Preparation method of antibacterial preservative film loaded with ZIF-8 nanoparticles

Abstract

The invention relates to a preparation method of an antibacterial preservative film loaded with ZIF-8 nanoparticles, which comprises the following steps: (1) adding PLA (polylactic acid) and PCL (polycaprolactone) into hexafluoroisopropanol, and stirring at room temperature to prepare a spinning solution; (2) adding PEO, and stirring and dissolving at room temperature; (3) feeding the solution, and applying voltage to perform electrostatic spinning to prepare a spinning membrane; (4) respectively dissolving Zn (NO3) 26H2O and 2-methylimidazole in deionized water; (5) adding CTAB (Cetyltrimethyl Ammonium Bromide) into the 2-methylimidazole solution, and heating; (6) adding the Zn (NO3) 26H2O solution into the 2-methylimidazole solution, and stirring the solution to form a milk white dispersion solution; (7) soaking the spinning membrane in the milky white dispersion solution; and (8) washing the spinning membrane with deionized water, and drying. The antibacterial preservative film prepared by the method has excellent thermal stability, mechanical property, hydrophobic surface, air permeability, water-retaining property, antibacterial activity and biological safety, and is a food packaging material with relatively strong activity.

Description

Technical Field

[0001] This invention relates to the field of antibacterial preservation film technology for fruit packaging, specifically to a method for preparing an antibacterial preservation film loaded with ZIF-8 nanoparticles. Background Technology

[0002] Post-harvest quality decline is a serious and recurring problem affecting fruit; one in five berries suffer quality loss during the post-harvest stage due to overripeness and spoilage. Therefore, it is essential to find a practical and environmentally friendly way to extend the shelf life of fruit. To ensure shelf life, storage, and service quality, food packaging protects fruit from environmental factors that can lead to spoilage, such as temperature, moisture, microorganisms, and oxygen. While plastics are commonly used as packaging materials, they are neither biodegradable nor sustainable, increasing waste and environmental problems. Therefore, non-toxic, biodegradable, antibacterial, and shelf-extending bioactive food packaging is a popular sustainable option. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing antibacterial food preservation film loaded with ZIF-8 nanoparticles.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing an antibacterial food preservation film loaded with ZIF-8 nanoparticles, comprising the following steps:

[0005] (1) Add PLA and PCL to hexafluoroisopropanol and stir at room temperature to prepare a uniform spinning solution;

[0006] (2) Add PEO to the spinning solution and stir to dissolve at room temperature;

[0007] (3) Feed the solution from step (2) and apply voltage at a certain collector distance to prepare a spun membrane by electrospinning.

[0008] (4) Synthesis of ZIF-8 nanoparticles: Zn(NO3)26H2O and 2-methylimidazole were dissolved in deionized water, respectively;

[0009] (5) Add hexadecyltrimethylammonium bromide to a deionized solution of 2-methylimidazole and heat the solution;

[0010] (6) Add Zn(NO3)26H2O solution to 2-methylimidazole solution and stir the solution during the addition process to form a milky white dispersion solution;

[0011] (7) Immerse the spun membrane from step (3) in a milky white dispersion solution;

[0012] (8) Wash the spinning film from step (7) with deionized water and then dry it to obtain the antibacterial preservation film loaded with ZIF-8 nanoparticles.

[0013] Preferably, in step (1), the PLA:PCL weight ratio is 2:1.

[0014] Preferably, in step (2), the weight ratio of PEO to spinning solution is 1:4.

[0015] Preferably, in step (3), the solution feed rate is 1.5 mL / h, and a voltage of 20 kV is applied at a collector distance of 12 cm to prepare a spun membrane by electrospinning. During this process, the ambient temperature is maintained at 25°C and the humidity at 35-40%.

[0016] Preferably, the solution is heated to 40°C in step (5).

[0017] Preferably, in step (6), the solution is stirred at 500 rpm for 15 minutes.

[0018] Preferably, in step (7), the soaking is carried out at 40°C for 1 hour.

[0019] Preferably, the washing is performed 3 times in step (8).

[0020] Preferably, in step (8), drying is performed at 60°C.

[0021] The beneficial effects of this invention compared to existing technologies are as follows: The nano-antibacterial preservation film prepared using this invention possesses excellent thermal stability, mechanical properties, hydrophobic surface, air permeability, water retention, antibacterial activity, and biosafety, making it a highly active food packaging material. In storage applications, this nanofiber film effectively maintained the post-harvest quality of blueberries when stored at 4°C and 70% humidity for 28 days. The nanofiber film exhibits good moisture retention properties, delaying water release and weight loss of blueberries during storage. Furthermore, this ZIF-8 nanoparticle-loaded antibacterial preservation film effectively promotes long-term storage applications at different temperatures, extending the shelf life of blueberries, and can be further extended to other types of fruits and vegetables; it also offers advantages such as biosafety, environmental friendliness, low cost, and large-scale production. Attached Figure Description

[0022] Figure 1 SEM images of Zif-8 nanoparticles synthesized under different conditions according to this invention;

[0023] Figure 2AL shows the morphology of electrospun PLA (A), PCL (B), PLA / PCL (C), 20% PEO / PLA / PCL (D), ZIF-8@PLA / PCL (E), and 20% ZIF-8@20% PEO / PLA / PCL (F), respectively; EDS analysis of ZIF-8@PLA / PCL (G) and 20% ZIF-8@20% PEO / PLA / PCL (J) and elemental mapping of all (H) and (K), Zn (I) and (L);

[0024] Figure 3 The average diameters of pure PLA and PCL fibers are shown;

[0025] Figure 4 The conformation and surface information of the nanofibers were analyzed using ATR and FTIR spectroscopy.

