PE-XC pipe as well as preparation method and application thereof

Abstract

The invention discloses a PE-XC pipe as well as a preparation method and application thereof, and relates to the technical field of high polymer materials. The PE-XC pipe comprises the following raw material components in percentage by weight: 1.2-2% of a cross-linking agent; 0.5 to 1.5 percent of nano filler; 0.6-1% of an antioxidant; 0.3%-0.8% of an anti-UV auxiliary agent; 0.8-1.5% of a dynamic vulcanizing agent; the balance is high-density polyethylene; the cross-linking agent is prepared from benzoyl peroxide, dicumyl peroxide and 2, 5-dimethyl-2, 5-di (tert-butyl peroxide) hexane, and the weight ratio of the benzoyl peroxide to the dicumyl peroxide to the 2, 5-dimethyl-2, 5-di (tert-butyl peroxide) hexane is (3 to 5) to (2 to 4) to (1 to 3). The PE-XC pipe provided by the invention has excellent high temperature resistance, impact resistance and long-term stability.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and in particular to a PE-XC pipe and a preparation method and application thereof. Background Art

[0002] While traditional radiation-cross-linked polyethylene (PE-XC) pipes offer excellent crosslinking and chlorine resistance, they suffer from insufficient creep resistance and toughness at high temperatures (>120°C) and under dynamic impact, making them susceptible to stress cracking. Existing technologies often improve performance by adjusting electron beam radiation, adjusting the crosslinker ratio, or introducing a single antioxidant, but these efforts struggle to achieve both high-temperature stability and impact resistance. Furthermore, crosslinker compounding in traditional processes is limited in efficiency and prone to problems such as uneven dispersion and internal pipe defects. Summary of the Invention

[0003] The present invention aims to overcome the deficiencies of the prior art and provide a PE-XC pipe and its preparation method and application. The PE-XC pipe of the present invention has excellent high temperature resistance, impact resistance and long-term stability.

[0004] To achieve the above object, the technical solution adopted by the present invention is: In a first aspect, the present invention provides a PE-XC pipe comprising the following raw material components in percentage by weight: Cross-linking agent 1.2-2%; nano filler 0.5-1.5%; antioxidant 0.6-1%; anti-UV additive 0.3-0.8%; dynamic vulcanizer 0.8-1.5%; the balance is high-density polyethylene (HDPE); the total weight percentage is 100%; The cross-linking agent includes benzoyl peroxide (BPO), dicumyl peroxide (DCP), and 2,5-dimethyl-2,5-di(tert-butyl peroxide) hexane, and the weight ratio of the benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide) hexane is (3-5): (2-4): (1-3).

[0005] In the present invention, the three crosslinking agents BPO, DCP, and 2,5-dimethyl-2,5-di(tert-butyl peroxide) hexane have different decomposition temperatures: BPO decomposition temperature is 80-100°C, DCP decomposition temperature is 120-140°C, and 2,5-dimethyl-2,5-di(tert-butyl peroxide) hexane decomposition temperature is 140-150°C. By releasing free radicals in stages, the surface layer of the pipe is preferentially crosslinked to form a dense network with a high crosslinking density; the core layer is subsequently crosslinked to retain toughness and have a low crosslinking density, thereby achieving gradient crosslinking, so that the PE-XC pipe has excellent high temperature resistance, impact resistance, and long-term stability.

[0006] If the blend ratio of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is too high, excessive crosslinking can lead to increased brittleness and reduced thermal stability of the pipe. If the blend ratio is too low, insufficient crosslinking can occur, reducing the pipe's impact resistance and temperature tolerance. Therefore, the present invention utilizes a specific blend of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane to achieve gradient crosslinking through the staged release of free radicals. This overcomes the efficiency bottleneck of traditional binary blends and helps improve the high-temperature resistance, impact resistance, and long-term stability of PE-XC pipes.

