Antibacterial food packaging bag and preparation process thereof

Abstract

The invention relates to the field of plastic packaging bags, in particular to an antibacterial food packaging bag and a preparation process thereof. The invention discloses a preparation process of an antibacterial food packaging bag. The preparation process comprises the following steps: preparing modified nitrogen-doped carbon quantum dots; preparing modified cellulose nanocrystals and modified chitosan nanofibers; preparing a composite filler; and preparing the antibacterial food packaging bag. The preparation method comprises the following steps: firstly, preparing nitrogen-doped carbon quantum dots by taking polyvinylpyrrolidone as a raw material through a hydrothermal reaction method, then preparing salicylic acid modified chitosan by taking salicylic acid and chitosan as raw materials, and grafting the salicylic acid modified chitosan on the surfaces of the nitrogen-doped carbon quantum dots to prepare the modified nitrogen-doped carbon quantum dots. After the salicylic acid modified chitosan is mixed with linear low-density polyethylene and other raw materials to prepare a food packaging bag, the dispersity of the nitrogen-doped carbon quantum dots in a matrix can be improved through the grafting modification effect of the salicylic acid modified chitosan, antibacterial components are not prone to being lost from the matrix, and therefore the long-acting antibacterial effect is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of plastic packaging bags, in particular to an antibacterial food packaging bag and a preparation process thereof. BACKGROUND

[0002] Polyethylene is a thermoplastic resin prepared by polymerization of ethylene, which is one of the most commonly used materials in the field of food packaging due to its characteristics such as no odor, no toxicity, low temperature resistance, good chemical stability, easy processing, etc.

[0003] However, the polyethylene molecular chain has a non-polar structure, the surface energy is extremely low, and it lacks antibacterial active groups, so it cannot inhibit the adhesion and reproduction of microorganisms. In the food packaging scenario, bacteria can grow on the surface of the packaging bag due to residual moisture, oil or food debris, leading to food spoilage and deterioration. The existing antibacterial modification methods (such as adding silver ions and chitosan) have problems such as migration risk, poor stability or high cost, and it is difficult to achieve long-term antibacterial effect.

[0004] In addition, the polyethylene molecular chain has high flexibility and low crystallinity, resulting in a tensile strength much lower than that of engineering plastics such as nylon. During transportation and storage, the packaging bag is prone to rupture due to external forces (such as extrusion and sharp object puncture), causing food leakage. Nano-layered double hydroxide has a unique layered nanostructure, a large specific surface area and a high surface energy. During stretching, the nano-layered double hydroxide platelets can effectively transfer external stress as a rigid reinforcing phase, dispersing the load on the polyethylene matrix to the self, reducing the local stress concentration and molecular chain rupture of the matrix, thereby improving the tensile strength of the material. In the puncture process, the two-dimensional structure of the nano-layered double hydroxide platelets can delay the crack propagation caused by the puncture force through the "blocking effect", thereby improving the puncture resistance. However, due to the large specific surface area and strong agglomeration effect of nano-layered double hydroxide, it is difficult to disperse uniformly in the polyethylene matrix, which limits its improvement on the tensile strength and puncture resistance of the polyethylene matrix.

[0005] Therefore, it is necessary to provide an antibacterial food packaging bag and a preparation process thereof capable of improving the tensile strength and puncture resistance to improve the service life. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide an antibacterial food packaging bag and a preparation process thereof.

[0007] The present application provides a preparation process of an antibacterial food packaging bag, comprising the following steps: S1: preparing modified nitrogen-doped carbon quantum dots First, polyvinylpyrrolidone is used as raw material to prepare nitrogen-doped carbon quantum dots, then chitosan and salicylic acid are used as raw materials to prepare salicylic acid modified chitosan, and finally the salicylic acid modified chitosan is grafted on the surface of the nitrogen-doped carbon quantum dots to obtain modified nitrogen-doped carbon quantum dots; S2: Preparation of modified cellulose nanocrystals and modified chitosan nanofibers First, the surface of the cellulose nanocrystals is modified by 3-aminopropyl triethoxysilane to obtain modified cellulose nanocrystals, and then the chitosan nanofiber is modified by lauric acid glycidyl ester to obtain modified chitosan nanofiber; S3: Preparation of composite filler S3.1: Disperse heavy calcium carbonate in 1-3wt% dilute hydrochloric acid at a ratio of 1g:(4-6)mL, stir for 20-30min, then filter, wash to neutral, and then dry to obtain activated heavy calcium carbonate; S3.2: Add magnesium nitrate hexahydrate and zinc chloride to deionized water at a ratio of (4.6-4.8)g:1g:(15-25)mL, stir to dissolve thoroughly to obtain a mixed metal salt solution; S3.3: Disperse the above activated heavy calcium carbonate in deionized water at a ratio of 1g:(20-30)mL, ultrasonic treatment for 20-30min to obtain an activated heavy calcium carbonate dispersion, then add nano-silicon dioxide, stir in a 50-60℃ water bath for 20-30min, then simultaneously add equal volume of the above mixed metal salt solution and mixed alkali liquid while stirring, stir at 60-70℃ for 12-16h, after cooling, filter, wash and dry to obtain a composite filler.