[0026] Figure 5 The mechanical properties of PLA / PCL nanofibers using PEO and ZIF-8 are shown.

[0027] Figure 6 The test information on the hydrophilicity and moisture barrier properties of the nanofiber membrane is displayed.

[0028] Figure 7 The growth curves of Escherichia coli and Staphylococcus aureus on various electrospun nanofiber membranes are shown.

[0029] Figure 8 The DPPH RSA percentages for various samples are shown.

[0030] Figure 9 The biosafety information of the nanofiber membrane is displayed. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] A method for preparing an antibacterial food preservation film loaded with ZIF-8 nanoparticles includes the following steps:

[0033] (1) Add PLA:PCL in a weight ratio of 2:1 to 10 mL of hexafluoroisopropanol, and then stir at 400 rpm for 6 hours at room temperature to prepare a uniform spinning solution;

[0034] (2) Add PEO slowly to the uniform spinning solution at a weight ratio of 1:4 between PEO and spinning solution, and then stir at room temperature for 4 hours to fully dissolve it.

[0035] (3) Using an automatic injection pump, maintain a solution feed rate of 1.5 mL / h, apply a voltage of 20 kV at a collector distance of 12 cm to prepare spun membranes by electrospinning. During this process, maintain an ambient temperature of 25℃ and an ambient humidity of 35-40%. The collector is a circular roller, which will produce a rectangular PEO / PLA / PCL electrospun nanofiber membrane of 28 cm × 17.5 cm.

[0036] (4) Synthesis of ZIF-8 nanoparticles: 1.2g Zn(NO3)26H2O and 84g 2-methylimidazole were dissolved in 600mL of deionized water.

[0037] (5) Add 4.5 mL of cetyltrimethylammonium bromide (CTAB) to a deionized solution of 2-methylimidazole and heat the solution to 40 °C;

[0038] (6) Add Zn(NO3)26H2O solution dropwise to 2-methylimidazole solution, and stir the solution continuously at 500 rpm for 15 minutes during the addition process to form a milky white dispersion solution;

[0039] (7) Then the PEO / PLA / PCL nanofiber membrane was immersed in the milky white dispersion and kept at 40°C for 1 hour;

[0040] (8) Wash the ZIF-8@PEO / PLA / PCL nanofiber membrane three times with deionized water and dry it overnight in a vacuum oven at 60°C. The preparation is now complete.

[0041] In this invention, PEO is combined with PLA and PCL to produce nanofibers, and ZIF-8 is attached to the surface of PEO / PL / PCL electrospun nanofibers for fruit packaging applications. First, the appearance and structural changes of the nanofiber membrane were observed using field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Second, the thermal stability of the nanofiber membrane was tested using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Third, the water vapor barrier of the nanofiber membrane was evaluated using two indicators: water contact angle (WCA) and water vapor permeability (WVP). Finally, mechanical, antibacterial, and biocompatibility tests were conducted to ensure the membrane's suitability for fruit packaging. Furthermore, the application of the nanofiber membrane (i.e., antibacterial preservation film) in postharvest blueberry preservation was established by measuring the effects of the nanofiber membrane on the appearance and storage quality of postharvest blueberries.

[0042] The experimental results are as follows:

[0043] 1.1 Materials and Instruments

[0044] 1.1.1 Experimental Materials and Reagents

[0045] Table 1.1 Main Reagents

[0046]

[0047] 1.1.2 Experimental Instruments and Equipment

[0048] Table 1.2 Experimental Apparatus

[0049]

[0050]

[0051] 1.1.3 Screening of Electrospun Nanofiber Membrane Substrate Formulations

[0052] Different substrates and formulations were mixed with 10 mL of hexafluoroisopropanol and stirred at 20 °C for 4 h until fully dissolved to prepare the electrospinning solution required for the experiment. 5 mL of the electrospinning solution was drawn into a syringe for spinning experiments, with a 0.9 mm inner diameter metal spinneret connected to the syringe end. The nanofibers were collected on a roller collector (rotation speed: 200 r / min) covered with nonwoven fabric (20 × 17.5 cm²). The electrospinning parameters were as follows: the distance between the metal nozzle and the nanofiber roller collector was set to 15 cm, the power supply was 18 kV, the propulsion speed of the spinning solution was 2.5 mL / h, the relative humidity (RH) of the external environment was controlled at 50 ± 5%, and the temperature was room temperature. After the spinning process, the nanofiber membrane was peeled off from the roller for characterization experiments.

