A modified pae film for degradable food inner packaging and a preparation method thereof

Abstract

This invention discloses a biodegradable modified PAE film for food inner packaging and its preparation method, belonging to the field of food packaging film technology. The biodegradable modified PAE film for food inner packaging prepared by this invention comprises modified PAE and antioxidants. The antioxidants include antioxidant 330, antioxidant CA, and biphenyl hydroquinone. The modified PAE is obtained by first acylating terminal hydroxyl polylactic acid acrylic acid, reacting it with N'-methyl-L-histidine methyl ester, and then reacting it with long-chain aliphatic bromoalkane. The antioxidants... The amount of N'-methyl-L-histidine methyl ester added is 0.4~0.8 wt%; the amount of N'-methyl-L-histidine methyl ester added is 15~25 wt% of the mass of terminal hydroxyl polylactic acid; the molar ratio of the long-chain aliphatic bromoalkane to N'-methyl-L-histidine methyl ester is (1~1.2):1; the carbon number of the long-chain aliphatic bromoalkane is 8~16; the modified PAE film for biodegradable food inner packaging prepared by the present invention has good degradability, good mechanical properties, strong antibacterial properties, and is not prone to the problem of easy migration of traditional added antibacterial agents.

Description

Technical Field

[0001] This invention relates to the field of food packaging film technology, specifically to a biodegradable modified PAE film for food inner packaging and its preparation method. Background Technology

[0002] As a barrier material that comes into direct contact with food, the performance and safety of food inner packaging are crucial to food shelf life, quality stability, and consumer health. Currently, traditional petroleum-based plastic packaging, such as polyethylene and polypropylene, is difficult to degrade naturally, leading to long-term accumulation of white pollution in the environment and driving the development of biodegradable packaging materials as an industry trend. Poly(β-amino ester) PAE, as an emerging class of biodegradable polymer materials, can be prepared through the conjugated addition polymerization of primary / secondary amine monomers and diacrylate monomers. Due to its easily hydrolyzable ester bond structure in the molecular chain, it possesses excellent biodegradability, aligning with the needs of green packaging development.

[0003] However, the application of PAE in food inner packaging still faces key technical bottlenecks: On the one hand, PAE film itself has insufficient water vapor barrier properties, which cannot effectively prevent the intrusion of external moisture, making it easy for food to become damp and deteriorate, thus limiting its application in packaging of high moisture-sensitive foods such as baked goods and dairy products; on the other hand, in order to endow packaging with antibacterial function to extend the shelf life of food, traditional processes often use the method of directly adding small molecule antibacterial agents, but these antibacterial agents have poor compatibility with the PAE matrix and are easy to migrate from the inside of the film material to the surface of the food during use or storage, which not only causes the antibacterial efficacy to decrease, but may also introduce food safety risks.

[0004] Therefore, there is an urgent need to develop a modified PAE film for biodegradable food inner packaging that combines good water vapor barrier properties with stable antibacterial properties. Summary of the Invention

[0005] The purpose of this invention is to provide a biodegradable modified PAE film for food inner packaging and its preparation method, so as to solve the technical problems mentioned in the background art.

[0006] The technical solution to achieve the objective of this invention is: In a first aspect, the present invention provides a modified PAE film for biodegradable food inner packaging, the raw material components including modified PAE and antioxidant; the modified PAE is obtained by first acrylating terminal hydroxyl polylactic acid to obtain acrylated polylactic acid, and then reacting the acrylated polylactic acid with N'-methyl-L-histidine methyl ester and then reacting it with long-chain aliphatic bromoalkane.

[0007] Polylactic acid (PLA) itself possesses excellent hydrophobicity and biodegradability. Using acrylated PLA as a diacrylate monomer to prepare poly(β-amino ester) effectively improves the degradability and hydrophobicity of the modified PAE film. Simultaneously, the selection of N'-methyl-L-histidine methyl ester, a biocompatible and safe non-toxic natural amino acid histidine derivative, as the primary amino monomer not only ensures the safety of food packaging but also further enhances the material's degradation performance. Furthermore, long-chain aliphatic brominated alkanes are introduced into the film. This not only strengthens the material's hydrophobicity, enabling it to effectively block water vapor, but also allows the alkyl bromides on the long-chain aliphatic brominated alkanes to react with the imidazole ring of N'-methyl-L-histidine methyl ester to generate imidazoleonium bromide salts. This endows the modified PAE film with excellent antibacterial properties, avoiding the migration problems associated with directly adding small-molecule antibacterial agents in traditional processes.

