A preparation method of a high-strength polyethylene blown film

Abstract

The present invention relates to the technical field of polyethylene films, and discloses a preparation method of a high-strength polyethylene blown film. Metallocene polyethylene, maleic anhydride and octavinyl-POSS are used to initiate polymerization to obtain polyethylene grafted polyene POSS, which is subjected to epoxidation treatment to obtain polyethylene grafted epoxy POSS. Its structure consists of an inorganic cage-like nucleus formed by silicon oxygen, which has a rigid structure and steric hindrance effect, hinders the movement of polyethylene chain segments, can form nano-inorganic microphase regions, avoids a large amount of agglomeration of inorganic particles, and enables them to be evenly dispersed in the polyethylene matrix; PBAT itself has high toughness, belongs to polar molecules, has good moisture permeability, presents a two-phase separation state in the co-blown film, improves the water resistance of the polyethylene matrix, can selectively slow down the gas exchange between O2 and the outside world, avoids the condensation phenomenon in fruit and vegetable packaging, and has good biodegradability.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene films, and particularly to a preparation method of a high-strength polyethylene blown film. Background Art

[0002] Blown films are plastic films produced by a blown film process and are widely used in packaging, printing, agriculture and other industries. Their production process involves heating plastic pellets to a molten state and then blowing them into a film shape through a blown film machine; polyethylene is the most widely used and largest-produced resin for packaging, and linear low-density polyethylene is a copolymer formed by the polymerization of ethylene and a small amount of higher α-olefins in the presence of a catalyst, with advantages such as low-temperature toughness, high modulus, resistance to bending and stress cracking, and better impact strength at low temperatures. It is a widely used blown film material. However, for a film made solely of low-density polyethylene material, its strength is limited, or in order to achieve the required load-bearing capacity of the product, it needs to be made into a thicker shape, increasing the production cost; therefore, the preparation of a high-strength polyethylene blown film has become a research hotspot at present.

[0003] Currently, the blow tensile strength of polyethylene blown film materials cannot meet the requirements of actual life production. In the prior art, inorganic nanoparticle filling modification is generally used, such as adding calcium carbonate, montmorillonite, etc. with good rigidity and heat resistance to fill the polyethylene matrix. After modification, the mechanical properties and thermal stability of the polyethylene film material have been improved to a certain extent. However, adding a small amount of inorganic particles has a very limited improvement in the properties of the polyethylene matrix, and adding a large amount of inorganic particles is prone to uneven dispersion and agglomeration; in addition, the polyethylene blown film has a low CO2 / O2 selectivity ratio, and when applied to fresh fruit and vegetable packaging, its water vapor permeability is poor, unable to maintain a low O2 and high CO2 packaging environment for fruits and vegetables with strong respiration, and is prone to condensation, resulting in rotting, and the polyethylene film is not easily degraded, easily causing white pollution.

[0004] Patent No. CN114103345B discloses a polyethylene blown film with high tensile strength and heat-sealing strength. The main body is made by optimizing the proportion of low-density polyethylene, linear low-density polyethylene, linear bimodal polyethylene, and metallocene polyethylene resin, and a composite layer, a base layer, and a heat-sealing layer are sequentially arranged from outside to inside. The obtained polyethylene film has excellent tensile properties, but the process is relatively complex, and the CO2 / O2 selectivity ratio of the polyethylene film is not significantly improved; polybutylene adipate terephthalate (PBAT) has good processability, impact resistance, and biodegradability, and its processing performance is similar to that of low-density polyethylene and can be used for blow molding; POSS is an inorganic-organic hybrid material with a cage structure, and its cage core has rigidity; the present invention utilizes the good moisture permeability of PBAT and the good blow molding performance of polyethylene, introduces the POSS hybrid structure into the polyethylene matrix, and prepares a blend blown composite film by melt extrusion, significantly improving the mechanical strength and moisture and gas permeability of the polyethylene blown film, and further broadening the application range of the polyethylene blown film. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing a high-strength polyethylene blown film. The polyethylene blown film has excellent mechanical properties and moisture and gas permeability functions, ensuring its corresponding excellent comprehensive properties when made into packaging materials.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The polyethylene blown film comprises the following components in parts by weight: 40-60 parts of linear low-density polyethylene, 20-35 parts of metallocene polyethylene, 10-30 parts of PBAT masterbatch, 3-15 parts of polyethylene grafted epoxy POSS, 0.2-0.5 part of antioxidant, and 0.05-0.1 part of heat stabilizer.

