation Example 3

[0054] The preparation steps of modified chitosan-C are as follows:

[0055] The difference between this preparation example and preparation example 1 is that 30 g of chlorogenic acid was used in step S2.

[0056] Preparation Example 4

[0057] The preparation steps of modified chitosan-D are as follows:

[0058] The difference between this preparation example and preparation example 1 is that 15 g of α-lipoic acid is used in step S3.

[0059] Preparation Example 5

[0060] The preparation steps of modified chitosan-E are as follows:

[0061] The difference between this preparation example and preparation example 1 is that 25 g of α-lipoic acid is used in step S3.

[0062] Preparation Example 6

[0063] The preparation steps of modified chitosan-F are as follows:

[0064] The difference between this preparation example and preparation example 1 is that step S3 uses 12g of anhydrous Na 2 SO 3 .

[0065] Preparation Example 7

[0066] The preparation steps of modified chitosan-G are as follows:

[0067] The difference between this preparation example and preparation example 1 is that step S3 uses 28g of anhydrous Na 2 SO 3 .

[0068] Example 1

[0069] A chitosan-modified highly transparent antibacterial polylactic acid film comprises the following raw materials by weight: 13 parts of modified chitosan-A, 15 parts of L-polylactic acid, 30 parts of racemic polylactic acid, 10 parts of casein, 180 parts of solvent and 40 parts of gelatin;

[0070] The solvent includes 120 parts of hexafluoroisopropanol and 60 parts of 3% by volume acetic acid solution.

[0071] The preparation steps of the chitosan-modified highly transparent antibacterial polylactic acid film in this embodiment are as follows:

[0072] (1) dissolving casein in hexafluoroisopropanol, adding L-polylactic acid and racemic polylactic acid, and stirring at 37° C. for 4 h to obtain a polylactic acid mixed solution;

[0073] (2) Dissolve the modified chitosan-A in a 4% acetic acid solution, add gelatin, and stir at 60°C for 1 hour, add the polylactic acid mixed solution in step (1), stir for 3 hours, and then ultrasonicate for 10 minutes. Pour the solution after ultrasonication on the film mold, dry it at room temperature for 24 hours, and then peel it off to obtain the highly transparent antibacterial polylactic acid film.

[0074] Example 2

[0075] A chitosan-modified highly transparent antibacterial polylactic acid film comprises the following raw materials by weight: 10 parts of modified chitosan-A, 14 parts of L-polylactic acid, 21 parts of racemic polylactic acid, 5 parts of casein, 130 parts of solvent and 30 parts of gelatin;

[0076] The solvent includes 80 parts of hexafluoroisopropanol and 50 parts of 2% by volume acetic acid solution.

[0077] The preparation steps of the chitosan-modified highly transparent antibacterial polylactic acid film in this embodiment are as follows:

[0078] (1) dissolving casein in hexafluoroisopropanol, adding L-polylactic acid and racemic polylactic acid, and stirring at 33° C. for 5 h to obtain a polylactic acid mixed solution;

[0079] (2) Dissolve the modified chitosan-A in a 4% acetic acid solution, add gelatin, and stir at 50°C for 1.5 hours, add the polylactic acid mixed solution in step (1) and stir for 3 hours, then ultrasonicate for 7 minutes, pour the ultrasonicated solution on the film mold, dry it at room temperature for 20 hours, and then peel it off to obtain the highly transparent antibacterial polylactic acid film.

[0080] Example 3

[0081] A chitosan-modified highly transparent antibacterial polylactic acid film comprises the following raw materials by weight: 16 parts of modified chitosan-A, 16 parts of L-polylactic acid, 39 parts of racemic polylactic acid, 15 parts of casein, 280 parts of solvent and 50 parts of gelatin;

[0082] The solvent includes 200 parts of hexafluoroisopropanol and 80 parts of 5% by volume acetic acid solution.

