Preparation method and application of immobilized nanometer copper sulfide carboxymethyl cellulose / polyvinyl alcohol high-barrier antibacterial composite film

Abstract

The application belongs to the field of functional materials, and provides a preparation method and application of a carboxymethyl cellulose / polyvinyl alcohol high-barrier antibacterial composite film immobilizing nano copper sulfide. The method comprises the following steps: dissolving carboxymethyl cellulose in an alkali-urea system, adding copper ammonia complex ion solution and sodium sulfide solution, and then performing reaction and dialysis to obtain a carboxymethyl cellulose solution immobilizing copper sulfide. Then, polyvinyl alcohol is added to the above solution, and a composite film is prepared by using a flow evaporation method. In the application, carboxymethyl cellulose is used as a fixing agent, a stabilizing agent and a growth template, and no surfactant or chemical stabilizer is added, so that the preparation method is green, non-toxic and low in cost. The long-chain stabilizing effect of carboxymethyl cellulose and the excellent film-forming property of polyvinyl alcohol greatly improve the fixing effect of copper sulfide. The copper sulfide can convert near-infrared light into heat energy to locally heat and achieve the purpose of sterilization. The composite film of the application is applied in the field of food antibacterial packaging.

Description

Technical Field

[0001] This invention belongs to the field of functional materials, specifically relating to a method for preparing a high-barrier antibacterial composite film of immobilized nano-copper sulfide carboxymethyl cellulose / polyvinyl alcohol, which can be used in related fields such as food antibacterial packaging. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] As the environmental problems caused by non-degradable petroleum-based plastic packaging products become increasingly serious, developing high-performance, green, and biodegradable antimicrobial food packaging materials for food antimicrobial preservation has become one of the major challenges facing the industry. Using green and biodegradable biomass raw materials to prepare food packaging films to replace traditional non-degradable petroleum-based plastic materials can effectively alleviate environmental problems and, by loading antimicrobial nanoparticles, achieve the antimicrobial preservation function of the packaging film, thereby extending the shelf life of food.

[0004] Copper sulfide is a transition metal sulfide with excellent optical properties, such as photothermal activity and visible light absorption. Nano-copper sulfide exhibits strong absorption in the near-infrared region, converting near-infrared light into heat energy to achieve localized heating and sterilization, demonstrating good killing and inhibitory effects on both Gram-positive and Gram-negative bacteria. Cellulose is the most widely distributed and abundant polysaccharide in nature, a green and biodegradable biomass resource. The cellulose molecular chain contains numerous hydroxyl groups, which can form supramolecular structures through hydrogen bonding, further serving as a green and harmless growth template for nano-copper sulfide. Simultaneously, cellulose has a good stabilizing effect on nano-copper sulfide, effectively preventing the aggregation of copper sulfide particles. Utilizing cellulose to synthesize nano-copper sulfide particles and then combining them with polyvinyl alcohol to form films not only allows for the exploration of green and efficient synthesis methods for nanoparticles but also enables the high-value utilization of biomass resources, showing broad application prospects and market demand.

[0005] Patent CN114957753A discloses a high-strength copper sulfide / nanocellulose / polyvinyl alcohol near-infrared shielding and heat insulation film. By adding toxic triethylamine, copper sulfide is deposited on nanocellulose. The heat insulation film prepared is mainly used for near-infrared shielding and heat insulation. Not only does it use toxic substances, but its antibacterial and barrier properties as an antibacterial and freshness-preserving packaging film also need to be improved.

[0006] Currently, there are multiple pathways for the formation of copper sulfide, and the curing effect of copper sulfate on cellulose varies significantly depending on the pathway. Even within the same pathway, different modified celluloses exhibit considerably different effects on promoting the curing of copper sulfate. Therefore, a method for preparing highly antibacterial and highly barrier copper sulfide / nanocellulose / polyvinyl alcohol films has not yet been found in the industry. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for preparing and applying a high-barrier antibacterial composite film for fruit and vegetable packaging that exhibits significant antibacterial effects, is environmentally friendly and biodegradable, and is non-toxic. This invention uses a green and non-toxic carboxymethyl cellulose solution to prepare copper sulfide. The preparation method is simple, efficient, environmentally friendly, and requires minimal requirements for the operating environment and equipment. Applying this high-barrier, high-strength antibacterial composite film to the packaging of fruits, vegetables, and other food products has great potential.