[0007] It should be noted that when the thickness of the pipe is 0.5mm, the thickness ratio of the core layer and the surface layer is (1.5-2.3):1; when the thickness of the pipe is 0.6mm, the thickness ratio of the core layer and the surface layer is (1.8-2.3):1; when the thickness of the pipe is 0.7mm, the thickness ratio of the core layer and the surface layer is 2.14:1; when the thickness of the pipe is 0.8mm, the thickness ratio of the core layer and the surface layer is (1.5-2.0):1; when the thickness of the pipe is 0.9mm, the thickness ratio of the core layer and the surface layer is 1.98:1; when the thickness of the pipe is ≥1.0mm, the thickness ratio of the core layer and the surface layer is ≤2.3:1.

[0008] Preferably, the weight ratio of the benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is 4:3:(1-2).

[0009] 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).

[0010] Preferably, the grafting rate of the maleic anhydride grafted polyethylene is 1.2-2%.

[0011] 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 toughness of the material. If the grafting rate of maleic anhydride-grafted polyethylene is less than 1.2%, insufficient interfacial bonding may occur. Therefore, the present invention improves the impact resistance of the pipe by controlling the grafting rate of maleic anhydride-grafted polyethylene.

[0012] 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, so that the pipe has both rigidity and toughness.

[0013] It should be noted that the grafting rate described in the present invention is measured by conventional chemical titration (acid-base titration), that is, the anhydride groups in the MAH graft chain are hydrolyzed to generate carboxylic acid, and the carboxylic acid content is determined by acid-base titration to calculate the grafting rate.

[0014] Preferably, the weight-average molecular weight of the maleic anhydride-grafted polyethylene is 100,000-150,000, and the polydispersity index (PDI) is ≤2.5, which can ensure uniformity of the grafting reaction. The molecular weight is determined by GPC (gel permeation chromatography) according to ASTM D6474-20.

[0015] 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 molecular weight distribution.

[0016] More preferably, the weight average molecular weight of the maleic anhydride grafted polyethylene is in the range of any one or both of 100,000, 110,000, 120,000, 130,000, 140,000 and 150,000.

[0017] Preferably, the maleic anhydride grafted polyethylene has a melt index of 5-15 g / 10 min at 190°C / 2.16 kg, matching the HDPE matrix and avoiding interfacial defects caused by differences in melt fluidity. The melt index is tested according to ASTM D1238-01.

[0018] More preferably, the maleic anhydride grafted polyethylene has a melt index of any one or both 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 under the test conditions of 190° C. / 2.16 kg.

[0019] Preferably, the grafting rate of the maleic anhydride grafted polypropylene is 1.2-1.8%, and the weight average molecular weight is 120,000-160,000.

[0020] Preferably, the maleic anhydride grafted polypropylene has a melt index of 8-15 g / 10 min under the test conditions of 230° C. / 2.16 kg.

[0021] 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.

[0022] Preferably, the epoxy resin grafted polyethylene has a melt index of 6-10 g / 10 min under the test conditions of 190° C. / 2.16 kg.

[0023] 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.

[0024] Preferably, the particle size of the nano-montmorillonite is in the range of 50-200 nm and the specific surface area is in the range of 800-1200 m 2 / g.

[0025] Preferably, the nano-montmorillonite is organically modified by the following steps: dispersing the montmorillonite in an aqueous solution of cetyltrimethylammonium bromide (CTAB) (concentration of 3-5 wt%) and stirring at 70-80°C for 20-24 hours to obtain the modified nano-montmorillonite.

[0026] Nano-montmorillonite is modified by intercalation with hexadecyltrimethylammonium bromide, which can optimize the interlayer spacing (interlayer spacing 2.5-3.5nm), which is beneficial to improving the dispersibility of nano-montmorillonite.

[0027] 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 m 2 / g.

[0028] Preferably, the carbon nanotubes are modified by carboxylation, and the steps are as follows: immersing the carbon nanotubes in a mixture of concentrated H2SO4 / HNO3 (volume ratio of 3:1), ultrasonically treating for 1-2 hours, and refluxing at 55-60°C for 5-6 hours, washing and drying to obtain the modified carbon nanotubes.

