Barrier, antibacterial and degradable preservative film as well as preparation method and application thereof

Abstract

The invention belongs to the field of new materials, and particularly relates to a barrier, antibacterial and degradable preservative film as well as a preparation method and application thereof, full-biodegradable resin is adopted as a preservative film base material, and the barrier, antibacterial and degradable preservative film is obtained through melt blending and extrusion blow molding of the full-biodegradable resin and a Zn-Al hydrotalcite / epsilon-polylysine hydrochloride composite material. Wherein the Zn-Al hydrotalcite / epsilon-polylysine hydrochloride composite material is prepared by loading epsilon-polylysine hydrochloride on Zn-Al hydrotalcite sheets, and the adopted hydrotalcite-like / epsilon-polylysine hydrochloride synergistically enhances the mechanical, barrier and antibacterial properties of the fresh-keeping film, so that the fresh-keeping effect of fruits and vegetables can be obviously improved, and the shelf life can be prolonged; meanwhile, the preparation method has the characteristics of environment friendliness, simple preparation process and low cost.

Description

Technical Field

[0001] The present invention belongs to the field of new materials, and particularly relates to a barrier, antibacterial and biodegradable fresh-keeping film, a preparation method thereof and an application thereof. Background Art

[0002] With the continuous improvement of people's requirements for food quality and safety, food fresh-keeping films have been widely used. The raw materials of traditional fresh-keeping films are mostly non-degradable polyethylene, polyvinyl chloride, polyvinylidene chloride, etc. If the used films are treated by incineration or burial, it will cause serious damage to the ecological environment. Biodegradable film materials can be degraded into carbon dioxide, water and inorganic substances in the natural environment after use, without causing environmental pollution, which is the future development trend.

[0003] Biodegradable PBAT / PLA film materials have been widely used due to their advantages such as rich raw materials, low cost and environmental friendliness. However, PBAT / PLA composite materials have single functions, poor mechanical properties and gas barrier properties, and lack antibacterial properties, which limit their development and application in food packaging.

[0004] Some Chinese patents have reported the preparation of degradable fresh-keeping films using PBAT and PLA. For example, in Chinese patents CN114395222A and CN118755241A, various additives such as antibacterial, breathable and anti-fogging, antioxidant, degradation-promoting, and compatibility-promoting additives are added to the substrate for modification, but their preparation processes are complex and costly, which is not conducive to industrial production; in Chinese patent CN118725372A, antibacterial and antioxidant agents are added to the PBAT / PLA matrix to endow the film with antibacterial and antioxidant functions and improve the mechanical properties of the film to a certain extent, but the gas barrier property of the film has not been improved; in Chinese patent CN116731489B, additives such as modified montmorillonite are added to effectively improve the dispersibility and stability of the composite and endow the film with antibacterial properties, but the barrier property of the film has not been improved either.

[0005] The gas barrier property is one of the core indicators of food packaging films, which directly affects the shelf life, flavor retention and safety of food. In Chinese patent CN112679928A, an antibacterial agent of talc-loaded ε-polylysine hydrochloride is added, which effectively retains the antibacterial property of ε-polylysine hydrochloride and improves the mechanical properties of the film, but this patent does not mention the improvement of the gas barrier property of the film; at the same time, there are also limitations in the multifunctionality of the carrier in this technical solution, such as not selecting more functional carriers to synergistically improve the barrier and longer-lasting antibacterial properties of the film, etc.

[0006] Existing degradable food wraps are difficult to meet the comprehensive requirements in terms of mechanical properties, barrier properties, antibacterial properties, etc., and are difficult to be promoted in the market. Therefore, there is an urgent need for a multifunctional degradable food wrap with good mechanical properties, excellent barrier and long-term antibacterial properties, as well as a preparation method with low cost. Summary of the Invention

[0007] To solve the problem that existing degradable food wraps are difficult to meet the comprehensive requirements in terms of mechanical properties, barrier properties, antibacterial properties, etc., the present invention provides a barrier and antibacterial degradable food wrap, its preparation method and application. A fully biodegradable resin is used as the matrix material of the food wrap, and a barrier and antibacterial degradable food wrap is obtained by melt blending and extrusion blowing with a Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material. Among them, the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material is prepared by loading ε-polylysine hydrochloride on Zn-Al hydrotalcite sheets. The used hydrotalcite-like / ε-polylysine hydrochloride composite material is not only a traditional carrier loaded with antibacterial agents, but also a multifunctional carrier and antibacterial agent that synergistically enhance the mechanical and barrier properties of the food wrap, and endow the film with a longer-lasting antibacterial effect, which can significantly improve the fresh-keeping effect of fruits and vegetables, extend the shelf life, and at the same time has the characteristics of environmental friendliness, simple preparation process and low cost, is suitable for industrial production, has both barrier and antibacterial properties, and has excellent mechanical properties.

[0008] The preparation method of the barrier and antibacterial degradable food wrap described in the present invention is to melt blend a Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and a fully biodegradable resin, and then obtain it by extrusion blowing. Among them, the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material is prepared by loading ε-polylysine hydrochloride on Zn-Al hydrotalcite sheets.

