High water resistance, high drug loading polyvinyl alcohol antibacterial packaging film and preparation method thereof

Abstract

The application discloses a kind of high water resistance, high drug loading polyvinyl alcohol antibacterial packaging film and preparation method thereof, utilize polyvinyl alcohol and bio-based aromatic aldehyde and carry out acetalization reaction, improve the water resistance of polyvinyl alcohol film, and utilize polyvinyl acetal and like eugenol natural plant essential oil strong π-π interaction, prepared with high water resistance and high, high drug loading polyvinyl alcohol antibacterial packaging film.The prepared polyvinyl alcohol packaging film is less than 45% in water swelling rate, the load capacity of eugenol natural plant essential oil is higher than 30 μg·mg ‑1 , especially when all using polyvinyl acetal to prepare polyvinyl alcohol packaging film, the swelling rate of the packaging film in water is only 1.12%, the load capacity of eugenol natural plant essential oil is as high as 39.69 μg·mg ‑1 , antibacterial effect can reach more than 98%, can extend the preservation period of fresh strawberry to 7 days, has potential application value in food packaging field.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer materials technology, specifically relating to a high water resistance, high drug loading polyvinyl alcohol antibacterial packaging film and its preparation method. Background Technology

[0002] As people's living standards improve, new demands are being placed on the quality and variety of food, promoting the inter-regional flow of many products (such as fresh fruit). Antimicrobial packaging can inhibit the growth of microorganisms on the surface of food, thus extending its shelf life. However, traditional plastic packaging brings environmental pressure and potential biological threats. Therefore, developing green and safe antimicrobial packaging is of great significance.

[0003] Currently developed green packaging materials include polybutylene succinate, polylactic acid, starch, cellulose, and chitosan. However, the mechanical properties of these materials are difficult to meet the needs of daily use, and their biocompatibility is also controversial. Polyvinyl alcohol (PVA) has received widespread attention due to its excellent biocompatibility and biodegradability. Simultaneously, PVA also possesses superior film-forming properties and mechanical properties, making PVA films a potential candidate for antibacterial packaging. However, pure PVA films have poor water resistance and lack antibacterial activity, typically requiring modification and loading with antibacterial substances. Chemical cross-linking is generally used to improve water resistance, but this method cannot effectively improve the film's antibacterial properties. Natural plant essential oils, as green and safe antibacterial agents, have limited application due to their low water solubility and volatility. Typically, to enhance the solubility of natural plant essential oils in PVA, additives (such as rare earth elements and Tween 80) are added. However, this method not only reduces the transparency and mechanical properties of the packaging film, but the additives can also migrate to the food surface during use, potentially harming health.

[0004] Therefore, without adding chemical additives, it is possible to simultaneously improve the water resistance and antibacterial substance loading of polyvinyl alcohol films, which has important theoretical and practical application value. Summary of the Invention

[0005] Objective of the Invention: To overcome the shortcomings of existing technologies, this invention provides a high-water-resistance, high-drug-loading polyvinyl alcohol (PVA) antibacterial packaging film and its preparation method. This is achieved by grafting bio-based aromatic aldehydes onto the PVA molecular chain, introducing hydrophobic groups and enhancing intermolecular interactions, thereby improving the water resistance of the PVA film. Bio-based aromatic aldehydes are natural compounds extracted from plants, and their structure is similar to some antibacterial natural plant essential oils such as eugenol. The aromatic aldehyde side groups grafted onto the PVA molecular chain exhibit strong π-π interactions with natural plant essential oils, which can improve the PVA film's loading capacity for plant essential oils, thus obtaining a PVA antibacterial packaging film with both high water resistance and high drug loading capacity.

[0006] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0007] The first objective of this invention is to provide a method for preparing a highly water-resistant polyvinyl alcohol packaging film, comprising the following steps:

[0008] (1) Polyvinyl alcohol and bio-based aromatic aldehyde were dissolved in dimethyl sulfoxide, and the two were mixed evenly to obtain a mixed solution. The mixture was heated and p-toluenesulfonic acid was added. After the reaction, the mixture was precipitated, washed with water and dried to obtain powdered polyvinyl alcohol acetal.

[0009] (2) Polyvinyl acetal or polyvinyl acetal and polyvinyl alcohol are dissolved in dimethyl sulfoxide to form a polymer solution. Natural plant essential oils are added to the polymer solution, mixed evenly, dried, and the solvent evaporated to obtain a polyvinyl alcohol antibacterial packaging film with high water resistance and high drug loading.

