A heat-resistant polyethylene composite packaging film and its preparation method

Abstract

The present invention relates to the technical field of packaging films, and specifically discloses a heat-resistant polyethylene composite packaging film and a preparation method thereof. The polyethylene composite packaging film comprises an inner layer, a middle layer and an outer layer. By mass, the raw materials of the inner layer include 100 parts of linear low-density polyethylene, 28-32 parts of polypropylene, and 8-10 parts of hydrotalcite-modified blend; the raw materials of the middle layer include 100 parts of low-density polyethylene, 40-60 parts of linear low-density polyethylene, 3-5 parts of coupling agent, and 0.5-1 part of antioxidant; the raw materials of the outer layer include 100 parts of modified PA6, 20-30 parts of metallocene polyethylene, and 5-8 parts of compatibilizer. The functional gradient distribution is realized by three-layer coextrusion and layered extrusion. The synergistic effect of PA6 and polypropylene endows the composite film with excellent heat resistance. The synergistic effect of hydrotalcite and graphene oxide, and the layered structure effectively blocks oxygen and water vapor. The obtained polyethylene composite packaging film has good barrier properties and excellent mechanical properties and heat resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging films, and particularly to a heat-resistant polyethylene composite packaging film and a preparation method thereof. Background Art

[0002] Polyethylene resin (PE), as a thermoplastic plastic, is rich in resources, low in price, safe and non-toxic, and has excellent chemical stability and processability. Among them, the polyethylene film made of polyethylene resin as the main raw material occupies an important position in the packaging industry, especially in the fields of food packaging, pharmaceutical packaging, and soft packaging of industrial products. The polyethylene film has excellent toughness and moisture-proof performance, but the heat resistance of ordinary polyethylene film is poor. It is easy to soften, deform or even melt under high temperature conditions, which not only greatly reduces the performance of the packaging material, but also may contaminate the packaged items. With the continuous progress of modern food processing technology, high-temperature sterilization is widely used, and the demand for high-temperature encapsulation in the industrial packaging field is also increasing day by day. The disadvantages of poor heat resistance of traditional polyethylene films are gradually exposed, which to a certain extent limits the application range of polyethylene films.

[0003] Chinese Patent Application CN111333991A discloses a high-temperature resistant composite packaging film, which is made of the following raw materials in parts by weight: 50-60 parts of modified polyethylene resin, 6-8 parts of modified talc powder, and 1.5-2 parts of liquid paraffin. Using modified polyethylene resin as the packaging film matrix and adding heat-resistant filler talc powder, the talc powder is modified to reduce the agglomeration of talc powder, and it has excellent heat resistance. The components of the packaging film are not easy to precipitate in a high-temperature environment. However, in the preparation process of the modified polyethylene resin in this packaging film, through cobalt source irradiation, the preparation cost is relatively high, which limits its application. Chinese Patent Application CN110330717A discloses an organic-inorganic hybrid material-modified high-temperature resistant PE film and a preparation method thereof. The high-temperature resistant PE film is composed of the following components in mass ratio: 10-15 parts of modified plant cellulose, 4-6 parts of porous organic-inorganic hybrid material, 1-3 parts of natural antioxidant, 1-3 parts of natural antibacterial agent, 70-80 parts of polyethylene matrix, and 3-5 parts of acrylic acid. This PE film has high safety and excellent antibacterial efficacy. However, under high temperature conditions, the natural antioxidant and natural antibacterial agent in this PE film are prone to decomposition or oxidation and precipitate from the PE film, affecting the mechanical properties of the PE film, and the compatibility between raw materials is general, resulting in problems such as delamination and cracking during processing and use, affecting the service life.

[0004] Therefore, it is urgent to develop a heat-resistant polyethylene composite packaging film with low cost and excellent mechanical properties to overcome the deficiencies of traditional polyethylene films in high-temperature environments and meet the market's demand for high-performance packaging materials.

[0005] ‌Summary of the Invention

[0006] (1) Technical problems to be solved

[0007] In view of the deficiencies of the prior art, the present invention provides a heat-resistant polyethylene composite packaging film and its preparation method, which solves the problems of poor heat resistance and general mechanical properties of polyethylene packaging films.

[0008] (2) Technical solutions

[0009] To achieve the above object, the present invention discloses a heat-resistant polyethylene composite packaging film, which includes an inner layer, a middle layer, and an outer layer;

[0010] By mass, the raw materials of the inner layer include: 100 parts of linear low-density polyethylene, 28 - 32 parts of polypropylene, and 8 - 10 parts of hydrotalcite modified blend;

[0011] By mass, the raw materials of the middle layer include: 100 parts of low-density polyethylene, 40 - 60 parts of linear low-density polyethylene, 3 - 5 parts of coupling agent, and 0.5 - 1 part of antioxidant;

[0012] By mass, the raw materials of the outer layer include: 100 parts of modified PA6, 20 - 30 parts of metallocene polyethylene, and 5 - 8 parts of compatibilizer.

[0013] Preferably, the preparation method of the hydrotalcite modified blend includes the following steps:

[0014] S1. Ultrasonically disperse hydrotalcite in a mixed solvent. After uniform dispersion, adjust the pH to 4 with glacial acetic acid, stir and mix, dropwise add γ-methacryloxypropyltrimethoxysilane, stir, and react. After the reaction is completed, perform suction filtration, wash with absolute ethanol and deionized water, and dry in a vacuum drying oven at 80°C for 12 h to obtain vinylated hydrotalcite;

[0015] S2. Mix acetone, maleic anhydride, polypropylene, polyethylene, vinylated hydrotalcite, and initiator uniformly. After the acetone volatilizes, transfer to a twin-screw extruder for melt blending, extrusion, and cooling to obtain a hydrotalcite modified blend.

[0016] Preferably, in S1, the mass ratio of hydrotalcite, mixed solvent, and γ-methacryloxypropyltrimethoxysilane is 100:3000 - 4000:12 - 25.

