High barrier antibacterial food packaging film and preparation method thereof

Abstract

The present invention belongs to the technical field of packaging materials, and specifically relates to a high-barrier antibacterial food packaging film and a preparation method thereof. The high-barrier antibacterial food packaging film comprises, from the inside to the outside, a polyethylene antibacterial inner layer, a first nylon / polyethylene blended layer, an ethylene-vinyl alcohol barrier layer, a second nylon / polyethylene blended layer, and a polyethylene outer layer; wherein the polyethylene antibacterial inner layer is added with polystyrene antibacterial microspheres, and the polyethylene outer layer is added with nano titanium dioxide modified with isocyanatepropyltriethoxysilane. The high-barrier antibacterial food packaging film prepared by the present invention has excellent barrier properties under both low humidity and high humidity conditions, and at the same time has good antibacterial properties, heat sealing properties, high and low temperature stability and mechanical properties, and can extend the shelf life of food.

Description

Technical Field

[0001] The invention belongs to the technical field of packaging materials, and in particular relates to a high-barrier antibacterial food packaging film and a preparation method thereof. Background Art

[0002] Food packaging film is a film used to package food, which has the functions of protecting food and extending shelf life. Common food packaging materials include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinylidene chloride (PVDC), nylon (PA), ethylene-vinyl alcohol copolymer (EVOH), etc.

[0003] In recent years, as people pay more and more attention to food safety, the industry has higher and higher requirements for the barrier properties, organic solvent resistance, high and low temperature resistance, antibacterial properties, heat sealing properties and mechanical properties of food packaging films. Among various film materials, EVOH has better barrier properties than other packaging materials due to the strong bonding between the hydroxyl groups in its molecular structure and the hydrogen bonds between molecules. It also has good organic solvent resistance, heat sealing and mechanical properties; but its hydrophilicity and hygroscopicity are high. In a high humidity environment, the bonding ability of hydrogen bonds in the EVOH molecular structure decreases, and the activity of chain segments increases, which will reduce its barrier properties, which to a certain extent limits its application range.

[0004] In order to improve the barrier properties of EVOH film under different environments, the prior art generally adopts a multi-layer film composite method. For example, patent CN117565499A provides an antibacterial high-strength high-barrier tear-resistant food packaging film, including a polyethylene outer layer, a first maleic anhydride high-strength adhesive layer, a high-barrier first polyamide layer, an ethylene-vinyl alcohol copolymer layer, a high-barrier second polyamide layer, a second maleic anhydride high-strength adhesive layer, and a polyethylene antibacterial inner layer. The invention improves the barrier properties of the packaging film under high humidity conditions by setting a polyamide layer, and bonds the polyethylene layer and the polyamide layer by setting a maleic anhydride high-strength adhesive layer; however, the maleic anhydride grafted modified polyethylene as the maleic anhydride high-strength adhesive layer has a low melting point, resulting in poor high temperature resistance of the food packaging film. In addition, the preparation of silver / Prussian blue loaded metal organic framework and chitosan-tannic acid gel as a composite antibacterial agent greatly increases the product cost, and the chitosan-tannic acid gel has good hydrophilicity, which is not conducive to improving the barrier properties of the composite film layer.

[0005] Patent CN117400610A discloses an ultra-high barrier multilayer co-extruded film for food packaging, including an upper surface layer, a core layer and a lower surface layer arranged in order from top to bottom, wherein the upper surface layer is composed of ethylene-vinyl alcohol copolymer, nylon 6, modified graphene and additives, the core layer is composed of ethylene-vinyl alcohol copolymer, modified polypropylene, modified graphene and additives, and the lower surface layer is composed of polyvinylidene fluoride, modified polypropylene, modified composite microspheres and additives. The invention improves the compatibility of graphene and composite microspheres by modifying them, and improves the hydrophilicity and air permeability of polypropylene by modifying polypropylene with maleic anhydride; however, the improvement of the hydrophilicity of the modified polypropylene leads to the improvement of the hydrophilicity of the lower surface layer and the core layer. As the use time of the film layer increases, the ethylene-vinyl alcohol copolymer of the core layer and the upper surface layer will be in high humidity conditions, thereby causing the barrier property of the film layer to decrease.

[0006] Therefore, it is necessary to study the composite properties of various materials of EVOH film in order to obtain a food packaging film with high barrier properties, antibacterial properties, high temperature stability and mechanical properties. Summary of the invention

[0007] In view of the deficiencies in the prior art, the object of the present invention is to provide a high-barrier antibacterial food packaging film, which has excellent barrier properties under both low and high humidity conditions, and at the same time has good antibacterial properties, high temperature stability and mechanical properties, and can extend the shelf life of food. The present invention also provides a simple and easy preparation method thereof.

