A plastic packaging bag with antibacterial functionality and a method for preparing the same

Abstract

The application belongs to the technical field of antibacterial plastic packaging preparation, and discloses a plastic packaging bag with antibacterial functionality and a preparation method thereof; three-layer co-extrusion structures of an inner contact layer, a function enhancement layer and an outer protective layer are sequentially arranged; the inner contact layer is food-grade modified linear low-density polyethylene, the function enhancement layer is a blow molding grade linear low-density polyethylene base material, antibacterial components of nano-silver loaded mesoporous silica and microcapsule embedded epsilon-polylysine are added, a double-sided maleic anhydride grafted polyolefin compatibility system is distributed between layers, and the outer protective layer is modified homopolymer polypropylene, which is prepared through a blow molding process. The application effectively improves the thermal processing stability of antibacterial peptides, enhances the interlayer bonding strength of the film material, prolongs the antibacterial effective period, and the silver migration amount is far lower than the food contact material limit value, and the comprehensive performance is excellent, and the application is suitable for the use requirements of various food packaging.

Description

Technical Field

[0001] This invention belongs to the field of antibacterial plastic packaging preparation technology, and in particular to a plastic packaging bag with antibacterial function and its preparation method. Background Technology

[0002] Antibacterial plastic packaging bags are widely used in fresh food, catering takeaway, and pharmaceutical consumable packaging. As downstream industries continue to increase their requirements for the anti-corrosion and preservation performance, food contact safety, and long-term stability of packaging materials, plastic packaging bags that combine long-lasting antibacterial function, excellent mechanical properties, and compliant migration characteristics have become the core research and development direction in the current packaging field.

[0003] Currently, most mainstream antibacterial plastic packaging bags are prepared using a process that directly adds antibacterial components. Commonly used antibacterial agents include nano-silver, quaternary ammonium compounds, and plant-derived antibacterial peptides. Among these, plant-derived antibacterial peptides have seen increasing application research in the food contact packaging field in recent years due to their advantages such as no biotoxicity, no risk of bacterial resistance, and broad antibacterial spectrum. However, the heat tolerance temperature of plant-derived antibacterial peptides generally does not exceed 80℃, while the temperatures in conventional plastic film processing steps such as melt blending, co-extrusion blow molding, and hot sealing are generally in the range of 130-210℃. Antibacterial peptides are prone to irreversible denaturation and inactivation during processing, resulting in extremely low retention of antibacterial activity after processing, failing to achieve the expected antibacterial effect. Some packaging bags that use nano-silver as a single antibacterial agent have problems such as short antibacterial effectiveness and excessive migration of silver ions, which do not meet the safety standards for food contact materials.

[0004] Another mainstream technology is the three-layer co-extruded plastic packaging bag, which typically features an inner contact layer, a functional layer, and an outer protective layer. The different components of each layer are designed to meet varying needs for contact safety, functionality, and external protection. However, existing three-layer packaging bags generally lack a targeted interfacial compatibility system. The polypropylene outer protective layer and the polyethylene functional layer have significant polarity differences, resulting in high interfacial tension and a high susceptibility to interlayer delamination and breakage during use, leading to a short actual lifespan. While existing research has explored the combined application of nano-silver and plant-derived antimicrobial peptides, it has not addressed the synergistic mechanism of their sustained-release properties, limiting the improvement in antimicrobial performance. Furthermore, it lacks thermal protection measures for the antimicrobial components during processing, making industrial-scale production highly impractical.

[0005] Current technologies cannot simultaneously meet the multiple requirements of antibacterial activity retention rate, interlayer bonding strength, and long-term antibacterial stability. The inherent contradiction between processing parameters and the thermal stability of antibacterial components, as well as the poor compatibility between different layer materials, have not been effectively resolved. There is an urgent need to develop antibacterial plastic packaging bag technologies that are compatible with existing mature processing technologies and whose comprehensive performance fully meets the needs of downstream industries. Summary of the Invention

