Preparation method and application of high water vapor barrier blown film

Abstract

The application relates to the technical field of packaging materials, and particularly discloses a preparation method and application of a high-water-vapor-barrier blown film. The preparation method of the high-water-vapor-barrier blown film is prepared through co-extrusion and blown forming of an outer layer, a secondary outer layer, a core layer, a secondary inner layer and an inner layer, and the core layer comprises the following raw materials in parts by weight: 85-95 parts of high-density polyethylene and 5-15 parts of a composite barrier modifier modified polyethylene master batch; the application forms a composite barrier modifier through a two-step method of ion exchange intercalation of inorganic flaky fillers by a long-chain alkyl quaternary ammonium salt modifier and introduction of polytetrafluoroethylene micro-powder to fill and expand the space of the flaky layer, and then the master batch is prepared through melt blending and granulation with maleic anhydride grafted high-density polyethylene as a carrier, so that the peeling and dispersing effect of the flaky fillers in the polyethylene matrix is improved, and then the water-vapor-barrier property and toughness of the blown film are improved.

Description

Technical Field

[0001] This application relates to the field of packaging materials technology, and more specifically, it relates to a method for preparing and applying a high moisture barrier blown film. Background Technology

[0002] Liquid bags are large-capacity flexible liquid packaging containers made primarily of polymer films. They are widely used in the international transportation and logistics distribution of food-grade liquids (such as wine, juice, and edible oil) and some industrial liquids (such as lubricating oil and chemicals).

[0003] Currently, the mainstream membrane material used in the liquid bag industry is multilayer co-extruded polyethylene (PE) film, which has advantages such as good toughness, low cost, and convenient recycling. However, polyethylene is a non-polar polymer with a loose molecular chain arrangement and limited crystallinity, allowing water molecules to easily penetrate through the gaps between the molecular chains, resulting in generally poor water vapor barrier properties. When transporting goods sensitive to moisture (such as edible oil, dairy products, and some chemical raw materials), moisture intrusion can easily lead to oxidation, spoilage, and mold growth. To address these issues, the market typically uses high-barrier materials such as aluminized film, ethylene-vinyl alcohol copolymer film, and polyvinylidene chloride film to laminate the outer layer of the polyethylene film to improve the overall water resistance. However, this type of lamination increases the cost by more than 50% compared to conventional PE film, and aluminized film has significant drawbacks such as poor toughness during use, easy breakage at creases, high breakage rate, and difficulty in recycling; ethylene-vinyl alcohol copolymer film and polyvinylidene chloride film are prone to delamination from the PE substrate, and the barrier performance of ethylene-vinyl alcohol copolymer film drops sharply in high humidity environments.

[0004] Patent application CN118222060A discloses a vacuum bag film with high barrier properties. By weight, its preparation raw materials include: 95-99 parts polyethylene, 1-5 parts nanosheet material, and 0.5-1 parts lubricant. This patent application uses nanosheet material, surface-modified with a coupling agent, to fill the voids in the polyethylene material itself, thus isolating the voids and filling the gaps where polyethylene molecules are disrupted due to cross-linking under high humidity conditions. This significantly enhances the sealing performance of the vacuum bag film. Although the operation is simple, the peeling and dispersion effect of the sheet material is poor, which affects its dispersion effect in the resin and reduces the barrier properties of the film.

[0005] Therefore, how to significantly improve the water vapor barrier performance of polyethylene liquid bag films while maintaining the advantages of low cost, high toughness, and easy recyclability brought by polyolefin main resins has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To overcome the shortcomings of existing polyethylene films for liquid bags, such as insufficient water vapor barrier properties and high cost and difficulty in recycling of traditional composite solutions, this application provides a method for preparing and applying a high water vapor barrier blown film.

[0007] In a first aspect, this application provides a method for preparing a high water vapor barrier blown film, employing the following technical solution: It is produced by co-extrusion and blow molding of outer layer, sub-outer layer, core layer, sub-inner layer and inner layer, wherein the core layer comprises the following raw materials in parts by weight: 85-95 parts of high-density polyethylene and 5-15 parts of composite barrier agent modified polyethylene masterbatch. The preparation method of the composite barrier agent modified polyethylene masterbatch includes the following steps: (1) Disperse 1-10 parts by weight of inorganic flake filler in 10-100 parts by weight of water and sonicate to form a suspension; add 0.4-4 parts by weight of long-chain alkyl quaternary ammonium salt modifier to 5-50 parts by weight of deionized water or ethanol aqueous solution to form a mixture; add the mixture to the suspension and sonicate at 60-80℃ for 1-3 hours, then add 1-3 parts by weight of polytetrafluoroethylene micro powder, sonicate and disperse, and obtain the composite barrier agent by filtration, washing, drying and pulverizing. (2) Mix 10-15 parts by weight of maleic anhydride-grafted high-density polyethylene, 2-5 parts by weight of composite barrier agent and 0.1%-0.5% by weight of antioxidant of maleic anhydride-grafted high-density polyethylene to obtain a mixture. Melt the mixture and extrude it into granules to obtain composite barrier agent modified polyethylene masterbatch.

[0008] By adopting the above technical solutions, inorganic sheet fillers are easy to peel off due to their own sheet crystal structure. The sheet structure is dense and has a large aspect ratio. When they are doped into polyethylene matrix, they can form a tortuous path effect, effectively extending the permeation path of water molecules and gases, and significantly improving the barrier performance of the matrix. Polytetrafluoroethylene (PTFE) has extremely low surface free energy and excellent hydrophobicity, which can block water vapor permeation and make up for the defect that polyethylene membrane interlayer interface is easily corroded by water vapor in high humidity environment.

