Long-acting slow-release antibacterial preservative paper based on Pickering emulsion and preparation method of long-acting slow-release antibacterial preservative paper

Abstract

The invention discloses long-acting slow-release antibacterial preservative paper based on Pickering emulsion and a preparation method of the long-acting slow-release antibacterial preservative paper. The long-acting slow-release antibacterial preservative paper comprises a paper-based carrier and an antibacterial functional layer, wherein the surface of the paper-based carrier is coated with the antibacterial functional layer; the antibacterial functional layer is formed by mixing a Pickering emulsion and a polyvinyl alcohol / gelatin composite base material to form a film; the Pickering emulsion is prepared by taking Tempo oxidized nanocellulose and ethyl lauroyl arginate hydrochloride water suspension as a water phase and performing ultrasonic emulsification on the water phase and origanum vulgare essential oil according to an oil-water volume ratio of 1: 9; wherein the mixing ratio of the Pickering emulsion to the composite base material is (30 to 50): 50; the mass percent concentration of the Tempo oxidized nanocellulose in the water-phase suspension liquid is 0.2 wt%, and the mass percent concentration of the ethyl lauroyl arginate hydrochloride in the water-phase suspension liquid is 0.01 wt%. Through material innovation and process optimization, the antibacterial property, the slow release property, the environmental protection property and the industrial application are remarkably superior to those of the prior art, and an efficient and reliable solution is provided for green packaging in the fields of food, medicine and the like.

Description

Technical Field

[0001] This invention belongs to the field of food preservation paper technology, specifically relating to a long-lasting, slow-release antibacterial food preservation paper based on Pickering emulsion and its preparation method. Background Technology

[0002] In recent years, the unsustainability and health threats posed by petroleum-based materials have forced the packaging industry to shift towards natural and biodegradable materials. With increasing consumer demand for food safety and environmental protection, antimicrobial packaging technology has become a research hotspot in the food, medical, and daily necessities sectors. Current mainstream antimicrobial packaging technologies mainly rely on the combination of petroleum-based materials and composite antimicrobial agents, but they have significant shortcomings in terms of environmental friendliness, safety, and long-term effectiveness, necessitating the development of new green antimicrobial packaging solutions.

[0003] While paper-based materials have the advantages of being biodegradable and renewable, their derivative technologies still present contradictions: inorganic antibacterial paper can cause ecotoxicity due to the leaching of metal ions; plant essential oils, as natural antibacterial agents, are safe and broad-spectrum, but they are volatile and their release is uncontrollable, resulting in short antibacterial effects.

[0004] Most studies use inorganic particles (such as TiO2), which do not meet food contact safety requirements. Nanocellulose (CNF) has limited emulsification efficiency when used alone, requiring high concentrations (>1 wt%) to stabilize the emulsion, which affects film-forming properties. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a long-lasting, sustained-release antibacterial preservation paper based on Pickering emulsion and its preparation method, thereby solving the aforementioned technical problems in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions: A long-lasting, slow-release antibacterial preservation paper based on Pickering emulsion includes a paper-based carrier and an antibacterial functional layer coated on its surface; the antibacterial functional layer is formed by mixing Pickering emulsion with a polyvinyl alcohol / gelatin composite substrate to form a film. The Pickering emulsion was prepared by ultrasonic emulsification of Tempo oxidized nanocellulose and lauroyl arginine ethyl ester hydrochloride aqueous suspension as aqueous phase and oregano essential oil at an oil-water volume ratio of 1:9. Wherein: the mixing ratio of the Pickering emulsion to the composite substrate is 30-50:50; The Tempo oxidized nanocellulose has a mass percentage concentration of 0.2 wt% in the aqueous suspension, and the lauroyl arginine ethyl ester hydrochloride has a mass percentage concentration of 0.01 wt% in the aqueous suspension.

