A natural polymer-based food packaging material and its preparation method and application

Abstract

The present invention provides a natural polymer-based food packaging material, a preparation method, and an application thereof, belonging to the technical field of food packaging materials. The present invention uses a chitosan derivative, chitosan quaternary ammonium salt, as a basis and uses the anions of docusate sodium to perform ion exchange on the chitosan quaternary ammonium salt. On the one hand, the chitosan quaternary ammonium salt takes advantage of its antibacterial and film-forming properties to impart good processing properties to the food packaging material and effectively solve the problem of bacterial growth in food packaging materials. On the other hand, the present invention uses the anions of docusate sodium to modify the chitosan quaternary ammonium salt, partially or completely replacing the chloride ions of the chitosan quaternary ammonium salt with the anions of docusate sodium. This can impart good hydrophobicity to the food packaging material, causing water vapor to accumulate on the surface of the material without penetrating, thereby imparting good water vapor barrier properties.

Description

Technical Field

[0001] The present invention relates to the technical field of food packaging materials, and in particular to a natural polymer-based food packaging material, a preparation method thereof, and an application thereof. Background Art

[0002] Plastic packaging materials have been widely used in the packaging industry due to their lightweight, durable, low-cost, and excellent protective and sealing properties. However, the increasing demand for raw materials due to the high volume of plastic packaging is exacerbating the depletion of natural resources. Therefore, the development of natural, renewable raw materials for plastic packaging is urgently needed.

[0003] Chitin is widely distributed in nature, with reserves ranking second only to cellulose, making it the second largest natural polymer. Approximately 10 billion tons of chitin are biosynthesized annually, making it a recyclable renewable resource. Chitosan quaternary ammonium salts, as advanced chitosan derivatives, possess excellent antibacterial properties. However, due to their high hydrophilicity and excellent water solubility, chitosan quaternary ammonium salts are not suitable for use as food packaging materials. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a natural polymer-based food packaging material and its preparation method and application. The natural polymer-based food packaging material provided by the present invention uses chitosan quaternary ammonium salt as raw material and has good hydrophobicity and antibacterial properties.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a natural polymer-based food packaging material having a structure shown in Formula 1:

[0007]

[0008] The anion R in formula 1 - Having the structure shown in Formula 2-1 and / or Formula 2-2; in the different structural units of Formula 1, the anion R - Not all of them are structures shown in formula 2-2:

[0009]

[0010] In formula 1, m>0, n>0, m+n=10-600, n / m+n=0.5-0.99, and m and n are both integers.

[0011] Preferably, in Formula 1, the anion R having the structure shown in Formula 2-1 - Accounting for all anions R - 50-100%;

[0012] Anion R having the structure shown in Formula 2-2 - Accounting for all anions R - 0~50%.

[0013] The present invention provides a method for preparing the above-mentioned natural polymer-based food packaging material, comprising the following steps:

[0014] Mixing a chitosan quaternary ammonium salt having a structure shown in Formula 3 with water to obtain a chitosan quaternary ammonium salt aqueous solution;

[0015]

[0016] In formula 3, m>0, n>0, m+n=10-600, n / m+n=0.5-0.99, m and n are both integers;

[0017] The chitosan quaternary ammonium salt aqueous solution is mixed with the docusate sodium aqueous solution and ion exchange is performed to obtain a natural polymer-based food packaging material having a structure shown in Formula 1.

[0018] Preferably, the mass concentration of the chitosan quaternary ammonium salt aqueous solution is 1 to 20%.

[0019] Preferably, the molecular weight of the chitosan quaternary ammonium salt is 10,000 to 300,000 g / mol;

[0020] The substitution degree of the chitosan quaternary ammonium salt is 50-99%.

[0021] Preferably, the mass concentration of the docusate sodium aqueous solution is 1 to 50%.

[0022] Preferably, the molar ratio of the quaternary ammonium salt functional group in the chitosan quaternary ammonium salt having the structure shown in Formula 3 to docusate sodium is 1:0.1-10.

