A high-pitch-resistance, high-density polyethylene pipe and a method for manufacturing the same

Abstract

The application belongs to the technical field of polyethylene pipe materials, and particularly relates to a high-melt-hanging-resistance high-density polyethylene pipe material and a preparation method thereof. The polyethylene pipe material comprises: 80-95 parts by weight of high-density polyethylene resin, and 5-20 parts by weight of directional crystallization nucleating agent. The directional crystallization nucleating agent comprises 85wt%-95wt% one-dimensional nanomaterial and 5wt%-15wt% nano inorganic nucleating agent, based on the total amount of the directional crystallization nucleating agent. The modified polyethylene pipe material has improved zero shear viscosity and melt strength, and can be applied to large-diameter and thick-wall pipe material products.

Description

Technical Field

[0001] This invention belongs to the field of polyethylene pipe technology, and particularly relates to a high-density polyethylene pipe with high anti-sagging properties and its preparation method. Background Technology

[0002] Large-diameter polyethylene (PE) pipes typically refer to solid-walled pipes with an outer diameter (DN) greater than 500 mm. In recent years, due to the excellent comprehensive performance of PE pipes, such as corrosion resistance, good flexibility, and good weldability, large-diameter PE pipes have been applied in various fields, including domestic water supply, nuclear power plant cooling systems, mariculture, seawater desalination projects, seabed waste discharge, transportation of corrosive media or slurries, corrosive soil environments, and the repair of old pipes using the internal lining method.

[0003] During the extrusion of large-diameter pipes, due to the thick pipe wall and slow cooling and solidification rate, the molten material sags under the influence of gravity, resulting in a thinner upper wall and a thicker lower wall, known as the "melt sag effect." This causes the resulting pipe wall to fail to meet the required tolerances, preventing the achievement of satisfactory butt welding. While adjusting the die gap (i.e., increasing the upper gap and decreasing the lower gap) can compensate for this to some extent, the effect is very limited.

[0004] Modifying high-density polyethylene (HDPE) is an effective way to improve its resistance to sag. Commonly used methods include organic / inorganic rigid material filling and composite, physical / chemical crosslinking, and increasing the crystallization rate and crystallinity. However, rigid particle filling and physical / chemical crosslinking significantly reduce the toughness of the material, increasing the brittleness of the processed pipe material and failing to meet the requirements for pipe transportation and use. Therefore, neither of these two technical improvement routes can improve the resistance to sag while ensuring the overall performance of HDPE.

[0005] Improving the crystallization rate and crystallinity of high-density polyethylene (HDPE) during pipe manufacturing allows the tubular polyethylene melt to rapidly crystallize and solidify under cooling water after extrusion, effectively reducing melt sag. Patent document CN 111607145A discloses a polyethylene material and polyethylene pipe. The provided polyethylene material contains cellulose modified with hyperbranched polyester, specifically a hyperbranched polyester containing cage-like polysilsesquioxanes. It also contains carbon black masterbatch, a coupling agent, and HDPE. The polyethylene pipe prepared from this material has advantages such as uniform carbon black dispersion, thicker walls, larger pipe diameter, stable quality, and longer service life. However, this method only involves modifying the anti-sag properties of polyethylene by utilizing the hydrogen bonds between cellulose and carbon black and the shear flowability of the hyperbranched polyester containing cage-like polysilsesquioxanes. The preparation process is cumbersome, costly, and has limited effectiveness in improving anti-sag properties.

[0006] Therefore, it is necessary to develop better methods to prepare high-density polyethylene pipe materials with superior anti-sagging properties. Summary of the Invention

[0007] The purpose of this invention is to address the limitations of existing high-density polyethylene (HDPE) in terms of poor anti-sagging properties and its inability to be used in large-diameter, thick-walled pipe materials. This invention provides a high-sagging-resistant HDPE pipe and its preparation method. The method utilizes the synergistic effect of one-dimensional nanomaterial orientation reinforcement and directional crystallization nucleating agents to modify HDPE for high anti-sagging properties. Compared with unmodified HDPE, the modified polyethylene pipe exhibits improved zero-shear viscosity and melt strength, making it suitable for use in large-diameter, thick-walled pipe materials.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] In the first aspect, a high-density polyethylene pipe with high resistance to sag is provided, comprising the following raw material components in parts by weight:

[0010] High-density polyethylene resin, 80 to 95 parts by weight (e.g., 82 parts by weight, 83 parts by weight, 84 parts by weight, 86 parts by weight, 88 parts by weight, 90 parts by weight, 92 parts by weight, 94 parts by weight), preferably 85 to 90 parts by weight;

[0011] Directional crystallization nucleating agent, 5 to 20 parts by weight (e.g., 6 parts by weight, 8 parts by weight, 10 parts by weight, 12 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 18 parts by weight), preferably 10 to 15 parts by weight;

[0012] The directional crystallization nucleating agent comprises, by total amount, 85 wt% to 95 wt% (e.g., 86 wt%, 88 wt%, 90 wt%, 92 wt%, 94 wt%) of one-dimensional nanomaterials and 5 wt% to 15 wt% (e.g., 6 wt%, 8 wt%, 9 wt%, 10 wt%, 12 wt%, 14 wt%) of nano-inorganic nucleating agent.

