High-strength weather-resistant polyethylene plastic for plastic pallets and method for preparing the same

Abstract

The application relates to the technical field of high polymer materials, and discloses a high-strength weather-resistant polyethylene plastic for plastic pallets and a preparation method thereof. The preparation steps are as follows: taking modified titanium dioxide with lignin, modifying the same with vinyl silane to obtain modified titanium dioxide with double bonds; taking ethylene octene copolymer and maleic anhydride modified ethylene octene copolymer, mixing the same uniformly in n-heptane, heating, keeping stirring, adding the modified titanium dioxide with double bonds in a condensation reflux state, stirring, and reducing to room temperature to obtain a suspension; dropping the suspension into hot water, cooling to room temperature, filtering, washing the obtained solid, and drying to obtain composite modified silicon dioxide; mixing polyethylene, PA6, ethylene octene copolymer, the composite modified silicon dioxide and modified mica, adding the mixture into a double-screw extruder, extruding, granulating, injection molding to obtain the polyethylene plastic, and the prepared polyethylene plastic has excellent strength and toughness and excellent weather resistance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and discloses a high-strength weather-resistant polyethylene plastic for plastic pallets and its preparation method. Background Technology

[0002] Plastic pallets, as core load-bearing devices in logistics warehousing, chemical transportation, and food cold chain industries, are an indispensable key component of the modern supply chain system. Polyethylene is a common thermoplastic with advantages such as low cost, non-toxicity, odorlessness, and ease of processing, making it the most widely used base material in plastic pallet production.

[0003] Existing polyethylene used in plastic pallets needs to possess both good mechanical properties and weather resistance. If the polyethylene plastic's strength is insufficient, the pallet is prone to deformation and breakage, affecting its service life and safety. On the other hand, some pallets are exposed to outdoor environments and subjected to long-term ultraviolet radiation. Poor weather resistance can lead to oxidative degradation, causing a decline in the material's mechanical properties and significantly reducing its service life. To improve the performance of polyethylene plastic, existing technologies often add inorganic fillers. However, these fillers have poor compatibility with the polyethylene matrix, which can negatively impact the material's performance. Therefore, researching a high-strength, weather-resistant polyethylene plastic for plastic pallets and its preparation method is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a high-strength, weather-resistant polyethylene plastic for plastic pallets and a method for preparing the same, in order to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing high-strength weather-resistant polyethylene plastic for plastic pallets, comprising the following steps: mixing polyethylene, PA6, ethylene octene copolymer, composite modified silica, and modified mica, adding to a twin-screw extruder, extruding, granulating, and injection molding to obtain polyethylene plastic.

[0006] More preferably, the polyethylene plastic comprises the following raw materials, by mass parts: 80-90 parts polyethylene, 10-15 parts PA6, 5-8 parts ethylene octene copolymer, 8-12 parts composite modified silica, and 3-5 parts modified mica.

[0007] In a more optimized manner, the preparation of the composite modified silica includes the following steps: Add lignin-modified titanium dioxide to an ethanol aqueous solution, heat to 50-60℃ and stir until homogeneous, add vinylsilane, adjust the pH to 4.5-5, stir for 3-6 hours, filter, wash and dry the obtained solid to obtain double bond-modified titanium dioxide. Take ethylene octene copolymer and maleic anhydride modified ethylene octene copolymer, add them to n-heptane and mix evenly. Heat to 110~120℃ and keep stirring. Under reflux, add double bond modified titanium dioxide and stir for 2~3 hours. Cool to room temperature to obtain a suspension. Drop the suspension into water at 90~95℃, cool to room temperature, filter, wash the obtained solid, and dry to obtain composite modified silica.

[0008] In a more optimized manner, the double-bonded modified titanium dioxide comprises the following raw materials, by mass parts: 10-15 parts lignin-modified titanium dioxide, 1-2 parts vinylsilane; The composite modified silica comprises the following raw materials, by mass parts: 3-5 parts ethylene octene copolymer, 6-8 parts maleic anhydride modified ethylene octene copolymer, and 4-6 parts double-bonded modified titanium dioxide.