[0008] The high barrier antibacterial food packaging film of the present invention comprises, from inside to outside, a polyethylene antibacterial inner layer, a first nylon / polyethylene blended layer, an ethylene-vinyl alcohol barrier layer, a second nylon / polyethylene blended layer, and a polyethylene outer layer;

[0009] The polyethylene antibacterial inner layer includes metallocene low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and polystyrene antibacterial microspheres;

[0010] The first nylon / polyethylene antibacterial blend layer and the second nylon / polyethylene antibacterial blend layer include nylon, linear low-density polyethylene, and maleic anhydride grafted polyethylene;

[0011] The ethylene-vinyl alcohol barrier layer comprises ethylene-vinyl alcohol copolymer;

[0012] The polyethylene outer layer includes metallocene low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and modified titanium dioxide;

[0013] Wherein, the preparation method of polystyrene antibacterial microspheres is as follows:

[0014] Place carbon nanotubes in concentrated acid solution, heat under reflux for 2-4 hours, separate solids, wash, and dry to obtain acidified carbon nanotubes; dissolve zinc acetate in anhydrous ethanol, add sodium hydroxide, heat under reflux for 1-2 hours to obtain zinc oxide sol; disperse the acidified carbon nanotubes in zinc oxide sol, heat under reflux for 1-2 hours, separate solids, wash, and dry to obtain antibacterial carbon nanotubes; dissolve polystyrene in ethyl acetate, add antibacterial carbon nanotubes and vanillin, disperse evenly, then slowly add to an aqueous solution containing a wetting dispersant, stir until a suspension is formed, separate solids, wash, and dry to obtain polystyrene antibacterial microspheres.

[0015] Preferably, the diameter of the carbon nanotubes is 1-3 nm and the length is 5-50 μm; the concentrated acid solution is concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1: (2-3), and the concentration of concentrated nitric acid and concentrated sulfuric acid is not less than 70wt.%; the mass volume ratio of the carbon nanotubes and the concentrated acid solution is 1g: (20-30)m1.

[0016] Preferably, the mass volume ratio of zinc acetate to anhydrous ethanol is 1 g: (20-30) ml; and the amount of sodium hydroxide added is 30-40% of the mass of zinc acetate.

[0017] Preferably, the mass ratio of carbon nanotubes to zinc acetate is 1:(1-1.2).

[0018] Preferably, the mass ratio of polystyrene, antibacterial carbon nanotubes and vanillin is 100:(1-2):(0.2-0.5); the mass volume ratio of polystyrene and ethyl acetate is (0.2-0.5) g:1 ml; in the aqueous solution containing the wetting dispersant, the concentration of the wetting dispersant is 1-2 wt.%; and the mass ratio of polystyrene and the wetting dispersant is 100:(3-5).

[0019] Preferably, the wetting and dispersing agent is polyethylene glycol, which functions to reduce the liquid-liquid and liquid-solid interfacial tension.

[0020] The present invention adopts concentrated acid to treat carbon nanotubes, the purpose is to introduce functional groups such as hydroxyl and carboxyl groups on the surface thereof, provide reactive sites for subsequent reaction with zinc oxide sol, thereby loading zinc oxide on the surface of carbon nanotubes, and giving carbon nanotubes antibacterial function. Then, polystyrene antibacterial microspheres are prepared by phase transition method, antibacterial carbon nanotubes and vanillin with the same antibacterial effect are dispersed in polystyrene organic solution, and then slowly added dropwise to polyethylene glycol aqueous solution, polyethylene glycol as a wetting dispersant, can significantly reduce liquid-liquid, liquid-solid interfacial tension, under high-speed stirring, water-insoluble polystyrene wraps antibacterial carbon nanotubes and vanillin to form polystyrene antibacterial microspheres, thereby carbon nanotubes loaded with zinc oxide and vanillin are uniformly dispersed and wrapped in polystyrene, not only improving the compatibility and stability of antibacterial carbon nanotubes and vanillin in the film layer, but also making zinc oxide antibacterial agent and vanillin have sustained release effect, improving the antibacterial stability and durability of food packaging film, thereby extending the shelf life of food. In addition, the addition of vanillin can make up for the lack of antibacterial effect of zinc oxide as a single antibacterial agent, greatly improving the antibacterial properties of food packaging film.

[0021] In the present invention, the linear low-density polyethylene has a melt index of 1 g / 10 min at 190°C and 2.16 kg, and a density of 0.92 g / cm 3 , preferably 2045G produced by Dow Chemical (China) Co., Ltd.;

[0022] The metallocene low-density polyethylene has a melt index of 0.5 g / 10 min at 190° C. and 2.16 kg, and a density of 0.863 g / cm 3 , preferably 8180 produced by Dow Chemical (China) Co., Ltd.;

[0023] The high-density polyethylene has a melt index of 20 g / 10 min at 190° C. and 2.16 kg, and a density of 0.954 g / cm 3 , preferably DMDA-8920 produced by Dushanzi Petrochemical Company;

[0024] The nylon is nylon 6;

[0025] The molar percentage of ethylene copolymer in the ethylene-vinyl alcohol copolymer is 32-38%.