[0008] S4: Preparation of antibacterial food packaging bag Put linear low density polyethylene, ethylene-vinyl acetate, the above modified nitrogen-doped carbon quantum dots, the above modified cellulose nanocrystals, the above modified chitosan nanofiber, the above composite filler and maleic anhydride grafted polyethylene into a banbury mixer, mix at 160-170℃, 40-50rpm for 8-10min, then add calcium stearate, continue to mix for 6-8min, then extrude and granulate, blow film forming to obtain an antibacterial food packaging bag.

[0009] Further, S1 specifically includes the following steps: S1.1: Dissolve polyvinylpyrrolidone in deionized water, stir to dissolve thoroughly, then transfer to a high-pressure reaction kettle, heat at 190-200℃ for 6-8h, cool, centrifuge to remove the precipitate, then filter the supernatant through a 0.22μm filter membrane, dialyze for 20-24h, then heat and evaporate at 80-90℃ to obtain nitrogen-doped carbon quantum dots; S1.2: chitosan is added into 2% acetic acid aqueous solution at 1 g: (75-85) mL, and stirred to dissolve to obtain a chitosan solution, then salicylic acid is dissolved in deionized water at 1 g: (35-40) mL, and equal molar amount of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide are added, and stirred to activate for 30-40 min to obtain an activated salicylic acid solution, wherein the mass ratio of N-hydroxysuccinimide to salicylic acid is (1.1-1.3): 1; S1.3: the activated salicylic acid solution is added into the chitosan solution, and heated to stir at 50-60℃ for 1-2 h, and then dialyzed and freeze-dried to obtain salicylic acid modified chitosan; S1.4: the nitrogen-doped carbon quantum dots are added into deionized water at 1 g: (180-200) mL, and ultrasonically dispersed for 20-30 min, and then equal molar amount of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide are added, and stirred to activate for 1-2 h to obtain an activated nitrogen-doped carbon quantum dot dispersion, wherein the mass ratio of N-hydroxysuccinimide to nitrogen-doped carbon quantum dots is 1:3; S1.5: the salicylic acid modified chitosan is dissolved in deionized water at 1 g: (200-300) mL, and the pH is adjusted to 6-6.5, and then the activated nitrogen-doped carbon quantum dot dispersion is added, and stirred to react at 40-50℃ for 5-6 h, and during the reaction, 0.1 mol / L sodium hydroxide solution is added to maintain the pH at 6-6.5, and after cooling, centrifugal separation, washing, dialysis and freeze-drying are performed to obtain modified nitrogen-doped carbon quantum dots.

[0010] Further, S2 specifically comprises the following steps: S2.1: cellulose nanocrystals are added into an ethanol solution with a volume fraction of 80%, and ultrasonically dispersed for 30-40 min to prepare a cellulose nanocrystal dispersion with a concentration of 1-3 wt%; S2.2: 3-aminopropyltriethoxysilane is added into the cellulose nanocrystal dispersion, and acetic acid is added to adjust the pH to 4-5, and then heated to stir at 50-60℃ for 4-6 h, and after cooling, centrifugal washing and freeze-drying are performed to obtain modified cellulose nanocrystals; S2.3: chitosan nanofibers are added into isopropanol at 1 g: (20-30) mL, and ultrasonically dispersed for 20-30 min, and then glycidyl laurate is added, and heated to stir at 70-80℃ for 6-8 h under nitrogen protection, and after cooling, filtration, washing and drying are performed to obtain modified chitosan nanofibers.

[0011] Further, the molar ratio of salicylic acid to chitosan is (0.7-0.8):1, and the mass ratio of nitrogen-doped carbon quantum dots to salicylic acid modified chitosan is (4.5-5.5):1.

[0012] Further, the addition amount of 3-aminopropyl triethoxysilane is 10-15% of the mass of cellulose nanocrystals.

[0013] Further, the addition amount of glycidyl laurate is 20-30% of the mass of chitosan nanofibers.

[0014] Further, the addition amount of nano-silicon dioxide is 8-10% of the mass of activated heavy calcium carbonate.

[0015] Further, the mixed alkali liquor includes 0.3 mol / L sodium carbonate and 1 mol / L sodium hydroxide, and the volume ratio of the mixed metal salt solution to the activated heavy calcium carbonate dispersion is 1:(4-5).

[0016] Further, the raw material composition of the antibacterial food packaging bag is 60-70 parts of linear low-density polyethylene, 15-20 parts of ethylene-vinyl acetate, 3-5 parts of modified nitrogen-doped carbon quantum dots, 6-8 parts of modified cellulose nanocrystals, 4-6 parts of modified chitosan nanofibers, 6-8 parts of maleic anhydride grafted polyethylene, and 1-3 parts of calcium stearate.

[0017] An antibacterial food packaging bag prepared by the preparation process of any one of the above-mentioned antibacterial food packaging bags.

[0018] The present application has the following advantages: 1、In the present application, nitrogen-doped carbon quantum dots are first prepared by hydrothermal reaction using polyvinylpyrrolidone as the raw material, then salicylic acid modified chitosan is prepared using salicylic acid and chitosan as the raw material, and the salicylic acid modified chitosan is grafted on the surface of the nitrogen-doped carbon quantum dots to prepare modified nitrogen-doped carbon quantum dots. After mixing with raw materials such as linear low-density polyethylene to make a food packaging bag, the chemical bacteriostatic effect of salicylic acid, the electrostatic adsorption and membrane damage of chitosan, and the active oxygen oxidation and physical puncture of nitrogen-doped carbon quantum dots synergistically work together to significantly improve the antibacterial property of the food packaging bag. At the same time, the graft modification of salicylic acid modified chitosan can improve the dispersibility of nitrogen-doped carbon quantum dots in the matrix, so that the antibacterial ingredients are not easily lost from the matrix, thereby achieving long-acting antibacterial effect.

