A pe / pa symmetric membrane and a method for preparing the same

Abstract

This application discloses a PE / PA symmetrical film and its preparation method, relating to the field of packaging film material technology. The PE / PA symmetrical film comprises, from the outside to the inside, an outer layer, an outer second layer, a first adhesive layer, a middle layer, a second adhesive layer, an inner layer, and an inner second layer. The outer first and inner second layers are made of modified high-density polyethylene, the outer second and inner first layers are made of linear low-density polyethylene, the first and second adhesive layers are made of TIE resin, and the middle layer is made of PA resin. The mass ratio of the raw materials in each layer is 0.156-0.168:0.195-0.203:0.077-0.087:0.113-0.0125:0.077-0.087:0.195-0.203:0.156-0.168. The PE / PA symmetrical film provided by this application has high mechanical properties and stiffness.

Description

Technical Field

[0001] This application relates to the field of packaging film material technology, and in particular to a PE / PA symmetrical film and its preparation method. Background Technology

[0002] In the field of polymer composite materials science and technology, PE (polyethylene) / PA (polyamide) symmetrical films, with their excellent physical properties such as good barrier properties, chemical resistance, and a certain degree of flexibility, have shown broad application potential in various fields such as food packaging, pharmaceutical packaging, and agricultural covering films. However, when traditional low-density polyethylene (LDPE) is used as the main matrix material for PE / PA films, although it offers significant processing convenience and cost-effectiveness, the resulting films have obvious shortcomings in mechanical properties, especially stiffness and tensile strength. This deficiency limits the application of PE / PA symmetrical films in the high-end packaging material market that requires higher strength support, tear resistance, or durability.

[0003] In existing technologies, polymer blending is commonly used to improve the mechanical properties of PE / PA symmetrical films. This involves blending LDPE with other specific engineering plastics, aiming to improve the film's mechanical properties through the interaction between different polymer chains. While this method improves the film's strength and stiffness to some extent, compatibility issues between different polymers during blending often lead to a deterioration in the film's processing performance. Therefore, providing a method that can effectively improve the mechanical properties of PE / PA symmetrical films without sacrificing their processing performance and long-term stability has become an urgent technical problem to be solved. Summary of the Invention

[0004] To improve the mechanical strength of PE / PA symmetrical films, this application provides a PE / PA symmetrical film and its preparation method.

[0005] This application provides a PE / PA symmetrical film, which adopts the following technical solution:

[0006] A PE / PA symmetrical film, wherein the PE / PA symmetrical film comprises, from the outside to the inside, an outer layer, an outer second layer, a first adhesive layer, a middle layer, a second adhesive layer, an inner layer, and an inner second layer; the outer first layer and the inner second layer are made of modified high-density polyethylene, the outer second layer and the inner first layer are made of linear low-density polyethylene, the first adhesive layer and the second adhesive layer are made of TIE resin, and the middle layer is made of PA resin.

[0007] By adopting the above technical solution, the PE / PA symmetrical film of this application adopts a seven-layer symmetrical structure. The raw materials are high-density polyethylene and linear low-density polyethylene instead of low-density polyethylene, which significantly improves the stiffness and strength of the PE / PA symmetrical film to meet the needs of high-performance packaging materials. Furthermore, by modifying the high-density polyethylene, the toughness of the high-density polyethylene is significantly improved, thereby further improving the mechanical properties and service life of the PE / PA symmetrical film.

[0008] Preferably, the mass ratio of the raw materials of the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer, and inner second layer is 0.156-0.168:0.195-0.203:0.077-0.087:0.113-0.0125:0.077-0.087:0.195-0.203:0.156-0.168.

[0009] Preferably, the mass ratio of the raw materials of the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer and inner second layer is 0.162:0.199:0.082:0.119:0.082:0.199:0.162.

[0010] Preferably, the modified high-density polyethylene is made from the following raw materials in parts by weight: 50-60 parts high-density polyethylene and 10-12 parts oxyalkylated organic solvent lignin-g-PLA graft copolymer.

[0011] By adopting the above technical solution, high-density polyethylene is modified with oxyalkylated organic solvent lignin-g-PLA graft copolymer. Lignin contains a large number of active functional groups such as phenolic hydroxyl groups and aliphatic hydroxyl groups, making it an ideal material for preparing green polymer materials. The oxyalkylated organic solvent lignin-g-PLA graft copolymer is prepared from the following raw materials in parts by weight: 0.01-0.03 parts oxyalkylated organic solvent lignin, 1-3 parts L-lactide, 0.05-0.15 parts 1,8-diazabicyclo[5.4.0]undec-7-ene, 10-20 parts acetic acid, and 45-60 parts methanol.

