Preparation method of degradable antibacterial packaging film based on ionic liquid functionalization

Abstract

The invention discloses a preparation method of a degradable antibacterial packaging film based on ionic liquid functionalization, and belongs to the technical field of polymer composite materials. The method comprises the following steps: mixing a natural polymer matrix and degradable polyester according to a certain mass ratio, adding choline or amino acid ionic liquid as a functional modifier, carrying out surface modification through ultrasonic assistance, grafting the ionic liquid to the surface of the natural polymer through chemical bonding, and carrying out melt blending on the modified natural polymer at 160-190 DEG C to obtain the biodegradable polyester composite material. And a composite film with the thickness of 20-100 microns is prepared through a film casting process. The 24-hour bacteriostasis rate of the prepared film on escherichia coli and staphylococcus aureus is larger than or equal to 99.5%, the tensile strength reaches 55-75 MPa, the elongation at break is 8.0-15.0%, the mass loss rate in a simulated soil environment within 60 days is larger than or equal to 90.0%, and degradation products are free of ecological toxicity. The method is simple in process, low in cost and suitable for efficient antibacterial packaging production in the fields of food, medicine and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite materials, and in particular to a method for preparing a degradable antibacterial packaging film based on ionic liquid functionalization. Background Art

[0002] The current mainstream packaging materials are still mainly based on traditional petroleum-based plastics such as polyethylene (PE) and polypropylene (PP). Because they are non-degradable and lack antibacterial properties, they are easily carriers of microbial growth, threatening the safety of food and medical supplies and causing serious environmental pollution problems. Although degradable polyesters (such as polylactic acid PLA and polybutylene succinate PBS) have made breakthroughs in environmental protection, they are brittle, poor in toughness, and insufficient in antibacterial function, making it difficult to meet actual needs. Existing technology attempts to improve degradability and antibacterial properties by adding natural polymers (such as chitosan and cellulose), but the polarity difference between natural polymers and polyesters leads to poor interfacial compatibility, and direct blending easily causes phase separation, resulting in a significant decrease in the mechanical strength of the material (tensile strength < 40 MPa). For example, the antibacterial packaging material disclosed in Chinese patent CN118307685A is prepared by sodium periodate oxidation of dialdehyde nanocellulose and grafted with guanidine salt. Although it shows good antibacterial properties, it needs a large amount of deionized water washing to remove residual oxidants after the reaction, resulting in increased wastewater treatment costs, significantly increasing environmental pressure, and limiting industrial production efficiency.

[0003] In recent years, ionic liquids have been introduced into the field of polymer materials due to their designable chemical structure and excellent antibacterial activity. However, in the existing technology, ionic liquids are mostly dispersed in the matrix through physical blending, which is easy to migrate due to non-bonding, resulting in attenuation of antibacterial performance (the inhibition rate drops by >20.0% after recycling) and environmental pollution risks. Some studies have attempted to graft ionic liquids onto polymer chains, but traditional grafting processes (such as high-temperature free radical initiation) are easy to destroy the active groups of natural polymers, and the process is complex and energy-intensive. In addition, it is difficult to balance the degradation efficiency and mechanical properties of existing composite materials. In order to increase the degradation rate, it is often necessary to increase the proportion of natural polymers, but this will lead to significant deterioration of the mechanical properties of the material.

[0004] To address these issues, the present invention proposes a method for preparing a biodegradable antimicrobial packaging material based on ionic liquid functionalization. Its innovation lies in the synergistic enhancement of antimicrobial and biodegradable properties achieved through the precise design of choline or amino acid ionic liquid functional groups. Choline cations (such as hydroxyethyltrimethylammonium) electrostatically bind to bacterial membrane phospholipids through the positive charge of the quaternary ammonium group, destroying their integrity. Amino acid anions (such as glutamic acid dicarboxylic acid group) achieve multi-target bactericidal effects by penetrating the membrane structure, chelating metal ions, and inducing reactive oxygen species (ROS). At the same time, ionic liquids and natural polymers (chitosan / cellulose) form stable grafts through ultrasound-assisted chemical bonding (hydrogen bonding, esterification / amidation), avoiding migration and ensuring synchronous degradation. Combined with low-temperature ultrasonic surface modification at 60-80°C (200-500W, 30-90min) to directionally activate the functional groups of the natural polymer, and ion-dipole entanglement regulation between the polyester matrix and the modified phase during melt blending at 160-190°C, the film is endowed with high mechanical strength (55-75MPa) and controllable degradability (weight loss ≥90.0% in 60 days). The degradation products (choline, amino acids, short-chain carboxylic acids) are metabolized by microorganisms into non-toxic small molecules, achieving high antibacterial efficiency (24h inhibition ≥99.5%). Through molecular design, interface modification and process innovation, this invention breaks through the technical bottleneck of traditional materials that are difficult to balance antibacterial properties, mechanical properties and environmental protection, and provides a new direction for high-performance degradable packaging materials. Summary of the Invention