[0019] 2. In this invention, cellulose nanocrystals are first modified with 3-aminopropyltriethoxysilane, and then chitosan nanofibers are modified with glycidyl laurate. After the modified cellulose nanocrystals and modified chitosan are mixed with linear low-density polyethylene and other raw materials to make food packaging bags, the uniformly dispersed cellulose nanocrystals can transfer external tensile force from the linear low-density polyethylene matrix to the cellulose nanocrystals through the "stress transfer" effect, using their rigidity to resist deformation. Meanwhile, the fibrous chitosan nanofibers can form an interwoven network in the linear low-density polyethylene matrix, dispersing local stress through the "bridging" effect, preventing crack propagation, and buffering the brittleness brought by the cellulose nanocrystals, balancing the "rigid-flexible" characteristics of the material. The combination of the two can synergistically improve the tensile strength of the food packaging bag. In addition, chitosan nanofibers have natural antibacterial properties. After modification with glycidyl laurate, the introduced lauric acid chains with fat-soluble antibacterial effects can work together with chitosan nanofibers to enhance the antibacterial effect.

[0020] 3. In this invention, heavy calcium carbonate is activated with dilute hydrochloric acid, then dispersed in deionized water, and then reacted with a mixed metal salt solution of magnesium nitrate and zinc chloride and a mixed alkaline solution to produce a composite filler of heavy calcium carbonate supported on nano-layered double hydroxides. When this composite filler is mixed with raw materials such as linear low-density polyethylene to produce food packaging bags, the heavy calcium carbonate, as a rigid inorganic filler, can be uniformly dispersed in the matrix to share external stress. Meanwhile, the nano-layered double hydroxides, with their layered structure and high specific surface area, can form a stronger interfacial interaction with the linear low-density polyethylene molecular chains, promoting effective stress transfer between the matrix and the filler. When the two are combined, the heavy calcium carbonate… Macroscopic particles of calcium carbonate can inhibit the overall deformation of materials, while the layered structure of nano-layered double hydroxides can hinder the propagation of microcracks, strengthen the network, and thus improve tensile strength. At the same time, using heavy calcium carbonate to load nano-layered double hydroxides can make them uniformly dispersed in the matrix with heavy calcium carbonate, reducing agglomeration. In addition, when subjected to puncture force, the layered structure of nano-layered double hydroxides will consume energy through interlayer sliding and the "physical barrier" effect, delaying stress concentration at the puncture point. Meanwhile, the rigid particles of heavy calcium carbonate can directly resist the impact of puncture force, reducing the plastic deformation of the matrix during puncture, thereby significantly improving the puncture resistance of food packaging bags. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the preparation process of the antibacterial food packaging bag used in an embodiment of the present invention. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0023] Example 1: A preparation process for an antibacterial food packaging bag, such as... Figure 1 As shown, it includes the following steps: S1: Preparation of modified nitrogen-doped carbon quantum dots S1.1: Polyvinylpyrrolidone was dissolved in deionized water and stirred thoroughly. The solution was then transferred to a high-pressure reactor and heated at 190°C for 6 hours. After cooling, the precipitate was removed by centrifugation. The supernatant was then filtered through a 0.22 μm filter membrane and dialyzed for 20 hours. Finally, it was heated at 80°C to dryness to obtain nitrogen-doped carbon quantum dots. S1.2: Chitosan was added to a 2% acetic acid aqueous solution at a ratio of 1 g: 75 mL and stirred thoroughly to dissolve, thus obtaining a chitosan solution. Then, salicylic acid was dissolved in deionized water at a ratio of 1 g: 35 mL, and equimolar amounts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide were added. The mixture was stirred and activated for 30 min to obtain an activated salicylic acid solution, wherein the mass ratio of N-hydroxysuccinimide to salicylic acid was 1.1:1. S1.3: The above salicylic acid activation solution was added to the above chitosan solution, and the mixture was heated and stirred at 50°C for 1 hour. Then, after dialysis and freeze-drying, salicylic acid modified chitosan was obtained, wherein the molar ratio of salicylic acid to chitosan was 0.7:1. S1.4: Add the above nitrogen-doped carbon quantum dots to deionized water at a ratio of 1g:180mL, sonicate for 20min, then add equimolar amounts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stir and activate for 1h to obtain an activated nitrogen-doped carbon quantum dot dispersion, wherein the mass ratio of N-hydroxysuccinimide to nitrogen-doped carbon quantum dots is 1:3; S1.5: The above salicylic acid modified chitosan was dissolved in deionized water at a ratio of 1g:200mL, the pH was adjusted to 6, and then added to the above activated nitrogen-doped carbon quantum dot dispersion. The mixture was stirred at 40℃ for 5h, and the pH was maintained at 6 by adding 0.1mol / L sodium hydroxide solution. After cooling, the modified nitrogen-doped carbon quantum dots were obtained by centrifugation, washing, dialyzing and freeze drying. The mass ratio of nitrogen-doped carbon quantum dots to salicylic acid modified chitosan was 4.5:1. S2: Preparation of modified cellulose nanocrystals and modified chitosan nanofibers S2.1: Add cellulose nanocrystals to an 80% ethanol solution and ultrasonically disperse for 30 min to prepare a cellulose nanocrystal dispersion with a concentration of 1 wt%. S2.2: 3-aminopropyl triethoxysilane is added to the above cellulose nanocrystal dispersion liquid, acetic acid is added to adjust the pH to 4, and then heated and stirred at 50℃ for 4h, after cooling, centrifugal washing and freeze-drying, modified cellulose nanocrystals are obtained, wherein the amount of 3-aminopropyl triethoxysilane added is 10% of the mass of cellulose nanocrystals; S2.3: The chitosan nanofiber is added to isopropanol at 1g:20mL, ultrasonic dispersion for 20min, then glycidyl laurate is added, and heated and stirred at 70℃ for 6h under nitrogen protection, after cooling, filtration, washing and drying, modified chitosan nanofiber is obtained, wherein the amount of glycidyl laurate added is 20% of the mass of chitosan nanofiber; S3: Preparation of composite filler S3.1: The heavy calcium carbonate is dispersed in 1wt% dilute hydrochloric acid at 1g:4mL, stirred for 20min, then filtered, washed to neutral, and dried to obtain activated heavy calcium carbonate; S3.2: The magnesium nitrate hexahydrate and zinc chloride are added to deionized water at 4.6g:1g:15mL, fully stirred and dissolved to obtain a mixed metal salt solution; S3.3: The above activated heavy calcium carbonate is dispersed in deionized water at 1g:20mL, ultrasonic treated for 20min to obtain an activated heavy calcium carbonate dispersion liquid, then nano-silica is added, stirred in a 50℃ water bath for 20min, then equal volume of the above mixed metal salt solution and mixed alkali solution are added while stirring, stirred at 60℃ for 12h, after cooling, filtered, washed and dried, a composite filler is obtained, wherein the amount of nano-silica added is 8% of the mass of activated heavy calcium carbonate, the mixed alkali solution includes 0.3mol / L sodium carbonate and 1mol / L sodium hydroxide, and the volume ratio of mixed metal salt solution to activated heavy calcium carbonate dispersion liquid is 1:4; S4: Preparation of antibacterial food packaging bag The linear low density polyethylene, ethylene-vinyl acetate, the above modified nitrogen-doped carbon quantum dots, the above modified cellulose nanocrystals, the above modified chitosan nanofiber, the above composite filler and the maleic anhydride grafted polyethylene are put into a mixing mill, mixed at 160℃, 40rpm for 8min, then calcium stearate is added, continue to mix for 6min, then extrusion granulation, film forming, an antibacterial food packaging bag is obtained, wherein the raw material composition of the antibacterial food packaging bag is: 60 parts of linear low density polyethylene, 15 parts of ethylene-vinyl acetate, 3 parts of modified nitrogen-doped carbon quantum dots, 6 parts of modified cellulose nanocrystals, 4 parts of modified chitosan nanofiber, 3 parts of composite filler, 6 parts of maleic anhydride grafted polyethylene and 1 part of calcium stearate.