[0083] The preparation steps of the chitosan-modified highly transparent antibacterial polylactic acid film in this embodiment are as follows:

[0084] (1) dissolving casein in hexafluoroisopropanol, adding L-polylactic acid and racemic polylactic acid, and stirring at 40° C. for 3 h to obtain a polylactic acid mixed solution;

[0085] (2) Dissolve the modified chitosan-A in a 4% acetic acid solution, add gelatin, and stir at 60°C for 1.5 hours, add the polylactic acid mixed solution in step (1) and stir for 3 hours, then ultrasonicate for 15 minutes, pour the ultrasonicated solution on the film mold, dry it at room temperature for 30 hours, and then peel it off to obtain the highly transparent antibacterial polylactic acid film.

[0086] Example 4

[0087] This embodiment provides a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the modified chitosan-A is replaced by an equal portion of modified chitosan-B.

[0088] Example 5

[0089] This embodiment provides a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the modified chitosan-A is replaced by an equal portion of modified chitosan-C.

[0090] Example 6

[0091] This embodiment provides a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the modified chitosan-A is replaced by an equal portion of modified chitosan-D.

[0092] Example 7

[0093] This embodiment provides a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the modified chitosan-A is replaced by an equal portion of modified chitosan-E.

[0094] Example 8

[0095] This embodiment provides a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the modified chitosan-A is replaced by an equal portion of modified chitosan-F.

[0096] Example 9

[0097] This embodiment provides a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the modified chitosan-A is replaced by an equal portion of modified chitosan-G.

[0098] Example 10

[0099] This embodiment provides a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the racemic polylactic acid is replaced by an equal portion of L-polylactic acid.

[0100] Embodiment 11

[0101] This embodiment provides a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the L-polylactic acid is replaced by an equal portion of racemic polylactic acid.

[0102] Comparative Example 1

[0103] A chitosan-modified highly transparent antibacterial polylactic acid film comprises the following raw materials by weight: 13 parts of modified chitosan-A, 15 parts of L-polylactic acid, 30 parts of racemic polylactic acid, 180 parts of solvent and 40 parts of gelatin;

[0104] The solvent contained 120 parts of hexafluoroisopropanol and 60 parts of acetic acid solution.

[0105] The preparation steps of the chitosan-modified highly transparent antibacterial polylactic acid film in this embodiment are as follows:

[0106] (1) dissolving L-polylactic acid and racemic polylactic acid in hexafluoroisopropanol and stirring at 37° C. for 4 h to obtain a polylactic acid mixed solution;

[0107] (2) Dissolve the modified chitosan-A in a 4% acetic acid solution, add gelatin, and stir at 60°C for 1 hour, add the polylactic acid mixed solution in step (1), stir for 3 hours, and then ultrasonicate for 10 minutes. Pour the solution after ultrasonication on the film mold, dry it at room temperature for 24 hours, and then peel it off to obtain the highly transparent antibacterial polylactic acid film.

[0108] Comparative Example 2

[0109] This comparative example provides a chitosan-modified highly transparent antibacterial polylactic acid film and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the modified chitosan-A is replaced by an equal portion of chitosan.

[0110] Performance Testing:

[0111] 1. Elongation at break test

[0112] Tested according to standard GB / T 1040.1-2018.

[0113] 2. Transparency test

[0114] The test is carried out according to standard GB T 2410-2008.

[0115] 3. Tensile strength test

[0116] Tested according to standard GB / T 1040.1-2018.

[0117] Elongation at break and tensile strength were used to evaluate the tensile strength and ductility of the films.

[0118] The results are shown in Table 1.