[0008] The method for preparing the high-strength polyethylene blown film is carried out according to the following steps: Vacuum dry the linear low-density polyethylene, metallocene polyethylene, and PBAT masterbatch at 50-70°C for 12-24 hours, place them in a high-speed mixer, add polyethylene grafted epoxy POSS, antioxidant, and heat stabilizer, stir at a stirring speed of 500-800 r / min and a temperature of 85-100°C for 5-10 minutes, place them in a twin-screw extruder, carry out melt extrusion and pelletization, and finally blow mold in a blown film machine. The film thickness is 20-25 μm to obtain the high-strength polyethylene blown film.

[0009] Further, the antioxidant is any one of phenolic antioxidants, amine antioxidants, or phosphite antioxidants.

[0010] Further, the heat stabilizer is any one of zinc stearate, dibutyltin dimaleate or tetrahydroxymethylcyclohexanol.

[0011] Further, the process parameters of blow molding are as follows: the temperature of the feed inlet is 145 - 155 °C, the front section is 160 - 170 °C, the middle section is 170 - 180 °C, the rear section is 150 - 160 °C, the die head temperature is 140 - 160 °C, the blow-up ratio is 1.5 - 2, and the draw ratio is 3 - 4.

[0012] Further, the preparation method of polyethylene grafted epoxy POSS is carried out according to the following steps:

[0013] Step (1): Under a nitrogen atmosphere, metallocene polyethylene, maleic anhydride and a solvent are added to a reaction flask. After stirring evenly, octavinyl-POSS and benzoyl peroxide are added, and stirring reaction is carried out. After the reaction is completed, acetone is added to precipitate a solid, which is filtered, extracted by Soxhlet extraction with acetone, and dried to obtain polyethylene grafted polyene POSS.

[0014] Step (2): Under a nitrogen atmosphere, polyethylene grafted polyene POSS and chloroform are added to a reaction flask. After stirring evenly, glacial acetic acid and concentrated sulfuric acid are added, and the temperature is raised to 50 - 65 °C. Hydrogen peroxide is added dropwise, and reflux reaction is carried out. The reaction solution is washed successively with sodium carbonate solution and deionized water, and the organic phase is concentrated and dried to obtain polyethylene grafted epoxy POSS.

[0015] Further, in step (1), the solvent is any one of methylcyclohexane, toluene or xylene.

[0016] Further, in step (1), the proportional relationship of metallocene polyethylene, maleic anhydride, solvent, octavinyl-POSS, and benzoyl peroxide is 100 g : (25 - 40) g : (120 - 150) mL : (10 - 20) g : (5 - 8) g.

[0017] Further, in step (1), the reaction temperature is 85 - 100 °C, and the reaction time is 2 - 5 h.

[0018] Further, in step (2), the proportional relationship of polyethylene grafted polyene POSS, chloroform, glacial acetic acid, concentrated sulfuric acid, and hydrogen peroxide is 100 g : (1500 - 1800) mL : (750 - 900) mL : (35 - 50) mL : (1550 - 1650) mL.

[0019] Further, in step (2), the reflux reaction temperature is 55 - 65 °C, and the reflux reaction time is 5 - 12 h.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] First, metallocene polyethylene, maleic anhydride, and octavinyl-POSS are used under the action of initiator benzoyl peroxide to obtain polyethylene-grafted polyene POSS. Then, the alkenyl groups in its structure are epoxidized to obtain polyethylene-grafted epoxy POSS. Subsequently, it is melt copolymerized with low-density polyethylene, metallocene polyethylene, and PBAT masterbatch, extruded into pellets, and blow-molded to obtain a high-strength polyethylene blown film.