[0024] Example 2, a preparation process of an antibacterial food packaging bag, as Figure 1As shown, comprising the following steps: S1: preparation of modified nitrogen-doped carbon quantum dots S1.1: polyvinylpyrrolidone is dissolved in deionized water, after fully stirring and dissolving, it is transferred to a high-pressure reaction kettle, heated at 195°C for 7h, cooled, centrifuged to remove the precipitate, then the supernatant is filtered through a 0.22μm filter membrane, dialyzed for 22h, and then evaporated to dryness at 85°C to obtain nitrogen-doped carbon quantum dots; S1.2: chitosan is added to 2% acetic acid solution at a ratio of 1g:80mL, fully stirred and dissolved to obtain a chitosan solution, then salicylic acid is dissolved in deionized water at a ratio of 1g:37.5mL, and equal molar amounts of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide are added, stirred and activated for 35min to obtain an activated salicylic acid solution, wherein the mass ratio of N-hydroxysuccinimide to salicylic acid is 1.2:1; S1.3: the above-mentioned activated salicylic acid solution is added to the above-mentioned chitosan solution, heated and stirred at 55°C for 1.5h, then dialyzed and freeze-dried to obtain salicylic acid-modified chitosan, wherein the molar ratio of salicylic acid to chitosan is 0.75:1; S1.4: the above-mentioned nitrogen-doped carbon quantum dots are added to deionized water at a ratio of 1g:190mL, ultrasonically dispersed for 25min, then equal molar amounts of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide are added, stirred and activated for 1.5h to obtain an activated nitrogen-doped carbon quantum dot dispersion, wherein the mass ratio of N-hydroxysuccinimide to nitrogen-doped carbon quantum dots is 1:3; S1.5: the above-mentioned salicylic acid-modified chitosan is dissolved in deionized water at a ratio of 1g:250mL, the pH is adjusted to 6, then the above-mentioned activated nitrogen-doped carbon quantum dot dispersion is added, stirred and reacted at 45°C for 5.5h, during which the pH is maintained at 6 by supplementing 0.1mol / L sodium hydroxide solution, after cooling, centrifuged, washed, dialyzed and freeze-dried to obtain modified nitrogen-doped carbon quantum dots, wherein the mass ratio of nitrogen-doped carbon quantum dots to salicylic acid-modified chitosan is 5:1; S2: preparation of modified cellulose nanocrystals and modified chitosan nanofibers S2.1: cellulose nanocrystals are added to an ethanol solution with a volume fraction of 80%, ultrasonically dispersed for 35min to prepare a cellulose nanocrystal dispersion with a concentration of 2wt%; S2.2: 3-aminopropyltriethoxysilane is added to the above-mentioned cellulose nanocrystal dispersion, and acetic acid is added to adjust the pH to 4.5, then heated and stirred at 55°C for 5h, after cooling, centrifuged, washed and freeze-dried to obtain modified cellulose nanocrystals, wherein the amount of 3-aminopropyltriethoxysilane added is 12.5% of the mass of the cellulose nanocrystals; S2.3: The chitosan nanofibers are added into isopropanol at 1 g:25 mL, ultrasonic dispersion for 25 min, then glycidyl laurate is added, heated and stirred at 75℃ for 7 h under nitrogen protection, after cooling, filtration, washing and drying, the modified chitosan nanofibers are obtained, wherein the addition amount of glycidyl laurate is 25% of the mass of the chitosan nanofibers; S3: Preparation of composite filler S3.1: The heavy calcium carbonate is dispersed in 2wt% dilute hydrochloric acid at 1 g:5 mL, stirred for 25 min, then filtered, washed to neutral, and dried to obtain activated heavy calcium carbonate; S3.2: The magnesium nitrate hexahydrate and zinc chloride are added into deionized water at 4.7 g:1 g:20 mL, fully stirred and dissolved to obtain a mixed metal salt solution; S3.3: The above activated heavy calcium carbonate is dispersed in deionized water at 1 g:25 mL, ultrasonic treated for 25 min to obtain an activated heavy calcium carbonate dispersion, then nano-silica is added, stirred in a 55℃ water bath for 25 min, then equal volume of the above mixed metal salt solution and mixed alkali solution are added while stirring, stirred at 65℃ for 14 h, after cooling, filtration, washing and drying, the composite filler is obtained, wherein the addition amount of nano-silica is 9% of the mass of the activated heavy calcium carbonate, the mixed alkali solution includes 0.3 mol / L sodium carbonate and 1 mol / L sodium hydroxide, and the volume ratio of the mixed metal salt solution to the activated heavy calcium carbonate dispersion is 1:4.5; S4: Preparation of antibacterial food packaging bag The linear low density polyethylene, ethylene-vinyl acetate, the above modified nitrogen-doped carbon quantum dots, the above modified cellulose nanocrystals, the above modified chitosan nanofibers, the above composite filler and the maleic anhydride grafted polyethylene are put into a mixing machine, mixed at 165℃, 45 rpm for 9 min, then calcium stearate is added, continue to mix for 7 min, then extrusion granulation, film forming, the antibacterial food packaging bag is obtained, wherein, according to mass fraction, the raw material composition of the antibacterial food packaging bag is: 65 parts of linear low density polyethylene, 17.5 parts of ethylene-vinyl acetate, 4 parts of modified nitrogen-doped carbon quantum dots, 7 parts of modified cellulose nanocrystals, 5 parts of modified chitosan nanofibers, 4 parts of composite filler, 7 parts of maleic anhydride grafted polyethylene and 2 parts of calcium stearate.

