A unidirectionally stretched polyethylene composite film material, its preparation method and application

Abstract

The present invention provides a unidirectionally stretched polyethylene composite film material, its preparation method and applications, belonging to the technical field of film materials. In the present invention, through ultrasonic exfoliation, modification with 3-aminopropyltriethoxysilane and intercalation with N,N-dimethyloctadecylammonium chloride, the dispersibility and interfacial compatibility of montmorillonite are improved, and zinc oxide is introduced to endow antibacterial and ultraviolet shielding functions; maleic anhydride grafting enhances its interfacial bonding force; in the modification of metallocene polyethylene, through the synergistic grafting of maleic anhydride and glycidyl methacrylate, polar groups are introduced to enhance its compatibility with polar nanomaterials, and the flexibility and processing performance are improved; magnesium chloride promotes the grafting efficiency, and tributyl phosphate improves the dispersibility and fluidity. The synergistic effect enhances the barrier properties, mechanical properties and processing performance of the composite material, meeting the application requirements of high-performance films.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin film materials, and relates to a unidirectionally stretched polyethylene composite thin film material, its preparation method and application. Background Art

[0002] Polyethylene is a thermoplastic plastic with excellent mechanical properties and chemical stability. Due to its excellent physical properties, it is widely used in many fields, including packaging, construction, and automotive. In the packaging industry, polyethylene films are favored for their light weight, durability, and economy, and can effectively meet various needs in daily life and industrial production. However, despite the good physical properties of polyethylene, traditional polyethylene films perform relatively poorly in terms of gas barrier properties, especially in the ability to block oxygen and water vapor. This defect limits its application in high-end packaging materials, especially in fields such as food and pharmaceuticals that have strict requirements for moisture and oxygen protection.

[0003] In order to improve the gas barrier properties of polyethylene films, researchers have introduced nanomaterials into the polyethylene matrix in order to achieve performance improvement. Among them, montmorillonite, as a widely studied nanomaterial, shows good modification potential due to its high specific surface area, layered structure, and excellent chemical stability. Researchers hope to significantly improve the barrier properties of polyethylene films by combining montmorillonite as a modifier with polyethylene, thereby expanding its application range.

[0004] However, simply introducing montmorillonite into polyethylene is not sufficient to ensure its effective dispersion in the polymer matrix. Traditional montmorillonite modification methods often result in insufficient dispersion in the polymer matrix, which not only affects the performance of montmorillonite, but may also cause the gas barrier properties and mechanical properties of polyethylene films to fail to achieve the expected effects. When montmorillonite particles cannot be evenly dispersed in polyethylene, aggregates may form inside the material. These aggregates will not only weaken the barrier effect of the material, but may also lead to a decrease in mechanical properties, affecting the durability and stability of the material. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a unidirectionally stretched polyethylene composite film material, its preparation method and application. The present invention synergistically optimizes the properties of montmorillonite and metallocene polyethylene through multiple modification strategies, significantly improving the comprehensive characteristics of the composite material. Through ultrasonic exfoliation, surface modification with 3-aminopropyltriethoxysilane, and intercalation modification with N,N-dimethyloctadecylammonium chloride, the dispersibility, interfacial compatibility, and interlayer stability of montmorillonite are improved. At the same time, zinc oxide is introduced to endow antibacterial and ultraviolet shielding functions; maleic anhydride grafting further enhances the interfacial binding force. Metallocene polyethylene is modified by synergistic grafting of maleic anhydride and glycidyl methacrylate to introduce polar groups to enhance the interfacial compatibility with polar nanomaterials and improve flexibility and processing performance. Magnesium chloride promotes the grafting efficiency, and tributyl phosphate improves the dispersibility and fluidity, enabling the modified metallocene polyethylene and montmorillonite to be evenly distributed, ultimately greatly improving the barrier properties, mechanical properties, and processing properties of the composite material to meet the application requirements of high-performance films.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a preparation method of a unidirectionally stretched polyethylene composite film material, and the preparation method of the unidirectionally stretched polyethylene composite film material includes:

[0008] S1: Ultrasonically treat the montmorillonite dispersion to obtain an exfoliated montmorillonite dispersion, and add 3-aminopropyltriethoxysilane to obtain pretreated montmorillonite;

[0009] S2: React the pretreated montmorillonite with N,N-dimethyloctadecylammonium chloride and zinc oxide to obtain ion-coordinated / intercalated modified montmorillonite; React it with maleic anhydride and diisopropylbenzene peroxide in toluene to obtain nanosheet powder grafted with polar groups;

[0010] S3: Melt-blend metallocene polyethylene with maleic anhydride, diisopropylbenzene peroxide, and antioxidant to obtain preliminarily grafted metallocene polyethylene; Co-extrude it with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate to obtain a modified polyethylene compatibilizer;

[0011] S4: Subject the polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, and additives to melt processing to obtain a unidirectionally stretched polyethylene composite film material.

[0012] Specifically, in S1: Ultrasonically treat the montmorillonite dispersion to exfoliate it to obtain an exfoliated montmorillonite dispersion, add 3-aminopropyltriethoxysilane to obtain reaction solution A, stir and react, then centrifuge, wash, and dry to obtain pretreated montmorillonite;

[0013] S2: Add N,N-dimethyloctadecylammonium chloride and zinc oxide to the pre-treated montmorillonite dispersion to obtain reaction solution B. After stirring and reacting, spray drying is carried out to obtain ion coordination / intercalation modified montmorillonite. Disperse maleic anhydride in toluene, add diisopropylbenzene peroxide and mix to obtain a grafting solution. Add the ion coordination / intercalation modified montmorillonite under an inert atmosphere to obtain reaction solution C. After reacting at a constant temperature, raise the temperature and react, and rotary evaporation is carried out to obtain nanosheet powder grafted with polar groups.

[0014] S3: Melt-blend and extrude metallocene polyethylene with maleic anhydride, diisopropylbenzene peroxide, and antioxidant to obtain preliminarily grafted metallocene polyethylene. Blend and extrude it with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate to obtain a modified polyethylene compatibilizer.

[0015] S4: Mix the polyethylene resin evenly with the nanosheet powder grafted with polar groups, the modified polyethylene compatibilizer, antioxidant, and lubricant, then put them into a twin-screw extruder to extrude and cast into sheets. Carry out unidirectional stretching, heat setting, and then cooling to obtain a unidirectionally stretched polyethylene composite film material.