[0013] In the aforementioned polyethylene pipe formulation, excessive use of the directional crystallization nucleating agent increases the crystallinity of the material, thereby reducing the pipe's resistance to environmental stress cracking and hydrostatic pressure; insufficient use will not achieve the anti-sagging effect. In the directional crystallization nucleating agent, controlling the ratio of one-dimensional nanomaterials to the inorganic nucleating agent within a suitable range ensures the uniform dispersion of these two nanomaterials in the solvent, thereby improving the bonding uniformity of the nano-inorganic nucleating agent on the one-dimensional nanomaterials.

[0014] In some embodiments of the polyethylene pipe provided by the present invention, the high-density polyethylene resin is a resin powder with low branching degree and an average particle size of 100-200 μm (e.g., 120 μm, 150 μm, 180 μm); the low branching degree here can be understood as having 0.5%-2% (e.g., 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%) of methyl groups per thousand carbons.

[0015] In some embodiments, the high-density polyethylene resin is a copolymer of ethylene and 1-butene as comonomers (1-butene monomer content is 0.5wt% to 1.5wt%, such as 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.3wt%, 1.4wt%), with a molecular weight of 20 × 10⁻⁶. 4 ~35×10 4 g / mol (e.g., 21 × 10⁻⁶ g / mol) 4 g / mol, 22×10 4 g / mol, 24×10 4 g / mol×10 4 g / mol, 25×10 4 g / mol, 28×10 4 g / mol, 30×10 4 g / mol, 32×10 4 g / mol, 34×10 4 The molecular weight distribution index is 17–34 (e.g., 18, 20, 22, 24, 25, 26, 28, 30, 32).

[0016] In some embodiments, the melt index of the high-density polyethylene resin under 21.6 kg conditions is 5 to 12 g / 10 min, for example, 6 g / 10 min, 8 g / 10 min, 10 g / 10 min, or 11 g / 10 min.

[0017] In some embodiments, the high-density polyethylene resin may be selected from one or more of 23050 powder, 23050-S powder, and 4731B powder.

[0018] In some embodiments, the directional crystallization nucleating agent is a product obtained by chemical modification of one-dimensional nanomaterials and nano-inorganic nucleating agents.

[0019] In some embodiments, the one-dimensional nanomaterial in the directional crystallization nucleating agent is selected from at least one of nanocellulose and / or carbon nanotubes; the one-dimensional nanomaterial is dispersed in the directional crystallization nucleating agent with a width of 10-50 nm (e.g., 15 nm, 20 nm, 30 nm, 40 nm) and a length of 0.5-3 μm (e.g., 0.8 μm, 1 μm, 2 μm, 2.5 μm).

[0020] Preferably, the one-dimensional nanomaterial is nanocellulose.

[0021] In some embodiments, the nano-inorganic nucleating agent in the directional crystallization nucleating agent is selected from at least one of nano-silica, nano-titanium dioxide and nano-talc; the particle size of the nano-inorganic nucleating agent dispersed in the directional crystallization nucleating agent is 1-100nm (e.g., 2nm, 5nm, 10nm, 20nm, 40nm, 50nm, 60nm, 80nm).

[0022] Preferably, the nano-inorganic nucleating agent is nano-silica.

[0023] In some embodiments, the method for preparing the directional crystallization nucleating agent includes the following steps:

[0024] i. According to the weight ratio of one-dimensional nanomaterial to nano-inorganic nucleating agent of 5 to 20:1 (e.g., 6:1, 8:1, 10:1, 12:1, 15:1, 18:1), the weight ratio of nanomaterial (i.e., the total weight of one-dimensional nanomaterial and nano-inorganic nucleating agent) to solvent of 1:20 to 50 (e.g., 1:22, 1:25, 1:30, 1:35, 1:40, 1:45), and the weight ratio of nanomaterial (i.e., the total weight of one-dimensional nanomaterial and nano-inorganic nucleating agent) to surface dispersant of 1:0.01 to 0.1 (e.g., 1:0.02, 1:0.04, 1:0.05, 1:0.06, 1:0.08), one-dimensional nanomaterial, nano-inorganic nucleating agent, solvent, and surface dispersant are added to a mixing container and dispersed in an ultrasonic oscillator to obtain a uniform dispersion.