[0025] Example 3, a preparation process of an antibacterial food packaging bag, as shown in Figure 1 , includes the following steps: S1: Preparation of modified nitrogen-doped carbon quantum dots S1.1: Polyvinylpyrrolidone was dissolved in deionized water, after fully stirring and dissolving, it was transferred to a high-pressure reaction kettle, heated at 200℃ for 8h, after cooling, the precipitate was removed by centrifugation, then the supernatant was filtered through a 0.22μm filter membrane, and dialyzed for 24h, then evaporated to dryness at 90℃, to obtain nitrogen-doped carbon quantum dots; S1.2: Chitosan was added to 2% acetic acid aqueous solution at 1g:85mL, fully stirred and dissolved to obtain a chitosan solution, then salicylic acid was dissolved in deionized water at 1g:40mL, and equal molar amounts of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide were added, stirred and activated for 40min to obtain an activated salicylic acid solution, wherein the mass ratio of N-hydroxysuccinimide to salicylic acid was 1.3:1; S1.3: The above-mentioned activated salicylic acid solution was added to the above-mentioned chitosan solution, heated and stirred at 60℃ for 2h, then dialyzed and freeze-dried to obtain salicylic acid-modified chitosan, wherein the molar ratio of salicylic acid to chitosan was 0.8:1; S1.4: The above-mentioned nitrogen-doped carbon quantum dots were added to deionized water at 1g:200mL, ultrasonically dispersed for 30min, then equal molar amounts of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide were added, stirred and activated for 2h to obtain activated nitrogen-doped carbon quantum dot dispersion, wherein the mass ratio of N-hydroxysuccinimide to nitrogen-doped carbon quantum dots was 1:3; S1.5: The above-mentioned salicylic acid-modified chitosan was dissolved in deionized water at 1g:300mL, the pH was adjusted to 6.5, then the above-mentioned activated nitrogen-doped carbon quantum dot dispersion was added, stirred and reacted at 50℃ for 6h, during which the pH was maintained at 6.5 by supplementing 0.1mol / L sodium hydroxide solution, after cooling, it was separated by centrifugation, washed, dialyzed and freeze-dried to obtain modified nitrogen-doped carbon quantum dots, wherein the mass ratio of nitrogen-doped carbon quantum dots to salicylic acid-modified chitosan was 5.5:1; S2: Preparation of modified cellulose nanocrystals and modified chitosan nanofibers S2.1: Cellulose nanocrystals were added to an ethanol solution with a volume fraction of 80%, ultrasonically dispersed for 40min to prepare a cellulose nanocrystal dispersion with a concentration of 3wt%; S2.2: 3-Aminopropyltriethoxysilane was added to the above-mentioned cellulose nanocrystal dispersion, and acetic acid was added to adjust the pH to 5, then heated and stirred at 60℃ for 6h, after cooling, it was washed by centrifugation and freeze-dried to obtain modified cellulose nanocrystals, wherein the amount of 3-aminopropyltriethoxysilane added was 15% of the mass of the cellulose nanocrystals; S2.3: The chitosan nanofibers are added into isopropanol at 1 g: 30 mL, ultrasonic dispersion for 30 min, then glycidyl laurate is added, heated and stirred at 80℃ for 8 h under nitrogen protection, after cooling, filtration, washing and drying, the modified chitosan nanofibers are obtained, wherein the added amount of glycidyl laurate is 30% of the mass of the chitosan nanofibers; S3: Preparation of composite filler S3.1: The heavy calcium carbonate is dispersed in 3 wt% dilute hydrochloric acid at 1 g: 6 mL, stirred for 30 min, then filtered, washed to neutral, and dried to obtain activated heavy calcium carbonate; S3.2: The magnesium nitrate hexahydrate and zinc chloride are added into deionized water at 4.8 g: 1 g: 25 mL, fully stirred and dissolved to obtain a mixed metal salt solution; S3.3: The above activated heavy calcium carbonate is dispersed in deionized water at 1 g: 30 mL, ultrasonic treatment for 30 min to obtain an activated heavy calcium carbonate dispersion, then nano-silica is added, stirred in a 60℃ water bath for 30 min, then equal volume of the above mixed metal salt solution and mixed alkali solution are added while stirring, stirred at 70℃ for 16 h, after cooling, filtration, washing and drying, the composite filler is obtained, wherein the added amount of nano-silica is 10% of the mass of the activated heavy calcium carbonate, the mixed alkali solution includes 0.3 mol / L sodium carbonate and 1 mol / L sodium hydroxide, and the volume ratio of the mixed metal salt solution to the activated heavy calcium carbonate dispersion is 1:5; S4: Preparation of antibacterial food packaging bag The linear low density polyethylene, ethylene-vinyl acetate, the above modified nitrogen-doped carbon quantum dots, the above modified cellulose nanocrystals, the above modified chitosan nanofibers, the above composite filler and the maleic anhydride grafted polyethylene are put into a mixing machine, mixed at 170℃, 50 rpm for 10 min, then calcium stearate is added, continue to mix for 8 min, then extrusion granulation, film forming, to obtain an antibacterial food packaging bag, wherein, in terms of mass parts, the raw material composition of the antibacterial food packaging bag is: 70 parts of linear low density polyethylene, 20 parts of ethylene-vinyl acetate, 5 parts of modified nitrogen-doped carbon quantum dots, 8 parts of modified cellulose nanocrystals, 6 parts of modified chitosan nanofibers, 5 parts of composite filler, 8 parts of maleic anhydride grafted polyethylene and 3 parts of calcium stearate.