[0012] Preferably, the oxyalkylated organic solvent lignin is prepared from the following raw materials in parts by weight: 5-10 parts organic solvent lignin, 0.6-1.2 parts 1,8-diazabicyclo[5.4.0]undec-7-ene, 79-108 parts propylene carbonate, and 200-300 parts water.

[0013] By adopting the above technical solution, this application uses propylene carbonate (PC) to oxyalkylate lignin (OL), increasing the number of aliphatic hydroxyl groups in the lignin. Then, the oxyalkylated lignin is ring-opened polymerized with L-lactide to prepare a graft copolymer. The resulting oxyalkylated organic solvent lignin-g-PLA graft copolymer can not only effectively improve the strength and toughness of high-density polyethylene, but also has good compatibility with high-density polyethylene and good processing performance.

[0014] Preferably, the method for preparing the oxyalkylated organic solvent lignin includes the following steps:

[0015] Organic solvent lignin, propylene carbonate and 1,8-diazabicyclo[5.4.0]undec-7-ene were added to a pressure-resistant tube, which was then filled with nitrogen and sealed. The tube was heated in an oil bath to 150-190°C and magnetically stirred for 3-5 hours. After the reaction was completed, the reaction solution was dropped into water and stirred for 1-3 hours. The solid product was obtained by vacuum filtration, washed several times and then freeze-dried to obtain oxyalkylated organic solvent lignin.

[0016] Preferably, the preparation method of the oxyalkylated organic solvent lignin-g-PLA graft copolymer includes the following steps:

[0017] Oxyalkylated organic solvent lignin, L-lactide and 1,8-diazabicyclo[5.4.0]undec-7-ene were added to a pressure-resistant tube, which was then filled with nitrogen and sealed. The tube was heated in an oil bath to 130-150℃ and magnetically stirred for 3-4 hours. Acetic acid was added to stop the reaction, followed by the addition of methanol and stirring for 1-2 hours. The solid product was obtained by centrifugation, washed several times, and dried in a vacuum drying oven at 50-60℃ for 24-30 hours to obtain an oxyalkylated organic solvent lignin-g-PLA graft copolymer.

[0018] Preferably, the method for preparing the modified high-density polyethylene includes the following steps:

[0019] High-density polyethylene is dried under vacuum at 75-85℃ for 12-15 hours; the dried high-density polyethylene and oxyalkylated organic solvent lignin-g-PLA graft copolymer are placed in a mixer and melt-blended at 160-180℃ and a screw speed of 60-80 rpm for 10-20 minutes to obtain modified high-density polyethylene.

[0020] This application also provides a method for preparing a PE / PA symmetrical film, using the following technical solution:

[0021] A method for preparing a PE / PA symmetrical film includes the following steps:

[0022] S1. Weigh the raw materials of the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer and inner second layer according to the mass ratio, put the raw materials into the hopper of the seven-layer co-extrusion blown film machine in sequence, set the screw barrel temperature corresponding to the hopper to 195-210℃, and then extrude through the screw to obtain the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer and inner second layer base film;

[0023] S2. The outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer and inner second layer base film are extruded and blown into a finished film under the action of a screw through the die head of a seven-layer co-extrusion blown film machine. The die head temperature of the seven-layer co-extrusion blown film machine is set to 195-210℃ and the blown ratio is 1:1.3-1.5.

[0024] By adopting the above technical solution and using a seven-layer co-extrusion blown film mechanism, it has many advantages such as high process stability, high production efficiency, excellent film performance and convenient operation, and can effectively obtain PE / PA symmetrical films with mechanical properties.

[0025] In summary, this application includes at least one of the following beneficial technical effects:

[0026] 1. By adopting the above technical solution, the PE / PA symmetrical film of this application adopts a seven-layer symmetrical structure. The raw material is high-density polyethylene and linear low-density polyethylene instead of low-density polyethylene, which significantly improves the stiffness and strength of the PE / PA symmetrical film to meet the needs of high-performance packaging materials. Furthermore, by modifying the high-density polyethylene, the toughness of the high-density polyethylene is significantly improved, thereby further improving the mechanical properties and service life of the PE / PA symmetrical film.

