Polyethylene powders, their preparation and use, and methods for improving the wear resistance of polyethylene articles

Abstract

The present application relates to a kind of polyethylene powder and its preparation and application, and the method for improving the wear resistance of polyethylene product, the polyethylene powder is prepared using single active catalyst, weight average molecular weight is 200-100 million, molecular weight distribution Mw / Mn≤3.5, thousand carbon short branch chain number SCB is 1-80;At 21.6kg load, 190 ℃, the melt index MI is 0.01-20g / 10min, the entanglement degree C of product prepared by powder preparation is 0.1-0.9 tan More than 10% can be reached. The polyethylene product prepared using the polyethylene powder of the present application is tested by mortar mill, and the average wear rate obtained can be less than 3.0%, which can be applied to fields with certain demand for wear resistance.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and relates to a polyethylene powder, its preparation and application, and a method for improving the wear resistance of polyethylene products. Background Technology

[0002] With the rapid development of science and technology, the engineering community has a certain demand for the wear resistance of materials. Wear-resistant products can improve the service life of products and endow them with superior performance. Currently, the wear resistance of conventional polyethylene materials is relatively poor. In order to enable polyolefin materials to have sufficient wear resistance, a large number of documents and patents have used various methods to enhance the wear resistance of polyethylene materials.

[0003] The most common method in the first category is to use ultra-high molecular weight polyethylene (UHMWPE) instead of polyethylene in the preparation of products. UHMWPE has excellent wear resistance and other superior mechanical properties, but its processing is very difficult due to the high degree of molecular chain entanglement, and conventional polyethylene processing equipment cannot process it. UHMWPE can only be used to prepare wear-resistant sheets through hot pressing. To obtain other profiles, it needs to be blended and modified with HDPE and other additives before further processing, and the processing efficiency is low, as shown in Chinese invention patents CN202011148416.X, CN201811178229.9, and CN111320797B.

[0004] The second type involves crosslinking polyethylene to increase the entanglement of the polyethylene molecular chains and improve its wear resistance. Crosslinking methods can be mainly divided into two forms: adding a crosslinking agent during extrusion and direct crosslinking on the surface of the product, as illustrated by Chinese invention patents CN112770789B and CN113045810B. These methods have certain limitations on the processing technology and the processed products, and require additional blending and crosslinking stages. Surface crosslinking has lower production efficiency and higher overall cost.

[0005] The third type involves adding inorganic nanoparticles to polyethylene to improve the wear resistance of polyethylene products, as illustrated by Chinese invention patents CN113045810B and CN103756088B. This method can improve the wear resistance of materials to some extent, but the added fillers need to undergo compatibility treatment beforehand, resulting in higher costs and potentially affecting the mechanical properties of the final product.

[0006] The fourth category combines the above methods, such as simultaneously incorporating crosslinking agent inorganic particles into the polyethylene, further crosslinking the ultra-high molecular weight polyethylene, or simultaneously incorporating ultra-high molecular weight polyethylene and inorganic fillers into the polyethylene, as exemplified by US Patent US11643511B2, and Chinese Patents CN113980160B, CN102492213B, CN101463156B, and CN101735505B. Products prepared using this method are intended for applications requiring extremely high wear resistance. While the production cost is high and the process is difficult, it yields excellent wear-resistant properties.

[0007] Of the four methods mentioned above for improving the wear resistance of polyethylene, the first method improves the wear resistance of the product by modifying the structure of the polyethylene molecular chain itself. The other three methods involve modifying the polyethylene resin or improving the processing technology to enhance the wear resistance of polyethylene. The improvement in wear resistance of these three types of products depends partly on the effectiveness of the modification and process improvement, and partly on the molecular chain structure of the resin raw material itself. Therefore, obtaining polyethylene resin with inherent wear-resistant properties is crucial for obtaining polyethylene products with excellent wear resistance.

[0008] The first method is to obtain ultra-high molecular weight polyethylene through polymerization. Although the wear resistance of the resulting resin product is greatly improved, the processing performance is greatly restricted. When processing such as extrusion, rotational molding, and blow molding, the resin must first be modified to improve its fluidity, which greatly increases the complexity and cost of product processing. Summary of the Invention

[0009] The purpose of this invention is to provide a polyethylene powder, its preparation and application, in order to solve the problem of insufficient wear resistance of current polyethylene products, especially when polyethylene products are processed by extrusion, rotational molding, blow molding and other means, which have insufficient wear resistance and need to be improved by modification or process improvement before they can be applied to some fields with high wear resistance requirements.