[0026] In the present invention, the thickness percentages of the polyethylene antibacterial inner layer, the first nylon / polyethylene blended layer, the ethylene-vinyl alcohol barrier layer, the second nylon / polyethylene blended layer, and the polyethylene outer layer are: 20-25%, 10-15%, 20-25%, 10-15%, and 30-35%. The total thickness of the food packaging film product is between 25-200 μm, and food packaging films of different thicknesses can be produced according to product requirements.

[0027] The polyethylene antibacterial inner layer includes 15-20wt.% of metallocene low-density polyethylene, 50-60wt.% of linear low-density polyethylene, 15-20wt.% of high-density polyethylene, and 10-15wt.% of polystyrene antibacterial microspheres.

[0028] The first nylon / polyethylene blend layer and the second nylon / polyethylene blend layer include 62-75 wt.% of nylon, 23-35 wt.% of linear low-density polyethylene, and 1-3 wt.% of maleic anhydride grafted polyethylene.

[0029] The polyethylene outer layer comprises 15-20 wt.% of metallocene low-density polyethylene, 55-60 wt.% of linear low-density polyethylene, 18-24 wt.% of high-density polyethylene, and 1-3 wt.% of modified titanium dioxide.

[0030] Preferably, the modified titanium dioxide is nano titanium dioxide modified with isocyanatepropyltriethoxysilane, and the preparation method is as follows:

[0031] Add nano titanium dioxide to N,N-dimethylformamide, fully stir at 60-70°C to form a suspension, then add isocyanatepropyltriethoxysilane and a catalyst, stir and react for 2-4 hours, separate the solid, wash, and dry to obtain modified titanium dioxide.

[0032] The catalyst is dibutyltin dilaurate or triethylenediamine, and the amount of the catalyst added is 0.01-0.05% of the mass of the nano-titanium dioxide; the mass ratio of nano-titanium dioxide to triethoxypropyl isocyanate silane is 1: (1.5-2); the mass volume ratio of nano-titanium dioxide to N,N-dimethylformamide is 1g: (20-30) ml.

[0033] The present invention uses isocyanate propyl triethoxysilane as a modification aid, and the isocyanate group contained in it can react chemically with the hydroxyl group on the surface of the nano silicon dioxide particles to form a stable covalent chemical bond instead of a hydrogen bond. At the same time, the present invention uses N,N-dimethylformamide as a dispersing solvent, which can provide a good suspension effect for inorganic titanium dioxide and siloxane and will not react with siloxane in any way, so that the limited hydroxyl groups of the inorganic titanium dioxide nanoparticles can be fully reacted with isocyanate propyl triethoxysilane to form a modification with the maximum grafting rate, ensuring that the role of the nano titanium dioxide particles in the system is maximized.

[0034] The present invention uses the EVOH film as the middle film layer, giving full play to its high barrier effect on gas and water vapor, and at the same time, in order to avoid the reduction of its barrier property under high humidity conditions, nylon / polyethylene blended layers are arranged on both sides of the EVOH film, and the hydrophobicity and low moisture permeability of nylon are used to isolate the EVOH film from contact with water, so that the EVOH film always maintains excellent barrier properties, and nylon and EVOH have good compatibility and good adhesion when co-extruded into film. In addition, adding a certain amount of polyethylene to the nylon / polyethylene blended layer can improve the compatibility of the nylon / polyethylene blended layer and the polyethylene outer layer, enhance the adhesion between the film layers, and thus reduce the setting of the adhesive layer.

[0035] The polyethylene antibacterial inner layer is used as the food contact layer. In order to improve its antibacterial stability and durability, the present invention uses zinc oxide, carbon nanotubes and vanillin as raw materials to prepare polystyrene antibacterial microspheres, wherein the synergistic effect of zinc oxide and vanillin can greatly improve the antibacterial property of the food packaging film, avoiding the insufficient antibacterial effect of a single antibacterial agent; the addition of carbon nanotubes can provide carriers for zinc oxide and vanillin on the one hand, and on the other hand, be embedded in the polymer molecular chain, thereby improving the barrier property, mechanical properties, thermal stability and antistatic property of the polyethylene antibacterial inner layer; the polystyrene microspheres can wrap the antibacterial agent, improve the compatibility of the antibacterial agent in the polyethylene layer, and realize the slow release of the antibacterial agent, thereby improving the antibacterial stability and durability of the food packaging film.

[0036] Adding nano titanium dioxide modified with isocyanatepropyltriethoxysilane to the polyethylene outer layer can graft the nano titanium dioxide onto siloxane through chemical bonds, greatly improving its compatibility and dispersion uniformity in the polyethylene resin. The addition of modified titanium dioxide can give the polyethylene outer layer antioxidant and antibacterial properties and improve the high temperature resistance of the polyethylene outer layer.

