EvoH high-barrier film for silage bag and method for manufacturing the same

Abstract

The application provides an EVOH high-barrier film for silage bags and a preparation method thereof, and relates to the technical field of multilayer films for packaging. The EVOH high-barrier film comprises an inner layer, a bonding inner layer, a barrier layer, a bonding outer layer and an outer layer. The raw material of the inner layer comprises acrylic acid grafted molybdenum disulfide, metallocene linear low-density polyethylene, low-density polyethylene, an antioxidant, a light stabilizer and a slip agent. The raw material of the bonding inner layer comprises ethylene-acrylic ester copolymer, maleic anhydride grafted polyethylene and linear low-density polyethylene. The raw material of the barrier layer comprises ethylene-vinyl alcohol copolymer, NiCo-MBO LDHs nanocomposite, an antioxidant, maleic anhydride grafted polyolefin and ethylene-acrylic ester copolymer. The raw material of the bonding outer layer comprises ethylene-acrylic ester copolymer, maleic anhydride grafted polyethylene and linear low-density polyethylene. The raw material of the outer layer comprises acrylic acid grafted molybdenum disulfide, high-density polyethylene, linear low-density polyethylene, an antioxidant, a light stabilizer and an anti-blocking agent. The application has excellent barrier property and stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of multi-layer film for packaging, in particular to an EVOH high-barrier film for silage bag and a preparation method thereof. BACKGROUND

[0002] As a key way to store green feed in animal husbandry, silage can effectively retain the nutritional components of feed and alleviate seasonal feed shortages, playing an important role in large-scale breeding. The core of the silage process is to promote lactic acid bacteria fermentation by creating an anaerobic environment, reduce the pH value of the feed, and inhibit the reproduction of spoilage bacteria and molds, thereby achieving long-term preservation.

[0003] Currently, ethylene-vinyl alcohol copolymer has strong barrier ability to oxygen and water vapor due to the presence of hydroxyl groups in its molecular structure, making it an ideal high-barrier substrate. However, single ethylene-vinyl alcohol copolymer material still cannot meet the actual use requirements of silage bags, and needs to be combined with other polymer materials through multi-layer composite process to optimize the overall performance.

[0004] The prior art with application number CN119858371A discloses a PA-EVOH multi-layer co-extruded film, its preparation method and a composite film. By adopting a five-layer composite structure, the core layer is EVOH, and the other layers are mainly PA resin with the addition of functional masterbatch, solving the problems of poor barrier property of traditional polyolefin film and insufficient thermal stability of existing film. However, this technology still has limitations such as poor mechanical property adaptability and insufficient barrier performance. The prior art with application number CN118752872B discloses an ultra-high barrier EVOH aluminum-coated composite sheet and its preparation method. By designing the barrier layer as "modified EVOH film layer + aluminum layer", it solves the problems of strong hydrophilicity and poor water resistance of EVOH film, but still has defects such as large brittleness of the barrier layer, single mechanical property and poor stability.

[0005] In summary, although the existing technical solutions have improved some properties of EVOH barrier film to some extent, they still have the following technical problems: poor barrier performance, insufficient mechanical property and stability. SUMMARY

[0006] To solve the above-mentioned problems in the prior art, the present application provides an EVOH high-barrier film for silage bag and a preparation method thereof, and achieves the following invention purposes: preparing a silage packaging material with high barrier property, excellent mechanical property and stability.

[0007] To achieve the above-mentioned purposes, the technical solutions adopted are as follows:

[0008] An EVOH high-barrier film for silage bag, which is composed of an inner layer, a bonding inner layer, a barrier layer, a bonding outer layer and an outer layer.

[0009] The inner layer raw material components include: acrylic acid grafted molybdenum disulfide 3-5 parts, metallocene linear low density polyethylene 45-55 parts, low density polyethylene 25-35 parts, antioxidant 0.2-0.5 parts, light stabilizer 0.1-0.3 parts, slip agent 0.1-0.2 parts.

[0010] The inner layer raw material components include: acrylic acid grafted molybdenum disulfide 3-5 parts, metallocene linear low density polyethylene 45-55 parts, low density polyethylene 25-35 parts, antioxidant 0.2-0.5 parts, light stabilizer 0.1-0.3 parts, slip agent 0.1-0.2 parts.

[0011] The inner layer raw material components include: acrylic acid grafted molybdenum disulfide 3-5 parts, metallocene linear low density polyethylene 45-55 parts, low density polyethylene 25-35 parts, antioxidant 0.2-0.5 parts, light stabilizer 0.1-0.3 parts, slip agent 0.1-0.2 parts.

[0012] The inner layer raw material components include: acrylic acid grafted molybdenum disulfide 3-5 parts, metallocene linear low density polyethylene 45-55 parts, low density polyethylene 25-35 parts, antioxidant 0.2-0.5 parts, light stabilizer 0.1-0.3 parts, slip agent 0.1-0.2 parts.

[0013] The inner layer raw material components include: acrylic acid grafted molybdenum disulfide 3-5 parts, metallocene linear low density polyethylene 45-55 parts, low density polyethylene 25-35 parts, antioxidant 0.2-0.5 parts, light stabilizer 0.1-0.3 parts, slip agent 0.1-0.2 parts.

[0014] The above parts are all calculated by weight.

[0015] The NiCo-MBO LDHs nanocomposite is prepared from Ni(NO3)2·6H2O, Co(NO3)2·6H2O and 2-mercaptobenzoxazole.

[0016] The acrylic acid grafted molybdenum disulfide is prepared from molybdenum disulfide, acrylic acid and potassium persulfate.

[0017] The density of the metallocene linear low density polyethylene is 0.914-0.922 g / cm 3 .

[0018] The density of the low density polyethylene is 0.917-0.925 g / cm 3 .