[0010] In one embodiment of the present invention, the polyvinyl alcohol is of type 1750, 1788, or 1799, preferably type 1799.

[0011] In one embodiment of the present invention, in the mixture of step (1), the mass fraction of polyvinyl alcohol is 0.01-0.1 g / mL, the mass fraction of bio-based aromatic aldehyde is 0.2-0.9 g / mL, and the molar ratio of polyvinyl alcohol to bio-based aromatic aldehyde is 10:1-1:1, preferably 4:1-1:1, and more preferably 4:1.

[0012] In one embodiment of the present invention, in step (1), the polymer is precipitated with sodium bicarbonate after the reaction.

[0013] In one embodiment of the present invention, the amount of p-toluenesulfonic acid added in step (2) is 0.5 to 2 wt.% of the reactants. It should be noted that the reactants here refer to polyvinyl alcohol and vanillin.

[0014] In one embodiment of the present invention, the reaction temperature in step (2) is 60-90°C and the reaction time is 2-8h. The reaction temperature can be any temperature such as 60°C, 70°C, 80°C, or 90°C, and the reaction time can be any time such as 2h, 3h, 4h, 5h, 6h, 7h, or 8h.

[0015] In one embodiment of the present invention, the polymer solution described in step (2),

[0016] When the polymer solution is a dimethyl sulfoxide solution of polyvinyl acetal, the mass fraction of polyvinyl acetal is 0.01–0.1 g / mL;

[0017] When the polymer solution is a polyvinyl acetal and a polyvinyl alcohol dimethyl sulfoxide solution, the mass fraction of polyvinyl acetal in the polyvinyl acetal and polyvinyl alcohol dimethyl sulfoxide solution is 0.01-0.1 g / mL, and the mass fraction of polyvinyl alcohol is 0.01-0.1 g / mL; the mass ratio of polyvinyl acetal to polyvinyl alcohol is 1:100-100:1.

[0018] In one embodiment of the present invention, the mass ratio of polyvinyl acetal to polyvinyl alcohol is not less than 1:1, and preferably, the mass ratio is not less than 3:1.

[0019] In one embodiment of the present invention, the natural plant essential oil mentioned in step (2) includes at least one of eugenol, thymol, cinnamaldehyde, and artemisinin, preferably eugenol, and its addition amount is 1-15% of the dry weight of the polymer. For example, the density of eugenol is 1.067 g / cm³. 3 Based on the calculation results of m=ρV, its dry weight is 1~15%, and the same applies to other natural plant essential oils.

[0020] A second objective of this invention is to provide a polyvinyl alcohol packaging film prepared according to any of the methods described above.

[0021] In one embodiment of the present invention, the polyvinyl alcohol packaging film has a swelling rate of less than 45% in water and a loading capacity of more than 30 μg·mg for natural plant essential oils, such as eugenol. -1 .

[0022] In one embodiment of the present invention, the polyvinyl alcohol packaging film has a swelling rate of only 1.12% in water and a loading capacity of up to 39.69 μg·mg for natural plant essential oils, represented by eugenol. -1 .

[0023] A third objective of this invention is to provide the application of the aforementioned polyvinyl alcohol packaging film in the field of food preservation.

[0024] In one embodiment of the present invention, the preparation method specifically includes the following steps:

[0025] Beneficial effects: The present invention provides a high water resistance and high drug loading polyvinyl alcohol antibacterial packaging film and its preparation method, which have the following advantages compared with the prior art:

[0026] This invention utilizes the acetalization reaction of polyvinyl alcohol (PVA) with bio-based aromatic aldehydes to improve the water resistance of PVA films. Furthermore, it leverages the strong π-π interactions between PVA acetals and natural plant essential oils such as eugenol to prepare an antibacterial PVA packaging film that exhibits both high water resistance and high drug loading capacity. The prepared PVA packaging film has a swelling rate of less than 45% in water and a loading capacity for natural plant essential oils such as eugenol exceeding 30 μg·mg. -1 In particular, when polyvinyl alcohol packaging films are prepared entirely using polyvinyl acetal, the swelling rate of the film in water is only 1.12%, and the loading capacity for natural plant essential oils, represented by eugenol, is as high as 39.69 μg·mg. -1 It has an antibacterial effect of over 98%, which can extend the shelf life of fresh strawberries to 7 days, and has potential application value in the food packaging field. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the packaging film prepared according to the present invention.