[0010] The objective of this invention can be achieved through the following technical solutions:

[0011] One technical solution of this invention provides a polyethylene powder prepared using a single active catalyst, with a weight-average molecular weight of 200,000 to 1,000,000, a molecular weight distribution Mw / Mn ≤ 3.5, and a short branch number (SCB) of 1-80 per thousand carbon atoms; at a loading of 21.6 kg and a temperature of 190 °C, the melt index (MI) is 0.01-20 g / 10 min. The degree of entanglement (C) of products prepared from this polyethylene powder is... tan It can reach over 10%.

[0012] Furthermore, the single active catalyst is a metallocene catalyst or a transition metal catalyst. Examples include the metallocene catalyst tetramethylcyclopentadiene dichlorozirconia (TMCP), the Schiff base single active center catalyst bis[N-cyclohexyl-(3-tert-butylsalicylaldehyde imino)]zirconia (FI), the ActivCAT catalyst produced by GRACE, and the new generation of post-metallocene catalysts jointly researched and developed by Mitsui Chemicals of Japan and Dow Chemical of the United States.

[0013] The invention team conducted an in-depth analysis of the polyethylene molecular chain structure and discovered a strong correlation between the degree of molecular chain entanglement and the wear resistance of polyethylene. Based on the characterization method for polyethylene entanglement in invention patent ZL201811419650.4, the calculated value of the entanglement degree of the polyethylene product in this invention is set as C. tan The invention team further investigated the entanglement degree C of sheet products prepared from ultra-high molecular weight polyethylene, low molecular weight polyethylene, and the polyethylene structure of this invention. tan The values ​​were analyzed, and the C of the sheet metal products was obtained through calculation and simulation. tan The relationship between the value and molecular weight Mw and the molecular weight distribution Mw / Mw is as follows: Figure 1 As shown in the figure. From the figure, we can see that C... tan The value can be determined by color; when Mw is low, C tan The gradient separation direction is arrow 2, at which point the C of the polyethylene sheet... tan The value is significantly affected by molecular weight, and when the molecular weight is large, C tan The value separation direction gradually shifts towards arrow 1, indicating that the C of the polyethylene sheet... tan The value is significantly affected by molecular weight distribution. Based on these characteristics, the invention team used computer simulations to screen for C... tan The value is comparable to that of 1 million ultra-high molecular weight polyethylene, but the Mw value is lower than 1 million. In this region, the corresponding Mw / Mn characteristics were obtained, and the corresponding polyethylene molecular chain structure type was determined.

[0014] After confirming the polyethylene structure type, the invention team obtained polyethylene powder with the molecular chain structure corresponding to the computer simulation results through laboratory ethylene polymerization, and then processed the powder into corresponding polyethylene products using post-processing technology. Surprisingly, through abrasion resistance testing of various products, C... tan The value has a good correlation with the wear resistance of polyethylene products, and polyethylene powder that can be used to prepare products with better wear resistance was obtained.

[0015] The second technical solution of the present invention provides a method for preparing polyethylene powder, which can be obtained by polymerization in a polyethylene reactor. The reactor is filled with raw materials such as a single active center catalyst, a co-catalyst, ethylene, hydrogen, and comonomer under anhydrous and oxygen-free conditions and nitrogen protection, and the polymerization reaction is carried out at high temperature.

[0016] Furthermore, the reactor is a slurry autoclave reactor, a slurry loop reactor, a gas-phase fluidized bed reactor, or a combination of the above reactors.

[0017] Furthermore, the molecular weight of the polyethylene powder can be controlled by the amount of hydrogen added. Depending on the characteristics of different catalysts, the addition amount ranges from 0 to 100 ppm. It should be noted that when the hydrogen addition amount is 0%, it means that no hydrogen is added; preferably, the hydrogen addition amount is not 0. The number of methyl groups per 1000 carbons can be controlled by the amount of comonomer added. Depending on the characteristics of different catalysts, the addition amount is 0% to 20% of the ethylene content. Similarly, when the comonomer addition amount is 0%, it means that no comonomer is added; preferably, the addition amount is not 0.