[0007] Furthermore, the polyvinyl alcohol / gelatin composite substrate has a polyvinyl alcohol concentration of 4.75 wt% and a gelatin concentration of 0.25 wt%. The PVA solution is dissolved at 95°C, cooled to 60°C, and then the gelatin is added. After cooling to room temperature, it is mixed with Pickering emulsion.

[0008] Furthermore, in the Pickering emulsion, the emulsion particle size distribution is 200-500 nm, and the Zeta potential is ≥+30mV.

[0009] The preparation method of long-acting sustained-release antibacterial preservative paper based on Pickering emulsion includes the following steps: S1. Preparation of aqueous suspension: First, dissolve 0.2 wt% Tempo oxidized nanocellulose and 0.01 wt% lauroyl arginine ethyl ester hydrochloride in water and stir until homogeneous; S2. Preparation of Pickering emulsion: The suspension obtained in S1 is mixed with oregano essential oil at a volume ratio of 1:9 (oil to water) and ultrasonically emulsified under ice bath conditions. S3. Preparation of composite substrate: Dissolve 4.75 wt% PVA solution at 95℃, cool to 60℃ and add 0.25 wt% gelatin, then cool to room temperature; S4. Mixing and film formation: Mix the emulsion obtained in S2 with the composite substrate obtained in S3 at a volume ratio of 30-50:50 to form a uniform coating liquid. S5. Coating and Drying: Apply the coating liquid to the paper base surface by scraping and air dry at room temperature.

[0010] Furthermore, in S2, the water bath temperature is 2-5℃ and the time is 2 minutes.

[0011] Furthermore, in step S2, the power density of the ultrasonic emulsification process is 100-150 W / cm². 2 The ultrasonic power was 40%, the pulse mode was 3 seconds working and 2 seconds pausing, and the total duration was 2 minutes.

[0012] Furthermore, in S2, the system temperature is maintained below 30°C during the ultrasonic emulsification process.

[0013] Furthermore, in step S5, the coating amount is controlled to be 2-4 g / m². 2 This allows the coating thickness to be 5-15 μm.

[0014] Furthermore, in step S4, the emulsion and the composite substrate are mixed at a volume ratio of 40:50, and the stirring speed is 200-400 rpm.

[0015] Furthermore, when applied to fruit and vegetable food packaging, the slow release of oregano essential oil achieves dynamic antibacterial activity. The antibacterial preservation paper exhibits an antibacterial rate of ≥90% against Escherichia coli and Staphylococcus aureus, and an inhibition rate of ≥70% against Aspergillus niger.

[0016] The beneficial effects of this invention are: 1. This invention uses a low concentration of Tempo oxidized CNF (0.2 wt%) and LAE (0.01 wt%) to form an interfacial complex through electrostatic interaction, which significantly improves the stability of the emulsion (the shelf life is extended by more than 2 times compared to the pure CNF system).

[0017] 2. In this invention, LAE is used as a cationic antibacterial agent and combined with negatively charged CNF to form a "CNF-LAE-essential oil" ternary sustained-release system, with the release rate matching the microbial growth curve (antibacterial effect ≥ 8 days).

[0018] 3. This invention improves the chemical stability of essential oils through Pickering emulsion encapsulation technology and integrates them uniformly with the coating substrate, thereby achieving a match between the release rate of antibacterial components and the dynamic reproduction of microorganisms.

[0019] 4. The room temperature coating and air drying process used in this invention avoids the destruction of essential oil activity by high temperature, and is suitable for industrial production.