[0029] In the present invention, the surface functional group density of the carbon nanotubes is increased after the carbon nanotubes are modified by carboxylation, which is beneficial to strengthening the interface bonding with the substrate.

[0030] The present invention can ensure directional distribution and synergistic enhancement effects by limiting the size of the nanofiller, and avoid the problem of agglomeration caused by uneven size.

[0031] Preferably, the aspect ratio of the nanofiller is 100-300.

[0032] When the aspect ratio of the nanofiller exceeds 300, the filler easily tangles, leading to uneven dispersion and affecting the mechanical properties of the pipe. When the aspect ratio of the nanofiller is less than 100, the dispersion is poor and the reinforcement effect is weak. Therefore, the present invention controls the aspect ratio of the nanofiller within the range of 100-300, which helps improve the impact strength of the pipe and also prevents shear fracture during processing.

[0033] Preferably, the antioxidant includes antioxidant 1010 and antioxidant DSTDP, and the weight ratio of the antioxidant 1010 to the antioxidant DSTDP is (3-5):1.

[0034] Preferably, the anti-UV auxiliary agent includes UV-326 and UV-234, and the weight ratio of UV-326 to UV-234 is (2-4):1.

[0035] Preferably, the weight average molecular weight of the high-density polyethylene is 180,000-220,000, and the molecular weight is measured by GPC according to ASTM D6474-20.

[0036] More preferably, the weight average molecular weight of the high-density polyethylene is in the range of any one or both of 180,000, 190,000, 200,000, 210,000 and 220,000.

[0037] Preferably, the high-density polyethylene has a melt index of 8-12 g / 10 min under the test conditions of 190° C. / 2.16 kg. The melt index is tested according to ASTM D1238-01.

[0038] More preferably, the melt index of the high-density polyethylene under the test conditions of 190°C / 2.16 kg is any one or both of 8g / 10min, 9g / 10min, 10g / 10min, 11g / 10min, and 12g / 10min.

[0039] In a second aspect, the present invention further provides a method for preparing a PE-XC pipe, comprising the following steps: (1) High-density polyethylene, dynamic vulcanizing agent and nanofiller are added into an internal mixer for dynamic vulcanization to obtain a premix; (2) adding a cross-linking agent, an antioxidant, and an anti-UV additive to the premix and mixing them uniformly to obtain a mixture; then, melt-extrude the mixture in a two-stage screw extruder; (3) The pipe extruded in step (2) is subjected to two different doses of electron beam irradiation to obtain the PE-XC pipe.

[0040] High-density polyethylene, a dynamic vulcanizer, and nanofillers are dynamically vulcanized in an internal mixer. This dynamic vulcanization forms a two-phase "sea-island" structure, where 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 forces of the internal mixer, the dynamic vulcanizer triggers in-situ crosslinking, forming micron-sized cross-linked particles (0.1-1μm in size). The nanofillers are anchored to the "island" phase interface via surface functional groups, inhibiting crack propagation and synergistically improving the pipe's impact resistance and temperature resistance. After extrusion, the pipe undergoes electron beam irradiation, triggering a secondary crosslinking between the residual crosslinker and electron-beam-excited free radicals, forming a gradient crosslinked network. This gradient structure, with a dense surface layer and a flexible core layer, addresses the brittleness issue caused by uniform crosslinking in traditional processes.

[0041] Preferably, in step (1), the temperature of the internal mixer is 160-180°C, the mixing time is 10-15 minutes, and the shear force is 5000-10000 s -1 .

[0042] Preferably, the two-stage screw extruder in step (2) comprises a first-stage screw and a second-stage screw, and the aspect ratio of the first-stage screw and the second-stage screw is (28-30):1, preferably 30:1.

[0043] It should be noted that the aspect ratio refers to the ratio of the length to the diameter of the screw.