[0008] Furthermore, the antioxidants include antioxidant 330, antioxidant CA, and biphenyl hydroquinone.

[0009] Furthermore, the amount of antioxidant added is 0.4~0.8 wt%.

[0010] The antioxidants of the present invention include antioxidant 330, antioxidant CA, and biphenyl hydroquinone, and the addition amount is 0.4~0.8wt%. It can effectively improve the crystallinity of polylactic acid segments in the modified PAE film for biodegradable food inner packaging, thereby effectively improving the heat resistance, mechanical properties and water vapor barrier properties of the modified PAE film.

[0011] Furthermore, the amount of N'-methyl-L-histidine methyl ester added is 15-25 wt% of the mass of acryloylated polylactic acid; Furthermore, the molar ratio of the long-chain aliphatic brominated alkane to N'-methyl-L-histidine methyl ester is (1~1.2):1.

[0012] Furthermore, the long-chain aliphatic bromoalkane has 8 to 16 carbon atoms; as the number of carbon atoms in the long-chain aliphatic bromoalkane increases, the hydrophobicity gradually increases, the thermal stability is less affected, the mechanical properties gradually increase, and the antibacterial properties show a trend of first increasing and then decreasing.

[0013] In a second aspect, the present invention provides a method for preparing a modified PAE film for biodegradable food inner packaging as described in the first aspect, the steps of which include: (1) Weigh and mix each raw material component and dry it; (2) The weighed raw material components are mixed, melted, extruded, granulated, and blown into a film to obtain a modified PAE film for biodegradable food inner packaging.

[0014] Further, the preparation steps of the modified PAE are as follows: Acrylamide-modified polylactic acid and N'-methyl-L-histidine methyl ester are dissolved in chloroform, heated to 50-60°C under inert gas protection, and reacted at this temperature for at least 48 hours. Then, the mixture is precipitated with diethyl ether at -4 to 0°C, filtered, and vacuum dried to obtain poly(β-amino ester). The poly(β-amino ester) is mixed with long-chain aliphatic bromoalkane, acetonitrile is added and mixing is continued for 10-20 minutes. Then, the mixture is stirred and reacted at 60-65°C for 23-25 ​​hours. After the reaction is completed, the acetonitrile is removed by rotary evaporation, washed 2-4 times with ethyl acetate, and then vacuum dried to obtain the modified PAE.

[0015] Further, the preparation method of the acrylamide polylactic acid is as follows: hydroxyl-terminated polylactic acid is dissolved in dichloromethane, then triethylamine and acryloyl chloride are added, the mixture is stirred at room temperature for at least 24 hours, the solvent is removed under reduced pressure, purified, dried, and acrylamide polylactic acid is obtained.

[0016] Furthermore, the ratio of the amount of hydroxyl groups in the terminal hydroxyl polylactic acid to the amount of triethylamine and acryloyl chloride is 1:(3~4):(2~3).

[0017] By adopting the above technical solution, the present invention has the following beneficial effects: The modified PAE film for biodegradable food inner packaging of the present invention comprises modified PAE and antioxidants. The modified PAE is prepared by first acrylating terminal hydroxyl polylactic acid to obtain acrylated polylactic acid, and then reacting the acrylated polylactic acid with N'-methyl-L-histidine methyl ester and then with long-chain aliphatic bromoalkane. The resulting modified PAE film for biodegradable food inner packaging has good water vapor barrier properties, stable antibacterial properties, as well as thermal stability and mechanical properties. Detailed Implementation

[0018] To better understand the above technical solution, the following will provide a detailed explanation of the technical solution in conjunction with specific implementation methods.

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0021] The hydroxyl-terminated polylactic acid used is DG-LOH100 hydroxyl-terminated L-polylactic acid from Jinan Daigang Bioengineering Co., Ltd., with a glass transition temperature of 60~65℃ and a melting point of 170~180℃.

