A PE-XC pipe, its preparation method and application

Abstract

This invention discloses a PE-XC pipe, its preparation method, and its applications, relating to the technical field of polymer materials. A PE-XC pipe comprises the following raw material components by weight percentage: crosslinking agent 1.2-2%; nanofiller 0.5-1.5%; antioxidant 0.6-1%; UV-resistant additive 0.3-0.8%; dynamic vulcanizing agent 0.8-1.5%; the balance being high-density polyethylene. The crosslinking agent includes benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane, and the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is (3-5):(2-4):(1-3). The PE-XC pipe of this invention exhibits excellent high-temperature resistance, impact resistance, and long-term stability.

Description

Technical Field

[0001] This invention relates to the technical field of polymer materials, and in particular to a PE-XC pipe, its preparation method, and its application. Background Technology

[0002] Traditional radiation-crosslinked polyethylene (PE-XC) pipes possess good crosslinking degree and chlorine resistance, but their creep resistance and toughness are insufficient under high-temperature (>120℃) and dynamic impact environments, making them prone to stress cracking. Existing technologies often improve performance by adjusting electron beam radiation or the crosslinking agent ratio, and by introducing a single antioxidant, but these methods struggle to balance high-temperature stability and impact resistance. Furthermore, the crosslinking agent compounding efficiency in traditional processes is limited, and problems such as uneven dispersion and internal pipe defects are easily encountered. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a PE-XC pipe, its preparation method, and its applications. The PE-XC pipe of this invention has excellent high-temperature resistance, impact resistance, and long-term stability.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] In a first aspect, the present invention provides a PE-XC pipe comprising the following raw material components by weight percentage:

[0006] Crosslinking agent 1.2-2%; nanofiller 0.5-1.5%; antioxidant 0.6-1%; UV resistant agent 0.3-0.8%; dynamic vulcanizing agent 0.8-1.5%; balance is high-density polyethylene (HDPE); total weight percentage is 100%.

[0007] The crosslinking agent includes benzoyl peroxide (BPO), dicumyl peroxide (DCP), and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane, and the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is (3-5):(2-4):(1-3).

[0008] In this invention, the three crosslinking agents—BPO, DCP, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane—have different decomposition temperatures. BPO decomposes at 80-100℃, DCP at 120-140℃, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane at 140-150℃. By releasing free radicals in stages, the surface layer of the pipe preferentially crosslinks to form a dense network with high crosslinking density; the core layer subsequently crosslinks to retain toughness with a low crosslinking density, achieving gradient crosslinking. This results in PE-XC pipes exhibiting excellent high-temperature resistance, impact resistance, and long-term stability.

[0009] If the ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane is too high, excessive cross-linking will lead to increased brittleness and a decrease in the thermal stability of the pipe. If the ratio is too low, insufficient cross-linking will result in a decrease in the impact resistance and temperature resistance of the pipe. Therefore, this invention uses benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane in a specific ratio to achieve gradient cross-linking through the staged release of free radicals. This breaks through the efficiency bottleneck of traditional binary compounding and is beneficial to improving the high-temperature resistance, impact resistance, and long-term stability of PE-XC pipes.

[0010] It should be noted that when the pipe thickness is 0.5mm, the thickness ratio of the core layer to the surface layer is (1.5-2.3):1; when the pipe thickness is 0.6mm, the thickness ratio is (1.8-2.3):1; when the pipe thickness is 0.7mm, the thickness ratio is 2.14:1; when the pipe thickness is 0.8mm, the thickness ratio is (1.5-2.0):1; when the pipe thickness is 0.9mm, the thickness ratio is 1.98:1; and when the pipe thickness is ≥1.0mm, the thickness ratio is ≤2.3:1.

[0011] Preferably, the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane is 4:3:(1-2).

[0012] Preferably, the dynamic vulcanizing agent includes at least one of maleic anhydride-grafted polyethylene (PE-g-MAH), maleic anhydride-grafted polypropylene (PP-g-MAH), and epoxy resin-grafted polyethylene (PE-g-EPOXY).

[0013] Preferably, the grafting rate of the maleic anhydride-grafted polyethylene is 1.2-2%.

[0014] If the grafting rate of maleic anhydride-grafted polyethylene exceeds 2.0%, the excessively long grafted chains may lead to molecular chain entanglement, reducing the material's toughness; if the grafting rate is below 1.2%, insufficient interfacial bonding will result. Therefore, this invention, by controlling the grafting rate of maleic anhydride-grafted polyethylene, helps to improve the impact resistance of the pipe.