[0020] 5. The raw materials used in this invention—CNF, LAE, oregano essential oil, PVA, and gelatin—are all biodegradable and pose no ecotoxicity risk. It can replace petroleum-based packaging, solving the problems of heavy metal leaching from traditional inorganic antibacterial agents (such as silver ions) and white pollution from synthetic plastics. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0022] Figure 1 This is a flowchart illustrating an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the antibacterial effect of Embodiment 1 of the present invention; Figure 3 This is a graph showing the antibacterial rate of Example 1 of the present invention; Figure 4 This is a diagram showing the changes in appearance during the preservation and storage period of Embodiment 2 of the present invention; Figure 5 A graph showing the spoilage changes during the preservation and storage period of Embodiment 2 of the present invention; Figure 6 This is a graph showing the weight change during the preservation and storage period of Embodiment 2 of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a long-lasting, sustained-release antibacterial preservation paper based on Pickering emulsion, comprising a paper-based carrier and an antibacterial functional layer coated on its surface; the antibacterial functional layer is formed by mixing Pickering emulsion with a polyvinyl alcohol / gelatin composite substrate to form a film; Pickering emulsion was prepared by ultrasonic emulsification of Tempo oxidized nanocellulose and lauroyl arginine ethyl ester hydrochloride aqueous suspension as aqueous phase with oregano essential oil at an oil-water volume ratio of 1:9. At this time, the emulsion particle size distribution was 200-500 nm and the zeta potential was ≥+30 mV.

[0025] Furthermore, the mixing ratio of Pickering emulsion to composite substrate is 30-50:50; The Tempo oxidized nanocellulose concentration in the aqueous suspension was 0.2 wt%, and the lauroyl arginine ethyl ester hydrochloride concentration in the aqueous suspension was 0.01 wt%.

[0026] At this point, Pickering emulsion encapsulation technology, combined with PVA / gelatin composite substrate, enables the controlled release of oregano essential oil, with a release cycle of ≥8 days, which is matched with the dynamic growth of microorganisms to avoid early burst release or late failure.

[0027] The CNF / LAE electrostatic complex enhances emulsion stability and reduces essential oil loss during processing and storage (essential oil retention is increased by 30% compared to high-temperature drying).

[0028] like Figure 1 As shown, a method for preparing a long-lasting, sustained-release antibacterial preservative paper based on Pickering emulsion includes the following steps: S1. Preparation of aqueous suspension: First, dissolve 0.2 wt% Tempo oxidized nanocellulose and 0.01 wt% lauroyl arginine ethyl ester hydrochloride in water and stir with a magnetic stirrer (500 rpm) for 30 min until completely dispersed and uniform.

[0029] S2. Preparation of Pickering emulsion: The suspension obtained in S1 is mixed with oregano essential oil at a volume ratio of 1:9 (oil to water) and ultrasonically emulsified under ice bath conditions. The mixture was placed in an ice bath and treated with an ultrasonic disruptor (40% power) for 2 minutes in pulse mode (3 seconds on / 2 seconds off) to prevent local overheating from causing demulsification.

[0030] The final result is a uniform O / W type Pickering emulsion with a droplet size distribution of 200-500 nm (measured by dynamic light scattering instrument).

[0031] S3. Preparation of composite substrate: Dissolve 4.75 wt% polyvinyl alcohol (PVA) in 50 mL of deionized water and heat and stir at 95°C until completely dissolved.

[0032] After cooling to 60℃, add 0.25 wt% gelatin and continue stirring for 10 min until homogeneous.

[0033] Cool to room temperature (25°C) before use.

[0034] Then, 40 mL of Pickering emulsion was slowly added to 50 mL of PVA / gelatin solution and mechanically stirred (300 rpm) for 20 min to form a stable and uniform coating solution.

[0035] S4. Mixing and film formation: The emulsion obtained in S2 and the composite substrate obtained in S3 are mixed and stirred at a volume ratio of 30-50:50, preferably the emulsion and the composite substrate are mixed at a volume ratio of 40:50, and the stirring speed is 200-400 rpm to form a uniform coating liquid. At the same time, a quantitative method of 80 g / m was selected. 2 Food-grade kraft paper, cut into 10 cm × 10 cm sizes, and surface treated with plasma for 30 seconds to improve coating adhesion.

[0036] The composite coating solution was uniformly applied to the paper substrate surface using a bar coater, controlling the wet film thickness to 100 μm, corresponding to a dry film coating weight of 3.5 g / m². 2 Air-dry at 25℃ and 50% relative humidity for 24 hours to form a preservative paper with antibacterial properties.

