Rosmarinic acid and zinc ion double cross-linked pva composite film, and preparation method and application thereof

Abstract

The application provides a rosmarinic acid and zinc ion double-crosslinked PVA composite film and a preparation method and application thereof. The preparation method of the rosmarinic acid and zinc ion double-crosslinked PVA composite film comprises the following steps: (1) mixing and reacting rosmarinic acid and a polyvinyl alcohol aqueous solution to obtain a polyvinyl alcohol / rosmarinic acid initial solution; (2) dialyzing the polyvinyl alcohol / rosmarinic acid initial solution to obtain a polyvinyl alcohol / rosmarinic acid pure solution; (3) mixing the polyvinyl alcohol / rosmarinic acid pure solution with a zinc chloride solution to obtain a polyvinyl alcohol / rosmarinic acid / Zn 2+ solution; and (4) drying and removing water from the polyvinyl alcohol / rosmarinic acid / Zn 2+ solution to obtain the rosmarinic acid and zinc ion double-crosslinked PVA composite film. The rosmarinic acid and zinc ion double-crosslinked PVA composite film prepared by the method has excellent antibacterial, antioxidant and ultraviolet resistance and good mechanical properties.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyvinyl alcohol composite film preparation, and particularly relates to a rosemary acid and zinc ion double-crosslinked PVA composite film and a preparation method and application thereof. BACKGROUND

[0002] Polyvinyl alcohol (PVA) is a hydrophilic semi-crystalline polymer used for food packaging film. However, it has low antibacterial, antioxidant and ultraviolet resistance. It is of great significance to improve the antibacterial, antioxidant and ultraviolet resistance of the food packaging film prepared from polyvinyl alcohol, to improve the application range of the polyvinyl alcohol film, and to prolong the shelf life and sensory characteristics of food. SUMMARY

[0003] The present application aims to at least partly solve one of the problems in the prior art. To this end, one object of the present application is to propose a rosemary acid and zinc ion double-crosslinked PVA composite film and a preparation method and application thereof.

[0004] In a first aspect, the present application proposes a preparation method of a rosemary acid and zinc ion double-crosslinked PVA composite film. According to an embodiment of the present application, the method comprises:

[0005] (1) mixing and reacting rosemary acid and a polyvinyl alcohol aqueous solution to obtain a polyvinyl alcohol / rosemary acid initial solution;

[0006] (2) dialyzing the polyvinyl alcohol / rosemary acid initial solution to obtain a polyvinyl alcohol / rosemary acid pure solution;

[0007] (3) mixing the polyvinyl alcohol / rosemary acid pure solution with a zinc chloride solution to obtain a polyvinyl alcohol / rosemary acid / Zn 2+ solution;

[0008] (4) drying and removing water from the polyvinyl alcohol / rosemary acid / Zn 2+ solution to obtain a rosemary acid and zinc ion double-crosslinked PVA composite film.

[0009] According to the preparation method of the rosmarinic acid and zinc ion double cross-linked PVA composite film in the above embodiment of the present application, firstly, the rosmarinic acid and the polyvinyl alcohol aqueous solution are mixed and reacted to obtain a polyvinyl alcohol / rosmarinic acid initial solution. The rosmarinic acid (RA) is a naturally occurring water-soluble phenolic compound and widely exists in various medicinal plants. The rosmarinic acid has various biological activities, such as antibacterial and antioxidant activities. The PVA is covalently coupled with the rosmarinic acid at 120°C to form a PVA / RA solution, which not only overcomes the problem of poor bioavailability of the rosmarinic acid, but also significantly improves the antibacterial, antioxidant and ultraviolet resistance of the polyvinyl alcohol film. The polyvinyl alcohol / rosmarinic acid initial solution is dialyzed to obtain a polyvinyl alcohol / rosmarinic acid pure solution. There is a small amount of unreacted rosmarinic acid in the polyvinyl alcohol / rosmarinic acid initial solution, which is removed by dialysis.