[0005] The present invention aims to provide a method for preparing a degradable antimicrobial packaging film based on ionic liquid functionalization. Through the dual functionalization of ionic liquids and the synergistic effect of ultrasonic melting, this method overcomes the shortcomings of traditional materials, such as low antimicrobial efficiency, poor mechanical properties, uncontrolled degradation, and solvent contamination, achieving the goals of high antimicrobial efficiency, mechanical enhancement, safety, and environmental protection.

[0006] A method for preparing a degradable antibacterial packaging film based on ionic liquid functionalization, characterized in that a natural polymer matrix (chitosan, cellulose or its derivatives) and a degradable polyester (polylactic acid PLA, polybutylene succinate PBS) are mixed in a mass ratio of 3:7-5:5, an ionic liquid modifier is added accounting for 0.5-3.0wt% of the total mass of the composite material, and ultrasonic-assisted surface modification (power 200-500W, treatment time 30-90min) is performed at 60-80°C. The ionic liquid is directionally grafted onto the surface of the natural polymer through chemical bonding to form a stable modified layer. The modified material is melt-blended with the polyester matrix at 160-190°C (shear rate 100-500s -1), a composite film with a thickness of 20-100 μm is prepared by a cast film process, and bubbles are eliminated by vacuum exhaust (pressure ≤-0.08 MPa) to ensure film uniformity and interfacial bonding strength. The prepared film has a 24-hour antibacterial rate of ≥99.5% against Escherichia coli and Staphylococcus aureus, a tensile strength of 55-75 MPa, an elongation at break of 8.0-15.0%, a mass loss rate of ≥90.0% within 60 days in a simulated soil environment, and the degradation products are non-ecotoxic. The ionic liquid is one of the choline ionic liquids choline acetate ([Choline][OAc]) and choline oleate ([Choline][Ole]), and one of the amino acid ionic liquids [1-ethyl-3-methylimidazole][glutamate] ([EMIM][Glu]) and [tetrabutylphosphine][lysine salt] ([TBP][Lys]).

[0007] The present invention solves this technical problem through the following technical solutions:

[0008] The specific technical solution is described by taking the chitosan to polylactic acid (PLA) mass ratio of 4:6 as an example:

[0009] Chitosan and polylactic acid (PLA) were mixed in a mass ratio of 4:6, and 2.0 wt% of choline acetate ([Choline][OAc]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at 400 W power for 60 minutes in a 70°C oil bath to allow the ionic liquid to be grafted onto the chitosan surface through chemical bonding. The modified material and PLA matrix were then put into a twin-screw extruder at 180°C and a shear rate of 300 s -1 The resulting composite film was melt-blended under various conditions and cast using a film-casting machine to a thickness of 50 μm. The film was ultrasonically cleaned in deionized water for 10 minutes, dried in a vacuum oven at 60°C for 12 hours, and then tested for performance. The resulting material demonstrated 24-hour antibacterial rates of 99.9% and 99.7% against Escherichia coli and Staphylococcus aureus, respectively, a tensile strength of 75.0 MPa, and an elongation at break of 12.5%. In a simulated soil environment (25°C, 60.0% humidity) over 55 days, the weight loss reached 93.5%.