[0053] Four types of nanofiber membranes with different substrate formulations were evaluated for their mechanical properties using an electronic universal testing machine (UTM6502, China) and a 50N pressure measuring element. Samples were cut to a length of 10 mm and a width of 5 mm for testing. The thickness of the sample was measured at three different locations, and the average value was calculated. During the mechanical testing, the machine crosshead traveled at a speed of 5 mm / min. Tensile strength, elastic modulus, and elongation at break were calculated from the linear region of the stress-strain curve.

[0054] The hydrophilicity of the nanofiber membrane was characterized using a contact angle meter (JC2000D1). Three different locations were randomly selected on the surface of the nanofiber membrane. Approximately 1 μL of water droplets were added to the membrane surface using a syringe. The contact angle meter was used to measure the two ends of the water droplet in contact with the nanofiber membrane and the tip of the droplet. The water contact angle of the nanofiber membrane was thus obtained. The data from each measurement were recorded, and the average of the three measurements was taken as the water contact angle of the nanofiber membrane.

[0055] 1.1.4 Analysis of Perilla Essential Oil Components

[0056] The components of PEO were detected using a trace intelligent single quadrupole (ISQ) 1300 gas chromatograph-mass spectrometer (Thermo Fisher Scientific, USA) equipped with a DB-5MS capillary column (30 m × 0.25 mm inner diameter (ID); 0.25 μm film thickness) and identified by comparison with a standard library. Quantification was performed using 2-octanol as an internal standard. The relative proportion of each PEO component was determined by the average peak area.

[0057] 1.1.5 Screening of Essential Oil Formulations for Electrospun Nanofiber Membranes

[0058] Different proportions of essential oils were added to a PLA / PCL 2:1 substrate formulation and mixed with 10 mL of hexafluoroisopropanol. The mixture was stirred at 20°C for 4 hours until fully dissolved to prepare the electrospinning solution required for the experiment. 5 mL of the electrospinning solution was drawn into a syringe for spinning experiments, with a 0.9 mm inner diameter metal spinneret connected to the syringe end. The nanofibers were collected on a roller collector (20 × 17.5 cm²) covered with nonwoven fabric (rotation speed: 200 r / min). The electrospinning parameters were as follows: the distance between the metal nozzle and the nanofiber roller collector was set to 15 cm, the power supply was 18 kV, the propulsion speed of the spinning solution was 2.5 mL / h, the relative humidity (RH) of the external environment was controlled at 50 ± 5%, and the temperature was room temperature. After the spinning process, the nanofiber membrane was peeled off from the roller for characterization experiments. SEM observation, mechanical properties, water contact angle measurement, and antibacterial performance comparison of nanofiber membranes with different proportions of essential oils were performed to determine the optimal essential oil addition amount.

[0059] 1.1.6 Characterization of Nanofiber Membrane Properties

[0060] 1.1.6.1 Microscopic morphology observation, EDS, FTIR, and XRD of electrospun nanofiber membranes

[0061] The nanofiber membrane was observed by SEM, XRD, and FTIR. The morphology of the prepared membrane was evaluated using a 3kV accelerating voltage and a cold field emission scanning electron microscope (Regulus 8100, Hitachi, Japan). Image J was used to calculate the average diameter of 100 nanofibers. Furthermore, the energy-dispersive spectroscopy (EDS) mapping of the nanofibers was detected using an electron microscope (Regulus 8100, Hitachi, Japan). FTIR spectra were recorded using a FTIR instrument with 32 scans in the wavenumber range of 4000–400 cm⁻¹, at a resolution of 4 cm⁻¹. X-ray diffraction analysis was performed using a Rigaku Ultima IV diffractometer equipped with Cu Kα radiation, operating at 40kV and 30mA, with a scanning angle (2θ) range of 10–50° and a scanning speed of 2°min⁻¹. 1.1.6.2 Thermodynamic Properties of Nanofiber Membranes

[0062] Thermal stability was measured using a DSC-1 instrument (Mettler-Toledo, Switzerland) at a scan rate of 10 °C, ranging from 20 °C to 200 °C. Heating from 50 °C to 600 °C was performed in a nitrogen atmosphere at a rate of 10 °C min⁻¹ using a TGA Q500 instrument (TA Instruments, Newcastle, USA).

[0063] 1.1.6.3 Mechanical properties of nanofiber membranes

[0064] The mechanical properties of the nanofiber membranes were studied using a mechanical testing apparatus (Instron 5944; USA) at 25°C. Tensile tests were performed using a 50 N load and an adjustment force distance of 10 mm min⁻¹. For testing, all nanofiber membranes were cut into rectangles approximately 20 mm by 7 mm.

[0065] 1.1.6.4 Hydrophilicity and moisture barrier properties of nanofiber membranes

[0066] The hydrophilicity of the nanofiber membrane was characterized using a contact angle goniometer (OCA20, Data Physics Instruments, Germany) to evaluate the contact angle (WCA). The contact angle was measured at the contact point between a drop of pure water (3.5 μL) and the nanofiber membrane. The WCA value was determined at three different locations on the same surface.

