CN117802696A - Zein nanofiber membrane and preparation method thereof - Google Patents

Abstract

The invention provides a zein nanofiber membrane and a preparation method thereof. The zein and the solvent are mixed uniformly to obtain a zein solution; the cationic surfactant and the zein solution are uniformly mixed to obtain a spinning solution; the spinning solution is obtained. The silk solution was electrospun to obtain zein nanofiber membrane. The zein nanofiber membrane of the present invention adds surfactant, and successfully obtains fibers with improved uniformity and smaller diameter. The addition of cationic surfactant significantly improves the mechanical properties, tensile strength, and fracture of the nanofiber membrane. The elongation and Young's modulus both increase, and at the same time, the water stability and hydrophilicity of the nanofiber membrane are significantly improved. The zein nanofiber membrane prepared by the present invention has wide applications in the field of food packaging. prospect.

Description

A zein nanofiber membrane and preparation method thereof

Technical Field

The invention belongs to the technical field of biomacromolecule materials, and in particular relates to a zein nanofiber membrane and a preparation method thereof.

Background technique

Electrospinning is a simple, economical, continuous, repeatable and scalable nonwoven fiber production technology. Fiber diameter is one of the most important structural characteristics of nanofiber materials. It affects the specific surface area, strength and other characteristics of nanofibers, and is an important indicator affecting the physical properties of nanofiber membranes. The preparation of nanofiber membranes with smaller diameters and better performance is a common pursuit of researchers. Existing studies have shown that the diameter and performance of electrospun fibers can be adjusted and optimized by changing electrospinning process parameters (such as applied electric field, spinning distance, flow rate) and solution properties (such as raw material concentration, conductivity, viscosity, surface tension). Among them, raw material concentration is an important factor affecting solution properties, and reducing polymer concentration usually leads to a decrease in fiber diameter. However, according to existing reports, due to the continuous dilution of the raw material solution, the stability of the Taylor cone is lost, resulting in the generation of nanoparticles by electrospray, so bio-based electrospun fibers with a fiber diameter of less than 200 nm are still difficult to obtain.

CN111850731A discloses a gliadin-based core-shell fiber membrane, food storage and preservation materials and a preparation method. After mixing a polyethylene oxide solution and a zein solution, coaxial electrospinning is performed to obtain a gliadin-based core-shell fiber membrane. , the diameter of the fiber prepared is 300nm, and the tensile strength is 20.0-25.0MPa, which cannot meet the needs of daily use.

CN113089185A discloses a conductive nanofiber membrane with bactericidal function, a preparation method and an application thereof. Pyrrole, zein, polyvinyl pyrrolidone and aminotrimethylenephosphonic acid are dissolved in acetic acid and electrospun into a nanofiber membrane. The prepared fiber has a diameter of 300 nm and a maximum tensile strength of 45.5±0.3 MPa, which limits the application of the zein nanofiber membrane.

So far, there is a lack of systematic research on the regulation of the diameter of bio-based polymer electrospun fibers, and there are bottlenecks in the preparation technology of electrospun fibers with small diameters and excellent physical properties.

Contents of the invention

In view of this, the present invention aims to propose a zein nanofiber membrane and a preparation method thereof to modify the solution by adding surfactants and by changing the parameters of the electrospinning process to achieve different diameters of zein nanofibers. Controlled preparation of nanofiber membranes.

In order to achieve the above objects, the technical solution of the present invention is implemented as follows:

In a first aspect, the present invention provides a method for reducing the diameter of zein nanofibers, comprising the following steps:

Mix zein and solvent evenly to obtain zein solution;

Mix the cationic surfactant and zein solution evenly to obtain a spinning solution;

The spinning solution was electrospun to obtain a zein nanofiber membrane.

Further, the added amount of the cationic surfactant is 1% to 20% of the zein mass; preferably 2%.

Further, the cationic surfactant is benzyltriethylammonium chloride (TEBAC).

Further, the solvent is an organic acid, preferably a monobasic acid, a dibasic acid and a polybasic acid, and more preferably acetic acid.

Further, the electrospinning conditions are: flow rate 0.5~3 mL/h, voltage 16-24 kv, receiving distance 8-12 cm, and drum speed 500-1500 rpm.

Further, the mass concentration of the zein solution is 30%~40%.

In a second aspect, the present invention provides a zein nanofiber membrane prepared according to the above method.

In a third aspect, the present invention provides a zein nanofiber film prepared according to the method as described above or an application of the zein nanofiber film as described above in product packaging.

