A fresh-keeping packaging bag, its preparation method and application

Abstract

The present invention discloses a fresh-keeping packaging bag, its preparation method and application, belonging to the technical field of packaging bags, and comprising the following raw materials in parts by weight: 70-90 parts of PLA, 10-30 parts of PBAT, 0.5-2 parts of Fe3O4-modified silver-loaded zirconium phosphate, 15-20 parts of modified MOF material, 0.5-2 parts of chain extender, 0.2-0.8 parts of antioxidant, and 0.2-0.6 parts of lubricant. The preparation method is as follows: After mixing the raw materials, melt extrusion, granulation, blown film are carried out, and then it is placed in a magnetic field environment at 80-100 °C for 6-12 h, and then cut and made into bags. The present invention uses Fe3O4-modified silver-loaded zirconium phosphate and modified MOF material as fillers, mixes them with PLA and PBAT, and cooperates with conventional additives to obtain a fresh-keeping packaging bag, which has biodegradability, and also has good barrier properties, mechanical properties and antibacterial properties, and has a good fresh-keeping effect on fruits and vegetables.

Description

Technical Field

[0001] The present invention belongs to the technical field of packaging bags, and particularly relates to a fresh-keeping packaging bag, a preparation method thereof and an application thereof. Background Art

[0002] At present, the fresh-keeping technologies for fruits and vegetables mainly include low-temperature storage, packaging with fresh-keeping bags (films), 1-MCP treatment, controlled atmosphere storage, etc. Among them, fresh-keeping packaging bags are the most commonly used. The fresh-keeping packaging bag regulates the contents of O2, CO2 and H20 in the surrounding environment of fruits and vegetables, inhibits the respiration of fruits and vegetables, delays the senescence of fruits and vegetables, and achieves the purpose of extending the shelf life.

[0003] Polyethylene (PE) is the most commonly used raw material for fresh-keeping packaging bags at present, which has a high water vapor barrier effect, but is difficult to degrade, and a large amount of use poses a huge threat to water and soil resources. Polylactic acid (PLA) is a green and environmentally friendly biodegradable polymer material with excellent mechanical properties, air permeability and carbon dioxide permeability. Polybutylene adipate / terephthalate (PBAT) is a thermoplastic biodegradable plastic with excellent ductility, impact resistance and film-forming properties, and is an excellent material for toughening PLA. However, the water vapor transmission rate of biodegradable materials such as PLA and PBAT is much greater than that of traditional PE. Therefore, when used for fruit and vegetable fresh-keeping, there will be more water loss compared with PE fresh-keeping materials, resulting in a decrease in color and fullness, and even spoilage. Summary of the Invention

[0004] The purpose of the present invention is to provide a fresh-keeping packaging bag, a preparation method thereof and an application thereof, so as to solve the problem of high water vapor transmission rate of fresh-keeping packaging bags made of existing PLA and PBAT materials.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A fresh-keeping packaging bag comprises the following raw materials in parts by weight:

[0007] 70-90 parts of PLA;

[0008] 10-30 parts of PBAT;

[0009] 0.5-2 parts of Fe3O4-modified silver-loaded zirconium phosphate;

[0010] 15-20 parts of modified MOF material;

[0011] 0.5-2 parts of chain extender;

[0012] 0.2-0.8 part of antioxidant;

[0013] 0.2-0.6 part of lubricant.

[0014] As a preferred technical solution of the present invention, the Fe3O4-modified silver-loaded zirconium phosphate is prepared through the following steps:

[0015] Mix the silver-loaded zirconium phosphate with deionized water, heat to 60 °C, add a mixed aqueous solution of ferric chloride hexahydrate and ferrous chloride tetrahydrate, stir evenly, then add ammonia water to adjust the pH value to 12, react at 80 °C for 0.5 - 1 h, filter, wash and dry the filter cake to obtain the Fe3O4-modified silver-loaded zirconium phosphate.

[0016] As a preferred technical solution of the present invention, in the above process, the dosage ratio of the silver-loaded zirconium phosphate, ferric chloride hexahydrate and ferrous chloride tetrahydrate is 30:1.16 - 3.48:1.7 - 5.1.