[0067] Water vapor transmission rate (WVP) was determined according to the ASTM E96 gravimetric method. Each nanofiber membrane was fixed on top of a permeation cup containing distilled water (100% RH) and placed in a desiccator containing dry silica gel (0% RH). After reaching steady-state conditions (i.e., after 30 minutes), the permeation cup was weighed every 12 hours for 5 days at 25°C and 90% RH, and the results were calculated using the following equation:

[0068]

[0069] Where ΔM / Δt is the weight of water lost per unit time (g h⁻¹), d is the thickness of the nanofiber membrane (mm), A is the area of ​​the nanofiber membrane exposed to water (m²), and Δp is the water vapor pressure difference of the environment in which the nanofiber membrane is located (3.1671 kPa at 25°C).

[0070] WVP values ​​were calculated using the gravimetric method according to ASTM E965. Each nanofiber membrane was cut into a square (85 mm × 85 mm) and fixed on top of a permeation cup containing distilled water at 100% relative humidity (RH). After permeation, the cup with the fixed nanofiber membrane was placed in a desiccator containing dry silica gel (0% RH) for approximately 30 minutes to maintain steady-state conditions. The permeation cup was then weighed every 24 hours for 7 days at 25°C and 90% RH. WVP was calculated using the following formula: where ΔM / Δt is the weight of water lost per unit time (g h⁻¹), d is the pad thickness (mm), A is the area of ​​the pad exposed to moisture (m²), and Δp is the water vapor pressure difference across the pad (3.1671 kPa at 25°C).

[0071] 1.1.6.5 Antibacterial properties of nanofiber membranes

[0072] The size of the inhibition zone of nanofiber membranes against *Alternaria alternata* and *Brachystomum buddingum* was determined using the disc diffusion method. 100 μL of diluted bacterial-fungal suspension (approximately 10⁶ CFU / mL) was transferred and uniformly dispersed on Luria-Bertani (LB) and PDA media. Nanofiber membranes with a diameter of 10 mm were sterilized by UV irradiation for 1 h and then placed in the center of the media. After incubating the bacteria and fungi at 37 °C and 28 °C for 24 h, respectively, the diameters were measured at three equidistant points from the center of the inhibition zone, and the average value was taken. The antibacterial properties of different nanofiber membranes were compared.

[0073] The antibacterial activity of ZIF-8@PEO / PLA / PCL membranes against Gram-positive Staphylococcus aureus (CMCC26003) and Gram-negative Escherichia coli (ATCC 25922) was evaluated using turbidimetric techniques. The nanofiber membranes were diced into 85 mm x 85 mm squares (approximately 87 mg) and incubated in 20 mL of liquid Luria-Bertani medium at 37 °C for 24 hours. Bacterial growth was monitored by measuring OD600 every 2 hours for 24 hours. A medium without the nanofiber membrane was used as a control. The inhibition rate was calculated as follows:

[0074]

[0075] in and These are the initial values ​​for the culture medium with and without pads, respectively. and It represents the values ​​for culture media with and without pads for culturing time t.

[0076] 1.1.6.6 Antioxidant properties of nanofiber membranes

[0077] The antioxidant capacity of the nanofiber membrane samples was confirmed by the increase in free radical scavenging activity (RSA%) in DPPH. The RSA% in DPPH was measured using the method outlined in Xu's paper. 50 mg of nanofiber membrane was chopped and vigorously shaken with 5 mL of DPPH free radical ethanol solution (final DPPH concentration: 0.1 mmol / L) to increase the contact area. The mixture was then incubated at room temperature and in the dark for different times (1, 12, 24 h) with stirring. The absorbance was measured at 517 nm using a UV-Vis spectrophotometer (UVmini-1240; Shimadzu, Japan). The RSA% was calculated using the following formula:

[0078]

[0079] Where Ac is the absorbance of the control, and As is the absorbance of the mixed solution of nanofiber membrane and free radical agent.

[0080] 1.1.6.7 Biosafety Evaluation of Nanofiber Membranes

[0081] Based on the article by Lu et al.6, this method was slightly modified. All zebrafish (Daniorerio) with a body length of 1.0±0.2 cm (Chinese Research Academy of Environmental Sciences, Beijing, China) were healthy and disease-free. The water used for acclimatization was pre-oxygenated at 23±1℃ for 12 hours. Ten zebrafish were placed in a blank culture medium containing 50 mg ZIF-8@PEO / PLA / PCL fibers with a diameter of 90 mm. Each treatment was repeated three times, with five zebrafish per treatment. Every five days, the zebrafish were photographed to determine their viability. Five zebrafish were placed in a 90 mm culture medium, with a 50 mg ZIF-8@PEO / PLA / PCL nanofiber membrane as the experimental group and no membrane as the control group. The zebrafish were photographed every five days for 15 days to determine their viability, and the treatment was repeated three times.

[0082] 1.1.7 Data Statistical Analysis

[0083] One-way ANOVA was performed using SPSS (version 19.0), and the separation of means was compared using Duncan's test. Differences were considered significant at p < 0.05.

[0084] 1.2 Results and Analysis

[0085] 1.2.1 Exploration and Adjustment of Electrospinning Conditions

[0086] The state of the electrospun nanofibers was adjusted by modifying parameters such as voltage, flow rate, receiving distance, humidity, and temperature to ensure uniformity, smoothness, and absence of beading. The optimal settings were: voltage 18-20 kV, flow rate 1.0-1.5 mL / h, receiving distance 10-15 cm, room temperature, and humidity below 40%.

