HDPE cable protection pipe for high-voltage cable buried laying and preparation method thereof

Abstract

The application discloses HDPE cable protection pipe for high-voltage cable buried laying and a preparation method thereof, belongs to the technical field of cable protection pipes, and aims to solve the technical problem that the ring stiffness, tensile strength, longitudinal shrinkage performance and notched impact performance of the HDPE cable protection pipe under low-temperature and thermal aging environment need to be further improved in the prior art. Specifically, the HDPE cable protection pipe comprises the following components in parts by weight: 70-80 parts of HDPE, 25-35 parts of toughening elastomer, 8-12 parts of a compatilizer and 2-3 parts of an additive. The toughening elastomer and HDPE-g-MA are used to enhance the HDPE, so that the ring stiffness and tensile strength of the HDPE cable protection pipe sample are improved, the longitudinal shrinkage rate is reduced, and the notched impact performance retention rate of the HDPE cable protection pipe sample after low-temperature and thermal aging is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of cable protection pipe technology, specifically to an HDPE cable protection pipe for underground laying of high-voltage cables and its preparation method. Background Technology

[0002] In high-voltage cable burial projects, cable protection pipes are used to provide mechanical protection for cables, isolate them from external soil / groundwater erosion, and facilitate cable threading and maintenance. They are subjected to complex service environments such as backfill soil compression, vehicle dynamic loads, uneven foundation settlement, and temperature cycling. Therefore, the protection pipes are usually required to have high ring stiffness and load-bearing stability, sufficient tensile strength and crack resistance, good low-temperature impact resistance, and the ability to maintain toughness after long-term thermo-oxidative aging. High-density polyethylene (HDPE) is widely used in the field of cable protection pipes due to its advantages such as corrosion resistance, light weight, convenient construction, and moderate cost.

[0003] However, HDPE pipes exhibit longitudinal shrinkage and dimensional fluctuations under temperature changes or long-term loads, affecting connection sealing and laying reliability. At the same time, HDPE's toughness decreases and notch sensitivity increases under low-temperature conditions, making it more prone to brittle fracture when subjected to external impacts or stress concentrations. Furthermore, under higher temperature and oxygen diffusion conditions, HDPE undergoes thermo-oxidative aging, resulting in chain breakage, changes in crystallinity, and microcrack initiation, leading to a decline in mechanical properties, especially impact toughness, over service time.

[0004] Currently, the common methods used are filler reinforcement and toughening modification, such as adding inorganic fillers such as talc and calcium carbonate or fiber reinforcement materials such as glass fiber and carbon fiber to improve ring stiffness and strength, adding elastomers such as POE, EVA, and EPDM or silicone oil-based flexible components to improve impact toughness, and using compatibilizers such as maleic anhydride-grafted polyethylene to enhance interphase adhesion.

[0005] However, the large difference in polarity between inorganic fillers or fibers and the HDPE matrix makes it easy for uneven dispersion, agglomeration, interface debonding, and pore defects to occur, resulting in insufficient stress transfer efficiency and crack formation. While improving impact performance, toughening components often reduce material stiffness and creep resistance, making it difficult to achieve both high ring stiffness and high toughness. Some low-molecular-weight toughening / lubricating components may also migrate, ooze, or weaken the interface under long-term thermal aging or load, causing continuous toughness decay.

[0006] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide an HDPE cable protection pipe for underground laying of high-voltage cables and its preparation method, in order to solve the technical problems that the ring stiffness, tensile strength, longitudinal shrinkage performance and notched impact performance of HDPE cable protection pipes in low temperature and thermal aging environments need to be further improved in the prior art.

[0008] The objective of this invention can be achieved through the following technical solution: an HDPE cable protection pipe for underground laying of high-voltage cables, comprising the following components by weight: 70-80 parts HDPE, 25-35 parts toughening elastomer, 8-12 parts compatibilizer, and 2-3 parts additives; The preparation method of the toughened elastomer is as follows: HDPE, unsaturated modified silicone oil, reinforcing filler, dicumyl peroxide and styrene are mixed evenly and then added to a twin-screw extruder. After melt extrusion, the mixture is water-cooled and pelletized to obtain the toughened elastomer. The compatibilizer is HDPE-g-MAH.