[0009] This application employs a two-step method to form a composite barrier agent: first, ion-exchange intercalation of an inorganic sheet-like filler with a long-chain alkyl quaternary ammonium salt modifier, and then introducing polytetrafluoroethylene (PTFE) micropowder to fill the enlarged sheet space. The first step utilizes the Na+ between the quaternary ammonium cations and the sheets. + The ion exchange of metal cations expands the interlayer spacing; at the same time, the long-chain alkyl ends of the modifier molecules are embedded in the interlayer to form steric hindrance; in the second step, small molecule PTFE powder enters the expanded interlayer spacing under ultrasonic assistance, and is uniformly dispersed in the polyethylene matrix along with the peeled-off sheets during subsequent melt blending and shearing action, forming a dual synergistic barrier network structure of sheet-like barrier and hydrophobic dots.

[0010] Meanwhile, maleic anhydride-grafted high-density polyethylene is used as the modified masterbatch matrix. The polar maleic anhydride groups on its molecular chain can undergo ring-opening esterification or hydrogen bonding with the hydroxyl groups on the sheet surface, achieving chemical bonding between the sheet filler and the polyethylene matrix. The long chain of the modifier has a matching solubility with the non-polar backbone of maleic anhydride-grafted high-density polyethylene, and can form inter-chain interlocking-entanglement and mutual solubility with the PE matrix during the melt blending stage. The two work synergistically to significantly improve the peeling degree and dispersion uniformity of the sheet filler in the non-polar polyethylene matrix, solving the technical problems of easy agglomeration and poor interfacial bonding of traditional sheet fillers in polyethylene.

[0011] Preferably, in step (1), the inorganic sheet filler is one or more of montmorillonite, kaolinite, hexagonal boron nitride, and vermiculite, and more preferably montmorillonite.

[0012] Preferably, the montmorillonite is sodium-based montmorillonite obtained by modifying natural montmorillonite with sodium salt via ion exchange; the sodium salt is one of sodium chloride, sodium sulfate, and sodium carbonate, and more preferably sodium chloride.

[0013] By adopting the above technical solutions, sodium-based montmorillonite has better cation exchange capacity, swelling capacity, dispersibility and thermal stability than calcium-based montmorillonite, which is more conducive to subsequent organic modification.

[0014] Sodium salts were inserted into the interlayer of natural montmorillonite using an ion exchange method to perform sodium-based treatment. The modified montmorillonite exhibited enhanced thermal stability and increased interlayer spacing, with sodium chloride showing the best modification effect. The exchange of sodium ions reduced the water absorption of montmorillonite, resulting in higher hydrophobicity, which provides favorable conditions for the further preparation of organically modified montmorillonite.

[0015] Preferably, in step (1), the long-chain alkyl quaternary ammonium salt modifier is one or more of octadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, dioctadecyldimethylammonium chloride, hexadecyltrimethylammonium bromide, and dodecyltrimethylammonium bromide.

[0016] By adopting the above technical solution, C 18 The long chain has a high solubility parameter matching with the PE matrix, and can "entangle and dissolve" with the PE molecular chain during the melt blending stage to form a three-level interface layer of inorganic sheet-modifier long chain-PE matrix, which significantly improves the dispersion uniformity and interfacial bonding force of the sheet filler in the non-polar PE matrix.

[0017] Preferably, in step (2), 10-15 parts by weight of maleic anhydride-grafted high-density polyethylene, 2-5 parts by weight of composite barrier agent, 1-3 parts by weight of nano-auxiliaries, and 0.1%-0.5% by weight of antioxidant of the maleic anhydride-grafted high-density polyethylene are mixed to obtain a mixture. The mixture is melted, extruded and granulated to obtain composite barrier agent modified polyethylene masterbatch. The nano-auxiliaries are a mixture of modified nanocellulose and modified nanosilica in a mass ratio of (3-5):1.

[0018] By adopting the above technical solutions, nanocellulose has nanoscale size and high specific surface area, which can form a dense network structure and effectively extend the diffusion path of gas and water vapor. Its crystallinity is as high as 50%-90%, and the crystalline region is composed of highly ordered cellulose molecular chains. The molecules are tightly bound by hydrogen bonds to form a dense barrier structure, which can effectively block the penetration of small molecules. At the same time, its surface is rich in hydroxyl groups, and its surface energy, hydrophobicity and interfacial interaction can be regulated after surface modification, thereby optimizing its barrier performance.

[0019] Nano-silica has a small particle size, large specific surface area, and a large number of hydroxyl groups on its surface. These hydroxyl groups make it easy for nano-silica particles to agglomerate and difficult to disperse in polymers. Modification not only gives silica good hydrophobicity, but also improves its dispersibility and compatibility in organic media.

[0020] This application improves the barrier properties of blown film by adding nano-additives that can fill the gaps in polyethylene molecules caused by the destruction of cross-linking structure under high humidity conditions, while simultaneously leveraging the hydrophobicity of modified nanocellulose and modified nanosilica.

[0021] Preferably, the method for preparing the modified nanocellulose includes the following steps: (a) Disperse nanocellulose in Tris-HCl buffer at pH=8.5, add dopamine hydrochloride to make the dopamine concentration 1-2 g / L, stir and react at 20-30℃ for 18-24 h, centrifuge, wash with water and freeze dry to obtain polydopamine-coated nanocellulose. (b) Disperse the product of step (a) in anhydrous ethanol, add octadecylamine at a mass ratio of 1:1 to polydopamine-coated nanocellulose, add triethylamine to adjust the pH to 8-9, stir the reaction at 60°C for 4-8 h under nitrogen protection, centrifuge, wash with ethanol, and vacuum dry to obtain modified nanocellulose with an average particle size of 80-100 nm.