[0022] The inorganic cage-like core formed by silicon oxygen in the structure of polyethylene-grafted epoxy POSS can form nano-inorganic microphase regions, avoiding the massive agglomeration of inorganic particles and enabling them to be uniformly dispersed in the polyethylene matrix. The rigid structure and steric hindrance effect of POSS hinder the movement of polyethylene chain segments. The metallocene polyethylene in its structure has characteristics such as high impact resistance, high extensibility, and high toughness, and can be miscible with the polyethylene matrix in a similar manner. During the melt blending process with polyethylene, the epoxy groups open the ring and react with the terminal carboxyl groups of PBAT to form nano-particles that are formally similar to a two-sided structure, playing a role of bridging connection, connecting the two incompatible systems of PBAT and polyethylene to form a cross-linked network structure, achieving efficient compatibilization, and thereby improving the mechanical properties of the blown film. At the same time, PBAT itself has high toughness, ductility, and impact strength. After melt blending with polyethylene, it significantly reduces the interfacial tension between the two, improving the ductility of the polyethylene blown film.

[0023] PBAT belongs to polar molecules, has a certain hydrophilicity, and has good moisture permeability. It presents a two-phase separation state in the co-blown film. Water molecules have more permeation channels to pass through the film, which is also beneficial to the permeation of water vapor to a certain extent, improving the water resistance of the polyethylene matrix and avoiding the condensation phenomenon inside the fruit and vegetable packaging. This makes the prepared polyethylene blown film more suitable for the packaging of fresh fruits. At the same time, PBAT endows the polyethylene blown film with selective gas permeability, which can selectively slow down the gas exchange of O2 with the outside world, maintain the slow respiration of fruits and vegetables in the bag, and the faster discharge of CO2 can prevent the poisoning of fruits and vegetables caused by excessive CO2, thereby prolonging the freshness period of fresh fruits and vegetables and having good biodegradability. Specific Embodiments

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0025] Unless otherwise specified, the raw materials and reagents used in this application are all commercially available products or can be prepared by known methods.

[0026] Octavinyl-POSS, with a CAS number of 69655-76-1.

[0027] Linear low density polyethylene, from Zhenhai Refining & Chemical Company, Sinopec.

[0028] Metallocene polyethylene, from ExxonMobil Chemical Company, USA.

[0029] PBAT masterbatch, from Hangzhou Xinfu Technology Co., Ltd.

[0030] The phenolic antioxidant is any one of 2,6-di-tert-butylphenol, antioxidant 1010 or antioxidant 1076.

[0031] The amine antioxidant is any one of naphthylamine, diphenylamine or p-phenylenediamine.

[0032] The phosphite antioxidant is triphenyl phosphite or tributyl sulfite.

[0033] Example 1

[0034] (1) Under a nitrogen atmosphere, add 45 g of metallocene polyethylene, 14.4 g of maleic anhydride and 61.2 mL of methylcyclohexane to a reaction flask. After stirring evenly, add 6.3 g of octavinyl-POSS and 3.24 g of dibenzoyl peroxide, and react at 95 °C for 4 h. Add acetone, precipitate, filter, perform Soxhlet extraction with acetone, and dry to obtain polyethylene-grafted polyenyl POSS.

[0035] (2) Under a nitrogen atmosphere, add 40 g of polyethylene-grafted polyenyl POSS and 660 mL of chloroform to a reaction flask. After stirring evenly, add 340 mL of glacial acetic acid and 170 mL of concentrated sulfuric acid, heat up to 55 °C, dropwise add 640 mL of hydrogen peroxide, and reflux and react at 60 °C for 10 h. Wash the reaction solution successively with sodium carbonate solution and deionized water, concentrate the organic phase, and dry to obtain polyethylene-grafted epoxidized POSS.