[0009] Furthermore, the weight ratio of HDPE, unsaturated modified silicone oil, reinforcing filler, dicumyl peroxide, and styrene is 40-50:20-30:15-20:0.2-0.3:5-8. The temperatures of the five sections of the twin-screw extruder are 175℃, 180℃, 180℃, 180℃, and 180℃ respectively, the die temperature is 185℃, and the spindle speed is 20-25 r / min.

[0010] Furthermore, the preparation method of unsaturated modified silicone oil is as follows: octamethylcyclotetrasiloxane, vinyldiethoxysilane, dodecylmethyldiethoxysilane and sulfuric acid are mixed, the reaction system is heated to 80-90℃, and the reaction is maintained at this temperature for 60-80 min. Tetramethyl-1,3-bis(3-aminopropyl)dimethylsilyl ether is added to the reaction system, and the reaction is maintained at this temperature for 2-3 h. After post-treatment, unsaturated modified silicone oil is obtained.

[0011] The synthesis reaction formula for unsaturated modified silicone oil is as follows: Furthermore, the ratio of octamethylcyclotetrasiloxane, vinyldiethoxysilane, dodecylmethyldiethoxysilane, sulfuric acid, and tetramethyl-1,3-bis(3-aminopropyl)dimethylsilyl ether is 15-18g:5-7g:6-8g:5mL:3-4g, and the concentration of sulfuric acid is 2-3mol / L. The post-treatment includes: after the reaction is complete, cooling the reaction system to room temperature, adding 2-3wt% sodium bicarbonate solution to the reaction system to adjust the pH of the system to 7, allowing it to stand and separate the liquids, washing the organic phase three times with purified water, and then transferring it to a rotary evaporator with a water bath temperature of 80-90℃ to remove low-boiling substances under reduced pressure to obtain unsaturated modified silicone oil.

[0012] Furthermore, the reinforcing filler is obtained by the following steps: A1. Mix and stir zinc oxide-loaded carbon fibers with Tris buffer at room temperature for 20-30 min. Add dopamine hydrochloride to the reaction system, heat the reaction system to 45-50℃, and keep the reaction at this temperature for 6-8 h. After post-treatment, PDA-modified carbon fibers are obtained. A2. Under an inert gas atmosphere, PDA-modified carbon fiber, acetone and triethylamine are mixed and stirred. The reaction system is cooled to 5-10℃, and the modification liquid is added to the reaction system. The reaction is kept at this temperature for 5-6 hours. After post-treatment, the reinforced filler is obtained.

[0013] The synthetic reactions involved in the preparation of reinforced fillers include: Further, in step A1, the ratio of the loaded carbon fiber, Tris buffer, 4-aminomethyl-2,2,6,6-tetramethylpiperidine, and dopamine hydrochloride is 5g:100mL:2-3g, the concentration of the Tris buffer is 0.1mol / L, and the pH is 8.3. The post-treatment includes: after the reaction is complete, the reaction system is cooled to room temperature, filtered, the filter cake is washed with purified water until neutral, dried, and the filter cake is transferred to a drying oven at 70-80℃ and dried to constant weight to obtain PDA modified carbon fiber.

[0014] Further, in step A2, the ratio of the amount of PDA-modified carbon fiber, acetone, triethylamine, and 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride solution is 5-6g:30mL:1g:5g. The modification solution is composed of 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride, 10-undecenoyl chloride, and acetone in a ratio of 1g:1g:15mL. The post-treatment includes: after the reaction is complete, the reaction system is cooled to room temperature, filtered, the filter cake is washed with purified water until neutral, dried, and the filter cake is transferred to a drying oven at a temperature of 70-80℃ and dried to constant weight to obtain the reinforcing filler.