[0018] Furthermore, the comonomer can be an α-olefin such as propylene, butene, hexene, or octene.

[0019] Furthermore, the co-catalyst is a catalyst such as triethylaluminum, triisobutylaluminum, or methylaluminoxane. The molar ratio of the co-catalyst to the single-active-site catalyst is 0-300, preferably, the amount of co-catalyst added is not zero.

[0020] Furthermore, as the polymerization temperature increases, the weight-average molecular weight of polyethylene decreases. With increasing hydrogen addition, the weight-average molecular weight of polyethylene decreases significantly.

[0021] The weight-average molecular weight Mw and the number of methyl groups per thousand carbons of the obtained polyethylene powder can be controlled by the amount of hydrogen and comonomer added. The molecular weight distribution value Mw / Mn of the polyethylene powder can be controlled by the selection of catalyst and the type of co-catalyst. When the obtained polyethylene powder reaches the molecular structure parameters of the polyethylene powder in the technical solution of this invention, wear resistance characteristics close to those of ultra-high molecular weight polyethylene can be obtained.

[0022] As the amount of hydrogen added increases, the molecular weight of polyethylene powder will gradually decrease. Lower molecular weight will increase the processing performance of the powder, but will reduce the wear resistance of products processed from polyethylene powder.

[0023] The third technical solution of the present invention provides an application of polyethylene powder, which is processed by hot pressing, extrusion molding, blow molding or rotational molding to prepare wear-resistant products.

[0024] Furthermore, during the hot pressing process, polyethylene powder is first mixed with an antioxidant and then processed at a temperature of 180–200°C for 30–90 minutes.

[0025] Furthermore, during the extrusion molding process, polyethylene powder is first blended with additives including antioxidants, release agents, and lubricants before being melt-processed. The processing temperature of the melt section is 180–240°C.

[0026] Furthermore, during the blow molding process, polyethylene powder is first blended with additives including antioxidants, release agents, and lubricants before processing, and the processing temperature of the molten section is 180–260°C.

[0027] Furthermore, during the rotational molding process, polyethylene powder is first blended with an antioxidant before processing at a temperature of 180–260°C and a hot-pressing time of 30–90 min.

[0028] Furthermore, in the above-mentioned polyethylene powder processing, the amount of each additive such as antioxidant, release agent, and lubricant added is less than 1% of the total mass of polyethylene powder.

[0029] The release agent used in the above-mentioned polyethylene powder processing is one or more of the following compounds: titanate, fluororubber, stearate or aluminate; the antioxidant is one or more of the following: 1010, 168, B215, 1076, 3114, 1135.

[0030] The fourth technical solution of the present invention provides a method for improving the wear resistance of polyethylene products. The method involves processing polyethylene powder through hot pressing, extrusion molding, blow molding, or rotational molding. The polyethylene powder used is prepared using a single active catalyst, with a weight-average molecular weight of 200,000 to 1,000,000, a molecular weight distribution Mw / Mn ≤ 3.5, and a short branch number (SCB) of 1-80 per thousand carbon atoms. Under a load of 21.6 kg and at 190 °C, the melt index (MI) is 0.01-20 g / 10 min.

[0031] This invention obtains polyethylene powder raw material with a suitable molecular chain structure through polymerization. This powder raw material has significantly better wear resistance than traditional polyethylene. It can be directly processed by extrusion, rotational molding, blow molding and other means to obtain polyethylene products with certain wear resistance. It can also obtain polyethylene products with better wear resistance through modification or process improvement. Attached Figure Description

[0032] Figure 1 C is the calculated value of the degree of molecular chain entanglement. tan Relationship with Mw and Mw / Mn values. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0034] In the following embodiments, the metallocene polyethylene catalyst used is the ActivCAT catalyst from GRACE.

[0035] The transition metal polyethylene catalyst was synthesized in the laboratory using the following methods:

[0036] Synthesis of support Mg1:

[0037] Add methanol (n):n(original support Mg(OH)2) = 10:1 to the reaction flask, heat to 100℃, add diisobutyl phthalate (n(diisobutyl phthalate):n(original support Mg(OH)2)) = 1:1, stir at high speed (500 rpm) for 4 hours, and after the reaction is complete, quickly press the resulting mixture into a large amount of -15℃ n-hexane for solidification to obtain a solid.