[0010] The inventors find that although the rosmarinic acid modified polyvinyl alcohol can improve the antibacterial, antioxidant and ultraviolet resistance of the polyvinyl alcohol film, the polyvinyl alcohol / rosmarinic acid is covalently coupled to form an ester group through esterification of the hydroxyl and carboxyl groups. The hydroxyl groups on the polyvinyl alcohol are reduced, resulting in weakened mechanical properties of the film. Therefore, the polyvinyl alcohol / rosmarinic acid pure solution is mixed with a zinc chloride solution to obtain a polyvinyl alcohol / rosmarinic acid / Zn 2+ solution. By chelating the covalent zinc ion to the rosmarinic acid through metal chelation, the mechanical properties of the film can be effectively improved, and the antibacterial performance of the film can be further improved. Finally, the polyvinyl alcohol / rosmarinic acid / Zn 2+ solution is dried to remove water to obtain the rosmarinic acid and zinc ion double cross-linked PVA composite film.

[0011] In some embodiments of the present application, in step (1), the mass ratio of the rosmarinic acid to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 1:(5-200). For example, the mass ratio of the rosmarinic acid to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 1:5, 1:10, 1:30, 1:50, 1:80, 1:100, 1:120, 1:140, 1:160, 1:180, 1:200, or any range between any two of the above-mentioned values. The inventors find that controlling the mass ratio of the rosmarinic acid to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution in the above range can improve the antibacterial, antioxidant and ultraviolet resistance of the polyvinyl alcohol film.

[0012] In some embodiments of the present application, the concentration of polyvinyl alcohol in the aqueous polyvinyl alcohol solution is 80-120 g / L. For example, the concentration of polyvinyl alcohol in the aqueous polyvinyl alcohol solution is 80 g / L, 83 g / L, 87 g / L, 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, or any range between any two of the aforementioned values. The inventors have found that the concentration of polyvinyl alcohol in the aqueous polyvinyl alcohol solution in the above range is conducive to better modification of polyvinyl alcohol by rosmarinic acid, and improves the antibacterial, antioxidant and ultraviolet resistance of the polyvinyl alcohol film.

[0013] In some embodiments of the present application, in step (1), the temperature of the mixing reaction is 110-120°C, and the time is 2-4 h. For example, the temperature of the reaction is 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, and the time is 2 h, 2.5 h, 3 h, 3.2 h, 3.5 h, 3.7 h, 4 h, etc. The temperature and time of the mixing reaction in the above range allows the rosmarinic acid and polyvinyl alcohol to react sufficiently, thereby improving the yield of rosmarinic acid-modified polyvinyl alcohol.

[0014] In some embodiments of the present application, in step (1), the preparation process of the aqueous polyvinyl alcohol solution comprises mixing polyvinyl alcohol and water and reacting at 90-100°C for 4-6 h. In this way, the polyvinyl alcohol can be fully dissolved in the aqueous solution, and an aqueous polyvinyl alcohol solution with a suitable concentration can be prepared.

[0015] In some embodiments of the present application, in step (2), the dialysis uses a dialysis bag with a molecular weight of 800-1000 and ultrapure water. In this way, the unreacted rosmarinic acid can be effectively removed.

[0016] In some embodiments of the present application, in step (3), the concentration of zinc chloride in the solution obtained after mixing the polyvinyl alcohol / rosmarinic acid pure solution and the zinc chloride solution is 0.8-15 g / L. For example, the concentration is 0.8 g / L, 1.0 g / L, 2 g / L, 5 g / L, 7 g / L, 9 g / L, 12 g / L, 15 g / L, or any range between any two of the aforementioned values. The inventors have found that controlling the concentration of zinc chloride in the solution after mixing in the above range is conducive to the action of zinc ions on rosmarinic acid, and meets a certain amount of zinc ions, thereby improving the mechanical properties of the film.

[0017] In some embodiments of the present application, in step (3), the concentration of the zinc chloride solution is 50-300 g / L. For example, the concentration of the zinc chloride solution is 50 g / L, 80 g / L, 100 g / L, 200 g / L, 300 g / L, or any range between any two of the aforementioned values.