[0009] The present invention first provides a barrier and antibacterial degradable food wrap, which includes the following components by weight: 95-99.5 parts of a fully biodegradable resin, and the fully biodegradable resin is a mixed resin of PBAT and PLA, wherein the mass ratio of PBAT to PLA is 93-97:3-7; based on the more excellent toughness and high temperature resistance of PBAT, the mass ratio of PBAT to PLA is more preferably 95∶5; in addition, it also includes 0.5-5 parts of a Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material. With the addition of the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material, the mechanical properties, barrier properties and antibacterial properties of the film are all significantly improved.

[0010] Preferably, the thickness of the barrier and antibacterial degradable food wrap is controlled at 25-35 μm.

[0011] The Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material is prepared by the following method: Zn-Al hydrotalcite and ε-polylysine hydrochloride are ball-milled. The specific process of ball-milling is as follows: the rotation speed is 200 - 400 rpm, ball-milling is carried out for 0.5 - 1.5 h, cooling is carried out for 0.5 - 1.5 h, then ball-milling is carried out for another 0.5 - 1.5 h, and then cooling is carried out for 0.5 - 1.5 h to obtain the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material, whose average particle size is 0.5 - 1.5 μm, more preferably 0.5 - 1.0 μm. Compared with other technologies, the preparation process of this technology is simple, time-consuming is short, and the cost is low.

[0012] Considering the antibacterial effect and material cost comprehensively, as a preference, Zn-Al hydrotalcite and ε-polylysine hydrochloride are ball-milled according to the mass ratio of 0.5 - 1:0.5 - 1.

[0013] Zn-Al hydrotalcite is a layered double hydroxide, which has the following advantages: (1) The preparation process is simple, the cost is low, the biocompatibility is good, and the chemical stability is high; (2) Introducing this two-dimensional layered material into the polymer matrix can extend the diffusion path of gas molecules through the distortion effect, which is beneficial to improving the gas barrier performance, thereby further extending the storage time of fruits; (3) Zn-Al hydrotalcite serves as a large Zn 2+ reservoir and has certain antibacterial activity; (4) The flaky structure of Zn-Al hydrotalcite is beneficial to the loading with other materials. Multifunctional Zn-Al hydrotalcite has great application potential in the field of food packaging.

[0014] ε-Polylysine hydrochloride is a microbially derived peptide composed of 25 - 30 lysine residues, which has the following advantages: (1) It has a broad antibacterial spectrum and a wide bacteriostatic pH range; (2) It has high safety. In Japan and the United States, ε-polylysine hydrochloride has been widely used in food preservation; (3) It has good thermal stability and is suitable for thermal processing; (4) A large number of amino groups are contained in its structure, which can form hydrogen bonds with PBAT with hydroxyl groups and has good compatibility with PBAT.

[0015] Utilizing the flaky structure of Zn-Al hydrotalcite, the water physically adsorbed between layers and on the surface, and the hydrophilic property of ε-polylysine hydrochloride, ε-polylysine hydrochloride is loaded onto the flaky structure of Zn-Al hydrotalcite to form a composite material, delaying the release of Zn 2+ , ε-polylysine hydrochloride with water vapor, thereby achieving longer-lasting antibacterial.

[0016] The existence of the flaky structure of Zn-Al hydrotalcite and the further loading of ε-polylysine hydrochloride prolong the diffusion path of gas molecules through the twisting effect, which is beneficial to improving the gas barrier performance. At the same time, the composite material has good compatibility with the fully biodegradable resin, and the intermolecular hydrogen bond interaction existing therein makes the film denser, further improving the gas barrier performance of the film, and thus prolonging the storage time of fruits and vegetables.

[0017] The Zn-Al hydrotalcite can be prepared by the following steps: The first reaction: React Na2CO3, NaOH, zinc nitrate hexahydrate, and aluminum nitrate nonahydrate in deionized water in the first reaction. After the reaction is completed, cool to room temperature, filter by suction and collect the solid. The second reaction: React the solid obtained from the first reaction with Na2CO3 again in the second reaction. After the reaction is completed, cool to room temperature, wash the turbid liquid with deionized water, filter by suction to collect the solid product, and dry and grind to obtain Zn-Al hydrotalcite.

[0018] Preferably, in the first reaction, the ratio of Na2CO3, NaOH, zinc nitrate hexahydrate, and aluminum nitrate nonahydrate is 4 - 18 mmol: 20 - 90 mmol: 8 - 10 g: 3 - 5 g, the concentration of zinc nitrate hexahydrate in the reaction system is 40 - 85 mg / mL, and the molar ratio of Na2CO3 in the first reaction to Na2CO3 in the second reaction is 4 - 18: 20 - 120.

[0019] More specifically, the specific steps for preparing Zn-Al hydrotalcite are as follows: 1) Weigh zinc nitrate hexahydrate and aluminum nitrate nonahydrate, add deionized water, and prepare a mixed nitrate solution to obtain a mixed nitrate solution.