[0006] To address the shortcomings of existing antibacterial plastic packaging bags, such as easy inactivation of antibacterial peptides during processing, easy peeling between layers, short antibacterial shelf life, and insufficient safety, this invention provides a plastic packaging bag with antibacterial function and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A plastic packaging bag with antibacterial function includes an inner contact layer, a functional reinforcement layer, and an outer protective layer stacked sequentially from the inside out. The inner contact layer is a modified polyethylene substrate that directly contacts the contents of the packaging bag and possesses migration characteristics that meet the safety standards for food contact materials. The functional reinforcement layer is a polyolefin co-extruded film loaded with a composite antibacterial agent, with the composite antibacterial agent evenly distributed internally, enabling the inactivation of bacteria and fungi that come into contact with and penetrate the inner contact layer. The side of the functional reinforcement layer closest to the outer protective layer contains 5%-10% by weight of maleic anhydride-grafted polypropylene as an interface compatibilizer. The outer protective layer is an abrasion-resistant modified polypropylene coating, located on the outermost side of the packaging bag, and can resist damage to the bag caused by external friction and scratches. The interface compatibilizer between the outer protective layer and the functional enhancement layer forms a chemical bond, with an interlayer peel strength of not less than 3.5 N / cm. The composite antibacterial agent is a compound of nano-silver-supported mesoporous silica and microcapsule-encapsulated plant-derived antimicrobial peptides. The wall material of the microcapsules is cross-linked polymethyl methacrylate with a temperature resistance of 180-230℃, and the core material is plant-derived antimicrobial peptides. This protects the antimicrobial peptides from thermal inactivation during processing. The activity retention rate of the plant-derived antimicrobial peptides after processing is not less than 90%. The composite antibacterial agent has an inactivation rate of not less than 99% against common foodborne pathogens. The packaging bag is sealed with a heat-pressed sealing edge, which is heat-melted and pressed to achieve a sealed preservation effect. The width of the heat-pressed sealing edge is 2-8 mm.

[0008] Preferably, the modified polyethylene of the inner contact layer is linear low-density polyethylene grafted with maleic anhydride, with a grafting rate of 0.2%-1.5%. The linear low-density polyethylene grafted with maleic anhydride can improve the surface wettability of the inner contact layer, enhance the interlayer bonding force with the functional reinforcement layer, and avoid the problem of interlayer peeling and falling off. At the same time, it can adsorb trace amounts of exudated antibacterial components, further reducing the risk of antibacterial components migrating into the built-in contents. The thickness of the inner contact layer is 15-30μm, which controls the overall bag thickness while ensuring mechanical strength and avoiding material waste.

[0009] Preferably, the polyolefin co-extruded film of the functional reinforcement layer is a blend of ethylene-octene copolymer and high-density polyethylene in a blending mass ratio of 1:2 to 1:4. The blend of ethylene-octene copolymer and high-density polyethylene can improve the tensile strength and puncture resistance of the functional reinforcement layer, which is suitable for the mechanical requirements of packaging bags containing various materials. The microcapsules of plant-derived antimicrobial peptides dispersed in the functional reinforcement layer have a particle size of 1-5 μm and no obvious agglomeration. The thickness of the functional reinforcement layer is 20-40 μm, which can ensure sufficient loading of composite antimicrobial agent without excessively increasing the thickness of the bag.

[0010] Preferably, the mass ratio of nano-silver-supported mesoporous silica to microcapsule-encapsulated plant-derived antimicrobial peptides in the composite antibacterial agent is 3:1-6:1. The pore size of the nano-silver-supported mesoporous silica is 2-5 nm, and the porosity of the microcapsule wall material is 15%-25%. The two can achieve gradient sustained release of antibacterial components, and the synergistic antibacterial effect is more than 40% higher than that of a single antibacterial component. The antibacterial effective period is not less than 12 months. The nano-silver-supported mesoporous silica has sustained-release characteristics, which can achieve long-lasting antibacterial effect. The microcapsule-encapsulated plant-derived antimicrobial peptides have the advantage of being non-biotoxic. The combination of the two can take into account both antibacterial durability and safety of use. The mass ratio of the composite antibacterial agent added to the functional enhancement layer is 1.2%-3.5%, which can ensure the antibacterial effect while avoiding negative impacts on the mechanical properties of the membrane material.

[0011] Preferably, the wear-resistant modified polypropylene coating of the outer protective layer is a homopolymer polypropylene coating with 0.5%-1.2% silicone wear-resistant agent added. The homopolymer polypropylene coating contains 3%-8% maleic anhydride-grafted polypropylene by mass, which chemically bonds with the interface compatibilizer of the functional reinforcement layer, further reducing interfacial tension and improving interlayer bonding. The silicone wear-resistant agent can be uniformly dispersed in the homopolymer polypropylene coating, reducing the surface friction coefficient of the outer protective layer and improving wear resistance. The thickness of the outer protective layer is 10-25μm, ensuring wear resistance while avoiding affecting the flexibility of the bag.

[0012] Preferably, the packaging bag has an easy-tear notch on its edge. The easy-tear notch is formed by stamping, and the edge is neat and burr-free. Users can quickly tear the bag along the easy-tear notch without the need for additional cutting tools, which improves the convenience of use. The depth of the easy-tear notch is 3-5mm, and it is located on one or both sides of the heat-sealed edge. The heat-sealed edge strength at the easy-tear notch is not lower than the sealing edge strength at other parts of the bag, which can prevent premature leakage at the notch.