[0036] (3) Vacuum dry 50 g of linear low density polyethylene, 25 g of metallocene polyethylene and 10 g of PBAT masterbatch at 65 °C for 16 h, place them in a high-speed mixer, add 3 g of polyethylene-grafted epoxidized POSS, 0.3 g of phenolic antioxidant and 0.08 g of zinc stearate, stir at a stirring speed of 700 r / min and a temperature of 95 °C for 8 min, place them in a twin-screw extruder, perform melt extrusion and pelletization, and finally blow-mold them in a blown film machine. The temperature of the feed inlet is 150 °C, the front section is 165 °C, the middle section is 175 °C, the rear section is 155 °C, the die head temperature is 150 °C, the blow-up ratio is 1.8, the draw ratio is 3.5, and the film thickness is 20 μm to obtain a high-strength polyethylene blown film.

[0037] Example 2

[0038] (1) Under a nitrogen atmosphere, 80 g of metallocene polyethylene, 20 g of maleic anhydride, and 96 mL of toluene were added to a reaction flask. After stirring evenly, 8 g of octavinyl-POSS and 4 g of dibenzoyl peroxide were added. The reaction was carried out at 100 °C for 2 h. Acetone was added to precipitate the product, which was then filtered, Soxhlet-extracted with acetone, and dried to obtain polyethylene-grafted polyene-based POSS.

[0039] (2) Under a nitrogen atmosphere, 60 g of polyethylene-grafted polyene-based POSS and 900 mL of chloroform were added to a reaction flask. After stirring evenly, 450 mL of glacial acetic acid and 210 mL of concentrated sulfuric acid were added. The temperature was raised to 65 °C, and 930 mL of hydrogen peroxide was added dropwise. The reaction was refluxed at 65 °C for 5 h. The reaction solution was washed successively with sodium carbonate solution and deionized water. The organic phase was concentrated and dried to obtain polyethylene-grafted epoxy POSS.

[0040] (3) 60 g of linear low-density polyethylene, 20 g of metallocene polyethylene, and 15 g of PBAT masterbatch were vacuum-dried at 70 °C for 12 h and placed in a high-speed mixer. 6 g of polyethylene-grafted epoxy POSS, 0.5 g of amine antioxidant, and 0.09 g of dibutyltin dimaleate were added. Stirring was carried out at a stirring speed of 800 r / min and a temperature of 100 °C for 5 min. The mixture was then placed in a twin-screw extruder for melt extrusion and pelletization. Finally, it was blown into a film using a blown film machine. The feeding port temperature was 155 °C, the front section was 170 °C, the middle section was 180 °C, the rear section was 160 °C, the die head temperature was 160 °C, the blow-up ratio was 2, the draw ratio was 4, and the film thickness was 22 μm to obtain a high-strength polyethylene blown film.

[0041] Example 3

[0042] (1) Under a nitrogen atmosphere, 30 g of metallocene polyethylene, 12 g of maleic anhydride, and 45 mL of xylene were added to a reaction flask. After stirring evenly, 6 g of octavinyl-POSS and 2.4 g of dibenzoyl peroxide were added. The reaction was carried out at 85 °C for 5 h. Acetone was added to precipitate the product, which was then filtered, Soxhlet-extracted with acetone, and dried to obtain polyethylene-grafted polyene-based POSS.

[0043] (2) Under a nitrogen atmosphere, 25 g of polyethylene-grafted polyene-based POSS and 450 mL of chloroform were added to a reaction flask. After stirring evenly, 225 mL of glacial acetic acid and 12.5 mL of concentrated sulfuric acid were added. The temperature was raised to 50 °C, and 412.5 mL of hydrogen peroxide was added dropwise. The reaction was refluxed at 55 °C for 2 h. The reaction solution was washed successively with sodium carbonate solution and deionized water. The organic phase was concentrated and dried to obtain polyethylene-grafted epoxy POSS.

