CN114805876B

CN114805876B - Preparation method of unidirectional water-blocking self-cleaning chitosan zein bilayer membrane

Info

Publication number: CN114805876B
Application number: CN202210524752.2A
Authority: CN
Inventors: 余达威; 张利铭; 董俊丽; 夏文水; 姜启兴; 许艳顺
Original assignee: Jiangnan University
Current assignee: Jiangnan University
Priority date: 2022-05-13
Filing date: 2022-05-13
Publication date: 2023-09-01
Anticipated expiration: 2042-05-13
Also published as: CN114805876A

Abstract

The application discloses a preparation method of a unidirectional water-blocking self-cleaning chitosan zein bilayer membrane, which comprises the steps of firstly dissolving chitosan in acetic acid to prepare chitosan solution, then adding nano particles which are used for embedding curcumin and nisin and plasticizer glycerol under a certain temperature condition, stirring and carrying out ultrasonic degassing to obtain active layer coating liquid; pouring the active layer coating liquid into a leveling mold to form gel at a certain temperature; dissolving zein in ethanol to obtain zein solution, adding glycerol as plasticizer, stirring, and ultrasonically degassing to obtain dampproof and self-cleaning coating film liquid; and finally, uniformly spreading the coating liquid of the dampproof and self-cleaning layers on the surface of the gel, and drying at a certain temperature to form a double-layer film. According to the application, zein is creatively used as a moisture-proof and self-cleaning layer, and nano particles with excellent antioxidant and antibacterial activities are added into a lower substrate of a double-layer film to be used as an active layer, so that the bioactivity and the service life of the chitosan film are effectively improved.

Description

Preparation method of unidirectional water-blocking self-cleaning chitosan zein bilayer membrane

Technical Field

The application belongs to the technical field of green packaging of foods, and particularly relates to a preparation method of a unidirectional water-blocking self-cleaning chitosan zein bilayer membrane.

Background

Petroleum-based synthetic polymers are widely used as packaging materials. However, the use of synthetic petroleum-based products poses health and environmental problems, and suitable alternatives are being sought. Biodegradable natural polymers are being widely studied. Among the different biodegradable polymers, chitosan stands out for its excellent film-forming properties and unique physicochemical properties (e.g. strong barrier ability and mechanical properties). However, pure chitosan films are difficult to resist the penetration of moisture from the external environment, stain is easily stained during application, favorable conditions are provided for the growth of microorganisms, and the functional properties of the chitosan films are low.

Therefore, it has been common to design and prepare chitosan films that both absorb excess moisture from the food itself and prevent the penetration of external environmental moisture into and carry away stains from the surface of the package.

At present, how to provide a technology for improving the applicability, the air-blocking performance and the heat sealing performance of a chitosan film is a technical problem to be solved urgently by those skilled in the art.

Disclosure of Invention

This section is intended to outline some aspects of embodiments of the application and to briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section as well as in the description of the application and in the title of the application, which may not be used to limit the scope of the application.

The present application has been made in view of the above and/or problems occurring in the prior art.

Therefore, the application aims to overcome the defects in the prior art and provide a preparation method of a unidirectional water-blocking self-cleaning chitosan zein bilayer membrane.

In order to solve the technical problems, the application provides the following technical scheme: a method for preparing a unidirectional water-blocking self-cleaning chitosan zein bilayer membrane, which comprises the following steps of,

respectively dissolving pectin, nisin and curcumin in pure water, acetic acid solution with pH of 4.0 and absolute ethyl alcohol to obtain pectin solution, nisin solution and curcumin solution;

then dropwise adding the nisin solution into the pectin solution, and stirring to obtain a compound solution;

then adding curcumin solution into the composite solution drop by drop to prepare a mixed solution system, stirring, and centrifuging and freeze-drying to obtain nano particles;

dissolving chitosan in acetic acid to prepare chitosan solution, adding nano particles and plasticizer into the chitosan solution, stirring, and performing ultrasonic degassing to obtain active layer coating liquid;

pouring the prepared active layer coating liquid into a leveling mold to form gel;

dissolving zein in ethanol, adding a plasticizer into the zein solution, stirring, and performing ultrasonic degassing to obtain a dampproof and self-cleaning layer coating liquid;

and uniformly spreading the prepared coating liquid on the surface of gel, cooling at room temperature to form double-layer hydrogel, and drying to form a double-layer film.