[0023] Preferably, the ion exchange temperature is 0°C to 100°C, and the time is 0.5 to 120 hours.

[0024] Preferably, after the ion exchange, the obtained ion exchange reaction liquid is washed and dried.

[0025] The present invention provides application of the above-mentioned natural polymer-based food packaging material in the field of food packaging.

[0026] The present invention provides a natural polymer-based food packaging material having a structure shown in Formula 1. Chitosan is widely distributed in nature and has high reserves. The present invention is based on a chitosan derivative - chitosan quaternary ammonium salt, and uses the anion of docusate sodium to perform ion exchange on it. On the one hand, the advantages of chitosan quaternary ammonium salt's good antibacterial and film-forming properties are utilized to give the food packaging material good processing performance, and effectively solve the problem that food packaging materials are prone to bacterial growth; on the other hand, the present invention uses the anion of docusate sodium to modify the chitosan quaternary ammonium salt, and uses the anion of docusate sodium to partially or completely replace the chloride ion of the chitosan quaternary ammonium salt, which can make the food packaging material have good hydrophobicity, so that water vapor will gather on the surface of the material without penetrating, thereby having good water vapor barrier performance. The natural polymer-based food packaging material provided by the present invention has good antibacterial properties, biocompatibility, mechanical strength and water vapor barrier performance at the same time, and can be used to preserve fruits, vegetables and other foods, extend their shelf life, and reduce food waste.

[0027] The present invention provides a method for preparing the above-mentioned natural polymer-based food packaging material. This method is based on the exchange reaction between the chloride ions of chitosan quaternary ammonium salt and the sodium ions of docusate, has simple operation, low cost, and is easy to achieve industrial batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the stress-strain curve of the natural polymer-based food packaging material in Example 1;

[0029] Figure 2 The cell compatibility test results of the natural polymer-based food packaging material in Example 1 are as follows;

[0030] Figure 3 These are the test results of the antibacterial properties of the natural polymer-based food packaging material in Example 3. DETAILED DESCRIPTION

[0031] The present invention provides a natural polymer-based food packaging material having a structure shown in Formula 1:

[0032]

[0033] The anion R in formula 1 - Having the structure shown in Formula 2-1 and / or Formula 2-2; in the different structural units of Formula 1, the anion R - Not all of them are structures shown in formula 2-2:

[0034]

[0035] In formula 1, m>0, n>0, m+n=10-600, n / m+n=0.5-0.99, and m and n are both integers.

[0036] In the present invention, m represents the number of repeating units of the ungrafted quaternary ammonium salt in the chitosan quaternary ammonium salt; m is preferably 0 to 225, more preferably 10 to 200. In the present invention, n represents the number of repeating units of the grafted quaternary ammonium salt in the complexed chitosan quaternary ammonium salt; m+n is preferably 100 to 600, more preferably 100 to 500. In the present invention, n / m+n is preferably 0.5 to 0.99, more preferably 0.7 to 0.99.

[0037] In the present invention, in Formula 1, the anion R having the structure shown in Formula 2-1 - Preferably, all anions R - 50 to 100%, more preferably 60 to 80%; anion R having the structure shown in formula 2-2 - Preferably, all anions R - 0 to 50%, more preferably 20 to 40%.

[0038] The present invention provides a method for preparing the above-mentioned natural polymer-based food packaging material, comprising the following steps:

[0039] Mixing a chitosan quaternary ammonium salt having a structure shown in Formula 3 with water to obtain a chitosan quaternary ammonium salt aqueous solution;

[0040]

[0041] In formula 3, m>0, n>0, m+n=10-600, n / m+n=0.5-0.99, m and n are both integers;

[0042] The chitosan quaternary ammonium salt aqueous solution is mixed with the docusate sodium aqueous solution and ion exchange is performed to obtain a natural polymer-based food packaging material having a structure shown in Formula 1.

