Low-precipitation polyethylene film and preparation method thereof

Abstract

The invention relates to the technical field of polyethylene films, and particularly discloses a low-precipitation polyethylene film and a preparation method thereof. The low-precipitation polyethylene film is prepared from the following raw materials: polyethylene, silicon carbide nanowires, nano talcum powder, an antioxidant and glyceryl stearate. The alkane precipitation amount of the obtained polyethylene film is 5 ppm or below, and precipitation of alkane molecules of the polyethylene film is obviously reduced.

Description

Technical Field

[0001] This application relates to the field of polyethylene films, and more specifically, to a low-exudation polyethylene film and a method for preparing the same. Background Technology

[0002] Polyethylene film is a thin and flexible plastic film made of polyethylene resin through processes such as blow molding, casting, or calendering. It is the most produced and widely used type of plastic film in the world, and is widely used in food, pharmaceuticals, daily consumer goods, and industrial packaging. Among them, low-emission polyethylene film is mainly used for special categories with packaging requirements, such as pharmaceutical raw materials, food, and food additives. In the actual application of packaging pharmaceutical raw materials, a large number of alkane molecules precipitate on the surface of the polyethylene film and migrate into the packaged pharmaceutical raw materials. This not only reduces the content of the active ingredients in the raw materials, but also increases the impurities in the raw materials, and even reduces the efficacy. It will have an adverse effect on the efficacy stability of pharmaceutical raw materials and the safety of subsequent medication.

[0003] In related technologies, nano-silica is added to the polyethylene film raw material to reduce the amount of low molecular weight alkanes released and improve the performance of the polyethylene film. However, nano-silica is prone to agglomeration, which leads to a decrease in the mechanical properties of the polyethylene film and makes it difficult to meet practical application requirements. Therefore, there is an urgent need to develop a low-release polyethylene film to meet practical application requirements. Summary of the Invention

[0004] To reduce the amount of low molecular weight alkanes precipitated from polyethylene films, this application provides a low-precipitation polyethylene film and a method for its preparation.

[0005] In a first aspect, this application provides a low-emission polyethylene membrane, which adopts the following technical solution: A low-emission polyethylene membrane comprises the following raw materials in parts by weight: 85-100 parts polyethylene, 0-5 parts silicon carbide nanowires, 0-8 parts nano talc, 0-1 parts antioxidant, and 0-1 parts glyceryl stearate.

[0006] The polyethylene film of this application uses any one of the following values: 85-100 parts polyethylene, 0-5 parts silicon carbide nanowires, 0-8 parts nano talc, 0-1 parts antioxidant, and 0-1 parts glyceryl stearate. The performance of the polyethylene film is predictable and can reduce the precipitation of low molecular weight alkanes from the polyethylene film to varying degrees.

[0007] By adopting the above scheme, polyethylene can be directly used as the raw material for polyethylene film, that is, low-density polyethylene can be used. The polyethylene film produced has an elution rate of 4.9 ppm, which is below 5 ppm, significantly reducing the elution rate of alkane molecules in polyethylene film.

[0008] Adding silicon carbide nanowires to polyethylene films, as a high aspect ratio inorganic nanomaterial, forms a three-dimensional interwoven network, diffusing the precipitation pathways of alkane molecules and thus reducing the amount of alkane precipitation in the polyethylene film. Nano-talc powder forms a two-dimensional barrier network, forcing alkane molecules to diffuse around the edges of the sheets, similarly diffusing their precipitation pathways and further reducing the amount of alkane precipitation in the polyethylene film. Furthermore, the three-dimensional interwoven network of silicon carbide nanowires in the polyethylene matrix extends the migration path of small alkane molecules, hindering their lateral diffusion, while nano-talc powder blocks the longitudinal migration channels of small molecules. The combination of these two materials constructs a multi-level barrier system, significantly increasing the difficulty of migration and substantially reducing the amount of low-molecular-weight alkane precipitation in the polyethylene film.

[0009] The long-chain ester groups of glyceryl stearate form a "polymer-like chain" entanglement with alkane molecules through hydrophobic interactions, constructing an "alkane adsorption network" in polyethylene. This effectively prevents the migration of low molecular weight alkanes and reduces the precipitation of low molecular weight alkanes from the polyethylene film.