[0018] In some embodiments of the present application, in step (3), the temperature of mixing is room temperature, and the time of mixing is 20-25 hours.

[0019] In some embodiments of the present application, the preparation of the zinc chloride solution comprises: dissolving zinc chloride powder with 0.07-0.1 mol / L hydrochloric acid, oscillating for 15-20 minutes, and standing for 20-30 hours.

[0020] In some embodiments of the present application, step (3) further comprises: dialyzing the polyvinyl alcohol / rosemary acid / Zn 2+ solution in 0.01-0.07 mol / L hydrochloric acid solution for 20-32 hours, thereby removing excess unreacted zinc ions.

[0021] In some embodiments of the present application, in step (4), the temperature of drying is 50-60℃, and the time is 24-32 hours, thereby effectively removing the moisture of the polyvinyl alcohol / rosemary acid / Zn 2+ solution while ensuring the stability of the prepared film.

[0022] It should be noted that the polyvinyl alcohol / rosemary acid / Zn 2+ solution can be placed in a mold of different shapes before drying to remove water, thereby obtaining a rosemary acid and zinc ion double-crosslinked PVA composite film of the desired shape.

[0023] In a second aspect of the present application, a rosemary acid and zinc ion double-crosslinked PVA composite film is provided. According to embodiments of the present application, the rosemary acid and zinc ion double-crosslinked PVA composite film is prepared by the above method. Thus, the rosemary acid and zinc ion double-crosslinked PVA composite film has excellent antibacterial, antioxidant and ultraviolet resistance and good mechanical properties.

[0024] In a third aspect of the present application, the above rosemary acid and zinc ion double-crosslinked PVA composite film is applied in the field of food packaging.

[0025] The present application has at least the following technical effects:

[0026] (1) The present application is based on the principle of esterification reaction. The carboxyl group of rosemary acid can be combined with the hydroxyl group of PVA at 120℃ to form a PVA / RA conjugate, thereby improving the antioxidant and ultraviolet resistance of the polyvinyl alcohol film. Zinc ions are combined with RA through metal chelation, thereby strengthening the mechanical properties of the film and further improving the antibacterial properties of the PVA film. The rosemary acid and zinc ion double-crosslinked PVA composite film prepared by the present application has excellent antibacterial, antioxidant and ultraviolet resistance and good mechanical properties.

[0027] (2) The method for preparing the rosmarinic acid and zinc ion double cross-linked PVA composite film has simple process, easy operation, low equipment requirement, easily available raw materials, environmental friendliness, and is suitable for large-area popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the present application or prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0029] Figure 1 PVA / RA / Zn of Example 1-5 2+ The actual figure of the solution;

[0030] Figure 2 The ultraviolet absorption spectrum of the solution of Example 1-5 and Comparative Examples 1, 3;

[0031] Figure 3 The comparison graph of the zinc ion chelation amount of the solution of Example 1, 7-10;

[0032] Figure 4 The ATR-FTIR spectrum of the solution of Example 1, Comparative Examples 1-3;

[0033] Figure 5 The ultraviolet-visible performance analysis result graph of the film of Example 1, Comparative Examples 1-2;

[0034] Figure 6 The antibacterial performance test result graph of the solution of Example 1, Comparative Examples 1-2;

[0035] Figure 7 The antioxidant performance test result graph of the film of Example 1, Comparative Examples 1-2;

[0036] Figure 8 The mechanical property test result graph of the film of Example 1 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0037] All other embodiments obtained by those skilled in the art without any creative effort on the basis of the embodiments in the present application belong to the protection scope of the present application. The present application will be described below with reference to specific embodiments, and it should be noted that these embodiments are merely descriptive, and do not limit the present application in any way.

[0038] The experimental materials and instruments used in the following examples and comparative examples are as follows:

[0039] Polyvinyl alcohol (type 1799), AR, purchased from Shanghai Titan Science and Technology Co., Ltd.