[0037] The method for preparing the high barrier antibacterial food packaging film of the present invention comprises the following steps:

[0038] The raw materials of the polyethylene antibacterial inner layer, the first nylon / polyethylene blended layer, the ethylene-vinyl alcohol barrier layer, the second nylon / polyethylene blended layer, and the polyethylene outer layer are respectively placed in the five feed hoppers of a five-layer co-extrusion film blowing machine, and the film is blown by melt extrusion to obtain a high barrier antibacterial food packaging film.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention uses EVOH film as the middle film layer, and arranges nylon / polyethylene blended layers and polyethylene functional layers on both sides of the EVOH film, which not only greatly improves the barrier properties of the multilayer film to oxygen and water vapor, composite peel strength, environmental resistance and fresh-keeping storage period, but also gives the multilayer film excellent high temperature resistance and antibacterial durability;

[0041] (2) The present invention utilizes the hydrophobicity and low moisture permeability of nylon to isolate the EVOH film from contact with water, and adds a certain amount of polyethylene to the nylon / polyethylene blend layer, which can improve the compatibility of the nylon / polyethylene blend layer with the polyethylene outer layer, enhance the adhesion between the film layers, and thus reduce the setting of the adhesive layer;

[0042] (3) The present invention uses zinc oxide, carbon nanotubes and vanillin as raw materials to prepare polystyrene antibacterial microspheres, wherein the synergistic effect of zinc oxide and vanillin can greatly improve the antibacterial property of the food packaging film, avoiding the insufficient antibacterial effect of a single antibacterial agent; the addition of carbon nanotubes can provide carriers for zinc oxide and vanillin on the one hand, and on the other hand, be embedded in the polymer molecular chain, thereby improving the barrier property, mechanical properties, thermal stability and antistatic property of the polyethylene antibacterial inner layer; the polystyrene microspheres can wrap the antibacterial agent, improve the compatibility of the antibacterial agent in the polyethylene layer, and realize the slow release of the antibacterial agent, thereby improving the antibacterial stability and durability of the food packaging film;

[0043] (4) The present invention adds nano titanium dioxide modified with isocyanatepropyltriethoxysilane to the polyethylene outer layer, so that the nano titanium dioxide can be grafted onto the siloxane through chemical bonds, greatly improving its compatibility and dispersion uniformity in the polyethylene resin. The addition of modified titanium dioxide can give the polyethylene outer layer antioxidant and antibacterial properties, thereby improving the high temperature resistance of the polyethylene outer layer.

[0044] (5) The polyethylene surface layer of the present invention is blended with linear low-density polyethylene, metallocene polyethylene and high-density polyethylene, which improves the tensile strength and crystallinity of the polyethylene surface layer. DETAILED DESCRIPTION

[0045] The technical scheme of the present invention is further described below in conjunction with the examples. Unless otherwise specified, all raw materials used in the examples are commercially available.

[0046] Some of the raw materials used in the examples are described as follows:

[0047] Linear low-density polyethylene, 2045G produced by Dow Chemical Company;

[0048] Metallocene low-density polyethylene, 8180 produced by Dow Chemical Company;

[0049] High-density polyethylene, DMDA-8920 produced by Dushanzi Petrochemical Company;

[0050] Nylon 6, CM1056 produced by Toray Industries, Ltd. of Japan;

[0051] Ethylene-vinyl alcohol copolymer, C109B produced by Kuraray Co., Ltd. of Japan;

[0052] Maleic anhydride grafted polyethylene, PE1040 produced by ExxonMobil.

[0053] Example 1

[0054] A high barrier antibacterial food packaging film, comprising, from inside to outside, a polyethylene antibacterial inner layer, a first nylon / polyethylene blended layer, an ethylene-vinyl alcohol barrier layer, a second nylon / polyethylene blended layer, and a polyethylene outer layer, wherein the thickness percentages of each layer are 20%, 10%, 25%, 10%, and 35% in sequence;

[0055] The polyethylene antibacterial inner layer includes 15wt.% of metallocene low-density polyethylene, 60wt.% of linear low-density polyethylene, 15wt.% of high-density polyethylene, and 10wt.% of polystyrene antibacterial microspheres;

[0056] The first nylon / polyethylene blend layer and the second nylon / polyethylene blend layer include 75 wt.% of nylon 6, 24 wt.% of linear low-density polyethylene, and 1 wt.% of maleic anhydride grafted polyethylene;

[0057] The ethylene-vinyl alcohol barrier layer includes 100 wt.% of ethylene-vinyl alcohol copolymer;

[0058] The polyethylene outer layer includes 15 wt.% of metallocene low-density polyethylene, 60 wt.% of linear low-density polyethylene, 24 wt.% of high-density polyethylene, and 1 wt.% of modified titanium dioxide.