[0020] 2) Pour the Na2CO3 solution into the reaction vessel, pour the mixed nitrate solution and the NaOH solution into the above Na2CO3 solution simultaneously, and carry out the first reaction under stirring. After the reaction is completed, cool to room temperature, filter by suction and collect the solid.

[0021] 3) Dissolve the obtained solid in the Na2CO3 solution, carry out the second reaction under stirring, then cool to room temperature, filter the obtained turbid liquid to obtain the solid, then wash the solid with deionized water until the washing liquid is neutral, filter by suction to collect the solid product, and dry and grind to obtain Zn-Al hydrotalcite.

[0022] Preferably, in step 1), the ratio of zinc nitrate hexahydrate to deionized water is 8 - 10 g: 40 - 60 mL; In step 2), the concentration of the Na2CO3 solution is 0.1 - 0.3 mol / L, and the volume is 40 - 60 mL; the concentration of the NaOH solution is 0.5 - 1.5 mol / L, and the volume is 40 - 60 mL; In step 3), the concentration of the Na2CO3 solution is 1 - 3 mol / L, and the volume is 20 - 40 mL.

[0023] Preferably, in the first reaction step, the reaction temperature is 50 - 70 °C, the reaction time is 2 - 4 h, during the reaction process, the pH of the reaction system is maintained at 9 - 11 by supplementing sodium hydroxide solution or deionized water, and the rotation speed is 800 - 1200 rpm; In the second reaction step, the reaction temperature is 30 - 50 °C, the reaction time is 10 - 14 h, and the rotation speed is 800 - 1200 rpm; The drying is carried out by drying at 60 - 80 °C for 7 - 9 h.

[0024] The present invention further provides a method for preparing the above-mentioned barrier, antibacterial and degradable fresh-keeping film, comprising the following steps: 1) Respectively drying 0.5 - 5 parts of Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and 95 - 99.5 parts of fully biodegradable resin particles at 60 - 90 °C for 7 - 14 h, adding the above-mentioned dried materials into a high-speed mixer respectively, with a rotation speed of 2000 - 3000 rpm, and mixing for 6 - 10 min for premixing to obtain a mixture, so that the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and the fully biodegradable resin are mixed evenly; 2) Adding the mixture obtained in 1) to the feeding port of a twin-screw extruder, with a feeding rate of 80 - 180 g / min, and setting the temperatures of the seven zones from the feeding port to the head of the extruder as: 165 - 170 / 170 - 175 / 170 - 180 / 170 - 180 / 165 - 175 / 160 - 165 / 155 - 160 °C, the screw rotation speed is 150 - 300 rpm, after melt blending by the twin-screw extruder, it passes through water cooling and air drying and then enters a pelletizer to form composite masterbatch.

[0025] 3) Drying the obtained composite masterbatch at 60 - 90 °C for 7 - 14 h, adding it to a single-screw extruder for melt extrusion, and then blowing it into a barrier, antibacterial and degradable fresh-keeping film with a thickness of 25 - 35 μm by a blown film machine; wherein, the temperatures of the head and the heating zone of the single-screw extruder are set as: 160 - 165 / 170 - 180 / 160 - 170 / 155 - 160 °C, and the screw rotation speed is 30 - 50 rpm.

[0026] The fully biodegradable resin particles are a mixture of PBAT particles and PLA particles, and preferably the mass ratio of PBAT to PLA is 95:5.

[0027] The obtained barrier, antibacterial and biodegradable fresh-keeping film is sealed with a black opaque plastic bag and stored in a dry, cool and dark place.

[0028] Preferably, the particle size of the fully biodegradable resin particles is 2-4 mm.

[0029] The barrier, antibacterial and biodegradable fresh-keeping film provided by the present invention can be used for food preservation.

[0030] The present invention has achieved the following beneficial effects: In the present invention, ε-polylysine hydrochloride is loaded onto Zn-Al hydrotalcite flakes to obtain a Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material. Different from traditional carrier-loaded antibacterial agents, Zn-Al hydrotalcite itself has certain antibacterial properties. The Zn-Al hydrotalcite / ε-polylysine hydrochloride synergistically enhances the antibacterial effect, and the tight combination of the two materials endows the film with a long-term antibacterial function. The existence of the flaky structure of Zn-Al hydrotalcite and the further loading of ε-polylysine hydrochloride extend the diffusion path of gas molecules through the twisting effect, which is beneficial to improving the gas barrier performance. At the same time, the composite material has good compatibility with the fully biodegradable resin. The intermolecular hydrogen bond interaction makes the film denser, further improving the gas barrier performance of the film, thereby further extending the storage time of fruits. The composite material and the fully biodegradable resin adopt a melt blending and extrusion blow molding process to prepare a degradable fresh-keeping film with both barrier and antibacterial properties, and this type of fresh-keeping film has excellent mechanical properties.

