A kind of composite preservative bag based on quaternary ammonium chitosan / polyvinyl alcohol aerogel and its application

Abstract

The application relates to a composite fresh-keeping bag based on quaternary ammonium chitosan / polyvinyl alcohol aerogel and application thereof, and belongs to the technical field of materials. The composite fresh-keeping bag based on quaternary ammonium chitosan / polyvinyl alcohol aerogel comprises a first non-woven fabric layer, a second non-woven fabric layer and a quaternary ammonium chitosan / polyvinyl alcohol aerogel layer arranged between the first non-woven fabric layer and the second non-woven fabric layer; the quaternary ammonium chitosan / polyvinyl alcohol aerogel layer is compounded between the first non-woven fabric layer and the second non-woven fabric layer through a hot-pressing process. The composite fresh-keeping bag based on quaternary ammonium chitosan / polyvinyl alcohol aerogel has stable modified atmosphere fresh-keeping effect; the quaternary ammonium chitosan / polyvinyl alcohol aerogel has uniform microporous structure and high gas adsorption capacity, can effectively fix gas components, maintain a stable modified atmosphere environment and prolong the fresh-keeping period of food.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, and in particular relates to a composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel and its application. Background Technology

[0002] Modified atmosphere packaging (MAP) is an important food preservation method that extends the shelf life of food by adjusting the gas composition of the food storage environment. This technology has been widely used in the food industry, for example, by controlling oxygen and carbon dioxide concentrations to inhibit food oxidation and microbial growth, thereby delaying food spoilage.

[0003] However, there are still some problems with the modified atmosphere packaging (MAP) technology on the market: the effect of MAP is unstable (traditional MAP methods may experience leakage or changes in gas components during long-term storage or transportation, leading to a decline in the quality and freshness of food), the cost of packaging materials is high (currently, the cost of commonly used MAP materials on the market is high, such as adsorbent films or packaging films, which limits their application in large-scale food packaging), and the preparation process of packaging materials is complex (existing MAP materials have complex preparation processes, requiring high-cost equipment and professional technology, which is not conducive to large-scale production and application), etc. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problem of unstable modified atmosphere preservation effect of composite preservation bags in the prior art.

[0005] To address the aforementioned technical problems, this invention provides a composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel and its application.

[0006] The first objective of this invention is to provide a composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel, comprising a first nonwoven fabric layer, a second nonwoven fabric layer, and a quaternized chitosan / polyvinyl alcohol aerogel layer disposed between the first and second nonwoven fabric layers; the quaternized chitosan / polyvinyl alcohol aerogel layer is composited between the first and second nonwoven fabric layers by a hot-pressing process.

[0007] In one embodiment of the present invention, the quaternized chitosan / polyvinyl alcohol aerogel comprises quaternized chitosan and polyvinyl alcohol, ensuring the structural stability and functional properties of the aerogel. This aerogel possesses an excellent hierarchical porous structure, which helps enhance CO2 adsorption efficiency and gives the aerogel a high surface area and adsorption capacity. The introduction of quaternary ammonium groups into the aerogel enhances its CO2 adsorption capacity, enabling reversible CO2 capture in the environment. Specifically, in low-humidity environments, CO2 can be adsorbed by the aerogel, while when the ambient humidity increases (respiration of fruits and vegetables leads to increased humidity inside the preservation bag), CO2 is desorbed, thereby increasing the CO2 concentration inside the preservation bag, inhibiting the respiration of fruits and vegetables, and achieving modified atmosphere preservation. The quaternized chitosan portion has excellent antibacterial properties, helping to extend the shelf life of food. The polyvinyl alcohol portion has good gas barrier properties, blocking the penetration of oxygen and water vapor, maintaining the freshness and quality of food.

[0008] In one embodiment of the present invention, the thickness of the quaternized chitosan / polyvinyl alcohol aerogel layer is 100μm-1000μm.