[0059] Wherein, the preparation method of polystyrene antibacterial microspheres is as follows:

[0060] The carbon nanotubes (diameter 1-3nm, length 5-50μm) were placed in a mixture of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:2, the mass volume ratio of the carbon nanotubes to the concentrated acid solution was 1g:25ml, and the mixture was heated at 110℃ for 3h. The solid was separated, washed, and dried to obtain acidified carbon nanotubes. Zinc acetate was dissolved in anhydrous ethanol, the mass volume ratio of zinc acetate to anhydrous ethanol was 1g:25ml, and then sodium hydroxide with a mass ratio of 40% of the mass of zinc acetate was added, and the mixture was heated at 90℃ for 2h to obtain zinc oxide sol. The acidified carbon nanotubes were dispersed in the zinc oxide sol, the mass ratio of the carbon nanotubes to zinc acetate was The mixture was heated at 100°C under reflux for 2 hours, the solid was separated, washed, and dried to obtain antibacterial carbon nanotubes; polystyrene was dissolved in ethyl acetate, the mass volume ratio of polystyrene and ethyl acetate was 0.3 g:1 ml, antibacterial carbon nanotubes and vanillin were added, the mass ratio of polystyrene, antibacterial carbon nanotubes, and vanillin was 100:1:0.2, and after uniform dispersion, they were slowly added into an aqueous solution with a polyethylene glycol concentration of 2 wt.%, the mass ratio of polystyrene and polyethylene glycol was 100:3, stirred to form a suspension, the solid was separated, washed, and dried to obtain polystyrene antibacterial microspheres.

[0061] The preparation method of modified titanium dioxide is as follows:

[0062] Add nano titanium dioxide to N,N-dimethylformamide, the mass volume ratio of nano titanium dioxide and N,N-dimethylformamide is 1g:20ml, stir thoroughly at 60°C to form a suspension, then add isocyanate propyl triethoxysilane and triethylenediamine accounting for 0.05% of the mass of nano titanium dioxide, the mass ratio of nano titanium dioxide and isocyanate propyl triethoxysilane is 1:1.5, stir the reaction for 2h, separate the solid, wash, and dry to obtain modified titanium dioxide.

[0063] The preparation method of high barrier antibacterial food packaging film is as follows:

[0064] The raw materials of the polyethylene antibacterial inner layer, the first nylon / polyethylene blended layer, the ethylene-vinyl alcohol barrier layer, the second nylon / polyethylene blended layer, and the polyethylene outer layer are respectively placed in the five feed hoppers of a five-layer co-extrusion film blowing machine, and the film is blown by melt extrusion to obtain a high barrier antibacterial food packaging film.

[0065] Example 2

[0066] A high barrier antibacterial food packaging film, comprising, from inside to outside, a polyethylene antibacterial inner layer, a first nylon / polyethylene blended layer, an ethylene-vinyl alcohol barrier layer, a second nylon / polyethylene blended layer, and a polyethylene outer layer, wherein the thickness percentages of each layer are 20%, 15%, 20%, 15%, and 30% in sequence;

[0067] The polyethylene antibacterial inner layer includes 15wt.% of metallocene low-density polyethylene, 53wt.% of linear low-density polyethylene, 20wt.% of high-density polyethylene, and 12wt.% of polystyrene antibacterial microspheres;

[0068] The first nylon / polyethylene blend layer and the second nylon / polyethylene blend layer include 75 wt.% of nylon 6, 23 wt.% of linear low-density polyethylene, and 2 wt.% of maleic anhydride grafted polyethylene;

[0069] The ethylene-vinyl alcohol barrier layer includes 100 wt.% of ethylene-vinyl alcohol copolymer;

[0070] The polyethylene outer layer includes 20 wt.% of metallocene low-density polyethylene, 60 wt.% of linear low-density polyethylene, 18 wt.% of high-density polyethylene, and 2 wt.% of modified titanium dioxide.

[0071] Wherein, the preparation method of polystyrene antibacterial microspheres is as follows:

[0072] The carbon nanotubes (diameter 1-3nm, length 5-50μm) were placed in a mixture of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3, the mass volume ratio of the carbon nanotubes to the concentrated acid solution was 1g: 30ml, and the mixture was heated at 110℃ for 2h, the solid was separated, washed, and dried to obtain acidified carbon nanotubes; zinc acetate was dissolved in anhydrous ethanol, the mass volume ratio of zinc acetate to anhydrous ethanol was 1g: 30ml, and then sodium hydroxide with a mass ratio of 35% of the zinc acetate was added, and the mixture was heated at 90℃ for 1h to obtain zinc oxide sol; the acidified carbon nanotubes were dispersed in the zinc oxide sol, the mass ratio of the carbon nanotubes to zinc acetate was 1: 1.1, and the mixture was heated at 100℃ for 1.5h, the solid was separated, washed, and dried to obtain Antibacterial carbon nanotubes; dissolve polystyrene in ethyl acetate, the mass volume ratio of polystyrene and ethyl acetate is 0.2g:1m1, add antibacterial carbon nanotubes and vanillin, the mass ratio of polystyrene, antibacterial carbon nanotubes and vanillin is 100:1.5:0.4, after uniform dispersion, slowly add into an aqueous solution of polyethylene glycol concentration of 1.5wt.%, the mass ratio of polystyrene and polyethylene glycol is 100:5, stir to form a suspension, separate the solid, wash and dry to obtain polystyrene antibacterial microspheres.