[0028] Figure 2 The image shows the 1H NMR spectrum of polyvinyl vanillin.

[0029] Figure 3 The antibacterial effect of the packaging films prepared in Examples 3 to 6 is shown.

[0030] Figure 4 Example 4 illustrates the preservation effect on fresh strawberries. Detailed Implementation

[0031] Example

[0032] This invention aims to provide a method for preparing a highly water-resistant polyvinyl alcohol packaging film, comprising the following steps:

[0033] (1) Dissolve polyvinyl alcohol and vanillin in dimethyl sulfoxide respectively to obtain dimethyl sulfoxide solutions of polyvinyl alcohol and vanillin, and mix them evenly to obtain a mixed solution;

[0034] (2) Add p-toluenesulfonic acid as a catalyst and increase the temperature to carry out the reaction to synthesize polyvinyl vanillin;

[0035] (3) The synthesized polyvinyl vanillin was precipitated with sodium bicarbonate and repeatedly washed with deionized water, and then freeze-dried to obtain powdered polyvinyl vanillin.

[0036] (4) Weigh out polyvinyl alcohol vanillin powder and dissolve it in dimethyl sulfoxide to prepare a polymer solution; or mix it evenly with a dimethyl sulfoxide solution of polyvinyl alcohol to prepare a polymer solution.

[0037] (5) Add natural plant essential oils such as eugenol to the polymer solution, shake thoroughly to mix evenly, and obtain film-forming solution. Place it in a 50°C oven for a period of time to dry. After the solvent evaporates, a high water-resistant polyvinyl alcohol packaging film can be obtained.

[0038] In one embodiment of the present invention, the polyvinyl alcohol in step (1) is of type 1750, 1788, or 1799, preferably type 1799.

[0039] In one embodiment of the present invention, the mass fraction of polyvinyl alcohol in step (1) is 0.01 to 0.1 g / mL, and the mass fraction of vanillin is 0.2 to 0.9 g / mL.

[0040] In one embodiment of the present invention, the molar ratio of polyvinyl alcohol to vanillin unit in step (1) is 10:1 to 1:1.

[0041] In one embodiment of the present invention, the amount of p-toluenesulfonic acid added in step (2) is 0.5 to 2 wt% of the reactants.

[0042] In one embodiment of the present invention, the reaction temperature in step (2) is 60-90°C and the reaction time is 2-8h.

[0043] In one embodiment of the present invention, the mass fraction of polyvinyl alcohol vanillin in step (4) is 0.01 to 0.1 g / mL, and the mass fraction of polyvinyl alcohol is 0.01 to 0.1 g / mL.

[0044] In one embodiment of the present invention, the mass ratio of polyvinyl alcohol vanillin to polyvinyl alcohol in step (4) is 1:100 to 100:1.

[0045] In one embodiment of the present invention, the natural plant essential oil in step (5) includes at least one of eugenol, thymol, cinnamaldehyde, and artemisinin, preferably eugenol; and its addition amount is 1-15% of the dry weight of the polymer. Eugenol is used as an example in the following examples, and other natural plant essential oils are similarly included within the scope of protection of the present invention.

[0046] The results of the determination of the degree of acetalization of polyvinyl vanillin involved were as follows: An appropriate amount of polyvinyl vanillin powder was weighed and dissolved in deuterated dimethyl sulfoxide, and its nuclear magnetic resonance hydrogen spectrum was measured. The degree of acetalization was calculated through its integrated area ratio.

[0047] Degree of acetalization = A -OCArHO- / 4A -OH

[0048] The results of the mechanical properties test of the packaging film involved: The composite film was cut into dumbbell shape, and the mechanical properties of the composite material were tested using a double-column benchtop testing system. The tensile speed was 50 mm / min, and each sample was tested five times, and the average value was taken.

