Antibacterial cellulose nanofiber, its preparation method and application in packaging paper

Abstract

The application discloses antibacterial cellulose nanofiber and a preparation method and application thereof in packaging paper, and belongs to the field of food packaging. The preparation method comprises the following steps: (1) dissolving cobalt nitrate hexahydrate and manganese nitrate in methanol to prepare solution A; dissolving 2-methyl imidazole in methanol to prepare solution B; (2) dispersing cellulose nanofiber in solution A, stirring, and enabling metal ions to be fully absorbed and coordinated into the cellulose nanofiber; (3) mixing the mixture obtained in the step (2) with solution B, ultrasonic treatment, centrifugal collection of blue precipitate, dispersion of the blue precipitate in methanol, mixing with solution A, reaction in a high-pressure reaction kettle, and obtaining antibacterial cellulose nanofiber. The obtained antibacterial cellulose nanofiber is applied to preparation of packaging paper. The packaging paper has certain flexibility, stability and excellent antibacterial capacity, is free of cytotoxicity, can be used for fruit and vegetable preservation, and remarkably prolongs the preservation period of fruits.

Description

Technical Field

[0001] This invention relates to the field of food packaging, specifically to an antibacterial cellulose nanofiber, its preparation method, and its application in packaging paper. Background Technology

[0002] Fruits and vegetables, as fresh foods, are particularly prone to spoilage from harvest to market consumption. Damaged fruits and vegetables, such as those whose stems accidentally detach during picking or those subjected to mechanical damage, are easily attacked by microorganisms, leading to rapid decay. This not only poses food safety issues but also results in significant waste. Fruit and vegetable packaging paper can protect fruits and vegetables from external environmental influences, such as sunlight, oxygen, and moisture. It can also, to some extent, prevent damage from collisions and compression during transportation, storage, and sales, thus protecting the integrity and quality of the produce. However, currently used packaging paper typically lacks antibacterial activity and is insufficient to prevent microbial contamination. Many research-developed paper-based antibacterial materials also have limitations. For example, mixing with antibacterial substances can lead to poor material compatibility and unsustainable antibacterial properties; doping with small antibacterial molecules can cause these molecules to leach out, resulting in potential toxicity and secondary environmental pollution; and the use of natural enzymes, polyphenols, essential oils, and other plant extracts has drawbacks such as relatively complex extraction processes, high costs, and poor stability under light, heat, and oxidation conditions. Patent applications 201510744994.2 ("A type of fruit preservation packaging paper and its preparation method") and 201910960460.1 ("A type of fruit and vegetable preservation paper and its preparation method") use as many as 16 and 11 different preservative components, respectively, and the processes are complex. Furthermore, patent application 201810829715.6 ("A type of fruit and vegetable preservation paper and its preparation method") uses caustic soda and borax, both of which are harmful chemicals, and the biosafety of the resulting preservation paper is unclear. Therefore, there is a need to further develop safe and stable antibacterial preservation papers for fruits and vegetables. Summary of the Invention

[0003] In view of the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide an antibacterial cellulose nanofiber, its preparation method and its application in packaging paper, which is a further breakthrough in addressing the deficiencies of the existing technology.

[0004] The objective of this invention is achieved through the following technical solutions.

[0005] A method for preparing antibacterial cellulose nanofibers includes the following steps;

[0006] (1) Dissolve cobalt nitrate hexahydrate and manganese nitrate in methanol to prepare solution A; dissolve 2-methylimidazole in methanol to prepare solution B;

[0007] (2) Disperse cellulose nanofibers (CNF) in solution A and stir to allow metal ions to be fully adsorbed and coordinated into the cellulose nanofibers;

[0008] (3) The mixture obtained in step (2) is mixed with solution B and ultrasonically treated. The blue precipitate is collected by centrifugation, dispersed in methanol, and mixed with solution A. The mixture is reacted in a high-pressure reactor, cooled, and separated by centrifugation to obtain a yellowish-brown product. After washing, antibacterial cellulose nanofibers are obtained.

[0009] Preferably, the mass ratio of cobalt nitrate hexahydrate to manganese nitrate in step (1) is 1-2:1.

[0010] Preferably, the mass ratio of cobalt nitrate hexahydrate to 2-methylimidazole in step (1) is 1:2-4.

[0011] Preferably, the proportion of cobalt nitrate hexahydrate in the methanol solution in step (1) is 1.8%.

[0012] Preferably, the 2-methylimidazolium in step (1) accounts for 4.1% of the methanol solution.

