A polyethylene composite material and a preparation method thereof

Abstract

The present invention belongs to the technical field of polymer materials, and particularly relates to a polyethylene composite material and a preparation method thereof. The composition of the polyethylene composite material comprises the following components in parts by weight: 60-70 parts of high-density polyethylene, 0.6-1 part of maleic anhydride, 6-10 parts of polyolefin elastomer, 3-5 parts of polypropylene microfiber, 4-6 parts of modified glass fiber, 2-3 parts of silane-modified montmorillonite, 1-2 parts of nano-silica, 0.6-1 part of zinc stearate, 0.5-1 part of polyethylene wax, 0.2-0.3 part of primary antioxidant and 0.2-0.3 part of secondary antioxidant. The present invention makes full use of recycled high-density polyethylene recovered from laundry detergent bottles as the base material, and through a multi-stage exhaust extrusion process, after effectively removing volatile substances, various components such as maleic anhydride, silane-modified montmorillonite, nano-silica, and polyolefin elastomer are added successively, and the strength, toughness and barrier properties of the material are improved through synergistic effects.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a polyethylene composite material and a preparation method thereof. Background Art

[0002] With the rapid development of the global economy and the continuous improvement of people's living standards, the usage of plastic products has increased explosively. High-density polyethylene (HDPE), as a widely used plastic material, plays an important role in many fields such as packaging, construction, agriculture, and automobiles. However, the traditional plastic treatment methods are mainly landfill and incineration. Landfilling will occupy a large amount of land resources, and plastics are difficult to degrade naturally. Long-term existence in the soil will affect the air permeability and fertility of the soil, causing damage to the ecological environment. Incineration can reduce the volume of plastic waste, but it will produce a large amount of harmful gases, posing a threat to the atmospheric environment and human health. As a thermoplastic polyethylene material with a relatively high crystallinity, HDPE has excellent chemical corrosion resistance, environmental stress cracking resistance, and good mechanical properties, such as high strength and good toughness. HDPE is often used in packaging films, containers, pipes, films, and injection-molded products (such as bottle caps, household sundries, toys, etc.), and is also widely used in fields such as automobiles, household appliances, agricultural pipes, and cable protective layers. Due to its large production and demand, a considerable number of waste plastic products are generated after the end of the usage cycle. If these waste plastics lack effective recycling means, they are likely to have an adverse impact on the ecological environment and also cause waste of resources. Recycling waste HDPE can significantly reduce the harm to the environment, reduce environmental pollution caused by landfilling and incineration, and at the same time effectively save petroleum resources. Through recycling and reuse, the demand for virgin plastics can be reduced, production costs can be saved, and economic benefits can be brought to the relevant industrial chains. By compounding and modifying with other polymers, inorganic fillers, toughening agents, and other materials, the mechanical properties, impact resistance, and thermal stability of recycled HDPE can be enhanced, effectively compensating for the deficiencies in the performance of recycled materials, and thus improving their comprehensive application value. In summary, based on the above problems, it is extremely necessary to study a high-strength and high-toughness polyethylene composite material based on recycled high-density polyethylene. Summary of the Invention

[0003] Aiming at the defects of the prior art, the purpose of the present invention is to provide a polyethylene composite material and a preparation method thereof.

[0004] The technical effects of the present invention are achieved through the following technical solutions: A polyethylene composite material, the composition of which comprises the following components in parts by weight: 60 to 70 parts of high-density polyethylene, 0.6 to 1 part of maleic anhydride, 6 to 10 parts of polyolefin elastomer, 3 to 5 parts of polypropylene microfiber, 4 to 6 parts of modified glass fiber, 2 to 3 parts of silane-modified montmorillonite, 1 to 2 parts of nano-silica, 0.6 to 1 part of zinc stearate, 0.5 to 1 part of polyethylene wax, 0.2 to 0.3 part of a primary antioxidant, and 0.2 to 0.3 part of a secondary antioxidant.

[0005] Preferably, the high-density polyethylene is prepared by washing, air-drying, pulverizing, and drying recycled laundry detergent bottles.

[0006] Preferably, the primary antioxidant is any one of dibutylhydroxytoluene, 2,4-ditert-butylphenol, and 2,6-ditert-butyl-p-cresol.

[0007] Preferably, the secondary antioxidant is any one of dilauryl thiodipropionate, tris(nonylphenyl) phosphite, and diphenyl phosphite.