[0015] More preferably, the grafting rate of the maleic anhydride-grafted polyethylene is 1.5-1.8%, which is beneficial to improving the notched impact strength of the pipe, making the pipe have both rigidity and toughness.

[0016] It should be noted that the grafting rate described in this invention is determined by conventional chemical titration (acid-base titration), which involves hydrolyzing the anhydride groups in the MAH graft chain to generate carboxylic acid, determining the carboxylic acid content by acid-base titration, and then calculating the grafting rate.

[0017] Preferably, the maleic anhydride-grafted polyethylene has a weight-average molecular weight of 100,000-150,000 and a distribution index (PDI) ≤ 2.5, which ensures the uniformity of the grafting reaction. Molecular weight is determined according to ASTM D6474-20, GPC (gel permeation chromatography).

[0018] Distribution Index (PDI): The ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (PDI=Mw / Mn), which characterizes the width of the molecular weight distribution.

[0019] More preferably, the weight-average molecular weight of the maleic anhydride-grafted polyethylene is any one or both of the following: 100,000, 110,000, 120,000, 130,000, 140,000, and 150,000.

[0020] Preferably, the maleic anhydride-grafted polyethylene has a melt index of 5-15 g / 10 min under the test conditions of 190℃ / 2.16 kg, which matches the HDPE matrix and can avoid interface defects caused by differences in melt flowability. The melt index is tested according to ASTM D1238-01.

[0021] More preferably, the melt index of the maleic anhydride-grafted polyethylene under the test conditions of 190°C / 2.16 kg is any one or a combination of 5 g / 10 min, 8 g / 10 min, 10 g / 10 min, 12 g / 10 min, 14 g / 10 min, and 15 g / 10 min.

[0022] Preferably, the maleic anhydride-grafted polypropylene has a grafting rate of 1.2-1.8% and a weight-average molecular weight of 120,000-160,000.

[0023] Preferably, the maleic anhydride-grafted polypropylene has a melt index of 8-15 g / 10 min under the test conditions of 230℃ / 2.16 kg.

[0024] Preferably, the epoxy resin grafted polyethylene has an epoxy value of 0.05-0.12 eq / 100g and a weight-average molecular weight of 100,000-150,000.

[0025] Preferably, the epoxy resin grafted polyethylene has a melt index of 6-10 g / 10 min under the test conditions of 190℃ / 2.16 kg.

[0026] Preferably, the nanofiller comprises nano-montmorillonite and carbon nanotubes, and the weight ratio of the nano-montmorillonite to the carbon nanotubes is (1-3):1.

[0027] Preferably, the nano-montmorillonite has a particle size range of 50-200 nm and a specific surface area of ​​800-1200 m². 2 / g.

[0028] Preferably, the nano-montmorillonite is modified by organic modification, and the steps are as follows: montmorillonite is dispersed in an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) (concentration of 3-5 wt%) and stirred at 70-80°C for 20-24 hours to obtain the modified nano-montmorillonite.

[0029] Nano-montmorillonite can be modified by intercalation of hexadecyltrimethylammonium bromide to optimize the interlayer spacing (2.5-3.5 nm), which is beneficial to improving the dispersibility of nano-montmorillonite.

[0030] Preferably, the carbon nanotubes have a diameter of 10-30 nm, a length of 1-5 μm, and a specific surface area of ​​250-400 m². 2 / g.

[0031] Preferably, the carbon nanotubes are modified by carboxylation, and the steps are as follows: immerse the carbon nanotubes in a mixture of concentrated H2SO4 / HNO3 (volume ratio of 3:1), sonicate for 1-2 hours, reflux at 55-60℃ for 5-6 hours, and then wash and dry to obtain the modified carbon nanotubes.

[0032] This invention improves the interfacial bonding between carbon nanotubes and the matrix by increasing the surface functional group density through carboxylation modification.

[0033] By limiting the size of the nanofiller, this invention can ensure directional distribution and synergistic enhancement effect, and avoid the problem of agglomeration caused by uneven size.

[0034] Preferably, the aspect ratio of the nanofiller is 100-300.

[0035] When the aspect ratio of the nanofiller exceeds 300, the filler is prone to entanglement, leading to uneven dispersion and affecting the mechanical properties of the pipe. When the aspect ratio of the nanofiller is less than 100, the dispersibility is poor, and the reinforcing effect is weak. Therefore, this invention, by controlling the aspect ratio of the nanofiller within the range of 100-300, is beneficial to improving the impact strength of the pipe and can also prevent shear fracture during the pipe processing.