[0017] Preferably, in S1, the reaction temperature is 55 - 65°C, and the reaction time is 1 - 2 h.

[0018] Preferably, in S1, the mixed solvent is obtained by mixing absolute ethanol and deionized water with a volume ratio of 9:1.

[0019] Preferably, in the step S2, the mass ratio of acetone, maleic anhydride, polypropylene, polyethylene, vinyl-functionalized hydrotalcite, and initiator is 400-450:10-14:20-30:100:5-8:2-5.

[0020] Preferably, in the step S2, the temperature of melt blending is 195-220 °C, and the time of melt blending is 8-12 min.

[0021] Preferably, the initiator in the step S2 is dicumyl peroxide.

[0022] Preferably, the preparation method of the modified PA6 includes the following steps:

[0023] Step (1): Ultrasonically disperse graphene oxide in N,N-dimethylformamide. After uniform dispersion, add triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine, raise the temperature, stir and mix, and react. After the reaction is completed, centrifuge at a rate of 6000 r / min for 8 min, wash with deionized water, and vacuum dry at 60 °C for 12 h to obtain amino-functionalized graphene oxide;

[0024] Step (2): Mix nanocellulose and deionized water evenly, add sodium periodate, stir and mix, raise the temperature, react in the dark, add ethylene glycol to terminate the reaction. After the reaction is completed, filter by suction, wash with deionized water, and freeze-dry to obtain aldehyde-functionalized cellulose;

[0025] Step (3): Vacuum dry PA6 in an oven at 90 °C for 12 h. Stir and mix the dried PA6, amino-functionalized graphene oxide, and aldehyde-functionalized cellulose evenly, add them to a twin-screw extruder, perform melt blending, extrusion, and cooling to obtain modified PA6.

[0026] Preferably, in the step (1), the mass ratio of graphene oxide, N,N-dimethylformamide, triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:9500-10500:400-500:42-50:4-5.

[0027] Preferably, in the step (1), the reaction temperature is 55-65 °C, and the reaction time is 10-15 h.

[0028] Preferably, in the step (2), the mass ratio of nanocellulose, deionized water, and sodium periodate is 100:6000-7000:120-150.

[0029] Preferably, in the step (2), the reaction temperature is 45-50 °C, and the reaction time is 18-20 h.

[0030] Preferably, in step (3), the mass ratio of the dried PA6, amino-functionalized graphene oxide, and aldehyde-functionalized cellulose is 100:4 - 7:3 - 5, and the temperature in the twin-screw extruder is set at 210 - 240 °C.

[0031] Preferably, the PA6 is nylon 6 resin with a melt index of 8 - 12 g / 10 min (test conditions: 230 °C / 2.16 kg).

[0032] Preferably, the coupling agent is a silane coupling agent.

[0033] Furthermore, the silane coupling agent is preferably vinyltrimethoxysilane.

[0034] Preferably, the antioxidant is composed of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1.

[0035] Preferably, the compatibilizer is maleic anhydride grafted POE.

[0036] A preparation method of a heat-resistant polyethylene composite packaging film includes the following steps:

[0037] Step 1: Weigh the raw materials for the inner layer, middle layer, and outer layer by mass parts, and respectively carry out batching, mixing, and drying pretreatment.

[0038] Step 2: Heat the raw materials for the inner layer, middle layer, and outer layer in the extruder barrel respectively to form a melt. After being transmitted through a pipeline and filtered by a filter, it is extruded into a sheet-like fluid by a three-layer coextrusion composite die head, cooled by a chill roll, then subjected to biaxial stretching. After the stretching is completed, it is drawn, wound, and slit to obtain the heat-resistant polyethylene composite packaging film.

[0039] Preferably, in step 2, the heating temperatures in the extruder barrel are 180 - 220 °C for the inner layer, 160 - 200 °C for the middle layer, and 240 - 280 °C for the outer layer respectively, and the temperature of the three-layer coextrusion composite die head is 210 - 240 °C.

[0040] Preferably, in step 2, during the biaxial stretching process, the transverse stretching ratio is 2 - 4 times, and the longitudinal stretching ratio is 1.5 - 3 times.

[0041] (III) Beneficial technical effects

[0042] In the present invention, γ-methacryloxypropyltrimethoxysilane is used to modify hydrotalcite, introducing carbon-carbon double bonds onto the surface of hydrotalcite to obtain vinylated hydrotalcite. Maleic anhydride, polypropylene, polyethylene, vinylated hydrotalcite, and initiator dicumyl peroxide are mixed. During the decomposition process of dicumyl peroxide, free radicals are generated. Under the action of dicumyl peroxide, polymerization occurs to obtain a hydrotalcite-modified mixture, improving the compatibility between hydrotalcite and the polyolefin matrix, forming chemical bonding, enhancing the interfacial bonding force, and inhibiting the agglomeration of hydrotalcite. Triethylenetetramine is used to modify graphene oxide. The amination reaction occurs between the amino group on triethylenetetramine and the carboxyl group on the surface of graphene oxide under the action of dicyclohexylcarbodiimide and 4-dimethylaminopyridine to obtain amino-functionalized graphene oxide. Sodium periodate is used to oxidize and modify nanocellulose to obtain aldehyde-functionalized cellulose. The dried PA6, amino-functionalized graphene oxide, and aldehyde-functionalized cellulose are mixed and melt-blended in a twin-screw extruder to obtain modified PA6.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] (1) In the present invention, a polyethylene composite packaging film is prepared by a three-layer coextrusion and biaxial stretching process. Linear low-density polyethylene is used as the main body for the inner layer, and polypropylene and a hydrotalcite-modified blend are added. The linear molecular structure and short branched-chain characteristics of linear low-density polyethylene endow it with excellent tensile and tear resistance, which can significantly improve the mechanical properties of the packaging film, and it has good compactness, which can simultaneously improve the barrier properties. The polypropylene molecular chain has high rigidity, a high melting point, good heat resistance and chemical resistance, and excellent mechanical properties, which can improve the heat resistance of the inner layer and prevent the composite film from softening and deforming. At the same time, it can also improve the mechanical properties, puncture resistance and tear resistance of the polyethylene composite film. Hydrotalcite has a layered structure, which can effectively block water vapor and oxygen, improve the barrier properties and thermal stability of the composite film, effectively reduce high-temperature heat shrinkage. After modification, the agglomeration of hydrotalcite is avoided, comprehensively improving the toughness and mechanical properties of the polyolefin composition. The hydrotalcite-modified blend can enhance the barrier properties and thermal stability.