[0049] The results of the water resistance test of the packaging film involved: the packaging film was cut into 2×2cm pieces. 2 The size and mass of the packaging film are recorded as m0 (mg); then it is soaked in deionized water and fully swollen for 24 hours, after which its weight is recorded as m1 (mg). The swelling rate of the packaging film in water is calculated using the formula:

[0050]

[0051] The results of determining the eugenol loading capacity of the packaging film were as follows: 40 mg of the film was weighed and placed in an ethanol-water solution, followed by thorough sonication. After the eugenol migration was complete, the absorbance at 282 nm was measured using a UV-Vis spectrophotometer, and the concentration was calculated based on the standard curve equation. The eugenol loading capacity of the packaging film was calculated using the following formula:

[0052]

[0053] In the formula, m e m is the mass (μg) of eugenol released into the solvent. m The mass (mg) of the packaging film weighed.

[0054] Results of the antibacterial effect test of the packaging film: The antibacterial activity was tested using the plate coating method. *Escherichia coli* and *Staphylococcus aureus* were incubated in nutrient broth at 37°C for 12 hours to achieve a bacterial concentration of 1×10⁻⁶. 8 CFU / mL. The bacterial culture was then diluted with sterile physiological saline and added to the sample, and incubated in a shaker at a constant temperature for 3 hours. The incubated bacterial culture was then evenly spread onto agar medium and incubated upside down at 37°C for 24 hours.

[0055] The results of the test on the effect of packaging film on strawberry preservation were as follows: After fresh strawberries were packaged, the packaging film was sealed by a hand-press sealing machine, and the strawberries were placed in a natural environment at room temperature (25℃). The condition of the strawberries was recorded using a digital camera. Traditional plastic packaging was used as a control group.

[0056] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the specific material ratios, process conditions, and results described in the embodiments are for illustrative purposes only and should not, and will not, limit the present invention as described in detail in the claims.

[0057] Comparative Example

[0058] Preparation of polyvinyl alcohol packaging film: Using 1 g (22.5 mmol) of polyvinyl alcohol, 20 mL of dimethyl sulfoxide, and 50 μL of eugenol, the method includes the following steps:

[0059] (1) Dissolve 1g of polyvinyl alcohol in 20mL of dimethyl sulfoxide to prepare a polymer solution.

[0060] (2) Add 50 μL of eugenol to the polymer solution, shake it thoroughly to mix it evenly, and dry it in an oven at 50°C to obtain polyvinyl alcohol antibacterial packaging film.

[0061] Example 1

[0062] Preparation of polyvinyl acetal: Using 1 g (22.5 mmol) of polyvinyl alcohol, 3.45 g (22.67 mmol) of vanillin, 15 mL of dimethyl sulfoxide, 0.077 g of p-toluenesulfonic acid, and a saturated sodium bicarbonate solution, the method includes the following steps:

[0063] (1) 1g (22.5mmol) of polyvinyl alcohol was dissolved in 10mL of dimethyl sulfoxide, and 3.45g (22.67mmol) of vanillin was dissolved in 5mL of dimethyl sulfoxide. After mixing the two evenly, the temperature was raised to 60℃, and 0.077g of p-toluenesulfonic acid was added. The reaction was carried out for 2h.

[0064] (2) After the reaction is complete, the polymer is precipitated with saturated sodium bicarbonate solution and repeatedly washed with deionized water. After freeze-drying, powdered polyvinyl alcohol acetal can be obtained.

[0065] Preparation of polyvinyl alcohol packaging film: Using 1g of polyvinyl acetal, 20mL of dimethyl sulfoxide, and 50μL of eugenol, the method includes the following steps:

[0066] (1) Dissolve 1g of polyvinyl acetal in 20mL of dimethyl sulfoxide to prepare a polymer solution.

[0067] (2) Add 50 μL of eugenol to the polymer solution, shake thoroughly to mix evenly, and dry it in an oven at 50°C to obtain a polyvinyl alcohol antibacterial packaging film with high water resistance and high drug loading.

[0068] Example 2

[0069] Preparation of polyvinyl acetal: Using 1 g (22.5 mmol) of polyvinyl alcohol, 1.72 g (11.33 mmol) of vanillin, 15 mL of dimethyl sulfoxide, 0.077 g of p-toluenesulfonic acid, and a saturated sodium bicarbonate solution, the method includes the following steps:

[0070] (1) 1 g (22.5 mmol) of polyvinyl alcohol was dissolved in 10 mL of dimethyl sulfoxide, and 1.72 g (11.33 mmol) of vanillin was dissolved in 5 mL of dimethyl sulfoxide. After mixing the two evenly, the temperature was raised to 60 °C, and 0.077 g of p-toluenesulfonic acid was added. The reaction was carried out for 2 h.