[0013] Preferably, the mass ratio of cobalt nitrate hexahydrate to cellulose nanofibers in step (2) is 2-4:1.

[0014] Preferably, the reaction in step (3) is carried out at a temperature of 110-140°C for 0.5-2 hours.

[0015] More preferably, the reaction in step (3) is carried out at a temperature of 120°C for 1 hour.

[0016] Preferably, in step (3), the mixture obtained in step (2) is mixed with solution B within 1 min and ultrasonically treated for 15 min, and then centrifuged to collect the blue precipitate.

[0017] Preferably, the yellowish-brown product obtained in step (3) is washed in methanol 3-4 times.

[0018] An antibacterial cellulose nanofiber prepared by any of the above preparation methods.

[0019] The above-described application of antibacterial cellulose nanofibers in the preparation of packaging paper involves preparing the antibacterial cellulose nanofibers into a suspension, which then self-assembles into antibacterial packaging paper.

[0020] Preferably, the packaging paper is fruit and vegetable preservation packaging paper.

[0021] The principle of this invention is as follows: An oxidase-like artificial enzyme based on a cobalt-manganese bimetallic organic framework (CNF) is grown in situ on a natural CNF. Furthermore, a solvothermal method is used to form a fungus-like metal-organic framework derivative with ultrathin nanosheets on the CNF. This structure, with its large surface area and porous network, provides more active sites, resulting in a CNF with excellent oxidase-like activity. In addition, cobalt and manganese exist in multiple oxidation states within the framework structure, enabling the obtained CNF with oxidase-like activity to undergo redox reactions. The resulting reactive oxygen species, such as singlet oxygen and superoxide anions, can kill foodborne pathogens such as Escherichia coli and Staphylococcus aureus.

[0022] Compared with existing methods, the present invention has the following advantages and beneficial effects:

[0023] (1) This invention grows an artificial enzyme with oxidase-like activity on CNF to obtain antibacterial CNF with oxidase-like activity, and further obtains antibacterial CNF paper with oxidase-like activity. Artificial enzymes are a sustainable, cost-effective and environmentally friendly substance. Compared with natural enzymes, artificial enzymes have more easily adjustable catalytic activity, higher stability against adverse conditions, lower cost, and the possibility of large-scale production.

[0024] (2) Artificial enzymes with oxidase-like activity can kill microorganisms by generating reactive oxygen species.

[0025] (3) By self-assembling the obtained antibacterial CNF into antibacterial paper, it has flexibility, stability and no cytotoxicity, and can be used for the preservation of fruits and vegetables. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the preparation of antibacterial CNF with oxidase-like activity according to the present invention.

[0027] Figure 2 This is a scanning electron microscope image of the antibacterial CNF with oxidase-like activity obtained in this invention.

[0028] Figure 3 This is a sample image of the antibacterial CNF paper with oxidase-like activity obtained in this invention.

[0029] Figure 4 The images show the packaging effect and the unpackaged effect of Korla pears in Embodiment 2 and Comparative Examples 1 and 2 of the present invention.

[0030] Figure 5 The images shown are of the packaging effect and the unpackaged effect of Crown Pears in Embodiment 2 and Comparative Examples 1 and 2 of the present invention. Detailed Implementation

[0031] The specific implementation of the present invention will be further described below with reference to examples and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0032] The antibacterial activity of the obtained CNF paper was evaluated using two bacterial strains: Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). First, 10 mL of bacteria (10 mL) was collected by centrifugation. 7 The bacterial sample was washed with phosphate buffer (CNF paper) and then dispersed in 10 mL of acetate buffer containing 0.02 g CNF paper. The samples were then incubated at 37°C with shaking for 2 h. A control group was used without CNF paper. The resulting bacterial suspension was then diluted and plated on agar plates for plate counting analysis. After incubation at 37°C for 24 h, the total bacterial count on each plate was recorded. The sterilization rate was calculated by comparing the total bacterial count with that of the control group.