[0010] Preferably, the weight ratio of the silicon carbide nanowires to the nano-talc powder is 1:(1.3-1.7).

[0011] By adopting the above scheme and controlling the weight ratio of silicon carbide nanowires to nano-talc powder, the composite effect of silicon carbide nanowires and nano-talc powder in polyethylene film can be further improved, thereby further improving the low precipitation characteristics of polyethylene film.

[0012] Preferably, the polyethylene film raw material further includes 1-3 parts of nano-silica-grafted sorbitol, which is prepared by the following steps: S1. Disperse nano-silica in an ethanol aqueous solution, sonicate, adjust pH to 4-5, heat to 60℃ and stir for 30 min, add 3-aminopropyltriethoxysilane, stir at 60℃ for 3 h, centrifuge and wash, and vacuum dry to obtain pretreated nano-silica. S2. Dissolve the pretreated nano-silica and sorbitol in ethanol, add p-toluenesulfonic acid, reflux at 80°C for 4-6 h, centrifuge, wash, and vacuum dry to obtain nano-silica grafted sorbitol.

[0013] The mass ratio of nano-silica to ethanol aqueous solution is 1:(5-6); the amount of 3-aminopropyltriethoxysilane is 5-8% of the mass of nano-silica; and the amount of p-toluenesulfonic acid is 2-3% of the mass of sorbitol.

[0014] By adopting the above scheme, the addition of nano-silica grafted with sorbitol can form a three-dimensional network structure in the polyethylene film. The diffusion path of alkane molecules is significantly extended, requiring them to pass through the dense interface layer, thereby reducing the alkane precipitation rate. Furthermore, the hydroxyl groups of sorbitol combine with the carbon chains of alkane molecules to form reversible adsorption, reducing the free energy of alkane and making it more difficult for them to precipitate from the surface of the polyethylene film.

[0015] First, nano-silica is dispersed in an aqueous ethanol solution, and then 3-aminopropyltriethoxysilane is added to react, which facilitates the grafting of sorbitol onto the nano-silica. Sorbitol molecules contain multiple hydroxyl groups, which react with the hydroxyl groups on the surface of nano-silica through chemical bonds, reducing the agglomeration of nano-silica and improving the dispersion uniformity of nano-silica.

[0016] Preferably, the mass ratio of sorbitol to nano-silica is 1:(1-1.5).

[0017] By adopting the above scheme and controlling the mass ratio of sorbitol to nano-silica, the effect of grafting sorbitol onto nano-silica is further optimized, thereby further improving the performance of sorbitol grafted onto nano-silica in polyethylene film raw materials and further reducing the precipitation of alkane molecules from the surface of polyethylene film.

[0018] Preferably, the polyethylene film raw material further includes 3-8 parts by weight of halloysite nanotubes and 10-15 parts by weight of polybenzimidazole.

[0019] By employing the above scheme, halloysite nanotubes can form a nanoscale tubular network in polyethylene membranes. Alkane molecules must diffuse around the tubes, thus extending the diffusion path and significantly reducing the amount of low-molecular-weight alkanes released from the polyethylene membrane. The nitrogen atoms of polybenzimidazole form weak hydrogen bonds with the hydrogen atoms of alkane molecules, creating a reversible adsorption complex that reduces the migration activity of alkanes. Halloysite nanotubes construct a nanoscale physical barrier, further extending the diffusion path, while polybenzimidazole chemically captures alkanes through polar interactions. Together, these two components synergistically reduce the amount of low-molecular-weight alkanes released from the polyethylene membrane.

[0020] Preferably, the weight ratio of halloysite nanotubes to polybenzimidazole is 1:(2-4).

[0021] By adopting the above scheme and controlling the weight ratio of halloysite nanotubes and polybenzimidazole, the precipitation of alkane molecules from the surface of polyethylene film can be further reduced.

[0022] Secondly, this application provides a method for preparing the low-exudation polyethylene film according to any one of claims 1-6, which is specifically achieved through the following technical solution: A method for preparing a low-exudation polyethylene film according to any one of claims 1-6, comprising the following steps: melting and extruding the various raw materials for polyethylene film, blowing compressed air into them while simultaneously pulling them upwards, cooling and shaping them, and pulling and winding them to obtain a polyethylene film.