[0087] 1.2.2 Screening of Electrospun Nanofiber Membrane Substrate Formulations

[0088] Table 2.1 Effect of PLA:PCL ratio on tensile properties and water contact angle of materials

[0089]

[0090] The study investigated seven substrates: PLA:PCL ratios of 3:1, 2:1, 1:1, 1:2, and 1:3, as well as pure PLA and pure PCL. The appropriate substrate ratio was determined based on mechanical properties and water contact angle. Ultimately, a PLA:PCL ratio of 2:1 was selected.

[0091] 1.2.3 Screening of Essential Oil Formulations for Electrospun Nanofiber Membranes

[0092] 1.2.3.1 Analysis and Identification of Perilla Essential Oil

[0093] Compared with the standard library, 26 compounds with an SI (identification similarity) value higher than 800 were identified. The most prevalent components in the PEO were perillaldehyde (45.88%), D-limonene (13.95%), and 2-octanol (7.62%). Perillaldehyde is a major component and functional agent of the essential oil, consistent with previous findings. Variations in this component are influenced by various factors such as plant growing area, temperature, humidity, and season. Due to the presence of volatile components such as perillaldehyde and limonene, perilla essential oil possesses antibacterial and antioxidant properties, making it suitable for food storage and addition to food packaging applications.

[0094] 1.2.3.2 Antibacterial test of essential oil films with different proportions

[0095] Table 2.2 Antibacterial rate (%) of nanofilms with different essential oils

[0096]

[0097] For the same bacterial species, different lowercase letters in the same column indicate that the antibacterial rate of nanofilms with different essential oil concentrations has statistical differences (P<0.05).

[0098] For the same bacterial species, different capital letters in the same row indicate that the antibacterial rate of nanofilms with different concentrations of the same essential oil has statistical differences (P<0.05).

[0099] 1.2.3.3 Study on the generation conditions of Zif-8 nanoparticles

[0100] Figure 1 In the middle: A. Zif-8 nanoparticles were synthesized hydrothermally at 20℃ for 5 hours. The particles are square, uniform, and have a side length of approximately 200 nm.

[0101] B. Zif-8 nanoparticles were synthesized hydrothermally at 20℃ for 10 hours. They were regular cubes, approximately 1 nm in size.

[0102] Zif-8 nanoparticles were synthesized hydrothermally at 40℃ for 5 hours. The particles were square, uniform, and neat, with a side length of approximately 200 nm.

[0103] D. Zif-8 nanoparticles were synthesized hydrothermally at 40℃ for 10 hours. Most were cubes, with a small number being elongated and irregular cubes.

[0104] Zif-8 nanoparticles were synthesized hydrothermally at 60℃ for 5 hours. The particles are irregular in shape, oval, with some rod-shaped and fewer cubic, ranging from 80-300 nm.

[0105] Zif-8 nanoparticles were synthesized hydrothermally at 60℃ for 10 hours. Most were cube-shaped, with a small number being elongated and irregular cube-shaped.

[0106] 1.2.4 Preparation and Characterization of Nanofiber Membranes

[0107] 1.2.4.1 Microstructure of Nanofiber Membranes

[0108] The microstructure of nanofibers affects the mechanical properties, thermal properties, and water vapor barrier properties of nanofilms. Figure 2 AF shows the morphology of electrospun PLA (A), PCL (B), PLA / PCL (C), 20% PEO / PLA / PCL (D), ZIF-8@PLA / PCL (E), and 20% ZIF-8@20% PEO / PLA / PCL (F), respectively. EDS analysis of ZIF-8@PLA / PCL (G) and 20% ZIF-8@20% PEO / PLA / PCL (J), as well as elemental mappings of all elements (H) and (K), and Zn (I) and (L), are shown in the figures. Figure 2 In GL, the surface of the PEO-loaded nanofibers was uniform, with no obvious beaded strands, indicating that the incorporation of PEO and ZIF-8 into the substrate did not affect the fiber morphology, similar to other researchers.

[0109] Figure 3The average diameters of pure PLA and PCL fibers were 689.9 nm and 200.3 nm, respectively. The average diameter of PLA / PCL fiber was 310.3 nm. 20% PEO / PLA / PCL fiber had a diameter of 410.1 nm, PLA / PCL fiber increased to 651.3 nm using ZIF-8, and ZIF-8@20% PEO / PLA / PCL fiber had a diameter of 759.1 nm. The continuous increase in nanofiber diameter can be attributed to the addition of PEO and ZIF-8 nanoparticles. Adding PEO to the spinning solution increases its viscosity. The nanofiber diameter increases due to ZIF-8 adhering to the nanofiber surface.