[0019] The density of the linear low density polyethylene is 0.918-0.922 g / cm 3 .

[0020] The density of the high density polyethylene is 0.941-0.955 g / cm 3 .

[0021] The ethylene-vinyl alcohol copolymer has an ethylene content of 40-44 mol% and a density of 1.0-1.5 g / cm³. 3 .

[0022] The ethylene-acrylate copolymer has an AA content of 15-20%.

[0023] The maleic anhydride-grafted polyethylene has a density of 0.92-0.94 g / cm³. 3 The grafting rate is 0.8-1.5%.

[0024] The maleic anhydride-grafted polyolefin has a density of 0.86-0.88 g / cm³. 3 The grafting rate is 1.2-1.5%.

[0025] The light stabilizer is a hindered phenolic light stabilizer, model number NOR356.

[0026] The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0027] The slip agent is erucamide.

[0028] The anti-blocking agent is nano-silica.

[0029] This invention also provides a method for preparing an EVOH high-barrier film for silage bags, the steps of which are as follows:

[0030] Step 1: Preparation of NiCo-MBO LDHs nanocomposites

[0031] Ni(NO3)2·6H2O and Co(NO3)2·6H2O were dissolved in deionized water to prepare nickel nitrate solution and cobalt nitrate solution with a concentration of 0.2-0.3 mol / L, respectively. The nickel nitrate solution and cobalt nitrate solution were mixed evenly at a volume ratio of (1-3):1 to obtain a nickel-cobalt mixed solution. 2-Mercaptobenzoxazole was dissolved in methanol to prepare a 2-mercaptobenzoxazole solution with a concentration of 0.1-0.2 mol / L.

[0032] 2-Mercaptobenzoxazole solution was added dropwise to a nickel-cobalt mixed solution, and stirring was started at a rate of 700-800 rpm. The volume ratio of 2-mercaptobenzoxazole solution to nickel-cobalt mixed solution was (0.2-0.5):1. NaOH solution was added dropwise to adjust the pH of the system to 8.5-9.5, and stirring was continued for 1-2 hours to obtain a suspension. The suspension was transferred to a reaction vessel and reacted at 120-160℃ for 18-24 hours. After the reaction, the mixture was allowed to cool naturally to room temperature and centrifuged at 8000-10000 rpm for 10-15 minutes. The precipitate was then washed alternately with deionized water and ethanol until the filtrate was neutral. After washing, the precipitate was dried at 60-80℃ for 18-24 hours to obtain NiCo-MBO LDHs nanocomposite material.

[0033] Step 2: Obtaining acrylic acid-grafted molybdenum disulfide

[0034] Molybdenum disulfide was added to DMF at a concentration of 1-1.2% of the DMF mass and subjected to ultrasonic treatment at a power of 300-500W for 4-6 hours. Then, it was centrifuged at 7000-8000 rpm for 15-20 minutes. After centrifugation, the supernatant was collected to obtain a molybdenum disulfide dispersion.

[0035] Acrylic acid was added to a molybdenum disulfide dispersion and stirred until homogeneous. The mass ratio of acrylic acid to molybdenum disulfide was (1-2):1. Nitrogen gas was introduced for 10-15 min at a flow rate of 20-30 mL / min. Then, potassium persulfate was added, with the amount of potassium persulfate being 5%-10% of the mass of acrylic acid. Under nitrogen protection, the reaction system was heated to 60-80℃ and stirred at 300-400 rpm for 6-8 h. After the reaction was completed, the mixture was centrifuged at 9000-10000 rpm for 15-20 min. Then, the mixture was washed repeatedly with deionized water and ethanol 3-5 times. After washing, the mixture was dried at 60-70℃ for 12-14 h to obtain acrylic acid grafted with molybdenum disulfide.

[0036] Step 3: Premixing of barrier layer raw materials

[0037] The NiCo-MBO LDHs nanocomposite material and ethylene-vinyl alcohol copolymer were added to a twin-screw extruder with a screw speed of 200-300 rpm. The extruder feeding section temperature was 160-170℃, the melting section temperature was 190-210℃, the mixing section temperature was 200-220℃, and the die head temperature was 180-190℃. The extruded material was air-cooled with an air ring cooling temperature of 20℃. The cooled material was then added to a granulator for granulation. After granulation, it was mixed evenly with antioxidants, maleic anhydride-grafted polyolefins, and ethylene-acrylate copolymers to obtain a barrier layer premix for later use.

[0038] Step 4: Co-extrusion molding

[0039] The raw materials for the inner layer, adhesive inner layer, adhesive outer layer, and outer layer are mixed separately according to the formula to form premixes for each layer. These premixes are then added to a five-layer co-extrusion extruder. The extruder temperatures for each section are as follows: feed section 145-170℃, compression section 165-200℃, melting section 180-210℃, homogenization section 185-210℃, connector section 180-210℃, transition section 175-210℃, distributor section 175-205℃, and die exit section 165-200℃. After extrusion, the film is blown, cooled, corona-treated, and dried to obtain an EVOH high-barrier film for silage bags. Blown film parameters: blow ratio 3.0, traction speed 20m / min; cooling parameters: air ring cooling temperature 20℃; corona treatment parameters: corona treatment power 10kW, treatment speed 15m / min; drying parameters: drying temperature 60℃. The resulting product thickness is 0.10mm±5%, and the thickness ratio of the inner layer, adhesive inner layer, barrier layer, adhesive outer layer, and outer layer is 3:1:3:1:2.

[0040] The beneficial effects of this invention are as follows:

[0041] 1. The EVOH high-barrier membrane prepared by this invention has excellent barrier properties, with an oxygen permeability of 0.06-0.09 cm⁻¹. 3 / (m 2 ·d), water vapor transmission rate is 0.09-0.15 g / (m 2 ·d).