[0037] S5. Coating and Drying: Apply the coating liquid to the paper base surface using a scraper, controlling the coating amount to 2-4 g / m². 2 This coating method achieves a coating thickness of 5-15 μm and air-dries at room temperature (no additional energy required). It eliminates the need for high temperatures or complex equipment, is suitable for existing paper production lines, and has a coating cost of ≤0.5 yuan / square meter, making it cost-effective.

[0038] Example 1 Suspension preparation: Dissolve 0.2 wt% Tempo nanocellulose (CNF) and 0.01 wt% lauroyl arginine ethyl ester hydrochloride (LAE) in deionized water, bring the volume to 18 mL, and stir with a magnetic stirrer (500 rpm) for 30 min until completely dispersed.

[0039] Pickering emulsion preparation: oil-to-water ratio: oil to suspension volume ratio (1:9). Ultrasonic treatment at 40% power for two minutes in pulse mode (3 seconds on / 2 seconds off). Simultaneous ultrasonic treatment with an ice bath to prevent demulsification due to excessive temperature. Coating preparation: Composite coating: After heating and mixing 50 ml of 4.75 wt% polyvinyl alcohol at 95℃, the mixture was cooled to 60℃ and 0.25% gelatin was added. After cooling to room temperature, 20 ml of pickering emulsion was added as experimental group 1, and 40 ml of pickering emulsion was added as experimental group 2. The mixture was stirred thoroughly during the process.

[0040] Coating method: Use the scraper coating method with a coating amount of 2-4 g / m². 2 .

[0041] Drying and curing: Air drying at room temperature. The blank control group used the original paper. The antibacterial rate was determined by shaking method according to GB-T42702-2023 (Determination of antibacterial properties of paper, paperboard and paper products).

[0042] Example 2 CNF and LAE were added to water at 0.2 wt% and 0.01 wt% solutions respectively to form a suspension with a total volume of 18 ml, and then thoroughly mixed. Pickering emulsion preparation: oil-to-water ratio: oil to suspension volume ratio (1:9). Ultrasonic treatment was performed at 40% power for two minutes (and 2 mL of oregano essential oil was added to the above aqueous suspension at an oil-to-water ratio of 1:9, followed by gentle agitation premixing), pulse mode (3 seconds on / 2 seconds off). An ice bath was used during ultrasonic treatment to prevent demulsification due to excessive temperature. Coating preparation: Composite coating: Heat and mix 50 ml of 4.75 wt% polyvinyl alcohol at 95℃, then cool to 60℃ and add 0.25% gelatin. After cooling to room temperature, add 40 ml of pickering emulsion, stirring thoroughly throughout the process. Control the coating amount to 2-4 g / m². 2 Air dry at room temperature.

[0043] Physical preservation test: Strawberries were placed in paper bags folded to A4 size and sealed with clips in both the control and experimental groups. The appearance of the strawberries was compared and recorded using photographs, and daily weight changes were observed. The blank control group used the original paper.

[0044] Refer to Table 1 below for a comparison with traditional technical solutions.

[0045] Table 1

[0046] This invention, through material innovation (CNF / LAE / PVA-gelatin) and process optimization (ultrasonic emulsification + room temperature coating), significantly outperforms existing technologies in terms of antibacterial properties, sustained release, environmental friendliness, and industrial application, providing an efficient and reliable solution for green packaging in the food, pharmaceutical, and other fields.

[0047] Antibacterial performance test: The tested bacterial strains were Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 6538), and Aspergillus niger (ATCC16404).

[0048] Test method: Cut the antibacterial preservation paper into 5 cm × 5 cm samples and mix with the bacterial suspension (10). 6 Co-culture (CFU / mL) for 24 h (bacteria) or 72 h (mold).

[0049] Antibacterial rate was calculated using the plate count method:

[0050] result: It exhibits an inhibition rate of ≥90% against Escherichia coli and Staphylococcus aureus, and an inhibition rate of ≥70% against Aspergillus niger.