[0010] Compared with the traditional method, the characteristics of the present invention are:

[0011] 1. Choline ionic liquids (such as [Choline][OAc]) are synthesized by quaternary ammonium cations (N + ) destroys the membrane potential, while the carboxylate anion (CH3COO - ) chelates Fe in the active center of bacterial enzymes 3+ / Mg 2+, blocking energy metabolism and forming a "charge-enzyme activity" dual-target inhibition; amino acid ionic liquids (such as [EMIM][Glu]) introduce glutamic acid dicarboxylic acid groups, reduce the Zeta potential of the membrane surface through pH regulation, enhance the cation permeation efficiency, and induce reactive oxygen species (ROS) to oxidatively damage DNA, thereby achieving efficient sterilization.

[0012] 2. Ultrasound-assisted hydrogen bonding is achieved by forming hydrogen bonds between the quaternary ammonium groups of the ionic liquid and the -NH2 of chitosan, while esterification occurs between the carboxylic acid groups and the C6-OH groups of cellulose, covalently anchoring the antimicrobial agent to the surface of the natural polymer. During degradation, the natural polymer chains are preferentially enzymatically degraded, triggering the breakage of the ionic liquid-polymer bond and the simultaneous release of choline and amino acids, thus avoiding secondary contamination caused by the asynchronous degradation of the antimicrobial residue and the matrix in traditional materials.

[0013] 3. The hydrophilic group of ionic liquid (-COO - , -OH) form micro-region hydrophilic channels under soil moisture, accelerate water penetration and hydrolysis reaction, increase the polyester ester bond breakage rate by 2-3 times, and increase the 60-day weight loss rate from 70% of traditional materials to ≥90%. The degradation products (lactic acid, choline) are quickly assimilated by microorganisms through the Krebs cycle without toxic accumulation.

[0014] 4. The entanglement between the long-chain alkyl groups of the ionic liquid (such as oleate C18 chains) and the polyester chain segments forms an ion-dipole cross-linked network during melt blending (160-190°C), which increases the tensile strength of the film to 55-75MPa and the elongation at break to 8.0-15.0%, breaking through the "trade-off effect" of strength and toughness of traditional materials. Specific implementation methods

[0015] The method of the present invention is further described below with reference to the embodiments, which are not intended to limit the present invention.

[0016] Example 1

[0017] Cellulose nanocrystals (CNC) and polybutylene succinate (PBS) were mixed in a mass ratio of 3:7, and 2.0 wt% of choline oleate ([Choline][Ole]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at 200 W power for 90 minutes in a 60°C oil bath to allow the ionic liquid to be grafted onto the surface of the cellulose nanocrystals through chemical bonding. The modified material and PBS matrix were then put into a twin-screw extruder at 160°C and a shear rate of 100 s -1The resulting composite film was melt-blended under various conditions and cast using a film-casting machine to form a 100 μm thick composite film. The film was ultrasonically cleaned in deionized water for 10 minutes, dried under vacuum at 60°C for 12 hours, and then tested for performance. The resulting material demonstrated 24-hour antibacterial rates of 99.5% and 99.6% against Escherichia coli and Staphylococcus aureus, respectively, with a tensile strength of 58.3 MPa and an elongation at break of 8.0%. The ionic liquid mobility was determined to be 0.08 ppm by HPLC, and the weight loss rate reached 91.5% over 55 days in a simulated soil environment (25°C, 60.0% humidity).

[0018] Comparative Example 1

[0019] This comparative example provides a preparation method of a degradable antibacterial packaging film based on ionic liquid functionalization. The difference between the comparative example and the embodiment is that the comparative example uses non-choline or amino acid ionic liquid 1-propyl-3-methylimidazolium bromide ([C3MIM][Br]) as a modifier, and the specific dosage is as follows: chitosan and polylactic acid (PLA) are mixed in a mass ratio of 4:6, and 2.0wt% of 1-propyl-3-methylimidazolium bromide ([C3MIM][Br]) is added as an ionic liquid modifier. The mixture is placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at a power of 400W for 60 minutes in a 70°C oil bath to allow the ionic liquid to be grafted to the surface of the chitosan through chemical bonding. The modified material and the PLA matrix are then put into a twin-screw extruder and extruded at 160°C and a shear rate of 100s -1 The composite films were melt-blended under the following conditions and cast using a tape-casting machine to a thickness of 50 μm. The films were ultrasonically cleaned in deionized water for 10 minutes and vacuum-dried at 60°C for 12 hours before performance testing. Due to the inability of the short-chain ionic liquid to effectively graft, the antibacterial rate was significantly reduced (85.2% for Escherichia coli and 83.7% for Staphylococcus aureus), the tensile strength dropped to 48.6 MPa, and the soil weight loss rate over 60 days was only 68.4%.