[0042] 2. The EVOH high-barrier membrane prepared by this invention has excellent mechanical properties, with a transverse tensile strength of 41.2-44.8 MPa, a longitudinal tensile strength of 43.7-47.5 MPa, a puncture strength of 52.4-60.7 N, and a right-angle tear strength of 145-152 N / mm.

[0043] 3. The EVOH high-barrier membrane prepared by this invention exhibits excellent stability. After low-temperature treatment, the transverse tensile strength remains at 39.9-43.1 MPa, and the longitudinal tensile strength remains at 41.8-45.6 MPa; after high-temperature aging, the transverse tensile strength remains at 38.2-42.0 MPa, and the longitudinal tensile strength remains at 40.3-44.6 MPa; after lactic acid immersion, the transverse tensile strength remains at 37.4-41.2 MPa, and the longitudinal tensile strength remains at 39.2-43.1 MPa.

[0044] 4. The silage bags prepared by this invention have excellent barrier properties. When the forage is placed in the silage bags for 1 to 3 months, the pH value of the forage remains stable between 3.8 and 4.2, and the appearance color remains basically unchanged, maintaining its green color. Attached Figure Description

[0045] Appendix Figure 1 This is a transmission electron microscope (TEM) image of the NiCo-MBO LDHs nanocomposite material in the "Preparation of NiCo-MBO LDHs Nanocomposite Material" step of the present invention. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0047] Example 1: An EVOH high-barrier film for silage bags

[0048] An EVOH high-barrier film for silage bags, the EVOH high-barrier film comprising an inner layer, an adhesive inner layer, a barrier layer, an adhesive outer layer, and an outer layer.

[0049] The inner layer raw material components include: 3 parts acrylic acid grafted molybdenum disulfide, 45 parts metallocene linear low-density polyethylene, 35 parts low-density polyethylene, 0.2 parts antioxidant, 0.3 parts light stabilizer, and 0.1 parts slip agent.

[0050] The adhesive inner layer raw material components include: 30 parts of ethylene-acrylate copolymer, 55 parts of maleic anhydride-grafted polyethylene, and 15 parts of linear low-density polyethylene.

[0051] The barrier layer raw material components include: 70 parts of ethylene-vinyl alcohol copolymer, 5 parts of NiCo-MBO LDHs nanocomposite material, 0.6 parts of antioxidant, 5 parts of maleic anhydride grafted polyolefin, and 10 parts of ethylene-acrylate copolymer.

[0052] The adhesive outer layer raw material components include: 25 parts of ethylene-acrylate copolymer, 50 parts of maleic anhydride-grafted polyethylene, and 20 parts of linear low-density polyethylene.

[0053] The outer layer raw material components include: 5 parts acrylic acid grafted molybdenum disulfide, 45 parts high-density polyethylene, 35 parts linear low-density polyethylene, 0.7 parts antioxidant, 0.3 parts light stabilizer, and 0.3 parts anti-blocking agent.

[0054] All the above quantities are by weight.

[0055] The light stabilizer is a hindered phenolic light stabilizer, model number NOR356.

[0056] The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0057] The slip agent is erucamide.

[0058] The anti-blocking agent is nano-silica with a particle size of 15-25nm.

[0059] A method for preparing an EVOH high-barrier film for silage bags, comprising the following steps:

[0060] Step 1: Preparation of NiCo-MBO LDHs nanocomposites

[0061] Ni(NO3)2·6H2O and Co(NO3)2·6H2O were dissolved in deionized water to prepare nickel nitrate solution and cobalt nitrate solution with a concentration of 0.2 mol / L, respectively. The nickel nitrate solution and cobalt nitrate solution were mixed evenly at a volume ratio of 1:1 to obtain a nickel-cobalt mixed solution. 2-Mercaptobenzoxazole was dissolved in methanol to prepare a 0.2 mol / L 2-mercaptobenzoxazole solution.

[0062] 2-Mercaptobenzoxazole solution was added dropwise to a nickel-cobalt mixed solution, and stirring was started at a rate of 700 rpm. The volume ratio of 2-mercaptobenzoxazole solution to nickel-cobalt mixed solution was 0.2:1. NaOH solution was added dropwise to adjust the pH of the system to 8.5, and stirring was continued for 1 h to obtain a suspension. The suspension was transferred to a reaction vessel and reacted at 120℃ for 24 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature and then centrifuged at 8000 rpm for 15 min. The precipitate was then washed alternately with deionized water and ethanol until the filtrate was neutral. After washing, the precipitate was dried at 60℃ for 24 h to obtain the NiCo-MBOLDHs nanocomposite material.

[0063] Step 2: Obtaining acrylic acid-grafted molybdenum disulfide

[0064] Molybdenum disulfide was added to DMF at a concentration of 1% of the DMF mass and subjected to ultrasonic treatment at a power of 300W for 6 hours. Then, it was centrifuged at 7000 rpm for 20 minutes. After centrifugation, the supernatant was collected to obtain a molybdenum disulfide dispersion.

[0065] Acrylic acid was added to a molybdenum disulfide dispersion and stirred until homogeneous. The mass ratio of acrylic acid to molybdenum disulfide was 1:1. Nitrogen gas was purged for 15 min at a flow rate of 20 mL / min. Then, potassium persulfate was added, at a concentration of 5% of the mass of acrylic acid. Under nitrogen protection, the reaction system was heated to 60°C and stirred at 400 rpm for 8 h. After the reaction was complete, the mixture was centrifuged at 9000 rpm for 20 min. The mixture was then washed three times with deionized water and ethanol. After washing, the mixture was dried at 60°C for 14 h to obtain acrylic acid-grafted molybdenum disulfide.