[0008] Preferably, the specific preparation steps of the silane-modified montmorillonite are as follows:

[0009] A1: Add montmorillonite to deionized water, and disperse it evenly by ultrasonic treatment to obtain a montmorillonite dispersion; add cetyltrimethylammonium bromide to deionized water, stir and mix evenly to obtain a 1-2 wt% surfactant solution; add γ-aminopropyltriethoxysilane to a 90 wt% ethanol solution, stir and mix evenly, adjust the pH to 4-5 with a 0.1 M hydrochloric acid solution, and hydrolyze at room temperature for 30 min to obtain a 4 wt% silanol solution;

[0010] A2: Slowly add the surfactant solution prepared in step A1 to the montmorillonite dispersion, control the temperature at 60-70 °C, stir and react for 4-6 h, wash with deionized water, and dry at 60 °C for 12-24 h to obtain organophilic montmorillonite; add the organophilic montmorillonite to the silanol solution prepared in step A1, stir and react at 50-60 °C for 2-4 h, wash with deionized water, and vacuum dry at 80 °C for 12 h to obtain silane-modified montmorillonite;

[0011] Preferably, in step A1, the dosage ratio of the montmorillonite to the deionized water is 1 g: 15-20 mL;

[0012] Preferably, in step A2, the volume dosage ratio of the surfactant solution to the montmorillonite dispersion is 1-1.5: 1; the dosage ratio of the organophilic montmorillonite to the silanol solution is 1 g: 6-8 mL.

[0013] Preferably, the specific preparation steps of the modified glass fiber are as follows:

[0014] B1: Immerse the glass fiber completely in deionized water, perform ultrasonic treatment at 100 W for 15 min, filter, and dry at 60 °C for 6 h to obtain pretreated glass fiber; add the pretreated glass fiber to concentrated nitric acid, stir and react at room temperature for 2 - 4 h. After the reaction is completed, wash with deionized water until neutral to obtain neutral glass fiber;

[0015] B2: Add the neutral glass fiber prepared in step B1 to a 70 wt% ethanol solution, soak for 30 min, then repeat washing with deionized water 3 times, and dry in vacuum at 80 °C for 12 - 24 h to obtain modified glass fiber;

[0016] Preferably, in step B1, the dosage ratio of the pretreated glass fiber to concentrated nitric acid is 1 g:5 - 6 mL;

[0017] Preferably, in step B2, the dosage ratio of the neutral glass fiber to the ethanol solution is 1 g:5 - 10 mL.

[0018] Preferably, on the other hand, the present invention provides a method for preparing a polyethylene composite material, and the specific preparation steps are as follows:

[0019] S1: Wash high - density polyethylene with deionized water and dry in vacuum at 80 °C for 12 h to obtain pretreated high - density polyethylene; stir and mix the pretreated high - density polyethylene, polyolefin elastomer, zinc stearate, polyethylene wax, primary antioxidant and auxiliary antioxidant evenly to obtain a pretreated mixture; ultrasonically treat and pre - disperse silane - modified montmorillonite, nano - silica and modified glass fiber into deionized water respectively; extrude polypropylene at 200 °C and perform stretching simultaneously to form polypropylene microfibers with a diameter of 2 - 3 mm;

[0020] S2: Add the pretreated mixture prepared in step S1 to an extruder, melt - blend at 190 - 200 °C, control the rotation speed at 60 rpm, and the mixing time at 3 - 5 min. Then slowly add maleic anhydride, raise the temperature to 200 - 210 °C, and react for 5 - 10 min;

[0021] S3: After completing the operation in step S2, sequentially add the silane - modified montmorillonite, nano - silica and modified glass fiber ultrasonically dispersed in step S1, raise the extrusion temperature to 220 °C, raise the rotation speed to 80 rpm, and the mixing time to 8 - 10 min;

[0022] S4: After completing the operation in step S3, slowly add the polypropylene microfibers prepared in step S1, reduce the rotation speed to 50 - 70 rpm, reduce the temperature to 200 °C at a rate of 5 °C / min, and the dispersion time is 5 - 6 min. After the dispersion is completed, reduce the temperature to 190 °C at a rate of 2 °C / min, extrude, and then cool the extrudate to room temperature to obtain a polyethylene composite material;

[0023] Preferably, in step S1, the stretching parameter of the polypropylene is a stretching ratio of 15 to 20;

[0024] Preferably, in step S2, after the maleic anhydride grafting reaction is completed, the first exhaust is carried out, the exhaust pressure is -0.08 MPa, and the time is 5 to 8 min;

[0025] Preferably, in step S4, after the polypropylene microfibers are added and mixed, the second exhaust is carried out, the exhaust pressure is -0.08 MPa, and the time is 5 to 8 min;

[0026] Preferably, in step S4, the extrusion cooling step is to first cool with 40°C water for 2 to 3 min, and then naturally cool to room temperature.

[0027] The beneficial effects of the present invention are as follows:

[0028] The present invention makes full use of recycled high-density polyethylene (HDPE) recovered from laundry detergent bottles as the base material. After effectively removing volatile substances through a multi-stage exhaust extrusion process, maleic anhydride (MAH), silane-modified montmorillonite, nano-silica (SiO 2 )), polyolefin elastomer (POE) and other components are added successively in a staged manner. Through the synergistic effect, the strength, toughness and barrier properties of the material are improved; at the same time, the high-value utilization of recycled high-density polyethylene is further realized by utilizing the orientation and fibrillation mechanism of polypropylene (PP) microfibers in secondary processing.