[0044] 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, the feeding section, the plasticizing section, the vacuum exhaust section, the pressurizing section, and the extrusion section is 2:6:13:1:2:6.

[0045] Preferably, the second-stage screw includes a clamping section, a feeding section, a plasticizing section, a double-helix groove compression section, a vacuum exhaust section, a boosting section, and an extrusion section, and the length ratio of the clamping section, the feeding section, the plasticizing section, the double-helix groove compression section, the vacuum exhaust section, the boosting section, and the extrusion section is 2:6:11:2:1:2:6.

[0046] The second-stage screw of the present invention is provided with a double-helical groove compression section in the plasticizing section compared to the first-stage screw. The compression section has a double-helical groove structure, which can significantly improve the shear dispersion efficiency, avoid the agglomeration of nanofillers, and thus improve the dispersibility of nanofillers.

[0047] Preferably, in step (2), the first-stage temperature is 160-180°C, and the second-stage temperature is 170-190°C.

[0048] Preferably, the dose of the two electron beam irradiations in step (3) is 80-180 kGy.

[0049] 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.

[0050] The present invention subjects the PE-XC tube blank to two different doses of radiation: first, pre-crosslinking is performed through low-dose radiation to form a basic network; then, high-dose radiation is performed to strengthen the crosslinking, which is beneficial to improving the crystallinity and making the tube have both high toughness and rigidity.

[0051] In a third aspect, the present invention further provides an application of a PE-XC pipe in an industrial fluid transportation system subject to extreme temperatures and high impact loads.

[0052] Specifically, the extreme temperature is: -50°C~150°C; the high impact load is: ≥10 MPa instantaneous pressure.

[0053] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention adopts benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide) hexane to form a ternary crosslinking system, and realizes gradient crosslinking by releasing free radicals in sections, breaking through the bottleneck of traditional binary compound efficiency.

[0054] 2. The present invention uses electron beam dosage control and dynamic vulcanization process to make the PE-XC pipe form a "rigid outside and tough inside" structure, solving the contradiction between the brittleness and temperature resistance of traditional PE-XC pipes.

[0055] 3. The present invention can significantly improve the shear dispersion efficiency by providing a double-helical groove compression section, avoid nanofiller agglomeration, and improve the dispersibility of the nanofiller. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a structural schematic diagram of the first-stage screw and the second-stage screw of the present invention, wherein L1 is the clamping section; L2 is the feeding section; L3 is the plasticizing section; L4 is the double-helix groove compression section; L5 is the vacuum exhaust section; L6 is the pressurizing section; and L7 is the extrusion section.

[0057] Figure 2 This is a scanning electron microscope image of the core layer of the PE-XC pipe in Example 1 of the present invention.

[0058] Figure 3 3 is a scanning electron microscope image of a radial cross section of the PE-XC pipe in Example 1 of the present invention.

[0059] Figure 4 This is a scanning electron microscope image of the surface layer of the PE-XC pipe in Example 1 of the present invention. DETAILED DESCRIPTION

[0060] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to specific embodiments, but the protection scope and implementation methods of the present invention are not limited thereto.

[0061] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0062] Example 1 This embodiment discloses a PE-XC pipe, comprising the following raw material components in percentage by weight: Cross-linking agent 1.8%; nano filler 1.0%; antioxidant 0.8%; anti-UV additive 0.5%; dynamic vulcanizer 1.2%; the balance is high-density polyethylene.

[0063] The cross-linking agent includes benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane, and the weight ratio of the benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is 4:3:2.

[0064] The benzoyl peroxide was purchased from AkzoNobel Perkadox CH-50; The dicumyl peroxide was purchased from Arkema Luperox 101; The 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was purchased from United Initiators Trigonox 101.

[0065] The dynamic vulcanizing agent includes maleic anhydride grafted polyethylene with a grafting rate of 1.5%; the maleic anhydride grafted polyethylene is purchased from DuPont Fusabond® E MB-226D, has a weight-average molecular weight of 120,000, and a melt index of 10 g / 10 min.