[0016] As a preferred technical solution of the present invention, in step S1, the mass fraction of the montmorillonite dispersion is 5-10 wt.%, for example, it can be 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5% or 10.0%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] In some alternative embodiments, the power of the ultrasonic treatment of the montmorillonite dispersion is 200-300 W, for example, it can be 200 W, 210 W, 220 W, 230 W, 240 W, 250 W, 260 W, 270 W, 280 W, 290 W or 300 W, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0018] In some alternative embodiments, the time of the ultrasonic treatment of the montmorillonite dispersion is 30-60 min, for example, it can be 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min or 60 min, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0019] In some alternative embodiments, the mass ratio of 3-aminopropyltriethoxysilane to montmorillonite is 0.03 - 0.05:1. For example, it can be 0.030:1, 0.032:1, 0.034:1, 0.036:1, 0.038:1, 0.040:1, 0.042:1, 0.044:1, or 0.050:1. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0020] In some alternative embodiments, the temperature for the stirring reaction of reaction solution A is 70 - 80 °C. For example, it can be 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C, or 80 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0021] In some alternative embodiments, the time for the stirring reaction of reaction solution A is 2 - 3 h. For example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h, or 3.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0022] As a preferred technical solution of the present invention, in step S2, the mass fraction of the pretreated montmorillonite dispersion is 2 - 4 wt.%. For example, it can be 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, or 4.0%. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0023] In some alternative embodiments, the mass ratio of N,N-dimethyloctadecylammonium chloride to the pretreated montmorillonite is 0.02 - 0.05:1. For example, it can be 0.020:1, 0.022:1, 0.024:1, 0.026:1, 0.028:1, 0.030:1, 0.032:1, 0.034:1, 0.036:1, 0.038:1, 0.040:1, 0.042:1, 0.044:1, or 0.050:1. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0024] In some alternative embodiments, the mass ratio of the zinc oxide to the pretreated montmorillonite is 0.01-0.03:1. For example, it can be 0.010:1, 0.012:1, 0.014:1, 0.016:1, 0.018:1, 0.020:1, 0.022:1, 0.024:1, 0.026:1, 0.028:1 or 0.030:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0025] In some alternative embodiments, the temperature of the stirring reaction of the reaction solution B is 70-80°C. For example, it can be 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0026] In some alternative embodiments, the time of the stirring reaction of the reaction solution B is 1-2 h. For example, it can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0027] In some alternative embodiments, the concentration of maleic anhydride in toluene is 0.05-0.15 g / mL. For example, it can be 0.05 g / mL, 0.06 g / mL, 0.07 g / mL, 0.08 g / mL, 0.09 g / mL, 0.10 g / mL, 0.11 g / mL, 0.12 g / mL, 0.13 g / mL, 0.14 g / mL or 0.15 g / mL. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0028] In some alternative embodiments, the mass ratio of the maleic anhydride to the ion-coordinated / intercalated modified montmorillonite is 0.05-0.1:1. For example, it can be 0.050:1, 0.055:1, 0.060:1, 0.065:1, 0.070:1, 0.075:1, 0.080:1, 0.085:1, 0.090:1, 0.095:1 or 0.100:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0029] In some alternative embodiments, the mass ratio of dicumyl peroxide to ion coordination / intercalation modified montmorillonite is 0.02 - 0.04:1. For example, it can be 0.020:1, 0.022:1, 0.024:1, 0.026:1, 0.028:1, 0.030:1, 0.032:1, 0.034:1, 0.036:1, 0.038:1 or 0.040:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] In some alternative embodiments, the first temperature for the constant-temperature reaction of reaction solution C is 100 - 120 °C. For example, it can be 100 °C, 102 °C, 104 °C, 106 °C, 108 °C, 110 °C, 112 °C, 114 °C, 116 °C, 118 °C or 120 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0031] In some alternative embodiments, the first time for the constant-temperature reaction of reaction solution C is 1 - 2 h. For example, it can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0032] In some alternative embodiments, the second temperature for the constant-temperature reaction of reaction solution C is 140 - 150 °C. For example, it can be 140 °C, 141 °C, 142 °C, 143 °C, 144 °C, 145 °C, 146 °C, 147 °C, 148 °C, 149 °C or 150 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0033] In some alternative embodiments, the second time for the constant-temperature reaction of reaction solution C is 1 - 2 h. For example, it can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0034] As a preferred technical solution of the present invention, in step S3, the mass ratio of maleic anhydride to metallocene polyethylene is 2 - 5:100. For example, it can be 2.0:100, 2.3:100, 2.6:100, 2.9:100, 3.2:100, 3.5:100, 3.8:100, 4.1:100, 4.4:100, 4.7:100 or 5.0:100. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0035] In some alternative embodiments, the mass ratio of dicumyl peroxide to metallocene polyethylene is 0.2 - 0.4:100. For example, it can be 0.20:100, 0.22:100, 0.24:100, 0.26:100, 0.28:100, 0.30:100, 0.32:100, 0.34:100, 0.36:100, 0.38:100 or 0.40:100. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] In some alternative embodiments, the mass ratio of the antioxidant to metallocene polyethylene is 0.1 - 0.2:100. For example, it can be 0.10:100, 0.11:100, 0.12:100, 0.13:100, 0.14:100, 0.15:100, 0.16:100, 0.17:100, 0.18:100, 0.19:100 or 0.20:100. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] In some alternative embodiments, the temperature of the melt blending is 180 - 200 °C. For example, it can be 180 °C, 182 °C, 184 °C, 186 °C, 188 °C, 190 °C, 192 °C, 194 °C, 196 °C, 198 °C or 200 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] In some alternative embodiments, the time of the melt blending is 5 - 10 min. For example, it can be 5.0 min, 5.5 min, 6.0 min, 6.5 min, 7.0 min, 7.5 min, 8.0 min, 8.5 min, 9.0 min, 9.5 min or 10.0 min. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] In some alternative embodiments, the mass ratio of glycidyl methacrylate to the preliminarily grafted metallocene polyethylene is 1 - 3:100. For example, it can be 1.0:100, 1.2:100, 1.4:100, 1.6:100, 1.8:100, 2.0:100, 2.2:100, 2.4:100, 2.6:100, 2.8:100 or 3.0:100. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0040] In some alternative embodiments, the mass ratio of ethyl acrylate to the preliminarily grafted metallocene polyethylene is 1-3:100. For example, it can be 1.0:100, 1.2:100, 1.4:100, 1.6:100, 1.8:100, 2.0:100, 2.2:100, 2.4:100, 2.6:100, 2.8:100 or 3.0:100. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0041] In some alternative embodiments, the mass ratio of magnesium chloride to the preliminarily grafted metallocene polyethylene is 0.5-1:100. For example, it can be 0.50:100, 0.55:100, 0.60:100, 0.65:100, 0.70:100, 0.75:100, 0.80:100, 0.85:100, 0.90:100, 0.95:100 or 1.00:100. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] In some alternative embodiments, the mass ratio of tributyl phosphate to the preliminarily grafted metallocene polyethylene is 0.5-1:100. For example, it can be 0.50:100, 0.55:100, 0.60:100, 0.65:100, 0.70:100, 0.75:100, 0.80:100, 0.85:100, 0.90:100, 0.95:100 or 1.00:100. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0043] As a preferred technical solution of the present invention, in step S4, the temperature of the twin-screw extruder is 200-210°C. For example, it can be 200°C, 201°C, 202°C, 203°C, 204°C, 205°C, 206°C, 207°C, 208°C, 209°C or 210°C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] In some alternative embodiments, the temperature of the heat setting is 80-100°C. For example, it can be 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C or 100°C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0045] In some alternative embodiments, the time for heat setting is 20 - 40 s. For example, it can be 20 s, 22 s, 24 s, 26 s, 28 s, 30 s, 32 s, 34 s, 36 s, 38 s or 40 s. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0046] In a second aspect, the present invention provides a unidirectionally stretched polyethylene composite film material. The unidirectionally stretched polyethylene composite film material comprises a polyethylene resin, a nanosheet powder grafted with polar groups, a modified polyethylene compatibilizer, an antioxidant and a lubricant. The mass ratio of the polyethylene resin, the nanosheet powder grafted with polar groups, the modified polyethylene compatibilizer, the antioxidant and the lubricant in the unidirectionally stretched polyethylene composite film material is: (75 - 85):(5 - 10):(5 - 15):(0.2 - 0.3):(0.05 - 0.15).

[0047] In the present invention, montmorillonite is introduced as a nanosheet barrier. Its main function is to form a "labyrinth effect" in the matrix material through its layered structure and high barrier performance, extending the diffusion path of gas or liquid molecules, thereby significantly improving the barrier performance of the material. Montmorillonite is a layered silicate mineral, and its crystal structure is composed of alternating stacks of silicon - oxygen tetrahedral layers and aluminum - oxygen octahedral layers, forming a nanosheet structure with regular interlayer spacing. This structure endows montmorillonite with a high specific surface area, a high cation - exchange capacity and good chemical stability. There are usually weak van der Waals forces and electrostatic interactions between the layers of montmorillonite. The interlayer cations can be displaced by other cations in the external environment through ion exchange, providing a good basis for its functional modification.