[0013] Preferably, the steps include: S1. Prepare the inner contact layer mixture, the functional reinforcement layer mixture, and the outer protective layer mixture according to the component ratio. Before preparing each layer mixture, all raw materials need to be dried to remove moisture and avoid bubbles and pores in the subsequent film formation process. Before preparing the functional reinforcement layer mixture, microcapsule-encapsulated plant-derived antimicrobial peptides are prepared by in-situ polymerization. The temperature during the mixing process is controlled at 60-70℃ to avoid premature rupture of the microcapsule wall material. S2. The three-layer mixture is fed into a three-layer co-extrusion blown film machine for co-extrusion blown film to obtain a three-layer composite film substrate. During the co-extrusion blown film process, the extrusion rate of each layer needs to be controlled synchronously to ensure that the thickness of each layer is uniform. At the same time, the screw shear rate is controlled at 100-300 / s to avoid high shear force from damaging the wall structure of the microcapsules. S3. The three-layer composite film substrate is hot-sealed, cut, and bagged to obtain the plastic packaging bag with antibacterial function. During the cutting process, the speed and pressure of the cutting blade need to be controlled to avoid burrs and warping defects on the edge of the bag. High-temperature contact exceeding 230°C should be avoided throughout the processing to ensure the integrity of the microcapsule structure.

[0014] Preferably, in S1, when preparing the functional reinforcement layer mixture, nano-silver-supported mesoporous silica, microcapsule-encapsulated plant-derived antimicrobial peptides, and polyethylene wax are first mixed to prepare an antimicrobial masterbatch. The preparation process of the antimicrobial masterbatch involves adding each component to a twin-screw extruder according to the ratio for melt blending and extrusion granulation. The twin-screw extrusion temperature is controlled at 170-190℃, which is lower than the tolerance temperature of the microcapsule wall material. The resulting antimicrobial masterbatch has a uniform particle size, which can improve the dispersibility of the composite antimicrobial agent in the functional reinforcement layer matrix and avoid the problem of antimicrobial agent agglomeration. Then, the antimicrobial masterbatch is mixed with polyolefin co-extruded film matrix raw material and maleic anhydride-grafted polypropylene in a high-speed mixer for 10-20 minutes. The mixing speed is set to 800-1000 rpm to ensure that each component is mixed evenly.

[0015] Preferably, the temperatures of each section of the co-extrusion blown film in S2 are 140-160℃ for the feeding section, 170-190℃ for the plasticizing section, and 195-210℃ for the die section. The temperatures of each section of the co-extrusion blown film are set in a gradient and are all lower than the tolerance temperature of the microcapsule wall material. This ensures that the raw materials of each layer are fully plasticized, avoids defects in the film material caused by incomplete plasticization, and does not damage the microcapsule structure. The blow-up ratio is 2.5-4.0, which ensures that the transverse and longitudinal mechanical properties of the film material are uniform and there is no problem of excessive performance deviation.

[0016] Preferably, the temperature of hot-pressing the edge in S3 is 130-150℃, the hot-pressing pressure is 0.2-0.5MPa, and the hot-pressing time is 2-5s. The parameter settings of the hot-pressing edge sealing can ensure that the three layers of film are fully heat-fused together, and the mechanical strength of the edge sealing is not lower than the mechanical strength of the bag itself, so as to avoid the problems of edge sealing cracking and leakage. During the hot-pressing process, the temperature of the hot-pressing plate needs to be uniformly controlled to avoid uneven edge sealing quality caused by local excessively high or low temperatures. The hot-pressing temperature is far lower than the tolerance temperature of the microcapsules, so it will not cause the antimicrobial peptides to be inactivated.

[0017] The present invention has the following beneficial effects: This invention employs a high-temperature resistant cross-linked polymer as the wall material to microencapsulate plant-derived antimicrobial peptides, enabling the antimicrobial peptides to withstand the high temperatures and high shear forces throughout the entire plastic processing process. The antimicrobial activity retention rate remains at a high level during processing, effectively solving the problems of poor thermal stability of plant-derived antimicrobial peptides, conflict with existing high-temperature processing parameters, and significant attenuation or even complete loss of antimicrobial function after processing in existing technologies.

[0018] This invention reduces the interfacial tension between the polypropylene outer protective layer and the polyolefin functional reinforcing layer, which have significant polarity differences, by setting a double-sided maleic anhydride-grafted polyolefin compatibility system at the interface between the functional reinforcement layer and the outer protective layer. This achieves chemical bonding at the interface, improves interlayer bonding strength, and effectively solves the defects of existing three-layer co-extruded packaging films, such as insufficient interlayer compatibility, easy delamination and peeling during use, structural damage, and short actual service life.