[0027] 2. By adopting the above technical solution, this application uses propylene carbonate (PC) to oxyalkylate lignin (OL), increasing the number of aliphatic hydroxyl groups in the lignin. Then, the oxyalkylated lignin is ring-opened polymerized with L-lactide to prepare a graft copolymer. The resulting oxyalkylated organic solvent lignin-g-PLA graft copolymer can not only effectively improve the strength and toughness of high-density polyethylene, but also has good compatibility with high-density polyethylene and good processing performance. Detailed Implementation

[0028] The present application will be further described in detail below with reference to the embodiments.

[0029] Preparation Example

[0030] Preparation Example 1

[0031] T1. Add 5g of organic solvent lignin, 79g of propylene carbonate and 0.6g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 150℃ and stir magnetically for 3h; after the reaction is complete, drop the reaction solution into 200g of water and stir for 1h, filter under vacuum to obtain a solid product, wash with deionized water 3 times and freeze dry to obtain oxyalkylated organic solvent lignin;

[0032] T2. Add 0.01g of oxyalkylated organic solvent lignin prepared by T1, 1g of L-lactide and 0.05g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 130℃ and stir magnetically for 3h, add 10g of acetic acid to stop the reaction, then add 45g of methanol and stir for 1h, centrifuge at 10000rpm to obtain a solid product, wash with deionized water 3 times and dry in a vacuum drying oven at 50℃ for 30h to obtain an oxyalkylated organic solvent lignin-g-PLA graft copolymer;

[0033] T3. Dry 50g of high-density polyethylene under vacuum at 75℃ for 12h; put the dried high-density polyethylene and 10g of the oxyalkylated organic solvent lignin-g-PLA graft copolymer obtained from T2 into a mixer, and melt-blend at 160℃ and a screw speed of 60rpm for 10min to obtain modified high-density polyethylene.

[0034] Preparation Example 2

[0035] T1. Add 7.5g of organic solvent lignin, 94g of propylene carbonate and 0.9g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 170℃ and stir magnetically for 4h; after the reaction is complete, drop the reaction solution into 250g of water and stir for 2h, filter under vacuum to obtain a solid product, wash with deionized water 3 times and freeze dry to obtain oxyalkylated organic solvent lignin;

[0036] T2. Add 0.01g of oxyalkylated organic solvent lignin prepared by T1, 1g of L-lactide and 0.05g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 130℃ and stir magnetically for 3h, add 10g of acetic acid to stop the reaction, then add 45g of methanol and stir for 1h, centrifuge at 10000rpm to obtain a solid product, wash with deionized water 3 times and dry in a vacuum drying oven at 50℃ for 30h to obtain an oxyalkylated organic solvent lignin-g-PLA graft copolymer;

[0037] T3. Dry 50g of high-density polyethylene under vacuum at 75℃ for 12h; put the dried high-density polyethylene and 10g of the oxyalkylated organic solvent lignin-g-PLA graft copolymer obtained from T2 into a mixer, and melt-blend at 160℃ and a screw speed of 60rpm for 10min to obtain modified high-density polyethylene.

[0038] Preparation Example 3

[0039] T1. Add 10g of organic solvent lignin, 108g of propylene carbonate and 1.2g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 190℃ and stir magnetically for 5h; after the reaction is complete, drop the reaction solution into 300g of water and stir for 3h, filter under vacuum to obtain a solid product, wash with deionized water 3 times and freeze dry to obtain oxyalkylated organic solvent lignin;

[0040] T2. Add 0.01g of oxyalkylated organic solvent lignin prepared by T1, 1g of L-lactide and 0.05g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 130℃ and stir magnetically for 3h, add 10g of acetic acid to stop the reaction, then add 45g of methanol and stir for 1h, centrifuge at 10000rpm to obtain a solid product, wash with deionized water 3 times and dry in a vacuum drying oven at 50℃ for 30h to obtain an oxyalkylated organic solvent lignin-g-PLA graft copolymer;

[0041] T3. Dry 50g of high-density polyethylene under vacuum at 75℃ for 12h; put the dried high-density polyethylene and 10g of the oxyalkylated organic solvent lignin-g-PLA graft copolymer obtained from T2 into a mixer, and melt-blend at 160℃ and a screw speed of 60rpm for 10min to obtain modified high-density polyethylene.