[0025] ii. At 40–70°C (e.g., 45°C, 50°C, 60°C, 65°C), the pH of the obtained uniform dispersion is adjusted to 3.5–5.5 (e.g., 4.0, 4.5, 5.0) by using an aqueous acetic acid solution. Magnetic stirring is added and the mixture is continuously stirred. After adding the silane coupling agent and reacting for 4–6 h (e.g., 4.5 h, 5 h, 5.5 h), the resulting reaction product is filtered.

[0026] iii. The powder obtained after filtration is dried to obtain the desired directional crystallization nucleating agent.

[0027] In some embodiments, in the method for preparing the directional crystallization nucleating agent, the dispersion time in step i in an ultrasonic oscillator can be 30 to 60 minutes (e.g., 40 minutes, 45 minutes, 50 minutes, 55 minutes).

[0028] In some embodiments, the drying process conditions in step iii of the method for preparing the directional crystallization nucleating agent include: drying in a vacuum oven at 70-90°C (e.g., 45°C, 50°C, 60°C, 80°C) for 24-48 hours (e.g., 28 hours, 30 hours, 32 hours, 36 hours, 40 hours, 42 hours, 45 hours).

[0029] In some embodiments, during the preparation of the directional crystallization nucleating agent, the silane coupling agent used is selected from one or more of KH172, KH540, KH550, KH560, KH570 and KH602, and its addition amount is 0.5% to 1.5% of the weight of the nano-inorganic nucleating agent.

[0030] In some embodiments, during the preparation of the directional crystallization nucleating agent, the solvent is selected from deionized water, methanol, or ethanol, preferably deionized water;

[0031] In some embodiments, during the preparation of the directional crystallization nucleating agent, the surface dispersant is selected from at least one of fatty acid glycerides, polyethylene glycol, and ammonium polyacrylate, preferably fatty acid glycerides.

[0032] According to the polyethylene pipe provided by the present invention, in some embodiments, based on the total amount of high-density polyethylene resin and directional crystallization nucleating agent, the high-sag-resistant high-density polyethylene pipe further includes the following raw material components:

[0033] The main antioxidant is present in an amount of 0.01 to 0.025 parts by weight (e.g., 0.015 parts by weight, 0.016 parts by weight, 0.02 parts by weight, or 0.024 parts by weight), preferably 0.012 to 0.018 parts by weight.

[0034] An auxiliary antioxidant, in the form of 0.003 to 0.015 parts by weight (e.g., 0.0035 parts by weight, 0.006 parts by weight, 0.008 parts by weight, 0.01 parts by weight, or 0.014 parts by weight), preferably 0.005 to 0.012 parts by weight.

[0035] Stearate, 0.005 to 0.025 parts by weight (e.g., 0.006 parts by weight, 0.008 parts by weight, 0.01 parts by weight, 0.012 parts by weight, 0.015 parts by weight, 0.02 parts by weight, 0.024 parts by weight), preferably 0.01 to 0.02 parts by weight.

[0036] In some embodiments, the primary antioxidant is a hindered phenolic primary antioxidant, preferably selected from one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenyl)benzene;

[0037] In some embodiments, the auxiliary antioxidant is a phosphite-based auxiliary antioxidant, preferably selected from one or more of tris[2,4-di-tert-butylphenyl] phosphite, tris(nonylphenyl) phosphite, and tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl)-bisphosphate;

[0038] In some embodiments, the stearate is at least one of calcium stearate and zinc stearate.

[0039] In some implementations, the zero-shear viscosity of the high-sag-resistant, high-density polyethylene pipe is 1.2 × 10⁻⁶. 6 Pa·s up to 2.5 × 10 6 Pa·s (e.g., 1.3 × 10⁻⁶) 6 Pa·s, 1.4 × 10 6 Pa·s, 1.5 × 10 6 Pa·s, 1.8 × 10 6 Pa·s, 2.0 × 10 6 Pa·s, 2.2 × 10 6 Pa·s, 2.4 × 10 6 The melt strength is 240 mN to 300 mN (e.g., 245 mN, 250 mN, 260 mN, 280 mN, 290 mN, 295 mN).

[0040] In a second aspect, a method for preparing high-density polyethylene pipe with high anti-sagging properties as described above is provided, comprising the following steps:

[0041] (1) Add each raw material component to a high-speed mixer and mix evenly;

[0042] (2) The uniformly mixed material is added to a twin-screw extruder for mixing, and then extruded and granulated to obtain the high-density polyethylene pipe with high resistance to sag.

[0043] According to the preparation method provided by the present invention, in some embodiments, the process conditions for mixing the raw material components in the high-speed mixer can be conventional choices in the art, and will not be elaborated here.

[0044] In some implementations, the operating and process conditions for mixing and extruding granulation in a twin-screw extruder are conventional choices in the art and will not be elaborated here.