[0045] (2) In the middle layer structure of the present invention, low-density polyethylene is used as the main body. Low-density polyethylene has good softness and extensibility, good impact resistance, and excellent processing fluidity. As the middle layer matrix, it can balance the overall flexibility and strength. When low-density polyethylene is mixed with linear low-density polyethylene and under the action of a coupling agent, it has excellent toughness, can play a role in structural support, promote the interfacial bonding of polymers, improve the uniformity of the middle layer, reduce stress concentration, improve the interlayer force, and the obtained composite film has excellent mechanical properties and heat resistance.

[0046] (3) In the present invention, modified PA6 is used as the main body in the outer layer. PA6 has a high melting point and excellent mechanical strength, which can improve the high-temperature resistance and puncture resistance of the outer layer. Graphene oxide has excellent heat resistance and mechanical properties. After modification, agglomeration is effectively avoided, and it can be evenly dispersed in the PA6 matrix. Nano-cellulose has an extremely low coefficient of thermal expansion, which can reduce the thermal expansion rate of the composite film. By enhancing the interaction between molecular chains, it delays the softening and deformation of polyethylene at high temperatures. When evenly dispersed into the matrix, it can form a reinforcing skeleton, significantly improving the tensile strength and elastic modulus of the composite film. At the same time, the cross-linked network structure can also absorb external stress and reduce the risk of film tearing. Further, the dense structure of nano-cellulose can effectively improve the barrier properties of the composite film. The amino groups on the amino-functionalized graphene oxide and the amino groups on PA6 in the modified PA6 can react with the aldehyde groups on the aldehyde-functionalized cellulose to construct a three-dimensional network structure, avoiding the problem of phase separation, having excellent compatibility, improving the mechanical properties and barrier properties of the composite film, and enhancing heat resistance. Metallocene polyethylene has the characteristics of high heat resistance, excellent mechanical properties and chemical stability, which can improve the toughness of the outer layer and effectively prevent brittle cracking. The compatibilizer maleic anhydride grafted POE has good compatibility with non-polar polyolefins, can promote the compatibility of PA6 and polyethylene, and is evenly dispersed, effectively avoiding delamination.

[0047] (4) In the present invention, the functional gradient distribution is realized through three-layer coextrusion and stratified extrusion, avoiding problems such as crystallization, cracking, uneven thickness or inability to form a film. Biaxial stretching can induce molecular chain orientation crystallization, improving mechanical properties and heat resistance. The synergistic effect of PA6 and PP endows the composite film with excellent heat resistance and enables it to withstand high-temperature environments. The synergistic effect of hydrotalcite and graphene oxide. The layered structure effectively blocks oxygen and water vapor, and as a filler, it can significantly improve the tensile strength and puncture resistance of the composite film. Specific embodiments

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the protection scope of the present invention. Example 1

[0049] A preparation method of a heat-resistant polyethylene composite packaging film includes the following steps:

[0050] Step 1: Weigh the raw materials for the inner layer, middle layer, and outer layer by mass parts. The raw materials for the inner layer include 100 parts of linear low-density polyethylene, 28 parts of polypropylene, and 8 parts of hydrotalcite-modified blend. The raw materials for the middle layer include: 100 parts of low-density polyethylene, 40 parts of linear low-density polyethylene, 3 parts of coupling agent vinyltrimethoxysilane, and 0.5 part of antioxidant. The antioxidant consists of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1. The raw materials for the outer layer include: 100 parts of modified PA6, 20 parts of metallocene polyethylene, and 5 parts of compatibilizer maleic anhydride-grafted POE. Carry out batching, mixing, and drying pretreatment respectively.

[0051] Step 2: Heat the raw materials for the inner layer, middle layer, and outer layer in the extruder barrel respectively. The heating temperatures in the extruder barrel are 180°C for the inner layer, 160°C for the middle layer, and 240°C for the outer layer. Process them into melts. After being transported through pipelines and filtered by filters, they are extruded into sheet-like fluids by a three-layer coextrusion composite die head. The temperature of the three-layer coextrusion composite die head is 210°C. After being cooled by a chill roll, carry out biaxial stretching. During the biaxial stretching process, the transverse stretching ratio is 4 times and the longitudinal stretching ratio is 3 times. After stretching is completed, carry out traction, winding, and slitting to obtain a heat-resistant polyethylene composite packaging film.

[0052] The preparation method of the hydrotalcite-modified blend includes the following steps:

[0053] S1: Ultrasonically disperse hydrotalcite in a mixed solvent. The mixed solvent is obtained by mixing anhydrous ethanol and deionized water with a volume ratio of 9:1. After uniform dispersion, adjust the pH to 4 with glacial acetic acid, stir and mix, and dropwise add γ-methacryloxypropyltrimethoxysilane. The mass ratio of hydrotalcite, mixed solvent, and γ-methacryloxypropyltrimethoxysilane is 100:3000:12. Stir and react at 55°C for 1 h. After the reaction is completed, carry out suction filtration, wash with anhydrous ethanol and deionized water, and dry in a vacuum drying oven at 80°C for 12 h to obtain vinyl-functionalized hydrotalcite.