[0031] During use, Zn 2+ and ε-polylysine hydrochloride in the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material will slowly release into the film matrix, then further release to the film surface, and finally contact with fruits and vegetables, achieving the effect of extending the shelf life of fruits and vegetables. The barrier, antibacterial and biodegradable fresh-keeping film prepared by the present invention has both barrier and antibacterial properties. Compared with the previous fresh-keeping films, the mechanical properties of the barrier, antibacterial and biodegradable fresh-keeping film of the present invention have also been improved. At the same time, it has the characteristics of green environmental protection, simple preparation process and low cost, and can be applied to the preservation of foods such as white button mushrooms, effectively extending the shelf life of foods such as white button mushrooms. The present invention has important economic, social and ecological benefits for the further development and application of degradable fresh-keeping films, meeting the requirements of sustainable development. Description of the Drawings

[0032] Figure 1In Figure a, it is the cumulative release result diagram of the ε-polylysine hydrochloride in the water of the fresh-keeping film prepared in Examples 1-3. In Figure b, it is the Zn of the fresh-keeping film prepared in Examples 2 and 3 and Comparative Examples 2 and 3. 2+ Cumulative release effect diagram in water; Figure 2 It is the diagram of the tensile strength and nominal strain at break of the fresh-keeping film prepared in Examples 2 and 3 and Comparative Examples 1-3. Among them, A is the diagram of the transverse tensile strength / nominal strain at break, and B is the diagram of the longitudinal tensile strength / nominal strain at break; Figure 3 It is the antibacterial performance result diagram of the fresh-keeping film prepared in Examples 2 and 3 and Comparative Examples 1-3; Figure 4 It is the gas barrier performance result diagram of the fresh-keeping film prepared in Examples 2 and 3 and Comparative Examples 1-4; Figure 5 It is the fresh-keeping effect photos at different times in the fresh-keeping test of Tricholoma gambosum of the fresh-keeping film prepared in Examples 2 and 3 and Comparative Examples 1-3. Detailed implementation manners

[0033] The technical solution of the present invention will be further described below in conjunction with specific embodiments. These embodiments are only used to more specifically illustrate the technical solution of the present invention and should not be construed as limiting the protection scope of the present invention.

[0034] All kinds of reagents and substances used in the following examples are generally commercially available products if not specifically stated.

[0035] Example 1 A barrier, antibacterial and degradable fresh-keeping film containing Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and its preparation method.

[0036] First, prepare Zn-Al hydrotalcite. The specific steps are as follows: S1. First, weigh 8.25 g of zinc nitrate hexahydrate and 3.60 g of aluminum nitrate nonahydrate and add them to 45 mL of deionized water to prepare a nitrate mixed solution.

[0037] S2. Pour 45 mL of 0.15 mol / L Na2CO3 solution into a flask, put in a rotor, and then pour the above nitrate solution and 50 mL of 0.5 mol / L NaOH solution into the Na2CO3 solution. Stir magnetically at 50 °C for 2 h, with a rotation speed of 800 rpm. During the stirring process, add sodium hydroxide solution or deionized water to maintain the solution pH at 10. After the reaction, cool to room temperature, filter by suction, and collect the solid.

[0038] S3. Redissolve the solid obtained in S2 in 25 mL of 1.5 mol / L Na2CO3, stir magnetically at 30 °C for 10 h at a rotation speed of 800 rpm. After cooling to room temperature, filter the resulting turbid solution to obtain the solid, then wash the solid with deionized water until the washing liquid is neutral, collect the solid product by suction filtration, dry it at 60 °C for 7 h, and grind it to obtain Zn-Al hydrotalcite powder.

[0039] Then, using the Zn-Al hydrotalcite prepared by the above method as the raw material, prepare the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material through the following steps: Ball mill Zn-Al hydrotalcite and ε-polylysine hydrochloride (purchased from Shandong Keyuan Biochemical Co., Ltd.) at a mass ratio of 0.5:1, with a rotation speed of 200 rpm. First, ball mill for 0.5 h, cool for 0.5 h, then ball mill for 1.5 h, and cool for 1.5 h to obtain the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material with an average particle size of 0.5 μm.

[0040] Then, using the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material prepared by the above method as the raw material, prepare a barrier and antibacterial degradable fresh-keeping film through the following method: 1) First, mix the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and the fully biodegradable resin PBAT / PLA mixed particles (where the mass ratio of PBAT to PLA is 95:5) (particle size range is 2 - 4 mm), dry at 60 °C for 10 h, and add the composite material and the fully biodegradable resin to a high-speed mixer at a mass ratio of 1:99 respectively, with a rotation speed of 2000 rpm, and mix for 6 min for pre-mixing to obtain a mixture, so that the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and the fully biodegradable resin are mixed evenly.

[0041] 2) Add the mixture to the feeding port of a twin-screw extruder, with a feeding rate of 100 g / min. The temperatures of the seven zones from the feeding port to the extruder head are set as: 165 / 175 / 170 / 170 / 165 / 160 / 155 °C, and the screw rotation speed is 180 rpm. After the resin is melt-blended, it passes through water cooling and air drying and enters a pelletizer to form composite masterbatches.

[0042] 3) Then dry the obtained composite masterbatches at 60 °C for 12 h, add them to a single-screw extruder for melt extrusion, and blow them into a barrier and antibacterial degradable fresh-keeping film through a blown film machine; Among them, the temperatures from the single-screw extruder head to the heating zone are set as: 160 / 170 / 160 / 155 °C, and the screw rotation speed is 30 rpm.