[0045] The high sag resistance of the above-mentioned high-density polyethylene pipe material or the high sag resistance of the high-density polyethylene pipe material prepared by the above-mentioned preparation method is obtained through the synergistic effect of one-dimensional nanomaterial orientation enhancement and directional crystallization nucleating agent. Compared with unmodified high-density polyethylene, its zero-shear viscosity and melt strength can be greatly improved.

[0046] Compared with the prior art, the beneficial effects of the technical solution of the present invention are at least as follows:

[0047] (1) This invention creatively employs the synergistic effect of one-dimensional nanomaterial orientation enhancement and directional crystallization nucleating agent to modify high-density polyethylene for high sag resistance. On the one hand, the directional nucleation effect of the directional crystallization nucleating agent is used to increase the crystallization temperature of the material, enabling the material to crystallize faster at a higher temperature during the cooling process, significantly shortening the molding cycle and thus improving the sag resistance of the material. On the other hand, one-dimensional nanomaterials are used to achieve directional crystallization. During the processing, the one-dimensional nanomaterials with ultra-large aspect ratio are oriented along the melt flow direction. After the melt is extruded from the extruder die, as the temperature decreases, the high-density polyethylene molecular chains undergo heterogeneous nucleation with the nucleating agent attached to the surface of the one-dimensional nanomaterial as the core, so that the crystals in the material are distributed along the melt extrusion direction, and the crystallization distribution direction is perpendicular to the sag direction, thereby further improving the sag resistance of the pipe material.

[0048] (2) The high-density polyethylene pipe with high anti-sag properties of the present invention has excellent comprehensive performance. Compared with unmodified high-density polyethylene, its anti-sag properties are greatly improved, especially its zero-shear viscosity and melt strength. For example, its zero-shear viscosity and melt strength can be increased by more than 340% and 30% respectively, and it can be applied to large-diameter, thick-walled pipe materials. Detailed Implementation

[0049] To provide a detailed understanding of the technical features and content of this invention, preferred embodiments will be described in more detail below. While preferred embodiments are described in the examples, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply.

[0050] In the following embodiments and comparative examples, "parts" refers to parts by weight.

[0051] The source information of the main raw materials in the following embodiments and comparative examples is as follows:

[0052] High-density polyethylene, a copolymer of ethylene and 1-butene as comonomers (1-butene content 0.8wt%), with a weight-average molecular weight of 300,000 g / mol and a molecular weight distribution index of 33; melt index at 21.6 kg is 6.2 g / 10 min; purchased from Wanhua Chemical Group Co., Ltd.

[0053] One-dimensional nanocellulose, with a width of 10-50 nm and a length of 0.5-3 μm, was purchased from Hubei Shineng Chemical Technology Co., Ltd.

[0054] Nano-silica, with a particle size of 30-80nm, was purchased from Shandong Sailike New Materials Co., Ltd.

[0055] Fatty acid glycerides were purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0056] Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] was purchased from Changzhou Xince Polymer Materials Co., Ltd.

[0057] Tris[2,4-di-tert-butylphenyl] phosphite, purchased from Changzhou Xince Polymer Materials Co., Ltd.;

[0058] Calcium stearate was purchased from Changzhou Xince Polymer Materials Co., Ltd.

[0059] Example 1

[0060] The preparation method of the directional crystallization nucleating agent includes the following steps:

[0061] i. According to the weight ratio of one-dimensional nanocellulose to nano silica nucleating agent of 15:1, the weight ratio of nanomaterial to water of 1:50, and the weight ratio of nanomaterial to fatty acid glyceride of 1:0.05, add each raw material into a container and place it in an ultrasonic oscillator for 50 minutes to disperse the nanomaterial evenly.

[0062] ii. Then, the obtained uniformly dispersed nanomaterial dispersion was placed in a water bath at 65°C. The pH of the dispersion was adjusted to about 4.5 by using an aqueous acetic acid solution. After continuous stirring with a magnetic stirrer, silane coupling agent KH550 was added and reacted for 6 hours. The resulting reaction solution was then filtered.

[0063] iii. Finally, the powder obtained by filtration is placed in a vacuum oven at 80°C and dried for 48 hours to obtain the desired directional crystallization nucleating agent.

[0064] The raw materials for high-density polyethylene pipes with high sag resistance include the following components in parts by weight:

[0065] 95 parts high-density polyethylene,

[0066] Five portions of the directional crystallization nucleating agent prepared above,

[0067] 0.012 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]

[0068] 0.005 parts of tris[2,4-di-tert-butylphenyl]phosphite,

[0069] 0.01 parts calcium stearate;

[0070] The preparation method of high-density polyethylene pipe with high resistance to sag is as follows: weigh each raw material component according to the above mass parts and add them to a high-speed mixer and mix them evenly; then add the evenly mixed material to a twin-screw extruder for mixing, extrusion and granulation to obtain high-density polyethylene pipe with high resistance to sag; wherein, the mixing time of each raw material in the high-speed mixer is 15 min, the temperature of the extruder is 220℃, and the screw speed of the extruder is 60 r / min.