[0009] In one embodiment of the present invention, the preparation of the quaternized chitosan / polyvinyl alcohol aerogel includes the following steps:

[0010] S1. Mix the polyvinyl alcohol solution and the quaternized chitosan solution, and adjust the pH to 4.5-5.5 to obtain a quaternized chitosan / polyvinyl alcohol mixture.

[0011] S2. Add a crosslinking agent to the quaternized chitosan / polyvinyl alcohol mixture described in S1 to carry out a crosslinking reaction, and obtain quaternized chitosan / polyvinyl alcohol hydrogel.

[0012] S3. The quaternized chitosan / polyvinyl alcohol hydrogel described in S2 is soaked in alkaline solution, washed with water, and freeze-dried to obtain the quaternized chitosan / polyvinyl alcohol aerogel.

[0013] In one embodiment of the present invention, in S1, the concentration of the quaternized chitosan solution is 0.5wt%-3.5wt%; the concentration of the polyvinyl alcohol solution is 3wt%-8wt%; and the mass ratio of the polyvinyl alcohol solution to the quaternized chitosan solution is 1:2-4.

[0014] Furthermore, the mass ratio of the polyvinyl alcohol solution to the quaternized chitosan solution is 1:2-3 to ensure the CO2 adsorption capacity and physical stability of the food preservation bag.

[0015] In one embodiment of the present invention, in S2, the crosslinking agent is selected from one or more of glutaraldehyde, epichlorohydrin and phenylenedialdehyde.

[0016] In one embodiment of the present invention, in S2, the temperature of the crosslinking reaction is 50°C-85°C and the time is 5h-8h.

[0017] In one embodiment of the present invention, in S3, the alkaline solution is selected from sodium hydroxide solution and / or potassium hydroxide solution; the concentration of the alkaline solution is 0.5 mol / L-2 mol / L.

[0018] In one embodiment of the present invention, in S3, the freeze-drying temperature is -60°C to -40°C, and the time is 36h to 48h.

[0019] In one embodiment of the present invention, the materials of the first nonwoven layer and the second nonwoven layer are independently selected from one or more of polyvinyl alcohol (PVA), polypropylene (PP), polyethylene (PE), polyester (PET) and polylactic acid (PLA) to improve the overall gas permeability and mechanical strength of the composite food preservation bag.

[0020] In one embodiment of the present invention, the first nonwoven layer and the second nonwoven layer are prepared by electrospinning. This nonwoven layer possesses excellent properties such as high specific surface area, high porosity, high strength, and flexibility, resulting in better performance in adsorbing and separating CO2.

[0021] Furthermore, the electrospinning conditions are as follows: spinning flow rate of 0.1 mL / h-0.3 mL / h, temperature of 15℃-45℃, and humidity of 45%-55%.

[0022] In one embodiment of the present invention, the hot-pressing process is performed under the following conditions: temperature 145℃-180℃, pressure 3MPa-5MPa, and time 5min-8min. Hot-pressing technology ensures edge sealing and accurate positioning (preventing slippage) between the non-woven fabric layer and the quaternized chitosan / polyvinyl alcohol aerogel layer, while also guaranteeing high gas permeability. Furthermore, the quaternized chitosan / polyvinyl alcohol aerogel layer and the non-woven fabric layer must be precisely cut before the hot-pressing process to ensure dimensional matching. The thickness and position of the quaternized chitosan / polyvinyl alcohol aerogel layer between the two non-woven fabric layers must also be determined in advance to ensure maximum gas exchange efficiency.

[0023] The second objective of this invention is to provide an application of the composite preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel in modified atmosphere storage.

[0024] The technical solution of the present invention has the following advantages compared with the prior art:

[0025] (1) The composite preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel described in this invention has a stable modified atmosphere preservation effect. The quaternized chitosan / polyvinyl alcohol aerogel has a uniform microporous structure and a high gas adsorption capacity, which can effectively fix gas components, maintain a stable modified atmosphere environment, and extend the shelf life of food.