[0029] The present invention acidifies glass fiber (GF), and by introducing hydroxyl polar groups, improves its compatibility and interfacial bonding force with the HDPE matrix. During the high-temperature extrusion process, maleic anhydride is added in stages. First, maleic anhydride reacts with the polyolefin segments in the HDPE matrix to form polyolefin chains with polar groups, improving the compatibility between HDPE and inorganic fillers. Inorganic fillers such as surface-treated modified montmorillonite and nano-silica can be more uniformly dispersed in the HDPE matrix, establishing a relatively stable interfacial bond. When the modified montmorillonite and nano-silica are well dispersed inside the matrix, a multi-level nanostructure can be constructed, slowing down the crack initiation and propagation, and enhancing the barrier performance. In addition, the surface of the glass fiber after nitric acid acidification is rich in hydroxyl groups (-OH), while the maleic anhydride-modified HDPE matrix introduces polar groups such as carboxylic acid groups (-COOH) through grafting reactions; through the hydrogen bond interaction between hydroxyl-carboxylic acid groups and the interaction between polar molecules, the compatibility between the glass fiber and the HDPE matrix is significantly improved, thereby enhancing the interfacial bonding force and the chimeric effect, and promoting the formation of a stable multi-strengthening network in the composite material. At this time, the uniformly dispersed modified montmorillonite provides a "lamellar" barrier in the matrix and cooperates with nano-silica to shape a multi-level nanostructure, significantly inhibiting crack propagation and improving the mechanical and barrier properties of the material.

[0030] In the preparation and processing of the present invention, polyethylene wax (PE wax) and zinc stearate (ZnSt) are used as organic lubricants to maintain good thermal stability and lubrication effect at relatively high processing temperatures. On the one hand, it reduces the viscosity of the polymer melt and the friction on the wall of the extruder, ensuring a smooth extrusion process; on the other hand, it helps the inorganic nanoparticles to be fully dispersed in the high-viscosity melt and avoid agglomeration. During secondary processing, polypropylene (PP) microfibers are used. Taking advantage of the fact that it belongs to the same olefin system as HDPE and has a relatively close processing temperature, by reasonably controlling the extrusion and subsequent stretching temperatures, the polypropylene can form highly oriented microfibers and be distributed in the high-density polyethylene matrix. The polypropylene microfibers not only significantly improve the tensile strength and rigidity of the material, but also block or interfere with the crack path during the crack propagation process, enhancing the fracture toughness and impact strength of the material. During the extrusion molding process, the high-density polyethylene matrix will melt again, while the polypropylene microfibers can maintain the fibrous state due to their appropriate melting point and partial crystalline structure; through temperature gradient control, premature softening of the polypropylene is avoided, and finally a stable fiber network is formed after cooling. Glass fibers provide higher overall stiffness and strength for the material, while polypropylene microfibers play an important role in enhancing toughness. The combination of the two achieves a balance between high stiffness and high toughness. The glass fibers and modified montmorillonite after nitric acid acidification treatment both contain enhanced polar groups, and their interfacial bonding degree with the polymer matrix can be greatly improved through the interaction of hydroxyl groups with the polyolefin matrix. At the same time, maleic anhydride introduces carboxylic acid groups into the HDPE chain segment through a melt grafting reaction. Its polar part not only forms physical interlocking with the non-polar HDPE main chain through intermolecular entanglement, but also generates chemical bonding with the polar groups of reinforcing phases such as glass fibers and montmorillonite, thus constructing a synergistic strengthening network at the multiphase interface and improving the overall structural stability of the composite material. In terms of improving toughness, polyolefin elastomers belong to the same olefin system as high-density polyethylene and have good compatibility at the molecular level, easily forming a relatively continuous elastic phase, which can absorb impact energy and relieve stress concentration. When the polypropylene microfibers and glass fibers jointly enhance the stiffness of the material, the elastic phase of the polyolefin elastomer can effectively offset the embrittlement or notch problem and combine with the crack interference effect of the microfibers / glass fibers to further improve the toughness of the material. The hierarchical synergistic structure between modified montmorillonite, nano-silica and other nanoparticles and the elastic phase of the polyolefin elastomer inhibits the ductile-brittle transition through the functions of barrier and local stress dispersion, effectively improving the toughness of the composite material. Brief Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only those of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 It is a test result diagram of the impact strength measurement and absorbed work of the polyethylene composites prepared in Example 2 and Comparative Examples 1-5 of the present invention;

[0033] Figure 2 It is a test result diagram of the anti-aging performance of the polyethylene composites prepared in Example 2 and Comparative Examples 1-5 of the present invention. Detailed implementation manners

[0034] Next, the technical solutions of the present invention will be clearly and completely described 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 the embodiments; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. It should be noted that unless otherwise specified, the raw materials involved in the present invention are purchased through conventional commercial channels.

[0035] Example 1: A polyethylene composite material, the composition of which includes the following components in parts by weight: 60 parts of high-density polyethylene, 0.6 part of maleic anhydride, 6 parts of polyolefin elastomer, 3 parts of polypropylene microfibers, 4 parts of modified glass fibers, 2 parts of silane-modified montmorillonite, 1 part of nano-silica, 0.6 part of zinc stearate, 0.5 part of polyethylene wax, 0.2 part of a primary antioxidant, and 0.2 part of a secondary antioxidant.