[0071] Example 2

[0072] The preparation method of the directional crystallization nucleating agent includes the following steps:

[0073] i. According to the weight ratio of one-dimensional nanocellulose to nano silica nucleating agent of 15:1, the weight ratio of nanomaterial to water of 1:50, and the weight ratio of nanomaterial to fatty acid glyceride of 1:0.05, add each raw material into a container and place it in an ultrasonic oscillator for 50 minutes to disperse the nanomaterial evenly.

[0074] ii. Then, the obtained uniformly dispersed nanomaterial dispersion was placed in a water bath at 65°C. The pH of the dispersion was adjusted to about 4.5 by using an aqueous acetic acid solution. After continuous stirring with a magnetic stirrer, silane coupling agent KH550 was added and reacted for 6 hours. The resulting reaction solution was then filtered.

[0075] iii. Finally, the powder obtained by filtration is placed in a vacuum oven at 80°C and dried for 48 hours to obtain the desired directional crystallization nucleating agent.

[0076] The raw materials for high-density polyethylene pipes with high sag resistance include the following components in parts by weight:

[0077] 90 parts high-density polyethylene,

[0078] 10 portions of the directional crystallization nucleating agent prepared as described above,

[0079] 0.012 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]

[0080] 0.005 parts of tris[2,4-di-tert-butylphenyl]phosphite,

[0081] 0.01 parts calcium stearate;

[0082] The preparation method of high-density polyethylene pipe with high resistance to sag is as follows: weigh each raw material component according to the above mass parts and add them to a high-speed mixer and mix them evenly; then add the evenly mixed material to a twin-screw extruder for mixing, extrusion and granulation to obtain high-density polyethylene pipe with high resistance to sag; wherein, the mixing time of each raw material in the high-speed mixer is 15 min, the temperature of the extruder is 220℃, and the screw speed of the extruder is 60 r / min.

[0083] Example 3

[0084] The preparation method of the directional crystallization nucleating agent includes the following steps:

[0085] i. According to the weight ratio of one-dimensional nanocellulose to nano silica nucleating agent of 15:1, the weight ratio of nanomaterial to water of 1:50, and the weight ratio of nanomaterial to fatty acid glyceride of 1:0.05, add each raw material into a container and place it in an ultrasonic oscillator for 50 minutes to disperse the nanomaterial evenly.

[0086] ii. Then, the obtained uniformly dispersed nanomaterial dispersion was placed in a water bath at 65°C. The pH of the dispersion was adjusted to about 4.5 by using an aqueous acetic acid solution. After continuous stirring with a magnetic stirrer, silane coupling agent KH550 was added and reacted for 6 hours. The resulting reaction solution was then filtered.

[0087] iii. Finally, the powder obtained by filtration is placed in a vacuum oven at 80°C and dried for 48 hours to obtain the desired directional crystallization nucleating agent.

[0088] The raw materials for high-density polyethylene pipes with high sag resistance include the following components in parts by weight:

[0089] 85 parts high-density polyethylene,

[0090] 15 portions of the directional crystallization nucleating agent prepared as described above,

[0091] 0.012 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]

[0092] 0.005 parts of tris[2,4-di-tert-butylphenyl]phosphite,

[0093] 0.01 parts calcium stearate;

[0094] The preparation method of high-density polyethylene pipe with high resistance to sag is as follows: weigh each raw material component according to the above mass parts and add them to a high-speed mixer and mix them evenly; then add the evenly mixed material to a twin-screw extruder for mixing, extrusion and granulation to obtain high-density polyethylene pipe with high resistance to sag; wherein, the mixing time of each raw material in the high-speed mixer is 15 min, the temperature of the extruder is 220℃, and the screw speed of the extruder is 60 r / min.

[0095] Example 4

[0096] The preparation method of the directional crystallization nucleating agent includes the following steps:

[0097] i. According to the weight ratio of one-dimensional nanocellulose to nano silica nucleating agent of 15:1, the weight ratio of nanomaterial to water of 1:50, and the weight ratio of nanomaterial to fatty acid glyceride of 1:0.05, add each raw material into a container and place it in an ultrasonic oscillator for 50 minutes to disperse the nanomaterial evenly.

[0098] ii. Then, the obtained uniformly dispersed nanomaterial dispersion was placed in a water bath at 65°C. The pH of the dispersion was adjusted to about 4.5 by using an aqueous acetic acid solution. After continuous stirring with a magnetic stirrer, silane coupling agent KH550 was added and reacted for 6 hours. The resulting reaction solution was then filtered.