[0048] In order to further improve the exfoliation degree and dispersibility of montmorillonite and enable it to better play the barrier performance in the composite material, the present invention performs ultrasonic treatment on montmorillonite. Ultrasonic treatment will trigger the cavitation effect, generating a large number of tiny bubbles in the liquid. These bubbles will produce an instantaneous local high - temperature and high - pressure environment during the formation and rupture process. This high - transient local pressure and temperature can break the van der Waals forces and electrostatic interactions between the layers of montmorillonite, promoting the exfoliation of the montmorillonite layered structure to form single - layer or multi - layer montmorillonite nanosheets. The exfoliated montmorillonite has a significantly increased specific surface area and more active sites, which can improve its interfacial interaction with the polymer matrix and provide active groups and reaction sites for subsequent chemical modification.

[0049] To further improve the compatibility and dispersion stability between montmorillonite and polymer matrix, 3-aminopropyltriethoxysilane is introduced in this invention to conduct surface modification on the exfoliated montmorillonite. 3-aminopropyltriethoxysilane is a typical silane coupling agent, and its molecular structure contains triethoxysilyl group and amino group. The triethoxysilyl group can undergo a condensation reaction with the surface of inorganic materials, while the amino group provides polar active sites for subsequent organic chemical modification. During the modification process, 3-aminopropyltriethoxysilane first undergoes a hydrolysis reaction to generate silanol, and the generated silanol then undergoes a condensation reaction with the hydroxyl groups on the surface of exfoliated montmorillonite, fixing 3-aminopropyltriethoxysilane on the surface of montmorillonite through covalent bonds.

[0050] This surface modification introduces amino functional groups, significantly improving the surface activity and polarity of montmorillonite. On the one hand, the amino functional groups can further enhance the interaction between montmorillonite and polymer matrix through hydrogen bonding or electrostatic interaction; on the other hand, the introduction of amino groups also provides active sites for subsequent organic chemical modification (such as intercalation or grafting modification).

[0051] In addition, through the modification of 3-aminopropyltriethoxysilane, the interlayer environment of montmorillonite changes from hydrophilic to partially hydrophobic. This change in surface properties improves the dispersion of montmorillonite in non-polar or weakly polar polymer matrices, effectively reducing the agglomeration phenomenon that may occur during the processing of composite materials. The modified montmorillonite not only has stronger interfacial adhesion ability but also can be more evenly dispersed in the polyethylene matrix, forming a stable nano-composite structure, thus greatly improving the barrier properties and mechanical properties of the material.

[0052] Montmorillonite, as a layered silicate mineral, has hydrophilicity and a small interlayer spacing in its interlayer. This property restricts its interfacial compatibility and dispersion with non-polar polymers to a certain extent. In a non-polar polymer matrix, unmodified montmorillonite is prone to agglomeration and difficult to disperse evenly, thus unable to fully exert its barrier properties and reinforcement effect of nano-sheets.

[0053] This invention introduces N,N-dimethyloctadecylammonium chloride to conduct intercalation modification on montmorillonite. N,N-dimethyloctadecylammonium chloride is a typical cationic surfactant, and its molecular structure contains an octadecyl long chain and a positively charged quaternary ammonium cation. During the intercalation modification process, its cationic part inserts into the interlayer of montmorillonite through electrostatic interaction and undergoes an ion exchange reaction with the cations in the interlayer.

[0054] Through ion exchange, quaternary ammonium cations replace the inorganic cations between the montmorillonite layers and are inserted into the interlayer space. Due to the hydrophobicity of the octadecyl long chain, this intercalation modification significantly changes the interlayer environment of montmorillonite. First, the intercalation modification significantly broadens the interlayer spacing of montmorillonite, making its layered structure looser, which provides a spatial basis for further intercalation and functionalization; second, the interlayer environment changes from hydrophilic to hydrophobic, greatly improving the compatibility and dispersibility of montmorillonite in the non-polar polyethylene matrix. In addition, more long-chain organic groups are exposed between the intercalated montmorillonite layers, and these groups can physically entangle or have weak interactions with the polyethylene matrix, thereby further enhancing the interfacial bonding force of the composite material.

[0055] Zinc oxide is an inorganic nanomaterial with excellent barrier properties, antibacterial properties, and ultraviolet shielding ability. Its introduction provides additional functionality for modified montmorillonite. In the present invention, by introducing zinc oxide into the montmorillonite interlayer, the functional modification of the interlayer space is further realized. Zinc oxide forms a stable montmorillonite-zinc oxide composite structure through the coordination of oxygen atoms on its surface with the negatively charged regions (partial negative charges from aluminum octahedra or silicon tetrahedra) between the montmorillonite layers. This coordination not only helps to stabilize the intercalation structure of montmorillonite but also endows the modified montmorillonite material with good barrier properties and antibacterial properties. In addition, zinc oxide may have weak interactions with the inserted organic long-chain cations, which further improves the modification effect of montmorillonite. Through the synergistic modification of zinc oxide, the interlayer structure of montmorillonite is more stable, and at the same time, its multifunctionality is significantly enhanced, providing support for the barrier properties and additional functions (such as antibacterial and ultraviolet shielding properties) of the final composite material.

[0056] Maleic anhydride is a highly active bifunctional compound with an anhydride ring in its molecular structure. Its chemical properties enable it to react with various active groups on the montmorillonite surface and the surface active sites of zinc oxide. The anhydride group in maleic anhydride can undergo an esterification reaction with the hydroxyl groups on the montmorillonite surface to form stable ester bonds. This chemical bonding improves the polarity and activity of the montmorillonite surface, providing a stronger chemical basis for its interfacial bonding with the polyethylene matrix. Maleic anhydride can also react with the active sites on the zinc oxide surface to form stable chemical bonds, further enhancing the stability of the modified montmorillonite composite structure.

[0057] At the same time, the anhydride ring of maleic anhydride undergoes a ring-opening reaction to generate carboxyl and hydroxyl groups. These polar groups can significantly improve the compatibility of montmorillonite with the non-polar polyethylene matrix. On the one hand, the carboxyl and hydroxyl groups can form hydrogen bonds or weak chemical bonds with the polar groups in the polyethylene matrix; on the other hand, these polar groups can also form a microscopic interfacial network structure in the polyethylene matrix, which helps to improve the mechanical properties and barrier properties of the composite material.

[0058] In the present invention, metallocene polyethylene is introduced as one of the matrix materials. Metallocene polyethylene is a high-performance polyethylene synthesized by metallocene catalysts. Its most significant feature lies in its narrow molecular weight distribution and regular molecular chain structure. Compared with polyethylene synthesized by traditional Ziegler-Natta catalysts, metallocene polyethylene has a higher crystallinity, and the arrangement of molecular chains is more orderly, thus showing excellent mechanical properties, thermal stability, and chemical inertness. In addition, metallocene polyethylene has superior processing properties and can meet the strict requirements for melt processing performance in film preparation. However, since metallocene polyethylene is a non-polar material and lacks polar groups in its molecular chains, its interfacial compatibility with polar nanomaterials is relatively poor. This characteristic results in weak interfacial forces between metallocene polyethylene and polar components, and polar nanomaterials are prone to agglomeration in the matrix and cannot be uniformly dispersed, thus limiting the overall performance of the composite material.

[0059] To overcome this problem, the present invention conducts functionalization treatment on metallocene polyethylene through chemical modification methods, aiming to introduce polar groups to improve its interfacial compatibility with polar components. Specifically, maleic anhydride is used to graft-modify metallocene polyethylene, introducing polar anhydride groups onto the molecular chains, thereby significantly improving its interfacial forces with polar nanomaterials.