[0017] When the present invention prepares the Fe3O4-modified silver-loaded zirconium phosphate, the mass ratio of the silver-loaded zirconium phosphate and the iron salt is limited within a suitable range. If the dosage of the iron salt is too low, the Fe3O4-modified silver-loaded zirconium phosphate will have low magnetism and it will be difficult to perform directional arrangement in the magnetic field, thus unable to achieve a better gain purpose; if the dosage of the iron salt is too high, the silver-loaded zirconium phosphate will be over-coated, reducing the contact area between the silver-loaded zirconium phosphate and the bacteria, resulting in poor antibacterial effect.

[0018] As a preferred technical solution of the present invention, the mass fraction of the ammonia water is 25 - 28%.

[0019] As a preferred technical solution of the present invention, the silver-loaded zirconium phosphate is silver-loaded zirconium phosphate HTB-032, with an average particle size of 1.6 μm. It is a broad-spectrum antibacterial agent with long-lasting bactericidal and bacteriostatic effects, harmless to humans, non-irritating to the skin, and is a safe and non-toxic product.

[0020] As a preferred technical solution of the present invention, the modified MOF material is prepared through the following steps:

[0021] Add the MOF material into the ethanol solution, disperse it evenly by ultrasonic wave, add epoxy poly(ethylene glycol) silane, stir and react at 15 - 75 °C for 6 - 8 h, filter, wash and dry the filter cake to obtain the modified MOF material.

[0022] As a preferred technical solution of the present invention, in the above process, the mass ratio of the MOF material and the epoxy poly(ethylene glycol) silane is 10:0.5 - 2, and the dosage of the ethanol solution is 8 - 15 times the mass of the MOF material.

[0023] When preparing the modified MOF material in the present invention, the mass ratio of the MOF material to the epoxy group polyethylene glycol silane is limited within a suitable range. If the dosage of the epoxy group polyethylene glycol is too low, the improvement effect on the dispersibility of the MOF material in the matrix is not obvious, and it is difficult to fully play the role of reinforcement, etc. If the dosage of the epoxy group polyethylene glycol is too high, it will block the pore structure in the MOF material, reduce the moisture absorption effect of the MOF material on water vapor, and affect the water vapor transmission rate of the fresh-keeping packaging bag.

[0024] As a preferred technical solution of the present invention, the mass fraction of the ethanol solution is 60-95%.

[0025] As a preferred technical solution of the present invention, the MOF material is MIL-101(Cr) and / or MOF-303. Both MIL-101(Cr) and MOF-303 are metal-organic framework materials with rich internal pores and have good hygroscopicity.

[0026] As a preferred technical solution of the present invention, the molecular weight of the epoxy group polyethylene glycol silane (Silane-PEG-EPO) is 0.4-10K.

[0027] As a preferred technical solution of the present invention, the chain extender is one or two of a dioxazoline-based chain extender and an isocyanate-based chain extender with a functionality greater than 2.

[0028] As a preferred technical solution of the present invention, the dioxazoline-based chain extender is selected from at least one of 2,2-bis(2-oxazoline), 2,2'-(1,3-phenylene)-dioxazoline, and 2,2'-(1,4-phenylene)-dioxazoline.

[0029] As a preferred technical solution of the present invention, the isocyanate-based chain extender is selected from at least one of hexamethylene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate.

[0030] As a preferred technical solution of the present invention, the antioxidant is selected from at least one of antioxidant 1010, antioxidant 168, and antioxidant 264.

[0031] As a preferred technical solution of the present invention, the lubricant is at least one of zinc stearate, N,N'-ethylenebisstearamide, and polyethylene wax.

[0032] The preparation method of the above-mentioned fresh-keeping packaging bag includes the following steps:

[0033] S1. Dry PLA and PBAT at 60 °C for 10 h, then add them together with Fe3O4-modified silver-loaded zirconium phosphate, modified MOF material, chain extender, antioxidant and lubricant into a mixer. After mixing evenly, add them into a twin-screw extruder for melt blending, and then water-cool and pelletize to obtain pellets.

[0034] S2. Add the pellets into a single-screw blown film machine for extrusion and blowing to obtain a fresh-keeping film.