[0038] The obtained solid was heated to 60°C under a nitrogen protective atmosphere and maintained for 5 hours to obtain the desired support Mg1, with an average particle size of 150 μm and a specific surface area of ​​450 m². 2 / g. Catalyst support: The transition metal titanium complex (with the following structure, 33.6 mg, 50 μmol, 673 g / mol) prepared according to CN 202010061212.6 was dissolved in 10 mL of toluene, and triethylaluminum (0.1 mL, 100 μmol, 1.0 mol / L) was added. The mixture was stirred at room temperature for 30 minutes to obtain the catalyst solution. Mg1 support (1.0 g) was added, and the mixture was stirred at room temperature for 1 hour. The mixture was filtered, washed with toluene, and dried under vacuum to obtain the supported catalyst C1.

[0039] Transition metal titanium complexes:

[0040]

[0041] The characterization data of the polyethylene raw material in the examples were obtained by the following methods:

[0042] Test methods

[0043] The abrasion resistance of polyethylene products was tested using the methods and equipment specified in GB 3960-83.

[0044] The molecular weight and molecular weight distribution of polyethylene powder were tested using the methods and equipment specified in ASTM D6474.

[0045] Unless otherwise specified, all other raw materials or processing techniques are commercially available and conventional in the field.

[0046] Example 1

[0047] Polyethylene polymerization was carried out in a 2L batch reactor. First, the polymerization reactor was purged several times with nitrogen to remove air, followed by several purgings with ethylene. After purging, nitrogen was introduced, and hexane, a transition metal catalyst, and co-catalysts triethylaluminum and methylaluminoxane were introduced into the purged reactor under nitrogen pressure. The amounts of hexane added were 1.5L, catalyst 0.2g, triethylaluminum 0.5g, and methylaluminoxane 0.3g. Ethylene was introduced through the transition metal catalyst, maintaining a set pressure of 0.8MPa. The reactor was stirred and gradually heated using heat transfer oil until it reached 80°C, which was maintained for 2 hours. At the initial stage of the reaction, 1% octene monomer (equivalent to 1% of the molar amount of ethylene) was added. After the reaction, the ethylene gas inlet was shut off, and the product was removed after cooling with cooling water to remove the upper layer of hexane. A polyethylene powder with a weight-average molecular weight of 300,000, Mw / Mn of 2.0, SCB of 1-10 per thousand carbon atoms, and MI of 4.6 g / 10 min was obtained. Polyethylene, antioxidant 1010, zinc stearate, and calcium stearate were added to a mixing tank at a ratio of 99.3%, 0.2%, 0.3%, and 0.2% (all by weight), respectively, and mixed for 3 minutes. The mixture was then fed into a single-screw extruder for polyethylene pipe extrusion. The feeding section temperature and extrusion temperature of the single screw were 60℃ and 190℃, respectively, and the screw speed was 60 rpm. The extruded pipe melt was passed through a water-cooling box and then drawn to obtain polyethylene pipes. The pipe extrusion rate could reach 1-2 m / min.

[0048] The abrasion resistance of polyethylene pipes was tested, C tan The value is 15, and the wear rate is 2.4%.

[0049] Example 2

[0050] Polyethylene polymerization was carried out in a 2L batch reactor. First, the polymerization reactor was purged several times with nitrogen to remove air, followed by several purgings with ethylene. After purging, nitrogen was introduced, and hexane, the post-metallocene catalyst, and the co-catalysts triisobutylaluminum and methylaluminoxane were introduced into the purged reactor under nitrogen pressure. The amounts of hexane added were 1.5L, catalyst 0.2g, triethylaluminum 0.5g, and methylaluminoxane 0.3g. Ethylene was introduced, and the pressure was maintained at 0.9MPa. The reactor was stirred and heated gradually using heat transfer oil until it reached 75°C, which was maintained for 2 hours. At the initial stage of the reaction, 4% butene monomer was added. After the reaction, the ethylene gas inlet was shut off, and the reactor was cooled with cooling water to remove the upper layer of hexane. The product was then collected. A polyethylene powder with a weight-average molecular weight of 500,000, Mw / Mn of 2.6, SCB of 10-30 per thousand carbon atoms, and MI of 1.2 g / 10 min was obtained. Polyethylene, antioxidant 176, fluororubber, and zinc stearate were added to a mixing tank at a ratio of 99.57%, 0.2%, 0.03%, and 0.2% (all by weight), respectively, and mixed for 3 minutes before being fed into a blow molding machine for blow molding. The melt temperature in the blow molding process was 210℃. The extruded melt was then extruded through a die to form hollow parts.