[0022] By adopting the above technical solution, after nanocellulose is coated with polydopamine and covalently grafted with octadecylamine, the exposed octadecyl segments on the outer layer have excellent compatibility with the non-polar polyethylene matrix, and the catechol groups of the inner polydopamine can undergo a bonding reaction with the anhydride groups of maleic anhydride grafted with high-density polyethylene to construct a four-level interface structure of nanocellulose core-polydopamine shell-octadecyl tail-matrix, which significantly improves the dispersibility and interfacial bonding of the filler in the matrix.

[0023] Preferably, the modified nano-silica is prepared by: ultrasonically dispersing nano-silica in ethanol to form a suspension; fully hydrolyzing a silane coupling agent in an ethanol / water mixed solvent to form a hydrolysate; adding the suspension to the hydrolysate, heating to 60-80℃ and stirring under reflux for 2-4 hours, washing and drying to obtain modified nano-silica with an average particle size of 30-50 nm; the amount of the silane coupling agent is 1-5 wt% of the mass of the nano-silica.

[0024] By adopting the above technical solution, the surface of silica is modified by silane coupling agent to obtain hydrophobic silica. The dispersibility of the modified silica in the organic phase is improved, which can better fill the gaps in polyethylene molecules caused by the destruction of the cross-linking structure under high humidity conditions. At the same time, its hydrophobicity can further improve the barrier properties of the blown film.

[0025] Preferably, the method for preparing the high water vapor barrier blown film includes the following steps: The raw materials for the outer layer, the second outer layer, the core layer, the second inner layer, and the inner layer are mixed evenly to obtain the material. The material of each layer is fed into five extruders and melt co-extruded and blown through the five-layer co-extrusion die, followed by air cooling, traction, and corona treatment to obtain the high water vapor barrier blown film. The raw materials for the outer layer and the inner layer are both linear low-density polyethylene, while the raw materials for the second outer layer and the second inner layer are both high-density polyethylene.

[0026] Preferably, the extrusion temperature of the extruder is controlled at 170-210℃, the die temperature is controlled at 200-220℃, and the air-cooling temperature is controlled at 15-25℃.

[0027] Secondly, this application provides an application of a high moisture barrier blown film, employing the following technical solution: The high water vapor barrier blown film is processed into liquid bags through slitting, bag making, and heat sealing welding.

[0028] By adopting the above technical solution, the blown film core layer prepared in this application serves as a barrier functional layer with a concentrated distribution of composite barrier agent and nano-additives. The outer and inner layers provide good heat sealing and contact safety, while the secondary outer and secondary inner layers provide sufficient longitudinal and transverse strength and toughness, ensuring that the liquid bag is not easily damaged and is reliably sealed during transportation and handling.

[0029] In summary, this application has the following beneficial effects: 1. This application uses a two-step method to prepare a composite barrier agent by intercalation modification of long-chain alkyl quaternary ammonium salts and filling the gaps between polytetrafluoroethylene (PTFE) micropowders. The inorganic sheet-like filler forms a tortuous path with a sheet structure to extend the permeation path. PTFE, with its high hydrophobicity, assists in blocking water vapor. At the same time, maleic anhydride-grafted high-density polyethylene, through bonding with the filler and mutual solubility and entanglement with the polyethylene matrix, synergistically improves the dispersibility and interfacial bonding of the filler, thereby improving the barrier properties of the blown film.

[0030] 2. This application improves the barrier properties of blown film by adding nano-additives that can fill the gaps in polyethylene molecules caused by the destruction of cross-linking structure under high humidity conditions, while also leveraging the hydrophobicity of modified nanocellulose and modified nanosilica.

[0031] 3. The modified nanocellulose in this application is polydopamine-coated and grafted with octadecylamine nanocellulose, which can construct a four-level interface structure of nanocellulose core-polydopamine shell-octadecyl tail-matrix, thereby improving the dispersibility and interfacial bonding of the filler in the matrix. Detailed Implementation

[0032] The present application will be further described in detail below with reference to the embodiments.

[0033] The raw materials used in the preparation examples, embodiments, and comparative examples of this application are all commercially available.

[0034] Preparation Example 1: Sodium-based montmorillonite This preparation example discloses a method for preparing montmorillonite, specifically: 5 kg of natural montmorillonite is treated with 100 L of deionized water, then washed three times with 50% ethanol solution, and 100 L of 1 mol / L sodium chloride solution is added. The mixture is then stirred at a constant temperature in a 60℃ water bath for 3 hours, allowed to cool naturally, centrifuged, and washed three times each with deionized water and 50% ethanol solution until the supernatant is free of Cl. - The sample was detected (AgNO3 test), dried in an 80℃ constant temperature drying oven to constant weight, and ground through a 200-mesh sieve to obtain sodium montmorillonite.

[0035] Preparation Examples 2-4 Modifiers Preparation Example 2 This preparation example discloses a method for preparing a modifier, specifically as follows: 7.3 kg of octadecyltrimethylammonium bromide (STAB) and 200 L of deionized water are added to a reaction vessel equipped with a mechanical stirrer, a thermometer, and a reflux condenser. The mixture is stirred in an 80°C water bath until completely dissolved to form a clear solution. A small amount of dilute hydrochloric acid is slowly added dropwise to adjust the pH to 3.5, and the mixture is kept warm and stirred for 30 min to obtain the modifier.

[0036] Preparation Example 3 Modifier This preparation example discloses a method for preparing a modifier, specifically: 12.0 kg of bis(octadecyl)dimethylammonium chloride (DODAC) is added to a reaction vessel, and 250 L of ethanol-water (volume ratio 1:1) mixed solvent is added. The mixture is stirred and dissolved in a 70°C water bath to form a homogeneous solution. A small amount of dilute hydrochloric acid is slowly added dropwise to adjust the pH to 3.5, and the mixture is kept warm and stirred for 30 min to obtain the modifier.