[0110] 1.2.4.2 FTIR Detection of Electrospun Nanofiber Membranes

[0111] The conformational and surface functional transitions of the nanofibers were analyzed using ATR and FTIR spectroscopy. Figure 4 In A, the FTIR spectrum of PEO showed characteristic peaks (815.21, 842.55, 911.28, and 775.2 cm⁻¹), with perillaldehyde being a rich component of PEO8. Furthermore, the peaks at 2923.87 and 2961.84 cm⁻¹ are attributed to CH stretching, a typical characteristic of essential oils. In the FTIR spectrum of the ZIF-8 aqueous dispersion, characteristic peaks appeared at 3329 cm⁻¹ (OH stretching), 1635.73 cm⁻¹ (CO stretching), and 1146.09 cm⁻¹ (CH stretching). The OH stretching vibration in PEO (3, 335 cm⁻¹) shifted to 2943.65 cm⁻¹, indicating that ZIF-8 adheres to the PLA / PCL fiber surface, forming intermolecular hydrogen bonds, which is beneficial for constructing a more stable, complex coating system.

[0112] Figure 4A shows a similar spectrum, indicating that the molecular and chemical structure did not change significantly after the addition of PEO and the attachment of ZIF-8 nanoparticles. The bands at approximately 2961.84 cm⁻¹ and 2923.87 cm⁻¹ in the PEO essential oil are assigned to the OH and CH stretching bonds in the hydroxyl and CH₃ groups. With PEO loading, the band intensity at 2961.84 cm⁻¹ gradually decreases to 2943.89 cm⁻¹, indicating that PEO has been well integrated into the nanofiber substrate. After the addition of PEO, the vibrational CO group and amide II (NH bending and CH stretching vibrations) PLA at 1754.08 cm⁻¹ increase, indicating enhanced intermolecular hydrogen bonding interactions. The peaks observed in the PEO / PLA / PCL nanofiber film at approximately 1365.33 and 1454.75 cm⁻¹ are related to the CH stretching of the aromatic ring. The peaks at 1182.68 and 1088.55 cm⁻¹, respectively, correspond to the glycoether groups of PLA / PCL. The addition of PEO increased the absorption rate intensities of the 869.94 and 733.65 cm⁻¹ peaks. The results indicate that PEO is incorporated into the PLA / PCL nanofiber film via hydrogen bonding.

[0113] 1.2.4.3 XRD Detection of Electrospun Nanofiber Membranes

[0114] exist Figure 4 In Figure B, PLA exhibits a diffraction peak at 15.88° superimposed on a broad amorphous peak background, while PCL shows two peaks at 21.18° and 23.48°, indicating that PCL is highly crystalline, while PLA is amorphous or microcrystalline. After blending, PLA / PCL nanofibers retain the PCL diffraction peaks (21.18° and 23.56°) superimposed on a relatively broad PLA peak background, with the peak at 16.26°. When PEO is blended with PLA / PCL, the peak intensity of the nanofiber film decreases slightly, mainly due to the decreased crystallinity of the nanofiber film formed by PEO and PLA / PCL. In contrast, the addition of PCL has a heterogeneous nucleation effect on PLA crystallization, providing nucleation sites for the arrangement of PLA chain segments and affecting the crystallinity of PLA, thus causing a shift in the diffraction peaks. The effect of ZIF-8 on the crystallinity and crystal structure of electrospun nanofibers was investigated. After ZIF-8 was attached to the surface, the characteristic peaks increased significantly, revealing its original crystal structure. The main characteristic diffraction peaks were between 10° and 40° (10.32°, 12.66°, 14.62°, 16.38°, 17.92°, 21.38°, 22.02°, 23.68°), indicating that ZIF-8 was attached to the surface of the composite fiber. According to the study by Chen et al.11, the crystallinity of the nanofibers decreased due to the interaction between the chain segments that induced hydrogen bonding.

[0115] 1.2.4.4 Thermal Performance Testing of Electrospun Nanofiber Membranes

[0116] Figure 4 Table C shows the DSC curves of PLA, PCL, and PLA / PCL nanofibers with different amounts of PEO and ZIF-8 nanoparticles. The glass transition temperature (Tm) of PLA fibers is 62.23 °C. The Tm values ​​of PCL and PLA fibers are 61.93 °C and 171.93 °C, respectively. In the DSC curve of PLA / PCL, two different endothermic peaks exist near the Tm of the PCL and PLA phases, revealing the thermodynamic immiscibility of the two polymer phases. Table 2.5 shows the DSC parameters of different nanofiber films. The Tm of nanofibers with added PEO and ZIF-8 is lower than that of PLA, PCL, and PLA / PCL nanofibers, indicating that the Tm increases with the addition of PEO and ZIF-8.

[0117] exist Figure 4 In D, the initial weight loss between 50 and 200°C is mainly due to the evaporation of residual water physically adsorbed in the nanofibers or PEO-loaded fibers. The addition of PEO improves the thermal stability of the electrospun nanofibers, as evidenced by these data. Furthermore, the attachment of ZIF-8 reduces the thermal stability of the nanofibers. Materials with low thermal stability are sensitive to structural deformation and thermal degradation, but are beneficial for thermal degradation. The widespread use of nanofibers in food packaging materials can be attributed to their high thermal stability. Although ZIF-8 reduces the thermal stability of nanofiber materials, it is still acceptable for use as a food packaging material.