[0026] (2) The composite preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel described in this invention has adjustable gas adsorption performance. The adsorption rate and adsorption amount of quaternized chitosan / polyvinyl alcohol aerogel for oxygen, carbon dioxide and water vapor can be adjusted according to the modified atmosphere preservation requirements of different foods, which improves its applicability and flexibility and has high application prospects and market potential.

[0027] (3) The composite preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel described in this invention achieves efficient and reversible capture of CO2 in ambient air through its unique layered pore structure and the introduction of quaternary ammonium groups, and can be applied to extend the shelf life of perishable foods and fruits and vegetables under controlled atmosphere conditions.

[0028] (4) The preparation of the quaternized chitosan / polyvinyl alcohol aerogel of the present invention uses quaternized chitosan and polyvinyl alcohol as raw materials, which has a low cost; moreover, it can be obtained through a simple preparation process, without the need for complex equipment and technology, which can reduce production costs, improve production efficiency, and achieve low cost and high efficiency, making it suitable for large-scale production and application. Attached Figure Description

[0029] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0030] Figure 1 This is a decay index scoring chart for Test Example 1 of the present invention;

[0031] Figure 2 This is a weight loss rate score chart for Test Example 1 of the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0033] In the description of this patent, it should be noted that the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of these terms in this patent based on the specific circumstances.

[0034] Example 1

[0035] The composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel of the present invention specifically includes the following steps:

[0036] S1. Preparation of quaternized chitosan:

[0037] S11. Suspend 5g of chitosan in 200mL of deionized water, then add 1mL of acetic acid to the suspension and stir for 30min. Gradually add 28g of glycidyltrimethylammonium chloride and continue the reaction at 55℃ for 18h to obtain a mixture.

[0038] S12. Centrifuge the mixture at 4000 rpm for 20 min at room temperature to remove undissolved chitosan. Then, filter the solution and add a pre-cooled acetone / ethanol mixture (volume ratio 1:1). Then, quaternize the chitosan to precipitate it. Repeat the above process three times and dry it in a vacuum oven at 35°C for 5 days to obtain purified quaternized chitosan.

[0039] S2, Preparation of Quaternized Chitosan / Polyvinyl Alcohol Aerogel

[0040] S21. Dissolve quaternized chitosan in deionized water to prepare a 2wt% quaternized chitosan solution; dissolve polyvinyl alcohol in deionized water and stir at 95°C to prepare a 5wt% polyvinyl alcohol solution; then add the polyvinyl alcohol solution to the quaternized chitosan solution at a mass ratio of 1:2.5 and stir until homogeneous; adjust the pH to 5 with dilute hydrochloric acid solution to form a quaternized chitosan / polyvinyl alcohol mixture.

[0041] S22. Add 2 mL of glutaraldehyde to the quaternized chitosan / polyvinyl alcohol mixture and stir continuously for 30 min. Then react at 60 °C for 6 h to obtain quaternized chitosan / polyvinyl alcohol hydrogel.

[0042] S23. The quaternized chitosan / polyvinyl alcohol hydrogel was immersed in a 1 mol / L sodium hydroxide solution for 24 h to undergo ion exchange with sodium hydroxide. During the ion exchange process, the free chloride ions in the hydrogel were replaced by hydroxide ions. Then, the sodium hydroxide was washed with deionized water and freeze-dried at -50℃ for 48 h to obtain the quaternized chitosan / polyvinyl alcohol aerogel.

[0043] S3. Preparation of composite food preservation bags based on quaternized chitosan / polyvinyl alcohol aerogel

[0044] S31. Electrospinning a 10wt% polyvinyl alcohol aqueous solution to form a polyvinyl alcohol nonwoven fabric; wherein the electrospinning conditions are: spinning flow rate of 0.2mL / h, temperature of 25℃, and humidity of 50%.