[0099] iii. Finally, the powder obtained by filtration is placed in a vacuum oven at 80°C and dried for 48 hours to obtain the desired directional crystallization nucleating agent.

[0100] The raw materials for high-density polyethylene pipes with high sag resistance include the following components in parts by weight:

[0101] 80 parts high-density polyethylene,

[0102] 20 portions of the directional crystallization nucleating agent prepared as described above,

[0103] 0.012 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]

[0104] 0.005 parts of tris[2,4-di-tert-butylphenyl]phosphite,

[0105] 0.01 parts calcium stearate;

[0106] The preparation method of high-density polyethylene pipe with high resistance to sag is as follows: weigh each raw material component according to the above mass parts and add them to a high-speed mixer and mix them evenly; then add the evenly mixed material to a twin-screw extruder for mixing, extrusion and granulation to obtain high-density polyethylene pipe with high resistance to sag; wherein, the mixing time of each raw material in the high-speed mixer is 15 min, the temperature of the extruder is 220℃, and the screw speed of the extruder is 60 r / min.

[0107] Example 5

[0108] The preparation method of the directional crystallization nucleating agent is the same as in Example 3, except that the weight ratio of one-dimensional nanocellulose to nanosilica nucleating agent in step i is 5:1, and the remaining steps are the same as in Example 3.

[0109] The raw material formulation for high-density polyethylene pipes with high anti-sagging properties is the same as that in Example 3.

[0110] The preparation method of high-density polyethylene pipe with high anti-sagging properties is the same as in Example 3.

[0111] Example 6

[0112] The preparation method of the directional crystallization nucleating agent is the same as in Example 3, except that the weight ratio of one-dimensional nanocellulose to nanosilica nucleating agent in step i is 20:1, and the remaining steps are the same as in Example 3.

[0113] The raw material formulation for high-density polyethylene pipes with high anti-sagging properties is the same as that in Example 3.

[0114] The preparation method of high-density polyethylene pipe with high anti-sagging properties is the same as in Example 3.

[0115] Example 7:

[0116] The preparation method of the directional crystallization nucleating agent is the same as in Example 3, except that: the temperature of the water bath in step ii is 55°C, and the pH of the dispersion is adjusted to about 5.0 by using an aqueous acetic acid solution; the remaining steps are the same as in Example 3.

[0117] The raw material formulation for high-density polyethylene pipes with high anti-sagging properties is the same as that in Example 3.

[0118] The preparation method of high-density polyethylene pipe with high anti-sagging properties is the same as in Example 3.

[0119] Comparative Example 1

[0120] The raw materials for polyethylene pipes include the following components in parts by weight:

[0121] 90 parts high-density polyethylene,

[0122] 0.012 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]

[0123] 0.005 parts of tris[2,4-di-tert-butylphenyl]phosphite,

[0124] 0.01 parts calcium stearate.

[0125] The preparation method of polyethylene pipe is as follows: weigh each raw material component according to the above mass parts and add them to a high-speed mixer and mix them evenly; then add the evenly mixed material to a twin-screw extruder for mixing, extrusion and granulation to obtain high-density polyethylene composite material; wherein, the mixing time of each raw material in the high-speed mixer is 15 min, the temperature of the extruder is 220℃, and the screw speed of the extruder is 60 r / min.

[0126] Comparative Example 2 (nucleating agent without one-dimensional nanomaterial modification)

[0127] The raw materials for polyethylene pipes include the following components in parts by weight:

[0128] 95 parts high-density polyethylene,

[0129] 5 parts of nano-silica nucleating agent,

[0130] 0.012 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]

[0131] 0.005 parts of tris[2,4-di-tert-butylphenyl]phosphite,

[0132] 0.01 parts calcium stearate.

[0133] The preparation method of polyethylene pipe is as follows: weigh each raw material component according to the above mass parts and add them to a high-speed mixer and mix them evenly; then add the evenly mixed material to a twin-screw extruder for mixing, extrusion and granulation to obtain high-density polyethylene pipe; wherein, the mixing time of each raw material in the high-speed mixer is 15 min, the temperature of the extruder is 220℃, and the screw speed of the extruder is 60 r / min.

[0134] Comparative Example 3

[0135] The preparation method of the directional crystallization nucleating agent includes the following steps:

[0136] i. According to the weight ratio of one-dimensional nanocellulose to nano silica nucleating agent of 4:1, the weight ratio of nanomaterial to water of 1:50, and the weight ratio of nanomaterial to fatty acid glyceride of 1:0.05, add each raw material into a container and place it in an ultrasonic oscillator for 50 minutes to disperse the nanomaterial evenly.

[0137] ii. Then, the obtained uniformly dispersed nanomaterial dispersion was placed in a water bath at 65°C. The pH of the dispersion was adjusted to about 4.5 by using an aqueous acetic acid solution. After continuous stirring with a magnetic stirrer, silane coupling agent KH550 was added and reacted for 6 hours. The resulting reaction solution was then filtered.