[0042] Preparation Example 4

[0043] T1. Add 5g of organic solvent lignin, 79g of propylene carbonate and 0.6g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 150℃ and stir magnetically for 3h; after the reaction is complete, drop the reaction solution into 200g of water and stir for 1h, filter under vacuum to obtain a solid product, wash with deionized water 3 times and freeze dry to obtain oxyalkylated organic solvent lignin;

[0044] T2. Add 0.02g of oxyalkylated organic solvent lignin prepared by T1, 2g of L-lactide and 0.1g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 140℃ and stir magnetically for 3.5h, add 15g of acetic acid to stop the reaction, then add 52g of methanol and stir for 1.5h. Centrifuge at 15000rpm to obtain a solid product, wash with deionized water 3 times and dry in a vacuum drying oven at 55℃ for 27h to obtain an oxyalkylated organic solvent lignin-g-PLA graft copolymer;

[0045] T3. Dry 50g of high-density polyethylene under vacuum at 75℃ for 12h; put the dried high-density polyethylene and 10g of the oxyalkylated organic solvent lignin-g-PLA graft copolymer obtained from T2 into a mixer, and melt-blend at 160℃ and a screw speed of 60rpm for 10min to obtain modified high-density polyethylene.

[0046] Preparation Example 5

[0047] T1. Add 5g of organic solvent lignin, 79g of propylene carbonate and 0.6g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 150℃ and stir magnetically for 3h; after the reaction is complete, drop the reaction solution into 200g of water and stir for 1h, filter under vacuum to obtain a solid product, wash with deionized water 3 times and freeze dry to obtain oxyalkylated organic solvent lignin;

[0048] T2. Add 0.03g of oxyalkylated organic solvent lignin obtained from T1, 3g of L-lactide and 0.15g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 150℃ and stir magnetically for 4h, add 20g of acetic acid to stop the reaction, then add 60g of methanol and stir for 2h, centrifuge at 20000rpm to obtain a solid product, wash with deionized water 3 times and dry in a vacuum drying oven at 60℃ for 24h to obtain an oxyalkylated organic solvent lignin-g-PLA graft copolymer;

[0049] T3. Dry 50g of high-density polyethylene under vacuum at 75℃ for 12h; put the dried high-density polyethylene and 10g of the oxyalkylated organic solvent lignin-g-PLA graft copolymer obtained from T2 into a mixer, and melt-blend at 160℃ and a screw speed of 60rpm for 10min to obtain modified high-density polyethylene.

[0050] Preparation Example 6

[0051] T1. Add 5g of organic solvent lignin, 79g of propylene carbonate and 0.6g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 150℃ and stir magnetically for 3h; after the reaction is complete, drop the reaction solution into 200g of water and stir for 1h, filter under vacuum to obtain a solid product, wash with deionized water 3 times and freeze dry to obtain oxyalkylated organic solvent lignin;

[0052] T2. Add 0.01g of oxyalkylated organic solvent lignin prepared by T1, 1g of L-lactide and 0.05g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 130℃ and stir magnetically for 3h, add 10g of acetic acid to stop the reaction, then add 45g of methanol and stir for 1h, centrifuge at 10000rpm to obtain a solid product, wash with deionized water 3 times and dry in a vacuum drying oven at 50℃ for 30h to obtain an oxyalkylated organic solvent lignin-g-PLA graft copolymer;

[0053] T3. Dry 55g of high-density polyethylene under vacuum at 80℃ for 13.5h; put the dried high-density polyethylene and 11g of the oxyalkylated organic solvent lignin-g-PLA graft copolymer obtained from T2 into a mixer and melt-blend at 170℃ and a screw speed of 70rpm for 15min to obtain modified high-density polyethylene.