[0022] Antioxidant 330, Antioxidant CA, Bisphenol Example 1

[0023] A method for preparing a biodegradable modified PAE film for food inner packaging, comprising the following steps: (1) Weigh and mix 99.2 parts by weight of modified PAE and 0.8 parts by weight of antioxidant 330 and dry them; (2) The modified PAE and antioxidant are mixed and put into a twin-screw extruder for melt extrusion granulation and blow molding to obtain a biodegradable modified PAE film for food inner packaging. The twin-screw extruder is preheated for 1 hour in advance. The temperature control program of the screw extruder is as follows: Zone 1 temperature 175℃, Zone 2 temperature 180℃, Zone 3 temperature 185℃, Zone 4 temperature 190℃, Zone 5 temperature 190℃, Zone 6 temperature 190℃, Zone 7 temperature 185℃, and the die head temperature 185℃. The feed device speed is set to 4r / min, and the screw speed is set to 150r / min. The temperature of each zone of the single-screw blown film machine is as follows: Zone 1 160℃, Zone 2 170℃, Zone 3 180℃, Zone 4 190℃, and the die head temperature 185℃. The blow ratio is 4:1, the traction speed is 10m / min, the screw speed is 150rpm, and the screw length-to-diameter ratio L / D = 32:1.

[0024] The preparation steps of the modified PAE are as follows: Acrylated polylactic acid and N'-methyl-L-histidine methyl ester are dissolved in chloroform, heated to 50°C under inert gas protection, and reacted for 48 h. Then, the mixture is precipitated with diethyl ether at -4°C, filtered, and vacuum dried to obtain poly(β-amino ester). Poly(β-amino ester) is mixed with bromododecane, acetonitrile is added and mixed for another 10 min, and then stirred at 60°C for 25 h. After the reaction is completed, the acetonitrile is removed by rotary evaporation, washed twice with ethyl acetate, and then vacuum dried to obtain the modified PAE. The amount of N'-methyl-L-histidine methyl ester added is 15 wt% of the mass of acrylated polylactic acid; the molar ratio of bromododecane to N'-methyl-L-histidine methyl ester is 1:1.

[0025] The preparation method of the acrylamide-modified polylactic acid is as follows: hydroxyl-terminated polylactic acid is dissolved in dichloromethane, then triethylamine and acryloyl chloride are added, the mixture is stirred at room temperature for 24 hours, dichloromethane is removed under reduced pressure, then dissolved in tetrahydrofuran and filtered. The filtrate is purified with diethyl ether to precipitate, and then dried under vacuum to obtain acrylamide-modified polylactic acid. The molar ratio of the hydroxyl groups in the hydroxyl-terminated polylactic acid to the molar ratio of triethylamine and acryloyl chloride is 1:3:2. Example 2

[0026] A method for preparing a biodegradable modified PAE film for food inner packaging, comprising the following steps: (1) Weigh and mix 99.2 parts by weight of modified PAE and 0.8 parts by weight of biphenyl hydroquinone and dry them; (2) Modified PAE and antioxidant are mixed and put into a twin-screw extruder for melt extrusion granulation and blow molding to obtain a biodegradable modified PAE film for food inner packaging. The twin-screw extruder is preheated for 1 hour in advance. The temperature control program of the screw extruder is as follows: Zone 1 temperature 175℃, Zone 2 temperature 180℃, Zone 3 temperature 185℃, Zone 4 temperature 190℃, Zone 5 temperature 190℃, Zone 6 temperature 190℃, Zone 7 temperature 185℃, and the die head temperature 185℃. The feed device speed is set to 4r / min, and the screw speed is set to 150r / min. The temperature of each zone of the single-screw blown film machine is as follows: Zone 1 160℃, Zone 2 170℃, Zone 3 180℃, Zone 4 190℃, and the die head temperature 185℃. The blow ratio is 4:1, the traction speed is 10m / min, the screw speed is 150rpm, and the screw length-to-diameter ratio L / D = 32:1.

[0027] The preparation steps of the modified PAE are as follows: Acrylated polylactic acid and N'-methyl-L-histidine methyl ester are dissolved in chloroform, heated to 60°C under inert gas protection, and reacted for 48 h. Then, the mixture is precipitated with diethyl ether at 0°C, filtered, and vacuum dried to obtain poly(β-amino ester). Poly(β-amino ester) is mixed with bromododecane, acetonitrile is added and mixing is continued for 20 min. Then, the mixture is stirred at 60°C for 24 h. After the reaction is completed, the acetonitrile is removed by rotary evaporation, washed three times with ethyl acetate, and then vacuum dried to obtain the modified PAE. The amount of N'-methyl-L-histidine methyl ester added is 20 wt% of the mass of acrylated polylactic acid. The molar ratio of bromododecane to N'-methyl-L-histidine methyl ester is 1.2:1.