[0040] Rosmarinic acid, zinc chloride (97%) purchased from Aladdin;

[0041] Anhydrous zinc chloride purchased from Shanghai Maikelin;

[0042] Autoclave purchased from Beijing Hutong Experimental Instrument Co., Ltd.

[0043] Magnetic stirrer (Eka), RCT bask set;

[0044] Vacuum drying oven (Linhai Yonggao), DZF-6024 type;

[0045] Rotary evaporator (Shanghai Yalong), RE-52A type;

[0046] Handheld high-speed stirrer (Zhan Yi), three-gear type, all purchased from Beijing Yanqiwang Biotechnology Co., Ltd.

[0047] Plastic vacuum dryer, HP-PC-150 type, purchased from Changde Bikeman Biotechnology Co., Ltd.; UV spectrophotometer, Q-6 type, purchased from Shanghai Yuanchi Instrument Co., Ltd.

[0048] Example 1

[0049] (1) Take 20 ml of PVA aqueous solution with a concentration of 100 g / L in a beaker, and weigh 163.6 mg of rosmarinic acid (mass ratio PVA:RA=12.2:1) into the beaker, and stir until dissolved.

[0050] (2) Set the temperature of the autoclave to 120°C and 300 rpm, heat the solution to 120°C, and stir with a small rotor for 2h to fully crosslink, to obtain a fully crosslinked PVA / RA solution.

[0051] (3) Dialysis bag treatment method: take 10 g of sodium bicarbonate and 186 mg of EDTA (ethylenediamine) and add them to 500 ml of ultrapure water; put the dialysis bag into the above solution, start timing when boiling, 10 min; take out the dialysis bag and wash it thoroughly with ultrapure water; put it into ultrapure water and start timing when boiling, 10 min; take out the dialysis bag and put it into the beaker of ultrapure water.

[0052] (4) Dialysis of the PVA / RA solution obtained in step (2) was performed using a dialysis bag with a molecular weight of 1000, and dialysis was performed in ultrapure water, dialysis for two days, and ultrapure water was changed three times a day (stirring).

[0053] (5) Take 10 ml of the PVA / RA solution after dialysis, add 1.2 ml of a 136 g / L ZnCl2 solution (weighed zinc chloride is added into 0.07 mol / L dilute hydrochloric acid), the concentration of ZnCl2 in the mixed solution is 14.6 g / L, fully stir for 15 minutes, then load into a centrifuge tube, crosslink at room temperature for 24 hours, to obtain a PVA / RA / Zn 2+ solution. Then dialyze with a 0.05 mol / L hydrochloric acid solution for 24 h.

[0054] (6) Take the PVA / RA / Zn 2+ solution into a small acrylic mold, vacuum degassing (horizontally close the air, clockwise open the vacuum, counterclockwise close the vacuum, after finishing, slowly open the air a small hole), after degassing, directly pour into the mold, dry at 50°C for 24 h, demold, to obtain a rosemary acid and zinc ion double crosslinked PVA composite film.

[0055] Example 2

[0056] The difference between Example 2 and Example 1 is:

[0057] In step (1) of Example 2, PVA:RA = 6.1:1.

[0058] Example 3

[0059] The difference between Example 3 and Example 1 is:

[0060] In step (1) of Example 3, PVA:RA = 24.4:1.

[0061] Example 4

[0062] The difference between Example 4 and Example 1 is:

[0063] In step (1) of Example 4, PVA:RA = 48.8:1.

[0064] Example 5

[0065] The difference between Example 5 and Example 1 is:

[0066] In step (1) of Example 5, PVA:RA = 97.6:1.

[0067] Example 6

[0068] The difference between Example 6 and Example 1 is:

[0069] In step (1) of Example 6, PVA:RA = 195.2:1.

[0070] Example 7

[0071] The difference between Example 7 and Example 1 is:

[0072] The concentration of ZnCl2 in the mixed solution was 7.3 g / L.

[0073] Example 8

[0074] The difference between Example 8 and Example 1 is:

[0075] The concentration of ZnCl2 in the mixed solution was 3.65 g / L.