[0015] Furthermore, the loaded carbon fiber is obtained by the following steps: B1. Mix and stir the chopped carbon fibers and the activation solution, heat the reaction system to 70-80℃, keep it at the temperature for 20-30 minutes, and then perform post-treatment to obtain activated fibers. B2. Mix and stir the activated fiber, zinc chloride, and anhydrous ethanol for 30-40 minutes. At room temperature, add sodium hydroxide solution to the reaction system to adjust the pH of the system to 9-10. Let it stand for aging for 6-8 hours, and then perform post-treatment to obtain the loaded carbon fiber.

[0016] Further, in step B1, the solid-liquid ratio of the chopped carbon fibers and the activation solution is 1:7-8, and the activation solution is composed of 10-15wt% sodium hydroxide and 20wt% hydrogen peroxide in a volume ratio of 5:1. The post-treatment includes: after the reaction is completed, the reaction system is cooled to room temperature, filtered, the filter cake is washed with purified water until neutral and then dried, the filter cake is transferred to a drying oven at a temperature of 70-80℃ and dried to constant weight to obtain activated fibers.

[0017] Further, in step B2, the ratio of activated fiber, zinc chloride, and anhydrous ethanol is 5g:0.8-1g:30mL, the concentration of sodium hydroxide solution is 0.6-0.8mol / L, and the post-treatment includes: after the reaction is complete, filtration is performed, the filter cake is washed with purified water until neutral and then dried, the filter cake is transferred to a drying oven at 70-80℃ and dried to constant weight, and then the fiber material is transferred to a tube furnace under an inert gas atmosphere, the tube furnace is heated to 300-350℃ and calcined for 120-150min, and then cooled naturally to room temperature to obtain loaded carbon fibers.

[0018] The present invention also proposes a method for preparing HDPE cable protection pipes for underground laying of high-voltage cables, comprising the following steps: HDPE, toughening elastomer, compatibilizer and additives are mixed evenly and then added to a twin-screw extruder, melt-extruded into a vacuum sizing box with a vacuum degree of -0.1MPa for sizing and forming, and after sizing, it enters a water spray cooling box for segmental cooling to obtain HDPE cable protection pipes.

[0019] Furthermore, the additives are composed of pigments, dispersants, lubricants and antioxidants in a weight ratio of 2:5:2:1; the pigment is carbon black, the dispersant is stearate, the lubricant is microcrystalline wax, and the antioxidant is antioxidant 1010.

[0020] The present invention has the following beneficial effects: This invention uses dicumyl peroxide as an initiator to melt-mix HDPE, unsaturated modified silicone oil, and reinforcing fillers to prepare a toughened elastomer. The grafted / mildly cross-linked structure formed in the toughened elastomer can constrain the orientation recovery of HDPE chain segments. Combined with the subsequently added HDPE-g-MAH, it further enhances the polar interface interaction or causes ring-opening reaction, making the multiphase interface more robust and the phase size more stable, thereby helping to reduce longitudinal shrinkage and improve dimensional stability. At the same time, the toughened elastomer fixes the unsaturated modified silicone oil and reinforcing fillers within the matrix network, reducing the toughness decay caused by phase migration and interface debonding during thermal aging. It also forms a dual protection mechanism with the antioxidant in the system, so that the sample can still maintain high notched impact strength and overall mechanical property stability after thermal aging.

[0021] This invention also uses an alkali / oxidation system to surface activate short-cut carbon fibers, giving the fibers more anchorable active sites and micro-rough structures, enhancing melt wetting and mechanical interlocking. After loading and calcination stabilization treatment, zinc oxide is stably loaded onto the short-cut carbon fibers. Then, a PDA universal adhesion layer is formed through dopamine self-polymerization, introducing polar groups capable of secondary reactions and improving dispersion stability. Acyl chloride modification is then used to directionally introduce hydrophobic segments and unsaturated alkenyl structures onto the PDA layer, reducing the interfacial tension between the filler and HDPE and endowing the interface with reactive bonding capabilities. This reduces interfacial debonding and pore defects, allowing for more complete stress transfer, improving the ring stiffness and tensile strength of the sample, while also resulting in a more uniform molding structure and lower shrinkage.