[0066] Step 3: Premixing of barrier layer raw materials

[0067] The NiCo-MBO LDHs nanocomposite material and ethylene-vinyl alcohol copolymer were added to a twin-screw extruder at a screw speed of 200 rpm. The extruder feeding section temperature was 160°C, the melting section temperature was 190°C, the mixing section temperature was 200°C, and the die head temperature was 180°C. The extruded material was air-cooled at a fan cooling temperature of 20°C. The cooled material was then added to a granulator for granulation. After granulation, it was mixed evenly with antioxidants, maleic anhydride-grafted polyolefins, and ethylene-acrylate copolymers to obtain a barrier layer premix for later use.

[0068] Step 4: Co-extrusion molding

[0069] The raw materials for the inner layer, the bonding inner layer, the bonding outer layer, and the outer layer are mixed according to the formula to form premixes for each layer. The premixes for the inner layer, the bonding inner layer, the barrier layer, the bonding outer layer, and the outer layer are added to a five-layer co-extrusion extruder. The temperature and process conditions for each zone of the extruder are detailed in Table 1.

[0070] Table 1 Temperature and process conditions in each zone of the extruder

[0071]

[0072] After extrusion through the die head, the film undergoes blown film blowing, cooling, corona treatment, and drying to finally obtain an EVOH high-barrier film for silage bags. Blown film parameters: blow-up ratio 3.0, traction speed 20 m / min; cooling parameters: air ring cooling temperature 20℃; corona treatment parameters: corona treatment power 10 kW, treatment speed 15 m / min; drying parameters: drying temperature 60℃. The resulting product has a thickness of 0.10 mm ± 5%, and the thickness ratio of the inner layer, adhesive inner layer, barrier layer, adhesive outer layer, and outer layer is 3:1:3:1:2.

[0073] Example 2: An EVOH high-barrier film for silage bags

[0074] An EVOH high-barrier film for silage bags, the EVOH high-barrier film comprising an inner layer, an adhesive inner layer, a barrier layer, an adhesive outer layer, and an outer layer.

[0075] The inner layer raw material components include: 4 parts acrylic acid grafted molybdenum disulfide, 50 parts metallocene linear low-density polyethylene, 30 parts low-density polyethylene, 0.4 parts antioxidant, 0.2 parts light stabilizer, and 0.2 parts slip agent.

[0076] The adhesive inner layer raw material components include: 35 parts of ethylene-acrylate copolymer, 50 parts of maleic anhydride-grafted polyethylene, and 20 parts of linear low-density polyethylene.

[0077] The barrier layer raw material components include: 65 parts of ethylene-vinyl alcohol copolymer, 8 parts of NiCo-MBO LDHs nanocomposite material, 0.6 parts of antioxidant, 10 parts of maleic anhydride grafted polyolefin, and 10 parts of ethylene-acrylate copolymer.

[0078] The adhesive outer layer raw material components include: 30 parts of ethylene-acrylate copolymer, 45 parts of maleic anhydride-grafted polyethylene, and 25 parts of linear low-density polyethylene.

[0079] The outer layer raw material components include: 6 parts of acrylic acid grafted molybdenum disulfide, 45 parts of high-density polyethylene, 40 parts of linear low-density polyethylene, 0.7 parts of antioxidant, 0.6 parts of light stabilizer, and 0.3 parts of anti-blocking agent.

[0080] All the above quantities are by weight.

[0081] The light stabilizer is a hindered phenolic light stabilizer, model number NOR356.

[0082] The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0083] The slip agent is erucamide.

[0084] The anti-blocking agent is nano-silica with a particle size of 15-25nm.

[0085] A method for preparing an EVOH high-barrier film for silage bags, comprising the following steps:

[0086] Step 1: Preparation of NiCo-MBO LDHs nanocomposites

[0087] Ni(NO3)2·6H2O and Co(NO3)2·6H2O were dissolved in deionized water to prepare nickel nitrate solution and cobalt nitrate solution with a concentration of 0.3 mol / L, respectively. The nickel nitrate solution and cobalt nitrate solution were mixed evenly at a volume ratio of 2:1 to obtain a nickel-cobalt mixed solution. 2-Mercaptobenzoxazole was dissolved in methanol to prepare a 0.2 mol / L 2-mercaptobenzoxazole solution.

[0088] 2-Mercaptobenzoxazole solution was added dropwise to a nickel-cobalt mixed solution, and stirring was started at 800 rpm. The volume ratio of 2-mercaptobenzoxazole solution to nickel-cobalt mixed solution was 0.4:1. NaOH solution was added dropwise to adjust the pH of the system to 9, and stirring was continued for 2 hours to obtain a suspension. The suspension was transferred to a reaction vessel and reacted at 140℃ for 24 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature and then centrifuged at 10,000 rpm for 10 minutes. The precipitate was then washed alternately with deionized water and ethanol until the filtrate was neutral. After washing, the precipitate was dried at 70℃ for 24 hours to obtain the NiCo-MBO LDHs nanocomposite material.

[0089] Step 2: Obtaining acrylic acid-grafted molybdenum disulfide

[0090] Molybdenum disulfide was added to DMF at a concentration of 1.2% of the DMF mass and subjected to ultrasonic treatment at a power of 400W for 6 hours. Then, it was centrifuged at 8000 rpm for 20 minutes. After centrifugation, the supernatant was collected to obtain a molybdenum disulfide dispersion.

[0091] Acrylic acid was added to a molybdenum disulfide dispersion and stirred until homogeneous. The mass ratio of acrylic acid to molybdenum disulfide was 2:1. Nitrogen gas was purged for 15 min at a flow rate of 30 mL / min. Then, potassium persulfate was added, at a concentration of 10% of the mass of acrylic acid. Under nitrogen protection, the reaction system was heated to 70°C and stirred at 400 rpm for 8 h. After the reaction was complete, the mixture was centrifuged at 10,000 rpm for 20 min. The mixture was then washed five times with deionized water and ethanol. After washing, the mixture was dried at 70°C for 14 h to obtain acrylic acid-grafted molybdenum disulfide.