[0066] The nanofiller comprises organically modified nano-montmorillonite and carboxylated carbon nanotubes, and the weight ratio of the organically modified nano-montmorillonite to the carboxylated carbon nanotubes is 1:1; The organic 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 m 2 / g; 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 m 2 / g.

[0067] The antioxidant includes antioxidant 1010 and antioxidant DSTDP, and the weight ratio of the antioxidant 1010 to the antioxidant DSTDP is 3:1; the antioxidant 1010 is Irganox® 1010, and the antioxidant DSTDP is purchased from BASF Irganox® DSTDP.

[0068] The anti-UV additive includes 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.

[0069] 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.

[0070] This embodiment discloses a method for preparing a PE-XC pipe, comprising the following steps: (1) High-density polyethylene, dynamic vulcanizing agent and nanofiller were added to an internal mixer for dynamic vulcanization to obtain a premix; wherein, the temperature of the internal mixer was 175°C, the internal mixing vulcanization time was 12 minutes, and the shear force was 5000 s -1 .

[0071] (2) Add the crosslinking agent, antioxidant and anti-UV additive to the premix and mix them evenly to obtain a mixture; then melt-extrude the mixture in a two-stage screw extruder with the first stage temperature at 170°C, the second stage temperature at 180°C and the screw speed at 18 r / min.

[0072] (3) The tube extruded in step (2) was subjected to electron beam irradiation twice to obtain the PE-XC tube. The first irradiation dose was 80 kGy, and the second irradiation dose was 100 kGy. The irradiation distance was 30 cm, the tube transmission line speed was 5 m / min, and the total irradiation time was controlled in stages according to the dose: the first irradiation dose of 80 kGy corresponded to 16 minutes, and the second irradiation dose of 100 kGy corresponded to 20 minutes.

[0073] The double-stage screw extruder of the present invention comprises a first-stage screw and a second-stage screw, 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.

[0074] like Figure 1 As shown, the first-stage 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.

[0075] The two-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.

[0076] Example 2 This embodiment discloses a PE-XC pipe, comprising the following raw material components in percentage by weight: Cross-linking agent 1.2%; nano filler 0.5%; antioxidant 0.6%; anti-UV additive 0.3%; dynamic vulcanizer 0.8%; the balance is high-density polyethylene.

[0077] The cross-linking agent includes benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane, and the weight ratio of the benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is 4:3:2.

[0078] The benzoyl peroxide was purchased from AkzoNobel Perkadox CH-50; The dicumyl peroxide was purchased from Arkema Luperox 101; The 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was purchased from United Initiators Trigonox 101.

[0079] The dynamic vulcanizing agent includes maleic anhydride grafted polyethylene with a grafting rate of 2%; the maleic anhydride grafted polyethylene is purchased from Arkema Orevac® 18302, has a weight-average molecular weight of 140,000, and a melt index of 8 g / 10 min.

[0080] The nanofiller comprises organically modified nano-montmorillonite and carboxylated carbon nanotubes, and the weight ratio of the organically modified nano-montmorillonite to the carboxylated carbon nanotubes is 3:1; The organic 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 m 2 / g; 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 m 2 / g.

[0081] The antioxidant includes antioxidant 1010 and antioxidant DSTDP, and the weight ratio of the antioxidant 1010 to the antioxidant DSTDP is 5:1; the antioxidant 1010 is Irganox® 1010, and the antioxidant DSTDP is purchased from BASF Irganox® DSTDP.

[0082] The anti-UV additive includes UV-326 and UV-234, and the weight ratio of UV-326 to UV-234 is 4: 1. The UV-326 is purchased from BASF Tinuvin® 326; the UV-234 is purchased from BASF Tinuvin® 234.

[0083] 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.