[0051] Abrasion resistance was tested by sampling in the middle space, C tan The value is 27, and the wear rate is 1.2%.

[0052] Example 3

[0053] Polyethylene polymerization was carried out in a 2L batch reactor. First, the polymerization reactor was purged several times with nitrogen to remove air, followed by several purgings with ethylene. After purging, nitrogen was introduced, and hexane, metallocene catalyst, and co-catalysts triethylaluminum and methylaluminoxane were introduced into the purged reactor under nitrogen pressure. The amounts of hexane added were 1.5L, catalyst 0.2g, triethylaluminum 0.5g, and methylaluminoxane 0.3g. Ethylene was introduced, and the pressure was maintained at 1MPa. The reactor was stirred and gradually heated using heat transfer oil. Once the reactor reached 85°C, the reaction was maintained for 2 hours. Propylene monomer (20%) was added at the initial stage of the reaction. After the reaction was completed, the ethylene gas inlet was shut off, and the product was removed after cooling with cooling water to remove the upper layer of hexane. A polyethylene powder with a weight-average molecular weight of 200,000, Mw / Mn of 3.5, SCB of 60-80 per thousand carbon atoms, and MI of 6.1 g / 10 min was obtained. Polyethylene and antioxidant B215 were added to a mixing tank at a ratio of 99.8 wt% and 0.2 wt%, respectively, and mixed for 3 minutes before being fed into a rotational molding machine for rotational molding. The melting temperature of the rotational molding process was 260℃.

[0054] Abrasion resistance tests were conducted on samples of the rotomolded parts.tan The value is 10, and the wear rate is 2.7%.

[0055] Example 4

[0056] Polyethylene polymerization was carried out in a 2L batch reactor. First, the polymerization reactor was purged several times with nitrogen to remove air, followed by several purgings with ethylene. After purging, nitrogen was introduced, and hexane, a transition metal catalyst, and co-catalysts triethylaluminum and methylaluminoxane were introduced into the purged reactor under nitrogen pressure. The amounts of hexane added were 1.5L, catalyst 0.2g, triethylaluminum 0.5g, and methylaluminoxane 0.3g. Ethylene was introduced, and the pressure was maintained at 0.8MPa. The reactor was stirred and heated gradually using heat transfer oil until it reached 83°C, which was then maintained for 2 hours. At the initial stage of the reaction, 8% octene monomer was added. After the reaction was completed, the ethylene gas inlet was shut off, and the product was removed after cooling with cooling water to remove the upper layer of hexane. Polyethylene with a weight-average molecular weight of 1 million, Mw / Mn of 3.0, SCB of 20-30 per thousand carbon atoms, and MI of 0.01 g / 10 min was obtained. Polyethylene and antioxidant 1076 were added to a mixing tank at a ratio of 99.5 wt% and 5 wt% respectively, and mixed for 5 min. The mixture was then placed in a molding die for sheet molding. The molding temperature was 220℃, and the molding time was 60 minutes.

[0057] Abrasion resistance tests were conducted on samples of the molded sheet material, C tan The value is 37, and the wear rate is 0.7%.

[0058] Comparative Example 1

[0059] First, the alumina powder was surface-treated: Ethanol was heated to 60°C in a three-necked flask, and then water and vinyltrimethoxysilane were added sequentially with stirring. The molar ratio of water to coupling agent (vinyltrimethoxysilane) was 3:1. One minute after adding the coupling agent, alumina powder was added, with a mass ratio of coupling agent to alumina powder of 1:100. Stirring continued at 60°C for 30 minutes. Then, the ethanol was distilled off at 60°C, and the powder was dried at 120°C for 1 hour to obtain surface-treated alumina powder for later use. Next, the polyolefin resin was prepared: The components of the system were premixed at high speed for 5 minutes in a high-speed mixer. The mixture was then extruded and granulated in an extruder with an inlet temperature of 60°C and an extrusion temperature of 200°C. The granules were then dried at 80°C for 1 hour and finally ground to obtain the finished powder. The raw material ratio is shown in Table 1, where the melt flow rate of LLDPE is 7.15 g / 10 min, Mw / Mn is greater than 4, and Mw is approximately 150,000. The flow rate of UHMWPE is 0 g / 10 min, Mw / Mn is greater than 4, and Mw is approximately 2.5 million.