As a preferable scheme of the preparation method of the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane, the application comprises the following steps: in the mixed solution system, the concentration of pectin, nisin and curcumin solution is respectively 1-3 mg/mL, 3-6 mg/mL and 3-6 mg/mL.

As a preferable scheme of the preparation method of the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane, the application comprises the following steps: the active layer coating liquid comprises 2-4% of chitosan, 1-3% of nano particles and 25-40% of plasticizer.

As a preferable scheme of the preparation method of the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane, the application comprises the following steps: the plasticizer comprises glycerol.

As a preferable scheme of the preparation method of the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane, the application comprises the following steps: the mass fraction of the nano particles is 2%.

As a preferable scheme of the preparation method of the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane, the application comprises the following steps: pouring the prepared active layer coating liquid into a leveling mold to form gel, wherein the gel forming temperature is 25-50 ℃.

As a preferable scheme of the preparation method of the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane, the application comprises the following steps: the ultrasonic degassing time is 10-20 minutes.

As a preferable scheme of the preparation method of the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane, the application comprises the following steps: and forming a double-layer film after drying, wherein the drying temperature is 40-50 ℃ and the drying time is 10-15 hours.

The application further aims to overcome the defects in the prior art and provide a double-layer film prepared by the preparation method of the unidirectional water-blocking self-cleaning chitosan zein double-layer film.

It is another object of the present application to overcome the deficiencies of the prior art and to provide the use of the bilayer film as a food packaging film.

The application has the beneficial effects that:

(1) According to the application, through the design of the double-layer film, hydrophobic zein is creatively added into the outer layer to serve as a dampproof and self-cleaning layer, nano particles with excellent antioxidant and antibacterial activities are added into the lower substrate of the double-layer film to serve as an active and hydration layer, and the application performance of the film is obviously improved; the mechanical property of the film is obviously improved by adding the nano particles, and the addition amount of the nano particles is preferably 2%, so that the mechanical property is optimal; films incorporating nanoparticles can significantly improve moisture barrier capability, higher opacity, as the nanoparticles can scatter transmitted light by occupying gaps in the polymer matrix, better protecting the food product.

(2) According to the application, the zein with excellent dampproof and self-cleaning capabilities is added to the upper layer of the double-layer film, so that the moisture blocking capability of the double-layer film is obviously improved, the service life of the chitosan film can be prolonged, and the double-layer film is natural and pollution-free, and can be widely applied to the fresh keeping of fruits, vegetables, meat and other foods.

(3) The application has simple operation, easy control and strong operability, and is suitable for industrial production.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art. Wherein:

FIG. 1 is a graph showing the mechanical properties of a bilayer membrane of a comparative example and each example in accordance with the present application;

FIG. 2 is a graph showing the moisture barrier of a bilayer film according to the comparative example and each example of the present application;

FIG. 3 is a graph showing the antioxidant activity of the bilayer films of the comparative examples and the examples of the present application;

FIG. 4 is a graph showing the bacteriostatic activity of the bilayer membrane according to the comparative example and each example in the present application;

FIG. 5 is a graph showing nisin and pectin levels versus nanoparticle encapsulation efficiency for comparative example 2 of the present application;

FIG. 6 is a graph showing nisin and pectin levels versus nanoparticle PDI for comparative example 2 of the present application;

FIG. 7 is a scanning electron microscope image of the nanoparticle of comparative example 2 in the present application.

Detailed Description

In order that the above-recited objects, features and advantages of the present application will become more apparent, a more particular description of the application will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application, but the present application may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present application is not limited to the specific embodiments disclosed below.

Further, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic can be included in at least one implementation of the application. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. The molecular weight of the chitosan is 500kDa, the deacetylation degree is 92%, and other raw materials are all common commercial products.

The key properties of the bilayer films referred to in the above examples and comparative examples were determined:

1. mechanical properties

Elongation at break and tensile strength were measured using a TA texture tester following ASTM standard (D882-02). The Tensile Strength (TS) and Elongation (EB) were measured after cutting the film samples into rectangular samples 10mm wide and 70mm long.