[0036] The high-density polyethylene is obtained by washing, drying, pulverizing, and drying recycled laundry detergent bottles;

[0037] The specific preparation steps of the silane-modified montmorillonite are as follows:

[0038] A1: Add 10 g of montmorillonite to 150 mL of deionized water, and ultrasonically disperse it evenly to obtain a montmorillonite dispersion; add 2 g of cetyltrimethylammonium bromide to 200 mL of deionized water, stir and mix evenly to obtain a 1 wt% surfactant solution; add 4 g of γ-aminopropyltriethoxysilane to 100 mL of 90 wt% ethanol solution, stir and mix evenly, and adjust the pH to 5 with 0.1 M hydrochloric acid solution, and hydrolyze at room temperature for 30 min to obtain a 4 wt% silanol solution;

[0039] A2: Slowly add the 150 mL of surfactant solution prepared in step A1 to 150 mL of the montmorillonite dispersion, control the temperature at 60 °C, stir and react for 6 h, wash with deionized water, and dry at 60 °C for 12 h to obtain organic montmorillonite; add 10 g of organic montmorillonite to the 60 mL of silanol solution prepared in step A1, stir and react at 50 °C for 4 h, wash with deionized water, and vacuum dry at 80 °C for 12 h to obtain silane-modified montmorillonite;

[0040] The specific preparation steps of the modified glass fiber are as follows:

[0041] B1: Immerse the glass fiber completely in deionized water, perform ultrasonic treatment at 100 W for 15 min, filter, and dry at 60 °C for 6 h to obtain pretreated glass fiber; add 10 g of the pretreated glass fiber to 50 mL of concentrated nitric acid, stir and react at room temperature for 2 h. After the reaction is completed, wash with deionized water until neutral to obtain neutral glass fiber;

[0042] B2: Add 10 g of the neutral glass fiber prepared in step B1 to 50 mL of 70 wt% ethanol solution, soak for 30 min, then wash repeatedly with deionized water 3 times, and dry in vacuum at 80 °C for 12 h to obtain modified glass fiber;

[0043] The specific preparation steps of the polyethylene composite material are as follows:

[0044] S1: Wash high-density polyethylene with deionized water and dry in vacuum at 80 °C for 12 h to obtain pretreated high-density polyethylene; stir and mix the pretreated high-density polyethylene, polyolefin elastomer, zinc stearate, polyethylene wax, dibutylhydroxytoluene, and dilauryl thiodipropionate evenly to obtain a pretreated mixture; ultrasonically disperse the silane-modified montmorillonite, nano-silica, and modified glass fiber into deionized water respectively; extrude polypropylene at 200 °C while performing stretching, and the stretching ratio parameter is 15 to form 2-mm polypropylene microfibers;

[0045] S2: Add the pretreated mixture prepared in step S1 to an extruder, melt and blend at 190 °C, control the rotation speed at 60 rpm, for 3 min, then slowly add maleic anhydride, raise the temperature to 200 °C, react for 5 min, perform the first exhaust, the exhaust pressure is -0.08 MPa, and the time is 5 min;

[0046] S3: After completing the operation in step S2, sequentially add the silane-modified montmorillonite, nano-silica, and modified glass fiber ultrasonically dispersed in step S1, raise the extrusion temperature to 220 °C, raise the rotation speed to 80 rpm, and the mixing time is 8 min;

[0047] S4: After completing the operation in step S3, slowly add the polypropylene microfibers prepared in step S1, reduce the rotation speed to 50 rpm, reduce the temperature to 200 °C at a rate of 5 °C / min, the dispersion time is 5 min. After the dispersion is completed, reduce the temperature to 190 °C at a rate of 2 °C / min, perform the second exhaust, the exhaust pressure is -0.08 MPa, and the time is 5 min, then extrude, and then cool the extrudate to room temperature. First, cool with 40 °C water for 2 min, and then naturally cool to room temperature to obtain the polyethylene composite material.

[0048] Example 2: A polyethylene composite material, the composition of which includes the following components in parts by weight: 65 parts of high-density polyethylene, 1 part of maleic anhydride, 10 parts of polyolefin elastomer, 5 parts of polypropylene microfiber, 6 parts of modified glass fiber, 3 parts of silane-modified montmorillonite, 2 parts of nano-silica, 1 part of zinc stearate, 1 part of polyethylene wax, 0.3 part of primary antioxidant and 0.3 part of auxiliary antioxidant.

[0049] The high-density polyethylene is obtained by washing the recycled laundry detergent bottles, drying them in the air, crushing them, and then drying.