[0036] Preferably, the antioxidant includes antioxidant 1010 and antioxidant DSTDP, and the weight ratio of antioxidant 1010 to antioxidant DSTDP is (3-5):1.

[0037] Preferably, the UV-resistant additives include UV-326 and UV-234, and the weight ratio of UV-326 to UV-234 is (2-4):1.

[0038] Preferably, the high-density polyethylene has a weight-average molecular weight of 180,000-220,000. The molecular weight is determined according to ASTM D6474-20, GPC testing.

[0039] More preferably, the weight-average molecular weight of the high-density polyethylene is any one or a combination of 180,000, 190,000, 200,000, 210,000, and 220,000.

[0040] Preferably, the high-density polyethylene has a melt index of 8-12 g / 10min under test conditions of 190°C / 2.16 kg. The melt index is tested according to ASTM D1238-01.

[0041] More preferably, the melt index of the high-density polyethylene under the test conditions of 190°C / 2.16 kg is any one or a combination of 8 g / 10 min, 9 g / 10 min, 10 g / 10 min, 11 g / 10 min, and 12 g / 10 min.

[0042] Secondly, the present invention also provides a method for preparing PE-XC pipes, comprising the following steps:

[0043] (1) High-density polyethylene, dynamic vulcanizing agent and nanofiller are added to a mixer for dynamic vulcanization to obtain a premix;

[0044] (2) Add crosslinking agent, antioxidant and anti-UV additive to premix and mix evenly to obtain mixture; then melt extrude the mixture in a two-stage screw extruder;

[0045] (3) The PE-XC pipe is obtained by subjecting the extruded pipe in step (2) to two electron beam irradiations with different doses.

[0046] High-density polyethylene (HDPE), a dynamic vulcanizing agent, and nanofillers undergo dynamic vulcanization in a Banbury mixer. After dynamic vulcanization, a "sea-island" two-phase structure is formed. The "island" phase consists of cross-linked maleic anhydride-grafted polyethylene or maleic anhydride-grafted polypropylene, uniformly dispersed within the "sea" phase of the HDPE matrix. Under the high shear force of the Banbury mixer, the dynamic vulcanizing agent initiates in-situ cross-linking, forming micron-sized cross-linked particles (0.1-1 μm in size). The nanofillers are anchored at the "island" phase interface through surface functional groups, inhibiting crack propagation and synergistically improving the impact resistance and temperature resistance of the pipe. After extrusion, the pipe undergoes secondary cross-linking triggered by electron beam radiation, involving the residual cross-linking agent and electron beam-excited free radicals. This forms a gradient cross-linking network, resulting in a dense surface layer and a flexible core, thus solving the brittleness problem caused by uniform cross-linking in traditional processes.

[0047] Preferably, in step (1), the temperature of the internal mixer is 160-180℃, the mixing time is 10-15 min, and the shear force is 5000-10000 s. -1 .

[0048] Preferably, the two-stage screw extruder in step (2) includes a first-stage screw and a second-stage screw, and the length-to-diameter ratio of the first-stage screw and the second-stage screw is (28-30):1, preferably 30:1.

[0049] It should be noted that the length-to-diameter ratio refers to the ratio of the screw's length to its diameter.

[0050] Preferably, the first-stage screw includes a clamping section, a feeding section, a plasticizing section, a vacuum exhaust section, a pressurizing section, and an extrusion section, and the length ratio of the clamping section, feeding section, plasticizing section, vacuum exhaust section, pressurizing section, and extrusion section is 2:6:13:1:2:6.

[0051] Preferably, the second-stage screw includes a clamping section, a feeding section, a plasticizing section, a twin-helix groove compression section, a vacuum exhaust section, a pressurizing section, and an extrusion section, and the length ratio of the clamping section, feeding section, plasticizing section, twin-helix groove compression section, vacuum exhaust section, pressurizing section, and extrusion section is 2:6:11:2:1:2:6.

[0052] The second-order screw of this invention has an additional double-helix groove compression section in the plasticizing section compared to the first-order screw. The compression section has a double-helix groove structure, which can significantly improve the shearing and dispersion efficiency, avoid the agglomeration of nanofillers, and thus improve the dispersibility of nanofillers.

[0053] Preferably, in step (2), the first-order temperature is 160-180℃ and the second-order temperature is 170-190℃.