[0054] S2: Mix acetone, maleic anhydride, polypropylene, polyethylene, vinyl-functionalized hydrotalcite, and initiator diisopropylbenzene peroxide with a mass ratio of 400:10:20:100:5:2 uniformly. After the acetone volatilizes, transfer it to a twin-screw extruder for melt blending. The temperature of the melt blending is 195°C and the time of the melt blending is 12 min. Extrude and cool to obtain the hydrotalcite-modified blend.

[0055] The preparation method of modified PA6 includes the following steps:

[0056] (1) Ultrasonically disperse graphene oxide in N,N-dimethylformamide. After uniform dispersion, add triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine. The mass ratio of graphene oxide, N,N-dimethylformamide, triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:9500:400:42:4. Heat up and stir to mix, and react. The reaction temperature is 55 °C and the reaction time is 15 h. After the reaction, centrifuge at a rate of 6000 r / min for 8 min, wash with deionized water, and dry in vacuum at 60 °C for 12 h to obtain amino-functionalized graphene oxide;

[0057] (2) Mix nanocellulose and deionized water evenly, and add sodium periodate. The mass ratio of nanocellulose, deionized water, and sodium periodate is 100:6000:120. Stir to mix, heat up, and react in the dark. The reaction temperature is 45 °C and the reaction time is 20 h. Add ethylene glycol to terminate the reaction. After the reaction, filter by suction, wash with deionized water, and freeze-dry to obtain aldehyde-functionalized cellulose;

[0058] (3) Vacuum-dry PA6 in an oven at 90 °C for 12 h. Stir and mix evenly the dried PA6, amino-functionalized graphene oxide, and aldehyde-functionalized cellulose with a mass ratio of 100:4:3, add them to a twin-screw extruder, melt and blend at 210 °C, extrude, and cool to obtain modified PA6. Example 2

[0059] A method for preparing a heat-resistant polyethylene composite packaging film, comprising the following steps:

[0060] Step 1: Weigh the raw materials for the inner layer, middle layer, and outer layer by mass parts. The raw materials for the inner layer include 100 parts of linear low-density polyethylene, 29 parts of polypropylene, and 8.5 parts of a hydrotalcite-modified blend. The raw materials for the middle layer include: 100 parts of low-density polyethylene, 45 parts of linear low-density polyethylene, 3.5 parts of a coupling agent vinyltrimethoxysilane, and 0.6 parts of an antioxidant. The antioxidant consists of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1. The raw materials for the outer layer include: 100 parts of modified PA6, 24 parts of metallocene polyethylene, and 6 parts of a compatibilizer maleic anhydride-grafted POE. Carry out batching, mixing, and drying pretreatment respectively;

[0061] Step 2: Heat the inner layer raw material, middle layer raw material, and outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 200°C for the inner layer, 180°C for the middle layer, and 250°C for the outer layer. After being processed into a melt, it is transmitted through a pipeline and filtered by a filter, and then extruded into a sheet-like fluid by a three-layer coextrusion die head. The temperature of the three-layer coextrusion die head is 220°C. After being cooled by a chill roll, it is subjected to biaxial stretching. During the biaxial stretching process, the transverse stretching ratio is 3 times and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, it is drawn, wound, and slit to obtain a heat-resistant polyethylene composite packaging film.

[0062] The preparation method of the hydrotalcite modified blend includes the following steps:

[0063] S1: Ultrasonically disperse hydrotalcite in a mixed solvent. The mixed solvent is obtained by mixing anhydrous ethanol and deionized water with a volume ratio of 9:1. After being dispersed evenly, adjust the pH to 4 with glacial acetic acid, stir and mix, and dropwise add γ-methacryloxypropyltrimethoxysilane. The mass ratio of hydrotalcite, mixed solvent, and γ-methacryloxypropyltrimethoxysilane is 100:3500:18. Stir and react at 60°C for 1.5 h. After the reaction is completed, filter by suction, wash with anhydrous ethanol and deionized water, and dry in a vacuum drying oven at 80°C for 12 h to obtain vinyl-functionalized hydrotalcite.

[0064] S2: Mix acetone, maleic anhydride, polypropylene, polyethylene, vinyl-functionalized hydrotalcite, and initiator diisopropyl peroxide with a mass ratio of 420:12:24:100:6:3 evenly. After the acetone volatilizes, transfer it to a twin-screw extruder for melt blending. The temperature of the melt blending is 205°C and the time of the melt blending is 9 min. Extrude and cool to obtain the hydrotalcite modified blend.

[0065] The preparation method of the modified PA6 includes the following steps:

[0066] (1) Ultrasonically disperse graphene oxide in N,N-dimethylformamide. After being dispersed evenly, add triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine. The mass ratio of graphene oxide, N,N-dimethylformamide, triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:10000:480:48:4.6. Heat up, stir and mix, and react. The reaction temperature is 60°C and the reaction time is 14 h. After the reaction is completed, centrifuge at a rate of 6000 r / min for 8 min, wash with deionized water, and dry in a vacuum at 60°C for 12 h to obtain amino-functionalized graphene oxide.