[0050] The specific preparation steps of the silane-modified montmorillonite are as follows:

[0051] A1: Add 10 g of montmorillonite to 200 mL of deionized water, and disperse it evenly by ultrasonic treatment to obtain a montmorillonite dispersion; add 6 g of cetyltrimethylammonium bromide to 300 mL of deionized water, stir and mix evenly to obtain a 2 wt% surfactant solution; add 4 g of γ-aminopropyltriethoxysilane to 100 mL of 90 wt% ethanol solution, stir and mix evenly, adjust the pH to 4 with 0.1 M hydrochloric acid solution, and hydrolyze at room temperature for 30 min to obtain a 4 wt% silanol solution.

[0052] A2: Slowly add the 300 mL of surfactant solution prepared in step A1 to the 200 mL of montmorillonite dispersion, control the temperature at 70 °C, stir and react for 4 h, wash with deionized water, and dry at 60 °C for 24 h to obtain organic montmorillonite; add 10 g of organic montmorillonite to the 80 mL of silanol solution prepared in step A1, stir and react at 60 °C for 2 h, wash with deionized water, and vacuum dry at 80 °C for 12 h to obtain silane-modified montmorillonite.

[0053] The specific preparation steps of the modified glass fiber are as follows:

[0054] B1: Immerse the glass fiber completely in deionized water, perform ultrasonic treatment at 100 W for 15 min, filter, and dry at 60 °C for 6 h to obtain pretreated glass fiber; add 10 g of pretreated glass fiber to 60 mL of concentrated nitric acid, stir and react at room temperature for 4 h, after the reaction is completed, wash with deionized water until neutral to obtain neutral glass fiber.

[0055] B2: Add 10 g of the neutral glass fiber prepared in step B1 to 100 mL of 70 wt% ethanol solution, soak for 30 min, then wash repeatedly with deionized water 3 times, and vacuum dry at 80 °C for 24 h to obtain modified glass fiber.

[0056] The specific preparation steps of the polyethylene composite material are as follows:

[0057] S1: Wash high-density polyethylene with deionized water, and dry it in vacuum at 80 °C for 12 h to obtain pretreated high-density polyethylene; stir and mix the pretreated high-density polyethylene, polyolefin elastomer, zinc stearate, polyethylene wax, 2,4-di-tert-butylphenol, and tris(nonylphenyl) phosphite evenly to obtain a pretreated mixture; ultrasonically treat and pre-disperse silane-modified montmorillonite, nano-silica, and modified glass fiber into deionized water respectively; extrude polypropylene at 200 °C while stretching, with a stretching ratio parameter of 20, to form 3-mm polypropylene microfibers.

[0058] S2: Add the pretreated mixture prepared in step S1 into an extruder, melt and blend at 200 °C, control the rotation speed at 60 rpm for 5 min, then slowly add maleic anhydride, raise the temperature to 210 °C, react for 10 min, conduct the first exhaust, with an exhaust pressure of -0.08 MPa and a time of 8 min.

[0059] S3: After completing the operation in step S2, sequentially add the silane-modified montmorillonite, nano-silica, and modified glass fiber that have been ultrasonically dispersed in step S1, raise the extrusion temperature to 220 °C, raise the rotation speed to 80 rpm, and mix for 10 min.

[0060] S4: After completing the operation in step S3, slowly add the polypropylene microfibers prepared in step S1, reduce the rotation speed to 70 rpm, reduce the temperature to 200 °C at a rate of 5 °C / min, with a dispersion time of 6 min. After the dispersion is completed, reduce the temperature to 190 °C at a rate of 2 °C / min, conduct the second exhaust, with an exhaust pressure of -0.08 MPa and a time of 8 min, then extrude, and then cool the extrudate to room temperature. First, cool it with 40 °C water for 3 min, and then naturally cool it to room temperature to obtain a polyethylene composite material.

[0061] Example 3: A polyethylene composite material, the composition of which includes the following components in parts by weight: 70 parts of high-density polyethylene, 0.8 part of maleic anhydride, 8 parts of polyolefin elastomer, 4 parts of polypropylene microfibers, 5 parts of modified glass fiber, 2.5 parts of silane-modified montmorillonite, 1.5 parts of nano-silica, 0.8 part of zinc stearate, 0.8 part of polyethylene wax, 0.25 part of primary antioxidant, and 0.25 part of auxiliary antioxidant.

[0062] The high-density polyethylene is prepared by washing recycled laundry detergent bottles, drying them in the air, crushing them, and then drying.

[0063] The specific preparation steps of the silane-modified montmorillonite are as follows:

[0064] A1: Add 10 g of montmorillonite to 180 mL of deionized water, and ultrasonically treat to disperse evenly to obtain a montmorillonite dispersion; add 4.5 g of cetyltrimethylammonium bromide to 300 mL of deionized water, stir and mix evenly to obtain a 1.5 wt% surfactant solution; add 4 g of γ-aminopropyltriethoxysilane to 100 mL of 90 wt% ethanol solution, stir and mix evenly, adjust the pH to 4.5 with 0.1 M hydrochloric acid solution, and hydrolyze at room temperature for 30 min to obtain a 4 wt% silanol solution;