[0009] In a more optimized manner, the preparation of the lignin-modified titanium dioxide includes the following steps: Alkali lignin was added to an aqueous sodium hydroxide solution and ultrasonically dispersed. Then, an aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, and the mixture was stirred at 80-85°C for 4-6 hours. After purification and freeze-drying, quaternized lignin was obtained. Quaternized lignin was added to water and stirred evenly. Titanium dioxide was added and the pH was adjusted to 4.5-5. The mixture was self-assembled for 1-2 hours and aged at 40-45℃ for 2-3 hours. The solvent was removed and the mixture was vacuum dried to obtain lignin-modified titanium dioxide. More preferably, the quaternized lignin comprises the following raw materials, by mass parts: 1-2 parts alkali lignin, 10-15 parts 15-20 wt% sodium hydroxide aqueous solution, and 1-1.5 parts 50-60 wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution; The lignin-modified titanium dioxide comprises the following raw materials, by mass: 5-8 parts quaternized lignin and 2-4 parts titanium dioxide.

[0010] In a more optimized manner, the preparation of the modified mica includes the following steps: Add mica to an ethanol-water solution, heat to 50-60℃ and stir until homogeneous, add aminosilane, adjust the pH to 4.5-5, stir for 3-6 hours, filter, wash and dry the obtained solid to obtain aminated mica. Aminated mica was added to toluene and dispersed evenly. Toluene-2,4-diisocyanate and octadecyl isocyanate were added, the temperature was raised to 70-80℃, and the mixture was stirred for 1-2 hours. The mixture was filtered, and the resulting solid was washed and dried to obtain modified mica.

[0011] More preferably, the aminated mica comprises the following raw materials, by mass parts: 10-15 parts mica, 1-2 parts aminosilane; The modified mica comprises the following raw materials, by mass parts: 10-15 parts aminated mica, 300-400 parts toluene, 2-3 parts toluene-2,4-diisocyanate, and 1-2 parts octadecyl isocyanate.

[0012] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) The matrix material is a mixture of polyethylene, PA6 and ethylene octene copolymer. PA6 has high tensile strength, and polyethylene and ethylene octene copolymer have good flexibility. After the three are mixed in a certain proportion, the matrix material can have the advantages of high strength and high toughness.

[0013] (2) Both lignin and titanium dioxide have good UV resistance. Quaternizing alkali lignin and then combining it with titanium dioxide through self-assembly not only improves its compatibility in polyethylene, but also allows lignin to inhibit the photocatalytic activity of titanium dioxide, thereby improving the stability of the material under UV irradiation. To further improve the compatibility of lignin-modified titanium dioxide in polyethylene, it was coated with ethylene octene copolymer and maleic anhydride-modified ethylene octene copolymer to obtain composite modified silica. The ethylene octene copolymer has excellent compatibility with polyethylene. At the same time, due to the presence of maleic anhydride-modified ethylene octene copolymer, the composite modified silica can also act as a compatibilizer to improve the compatibility of various substances in the matrix material and optimize the overall performance.

[0014] (3) Modified mica is introduced and modified with toluene-2,4-diisocyanate and octadecyl isocyanate to obtain: The introduction of toluene-2,4-diisocyanate can increase the crosslinking sites, increase the compatibility of modified mica in the matrix material, and increase the overall crosslinking degree to improve mechanical properties and weather resistance. However, excessive crosslinking degree will make the overall local viscosity too high, which is not conducive to the dispersion of raw materials during processing. Therefore, octadecyl isocyanate is introduced to alleviate the above problems by utilizing its long chain structure. The amount of toluene-2,4-diisocyanate and octadecyl isocyanate added needs to be controlled in order to obtain polyethylene material with sufficient crosslinking degree and excellent dispersion of raw materials inside.