[0071] (2) After the reaction is complete, the polymer is precipitated with saturated sodium bicarbonate solution and repeatedly washed with deionized water. After freeze-drying, powdered polyvinyl alcohol acetal can be obtained.

[0072] Preparation of polyvinyl alcohol packaging film: Using 1g of polyvinyl acetal, 20mL of dimethyl sulfoxide, and 50μL of eugenol, the method includes the following steps:

[0073] (1) Dissolve 1g of polyvinyl acetal in 20mL of dimethyl sulfoxide to prepare a polymer solution.

[0074] (2) Add 50 μL of eugenol to the polymer solution, shake thoroughly to mix evenly, and dry it in an oven at 50°C to obtain a polyvinyl alcohol antibacterial packaging film with high water resistance and high drug loading.

[0075] Example 3

[0076] Preparation of polyvinyl acetal: Using 1 g (22.5 mmol) of polyvinyl alcohol, 0.86 g (5.67 mmol) of vanillin, 15 mL of dimethyl sulfoxide, 0.077 g of p-toluenesulfonic acid, and a saturated sodium bicarbonate solution, the method includes the following steps:

[0077] (1) 1 g (22.5 mmol) of polyvinyl alcohol was dissolved in 10 mL of dimethyl sulfoxide, and 0.86 g (5.67 mmol) of vanillin was dissolved in 5 mL of dimethyl sulfoxide. After mixing the two evenly, the temperature was raised to 60 °C, and 0.077 g of p-toluenesulfonic acid was added. The reaction was carried out for 2 h.

[0078] (2) After the reaction is complete, the polymer is precipitated with saturated sodium bicarbonate solution and repeatedly washed with deionized water. After freeze-drying, powdered polyvinyl alcohol acetal can be obtained.

[0079] Preparation of polyvinyl alcohol packaging film: Using 1g of polyvinyl acetal, 20mL of dimethyl sulfoxide, and 50μL of eugenol, the method includes the following steps:

[0080] (1) Dissolve 1g of polyvinyl acetal in 20mL of dimethyl sulfoxide to prepare a polymer solution.

[0081] (2) Add 50 μL of eugenol to the polymer solution, shake thoroughly to mix evenly, and dry it in an oven at 50°C to obtain a polyvinyl alcohol antibacterial packaging film with high water resistance and high drug loading.

[0082] Example 4

[0083] Preparation of polyvinyl acetal: Using 1 g (22.5 mmol) of polyvinyl alcohol, 0.86 g (5.67 mmol) of vanillin, 15 mL of dimethyl sulfoxide, 0.077 g of p-toluenesulfonic acid, and a saturated sodium bicarbonate solution, the method includes the following steps:

[0084] (1) 1 g (22.5 mmol) of polyvinyl alcohol was dissolved in 20 mL of dimethyl sulfoxide, and 0.86 g (5.67 mmol) of vanillin was dissolved in 5 mL of dimethyl sulfoxide. After mixing the two evenly, the temperature was raised to 60 °C, and 0.077 g of p-toluenesulfonic acid was added. The reaction was carried out for 2 h.

[0085] (2) After the reaction is complete, the polymer is precipitated with saturated sodium bicarbonate solution and repeatedly washed with deionized water. After freeze-drying, powdered polyvinyl alcohol acetal can be obtained.

[0086] Preparation of polyvinyl alcohol packaging film: Using 0.75 g of polyvinyl acetal, 0.25 g of polyvinyl alcohol, 20 mL of dimethyl sulfoxide, and 50 μL of eugenol, the method includes the following steps:

[0087] (1) Dissolve 0.75g of polyvinyl acetal and 0.25g of polyvinyl alcohol in 10mL of dimethyl sulfoxide and mix them thoroughly to prepare a polymer solution.

[0088] (2) Add 50 μL of eugenol to the polymer solution, shake thoroughly to mix evenly, and dry it in an oven at 50°C to obtain a polyvinyl alcohol antibacterial packaging film with high water resistance and high drug loading.