[0060] Under high-temperature conditions, dicumyl peroxide decomposes to generate free radicals. These free radicals can extract hydrogen atoms from the molecular chains of metallocene polyethylene to generate polyethylene chain radicals. The formed polyethylene chain radicals have strong reactivity and are the core intermediates of the grafting reaction. Subsequently, the polyethylene chain radicals undergo free radical addition reactions with the double bonds in maleic anhydride molecules, grafting the anhydride groups onto the polyethylene molecular chains. The anhydride group is a highly polar functional group, and its molecular structure contains two carbonyl groups that can form strong interfacial bonds with other polar components (such as hydroxyl or amino groups in modified montmorillonite) through hydrogen bonding, coordination, or chemical bonding.

[0061] Through graft modification, metallocene polyethylene is partially transformed from a highly non-polar material into a modified material with polar functions. These grafted anhydride groups significantly increase the polarity of metallocene polyethylene, enabling it to form stronger interfacial forces with intercalated / ion-coordinated modified montmorillonite. At the same time, the grafting of maleic anhydride also improves the dispersion ability of the metallocene polyethylene matrix for montmorillonite, thus effectively avoiding the agglomeration of nanosheets, improving the uniformity and interfacial adhesion performance of the composite material, and also enhancing the barrier properties and mechanical properties of the material.

[0062] In order to further optimize the polarity and interfacial properties of metallocene polyethylene, glycidyl methacrylate is also introduced as a co-modifying agent in the present invention. Glycidyl methacrylate is a bifunctional compound that contains both an epoxy group and an acrylate group in its molecule. The epoxy group has high reactivity and can undergo ring-opening addition reactions with polar groups (such as anhydride groups, hydroxyl groups or amino groups), while the acrylate group can copolymerize with polyethylene chain radicals under free radical initiation. This enables glycidyl methacrylate to chemically interact with metallocene polyethylene and polar components through multiple reaction mechanisms.

[0063] Under the initiation of dicumyl peroxide, the acrylate group of glycidyl methacrylate can copolymerize with metallocene polyethylene chain radicals to graft glycidyl methacrylate onto the polyethylene molecular chain. The epoxy group in the grafted glycidyl methacrylate molecule can further undergo ring-opening reactions with the anhydride group or hydroxyl group in the grafted maleic anhydride to generate more polar groups. Through the introduction of glycidyl methacrylate, polar functional groups such as ester groups and hydroxyl groups are simultaneously introduced onto the metallocene polyethylene molecular chain. The hydroxyl group can form hydrogen bonds with the polar hydroxyl groups on the surface of montmorillonite, and the polar ester group can interact with the functional groups of montmorillonite or the surface active sites of zinc oxide. These polar groups further enhance the interfacial interaction between metallocene polyethylene and modified montmorillonite. In addition, the introduction of glycidyl methacrylate also improves the processing performance and toughness of the modified polyethylene by forming a flexible molecular chain structure, making it have better fluidity and ductility during the melt processing.

[0064] Through the synergistic graft modification of maleic anhydride and glycidyl methacrylate, metallocene polyethylene is transformed from a non-polar material into a modified material with polar functions. By introducing polar groups such as anhydride groups, hydroxyl groups and ester groups, the polarity of metallocene polyethylene is significantly improved, enabling it to form stronger interfacial binding forces with polar components such as modified montmorillonite and zinc oxide. Secondly, the polar groups can form stable chemical bonds through hydrogen bonds, chemical bonds or coordination interactions with the polar groups (such as hydroxyl groups, amino groups) in modified montmorillonite or the surface active sites of zinc oxide, thus significantly improving the interfacial adhesion performance of the composite material. The modified metallocene polyethylene can better disperse the montmorillonite platelets, avoiding the agglomeration of montmorillonite in the non-polar polyethylene matrix, and thus forming a uniformly distributed nanocomposite structure. The barrier properties, mechanical properties and processing properties of the composite material have all been significantly improved, meeting the requirements of high-performance packaging films for comprehensive properties.

[0065] Ethyl acrylate is a flexible monomer. Its molecular structure contains both an acrylate group and a flexible ethoxyalkyl chain. This structural feature endows ethyl acrylate with a certain polarity and enables it to endow the modified material with better flexibility and processing performance through its flexible chain segments. Through a free radical-initiated grafting reaction, ethyl acrylate is grafted onto the molecular chain of metallocene polyethylene. After grafting, a flexible ethoxyalkyl chain is introduced onto the polyethylene molecular chain, while the polar ester group is retained. The flexible ethoxyalkyl chain of ethyl acrylate imparts higher flexibility to the modified metallocene polyethylene, making the material exhibit better ductility and fluidity during processing. This flexible chain segment can play a "lubricating" role between the polyethylene molecular chains, significantly reducing the cohesive force of the material, thereby improving the melt processing performance.

[0066] Magnesium chloride, as a typical Lewis acid, is used in this invention to promote the grafting modification reaction. The characteristic of a Lewis acid is that it can accept an electron pair and interact with polar groups in the material system, thereby regulating the reaction behavior at the interface. During the grafting process, magnesium chloride can coordinate with the anhydride group in maleic anhydride, reducing the electron density of the anhydride group and thus increasing its reactivity with the polyethylene chain radical. This effect promotes the grafting efficiency of maleic anhydride, enabling more anhydride groups to be successfully introduced onto the metallocene polyethylene molecular chain. Secondly, magnesium chloride can also have a weak coordination effect with the epoxy group of glycidyl methacrylate, reducing the ring tension of the epoxy group and thus promoting the ring-opening reaction. After ring-opening, glycidyl methacrylate can further react with polar groups on the surface of maleic anhydride or montmorillonite to form a more stable interfacial bond.

[0067] The introduction of magnesium chloride not only improves the efficiency of the grafting reaction but also enhances the polarity of the metallocene polyethylene after grafting modification, improving its compatibility with montmorillonite. At the same time, magnesium chloride provides additional stability for the interfacial chemical bonding of the composite material by regulating the interfacial reaction behavior.

[0068] Tributyl phosphate is a commonly used plasticizer and dispersant. In the melt blending system, it can significantly reduce the viscosity of the material, thereby improving the processing performance. In the present invention, the introduction of tributyl phosphate has the following effects: Tributyl phosphate plays a lubricating role through its flexible molecular structure, reducing the cohesion between polyethylene molecular chains in the molten system. This effect can significantly reduce the viscosity during the melt blending process, thereby improving the fluidity and processing performance of the material; Secondly, due to the certain polarity of tributyl phosphate, it can have weak interactions with the polar groups of modified montmorillonite, thereby improving the dispersibility of montmorillonite in the polyethylene matrix. This effect can effectively prevent the aggregation of montmorillonite in the matrix and ensure the uniform distribution of nanosheets in the composite material; In addition, as a plasticizer, tributyl phosphate can play a "lubricating" role between polyethylene molecular chains, endowing the material with higher flexibility and ductility.

[0069] Through the above modification, montmorillonite is uniformly dispersed in the polyethylene matrix. The exfoliated montmorillonite is uniformly distributed in the matrix in the form of single or multiple nanosheets, and its layered structure forms a "labyrinth effect" in the composite material. When gas molecules attempt to pass through the film, the nanosheets of montmorillonite will significantly extend the diffusion path of gas molecules, thereby reducing the gas permeation rate and ultimately significantly improving the barrier performance of the composite material. At the same time, the interfacial binding force between the polar groups (such as anhydride groups, hydroxyl groups) in the modified polyethylene matrix and montmorillonite is enhanced, making the dispersion of montmorillonite in the matrix more uniform, thereby further improving the overall performance of the nanocomposite.