[0092] Step 3: Premixing of barrier layer raw materials

[0093] The NiCo-MBO LDHs nanocomposite material and ethylene-vinyl alcohol copolymer were added to a twin-screw extruder at a screw speed of 300 rpm. The extruder feeding section temperature was 170°C, the melting section temperature was 200°C, the mixing section temperature was 210°C, and the die head temperature was 190°C. The extruded material was air-cooled at a fan cooling temperature of 20°C. The cooled material was then added to a granulator for granulation. After granulation, it was mixed evenly with antioxidants, maleic anhydride-grafted polyolefins, and ethylene-acrylate copolymers to obtain a barrier layer premix for later use.

[0094] Step 4: Co-extrusion molding

[0095] The raw materials for the inner layer, the bonding inner layer, the bonding outer layer, and the outer layer are mixed according to the formula to form premixes for each layer. The premixes for the inner layer, the bonding inner layer, the barrier layer, the bonding outer layer, and the outer layer are added to a five-layer co-extrusion extruder. The temperature and process conditions for each zone of the extruder are detailed in Table 2.

[0096] Table 2 Temperature and process conditions in each zone of the extruder

[0097]

[0098] After extrusion through the die head, the film undergoes blown film blowing, cooling, corona treatment, and drying to finally obtain an EVOH high-barrier film for silage bags. Blown film parameters: blow-up ratio 3.0, traction speed 20 m / min; cooling parameters: air ring cooling temperature 20℃; corona treatment parameters: corona treatment power 10 kW, treatment speed 15 m / min; drying parameters: drying temperature 60℃. The resulting product has a thickness of 0.10 mm ± 5%, and the thickness ratio of the inner layer, adhesive inner layer, barrier layer, adhesive outer layer, and outer layer is 3:1:3:1:2.

[0099] Example 3: An EVOH high-barrier film for silage bags

[0100] An EVOH high-barrier film for silage bags, the EVOH high-barrier film comprising an inner layer, an adhesive inner layer, a barrier layer, an adhesive outer layer, and an outer layer.

[0101] The inner layer raw material components include: 5 parts acrylic acid grafted molybdenum disulfide, 55 parts metallocene linear low-density polyethylene, 25 parts low-density polyethylene, 0.5 parts antioxidant, 0.1 parts light stabilizer, and 0.2 parts slip agent.

[0102] The adhesive inner layer raw material components include: 35 parts of ethylene-acrylate copolymer, 45 parts of maleic anhydride-grafted polyethylene, and 20 parts of linear low-density polyethylene.

[0103] The barrier layer raw material components include: 60 parts of ethylene-vinyl alcohol copolymer, 8 parts of NiCo-MBO LDHs nanocomposite material, 0.3 parts of antioxidant, 10 parts of maleic anhydride grafted polyolefin, and 5 parts of ethylene-acrylate copolymer.

[0104] The adhesive outer layer raw material components include: 35 parts of ethylene-acrylate copolymer, 45 parts of maleic anhydride-grafted polyethylene, and 25 parts of linear low-density polyethylene.

[0105] The outer layer raw material components include: 8 parts of acrylic acid grafted molybdenum disulfide, 40 parts of high-density polyethylene, 40 parts of linear low-density polyethylene, 0.5 parts of antioxidant, 0.6 parts of light stabilizer, and 0.1 parts of anti-blocking agent.

[0106] All the above quantities are by weight.

[0107] The light stabilizer is a hindered phenolic light stabilizer, model number NOR356.

[0108] The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0109] The slip agent is erucamide.

[0110] The anti-blocking agent is nano-silica with a particle size of 15-25nm.

[0111] A method for preparing an EVOH high-barrier film for silage bags, comprising the following steps:

[0112] Step 1: Preparation of NiCo-MBO LDHs nanocomposites

[0113] Ni(NO3)2·6H2O and Co(NO3)2·6H2O were dissolved in deionized water to prepare nickel nitrate solution and cobalt nitrate solution with a concentration of 0.3 mol / L, respectively. The nickel nitrate solution and cobalt nitrate solution were mixed evenly at a volume ratio of 3:1 to obtain a nickel-cobalt mixed solution. 2-Mercaptobenzoxazole was dissolved in methanol to prepare a 0.1 mol / L 2-mercaptobenzoxazole solution.

[0114] 2-Mercaptobenzoxazole solution was added dropwise to a nickel-cobalt mixed solution, and stirring was started at 800 rpm. The volume ratio of 2-mercaptobenzoxazole solution to nickel-cobalt mixed solution was 0.5:1. NaOH solution was added dropwise to adjust the pH of the system to 9.5, and stirring was continued for 2 hours to obtain a suspension. The suspension was transferred to a reaction vessel and reacted at 160℃ for 18 hours. After the reaction, the mixture was allowed to cool naturally to room temperature and then centrifuged at 10,000 rpm for 10 minutes. The precipitate was then washed alternately with deionized water and ethanol until the filtrate was neutral. After washing, the precipitate was dried at 80℃ for 18 hours to obtain the NiCo-MBOLDHs nanocomposite material.

[0115] Step 2: Obtaining acrylic acid-grafted molybdenum disulfide

[0116] Molybdenum disulfide was added to DMF at a concentration of 1.2% of the DMF mass and subjected to ultrasonic treatment at a power of 500W for 4 hours. Then, it was centrifuged at 8000 rpm for 15 minutes. After centrifugation, the supernatant was collected to obtain a molybdenum disulfide dispersion.