[0015] (4) The filler used in this scheme is a composite modified silica and modified mica in a certain mass ratio. The two fillers have complementary forms: mica is in sheet form, which can improve the overall mechanical strength to a greater extent, while silica is in granular form, which can reduce the brittleness caused by the agglomeration of sheet fillers by dispersing stress through sliding. Under the synergistic effect, high-strength, high-toughness, and high-weather-resistant polyethylene plastic is finally obtained. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] It should be noted that there are no special restrictions on the manufacturers from which the raw materials involved in this invention can be purchased. Exemplary examples include: alkali lignin (ALDRICH 471003); titanium dioxide (20nm, rutile type); vinyl silane (vinyltrimethoxysilane); mica (5000 mesh); aminosilane (3-aminopropyltriethoxysilane); ethylene octene copolymer (Dow 8150); maleic anhydride modified ethylene octene copolymer (Dow R905); PA6 (CM1007); polyethylene (Y45330, meltflow rate: 2.01g / 10min). Example 1: S1: 1 part of alkali lignin was added to 15 parts of 20 wt% sodium hydroxide aqueous solution, ultrasonically dispersed for 15 min, 1 part of 60 wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution was added, and the mixture was stirred at 85 °C for 5 h. Small molecule impurities were removed by dialysis purification, and the mixture was freeze-dried for 48 h to obtain quaternized lignin. Six parts of quaternized lignin were added to 100 parts of water and stirred evenly. Four parts of titanium dioxide were added, the pH was adjusted to 5, and the mixture was self-assembled for 1 hour. The mixture was aged at 40°C for 2 hours, the solvent was removed, and the mixture was vacuum dried at 50°C for 24 hours to obtain lignin-modified titanium dioxide. S2: Take 10 parts of lignin-modified titanium dioxide and add it to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of vinyltrimethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash and dry the obtained solid to obtain double bond modified titanium dioxide. Take 5 parts of ethylene octene copolymer and 6 parts of maleic anhydride modified ethylene octene copolymer, add them to 100 parts of n-heptane and mix well. Heat to 115℃ and keep stirring. Under reflux, add 6 parts of double bond modified titanium dioxide and stir for 3 hours. Cool to room temperature to obtain a suspension. Drop the suspension into 200 parts of water at 90℃ at a rate of 0.1 mL / s. Cool to room temperature, filter, wash and dry the obtained solid to obtain composite modified silica. S3: Take 10 parts of mica and add them to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of 3-aminopropyltriethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash the obtained solid, and dry to obtain aminated mica. 15 parts of aminated mica were added to 400 parts of toluene and dispersed evenly. 2 parts of toluene-2,4-diisocyanate and 2 parts of octadecyl isocyanate were added. The mixture was heated to 75°C and stirred for 2 hours. After filtration, the obtained solid was washed and dried to obtain modified mica. S4: Add 85 parts polyethylene, 15 parts PA6, 5 parts ethylene octene copolymer, 10 parts composite modified silica, and 4 parts modified mica to a twin-screw extruder, extrude at 200℃, with a screw speed of 60 r / min, granulate, and injection mold to obtain polyethylene plastic.