[0035] S3. Place the fresh-keeping film in an environment at 60 - 80 °C, then apply a magnetic field perpendicular to the fresh-keeping film with a magnetic field intensity of 0.1 - 0.5 T, keep it warm for 6 - 12 h, then remove the magnetic field, cut and bag the obtained fresh-keeping film to obtain a fresh-keeping packaging bag.

[0036] As a preferred technical solution of the present invention, the temperatures of the twin-screw extruder are 135 °C, 150 °C, 160 °C, 170 °C, 165 °C, 160 °C, 150 °C in sequence, and the screw speed is 100 r / min.

[0037] As a preferred technical solution of the present invention, the temperatures of each heating section of the blown film machine from the feed port to the die are 130 °C, 160 °C, 165 °C, 140 °C respectively, and the screw speed is 30 r / min.

[0038] Application of the above fresh-keeping packaging bag in fruit and vegetable fresh-keeping.

[0039] Advantages of the present invention:

[0040] 1. The present invention provides a fresh-keeping packaging bag, which uses Fe3O4-modified silver-loaded zirconium phosphate and modified MOF material as fillers, mixes them with PLA and PBAT, and cooperates with conventional additives, and is obtained by melt extrusion and blowing. It has good biodegradability, is environmentally friendly and healthy. In addition, it has good barrier properties, mechanical properties and antibacterial properties, and has a good fresh-keeping effect on fruits and vegetables.

[0041] 2. The present invention modifies iron oxide on the surface of sheet silver-loaded zirconium phosphate, and performs magnetic field induction during the preparation process of the fresh-keeping film, so that Fe3O4-modified silver-loaded zirconium phosphate is arranged regularly and directionally in the film, reducing the agglomeration problem of Fe3O4-modified silver-loaded zirconium phosphate, enabling it to give full play to the antibacterial effect and strengthening effect of silver-loaded zirconium phosphate. In addition, the uniformly distributed Fe3O4-modified silver-loaded zirconium phosphate forms an inorganic barrier layer in the film. Combining with the strong hygroscopicity of Fe3O4 itself, finally, the water vapor transmission rate of the fresh-keeping packaging bag is greatly reduced through the barrier effect and hygroscopic effect, effectively solving the problem of high water vapor transmission rate of the existing fresh-keeping packaging bags made of PLA and PBAT materials.

[0042] 3. The present invention modifies the highly hygroscopic MOF material with epoxy group polyethylene glycol silane. On the one hand, it improves the dispersion of the MOF material in the matrix, enables the MOF material to fully exert its hygroscopic effect, and further reduces the water vapor transmission rate of the fresh-keeping packaging bag. On the other hand, by means of the active epoxy groups in the epoxy group polyethylene glycol silane, it reacts with the hydroxyl and carboxyl groups of PLA and PBAT, improves the compatibility between PLA and PBAT, enhances the adhesion strength between interfaces, and realizes the improvement of mechanical properties. In addition, the flexible polyethylene glycol chain carried by the epoxy group polyethylene glycol silane also has a beneficial effect on the mechanical properties of the fresh-keeping packaging bag. Detailed implementation manners

[0043] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the following further details the present application in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0044] In the present application, the silver-loaded zirconium phosphate is silver-loaded zirconium phosphate HTB-032, with an average particle size of 1.6 μm, the grade of PLA is Lx-175, the melt index is 6.2 g / 10 min (210 °C / 2.16 kg), and the density is 1.25 g / cm 3 , the grade of PBAT is TH-801T, the melt index is 3.4 g / 10 min (190 °C / 2.16 kg), and the density is 1.24 g / cm 3 .

[0045] The following illustrates the technical solutions of the present application through specific examples and comparative examples.

[0046] Preparation Example 1

[0047] The preparation of Fe3O4-modified silver-loaded zirconium phosphate is as follows:

[0048] Mix 30 g of silver-loaded zirconium phosphate with 300 mL of deionized water and heat to 60 °C. Add a mixed solution composed of 1.16 g of ferric chloride hexahydrate, 1.7 g of ferrous chloride tetrahydrate and 50 mL of deionized water. After stirring evenly, add 25 wt% ammonia water to adjust the pH value to 12, react at 80 °C for 0.5 h, filter, wash and dry the filter cake to obtain Fe3O4-modified silver-loaded zirconium phosphate.