[0138] iii. Finally, the powder obtained by filtration is placed in a vacuum oven at 80°C and dried for 48 hours to obtain the desired directional crystallization nucleating agent.

[0139] The raw materials for polyethylene pipes include the following components in parts by weight:

[0140] 95 parts high-density polyethylene,

[0141] Five portions of the directional crystallization nucleating agent prepared above,

[0142] 0.012 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]

[0143] 0.005 parts of tris[2,4-di-tert-butylphenyl]phosphite,

[0144] 0.01 parts calcium stearate.

[0145] The preparation method of polyethylene pipe is as follows: weigh each raw material component according to the above mass parts and add them to a high-speed mixer and mix them evenly; then add the evenly mixed material to a twin-screw extruder for mixing, extrusion and granulation to obtain high-density polyethylene pipe with high resistance to sag; wherein, the mixing time of each raw material in the high-speed mixer is 15 min, the temperature of the extruder is 220℃, and the screw speed of the extruder is 60 r / min.

[0146] Performance testing:

[0147] The polyethylene pipes prepared in Examples 1-7 and Comparative Examples 1-3 were subjected to performance tests according to the following methods:

[0148] (1) Crystallinity, crystallization temperature, melting temperature, and semi-crystallization time shall be tested in accordance with the requirements of GB / T 19466;

[0149] (2) The prepared polyethylene pipe was made into a strip, and the tensile strength and elongation at break were tested according to the method of GB / T1040-92.

[0150] The flexural modulus was tested according to the method in GB / T 1449-2005.

[0151] The notched impact strength of simply supported beams was tested according to the requirements of the national standard GB / T 1043.1-2008 Impact Test Method.

[0152] Melt strength testing shall be conducted in accordance with the method of GB / T 2951.41-2008;

[0153] Zero-shear viscosity was tested according to GB / T 21989-2008.

[0154] The specific test results are shown in Tables 1 and 2.

[0155] Table 1 Performance test results of Examples 1-4 and Comparative Examples 1-3

[0156]

[0157]

[0158] Table 2 Performance test results of Examples 5-7

[0159] Test Project Example 5 Example 6 Example 7 Semi-crystallization time (min) 15.33 12.66 13.64 Zero-shear viscosity (Pa·s) 1417232 1638736 1593753 Melt strength (mN) 231.7 268.4 252.2 Crystallization temperature (°C) 115.94 117.02 116.93 Melting temperature (°C) 128.39 128.36 128.03 Crystallinity (%) 56.62 60.17 60.76 Tensile strength (MPa) 21.8 22.9 22.6 Elongation at break (%) 513 605 595 Flexural modulus (MPa) 1175 1211 1103 <![CDATA[Notched impact strength of simply supported beam at room temperature (kJ / m 2 )]]> 20.21 26.28 25.42

[0160] As can be seen from the test data of Examples 1-4 and Comparative Examples 1-3 in Table 1, compared with Comparative Example 1 without the addition of a directional nucleating agent, the comprehensive performance of the high-density polyethylene pipes with high anti-sagging properties prepared in Examples 1-4 gradually improves with the increase of the amount of directional nucleating agent added. In particular, the improvement in zero-shear viscosity, melt strength and semi-crystallization time is obvious. This is because the directional nucleation effect of the directional nucleating agent increases the crystallization temperature of the pipe material, enabling the material to crystallize faster at a higher temperature during the cooling process, significantly shortening the molding cycle and thus improving the anti-sagging properties of the pipe material. One-dimensional nanomaterials achieve directional crystallization of the pipe. During the processing, the one-dimensional nanomaterials with ultra-large aspect ratio are oriented along the melt flow direction. After the melt is extruded from the extruder die, as the temperature decreases, the high-density polyethylene molecular chains undergo heterogeneous nucleation with the nucleating agent attached to the surface of the one-dimensional nanomaterial as the core, so that the crystals in the material are distributed along the melt extrusion direction, and the crystal distribution direction is perpendicular to the sagging direction, thereby further improving the anti-sagging properties of the material. Comparative Example 2 lacked directional nucleation, while Comparative Example 3 suffered from weakened directional nucleation due to an unsuitable ratio of one-dimensional nanomaterials to nano-inorganic nucleating agents. Consequently, the anti-sagging properties of these two groups of samples were not significantly improved.

[0161] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the spirit of the invention.

Claims

1. A high-density polyethylene pipe with high resistance to sag, characterized in that, It includes the following raw material components in parts as follows: High-density polyethylene resin, 80-95 parts by weight, preferably 85-90 parts by weight; Directional crystallization nucleating agent, 5-20 parts by weight, preferably 10-15 parts by weight; The directional crystallization nucleating agent comprises 85wt% to 95wt% of one-dimensional nanomaterials and 5wt% to 15wt% of nano-inorganic nucleating agent, based on the total amount of the directional crystallization nucleating agent.