[0117] Acrylic acid was added to a molybdenum disulfide dispersion and stirred until homogeneous. The mass ratio of acrylic acid to molybdenum disulfide was 2:1. Nitrogen gas was purged for 10 min at a flow rate of 30 mL / min. Then, potassium persulfate was added, at a concentration of 10% of the mass of acrylic acid. Under nitrogen protection, the reaction system was heated to 80°C and stirred at 300 rpm for 6 h. After the reaction was complete, the mixture was centrifuged at 10,000 rpm for 15 min. The mixture was then washed five times with deionized water and ethanol. After washing, the mixture was dried at 70°C for 12 h to obtain acrylic acid-grafted molybdenum disulfide.

[0118] Step 3: Premixing of barrier layer raw materials

[0119] The NiCo-MBO LDHs nanocomposite material and ethylene-vinyl alcohol copolymer were added to a twin-screw extruder at a screw speed of 300 rpm. The extruder feeding section temperature was 170°C, the melting section temperature was 210°C, the mixing section temperature was 220°C, and the die head temperature was 190°C. The extruded material was air-cooled at a fan cooling temperature of 20°C. The cooled material was then added to a granulator for granulation. After granulation, it was mixed evenly with antioxidants, maleic anhydride-grafted polyolefins, and ethylene-acrylate copolymers to obtain a barrier layer premix for later use.

[0120] Step 4: Co-extrusion molding

[0121] The raw materials for the inner layer, the bonding inner layer, the bonding outer layer, and the outer layer are mixed according to the formula to form premixes for each layer. The premixes for the inner layer, the bonding inner layer, the barrier layer, the bonding outer layer, and the outer layer are added to a five-layer co-extrusion extruder. The temperature and process conditions for each zone of the extruder are detailed in Table 3.

[0122] Table 3 Temperature and process conditions in each zone of the extruder

[0123]

[0124] After extrusion through the die head, the film undergoes blown film blowing, cooling, corona treatment, and drying to finally obtain an EVOH high-barrier film for silage bags. Blown film parameters: blow-up ratio 3.0, traction speed 20 m / min; cooling parameters: air ring cooling temperature 20℃; corona treatment parameters: corona treatment power 10 kW, treatment speed 15 m / min; drying parameters: drying temperature 60℃. The resulting product has a thickness of 0.10 mm ± 5%, and the thickness ratio of the inner layer, adhesive inner layer, barrier layer, adhesive outer layer, and outer layer is 3:1:3:1:2.

[0125] Comparative Example 1

[0126] An EVOH high-barrier membrane, the EVOH high-barrier membrane being composed of an inner layer, an adhesive inner layer, a barrier layer, an adhesive outer layer, and an outer layer.

[0127] The inner layer raw material components include: 4 parts acrylic acid grafted molybdenum disulfide, 50 parts metallocene linear low-density polyethylene, 30 parts low-density polyethylene, 0.4 parts antioxidant, 0.2 parts light stabilizer, and 0.2 parts slip agent.

[0128] The adhesive inner layer raw material components include: 35 parts of ethylene-acrylate copolymer, 50 parts of maleic anhydride-grafted polyethylene, and 20 parts of linear low-density polyethylene.

[0129] The barrier layer raw material components include: 65 parts of ethylene-vinyl alcohol copolymer, 0.6 parts of antioxidant, 10 parts of maleic anhydride grafted polyolefin, and 10 parts of ethylene-acrylate copolymer.

[0130] The adhesive outer layer raw material components include: 30 parts of ethylene-acrylate copolymer, 45 parts of maleic anhydride-grafted polyethylene, and 25 parts of linear low-density polyethylene.

[0131] The outer layer raw material components include: 6 parts of acrylic acid grafted molybdenum disulfide, 45 parts of high-density polyethylene, 40 parts of linear low-density polyethylene, 0.7 parts of antioxidant, 0.6 parts of light stabilizer, and 0.3 parts of anti-blocking agent.

[0132] All the above quantities are by weight.

[0133] The light stabilizer is a hindered phenolic light stabilizer, model number NOR356.

[0134] The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0135] The slip agent is erucamide.

[0136] The anti-blocking agent is nano-silica with a particle size of 15-25nm.

[0137] A method for preparing an EVOH high-barrier membrane, comprising the following steps:

[0138] Step 1: Obtaining acrylic acid-grafted molybdenum disulfide

[0139] This step is the same as the "Preparation of acrylic acid grafted molybdenum disulfide" step in Example 2.

[0140] Step 2: Premixing of barrier layer raw materials

[0141] This step is the same as the "barrier layer raw material premixing" step in Example 2.

[0142] Step 3: Co-extrusion molding

[0143] This step is the same as the "co-extrusion molding" step in Example 2.

[0144] Comparative Example 2

[0145] An EVOH high-barrier membrane, the EVOH high-barrier membrane being composed of an inner layer, an adhesive inner layer, a barrier layer, an adhesive outer layer, and an outer layer.

[0146] The inner layer raw material components include: 50 parts of metallocene linear low-density polyethylene, 30 parts of low-density polyethylene, 0.4 parts of antioxidant, 0.2 parts of light stabilizer, and 0.2 parts of slip agent.

[0147] The adhesive inner layer raw material components include: 35 parts of ethylene-acrylate copolymer, 50 parts of maleic anhydride-grafted polyethylene, and 20 parts of linear low-density polyethylene.

[0148] The barrier layer raw material components include: 65 parts of ethylene-vinyl alcohol copolymer, 8 parts of NiCo-MBO LDHs nanocomposite material, 0.6 parts of antioxidant, 10 parts of maleic anhydride grafted polyolefin, and 10 parts of ethylene-acrylate copolymer.

[0149] The adhesive outer layer raw material components include: 30 parts of ethylene-acrylate copolymer, 45 parts of maleic anhydride-grafted polyethylene, and 25 parts of linear low-density polyethylene.