[0049] Preparation Example 2

[0050] The preparation of Fe3O4-modified silver-loaded zirconium phosphate is as follows:

[0051] Mix 30 g of silver-loaded zirconium phosphate with 300 mL of deionized water, heat the mixture to 60 °C, add a mixed solution composed of 2.32 g of ferric chloride hexahydrate, 3.4 g of ferrous chloride tetrahydrate and 100 mL of deionized water. After stirring evenly, add 28 wt% ammonia water to adjust the pH value to 12, react at 80 °C for 1 h, filter, wash and dry the filter cake to obtain silver-loaded zirconium phosphate modified with Fe3O4.

[0052] Preparation Example 3

[0053] The preparation of silver-loaded zirconium phosphate modified with Fe3O4 is as follows:

[0054] Mix 30 g of silver-loaded zirconium phosphate with 300 mL of deionized water, heat the mixture to 60 °C, add a mixed solution composed of 3.48 g of ferric chloride hexahydrate, 5.1 g of ferrous chloride tetrahydrate and 100 mL of deionized water. After stirring evenly, add 28 wt% ammonia water to adjust the pH value to 12, react at 80 °C for 1 h, filter, wash and dry the filter cake to obtain silver-loaded zirconium phosphate modified with Fe3O4.

[0055] Control Example 1

[0056] The preparation of silver-loaded zirconium phosphate modified with Fe3O4 is different from Preparation Example 1 only in that the amount of ferric chloride hexahydrate is adjusted from "1.16 g" to "0.58 g", and the amount of ferrous chloride tetrahydrate is adjusted from "1.7 g" to "0.85 g".

[0057] Control Example 2

[0058] The preparation of silver-loaded zirconium phosphate modified with Fe3O4 is different from Preparation Example 3 only in that the amount of ferric chloride hexahydrate is adjusted from "3.48 g" to "4.64 g", and the amount of ferrous chloride tetrahydrate is adjusted from "5.1 g" to "6.8 g".

[0059] Control Example 3

[0060] This control example is silver-loaded zirconium phosphate.

[0061] Preparation Example 4

[0062] The preparation of the modified MOF material is as follows:

[0063] Add 10 g of MIL-101(Cr) to 80 mL of 60 wt% ethanol solution, disperse it evenly by ultrasonic wave, add 0.5 g of epoxy poly(ethylene glycol) silane, stir and react at 15 °C for 6 h, filter, wash and dry the filter cake to obtain the modified MOF material, and the molecular weight of the epoxy poly(ethylene glycol) silane is 0.4K.

[0064] Preparation Example 5

[0065] The preparation of the modified MOF material is as follows:

[0066] 10 g of MIL-101(Cr) was added to 120 mL of 85 wt% ethanol solution, ultrasonically dispersed evenly, 1 g of epoxy poly(ethylene glycol) silane was added, and the mixture was stirred and reacted at 65 °C for 7 h, filtered, and the filter cake was washed and dried to obtain a modified MOF material. The epoxy poly(ethylene glycol) silane had a molecular weight of 5K.

[0067] Preparation Example 6

[0068] The preparation of the modified MOF material was carried out as follows:

[0069] 10 g of MIL-101(Cr) was added to 150 mL of 95 wt% ethanol solution, ultrasonically dispersed evenly, 2 g of epoxy poly(ethylene glycol) silane was added, and the mixture was stirred and reacted at 75 °C for 8 h, filtered, and the filter cake was washed and dried to obtain a modified MOF material. The epoxy poly(ethylene glycol) silane had a molecular weight of 10K.

[0070] Preparation Example 7

[0071] The preparation of the modified MOF material was the same as that of Preparation Example 4, except that an equal mass of MOF-303 was used to replace an equal mass of MIL-101(Cr).

[0072] Control Example 4

[0073] The preparation of the modified MOF material was the same as that of Preparation Example 4, except that the amount of epoxy poly(ethylene glycol) silane was adjusted from "0.5 g" to "0.3 g".