[0084] This embodiment discloses a method for preparing a PE-XC pipe, comprising the following steps: (1) High-density polyethylene, dynamic vulcanizing agent and nanofiller were added to an internal mixer for dynamic vulcanization to obtain a premix; wherein, the temperature of the internal mixer was 175°C, the internal mixing vulcanization time was 12 minutes, and the shear force was 10,000 s -1 .

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

[0086] (3) The tube extruded in step (2) was subjected to electron beam irradiation twice to obtain the PE-XC tube. The first irradiation dose was 100 kGy, and the second irradiation dose was 180 kGy. The irradiation distance was 30 cm, the tube transmission line speed was 5 m / min, and the total irradiation time was controlled in stages according to the dose: the first irradiation of 100 kGy corresponded to 20 minutes, and the second irradiation of 180 kGy corresponded to 36 minutes.

[0087] The structure of the double-stage screw extruder is the same as that of Example 1.

[0088] Example 3 A PE-XC pipe, which differs from Example 1 in that the PE-XC pipe comprises the following raw material components in the following weight percentages: Cross-linking agent 2%; nano filler 1.5%; antioxidant 1%; anti-UV additive 0.8%; dynamic vulcanizing agent 1.5%; the balance is high-density polyethylene.

[0089] The dynamic vulcanizing agent includes 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.

[0090] Example 4 A PE-XC pipe is different from Example 1 in that the weight ratio of the benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is 3:4:1.

[0091] Example 5 A PE-XC pipe is different from Example 1 in that the weight ratio of the benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is 5:2:3.

[0092] Example 6 A PE-XC pipe is different from Example 1 in that the weight ratio of the benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is 4:3:1.

[0093] Example 7 A method for preparing a PE-XC pipe differs from Example 1 in that the first radiation dose in step (3) is 120 kGy, and the second radiation dose is 180 kGy. The radiation distance is 30 cm, the pipe transmission line speed is 5 m / min, and the total radiation time is controlled in stages according to the dose: the first radiation dose of 120 kGy corresponds to 24 minutes, and the second radiation dose of 180 kGy corresponds to 36 minutes.

[0094] Comparative Example 1 A PE-XC pipe, which is different from Example 1 in that benzoyl peroxide is not added to the cross-linking agent.

[0095] Comparative Example 2 A PE-XC pipe, which is different from Example 1 in that dicumyl peroxide is not added to the cross-linking agent.

[0096] Comparative Example 3 A PE-XC pipe is different from Example 1 in that 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane is not added to the cross-linking agent.

[0097] Comparative Example 4 A PE-XC pipe, which differs from Example 1 in that an equal mass of dicumyl peroxide is used in the cross-linking agent instead of benzoyl peroxide.

[0098] Comparative Example 5 A PE-XC pipe differs from Example 1 in that an equal mass of dicumyl peroxide (DCPD) is used in the cross-linking agent instead of dicumyl peroxide (DCP).

[0099] Comparative Example 6 A PE-XC pipe is different from Example 1 in that the weight ratio of the benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is 1:1:4.

[0100] Comparative Example 7 A PE-XC pipe is different from Example 1 in that the weight ratio of the benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is 6:5:1.

[0101] Comparative Example 8 A PE-XC pipe, which differs from Example 1 in that the PE-XC pipe comprises the following raw material components in the following weight percentages: Cross-linking agent 0.8%; nano filler 1.0%; antioxidant 0.8%; anti-UV additive 0.5%; dynamic vulcanizer 1.2%; the balance is high-density polyethylene.

[0102] Comparative Example 9 A PE-XC pipe, which differs from Example 1 in that the PE-XC pipe comprises the following raw material components in the following weight percentages: Cross-linking agent 2.5%; nano filler 1.0%; antioxidant 0.8%; anti-UV additive 0.5%; dynamic vulcanizer 1.2%; the balance is high-density polyethylene.