[0043] The obtained barrier, antibacterial and degradable fresh-keeping film is sealed with a black opaque plastic bag and stored in a dry, cool and dark place; the thickness of the barrier, antibacterial and degradable fresh-keeping film is controlled between 28 ± 1 μm.

[0044] Example 2 A barrier, antibacterial and degradable fresh-keeping film containing Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and its preparation method.

[0045] First, prepare Zn-Al hydrotalcite, and the specific steps are as follows: S1. First, weigh 8.50 g of zinc nitrate hexahydrate and 3.80 g of aluminum nitrate nonahydrate and add them to 55 mL of deionized water to prepare a nitrate mixed solution.

[0046] S2. Pour 40 mL of 0.2 mol / L Na2CO3 solution into a flask, put in a rotor, and then pour the nitrate solution and 50 mL of 0.8 mol / L NaOH solution into the Na2CO3 solution. Stir magnetically at 55 °C for 2 h, with a rotation speed of 900 rpm. During the stirring process, add sodium hydroxide solution or deionized water to maintain the solution pH at 11. After the reaction, cool to room temperature, filter by suction, and collect the solid.

[0047] S3. Dissolve the solid obtained in S2 again in 20 mL of 1.8 mol / L Na2CO3, stir magnetically at 30 °C for 12 h, with a rotation speed of 1000 rpm. After cooling to room temperature, filter the obtained turbid solution to obtain the solid, then wash the solid with deionized water until the washing liquid is neutral, filter by suction to collect the solid product, dry at 65 °C for 7 h, and grind to obtain Zn-Al hydrotalcite powder.

[0048] Then, using the Zn-Al hydrotalcite prepared by the above method as the raw material, prepare the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material through the following steps: Ball-mill Zn-Al hydrotalcite and ε-polylysine hydrochloride (purchased from Shandong Keyuan Biochemical Co., Ltd.) according to a mass ratio of 1:0.5, with a rotation speed of 200 rpm. First, ball-mill for 1 h, cool for 1 h, then ball-mill for 1 h, and cool for 1 h to obtain the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material, with an average particle size of 1 μm.

[0049] Then, using the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material prepared by the above method as the raw material, prepare the barrier, antibacterial and degradable fresh-keeping film through the following method: 1) First, mix the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and the fully biodegradable resin PBAT / PLA mixed particles (where the mass ratio of PBAT to PLA is 95:5) (particle size range is 2 - 4 mm), and dry them at 70 °C for 11 h. Then, add the composite material and the fully biodegradable resin to a high-speed mixer at a mass ratio of 3:97, with a rotation speed of 2500 rpm, and mix for 7 min for pre-mixing to obtain a mixture, making the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and the fully biodegradable resin evenly mixed.

[0050] 2) Add the mixture to the feeding port of a twin-screw extruder, with a feeding rate of 120 g / min. Set the temperatures of the seven zones from the feeding port to the extruder head to: 170 / 175 / 170 / 170 / 165 / 160 / 160 °C, and the screw rotation speed to 200 rpm. After the resin is melt-blended, it passes through water cooling and air drying and then enters a pelletizer for pelletizing to obtain composite masterbatch.

[0051] 3) Then dry the obtained composite masterbatch at 70 °C for 11 h, add it to a single-screw extruder for melt extrusion, and blow it into a barrier, antibacterial and biodegradable fresh-keeping film through a blown film machine; Among them, set the temperatures from the head of the single-screw extruder to the heating zone to: 165 / 170 / 160 / 155 °C, and the screw rotation speed to 35 rpm.

[0052] Package the obtained barrier, antibacterial and biodegradable fresh-keeping film with a black opaque plastic bag and store it in a dry, cool and dark place; control the thickness of the barrier, antibacterial and biodegradable fresh-keeping film between 32 ± 1 μm.

[0053] Example 3 A barrier, antibacterial and biodegradable fresh-keeping film containing Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and its preparation method.

[0054] First, prepare Zn-Al hydrotalcite, and the specific steps are as follows: S1. First, weigh 8.91 g of zinc nitrate hexahydrate and 3.75 g of aluminum nitrate nonahydrate and add them to 50 mL of deionized water to prepare a nitrate mixed solution.

[0055] S2. Pour 50 mL of 0.16 mol / L Na2CO3 solution into a flask, place a rotor, and then pour the nitrate solution and 50 mL of 1 mol / L NaOH solution into the Na2CO3 solution. Stir magnetically at 60 °C for 3 h, with a rotation speed of 1100 rpm. During the stirring process, add sodium hydroxide solution or deionized water to maintain the solution pH at 10. After the reaction, cool to room temperature, filter by suction, and collect the solid.

[0056] S3. Redissolve the solid obtained in S2 in 30 mL of 2 mol / L Na2CO3, stir magnetically at 40 °C for 12 h at a rotation speed of 1100 rpm. After cooling to room temperature, filter the resulting turbid liquid to obtain the solid, then wash the solid with deionized water until the washing liquid is neutral, collect the solid product by suction filtration, dry it at 70 °C for 7 h, and grind it to obtain Zn-Al hydrotalcite powder.