[0018] Example 2: S1: Add 1 part of alkali lignin to 10 parts of 20wt% sodium hydroxide aqueous solution, ultrasonically disperse for 15 min, add 1 part of 60wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution, stir and react at 85℃ for 5 h, dialysis to remove small molecule impurities, freeze dry for 48 h to obtain quaternized lignin. Add 5 parts of quaternized lignin to 100 parts of water and stir evenly. Add 2 parts of titanium dioxide, adjust the pH to 5, mix and self-assemble for 1 hour, age at 40℃ for 2 hours, remove the solvent, and vacuum dry at 50℃ for 24 hours to obtain lignin-modified titanium dioxide. S2: Take 10 parts of lignin-modified titanium dioxide and add it to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 1 part of vinyltrimethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash and dry the obtained solid to obtain double bond modified titanium dioxide. Take 3 parts of ethylene octene copolymer and 6 parts of maleic anhydride modified ethylene octene copolymer, add them to 100 parts of n-heptane and mix well. Heat to 115℃ and keep stirring. Under reflux, add 4 parts of double bond modified titanium dioxide and stir for 3 hours. Cool to room temperature to obtain a suspension. Add the suspension dropwise to 200 parts of water at 90℃ at a rate of 0.1 mL / s. Cool to room temperature, filter, wash and dry the obtained solid to obtain composite modified silica. S3: Take 10 parts of mica and add them to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 1 part of 3-aminopropyltriethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash and dry the obtained solid to obtain aminated mica. 10 parts of aminated mica were added to 400 parts of toluene and dispersed evenly. 2 parts of toluene-2,4-diisocyanate and 1 part of octadecyl isocyanate were added. The mixture was heated to 75°C and stirred for 2 hours. After filtration, the obtained solid was washed and dried to obtain modified mica. S4: Add 90 parts polyethylene, 15 parts PA6, 8 parts ethylene octene copolymer, 12 parts composite modified silica, and 5 parts modified mica to a twin-screw extruder, extrude at 200℃, with a screw speed of 60 r / min, granulate, and injection mold to obtain polyethylene plastic.

[0019] Example 3: S1: Add 2 parts of alkali lignin to 15 parts of 20wt% sodium hydroxide aqueous solution, ultrasonically disperse for 15 min, add 1.5 parts of 60wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution, stir and react at 85℃ for 5 h, dialysis to remove small molecule impurities, freeze dry for 48 h to obtain quaternized lignin. Eight parts of quaternized lignin were added to 100 parts of water and stirred evenly. Four parts of titanium dioxide were added, the pH was adjusted to 5, and the mixture was self-assembled for 1 hour. The mixture was aged at 40°C for 2 hours, the solvent was removed, and the mixture was vacuum dried at 50°C for 24 hours to obtain lignin-modified titanium dioxide. S2: Take 15 parts of lignin-modified titanium dioxide and add it to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of vinyltrimethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash and dry the obtained solid to obtain double bond modified titanium dioxide. Take 5 parts of ethylene octene copolymer and 8 parts of maleic anhydride modified ethylene octene copolymer, add them to 100 parts of n-heptane and mix well. Heat to 115℃ and keep stirring. Under reflux, add 6 parts of double bond modified titanium dioxide and stir for 3 hours. Cool to room temperature to obtain a suspension. Drop the suspension into 200 parts of water at 90℃ at a rate of 0.1 mL / s. Cool to room temperature, filter, wash and dry the obtained solid to obtain composite modified silica. S3: Take 15 parts of mica and add them to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of 3-aminopropyltriethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash and dry the obtained solid to obtain aminated mica. 15 parts of aminated mica were added to 400 parts of toluene and dispersed evenly. 2 parts of toluene-2,4-diisocyanate and 1 part of octadecyl isocyanate were added. The mixture was heated to 75°C and stirred for 2 hours. After filtration, the obtained solid was washed and dried to obtain modified mica. S4: Add 80 parts polyethylene, 10 parts PA6, 5 parts ethylene octene copolymer, 8 parts composite modified silica, and 3 parts modified mica to a twin-screw extruder, extrude at 200℃, with a screw speed of 60 r / min, granulate, and injection mold to obtain polyethylene plastic.