Furthermore, the products may be food, medicine, or cosmetics.

In a fourth aspect, the present invention provides the application of TEBAC for improving the performance of zein nanofiber membrane, which is characterized in that the improvement of the performance of zein nanofiber membrane includes at least one of the following:

(1) Reduce the diameter of zein nanofibers;

(2) Increase the tensile strength of zein nanofiber membranes;

(3) Increase the elongation at break of zein nanofiber membrane;

(4) Increase the Young’s modulus of zein nanofiber membrane;

(5) Improve the water stability of zein nanofiber membrane;

(6) Increase the hydrophilicity of zein nanofiber membrane.

Compared with the existing technology, the zein nanofiber membrane and its preparation method according to the present invention have the following advantages:

The zein nanofiber membrane of the present invention adds surfactant, and successfully obtains fibers with improved uniformity and smaller diameter (100 nm). The addition of cationic surfactant significantly improves the mechanical properties of the nanofiber membrane, and the tensile strength of the nanofiber membrane is improved. The tensile strength, elongation at break and Young's modulus are all increased. At the same time, the water stability and hydrophilicity of the nanofiber membrane are significantly improved. The zein nanofiber membrane prepared by the present invention has great application in the field of food packaging. It has broad application prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings forming a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached picture:

Figure 1 is the scanning electron microscope image of different zein nanofiber membranes; among them, a is ZNF_200; b is ZNF_400; c is ZNF_600; d is ZNF_1000; e is TEBAC/ZNF; f is SDS/ZNF; g is span-80/ZNF ;

Figure 2 is the diameter distribution histogram of different zein nanofiber membranes, where A is ZNF_200; B is ZNF_400; C is ZNF_600; D is ZNF_1000; E is TEBAC/ZNF; F is SDS/ZNF; G is span-80/ ZNF;

Figure 3 is a comparison diagram of the mechanical properties of different zein nanofiber membranes. A is a comparison diagram of the mechanical properties of zein nanofiber membranes with different diameters, and B is a comparison diagram of the mechanical properties of zein nanofiber membranes assisted by different surfactants;

Figure 4 is a comparison diagram of the volume changes of different zein nanofiber membranes after being immersed in water for 24 hours. A is a comparison diagram of the volume changes of zein nanofiber membranes with different diameters after being immersed in water for 24 hours. B is a comparison diagram of zein nanofibers assisted by different surfactants. Comparison of volume changes of the fiber membrane after being immersed in water for 24 hours;

Figure 5 is a microscopic morphology of zein nanofiber membranes with different diameters (200-1000 nm) after being immersed in water for 24 h;

Figure 6 shows the micromorphology of different types of surfactant-assisted zein nanofiber membranes after being infiltrated in water for 24 hours;

Figure 7 is a schematic diagram comparing the water contact angles of different zein nanofiber membranes;

Figure 8 is an infrared spectrum of different zein nanofiber membranes; wherein A is an infrared spectrum of zein nanofiber membranes of different diameters in Comparative Examples 1 to 4; B is an infrared spectrum of a cationic surfactant TEBAC, a zein nanofiber membrane (ZNF), and a TEBAC-assisted zein nanofiber membrane (TEBAC/ZNF); C is an infrared spectrum of an anionic surfactant SDS, a zein nanofiber membrane (ZNF), and a SDS-assisted zein nanofiber membrane (SDS/ZNF); D is an infrared spectrum of a nonionic surfactant span-80, a zein nanofiber membrane (ZNF), and a span-80-assisted zein nanofiber membrane (span-80/ZNF);

Figure 9 is a schematic diagram of the formation of different zein nanofiber membranes and the distribution of different surfactants in the solution and nanofibers in Example 1 and Comparative Examples 1 to 6.

Detailed ways

It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

The main reagents and test instruments used in the following examples are shown in Table 1 and Table 2.

Table 1 Main test reagents

Table 2 Main test instruments

The detection methods involved in the following embodiments include:

1. Characteristics of spinning solution

The conductivity of the spinning solution was measured at 25° C. using a digital conductivity tester; the viscosity of the spinning solution was measured using a rotational rheometer; and the surface tension of the spinning solution was measured using a surface tension meter.

2. Physical properties of zein nanofiber membrane

(1) Shape and size distribution

The surface morphology of the zein nanofiber membrane was observed using a scanning electron microscope. All samples were gold sprayed under vacuum before observation. The image analysis software Image J was used to collect statistics on 200 random fibers from each sample to obtain the average fiber diameter and diameter distribution.