[0150] The outer layer raw material components include: 45 parts high-density polyethylene, 40 parts linear low-density polyethylene, 0.7 parts antioxidant, 0.6 parts light stabilizer, and 0.3 parts anti-blocking agent.

[0151] All the above quantities are by weight.

[0152] The light stabilizer is a hindered phenolic light stabilizer, model number NOR356.

[0153] The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0154] The slip agent is erucamide.

[0155] The anti-blocking agent is nano-silica with a particle size of 15-25nm.

[0156] A method for preparing an EVOH high-barrier membrane, comprising the following steps:

[0157] Step 1: Preparation of NiCo-MBO LDHs nanocomposites

[0158] This step is the same as the "Preparation of NiCo-MBO LDHs Nanocomposite Materials" step in Example 2.

[0159] Step 2: Premixing of barrier layer raw materials

[0160] This step is the same as the "barrier layer raw material premixing" step in Example 2.

[0161] Step 3: Co-extrusion molding

[0162] This step is the same as the "co-extrusion molding" step in Example 2.

[0163] Example 4 Performance Testing

[0164] (a) Barrier performance test

[0165] The EVOH high-barrier membranes prepared in Examples 1-3 and Comparative Examples 1-2 were tested for oxygen permeability according to the test method provided in GB / T 19789-2005; and for water vapor permeability according to the test method provided in GB / T 26253-2010. The specific test results are shown in Table 4.

[0166] Table 4

[0167]

[0168] As shown in Table 4, the oxygen permeability of the EVOH high-barrier membranes prepared in Examples 1-3 is 0.06-0.09 cm⁻¹. 3 / (m 2 ·d), water vapor transmission rate is 0.09-0.15 g / (m 2 (d) shows a significant reduction compared to the comparative example. This demonstrates that the EVOH high-barrier membrane prepared in this invention possesses excellent barrier properties.

[0169] (ii) Mechanical performance testing

[0170] The EVOH high-barrier films prepared in Examples 1-3 and Comparative Examples 1-2 were tested for transverse and longitudinal tensile strength according to the test method provided in GB / T 1040-2006, for puncture strength according to the test method provided in GB / T 10004-2008, and for right-angle tear strength according to the test method provided in GB / T 16578.2-2009. The specific test results are shown in Table 5.

[0171] Table 5

[0172]

[0173] As shown in Table 5, the EVOH high-barrier membranes prepared in Examples 1-3 exhibit a transverse tensile strength of 41.2-44.8 MPa, a longitudinal tensile strength of 43.7-47.5 MPa, a puncture strength of 52.4-60.7 N, and a right-angle tear strength of 145-152 N / mm. This demonstrates that the EVOH high-barrier membranes prepared in this invention possess excellent mechanical properties.

[0174] (III) Stability Testing

[0175] The EVOH high-barrier membranes prepared in Examples 1-3 and Comparative Examples 1-2 were tested for low-temperature resistance, high-temperature aging resistance, and corrosion resistance. The EVOH high-barrier membranes were placed at -20℃ for 12 hours, and their tensile strength was tested immediately after removal. The EVOH high-barrier membranes were then subjected to thermal aging at 80℃ for 168 hours, and their tensile strength was tested after aging. The EVOH high-barrier membranes were also immersed in a 3% lactic acid solution at 30℃ for 72 hours, and after drying, their tensile strength was tested. Specific test results are shown in Table 6.

[0176] Table 6

[0177]

[0178] As shown in Table 6, the EVOH high-barrier membranes prepared in Examples 1-3, after low-temperature treatment, maintained a transverse tensile strength of 39.9-43.1 MPa and a longitudinal tensile strength of 41.8-45.6 MPa; after high-temperature aging, the transverse tensile strength remained at 38.2-42.0 MPa and the longitudinal tensile strength at 40.3-44.6 MPa; and after lactic acid immersion, the transverse tensile strength remained at 37.4-41.2 MPa and the longitudinal tensile strength at 39.2-43.1 MPa. This demonstrates that the EVOH high-barrier membrane prepared by this invention possesses excellent stability.

[0179] (iv) The EVOH high-barrier films prepared in Examples 1-3 and Comparative Examples 1-2 were used to make silage bags. The prepared EVOH high-barrier films were cut into widths of 800-1200 mm; then, the bags were heat-sealed on three sides. The heat-sealing parameters were: temperature 180-220℃, pressure 0.3-0.5 MPa, time 0.5-1.5 s, and sealing width 8-12 mm. A one-way exhaust valve was installed on the top or side of the bag. The forage was added into the silage bags and vacuumed. The pH value of the forage was tested regularly (every week, every month, and every 3 months), and the color change was observed. The specific test results are shown in Table 7.

[0180] Table 7

[0181]

[0182] As shown in Table 7, the pH value of the forage remained stable between 3.8 and 4.2 during the period of 1 to 3 months after being placed in the silage bags, and its appearance color remained basically unchanged, maintaining its green color. This proves that the silage bags prepared by this invention have excellent barrier properties.

[0183] The specific parameters of the raw materials used in this invention are as follows:

[0184] The density of the metallocene linear low-density polyethylene is 0.914-0.922 g / cm³. 3 .

[0185] The density of the low-density polyethylene is 0.917-0.925 g / cm³. 3 .

[0186] The linear low-density polyethylene has a density of 0.918-0.922 g / cm³. 3 .

[0187] The density of the high-density polyethylene is 0.941-0.955 g / cm³. 3 .

[0188] The ethylene-vinyl alcohol copolymer has an ethylene content of 40-44 mol% and a density of 1.0-1.5 g / cm³. 3 .

[0189] The ethylene-acrylate copolymer has an AA content of 15-20%.

[0190] The maleic anhydride-grafted polyethylene has a density of 0.92-0.94 g / cm³. 3 The grafting rate is 0.8-1.5%.