[0026] Comparative Example 1, the difference between this comparative example 1 and example 1 is that steps S1.2-S1.5 are removed, and the modified nitrogen-doped carbon quantum dots in step S4 are replaced by equal amount of nitrogen-doped carbon quantum dots.

[0027] Comparative Example 2, the difference between this comparative example 2 and example 1 is that the modified cellulose nanocrystals in step S4 are replaced by equal amount of modified chitosan nanofibers.

[0028] Comparative Example 3, the difference between Comparative Example 3 and Example 1 is that the modified chitosan nanofiber in step S4 is replaced by an equal amount of modified cellulose nanocrystal.

[0029] Comparative Example 4, the difference between Comparative Example 4 and Example 1 is that the activated heavy calcium carbonate dispersion solution in step S3.3 is removed to prepare nanometer layered double hydroxide, and the composite filler in step S4 is replaced by an equal amount of nanometer layered double hydroxide.

[0030] Comparative Example 5, the difference between Comparative Example 5 and Example 1 is that the composite filler in step S4 is removed.

[0031] Test Example: Test 1: Staphylococcus aureus is used as the test strain to test the initial antibacterial rate and 90-day antibacterial rate of the food packaging bags prepared in Examples 1-3 and Comparative Examples 1 and 3, repeated three times, and the average value is taken, and the results are shown in Table 1.