2. Permeability to water vapor

3g of anhydrous CaCl was weighed ₂ Covering the mouth of the weighing bottle with a composite film, weighing again and recording m ₀ Placing into a constant temperature and humidity box, maintaining 90% relative humidity at 23deg.C, weighing again after 24 hr, and recording m ₁ The water vapor permeability was calculated from the front-to-back mass change. The water vapor permeability is calculated according to the following formula:

WVP＝(Δm×d)/(A×t×P)

wherein Deltam (kg) -the difference in mass of the weighing bottle, d (mm) -the thickness of the film; t(s) -time; a (m) ² ) -an effective area of the membrane; p (KPa) -pressure difference between water vapor and vapor inside and outside the membrane.

3. Moisture content, water solubility, swelling degree and Water contact Angle

Weigh 2X 2cm of film (W) ₀ ) After drying at 105℃for 24 hours, weighing (W ₁ ). Then, the dried film was immersed in 50mL of distilled water for 24 hours, and the surface water was removed with a water absorbing paper, and then the weight (W) ₂ ) Oven-drying at 105deg.C to constant weight (W) ₃ ). The moisture content, water solubility and swelling value of the film are determined by the following formula:

the water contact angle of the films was tested using a contact angle analyzer (OCA 15EC, datphysicalinstruments GmbH, filderstadt, germany). A droplet of 2. Mu.L of distilled water was applied to the surface of the film by a micro-syringe, and the WCA was measured after 0 and 60 seconds.

4. Color and opacity

The color of the film was measured by a color difference meter (SC-80C, beijing, china). The L (brightness), a (red-gray) and b (yellow-blue) parameters are determined by reflectance measurements. Opacity was measured with an ultraviolet spectrophotometer. The dimensions of the film were 10mm by 40mm. A void Dan Yingmin is used as a reference. Opacity was calculated as follows:

wherein A is ₆₀₀ The absorbance, d (mm), is the film thickness.

5. Measurement of antioxidant Activity of Membrane

The double-layer film was cut into squares of 2cm×2cm, placed in a sample bottle containing 10mL of distilled water, placed on a magnetic stirrer at room temperature and stirred for 30 minutes, 1mL of the sample was taken and added into 4mL of DPPH solution (150 μmol/L) to be mixed with shaking. The reaction was allowed to stand in the dark for 30 minutes to allow radical scavenging to take place sufficiently, and the absorbance was measured at 517nm using a visible spectrophotometer (VIS-7220N, rayleigh analytical instruments).

Will contain 2.4mM K ₂ S ₂ O ₈ And ABTS of 7.0mM ASTS ⁺ The free radical stock solution was incubated in the dark for 12-16 hours. Dilution of ABTS with 5mM phosphate buffer (pH 7.4) ⁺ Free radical stock solution, causing its absorption at 730nmThe luminosity is 0.70+ -0.02. The film samples were immersed in 5ml of phosphate buffer. Mu.l of sample solution was combined with 2mL of ABTS ⁺ The solutions were mixed as samples. A mixture of 2mL of phosphate buffered saline and 200. Mu.L of sample solution was used as a control, and a mixture of 200. Mu.L of distilled water and 2mL of ABTS working solution was used as a blank. The mixture was incubated in the dark for 20 minutes. Absorbance was measured at 730nm using an ultraviolet-visible spectrophotometer.

6. Determination of antimicrobial Activity of films

The antibacterial activity of the bilayer membrane against staphylococcus aureus and escherichia coli was determined using an agar plate assay. After all films were sterilized under ultraviolet irradiation for 20 minutes, they were cut into 2 cm. Times.2 cm pieces and placed in 6-well plates. Then 500. Mu.L of sterilized LB medium was added to each well, followed by 100. Mu.L of bacterial suspension (. About.10) ⁷ CFU·mL ^-1 ) The culture was performed under white light irradiation and darkness at 37℃for 24 hours with gentle shaking. Samples were removed after incubation for 3, 6, 9, 12 and 15 hours, diluted and plated on agar plates to determine the number of viable cells.

The preparation method of the nano-particles comprises the following steps:

respectively dissolving pectin, nisin and curcumin in pure water, acetic acid solution with pH of 4.0 and absolute ethyl alcohol to respectively prepare pectin solution (1 mg/mL), nisin solution (3 mg/mL) and curcumin solution (3 mg/mL);

and then dropwise adding the curcumin solution into the composite solution to prepare a mixed solution system, wherein the concentrations of pectin, nisin and curcumin solution in the mixed solution system are respectively 1mg/mL, 6mg/mL and 4mg/mL, stirring, and centrifuging and freeze-drying to obtain the nano particles.