[0070] Unidirectional stretching is a key step in the formation of composite films and plays a role in optimizing the microstructure of the material in the present invention: During unidirectional stretching, the polyethylene molecular chains are highly oriented along the stretching direction. This directional arrangement of molecular chains not only improves the tensile strength of the film but also optimizes the mechanical properties of the material; The unidirectional stretching process also promotes the ordered arrangement of montmorillonite nanosheets in the film. The directional arrangement of montmorillonite sheets further enhances the "labyrinth effect", making the diffusion path of gas molecules more tortuous, thereby significantly improving the barrier performance of the film. The stretched film is subjected to heat setting treatment to fix the orientation structure of polyethylene molecular chains and montmorillonite sheets, avoiding a decrease in performance caused by the relaxation and retraction of molecular chains during the cooling process.

[0071] There is also a synergistic enhancement effect in the present invention. Maleic anhydride introduces polar anhydride groups onto the molecular chain of metallocene polyethylene through a grafting reaction. These anhydride groups not only significantly improve the polarity of polyethylene but also generate carboxyl and hydroxyl groups through ring-opening reactions, providing active sites for further interfacial reactions. The epoxy group in glycidyl methacrylate can undergo a ring-opening reaction with the anhydride group or carboxyl group of maleic anhydride, thereby introducing more polar groups onto the polyethylene molecular chain. The synergistic effect of maleic anhydride and glycidyl methacrylate increases the interfacial binding force between the modified polyethylene and montmorillonite or other polar components by constructing various polar groups on the polyethylene molecular chain. The flexible molecular structure of glycidyl methacrylate can also reduce the rigidity of the grafted polyethylene and alleviate the brittleness problem of the material caused by the introduction of rigid groups.

[0072] Ethyl acrylate introduces flexible ethoxyalkyl chains and polar ester groups onto the polyethylene molecular chain through a free radical grafting reaction. Grafting maleic anhydride provides anhydride groups and carboxyl groups, increasing the polarity of polyethylene. The flexible chain segment of ethyl acrylate alleviates the rigidity and processing difficulties of the polyethylene matrix caused by the introduction of polar groups after maleic anhydride grafting, thus balancing the flexibility and strength of the material. The simultaneous presence of ester groups and carboxyl groups provides more binding sites for the interfacial interaction between polyethylene and modified montmorillonite, enhancing the interfacial binding force.

[0073] After the intercalation modification of montmorillonite, the interlayer environment changes from hydrophilic to hydrophobic, and at the same time, the interlayer spacing increases, providing more space for the polar groups of the modified polyethylene to interact with it. The anhydride groups, hydroxyl groups, and ester groups introduced into the modified polyethylene through maleic anhydride, glycidyl methacrylate, and ethyl acrylate can form stable interfacial bindings with the polar groups (such as hydroxyl groups and amino groups) on the surface of the modified montmorillonite through hydrogen bonds, van der Waals forces, or chemical bonds. The intercalated structure of the modified montmorillonite and the polar groups of the modified polyethylene complement each other, ensuring the uniform dispersion of montmorillonite in the polyethylene matrix. This enhanced interfacial binding force significantly improves the mechanical properties, barrier properties, and thermal stability of the composite material.

[0074] The exfoliated montmorillonite is uniformly distributed in the polyethylene matrix in the form of single or multi-layer nanosheets, and its layered structure forms a "labyrinth effect" in the material, extending the diffusion path of gas molecules. The polar groups in the modified polyethylene further promote the uniform distribution of montmorillonite in the matrix through interfacial binding. The binding of the polar groups of the modified polyethylene to montmorillonite optimizes its dispersion and lamellar orientation, ensuring the maximization of the "labyrinth effect", thereby significantly improving the barrier properties of the film. The uniform dispersion of montmorillonite also enhances the mechanical properties of the composite material, making it exhibit higher strength and toughness.

[0075] In a third aspect, the present invention provides an application of a unidirectionally stretched polyethylene composite film material in the preparation of packaging materials.

[0076] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0077] The present invention optimizes the dispersion and interfacial compatibility of montmorillonite in the polyethylene matrix through multiple modification strategies, significantly improving the properties of the composite material. Ultrasonic exfoliation increases its specific surface area and active sites; modification with 3-aminopropyltriethoxysilane introduces amino functional groups, enhancing surface polarity and converting the interlayer environment from hydrophilic to hydrophobic; intercalation with N,N-dimethyloctadecylammonium chloride widens the layer spacing, enhancing physical entanglement and interfacial binding force with polyethylene; introduction of zinc oxide further stabilizes the intercalated structure and imparts antibacterial and ultraviolet shielding functions; maleic anhydride strengthens the interfacial binding force through chemical bonding. These synergistic effects enable the uniform dispersion of montmorillonite in the composite material, improving the barrier properties, mechanical properties, and functional characteristics.

[0078] The present invention functionalizes metallocene polyethylene through the synergistic grafting of maleic anhydride and glycidyl methacrylate, introducing polar groups, significantly improving its interfacial compatibility and dispersion with polar nanomaterials, and simultaneously improving flexibility and processing performance. Combining magnesium chloride to promote grafting efficiency and tributyl phosphate to improve dispersion and fluidity, the modified metallocene polyethylene achieves uniform distribution of nanosheets, significantly enhancing the barrier properties, mechanical properties, and processing performance of the composite material, meeting the application requirements of high-performance films. Description of the Drawings

[0079] Figure 1 It is a flow chart of the preparation method of the unidirectionally stretched polyethylene composite film material provided in Example 1 of the present invention. Detailed Embodiments

[0080] The technical solutions of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary, and should not be construed as a limitation on the embodiments of the present invention and the protection scope of the present invention. Except for the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of the present application, and these technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments recorded herein.

[0081] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products and have not been further purified or treated.

[0082] Example 1

[0083] This embodiment provides a unidirectionally stretched polyethylene composite film material and a preparation method thereof. The preparation method specifically includes the following steps:

[0084] S1: Ultrasonically treat the montmorillonite dispersion to obtain an exfoliated montmorillonite dispersion, and add 3-aminopropyltriethoxysilane to obtain pretreated montmorillonite.

[0085] Specifically, S1: Ultrasonically treat a montmorillonite dispersion with a mass fraction of 8 wt.% for 30 min at a power of 200 W to obtain an exfoliated montmorillonite dispersion. Add 3-aminopropyltriethoxysilane with a mass ratio of 0.04:1 to the montmorillonite to obtain reaction solution A. Stir and react at 78 °C for 2 h, then centrifuge, wash, and dry to obtain pretreated montmorillonite.

[0086] S2: React the pretreated montmorillonite with N,N-dimethyloctadecylammonium chloride and zinc oxide to obtain ion-coordinated / intercalated modified montmorillonite; react it with maleic anhydride and dicumyl peroxide in toluene to obtain nanosheet powder grafted with polar groups.

[0087] Specifically, S2: Add N,N-dimethyloctadecylammonium chloride with a mass ratio of 0.04:1 to the pretreated montmorillonite and zinc oxide with a mass ratio of 0.03:1 to the pretreated montmorillonite to a 2 wt.% pretreated montmorillonite dispersion to obtain reaction solution B. Stir and react at 70 °C for 1 h, then spray dry to obtain ion-coordinated / intercalated modified montmorillonite; Disperse maleic anhydride in toluene, where the concentration of maleic anhydride in toluene is 0.1 g / mL, and the mass ratio of maleic anhydride to ion-coordinated / intercalated modified montmorillonite is 0.08:1. Add dicumyl peroxide with a mass ratio of 0.03:1 to the ion-coordinated / intercalated modified montmorillonite and mix to obtain a grafting solution. Add the ion-coordinated / intercalated modified montmorillonite under an inert atmosphere to obtain reaction solution C. React at a constant temperature of 100 °C for 1 h, then raise the temperature to 145 °C and react for 1 h, and rotary evaporate to obtain nanosheet powder grafted with polar groups.