[0057] Then, using the Zn-Al hydrotalcite prepared by the above method as the raw material, prepare the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material through the following steps: Ball-mill Zn-Al hydrotalcite and ε-polylysine hydrochloride (purchased from Shandong Keyuan Biochemical Co., Ltd.) at a mass ratio of 1:1 at a rotation speed of 300 rpm. First, ball-mill for 1 h, cool for 1 h, then ball-mill for 1.5 h, and cool for 1.5 h to obtain the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material with an average particle size of 0.8 μm.

[0058] Then, using the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material prepared by the above method as the raw material, prepare a barrier and antibacterial degradable fresh-keeping film through the following method: 1) First, mix the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and the fully biodegradable resin PBAT / PLA mixed particles (where the mass ratio of PBAT to PLA is 95:5) (particle size range is 2 - 4 mm), dry at 70 °C for 8 h. The composite material and the fully biodegradable resin are added to a high-speed mixer at a mass ratio of 5:95 respectively, and mixed at a rotation speed of 3000 rpm for 10 min for pre-mixing to obtain a mixture, so that the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and the fully biodegradable resin are mixed evenly.

[0059] 2) Add the mixture to the feeding port of a twin-screw extruder at a feeding rate of 160 g / min. The temperatures of the seven zones from the feeding port to the head of the extruder are set as: 170 / 175 / 180 / 170 / 165 / 160 / 155 °C, and the screw rotation speed is 260 rpm. After the resin is melt-blended, it passes through water cooling and air drying and enters a pelletizer to form composite masterbatches.

[0060] 3) Then dry the obtained composite masterbatches at 70 °C for 10 h, add them to a single-screw extruder for melt extrusion, and blow them into a barrier and antibacterial degradable fresh-keeping film through a blown film machine; Among them, the temperatures from the head of the single-screw extruder to the heating zone are set as: 165 / 175 / 160 / 155 °C, and the screw rotation speed is 40 rpm.

[0061] The obtained barrier, antibacterial and degradable fresh-keeping film is sealed with a black opaque plastic bag and stored in a dry, cool and dark place; the thickness of the barrier, antibacterial and degradable fresh-keeping film is controlled between 30 ± 1 μm.

[0062] Comparative Example 1 The barrier, antibacterial and degradable fresh-keeping film was prepared by the same steps as in Example 1, except that no Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material was added in Comparative Example 1, and the other steps were the same as in Example 1.

[0063] Comparative Example 2 The barrier, antibacterial and degradable fresh-keeping film was prepared by the same steps as in Example 1, except that Zn-Al hydrotalcite was directly used as the barrier antibacterial agent in Comparative Example 2. The Zn-Al hydrotalcite and the fully biodegradable resin PBAT / PLA mixed particles (where the mass ratio of PBAT to PLA is 95:5) (particle size range is 2-4 mm) were mixed at a mass ratio of 1:99 and then sent to the feed inlet of the twin-screw extruder. The other steps were the same as in Example 1.

[0064] Comparative Example 3 The barrier, antibacterial and degradable fresh-keeping film was prepared by the same steps as in Example 1, except that Zn-Al hydrotalcite was directly used as the barrier antibacterial agent in Comparative Example 3. The Zn-Al hydrotalcite and the fully biodegradable resin PBAT / PLA mixed particles (where the mass ratio of PBAT to PLA is 95:5) (particle size range is 2-4 mm) were mixed at a mass ratio of 3:97 and then sent to the feed inlet of the twin-screw extruder. The other steps were the same as in Example 1.

[0065] Comparative Example 4 The barrier, antibacterial and degradable fresh-keeping film was prepared by the same steps as in Example 1, except that talcum powder was used as the barrier antibacterial agent in Comparative Example 4. The talcum powder and the fully biodegradable resin PBAT / PLA mixed particles (where the mass ratio of PBAT to PLA is 95:5) (particle size range is 2-4 mm) were mixed at a mass ratio of 5:95 and then sent to the feed inlet of the twin-screw extruder. The other steps were the same as in Example 1.

[0066] Experimental Example 1 Accelerated Release Test of the Antibacterial Component of the Fresh-Keeping Film in Water Take the barrier, antibacterial and degradable fresh-keeping films prepared in Examples 1-3 as fresh-keeping film samples. Accurately weigh 0.5 g of the fresh-keeping film samples, soak the fresh-keeping film samples in a 150 mL ground conical flask containing 50 mL of pure water, cover the stopper, place the conical flask in a constant temperature air bath oscillator, set the temperature to 40 °C, and the amplitude to 20 mm. At 10, 20, 30, 40, 50, 60, 120, 180, 300, 360, 720, and 1440 min of soaking, respectively, pipette 3 mL of the release solution and replenish 3 mL of pure water to ensure that the total volume remains unchanged. The release of ε-polylysine hydrochloride from the composite film was evaluated by ultraviolet-visible absorption spectroscopy. According to the characteristic ultraviolet absorption peak at 309 nm, the ε-polylysine hydrochloride in the solution was quantified, and the standard curve of ε-polylysine hydrochloride was plotted. Then, by comparing the absorbance data of the standard curve and the experimental samples, the concentration of ε-polylysine hydrochloride in the samples could be accurately calculated. The final cumulative release rate = the actually measured concentration of ε-polylysine hydrochloride / the theoretical concentration of ε-polylysine hydrochloride × 100%. The results are shown in Figure 1 a.