[0023] Preferably, the twin-screw extruder has an aspect ratio of 44, and the temperatures of the conveying section, melting section, mixing section, venting section, and homogenizing section are 195-205℃, 208-212℃, 212-218℃, 218-222℃, and 208-212℃, respectively, while the screw rotation speed is 440 r / min.

[0024] By adopting the above scheme, during the twin-screw extrusion process of polyethylene film, high temperature will exacerbate the breakage of polyethylene molecular chains and the volatilization and precipitation of low molecular weight alkanes. Therefore, the temperatures of the conveying section, melting section, mixing section, exhaust section, and homogenization section need to be controlled at 195-205℃, 208-212℃, 212-218℃, 218-222℃, and 208-212℃, respectively, to prevent the volatilization and precipitation of low molecular weight alkanes in low-density polyethylene caused by high temperature, thereby reducing the amount of low molecular weight alkanes released from the polyethylene film.

[0025] In summary, this application includes at least one of the following beneficial technical effects: 1. This application directly uses low-density polyethylene as polyethylene raw material, and the amount of alkane precipitation in the polyethylene film is 4.9 ppm, which is below 5 ppm, significantly reducing the amount of alkane molecules precipitated from the polyethylene film.

[0026] 2. This application further reduces the amount of alkane molecules released from polyethylene film by adjusting the types and amounts of raw materials used in polyethylene film, resulting in an alkane release of 4.3-4.6 ppm.

[0027] 3. This application reduces the amount of alkane precipitated from polyethylene film by adding self-made nano-silica grafted with sorbitol to polyethylene film raw materials and controlling the mass ratio of sorbitol to nano-silica, thereby reducing the amount of alkane precipitated from polyethylene film to 3.5-3.8 ppm.

[0028] 4. This application reduces the amount of alkane molecules released from polyethylene film by adding halloysite nanotubes and polybenzimidazole to polyethylene film raw materials and adjusting the weight ratio of halloysite nanotubes and polybenzimidazole to achieve a hydrocarbon release of 3.0-3.3 ppm.

[0029] 5. The polyethylene film obtained in this application has the highest tensile strength and elongation at break of 41.0 MPa and 1412%, respectively, and has high basic properties. Detailed Implementation

[0030] The following detailed description, in conjunction with specific embodiments, further illustrates this application. All the raw materials used in this application are commercially available products and are intended to fully disclose the raw materials used in this application; they should not be construed as limiting the source of the raw materials. Specifically: the polyethylene used is low-density polyethylene, with a melt flow index of 2 g / 10 min under test conditions of 190℃ and 2.16 kg; silicon carbide nanowires with an effective component content of 99%; nano-talc powder with a particle size of 1250 mesh; antioxidant, model 1010; glyceryl stearate with an effective component content of 99%; halloysite nanotubes with an outer tube size of 10-50 nm, an inner diameter of 5-20 nm, a length of 0.5-3 μm, and 15-40 crystal layers; polybenzimidazole, brand Dinghang.

[0031] The following are examples of the preparation of nano-silica grafted with sorbitol: Preparation Example 1 The preparation of nano-silica grafted sorbitol in Example 1 was specifically as follows: S1. Disperse 1 kg of 20 nm nano-silica in 5 L of 50% ethanol aqueous solution, sonicate, adjust pH to 4, heat to 60 °C and stir for 30 min, add 70 g of 3-aminopropyltriethoxysilane, stir at 60 °C for 3 h, centrifuge and wash, vacuum dry to obtain pretreated nano-silica. S2. Dissolve 1 kg of pretreated nano-silica and 1.25 kg of sorbitol in ethanol, add 25 g of p-toluenesulfonic acid, reflux at 80 °C for 4 h, centrifuge, wash, and vacuum dry to obtain nano-silica grafted sorbitol.

[0032] Preparation Examples 2-5 The nano-silica grafted sorbitol in Preparation Examples 2-5 were exactly the same as those in Preparation Example 1 in terms of raw material types and preparation methods. The difference was in the amount of sorbitol and p-toluenesulfonic acid used, specifically 1 kg and 20 g, 0.77 kg and 15.4 g, 0.67 kg and 13.4 g, and 0.62 kg and 12.4 g. The remaining steps were the same as those in Preparation Example 1.