[0044] (3) Vacuum dry 40 g of linear low-density polyethylene, 35 g of metallocene polyethylene, and 20 g of PBAT masterbatch at 50 °C for 24 h. Place them in a high-speed mixer, add 9 g of polyethylene-grafted epoxidized POSS, 0.2 g of phosphite antioxidant, and 0.09 g of tetrahydroxymethylcyclohexanol. Stir at a stirring speed of 500 r / min and a temperature of 85 °C for 10 min. Then place it in a twin-screw extruder for melt extrusion and pelletization. Finally, place it in a blown film machine for blow molding. The feed port temperature is 145 °C, the front section is 160 °C, the middle section is 170 °C, the rear section is 150 °C, the die head temperature is 140 °C, the blow-up ratio is 1.5, the draw ratio is 3, and the film thickness is 23 μm to obtain a high-strength polyethylene blown film.

[0045] Example 4

[0046] (1) Under a nitrogen atmosphere, add 20 g of metallocene polyethylene, 7 g of maleic anhydride, and 28.5 mL of methylcyclohexane to a reaction flask. After stirring evenly, add 3.3 g of octavinyl-POSS and 1.5 g of dibenzoyl peroxide. React at 90 °C for 5 h. Add acetone to precipitate the solid, filter, perform Soxhlet extraction with acetone, and dry to obtain polyethylene-grafted polyene-based POSS.

[0047] (2) Under a nitrogen atmosphere, add 10 g of polyethylene-grafted polyene-based POSS and 170 mL of chloroform to a reaction flask. After stirring evenly, add 85 mL of glacial acetic acid and 5 mL of concentrated sulfuric acid. Heat up to 60 °C and dropwise add 165 mL of hydrogen peroxide. Reflux and react at 65 °C for 9 h. Wash the reaction solution successively with sodium carbonate solution and deionized water. Concentrate the organic phase and dry to obtain polyethylene-grafted epoxidized POSS.

[0048] (3) Vacuum dry 55 g of linear low-density polyethylene, 30 g of metallocene polyethylene, and 25 g of PBAT masterbatch at 65 °C for 24 h. Place them in a high-speed mixer, add 12 g of polyethylene-grafted epoxidized POSS, 0.5 g of phenolic antioxidant, and 0.06 g of zinc stearate. Stir at a stirring speed of 720 r / min and a temperature of 90 °C for 10 min. Then place it in a twin-screw extruder for melt extrusion and pelletization. Finally, place it in a blown film machine for blow molding. The feed port temperature is 145 °C, the front section is 170 °C, the middle section is 180 °C, the rear section is 155 °C, the die head temperature is 160 °C, the blow-up ratio is 2, the draw ratio is 4, and the film thickness is 24 μm to obtain a high-strength polyethylene blown film.

[0049] Example 5

[0050] (1) Under a nitrogen atmosphere, 12 g of metallocene polyethylene, 4.2 g of maleic anhydride, and 17.5 mL of xylene were added to a reaction flask. After stirring evenly, 2.22 g of octavinyl-POSS and 0.78 g of benzoyl peroxide were added. The reaction was carried out at 95 °C for 3 h. Acetone was added to precipitate the product, which was then filtered, extracted with acetone in a Soxhlet extractor, and dried to obtain polyethylene-grafted polyvinyl POSS.

[0051] (2) Under a nitrogen atmosphere, 8 g of polyethylene-grafted polyvinyl POSS and 140 mL of chloroform were added to a reaction flask. After stirring evenly, 68 mL of glacial acetic acid and 3.5 mL of concentrated sulfuric acid were added. The temperature was raised to 55 °C, and 120 mL of hydrogen peroxide was added dropwise. The reaction was refluxed at 60 °C for 12 h. The reaction solution was washed successively with sodium carbonate solution and deionized water. The organic phase was concentrated and dried to obtain polyethylene-grafted epoxidized POSS.