[0020] Comparative Example 2

[0021] This comparative example provides a preparation method of a degradable antibacterial packaging material film based on ionic liquid functionalization. The difference between the comparative example and the embodiment is that the comparative example uses a non-functionalized ionic liquid as a modifier. The specific method is as follows: chitosan and polylactic acid (PLA) are mixed in a mass ratio of 4:6, and 2.0wt% of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) is added. The mixture is placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at a power of 400W for 60 minutes in an 80°C oil bath. The modified material and the PLA matrix are put into a twin-screw extruder and extruded at 160°C and a shear rate of 300s. -1The PLA was melt-blended under the following conditions and cast into a 50 μm thick film. The film was ultrasonically cleaned in deionized water for 10 minutes and dried in a vacuum oven at 60°C for 12 hours before testing its performance. Because [BMIM][PF6] lacks antimicrobial active groups (such as carboxylates or amino groups) and high-temperature ultrasound damages the chitosan structure, the inhibition rate was only 87.4%. Furthermore, incomplete PLA plasticization and poor compatibility between the ionic liquid and the matrix weakened the interfacial bonding, resulting in a tensile strength of only 34.1 MPa, an elongation at break of 4.5%, and a soil weight loss rate of only 65.3% over 60 days.

[0022] Example 2

[0023] Chitosan and polylactic acid (PLA) were mixed in a mass ratio of 5:5, and 0.5 wt% of choline oleate ([Choline][Ole]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at 500 W power for 30 minutes in an 80°C oil bath to allow the ionic liquid to be grafted onto the chitosan surface through chemical bonding. The modified material and PLA matrix were then put into a twin-screw extruder at 190°C and a shear rate of 500 s -1 The resulting composite film was melt-blended under various conditions and cast using a film-casting machine to a thickness of 50 μm. The film was ultrasonically cleaned in deionized water for 10 minutes, dried in a vacuum oven at 60°C for 12 hours, and then tested for performance. The resulting material demonstrated 24-hour antibacterial rates of 99.5% and 99.5% against Escherichia coli and Staphylococcus aureus, respectively, a tensile strength of 72.1 MPa, and an elongation at break of 15.0%. In a simulated soil environment (25°C, 60.0% humidity), the weight loss reached 90.8% over 60 days.

[0024] Example 3

[0025] Chitosan and polylactic acid (PLA) were mixed in a mass ratio of 4:6, and 2.0 wt% of choline acetate ([Choline][OAc]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at 400 W power for 60 minutes in a 70°C oil bath to allow the ionic liquid to be grafted onto the chitosan surface through chemical bonding. The modified material and PLA matrix were then put into a twin-screw extruder at 180°C and a shear rate of 300 s -1 The resulting composite film was melt-blended under various conditions and cast using a film-casting machine to a thickness of 50 μm. The film was ultrasonically cleaned in deionized water for 10 minutes, dried in a vacuum oven at 60°C for 12 hours, and then tested for performance. The resulting material demonstrated 24-hour antibacterial rates of 99.9% and 99.7% against Escherichia coli and Staphylococcus aureus, respectively, a tensile strength of 75.0 MPa, and an elongation at break of 12.5%. In a simulated soil environment (25°C, 60.0% humidity) over 55 days, the weight loss reached 93.5%.

[0026] Example 4

[0027] Carboxymethyl cellulose (CMC) and polylactic acid (PLA) were mixed in a mass ratio of 4:6, and 3.0 wt% of [1-ethyl-3-methylimidazole][glutamate] ([EMIM][Glu]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at 200 W power for 30 minutes in a 70°C oil bath to allow the ionic liquid to be grafted onto the surface of the carboxymethyl cellulose through chemical bonding. The modified material and the PLA matrix were then put into a twin-screw extruder at 160°C and a shear rate of 100s. -1 The composite film was melt-blended under various conditions and cast using a film-casting machine to a thickness of 100 μm. The film was ultrasonically cleaned in deionized water for 10 minutes and vacuum-dried at 60°C for 12 hours before performance testing. The resulting material demonstrated 24-hour antibacterial rates of 99.5% and 99.7% against Escherichia coli and Staphylococcus aureus, respectively, with a tensile strength of 55.0 MPa and an elongation at break of 8.0%. In a simulated soil environment (25°C, 60.0% humidity) over 50 days, the weight loss reached 90.0%.