[0037] Preparation Example 4 Modifier This preparation example discloses a method for preparing a modifier, specifically: 7.3 kg of cetyltrimethylammonium bromide (CTAB) is added to a reaction vessel, 200 L of deionized water is added, and the mixture is stirred and dissolved in a 70 °C water bath; a small amount of dilute hydrochloric acid is slowly added dropwise to adjust the pH to 3.5, and the mixture is kept warm and stirred for 30 min to obtain the modifier.

[0038] Preparation Examples 5-10: Polyethylene Masterbatch Modified with Composite Barrier Agent This preparation example discloses a method for preparing a composite barrier agent modified polyethylene masterbatch, specifically including the following steps: (1) 1 kg of sodium montmorillonite (prepared according to Preparation Example 1) was added to 30 L of deionized water, stirred at high speed (500 r / min) in a water bath at 70 °C and ultrasonically dispersed for 45 min to form a uniform suspension; 11.5 L of modifier containing 0.4 kg STAB (prepared according to Preparation Example 2) was added, and the mixture was mechanically stirred at 70 °C for 3 h; 1 kg of polytetrafluoroethylene micro powder with a particle size of 1-5 μm was added, and ultrasonically dispersed for 60 min to form mixture A; after the reaction was completed, the mixture was filtered and washed with 50% ethanol aqueous solution until no Br was found. - The compound barrier agent was obtained by detecting AgNO3, vacuum drying at 80℃ to constant weight, and mechanically pulverizing it through a 200-mesh sieve.

[0039] (2) 10 kg of maleic anhydride-grafted high-density polyethylene, 2 kg of the composite barrier agent obtained in step (1), 0.02 kg of antioxidant 1010, and 0.02 kg of antioxidant 168 were premixed in a high-speed mixer for 5 min; then fed into a co-rotating twin-screw extruder (φ35 mm, L / D=40) for melt blending. The temperatures of each section were set as follows: feeding section 170℃, conveying section 190℃, melting section 200℃, mixing section 210℃, metering section 215℃, and die head 220℃; the screw speed was 250 r / min; the melt was pelletized by water ring cutting, vibrating sieve, and dried at 80℃ for 4 h to obtain composite barrier agent modified polyethylene masterbatch.

[0040] Preparation Example 6 This preparation example discloses a method for preparing a composite barrier agent modified polyethylene masterbatch, specifically including the following steps: (1) Add 5 kg of sodium montmorillonite (prepared according to the method of Preparation Example 1) to 60 L of deionized water, stir at high speed (500 r / min) in a water bath at 70 °C and ultrasonically disperse for 45 min to form a uniform suspension; add 42 L of modifier containing 2 kg of DODAC (prepared according to the method of Preparation Example 3), and react mechanically at 70 °C for 3 h; add 2 kg of polytetrafluoroethylene micro powder with a particle size of 1-5 μm, and ultrasonically disperse for 60 min to form mixture A; after the reaction is completed, filter and wash with 50% ethanol aqueous solution until Cl is removed. - The compound barrier agent was obtained by detecting AgNO3, vacuum drying at 80℃ to constant weight, and mechanically pulverizing it through a 200-mesh sieve.

[0041] (2) 12 kg of maleic anhydride-grafted high-density polyethylene, 3 kg of the composite barrier agent obtained in step (1), 0.03 kg of antioxidant 1010, and 0.03 kg of antioxidant 168 were premixed in a high-speed mixer for 5 min; then fed into a co-rotating twin-screw extruder (φ35 mm, L / D=40) for melt blending. The temperatures of each section were set as follows: feeding section 170℃, conveying section 190℃, melting section 200℃, mixing section 210℃, metering section 215℃, and die head 220℃; the screw speed was 250 r / min; the melt was pelletized by water ring cutting, vibrating sieve, and dried at 80℃ for 4 h to obtain composite barrier agent modified polyethylene masterbatch.

[0042] Preparation Example 7 This preparation example discloses a method for preparing a composite barrier agent modified polyethylene masterbatch, specifically including the following steps: (1) 10 kg of sodium montmorillonite (prepared according to the method of Preparation Example 1) was added to 100 L of deionized water, stirred at high speed (500 r / min) in a water bath at 70 °C and ultrasonically dispersed for 45 min to form a uniform suspension; 110 L of modifier containing 4 kg of CTAB (prepared according to the method of Preparation Example 4) was added, and the mixture was mechanically stirred at 70 °C for 3 h; 3 kg of polytetrafluoroethylene micro powder with a particle size of 1-5 μm was added, and ultrasonically dispersed for 60 min to form mixture A; after the reaction was completed, the mixture was filtered and washed with 50% ethanol aqueous solution until no Br was found. - The compound barrier agent was obtained by detecting AgNO3, vacuum drying at 80℃ to constant weight, and mechanically pulverizing it through a 200-mesh sieve.

[0043] (2) 15 kg of maleic anhydride-grafted high-density polyethylene, 5 kg of the composite barrier agent obtained in step (1), 0.04 kg of antioxidant 1010, and 0.04 kg of antioxidant 168 were premixed in a high-speed mixer for 5 min; then fed into a co-rotating twin-screw extruder (φ35 mm, L / D=40) for melt blending. The temperatures of each section were set as follows: feeding section 170℃, conveying section 190℃, melting section 200℃, mixing section 210℃, metering section 215℃, and die head 220℃; the screw speed was 250 r / min; the melt was pelletized by water ring cutting, vibrating sieve, and dried at 80℃ for 4 h to obtain composite barrier agent modified polyethylene masterbatch.