[0054] Preparation Example 7

[0055] T1. Add 5g of organic solvent lignin, 79g of propylene carbonate and 0.6g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 150℃ and stir magnetically for 3h; after the reaction is complete, drop the reaction solution into 200g of water and stir for 1h, filter under vacuum to obtain a solid product, wash with deionized water 3 times and freeze dry to obtain oxyalkylated organic solvent lignin;

[0056] T2. Add 0.01g of oxyalkylated organic solvent lignin prepared by T1, 1g of L-lactide and 0.05g of 1,8-diazabicyclo[5.4.0]undec-7-ene to a pressure-resistant tube, fill with nitrogen and seal, heat in an oil bath to 130℃ and stir magnetically for 3h, add 10g of acetic acid to stop the reaction, then add 45g of methanol and stir for 1h, centrifuge at 10000rpm to obtain a solid product, wash with deionized water 3 times and dry in a vacuum drying oven at 50℃ for 30h to obtain an oxyalkylated organic solvent lignin-g-PLA graft copolymer;

[0057] T3. Dry 60g of high-density polyethylene under vacuum at 85℃ for 15h; put the dried high-density polyethylene and 12g of oxyalkylated organic solvent lignin-g-PLA graft copolymer obtained from T2 into a mixer and melt-blend at 180℃ and a screw speed of 80rpm for 20min to obtain modified high-density polyethylene.

[0058] Example

[0059] Example 1

[0060] S1. A PE / PA symmetrical film, comprising, from the outside to the inside, an outer layer, an outer second layer, a first adhesive layer, a middle layer, a second adhesive layer, an inner layer, and an inner second layer; 0.156g of modified high-density polyethylene for the outer layer, 0.195g of linear low-density polyethylene for the outer second layer, 0.077g of TIE resin for the first adhesive layer, 0.113g of PA resin for the middle layer, 0.077g of TIE resin for the second adhesive layer, 0.195g of linear low-density polyethylene for the inner layer, and 0.156g of modified high-density polyethylene for the inner second layer are weighed according to mass. In this embodiment, the TIE resin used is an anhydride-modified ethylene-vinyl acetate copolymer, and the modified high-density polyethylene used is from Preparation Example 1; the raw materials are sequentially placed into the hopper of a seven-layer co-extrusion blown film machine, the screw barrel temperature corresponding to the hopper is set to 195°C, and then the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner layer, and inner second layer base film are obtained by screw extrusion;

[0061] S2. The outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer and inner second layer base film are extruded and blown into a finished film under the action of a screw through the die head of a seven-layer co-extrusion blown film machine. The die head temperature of the seven-layer co-extrusion blown film machine is set to 195℃ and the blown ratio is 1:1.3.

[0062] Example 2

[0063] S1. A PE / PA symmetrical film, comprising, from the outside to the inside, an outer layer, an outer second layer, a first adhesive layer, a middle layer, a second adhesive layer, an inner layer, and an inner second layer; 0.162g of modified high-density polyethylene for the outer layer, 0.199g of linear low-density polyethylene for the outer second layer, 0.082g of TIE resin for the first adhesive layer, 0.118g of PA resin for the middle layer, 0.082g of TIE resin for the second adhesive layer, 0.199g of linear low-density polyethylene for the inner layer, and 0.162g of modified high-density polyethylene for the inner second layer are weighed according to mass. In this embodiment, the TIE resin used is an anhydride-modified ethylene-vinyl acetate copolymer, and the modified high-density polyethylene used is from Preparation Example 1; the raw materials are sequentially placed into the hopper of a seven-layer co-extrusion blown film machine, the screw barrel temperature corresponding to the hopper is set to 200°C, and then the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner layer, and inner second layer base film are obtained by screw extrusion;

[0064] S2. The outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer and inner second layer base film are extruded and blown into a finished film under the action of a screw through the die head of a seven-layer co-extrusion blown film machine. The die head temperature of the seven-layer co-extrusion blown film machine is set to 200℃ and the blown ratio is 1:1.4.

[0065] Example 3

[0066] S1. A PE / PA symmetrical film, comprising, from the outside to the inside, an outer layer, an outer second layer, a first adhesive layer, a middle layer, a second adhesive layer, an inner layer, and an inner second layer; 0.168g of modified high-density polyethylene for the outer layer, 0.203g of linear low-density polyethylene for the outer second layer, 0.087g of TIE resin for the first adhesive layer, 0.125g of PA resin for the middle layer, 0.087g of TIE resin for the second adhesive layer, 0.203g of linear low-density polyethylene for the inner layer, and 0.168g of modified high-density polyethylene for the inner second layer are weighed according to mass. In this embodiment, the TIE resin used is an anhydride-modified ethylene-vinyl acetate copolymer, and the modified high-density polyethylene used is from Preparation Example 1; the raw materials are sequentially placed into the hopper of a seven-layer co-extrusion blown film machine, the screw barrel temperature corresponding to the hopper is set to 210°C, and then the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner layer, and inner second layer base film are obtained by screw extrusion;

[0067] S2. The outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer and inner second layer base film are extruded and blown into a finished film under the action of a screw through the die head of a seven-layer co-extrusion blown film machine. The die head temperature of the seven-layer co-extrusion blown film machine is set to 210℃ and the blown ratio is 1:1.5.