[0103] Comparative Example 10 A method for preparing a PE-XC pipe, which differs from Example 1 in that the extruder in step (2) is different from that in Example 1, that is, in step (2), the mixed material is melt-extruded in a single-screw extruder, wherein the barrel temperature in the single-screw extruder is: first section: 160°C, second section: 170°C, third section: 180°C, fourth section: 180°C); the screw speed is 18 r / min.

[0104] Comparative Example 11 A method for preparing a PE-XC pipe is different from that in Example 1 in that step (3) is different from that in Example 1, the pipe extruded in step (2) is subjected to electron beam irradiation only once to obtain the PE-XC pipe, and the irradiation dose is 80 kGy.

[0105] Performance testing 1. Gradient cross-linking structure characterization method 1. Cross-linking degree layered test method Thin slices with a thickness of 0.5 mm were cut along the cross section of the tube; the surface layer (0-0.2 mm) and the core layer (0.2-0.5 mm) were separated using microdissection technology; and samples (1 g) were weighed for crosslinking degree testing.

[0106] The degree of crosslinking was tested according to ASTM D2765-01 (2006), and the insoluble matter content was determined by solvent extraction (xylene, boiling for 24 h).

[0107] 2. Characterization of gradient structure morphology Scanning electron microscope analysis was performed on the surface, radial section and core layer of the pipe. Figure 2-4 As can be seen in the figure, the surface layer exhibits a dense cross-linked network, while flexible segments are visible in the core layer. This indicates that the present invention utilizes 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.

[0108] 3. Mechanical properties gradient verification The hardness of the surface and core layers was measured using a Keysight G200 nanoindenter with a Berkovich diamond indenter at a penetration depth of 500 nm. The hardness was calculated according to ISO 14577-5.

[0109] 2. Heat Deflection Temperature: Tested in accordance with ASTM D648-18 (0.45 MPa).

[0110] 3. Notched impact strength: tested in accordance with ASTM D256-24 (23°C).

[0111] 4. Chlorine resistance: According to the ASTM F2023-21 (95℃ / 1000h) test, the higher the tensile strength retention rate, the better the chlorine resistance of the pipe.

[0112] 5. Anti-UV performance: According to the ASTM G154-23 (QUV 3000h) test, the smaller the color difference ΔE, the better the UV resistance of the pipe.

[0113] The above test results are shown in Table 1.

[0114] Table 1 As shown in Table 1, the present invention adopts a compound of benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide) hexane to achieve gradient crosslinking. In addition, by adopting a dynamic vulcanization process and electron beam radiation for secondary crosslinking, a structure with a dense surface layer and a flexible core layer is formed, so that the pipe has excellent high temperature resistance, impact resistance and long-term stability.

[0115] By comparing Comparative Examples 1-3 with Example 1, it can be seen that no benzoyl peroxide was added in Comparative Example 1, no dicumyl peroxide was added in Comparative Example 2, and no 2,5-dimethyl-2,5-di(tert-butyl peroxide) hexane was added in Comparative Example 3. The crosslinking degree of the surface layer and the core layer of the pipe were lower than that of Example 1, and the hardness was also lower than that of Example 1. This shows that only by compounding benzoyl peroxide, dicumyl peroxide and 2,5-dimethyl-2,5-di(tert-butyl peroxide) hexane and releasing free radicals in stages can gradient crosslinking be achieved, so that the pipe has excellent high temperature resistance, impact resistance and long-term stability.

[0116] By comparing Comparative Example 4 with Example 1, it can be seen that in Comparative Example 4, when an equal mass of dicumyl peroxide is used to replace benzoyl peroxide, the impact strength, chlorine resistance, and UV resistance of the pipe are not as good as those in Example 1, indicating that the compounding 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.

[0117] By comparing Comparative Example 5 with Example 1, it can be seen that dicumyl peroxide is used instead of dicumyl peroxide in Comparative Example 5. The decomposition temperature of dicumyl peroxide is 120-125°C, but because its free radical activity is lower than that of dicumyl peroxide, it cannot form a dense surface network, so that the high temperature resistance, impact resistance and long-term stability of the pipe are affected. This shows that not all cross-linking agents can be compounded 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.