[0028] The preparation method of the acrylamide-modified polylactic acid is as follows: hydroxyl-terminated polylactic acid is dissolved in dichloromethane, then triethylamine and acryloyl chloride are added, the mixture is stirred at room temperature for 24 hours, dichloromethane is removed under reduced pressure, then dissolved in tetrahydrofuran and filtered. The filtrate is purified and precipitated with diethyl ether, and dried under vacuum to obtain acrylamide-modified polylactic acid; wherein, the molar ratio of the hydroxyl groups in the hydroxyl-terminated polylactic acid to the molar ratio of triethylamine and acryloyl chloride is 1:4:3. Example 3

[0029] A method for preparing a biodegradable modified PAE film for food inner packaging, comprising the following steps: (1) Weigh and mix 99.6 parts by weight of modified PAE and 0.4 parts by weight of antioxidant CA and dry them; (2) Modified PAE and antioxidant are mixed and put into a twin-screw extruder for melt extrusion granulation and blow molding to obtain a biodegradable modified PAE film for food inner packaging. The twin-screw extruder is preheated for 1 hour in advance. The temperature control program of the screw extruder is as follows: Zone 1 temperature 175℃, Zone 2 temperature 180℃, Zone 3 temperature 185℃, Zone 4 temperature 190℃, Zone 5 temperature 190℃, Zone 6 temperature 190℃, Zone 7 temperature 185℃, and the die head temperature 185℃. The feed device speed is set to 4r / min, and the screw speed is set to 150r / min. The temperature of each zone of the single-screw blown film machine is as follows: Zone 1 160℃, Zone 2 170℃, Zone 3 180℃, Zone 4 190℃, and the die head temperature 185℃. The blow ratio is 4:1, the traction speed is 10m / min, the screw speed is 150rpm, and the screw length-to-diameter ratio L / D = 32:1.

[0030] The preparation steps of the modified PAE are as follows: Acrylated polylactic acid and N'-methyl-L-histidine methyl ester are dissolved in chloroform, heated to 60°C under inert gas protection, and reacted for 48 h. Then, the mixture is precipitated with diethyl ether at -4°C, filtered, and vacuum dried to obtain poly(β-amino ester). Poly(β-amino ester) is mixed with bromododecane, acetonitrile is added and mixing is continued for 20 min. Then, the mixture is stirred at 65°C for 23 h. After the reaction is completed, the acetonitrile is removed by rotary evaporation, washed four times with ethyl acetate, and then vacuum dried to obtain the modified PAE. The amount of N'-methyl-L-histidine methyl ester added is 25 wt% of the mass of acrylated polylactic acid. The molar ratio of bromododecane to N'-methyl-L-histidine methyl ester is 1.2:1.

[0031] The preparation method of the acrylamide-modified polylactic acid is as follows: hydroxyl-terminated polylactic acid is dissolved in dichloromethane, then triethylamine and acryloyl chloride are added, and the mixture is stirred at room temperature for at least 24 hours. Dichloromethane is removed under reduced pressure, and the mixture is then dissolved in tetrahydrofuran and filtered. The filtrate is purified and precipitated with diethyl ether, and then dried under vacuum to obtain acrylamide-modified polylactic acid. The molar ratio of the hydroxyl groups in the hydroxyl-terminated polylactic acid to the molar ratio of triethylamine and acryloyl chloride is 1:4:3. Examples 4-7

[0032] The only difference between Examples 4-7 and Example 2 is that the long-chain aliphatic brominated alkanes are bromooctane, bromodecane, bromotetradecane, and bromohexadecane, respectively. Examples 8-11

[0033] The only difference between Examples 8-11 and Example 2 is that the amount of N'-methyl-L-histidine methyl ester added is 10 wt%, 15 wt%, 25 wt%, and 30 wt% of the mass of acryloylated polylactic acid, respectively. Comparative Example 1