[0019] This invention employs a gradient compounding technique of nano-silver-supported mesoporous silica and microcapsule-encapsulated plant-derived antimicrobial peptides to achieve a sustained-release synergistic effect between the two antimicrobial components. The antimicrobial spectrum covers the vast majority of common foodborne pathogens, extending the antimicrobial efficacy period. At the same time, it avoids the risk of excessive migration of active components present with single nano-silver antimicrobial agents, meets the safety standards for food contact materials, and effectively solves the defects of existing compound antimicrobial systems, such as the lack of a clear synergistic mechanism, limited antimicrobial effect, and insufficient safety.

[0020] The antibacterial plastic packaging bag and its preparation method of the present invention are compatible with the existing mature three-layer co-extrusion blown film processing technology. No additional special processing equipment or modification of existing production lines is required. It can achieve large-scale mass production and is widely used in various packaging scenarios such as fresh food, pre-cooked meals, catering takeaway, and medical consumables. It is suitable for various temperature and humidity environments and has strong applicability for industry promotion. Attached Figure Description

[0021] Figure 1 This is a flowchart of a method for preparing an antibacterial plastic packaging bag according to the present invention; Figure 2This is a composite diagram showing the effect of the crosslinking degree of the microcapsule wall material proposed in this invention on its antibacterial properties. Figure 3 This is a graph showing the trend of long-term antibacterial performance of different samples proposed in this invention; Figure 4 Radar charts showing the comprehensive performance of different samples proposed in this invention. Detailed Implementation

[0022] The following will refer to the appendices in the embodiments of the present invention. Figure 1-4 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 The antibacterial plastic packaging bag in this embodiment has a three-layer structure consisting of an inner contact layer, a functional enhancement layer, and an outer protective layer. The inner contact layer is made of food-grade modified linear low-density polyethylene with a thickness of 20 μm, and contains 1 wt% erucamide opening agent and 0.5 wt% zinc stearate stabilizer, which meets the safety requirements for food contact materials. The functional reinforcement layer is a 30μm thick blow-molded linear low-density polyethylene substrate with 2wt% added compound antibacterial components. The compound antibacterial components are nano-silver-supported mesoporous silica and microcapsule-encapsulated ε-polylysine in a 1:2 mass ratio. The microcapsules are prepared using chitosan with 60% crosslinking degree as the wall material, with a core-to-wall mass ratio of 1:3, and are prepared by sodium tripolyphosphate crosslinking method to encapsulate ε-polylysine inside. At the interface between the functional reinforcement layer and the outer protective layer, there is a 1.5wt% double-sided maleic anhydride-grafted polyolefin compatibility system. The compatibility system is a 1.2% grafted maleic anhydride-grafted polypropylene and a 1.5% grafted maleic anhydride-grafted polyethylene in a 1:1 mass ratio. The outer protective layer is a 25μm thick modified homopolymer polypropylene substrate with 2wt% added light stabilizer UV-327 and 1wt% antioxidant 1010.

[0024] The preparation steps are as follows: S1 raw material pretreatment: The raw materials of the inner contact layer, functional enhancement layer and outer protective layer are respectively put into a high-speed mixer and mixed at 40°C for 5 minutes to obtain the premix of each layer. S2 three-layer co-extrusion feeds each layer of premixed material into three extruders. The extrusion temperature range for the inner contact layer is 140℃ to 150℃, the extrusion temperature range for the functional reinforcement layer is 145℃ to 155℃, and the extrusion temperature range for the outer protective layer is 150℃ to 145℃. The melt flows through the three-layer co-extrusion die. S3 blow molding, controlling the blow ratio at 2.5, the traction speed at 15m / min, and the cooling air temperature at 20℃, to obtain the molded film material; S4 slitting and bag making involves slitting the film material and then heat-sealing it at 120℃ for 0.5 seconds to obtain the finished packaging bag.

[0025] Example 2 In this embodiment, the antibacterial plastic packaging bag is constructed with three layers: an inner contact layer, a functional enhancement layer, and an outer protective layer. The inner contact layer is made of 20 μm thick food-grade modified linear low-density polyethylene with 1 wt% erucamide opening agent and 0.5 wt% zinc stearate stabilizer. The functional enhancement layer is made of 30 μm thick blow-molded linear low-density polyethylene substrate with 3.5 wt% compound antibacterial component. The compound antibacterial component is a mixture of nano-silver-supported mesoporous silica and microcapsule-encapsulated ε-polylysine in a mass ratio of 1:2. The microcapsules are made of chitosan with a cross-linking degree of 72% as the wall material, with a core-to-wall mass ratio of 1:3, and are prepared using the sodium tripolyphosphate cross-linking method to encapsulate ε-polylysine inside. At the interface between the functional enhancement layer and the outer protective layer, there is a 2.2 wt% double-sided maleic anhydride-grafted polyolefin compatibility system. The compatibility system is a 1:1 mass ratio of maleic anhydride-grafted polypropylene with a grafting rate of 1.2% and maleic anhydride-grafted polyethylene with a grafting rate of 1.5%. The outer protective layer is a 25 μm thick modified homopolymer polypropylene substrate with 2 wt% light stabilizer UV-327 and 1 wt% antioxidant 1010 added.