[0076] Example 9

[0077] The difference between Example 9 and Example 1 is:

[0078] The concentration of ZnCl2 in the mixed solution was 1.83 g / L.

[0079] Example 10

[0080] The difference between Example 10 and Example 1 is:

[0081] The concentration of ZnCl2 in the mixed solution was 0.92 g / L.

[0082] Comparative Example 1

[0083] (1) 10.0 g of PVA was added to 100 ml of aqueous solution, and rotary evaporation was performed at 95°C for 2h until the PVA was completely dissolved, to obtain a PVA aqueous solution.

[0084] (2) The PVA solution was mixed and shaken and ultrasonically treated, and then vacuumized to remove bubbles. Finally, it was dried at 60°C to obtain a polyvinyl alcohol material.

[0085] Comparative Example 2

[0086] (1) 20 ml of PVA aqueous solution with a concentration of 100 g / L was taken in a beaker, and 163.6 mg of rosmarinic acid (mass ratio PVA:RA = 12.2:1) was weighed into the beaker using a weighing instrument, and stirred until dissolved.

[0087] (2) The solution was heated to 120°C using a high-pressure kettle set at 120°C and 300 rpm, and the solution was stirred with a small rotor for 2h to fully crosslink, to obtain a fully crosslinked PVA / RA solution.

[0088] (3) Dialysis bag treatment method: 10 g of sodium bicarbonate and 186 mg of EDTA (ethylenediamine) were added to 500 ml of ultrapure water; the dialysis bag was placed in the above solution, and boiling was started to start timing, 10 min; the dialysis bag was taken out and washed thoroughly with ultrapure water; it was placed in ultrapure water and boiled to start timing for 10 min; the dialysis bag was taken out and placed in a beaker of ultrapure water.

[0089] (4) dialysis of the PVA / RA solution obtained in step (2) is performed using a dialysis bag with a molecular weight of 1000, which is placed in ultrapure water, dialysis is performed, and the dialysis is performed for two days, with the ultrapure water being replaced three times a day (stirring).

[0090] (5) the PVA / RA solution after dialysis is taken into a small acrylic mold, vacuum is applied to remove bubbles (air is applied horizontally, vacuum is applied clockwise, vacuum is closed counterclockwise, after completion, air is slowly opened a small hole), the bubbles are removed and directly poured into the mold, dried at 50°C for 24 h, demolded, and a rosmarinic acid and zinc ion double-crosslinked PVA composite film is obtained.

[0091] Comparative Example 3

[0092] 20 ml of a PVA aqueous solution with a concentration of 100 g / L is taken in a beaker, 163.6 mg of rosmarinic acid (mass ratio PVA:RA = 12.2:1) is weighed into the beaker using a weighing instrument, and stirring is performed until dissolution, and a PVA+RA solution is obtained.

[0093] The product performance of Examples 1-10 and Comparative Examples 1-3 is detected.

[0094] (1) the actual figure of the PVA / RA solution of Examples 1-5 is as shown in Figure 1 , it can be seen from Figure 1 that as the amount of RA added increases, the color of the solution gradually changes from light yellow to dark yellow, and finally presents a turbid state, and the turbid state of Example 2 is due to the increase in the content of rosmarinic acid, which reduces the hydroxyl group of PVA, increases the hydrophobicity, and causes a part of PVA to precipitate, so that the solution becomes turbid.

[0095] (2) the ultraviolet absorption spectrum of the PVA / RA solution of Examples 1-5 and the PVA aqueous solution of Comparative Example 1 and the PVA+RA solution of Comparative Example 3 is as shown in Figure 2 , it can be seen from Figure 2 that the ultraviolet absorption of the solution of Example 1 is the highest. The ultraviolet absorption of the solution of Comparative Example 1 is the worst, and as the amount of RA added decreases, the ultraviolet absorption of the solution also decreases, the absorption of the solution of Example 1 is the highest, and there is no big difference with the PVA+RA solution (Comparative Example 3) mixed alone, which shows that the processing method does not affect the performance of rosmarinic acid.