[0054] Preferably, the dose of the two electron beam radiations in step (3) is 80-180 kGy.

[0055] More preferably, the dose of the first radiation in step (3) is 80-100 kGy, and the dose of the second radiation is 100-180 kGy.

[0056] This invention involves subjecting PE-XC pipe blanks to two different doses of radiation. First, a low-dose radiation is used for pre-crosslinking to form a basic network. Then, a high-dose radiation is used to strengthen the crosslinking, which helps to improve the crystallinity and gives the pipe both high toughness and rigidity.

[0057] Thirdly, the present invention also provides an application of PE-XC pipes in industrial fluid transport systems subjected to extreme temperatures and high impact loads.

[0058] Specifically, the extreme temperature is -50℃ to 150℃; the high impact load is ≥10 MPa instantaneous pressure.

[0059] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0060] 1. This invention uses benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane to form a ternary crosslinking system. Gradient crosslinking is achieved by releasing free radicals in stages, which breaks through the bottleneck of efficiency of traditional binary composites.

[0061] 2. This invention uses electron beam dosage control and dynamic vulcanization process to enable PE-XC pipes to form an "outer rigid and inner tough" structure, thus solving the contradiction between the brittleness and temperature resistance of traditional PE-XC pipes.

[0062] 3. By setting a double-helix groove compression section, the present invention can significantly improve the shear dispersion efficiency, avoid the agglomeration of nanofillers, and improve the dispersibility of nanofillers. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of the structure of the first-order screw and the second-order screw described in this invention, wherein L1 is the clamping section; L2 is the feeding section; L3 is the plasticizing section; L4 is the double spiral groove compression section; L5 is the vacuum exhaust section; L6 is the pressurization section; and L7 is the extrusion section.

[0064] Figure 2 This is a scanning electron microscope image of the core layer of the PE-XC pipe in Embodiment 1 of the present invention.

[0065] Figure 3 This is a scanning electron microscope image of the radial cross-section of the PE-XC pipe in Embodiment 1 of the present invention.

[0066] Figure 4 This is a scanning electron microscope image of the surface layer of the PE-XC pipe in Embodiment 1 of the present invention. Detailed Implementation

[0067] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the scope of protection and implementation of the present invention are not limited thereto.

[0068] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0069] Example 1

[0070] This embodiment discloses a PE-XC pipe, comprising the following raw material components by weight percentage:

[0071] Crosslinking agent 1.8%; nanofiller 1.0%; antioxidant 0.8%; UV resistant agent 0.5%; dynamic vulcanizing agent 1.2%; balance is high-density polyethylene.

[0072] The crosslinking agent includes benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane, and the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is 4:3:2.

[0073] The benzoyl peroxide was purchased from AkzoNobel Perkadox CH-50;

[0074] The dicumyl peroxide was purchased from Arkema Luperox 101;

[0075] The 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane was purchased from United Initiators Trigonox 101.

[0076] The dynamic vulcanizing agent comprises maleic anhydride-grafted polyethylene with a grafting rate of 1.5%; the maleic anhydride-grafted polyethylene is purchased from DuPont Fusabond® E MB-226D, with a weight-average molecular weight of 120,000 and a melt index of 10 g / 10 min.

[0077] The nanofiller includes organically modified montmorillonite nanoparticles and carboxylated carbon nanotubes, and the weight ratio of the organically modified montmorillonite nanoparticles to the carboxylated carbon nanotubes is 1:1.

[0078] The organically modified nano-montmorillonite was purchased from Nanocor I.30E, with a particle size range of 80-120 nm and a specific surface area of ​​900-1100 m². 2 / g;

[0079] The carboxylated carbon nanotubes were purchased from Cheap Tubes COOH-10-20, with a diameter of 10-20 nm, a length of 1-3 μm, and a specific surface area of ​​280-350 m². 2 / g.

[0080] The antioxidants include antioxidant 1010 and antioxidant DSTDP, and the weight ratio of antioxidant 1010 to antioxidant DSTDP is 3:1; antioxidant 1010 is Irganox® 1010, and antioxidant DSTDP is purchased from BASF Irganox® DSTDP.

[0081] The UV-resistant additives include UV-326 and UV-234, and the weight ratio of UV-326 to UV-234 is 2:1. The UV-326 is purchased from BASF Tinuvin® 326; the UV-234 is purchased from BASF Tinuvin® 234.

[0082] The high-density polyethylene was purchased from Dow Chemical (DOW 5502), with a weight-average molecular weight of 200,000 and a melt index of 10 g / 10 min.