[0073] The preparation method of modified titanium dioxide is as follows:

[0074] Add nano titanium dioxide to N,N-dimethylformamide, the mass volume ratio of nano titanium dioxide and N,N-dimethylformamide is 1g:30ml, and stir thoroughly at 70°C to form a suspension, then add isocyanate propyl triethoxysilane and triethylenediamine accounting for 0.02% of the mass of nano titanium dioxide, the mass ratio of nano titanium dioxide and isocyanate propyl triethoxysilane is 1:1.8, stir the reaction for 3h, separate the solid, wash, and dry to obtain modified titanium dioxide.

[0075] The preparation method of high barrier antibacterial food packaging film is as follows:

[0076] The raw materials of the polyethylene antibacterial inner layer, the first nylon / polyethylene blended layer, the ethylene-vinyl alcohol barrier layer, the second nylon / polyethylene blended layer, and the polyethylene outer layer are respectively placed in the five feed hoppers of a five-layer co-extrusion film blowing machine, and the film is blown by melt extrusion to obtain a high barrier antibacterial food packaging film.

[0077] Example 3

[0078] A high barrier antibacterial food packaging film, comprising, from inside to outside, a polyethylene antibacterial inner layer, a first nylon / polyethylene blended layer, an ethylene-vinyl alcohol barrier layer, a second nylon / polyethylene blended layer, and a polyethylene outer layer, wherein the thickness percentages of each layer are 25%, 12%, 21%, 12%, and 30% in sequence;

[0079] The polyethylene antibacterial inner layer includes 20wt.% of metallocene low-density polyethylene, 50wt.% of linear low-density polyethylene, 15wt.% of high-density polyethylene, and 15wt.% of polystyrene antibacterial microspheres;

[0080] The first nylon / polyethylene blend layer and the second nylon / polyethylene blend layer include 62 wt.% of nylon 6, 35 wt.% of linear low-density polyethylene, and 3 wt.% of maleic anhydride grafted polyethylene;

[0081] The ethylene-vinyl alcohol barrier layer includes 100 wt.% of ethylene-vinyl alcohol copolymer;

[0082] The polyethylene outer layer includes 20 wt.% of metallocene low-density polyethylene, 55 wt.% of linear low-density polyethylene, 22 wt.% of high-density polyethylene, and 3 wt.% of modified titanium dioxide.

[0083] Wherein, the preparation method of polystyrene antibacterial microspheres is as follows:

[0084] The carbon nanotubes (diameter 1-3nm, length 5-50μm) were placed in a mixture of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:2.5, the mass volume ratio of the carbon nanotubes to the concentrated acid solution was 1g:20ml, and the mixture was heated at 110℃ for 4h. The solid was separated, washed, and dried to obtain acidified carbon nanotubes. Zinc acetate was dissolved in anhydrous ethanol, the mass volume ratio of zinc acetate to anhydrous ethanol was 1g:20ml, and sodium hydroxide with a mass ratio of 30% of the mass of zinc acetate was added, and the mixture was heated at 90℃ for 1.5h to obtain zinc oxide sol. The acidified carbon nanotubes were dispersed in the zinc oxide sol. The mass ratio is 1:1, heated to reflux at 100°C for 1h, the solid is separated, washed, and dried to obtain antibacterial carbon nanotubes; polystyrene is dissolved in ethyl acetate, the mass volume ratio of polystyrene and ethyl acetate is 0.5g:1m1, antibacterial carbon nanotubes and vanillin are added, the mass ratio of polystyrene, antibacterial carbon nanotubes, and vanillin is 100:2:0.5, after uniform dispersion, slowly add to an aqueous solution with a polyethylene glycol concentration of 1wt.%, the mass ratio of polystyrene and polyethylene glycol is 100:4, stir to form a suspension, separate the solid, wash, and dry to obtain polystyrene antibacterial microspheres.

[0085] The preparation method of modified titanium dioxide is as follows:

[0086] Add nano titanium dioxide to N,N-dimethylformamide, the mass volume ratio of nano titanium dioxide and N,N-dimethylformamide is 1g:25ml, and stir thoroughly at 65°C to form a suspension, then add isocyanatepropyltriethoxysilane and dibutyltin dilaurate accounting for 0.01% of the mass of nano titanium dioxide, the mass ratio of nano titanium dioxide and isocyanatepropyltriethoxysilane is 1:2, stir the reaction for 4h, separate the solid, wash, and dry to obtain modified titanium dioxide.