[0068] Example 4

[0069] The difference between Example 4 and Example 1 is that the raw materials used for the outer layer and inner second layer in Example 4 are from Preparation Example 2.

[0070] Example 5

[0071] The difference between Example 5 and Example 1 is that the raw materials used for the outer layer and the inner second layer in Example 5 are from Preparation Example 3.

[0072] Example 6

[0073] The difference between Example 6 and Example 1 is that the raw materials used for the outer layer and the inner second layer in Example 6 are from Preparation Example 4.

[0074] Example 7

[0075] The difference between Example 7 and Example 1 is that the raw materials used for the outer layer and the inner second layer in Example 7 are from Preparation Example 5.

[0076] Example 8

[0077] The difference between Example 8 and Example 1 is that the raw materials used for the outer layer and the inner second layer in Example 8 are from Preparation Example 6.

[0078] Example 9

[0079] The difference between Example 9 and Example 1 is that the raw materials used for the outer layer and the inner second layer in Example 9 are from Preparation Example 7.

[0080] Comparative Example

[0081] Comparative Example 1

[0082] The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, the outer layer material is modified high-density polyethylene 0.150g, the outer second layer material is linear low-density polyethylene 0.191g, the first adhesive layer material is TIE resin 0.072g, the middle layer material is PA resin 0.107g, the second adhesive layer material is TIE resin 0.072g, the inner layer material is linear low-density polyethylene 0.191g, and the inner second layer material is modified high-density polyethylene 0.150g.

[0083] Comparative Example 2

[0084] The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, the outer layer material is modified high-density polyethylene 0.174g, the outer second layer material is linear low-density polyethylene 0.207g, the first adhesive layer material is TIE resin 0.092g, the middle layer material is PA resin 0.131g, the second adhesive layer material is TIE resin 0.092g, the inner layer material is linear low-density polyethylene 0.207g, and the inner second layer material is modified high-density polyethylene 0.174g.

[0085] Comparative Example 3

[0086] The difference between Comparative Example 3 and Example 1 is that the outer layer and inner two layers in Comparative Example 3 are made of unmodified high-density polyethylene.

[0087] Performance testing

[0088] 1. The tensile strength and elongation at break of the PE / PA symmetrical films obtained in Examples 1-9 and Comparative Examples 1-3 were tested using GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films / sheets". The results are shown in Table 1.

[0089] 2. While ensuring the flatness of the PE / PA symmetrical film, take a long strip of polyester film measuring 15mm × 160mm along the longitudinal direction, place it horizontally, and clamp it with a length of 20mm. The horizontal difference between the free end and the clamped end is used as the evaluation standard for the stiffness of the PE / PA symmetrical film. The smaller the horizontal difference, the better the stiffness of the PE / PA symmetrical film. The results are shown in Table 1.

[0090] The specific test results are as follows:

[0091] Table 1 Performance Test Results

[0092] Tensile strength / MPa Elongation at break / % stiffness / mm Example 1 51 665 26 Example 2 67 695 12 Example 3 58 680 18 Example 4 54 670 24 Example 5 52 662 25 Example 6 53 667 25 Example 7 51 662 27 Example 8 60 672 20 Example 9 54 668 22 Comparative Example 1 28 580 75 Comparative Example 2 31 593 80 Comparative Example 3 35 376 90

[0093] As can be seen from the test results in Table 1, the PE / PA symmetrical film and its preparation method provided in this application have high tensile strength and elongation at break, indicating that the PE / PA symmetrical film provided in this application has strong mechanical strength; the horizontal position difference between the free end and the clamping end of the film is small, indicating that the PE / PA symmetrical film provided in this application has good stiffness.

[0094] 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 PE / PA symmetric film characterized in that: The PE / PA symmetrical film comprises, from the outside to the inside, an outer layer, an outer second layer, a first adhesive layer, a middle layer, a second adhesive layer, an inner layer, and an inner second layer; the outer first layer and the inner second layer are made of modified high-density polyethylene, the outer second layer and the inner first layer are made of linear low-density polyethylene, the first adhesive layer and the second adhesive layer are made of TIE resin, and the middle layer is made of PA resin.