[0083] This embodiment discloses a method for preparing PE-XC pipes, including the following steps:

[0084] (1) High-density polyethylene, dynamic vulcanizing agent and nanofiller are added to a mixer for dynamic vulcanization to obtain a premix; wherein the temperature of the mixer is 175℃, the mixing and vulcanization time is 12min, and the shear force is 5000 s. -1 .

[0085] (2) Add crosslinking agent, antioxidant and anti-UV additive to the premix and mix evenly to obtain a mixture; then melt extrude the mixture in a two-stage screw extruder with a first-stage temperature of 170℃, a second-stage temperature of 180℃ and a screw speed of 18r / min.

[0086] (3) The PE-XC pipe is obtained by subjecting the extruded pipe in step (2) to two electron beam irradiations. The dose of the first irradiation is 80 kGy and the dose of the second irradiation is 100 kGy. The irradiation distance is 30 cm, the pipe transmission line speed is 5 m / min, and the total irradiation time is controlled in segments according to the dose: 16 min for the first irradiation of 80 kGy and 20 min for the second irradiation of 100 kGy.

[0087] The two-stage screw extruder of the present invention includes a first-stage screw and a second-stage screw, wherein the length-to-diameter ratio of the first-stage screw is 30:1 and the length-to-diameter ratio of the second-stage screw is 30:1.

[0088] like Figure 1As shown, the first-order screw includes a clamping section L1, a feeding section L2, a plasticizing section L3, a vacuum exhaust section L5, a pressurizing section L6, and an extrusion section L7, and the length ratio of L1, L2, L3, L5, L6, and L7 is 2:6:13:1:2:6.

[0089] The second-stage screw includes a clamping section L1, a feeding section L2, a plasticizing section L3, a double-helix groove compression section L4, a vacuum exhaust section L5, a pressurizing section L6, and an extrusion section L7, and the length ratio of L1, L2, L3, L4, L5, L6, and L7 is 2:6:11:2:1:2:6.

[0090] Example 2

[0091] This embodiment discloses a PE-XC pipe, comprising the following raw material components by weight percentage:

[0092] Crosslinking agent 1.2%; nanofiller 0.5%; antioxidant 0.6%; UV resistant agent 0.3%; dynamic vulcanizing agent 0.8%; balance is high-density polyethylene.

[0093] The crosslinking agent includes benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane, and the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is 4:3:2.

[0094] The benzoyl peroxide was purchased from AkzoNobel Perkadox CH-50;

[0095] The dicumyl peroxide was purchased from Arkema Luperox 101;

[0096] The 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane was purchased from United Initiators Trigonox 101.

[0097] The dynamic vulcanizing agent comprises maleic anhydride-grafted polyethylene with a grafting rate of 2%; the maleic anhydride-grafted polyethylene is purchased from Arkema Orevac® 18302, with a weight-average molecular weight of 140,000 and a melt index of 8 g / 10 min.

[0098] The nanofiller comprises organically modified montmorillonite nanoparticles and carboxylated carbon nanotubes, and the weight ratio of the organically modified montmorillonite nanoparticles to the carboxylated carbon nanotubes is 3:1.

[0099] The organically modified nano-montmorillonite was purchased from Nanocor I.30E, with a particle size range of 80-120 nm and a specific surface area of ​​900-1100 m². 2 / g;

[0100] The carboxylated carbon nanotubes were purchased from Cheap Tubes COOH-10-20, with a diameter of 10-20 nm, a length of 1-3 μm, and a specific surface area of ​​280-350 m². 2 / g.

[0101] The antioxidants include antioxidant 1010 and antioxidant DSTDP, and the weight ratio of antioxidant 1010 to antioxidant DSTDP is 5:1; antioxidant 1010 is Irganox® 1010, and antioxidant DSTDP is purchased from BASF Irganox® DSTDP.

[0102] The UV-resistant additives include UV-326 and UV-234, and the weight ratio of UV-326 to UV-234 is 4:1. UV-326 is purchased from BASF Tinuvin® 326; UV-234 is purchased from BASF Tinuvin® 234.

[0103] The high-density polyethylene was purchased from ExxonMobil HD6704, with a weight-average molecular weight of 180,000 and a melt index of 12 g / 10 min.

[0104] This embodiment discloses a method for preparing PE-XC pipes, including the following steps:

[0105] (1) High-density polyethylene, dynamic vulcanizing agent and nanofiller are added to a mixer for dynamic vulcanization to obtain a premix; wherein the temperature of the mixer is 175℃, the mixing and vulcanization time is 12min, and the shear force is 10000 s. -1 .