[0191] The maleic anhydride-grafted polyolefin has a density of 0.86-0.88 g / cm³. 3 The grafting rate is 1.2-1.5%.

[0192] Obviously, there are many other possible implementation methods under the concept of this invention. It should be stated here that any changes made under the inventive concept of this invention will fall within the protection scope of this invention.

Claims

1. An EVOH high-barrier film for silage bags, characterized in that: The EVOH high-barrier membrane consists of an inner layer, an adhesive inner layer, a barrier layer, an adhesive outer layer, and an outer layer. The inner layer raw material components include: 3-5 parts of acrylic acid grafted with molybdenum disulfide, 45-55 parts of metallocene linear low-density polyethylene, 25-35 parts of low-density polyethylene, 0.2-0.5 parts of antioxidant, 0.1-0.3 parts of light stabilizer, and 0.1-0.2 parts of slip agent; the slip agent is erucamide. The adhesive inner layer raw material components include: 30-35 parts of ethylene-acrylate copolymer, 45-55 parts of maleic anhydride grafted polyethylene, and 15-20 parts of linear low-density polyethylene. The barrier layer raw material components include: 60-70 parts of ethylene-vinyl alcohol copolymer, 5-8 parts of NiCo-MBO LDHs nanocomposite material, 0.3-0.6 parts of antioxidant, 5-10 parts of maleic anhydride grafted polyolefin, and 5-10 parts of ethylene-acrylate copolymer. The adhesive outer layer raw material components include: 25-35 parts of ethylene-acrylate copolymer, 45-50 parts of maleic anhydride grafted polyethylene, and 20-25 parts of linear low-density polyethylene. The outer layer raw material components include: 5-8 parts of acrylic acid grafted molybdenum disulfide, 40-45 parts of high-density polyethylene, 35-40 parts of linear low-density polyethylene, 0.5-0.7 parts of antioxidant, 0.3-0.6 parts of light stabilizer, and 0.1-0.3 parts of anti-blocking agent; the anti-blocking agent is nano-silica; All the above quantities are by weight. Preparation of the NiCo-MBO LDHs nanocomposite material: Ni(NO3)2·6H2O and Co(NO3)2·6H2O were dissolved in deionized water to prepare nickel nitrate solution and cobalt nitrate solution, respectively; the nickel nitrate solution and cobalt nitrate solution were mixed evenly at a volume ratio of (1-3):1 to obtain a nickel-cobalt mixed solution; 2-mercaptobenzoxazole was dissolved in methanol to prepare a 2-mercaptobenzoxazole solution; the 2-mercaptobenzoxazole solution was added dropwise to the nickel-cobalt mixed solution, the pH value of the system was adjusted, and stirring was continued for 1-2 h to obtain a suspension; the suspension was transferred to a reaction vessel, and the temperature was 120-160℃ for 18-24 h; after the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, washed, and dried to obtain the NiCo-MBO LDHs nanocomposite material; Preparation of the acrylic acid-grafted molybdenum disulfide: Molybdenum disulfide is added to DMF, the amount of molybdenum disulfide being 1-1.2% of the mass of DMF, and ultrasonic treatment is performed for 4-6 hours; then centrifugation is performed to obtain a molybdenum disulfide dispersion. Acrylic acid was added to the molybdenum disulfide dispersion and stirred until homogeneous. Nitrogen gas was introduced, potassium persulfate was added, and the reaction system was heated to 60-80℃ under nitrogen protection and stirred for 6-8 hours. After the reaction was completed, the acrylic acid-grafted molybdenum disulfide was obtained by centrifugation, washing, and drying.

2. The method for preparing an EVOH high-barrier film for silage bags according to claim 1, characterized in that: The volume ratio of the 2-mercaptobenzoxazole solution to the nickel-cobalt mixed solution is (0.2-0.5):

1.

3. The method for preparing an EVOH high-barrier film for silage bags according to claim 1, characterized in that: The pH value of the system is adjusted by adding NaOH solution dropwise to adjust the pH value to 8.5-9.

5.

4. The method for preparing an EVOH high-barrier film for silage bags according to claim 1, characterized in that: The mass ratio of acrylic acid to molybdenum disulfide is (1-2):

1.

5. The method for preparing an EVOH high-barrier film for silage bags according to claim 1, characterized in that: The potassium persulfate is 5%-10% of the mass of acrylic acid.

6. The method for preparing an EVOH high-barrier film for silage bags according to claim 1, characterized in that: The process includes the preparation of NiCo-MBO LDHs nanocomposites, the preparation of acrylic acid-grafted molybdenum disulfide, the premixing of barrier layer raw materials, and co-extrusion molding steps.

7. The method for preparing an EVOH high-barrier film for silage bags according to claim 6, characterized in that: The barrier layer raw material premix: NiCo-MBO LDHs nanocomposite material and ethylene-vinyl alcohol copolymer are added to a twin-screw extruder. The extruder feeding section temperature is 160-170℃, the melting section temperature is 190-210℃, the mixing section temperature is 200-220℃, and the die head temperature is 180-190℃. The extruded material is cooled and granulated, and then mixed evenly with antioxidant, maleic anhydride grafted polyolefin, and ethylene-acrylate copolymer to obtain the barrier layer premix.

8. The method for preparing an EVOH high-barrier film for silage bags according to claim 6, characterized in that: The co-extrusion molding process involves pre-mixing each layer of raw materials and then adding them to a five-layer co-extrusion extruder. The temperatures of each section of the extruder are as follows: feeding section 145-170℃, compression section 165-200℃, melting section 180-210℃, homogenization section 185-210℃, connector section 180-210℃, transition section 175-210℃, distributor section 175-205℃, and die outlet section 165-200℃. After extrusion through the die, the film is blown, cooled, corona-treated, and dried to finally obtain an EVOH high-barrier film for silage bags.

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