(2) Mechanical properties

The zein nanofiber membrane was cut into a size of 30 mm × 3 mm, and a universal testing machine was used to analyze the static mechanical properties of the zein nanofiber membrane at a tensile speed of 1 mm/s. The results of five determinations for each zein nanofiber membrane sample were averaged.

The tensile strength ( TS ), elongation at break ( EB ) and Young's modulus ( YM ) were calculated as follows:

where, Fm is the maximum recorded load (N), S is the cross-sectional area of the specimen, Lb is the _length at the breaking point (mm), L0 is the initial length of the specimen, _and Lm is the length corresponding _to the maximum load _. Corresponding test length (mm).

(3) Water stability

The zein nanofiber membrane sample was cut into a size of 3 cm × 3 cm, and then immersed in 40 mL of deionized water for 24 h. Take pictures of the sample before and after infiltration with deionized water, and observe the dimensional changes of the zein nanofiber membrane sample.

Zein nanofiber membrane samples of appropriate size were cut and immersed in 40 mL of deionized water for 0.5 h, 1 h, 3 h, 6 h, and 24 h, respectively. After that, the water was removed and freeze-dried, and the surface morphology was observed using a scanning electron microscope.

(4) Surface wettability

The water contact angle of the zein nanofiber membrane samples was measured using an OCA 25 contact angle meter at room temperature. Place the nanofiber membrane to be tested on a glass slide, drop 3 µL of deionized water on the sample surface, and then record it immediately with an instrument and automatically measure the contact angle value. Measurements for each sample were repeated five times.

3. Molecular structure of zein nanofiber membrane

The functional groups and intermolecular interactions between components in zein nanofiber membranes with different diameters and surfactant-assisted zein nanofiber membranes were analyzed by Fourier transform infrared spectroscopy in ATR mode. Place the sample to be tested on the ATR accessory and carefully press the accessory down to ensure good contact between the sample and the ATR crystal. The wavelength scan range is 400-4000 cm ^-1 with a resolution of 4 cm ^-1 , and the spectrum of each sample is collected after an average of 32 scans, with an empty ATR crystal as a reference.

4. Data statistics and analysis

All data were statistically analyzed using SPSS 20 software, and the data obtained were expressed as mean ± standard deviation. Comparisons between means were performed by one-way ANOVA and Duncan's multiple range test at a confidence level of 0.05.

Example 1

This embodiment provides a method for preparing a zein nanofiber membrane with controllable diameter, which includes the following steps: adding zein (zein) to acetic acid, and magnetically stirring at room temperature (25±2°C) overnight. , fully dissolve it, and prepare a zein solution with a concentration of 30% (w/v). Then, 2% (w/w, based on zein) TEBAC was added to the zein solution, stirred at room temperature for 2 h to fully dissolve TEBAC, and prepare the resulting spinning solution. The spinning solution was allowed to stand to remove air bubbles, and then a certain amount of the spinning solution was put into a 10 mL syringe, and electrospinning was performed according to the electrospinning parameters in Table 3 to prepare a TEBAC-assisted zein nanofiber membrane ( TEBAC/ZNF).

Table 3 Electrospinning parameters of zein nanofiber membranes

Comparative Example 1 No surfactant is added, the concentration of zein spinning solution is 30%

Add zein to acetic acid and stir it overnight with magnetic stirring at room temperature (25±2°C) to fully dissolve it to prepare a zein spinning solution with a concentration of 30% (w/v). Let the spinning solution sit for 10 minutes to remove air bubbles. After that, draw a certain amount of spinning solution into a 10 mL syringe, perform electrospinning according to the electrospinning parameters in Table 3, and prepare a zein nanofiber membrane with a fiber diameter of about 200 nm.

Comparative Example 2 No surfactant is added, the concentration of zein spinning solution is 35%

Add zein to acetic acid and stir it overnight with magnetic stirring at room temperature (25±2°C) to fully dissolve it to prepare a zein spinning solution with a concentration of 35% (w/v). Let the spinning solution sit for 10 minutes to remove air bubbles. After that, draw a certain amount of spinning solution into a 10 mL syringe, perform electrospinning according to the electrospinning parameters in Table 3, and prepare a zein nanofiber membrane with a fiber diameter of about 400 nm.

Comparative Example 3 No surfactant is added, the concentration of zein spinning solution is 40%

Add zein to acetic acid and stir it overnight with magnetic stirring at room temperature (25±2°C) to fully dissolve it to prepare a zein spinning solution with a concentration of 40% (w/v). Let the spinning solution sit for 10 minutes to remove air bubbles. After that, draw a certain amount of spinning solution into a 10 mL syringe, perform electrospinning according to the electrospinning parameters in Table 3, and prepare zein nanofibers with a fiber diameter of about 600 nm.