[0034] The only difference between Comparative Example 1 and Example 2 is that the modified PAE first acrylates the terminal hydroxyl polylactic acid to obtain acrylated polylactic acid, and then reacts the acrylated polylactic acid with N'-methyl-L-histidine methyl ester to obtain the antibacterial agent 1-methyl-3-dodecylimidazolium bromide. Example of effect

[0035] Table 1 below shows the initial decomposition temperatures of the membranes in Examples 1-11, Comparative Example 1, and the blank example. The blank example's raw materials were 99.2 parts by mass of terminal hydroxyl-terminated polylactic acid (L-lactic acid) and 0.8 parts by mass of nucleating agent biphenyl hydroquinone. Table 1

[0036] Table 1 shows that the initial decomposition temperatures of the modified PAE films in Examples 1-3 under different nucleating agents were 351.95℃, 357.71℃, and 350.64℃, respectively, which are higher than the initial decomposition temperature of 338.1℃ for L-terminated polylactic acid. In Examples 4-7, the long-chain aliphatic bromoalkanes used were bromooctane, bromodecane, bromotetradecane, and bromohexadecane, respectively, and the increase in alkane chain had a relatively small impact on thermal stability. In Examples 8-11, the amount of N'-methyl-L-histidine methyl ester added was 10wt%, 15wt%, 25wt%, and 30wt% of the mass of acryloylated polylactic acid, respectively. With the increase of the amount of N'-methyl-L-histidine methyl ester added, the initial decomposition temperatures were 350.20℃, 353.42℃, 349.84℃, and 350.64℃, respectively. The thermal stability of the modified PAE film initially increased and then decreased at 40.90℃, especially after the addition amount exceeded 20%. The modified PAE in Comparative Example 1 was prepared by first acrylating terminal hydroxyl polylactic acid to obtain acrylated polylactic acid, which was then reacted with N'-methyl-L-histidine methyl ester. The antibacterial agent 1-methyl-3-dodecylimidazolium bromide was directly added. It can be seen that the direct addition of the antibacterial agent 1-methyl-3-dodecylimidazolium bromide significantly reduced the initial decomposition temperature of the modified PAE film. The blank example used 99.2 parts by weight of terminal hydroxyl L-polylactic acid and 0.8 parts by weight of nucleating agent biphenyl hydroquinone. Compared with Example 2, the initial decomposition temperature of Example 2 was less different from that of the blank example, indicating that the thermal stability of the modified PAE film was better maintained under the conditions of Example 2.

[0037] Table 2 below shows the mechanical properties and water vapor transmission rate test results of the modified PAE membranes of Examples 1-11 and Comparative Example 1: Table 2

[0038] As shown in Table 2, the modified PAE membranes of Examples 1-3 have high tensile strength, high elongation at break, and low water vapor permeability. The long-chain aliphatic brominated alkanes used in Examples 4-7 are bromooctane, bromodecane, bromotetradecane, and bromohexadecane. As the alkane chain length increases, the tensile strength and elongation at break gradually increase, while the water vapor permeability decreases and tends to stabilize.

[0039] In Examples 8-11, the amount of N'-methyl-L-histidine methyl ester added was 10 wt%, 15 wt%, 25 wt%, and 30 wt% of the mass of acryloylated polylactic acid, respectively. As the amount of N'-methyl-L-histidine methyl ester added increased, the tensile strength and elongation at break showed a trend of first increasing and then decreasing, while the water vapor permeability decreased.

[0040] The modified PAE of Comparative Example 1 was prepared by first acrylating the terminal hydroxyl polylactic acid to obtain acrylated polylactic acid, and then reacting the acrylated polylactic acid with N'-methyl-L-histidine methyl ester. The antibacterial agent 1-methyl-3-dodecylimidazolium bromide was directly added. It can be seen that the direct addition of the antibacterial agent 1-methyl-3-dodecylimidazolium bromide significantly reduced the tensile strength and elongation at break of the modified PAE film, while the water vapor permeability was not significantly affected.

[0041] Antimicrobial stability: Migration experiments were conducted according to GB 31604.1-2023, and the diameter of the inhibition zone of Escherichia coli before and after migration was tested using the inhibition zone method.