[0118] 1.2.4.5 Mechanical property testing of electrospun nanofiber membranes

[0119] Figure 5The mechanical properties of PLA / PCL nanofibers using PEO and ZIF-8 are shown. The tensile strengths of pure PLA and PCL are 5.23 MPa and 8.19 MPa, respectively, and their elastic moduli are 5.84 and 42.93 MPa, respectively. After mixing, the tensile strength and elastic modulus of the PLA / PCL film are 7.69 and 9.38 MPa, respectively. The addition of PEO significantly decreased both tensile strength and elastic modulus (P < 0.05). Furthermore, the elastic modulus significantly increased with the addition of ZIF-8. The final elastic modulus of the nanofiber film is significantly higher than that of PLA / PCL. A high intermolecular hydrogen bond density is generated due to the interaction between PLA and PCL. Adding PCL to PLA has a beneficial effect on improving the elasticity of the PLA matrix by making the molecular chains more rigid. These modifications improve the tensile strength and elastic modulus of PLA / PCL nanofibers. Mechanical properties vary depending on the added PEO and ZIF-8. The polymer network may be disrupted by the introduction of PEO. Furthermore, the elongation at break of PLA / PCL fiber membranes was higher than that of PCL, but much lower than that of PLA fiber membranes. The elongation at break of PLA / PCL increased from 78.47% to 82.55% with the addition of 20% PEO. However, the mechanical strength of ZIF-8@20% PEO / PL / PCL nanofiber membranes was higher than that of ZIF-8@PLA / PCL membranes. This is because the presence of pure ZIF-8 on the fiber surface disrupts its surface properties, while the presence of PEO preserves them.

[0120] 1.2.4.6 Testing of the hydrophilicity and moisture barrier properties of electrospun nanofiber membranes

[0121] The hydrophobicity of material surfaces in humid environments is crucial in practice. WCA, such as PLA / PCL electrospun nanofibers with PEO and ZIF-8, is an example. Figure 6As shown in Figure A, hydrophobic surfaces exist on pure PLA and PCL electrospun nanofibers with WCA values ​​of 127.34° and 123.04°, respectively. After blending, the WCA of the PLA / PCL fiber membrane remained relatively slightly increased to 124.59°. According to the results of ART spectroscopy, the reduction of hydrophilic groups (CO bending and OH groups) may contribute to the increase in WCA in the PLA / PCL membrane. Furthermore, when PEO was added to the PLA / PCL membrane, the WCA decreased from 124.59° to 121.77°. The WCA value of the nanofiber membrane linked to ZIF-8 decreased significantly to 47.82°, indicating that the membrane transitioned from hydrophobic to hydrophilic. After the addition of PEO and subsequent attachment of ZIF-8 nanoparticles, the WCA value did not change significantly; it remained hydrophobic (118.41°), which may be attributed to the bonds linked to the nanoparticles and the roughness of the membrane surface. The polymer is considered hydrophobic when the contact angle is 90° or greater. The hydrophobic surface effectively repels water, thus preventing the diffusion of water and even corrosive solutions in the porous nanofiber composite.

[0122] WVP (Wetness Verification) involves the transfer and exchange of moisture between food and its surrounding environment, which is a fundamental property of food packaging materials. Figure 6 B indicates that the water vapor barrier properties (WVP) of the PLA / PCL nanofiber membrane is 0.1901 g mm / m² h kPa, which is lower than that of both PLA and PCL nanofiber membranes. The value decreases upon the addition of PEO, similar to that of a single PEO@PLA / PCL nanofiber membrane. However, when ZIF-8 nanoparticles are bonded to the PEO / PLA / PCL nanofiber membrane, the water vapor barrier performance is enhanced, likely due to increased hydrogen bonding, which reduces hydrogen bonding interactions between the components and water, leading to a decrease in WVP. The hydrophobic surface reduces the packaging material's ability to regulate water vapor transmission. Water vapor permeability directly affects the interaction between food and its surrounding environment, reducing chemical, physical, and microbiological changes in food and protecting its safety for human consumption. Generally, food packaging should prevent or reduce water transfer to the outer surface. Therefore, WVP needs to be as low as possible. The WVP of ZIF-8@20% PEO / PLA / PCL indicates good moisture-proof performance and suggests its potential for use in food packaging.

[0123] 1.2.4.7 Antibacterial properties of electrospun nanofiber membranes

[0124] Growth curves of Escherichia coli and Staphylococcus aureus on various electrospun nanofiber membranes are as follows: Figure 7As shown in the figure, compared with pure PLA, pure PCL, and PLA / PCL membranes, nanofiber membranes containing PEO and linked ZIF-8 exhibited antimicrobial activity against the tested microorganisms. Bacteria were initially inhibited on all nanofiber membranes for the first 2 hours, after which they rapidly multiplied (2–6 hours). Bacteria exposed to the PEO nanofiber membrane grew more slowly than those exposed to PLA / PCL and the control group. Notably, *Escherichia coli* and *Staphylococcus aureus* showed almost no development on the nanofiber membrane linked to ZIF-8 nanoparticles, exhibiting remarkable antimicrobial properties. After 24 hours, the inhibition rates of ZIF-8@PLA / PCL and ZIF-8@PEO / PLA / PCL nanofiber membranes against *Escherichia coli* and *Staphylococcus aureus* remained at 100%, indicating that the ZIF-8@PLA / PCL and ZIF-8@PEO / PLA / PCL membranes possess extremely strong antimicrobial activity. The PEO / PLA / PCL membrane disappeared after 24 hours on *E. coli*, but still showed inhibitory activity against *Staphylococcus aureus*, with an inhibition rate of 26.09%. These results indicate that the nanofiber membrane in this study has a stronger effect against Gram-positive bacteria. This is consistent with the research of Li et al. ZIF-8@PEO / PLA / PCL exhibited antibacterial activity to prevent food spoilage caused by microorganisms. Therefore, it can be used as an antibacterial food packaging material.