[0074] Control Example 5

[0075] The preparation of the modified MOF material was the same as that of Preparation Example 6, except that the amount of epoxy poly(ethylene glycol) silane was adjusted from "2 g" to "2.2 g".

[0076] Control Example 6

[0077] The preparation of the modified MOF material was the same as that of Preparation Example 4, except that an equal mass of 3-(2,3-epoxypropoxy)propyltrimethoxysilane was used to replace an equal mass of epoxy poly(ethylene glycol) silane.

[0078] Example 1

[0079] A fresh-keeping packaging bag comprises the following raw materials in parts by weight:

[0080] 70 parts of PLA;

[0081] 30 parts of PBAT;

[0082] 0.5 part of Fe3O4-modified silver-loaded zirconium phosphate of Preparation Example 1;

[0083] 15 parts of the modified MOF material of Preparation Example 4;

[0084] 0.5 part of chain extender;

[0085] 0.2 part of antioxidant 1010;

[0086] 0.2 part of zinc stearate.

[0087] The chain extender is composed of 2,2-bis(2-oxazoline) and hexamethylene diisocyanate in a mass ratio of 1:1.

[0088] The preparation method of the above fresh-keeping packaging bag includes the following steps:

[0089] S1. Dry PLA and PBAT at 60 °C for 10 h, then add them together with Fe3O4-modified silver-loaded zirconium phosphate, modified MOF material, chain extender, antioxidant and lubricant into a mixer. After mixing evenly, add them into a twin-screw extruder, melt and blend, and cool and pelletize to obtain pellets;

[0090] S2. Add the pellets into a single-screw blown film machine to extrude and blow film to obtain a 40-μm-thick fresh-keeping film;

[0091] S3. Place the fresh-keeping film in an environment at 60 °C, then apply a magnetic field perpendicular to the fresh-keeping film with a magnetic field strength of 0.1 T, keep it warm for 6 h, remove the magnetic field, cut and bag the obtained fresh-keeping film to obtain a fresh-keeping packaging bag.

[0092] The temperatures of the twin-screw extruder are 135 °C, 150 °C, 160 °C, 170 °C, 165 °C, 160 °C, 150 °C in sequence, and the screw speed is 100 r / min.

[0093] The temperatures of each heating section of the blown film machine from the feed inlet to the die are 130 °C, 160 °C, 165 °C, 140 °C respectively, and the screw speed is 30 r / min.

[0094] Example 2

[0095] A fresh-keeping packaging bag, comprising the following raw materials in parts by weight:

[0096] 80 parts of PLA;

[0097] 20 parts of PBAT;

[0098] 1 part of Fe3O4-modified silver-loaded zirconium phosphate of Preparation Example 1;

[0099] 18 parts of the modified MOF material of Preparation Example 4;

[0100] 1 part of chain extender;

[0101] 0.6 parts of antioxidant 1010;

[0102] 0.4 parts of zinc stearate.

[0103] The chain extender is composed of 2,2-bis(2-oxazoline) and hexamethylene diisocyanate in a mass ratio of 1:1.

[0104] The preparation method of the above fresh-keeping packaging bag includes the following steps:

[0105] S1. Dry PLA and PBAT at 60 °C for 10 h, then add them together with Fe3O4-modified silver-loaded zirconium phosphate, modified MOF material, chain extender, antioxidant and lubricant into a mixer. After mixing evenly, add them into a twin-screw extruder, melt-blend, cool and pelletize to obtain pellets;

[0106] S2. Add the pellets into a single-screw blown film machine to extrude and blow film to obtain a 40-μm-thick fresh-keeping film;

[0107] S3. Place the fresh-keeping film in an environment at 70 °C, then apply a magnetic field perpendicular to the fresh-keeping film with a magnetic field strength of 0.3 T, keep it warm for 8 h, then remove the magnetic field, cut and make bags for the obtained fresh-keeping film to obtain a fresh-keeping packaging bag.

[0108] The temperature settings of the twin-screw extruder and the blown film machine are the same as those in Preparation Example 1.