Comparative Example 4 No surfactant is added, the concentration of zein spinning solution is 40%

Add zein to acetic acid and stir it overnight with magnetic stirring at room temperature (25±2°C) to fully dissolve it to prepare a zein spinning solution with a concentration of 40% (w/v). Let the spinning solution sit for 10 minutes to remove air bubbles. After that, draw a certain amount of spinning solution into a 10 mL syringe, perform electrospinning according to the electrospinning parameters in Table 3, and prepare zein nanofibers with a fiber diameter of about 1000 nm.

Comparative Example 5 Addition of anionic surfactant SDS

In this comparative example, the zein solution was prepared using the same method as Example 1. Add 2% (w/w, based on zein) anionic surfactant SDS to the zein solution, stir at room temperature for 2 h to fully dissolve the anionic surfactant, and prepare the spinning solution. The spinning solution was left to stand for 10 minutes to remove air bubbles, and then a certain amount of the spinning solution was sucked into a syringe and electrospinning was performed (see Table 3 for parameters) to obtain SDS-assisted zein nanofiber membranes (SDS/ ZNF).

Comparative Example 6 Adding nonionic surfactant span-80

In this comparative example, the zein solution was prepared using the same method as Example 1. Add 2% (w/w, based on zein) nonionic surfactant span-80 to the zein solution, stir at room temperature for 2 hours to fully dissolve the nonionic surfactant, and prepare the spinning solution. Let the spinning solution stand for 10 minutes to remove air bubbles, then draw a certain amount of the spinning solution into a syringe and perform electrospinning (see Table 3 for parameters) to obtain a span-80-assisted zein nanofiber membrane ( span-80/ZNF).

Test Example 1 Measurement of Spinning Solution Characteristics

The viscosity, conductivity, and surface tension of the spinning solution play a key role in the shape and diameter of the nanofiber membrane. In this test example, the physical and rheological properties of each group of zein spinning solutions in Example 1 and Comparative Examples 1 to 6 were measured. Table 4 shows the physical and rheological properties of the spinning solution with different zein concentrations and the addition of different surfactants. Table 5 shows the physical and rheological properties of the spinning solutions after adding different concentrations and types of surfactants.

Table 4 Physical and rheological properties of zein spinning solution

Note: Different lowercase letters in each column indicate that there are significant differences in the spinning solution properties of zein nanofiber membranes with different diameters (p < 0.05); different uppercase letters in each column indicate that there are significant differences in the spinning solution properties without adding and with adding different surfactants (p < 0.05).

The results show that the viscosity of the 30% zein solution in Comparative Example 1 is 0.32 Pa·s, the conductivity is 103.73 µS/cm, and the surface tension is 46.10 mN/m. As the zein concentration increases to 40%, the viscosity of the spinning solutions in Comparative Examples 3 and 4 increases significantly (1.06 Pa·s), the surface tension also increases (47.98 mN/m), and the conductivity first increases and then decreases. There is a small change trend, among which the conductivity of the 35% zein solution in Comparative Example 2 is the largest, which is 113.67 µS/cm.

After adding each of the three surfactants, the conductivity increased significantly and the surface tension decreased significantly. Among them, after adding the cationic surfactant TEBAC in Example 1, the conductivity is the largest (225.67 µS/cm) and the surface tension is the smallest (38.11 mN/m). In addition, except for the addition of SDS in Comparative Example 5, which significantly increased the viscosity of the spinning solution, other surfactants did not cause changes in the viscosity. These results indicate that zein interacts with surfactants.

The viscosity of the pure zein solution in Comparative Example 1 was 0.32 Pa·s. When 2% SDS and TEBAC were added to Comparative Example 5 and Example 1 respectively, the viscosity of the zein solution increased to 0.38 Pa·s and 0.34 Pa·s respectively; And as shown in the results in Table 5, as the concentration of the two surfactants increases, the viscosity of the mixed solution first decreases and then increases, but its viscosity is still higher than that of the zein solution alone. When 2% of the nonionic surfactant span-80 was added to Comparative Example 6, the viscosity of the zein mixed solution did not change significantly; as shown in Table 5, when the added concentration was increased to 10%, the viscosity of the zein mixed solution decreased significantly. ; As the surfactant concentration continues to increase to 20%, the viscosity of the zein/span-80 mixed solution increases.