[0033] Example 1 Example 1: Polyethylene film was prepared by the following steps: 100 kg of polyethylene was melted and extruded in a twin-screw extruder with an aspect ratio of 44. The temperatures of the conveying section, melting section, mixing section, venting section, and homogenizing section were 200°C, 210°C, 215°C, 220°C, and 210°C, respectively. The screw speed was 440 r / min. Compressed air was blown in at a pressure of 0.03–0.06 MPa, and the film was simultaneously pulled upwards at a speed of 50 m / min and a temperature of 50°C. After cooling and shaping, the film was pulled and wound up to obtain a polyethylene film.

[0034] Example 2 Example 2: A polyethylene film was prepared by the following steps: According to the dosage in Table 1, the raw materials for polyethylene film are melted and placed in a twin-screw extruder for extrusion. The length-to-diameter ratio of the twin-screw extruder is 44. The temperatures of the conveying section, melting section, mixing section, venting section, and homogenizing section are 200℃, 210℃, 215℃, 220℃, and 210℃, respectively. The screw speed is 440 r / min. Compressed air is blown in at a pressure of 0.03~0.06MPa and simultaneously pulled upwards at a speed of 50 m / min and a temperature of 50℃. After cooling and shaping, the film is pulled and wound up to obtain the polyethylene film.

[0035] Examples 3-6 The polyethylene films in Examples 3-6 were prepared using the same methods and raw materials as those in Example 1, except for the different amounts of each raw material. See Table 1 for details.

[0036] Table 1. Raw material dosage for polyethylene films in Examples 2-6 (unit: kg) raw material Example 2 Example 3 Example 4 Example 5 Example 6 polyethylene 88 87.5 89 88.2 87.8 silicon carbide nanowires 5 5 4 4 4 Nano talc 6 6.5 6 6.8 7.2 antioxidants 0.8 0.8 0.8 0.8 0.8 Glyceryl stearate 0.2 0.2 0.2 0.2 0.2 Examples 7-11 The preparation methods of polyethylene films in Examples 7-11 are the same as those in Example 4, except that the nano-silica grafted sorbitol is prepared using the nano-silica grafted sorbitol prepared in Examples 1-5, and the other raw materials and dosages are the same as in Example 4.

[0037] Examples 12-16 The preparation methods of polyethylene films in Examples 12-16 are the same as those in Example 9, except that the polyethylene film raw materials also include halloysite nanotubes and polybenzimidazole, with specific dosages of each. The types and dosages of the remaining raw materials are the same as those in Example 9.

[0038] Example 17 The preparation method of the polyethylene film in Example 17 is exactly the same as that in Example 2, except that silicon carbide nanowires are replaced with nano-talc powder in equal amounts, and the other raw materials and dosages are the same as in Example 2.

[0039] Example 18 The preparation method of the polyethylene film in Example 18 is exactly the same as that in Example 2, except that the nano-talc powder is replaced with silicon carbide nanowires in equal amounts, and the other raw materials and dosages are the same as in Example 2.

[0040] Performance Testing (Part 1) The performance of the polyethylene films obtained in different Examples 1-18 was tested using the following testing standards or methods. The test results are shown in Table 2.

[0041] Tensile strength and elongation at break: The tensile strength and elongation at break of polyethylene film were tested according to YBB00112003-2015 "Method for Determination of Tensile Properties".

[0042] Alkane precipitation: The amount of alkane precipitated from the polyethylene film was determined by gas chromatography-mass spectrometry.

[0043] Table 2 Performance test results of different polyethylene films The test results in Table 2 show that the amount of alkane precipitated in the polyethylene film obtained in this application is less than 5 ppm, which significantly reduces the amount of alkane molecules precipitated in the polyethylene film. Furthermore, the polyethylene film obtained in this application has the highest tensile strength and elongation at break of 41.0 MPa and 1412%, respectively, and has high basic properties.

[0044] Based on the performance test data of the polyethylene film in Example 1, it was found that the alkane precipitation amount of the polyethylene film in Example 1 was 4.9 ppm, which is below 5 ppm. This significantly reduced the precipitation amount of alkane molecules in the polyethylene film, indicating that directly using high-pressure low-density polyethylene as the polyethylene raw material can significantly reduce the precipitation amount of alkane molecules in the polyethylene film.