[0008] This invention has found that during the reaction of copper ammonia complex solution and sodium sulfide, the long-chain stabilizing effect of carboxymethyl cellulose can effectively promote the curing of copper sulfate on carboxymethyl cellulose, significantly improving the antibacterial and barrier properties of the composite film. Test results show that the composite film of this invention has high barrier properties against water vapor, oxygen, and air, and has a significant antibacterial effect against bacteria and other microorganisms.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a high-barrier antibacterial composite membrane of immobilized copper sulfide nanoparticles and carboxymethyl cellulose / polyvinyl alcohol, comprising:

[0011] Carboxymethyl cellulose was dissolved in an alkaline urea system, and then copper ammonium complex ion solution and sodium sulfide solution were added and mixed evenly to obtain the first mixed solution.

[0012] The mixed solution was heated to allow it to react. After the reaction was complete, it was dialyzed to obtain a carboxymethyl cellulose-immobilized copper sulfide solution.

[0013] The polyvinyl alcohol solution and the carboxymethyl cellulose immobilized copper sulfide solution were mixed evenly to obtain a second mixed solution;

[0014] The second mixed solution is cast into a film using a casting method to obtain the final product.

[0015] In some embodiments, the mass ratio of the carboxymethyl cellulose to the copper ammonia complex solution and the sodium sulfide solution is 2:1:1-1.5.

[0016] Preferably, the mass ratio of carboxymethyl cellulose solution to copper ammonia complex solution and sodium sulfide solution is 2:1:1.

[0017] In some embodiments, the carboxymethyl cellulose is in powder form with a fiber size of 180 μm.

[0018] In some embodiments, the alkali-urea system solution contains 5-12% sodium hydroxide by mass, 7-12% urea by mass, and the remainder is water.

[0019] In some embodiments, the mass-to-volume ratio of the carboxymethyl cellulose to the alkaline urea solution is 1–5 g: 100 mL.

[0020] In some embodiments, the concentration of the copper ammonia complex solution is 0.02M to 0.04M.

[0021] In some embodiments, the concentration of the sodium sulfide solution is 0.025M to 0.04M.

[0022] In some embodiments, a copper ammonia complex solution is added to a carboxymethyl cellulose solution and stirred for 1.5–2 hours. After homogeneous mixing, a sodium sulfide solution is added to the mixture and stirred for 0.5–1 hour.

[0023] In some embodiments, the reaction is carried out at 30–80°C for 30–60 min.

[0024] In some implementations, microwave heating is used, with a microwave power of 700–1000W.

[0025] In some embodiments, after the carboxymethyl cellulose solution is thoroughly mixed with the copper ammonia complex solution and the sodium sulfide solution, the reaction should be carried out in a microwave reactor under heating and stirring.

[0026] In some implementations, dialysis is performed to ensure that unreacted sulfide ions are completely precipitated, which takes 72 to 96 hours.

[0027] In some embodiments, the mass ratio of carboxymethyl cellulose to polyvinyl alcohol is 1-5:1-10.

[0028] In some embodiments, 1–10 g of polyvinyl alcohol is dissolved in 100 mL of deionized water.

[0029] In some embodiments, the carboxymethyl cellulose solution immobilized with copper sulfide is mixed with a polyvinyl alcohol solution and then stirred using a magnetic stirrer at a speed of 300-450 r / min for 5 min.

[0030] In some embodiments, the mixed solution is placed in a vacuum drying oven for degassing.

[0031] In some embodiments, the mixed solution is dried at a temperature of 45–60°C for 6–10 hours.

[0032] More specifically, including:

[0033] A certain amount of carboxymethyl cellulose was uniformly dissolved in an alkaline urea system, and a certain amount of copper ammonia complex solution and sodium sulfide solution were added. The mixture was then placed in a microwave reactor for reaction. After the reaction was completed, the solution was poured into a dialysis bag to remove unreacted sulfide ions, obtaining a carboxymethyl cellulose immobilized copper sulfide solution. Then, a certain amount of polyvinyl alcohol was dissolved in deionized water, and a quantitative amount of the above-prepared carboxymethyl cellulose immobilized copper sulfide solution was added. After uniform mixing, the mixture was poured into a mold using a casting evaporation method and dried to obtain a carboxymethyl cellulose immobilized copper sulfide / polyvinyl alcohol composite membrane.

[0034] Furthermore, the preparation method of the high-barrier antibacterial composite membrane specifically includes the following steps:

[0035] (1) Preparation of carboxymethyl cellulose immobilized with copper sulfide: Dissolve 1-5g of carboxymethyl cellulose powder in 100mL of alkaline urea solution, then add 0.02M-0.04M of copper ammonia complex ion solution and 0.025M-0.04M of sodium sulfide solution in a mass ratio of 2:1:1. After uniform mixing, place the mixture in a microwave reactor and react for 30-60min at a power of 700-1000W and a temperature of 30-80℃. After the reaction is completed, dialyze out the unreacted sulfide ions to obtain a carboxymethyl cellulose solution immobilized with copper sulfide.