[0052] (3) 45 g of linear low-density polyethylene, 30 g of metallocene polyethylene, and 30 g of PBAT masterbatch were vacuum dried at 70 °C for 16 h, placed in a high-speed mixer, and 15 g of polyethylene-grafted epoxidized POSS, 0.4 g of phenolic antioxidant, and 0.05 g of tetramethylolcyclohexanol were added. Stirring was carried out at a stirring speed of 800 r / min and a temperature of 90 °C for 10 min. Then it was placed in a twin-screw extruder for melt extrusion and pelletization. Finally, it was blown into a film in a blown film machine. The feed port temperature was 155 °C, the front section was 160 °C, the middle section was 180 °C, the rear section was 155 °C, the die head temperature was 150 °C, the blow-up ratio was 2, the draw ratio was 3, and the film thickness was 25 μm to obtain a high-strength polyethylene blown film.

[0053] Comparative Example 1

[0054] (1) Under a nitrogen atmosphere, 45 g of metallocene polyethylene, 14.4 g of maleic anhydride, and 61.2 mL of methylcyclohexane were added to a reaction flask. After stirring evenly, 3.24 g of benzoyl peroxide was added. The reaction was carried out at 95 °C for 4 h. Acetone was added to precipitate the product, which was then filtered, extracted with acetone in a Soxhlet extractor, and dried to obtain polyethylene-grafted maleic anhydride.

[0055] (2) 50 g of linear low-density polyethylene, 25 g of metallocene polyethylene, and 10 g of PBAT masterbatch were vacuum dried at 65 °C for 16 h, placed in a high-speed mixer, and 3 g of polyethylene-grafted maleic anhydride, 0.3 g of phenolic antioxidant, and 0.08 g of zinc stearate were added. Stirring was carried out at a stirring speed of 700 r / min and a temperature of 95 °C for 8 min. Then it was placed in a twin-screw extruder for melt extrusion and pelletization. Finally, it was blown into a film in a blown film machine. The feed port temperature was 150 °C, the front section was 165 °C, the middle section was 175 °C, the rear section was 155 °C, the die head temperature was 150 °C, the blow-up ratio was 1.8, the draw ratio was 3.5, and the film thickness was 20 μm to obtain a polyethylene blown film.

[0056] Comparative Example 2

[0057] 50 g of linear low-density polyethylene and 25 g of metallocene polyethylene were vacuum dried at 65 °C for 16 h, placed in a high-speed mixer, 3 g of polyethylene-grafted epoxidized POSS (prepared in Example 1), 0.3 g of phenolic antioxidant and 0.08 g of zinc stearate were added, and stirred at a stirring speed of 700 r / min and a temperature of 95 °C for 8 min. Then it was placed in a twin-screw extruder for melt extrusion and pelletization. Finally, it was placed in a blown film machine for blow molding. The temperature of the feed inlet was 150 °C, the front section was 165 °C, the middle section was 175 °C, the rear section was 155 °C, the die head temperature was 150 °C, the blow-up ratio was 1.8, the draw ratio was 3.5, and the film thickness was 20 μm to obtain a polyethylene blown film.

[0058] Comparative Example 3

[0059] 50 g of linear low-density polyethylene and 25 g of metallocene polyethylene were vacuum dried at 65 °C for 16 h, placed in a high-speed mixer, 0.3 g of phenolic antioxidant and 0.08 g of zinc stearate were added, and stirred at a stirring speed of 700 r / min and a temperature of 95 °C for 8 min. Then it was placed in a twin-screw extruder for melt extrusion and pelletization. Finally, it was placed in a blown film machine for blow molding. The temperature of the feed inlet was 150 °C, the front section was 165 °C, the middle section was 175 °C, the rear section was 155 °C, the die head temperature was 150 °C, the blow-up ratio was 1.8, the draw ratio was 3.5, and the film thickness was 20 μm to obtain a polyethylene blown film.

[0060] Mechanical property test: Referring to the standard GB / T1040.3-2006, a universal tensile machine was used to test the mechanical properties of the film. The prepared polyethylene blown film was made into dumbbell shapes, with 10 parallel specimens in each group, and the tensile speed was 50 mm / min.