[0043] Unless otherwise specified, the raw materials used in the present invention are all commercially available.

[0044] The present invention mixes a chitosan quaternary ammonium salt having a structure shown in Formula 3 with water to obtain a chitosan quaternary ammonium salt aqueous solution. In the present invention, the molecular weight of the chitosan quaternary ammonium salt is preferably 10,000 to 300,000 g / mol, more preferably 50,000 to 200,000 g / mol, and further preferably 100,000 to 150,000 g / mol. In the present invention, the degree of substitution of the chitosan quaternary ammonium salt is preferably 50 to 99%, more preferably 70 to 99%.

[0045] In the present invention, the water is preferably deionized water. In the present invention, the mixing is preferably heated mixing, and the temperature of the heated mixing is preferably 45°C. In the present invention, the mass concentration of the chitosan quaternary ammonium salt aqueous solution is preferably 1-20%, more preferably 5-10%; as a specific embodiment of the present invention, the mass concentration of the chitosan quaternary ammonium salt aqueous solution is 1%, 5%, 8%, 10%, 15% or 20%.

[0046] The present invention mixes the chitosan quaternary ammonium salt aqueous solution with the docusate sodium aqueous solution and performs ion exchange to obtain a natural polymer-based food packaging material having a structure shown in Formula 1. In the present invention, the docusate sodium has a structure shown in Formula 4:

[0047]

[0048] In the present invention, the mass concentration of the docusate sodium aqueous solution is preferably 1-50%, more preferably 10-40%; as a specific embodiment of the present invention, the mass concentration of the docusate sodium aqueous solution is 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%.

[0049] In the present invention, the molar ratio of the quaternary ammonium salt functional group in the chitosan quaternary ammonium salt having the structure shown in Formula 3 to docusate sodium is preferably 1:0.1-10, more preferably 1:0.5-5, and further preferably 1:1-3.

[0050] The present invention has no particular requirements for the mixing method; any mixing method known in the art, such as stirring, may be used. In the present invention, the ion exchange temperature is preferably 0-100°C, more preferably 20-60°C, and even more preferably room temperature; the ion exchange time is preferably 0.5-120 hours, more preferably 10-60 hours. Chitosan quaternary ammonium salt is water-soluble, and after ion exchange with docusate sodium, the ion exchange product precipitates from water, exhibiting good hydrophobicity.

[0051] In the present invention, after the ion exchange, the ion exchange reaction solution is preferably washed and dried. In the present invention, the washing is preferably water washing, and the drying is preferably freeze drying.

[0052] The present invention provides application of the above-mentioned natural polymer-based food packaging material in the field of food packaging.

[0053] The natural polymer-based food packaging material provided by the present invention, its preparation method and application are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0054] Example 1

[0055] (1) 1.4 g of chitosan quaternary ammonium salt with a molecular weight of 100,000 g / mol and a degree of substitution of 90% and 100 g of deionized water were added to a 250 mL round-bottom flask and heated at 45°C for 24 h until completely dissolved.

[0056] (2) Dissolve 1.9 g of the sodium docusate in 20 mL of deionized water to obtain a sodium docusate aqueous solution.

[0057] (3) The two aqueous solutions were mixed and ion exchanged at room temperature for 72 h (the molar ratio of quaternary ammonium salt group to sodium docusate was 1:1). The resulting product was washed and dried multiple times to obtain a natural polymer-based food packaging material.

[0058] Example 2

[0059] (1) Add 1.5 g of chitosan quaternary ammonium salt with a molecular weight of 300,000 g / mol and a degree of substitution of 90% and 100 g of deionized water to a 250 mL round-bottom flask and heat at 45°C for 24 h until completely dissolved.

[0060] (2) Dissolve 4.0 g of the sodium docusate in 20 mL of deionized water to obtain a sodium docusate aqueous solution.

[0061] (3) After mixing the above two aqueous solutions, ion exchange was carried out at room temperature for 72 h (the molar ratio of quaternary ammonium salt group to sodium docusate was 1:2), and the resulting product was washed and dried multiple times to obtain a natural polymer-based food packaging material.