[0020] Comparative Example 1 (Ethylene octene copolymer replaced maleic anhydride modified ethylene octene copolymer, the rest is the same as Example 1): S1: 1 part of alkali lignin was added to 15 parts of 20 wt% sodium hydroxide aqueous solution, ultrasonically dispersed for 15 min, 1 part of 60 wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution was added, and the mixture was stirred and reacted at 85 °C for 5 h. Small molecule impurities were removed by dialysis purification, and the mixture was freeze-dried for 48 h to obtain quaternized lignin. Six parts of quaternized lignin were added to 100 parts of water and stirred evenly. Four parts of titanium dioxide were added, the pH was adjusted to 5, and the mixture was self-assembled for 1 hour. The mixture was aged at 40°C for 2 hours, the solvent was removed, and the mixture was vacuum dried at 50°C for 24 hours to obtain lignin-modified titanium dioxide. S2: Take 10 parts of lignin-modified titanium dioxide and add it to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of vinyltrimethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash and dry the obtained solid to obtain double bond modified titanium dioxide. Take 11 parts of ethylene octene copolymer, add it to 100 parts of n-heptane and mix well. Heat to 115℃ and keep stirring. Under reflux, add 6 parts of double bond modified titanium dioxide and stir for 3 hours. Cool to room temperature to obtain a suspension. Drop the suspension into 200 parts of water at 90℃ at a rate of 0.1 mL / s. Cool to room temperature, filter, wash and dry the obtained solid to obtain composite modified silica. S3: Take 10 parts of mica and add them to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of 3-aminopropyltriethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash the obtained solid, and dry to obtain aminated mica. 15 parts of aminated mica were added to 400 parts of toluene and dispersed evenly. 2 parts of toluene-2,4-diisocyanate and 2 parts of octadecyl isocyanate were added. The mixture was heated to 75°C and stirred for 2 hours. After filtration, the obtained solid was washed and dried to obtain modified mica. S4: Add 85 parts polyethylene, 15 parts PA6, 5 parts ethylene octene copolymer, 10 parts composite modified silica, and 4 parts modified mica to a twin-screw extruder, extrude at 200℃, with a screw speed of 60 r / min, granulate, and injection mold to obtain polyethylene plastic.

[0021] Comparative Example 2 (toluene-2,4-diisocyanate is used instead of octadecyl isocyanate, and the rest is the same as in Example 1): S1: 1 part of alkali lignin is added to 15 parts of 20 wt% sodium hydroxide aqueous solution, ultrasonically dispersed for 15 min, 1 part of 60 wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is added, the mixture is stirred at 85 °C for 5 h, small molecule impurities are removed by dialysis purification, and the mixture is freeze-dried for 48 h to obtain quaternized lignin; Six parts of quaternized lignin were added to 100 parts of water and stirred evenly. Four parts of titanium dioxide were added, the pH was adjusted to 5, and the mixture was self-assembled for 1 hour. The mixture was aged at 40°C for 2 hours, the solvent was removed, and the mixture was vacuum dried at 50°C for 24 hours to obtain lignin-modified titanium dioxide. S2: Take 10 parts of lignin-modified titanium dioxide and add it to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of vinyltrimethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash and dry the obtained solid to obtain double bond modified titanium dioxide. Take 5 parts of ethylene octene copolymer and 6 parts of maleic anhydride modified ethylene octene copolymer, add them to 100 parts of n-heptane and mix well. Heat to 115℃ and keep stirring. Under reflux, add 6 parts of double bond modified titanium dioxide and stir for 3 hours. Cool to room temperature to obtain a suspension. Drop the suspension into 200 parts of water at 90℃ at a rate of 0.1 mL / s. Cool to room temperature, filter, wash and dry the obtained solid to obtain composite modified silica. S3: Take 10 parts of mica and add them to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of 3-aminopropyltriethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash the obtained solid, and dry to obtain aminated mica. 15 parts of aminated mica were added to 400 parts of toluene and dispersed evenly. 4 parts of toluene-2,4-diisocyanate were added, the temperature was raised to 75°C, and the mixture was stirred for 2 hours. The mixture was filtered, and the resulting solid was washed and dried to obtain modified mica. S4: Add 85 parts polyethylene, 15 parts PA6, 5 parts ethylene octene copolymer, 10 parts composite modified silica, and 4 parts modified mica to a twin-screw extruder, extrude at 200℃, with a screw speed of 60 r / min, granulate, and injection mold to obtain polyethylene plastic.