2. The polyethylene pipe according to claim 1, characterized in that, The high-density polyethylene resin is a resin powder with low branching degree and an average particle size of 100-200 μm. Preferably, the high-density polyethylene resin is a copolymer of ethylene and 1-butene as comonomers, with a molecular weight of 20 × 10⁻⁶. 4 ~35×10 4 g / mol, with a molecular weight distribution index of 17–34; Preferably, the melt index of the high-density polyethylene resin under 21.6 kg conditions is 5-12 g / 10 min.

3. The polyethylene pipe according to claim 1 or 2, characterized in that, The directional crystallization nucleating agent is a product obtained by chemical modification of one-dimensional nanomaterials and nano-inorganic nucleating agents.

4. The polyethylene pipe according to any one of claims 1-3, characterized in that, In the directional crystallization nucleating agent, the one-dimensional nanomaterial is selected from at least one of nanocellulose and / or carbon nanotubes; the one-dimensional nanomaterial is dispersed in the directional crystallization nucleating agent with a width of 10-50 nm and a length of 0.5-3 μm; Preferably, the one-dimensional nanomaterial is nanocellulose.

5. The polyethylene pipe according to any one of claims 1-4, characterized in that, In the directional crystallization nucleating agent, the nano-inorganic nucleating agent is selected from at least one of nano-silica, nano-titanium dioxide and nano-talc; the particle size of the nano-inorganic nucleating agent dispersed in the directional crystallization nucleating agent is 1-100 nm; Preferably, the nano-inorganic nucleating agent is nano-silica.

6. The polyethylene pipe according to any one of claims 1-5, characterized in that, The method for preparing the directional crystallization nucleating agent includes the following steps: i. According to the weight ratio of one-dimensional nanomaterial to nano-inorganic nucleating agent of 5 to 20:1, the weight ratio of nanomaterial to solvent of 1:20 to 50, and the weight ratio of nanomaterial to surface dispersant of 1:0.01 to 0.1, add one-dimensional nanomaterial, nano-inorganic nucleating agent, solvent and surface dispersant into a mixing container and disperse in an ultrasonic oscillator to obtain a uniform dispersion. ii. At 40-70℃, adjust the pH of the obtained uniform dispersion to 3.5-5.5 with acetic acid aqueous solution, add magnetic stirrer and stir continuously, add silane coupling agent and react for 4-6 hours, then filter the obtained reaction product. iii. The powder obtained after filtration is dried to obtain the desired directional crystallization nucleating agent.

7. The polyethylene pipe according to claim 6, characterized in that, In the preparation of the directional crystallization nucleating agent, the silane coupling agent used is selected from one or more of KH172, KH540, KH550, KH560, KH570 and KH602, and its addition amount is 0.5% to 1.5% of the weight of the nano-inorganic nucleating agent. The solvent is selected from deionized water, methanol, or ethanol, preferably deionized water; The surface dispersant is selected from at least one of fatty acid glycerides, polyethylene glycol, and ammonium polyacrylate, preferably fatty acid glycerides.

8. The polyethylene pipe according to any one of claims 1-7, characterized in that, The high-density polyethylene pipe with high resistance to sag also includes the following raw material components: The main antioxidant, 0.01 to 0.025 parts by weight, preferably 0.012 to 0.018 parts by weight, An auxiliary antioxidant, 0.003 to 0.015 parts by weight, preferably 0.005 to 0.012 parts by weight. Stearate, 0.005 to 0.025 parts by weight, preferably 0.01 to 0.02 parts by weight; Preferably, the primary antioxidant is a hindered phenolic primary antioxidant, preferably selected from one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenyl)benzene; Preferably, the auxiliary antioxidant is a phosphite-based auxiliary antioxidant, preferably selected from one or more of tris[2,4-di-tert-butylphenyl] phosphite, tris(nonylphenyl) phosphite, and tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl)-bisphosphate; Preferably, the stearate is at least one of calcium stearate and zinc stearate.

9. The polyethylene pipe according to any one of claims 1-8, characterized in that, The high-density polyethylene pipe with high anti-sagging properties has a zero-shear viscosity of 1.2 × 10⁻⁶. 6 Pa·s up to 2.5 × 10 6 Pa·s, melt strength of 240 mN to 300 mN.

10. A method for preparing high-density polyethylene pipe with high anti-sagging properties as described in any one of claims 1-9, comprising the following steps: (1) Add each raw material component to a high-speed mixer and mix evenly; (2) The uniformly mixed material is added to a twin-screw extruder for mixing, and then extruded and granulated to obtain the high-density polyethylene pipe with high resistance to sag.

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