[0033] Example 1

[0034] Figure 1 This is a schematic diagram of the preparation of antibacterial CNF with oxidase-like activity. The specific steps are as follows: Solution A is obtained by dissolving 0.548 g of cobalt nitrate hexahydrate and 0.540 mL of manganese nitrate solution (containing 50% water) in 30 mL of methanol. Solution B is obtained by dissolving 1.096 g of 2-methylimidazole in 27 mL of methanol. 0.270 g of CNF is dispersed in solution A, and the mixture is magnetically stirred at room temperature to allow the metal ions to be fully adsorbed and coordinated into the CNF. Subsequently, the mixture is mixed with solution B within 1 min and ultrasonically treated for 15 min. The blue precipitate is collected by centrifugation, dispersed in 30 mL of methanol, and mixed with solution A (0.548 g of cobalt nitrate hexahydrate and 0.540 mL of manganese nitrate solution (containing 50% water) dissolved in 30 mL of methanol). The resulting mixture is transferred to a PTFE-lined high-pressure reactor and reacted at 120 °C for 1 h. After cooling, a yellowish-brown product is obtained by centrifugation. After washing four times with methanol, the antibacterial CNF (surface morphology as shown) is obtained. Figure 2 (As shown). The resulting antibacterial CNF suspension was further self-assembled into CNF paper (e.g., Figure 3 (As shown). The obtained packaging paper is flexible, stable, and non-cytotoxic, with bactericidal rates of 64.76% and 77.98% against Escherichia coli and Staphylococcus aureus, respectively. Korla pears with the stem removed, packaged in the obtained CNF paper, can be stored for more than 10 days without spoilage at 30±2℃ and 70% relative humidity; Crown pears with the stem removed, packaged in the obtained CNF paper, can be stored for more than 25 days without spoilage at 30±2℃ and 70% relative humidity.

[0035] Example 2

[0036] Solution A was obtained by dissolving 0.548 g of cobalt nitrate hexahydrate and 0.440 mL of manganese nitrate solution (containing 50% water) in 30 mL of methanol. Solution B was obtained by dissolving 1.232 g of 2-methylimidazole in 30 mL of methanol. 0.160 g of CNF was dispersed in solution A, and the mixture was magnetically stirred at room temperature to allow the metal ions to be fully adsorbed and coordinated into the CNF. Subsequently, the mixture was mixed with solution B within 1 min and sonicated for 15 min. The blue precipitate was collected by centrifugation, dispersed in 30 mL of methanol, and mixed with solution A (0.548 g of cobalt nitrate hexahydrate and 0.440 mL of manganese nitrate solution (containing 50% water) dissolved in 30 mL of methanol). The resulting mixture was transferred to a PTFE-lined high-pressure reactor and reacted at 120 °C for 1 h. After cooling, a yellowish-brown product was obtained by centrifugation and washed four times with methanol to obtain antibacterial CNF. The obtained antibacterial CNF suspension was further self-assembled into CNF paper. The obtained packaging paper is flexible, stable, and non-cytotoxic, with bactericidal rates of 73.32% and 83.21% against Escherichia coli and Staphylococcus aureus, respectively. Korla pears with their stems removed, packaged in the obtained CNF paper, can be stored for more than 10 days without spoilage at 30±2℃ and 70% relative humidity; Crown pears with their stems removed, packaged in the obtained CNF paper, can be stored for more than 30 days without spoilage at 30±2℃ and 70% relative humidity.

[0037] Example 3

[0038] Solution A was obtained by dissolving 0.548 g of cobalt nitrate hexahydrate and 0.300 mL of manganese nitrate solution (containing 50% water) in 30 mL of methanol. Solution B was obtained by dissolving 2.082 g of 2-methylimidazole in 50 mL of methanol. 0.130 g of CNF was dispersed in solution A, and the mixture was magnetically stirred at room temperature to allow the metal ions to be fully adsorbed and coordinated into the CNF. Subsequently, the mixture was mixed with solution B within 1 min and sonicated for 15 min. The blue precipitate was collected by centrifugation, dispersed in 30 mL of methanol, and mixed with solution A (0.548 g of cobalt nitrate hexahydrate and 0.300 mL of manganese nitrate solution (containing 50% water) dissolved in 30 mL of methanol). The resulting mixture was transferred to a PTFE-lined high-pressure reactor and reacted at 120 °C for 1 h. After cooling, a yellowish-brown product was obtained by centrifugation and washed four times with methanol to obtain antibacterial CNF. The obtained antibacterial CNF suspension was further self-assembled into CNF paper. The obtained packaging paper is flexible, stable, and non-cytotoxic, with bactericidal rates of 84.96% and 91.11% against Escherichia coli and Staphylococcus aureus, respectively. Korla pears with their stems removed, packaged in the obtained CNF paper, can be stored for more than 15 days without spoilage at 30±2℃ and 70% relative humidity; Crown pears with their stems removed, packaged in the obtained CNF paper, can be stored for more than 30 days without spoilage at 30±2℃ and 70% relative humidity.