[0089] Example 5

[0090] Preparation of polyvinyl acetal: Using 1 g (22.5 mmol) of polyvinyl alcohol, 0.86 g (5.67 mmol) of vanillin, 15 mL of dimethyl sulfoxide, 0.077 g of p-toluenesulfonic acid, and a saturated sodium bicarbonate solution, the method includes the following steps:

[0091] (1) 1 g (22.5 mmol) of polyvinyl alcohol was dissolved in 20 mL of dimethyl sulfoxide, and 0.86 g (5.67 mmol) of vanillin was dissolved in 5 mL of dimethyl sulfoxide. After mixing the two evenly, the temperature was raised to 60 °C, and 0.077 g of p-toluenesulfonic acid was added. The reaction was carried out for 2 h.

[0092] (2) After the reaction is complete, the polymer is precipitated with saturated sodium bicarbonate solution and repeatedly washed with deionized water. After freeze-drying, powdered polyvinyl alcohol acetal can be obtained.

[0093] Preparation of polyvinyl alcohol packaging film: Using 0.5g polyvinyl acetal, 0.5g polyvinyl alcohol, 20mL dimethyl sulfoxide, and 50μL eugenol, the method includes the following steps:

[0094] (1) Dissolve 0.5g of polyvinyl acetal and 0.5g of polyvinyl alcohol in 10mL of dimethyl sulfoxide and mix them thoroughly to prepare a polymer solution.

[0095] (2) Add 50 μL of eugenol to the polymer solution, shake thoroughly to mix evenly, and dry it in an oven at 50°C to obtain a polyvinyl alcohol antibacterial packaging film with high water resistance and high drug loading.

[0096] Example 6

[0097] Preparation of polyvinyl acetal: Using 1 g (22.5 mmol) of polyvinyl alcohol, 0.86 g (5.67 mmol) of vanillin, 15 mL of dimethyl sulfoxide, 0.077 g of p-toluenesulfonic acid, and a saturated sodium bicarbonate solution, the method includes the following steps:

[0098] (1) 1 g (22.5 mmol) of polyvinyl alcohol was dissolved in 20 mL of dimethyl sulfoxide, and 0.86 g (5.67 mmol) of vanillin was dissolved in 5 mL of dimethyl sulfoxide. After mixing the two evenly, the temperature was raised to 60 °C, and 0.077 g of p-toluenesulfonic acid was added. The reaction was carried out for 2 h.

[0099] (2) After the reaction is complete, the polymer is precipitated with saturated sodium bicarbonate solution and repeatedly washed with deionized water. After freeze-drying, powdered polyvinyl alcohol acetal can be obtained.

[0100] Preparation of polyvinyl alcohol packaging film: Using 0.25 g of polyvinyl acetal, 0.75 g of polyvinyl alcohol, 20 mL of dimethyl sulfoxide, and 50 μL of eugenol, the method includes the following steps:

[0101] (1) Dissolve 0.25g of polyvinyl acetal and 0.75g of polyvinyl alcohol in 10mL of dimethyl sulfoxide and mix them thoroughly to prepare a polymer solution.

[0102] (2) Add 50 μL of eugenol to the polymer solution, shake thoroughly to mix evenly, and dry it in an oven at 50°C to obtain a polyvinyl alcohol antibacterial packaging film with high water resistance and high drug loading.

[0103] Example 7

[0104] Preparation of polyvinyl acetal: Using 1 g (22.5 mmol) of polyvinyl alcohol, 0.86 g (5.67 mmol) of vanillin, 15 mL of dimethyl sulfoxide, 0.077 g of p-toluenesulfonic acid, and a saturated sodium bicarbonate solution, the method includes the following steps:

[0105] (1) 1 g (22.5 mmol) of polyvinyl alcohol was dissolved in 20 mL of dimethyl sulfoxide, and 0.86 g (5.67 mmol) of vanillin was dissolved in 5 mL of dimethyl sulfoxide. After mixing the two evenly, the temperature was raised to 60 °C, and 0.077 g of p-toluenesulfonic acid was added. The reaction was carried out for 2 h.

[0106] (2) After the reaction is complete, the polymer is precipitated with saturated sodium bicarbonate solution and repeatedly washed with deionized water. After freeze-drying, powdered polyvinyl alcohol acetal can be obtained.

[0107] Preparation of polyvinyl alcohol packaging film: Using 0.25 g of polyvinyl acetal, 0.75 g of polyvinyl alcohol, 20 mL of dimethyl sulfoxide, and 50 μL of cinnamaldehyde, the method includes the following steps:

[0108] (1) Dissolve 0.25g of polyvinyl acetal and 0.75g of polyvinyl alcohol in 10mL of dimethyl sulfoxide and mix them thoroughly to prepare a polymer solution.