[0044] Preparation Example 8 This preparation example is basically the same as Preparation Example 6, except that (2) 12 kg of maleic anhydride-grafted high-density polyethylene, 3 kg of the composite barrier agent obtained in step (1), 0.75 kg of modified nanocellulose, 0.25 kg of modified nanosilica, 0.03 kg of antioxidant 1010, and 0.03 kg of antioxidant 168 are premixed in a high-speed mixer for 5 min; then fed into a co-rotating twin-screw extruder (φ35 mm, L / D=40) for melt blending. The temperatures of each section are set as follows: feeding section 170℃, conveying section 190℃, melting section 200℃, mixing section 210℃, metering section 215℃, and die head 220℃; the screw speed is 250 r / min; the melt is granulated by water ring cutting, vibrating sieve, and dried at 80℃ for 4 h to obtain composite barrier agent modified polyethylene masterbatch.

[0045] The modified nanocellulose was prepared as follows: (a) 1 kg of nanocellulose with a particle size of 20-30 nm was weighed and added to 100 L of 10 mmol / L Tris-HCl buffer solution with pH=8.5, and ultrasonically dispersed for 30 min under ice bath conditions; 200 g of dopamine hydrochloride (final concentration approximately 1 g / L) was added; the mixture was mechanically stirred at 25 °C for 24 h under open conditions; centrifuged at 10000 r / min for 15 min, washed with deionized water until the supernatant was colorless, and freeze-dried at -50 °C for 48 h to obtain polydopamine-coated nanocellulose; (b) 500 g of polydopamine-coated nanocellulose was dispersed in 15 L of anhydrous ethanol and ultrasonically dispersed to form a suspension; 500 g of octadecylamine was dissolved in 5 L of anhydrous ethanol and slowly added dropwise to the suspension; triethylamine was added to adjust the pH to 8.5; the mixture was magnetically stirred at 60 °C for 6 h under nitrogen protection; 10000 r / min was centrifuged at 10000 r / min for 15 min, washed with deionized water until the supernatant was colorless, and freeze-dried at -50 °C for 48 h to obtain polydopamine-coated nanocellulose; (c) 500 g of polydopamine-coated nanocellulose was dispersed in 15 L of anhydrous ethanol and ultrasonically dispersed to form a suspension; 500 g of octadecylamine was dissolved in 5 L of anhydrous ethanol and slowly added dropwise to the suspension; triethylamine was added to adjust the pH to 8.5; the mixture was magnetically stirred at 60 °C for 6 h under nitrogen protection; 10000 r / min was centrifuged at 10000 r / min for 15 min, Centrifuge at 1 r / min for 15 min, wash three times with anhydrous ethanol, and vacuum dry at 50℃ for 12 h to obtain modified nanocellulose with an average particle size of about 80 nm.

[0046] The modified nano-silica was prepared as follows: 180 mL of ethanol and 20 mL of deionized water were mixed, and 10 g of KH550 was added dropwise while stirring. The mixture was stirred for 30 min to form a hydrolysate. 1 kg of fumed nano-silica with a particle size of 20-30 nm was added to 20 kg of 90 wt% ethanol solution and ultrasonically dispersed for 30 min. The hydrolysate was added while stirring, and the mixture was heated to 60 °C and refluxed for 2 h. The product was centrifuged at 10000 r / min, washed three times with ethanol, and dried at 60 °C to obtain modified nano-silica with an average particle size of about 30 nm.

[0047] Preparation Example 9 This preparation example is basically the same as Preparation Example 6, except that (2) 12 kg of maleic anhydride-grafted high-density polyethylene, 3 kg of the composite barrier agent obtained in step (1), 1.6 kg of modified nanocellulose, 0.4 kg of modified nanosilica, 0.03 kg of antioxidant 1010, and 0.03 kg of antioxidant 168 are premixed in a high-speed mixer for 5 min; then fed into a co-rotating twin-screw extruder (φ35 mm, L / D=40) for melt blending. The temperatures of each section are set as follows: feeding section 170℃, conveying section 190℃, melting section 200℃, mixing section 210℃, metering section 215℃, and die head 220℃; the screw speed is 250 r / min; the melt is pelletized by water ring cutting, vibrating sieve, and dried at 80℃ for 4 h to obtain composite barrier agent modified polyethylene masterbatch.

[0048] The modified nanocellulose was prepared as follows: (a) 1 kg of nanocellulose with a particle size of 20-30 nm was weighed and added to 100 L of 10 mmol / L Tris-HCl buffer solution with pH=8.5, and ultrasonically dispersed for 30 min under ice bath conditions; 300 g of dopamine hydrochloride (final concentration approximately 1.5 g / L) was added; the mixture was mechanically stirred at 25 °C for 24 h under open conditions; centrifuged at 10000 r / min for 15 min, washed with deionized water until the supernatant was colorless, and freeze-dried at -50 °C for 48 h to obtain polydopamine-coated nanocellulose; (b) 500 g of polydopamine-coated nanocellulose was dispersed in 15 L of anhydrous ethanol and ultrasonically dispersed to form a suspension; 500 g of octadecylamine was dissolved in 5 L of anhydrous ethanol and slowly added dropwise to the suspension; triethylamine was added to adjust the pH to 8.5; the mixture was magnetically stirred at 60 °C for 6 h under nitrogen protection; 10000 Centrifuge at 1 r / min for 15 min, wash three times with anhydrous ethanol, and vacuum dry at 50℃ for 12 h to obtain modified nanocellulose with an average particle size of about 90 nm.