[0045] S32. Stack the first polyvinyl alcohol nonwoven fabric, the quaternized chitosan / polyvinyl alcohol aerogel, and the second polyvinyl alcohol nonwoven fabric in that order, and then assemble them by hot pressing at 160°C and 5MPa for 6 minutes to obtain a composite food storage bag based on quaternized chitosan / polyvinyl alcohol aerogel (the thickness of the quaternized chitosan / polyvinyl alcohol aerogel layer is about 300μm±10μm).

[0046] Comparative Example 1 is basically the same as Example 1, except that quaternized chitosan is replaced with methylated chitosan.

[0047] The preparation of methylated chitosan specifically includes the following steps: 5g of chitosan is suspended in 200mL of deionized water, then 1mL of acetic acid is added to the suspension and stirred for 30min. Sodium hydroxide is slowly added until the pH of the solution is 10-11, and then 10mL of iodomethane is slowly added. The reaction is controlled at 0℃ for 2h. After the reaction is completed, a large amount of ethanol is added to precipitate the methylated chitosan. The precipitate is collected by filtration, and the precipitate is washed with ethanol to remove unreacted reagents and byproducts. After drying, methylated chitosan is obtained.

[0048] Comparative Example 2 is basically the same as Example 1, except that polyvinyl alcohol is replaced with polyvinylpyrrolidone.

[0049] Test Example 1

[0050] Based on Example 1, the effects of quaternized chitosan / polyvinyl alcohol aerogels (named 1-0.5, 1-1, 1-2, 1-2.5, 1-3, 1-4, respectively) prepared from polyvinyl alcohol solutions and quaternized chitosan solutions with different mass ratios (1:0.5, 1:1, 1:2, 1:2.5, 1:3, 1:4) on composite food preservation bags were investigated.

[0051] Strawberries were randomly divided into 8 groups, totaling 30 groups. The experimental groups (1-0.5, 1-1, 1-2, 1-2.5, 1-3, 1-4) were sealed and placed in commercially available polyethylene preservation bags (purchased from Miaojie) and ordinary plastic bags (purchased from Hongshengyuan, model: starch-based vest bag). The strawberries were stored at 25±3℃. Every 24 hours, the strawberries in each group were observed, evaluated, and photographed to compare the preservation effects.

[0052] (1) Determination of Rot Index: The fruit rot index was evaluated using a sensory grading method: Grade 0 indicates no rot and normal pulp tissue; Grade 1 indicates slight rot but no rotten color bands; Grade 2 indicates obvious rot with rotten color bands and a rotten area of ​​less than 1 / 5; Grade 3 indicates obvious rot with a rotten area of ​​less than 1 / 3; Grade 4 indicates rotten area of ​​more than 1 / 3. The formula for calculating the rot index is as follows: Rot Index (%) = ∑(Number of rotten fruits × Rotten grade value) / (Total number of fruits × Highest rotten grade value) × 100%. The scoring mechanism for the rot index is shown in Table 1.

[0053] Table 1

[0054] Decay Index (%) Rating (points) evaluate 0-10 90-100 Excellent 11-20 80-89 very good 21-30 70-79 good 31-40 60-69 generally 41-50 50-59 Poor 51-60 40-49 Difference 61-70 30-39 Very bad 71-80 20-29 Range 81-90 10-19 Almost no preservation effect 91-100 0-9 No preservation effect

[0055] Respiration, water loss, and infection by putrefactive bacteria are the main factors promoting fruit rot in strawberries. The rot rate gradually increases with prolonged storage. The rot index directly affects the storage life of strawberries. By observing 30 strawberries in each group, the rot index was calculated and statistically analyzed according to the formula. The rot index scores are as follows: Figure 1 As shown. From Figure 1 It can be seen that the composite preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel has a better preservation effect than the control group, especially the composite preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel with a mass ratio of 1:2-4. Among them, the composite preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel with a mass ratio of 1:2.5 has the highest inhibition rate of strawberry rot. This is because when the proportion of polyvinyl alcohol is too low, the structural stability and mechanical strength of the aerogel are insufficient, affecting its ability to effectively encapsulate and regulate internal gas, thereby reducing the preservation effect. When the proportion of polyvinyl alcohol is too high, the porosity of the aerogel decreases, reducing its ability to adsorb and desorb CO2, and affecting the gas exchange efficiency.