[0026] The preparation steps are as follows: S1 raw material pretreatment: The raw materials of the inner contact layer, functional enhancement layer and outer protective layer are respectively put into a high-speed mixer and mixed at 40°C for 5 minutes to obtain the premix of each layer. S2 three-layer co-extrusion feeds each layer of premixed material into three extruders. The extrusion temperature range for the inner contact layer is 150°C to 165°C, the extrusion temperature range for the functional reinforcement layer is 155°C to 175°C, and the extrusion temperature range for the outer protective layer is 165°C to 170°C. The melt flows through the three-layer co-extrusion die. S3 blow molding: control the blow ratio at 2.5, the traction speed at 15m / min, and the cooling air temperature at 20℃ to obtain the molded film material; S4 slitting and bag making: cut the film material and heat seal it at 120℃ for 0.5s to obtain the finished packaging bag.

[0027] Example 3 The antibacterial plastic packaging bag in this embodiment has a three-layer structure consisting of an inner contact layer, a functional reinforcement layer, and an outer protective layer. The inner contact layer is made of 20 μm thick food-grade modified linear low-density polyethylene, with 1 wt% erucamide opening agent and 0.5 wt% zinc stearate stabilizer added. The functional reinforcement layer is made of 30 μm thick blow-molding grade linear low-density polyethylene substrate, with 5 wt% compound antibacterial component added. The compound antibacterial component is a mixture of nano-silver-supported mesoporous silica and microcapsule-encapsulated ε-polylysine in a mass ratio of 1:2; wherein the microcapsules have a cross-linking degree of 85%. Chitosan is used as the wall material, with a core-to-wall mass ratio of 1:3. It is prepared by sodium tripolyphosphate crosslinking method, encapsulating ε-polylysine inside. At the interface between the functional reinforcement layer and the outer protective layer, there is a 3wt% double-sided maleic anhydride-grafted polyolefin compatibility system. The compatibility system is a 1:1 mass ratio of maleic anhydride-grafted polypropylene with a grafting rate of 1.2% and maleic anhydride-grafted polyethylene with a grafting rate of 1.5%. The outer protective layer is a 25μm thick modified homopolymer polypropylene substrate with 2wt% light stabilizer UV-327 and 1wt% antioxidant 1010 added.

[0028] The preparation steps are as follows: S1 raw material pretreatment: The raw materials of the inner contact layer, functional enhancement layer and outer protective layer are respectively put into a high-speed mixer and mixed at 40°C for 5 minutes to obtain the premix of each layer. S2 three-layer co-extrusion feeds each layer of premixed material into three extruders. The extrusion temperature range for the inner contact layer is 160°C to 180°C, the extrusion temperature range for the functional reinforcement layer is 170°C to 190°C, and the extrusion temperature range for the outer protective layer is 180°C to 200°C. The melt flows through the three-layer co-extrusion die. S3 blow molding, controlling the blow ratio at 2.5, the traction speed at 15m / min, and the cooling air temperature at 20℃, to obtain the molded film material; S4 slitting and bag making involves slitting the film material and then heat-sealing it at 120℃ for 0.5 seconds to obtain the finished packaging bag.

[0029] Comparative Example 1 This comparative example uses the existing process of directly adding unencapsulated antimicrobial peptides. Except for the fact that the antimicrobial peptides were not microencapsulated, the other components and parameters are completely consistent with those in Example 2. This comparative example is used to verify the effect of microencapsulation structure on improving the thermal stability of antimicrobial peptides, thereby addressing the defect of antimicrobial peptide processing inactivation.

[0030] Comparative Example 2 This comparative example uses an existing three-layer co-extrusion process without interfacial compatibilizers. Except for the absence of the double-sided maleic anhydride-grafted polyolefin compatibilizer system, the other components and parameters are completely consistent with those in Example 2. This comparative example is used to verify the effect of the interfacial compatibilizer system on improving the interlayer bonding strength, thereby addressing the defect of easy peeling between layers.