[0032] Table 1: Test results of antibacterial rate of food packaging bags

[0033] From Table 1 above, it can be seen that after the nitrogen-doped carbon quantum dots are modified by salicylic acid-modified chitosan in Comparative Example 1, the initial antibacterial rate and 90-day antibacterial rate of the food packaging bags prepared are lower than those of Example 1. Therefore, by first preparing nitrogen-doped carbon quantum dots from polyvinylpyrrolidone using a hydrothermal reaction method, then preparing salicylic acid-modified chitosan from salicylic acid and chitosan, and then grafting the salicylic acid-modified chitosan onto the surface of the nitrogen-doped carbon quantum dots to prepare modified nitrogen-doped carbon quantum dots, and then mixing the modified nitrogen-doped carbon quantum dots with linear low-density polyethylene and other raw materials to prepare food packaging bags, the chemical antibacterial effect of salicylic acid, the electrostatic adsorption and membrane damage of chitosan, and the active oxygen oxidation and physical puncture of nitrogen-doped carbon quantum dots can synergistically enhance the antibacterial properties of the food packaging bags. At the same time, the grafting modification of salicylic acid-modified chitosan can improve the dispersibility of nitrogen-doped carbon quantum dots in the matrix, so that the antibacterial components are not easily lost from the matrix, thereby achieving long-acting antibacterial effect. In addition, after replacing the modified chitosan nanofiber with an equal amount of modified cellulose nanocrystal in Comparative Example 3, the initial antibacterial rate of the food packaging bags prepared is also lower than that of Example 1. Therefore, the addition of modified chitosan nanofiber can further enhance the antibacterial effect of the food packaging bags.

[0034] Test 2: The tensile strength of the food packaging bags prepared in Examples 1-3 and Comparative Examples 2-4 is tested, repeated three times, and the average value is taken, and the results are shown in Table 2.

[0035] Table 2: Test results of tensile strength of food packaging bags

[0036] From the above Table 2, it can be seen that when only one of the modified chitosan nanofiber or the modified cellulose nanocrystal is added in Comparative Example 2 and Comparative Example 3, the tensile strength of the food packaging bag prepared is lower than that of Example 1, thus it can be seen that after the cellulose nanocrystal is modified by 3-aminopropyl triethoxysilane and the chitosan nanofiber is modified by glycidyl laurate, then the modified cellulose nanocrystal and the modified chitosan are mixed with linear low-density polyethylene and other raw materials to prepare the food packaging bag, the cellulose nanocrystal and the chitosan nanofiber can synergistically improve the tensile strength of the food packaging bag after being combined; In addition, after the composite filler is replaced by an equal amount of nanometer layered double hydroxide in Comparative Example 4, and after the composite filler is removed in Comparative Example 5, the tensile strength of the food packaging bag prepared is lower than that of Example 1, thus it can be seen that after the heavy calcium carbonate is activated by dilute hydrochloric acid and then dispersed in deionized water, a mixed metal salt solution of magnesium nitrate and zinc chloride and a mixed alkali solution are added and reacted to prepare the composite filler of heavy calcium carbonate loaded with nanometer layered double hydroxide, which is mixed with linear low-density polyethylene and other raw materials to prepare the food packaging bag, the heavy calcium carbonate loaded with nanometer layered double hydroxide can be uniformly dispersed in the matrix with the heavy calcium carbonate, reducing agglomeration, and the combination of the two can enhance the network, thereby improving the tensile strength.

[0037] Test 3: The puncture strength of the food packaging bags prepared in Examples 1-3 and Comparative Example 5 was tested, repeated three times, and the average value was taken, and the results are shown in Table 3.

[0038] Table 3: Puncture strength test results of food packaging bags

[0039] From the above Table 3, it can be seen that after the composite filler is removed in Comparative Example 5, the puncture strength of the food packaging bag prepared is lower than that of Example 1, thus it can be seen that the addition of the composite filler can significantly improve the puncture resistance of the food packaging bag.

[0040] It should be understood that those of ordinary skill in the art can make improvements or changes according to the above description, and all these improvements and changes shall fall within the protection scope of the appended claims of the present application. Parts not described in detail in the specification belong to the prior art known to those skilled in the art.

Claims

1. A preparation process for an antibacterial food packaging bag, characterized in that, Includes the following steps: S1: Preparation of modified nitrogen-doped carbon quantum dots First, nitrogen-doped carbon quantum dots were prepared using polyvinylpyrrolidone as a raw material. Then, salicylic acid-modified chitosan was prepared using chitosan and salicylic acid as raw materials. Finally, the salicylic acid-modified chitosan was grafted onto the surface of nitrogen-doped carbon quantum dots to obtain modified nitrogen-doped carbon quantum dots. S2: Preparation of modified cellulose nanocrystals and modified chitosan nanofibers First, cellulose nanocrystals were surface modified with 3-aminopropyltriethoxysilane to obtain modified cellulose nanocrystals. Then, chitosan nanofibers were modified with glycidyl laurate to obtain modified chitosan nanofibers. S3: Preparation of composite fillers S3.1: Disperse heavy calcium carbonate in 1-3wt% dilute hydrochloric acid at a ratio of 1g:(4-6)mL, stir for 20-30min, then filter, wash until neutral, and dry to obtain activated heavy calcium carbonate; S3.2: Add magnesium nitrate hexahydrate and zinc chloride to deionized water at a ratio of (4.6-4.8) g: 1 g: (15-25) mL, stir thoroughly to dissolve, and obtain a mixed metal salt solution; S3.3: Disperse the above activated heavy calcium carbonate in deionized water at a ratio of 1g:(20-30)mL, sonicate for 20-30min to obtain activated heavy calcium carbonate dispersion, then add nano silica, stir in a water bath at 50-60℃ for 20-30min, then add an equal volume of the above mixed metal salt solution and mixed alkali solution while stirring, stir at 60-70℃ for 12-16h, cool, filter, wash and dry to obtain composite filler. S4: Preparation of antibacterial food packaging bags Linear low-density polyethylene, ethylene-vinyl acetate, the above-mentioned modified nitrogen-doped carbon quantum dots, the above-mentioned modified cellulose nanocrystals, the above-mentioned modified chitosan nanofibers, the above-mentioned composite filler, and maleic anhydride-grafted polyethylene are put into a mixer and mixed at 160-170℃ and 40-50rpm for 8-10 minutes. Then calcium stearate is added and the mixing continues for 6-8 minutes. The mixture is then extruded, granulated, and blown into a film to obtain an antibacterial food packaging bag.