[0087] The preparation method of high barrier antibacterial food packaging film is as follows:

[0088] The raw materials of the polyethylene antibacterial inner layer, the first nylon / polyethylene blended layer, the ethylene-vinyl alcohol barrier layer, the second nylon / polyethylene blended layer, and the polyethylene outer layer are respectively placed in the five feed hoppers of a five-layer co-extrusion film blowing machine, and the film is blown by melt extrusion to obtain a high barrier antibacterial food packaging film.

[0089] Comparative Example 1

[0090] The only difference between this comparative example and Example 1 is that the polystyrene antibacterial microspheres in the polyethylene antibacterial inner layer are replaced with polystyrene, antibacterial carbon nanotubes and vanillin in an equal mass ratio.

[0091] Comparative Example 2

[0092] The only difference between this comparative example and Example 1 is that vanillin is not added when preparing the polystyrene antibacterial microspheres.

[0093] Comparative Example 3

[0094] The only difference between this comparative example and Example 1 is that the linear low-density polyethylene is replaced with an equal mass of nylon 6 in the first nylon / polyethylene blended layer and the second nylon / polyethylene blended layer.

[0095] During co-extrusion blown film, due to the poor compatibility of nylon and polyethylene, the adhesion between the film layers is poor, and the obtained 5-layer co-extruded film is difficult to form.

[0096] Comparative Example 4

[0097] The difference between this comparative example and Example 1 is that, when preparing the modified titanium dioxide, isocyanatepropyltriethoxysilane is replaced by γ-methacryloxypropyltrimethoxysilane, and the catalyst triethylenediamine is not added.

[0098] Comparative Example 5

[0099] The only difference between this comparative example and Example 1 is that in the polyethylene outer layer, the modified titanium dioxide is replaced by an equal mass of linear low-density polyethylene.

[0100] The food packaging films prepared in the embodiments and comparative examples were subjected to performance tests, and the tests were performed after being placed for 48 hours under normal indoor environment and high temperature and high humidity conditions (temperature 100°C, humidity 80%); wherein, the oxygen permeability was tested with reference to the standard GB / T1038-2000; the water vapor permeability was tested with reference to the standard GB / T1037-1988; the antibacterial rate was tested with reference to the standard GB / T31402-2015; and the tensile strength was tested with reference to the standard GB / T1040.3-2006.

[0101] The test results are shown in Table 1.

[0102] Table 1 Test results of food packaging films performance of various embodiments and comparative examples

[0103] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 4 Comparative Example 5 <![CDATA[Oxygen transmission rate (at room temperature, humidity 20%), cm 3 / m 2 ·24 h·0.1 MPa]]> 0.23 0.25 0.24 0.45 0.24 0.26 0.53 <![CDATA[Water vapor transmission rate (at room temperature, humidity 20%), g / m 2 ·24h]]> 0.04 0.05 0.04 0.08 0.04 0.06 0.14 <![CDATA[Oxygen Permeability (100°C, 90% Humidity), cm 3 / m 2 ·24h·0.1MPa]]> 0.39 0.33 0.31 0.60 0.41 0.52 0.79 <![CDATA[Water vapor transmission rate (100 °C, 90% humidity), g / m 2 ·24 h]]> 0.10 0.12 0.10 0.24 0.10 0.16 0.27 Escherichia coli inhibition rate, % 99.7 99.8 100 99.3 92.3 98.5 97.2 Inhibition rate of Staphylococcus aureus, % 99.5 99.6 100 98.9 91.6 97.2 96.7 Escherichia coli inhibition rate (after 30 days of immersion), % 99.5 99.6 99.9 82.5 92.0 95.2 96.9 Inhibition rate of Staphylococcus aureus (after 30 days of immersion), % 99.4 99.5 99.8 80.2 91.1 94.0 96.2 Tensile strength, MPa 34.6 35.4 35.7 32.8 34.5 34.2 35.8

[0104] As can be seen from Table 1, in Comparative Example 1, antibacterial carbon nanotubes and vanillin are directly incorporated into the polyethylene system. Due to the poor compatibility of antibacterial carbon nanotubes with polyethylene, they are unevenly dispersed and easily precipitated, which affects the mechanical properties and barrier properties of the film, and the antibacterial durability is also greatly reduced. Comparative Example 2 does not add the organic antibacterial agent vanillin, which has little effect on the mechanical properties and barrier properties of the film, but the use of a single antibacterial agent causes the antibacterial property of the film to be reduced. Comparative Example 3 is difficult to form a film, and no performance test was performed. Comparative Example 4 uses hydrogen bonding when modifying nano-titanium dioxide, which is not firmly bonded by chemical bonds, resulting in nano-titanium dioxide being relatively easy to precipitate, affecting the heat resistance and antibacterial durability of the film. Comparative Example 5 does not add modified titanium dioxide, and the tensile strength of the film is increased, but the antibacterial and barrier properties are reduced.