[0060]

[0061] The polyethylene modified material obtained in Comparative Example 1 yielded a product with an abrasion rate of 2.9%.

[0062] Comparative Example 2

[0063] A rotational molding grade cross-linked polyethylene wear-resistant composite material, the raw material formulation of which is as follows:

[0064]

[0065]

[0066] First, molybdenum disulfide is surface-treated: a certain amount of coupling agent (i.e., DCP+TAIC) is weighed according to the experimental scheme, and a small amount of ethanol aqueous solution is added to prepare a 20% concentration solution. Inorganic filler (i.e., molybdenum disulfide) is weighed according to the above proportion and placed in a high-speed mixer. While stirring at high speed, the temperature is raised to 60℃, and the coupling agent solution is added dropwise using a dropper. After the addition is complete, high-speed mixing continues for 20 minutes. After mixing, the treated filler is removed and dried in a forced-air drying oven at 120℃ for 1 hour to obtain the surface-treated inorganic filler. Next, the wear-resistant composite material is prepared: linear low-density polyethylene, ultra-high molecular weight polyethylene, crosslinking agent, and co-crosslinking agent are mixed evenly and absorbed at 85℃ for 80–120 minutes. Then, the surface-treated inorganic filler, antioxidant, etc., are added and mixed evenly using a high-speed mixer. The mixture is then extruded and granulated using a twin-screw extruder at 190℃, dried at 80–90℃ for 2 hours, and ground to obtain the finished powder.

[0067] The linear low-density polyethylene used had a melt flow rate of 7.24 g / 10 min and a Mw / Mn ratio greater than 4. Other fillers, crosslinking agents, and antioxidants were all commercially available. The wear rate of LLDPE was 10.48%, and the wear rate after modification was 7.83%.

[0068] Comparative Example 3

[0069] A type of ultra-high molecular weight polyethylene pipe, the pipe comprising the following raw materials in parts by weight: 80 parts ultra-high molecular weight polyethylene (2.5 million, Mw / Mn greater than 4), 5 parts clay, 2 parts carbon black, 0.1 parts stearic acid, 0.1 parts zinc borate, 0.1 parts antistatic agent, and 0.1 parts antioxidant.

[0070] Its preparation method includes the following steps:

[0071] (1) Weigh 80 parts of ultra-high molecular weight polyethylene, 5 parts of clay, 2 parts of carbon black, 0.1 parts of stearic acid, 0.1 parts of zinc borate, 0.1 parts of antistatic agent and 0.1 parts of antioxidant, mix and stir evenly to obtain a mixture, wherein the mixing speed is 35 r / min and the stirring time is 20 min;

[0072] (2) The mixture is fed into an extruder and extruded. The temperatures of each section of the extruder are as follows: Section 1: 90℃, Section 2: 180℃, Section 3: 190℃, Section 4: 200℃. The main machine speed is 45r / min and the extruder pressure is 35MPa.

[0073] (3) Cooling: Cool with water at 70°C to set the shape.

[0074] The wear rate of the pipe obtained in the comparative example was 0.9%, but the pipe extrusion speed was slow, about 1-2 cm / min, while the pipe extrusion rate in the embodiment could reach 1-2 m / min.

[0075] Comparative Example 4

[0076] Polyethylene polymerization was carried out in a 2L batch reactor. First, the polymerization reactor was purged several times with nitrogen to remove air, followed by several purgings with ethylene. After purging, nitrogen was introduced, and hexane, Zn catalyst, and triisobutylaluminum co-catalyst were pressurized into the purged reactor through nitrogen. The amounts of hexane added were 1.5L, catalyst 0.2g, and triethylaluminum 0.8g. Ethylene was introduced, and the pressure was maintained at 0.9MPa. The reactor was stirred and heated gradually using heat transfer oil until it reached 80°C, at which point the reaction was maintained for 2 hours. At the initial stage of the reaction, 4% butene monomer was added. After the reaction was completed, the ethylene gas inlet was shut off, and the reactor was cooled with cooling water to remove the upper layer of hexane. The product was then collected. Polyethylene with a weight-average molecular weight of 3.5 million, Mw / Mn of 5.5, SCB of 20-30 per thousand carbon atoms, and MI of 0 g / 10 min was obtained. Antioxidant 1076 was added to a mixing tank at a ratio of 99.5% to 5% and mixed for 5 minutes. The mixture was then placed in a molding die for sheet molding. The molding temperature was 220℃, and the molding time was 60 minutes.