[0039] Comparative Example 1

[0040] The original CNF suspension self-assembled into CNF paper. It had no bactericidal effect against Escherichia coli and Staphylococcus aureus. Korla pears, after having their stems removed, were packaged in the original CNF paper and stored at 30±2℃ and 70% relative humidity for 6 days, showing obvious blackening and shrinkage (e.g., ...). Figure 4 (As shown); Crown pears with the stem removed, wrapped in the original CNF paper, did not rot for 10 days when stored at 30±2℃ and 70% relative humidity, but the part where the stem was removed showed obvious blackening (as shown). Figure 5 (As shown).

[0041] Comparative Example 2

[0042] Commercially available polyethylene (PE) plastic film. It has no bactericidal effect against Escherichia coli and Staphylococcus aureus. Korla pears, after the stems have been removed, packaged in PE film and stored at 30±2℃ and 70% relative humidity for 2 days without spoiling (e.g., Figure 4 (As shown); Crown pears with the stem removed were packaged in PE film and stored at 30±2℃ and 70% relative humidity for 6 days without rotting, but the part where the stem was removed showed obvious blackening (as shown). Figure 5 (As shown).

[0043] Comparative Example 3

[0044] Solution A was prepared by dissolving 0.548 g of cobalt nitrate hexahydrate and 0.440 mL of manganese nitrate solution (containing 50% water) in 30 mL of methanol. Solution B was prepared by dissolving 1.232 g of 2-methylimidazole in 30 mL of methanol. 0.160 g of CNF was dispersed in solution A, and the mixture was magnetically stirred at room temperature to allow for sufficient adsorption and coordination of metal ions into the CNF. Subsequently, the mixture was mixed with solution B within 1 min and sonicated for 15 min. The blue precipitate was collected by centrifugation and washed four times with methanol to obtain CNF with a cobalt-manganese metal-organic framework grown on its surface. The obtained CNF suspension was further self-assembled into CNF paper. The resulting packaging paper showed bactericidal rates of 33.61% against Escherichia coli and 48.48% against Staphylococcus aureus.

[0045] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. The application of antibacterial cellulose nanofibers in the preparation of packaging paper, characterized in that, The antibacterial cellulose nanofibers are formulated into a suspension and then self-assembled into antibacterial packaging paper. The method for preparing the antibacterial cellulose nanofibers includes the following steps; (1) Prepare solution A by dissolving cobalt nitrate hexahydrate and manganese nitrate in methanol; Solution B is prepared by dissolving 2-methylimidazole in methanol; (2) Disperse cellulose nanofibers in solution A and stir to allow metal ions to be fully adsorbed and coordinated into the cellulose nanofibers; (3) The mixture obtained in step (2) is mixed with solution B and ultrasonically treated. The blue precipitate is collected by centrifugation, dispersed in methanol, and mixed with solution A. The mixture is reacted in a high-pressure reactor, cooled, and separated by centrifugation to obtain a yellowish-brown product. After washing, antibacterial cellulose nanofibers are obtained.

2. The application of the antibacterial cellulose nanofiber according to claim 1 in the preparation of packaging paper, characterized in that, The mass ratio of cobalt nitrate hexahydrate to manganese nitrate in step (1) is 1-2:

1.

3. The application of the antibacterial cellulose nanofiber according to claim 1 in the preparation of packaging paper, characterized in that, The mass ratio of cobalt nitrate hexahydrate to 2-methylimidazole in step (1) is 1:2-4.

4. The application of the antibacterial cellulose nanofiber according to claim 1 in the preparation of packaging paper, characterized in that, In step (2), the mass ratio of cobalt nitrate hexahydrate to cellulose nanofibers is 2-4:

1.

5. The application of the antibacterial cellulose nanofiber according to claim 1 in the preparation of packaging paper, characterized in that, The composition and amount of solution A in step (3) are exactly the same as those of solution A in step (1).

6. The application of the antibacterial cellulose nanofiber according to claim 1 in the preparation of packaging paper, characterized in that, The reaction in step (3) is carried out at a temperature of 110-140℃ for 0.5-2 h.

7. The application of the antibacterial cellulose nanofiber according to claim 1 in the preparation of packaging paper, characterized in that, In step (3), the mixture obtained in step (2) is mixed with solution B within 1 min and ultrasonically treated for 15 min, and then centrifuged to collect the blue precipitate.

8. The application of the antibacterial cellulose nanofiber according to claim 1 in the preparation of packaging paper, characterized in that, The packaging paper is for preserving and protecting fruits and vegetables.

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