[0036] (2) Preparation of carboxymethyl cellulose / polyvinyl alcohol high-barrier antibacterial composite membrane with immobilized copper sulfide: Dissolve 1-10g of polyvinyl alcohol in 100mL of deionized water and stir with a magnetic stirrer for 1h until the polyvinyl alcohol is completely dissolved. Add 20-40mL of carboxymethyl cellulose solution with immobilized copper sulfide obtained in step (1), mix evenly, and then prepare and dry the carboxymethyl cellulose / polyvinyl alcohol high-barrier antibacterial composite membrane with immobilized copper sulfide by casting evaporation method.

[0037] In a second aspect, the present invention provides a high-barrier antibacterial composite membrane of immobilized copper sulfide nanoparticles and carboxymethyl cellulose / polyvinyl alcohol prepared by the above method.

[0038] A third aspect of the present invention provides the application of the above-mentioned immobilized copper nanoparticle carboxymethyl cellulose / polyvinyl alcohol high-barrier antibacterial composite film in the preparation of antibacterial packaging, the applicable objects of which include: food.

[0039] Preferably, the immobilized copper sulfide nanocarboxymethyl cellulose / polyvinyl alcohol high-barrier composite antibacterial film can be applied to biodegradable antibacterial packaging materials for fruits and vegetables such as grapes, longan, tomatoes, bananas, cucumbers, and celery. This composite film has high barrier properties against water vapor, oxygen, and air, and exhibits significant antibacterial effects against bacteria and other microorganisms.

[0040] Beneficial effects of the present invention

[0041] (1) This invention uses carboxymethyl cellulose, a biomass resource, as a stabilizer, fixative and growth template, so that no other chemical surfactants are added. The preparation method is simple, efficient, green and pollution-free, and has low requirements for the operating environment and equipment.

[0042] (2) Copper sulfide is an important transition metal sulfide with excellent optical properties. It has strong absorption in the near-infrared light and can convert near-infrared light into heat energy to achieve local temperature rise and sterilization. It can effectively avoid the problem of drug resistance of pathogenic microorganisms caused by the overuse of antibiotics.

[0043] (3) The polyvinyl alcohol used in this invention is water-soluble, environmentally friendly, and has excellent film-forming properties. The film exhibits superior physical properties, high strength, and good barrier properties, making it suitable as a functional material for food packaging. Polyvinyl alcohol is a biocompatible and biodegradable green polymer material. Film formation can further fix copper sulfide, enhancing the sustained-release antibacterial effect of nanoparticles, thus enabling the composite film to be applied in the field of antibacterial food packaging.

[0044] (4) This invention relies on the long-chain stabilizing effect of carboxymethyl cellulose and the excellent film-forming properties of polyvinyl alcohol to greatly improve the fixation effect of copper sulfide. The preparation method of this invention is simple, practical, and easy to promote. Attached Figure Description

[0045] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0046] Figure 1 Carboxymethyl cellulose solutions of immobilized copper sulfide at different dilution ratios.

[0047] Figure 2 Electron micrographs of the surface of the carboxymethyl cellulose / polyvinyl alcohol high-barrier antibacterial composite membrane with immobilized copper sulfide and the immobilized copper sulfide.

[0048] Figure 3 The graph shows the antibacterial effect of the composite membrane against Staphylococcus aureus and Escherichia coli. Detailed Implementation

[0049] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0050] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0051] Based on the final requirements for high-barrier antibacterial packaging materials, the main focus is on testing the antibacterial ability of the prepared high-barrier antibacterial composite film against Gram-positive and Gram-negative bacteria (taking Staphylococcus aureus and Escherichia coli as examples) and its food packaging barrier performance after near-infrared light irradiation. The initial amount of carboxymethyl cellulose-immobilized copper sulfide and the copper ammonia complex solution and sodium sulfide solution are adjusted according to different actual conditions. Specifically, this includes:

[0052] (1) Antibacterial experiments were conducted using Staphylococcus aureus and Escherichia coli, respectively. The carboxymethyl cellulose immobilized copper sulfide / polyvinyl alcohol high-barrier antibacterial composite membranes prepared in Examples 1-4 were placed on a glass slide (2×2cm). 2 The bacterial culture was used as a sample. Antimicrobial test: The bacterial culture was diluted to 10 g / L in LB liquid medium. 8 CFU / mL, poured into petri dishes, and then added 10 mL of diluted bacterial suspension. The petri dishes containing the sample and bacterial suspension were placed in a constant temperature incubator and incubated at 30°C for 12 hours. After incubation, the solution was serially diluted 10⁻¹⁰ times with LB. 3 The diluted liquid culture medium sample (10 μL) was evenly scraped onto LB solid medium and incubated at 30°C for 48 h. The number of colonies adhering to different samples was determined by plate counting. The number of colonies growing on the solid medium was recorded as N1, and the number of colonies in the control group was recorded as N2. The antimicrobial efficiency (AE) was calculated according to formula (1):