[0077] Abrasion resistance tests were conducted on samples of the molded sheet material, and the abrasion rate was 1.0%.

[0078] Comparative Example 5

[0079] Polyethylene polymerization was carried out in a 2L batch reactor. First, the polymerization reactor was purged several times with nitrogen to remove air, followed by several purgings with ethylene. After purging, nitrogen was introduced, and hexane, zinc catalyst, and triethylaluminum co-catalyst were then introduced into the purged reactor under nitrogen pressure. The amounts of hexane added were 1.5L, catalyst 0.2g, and triethylaluminum 0.8g. Ethylene was introduced, and the pressure was maintained at 0.8MPa. The reactor was stirred and heated gradually using heat transfer oil. Once the reactor reached 80°C, the reaction was maintained for 2 hours. At the initial stage of the reaction, 1% octene monomer was added. After the reaction was completed, the ethylene gas inlet was shut off, and the product was removed after cooling with cooling water to remove the upper layer of hexane. A polyethylene powder with a weight-average molecular weight of 300,000, Mw / Mn of 6.0, SCB of 1-10 per thousand carbon atoms, and MI of 8.9 g / 10 min was obtained. Polyethylene, antioxidant 1010, zinc stearate, and calcium stearate were added to a mixing tank at a ratio of 99.3%, 0.2%, 0.3%, and 0.2% (all by weight), respectively, and mixed for 3 minutes. The mixture was then fed into a single-screw extruder for polyethylene pipe extrusion. The single screw was set at a feeding section temperature of 60℃ and an extrusion temperature of 190℃, with a rotation speed of 60 rpm. The extruded pipe melt was passed through a water-cooling box and then drawn to obtain polyethylene pipes. The pipe extrusion rate could reach 1-2 m / min.

[0080] The abrasion resistance of polyethylene pipes was tested, C tan The value is 6, and the wear rate is 7.4%.

[0081]

[0082]

[0083] As shown in the table above, this invention, by using polyethylene powder with a suitable molecular structure, can directly process polyethylene products with an abrasion rate of less than 3.0%, while the abrasion rate of commercially available polyethylene in the same molecular weight range is around 10.0%. The abrasion resistance of this invention is far superior to that of commercially available polyethylene. Furthermore, compared to ultra-high molecular weight polyethylene extruded products, this invention has lower processing costs and higher processing efficiency. Compared to ultra-high molecular weight polyethylene sheets, the abrasion resistance of the 1 million molecular weight sheet products of this invention is even slightly better than that of sheet products prepared from traditional ultra-high molecular weight polyethylene with a molecular weight of 3.5 million. Therefore, it is evident that the polyethylene with the specific structure prepared by this invention has superior abrasion resistance compared to similar products currently available.

[0084] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A polyethylene powder, characterized in that, It was prepared using a single active catalyst, with a weight-average molecular weight of 200,000 to 1,000,000, a molecular weight distribution Mw / Mn≤3.5, and a short branch number (SCB) of 1-80 per thousand carbon atoms; at a loading of 21.6 kg and a temperature of 190 °C, the melt index (MI) is 0.01-20 g / 10 min. The single active catalyst is a metallocene catalyst or a transition metal catalyst. The metallocene catalyst used is ActivCAT catalyst from GRACE. The transition metal catalyst was synthesized through the following steps: Synthesis of S1 and Mg1 support: Methanol and the original support Mg(OH)2 were added to a reaction flask at a molar ratio of 10:

1. The temperature was raised to 100°C, and diisobutyl phthalate was added. The molar ratio of diisobutyl phthalate to the original support Mg(OH)2 was 1:

1. The mixture was stirred at a high speed of 500 rpm for 4 hours. After the reaction was completed, the resulting mixture was quickly pressed into a large amount of -15°C n-hexane for solidification to obtain a solid. The obtained solid was heated to 60°C under a nitrogen protective atmosphere and maintained for 5 hours to obtain the desired support Mg1, with an average particle size of 150 μm and a specific surface area of ​​450 m². 2 / g; S2, Catalyst Support: 33.6 mg of the transition metal titanium complex was dissolved in 10 mL of toluene, and 100 mg of triethylaluminum was added. mol, stirred at room temperature for 30 minutes to obtain a catalyst solution; 1.0 g of support Mg1 was added, stirred at room temperature for 1 hour, filtered, washed with toluene, and dried under vacuum to obtain the transition metal catalyst; The chemical structural formula of the transition metal titanium complex is: 。 2. The method for preparing polyethylene powder as described in claim 1, characterized in that, A single-active-center catalyst, a co-catalyst, ethylene, hydrogen, and a comonomer are added to a reactor that is anhydrous, oxygen-free, and filled with inert gas for protection. The polymerization reaction is carried out at high temperature to obtain the target product, polyethylene powder.

3. The method for preparing polyethylene powder as described in claim 2, characterized in that, The amount of hydrogen added is 0-100 ppm; The amount of the comonomer added is 0% to 20% of the molar amount of ethylene; The molar ratio of the co-catalyst to the single-active-center catalyst is 0-300; The comonomer is propylene, butene, hexene, or octene; The co-catalyst is triethylaluminum, triisobutylaluminum, or methylaluminoxane.

4. The application of a polyethylene powder as described in claim 1, characterized in that, The polyethylene powder is processed into wear-resistant products through hot pressing, extrusion molding, blow molding or rotational molding.

5. The application of a polyethylene powder according to claim 4, characterized in that, During the hot pressing process, polyethylene powder is first mixed with an antioxidant and then processed at a temperature of 180~200℃ for 30~90 minutes.

6. The application of a polyethylene powder according to claim 4, characterized in that, During the extrusion molding process, polyethylene powder is first blended with additives including antioxidants, release agents, and lubricants before being melt-processed. The processing temperature of the melt section is 180~240℃.

7. The application of a polyethylene powder according to claim 4, characterized in that, During the blow molding process, polyethylene powder is first blended with additives including antioxidants, release agents, and lubricants before processing. The processing temperature in the molten section is 180~260℃.

8. The application of a polyethylene powder according to claim 4, characterized in that, During rotational molding, polyethylene powder is first mixed with an antioxidant and then processed at a temperature of 180~260℃ and a hot pressing time of 30~90min.

9. A method for improving the abrasion resistance of polyethylene products, characterized in that, The process involves powder processing of polyethylene powder through hot pressing, extrusion molding, blow molding, or rotational molding. The polyethylene powder used is prepared using a single active catalyst, with a weight-average molecular weight of 200,000 to 1,000,000, a molecular weight distribution Mw / Mn ≤ 3.5, and a short branch number (SCB) of 1-80 per thousand carbon atoms. At a loading of 21.6 kg and a temperature of 190 °C, the melt index (MI) is 0.01-20 g / 10 min. The single active catalyst is a metallocene catalyst or a transition metal catalyst. The metallocene catalyst used is ActivCAT catalyst from GRACE. The transition metal catalyst was synthesized through the following steps: Synthesis of S1 and Mg1 support: Methanol and the original support Mg(OH)2 were added to a reaction flask at a molar ratio of 10:

1. The temperature was raised to 100°C, and diisobutyl phthalate was added. The molar ratio of diisobutyl phthalate to the original support Mg(OH)2 was 1:

1. The mixture was stirred at a high speed of 500 rpm for 4 hours. After the reaction was completed, the resulting mixture was quickly pressed into a large amount of -15°C n-hexane for solidification to obtain a solid. The obtained solid was heated to 60°C under a nitrogen protective atmosphere and maintained for 5 hours to obtain the desired support Mg1, with an average particle size of 150 μm and a specific surface area of ​​450 m². 2 / g; S2, Catalyst Support: 33.6 mg of the transition metal titanium complex was dissolved in 10 mL of toluene, and 100 mg of triethylaluminum was added. mol, stirred at room temperature for 30 minutes to obtain a catalyst solution; 1.0 g of support Mg1 was added, stirred at room temperature for 1 hour, filtered, washed with toluene, and dried under vacuum to obtain the transition metal catalyst; The chemical structural formula of the transition metal titanium complex is: 。

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