As expected, mixtures of zein and surfactants had lower surface tension than the zein solution itself in all cases, and anionic and cationic surfactants can significantly reduce the surface tension of the zein solution. However, as the concentration of surfactant increases from 2% to 20%, the surface tension gradually increases. This surface behavior is considered to be evidence of zein-surfactant interaction, which will increase with the surfactant. changes with increasing content.

Table 5 Physical and rheological properties of zein solutions after adding different concentrations and types of surfactants

Note: Different lowercase letters indicate significant differences between zein solutions with different types and concentrations of surfactants ( p <0.05); different capital letters indicate significant differences between zein solutions with different concentrations of surfactants ( p < 0.05).

According to Table 5, the conductivity of the zein solution is 103.73 µS/cm. After adding 2% of the surfactants TEBAC, SDS and span-80, the conductivity of the solution increases to 225.67, 154.37 and 120.23 µS/cm, respectively. As the surfactant concentration increases to 20%, the conductivity of the zein/TEBAC mixed solution gradually increases to 662.00 µS/cm; the conductivity of the zein/SDS mixed solution shows a trend of decreasing first and then increasing, and the conductivity of the mixed solution is 200.83 µS/cm when the SDS concentration is 20%; however, the conductivity of the zein/span-80 mixed solution decreases with the increase of the surfactant concentration, and when the surfactant concentration is 20%, the conductivity is 73.73 µS/cm.

Test Example 2 Measurement results of physical properties of zein nanofiber membrane

In this test example, the morphology and diameter distribution, mechanical properties, water stability, and surface wettability of each group of zein nanofiber membranes prepared in Example 1 and Comparative Examples 1 to 6 were measured.

1. Shape and diameter distribution of zein nanofiber membrane

Figure 1 shows SEM images of zein nanofiber membranes with different diameters. It can be seen from Figure 1 a-d that the fiber diameter depends largely on the mass concentration of zein, and the diameter of zein nanofibers increases with the increase of zein concentration, which can be attributed to the increase in the viscosity of the spinning solution. Although the four spinning solutions in Comparative Examples 1-4 had different conductivities and viscosities, all the zein nanofibers produced were rod-shaped and showed uniform morphology, indicating that although the changes in zein mass concentration and flow rate affected spinning solution properties and the average diameter of the nanofibers, but does not affect the shape of the nanofibers.

Modification of the zein spinning solution by adding surfactants also leads to changes in the morphology of zein nanofibers. As shown in Figure 1 e-g, compared with the sample without surfactant (Figure 1 a), the morphology of the fibers is more uniform after adding surfactants, which is specifically manifested as a narrowing of the diameter distribution of the fibers (Figure 2 E-G). In addition, Example 1 and Comparative Examples 5-6 respectively added three kinds of surfactants to the zein nanofiber membrane, which significantly reduced the fiber diameter. The addition of 2% TEBAC, SDS and span-80 reduced the average fiber diameter of the zein nanofiber membrane from 208.22 ± 46.93 nm to 106.10 ± 18.58 nm, 98.92 ± 15.20 nm and 106.11 ± 17.98 nm, respectively.

2. Mechanical properties of zein nanofiber membrane

The tensile strength, elongation at break and Young's modulus of zein nanofiber membranes with different diameters are shown in A in Figure 3. The tensile strength of the zein nanofiber membrane with a fiber diameter of 200 nm is 11.08 MPa, the elongation at break is 4.21%, and the Young's modulus is 0.97 GPa. As the average fiber diameter increases, the tensile strength of the zein nanofiber membrane first increases and then decreases. The fiber membrane with a fiber diameter of 600 nm has the largest tensile strength value of 35.55 MPa. Similarly, the Young's modulus of zein nanofiber membrane gradually increased from 0.97 GPa to 6.77 GPa with the increase of fiber diameter. However, the elongation at break of the zein nanofiber membrane gradually decreases as the fiber diameter increases. The fiber membrane with a diameter of 1000 nm has the smallest elongation at break, which is 1.86%.

B in Figure 3 shows the mechanical properties of zein nanofiber membrane and three surfactants-assisted zein nanofiber membrane. It can be seen that the mechanical properties of zein nanofiber membranes are greatly affected by the surfactant type. With the addition of the cationic surfactant TEBAC, the tensile strength, elongation at break and Young's modulus all increased to 63.26MPa, 6.50% and 2.86 MPa respectively, indicating that the addition of TEBAC improved the mechanics of zein nanofiber membranes. performance. In addition, the addition of the anionic surfactant SDS and the nonionic surfactant span-80 caused the elongation at break of the zein nanofiber membrane to increase to 11.86% and 9.10% respectively; while the tensile strength and Young's modulus both decreased, respectively. are 1.78 MPa, 1.55 MPa and 0.05 GPa, 0.06 GPa.