[0065] A2: Slowly add 250 mL of the surfactant solution prepared in step A1 to 180 mL of the montmorillonite dispersion, control the temperature at 65 °C, stir and react for 5 h, wash with deionized water, and dry at 60 °C for 18 h to obtain organic montmorillonite; add 10 g of organic montmorillonite to 70 mL of the silanol solution prepared in step A1, stir and react at 55 °C for 3 h, wash with deionized water, and vacuum dry at 80 °C for 12 h to obtain silane-modified montmorillonite;

[0066] The specific preparation steps of the modified glass fiber are as follows:

[0067] B1: Immerse the glass fiber completely in deionized water, ultrasonically treat at 100 W for 15 min, filter, and dry at 60 °C for 6 h to obtain pretreated glass fiber; add 10 g of pretreated glass fiber to 55 mL of concentrated nitric acid, stir and react at room temperature for 3 h, after the reaction is completed, wash with deionized water until neutral to obtain neutral glass fiber;

[0068] B2: Add 10 g of the neutral glass fiber prepared in step B1 to 80 mL of 70 wt% ethanol solution, soak for 30 min, then repeat washing with deionized water 3 times, and vacuum dry at 80 °C for 18 h to obtain modified glass fiber;

[0069] The specific preparation steps of the polyethylene composite are as follows:

[0070] S1: Wash the high-density polyethylene with deionized water and vacuum dry at 80 °C for 12 h to obtain pretreated high-density polyethylene; stir and mix the pretreated high-density polyethylene, polyolefin elastomer, zinc stearate, polyethylene wax, 2,6-di-tert-butyl-p-cresol, and diphenyl phosphite evenly to obtain a pretreated mixture; ultrasonically treat and pre-disperse the silane-modified montmorillonite, nano-silica, and modified glass fiber into deionized water respectively; extrude the polypropylene at 200 °C and simultaneously perform stretching, with the stretching ratio parameter being 18, to form 2.5 mm polypropylene microfibers;

[0071] S2: Add the pretreatment mixture prepared in step S1 into an extruder, melt and blend at 195 °C, control the rotation speed at 60 rpm, for 4 min, then slowly add maleic anhydride, raise the temperature to 205 °C, react for 8 min, conduct the first exhaust, the exhaust pressure is -0.08 MPa, for 6 min;

[0072] S3: After completing the operation in step S2, sequentially add the silane-modified montmorillonite, nano-silica, and modified glass fiber after ultrasonic dispersion in step S1, raise the extrusion temperature to 220 °C, raise the rotation speed to 80 rpm, and the mixing time is 9 min;

[0073] S4: After completing the operation in step S3, slowly add the polypropylene microfiber prepared in step S1, reduce the rotation speed to 60 rpm, reduce the temperature to 200 °C at a rate of 5 °C / min, the dispersion time is 5.5 min, after the dispersion is completed, reduce the temperature to 190 °C at a rate of 2 °C / min, conduct the second exhaust, the exhaust pressure is -0.08 MPa, for 6 min, extrude, and then cool the extrudate to room temperature, first cool with 40 °C water for 2.5 min, and then naturally cool to room temperature to obtain the polyethylene composite material.

[0074] Comparative Example 1: The operation of Comparative Example 1 is basically the same as that of Example 2, the difference is that maleic anhydride is not added in Comparative Example 1.

[0075] Comparative Example 2: The operation of Comparative Example 2 is basically the same as that of Example 2, the difference is that polypropylene microfiber is not added in Comparative Example 2.

[0076] Comparative Example 3: The operation of Comparative Example 3 is basically the same as that of Example 2, the difference is that silane-modified montmorillonite and nano-silica are not added in Comparative Example 3.

[0077] Comparative Example 4: The operation of Comparative Example 4 is basically the same as that of Example 2, the difference is that polyolefin elastomer is not added in Comparative Example 4.

[0078] Comparative Example 5: The operation of Comparative Example 5 is basically the same as that of Example 2, the difference is that in Comparative Example 5, polypropylene microfiber is not added in stages, but is added and mixed with glass fiber at the same time.

[0079] Performance test:

[0080] Mechanical strength test: The tensile strength and flexural strength of the polyethylene composite samples prepared in Examples 1-3 and Comparative Examples 1-5 were tested using a universal material testing machine RH-5000. The tensile strength was tested in accordance with GB / T 1040.1-2018; the flexural strength was tested in accordance with GB / T 9341-2008; the impact strength and absorbed energy were determined using a plastic pendulum impact testing machine in accordance with GB / T 1843-2008. The results of the tensile strength, flexural strength and impact strength are shown in Table 1 below; the test results of the comparison of the impact strength and absorbed energy are as Figure 1 shown.