[0062] Example 3

[0063] (1) 1.4 g of chitosan quaternary ammonium salt with a molecular weight of 200,000 g / mol and a degree of substitution of 99% and 100 g of deionized water were added to a 250 mL round-bottom flask and heated at 45°C for 24 h until completely dissolved.

[0064] (2) Dissolve 1.0 g of the sodium docusate in 20 mL of deionized water to obtain a sodium docusate aqueous solution.

[0065] (3) After mixing the above two aqueous solutions, ion exchange was carried out at room temperature for 72 h (the molar ratio of quaternary ammonium salt group to sodium docusate was 1:0.6), and the resulting product was washed and dried multiple times to obtain a natural polymer-based food packaging material.

[0066] Performance Testing

[0067] (1) Tensile performance test: The natural polymer-based food packaging material obtained in the example was dissolved in DMF, spread into a film, and then dried in an oven to obtain a test sample. The completely dried test sample was cut into 20 mm × 4 mm × 1 mm dumbbell-shaped specimens with a cutter. At least 5 dumbbell-shaped specimens were prepared for each test sample as parallel comparisons. The test sample was subjected to a tensile test on a universal testing machine. The tensile rate was 10 mm / min, the test temperature was 25 ± 2 ° C, and at least 5 parallel samples were tested for each test sample.

[0068] (2) Cytotoxicity test: The test sample was cut into 3 cm × 2 cm rectangular strips, washed and dried, and then placed in 2 mL of complete culture medium for immersion at 37 ° C for 24 h to obtain the extract. The cytotoxicity test of the material extract was performed using the CCK-8 method. L929 cells in the logarithmic growth phase were taken and the cell count was performed, and the cell concentration was adjusted to 1 × 10 5 / mL, take 100μL and inoculate into 96-well plates, culture overnight at 37°C in a 5% CO2 constant temperature incubator to allow cells to grow attached to the wall. Add 100μL of extract and culture for 24h, then remove the culture medium, wash three times with sterile PBS buffer, add 100μL of 10% concentration CCK-8 solution to each well, add 100μL of complete culture medium to the blank wells around the test well as the background group, culture in a constant temperature incubator at 5% CO2, 37°C for 2h, take out and use a microplate reader to detect the absorbance value of each well at 450nm. The cytotoxicity of the sample was tested by calculating the cell viability. The calculation formula for cell viability is shown in Formula 1:

[0069]

[0070] (3) Antibacterial performance test: Escherichia coli and Staphylococcus aureus were used as experimental strains. First, the bacteria were inoculated into MH broth medium and cultured at 37°C for 12 hours to allow the bacteria to reach the logarithmic growth phase. After centrifugation, the bacterial solution was diluted with MH broth to 5×10 5 CFU / mL is set aside. Cut the test sample into a 1.5cm×1.5cm square membrane and place it in a 6-well plate. Add 25μL of the above bacterial suspension to the center area of ​​the membrane surface and cover it with a 1cm×1cm polyethylene (PE) film. Place the test sample in a constant temperature and humidity incubator at 37°C and 90% humidity and incubate for 24 hours. Then take out the test sample together with the PE cover film and place it in a 50mL sterile centrifuge tube. Add 5mL of PBS solution and vortex for 1.5 minutes to make the bacteria adhering to the surface of the test sample fall off. Then spread the PBS solution containing bacteria on LB agar culture, culture at 37°C overnight, and count the number of colonies. The calculation formula for the antibacterial rate is shown in Formula 2:

[0071] Antibacterial rate (%) = (BC) / B × 100 Formula 2;

[0072] In formula 2, B: average number of bacteria recovered from blank control samples;

[0073] C: Average number of bacteria recovered from antibacterial samples.