[0109] (2) Add 50 μL of cinnamaldehyde to the polymer solution, shake thoroughly to mix evenly, and dry in a 50°C oven to obtain a polyvinyl alcohol antibacterial packaging film with high water resistance and high drug loading. The above examples are only to illustrate the inventor's inventive concept. Any variations and improvements based on the inventive concept of this invention are within the scope of protection of this invention.

[0110] Test case

[0111] (1) The water resistance of the packaging film and its load-bearing capacity for plant essential oils.

[0112] The degree of acetalization of polyvinyl alcohol (PVA) acetal affects the water resistance and loading capacity of the membrane for plant essential oils. Therefore, the degree of acetalization was first investigated when the molar ratio of PVA to vanillin was 4:1 to 1:1. The membrane was then prepared by mixing PVA with eugenol. The test results showed that when the ratio was 4:1, the degree of acetalization of PVA acetal was 57%, the swelling ratio of the membrane in water was only 1.12%, and the loading capacity for eugenol was 39.69 μg·mg. -1 A lower degree of acetalization results in a higher eugenol loading capacity, possibly because a higher degree of acetalization leads to stronger intermolecular interactions and greater steric hindrance, confining eugenol primarily to the molecular surface. Conversely, a lower degree of acetalization results in weaker intermolecular interactions, allowing eugenol to aggregate between molecular chains, thus increasing the loading capacity. Therefore, a polyvinyl alcohol acetalization degree of 57% was chosen for subsequent performance testing in packaging film preparation.

[0113] The dosage of polyvinyl alcohol acetal was then investigated, exploring the antibacterial properties and preservation effect on fresh fruit when the mass ratio of polyvinyl alcohol to polyvinyl alcohol acetal was 75:25, 50:50, 25:75, and 0:100. The results showed that when the ratio of polyvinyl alcohol to polyvinyl alcohol acetal was 25:75, the film achieved an antibacterial effect of over 98% against both *Escherichia coli* and *Staphylococcus aureus*, extending the shelf life of fresh strawberries to 7 days.

[0114] Table 1 shows the degree of acetalization of polyvinyl alcohol acetal in Examples 1-6, as well as the corresponding membrane's loading capacity for plant essential oils and water resistance.

[0115]

[0116] (2) Mechanical properties of packaging film

[0117] The content of polyvinyl acetal affects the mechanical properties of the packaging film. As the content of polyvinyl acetal decreases, the tensile strength of the packaging film first decreases and then increases. When the ratio of polyvinyl alcohol to polyvinyl acetal is 25:75, the tensile strength is 33.59 MPa. At this point, the packaging film still has good flexibility, and its elongation at break is 220.67%.

[0118] Table 2 Mechanical properties of packaging films in Examples 3-6

[0119]

[0120] (3) The antibacterial effect and packaging effect of the packaging film

[0121] Figure 3 The antibacterial effect of the packaging films prepared in Examples 3 to 6 is shown in the figure. As can be seen from the figure, the antibacterial effect of the packaging film increases with the increase of eugenol content. In Example 4, the packaging film was loaded with 38 μg / mg of eugenol, and its antibacterial effect was as high as 98% or more, which has good antibacterial properties.

[0122] Figure 4 As shown in the figure, the packaging film prepared by the present invention can extend the shelf life of fresh strawberries to 7 days and still keep them fresh and edible.

[0123] In summary, the method for preparing the high water resistance and high drug loading capacity polyvinyl alcohol antibacterial packaging film of the present invention is simple, and the raw materials are green, safe, and widely available. The polyvinyl alcohol packaging film prepared by the present invention has a swelling rate of less than 45% in water and a loading capacity of eugenol exceeding 30 μg·mg. -1 In particular, when polyvinyl alcohol packaging films are prepared entirely using polyvinyl acetal, the resulting packaging films exhibit a swelling rate of only 1.12% in water, and their eugenol loading capacity can reach as high as 39.69 μg·mg.-1 The antibacterial effect against Escherichia coli and Staphylococcus aureus can reach over 98%, extending the shelf life of fresh strawberries by 7 days. Therefore, the high water resistance and high drug loading polyvinyl alcohol antibacterial packaging film prepared by this invention has potential application value in the field of food preservation.