Example 1

(1) Dissolving chitosan in 1% (v/v) acetic acid solution to prepare a solution with the mass concentration of 2g/100mL, adding nano particles with the mass percent of 1% and 25% of glycerol based on the mass percent of the chitosan into the chitosan solution at 55 ℃, stirring for 1 hour, and then performing ultrasonic degassing for 15 minutes to obtain a chitosan-nano particle active layer coating solution;

(2) Pouring the active layer coating liquid prepared in the first step into a leveling mold to form gel at 40 ℃;

(3) Dissolving zein in 90% (v/v) ethanol solution to prepare a solution with the mass concentration of 10g/100mL, adding 25% of glycerol based on the mass of zein into the zein solution, stirring for 2 hours, and performing ultrasonic degassing for 20 minutes to obtain zein dampproof and self-cleaning layer coating liquid.

(4) And pouring the zein dampproof and self-cleaning layer coating liquid prepared in the third step onto the chitosan-nanoparticle gel formed in the second step, and then drying in an oven at 40 ℃ for 12 hours to form a double-layer film.

Example 2

(1) Dissolving chitosan in 1% (v/v) acetic acid solution to prepare a solution with the mass concentration of 2g/100mL, adding nano particles with the mass of 2% based on the chitosan and 25% of glycerol into the chitosan solution at 55 ℃, stirring for 1 hour, and then performing ultrasonic degassing for 15 minutes to obtain a chitosan-nano particle active layer coating solution;

Example 3

(1) Dissolving chitosan in 1% (v/v) acetic acid solution to prepare a solution with the mass concentration of 2g/100mL, adding nano particles with the mass percent of 3% and 25% of glycerol based on the mass percent of chitosan into the chitosan solution at 55 ℃, stirring for 1 hour, and then performing ultrasonic degassing for 15 minutes to obtain a chitosan-nano particle active layer coating solution;

Comparative example 1

In comparison with examples 1, 2, 3, the difference is that no nanoparticles are added, the procedure is as follows:

(1) Dissolving chitosan in 1% (v/v) acetic acid solution to prepare a solution with the mass concentration of 2g/100mL, adding glycerol accounting for 25% of the mass of the chitosan into the chitosan solution at 55 ℃, stirring for 1 hour, and then performing ultrasonic degassing for 15 minutes to obtain a chitosan layer coating solution;

(4) And pouring the zein dampproof and self-cleaning layer coating liquid prepared in the third step onto the chitosan gel formed in the second step, and then drying the chitosan gel in an oven at 40 ℃ for 12 hours to form a double-layer film.

The performance of the double-layered films provided in comparative example 1 and examples 1 to 3 of the present application is tested as shown in fig. 1, a is a comparison of tensile strength and elongation of the comparative example and the examples, and B is a comparison of mechanical properties with the existing polymer films.

As can be seen from fig. 1, the tensile strength and elongation of the example bilayer film were higher than those of the control bilayer film, indicating that the addition of nanoparticles significantly improved the mechanical properties of the film, with the tensile strength and elongation of example 2 being the highest. And the tensile strength value of the nanoparticle-added double-layer film is comparable to that of a typical packaging plastic such as low density polyethylene (LDPE, 45.2-58.6 MPa), but slightly lower than Polystyrene (PS) (45-63 MPa), showing high potential as a packaging material.

Comparative examples and examples: (A) moisture content, (B) water solubility, (C) swelling degree, (D) water vapor permeability, (E) water contact angle on C side (chitosan side), and (F) water contact angle on Z side (zein side), see FIG. 2.

As can be seen from fig. 2, the film incorporating the nanoparticles can significantly improve the moisture blocking ability of the control, and the reason for this phenomenon is that the nanoparticles occupy the hydroxyl groups of the chitosan molecules and block the binding of water molecules due to the interaction of the nanoparticles with the chitosan matrix through hydrogen bonds. The water vapor transmission rate was also measured on both sides of the double-layered film, and it was found that the double-layered film had different water vapor transmission rates on both sides, which is consistent with the double-layered film having unidirectional water blocking properties as referred to in the present application.