3. Water stability of zein nanofiber membrane

In order to observe the morphology of the nanofiber membrane after absorbing water, this test example soaked the zein nanofiber membrane samples of the above-mentioned embodiment 1 and comparative examples 1 to 6 in deionized water for 24 hours. Figure 4 shows the volume changes of zein nanofiber membranes with different diameters and surfactant-assisted zein nanofiber membranes after soaking in deionized water for 24 hours. It can be seen from the figure that all nanofiber membrane samples showed shrinkage when initially exposed to deionized water. Among them, the volume of the nanofiber membrane with an average fiber diameter of 200-1000 nm changed to 28.83%, 46.41%, 73.45% and 76.58% of the initial volume, respectively. With the increase of exposure time, the volume of the zein nanofiber membrane with a fiber diameter of 200 nm, 400 nm and 600 nm gradually decreased. After soaking in deionized water for 24 hours, the volume of the nanofiber membrane changed to 20.60%, 15.00% and 29.68% of the initial volume, respectively. However, the zein nanofiber membrane with a fiber diameter of 1000 nm swelled after exposure to deionized water, that is, the volume gradually increased with the increase of exposure time; after 6 h of exposure to deionized water, the volume of the zein nanofiber membrane was 93.60% of the initial volume. However, as the exposure time continued to increase, the zein nanofiber membrane became incomplete due to dissolution. These results show that the diameter of the zein nanofiber membrane has a great influence on its stability in aqueous media.

After the introduction of surfactants, the swelling behavior of zein nanofiber membranes in water changed significantly. The results of B in Figure 4 show that the presence of the cationic surfactant TEBAC caused the volume of the zein nanofiber membrane to increase from 28.83% of the initial volume to 32.41% when initially exposed to deionized water; after 24 h of exposure to deionized water, The volume of the TEBAC-assisted zein nanofiber membrane is 31.43% of the initial volume, which is significantly higher than the 20.60% of the zein nanofiber membrane. Different from the cationic surfactant, the addition of the anionic surfactant SDS causes the zein nanofiber membrane to shrink more severely when exposed to deionized water. When the exposure time is 24 h, the volume of the SDS-assisted zein nanofiber membrane is only 2.07% of initial volume. However, the addition of the nonionic surfactant span-80 has no obvious effect on the swelling behavior of the zein nanofiber membrane in water. After being exposed to deionized water for 24 hours, the volume of the zein nanofiber membrane assisted by span-80 is equal to the initial volume. 23.63%.

Figures 5 and 6 show the changes in the surface morphology of zein nanofiber membranes with different diameters and surfactants after immersion in deionized water for 24 hours. It can be seen that after immersion in deionized water for 0.5 hours, the fiber structure of the fiber membrane with a diameter of 200 nm disappears due to the adhesion between the fibers, and only some pores formed by incomplete adhesion between the fibers can be observed; as the exposure time increases to 3 hours, the number of pores gradually decreases; when the exposure time increases further, large holes are observed to appear, and the number gradually increases. After exposure to deionized water for 0.5 hours, the fiber membrane with a diameter of 400 nm swells and the pores between the fibers become smaller; after immersion in deionized water for 3 hours, the fiber structure disappears and some pores exist; as the exposure time continues to increase, the number of pores decreases; after immersion in deionized water for 24 hours, holes formed after the sample dissolves are observed. According to Figure 5, as the exposure time of the fiber membrane with a diameter of 600 nm in deionized water increases, the fiber diameter gradually increases due to water absorption and swelling, the pores between fibers decrease, and the size and number of pores formed by the fiber dissolution also increase; after immersion in deionized water for 24 h, adhesion occurs between the fibers. For the fiber membrane with a diameter of 1000 nm, as the exposure time in deionized water increases, it is observed that the fiber diameter gradually increases, the pores between fibers decrease, and the size and number of pores on the fibers increase, and there is basically no adhesion between the fibers.