[0106] (2) Add crosslinking agent, antioxidant and anti-UV additive to the premix and mix evenly to obtain a mixture; then melt extrude the mixture in a two-stage screw extruder with a first-stage temperature of 170℃, a second-stage temperature of 180℃ and a screw speed of 18r / min.

[0107] (3) The PE-XC pipe is obtained by subjecting the extruded pipe in step (2) to two electron beam irradiations. The dose of the first irradiation is 100 kGy and the dose of the second irradiation is 180 kGy. The irradiation distance is 30 cm, the pipe transmission line speed is 5 m / min, and the total irradiation time is controlled according to the dose segments: 20 min for the first irradiation of 100 kGy and 36 min for the second irradiation of 180 kGy.

[0108] The structure of the two-stage screw extruder is the same as that in Example 1.

[0109] Example 3

[0110] A PE-XC pipe, differing from Example 1 in that the PE-XC pipe comprises the following raw material components by weight percentage:

[0111] Crosslinking agent 2%; nanofiller 1.5%; antioxidant 1%; UV resistant agent 0.8%; dynamic vulcanizing agent 1.5%; balance is high-density polyethylene.

[0112] The dynamic vulcanizing agent comprises maleic anhydride-grafted polypropylene with a grafting rate of 1.6%; the maleic anhydride-grafted polypropylene is purchased from Sanyo Chemical Umex 1010, with a weight-average molecular weight of 140,000 and a melt index of 10 g / 10 min.

[0113] Example 4

[0114] A PE-XC pipe differs from Example 1 in that the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane is 3:4:1.

[0115] Example 5

[0116] A PE-XC pipe differs from Example 1 in that the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane is 5:2:3.

[0117] Example 6

[0118] A PE-XC pipe differs from Example 1 in that the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane is 4:3:1.

[0119] Example 7

[0120] A method for preparing PE-XC pipe differs from Example 1 in that the dose of the first radiation in step (3) is 120 kGy, and the dose of the second radiation is 180 kGy. The radiation distance is 30 cm, the pipe transmission linear velocity is 5 m / min, and the total radiation time is controlled in segments according to the dose: the first radiation of 120 kGy corresponds to 24 min, and the second radiation of 180 kGy corresponds to 36 min.

[0121] Comparative Example 1

[0122] A PE-XC pipe, which differs from Example 1 in that benzoyl peroxide is not added to the crosslinking agent.

[0123] Comparative Example 2

[0124] A PE-XC pipe, which differs from Example 1 in that the crosslinking agent does not contain dicumyl peroxide.

[0125] Comparative Example 3

[0126] A PE-XC pipe, which differs from Example 1 in that the crosslinking agent does not contain 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane.

[0127] Comparative Example 4

[0128] A PE-XC pipe differs from Example 1 in that an equal mass of dicumyl peroxide is used instead of benzoyl peroxide in the crosslinking agent.

[0129] Comparative Example 5

[0130] A PE-XC pipe, which differs from Example 1 in that the crosslinking agent uses an equal mass of dicumyl peroxide (DCPD) instead of dicumyl peroxide (DCP).

[0131] Comparative Example 6

[0132] A PE-XC pipe differs from Example 1 in that the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane is 1:1:4.

[0133] Comparative Example 7

[0134] A PE-XC pipe differs from Example 1 in that the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane is 6:5:1.

[0135] Comparative Example 8

[0136] A PE-XC pipe, differing from Example 1 in that the PE-XC pipe comprises the following raw material components by weight percentage:

[0137] Crosslinking agent 0.8%; nanofiller 1.0%; antioxidant 0.8%; UV resistant agent 0.5%; dynamic vulcanizing agent 1.2%; balance is high-density polyethylene.

[0138] Comparative Example 9

[0139] A PE-XC pipe, differing from Example 1 in that the PE-XC pipe comprises the following raw material components by weight percentage:

[0140] Crosslinking agent 2.5%; nanofiller 1.0%; antioxidant 0.8%; UV resistant agent 0.5%; dynamic vulcanizing agent 1.2%; balance is high-density polyethylene.

[0141] Comparative Example 10

[0142] A method for preparing PE-XC pipes differs from Example 1 in that the extruder in step (2) is different from that in Example 1. In step (2), the mixture is melt-extruded in a single-screw extruder, wherein the barrel temperature in the single-screw extruder is: first section: 160℃, second section: 170℃, third section: 180℃, fourth section: 180℃); and the screw speed is 18r / min.