With the addition of the nanoparticles, the chitosan-side water contact angle value slightly increased, possibly due to interactions between chitosan and the nanoparticles. And after 60s of water drop deposition, the water contact angle value of the chitosan layer is obviously reduced, and the water contact angle value of the zein layer is not greatly changed, which indicates that the hydrophobic group of the zein blocks the penetration of water, and the hydrophilicity of the chitosan accelerates the penetration of water.

Table 1 comparative and examples bilayer film color values and opacity

As can be seen from Table 1, all of the bilayer films had smooth and uniform surfaces. After addition of nanoparticles, Δe of the bilayer membrane increased, mainly due to the decrease in L, the increase in a and b. Notably, the value of b shows a larger variation and, depending on the concentration effect of the nanoparticles, a lighter yellow color, since the nanoparticles appear yellowish.

In terms of opacity, the opacity of all films was between 1.03 and 1.29, similar to the opacity value (1.67) of commercial films used for packaging. The increase in the mass ratio of the nanoparticles results in higher opacity, since the nanoparticles can scatter transmitted light by occupying the gaps in the polymer matrix, indicating that the presence of the nanoparticles better protects the food product.

The antioxidant activity of the bilayer films of the control and examples is shown in FIG. 3. It can be seen that the DPPH radical activity of the control example was significantly improved after the nanoparticles were added, because curcumin had a strong antioxidant activity. This suggests that nano-encapsulated curcumin is an effective way to maintain its structural integrity and antioxidant activity. Similar to DPPH assay, ABTS radical scavenging activity was significantly improved after addition of nanoparticles, due to the good scavenging effect of nanoparticles on OH radicals. The nanocomposite film has high antioxidant activity, and can be used for active packaging application to prevent oxidation of food, maintain food quality and prolong shelf life of food.

The bacteriostatic activity of the bilayer membranes of the control and examples is shown in figure 4.

Curcumin can efficiently generate Reactive Oxygen Species (ROS) under white light, thereby exhibiting enhanced antibacterial effects. The film is used as a packaging material and is easily affected by light in the use process. In light of this, the antimicrobial properties of the films under light and dark conditions were analyzed (fig. 4). Under the illumination condition, all the nano composite films show effective killing effect on bacteria, and the inhibition effect is enhanced along with the extension of the illumination time. This is probably due to the fact that curcumin generates active oxygen during illumination, which may cause oxidative stress, and destroy the integrity of bacterial films, thereby enhancing antibacterial action. In addition, the inhibition of gram-positive staphylococcus aureus by the film containing the nano-particles is stronger than that of gram-negative escherichia coli mainly because nisin has stronger inhibition on gram-positive bacteria, which indicates that nisin not only mediates the interaction of curcumin and pectin, but also has good antibacterial capability. Therefore, the nanoparticle film developed by the research has the application potential of prolonging the shelf life of packaged foods.

Comparative example 2

The testing method comprises the following steps: a suitable amount of sample was taken and the particle size and dispersibility (PDI) of the nanoparticles were determined using dynamic light scattering techniques. The sample was equilibrated at 25℃for 1 minute before measurement, the detection angle was 173℃and the refractive index of the protein was set to 1.45, the refractive index of water was set to 1.33, and the measurement time was 180 seconds. All sample assays were repeated three times.

Determination of Encapsulation Efficiency (EE): centrifuging the nanoparticle suspension to obtain free curcumin, and measuring at 426nm with an ultraviolet wind-light photometer; the free nisin was assayed by a micro-protein kit.

Scanning Electron Microscope (SEM) method of measurement: nanoparticle suspensions were dropped onto silicon wafers and after gold was sprayed with a vacuum sputter coater (108Auto,TedPella Inc, redding, CA, USA), photographed at an accelerating voltage of 10 kv using a scanning electron microscope (S-4800, hitachi, tokyo, japan).

Based on the preparation of the nano-particles, the influence of pectin content on the nano-particles is explored.