[0031] Performance testing methods Antimicrobial peptide activity retention rate test: This test was used to determine the proportion of antimicrobial activity retained by the microcapsules containing ε-polylysine after processing. The Oxford cup inhibition zone method combined with extraction recovery rate correction was used. The specific steps are as follows: Initial activity assay: Unprocessed microcapsules containing ε-polylysine standard were prepared into gradient concentration solutions using phosphate-buffered saline (PBS) at pH 7.2-7.4. Using Escherichia coli ATCC25922 as an indicator bacterium, the diameter of the inhibition zone was determined using the Oxford cup method, and a standard curve of inhibition zone diameter versus antimicrobial peptide concentration was plotted. Sample extraction after processing: Take the functional enhancement layer sample of the packaging bag to be tested, cut it into 5mm×5mm fragments, accurately weigh 1.0g, add 50mL PBS buffer, and extract by shaking at 37℃ and 150rpm for 24h. Filter the extract through a 0.22μm filter membrane for later use. Activity determination and calculation: Take the above filtrate and determine the diameter of the inhibition zone using the same Oxford cup method. Calculate the effective concentration of antimicrobial peptides in the extract according to the standard curve. Combine this with the extraction recovery rate (previously determined by the spiked recovery method, the extraction recovery rate of this system is 85%~92%) to obtain the actual antimicrobial peptide activity content in the membrane material. Retention rate calculation: Antimicrobial peptide activity retention rate = (Actual active content of antimicrobial peptide in the processed membrane material / Theoretical added active content) × 100%.

[0032] The interlayer peel strength test was performed according to the T-type peel method in GB / T8808-1988 "Peel Test Method for Flexible Composite Plastic Materials", and the test was conducted on the interface between the functional reinforcement layer and the outer protective layer of this application. Sample preparation: Cut a rectangular sample with a width of 15mm and a length of 150mm from the packaging bag to be tested. Beforehand, manually peel about 50mm of the functional reinforcement layer from the outer protective layer at one end of the sample to ensure that the peeling interface is clear and undamaged. Test conditions: A universal testing machine was used. The two peeled layers were clamped in upper and lower fixtures with a fixture spacing of 50 mm. The tensile speed was 300 mm / min. The ambient temperature was 23±2℃ and the relative humidity was 50±5%. Data processing: Record the average peeling force during the peeling process, in N / 15mm. Five samples were tested in each group, and the arithmetic mean was taken. The inhibition rate test for Escherichia coli and Staphylococcus aureus was performed according to the film application method in GB / T31402-2015: Sample preparation: Cut 50mm×50mm square samples, with 3 parallel samples per group. At the same time, prepare sterile polyethylene films of the same size as negative controls. Preparation of bacterial culture: Escherichia coli ATCC25922 and Staphylococcus aureus ATCC6538 were inoculated into nutrient agar medium and cultured at 37°C for 24 h. The cultures were then washed with PBS buffer and diluted to a concentration of 1×10⁻⁶. 5 ~5×10 5 CFU / mL bacterial suspension; Inoculation and culture: Take 0.1 mL of bacterial suspension and drop it evenly onto the sample surface, cover it with a sterile polyethylene film to ensure that the bacterial suspension is in uniform contact with the sample surface, and culture for 24 h at 37℃ and relative humidity ≥90%. Viable cell count and calculation: After incubation, rinse the sample and covering membrane with 10 mL PBS buffer, collect the eluent, and determine the viable cell count using the plate count method. Inhibition rate = (Negative control viable cell count - Sample viable cell count) / Negative control viable cell count × 100%.

[0033] The silver migration test shall be conducted in accordance with the migration test method in GB4806.7-2016 "Plastic Materials and Products for Food Contact". Sample preparation: Take the inner contact layer surface of the packaging bag to be tested, and cut the corresponding area of ​​the sample according to the ratio of contact area to food simulant volume of 6dm² / L. Migration test: A 4% (v / v) acetic acid aqueous solution was used as a food simulant and soaked at 60°C for 10 days. During the soaking process, the samples were ensured to be completely submerged and not in contact with each other. Content determination: After soaking, the soaking solution was taken and the silver content was determined by graphite furnace atomic absorption spectrophotometer. The silver migration amount was calculated in mg / dm². The method detection limit was 0.0005 mg / dm².

[0034] Long-term performance testing methods Antibacterial rate test at 30 days / 90 days / 180 days Sample aging treatment: Place the packaging bag sample to be tested in a constant temperature and humidity chamber and place it for 30 days, 90 days and 180 days respectively under normal temperature and humidity conditions of 23±2℃ and 50±5% relative humidity, avoiding direct sunlight and external force damage. Antibacterial rate determination: After the aging treatment, the same method as the above "Antibacterial rate test of Escherichia coli and Staphylococcus aureus" was used to test the antibacterial rate and record the antibacterial rate after different aging times.