[0074] (4) Water vapor transmission rate test: The material was wrapped in a cylindrical cup containing deionized water. A blank control group was used as a control. The cup was kept in a constant temperature and humidity chamber (37°C, 95%) for 24 hours. The mass loss of water in the cup was measured, and the calculation formula is shown in Equation 3:

[0075] X = (W1-W2) × 1000 × 24 / T (Equation 3);

[0076] In formula 3, X is water vapor transmission rate, in grams per square meter per 24 hours (g·m -2 24h -1 );

[0077] W1: mass of container, sample and liquid, unit (g);

[0078] W2: mass of container, sample and liquid after the test period, in g;

[0079] T: test period, in hours (h).

[0080] The performance test results of the natural polymer-based food packaging materials obtained in Examples 1 to 3 are shown in Table 1.

[0081] Table 1 Performance test results of natural polymer-based food packaging materials obtained in Examples 1 to 3

[0082]

[0083] Among them, the stress-strain curve of the natural polymer-based food packaging material in Example 1 is as follows: Figure 1 As shown, it can be seen that the tensile strength of this material is 13.8 MPa and the elongation at break is 67%.

[0084] Example 1 Cell compatibility test results of natural polymer-based food packaging materials are as follows Figure 2 As shown, Figure 2 The control group was a cell sample to which no material extract was added.

[0085] Example 3: The antibacterial performance test results of natural polymer-based food packaging materials are as follows: Figure 3 As shown. Figure 3 It can be seen that compared with the control group, the antibacterial rate of the material prepared in Example 3 against Escherichia coli is 96.0%; the antibacterial rate against Staphylococcus aureus is 99.99%.

[0086] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A natural polymer-based food packaging material, characterized in that: It has the structure shown in formula 1: The anion R in formula 1 - Having the structure shown in Formula 2-1 and / or Formula 2-2; in the different structural units of Formula 1, the anion R - Not all of them are structures shown in formula 2-2: In formula 1, m>0, n>0, m+n=10-600, n / m+n=0.5-0.99, and m and n are both integers.

2. The natural polymer-based food packaging material according to claim 1, characterized in that: In Formula 1, the anion R having the structure shown in Formula 2-1 - Accounting for all anions R - 50-100%; Anion R having the structure shown in Formula 2-2 - Accounting for all anions R - 0~50%.

3. The method for preparing the natural polymer-based food packaging material according to claim 1 or 2, characterized in that: The following steps are involved: Mixing a chitosan quaternary ammonium salt having a structure shown in Formula 3 with water to obtain a chitosan quaternary ammonium salt aqueous solution; In formula 3, m>0, n>0, m+n=10-600, n / m+n=0.5-0.99, m and n are both integers; The chitosan quaternary ammonium salt aqueous solution is mixed with the docusate sodium aqueous solution and ion exchange is performed to obtain a natural polymer-based food packaging material having a structure shown in Formula 1.

4. The preparation method according to claim 3, characterized in that The mass concentration of the chitosan quaternary ammonium salt aqueous solution is 1-20%.

5. The preparation method according to claim 3 or 4, characterized in that The molecular weight of the chitosan quaternary ammonium salt is 10,000 to 300,000 g / mol; The substitution degree of the chitosan quaternary ammonium salt is 50-99%.

6. The preparation method according to claim 3, characterized in that The mass concentration of the docusate sodium aqueous solution is 1-50%.

7. The preparation method according to claim 3, characterized in that The molar ratio of the quaternary ammonium salt functional group in the chitosan quaternary ammonium salt having the structure shown in Formula 3 to docusate sodium is 1:0.1-10.

8. The preparation method according to claim 3, characterized in that The temperature of the ion exchange is 0° C. to 100° C., and the time is 0.5 to 120 hours.

9. The preparation method according to claim 3, characterized in that After the ion exchange, the method further includes washing and drying the obtained ion exchange reaction liquid.

10. Use of the natural polymer-based food packaging material according to claim 1 or 2, or the natural polymer-based food packaging material prepared by the preparation method according to any one of claims 3 to 9 in the field of food packaging.

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