[0028] Example 5

[0029] Chitosan and polylactic acid (PLA) were mixed in a mass ratio of 3:7, and 0.5 wt% of choline acetate ([Choline][OAc]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at 400 W power for 60 minutes in a 60°C oil bath to allow the ionic liquid to be grafted onto the chitosan surface through chemical bonding. The modified material and the PLA matrix were then put into a twin-screw extruder at 180°C and a shear rate of 500 s -1 The resulting composite film was melt-blended under various conditions and cast using a film-casting machine to a thickness of 50 μm. The film was ultrasonically cleaned in deionized water for 10 minutes, dried in a vacuum oven at 60°C for 12 hours, and then tested for performance. The resulting material demonstrated 24-hour antibacterial rates of 99.5% and 99.6% against Escherichia coli and Staphylococcus aureus, respectively, a tensile strength of 64.7 MPa, and an elongation at break of 11.2%. In a simulated soil environment (25°C, 60.0% humidity) over 55 days, the weight loss reached 91.0%.

[0030] Example 6

[0031] Chitosan and polybutylene succinate (PBS) were mixed in a mass ratio of 5:5, and 2.0 wt% of [tetrabutylphosphine] [lysine salt] ([TBP] [Lys]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at 400 W power for 60 minutes in a 70°C oil bath to allow the ionic liquid to be grafted onto the chitosan surface through chemical bonding. The modified material and PBS matrix were then put into a twin-screw extruder at 190°C and a shear rate of 300 s -1 The resulting composite film was melt-blended under various conditions and cast using a film-casting machine to a thickness of 70 μm. The film was ultrasonically cleaned in deionized water for 10 minutes, vacuum-dried at 60°C for 12 hours, and then tested for performance. The resulting material demonstrated 24-hour antibacterial rates of 99.5% and 99.5% against Escherichia coli and Staphylococcus aureus, respectively, a tensile strength of 61.2 MPa, and an elongation at break of 10.5%. In a simulated soil environment (25°C, 60.0% humidity), the weight loss reached 91.0% over 60 days.

[0032] Example 7

[0033] Cellulose and polylactic acid (PLA) were mixed in a mass ratio of 4:6, and 3.0 wt% of choline acetate ([Choline][OAc]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer and ultrasonically treated at 400 W power for 60 minutes in a 70°C oil bath to allow the ionic liquid to be grafted onto the cellulose surface through chemical bonding. The modified material and the PLA matrix were then put into a twin-screw extruder at 180°C and a shear rate of 300 s -1 The resulting composite film was melt-blended under various conditions and cast using a film-casting machine to a thickness of 70 μm. The film was ultrasonically cleaned in deionized water for 10 minutes, dried in a vacuum oven at 60°C for 12 hours, and then tested for performance. The resulting material demonstrated 24-hour antibacterial rates of 99.7% and 99.5% against Escherichia coli and Staphylococcus aureus, respectively, a tensile strength of 67.5 MPa, and an elongation at break of 12.8%. In a simulated soil environment (25°C, 60.0% humidity) over 58 days, the weight loss reached 92.1%.

[0034] Example 8

[0035] Chitosan and polylactic acid (PLA) were mixed in a mass ratio of 4:6, and 2.0 wt% of [1-ethyl-3-methylimidazole][glutamate] ([EMIM][Glu]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at 400 W power for 60 minutes in an 80°C oil bath to allow the ionic liquid to be grafted onto the chitosan surface through chemical bonding. The modified material and the PLA matrix were then put into a twin-screw extruder at 160°C and a shear rate of 300 s -1The resulting composite film was melt-blended under various conditions and cast using a film-casting machine to a thickness of 50 μm. The film was ultrasonically cleaned in deionized water for 10 minutes, dried in a vacuum oven at 60°C for 12 hours, and then tested for performance. The resulting material demonstrated 24-hour antibacterial rates of 99.7% and 99.6% against Escherichia coli and Staphylococcus aureus, respectively, a tensile strength of 69.4 MPa, and an elongation at break of 13.1%. In a simulated soil environment (25°C, 60.0% humidity) over 52 days, the weight loss reached 92.8%.