[0088] S3: Melt-blend metallocene polyethylene with maleic anhydride, dicumyl peroxide, and an antioxidant to obtain preliminarily grafted metallocene polyethylene; co-extrude it with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate to obtain a modified polyethylene compatibilizer.

[0089] Specifically, S3: Melting and blending metallocene polyethylene, maleic anhydride, dicumyl peroxide, and antioxidant 1010 at 180°C for 5 min, and then extruding to obtain preliminarily grafted metallocene polyethylene. The mass ratio of maleic anhydride to metallocene polyethylene is 3:100, the mass ratio of dicumyl peroxide to metallocene polyethylene is 0.35:100, and the mass ratio of antioxidant 1010 to metallocene polyethylene is 0.15:100. Blending and extruding it with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate to obtain a modified polyethylene compatibilizer. The mass ratio of glycidyl methacrylate to the preliminarily grafted metallocene polyethylene is 2:100, the mass ratio of ethyl acrylate to the preliminarily grafted metallocene polyethylene is 1.8:100, the mass ratio of magnesium chloride to the preliminarily grafted metallocene polyethylene is 0.8:100, and the mass ratio of tributyl phosphate to the preliminarily grafted metallocene polyethylene is 0.7:100;

[0090] S4: Melting and processing polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, and additives to obtain a unidirectionally stretched polyethylene composite film material.

[0091] Specifically, S4: Mixing polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, antioxidant 1010, and lubricant zinc stearate evenly, then feeding them into a twin-screw extruder to extrude and cast into a sheet at 200°C, subjecting it to unidirectional stretching, heat setting at 80°C for 20 s, and then cooling to obtain a unidirectionally stretched polyethylene composite film material. The mass ratio of polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, antioxidant 1010, and lubricant zinc stearate is 80:8:10:0.25:0.1.

[0092] Example 2

[0093] This example provides a unidirectionally stretched polyethylene composite film material and its preparation method. The preparation method specifically includes the following steps:

[0094] S1: Ultrasonically treating the montmorillonite dispersion to obtain a delaminated montmorillonite dispersion, and adding 3-aminopropyltriethoxysilane to obtain pretreated montmorillonite;

[0095] Specifically, S1: Ultrasonically treating a 5 wt.% montmorillonite dispersion at a power of 270 W for 50 min to obtain a delaminated montmorillonite dispersion, adding 3-aminopropyltriethoxysilane with a mass ratio to montmorillonite of 0.045:1 to obtain reaction solution A, stirring and reacting at 75°C for 2.5 h, then centrifuging, washing, and drying to obtain pretreated montmorillonite;

[0096] S2: React the pretreated montmorillonite with N,N-dimethyloctadecylammonium chloride and zinc oxide to obtain ion coordination / intercalation modified montmorillonite; react it with maleic anhydride and diisopropylbenzene peroxide in toluene to obtain a nanosheet powder grafted with polar groups;

[0097] Specifically, S2: Add N,N-dimethyloctadecylammonium chloride with a mass ratio of 0.02:1 to the pretreated montmorillonite and zinc oxide with a mass ratio of 0.02:1 to the pretreated montmorillonite to the pretreated montmorillonite dispersion with a mass fraction of 3 wt.% to obtain reaction solution B. Stir and react at 80 °C for 1.2 h and then spray dry to obtain ion coordination / intercalation modified montmorillonite; Disperse maleic anhydride in toluene, where the concentration of maleic anhydride in toluene is 0.05 g / mL, and the mass ratio of maleic anhydride to ion coordination / intercalation modified montmorillonite is 0.1:1. Add diisopropylbenzene peroxide with a mass ratio of 0.02:1 to the ion coordination / intercalation modified montmorillonite and mix to obtain a grafting solution. Add the ion coordination / intercalation modified montmorillonite under an inert atmosphere to obtain reaction solution C. React at a constant temperature of 110 °C for 1.5 h and then raise the temperature to 140 °C and react for 1.6 h. Rotary evaporate to obtain a nanosheet powder grafted with polar groups;

[0098] S3: Melt-blend metallocene polyethylene with maleic anhydride, diisopropylbenzene peroxide, and antioxidant to obtain preliminarily grafted metallocene polyethylene; co-extrude it with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate to obtain a modified polyethylene compatibilizer;

[0099] Specifically, S3: Melt-blend metallocene polyethylene with maleic anhydride, diisopropylbenzene peroxide, and antioxidant 1076 at 190 °C for 8 min and extrude to obtain preliminarily grafted metallocene polyethylene, where the mass ratio of maleic anhydride to metallocene polyethylene is 2:100, the mass ratio of diisopropylbenzene peroxide to metallocene polyethylene is 0.2:100, and the mass ratio of antioxidant 1076 to metallocene polyethylene is 0.17:100; Co-extrude it with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate to obtain a modified polyethylene compatibilizer, where the mass ratio of glycidyl methacrylate to preliminarily grafted metallocene polyethylene is 1:100, the mass ratio of ethyl acrylate to preliminarily grafted metallocene polyethylene is 3:100, the mass ratio of magnesium chloride to preliminarily grafted metallocene polyethylene is 1:100, and the mass ratio of tributyl phosphate to preliminarily grafted metallocene polyethylene is 0.6:100;

[0100] S4: Process the polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, and additives through melt processing to obtain a unidirectionally stretched polyethylene composite film material.

[0101] Specifically, S4: Mix the polyethylene resin with the nanosheet powder grafted with polar groups, the modified polyethylene compatibilizer, antioxidant 1076, and lubricant calcium stearate evenly, then put them into a twin-screw extruder and extrude and cast into sheets at 208 °C. Perform unidirectional stretching on it, heat-set at 90 °C for 30 s, and then cool to obtain the unidirectionally stretched polyethylene composite film material, where the mass ratio of the polyethylene resin, the nanosheet powder grafted with polar groups, the modified polyethylene compatibilizer, antioxidant 1076, and lubricant calcium stearate is 82:5:5:0.2:0.12.

[0102] Example 3

[0103] This example provides a unidirectionally stretched polyethylene composite film material and a preparation method thereof. The preparation method specifically includes the following steps:

[0104] S1: Ultrasonically treat the montmorillonite dispersion to obtain a delaminated montmorillonite dispersion, and add 3-aminopropyltriethoxysilane to obtain pretreated montmorillonite;

[0105] Specifically, S1: Ultrasonically treat the montmorillonite dispersion with a mass fraction of 7 wt.% at a power of 240 W for 40 min to obtain a delaminated montmorillonite dispersion. Add 3-aminopropyltriethoxysilane with a mass ratio of 0.03:1 to the montmorillonite to obtain reaction solution A. Stir and react at 70 °C for 2.7 h, then centrifuge, wash, and dry to obtain pretreated montmorillonite;

[0106] S2: React the pretreated montmorillonite with N,N-dimethyloctadecylammonium chloride and zinc oxide to obtain ion-coordinated / intercalated modified montmorillonite; React it with maleic anhydride and diisopropylbenzene peroxide in toluene to obtain the nanosheet powder grafted with polar groups;