[0143] Comparative Example 11

[0144] A method for preparing PE-XC pipes differs from Example 1 in that step (3) is different from that in Example 1, the pipes extruded in step (2) are subjected to electron beam irradiation only once to obtain the PE-XC pipes, and the irradiation dose is 80 kGy.

[0145] Performance testing

[0146] I. Characterization Methods for Gradient Crosslinking Structures

[0147] 1. Crosslinking Degree Layering Test Method

[0148] Cut a 0.5 mm thick sheet along the cross-section of the pipe; use micro-cutting technology to separate the surface layer (0-0.2 mm) and the core layer (0.2-0.5 mm); weigh 1 g of each sample for cross-linking degree testing.

[0149] The degree of crosslinking was tested according to ASTM D2765-01 (2006), and the content of insoluble matter was determined by solvent extraction (xylene, boiling for 24 hours).

[0150] 2. Gradient structure morphology characterization

[0151] Scanning electron microscopy (SEM) analysis was performed on the surface layer, radial section, and core layer of the pipe, respectively. Figure 2-4 As can be seen, the surface layer exhibits a dense cross-linked network, while the core layer shows flexible chain segments. This indicates that the present invention uses a compound of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane to achieve gradient cross-linking through the segmented release of free radicals, resulting in PE-XC pipes with excellent high-temperature resistance, impact resistance, and long-term stability.

[0152] 3. Gradient verification of mechanical properties

[0153] The surface and core hardness were determined using a Keysight G200 nanoindenter with a Berkovich diamond indenter and an indentation depth of 500 nm. The hardness was calculated according to ISO 14577-5 standard.

[0154] 2. Heat distortion temperature: Tested according to ASTM D648-18 (0.45 MPa).

[0155] III. Notched impact strength: Tested according to ASTM D256-24 (23℃).

[0156] IV. Chlorine resistance: According to ASTM F2023-21 (95℃ / 1000h) test, the higher the tensile strength retention rate, the better the chlorine resistance of the pipe.

[0157] V. UV resistance: According to ASTM G154-23 (QUV 3000h) test, the smaller the color difference ΔE, the better the UV resistance of the pipe.

[0158] The test results are shown in Table 1.

[0159] Table 1

[0160]

[0161] As shown in Table 1, the present invention uses benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane to achieve gradient crosslinking. Furthermore, by employing dynamic vulcanization and electron beam radiation for secondary crosslinking, a structure with a dense surface layer and a flexible core layer is formed, giving the pipe excellent high-temperature resistance, impact resistance, and long-term stability.

[0162] Comparing Comparative Examples 1-3 with Example 1, it can be seen that Comparative Example 1 did not contain benzoyl peroxide, Comparative Example 2 did not contain dicumyl peroxide, and Comparative Example 3 did not contain 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane. The crosslinking degree of the surface and core layers of the pipes was lower than that of Example 1, and the hardness was also lower than that of Example 1. This indicates that only by using benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane to form a compound and releasing free radicals in stages can gradient crosslinking be achieved, resulting in pipes with excellent high-temperature resistance, impact resistance, and long-term stability.

[0163] Comparing Comparative Example 4 with Example 1, it can be seen that in Comparative Example 4, the impact strength, chlorine resistance, and UV resistance of the pipe are all inferior to those of Example 1 when dicumyl peroxide is used to replace benzoyl peroxide of equal mass. This indicates that the combination of dicumyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane cannot make the pipe have excellent high temperature resistance, impact resistance, and long-term stability at the same time.

[0164] Comparing Comparative Example 5 with Example 1, it can be seen that in Comparative Example 5, dicumyl peroxide was used instead of dicumyl peroxide. The decomposition temperature of dicumyl peroxide is 120-125℃, but because its free radical activity is lower than that of dicumyl peroxide, it cannot form a dense surface network. This affects the high temperature resistance, impact resistance, and long-term stability of the pipe. This shows that it is not possible to use any crosslinking agent combined with benzoyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane to make the pipe have excellent high temperature resistance, impact resistance, and long-term stability.

[0165] Comparing Comparative Examples 6-7 with Example 1, it can be seen that if the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is too large or too small, the high temperature resistance, impact resistance, and long-term stability of the pipe are not as good as those of Example 1. This indicates that by controlling the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane within the range of (3-5):(2-4):(1-3), the present invention is beneficial to improving the high temperature resistance, impact resistance, and long-term stability of the pipe.