[0096] (3) the comparison chart of the zinc ion chelation amount of the solutions of Examples 1, 7-10 is as shown in Figure 3 . Since zinc ions are chelated by two phenolic hydroxyl groups on rosmarinic acid, the content of zinc ions added will have a saturation value. The comparison chart of the zinc ion chelation amount of the solutions of Examples 1 / 7-10 is as shown in Figure 3 , it can be seen from Figure 3It can be seen that when the zinc ion content is 163.2 mg, the chelating amount reaches the saturation value.

[0097] (4) The ATR-FTIR spectra of the solutions of Example 1 and Comparative Examples 1-3 are as follows: Figure 4 As shown, from Figure 4 Yes, the characteristic absorption peaks of PVA in Comparative Example 1 are 3340 cm −1 (OH stretching), 2940 cm −1 (hydrocarbon CH stretching), 1426 cm −1 (CH2 bending vibration) and 1084 cm −1 (CO stretching). Compared with PVA, the PVA / RA of Comparative Example 2 has a −1 The absorption peak at 53.54eV is enhanced, indicating that the CO content increases. This indicates that an esterification cross-linking reaction occurs between the hydroxyl groups of polyvinyl alcohol and the carboxyl groups of rosmarinic acid to form an ester group. The C-OH peak of the PVA+RA solution of Comparative Example 3 shifts to 532.52eV. At the same time, new peaks appear at 533.47 and 531.32, which are attributed to C=O and -COO-. The PVA / RA / Zn solution of Example 1 2+ 1265 cm in the spectrum −1 The strong peak at 1259 cm in the PVA / RA spectrum corresponds to −1 The vibration of the CO group of catechol and the change of its chemical shift suggest that the catechol structure in PVA / RA may be the site of metal ion coordination, which indicates that the phenolic hydroxyl group in RA is involved in metal chelation.

[0098] (5) The UV-visible performance of the films of Example 1 and Comparative Examples 1-2 is analyzed as follows: Figure 5 As shown, from Figure 5 It can be seen that PVA alone does not show any significant UV protection as evidenced by the 85-90% transmittance in the UV region. On the other hand, the composite films of Example 1 and Comparative Example 2 show broad and significant UV absorption (protection) and high visible light transmittance.

[0099] (6) Example 1, Comparative Example 1-2 solution antibacterial performance test, the specific process is as follows: LB (TSA) liquid culture medium, LB Escherichia coli (TSA Staphylococcus aureus) liquid culture medium for liquid culture test, according to the number of colonies in the culture medium to judge the antibacterial effect of the liquid, the fewer the number of colonies, the stronger the antibacterial effect. The antibacterial performance test results are as follows Figure 6 As shown, from Figure 6 It can be seen that by testing PVA (Comparative Example 1), PVA / RA (Comparative Example 2) and PVA / RA / Zn 2+(Example 1) The number of strains in the solution was found to be PVA / RA and PVA / RA / Zn 2+ The number of bacterial beads in the PVA / RA / Zn composite film decreased compared with the blank control and pure PVA, and the antibacterial effect was good, indicating that the composite film had good antibacterial properties. 2+ Compared with PVA / RA solution, the antibacterial effect of the solution is significantly improved.

[0100] (7) Example 1, Comparative Example 1-2 Film Antioxidant Performance Test, the specific process is as follows: add the solution to the DPPH solution, and test the absorbance of DPPH after 30-40 minutes. The lower the absorbance, the stronger the antioxidant property. The test results are as follows: Figure 7 As shown, from Figure 7 It can be seen that PVA, PVA / RA and PVA / RA / Zn 2+ The DPPH scavenging rate of the solution was found to be PVA / RA and PVA / RA / Zn 2+ The solution has good free radical scavenging ability and good antioxidant effect, indicating that the film of the present application has good antioxidant properties.