[0067] (2) Mix nanocellulose and deionized water evenly, add sodium periodate, where the mass ratio of nanocellulose, deionized water, and sodium periodate is 100:6500:135. Stir and mix, heat up, and react in the dark. The reaction temperature is 48 °C and the reaction time is 19 h. Add ethylene glycol to terminate the reaction. After the reaction ends, perform suction filtration, wash with deionized water, and freeze-dry to obtain aldehyde-functionalized cellulose;

[0068] (3) Vacuum-dry PA6 in an oven at 90 °C for 12 h. Stir and mix the dried PA6, amino-functionalized graphene oxide, and aldehyde-functionalized cellulose with a mass ratio of 100:5:3.5 evenly, add them to a twin-screw extruder, and perform melt blending at 225 °C, then extrude and cool to obtain modified PA6. Example 3

[0069] A preparation method of a heat-resistant polyethylene composite packaging film includes the following steps:

[0070] Step 1: Weigh the raw materials for the inner layer, middle layer, and outer layer by mass parts. The raw materials for the inner layer include 100 parts of linear low-density polyethylene, 29 parts of polypropylene, and 8.5 parts of a hydrotalcite-modified blend. The raw materials for the middle layer include: 100 parts of low-density polyethylene, 45 parts of linear low-density polyethylene, 3.5 parts of a coupling agent vinyltrimethoxysilane, and 0.6 parts of an antioxidant. The antioxidant is composed of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1. The raw materials for the outer layer include: 100 parts of modified PA6, 24 parts of metallocene polyethylene, and 6 parts of a compatibilizer maleic anhydride-grafted POE. Perform batching, mixing, and drying pretreatment respectively;

[0071] Step 2: Heat the raw materials for the inner layer, middle layer, and outer layer in the extruder barrel respectively. The heating temperatures in the extruder barrel are 200 °C for the inner layer, 180 °C for the middle layer, and 250 °C for the outer layer. Process them into melts, and after being transmitted through a pipeline and filtered by a filter, extrude them into a sheet-like fluid through a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 220 °C. After cooling by a chill roll, perform biaxial stretching. During the biaxial stretching process, the transverse stretching ratio is 3 times and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, perform traction, winding, and slitting to obtain the heat-resistant polyethylene composite packaging film.

[0072] The preparation method of the hydrotalcite-modified blend includes the following steps:

[0073] S1. Ultrasonically disperse hydrotalcite in a mixed solvent, which is obtained by mixing anhydrous ethanol and deionized water with a volume ratio of 9:1. After uniform dispersion, adjust the pH to 4 using glacial acetic acid, stir and mix, and then dropwise add γ-methacryloxypropyltrimethoxysilane. The mass ratio of hydrotalcite, mixed solvent, and γ-methacryloxypropyltrimethoxysilane is 100:3500:24. Stir and react at 60 °C for 1.5 h. After the reaction, perform suction filtration, wash with anhydrous ethanol and deionized water, and dry in a vacuum drying oven at 80 °C for 12 h to obtain vinyl-functionalized hydrotalcite;

[0074] S2. Mix acetone, maleic anhydride, polypropylene, polyethylene, vinyl-functionalized hydrotalcite, and initiator diisopropyl peroxide with a mass ratio of 420:13:24:100:6:4 uniformly. After the acetone volatilizes, transfer it to a twin-screw extruder for melt blending. The melt blending temperature is 215 °C, and the melt blending time is 10 min. Extrude and cool to obtain a hydrotalcite-modified blend.

[0075] The preparation method of modified PA6 includes the following steps:

[0076] (1) Ultrasonically disperse graphene oxide in N,N-dimethylformamide. After uniform dispersion, add triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine. The mass ratio of graphene oxide, N,N-dimethylformamide, triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:10000:480:48:4.6. Heat up, stir and mix, and react. The reaction temperature is 60 °C, and the reaction time is 14 h. After the reaction, centrifuge at a rate of 6000 r / min for 8 min, wash with deionized water, and dry in a vacuum at 60 °C for 12 h to obtain amino-functionalized graphene oxide;

[0077] (2) Mix nanocellulose and deionized water uniformly, and add sodium periodate. The mass ratio of nanocellulose, deionized water, and sodium periodate is 100:6500:135. Stir and mix, heat up, and react in the dark. The reaction temperature is 48 °C, and the reaction time is 19 h. Add ethylene glycol to terminate the reaction. After the reaction, perform suction filtration, wash with deionized water, and freeze-dry to obtain aldehyde-functionalized cellulose;

[0078] (3) Vacuum-dry PA6 in an oven at 90 °C for 12 h. Stir and mix the dried PA6, amino-functionalized graphene oxide, and aldehyde-functionalized cellulose with a mass ratio of 100:6:4.5 uniformly, add them to a twin-screw extruder, and perform melt blending at 235 °C. Extrude and cool to obtain modified PA6. Example 4

[0079] A preparation method of a heat-resistant polyethylene composite packaging film, comprising the following steps:

[0080] Step 1: Weigh the raw materials for the inner layer, middle layer, and outer layer by mass. The raw materials for the inner layer include 100 parts of linear low-density polyethylene, 31 parts of polypropylene, and 9.5 parts of a hydrotalcite-modified blend. The raw materials for the middle layer include: 100 parts of low-density polyethylene, 55 parts of linear low-density polyethylene, 4 parts of the coupling agent vinyltrimethoxysilane, and 0.8 part of an antioxidant. The antioxidant is composed of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1. The raw materials for the outer layer include: 100 parts of modified PA6, 28 parts of metallocene polyethylene, and 7 parts of the compatibilizer maleic anhydride-grafted POE. Carry out batching, mixing, and drying pretreatment respectively;

[0081] Step 2: Heat the raw materials for the inner layer, middle layer, and outer layer in the extruder barrel respectively. The heating temperatures in the extruder barrel are 215°C for the inner layer, 190°C for the middle layer, and 265°C for the outer layer. Process them into melts, and after pipeline transmission and filtration through a filter, extrude them into a sheet-like fluid through a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 230°C. After cooling by a chill roll, perform biaxial stretching. During the biaxial stretching process, the transverse stretching ratio is 3 times and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, carry out traction, winding, and slitting to obtain the heat-resistant polyethylene composite packaging film.