[0107] Specifically, S2: Add N,N-dimethyloctadecylammonium chloride with a mass ratio of 0.03:1 to the pretreated montmorillonite and zinc oxide with a mass ratio of 0.01:1 to the pretreated montmorillonite in the pretreated montmorillonite dispersion with a mass fraction of 3.5 wt.% to obtain reaction solution B. Stir and react at 78 °C for 1.6 h, then spray dry to obtain ion-coordinated / intercalated modified montmorillonite; Disperse maleic anhydride in toluene, where the concentration of maleic anhydride in toluene is 0.12 g / mL, the mass ratio of maleic anhydride to ion-coordinated / intercalated modified montmorillonite is 0.05:1. Add diisopropylbenzene peroxide with a mass ratio of 0.035:1 to the ion-coordinated / intercalated modified montmorillonite and mix to obtain a grafting solution. Add the ion-coordinated / intercalated modified montmorillonite under an inert atmosphere to obtain reaction solution C. React at a constant temperature of 115 °C for 1.8 h, then raise the temperature to 147 °C and react for 1.4 h, and rotary evaporate to obtain the nanosheet powder grafted with polar groups;

[0108] S3: Melting and blending metallocene polyethylene with maleic anhydride, diisopropylbenzene peroxide, and antioxidant to obtain preliminarily grafted metallocene polyethylene; blending and extruding it with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate to obtain a modified polyethylene compatibilizer;

[0109] Specifically, S3: Melting and blending metallocene polyethylene with maleic anhydride, diisopropylbenzene peroxide, and antioxidant 1010 at 195 °C for 7 min and extruding to obtain preliminarily grafted metallocene polyethylene, where the mass ratio of maleic anhydride to metallocene polyethylene is 4:100, the mass ratio of diisopropylbenzene peroxide to metallocene polyethylene is 0.38:100, and the mass ratio of antioxidant 1010 to metallocene polyethylene is 0.1:100; blending and extruding it with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate to obtain a modified polyethylene compatibilizer, where the mass ratio of glycidyl methacrylate to preliminarily grafted metallocene polyethylene is 2.5:100, the mass ratio of ethyl acrylate to preliminarily grafted metallocene polyethylene is 2:100, the mass ratio of magnesium chloride to preliminarily grafted metallocene polyethylene is 0.5:100, and the mass ratio of tributyl phosphate to preliminarily grafted metallocene polyethylene is 1:100;

[0110] S4: Melting, processing, and treating polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, and additives to obtain a unidirectionally stretched polyethylene composite film material.

[0111] Specifically, S4: Mixing polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, antioxidant 1010, and lubricant calcium stearate evenly, then feeding them into a twin-screw extruder to extrude and cast into a sheet at 204 °C, subjecting it to unidirectional stretching, heat setting at 95 °C for 35 s, and then cooling to obtain a unidirectionally stretched polyethylene composite film material, where the mass ratio of polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, antioxidant 1010, and lubricant calcium stearate is 75:7:12:0.28:0.05.

[0112] Example 4

[0113] This example provides a unidirectionally stretched polyethylene composite film material and its preparation method. The preparation method specifically includes the following steps:

[0114] S1: Ultrasonically treating the montmorillonite dispersion to obtain a delaminated montmorillonite dispersion, and adding 3-aminopropyltriethoxysilane to obtain pretreated montmorillonite;

[0115] Specifically, S1: The montmorillonite dispersion with a mass fraction of 10 wt.% is ultrasonically treated at a power of 300 W for 60 min to obtain a delaminated montmorillonite dispersion. 3-aminopropyltriethoxysilane with a mass ratio of 0.05:1 to montmorillonite is added to obtain reaction solution A. After stirring and reacting at 80 °C for 3 h, it is centrifuged, washed, and dried to obtain pretreated montmorillonite;

[0116] S2: The pretreated montmorillonite reacts with N,N-dimethyloctadecylammonium chloride and zinc oxide to obtain ion-coordination / intercalation modified montmorillonite; it reacts with maleic anhydride and diisopropylbenzene peroxide in toluene to obtain nanosheet powder grafted with polar groups;

[0117] Specifically, S2: N,N-dimethyloctadecylammonium chloride with a mass ratio of 0.05:1 to the pretreated montmorillonite and zinc oxide with a mass ratio of 0.023:1 to the pretreated montmorillonite are added to a 4 wt.% pretreated montmorillonite dispersion to obtain reaction solution B. After stirring and reacting at 75 °C for 2 h, it is spray-dried to obtain ion-coordination / intercalation modified montmorillonite; maleic anhydride is dispersed in toluene, where the concentration of maleic anhydride in toluene is 0.15 g / mL, and the mass ratio of maleic anhydride to ion-coordination / intercalation modified montmorillonite is 0.07:1. Diisopropylbenzene peroxide with a mass ratio of 0.04:1 to ion-coordination / intercalation modified montmorillonite is added and mixed to obtain a grafting solution. The ion-coordination / intercalation modified montmorillonite is added under an inert atmosphere to obtain reaction solution C. After reacting at a constant temperature of 120 °C for 2 h, the temperature is raised to 150 °C and reacted for 2 h, and rotary evaporation is performed to obtain nanosheet powder grafted with polar groups;

[0118] S3: Metallocene polyethylene is melt-blended with maleic anhydride, diisopropylbenzene peroxide, and an antioxidant to obtain preliminarily grafted metallocene polyethylene; it is melt-extruded with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate to obtain a modified polyethylene compatibilizer;

[0119] Specifically, in S3: melt blend metallocene polyethylene, maleic anhydride, dicumyl peroxide, and antioxidant 1076 at 200°C for 10 min and extrude to obtain preliminarily grafted metallocene polyethylene, where the mass ratio of maleic anhydride to metallocene polyethylene is 5:100, the mass ratio of dicumyl peroxide to metallocene polyethylene is 0.4:100, and the mass ratio of antioxidant 1076 to metallocene polyethylene is 0.2:100; blend it with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate and extrude to obtain a modified polyethylene compatibilizer, where the mass ratio of glycidyl methacrylate to the preliminarily grafted metallocene polyethylene is 3:100, the mass ratio of ethyl acrylate to the preliminarily grafted metallocene polyethylene is 2.5:100, the mass ratio of magnesium chloride to the preliminarily grafted metallocene polyethylene is 0.7:100, and the mass ratio of tributyl phosphate to the preliminarily grafted metallocene polyethylene is 0.5:100;

[0120] S4: subject polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, and additives to melt processing to obtain a unidirectionally stretched polyethylene composite film material.

[0121] Specifically, in S4: mix polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, and antioxidant 1076 and zinc stearate lubricant evenly, then feed them into a twin-screw extruder and extrude and cast into sheets at 210°C, subject the sheets to unidirectional stretching, heat set them at 100°C for 40 s, and then cool to obtain a unidirectionally stretched polyethylene composite film material, where the mass ratio of polyethylene resin, nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, antioxidant 1076, and zinc stearate lubricant is 85:10:15:0.3:0.15.

[0122] Comparative Example 1

[0123] This comparative example provides a unidirectionally stretched polyethylene composite film material. The difference from Example 1 is that in S2, the mass ratio of N,N-dimethyloctadecylammonium chloride to pretreated montmorillonite is 0.1:1, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0124] Comparative Example 2

[0125] This comparative example provides a unidirectionally stretched polyethylene composite film material. The difference from Example 1 is that in S2, the mass ratio of N,N-dimethyloctadecylammonium chloride to pretreated montmorillonite is 0.01:1, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0126] Comparative Example 3

[0127] This comparative example provides a unidirectionally stretched polyethylene composite film material. The difference from Example 1 is that in S2, the mass ratio of maleic anhydride to ion-coordinated / intercalated modified montmorillonite is 0.2:1, and other operation steps and process parameters are exactly the same as those in Example 1.

[0128] Comparative Example 4

[0129] This comparative example provides a unidirectionally stretched polyethylene composite film material. The difference from Example 1 is that in S2, the mass ratio of maleic anhydride to ion-coordinated / intercalated modified montmorillonite is 0.01:1, and other operation steps and process parameters are exactly the same as those in Example 1.