[0124] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a polyvinyl alcohol antibacterial packaging film with high water resistance and high drug loading capacity, characterized in that, The method includes the following steps: (1) Polyvinyl alcohol and bio-based aromatic aldehyde are dissolved in dimethyl sulfoxide, and the two are mixed evenly to obtain a mixed solution. The solution is heated to 60~90℃, p-toluenesulfonic acid is added, and after reaction, after precipitation, washing with water and drying, powdered polyvinyl alcohol acetal is obtained; the molecular structure of the bio-based aromatic aldehyde contains an aromatic ring and is selected from one of vanillin, isovanillin, ortho-vanillin, ethylvanillin, cinnamaldehyde, salicylaldehyde and benzaldehyde. (2) Polyvinyl acetal, or polyvinyl acetal and polyvinyl alcohol, dissolved in dimethyl sulfoxide to form a polymer solution, natural plant essential oil is added to the polymer solution, mixed evenly, dried, and the solvent evaporated to obtain a polyvinyl alcohol antibacterial packaging film with high water resistance and high drug loading; the molecular structure of the natural plant essential oil contains an aromatic ring, including at least one of eugenol, thymol, cinnamaldehyde, and artemisinin; The prepared polyvinyl alcohol antibacterial packaging film has a swelling rate of less than 45% in water and a loading capacity of more than 30 μg·mg for natural plant essential oils. -1 .

2. The method according to claim 1, characterized in that, The polyvinyl alcohol is of type 1750, 1788, or 1799.

3. The method according to claim 2, characterized in that, The polyvinyl alcohol in question is of type 1799.

4. The method according to claim 1, characterized in that, The bio-based aromatic aldehyde in step (1) is vanillin.

5. The method according to claim 1, characterized in that, In the mixture of step (1), the mass fraction of polyvinyl alcohol is 0.01~0.1 g / mL, the mass fraction of bio-based aromatic aldehyde is 0.2~0.9 g / mL, and the molar ratio of polyvinyl alcohol to bio-based aromatic aldehyde is 10:1~1:

1.

6. The method according to claim 5, characterized in that, In step (1), the molar ratio of polyvinyl alcohol to bio-based aromatic aldehyde unit is 4:1 to 1:

1.

7. The method according to claim 6, characterized in that, In step (1), the molar ratio of polyvinyl alcohol to bio-based aromatic aldehyde unit is 4:

1.

8. The method according to claim 1, characterized in that, The amount of p-toluenesulfonic acid added in step (1) is 0.5~2 wt.% of the reactants.

9. The method according to claim 1, characterized in that, The heating mentioned in step (1) refers to heating to the reaction temperature of 60~90℃ and the reaction time is 2~8 h.

10. The method according to claim 1, characterized in that, The polymer solution described in step (2), When the polymer solution is a dimethyl sulfoxide solution of polyvinyl acetal, the mass fraction of polyvinyl acetal is 0.01~0.1 g / mL; When the polymer solution is a polyvinyl acetal and a polyvinyl alcohol dimethyl sulfoxide solution, the mass fraction of polyvinyl acetal in the polyvinyl acetal and polyvinyl alcohol dimethyl sulfoxide solution is 0.01~0.1 g / mL, and the mass fraction of polyvinyl alcohol is 0.01~0.1 g / mL; the mass ratio of polyvinyl acetal to polyvinyl alcohol is 1:100~100:

1.

11. The method according to claim 10, characterized in that, The mass ratio of polyvinyl acetal to polyvinyl alcohol is not less than 1:

1.

12. The method according to claim 11, characterized in that, The mass ratio of polyvinyl acetal to polyvinyl alcohol is not less than 3:

1.

13. The method according to claim 1, characterized in that, The natural plant essential oil mentioned in step (2) is eugenol; and its addition amount is 1 to 15% of the dry weight of the polymer.

14. The method according to claim 1, characterized in that, The polyvinyl alcohol packaging film exhibits a swelling rate of 1.12% in water and a loading capacity of up to 39.69 μg·mg for natural plant essential oils, primarily eugenol. -1 .

15. A polyvinyl alcohol packaging film, prepared according to any one of claims 1-14.

16. The application of the polyvinyl alcohol packaging film according to claim 15 in the field of food preservation.

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