[0166] Comparing Comparative Examples 8-9 with Example 1, it can be seen that if the content of crosslinking agent in the PE-XC pipe is too low, the pipe's high temperature resistance, impact resistance, and long-term stability are all inferior to those of Example 1. If the content of crosslinking agent in the PE-XC pipe is too high, although the degree of crosslinking and hardness of the pipe are higher than those of Example 1, the pipe's impact strength, chlorine resistance, and UV resistance are all inferior to those of Example 1. This indicates that only by controlling the content of crosslinking agent in the PE-XC pipe to 1.2-2% can the pipe simultaneously possess excellent high temperature resistance, impact resistance, and long-term stability.

[0167] Comparing Comparative Example 10 with Example 1, it can be seen that the impact strength, chlorine resistance, and UV resistance of the pipe material in Comparative Example 10, which uses a single screw extruder for melt extrusion, are not as good as those in Example 1. This indicates that the present invention uses a two-stage screw extruder for melt extrusion, which is beneficial to improving the dispersibility of nanofillers and thus improving the high temperature resistance, impact resistance, and long-term stability of the pipe material.

[0168] Comparing Comparative Example 11 with Example 1, it can be seen that the pipe extruded in step (2) of Comparative Example 11 was only subjected to electron beam irradiation once, the electron beam irradiation dose was not controlled in layers, the crosslinking network was uniform, and it was impossible to balance the surface hardness and the core toughness. Therefore, by subjecting the PE-XC pipe blank to two irradiations with different doses, the present invention can make the pipe have both high toughness and rigidity.

[0169] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A PE-XC pipe, characterized in that, The raw material components include the following weight percentages: Crosslinking agent 1.2-2%; nanofiller 0.5-1.5%; antioxidant 0.6-1%; UV resistant agent 0.3-0.8%; dynamic vulcanizing agent 0.8-1.5%; balance is high-density polyethylene; The crosslinking agent includes benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane, and the weight ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is (3-5):(2-4):(1-3). The dynamic vulcanizing agent includes at least one of maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, and epoxy resin-grafted polyethylene. The method for preparing the PE-XC pipe includes the following steps: (1) High-density polyethylene, dynamic vulcanizing agent and nanofiller are added to a mixer for dynamic vulcanization to obtain a premix; (2) Add crosslinking agent, antioxidant and anti-UV additive to premix and mix evenly to obtain mixture; then melt extrude the mixture in a two-stage screw extruder; wherein, the second-stage screw in the two-stage screw extruder has a double spiral groove compression section in the plasticizing section compared to the first-stage screw. (3) The PE-XC pipe is obtained by subjecting the extruded pipe in step (2) to two electron beam irradiations with different doses; In step (3), the dose of the first radiation is 80-100 kGy, and the dose of the second radiation is 100-180 kGy.

2. The PE-XC pipe as described in claim 1, characterized in that, The grafting rate of the maleic anhydride-grafted polyethylene is 1.2-2%, and the weight-average molecular weight is 100,000-150,000. And / or, the maleic anhydride-grafted polypropylene has a grafting rate of 1.2-1.8% and a weight-average molecular weight of 120,000-160,000.

3. The PE-XC pipe as described in claim 1, characterized in that, The nanofiller includes nano-montmorillonite and carbon nanotubes, and the weight ratio of nano-montmorillonite to carbon nanotubes is (1-3):

1.

4. The PE-XC pipe as described in claim 1, characterized in that, The antioxidants include antioxidant 1010 and antioxidant DSTDP, and the weight ratio of antioxidant 1010 to antioxidant DSTDP is (3-5):1; And / or, the UV-resistant additives include UV-326 and UV-234, and the weight ratio of UV-326 to UV-234 is (2-4):

1.

5. The PE-XC pipe as described in claim 1, characterized in that, The weight-average molecular weight of the high-density polyethylene is 180,000-220,000. And / or, the melt index of the high-density polyethylene under the test conditions of 190°C / 2.16 kg is 8-12 g / 10 min.

6. The PE-XC pipe as described in claim 1, characterized in that, In step (1), the temperature of the internal mixer is 160-180℃, the mixing time is 10-15 minutes, and the shear force is 5000-10000 s. -1 .

7. The application of a PE-XC pipe as described in any one of claims 1-6 in an industrial fluid transport system under extreme temperatures and high impact loads.

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