[0036] Example 9

[0037] Lignin and polybutylene succinate (PBS) were mixed in a mass ratio of 3:7, and 2.0 wt% of choline oleate ([Choline][Ole]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at 400 W power for 90 minutes in a 60°C oil bath to allow the ionic liquid to be grafted onto the lignin surface through chemical bonding. The modified material and PBS matrix were then put into a twin-screw extruder and extruded at 180°C and a shear rate of 300 s -1 The resulting composite film was melt-blended under various conditions and cast using a film-casting machine to a thickness of 100 μm. The film was ultrasonically cleaned in deionized water for 10 minutes and vacuum-dried at 60°C for 12 hours before performance testing. The resulting material demonstrated 24-hour antibacterial rates of 99.6% and 99.7% against Escherichia coli and Staphylococcus aureus, respectively, with a tensile strength of 56.8 MPa and an elongation at break of 9.1%. In a simulated soil environment (25°C, 60.0% humidity), the weight loss reached 90.5% over 60 days.

[0038] Example 10

[0039] Chitosan and polylactic acid (PLA) were mixed in a mass ratio of 4:6, and 3.0 wt% of [tetrabutylphosphine] [lysine salt] ([TBP] [Lys]) was added as an ionic liquid modifier. The mixture was placed in a three-necked flask equipped with a magnetic stirrer and a thermometer, and ultrasonically treated at 500 W power for 30 minutes in a 70°C oil bath to allow the ionic liquid to be grafted onto the chitosan surface through chemical bonding. The modified material and the PLA matrix were then put into a twin-screw extruder at 190°C and a shear rate of 500 s -1 The resulting composite film was melt-blended under various conditions and cast using a film-casting machine to a thickness of 50 μm. The film was ultrasonically cleaned in deionized water for 10 minutes, dried under vacuum at 60°C for 12 hours, and then tested for performance. The resulting material demonstrated 24-hour antibacterial rates of 99.7% and 99.5% against Escherichia coli and Staphylococcus aureus, respectively, a tensile strength of 74.3 MPa, and an elongation at break of 15.0%. In a simulated soil environment (25°C, 60.0% humidity) over 58 days, the weight loss reached 92.5%.

[0040] Antibacterial performance test

[0041] Escherichia coli and Staphylococcus aureus were used as test bacteria, representing Gram-negative and Gram-positive bacteria, respectively. Nutrient broth (NB) and nutrient agar (NA) were used as culture media. The prepared films were cut into (50±1) mm × (50±1) mm square specimens (thickness 20-100 μm) and sterilized by double-sided irradiation with UV light (254 nm) for 30 minutes. A sterile polypropylene film of the same size served as a blank control. After activation on NA plates, single colonies were selected and cultured in NB medium at 37°C with shaking until the logarithmic growth phase (OD600 ≈ 0.6). The cells were harvested by centrifugation and resuspended in PBS buffer (pH 7.4) to a concentration of (1.0-3.0) × 105 CFU / mL. 100 μL of bacterial suspension was evenly dripped onto the film surface, covered with a sterile polyethylene film, and left in contact at 37°C for 24 hours. The cells were then eluted with ultrasonic vibration in a neutralizing solution containing 0.5% Tween-80 in PBS. After gradient dilution, the suspension was spread on NA plates and incubated at 37°C for 24 hours to count the viable bacterial counts (CFU). The results showed that the prepared film had a 24-hour antibacterial rate of ≥99.5% against Escherichia coli and Staphylococcus aureus. The entire experiment was performed in a biological safety cabinet, and the neutralizer's effect on the ionic liquid's activity was pre-verified, and the film's surface integrity was examined by SEM to ensure data reliability.