2. The PE / PA symmetrical film according to claim 1, characterized in that: The mass ratio of the raw materials for the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer, and inner second layer is 0.156-0.168:0.195-0.203:0.077-0.087:0.113-0.0125:0.077-0.087:0.195-0.203:0.156-0.

168.

3. The PE / PA symmetric film according to claim 2, characterized in that: The mass ratio of the raw materials for the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer, and inner second layer is 0.162:0.199:0.082:0.119:0.082:0.199:0.

162.

4. The PE / PA symmetrical film according to claim 1, characterized in that: The modified high-density polyethylene is prepared from the following raw materials in parts by weight: 50-60 parts high-density polyethylene and 10-12 parts oxyalkylated organic solvent lignin-g-PLA graft copolymer.

5. A PE / PA symmetrical film according to claim 4, characterized in that: The oxyalkylated organic solvent lignin-g-PLA graft copolymer is prepared from the following raw materials in parts by weight: 0.01-0.03 parts oxyalkylated organic solvent lignin, 1-3 parts L-lactide, 0.05-0.15 parts 1,8-diazabicyclo[5.4.0]undec-7-ene, 10-20 parts acetic acid, and 45-60 parts methanol.

6. The PE / PA symmetrical film according to claim 5, characterized in that: The oxyalkylated organic solvent lignin is prepared from the following raw materials in parts by weight: 5-10 parts organic solvent lignin, 0.6-1.2 parts 1,8-diazabicyclo[5.4.0]undec-7-ene, 79-108 parts propylene carbonate, and 200-300 parts water.

7. A PE / PA symmetrical film according to claim 6, characterized in that: The method for preparing the oxyalkylated organic solvent lignin includes the following steps: Organic solvent lignin, propylene carbonate and 1,8-diazabicyclo[5.4.0]undec-7-ene were added to a pressure-resistant tube, which was then filled with nitrogen and sealed. The tube was heated in an oil bath to 150-190°C and magnetically stirred for 3-5 hours. After the reaction was completed, the reaction solution was dropped into water and stirred for 1-3 hours. The solid product was obtained by vacuum filtration, washed several times and then freeze-dried to obtain oxyalkylated organic solvent lignin.

8. The PE / PA symmetric film according to claim 5, characterized in that: The preparation method of the oxyalkylated organic solvent lignin-g-PLA graft copolymer includes the following steps: Oxyalkylated organic solvent lignin, L-lactide and 1,8-diazabicyclo[5.4.0]undec-7-ene were added to a pressure-resistant tube, which was then filled with nitrogen and sealed. The tube was heated in an oil bath to 130-150℃ and magnetically stirred for 3-4 hours. Acetic acid was added to stop the reaction, followed by the addition of methanol and stirring for 1-2 hours. The solid product was obtained by centrifugation, washed several times, and dried in a vacuum drying oven at 50-60℃ for 24-30 hours to obtain an oxyalkylated organic solvent lignin-g-PLA graft copolymer.

9. The PE / PA symmetric film according to claim 4, characterized in that: The method for preparing the modified high-density polyethylene includes the following steps: High-density polyethylene is dried under vacuum at 75-85℃ for 12-15 hours; the dried high-density polyethylene and oxyalkylated organic solvent lignin-g-PLA graft copolymer are placed in a mixer and melt-blended at 160-180℃ and a screw speed of 60-80 rpm for 10-20 minutes to obtain modified high-density polyethylene.

10. A method for preparing a PE / PA symmetrical film according to any one of claims 1-9, characterized in that: Includes the following steps: S1. Weigh the raw materials of the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer and inner second layer according to the mass ratio, put the raw materials into the hopper of the seven-layer co-extrusion blown film machine in sequence, set the screw barrel temperature corresponding to the hopper to 195-210℃, and then extrude through the screw to obtain the outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer and inner second layer base film; S2. The outer layer, outer second layer, first adhesive layer, middle layer, second adhesive layer, inner first layer and inner second layer base film are extruded and blown into a finished film under the action of a screw through the die head of a seven-layer co-extrusion blown film machine. The die head temperature of the seven-layer co-extrusion blown film machine is set to 195-210℃ and the blown ratio is 1:1.3-1.5.