[0125] 1.2.4.8 Antioxidant properties of electrospun nanofiber membranes

[0126] exist Figure 8 The data show the DPPH RSA% of various samples. The antioxidant activity of PLA, PCL, and PLA / PCL nanofiber mats incubated for 24 hours was approximately 20%, but this changed little over time. However, the antioxidant activity increased significantly upon the addition of PEO or Zif-8. After 24 hours of incubation, the antioxidant activity rose to 72.45% with only 20% PEO. However, the antioxidant activity of nanofibers fully bonded to ZIF-8 increased to 58.34%. Furthermore, nanofibers with 20% PEO and Zif-8 attachment increased the DPPH RSA% to 79.05%. Many terpenoids found in PEO, including perillaldehyde, limonene, and pinene, have been shown to possess antioxidant properties. Notably, the antioxidant activity of nanofibers bonded only to ZI-8 was 58% lower than that of nanofiber membranes containing essential oils, indicating that the primary antioxidant activity of the nanofiber membranes is perillaldehyde essential oil.

[0127] 1.2.4.9 Biosafety of Electrospun Nanofiber Membranes

[0128] ZIF-8@PEO / PLA / PCL membranes must be organically safe for packaging active foods. This study used zebrafish to evaluate the biocompatibility of ZIF-8@PEO / PLA / PCL nanofiber membranes. Zebrafish were implanted into a culture medium containing 50 mg of ZIF-8@PEO / PLA / PCL nanofiber membrane for 15 days. The results are as follows: Figure 9 As shown in AC, zebrafish co-cultured with ZIF-8@PEO / PLA / PCL maintained high viability after 15 days of culture, demonstrating the biosafety and non-toxicity of the nanofiber membrane. Figure 9 D). Based on the results, the ZIF-8@PEO / PLA / PCL nanofiber membrane is biocompatible and can be used for food packaging.

Claims

1. A method for preparing an antibacterial food preservation film loaded with ZIF-8 nanoparticles, characterized in that, Includes the following steps: (1) Add PLA and PCL to hexafluoroisopropanol and stir at room temperature to prepare a uniform spinning solution; (2) Add PEO to the spinning solution and stir to dissolve at room temperature; (3) Feed the solution from step (2) and apply voltage at a certain collector distance to prepare a spun membrane by electrospinning. (4) Synthesis of ZI F-8 nanoparticles: Zn(NO3)26H2O and 2-methylimidazole were dissolved in deionized water, respectively; (5) Add hexadecyltrimethylammonium bromide to a deionized solution of 2-methylimidazole and heat the solution; (6) Add Zn(NO3)26H2O solution to 2-methylimidazole solution and stir the solution during the addition process to form a milky white dispersion solution; (7) Immerse the spun membrane from step (3) in a milky white dispersion solution; (8) Wash the spinning film from step (7) with deionized water and then dry it to obtain the antibacterial preservation film loaded with ZIF-8 nanoparticles.

2. The method for preparing ZIF-8 nanoparticle-loaded antibacterial preservation film according to claim 1, characterized in that: In step (1), the PLA:PCL weight ratio is 2:

1.

3. The method for preparing ZIF-8 nanoparticle-loaded antibacterial preservation film according to claim 1, characterized in that: In step (2), the weight ratio of PEO to spinning solution is 1:

4.

4. The method for preparing ZIF-8 nanoparticle-loaded antibacterial preservation film according to claim 1, characterized in that: In step (3), the solution feed rate is 1-1.5 mL / h, and a voltage of 18-20 kV is applied at a collector distance of 10-15 cm to prepare a spun membrane by electrospinning. During this process, the ambient temperature is maintained at 25℃ and the humidity at 35-40%.

5. The method for preparing ZIF-8 nanoparticle-loaded antibacterial preservation film according to claim 1, characterized in that: In step (5), the solution is heated to 40°C.

6. The method for preparing ZIF-8 nanoparticle-loaded antibacterial preservation film according to claim 1, characterized in that: In step (6), the solution is stirred at 500 rpm for 15 minutes.

7. The method for preparing ZIF-8 nanoparticle-loaded antibacterial food preservation film according to claim 1, characterized in that: In step (7), soak at 40°C for 1 hour.

8. The method for preparing ZIF-8 nanoparticle-loaded antibacterial preservation film according to claim 1, characterized in that: Wash three times in step (8).

9. The method for preparing the ZIF-8 nanoparticle-loaded antibacterial preservation film according to claim 8, characterized in that: In step (8), the product is dried at 60°C.

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