[0053] AE = (1 - N1 / N2) × 100% (1)

[0054] (2) The oxygen permeability and water vapor permeability of the composite membrane were determined according to GB / T 19789-2021 and GB1037.

[0055] Example 1:

[0056] 1g of carboxymethyl cellulose powder was added to 100mL of alkali urea solution, dispersed evenly, and then freeze-thawed in a refrigerator. Next, 0.02M copper ammonia complex solution and 0.025M sodium sulfide solution were added at a mass ratio of 2:1:1. After thorough mixing, the mixture was placed in a microwave reactor and reacted at 1000W and 80℃ for 60 minutes. After the reaction, unreacted sulfide ions were dialyzed off to obtain a carboxymethyl cellulose immobilized copper sulfide solution. 1g of polyvinyl alcohol was dissolved in 100mL of deionized water and stirred with a magnetic stirrer for 1 hour until the polyvinyl alcohol was completely dissolved. 20mL of the carboxymethyl cellulose immobilized copper sulfide solution was mixed evenly with the above polyvinyl alcohol solution. The mixture was then placed in a mold using a casting evaporation method and dried to obtain a carboxymethyl cellulose immobilized copper sulfide / polyvinyl alcohol high-barrier antibacterial composite membrane.

[0057] The prepared composite membrane exhibited a 99.2% inhibition rate against Staphylococcus aureus and a 99.0% inhibition rate against Escherichia coli. The oxygen permeability of the composite membrane, as determined by GB / T 19789-2021 and GB 1037, was 0.15 cc / m³. 2 / day, water vapor transmission rate is 201.8 g / m 2 / day.

[0058] Example 2:

[0059] 2g of carboxymethyl cellulose powder was added to 100mL of alkali urea solution, dispersed evenly, and then freeze-thawed in a refrigerator. Next, 0.025M copper ammonia complex solution and 0.03M sodium sulfide solution were added at a mass ratio of 2:1:1. After uniform mixing, the mixture was placed in a microwave reactor and reacted at 900W and 60℃ for 50 minutes. After the reaction, unreacted sulfide ions were dialyzed off to obtain a cellulose-immobilized copper sulfide solution. 3g of polyvinyl alcohol was dissolved in 100mL of deionized water and stirred with a magnetic stirrer for 1 hour until the polyvinyl alcohol was completely dissolved. 25mL of the cellulose-immobilized copper sulfide solution was mixed evenly with the above polyvinyl alcohol solution. The mixture was then placed in a mold using a casting evaporation method and dried to obtain a cellulose-immobilized copper sulfide / polyvinyl alcohol high-barrier antibacterial composite membrane.

[0060] The prepared composite membrane exhibited a 99.2% inhibition rate against Staphylococcus aureus and a 99.0% inhibition rate against Escherichia coli; its oxygen permeability was 0.08 cc / m³. 2 / day, water vapor transmission rate is 191.3 g / m 2 / day.

[0061] Example 3:

[0062] 3g of carboxymethyl cellulose powder was added to 100mL of alkali urea solution, dispersed evenly, and then freeze-thawed in a refrigerator. Next, 0.03M copper ammonia complex solution and 0.035M sodium sulfide solution were added at a mass ratio of 2:1:1. After thorough mixing, the mixture was placed in a microwave reactor and reacted at 800W and 40℃ for 40 minutes. After the reaction, unreacted sulfide ions were dialyzed off to obtain a cellulose-immobilized copper sulfide solution. 5g of polyvinyl alcohol was dissolved in 100mL of deionized water and stirred with a magnetic stirrer for 1 hour until the polyvinyl alcohol was completely dissolved. 30mL of the cellulose-immobilized copper sulfide solution was mixed evenly with the above polyvinyl alcohol solution. The mixture was then placed in a mold using a casting evaporation method and dried to obtain a cellulose-immobilized copper sulfide / polyvinyl alcohol high-barrier antibacterial composite membrane.

[0063] The prepared composite membrane exhibited a 99.4% inhibition rate against Staphylococcus aureus and a 99.3% inhibition rate against Escherichia coli; its oxygen permeability was 0.05 cc / m³. 2 / day, water vapor transmission rate is 182.3 g / m 2 / day.