[0082] The preparation methods of the hydrotalcite-modified blend and modified PA6 are the same as those of the hydrotalcite-modified blend and modified PA6 in Example 3. Example 5

[0083] A preparation method of a heat-resistant polyethylene composite packaging film, comprising the following steps:

[0084] Step 1: Weigh the raw materials for the inner layer, middle layer, and outer layer by mass. The raw materials for the inner layer include 100 parts of linear low-density polyethylene, 32 parts of polypropylene, and 10 parts of a hydrotalcite-modified blend. The raw materials for the middle layer include: 100 parts of low-density polyethylene, 60 parts of linear low-density polyethylene, 5 parts of the coupling agent vinyltrimethoxysilane, and 1 part of an antioxidant. The antioxidant is composed of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1. The raw materials for the outer layer include: 100 parts of modified PA6, 30 parts of metallocene polyethylene, and 8 parts of the compatibilizer maleic anhydride-grafted POE. Carry out batching, mixing, and drying pretreatment respectively;

[0085] Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 220°C for the inner layer, 200°C for the middle layer, and 280°C for the outer layer. The raw materials are processed into a melt, and after being transmitted through a pipeline and filtered by a filter, they are extruded into a sheet-like fluid and flow out through a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 240°C. After being cooled by a chilled roller, they are biaxially stretched. During the biaxial stretching process, the transverse stretching ratio is 2 times, and the longitudinal stretching ratio is 1.5 times. After the stretching is completed, the film is pulled, rolled, and slit to obtain a heat-resistant polyethylene composite packaging film.

[0086] The preparation method of the hydrotalcite modified blend comprises the following steps:

[0087] S1. Ultrasonic dispersion of hydrotalcite in a mixed solvent, wherein the mixed solvent is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 9:1. After uniform dispersion, the pH value is adjusted to 4 using glacial acetic acid, and the mixture is stirred and mixed. γ-methacryloxypropyltrimethoxysilane is added dropwise, wherein the mass ratio of hydrotalcite, mixed solvent, and γ-methacryloxypropyltrimethoxysilane is 100:4000:25. The mixture is stirred and reacted at 65° C. for 1 h. After the reaction is completed, the mixture is filtered, washed with anhydrous ethanol and deionized water, and dried in a vacuum drying oven at 80° C. for 12 h to obtain olefinated hydrotalcite.

[0088] S2. Acetone, maleic anhydride, polypropylene, polyethylene, olefinated hydrotalcite and initiator dicumyl peroxide in a mass ratio of 450:14:30:100:8:5 are mixed evenly, and after the acetone is volatilized, the mixture is transferred to a twin-screw extruder for melt blending at a temperature of 220° C. for 8 min, extruded, and cooled to obtain a hydrotalcite-modified blend.

[0089] The preparation method of modified PA6 comprises the following steps:

[0090] (1) Ultrasonic dispersion of graphene oxide in N,N-dimethylformamide, after uniform dispersion, adding triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine, wherein the mass ratio of graphene oxide, N,N-dimethylformamide, triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:10500:500:50:5, heating, stirring and mixing, reacting, the reaction temperature is 65°C, the reaction time is 10 hours, after the reaction is completed, centrifugation, the centrifugation speed is 6000 r / min, the centrifugation time is 8 minutes, washing with deionized water, and vacuum drying at 60°C for 12 hours to obtain amino graphene oxide;

[0091] (2) Mix nanocellulose and deionized water evenly, add sodium periodate, where the mass ratio of nanocellulose, deionized water, and sodium periodate is 100:7000:150. Stir and mix, heat up, and react in the dark. The reaction temperature is 50 °C and the reaction time is 18 h. Add ethylene glycol to terminate the reaction. After the reaction, perform suction filtration, wash with deionized water, and freeze-dry to obtain aldehyde-functionalized cellulose.

[0092] (3) Vacuum-dry PA6 in an oven at 90 °C for 12 h. Stir and mix the dried PA6, amino-functionalized graphene oxide, and aldehyde-functionalized cellulose with a mass ratio of 100:7:5 evenly, and add them to a twin-screw extruder. Perform melt blending at 240 °C, extrude, and cool to obtain modified PA6. Comparative Example 1

[0093] A method for preparing a polyethylene composite packaging film includes the following steps:

[0094] Step 1: Weigh the raw materials for the inner layer, middle layer, and outer layer by mass parts. The raw materials for the inner layer include 100 parts of linear low-density polyethylene, 31 parts of polypropylene, 0.5 part of hydrotalcite, and 9 parts of modified blend. The raw materials for the middle layer include: 100 parts of low-density polyethylene, 55 parts of linear low-density polyethylene, 4 parts of coupling agent vinyltrimethoxysilane, and 0.8 part of antioxidant. The antioxidant is composed of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1. The raw materials for the outer layer include: 100 parts of modified PA6, 28 parts of metallocene polyethylene, and 7 parts of compatibilizer maleic anhydride grafted POE. Perform batching, mixing, and drying pretreatment respectively.

[0095] Step 2: Heat the raw materials for the inner layer, middle layer, and outer layer in the extruder barrel respectively. The heating temperatures in the extruder barrel are 215 °C for the inner layer, 190 °C for the middle layer, and 265 °C for the outer layer. Process them into melts, transfer through pipelines, filter through filters, and then extrude into a sheet-like fluid through a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 230 °C. After cooling by a chill roll, perform biaxial stretching. During the biaxial stretching process, the transverse stretching ratio is 3 times and the longitudinal stretching ratio is 2.5 times. After stretching, perform traction, winding, and slitting to obtain the polyethylene composite packaging film.

[0096] The preparation method of the modified blend includes the following steps:

[0097] Mix acetone, maleic anhydride, polypropylene, polyethylene, and initiator diisopropylbenzene peroxide with a mass ratio of 420:13:24:106:4 evenly. After the acetone volatilizes, transfer to a twin-screw extruder and perform melt blending. The melt blending temperature is 215 °C and the melt blending time is 10 min. Extrude and cool to obtain the modified blend.