[0130] Comparative Example 5

[0131] This comparative example provides a unidirectionally stretched polyethylene composite film material. The difference from Example 1 is that in S4, the mass ratio of polyethylene resin to nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, antioxidant 1010, and lubricant zinc stearate is 80:8:20:0.25:0.1, and other operation steps and process parameters are exactly the same as those in Example 1.

[0132] Comparative Example 6

[0133] This comparative example provides a unidirectionally stretched polyethylene composite film material. The difference from Example 1 is that in S4, the mass ratio of polyethylene resin to nanosheet powder grafted with polar groups, modified polyethylene compatibilizer, antioxidant 1010, and lubricant zinc stearate is 80:8:2:0.25:0.1, and other operation steps and process parameters are exactly the same as those in Example 1.

[0134] Perform performance tests on the unidirectionally stretched polyethylene composite film materials of the above Examples 1-4 and Comparative Examples 1-6. The specific process is as follows:

[0135] Test the water vapor transmission rate of the samples according to GB / T1037-2021;

[0136] Test the oxygen transmission rate of the samples according to GB / T1038.1-2022;

[0137] Use a universal tensile testing machine to test the tensile strength of the samples;

[0138] The test results are shown in Table 1.

[0139] Table 1: Performance test results of unidirectionally stretched polyethylene composite film materials of Examples 1-4 and Comparative Examples 1-6

[0140]

[0141] From the test results of Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that when the mass ratio of N,N-dimethyloctadecylammonium chloride to pretreated montmorillonite is too high, the excessive organic modifier accumulates in the interlayer to form a continuous phase, destroying the layered structure of montmorillonite and causing the water vapor transmission rate to increase to 3.42 ; at the same time, due to the unstable interlayer structure and the increase in gas diffusion channels, the oxygen transmission rate increases to 2.84 , and the tensile strength of the material also decreases to 38.6 MPa; while when the mass ratio is too low, the modification effect is insufficient, resulting in poor dispersion of montmorillonite and the formation of agglomerated regions. Although the water vapor transmission rate is 2.68 , due to the increase in interface defects, the oxygen transmission rate rises to 2.23 , and the tensile strength also decreases to 42.3 MPa;

[0142] From the test results of Example 1, Comparative Example 3, and Comparative Example 4, it can be seen that when the mass ratio of maleic anhydride to ion coordination / intercalation modified montmorillonite is too high, the excessive maleic anhydride undergoes a self-crosslinking reaction and accumulates at the interface, causing the water vapor transmission rate to increase to 3.15 ; at the same time, due to the damage of the interlayer structure, the oxygen transmission rate increases to 2.45 , and excessive crosslinking leads to embrittlement of the material, and the tensile strength decreases to 35.8 MPa; while when the mass ratio is too low, the grafting degree is insufficient, affecting the interfacial compatibility. Although the water vapor transmission rate is 2.48 , insufficient interfacial bonding causes the oxygen transmission rate to rise to 2.12 , and the tensile strength also decreases to 41.5 MPa;

[0143] From the test results of Example 1, Comparative Example 5, and Comparative Example 6, it can be seen that when the addition amount of the modified polyethylene compatibilizer is too high, the excessive compatibilizer reduces the matrix crystallinity, resulting in the water vapor transmission rate increasing to 3.25 ; at the same time, due to the increase in amorphous regions, the oxygen transmission rate increases to 2.38 , and the tensile strength of the material also decreases to 39.2 MPa; while when the addition amount is too low, insufficient compatibility leads to uneven dispersion. Although the water vapor transmission rate is 2.85 , insufficient interfacial bonding causes the oxygen transmission rate to rise to 2.32 , and the tensile strength also decreases to 36.8 MPa.

[0144] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a unidirectionally stretched polyethylene composite film material, characterized in that The preparation method includes: S1: Ultrasonically treat the montmorillonite dispersion to obtain an exfoliated montmorillonite dispersion, and add 3-aminopropyltriethoxysilane to obtain pretreated montmorillonite; S2: React the pretreated montmorillonite with N,N-dimethyloctadecylammonium chloride and zinc oxide to obtain ion-coordinated / intercalated modified montmorillonite; React it with maleic anhydride and diisopropylbenzene peroxide in toluene to obtain a nanosheet powder grafted with polar groups; S3: Melt-blend metallocene polyethylene with maleic anhydride, diisopropylbenzene peroxide, and an antioxidant to obtain preliminarily grafted metallocene polyethylene; Co-extrude it with glycidyl methacrylate, ethyl acrylate, magnesium chloride, and tributyl phosphate to obtain a modified polyethylene compatibilizer; S4: Subject the polyethylene resin, the nanosheet powder grafted with polar groups, the modified polyethylene compatibilizer, and the additives to melt processing to obtain a unidirectionally stretched polyethylene composite film material; The mass ratio of the N,N-dimethyloctadecylammonium chloride to the pretreated montmorillonite is 0.02-0.05:1; The mass ratio of the maleic anhydride to the ion-coordinated / intercalated modified montmorillonite is 0.05-0.1:1; In the unidirectionally stretched polyethylene composite film material, the mass ratio of the polyethylene resin, the nanosheet powder grafted with polar groups, the modified polyethylene compatibilizer, the antioxidant, and the lubricant is: (75-85):(5-10):(5-15):(0.2-0.3):(0.05-0.15).

2. The preparation method of a unidirectionally stretched polyethylene composite film material according to claim 1, characterized in that, In S1: The mass ratio of the 3-aminopropyltriethoxysilane to the montmorillonite is 0.03-0.05:

1.

3. The preparation method of a unidirectionally stretched polyethylene composite film material according to claim 1, characterized in that, In S2: The mass ratio of the zinc oxide to the pretreated montmorillonite is 0.01-0.03:

1.

4. The preparation method of a unidirectionally stretched polyethylene composite film material according to claim 1, characterized in that, In S2: The mass ratio of the diisopropylbenzene peroxide to the ion-coordinated / intercalated modified montmorillonite is 0.02-0.04:

1.

5. The preparation method of a unidirectionally stretched polyethylene composite film material according to claim 1, characterized in that, In S3: The mass ratio of the maleic anhydride to the metallocene polyethylene is 2-5:100; The mass ratio of the diisopropylbenzene peroxide to the metallocene polyethylene is 0.2-0.4:

100.

6. The preparation method of a unidirectionally stretched polyethylene composite film material according to claim 1, characterized in that, In S3: The antioxidant is antioxidant 1010 or antioxidant 1076; The mass ratio of the antioxidant to the metallocene polyethylene is 0.1-0.2:

100.

7. The preparation method of a unidirectionally stretched polyethylene composite film material according to claim 1, characterized in that, In S3: The mass ratio of the glycidyl methacrylate to the preliminarily grafted metallocene polyethylene is 1-3:100; The mass ratio of the ethyl acrylate to the preliminarily grafted metallocene polyethylene is 1-3:100; The mass ratio of the magnesium chloride to the preliminarily grafted metallocene polyethylene is 0.5-1:100; The mass ratio of the tributyl phosphate to the preliminarily grafted metallocene polyethylene is 0.5-1:

100.

8. The preparation method of a unidirectionally stretched polyethylene composite film material according to claim 1, characterized in that, In S4: The additive is an antioxidant and a lubricant; The lubricant is zinc stearate or calcium stearate.

9. A unidirectionally stretched polyethylene composite film material prepared by using the preparation method according to any one of claims 1-8.

10. Application of a unidirectionally stretched polyethylene composite film material prepared by using the preparation method according to any one of claims 1-8 in the preparation of packaging materials.

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