The changes in surface morphology of the surfactant-assisted zein nanofiber membrane after being soaked in deionized water for 24 h are shown in Figure 6. After the cationic surfactant TEBAC assisted zein nanofiber membrane was soaked in deionized water for 0.5 h, the fiber structure had completely disappeared, and the film formed by adhesion between fibers was distributed with pits left after the water was removed; after being soaked in deionized water for 3 h Afterwards, block-like protrusions resulting from further aggregation of the fiber membrane were observed; when infiltrated in deionized water for 24 h, the membrane dissolved, resulting in a large number of holes. As the infiltration time in deionized water increases, the anionic surfactant SDS assists the fibers of the zein nanofiber membrane to absorb water and swell, so the fiber diameter gradually increases and the pores between fibers continue to decrease; after infiltration in deionized water for 3 hours, Most of the fibers were adhered, and only a small part of the fibers still maintained the fiber structure; after being soaked in deionized water for 24 hours, a smooth surface film was formed. When the nonionic surfactant span-80 assisted the zein nanofiber membrane to be infiltrated in deionized water for 0.5 h, the fiber structure disappeared, and a large number of pores formed by incomplete fiber adhesion were distributed on the surface of the membrane; as the infiltration time increased, the pores gradually decreased .

4. Surface wettability of zein nanofiber membrane

Contact angle is a useful method to characterize the wettability of a material surface. In this study, water was used as the medium for contact angle measurement. It is reported that a large water contact angle (θ>90°) indicates a hydrophobic surface, while a small water contact angle (θ<90°) indicates a hydrophilic surface. The water contact angle values of zein nanofiber membranes with different diameters are shown in Figure 7. From the results, it can be seen that in Comparative Examples 1 to 4, as the fiber diameter increases from 200 nm to 1000 nm, the water contact angle value of the zein nanofiber membrane decreases from 120.88° to 80.65°. This may be because as the fiber diameter increases, the gap between fibers in the zein nanofiber membrane increases, which is more conducive to water penetration.

Compared with the nanofiber membrane without surfactant (Comparative Example 1), after adding 2% TEBAC, SDS and span-80 in Example 1 and Comparative Examples 5~6, the water contact angle of the zein nanofiber membrane decreased from 120.88° to 95.43°, 90.88° and 88.73° respectively; after adding the surfactant, the water contact angle of the zein nanofiber membrane decreased, indicating that the surfactant increased the hydrophilicity of the zein nanofiber membrane.

Test Example 3 Molecular Structure of Zein Nanofiber Membrane

Infrared spectroscopy is a useful technique for characterizing interactions between components of nanofibrous membranes. In this test example, the infrared spectra of the zein nanofiber membrane samples of each group of Example 1 and Comparative Examples 1 to 6 were measured.

The infrared spectra of zein nanofiber membranes with fiber diameters of 200-1000 nm in Comparative Examples 1 to 4 are shown in A in Figure 8. It can be seen that zein nanofiber membranes with different diameters have similar spectral characteristics, indicating that the diameter does not change the basic structure of the zein nanofiber membrane. Compared with the fiber membrane with a diameter of 200 nm, new characteristic peaks appear at 2901 cm ^-1 and 2334-2364 cm ^-1 in the infrared spectrum of the zein fiber membrane with a diameter of 400-1000 nm; and it can be observed at 1066 cm ^- The peak intensity at ¹ and 1541 cm ^-1 gradually increases with the increase of the average fiber diameter. In addition, as the average fiber diameter increases, the characteristic peaks at 1243 cm ^-1 , 1455 cm ^-1 and 2966 cm ^-1 undergo a blue shift, while the characteristic peak at 1654 cm ^-1 undergoes a red shift. These results indicate that the interactions of zein-zein molecular chains in nanofibers with different diameters are different. During the electrospinning process, under the same stretching effect, the higher the polymer concentration, the more entangled molecular chains exist, resulting in stronger molecular chain interactions. The amide I band is a complex secondary structure composed of multiple overlapping substructures such as protein side chains, β-sheets, α-helices, random coils, and β-turns. The secondary structure content of the zein nanofiber membrane was obtained by fitting the second derivative and Gaussian curve of the amide I band in the range of 1700-1600 cm ^-1 .