[0081] Table 1. Mechanical strength test results of polyethylene composites

[0082]

[0083] As can be seen from Table 1 and Figure 1 the results, the polyethylene composites prepared by the present invention have good tensile strength, flexural strength and impact strength, and excellent mechanical properties; from the results of Comparative Example 1 and Example 2, it can be seen that the graft modification effect of maleic anhydride is missing, the compatibility between the inorganic filler and the HDPE matrix is significantly affected, the interfacial bonding force is significantly reduced, and the chimeric effect between the glass fiber and the matrix may also be weakened, resulting in a significant decrease in the overall strength; from the results of Comparative Example 2 and Example 2, it can be seen that the lack of drawn polypropylene microfibers leads to the lack of an important reinforcing phase in the matrix, the load-bearing capacity at fracture is weakened, and the interference effect on the crack propagation path disappears, resulting in a significant decrease in the material's ability to absorb dynamic loads; from the results of Comparative Example 3 and Example 2, it can be seen that after the montmorillonite and nano-SiO 2 are missing, the composite material loses the support of nano-reinforcement and multi-level structure, cracks are easy to expand, the tensile strength and flexural properties are greatly weakened. In addition, the crack resistance and local stress dispersion effects of the inorganic filler are missing, and the crack propagation is more rapid, resulting in the material being more prone to fracture; from the results of Comparative Example 4 and Example 2, it can be seen that the lack of the toughening effect of the polyolefin elastomer results in a significant reduction in the energy absorption capacity under dynamic loads and a significant decrease in the impact strength of the material; from the results of Comparative Example 5 and Example 2, it can be seen that when the polypropylene microfibers and glass fibers are added simultaneously, the dispersion is uneven, which may lead to a weakening of the reinforcement effect, and the simultaneous addition of the polypropylene microfibers may cause local agglomeration, resulting in a significant decrease in the toughness effect.

[0084] Thermal property test: The polyethylene composites prepared in Example 2 and Comparative Examples 1-5 were placed in a thermogravimetric analyzer, the heating rate was set at 10 °C / min, the temperature was raised to 600 °C, and the initial decomposition temperature (Tonset) and the maximum decomposition rate temperature (Tmax) of the material were recorded. At the same time, the percentage of the remaining mass of the sample at high temperature was recorded. The results are shown in Table 2 below.

[0085] Table 2. Thermal property test results of polyethylene composites

[0086]

[0087] As can be seen from the results in Table 2, the polyethylene composites prepared by the present invention have a relatively high initial decomposition temperature and maximum decomposition rate temperature, and also a relatively large residual mass percentage, indicating that the inorganic fillers are effectively and uniformly dispersed, the interfacial bonding force is strong, and the overall thermal stability of the material is good; from the results of Comparative Example 1 and Example 2, it can be seen that without maleic anhydride graft modification, the interfacial bonding force is poor, the dispersibility of inorganic fillers is reduced, and the thermal stability of the fillers may not be fully exerted, which leads to an obvious influence on the thermal decomposition performance; from the results of Comparative Example 2 and Example 2, it can be seen that without polypropylene microfiber reinforcement, the effect of the crystal structure of the microfibers on thermal stability is missing, and the thermal stability is affected to a certain extent; from the results of Comparative Example 3 and Example 2, it can be seen that without the barrier effect of nano-fillers, this may lead to easier migration of volatile components, and without the high-temperature support effect of montmorillonite and nano-silica, the overall thermal stability of the material is reduced, and at the same time, due to the reduction of the filler mass, the residual inorganic components are significantly reduced; from the results of Comparative Example 5 and Example 2, it can be seen that the polypropylene microfibers are not evenly dispersed, the interfacial bonding force between the matrix and the fibers is weakened, and the thermal stability is affected to a certain extent.

[0088] Anti-aging test: The polyethylene composite samples prepared in Example 2 and Comparative Examples 1-5 were subjected to ultraviolet lamp aging test. The test parameters were UVA-340 lamp tube to simulate ultraviolet rays (0.35 W / m 2 ), temperature 60 °C, humidity 75%, and the light cycle was 12 h of light and 12 h of darkness. The test was carried out for 800 h, and the percentage change in the tensile strength of the samples was recorded at 96 h, 240 h, 500 h and 800 h (tensile strength change = (tensile strength before test - tensile strength after test) / tensile strength before test × 100%), and the results are as Figure 2 shown.

[0089] From Figure 2The results show that the polyethylene composite prepared by the present invention has good anti-aging performance and can be effectively used for a long time under outdoor exposure. From the results of Comparative Example 1 and Example 2, it can be seen that the lack of maleic anhydride leads to poor interfacial bonding between the filler and the matrix, and the filler may fall off after aging, resulting in performance degradation. From the results of Comparative Example 2 and Example 2, it can be seen that without the effect of polypropylene microfibers, the anti-crack and degradation-retarding effects of the microfiber distribution disappear, which may lead to obvious aging. From the results of Comparative Example 3 and Example 2, it can be seen that the lack of the ultraviolet barrier effect of modified montmorillonite and nano-silica may lead to aggravated photo-oxidative degradation and significant impact on mechanical properties. From the results of Comparative Example 4 and Example 2, it can be seen that without the toughening of polyolefin elastomer, the crack propagation is aggravated after aging, and the ultraviolet barrier and antioxidant effects of the remaining fillers are still there, and the overall decline is small. From the results of Comparative Example 5 and Example 2, it can be seen that the polypropylene microfibers are unevenly dispersed, the microfiber reinforcement network effect is weakened, and the anti-aging performance is affected to a certain extent, and the mechanical strength decreases.