[0056] (2) Weight loss rate determination: The weighing method was used, and the formula for calculating the weight loss rate is as follows: Weight loss rate = (Pre-storage mass - Mass at measurement) / Pre-storage mass × 100%. The scoring mechanism for the weight loss rate is shown in Table 2.

[0057] Table 2

[0058] Weight loss rate (%) Rating (points) evaluate 0-10 90-100 Excellent 11-20 80-89 very good 21-30 70-79 good 31-40 60-69 generally 41-50 50-59 Poor 51-60 40-49 Difference 61-70 30-39 Very bad 71-80 20-29 Range 81-90 10-19 Almost no preservation effect 91-100 0-9 No preservation effect

[0059] By observing 30 strawberries in each group, the weight loss rate was calculated and statistically analyzed according to the formula for calculating the weight loss rate. The weight loss rate score results are as follows: Figure 2 As shown. From Figure 2It can be seen that the composite preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel has a better preservation effect than the control group, and the composite preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel with a mass ratio of 1:2.5 has the lowest weight loss rate for strawberries.

[0060] Test Example 2: Adsorption and Desorption Performance of Quaternized Chitosan / Polyvinyl Alcohol Aerogel for CO2

[0061] The CO2 adsorption and desorption performance of quaternized chitosan / polyvinyl alcohol aerogel was tested based on Example 1: First, a closed system with precisely regulated temperature and humidity was provided, maintaining a constant total CO2 concentration. The initial CO2 concentration in the closed system was adjusted using CO2 and N2 gas cylinders. The initial CO2 concentration was adjusted to 400 ppm, the same as the atmospheric CO2 concentration. The quaternized chitosan / polyvinyl alcohol aerogel was first dried in an oven at 30°C for 48 hours to saturate CO2 absorption, and then placed in the device to trigger reversible CO2 capture under humid and dry conditions. A CO2 adsorption reaction occurred, converting hydroxide ions to bicarbonate ions, and the adsorbent entered an adsorption-desorption cycle.

[0062] (1) The effect of humidity variation on CO2 adsorption and desorption of quaternized chitosan / polyvinyl alcohol aerogel under room temperature (20℃) conditions was studied. CO2-saturated quaternized chitosan / polyvinyl alcohol aerogel was placed in the device, and the relative humidity of the sample chamber was increased from 3% to 95%. CO2 was desorbed from the aerogel, with the highest desorption amount being 0.181 mmol / g. Nine adsorption and desorption processes were carried out using the variable humidity method, and no performance degradation was observed, demonstrating that the quaternized chitosan / polyvinyl alcohol aerogel has high stability.

[0063] (2) The effect of temperature change on CO2 adsorption and desorption of quaternized chitosan / polyvinyl alcohol aerogel under humidity conditions of 3%-95% was studied. The temperature of the sample chamber was set to 10℃, 20℃ and 30℃ respectively. The adsorption rate of CO2 at 10℃ was measured to be approximately 0.83×10⁻⁶. -4 mmolg -1 s -1 The adsorption rate of CO2 at 20℃ is approximately 1.75 × 10⁻⁶. -4 mmolg -1 s -1 The adsorption rate of CO2 at 30℃ is approximately 2.78 × 10⁻⁶. -4 mmolg -1 s -1Clearly, the CO2 adsorption rate increases significantly with increasing temperature. Increased temperature enhances the thermodynamic energy of molecules within the aerogel, thereby promoting the collision and adsorption of CO2 molecules with active sites on the aerogel surface. Simultaneously, rising temperature may also alter the microstructure of the aerogel, increasing its porosity and specific surface area, providing more adsorption sites for CO2 molecules.