[0101] (8) Mechanical property test of the film of Example 1 and Comparative Example 2. The specific process is as follows: the film is cut into strips of 1-4 cm wide and 2-4 cm long for mechanical property test. The four indicators of tensile strength, elongation at break, elastic modulus and tensile stress at break are tested. The film is subjected to the test at 20 mm min. -1 The strain rate is set to 0.05, and the tensile load is applied to the fracture. Figure 8 ,from Figure 8 It can be seen that the tensile strength, elongation at break, modulus and tensile stress at break of PVA film are 47MPa, 151%, 2080.76645MPa and 4.0823MPa respectively; the tensile strength, elongation at break, modulus and tensile stress at break of PVA / RA film are 36MPa, 93%, 1781.0437MPa and 3.40915MPa respectively; 2+ The tensile strength, elongation at break, modulus and tensile stress at break of the film are 67 MPa, 266%, 2534.2522 MPa and 6.4344 MPa respectively. 2+ The tensile strength of the film increased by 29.85MPa compared with the PVA film and 46.27MPa compared with the PVA / RA film; 2+ The elongation at break of the film increased by 65.04% compared with the PVA film and by 42.23% compared with the PVA / RA film, which shows that the addition of zinc ions can greatly improve the decline in the mechanical properties of the PVA film caused by the addition of rosmarinic acid. Figure 8 It can be seen that PVA / RA / Zn2+ showed strong tensile strength, elongation at break, elastic modulus and tensile stress at break.

[0102] Finally, it should be noted that the above examples are intended to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a double-crosslinked PVA composite film of rosmarinic acid and zinc ions, characterized in that: include: (1) mixing rosmarinic acid and polyvinyl alcohol aqueous solution to react and obtain polyvinyl alcohol / rosmarinic acid initial solution; (2) dialyzing the polyvinyl alcohol / rosmarinic acid initial solution to obtain a polyvinyl alcohol / rosmarinic acid pure solution; (3) Mixing the polyvinyl alcohol / rosmarinic acid pure solution with zinc chloride solution to obtain polyvinyl alcohol / rosmarinic acid / Zn 2+ solution; (4) the polyvinyl alcohol / rosmarinic acid / Zn 2+ The solution is dried to remove water, thereby obtaining a rosmarinic acid and zinc ion double-crosslinked PVA composite film.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of the rosmarinic acid to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 1:(5-200); And / or, the concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 80-120 g / L; And / or, the temperature of the mixed reaction is 110° C. to 120° C., and the time is 2 h to 4 h.

3. The method according to claim 1 or 2, characterized in that In step (1), the preparation process of the polyvinyl alcohol aqueous solution includes: mixing polyvinyl alcohol and water and reacting them at 90° C. to 100° C. for 4 h to 6 h.

4. The method according to claim 1, characterized in that In step (2), the dialysis uses a dialysis bag with a molecular weight of 800-1000 and ultrapure water.

5. The method according to claim 1, characterized in that: In step (3), the concentration of zinc chloride in the solution after the polyvinyl alcohol / rosmarinic acid pure solution and the zinc chloride solution are mixed is 0.8 g / L to 15 g / L; And / or, the concentration of the zinc chloride solution is 50 g / L to 300 g / L; And / or, the mixing temperature is room temperature, and the mixing time is 20h~25h.

6. The method according to claim 1 or 5, characterized in that The preparation process of the zinc chloride solution comprises: dissolving zinc chloride powder with 0.07-0.1 mol / L hydrochloric acid, shaking for 15-20 minutes, and allowing to react for 20-30 hours.

7. The method according to claim 1 or 5, characterized in that Step (3) also includes: polyvinyl alcohol / rosmarinic acid / Zn 2+ The solution was dialyzed against 0.01~0.07mol / L hydrochloric acid solution for 20h~32h.

8. The method according to claim 1, characterized in that: In step (4), the drying temperature is 50°C to 60°C, and the drying time is 24h to 32h.

9. A double-crosslinked PVA composite film of rosmarinic acid and zinc ions, characterized in that: Prepared by the method according to any one of claims 1 to 8.

10. Use of the double-crosslinked PVA composite film of rosmarinic acid and zinc ions according to claim 9 in the field of food packaging.

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