[0090] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made in these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polyethylene composite material, characterized in that: The composition includes the following components in parts by weight: 60-70 parts of high-density polyethylene, 0.6-1 parts of maleic anhydride, 6-10 parts of polyolefin elastomer, 3-5 parts of polypropylene microfiber, 4-6 parts of modified glass fiber, 2-3 parts of silane-modified montmorillonite, 1-2 parts of nano silicon dioxide, 0.6-1 parts of zinc stearate, 0.5-1 parts of polyethylene wax, 0.2-0.3 parts of primary antioxidant and 0.2-0.3 parts of auxiliary antioxidant; The primary antioxidant is any one of butylated hydroxytoluene, 2,4-di-tert-butylphenol and 2,6-di-tert-butyl-p-cresol; The auxiliary antioxidant is any one of didodecanediol thiodipropionate, tris(nonylphenyl)phosphite, and diphenylphosphite; The specific preparation steps of the silane-modified montmorillonite are as follows: A1: Add montmorillonite to deionized water, disperse it evenly by ultrasonic treatment, and obtain a montmorillonite dispersion; add hexadecyltrimethylammonium bromide to deionized water, stir and mix evenly, and obtain a 1-2wt% active agent solution; add γ-aminopropyltriethoxysilane to the ethanol solution, stir and mix evenly, adjust the pH to 4-5 with 0.1M hydrochloric acid solution, and hydrolyze at room temperature to obtain a 4wt% silanol solution; A2: slowly adding the active agent solution prepared in step A1 to the montmorillonite dispersion, controlling the temperature at 60-70°C, stirring the reaction, washing with deionized water, and drying to obtain an organic montmorillonite; adding the organic montmorillonite to the silanol solution prepared in step A1, stirring the reaction, washing with deionized water, and vacuum drying to obtain a silane-modified montmorillonite; In step A1, the ratio of the amount of montmorillonite to deionized water is 1 g: 15-20 mL; in step A2, the volume ratio of the active agent solution to the montmorillonite dispersion is 1-1.5:1; the ratio of the amount of the organic montmorillonite to the silanol solution is 1 g: 6-8 mL; The specific preparation steps of the modified glass fiber are as follows: B1: The glass fiber is completely immersed in deionized water, subjected to ultrasonic treatment, filtered, and dried to obtain pretreated glass fiber; the pretreated glass fiber is added to concentrated nitric acid, stirred and reacted at room temperature, and after the reaction is completed, washed with deionized water until neutral to obtain neutral glass fiber; B2: adding the neutral glass fiber prepared in step B1 into an ethanol solution, soaking, then repeatedly washing with deionized water, and vacuum drying to obtain a modified glass fiber; In step B1, the ratio of the amount of the pretreated glass fiber to the concentrated nitric acid is 1 g: 5-6 mL; in step B2, the ratio of the amount of the neutral glass fiber to the ethanol solution is 1 g: 5-10 mL; the specific preparation steps of the polyethylene composite material are as follows: S1: washing high-density polyethylene with deionized water and vacuum drying to obtain pretreated high-density polyethylene; stirring and mixing the pretreated high-density polyethylene, polyolefin elastomer, zinc stearate, polyethylene wax, primary antioxidant and auxiliary antioxidant to obtain a pretreated mixture; pre-dispersing silane-modified montmorillonite, nano-silica and modified glass fiber in deionized water by ultrasonic treatment respectively; extruding polypropylene through an extruder and stretching it at the same time to form polypropylene microfibers; S2: adding the pretreated mixture prepared in step S1 into an extruder, melt blending at 190-200° C., controlling the speed to 60 rpm, mixing time 3-5 min, then slowly adding maleic anhydride, raising the temperature to 200-210° C., and reacting for 5-10 min; S3: After completing the operation in step S2, add the silane-modified montmorillonite, nano-silica and modified glass fiber after ultrasonic dispersion in step S1 in sequence, increase the extrusion temperature to 220° C., increase the rotation speed, and mix for 8 to 10 minutes; S4: After completing the operation in step S3, slowly add the polypropylene microfiber prepared in step S1, reduce the rotation speed, reduce the temperature to 200°C at a rate of 5°C / min, and disperse for 5 to 6 minutes. After dispersion, reduce the temperature to 190°C at a rate of 2°C / min, extrude, and then cool the extrudate to room temperature to obtain a polyethylene composite material; In step S1, the stretching parameter of the polypropylene is a stretching ratio of 15 to 20; in step S2, after the maleic anhydride grafting reaction is completed, the first exhaust is performed, the exhaust pressure is -0.08 MPa, and the time is 5 to 8 minutes; In step S4, after the polypropylene microfibers are added and mixed, a second exhaust is performed with an exhaust pressure of -0.08 MPa for 5 to 8 minutes; the extrudate cooling step is firstly cooling with 40° C. water for 2 to 3 minutes, and then naturally cooling to room temperature.

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