[0118] By 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 in Example 1. This shows that the present invention is beneficial to improving the high temperature resistance, impact resistance, and long-term stability of the pipe 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).

[0119] Comparison of Comparative Examples 8-9 with Example 1 shows that if the cross-linking agent content in the PE-XC pipe is too low, the high temperature resistance, impact resistance, and long-term stability of the pipe are inferior to those of Example 1. If the cross-linking agent content in the PE-XC pipe is too high, although the cross-linking degree and hardness of the pipe are higher than those of Example 1, the impact strength, chlorine resistance, and UV resistance of the pipe are inferior to those of Example 1. This indicates that only by controlling the cross-linking agent content in the PE-XC pipe to 1.2-2% can the pipe simultaneously have excellent high temperature resistance, impact resistance, and long-term stability.

[0120] By comparing Comparative Example 10 with Example 1, it can be seen that in Comparative Example 10, a single-screw extruder is used for melt extrusion, and the impact strength, chlorine resistance and UV resistance of the pipe are not as good as those in Example 1. This shows that the present invention uses a two-stage screw extruder for melt extrusion, which is beneficial to improving the dispersibility of the nanofiller, thereby improving the high temperature resistance, impact resistance and long-term stability of the pipe.

[0121] Comparison of Comparative Example 11 with Example 1 shows that the extruded pipe in step (2) of Comparative Example 11 was subjected to electron beam irradiation only once, and the electron beam irradiation dose was not controlled in layers, resulting in a uniform cross-linked network and an inability to balance the surface hardness and core toughness. Therefore, the present invention can achieve both high toughness and rigidity by irradiating the PE-XC pipe blank twice at different doses.

[0122] 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 the technical solutions of the present invention may be modified or replaced by equivalents 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: Cross-linking agent 1.2-2%; nano filler 0.5-1.5%; antioxidant 0.6-1%; anti-UV additive 0.3-0.8%; dynamic vulcanizing agent 0.8-1.5%; the balance is high-density polyethylene; The cross-linking agent includes benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane, and the weight ratio of the benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane is (3-5):(2-4):(1-3).

2. The PE-XC pipe according to claim 1, characterized in that: The dynamic vulcanizing agent includes at least one of maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, and epoxy resin grafted polyethylene.

3. The PE-XC pipe according to claim 2, 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 grafting rate of the maleic anhydride grafted polypropylene is 1.2-1.8%, and the weight average molecular weight is 120,000-160,000.

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

1.

5. The PE-XC pipe according to claim 1, characterized in that: The antioxidant includes antioxidant 1010 and antioxidant DSTDP, and the weight ratio of the antioxidant 1010 to the antioxidant DSTDP is (3-5):1; And / or, the anti-UV auxiliary agent includes UV-326 and UV-234, and the weight ratio of UV-326 to UV-234 is (2-4):

1.

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

7. A method for preparing a PE-XC pipe according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) High-density polyethylene, dynamic vulcanizing agent and nanofiller are added into an internal mixer for dynamic vulcanization to obtain a premix; (2) adding a cross-linking agent, an antioxidant, and an anti-UV additive to the premix and mixing them uniformly to obtain a mixture; then, melt-extrude the mixture in a two-stage screw extruder; (3) The pipe extruded in step (2) is subjected to two different doses of electron beam irradiation to obtain the PE-XC pipe.

8. The method for preparing a PE-XC pipe according to claim 7, wherein: In step (1), the temperature of the internal mixer is 160-180°C, the mixing time is 10-15 minutes, and the shear force is 5000-10000 s -1 .

9. The method for preparing a PE-XC pipe according to claim 7, wherein: The dose of the first radiation in step (3) is 80-100 kGy, and the dose of the second radiation is 100-180 kGy.

10. Use of the PE-XC pipe according to any one of claims 1 to 6 in an industrial fluid transportation system subject to extreme temperatures and high impact loads.

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