B in Figure 8 shows the infrared spectra of TEBAC, zein nanofiber membranes and TEBAC-assisted zein nanofiber membranes. It can be seen that due to the interaction between TEBAC and zein, the intensity of the characteristic peaks at 1654 cm ^-1 , 1541 cm ^-1 , 1455 cm ^-1 and 1243 cm ^-1 in the infrared spectrum of the TEBAC-assisted zein nanofiber membrane is greatly reduced. . In addition, the addition of TEBAC caused the characteristic peaks located at 3296 cm ^-1 and 2966 cm ^-1 in the zein nanofiber membrane to move to 3311 cm ^-1 and 2988 cm ^-1 respectively, indicating that a micelle structure was also formed between TEBAC and zein. The infrared spectrum of the SDS-assisted zein nanofiber membrane (C in Figure 8) shows that new characteristic peaks appear at 3749 cm ^-1 , 2366 cm ^-1 and 1066 cm ^{-1 .} After adding SDS, the zein nanofiber membrane has a peak at 2966 cm The intensity of the characteristic peaks ^-1 , 1541 cm ^-1 and 1243 cm ^-1 increased significantly. These are the characteristic peaks in the SDS spectrum, indicating good compatibility between SDS and zein. In addition, the addition of SDS caused the characteristic peak located at 1654 cm ^-1 in the zein nanofiber membrane to move to 1652 cm ^-1 . According to D in Figure 8, after adding span-80, new characteristic peaks appear at 3749 cm ^-1 , 2359 cm ^-1 , and 1066 cm ^-1 in the infrared spectrum of the zein nanofiber membrane, and are located at 2967 cm ^-1 and 1541 The peak intensity of the characteristic peak at cm ^-1 increases. These are the characteristic peaks of span-80, indicating the presence of span-80 in the zein nanofiber membrane and the good compatibility between span-80 and zein. In addition, the addition of span-80 causes the characteristic peaks located at 3296 cm ^-1 , 2966 cm ^-1 , and 1455 cm ^-1 in the zein nanofiber membrane to blue shift.

According to Table 6, as the fiber diameter increases, the α-helix and β-sheet structure content of the zein nanofiber membrane increases, while the β-turn structure content decreases significantly. In addition, after adding different surfactants, the β-turn structure content of zein nanofiber membranes decreased to varying degrees, while the α-helical structure content increased accordingly. Among them, after adding the anionic surfactant SDS, the secondary structure of the zein nanofiber membrane changed most significantly, while after adding the cationic surfactant TEBAC, the secondary structure changed the least. The above results indicate that cationic, anionic, and nonionic surfactants behave differently in polymer solutions, depending on the inherent properties of the solvent and polymer and their interactions.

Table 6 Secondary structure content of different diameters and surfactant-assisted zein nanofiber membranes

Figure 9 shows the formation of different zein nanofiber membranes in Example 1 and Comparative Examples 1 to 6 of the present application and the distribution of different surfactants in the solution and nanofibers.

The above results indicate that controllable adjustment of fiber diameter can be achieved by changing electrospinning parameters and using surfactant-assisted methods. After the addition of the anionic surfactant SDS and the nonionic surfactant span-80, the elongation at break of the zein nanofiber membrane increased, but the tensile strength and Young's modulus decreased; while the addition of the cationic surfactant TEBAC significantly improved the zein nanofiber membrane. The mechanical properties of the nanofiber membrane, tensile strength, elongation at break and Young's modulus all increased.

Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to the preferred arrangement, those of ordinary skill in the art will understand that the technical solution of the present invention can be modified. Or equivalent substitutions may be made without departing from the spirit and scope of the technical solution of the present invention.

Claims (6)

1. A method for reducing the diameter of zein nanofibers, characterized by: comprising the following steps: Mix zein and solvent evenly to obtain zein solution; Mix the cationic surfactant and the zein solution evenly to obtain a spinning solution, the cationic surfactant is TEBAC, and the addition amount of the cationic surfactant is 2% to 20% of the zein mass; The spinning solution is electrospun to obtain a zein nanofiber membrane. The electrospinning conditions are: flow rate 0.5~3 mL/h, voltage 16-24 kv, receiving distance 8-12 cm, drum speed 500-1500 rpm. 2. The method according to claim 1, characterized in that the solvent is an organic acid. 3. The method according to claim 1, characterized in that the mass concentration of the zein solution is 30%~40%. 4. A zein nanofiber membrane prepared according to any one of claims 1 to 3. 5. Application of the zein nanofiber film prepared by the method of any one of claims 1 to 3 or the zein nanofiber film of claim 4 in product packaging. 6. The application of TEBAC in improving the properties of zein nanofiber membranes, characterized in that the application includes at least one of the following: (1) Application in reducing the fiber diameter of zein nanofiber membrane; (2) Application in increasing the tensile strength of zein nanofiber membranes; (3) Application in increasing the elongation at break of zein nanofiber membranes; (4) Application in increasing the Young’s modulus of zein nanofiber membranes; (5) Application in improving the water stability of zein nanofiber membranes; (6) Application in increasing the hydrophilicity of zein nanofiber membranes.