[0098] The preparation method of the modified PA6 is the same as that of the modified PA6 in Example 3. Comparative Example 2

[0099] A preparation method of a polyethylene composite packaging film includes the following steps:

[0100] Step 1: Weigh the raw materials for the inner layer, middle layer, and outer layer by mass. The raw materials for the inner layer include 100 parts of linear low-density polyethylene, 31 parts of polypropylene, and 9.5 parts of a hydrotalcite-modified blend. The raw materials for the middle layer include: 100 parts of low-density polyethylene, 55 parts of linear low-density polyethylene, 4 parts of the coupling agent vinyltrimethoxysilane, and 0.8 parts of an antioxidant. The antioxidant consists of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1. The raw materials for the outer layer include: 90.5 parts of PA6, 5.5 parts of graphene oxide, 4 parts of nanocellulose, 28 parts of metallocene polyethylene, and 7 parts of the compatibilizer maleic anhydride-grafted POE. Carry out batching, mixing, and drying pretreatment respectively.

[0101] Step 2: Heat the raw materials for the inner layer, middle layer, and outer layer in the extruder barrel respectively. The heating temperatures in the extruder barrel are 215°C for the inner layer, 190°C for the middle layer, and 265°C for the outer layer. Process them into melts. After being transported through pipelines and filtered by filters, they are extruded into sheet-like fluids by a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 230°C. After being cooled by a chill roll, carry out biaxial stretching. During the biaxial stretching process, the transverse stretching ratio is 3 times and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, carry out traction, winding, and slitting to obtain the polyethylene composite packaging film.

[0102] The preparation method of the hydrotalcite-modified blend is the same as that of the hydrotalcite-modified blend in Example 3. Comparative Example 3

[0103] A preparation method of a polyethylene composite packaging film includes the following steps:

[0104] Step 1: Weigh the raw materials for the inner layer, middle layer, and outer layer by mass. The raw materials for the inner layer include 100 parts of linear low-density polyethylene, 31 parts of polypropylene, and 9.5 parts of a modified blend. The raw materials for the middle layer include: 100 parts of low-density polyethylene, 55 parts of linear low-density polyethylene, 4 parts of the coupling agent vinyltrimethoxysilane, and 0.8 parts of an antioxidant. The antioxidant consists of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1. The raw materials for the outer layer include: 100 parts of PA6, 28 parts of metallocene polyethylene, and 7 parts of the compatibilizer maleic anhydride-grafted POE. Carry out batching, mixing, and drying pretreatment respectively.

[0105] Step 2: Heat the inner layer raw material, middle layer raw material, and outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 215°C for the inner layer, 190°C for the middle layer, and 265°C for the outer layer. Process them into melts. After being transmitted through pipelines and filtered by filters, they are extruded into sheet-like fluids by a three-layer coextrusion composite die head. The temperature of the three-layer coextrusion composite die head is 230°C. After being cooled by a chill roll, biaxial stretching is carried out. During the biaxial stretching process, the transverse stretching ratio is 3 times and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, it is drawn, wound up, and slit to obtain a polyethylene composite packaging film.

[0106] The preparation method of the modified blend includes the following steps:

[0107] Mix acetone, maleic anhydride, polypropylene, polyethylene, and the initiator diisopropylbenzene peroxide with a mass ratio of 420:13:24:106:4 evenly. After the acetone volatilizes, transfer it to a twin-screw extruder for melt blending. The temperature of the melt blending is 215°C and the time of the melt blending is 10 min. Then extrude and cool to obtain the modified blend.

[0108] The linear low-density polyethylene used in the examples and comparative examples of the present invention is purchased from Shanghai Qianyi Plasticization Technology Co., Ltd., with the product number px-21; the polypropylene is purchased from PetroChina Daqing Petrochemical Company, with the model T30S; the hydrotalcite is purchased from Tai'an Boyang Chemical Technology Co., Ltd.; the low-density polyethylene is purchased from Sinopec Maoming Petrochemical Company, with the model LDPE2426H; the graphene oxide is purchased from Suzhou Carbon Feng Graphite Technology Co., Ltd.; the nanocellulose is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a particle size ≤ 25 μm; the PA6 is purchased from Sinopec Baling Petrochemical Company, with the model YH800; the metallocene polyethylene is purchased from Dongguan Mingyuan Plastic Co., Ltd., with the brand Dow NG5401B; the maleic anhydride grafted POE is purchased from Jia Yirong Polymer (Shanghai) Co., Ltd., with the model CMG5805-L; other reagents are all commercially available.

[0109] Take the polyethylene composite packaging films prepared in Examples 1-5 and Comparative Examples 1-3 as samples for relevant performance tests. The test results are as follows:

[0110] (1) Heat resistance test: Cut the sample into 100 mm × 100 mm, record it as the original size, place it in an oven at 120°C for 30 min, and after cooling, measure the size after heating and calculate the heat shrinkage rate. The heat shrinkage rate = (original size - size after heating) / original size × 100%; Adopt the test standard GB / T 19466.1-2004 "Plastics - Differential scanning calorimetry (DSC) - Part 1: General principles" to test the melting peak temperature of the sample; The test results are shown in Table 1:

[0111] Table 1

[0112]

[0113] It can be seen from the test results in Table 1 that the polyethylene composite packaging films corresponding to Examples 1-5 have excellent heat resistance, with a small heat shrinkage rate and a high melting temperature. In Comparative Example 1, hydrotalcite and a modified blend were added to replace the hydrotalcite-modified blend as the raw material for the inner layer film, and the hydrotalcite was not modified. The dispersibility of the hydrotalcite in the composite packaging film became poor, and the compatibility was greatly reduced, resulting in heat stress concentration and an increased heat shrinkage rate. In Comparative Example 2, PA6, graphene oxide, and nanocellulose were added to replace the modified PA6 as the raw material for the outer layer film. The heat shrinkage rate of the composite packaging film decreased, and the melting temperature decreased. In Comparative Example 3, the modified blend was added to replace the hydrotalcite-modified blend, and PA6 was added to replace the modified PA6, resulting in poor thermal stability and a significant reduction in heat resistance.