[0049] The modified nano-silica was prepared as follows: 180 mL of ethanol and 20 mL of deionized water were mixed, and 30 g of KH550 was added dropwise while stirring. The mixture was stirred for 30 min to form a hydrolysate. 1 kg of fumed nano-silica with a particle size of 20-30 nm was added to 20 kg of 90 wt% ethanol solution and ultrasonically dispersed for 30 min. The hydrolysate was added while stirring, and the mixture was heated to 70 °C and refluxed for 3 h. The product was centrifuged at 10000 r / min, washed three times with ethanol, and dried at 60 °C to obtain modified nano-silica with an average particle size of about 40 nm.

[0050] Preparation Example 10 This preparation example is basically the same as Preparation Example 6, except that (2) 12 kg of maleic anhydride-grafted high-density polyethylene, 3 kg of the composite barrier agent obtained in step (1), 2.5 kg of modified nanocellulose, 0.5 kg of modified nanosilica, 0.03 kg of antioxidant 1010, and 0.03 kg of antioxidant 168 are premixed in a high-speed mixer for 5 min; then fed into a co-rotating twin-screw extruder (φ35 mm, L / D=40) for melt blending. The temperatures of each section are set as follows: feeding section 170℃, conveying section 190℃, melting section 200℃, mixing section 210℃, metering section 215℃, and die head 220℃; the screw speed is 250 r / min; the melt is granulated by water ring cutting, vibrating sieve, and dried at 80℃ for 4 h to obtain composite barrier agent modified polyethylene masterbatch.

[0051] The modified nanocellulose was prepared as follows: (a) 1 kg of nanocellulose with a particle size of 20-30 nm was weighed and added to 100 L of 10 mmol / L Tris-HCl buffer solution with pH=8.5, and ultrasonically dispersed for 30 min under ice bath conditions; 400 g of dopamine hydrochloride (final concentration approximately 2 g / L) was added; the mixture was mechanically stirred at 25 °C for 24 h under open conditions; centrifuged at 10000 r / min for 15 min, washed with deionized water until the supernatant was colorless, and freeze-dried at -50 °C for 48 h to obtain polydopamine-coated nanocellulose; (b) 500 g of polydopamine-coated nanocellulose was dispersed in 15 L of anhydrous ethanol and ultrasonically dispersed to form a suspension; 500 g of octadecylamine was dissolved in 5 L of anhydrous ethanol and slowly added dropwise to the suspension; triethylamine was added to adjust the pH to 8.5; the mixture was magnetically stirred at 60 °C for 6 h under nitrogen protection; 10000 r / min was centrifuged at 10000 r / min for 15 min, washed with deionized water until the supernatant was colorless, and freeze-dried at -50 °C for 48 h to obtain polydopamine-coated nanocellulose; (c) 500 g of polydopamine-coated nanocellulose was dispersed in 15 L of anhydrous ethanol and ultrasonically dispersed to form a suspension; 500 g of octadecylamine was dissolved in 5 L of anhydrous ethanol and slowly added dropwise to the suspension; triethylamine was added to adjust the pH to 8.5; the mixture was magnetically stirred at 60 °C for 6 h under nitrogen protection; 10000 r / min was centrifuged at 10000 r / min for 15 min, Centrifuge at 1 r / min for 15 min, wash three times with anhydrous ethanol, and vacuum dry at 50℃ for 12 h to obtain modified nanocellulose with an average particle size of about 90 nm.

[0052] The modified nano-silica was prepared as follows: 180 mL of ethanol and 20 mL of deionized water were mixed, and 50 g of KH550 was added dropwise while stirring. The mixture was stirred for 30 min to form a hydrolysate. 1 kg of fumed nano-silica with a particle size of 20-30 nm was added to 20 kg of 90 wt% ethanol solution and ultrasonically dispersed for 30 min. The hydrolysate was added while stirring, and the mixture was heated to 80 °C and refluxed for 4 h. The product was centrifuged at 10000 r / min, washed three times with ethanol, and dried at 60 °C to obtain modified nano-silica with an average particle size of about 50 nm.

[0053] Example 1 This embodiment provides a high moisture barrier blown film formulation as follows: Outer layer: 100kg linear low-density polyethylene; Second outer layer: 100kg high-density polyethylene; Core layer: 95 kg of high-density polyethylene and 5 kg of composite barrier agent modified polyethylene masterbatch (obtained from Preparation Example 5); Inner layer: 100kg high-density polyethylene; Inner layer: 100kg linear low-density polyethylene; This embodiment also provides a method for preparing the above-mentioned high water vapor barrier blown film, including the following steps: Material mixing: Mix each layer of resin and masterbatch evenly in a high-speed mixer according to the above formula.

[0054] Five-layer co-extrusion blow molding: Five extruders correspond to five layers respectively, with extrusion temperatures controlled at 170℃-210℃; the temperature of the five-layer co-extrusion die is 210℃; the melt is extruded and blown after converging at the die, with a blow-up ratio of 2.5-3.0 and a draw ratio of 4-5; dual-air ring cooling is adopted, with a cooling air temperature of 20℃; after traction stabilization, it undergoes corona treatment, edge trimming, online thickness measurement, and winding to obtain a five-layer co-extrusion blow-molded film with a total thickness of 100μm, of which the core layer thickness accounts for 40%.

[0055] This embodiment also discloses a method for preparing a liquid bag: the above-mentioned high water vapor barrier blown film is slit into rolls with a width of 2400mm along the longitudinal direction (MD direction) of the film surface by a slitting machine, and then cut into pieces according to the design capacity of 1000L of the liquid bag (the single piece cutting size is about 2400mm×4800mm) to obtain liquid bag film sheets; two film sheets are flatly stacked with the inner LLDPE surfaces facing each other, and the edges are sealed by a four-sided heat sealing welding process. The heat sealing is carried out using a constant temperature hot press welding machine, the welding temperature is controlled at 150℃, the welding pressure is 0.4MPa, the welding time is 3s, and the weld width is 15mm to form a bag body.