[0042] Table 3 below shows the performance test results of the antibacterial properties and antibacterial stability of the modified PAE films of Examples 1-11 and Comparative Example 1: Table 3

[0043] As shown in Table 3, the modified PAE films of Examples 1-3 have better antibacterial properties and antibacterial stability.

[0044] The long-chain aliphatic brominated alkanes in Examples 4-7 are bromooctane, bromodecane, bromotetradecane, and bromohexadecane. As the alkane chain length increases, the antibacterial activity first increases and then decreases, while the antibacterial stability is not significantly affected.

[0045] The amount of N'-methyl-L-histidine methyl ester added in Examples 8-11 was 10 wt%, 15 wt%, 25 wt%, and 30 wt% of the mass of acryloylated polylactic acid, respectively. The antibacterial properties were enhanced as the amount of N'-methyl-L-histidine methyl ester added increased.

[0046] The modified PAE of Comparative Example 1 was obtained by first acrylating the terminal hydroxyl polylactic acid to obtain acrylated polylactic acid, and then reacting the acrylated polylactic acid with N'-methyl-L-histidine methyl ester. The antibacterial agent 1-methyl-3-dodecylimidazolium bromide was directly added, but the antibacterial stability was poor and migration occurred.

[0047] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A modified PAE film for biodegradable food inner packaging, characterized in that, The raw material components include modified PAE and antioxidants; the modified PAE is obtained by first acrylating terminal hydroxyl polylactic acid to obtain acrylated polylactic acid, and then reacting the acrylated polylactic acid with N'-methyl-L-histidine methyl ester and then reacting it with long-chain aliphatic bromoalkane.

2. The modified PAE film for biodegradable food inner packaging according to claim 1, characterized in that, The antioxidants include antioxidant 330, antioxidant CA, and biphenyl hydroquinone.

3. The modified PAE film for biodegradable food inner packaging according to claim 2, characterized in that, The amount of antioxidant added is 0.4~0.8wt%.

4. The modified PAE film for biodegradable food inner packaging according to claim 1, characterized in that, The amount of N'-methyl-L-histidine methyl ester added is 15-25 wt% of the mass of acryloylated polylactic acid.

5. The modified PAE film for biodegradable food inner packaging according to claim 1, characterized in that, The molar ratio of the long-chain aliphatic brominated alkanes to N'-methyl-L-histidine methyl is (1~1.2):

1.

6. The modified PAE film for biodegradable food inner packaging according to claim 1, characterized in that, The long-chain aliphatic brominated alkanes have 8 to 16 carbon atoms.

7. A method for preparing a modified PAE film for biodegradable food inner packaging as described in any one of claims 1 to 6, characterized in that, step include: (1) Weigh and mix each raw material component and dry it; (2) The weighed raw material components are mixed, melted, extruded, granulated, and blown into a film to obtain a modified PAE film for biodegradable food inner packaging.

8. The method for preparing the modified PAE film for biodegradable food inner packaging according to claim 7, characterized in that, The preparation steps of the modified PAE are as follows: Acrylate-modified polylactic acid and N'-methyl-L-histidine methyl ester are dissolved in chloroform, heated to 50-60℃ under inert gas protection, and reacted at this temperature for at least 48h. Then, the mixture is precipitated with diethyl ether at -4-0℃, filtered, and vacuum dried to obtain poly(β-amino ester). Poly(β-amino ester) is mixed with long-chain aliphatic bromoalkane, acetonitrile is added and mixing is continued for 10-20min. Then, the mixture is stirred at 60-65℃ for 23-25h. After the reaction is completed, the acetonitrile is removed by rotary evaporation, washed 2-4 times with ethyl acetate, and then vacuum dried to obtain the modified PAE.

9. The method for preparing the modified PAE film for biodegradable food inner packaging according to claim 8, characterized in that, The preparation method of the acrylamide-modified polylactic acid is as follows: hydroxyl-terminated polylactic acid is dissolved in dichloromethane, then triethylamine and acryloyl chloride are added, the mixture is stirred at room temperature for at least 24 hours, the solvent is removed under reduced pressure, purified, and dried to obtain acrylamide-modified polylactic acid.

10. The method for preparing the modified PAE film for biodegradable food inner packaging according to claim 9, characterized in that, The ratio of the amount of hydroxyl groups in the terminal hydroxyl polylactic acid to the amount of triethylamine and acryloyl chloride is 1:(3~4):(2~3).

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