[0061] Table 1 Mechanical Property Test

[0062]

[0063]

[0064] As can be seen from the test results in the above table, as the content of polyethylene-grafted epoxidized POSS and PBAT masterbatch increases, the mechanical properties of the polyethylene blown film gradually increase. Among them, the longitudinal tensile strength in the examples is 37.5 MPa, and the transverse tensile strength is 22.0 MPa. This is because on the one hand, PBAT itself has high toughness, ductility and impact strength. After melt blending with polyethylene, the interfacial tension between the two is significantly reduced, improving the ductility of the polyethylene blown film; on the other hand, polyethylene-grafted epoxidized POSS is an inorganic hybrid material composed of a silicon-oxygen skeleton with alternating Si-O bonds. The energy required to break the bond energy in the POSS core is relatively large, which can effectively inhibit the chain movement of polyethylene molecules. The metallocene polyethylene in its structure is similar and compatible with the polyethylene matrix. During the melt blending process with polyethylene, the epoxy group opens the ring and reacts with the terminal carboxyl group of PBAT to form a nanoparticle similar to a two-sided structure in form, playing a role of bridge connection, connecting the two incompatible systems of PBAT and polyethylene, forming a cross-linked network structure, achieving efficient compatibilization, and thus showing an improvement in the mechanical properties of the blown film.

[0065] In Comparative Example 1, there is no POSS group, so there is no hybrid particle strengthening effect. However, polyethylene-grafted maleic anhydride can improve the compatibility between polyethylene and PBAT, and has a certain improvement effect on the tensile properties of the film; in Comparative Example 2, there is no PBAT masterbatch, and no cross-linked network structure is formed, so the improvement of the tensile properties is not obvious; in Comparative Example 3, it is a common polyethylene blown film material, and its mechanical properties are the worst.

[0066] Water vapor transmission performance test: Referring to the standard GB / T 26253-2010, the prepared polyethylene blown film was cut into circles with an area of 10 cm 2 each, with 10 parallel specimens in each group. The test temperature was 23 °C and the humidity was 65% RH.

[0067] CO2 / O2 selectivity ratio test: The O2 and CO2 transmission performance of the film was tested using a differential pressure permeation meter. The prepared polyethylene blown film was cut into rectangles with a length of 18 cm and a width of 10 cm, with 5 parallel specimens in each group. The test temperature was 23 °C.

[0068] Table 2 Test of moisture permeability and gas permeability of the film

[0069]

[0070] For the packaging of fresh fruits and vegetables, maintaining a certain humidity environment is crucial for keeping the freshness of the products. If the water vapor barrier property of the packaging film is too high, a large amount of water droplets will condense in the internal environment and drip onto the surface of the products, which will cause the products to rot faster. However, too low a barrier property is also not conducive to maintaining the moisture of fruits and vegetables. It can be seen from the test results in the above table that as the PBAT content increases, the water vapor transmission rate of the polyethylene blown film gradually increases. This is because PBAT belongs to polar molecules, has certain hydrophilicity, and has good moisture permeability. It presents a two-phase separation state in the co-blown film, and water molecules have more permeation channels to pass through the film, which also facilitates the permeation of water vapor to a certain extent, improves the water resistance of the polyethylene matrix, avoids the dew condensation phenomenon inside the fruit and vegetable packaging, and makes the prepared polyethylene blown film more suitable for the packaging of fresh fruits.

[0071] The CO2 / O2 selectivity of the blown film is an important indicator for evaluating the freshness preservation performance of the film. As the PBAT content increases, the CO2 / O2 selectivity of the polyethylene blown film gradually increases. This is because PBAT endows the polyethylene blown film with selective gas permeability, which can selectively slow down the gas exchange between O2 and the outside world, maintain the slow respiration of the fruits and vegetables in the bag, and the faster CO2 discharge can prevent the poisoning of fruits and vegetables caused by excessive CO2, thereby prolonging the freshness preservation period of fresh fruits and vegetables.