[0022] Comparative Example 3 (Using a mixture of alkali lignin and titanium dioxide instead of lignin to modify titanium dioxide, the rest is the same as in Example 2): S1: Take 6 parts of alkali lignin and 4 parts of titanium dioxide, mix them to obtain a mixture of alkali lignin and titanium dioxide. S2: Take 10 parts of the mixture of alkali lignin and titanium dioxide and add it to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of vinyltrimethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash the obtained solid, dry it, and obtain double bond modified titanium dioxide. Take 5 parts of ethylene octene copolymer and 6 parts of maleic anhydride modified ethylene octene copolymer, add them to 100 parts of n-heptane and mix well. Heat to 115℃ and keep stirring. Under reflux, add 6 parts of double bond modified titanium dioxide and stir for 3 hours. Cool to room temperature to obtain a suspension. Drop the suspension into 200 parts of water at 90℃ at a rate of 0.1 mL / s. Cool to room temperature, filter, wash and dry the obtained solid to obtain composite modified silica. S3: Take 10 parts of mica and add them to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of 3-aminopropyltriethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash the obtained solid, and dry to obtain aminated mica. 15 parts of aminated mica were added to 400 parts of toluene and dispersed evenly. 2 parts of toluene-2,4-diisocyanate and 2 parts of octadecyl isocyanate were added. The mixture was heated to 75°C and stirred for 2 hours. After filtration, the obtained solid was washed and dried to obtain modified mica. S4: Add 85 parts polyethylene, 15 parts PA6, 5 parts ethylene octene copolymer, 10 parts composite modified silica, and 4 parts modified mica to a twin-screw extruder, extrude at 200℃, with a screw speed of 60 r / min, granulate, and injection mold to obtain polyethylene plastic.

[0023] Comparative Example 4 (composite modified silica replaces modified mica, the rest is the same as Example 1): S1: 1 part of alkali lignin is added to 15 parts of 20 wt% sodium hydroxide aqueous solution, ultrasonically dispersed for 15 min, 1 part of 60 wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is added, the mixture is stirred at 85 °C for 5 h, small molecule impurities are removed by dialysis purification, and the mixture is freeze-dried for 48 h to obtain quaternized lignin; Six parts of quaternized lignin were added to 100 parts of water and stirred evenly. Four parts of titanium dioxide were added, the pH was adjusted to 5, and the mixture was self-assembled for 1 hour. The mixture was aged at 40°C for 2 hours, the solvent was removed, and the mixture was vacuum dried at 50°C for 24 hours to obtain lignin-modified titanium dioxide. S2: Take 10 parts of lignin-modified titanium dioxide and add it to 80 parts of 75wt% ethanol aqueous solution. Heat to 60℃ and stir evenly. Add 2 parts of vinyltrimethoxysilane, adjust the pH to 5, stir for 5 hours, filter, wash and dry the obtained solid to obtain double bond modified titanium dioxide. Take 5 parts of ethylene octene copolymer and 6 parts of maleic anhydride modified ethylene octene copolymer, add them to 100 parts of n-heptane and mix well. Heat to 115℃ and keep stirring. Under reflux, add 6 parts of double bond modified titanium dioxide and stir for 3 hours. Cool to room temperature to obtain a suspension. Drop the suspension into 200 parts of water at 90℃ at a rate of 0.1 mL / s. Cool to room temperature, filter, wash and dry the obtained solid to obtain composite modified silica. S3: Add 85 parts of polyethylene, 15 parts of PA6, 5 parts of ethylene octene copolymer, and 14 parts of composite modified silica to a twin-screw extruder, extrude at 200°C, with a screw speed of 60 r / min, granulate, and injection mold to obtain polyethylene plastic.