[0109] Example 3

[0110] A fresh-keeping packaging bag, comprising the following raw materials in parts by weight:

[0111] 90 parts of PLA;

[0112] 10 parts of PBAT;

[0113] 2 parts of Fe3O4-modified silver-loaded zirconium phosphate of Preparation Example 1;

[0114] 20 parts of the modified MOF material of Preparation Example 4;

[0115] 2 parts of chain extender;

[0116] 0.8 parts of antioxidant 1010;

[0117] 0.6 parts of zinc stearate.

[0118] The chain extender is composed of 2,2-bis(2-oxazoline) and hexamethylene diisocyanate in a mass ratio of 1:1.

[0119] The preparation method of the above fresh-keeping packaging bag includes the following steps:

[0120] S1. Dry PLA and PBAT at 60 °C for 10 h, then add them together with Fe3O4-modified silver-loaded zirconium phosphate, modified MOF material, chain extender, antioxidant and lubricant into a mixer. After mixing evenly, add them into a twin-screw extruder for melt blending, followed by water cooling and pelletizing to obtain pellets;

[0121] S2. Add the pellets into a single-screw blown film machine for extrusion and blowing to obtain a 40-μm-thick fresh-keeping film;

[0122] S3. Place the fresh-keeping film in an environment at 80 °C, then apply a magnetic field perpendicular to the fresh-keeping film with a magnetic field strength of 0.5 T for heat preservation treatment for 12 h. After that, remove the magnetic field, cut and bag the obtained fresh-keeping film to obtain a fresh-keeping packaging bag.

[0123] The temperature settings of the twin-screw extruder and the blown film machine are the same as those in Preparation Example 1.

[0124] Example 4

[0125] A fresh-keeping packaging bag, which is different from Example 1 only in that the Fe3O4-modified silver-loaded zirconium phosphate in Example 1 is replaced with the product prepared in Preparation Example 2.

[0126] Example 5

[0127] A fresh-keeping packaging bag, which is different from Example 1 only in that the Fe3O4-modified silver-loaded zirconium phosphate in Example 1 is replaced with the product prepared in Preparation Example 3.

[0128] Example 6

[0129] A fresh-keeping packaging bag, which is different from Example 1 only in that the modified MOF material in Example 1 is replaced with the product prepared in Preparation Example 5.

[0130] Example 7

[0131] A fresh-keeping packaging bag, which is different from Example 1 only in that the modified MOF material in Example 1 is replaced with the product prepared in Preparation Example 6.

[0132] Example 8

[0133] A fresh-keeping packaging bag, which is different from Example 1 only in that the modified MOF material in Example 1 is replaced with the product prepared in Preparation Example 7.

[0134] Comparative Example 1

[0135] A fresh-keeping packaging bag, which is different from Example 1 only in that the Fe3O4-modified silver-loaded zirconium phosphate in Example 1 is replaced with the product prepared in Comparative Example 1.

[0136] Comparative Example 2

[0137] A fresh-keeping packaging bag, compared with Example 5, the difference is only that the Fe3O4-modified silver-loaded zirconium phosphate in Example 5 is replaced with the product prepared in Comparative Example 2.

[0138] Comparative Example 3

[0139] A fresh-keeping packaging bag, compared with Example 1, the difference is only that the Fe3O4-modified silver-loaded zirconium phosphate in Example 1 is replaced with the substance in Comparative Example 3.

[0140] Comparative Example 4

[0141] A fresh-keeping packaging bag, compared with Example 1, the difference is only that the modified MOF material in Example 1 is replaced with the product prepared in Comparative Example 4.

[0142] Comparative Example 5

[0143] A fresh-keeping packaging bag, compared with Example 7, the difference is only that the modified MOF material in Example 7 is replaced with the product prepared in Comparative Example 5.

[0144] Comparative Example 6

[0145] A fresh-keeping packaging bag, compared with Example 1, the difference is only that the modified MOF material in Example 1 is replaced with the product prepared in Comparative Example 6.

[0146] Comparative Example 7

[0147] A fresh-keeping packaging bag, compared with Example 1, the preparation method of the fresh-keeping packaging bag is different. Without magnetic field treatment, the fresh-keeping film obtained in step S2 is directly cut and made into bags to obtain the fresh-keeping packaging bag.