[0051] Strawberry preservation application test. See details in the attached document. Figure 2 , Figure 3 As shown.

[0052] like Figure 2 and Figure 3 The control group and experimental group 1 and experimental group 2 shown are, from left to right, the experimental group, control group 1, and control group 2. As can be seen from the figure, almost no visible colonies were found in the culture dishes of experimental group 2 for *Escherichia coli* and *Staphylococcus aureus*. The antibacterial preservative paper has a strong inhibitory effect on both Gram-negative and Gram-positive bacteria, with an inhibition rate ≥90%. In contrast, the experimental group corresponding to *Aspergillus niger* showed a small number of tiny colonies, indicating that the antibacterial material has a relatively weak inhibitory effect on fungi, with an inhibition rate ≥70%. Furthermore, the antibacterial ability of the three types of colonies increased with the increase of the amount of emulsion added.

[0053] Note: Figure 3 The indicators from left to right are for Escherichia coli, Staphylococcus aureus, and Aspergillus niger.

[0054] Sample preparation Antibacterial preservation paper was prepared using the method in Example 1 and folded into A4-sized paper bags.

[0055] Fresh strawberries (variety "Hongyan") were randomly divided into two groups (refer to...). Figure 4 (as shown) Experimental group: packaged in antibacterial paper bags; control group: packaged in ordinary kraft paper bags.

[0056] All samples were stored at 25°C and 60% relative humidity.

[0057] Evaluation indicators Sensory changes: Take photos daily to record the mold growth, water loss, and shrinkage on the surface of the strawberries.

[0058] Weightlessness rate: Weigh yourself daily and calculate the weight loss rate: .

[0059] Corruption rate: The percentage of strawberries with mold or soft rot was counted.

[0060] .

[0061] On day 8, the experimental group of strawberries: The decay rate is ≤20%, the weight loss rate is ≤5%, and the color and hardness are well maintained.

[0062] The strawberries in the control group showed obvious mold on the 4th day, and the spoilage rate was ≥80% on the 6th day.

[0063] Validation of sustained-release performance: Essential oil release kinetics testing methods: Immerse the antibacterial preservation paper in 50 mL of 10% ethanol solution (simulating a moist environment for food) and let it stand at 25°C.

[0064] Samples were taken every 24 hours, and the release of carvacrol in oregano essential oil was determined by gas chromatography (GC).

[0065] result: The release curve conforms to a first-order kinetic model, with a sustained-release period of ≥8 days, matching the microbial growth cycle. Figure 1 ).

[0066] Weight loss rate: The weight change of the sample after the experiment was observed, and the weight loss rate was calculated as follows: .

[0067] like Figure 4 As shown in 5 and 6, Figure 4In the blank control group: obvious rotten spots appeared on day 6, and the fruit was completely rotten on day 9 with blackened skin and spreading mold; while in the experimental group: the strawberries still maintained an intact appearance on day 9 with bright green stems and no mold spots on the surface, and the shelf life was extended to ≥8 days. Figure 4 In the study of spoilage rates, the spoilage rate in the blank control group increased sharply with storage time, reaching 45% on day 9.

[0068] The rate of spoilage in the experimental group slowed significantly, reaching only 20% on day 9, with a spoilage inhibition efficiency of over 55%. This indicates that the experimental group effectively inhibited microbial growth and delayed the spoilage process through the slow-release mechanism of antibacterial components. Figure 5 In the comparison of weight loss rates shown, the control group lost nearly 40% of its weight on day 8, indicating that rapid water loss led to fruit shrinkage; while the experimental group lost about 30% of its weight during the same period, with a 25% improvement in water retention.