[0064] Example 4:

[0065] 4g of carboxymethyl cellulose powder was added to 100mL of alkali urea solution, dispersed evenly, and then freeze-thawed in a refrigerator. Next, 0.035M copper ammonia complex solution and 0.04M sodium sulfide solution were added at a mass ratio of 2:1:1, and mixed evenly. The mixture was then placed in a microwave reactor and reacted at 700W and 20℃ for 30 minutes. After the reaction, unreacted sulfide ions were dialyzed off to obtain a cellulose-immobilized copper sulfide solution. 7g of polyvinyl alcohol was dissolved in 100mL of deionized water and stirred with a magnetic stirrer for 1 hour until the polyvinyl alcohol was completely dissolved. 35mL of the cellulose-immobilized copper sulfide solution was mixed evenly with the above polyvinyl alcohol solution. The mixture was then placed in a mold using a casting evaporation method and dried to obtain a cellulose-immobilized copper sulfide / polyvinyl alcohol high-barrier antibacterial composite membrane.

[0066] The prepared composite membrane exhibited a 99.5% inhibition rate against Staphylococcus aureus and a 99.4% inhibition rate against Escherichia coli; its oxygen permeability was 0.03 cc / m³. 2 / day, water vapor transmission rate is 163.3 g / m 2 / day.

[0067] Comparative Example 1

[0068] The difference from Example 4 is that nanofibers were used instead of carboxymethyl cellulose. Furthermore, toxic triethylamine was added during the experiment; this substance irritates the human respiratory tract and can cause chemical burns if it comes into contact with the eyes or skin. In contrast, Example 4 used a carboxymethyl cellulose solution as a template and stabilizer to synthesize copper sulfide; this process is non-toxic and possesses advantages such as safety and being environmentally friendly.

[0069] Comparative Example 2

[0070] The difference from Example 4 is that carboxymethyl cellulose was blended with polyvinyl alcohol to prepare nanofibers, and copper sulfide nanoparticles were not introduced during the experiment, therefore it did not possess antibacterial properties. In contrast, in Example 4, copper sulfide was synthesized using carboxymethyl cellulose as a template and stabilizer, and then blended with polyvinyl alcohol to prepare a composite membrane. This composite membrane exhibited an inhibition rate of 99.5% against Staphylococcus aureus and 99.4% against Escherichia coli.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-barrier antibacterial composite membrane of immobilized copper sulfide nanoparticles and carboxymethyl cellulose / polyvinyl alcohol, characterized in that, It consists of the following steps: Carboxymethyl cellulose was dissolved in an alkaline urea system, and then copper ammonium complex ion solution and sodium sulfide solution were added and mixed evenly to obtain the first mixed solution. The mass ratio of the carboxymethyl cellulose to the copper ammonia complex solution and the sodium sulfide solution is 2:1:1-1.5; The mass-to-volume ratio of the carboxymethyl cellulose to the alkaline urea solution is 1-5 g: 100 mL; The concentration of the copper ammonia complex solution is 0.02 M to 0.04 M; The concentration of the sodium sulfide solution is 0.025 M to 0.04 M; The mixed solution was heated to allow it to react. After the reaction was complete, it was dialyzed to obtain a carboxymethyl cellulose-immobilized copper sulfide solution. The polyvinyl alcohol solution and the carboxymethyl cellulose immobilized copper sulfide solution were mixed evenly to obtain a second mixed solution; The mass ratio of carboxymethyl cellulose to polyvinyl alcohol is 1~5:1~7; The second mixed solution is cast into a film using a casting method to obtain the final product; The term "high barrier" refers to its high barrier properties against water vapor, oxygen, and air.

2. The method for preparing the immobilized copper sulfide nanocarboxymethyl cellulose / polyvinyl alcohol high-barrier antibacterial composite membrane as described in claim 1, characterized in that, The reaction conditions are 30~80℃ for 30~60 min.

3. The method for preparing the immobilized copper sulfide nanocarboxymethyl cellulose / polyvinyl alcohol high-barrier antibacterial composite membrane as described in claim 1, characterized in that, Microwave heating is used, with a microwave power of 700~1000 W.

4. The carboxymethyl cellulose / polyvinyl alcohol high-barrier antibacterial composite membrane with immobilized copper nanoparticles prepared by the method according to any one of claims 1-3.

5. The application of the immobilized copper nanoparticle cellulose / polyvinyl alcohol high-barrier antibacterial composite film according to claim 4 in the preparation of antibacterial packaging, characterized in that, The antimicrobial packaging is applicable to food products.

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