[0148] The fresh-keeping films obtained in Examples 1 - 8 and Comparative Examples 1 - 7 were tested, and the test process is as follows:

[0149] Water vapor permeability test: According to the national standard GB / T1037 - 1988, the water vapor permeability of each group of fresh-keeping films was tested using a W3 / 031 type water vapor transmission rate tester from LanGuang Electromechanical Technology Co., Ltd. The test temperature was 38 °C and the humidity was 90%RH. Three parallel samples were tested for each group, and the water vapor transmission coefficient was calculated by Equation (1):

[0150] WVP = (△m × d) / (A × t × △p) (1)

[0151] In the formula: WVP is the water vapor transmission coefficient, with the unit of g·cm / (cm 2 •s·Pa); △m is the increased mass during the test time, with the unit of g; d is the sample thickness, with the unit of cm; A is the test area, with the unit of cm 2, where \(t\) is the test time in hours; \(\Delta p\) is the steam pressure difference on both sides of the sample in Pa;

[0152] Mechanical properties: Place the test specimens on a commercially available CMT4204 universal mechanical testing machine, and conduct tensile property tests on the specimens according to the national standard GB / T 1040 - 2003. The tensile speed is 250 mm / min, and 5 parallel samples are tested for each group of samples;

[0153] Antibacterial properties: The antibacterial properties of the films were tested by the plate colony counting method. Escherichia coli and Staphylococcus aureus were used as the test strains. Cut the fresh-keeping films of each group into squares with a side length of 50 mm, and at the same time cut the non-antibacterial PE film into squares with a side length of 40 mm as the covering film. Use a pipette to accurately aspirate 0.2 mL (about 10 5 cfu / mL) of the bacterial suspension and drop it onto the test pieces in each petri dish. Cover the covering film above the bacterial suspension and incubate in a constant temperature incubator for 24 h at a temperature of 37 °C and a relative humidity of 90%. After 24 h, elute the bacterial suspension with the eluent, and count the eluent by the plate counting method. 3 parallel samples are tested for each group of samples, and the results are averaged;

[0154] Fresh-keeping properties: Purchase fresh cherries as samples, put the cherries into the fresh-keeping packaging bags prepared from the fresh-keeping films of each group in equal amounts, seal them and store them in a 4 °C refrigerator. Take them out after 11 days and calculate the good fruit rate to evaluate the fresh-keeping effect;

[0155] The results are shown in Table 1:

[0156]

[0157] It can be seen from the analysis of the data in Table 1 that the water vapor transmission rate of the fresh-keeping films obtained in Examples 1 - 8 is 2.07 - 2.23×10 -14 g·cm / (cm 2 •s·Pa), the tensile strength is 37.4 - 43.2 MPa, the elongation at break is 536 - 674%, the antibacterial rate against Escherichia coli is ≥99.1%, the antibacterial rate against Staphylococcus aureus is ≥98.2%, and the good fruit rate of cherries after 11 days of fresh-keeping is 95.4 - 96.8%. This shows that the fresh-keeping films and fresh-keeping packaging bags prepared by the present invention have a low water vapor transmission rate, can slow down the water loss of fruits and vegetables, have a good fresh-keeping effect, and in addition, also have good mechanical properties and antibacterial properties.

[0158] More specifically, it can be seen from the test results of Example 1 and Comparative Example 1, Example 5 and Comparative Example 2 that when preparing Fe3O4-modified silver-loaded zirconium phosphate in the present invention, limiting the mass ratio of silver-loaded zirconium phosphate to iron salt within a suitable range is more conducive to obtaining a fresh-keeping film with good comprehensive performance; it can be seen from the test results of Example 1 and Comparative Example 3 that modifying the surface of flaky silver-loaded zirconium phosphate with magnetite can significantly reduce the water vapor transmission rate of the fresh-keeping film and improve the mechanical properties of the fresh-keeping film; it can be seen from the test results of Example 1 and Comparative Example 4, Example 7 and Comparative Example 5 that when preparing the modified MOF material, limiting the mass ratio of the MOF material to epoxy group polyethylene glycol silane within a suitable range can significantly reduce the water vapor transmission rate of the fresh-keeping film. It can be seen from the test results of Example 1 and Comparative Example 6 that when 3-(2,3-epoxypropoxy)propyltrimethoxysilane is used to replace an equal mass of epoxy group polyethylene glycol silane, the elongation at break of the finally obtained fresh-keeping film is significantly reduced. It can be seen from the test results of Example 1 and Comparative Example 7 that without magnetic field induction treatment during the preparation of the fresh-keeping film, the water vapor transmission rate and mechanical properties of the obtained fresh-keeping film are significantly deteriorated.