[0042] Tensile strength and elongation at break test

[0043] The film was cut into standard dumbbell-shaped specimens (gauge section width 15±0.5mm, thickness 20-100μm), and balanced in an environment of 23±2℃ and 50±5% humidity for 24 hours. Using a calibrated universal material testing machine, set the clamping spacing to 50mm, stretch it at a speed of 50mm / min until it breaks, and record the maximum load value. Track and record the gauge section length at the time of fracture in real time, while ensuring that the specimen fracture is within the gauge section, and eliminate samples with fractures in the clamping area or abnormal data. The accuracy of the load sensor of the testing machine must meet the requirements of ISO7500-1 Grade 1. The results show that the tensile strength of the prepared film reaches 55-75MPa, and the elongation at break is 8.0-15.0%.

[0044] Degradation performance test

[0045] A simulated soil environment was prepared by mixing humus, sand, and organic matter in a mass ratio of 3:2:1. The humidity was adjusted to 40-60% (mass moisture content) and a pH of 6.5-7.5. The soil was then inoculated with an active soil microbial community. The film was cut into square specimens (20±1) mm × (20±1) mm (thickness 20-100 μm) and dried in a 50°C vacuum oven to constant weight. The initial mass (W0) was recorded. The specimens were spread 5 cm below the soil surface and placed in a constant temperature and humidity chamber (25±2°C, 70% humidity). Deionized water was added every 10 days to maintain a constant humidity. The specimens were removed periodically, rinsed with deionized water, and then vacuum-dried at 50°C to constant weight. The remaining mass (W1) was measured. A blank soil control was also maintained to verify the effectiveness of the environment. Microbial activity in the soil was ensured (as determined by ATP bioluminescence). Scanning electron microscopy (SEM) was used to observe changes in the pore structure of the specimen surface to eliminate interference from non-biodegradable factors. The results showed that the mass loss rate was ≥90.0% within 60 days in a simulated soil environment.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions claimed to be protected by the present invention.

Claims

1. A method for preparing a degradable antibacterial packaging film based on ionic liquid functionalization, characterized in that: The following steps are involved: (1) mixing a natural polymer matrix and a biodegradable polyester in a mass ratio of 3:7-5:5, and adding an ionic liquid modifier in an amount of 0.5-3.0 wt% of the total mass of the composite material; (2) Ultrasonic-assisted surface modification of the mixed material is performed at 60-80°C, so that the ionic liquid is grafted onto the surface of the natural polymer through chemical bonding; (3) The modified natural polymer is melt-blended with the biodegradable polyester and a composite film is prepared by a cast film forming process.

2. The preparation method according to claim 1, characterized in that The natural polymer matrix is ​​one of chitosan, cellulose or derivatives thereof, and the degradable polyester is one of polylactic acid (PLA) and polybutylene succinate (PBS).

3. The preparation method according to claim 1, characterized in that The choline ionic liquid is one of choline acetate ([Choline][OAc]) and choline oleate ([Choline][Ole]), and the amino acid ionic liquid is one of [1-ethyl-3-methylimidazole][glutamate] ([EMIM][Glu]) and [tetrabutylphosphine][lysine salt] ([TBP][Lys]).

4. The preparation method according to claim 1, characterized in that In step (2), the ultrasonic power is 200-500W, and the treatment time is 30-90min.

5. The preparation method according to claim 1, characterized in that The film-making equipment in step (3) is a twin-screw extruder, the melt blending temperature is 160-190° C., the shear rate is 100-500 s-1, and the thickness of the cast film is 20-100 μm.

6. The degradable antibacterial packaging film prepared according to any one of claims 1 to 5, characterized in that: The 24-hour antibacterial rate against Escherichia coli and Staphylococcus aureus is ≥99.5%, the tensile strength is 55-75 MPa, and the elongation at break is 8.0-15.0%.

7. The degradable antibacterial packaging film according to claim 6, characterized in that: The weight loss rate in a simulated soil environment within 60 days is ≥90.0%.

8. The ionic liquid according to claim 3, characterized in that The cation of the choline ionic liquid is hydroxyethyltrimethylammonium ([N + (CH3)3CH2CH2OH]), the anion is carboxylate (RCOO - , R=C1-C18 alkyl / alkenyl) or amino acid root (such as glycine root, lysine root).

9. The ionic liquid according to claim 3, characterized in that The anion of the amino acid ionic liquid is α-aminocarboxylate (such as [Glu] - , [Lys] - ), the cation is 1-alkyl-3-methylimidazole (such as [EMIM] + ) or tetraalkylphosphine (such as [TBP] + ).