[0064] Test Example 3

[0065] The composite preservation bags prepared in Comparative Examples 1-2 were tested for decay index and weight loss rate according to the test method of Test Example 1, and compared with Example 1. The decay index score and weight loss rate score on days 1, 3, 5, 7, and 9 are shown in Table 3:

[0066] Table 3

[0067]

[0068] As shown in Table 3, the decay index and weight loss scores of the composite preservation bags in the examples were significantly better than those in the comparative examples. This is because the methylated chitosan used in Comparative Example 1 has weaker antibacterial properties than quaternized chitosan. Quaternary ammonium groups can effectively disrupt the cell walls of bacteria, thereby more effectively inhibiting microbial growth. Compared to polyvinylpyrrolidone, the polyvinyl alcohol used in Comparative Example 2 is less effective in gas regulation and moisture retention. This is because polyvinyl alcohol may provide a more stable microporous structure when forming an aerogel, which helps to more effectively regulate the gas environment inside the packaging and retain moisture, thus better maintaining the freshness of food.

[0069] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel, characterized in that, It includes a first nonwoven fabric layer, a second nonwoven fabric layer, and a quaternized chitosan / polyvinyl alcohol aerogel layer disposed between the first nonwoven fabric layer and the second nonwoven fabric layer; the quaternized chitosan / polyvinyl alcohol aerogel layer is composited between the first nonwoven fabric layer and the second nonwoven fabric layer by a hot pressing process. The preparation of the quaternized chitosan / polyvinyl alcohol aerogel includes the following steps: S1. Mix the polyvinyl alcohol solution and the quaternized chitosan solution, and adjust the pH to 4.5-5.5 to obtain a quaternized chitosan / polyvinyl alcohol mixture. S2. Add a crosslinking agent to the quaternized chitosan / polyvinyl alcohol mixture described in S1 to carry out a crosslinking reaction, thereby obtaining a quaternized chitosan / polyvinyl alcohol hydrogel; the concentration of the quaternized chitosan solution is 0.5wt%-3.5wt%; the concentration of the polyvinyl alcohol solution is 3wt%-8wt%; and the mass ratio of the polyvinyl alcohol solution to the quaternized chitosan solution is 1:2-4. S3. The quaternized chitosan / polyvinyl alcohol hydrogel described in S2 is soaked in alkaline solution, washed with water, and freeze-dried to obtain the quaternized chitosan / polyvinyl alcohol aerogel.

2. The composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel according to claim 1, characterized in that, In S2, the crosslinking agent is selected from one or more of glutaraldehyde, epichlorohydrin, and benzodialdehyde.

3. The composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel according to claim 1, characterized in that, In S2, the crosslinking reaction is carried out at a temperature of 50°C-85°C for 5-8 hours.

4. The composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel according to claim 1, characterized in that, In S3, the alkaline solution is selected from sodium hydroxide solution and / or potassium hydroxide solution; the concentration of the alkaline solution is 0.5 mol / L-2 mol / L.

5. The composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel according to claim 1, characterized in that, In S3, the freeze-drying temperature is -60°C to -40°C, and the time is 36h to 48h.

6. The composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel according to claim 1, characterized in that, The materials of the first nonwoven layer and the second nonwoven layer are independently selected from one or more of polyvinyl alcohol, polypropylene, polyethylene, polyester and polylactic acid.

7. The composite food preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel according to claim 1, characterized in that, The first nonwoven layer and the second nonwoven layer are prepared by electrospinning.

8. The application of the composite preservation bag based on quaternized chitosan / polyvinyl alcohol aerogel as described in any one of claims 1-7 in modified atmosphere preservation.

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