[0069] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A long-lasting, sustained-release antibacterial preservative paper based on Pickering emulsion, comprising a paper-based carrier and an antibacterial functional layer coated on its surface; characterized in that, The antibacterial functional layer is formed by mixing Pickering emulsion with a polyvinyl alcohol / gelatin composite substrate to form a film. The Pickering emulsion was prepared by ultrasonic emulsification of Tempo oxidized nanocellulose and lauroyl arginine ethyl ester hydrochloride aqueous suspension as aqueous phase and oregano essential oil at an oil-water volume ratio of 1:

9. Wherein: the mixing ratio of the Pickering emulsion to the composite substrate is 30-50:50; The Tempo oxidized nanocellulose has a mass percentage concentration of 0.2 wt% in the aqueous suspension, and the lauroyl arginine ethyl ester hydrochloride has a mass percentage concentration of 0.01 wt% in the aqueous suspension.

2. The long-lasting, sustained-release antibacterial preservative paper based on Pickering emulsion according to claim 1, characterized in that, The polyvinyl alcohol / gelatin composite substrate has a polyvinyl alcohol concentration of 4.75 wt% and a gelatin concentration of 0.25 wt%. The PVA solution is dissolved at 95°C, cooled to 60°C, and then gelatin is added. After cooling to room temperature, it is mixed with Pickering emulsion.

3. The long-lasting, sustained-release antibacterial preservative paper based on Pickering emulsion according to claim 1, characterized in that, The Pickering emulsion has a particle size distribution of 200-500 nm and a zeta potential ≥ +30 mV.

4. The method for preparing long-lasting, sustained-release antibacterial preservative paper based on Pickering emulsion according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Preparation of aqueous suspension: First, dissolve 0.2 wt% Tempo oxidized nanocellulose and 0.01 wt% lauroyl arginine ethyl ester hydrochloride in water and stir until homogeneous; S2. Preparation of Pickering emulsion: The suspension obtained in S1 is mixed with oregano essential oil at a volume ratio of 1:9 (oil to water) and ultrasonically emulsified under ice bath conditions. S3. Preparation of composite substrate: Dissolve 4.75 wt% PVA solution at 95℃, cool to 60℃ and add 0.25 wt% gelatin, then cool to room temperature; S4. Mixing and film formation: Mix the emulsion obtained in S2 with the composite substrate obtained in S3 at a volume ratio of 30-50:50 to form a uniform coating liquid. S5. Coating and Drying: Apply the coating liquid to the paper base surface by scraping and air dry at room temperature.

5. The method for preparing long-lasting, sustained-release antibacterial preservative paper based on Pickering emulsion according to claim 4, characterized in that, In S2, the water bath temperature is 2-5℃ and the time is 2 minutes.

6. The method for preparing long-lasting sustained-release antibacterial preservative paper based on Pickering emulsion according to claim 4, characterized in that, In step S2, the power density of the ultrasonic emulsification process is 100-150 W / cm². 2 The ultrasonic power was 40%, the pulse mode was 3 seconds working and 2 seconds pausing, and the total duration was 2 minutes.

7. The method for preparing long-lasting sustained-release antibacterial preservative paper based on Pickering emulsion according to claim 6, characterized in that, In step S2, the system temperature is maintained below 30°C during ultrasonic emulsification.

8. The method for preparing long-lasting sustained-release antibacterial preservative paper based on Pickering emulsion according to claim 4, characterized in that, In step S5, the coating amount is controlled at 2-4 g / m². 2 This allows the coating thickness to be 5-15 μm.

9. The long-lasting, sustained-release antibacterial preservative paper based on Pickering emulsion according to claim 1, characterized in that, In step S4, the emulsion and the composite substrate are mixed at a volume ratio of 40:50, and the stirring speed is 200-400 rpm.

10. The long-lasting, sustained-release antibacterial preservative paper based on Pickering emulsion according to claim 1, characterized in that, When applied to fruit and vegetable food packaging, it achieves dynamic antibacterial effect through the slow release of oregano essential oil. The antibacterial preservation paper has an antibacterial rate of ≥90% against Escherichia coli and Staphylococcus aureus, and an inhibition rate of ≥70% against Aspergillus niger.

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