Analysis: see fig. 5, where the particle size of the nanoparticles gradually decreases with increasing pectin content, where nisin: pectin=1: the particle size is smallest at 6 (mass ratio), since when the amount of pectin added is small, there is insufficient pectin to bind to nisin, resulting in complete exposure of the hydrophobic region of nisin, so that the hydrophobic interaction of nisin with curcumin is weak, the nanoparticle size is large, whereas when the proportion of pectin is increased, a large amount of pectin can thoroughly bind to the hydrophilic region of nisin, so that the hydrophobic region of nisin is fully exposed, the hydrophobic effects of nisin and curcumin become stronger, so that the size of the synthetic nanoparticle is very small.

See fig. 6, when the ratio increases to 1:6, too much pectin will adhere to the nisin surface, increasing the particle size of the nanocomposite. PDI also showed the same trend, and in general, PDI <0.3 was considered stable for the system, nisin: pectin=1: 6, the lowest PDI and highest encapsulation efficiency, so that the optimal design of the nanoparticle can be obtained by optimization experiments as pectin: nisin = 1:6. referring to fig. 7, it can be seen in the scanning electron microscope that the nanoparticles exhibit a uniform spherical shape and the surface is smooth without cracks, so that the nanoparticles are considered to be successfully prepared.

It can be seen from the above that: compared with a chitosan/zein double-layer film prepared without nano particles, the double-layer film prepared with nano particles has better mechanical property, moisture resistance, oxidation resistance and bacteriostasis, and has stronger applicability.

The layer-by-layer self-assembly solution casting technology of the application can control the thickness of the film by utilizing the sequential adsorption principle of materials with opposite charges on a matrix, and is an ideal method for preparing the double-layer film. In addition, such a bilayer film substrate may be further formed into an active packaging material by combining an antibacterial agent and an antioxidant.

According to the application, a layer-by-layer self-assembly casting method is utilized, a chitosan film containing nanoparticles of the embedded curcumin and nisin is taken as a hydration active inner layer, and a zein film is taken as a dampproof and self-cleaning outer layer, so that an attempt is made to prepare the preservative film with excellent physicochemical properties. The method is mainly used for packaging and preserving foods with high moisture content, and effectively prolongs the shelf life of the foods. The method does not introduce exogenous reagent, and the preparation process has the characteristics of green, safety and convenience, and the technology can provide a reliable strategy for improving the applicability of the chitosan film.

It should be noted that the above embodiments are only for illustrating the technical solution of the present application and not for limiting the same, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present application may be modified or substituted without departing from the spirit and scope of the technical solution of the present application, which is intended to be covered in the scope of the claims of the present application.

Claims

1. A preparation method of a unidirectional water-blocking self-cleaning chitosan zein bilayer membrane is characterized by comprising the following steps of: comprising the steps of (a) a step of,

then adding curcumin solution dropwise into the composite solution to prepare a mixed solution system, stirring, and centrifuging and freeze-drying to obtain nano particles, wherein the concentration of pectin, nisin and curcumin solution in the mixed solution system is respectively 1-3 mg/mL, 3-6 mg/mL and 3-6 mg/mL;

dissolving chitosan in acetic acid to prepare chitosan solution, adding nano particles and plasticizer into the chitosan solution, stirring, and performing ultrasonic degassing to obtain active layer coating liquid; wherein the mass fraction of chitosan in the active layer coating liquid is 2-4%, the mass fraction of nano particles is 1-3%, the mass fraction of plasticizer is 25-40%, and the plasticizer comprises glycerin;

dissolving zein in ethanol, adding a plasticizer into the zein solution, stirring, and performing ultrasonic degassing to obtain a dampproof and self-cleaning layer coating liquid, wherein the plasticizer comprises glycerol;

2. The method for preparing the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane according to claim 1, which is characterized in that: the mass fraction of the nano particles is 2%.

3. The method for preparing the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane according to claim 1, which is characterized in that: pouring the prepared active layer coating liquid into a leveling mold to form gel, wherein the gel forming temperature is 25-50 ℃.

4. The method for preparing the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane according to claim 1, which is characterized in that: the ultrasonic degassing time is 10-20 minutes.

5. The method for preparing the unidirectional water-blocking self-cleaning chitosan zein bilayer membrane according to claim 1, which is characterized in that: and forming a double-layer film after drying, wherein the drying temperature is 40-50 ℃ and the drying time is 10-15 hours.

6. The unidirectional water-blocking self-cleaning chitosan zein bilayer membrane prepared by the preparation method of any one of claims 1 to 5.

7. Use of the bilayer film according to claim 6 as a food packaging film.