Claims

1. A high barrier antibacterial food packaging film, characterized in that: The high barrier antibacterial food packaging film comprises, from inside to outside, a polyethylene antibacterial inner layer, a first nylon / polyethylene blended layer, an ethylene-vinyl alcohol barrier layer, a second nylon / polyethylene blended layer, and a polyethylene outer layer; The polyethylene antibacterial inner layer comprises 15-20wt.% of metallocene low-density polyethylene, 50-60wt.% of linear low-density polyethylene, 15-20wt.% of high-density polyethylene, and 10-15wt.% of polystyrene antibacterial microspheres; The first nylon / polyethylene blend layer and the second nylon / polyethylene blend layer include 62-75 wt.% of nylon, 23-35 wt.% of linear low-density polyethylene, and 1-3 wt.% of maleic anhydride grafted polyethylene; The ethylene-vinyl alcohol barrier layer comprises ethylene-vinyl alcohol copolymer; The polyethylene outer layer comprises 15-20wt.% of metallocene low-density polyethylene, 55-60wt.% of linear low-density polyethylene, 18-24wt.% of high-density polyethylene, and 1-3wt.% of modified titanium dioxide; The preparation method of polystyrene antibacterial microspheres is as follows: The carbon nanotubes are placed in a concentrated acid solution, heated under reflux for 2-4 hours, the solid is separated, washed, and dried to obtain acidified carbon nanotubes; zinc acetate is dissolved in anhydrous ethanol, sodium hydroxide is added, and the mixture is heated under reflux for 1-2 hours to obtain zinc oxide sol; the acidified carbon nanotubes are dispersed in the zinc oxide sol, heated under reflux for 1-2 hours, the solid is separated, washed, and dried to obtain antibacterial carbon nanotubes; polystyrene is dissolved in ethyl acetate, antibacterial carbon nanotubes and vanillin are added, and after uniform dispersion, the mixture is slowly added to an aqueous solution containing a wetting dispersant, stirred to form a suspension, the solid is separated, washed, and dried to obtain polystyrene antibacterial microspheres; the mass ratio of polystyrene, antibacterial carbon nanotubes, and vanillin is 100:(1-2):(0.2-0.5); The modified titanium dioxide is nano titanium dioxide modified by isocyanatepropyltriethoxysilane.

2. The high barrier antibacterial food packaging film according to claim 1, characterized in that: The concentrated acid solution is concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1: (2-3), and the concentrations of the concentrated nitric acid and concentrated sulfuric acid are not less than 70wt.%; the mass volume ratio of the carbon nanotubes and the concentrated acid solution is 1g: (20-30)mL.

3. The high barrier antibacterial food packaging film according to claim 1, characterized in that: The mass volume ratio of zinc acetate and anhydrous ethanol is 1g: (20-30)mL; the amount of sodium hydroxide added is 30-40% of the mass of zinc acetate.

4. The high barrier antibacterial food packaging film according to claim 1, characterized in that: The mass ratio of carbon nanotubes to zinc acetate is 1:(1-1.2).

5. The high barrier antibacterial food packaging film according to claim 1, characterized in that: The mass volume ratio of polystyrene and ethyl acetate is (0.2-0.5) g:1 mL; in the aqueous solution containing the wetting and dispersing agent, the concentration of the wetting and dispersing agent is 1-2 wt.%; and the mass ratio of polystyrene and the wetting and dispersing agent is 100:(3-5).

6. The high barrier antibacterial food packaging film according to claim 1, characterized in that: The melt index of linear low-density polyethylene at 190°C and 2.16 kg is 1 g / 10 min, and the density is 0.92 g / cm 3 The melt index of metallocene low-density polyethylene at 190°C and 2.16 kg is 0.5 g / 10 min, and the density is 0.863 g / cm 3 The melt index of high-density polyethylene at 190°C and 2.16 kg is 20 g / 10 min, and the density is 0.954 g / cm 3 .

7. The high barrier antibacterial food packaging film according to claim 1, characterized in that: The thickness percentages of the polyethylene antibacterial inner layer, the first nylon / polyethylene blended layer, the ethylene-vinyl alcohol barrier layer, the second nylon / polyethylene blended layer, and the polyethylene outer layer are: 20-25%, 10-15%, 20-25%, 10-15%, and 30-35%.

8. A method for preparing the high barrier antibacterial food packaging film according to any one of claims 1 to 7, characterized in that: The following steps are involved: The raw materials of the polyethylene antibacterial inner layer, the first nylon / polyethylene blended layer, the ethylene-vinyl alcohol barrier layer, the second nylon / polyethylene blended layer, and the polyethylene outer layer are respectively placed in the five feed hoppers of a five-layer co-extrusion film blowing machine, and the film is blown by melt extrusion to obtain a high barrier antibacterial food packaging film.