2. The preparation process of an antibacterial food packaging bag according to claim 1, characterized in that, S1 specifically includes the following steps: S1.1: Dissolve polyvinylpyrrolidone in deionized water, stir thoroughly to dissolve, transfer to a high-pressure reactor, heat at 190-200℃ for 6-8 hours, cool, centrifuge to remove precipitate, filter the supernatant through a 0.22μm filter membrane, dialyze for 20-24 hours, and then heat at 80-90℃ to dryness to obtain nitrogen-doped carbon quantum dots; S1.2: Add chitosan to a 2% acetic acid aqueous solution at a ratio of 1 g: (75-85) mL, stir thoroughly to dissolve, and obtain a chitosan solution. Then, dissolve salicylic acid in deionized water at a ratio of 1 g: (35-40) mL, add equimolar amounts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stir and activate for 30-40 min to obtain an activated salicylic acid solution, wherein the mass ratio of N-hydroxysuccinimide to salicylic acid is (1.1-1.3):1; S1.3: Add the above salicylic acid activation solution to the above chitosan solution, heat and stir at 50-60℃ for 1-2 hours, and then dialyze and freeze dry to obtain salicylic acid modified chitosan. S1.4: Add the above nitrogen-doped carbon quantum dots to deionized water at a ratio of 1g:(180-200)mL, disperse by ultrasonication for 20-30min, then add equimolar amounts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stir and activate for 1-2h to obtain an activated nitrogen-doped carbon quantum dot dispersion, wherein the mass ratio of N-hydroxysuccinimide to nitrogen-doped carbon quantum dots is 1:3; S1.5: Dissolve the above salicylic acid modified chitosan in deionized water at a ratio of 1g:(200-300)mL, adjust the pH to 6-6.5, and then add it to the above activated nitrogen-doped carbon quantum dot dispersion. Stir the reaction at 40-50℃ for 5-6 hours, and maintain the pH at 6-6.5 by adding 0.1mol / L sodium hydroxide solution during the reaction. After cooling, the modified nitrogen-doped carbon quantum dots are obtained by centrifugation, washing, dialyzing and freeze-drying.

3. The preparation process of an antibacterial food packaging bag according to claim 2, characterized in that, S2 specifically includes the following steps: S2.1: Add cellulose nanocrystals to an 80% (v / v) ethanol solution and ultrasonically disperse for 30-40 min to prepare a cellulose nanocrystal dispersion with a concentration of 1-3 wt%. S2.2: Add 3-aminopropyltriethoxysilane to the above cellulose nanocrystal dispersion, and add acetic acid to adjust the pH to 4-5. Then heat and stir at 50-60℃ for 4-6 hours. After cooling, centrifuge, wash and freeze dry to obtain modified cellulose nanocrystals. S2.3: Add chitosan nanofibers to isopropanol at a ratio of 1g:(20-30)mL, disperse ultrasonically for 20-30min, then add glycidyl laurate, and heat and stir at 70-80℃ for 6-8h under nitrogen protection. After cooling, filter, wash and dry to obtain modified chitosan nanofibers.

4. The preparation process of an antibacterial food packaging bag according to claim 2, characterized in that, The molar ratio of salicylic acid to chitosan is (0.7-0.8):1, and the mass ratio of nitrogen-doped carbon quantum dots to salicylic acid-modified chitosan is (4.5-5.5):

1.

5. The preparation process of an antibacterial food packaging bag according to claim 3, characterized in that, The amount of 3-aminopropyltriethoxysilane added is 10-15% of the mass of the cellulose nanocrystals.

6. The preparation process of an antibacterial food packaging bag according to claim 3, characterized in that, The amount of glycidyl laurate added is 20-30% of the mass of chitosan nanofibers.

7. The preparation process of an antibacterial food packaging bag according to claim 1, characterized in that, The amount of nano-silica added is 8-10% of the mass of activated heavy calcium carbonate.

8. The preparation process of an antibacterial food packaging bag according to claim 1, characterized in that, The mixed alkaline solution includes 0.3 mol / L sodium carbonate and 1 mol / L sodium hydroxide, and the volume ratio of the mixed metal salt solution to the activated heavy calcium carbonate dispersion is 1:(4-5).

9. The preparation process of an antibacterial food packaging bag according to claim 1, characterized in that, By weight, the raw material composition of antibacterial food packaging bags is as follows: 60-70 parts linear low-density polyethylene, 15-20 parts ethylene-vinyl acetate, 3-5 parts modified nitrogen-doped carbon quantum dots, 6-8 parts modified cellulose nanocrystals, 4-6 parts modified chitosan nanofibers, 3-5 parts composite filler, 6-8 parts maleic anhydride-grafted polyethylene, and 1-3 parts calcium stearate.

10. An antibacterial food packaging bag, characterized in that, It is prepared by the preparation process of an antibacterial food packaging bag as described in any one of claims 1-9.

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