[0114] (2) Mechanical property test: The tensile strength and elongation at break of the samples were tested according to the test standard of GB / T 1040.3-2006 "Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets"; referring to the ASTM F1306 test standard, the puncture resistance strength of the samples was tested. The diameter of the puncture needle used was 1 mm, and the puncture speed was 50 mm / min. The maximum force value was recorded; each of the above tests was performed three times, and the test results were averaged;

[0115] The above test results are shown in Table 2:

[0116] Table 2

[0117]

[0118] It can be seen from the test results in Table 2 that the polyethylene packaging composite films corresponding to Examples 1-5 have excellent mechanical properties, with a large tensile strength, are not easily broken, and have good puncture resistance strength. There are interface defects in the polyethylene composite packaging films corresponding to Comparative Example 1 and Comparative Example 2, and the mechanical properties are somewhat reduced. In Comparative Example 3, the tensile strength, elongation at break, and puncture resistance strength of the polyethylene composite packaging film are all significantly reduced.

[0119] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the claims of the present invention shall still fall within the scope covered by the present invention.

Claims

1. A heat-resistant polyethylene composite packaging film, characterized in that: Including inner layer, middle layer and outer layer; In parts by mass, the raw materials of the inner layer include: 100 parts of linear low-density polyethylene, 28-32 parts of polypropylene, and 8-10 parts of hydrotalcite modified blend; The raw materials of the middle layer include, by weight: 100 parts of low-density polyethylene, 40-60 parts of linear low-density polyethylene, 3-5 parts of coupling agent, and 0.5-1 part of antioxidant; In parts by mass, the raw materials of the outer layer include: 100 parts of modified PA6, 20-30 parts of metallocene polyethylene, and 5-8 parts of compatibilizer; The preparation method of the hydrotalcite modified blend comprises the following steps: S1. Ultrasonic dispersion of hydrotalcite in a mixed solvent. After uniform dispersion, use glacial acetic acid to adjust the pH to 4, stir and mix, dropwise add γ-methacryloxypropyltrimethoxysilane, stir and react. After the reaction is completed, filter, wash with anhydrous ethanol and deionized water, and dry in a vacuum drying oven at 80° C. for 12 h to obtain olefinated hydrotalcite; S2, acetone, maleic anhydride, polypropylene, polyethylene, olefinic hydrotalcite, and initiator are uniformly mixed, and after the acetone is volatilized, the mixture is transferred to a twin-screw extruder for melt blending, extrusion, and cooling to obtain a hydrotalcite-modified blend; The preparation method of the modified PA6 comprises the following steps: Step (1), ultrasonically dispersing graphene oxide in N,N-dimethylformamide, after uniform dispersion, adding triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine, heating, stirring and mixing, reacting, and after the reaction is completed, centrifuging at a rate of 6000 r / min for 8 min, washing with deionized water, and vacuum drying at 60° C. for 12 h to obtain amino-modified graphene oxide; Step (2), mixing the nanocellulose and deionized water evenly, adding sodium periodate, stirring and mixing, heating, reacting in the dark, adding ethylene glycol to terminate the reaction, and after the reaction is completed, filtering, washing with deionized water, and freeze-drying to obtain aldehyded cellulose; Step (3), vacuum drying PA6 in an oven at 90° C. for 12 h, stirring and mixing the dried PA6, amino-modified graphene oxide, and formaldehyde-modified cellulose, adding the mixture to a twin-screw extruder, melt blending, extruding, and cooling to obtain modified PA6.

2. The heat-resistant polyethylene composite packaging film according to claim 1, characterized in that: The mass ratio of hydrotalcite, mixed solvent and γ-methacryloxypropyltrimethoxysilane in S1 is 100:3000-4000:12-25, the reaction temperature is 55-65° C., and the reaction time is 1-2 h.

3. The heat-resistant polyethylene composite packaging film according to claim 1, characterized in that: The mass ratio of acetone, maleic anhydride, polypropylene, polyethylene, olefinic hydrotalcite and initiator in S2 is 400-450:10-14:20-30:100:5-8:2-5, the temperature of melt blending is 195-220°C, and the time of melt blending is 8-12min.

4. The heat-resistant polyethylene composite packaging film according to claim 1, characterized in that: In the step (3), the mass ratio of the dried PA6, amino-modified graphene oxide, and formaldehyde-modified cellulose is 100:4-7:3-5, and the temperature in the twin-screw extruder is set at 210-240°C.

5. The heat-resistant polyethylene composite packaging film according to claim 1, characterized in that: The coupling agent is a silane coupling agent; the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1; and the compatibilizer is maleic anhydride grafted POE.

6. A method for preparing the heat-resistant polyethylene composite packaging film according to any one of claims 1 to 5, characterized in that: The steps include: Step 1: weigh the raw materials of the inner layer, the middle layer and the outer layer by weight, and perform batching, mixing and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively, process them into melts, transmit through pipelines, filter through filters, extrude into sheet-like fluids out through the three-layer co-extrusion composite die head, cool through chilled rollers, and then perform biaxial stretching. After the stretching is completed, pull, roll, and slit to obtain a heat-resistant polyethylene composite packaging film.

7. The method for preparing a heat-resistant polyethylene composite packaging film according to claim 6, characterized in that: In the step 2, the heating temperatures in the extruder barrel are 180-220°C for the inner layer, 160-200°C for the middle layer, and 240-280°C for the outer layer, and the temperature of the three-layer co-extrusion composite die is 210-240°C.

8. The method for preparing a heat-resistant polyethylene composite packaging film according to claim 6, characterized in that: In the step 2, during the biaxial stretching process, the transverse stretching ratio is 2-4 times, and the longitudinal stretching ratio is 1.5-3 times.

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