[0024] Performance Test 1: Polyethylene plastics prepared in Examples 1-3 and Comparative Examples 1-4 were used; (1) Tensile strength and elongation at break were tested according to GB / T1040.1-2018; (2) A UV aging test chamber was used to test the tensile strength and elongation at break at an ultraviolet irradiation intensity of 5000 μw / cm. 2 Accelerated aging tests were conducted at 70℃, and the tensile strength was tested after 360 hours. The retention rate was calculated. See Table 1 for details. Table 1: Comparative Example 1 uses ethylene octene copolymer instead of maleic anhydride-modified ethylene octene copolymer; the overall compatibility decreases, leading to a decline in performance. Comparative Example 2 uses toluene-2,4-diisocyanate instead of octadecyl isocyanate, further increasing crosslinking; the reduced flowability may lead to uneven internal dispersion, resulting in performance degradation. Comparative Example 3 uses a mixture of alkali lignin and titanium dioxide instead of lignin-modified titanium dioxide; simple blending leads to reduced dispersibility, and the high photocatalytic activity of unmodified titanium dioxide also reduces weather resistance. Comparative Example 4 uses composite modified silica instead of modified mica; the performance of a single filler is not as good as the synergistic effect of the two. In summary, the polyethylene plastic prepared by this method possesses excellent strength and toughness as well as excellent weather resistance.

[0025] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-strength, weather-resistant polyethylene plastic for plastic pallets, characterized in that: Includes the following steps: By weight, 80-90 parts of polyethylene, 10-15 parts of PA6, 5-8 parts of ethylene octene copolymer, 8-12 parts of composite modified titanium dioxide, and 3-5 parts of modified mica are mixed, added to a twin-screw extruder, extruded, granulated, and injection molded to obtain polyethylene plastic. The preparation of the composite modified titanium dioxide includes the following steps: by mass, take 10-15 parts of lignin-modified titanium dioxide and add it to an ethanol aqueous solution, heat it to 50-60℃ and stir it evenly, add 1-2 parts of vinylsilane, adjust the pH to 4.5-5, stir for 3-6 hours, filter, wash the obtained solid, dry it, and obtain double bond modified titanium dioxide. Take 3-5 parts of ethylene octene copolymer and 6-8 parts of maleic anhydride modified ethylene octene copolymer, add them to n-heptane and mix evenly. Heat to 110-120℃ and keep stirring. Under reflux, add 4-6 parts of double bond modified titanium dioxide and stir for 2-3 hours. Cool to room temperature to obtain a suspension. Drop the suspension into water at 90-95℃, cool to room temperature, filter, wash the obtained solid, and dry to obtain composite modified titanium dioxide. The preparation of the modified mica includes the following steps: by mass, 10-15 parts of mica are added to an ethanol aqueous solution, heated to 50-60°C and stirred evenly, 1-2 parts of aminosilane are added, the pH is adjusted to 4.5-5, stirred for 3-6 hours, filtered, the obtained solid is washed and dried to obtain aminated mica; 10-15 parts of aminated mica are added to 300-400 parts of toluene and dispersed evenly, 2-3 parts of toluene-2,4-diisocyanate and 1-2 parts of octadecyl isocyanate are added, heated to 70-80°C, stirred for 1-2 hours, filtered, the obtained solid is washed and dried to obtain modified mica; The preparation of the lignin-modified titanium dioxide includes the following steps: alkali lignin is added to an aqueous sodium hydroxide solution, ultrasonically dispersed, and an aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride is added. The mixture is stirred at 80-85°C for 4-6 hours, purified, and freeze-dried to obtain quaternized lignin; the quaternized lignin is added to water and stirred evenly, titanium dioxide is added, the pH is adjusted to 4.5-5, and the mixture is blended and self-assembled for 1-2 hours. The mixture is aged at 40-45°C for 2-3 hours, the solvent is removed, and the mixture is vacuum-dried to obtain lignin-modified titanium dioxide.

2. The method for preparing high-strength weather-resistant polyethylene plastic for plastic pallets according to claim 1, characterized in that: The quaternized lignin comprises the following raw materials, by mass parts: 1-2 parts alkali lignin, 10-15 parts 15-20 wt% sodium hydroxide aqueous solution, and 1-1.5 parts 50-60 wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution. The lignin-modified titanium dioxide comprises the following raw materials, by mass: 5-8 parts quaternized lignin and 2-4 parts titanium dioxide.

3. The polyethylene plastic prepared by the method for preparing high-strength weather-resistant polyethylene plastic for plastic pallets according to any one of claims 1 to 2.

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