[0159] In summary, the present invention uses Fe3O4-modified silver-loaded zirconium phosphate and modified MOF material as fillers, mixes them with PLA and PBAT, and combines with conventional additives to obtain a fresh-keeping packaging bag through melt extrusion and blowing. It has good biodegradability, is environmentally friendly and healthy. In addition, it has good barrier properties, mechanical properties and antibacterial properties, and has a good fresh-keeping effect on fruits and vegetables.

[0160] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0161] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A fresh-keeping packaging bag, characterized in that: It includes the following raw materials in parts by weight: PLA 70-90 parts; PBAT 10-30 parts; 0.5-2 parts of Fe3O4 modified silver-loaded zirconium phosphate; 15-20 parts of modified MOF material; Chain extender 0.5-2 parts; Antioxidant 0.2-0.8 parts; Lubricant 0.2-0.6 parts; The modified MOF material is prepared by the following steps: The MOF material is added to an ethanol solution, dispersed uniformly by ultrasonication, epoxy polyethylene glycol silane is added, stirred and reacted at 15-75° C. for 6-8 hours, filtered, and the filter cake is washed and dried to obtain a modified MOF material; The MOF material is Cr-MIL-101 and / or MOF-303.

2. A fresh-keeping packaging bag according to claim 1, characterized in that: The Fe3O4 modified silver-loaded zirconium phosphate is prepared by the following steps: The silver-loaded zirconium phosphate was mixed with deionized water and heated to 60°C, and a mixed aqueous solution of ferric chloride hexahydrate and ferrous chloride tetrahydrate was added. After stirring evenly, ammonia water was added to adjust the pH value to 12, and the mixture was reacted at 80°C for 0.5-1h. The mixture was filtered, and the filter cake was washed and dried to obtain Fe3O4-modified silver-loaded zirconium phosphate.

3. A fresh-keeping packaging bag according to claim 2, characterized in that: The dosage ratio of silver-loaded zirconium phosphate, ferric chloride hexahydrate and ferrous chloride tetrahydrate is 30:1.16-3.48:1.7-5.

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4. A fresh-keeping packaging bag according to claim 1, characterized in that: The mass ratio of MOF material to epoxy polyethylene glycol silane is 10:0.5-2.

5. A fresh-keeping packaging bag according to claim 1, characterized in that: The molecular weight of the epoxy polyethylene glycol silane is 0.4-10K.

6. A method for preparing a fresh-keeping packaging bag, characterized in that: The method for preparing the fresh-keeping packaging bag according to any one of claims 1 to 5 comprises the following steps: S1, PLA and PBAT were dried at 60°C for 10 h, and then added into a mixer together with Fe3O4-modified silver-loaded zirconium phosphate, modified MOF material, chain extender, antioxidant and lubricant, mixed evenly and then added into a twin-screw extruder, melt blended, water-cooled and pelletized to obtain pellets; S2, adding the pellets into a single screw film blowing machine for extrusion and film blowing to obtain a fresh-keeping film; S3, placing the cling film in an environment of 60-80°C, then applying a magnetic field perpendicular to the cling film, and heat-treating for 6-12 hours, then removing the magnetic field, cutting and bagging the obtained cling film, and obtaining a fresh-keeping packaging bag.

7. The method for preparing a fresh-keeping packaging bag according to claim 6, characterized in that: The magnetic field strength is 0.1-0.5T.

8. Use of a fresh-keeping packaging bag as claimed in any one of claims 1 to 5 in preserving fruits and vegetables.

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