[0067] Take the barrier, antibacterial and degradable fresh-keeping films prepared in Example 2, Example 3, Comparative Example 2 and Comparative Example 3 as fresh-keeping film samples. Accurately weigh 0.5 g of the fresh-keeping film samples, soak the fresh-keeping film samples in a 50 mL ground conical flask containing 10 mL of pure water, cover the stopper, place the conical flask in a constant temperature air bath oscillator, set the temperature to 25 °C, and the amplitude to 20 mm. At 30, 60, 120, 180, 240, 300, 360, 420, and 480 min of soaking, respectively, perform ICP analysis on the soaked solution to determine the Zn 2+ content. The results are shown in Figure 1 b.

[0068] The results show that the tight combination of Zn-Al hydrotalcite / ε-polylysine hydrochloride realizes the slow release of ε-polylysine hydrochloride and Zn 2+ with water vapor, thus achieving long-term antibacterial.

[0069] Experimental Example 2 Mechanical Property Test Take the barrier, antibacterial and degradable fresh-keeping films prepared in Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 as fresh-keeping film samples, and conduct mechanical property tests. The test method refers to GB 13022-91. The results are shown in Figure 2 , where A in the figure is the result graph of transverse tensile strength / breaking nominal strain, and B is the result graph of longitudinal tensile strength / breaking nominal strain.

[0070] The results show that the presence of Zn-Al hydrotalcite / ε-polylysine hydrochloride improves the dispersibility and interfacial interaction with the fully biodegradable resin, and the intermolecular hydrogen bonds make the film denser, thus enhancing the mechanical properties of the film.

[0071] Experimental Example 3 Antibacterial Performance Test The barrier and antibacterial degradable fresh-keeping films prepared in Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were used as fresh-keeping film samples for antibacterial performance testing. Escherichia coli and Staphylococcus aureus were cultured at 37 °C for 24 h and diluted to 106 colony-forming units (CFU) per milliliter. Then, 0.1 mL of the solution was dropped onto an AGAR plate, spread evenly with a sterilized wire, a cut film with a diameter of 6 mm was placed, and then the plate was placed at 37 °C for 12 h. Finally, the diameter of the inhibition zone was measured, and the average value was taken for three groups. The results are shown in Figure 3 。

[0072] The results show that Examples 2 and 3 have better antibacterial performance, indicating that the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material can significantly improve the antibacterial performance of the film.

[0073] Experimental Example 4 Gas Barrier Performance Test The barrier and antibacterial degradable fresh-keeping films prepared in Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 were used as fresh-keeping film samples for gas barrier performance testing. The permeability of oxygen and carbon dioxide of the composite film was tested using a differential pressure method gas permeation instrument. The water vapor transmission rate (WVT) of the film was tested on an automatic moisture permeability tester. The cup method was used for the test. The film was cut into circular sample films with an area of 3.3×10 -3 m 2 . The experimental temperature was 38 °C, the experimental humidity was 90% RH, and the preheating time was 1 h. The results are shown in Figure 4 。

[0074] The results show that, compared with Comparative Example 1, the addition of Zn-Al hydrotalcite (Comparative Examples 2 and 3), talcum powder (Comparative Example 4), and Zn-Al hydrotalcite / ε-polylysine hydrochloride composite materials (Examples 2 and 3) all play a certain barrier role. Compared with the addition of talcum powder, the addition of Zn-Al hydrotalcite has better water vapor barrier performance. Generally speaking, Examples 2 and 3 have better barrier performance, with their oxygen transmission rates lower than those of Comparative Examples 2 and 3, and their carbon dioxide and water vapor transmission rates lower than those of Comparative Example 4. Comparing the barrier performance of Examples 2 and 3, it is found that the performance of Example 3 is better, which indicates that with the addition of Zn-Al hydrotalcite / ε-polylysine hydrochloride composite materials, the diffusion path of gas through the film becomes longer, the film structure becomes denser, further reducing the transmission rate of water vapor and gas, making it more difficult for gas molecules to pass through.

[0075] Experimental Example 5 Fresh-keeping Test of Tricholoma gambosum Using PE fresh-keeping film, the barrier, antibacterial and biodegradable fresh-keeping films prepared in Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 as fresh-keeping film samples to conduct a fresh-keeping test on Tricholoma gambosum, the test design is as follows: Select fresh Tricholoma gambosum with uniform size and no obvious damage, cut different kinds of fresh-keeping films of 15 cm×18 cm to wrap Tricholoma gambosum, seal with a sealing machine, and store at 25 °C and 43% humidity for 6 days. Observe the appearance every day and record any obvious changes. The results are shown in Figure 5 .