[0072] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all belong to the protection scope of the present invention. In addition, it should be noted that in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

Claims

1. A method for preparing a high-strength polyethylene blown film, characterized in that, The polyethylene blown film comprises the following components in parts by weight: 40 - 60 parts of linear low density polyethylene, 20 - 35 parts of metallocene polyethylene, 10 - 30 parts of PBAT masterbatch, 3 - 15 parts of polyethylene grafted epoxidized POSS, 0.2 - 0.5 part of antioxidant, and 0.05 - 0.1 part of heat stabilizer; The preparation method is carried out according to the following steps: Vacuum dry the linear low density polyethylene, metallocene polyethylene and PBAT masterbatch at 50 - 70 °C for 12 - 24 h, place them in a high-speed mixer, add polyethylene grafted epoxidized POSS, antioxidant and heat stabilizer, stir at a stirring speed of 500 - 800 r / min and a temperature of 85 - 100 °C for 5 - 10 min, place them in a twin-screw extruder for melt extrusion and pelletizing, and finally place them in a blown film machine for blow molding. The film thickness is 20 - 25 μm to obtain a high-strength polyethylene blown film; The preparation method of the polyethylene grafted epoxidized POSS is carried out according to the following steps: Step (1), Under a nitrogen atmosphere, add metallocene polyethylene, maleic anhydride and a solvent to a reaction flask. After stirring evenly, add octavinyl-POSS and benzoyl peroxide, stir and react. After the reaction is completed, add acetone to precipitate, filter, perform Soxhlet extraction with acetone, and dry to obtain polyethylene grafted polyene-based POSS; Step (2), Under a nitrogen atmosphere, add polyethylene grafted polyene-based POSS and chloroform to a reaction flask. After stirring evenly, add glacial acetic acid and concentrated sulfuric acid, heat up to 50 - 65 °C, dropwise add hydrogen peroxide, and carry out reflux reaction. The reaction solution is washed successively with sodium carbonate solution and deionized water, and the organic phase is concentrated and dried to obtain polyethylene grafted epoxidized POSS.

2. The preparation method of the high-strength polyethylene blown film according to claim 1, characterized in that, The antioxidant is any one of phenolic antioxidants, amine antioxidants or phosphite antioxidants.

3. The preparation method of the high-strength polyethylene blown film according to claim 1, characterized in that, The heat stabilizer is any one of zinc stearate, dibutyltin dimaleate or tetrahydroxymethylcyclohexanol.

4. The preparation method of the high-strength polyethylene blown film according to claim 1, characterized in that, The process parameters of the blow molding are as follows: the temperature of the feed inlet is 145 - 155 °C, the front section is 160 - 170 °C, the middle section is 170 - 180 °C, the rear section is 150 - 160 °C, the die head temperature is 140 - 160 °C, the blow-up ratio is 1.5 - 2, and the draw ratio is 3 - 4.

5. The preparation method of the high-strength polyethylene blown film according to claim 1, characterized in that, The solvent in step (1) is any one of methylcyclohexane, toluene or xylene.

6. The preparation method of the high-strength polyethylene blown film according to claim 1, characterized in that, The proportional relationship of metallocene polyethylene, maleic anhydride, solvent, octavinyl-POSS, benzoyl peroxide in step (1) is 100 g : (25 - 40) g : (120 - 150) mL : (10 - 20) g : (5 - 8) g.

7. The preparation method of the high-strength polyethylene blown film according to claim 1, characterized in that The reaction temperature in step (1) is 85 - 100 °C, and the reaction time is 2 - 5 h.

8. The preparation method of the high-strength polyethylene blown film according to claim 1, characterized in that, The proportional relationship of polyethylene grafted polyene-based POSS, chloroform, glacial acetic acid, concentrated sulfuric acid, hydrogen peroxide in step (2) is 100 g : (1500 - 1800) mL : (750 - 900) mL : (35 - 50) mL : (1550 - 1650) mL.

9. The preparation method of the high-strength polyethylene blown film according to claim 1, characterized in that, In the step (2), the reflux reaction temperature is 55 - 65 °C and the reflux reaction time is 5 - 12 h.

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