[0035] 180-day interlayer integrity test Sample aging treatment: The same aging conditions as the long-term antibacterial rate test were used, and the samples were placed for 180 days.

[0036] Integrity check: Visual inspection: Directly observe whether there are phenomena such as delamination, blistering, edge curling, or peeling on the sample surface; Auxiliary verification: For samples with no obvious visual abnormalities, the peel strength is measured according to the above-mentioned "interlayer peel strength test" method. If the peel strength is still ≥3.5N / cm (technical requirement of this application) and there is no interface breakage, it is judged to be interlayer intact.

[0037] Result determination: If any delamination or peel strength is less than 3.5 N / cm, the interlayer integrity is deemed unqualified.

[0038] Test data table and explanation Table 1. Test Results of Core Performance of Antibacterial Packaging Bags

[0039] As shown in Table 1, the antimicrobial peptide activity retention rates of Examples 1-3 were significantly higher than those of Comparative Example 1 (which did not use microencapsulation), indicating that the microencapsulation structure effectively prevented the thermal inactivation of the antimicrobial peptides during processing. The interlayer peel strength of the examples was significantly higher than that of Comparative Example 2 (which did not add an interfacial compatibilizer), meeting the requirements for interlayer bonding strength in packaging materials. All examples achieved antibacterial rates meeting the requirements for food packaging antibacterial properties, and the silver migration was significantly lower than the food contact material limit of 0.01 mg / dm³. 2 Safety standards are met.

[0040] Table 2. Results of Long-Term Performance Tests on Antimicrobial Packaging Bags

[0041] As shown in Table 2, Examples 1-3 maintained a high antibacterial rate after 180 days of use. The sustained-release effect of the compound antibacterial system effectively extended the antibacterial efficacy period, which was far superior to Comparative Example 1 without encapsulated antimicrobial peptides. No interlayer delamination phenomenon was observed in any of the examples after 180 days of use, which was better than Comparative Example 2 without compatibilizer, verifying that the interfacial compatibility system can effectively improve the long-term structural stability.

[0042] refer to Figure 2 This figure visually illustrates the correlation between the cross-linking degree of the microcapsule wall material and two core antibacterial properties. It clearly shows that at a cross-linking degree of 72%, both the heat retention rate of the antimicrobial peptide and the effective antibacterial period reach their optimal values. When the cross-linking degree is below 60%, the wall material lacks density, making the antimicrobial peptide susceptible to high-temperature degradation and inactivation during processing, and the excessively rapid release leads to a short effective period. When the cross-linking degree is above 85%, the wall material is too thick, making it difficult for the antimicrobial components to be released from the inside, thus reducing the long-term antibacterial effect. This figure clarifies the optimal process range for microcapsule preparation and visually verifies that the microcapsule encapsulation structure can simultaneously solve the core defects of antimicrobial peptide processing inactivation and short antibacterial effective period in existing technologies, providing a clear basis for parameter control in industrial production.

[0043] refer to Figure 3This figure visually illustrates the trend of E. coli inhibition rate changes in each test sample over a 180-day usage period. It clearly shows that the inhibition rate decay rate of the three embodiments of this invention is extremely slow, maintaining an inhibition rate of over 92% after 180 days. This indicates that the sustained-release effect of the compound antibacterial system is significant, effectively extending the antibacterial shelf life. Comparative Example 1, without encapsulated antimicrobial peptides, showed a rapid decrease in inhibition rate over time, with an inhibition rate of less than 30% after 180 days. Comparative Example 2, without compatibilizers, also experienced a higher rate of inhibition rate decline than the embodiments of this invention due to the shedding of antimicrobial components caused by later interlayer peeling. This further verifies the long-term stability of this solution.

[0044] refer to Figure 4 This figure visually demonstrates the comprehensive performance of each test sample. It clearly shows that the performance polygons of the three embodiments of the present invention are close to regular pentagons, with scores above 7 in all dimensions, indicating no obvious performance shortcomings and meeting the full performance requirements of antibacterial food packaging. Comparative Example 1 scored extremely low in both antimicrobial peptide retention rate and long-term antibacterial rate, failing to meet the requirements for long-term antibacterial effects; Comparative Example 2 scored extremely low in interlayer peel strength, making it prone to delamination and damage during use, failing to meet the requirements for long-term structural stability. This directly reflects the comprehensive performance advantages of the present invention compared to existing technologies.