[0076] The results show that: as the fresh-keeping time prolongs, compared with the Tricholoma gambosum packaged with the fresh-keeping film of the example, the Tricholoma gambosum of the comparative example changes color, shrinks and wrinkles significantly, while the Tricholoma gambosum samples of the example are still relatively fresh after 6 days of storage. It shows that the barrier, antibacterial and biodegradable fresh-keeping film prepared by the present invention can effectively prolong the fresh-keeping time of Tricholoma gambosum. Therefore, the barrier, antibacterial and biodegradable fresh-keeping film provided by the present invention has certain popularization and application value.

[0077] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any equivalent replacement, modification, etc. made by those skilled in the art within the spirit and principle of the present invention without any creative work shall be included in the protection scope of the present invention.

Claims

1. A barrier, antibacterial and degradable cling film, characterized in that: The invention comprises the following components by weight: 95-99.5 parts of a fully biodegradable resin, wherein the fully biodegradable resin is a mixed resin of PBAT and PLA, wherein the mass ratio of PBAT to PLA is 93-97:3-7; and 0.5-5 parts of a Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material.

2. The barrier, antibacterial and degradable cling film according to claim 1, characterized in that: The thickness of the plastic wrap is 25-35 μm.

3. The barrier, antibacterial and degradable cling film according to claim 1, characterized in that: The mass ratio of PBAT to PLA in the PBAT and PLA mixed resin is 95:

5.

4. The barrier, antibacterial and degradable cling film according to claim 1, characterized in that: The Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material is prepared by the following method: ball milling Zn-Al hydrotalcite and ε-polylysine hydrochloride, wherein the specific process of ball milling is: rotating speed 200-400 rpm, ball milling 0.5-1.5 h, cooling 0.5-1.5 h, then ball milling 0.5-1.5 h, and cooling 0.5-1.5 h to obtain the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material, wherein the average particle size is 0.5-1.5 μm; The Zn-Al hydrotalcite and ε-polylysine hydrochloride are ball-milled in a mass ratio of 0.5-1:0.5-1.

5. The barrier, antibacterial and degradable cling film according to claim 1, characterized in that: The Zn-Al hydrotalcite is prepared by the following steps: First step reaction: Na2CO3, NaOH, zinc nitrate hexahydrate and aluminum nitrate nonahydrate are reacted in deionized water. After the reaction is completed, the mixture is cooled to room temperature, and the solid is filtered and collected. Second step reaction: the solid obtained from the first step reaction is reacted with Na2CO3 again for the second step reaction. After the reaction is completed, it is cooled to room temperature, the turbid liquid is washed with deionized water, the solid product is collected by filtration, and dried and ground to obtain Zn-Al hydrotalcite.

6. The barrier, antibacterial and degradable cling film according to claim 5, characterized in that: The ratio of Na2CO3, NaOH, zinc nitrate hexahydrate and aluminum nitrate nonahydrate in the first step reaction is 4-18 mmol:20-90 mmol:8-10 g:3-5 g, the concentration of zinc nitrate hexahydrate in the reaction system is 40-85 mg / mL, and the molar ratio of Na2CO3 in the first step reaction to Na2CO3 in the second step reaction is 4-18:20-120.

7. The method for preparing the barrier, antibacterial and degradable cling film according to claim 1, characterized in that: The following steps are involved: 1) Dry the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and the fully biodegradable resin particles at 60-90°C for 7-14h, respectively, add the dried materials into a high-speed mixer at a speed of 2000-3000rpm, mix for 6-10min to obtain a mixture, and mix the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material and the fully biodegradable resin uniformly. The total weight of the fully biodegradable resin is 95-99.5 parts, and the weight of the Zn-Al hydrotalcite / ε-polylysine hydrochloride composite material is 0.5-5 parts; 2) adding the mixture obtained in 1) to the feed port of a twin-screw extruder at a feed rate of 80-180 g / min, setting the temperatures of seven zones from the feed port to the extruder head to 165-170 / 170-175 / 170-180 / 170-180 / 165-175 / 160-165 / 155-160°C, and the screw speed to 150-300 rpm; after melt blending in the twin-screw extruder, water cooling and air drying are performed and then the mixture is pelletized in a pelletizer to obtain a composite masterbatch; 3) Dry the obtained composite masterbatch at 60-90° C. for 7-14 h, add it into a single screw extruder for melt extrusion, and then blow it into a barrier, antibacterial and degradable cling film with a thickness of 25-35 μm through a film blowing machine.

8. The method for preparing the barrier, antibacterial and degradable cling film according to claim 7, characterized in that: The particle size of the fully biodegradable resin particles is 2-4 mm.

9. The method for preparing the barrier, antibacterial and degradable cling film according to claim 7, characterized in that: In step 3), the temperature of the single screw extruder head and the heating zone is set to: 160-165 / 170-180 / 160-170 / 155-160°C, and the screw speed is 30-50 rpm.

10. Use of the barrier, antibacterial and degradable cling film according to claim 1 in food preservation.

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