[0056] Example 2 The difference between this embodiment and Embodiment 1 is that: Core layer: 93 kg of high-density polyethylene and 7 kg of composite barrier modified polyethylene masterbatch (obtained from Preparation Example 5), other components are the same as in Example 1.

[0057] Example 3 The difference between this embodiment and Embodiment 1 is that: Core layer: 90 kg of high-density polyethylene and 10 kg of composite barrier agent modified polyethylene masterbatch (obtained from Preparation Example 5), other components are the same as in Example 1.

[0058] Example 4 The difference between this embodiment and Embodiment 2 is as follows: The composite barrier agent modified polyethylene masterbatch was obtained from Preparation Example 6, and the rest was the same as in Example 2.

[0059] Example 5 The difference between this embodiment and Embodiment 2 is as follows: The composite barrier agent modified polyethylene masterbatch was obtained from Preparation Example 7, and the rest was the same as in Example 2.

[0060] Example 6 The difference between this embodiment and embodiment 4 is that: The composite barrier agent modified polyethylene masterbatch was obtained from Preparation Example 8, and the rest was the same as in Example 4.

[0061] Example 7 The difference between this embodiment and embodiment 4 is that: The composite barrier agent modified polyethylene masterbatch was obtained from Preparation Example 9, and the rest was the same as in Example 4.

[0062] Example 8 The difference between this embodiment and embodiment 4 is that: The composite barrier agent modified polyethylene masterbatch was obtained from Preparation Example 10, and the rest was the same as in Example 4.

[0063] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: Core layer: 95 kg high-density polyethylene and 5 kg silane coupling agent modified montmorillonite, other components are the same as in Example 1; The specific method for modifying montmorillonite with silane coupling agent is as follows: 1.8 L of anhydrous ethanol and 0.2 L of deionized water are mixed at a volume ratio of 9:1. 200 g of γ-aminopropyltriethoxysilane is slowly added dropwise under stirring. The pH of the system is adjusted to 4.5 with glacial acetic acid, and the mixture is stirred at room temperature for 30 min to obtain a hydrolysate. 10 kg of montmorillonite (obtained from Preparation Example 1) is added to 10 L of 90 wt% ethanol aqueous solution and ultrasonically dispersed for 30 min to form a uniform suspension. The hydrolysate is slowly added dropwise to the montmorillonite suspension, and the mixture is heated to 80 °C and mechanically stirred under reflux for 4 h. After the reaction is completed, the mixture is centrifuged at 10000 r / min, washed three times with anhydrous ethanol, vacuum dried at 80 °C to constant weight, and ground through a 200-mesh sieve to obtain silane coupling agent modified montmorillonite.

[0064] Comparative Example 2 This comparative example discloses a barrier blown film, which is prepared using a dry lamination process to create a PE / metallized PET composite film. The specific steps are as follows: Step 1: Dilute the two-component polyurethane adhesive with ethyl acetate to a solid content of 30wt%. At the coating station of the dry laminating machine, apply the diluted adhesive to the aluminized surface of the 12μm aluminized PET film using a gravure roller. The coating amount is controlled at 3.5 g / m². Step 2: The coated aluminized PET film enters the drying oven channel of the dry laminating machine. The oven is temperature controlled in three sections (50℃→70℃→80℃) to obtain an aluminized PET film with a residual adhesive layer on the surface. Step 3: The inner and outer layers are both linear low-density polyethylene, and the middle layer is high-density polyethylene. Three extruders are used for each of the three layers, with extrusion temperatures controlled at 170℃-210℃ respectively. The temperature of the three-layer co-extrusion die is 210℃. After the melt converges at the die, it is extruded and blown, with a blow-up ratio of 2.5-3.0 and a draw ratio of 4-5. Dual-air ring cooling is used, with a cooling air temperature of 20℃. After traction stabilization, it undergoes corona treatment, edge trimming, online thickness measurement, and winding to obtain a three-layer co-extruded blown film with a total thickness of 100μm, of which the core layer accounts for 40%. The 100μm three-layer co-extruded PE film is then bonded to the above-mentioned coated aluminized PET film at the composite steel roller of a dry laminating machine (the outer layer of the PE film is in contact with the coated aluminized surface of the aluminized PET film). The lamination temperature is 80℃, the lamination pressure is 0.4 MPa, and the lamination speed is 80 m / min to obtain a composite film semi-finished product. Step 4: Transfer the above composite film semi-finished product to a 45℃ constant temperature curing chamber and cure for 48 hours to obtain a barrier blown film.

[0065] Performance testing 1. Water vapor transmission rate (WVTR): Determined according to the cup method of GB / T 1037-2021, at a temperature of 38℃ and a relative humidity of 90%. The test results are shown in Table 1.

[0066] 2. Tensile strength and elongation at break: determined according to GB / T 1040.3-2006, with a tensile speed of 500 mm / min, and tested in the longitudinal direction (MD) and transverse direction (TD). The test results are shown in Table 1.

[0067] Performance test data of Examples 1-8 and Comparative Examples 1-2

[0068] Combined with Example 1 and Comparative Example 1 and referring to Table 1, it can be seen that this application forms a composite barrier agent by using a two-step method (first, long-chain alkyl quaternary ammonium salt ion exchange intercalation, and then PTFE filling the expanded interlayer space) with polytetrafluoroethylene and inorganic sheet filler, and then uses maleic anhydride-grafted high-density polyethylene as a carrier for melt blending and granulation to prepare masterbatch. The peeling and dispersion effect of sheet filler in polyethylene matrix is ​​significantly better than that of direct blending of montmorillonite modified with a single silane coupling agent. The water vapor permeability of the membrane material decreases, while the tensile strength and elongation at break are significantly improved.