[0119] Table 1 Performance test results

[0120]

[0121]

[0122] From the data in Table 1, it can be seen that the polylactic acid films of Examples 1-3 have good toughness, tensile strength and transparency; from Example 1 and Comparative Example 1, it can be seen that the addition of casein can improve the transparency of the polylactic acid film, which may be due to the breaking of the regular and orderly structure inside the polylactic acid or the reduction of the crystal size of the polylactic acid film. From Example 1 and Examples 6-7, it can be seen that chitosan can improve the elongation at break and tensile strength of the polylactic acid film by condensing with α-lipoic acid on the basis of grafting specific chlorogenic acid, indicating that its toughness and tensile strength have been enhanced; from Examples 1 and Examples 8-9, it can be seen that the anhydrous Na in the modified chitosan 2 SO 3 The amount of use has an impact on the toughness, tensile strength and transparency of the polylactic acid film. The possible reason is that the specific anhydrous Na 2 SO 3 The amount used determines whether the disulfide bonds on the α-lipoic acid can be reduced to thiol groups, thereby carrying out the next reaction; it can be seen from Example 1 and Examples 10-11 that the compounding of L-polylactic acid and racemic polylactic acid can effectively improve the toughness and tensile strength of the polylactic acid film; it can be seen from Example 1 and Comparative Example 2 that the modified chitosan can effectively improve the toughness and tensile strength of the polylactic acid film.

[0123] The embodiments and comparative examples described above do not impose any form of limitation on the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A chitosan-modified highly transparent antibacterial polylactic acid film, characterized in that: The composition comprises the following raw materials by weight: 10 to 16 parts of modified chitosan, 35 to 55 parts of polylactic acid, 5 to 15 parts of casein, 50 to 300 parts of solvent and 30 to 50 parts of gelatin; wherein the solvent comprises hexafluoroisopropanol and acetic acid solution; The preparation steps of the modified chitosan are as follows: S1, preparing a chitosan solution with a pH of 2.8 to 3.4 using chitosan, water and hydrochloric acid solution; S2, dissolving chlorogenic acid and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride in a 60-80% by volume ethanol solution, then adding N-hydroxysuccinimide, stirring at -2°C to 2°C for 1 to 2 hours, to obtain a reaction solution 1; S3, dissolving α-lipoic acid and anhydrous Na2SO3 in deionized water, then adding 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, stirring at room temperature for 40 to 60 minutes, to obtain reaction solution 2; S4, at -2°C to 2°C, dropwise add the reaction solution 1 of step S2 into the chitosan solution of step S1, stir for 16 to 24 hours after the dropwise addition, then add the reaction solution 2 of step S3, raise the temperature to 25 to 28°C, adjust the pH to 6.0 to 6.6, stir for 3 to 5 hours, centrifuge and dry to obtain the modified chitosan; The mass ratio of chlorogenic acid in step S2 to chitosan in step S1 is (0.22-0.28):1; The mass ratio of α-lipoic acid in step S3 to chitosan in step S1 is (0.18-0.22):1; In step S3, the mass ratio of α-lipoic acid to anhydrous Na2SO3 is 1:(0.8-1.2); The protein content of the casein is >92wt%; The polylactic acid is compounded by mixing left-handed polylactic acid and racemic polylactic acid in a mass ratio of 1:(1.5-2.5).

2. A method for preparing the chitosan-modified highly transparent antibacterial polylactic acid film according to claim 1, characterized in that: The following steps are involved: (1) dissolving casein in hexafluoroisopropanol, then adding polylactic acid, and stirring at 33-40° C. for 3-5 hours to obtain a polylactic acid mixed solution; (2) Dissolve the modified chitosan in acetic acid solution, add gelatin, and stir at 50-60° C. for 0.5-1.5 h, add the polylactic acid mixed solution in step (1) and stir for 2-3 h, then ultrasonicate for 5-15 min, pour the solution after ultrasonication on the film mold, dry it at room temperature for 20-30 h, and then peel it off to obtain the chitosan-modified highly transparent antibacterial polylactic acid film.

3. Use of the chitosan-modified highly transparent antibacterial polylactic acid film according to claim 1 or the highly transparent antibacterial polylactic acid film obtained by the preparation method according to claim 2 in food packaging.

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