[0045] Based on the performance test data of polyethylene films in Examples 2-6, it was found that the alkane precipitation of polyethylene films in Examples 3-5 was 4.3-4.5 ppm, which was lower than that in Examples 2 and 6. This indicates that the weight ratio of silicon carbide nanowires to nano-talc powder in the polyethylene film raw material is more suitable at 1:(1.3-1.7), which reduces the precipitation of alkane molecules in polyethylene films.

[0046] Based on the performance test data of polyethylene films in Examples 7-11, it was found that the alkane precipitation of polyethylene films in Examples 8-10 was 3.5-3.8 ppm, which was lower than that in Examples 7 and 11. This indicates that adding self-made nano-silica grafted with sorbitol to polyethylene film raw materials, with a mass ratio of sorbitol to nano-silica of 1:(1-1.5), is more suitable and reduces the precipitation of alkane molecules in polyethylene films.

[0047] Based on the performance test data of polyethylene films in Examples 12-16, it was found that the hydrocarbon precipitation of polyethylene films in Examples 13-15 was 3.0-3.3 ppm, which was lower than that in Examples 12 and 16. This indicates that the addition of halloysite nanotubes and polybenzimidazole to the polyethylene film raw materials, and the further reduction of alkane precipitation in polyethylene films when the weight ratio of halloysite nanotubes to polybenzimidazole was 1:(2-4).

[0048] Based on the performance test data of polyethylene films from Examples 1 and 17-18, it was found that adding silicon carbide nanowires and nano-talc powder to the polyethylene film raw materials can reduce the amount of alkane molecules released from the polyethylene film to varying degrees.

[0049] 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 low-exudation polyethylene film characterized by, It comprises the following raw materials by weight: polyethylene 85-100 parts, silicon carbide nanowires 0-5 parts, nano-talc powder 0-8 parts, antioxidant 0-1 part, glyceryl stearate 0-1 part.

2. The low-exudation polyethylene film according to claim 1, characterized in that, The weight ratio of the silicon carbide nanowires to the nano-talc powder is 1: (1.3-1.7).

3. The low-exudation polyethylene film according to claim 1, characterized in that, The polyethylene film raw material further comprises 1-3 parts of nano-silicon dioxide grafted sorbitol, and the nano-silicon dioxide grafted sorbitol is prepared by the following steps: S1, dispersing nano-silicon dioxide in an ethanol aqueous solution, ultrasonic treatment, adjusting pH 4-5, heating to 60℃ and stirring for 30 min, adding 3-aminopropyl triethoxysilane, stirring at 60℃ for 3h, centrifugal washing, vacuum drying, and obtaining pretreated nano-silicon dioxide; S2, dissolving the pretreated nano-silicon dioxide and sorbitol in ethanol, adding p-toluenesulfonic acid, refluxing at 80℃ for 4-6h, centrifugal washing, vacuum drying, and obtaining nano-silicon dioxide grafted sorbitol.

4. The low-exudation polyethylene film according to claim 3, characterized in that, The mass ratio of the sorbitol to the nano-silicon dioxide is 1: (1-1.5).

5. The low-exudation polyethylene film according to claim 1, wherein, The polyethylene film raw material further comprises 3-8 parts by weight of halloysite nanotubes and 10-15 parts by weight of polybenzimidazole.

6. The low-exudation polyethylene film according to claim 5, characterized in that, The weight ratio of the halloysite nanotubes to the polybenzimidazole is 1: (2-4).

7. A process for the production of a low-exudation polyethylene film as claimed in any one of claims 1 to 6, characterized in that, It comprises the following operation steps: melting the polyethylene film raw materials and placing them in a double screw extruder for extrusion, blowing in compressed air, simultaneously pulling upwards, cooling and shaping, pulling and winding, and obtaining a polyethylene film.

8. The method for producing a low-extraction polyethylene film according to claim 7, characterized by, The length-diameter ratio of the double screw extruder is 44, the temperatures of the conveying section, the melting section, the mixing section, the exhaust section, and the homogenizing section are 195-205℃, 208-212℃, 212-218℃, 218-222℃, and 208-212℃ respectively, and the rotation speed of the screw is 440r / min.

Images