[0069] Referring to Example 1 and Comparative Example 2 and Table 1, it can be seen that although the water vapor barrier performance of the present application is slightly lower than that of the traditional aluminized composite membrane, the membrane material is entirely composed of polyolefins and has no metal interlayer, thus possessing better toughness, higher recyclability, and lower cost.

[0070] Referring to Examples 4 and 6-8 and Table 1, it can be seen that by further adding a nano-additive composed of modified nanocellulose and modified nanosilica on the basis of the composite barrier agent, the water vapor permeability can be further reduced, demonstrating the advantages of multi-scale synergistic barrier of sheet-line-point.

[0071] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A process for the production of a high water vapor barrier blown film, characterized in that, It is produced by co-extrusion and blow molding of outer layer, sub-outer layer, core layer, sub-inner layer and inner layer, wherein the core layer comprises the following raw materials in parts by weight: 85-95 parts of high-density polyethylene and 5-15 parts of composite barrier agent modified polyethylene masterbatch. The preparation method of the composite barrier agent modified polyethylene masterbatch includes the following steps: (1) Disperse 1-10 parts by weight of inorganic flake filler in 10-100 parts by weight of water and sonicate to form a suspension; add 0.4-4 parts by weight of long-chain alkyl quaternary ammonium salt modifier to 5-50 parts by weight of deionized water or ethanol aqueous solution to form a mixture; add the mixture to the suspension and sonicate at 60-80℃ for 1-3 hours, then add 1-3 parts by weight of polytetrafluoroethylene micro powder, sonicate and disperse, and obtain the composite barrier agent by filtration, washing, drying and pulverizing. (2) Mix 10-15 parts by weight of maleic anhydride-grafted high-density polyethylene, 2-5 parts by weight of composite barrier agent and 0.1%-0.5% by weight of antioxidant of maleic anhydride-grafted high-density polyethylene to obtain a mixture. Melt the mixture and extrude it into granules to obtain composite barrier agent modified polyethylene masterbatch.

2. The method of making a high water vapor barrier blown film according to claim 1, wherein, In step (1), the inorganic sheet filler is one or more of montmorillonite, kaolinite, hexagonal boron nitride, and vermiculite.

3. The method of claim 2, wherein the high water vapor barrier blown film is prepared by a process comprising: The montmorillonite is sodium-based montmorillonite obtained by modifying natural montmorillonite with sodium salts via ion exchange.

4. The method of making a high water vapor barrier blown film according to claim 1, wherein, In step (1), the long-chain alkyl quaternary ammonium salt modifier is one or more of octadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, bis(octadecyldimethylammonium chloride), hexadecyltrimethylammonium bromide, and dodecyltrimethylammonium bromide.

5. The method of claim 1, wherein the high water vapor barrier blown film is prepared by a process comprising: Step (2) Mix 10-15 parts by weight of maleic anhydride-grafted high-density polyethylene, 2-5 parts by weight of composite barrier agent, 1-3 parts by weight of nano-auxiliaries, and 0.1%-0.5% by weight of antioxidant of the maleic anhydride-grafted high-density polyethylene to obtain a mixture. Melt the mixture and extrude it into granules to obtain composite barrier agent modified polyethylene masterbatch. The nano-auxiliaries are a mixture of modified nanocellulose and modified nanosilica in a mass ratio of (3-5):

1.

6. The method of claim 5, wherein the high water vapor barrier blown film is prepared by a process comprising: The method for preparing the modified nanocellulose includes the following steps: (a) Disperse nanocellulose in Tris-HCl buffer at pH=8.5, add dopamine hydrochloride to make the dopamine concentration 1-2 g / L, stir and react at 20-30℃ for 18-24 h, centrifuge, wash with water and freeze dry to obtain polydopamine-coated nanocellulose. (b) Disperse the product of step (a) in anhydrous ethanol, add octadecylamine at a mass ratio of 1:1 to polydopamine-coated nanocellulose, add triethylamine to adjust the pH to 8-9, stir the reaction at 60°C for 4-8 h under nitrogen protection, centrifuge, wash with ethanol, and vacuum dry to obtain modified nanocellulose with an average particle size of 80-100 nm.

7. The method for preparing a high water vapor barrier blown film according to claim 5, characterized in that, The modified nano-silica is prepared by: ultrasonically dispersing nano-silica in ethanol to form a suspension; fully hydrolyzing a silane coupling agent in an ethanol / water mixed solvent to form a hydrolysate; adding the suspension to the hydrolysate, heating to 60-80℃ and stirring under reflux for 2-4 hours, washing and drying to obtain modified nano-silica with an average particle size of 30-50 nm; the amount of silane coupling agent used is 1-5 wt% of the mass of nano-silica.

8. The method for preparing a high water vapor barrier blown film according to claim 1, characterized in that, Includes the following steps: The raw materials for the outer layer, the second outer layer, the core layer, the second inner layer, and the inner layer are mixed evenly to obtain the material. The material of each layer is fed into five extruders and melt co-extruded and blown through the five-layer co-extrusion die, followed by air cooling, traction, and corona treatment to obtain the high water vapor barrier blown film. The raw materials for the outer layer and the inner layer are both linear low-density polyethylene, while the raw materials for the second outer layer and the second inner layer are both high-density polyethylene.

9. The method for preparing a high water vapor barrier blown film according to claim 8, characterized in that, The extruder's extrusion temperature is controlled at 170-210℃, the die head temperature at 200-220℃, and the air-cooling temperature at 15-25℃.

10. The application of the high moisture barrier blown film according to any one of claims 1-9, characterized in that, The high water vapor barrier blown film is processed into liquid bags through slitting, bag making, and heat sealing welding.

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