[0045] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A plastic packaging bag with antibacterial function, characterized in that, The packaging bag comprises an inner contact layer, a functional reinforcement layer, and an outer protective layer, stacked sequentially from the inside out. The inner contact layer is a modified polyethylene substrate. The functional reinforcement layer is a polyolefin co-extruded film loaded with a composite antibacterial agent. The side of the functional reinforcement layer closest to the outer protective layer contains 5%-10% by weight of maleic anhydride-grafted polypropylene as an interface compatibilizer. The outer protective layer is a wear-resistant modified polypropylene coating, located on the outermost side of the packaging bag. The composite antibacterial agent is a compound of nano-silver-loaded mesoporous silica and microcapsule-encapsulated plant-derived antimicrobial peptides. The wall material of the microcapsules is cross-linked polymethyl methacrylate with a temperature resistance of 180-230℃, and the core material is a plant-derived antimicrobial peptide. The packaging bag has a heat-sealed edge with a width of 2-8 mm at the sealing point.

2. The plastic packaging bag with antibacterial function according to claim 1, characterized in that, The modified polyethylene of the inner contact layer is linear low-density polyethylene grafted with maleic anhydride, with a grafting rate of 0.2%-1.5% and a thickness of 15-30 μm.

3. The plastic packaging bag with antibacterial function according to claim 1 or 2, characterized in that, The polyolefin co-extruded film of the functional reinforcement layer is a blend of ethylene-octene copolymer and high-density polyethylene with a blending mass ratio of 1:2-1:

4. The microcapsules encapsulating plant-derived antimicrobial peptides dispersed in the functional reinforcement layer have a particle size of 1-5 μm, and the thickness of the functional reinforcement layer is 20-40 μm.

4. The plastic packaging bag with antibacterial function according to claim 1, characterized in that, The mass ratio of nano-silver-supported mesoporous silica to microcapsule-encapsulated plant-derived antimicrobial peptides in the composite antibacterial agent is 3:1-6:

1. The pore size of the nano-silver-supported mesoporous silica is 2-5 nm, the porosity of the microcapsule wall material is 15%-25%, and the mass percentage of the composite antibacterial agent added to the functional enhancement layer is 1.2%-3.5%.

5. The plastic packaging bag with antibacterial function according to claim 1, characterized in that, The wear-resistant modified polypropylene coating of the outer protective layer is a homopolymer polypropylene coating with 0.5%-1.2% silicone wear-resistant agent added. The homopolymer polypropylene coating contains 3%-8% maleic anhydride grafted polypropylene by mass, and the thickness of the outer protective layer is 10-25μm.

6. The plastic packaging bag with antibacterial function according to claim 1, characterized in that, The packaging bag has an easy-tear notch on its edge, the notch being 3-5mm deep and located on one or both sides of the heat-sealed edge.

7. A method for preparing a plastic packaging bag with antibacterial function, used to prepare a plastic packaging bag with antibacterial function as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Prepare the inner contact layer mixture, the functional reinforcement layer mixture and the outer protective layer mixture according to the component ratio. Before preparing each layer mixture, all raw materials need to be dried. Before preparing the functional reinforcement layer mixture, microcapsule-encapsulated plant-derived antimicrobial peptides are prepared by in-situ polymerization. The temperature during the mixing process is controlled at 60-70℃. S2. The three-layer mixture is fed into a three-layer co-extrusion blown film machine for co-extrusion blown film to obtain a three-layer composite film substrate. During the co-extrusion blown film process, the extrusion rate of each layer is synchronously controlled, and the screw shear rate is controlled at 100-300 / s. S3. The three-layer composite film substrate is hot-sealed, cut, and bag-made to obtain the plastic packaging bag with antibacterial function.

8. The method for preparing a plastic packaging bag with antibacterial function according to claim 7, characterized in that, When preparing the functional enhancement layer mixture in S1, firstly, nano-silver loaded mesoporous silica, microcapsule-encapsulated plant-derived antimicrobial peptides, and polyethylene wax are mixed to prepare an antimicrobial masterbatch. The preparation process of the antimicrobial masterbatch is to add each component according to the ratio to a twin-screw extruder for melt blending, extrusion granulation, and control the twin-screw extrusion temperature at 170-190℃. Then, the antimicrobial masterbatch, polyolefin co-extruded film matrix raw material, and maleic anhydride grafted polypropylene are mixed in a high-speed mixer for 10-20 minutes, and the mixing speed is set to 800-1000 rpm.

9. The method for preparing a plastic packaging bag with antibacterial function according to claim 7, characterized in that, The temperatures of each section of the S2 co-extrusion blown film are as follows: feeding section 140-160℃, plasticizing section 170-190℃, die head section 195-210℃, and blow-up ratio 2.5-4.

0.

10. The method for preparing a plastic packaging bag with antibacterial function according to claim 7, characterized in that, The temperature for hot-pressing the edge in S3 is 130-150℃, the hot-pressing pressure is 0.2-0.5MPa, and the hot-pressing time is 2-5s.

Images