[0022] This invention also prepares an unsaturated modified silicone oil with both unsaturated olefins and long alkyl hydrophobic side chains. Its flexible siloxane backbone provides an energy-dissipating phase that remains in a rubbery state at low temperatures. The unsaturated olefin structure, under peroxide-initiated conditions, undergoes grafting / branching / micro-crosslinking with styrene and HDPE segments, resulting in a network-bound silicone oil that reduces migration and failure risks. Simultaneously, the alkenyl structure on the surface of the reinforcing filler provides an interfacial co-reaction inlet for the same free radical reaction system, enabling chemical or strong entanglement between the reinforcing phase and the toughening phase / matrix. The long alkyl hydrophobic side chains reduce the interfacial tension between the silicone oil phase and HDPE and improve compatibility. The properties of ZnO make it easier for the toughening phase to form a fine and uniform dispersion morphology, which promotes energy-consuming processes such as shear yielding, cavitation and crack deflection from a mechanistic perspective. This maintains the notched impact strength of HDPE cable protection pipes at low temperatures. The sterically hindered phenolic structure grafted on the filler surface provides free radical termination ability near the interface, which can preferentially inhibit the chain oxidation reaction caused by stress concentration and oxygen diffusion at the interface, reduce interface embrittlement and microcrack initiation. By stabilizing the interface, enriching polar groups and providing adsorption sites, ZnO enables the sterically hindered phenol to more effectively cover the weak area of ​​the interface, thus maintaining the impact strength after thermal aging more effectively, so that the material still maintains a high level after thermal aging. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] In this invention, the chopped carbon fiber is selected from commercially available products of Carbonene Technology (Shenzhen) Co., Ltd., and the length of the chopped carbon fiber is 0.5-1mm.

[0025] In this invention, HDPE is high-density polyethylene, brand name is Sinopec Maoming, and property grade is injection molding grade; In this invention, HDPE-g-MAH is maleic anhydride-grafted polyethylene with a maleic anhydride grafting rate of 1%, brand name DOW, and processing grade is injection molding grade.

[0026] Example 1 This embodiment provides a method for preparing HDPE cable protection pipes for underground laying of high-voltage cables, specifically including the following steps: Step 1: Preparation of supported carbon fibers 10wt% sodium hydroxide and 20wt% hydrogen peroxide were mixed evenly at a volume ratio of 5:1 to obtain an activation solution; Short carbon fibers and activation solution were added to a reaction flask at a solid-liquid ratio of 1:7 and stirred. The reaction flask was heated to 70°C and kept at that temperature for 20 minutes. The reaction flask was then cooled to room temperature and filtered. The filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 70°C and dried to constant weight to obtain activated fibers. Weigh out 50g of activated fiber, 8g of zinc chloride, and 300mL of anhydrous ethanol and add them to a reaction flask. Stir for 30min. At room temperature, add 0.6mol / L sodium hydroxide solution to the reaction flask to adjust the pH of the system to 9. Let it stand for 6h for aging. Filter the mixture. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight. Then transfer the fiber material to a tube furnace under argon protection. Heat the tube furnace to 300℃ and calcine it for 120min. Let it cool naturally to room temperature to obtain the loaded carbon fiber.

[0027] During the preparation process, an activation solution composed of sodium hydroxide and hydrogen peroxide is used to perform alkaline etching and oxidative etching on the surface of chopped carbon fibers at high temperature. This removes the sizing / weak boundary layer of the chopped carbon fibers while introducing oxygen-containing functional groups at the graphite edges and defect sites, forming micro-roughness. Subsequently, zinc chloride is introduced into the ethanol system and the pH is adjusted to alkalinity with NaOH, allowing Zn to... 2+ Hydrolysis occurs to generate Zn(OH)2 salt, which is deposited heterogeneously on the fiber surface. Under argon protection, calcination at 300℃ dehydrates the deposit and transforms it into stable loaded ZnO nanoparticles, which are then more strongly anchored to the activated surface defects / functional groups.

[0028] Step 2: Preparation of reinforcing filler Weigh 50g of loaded carbon fiber and 1000mL of Tris buffer into a reaction flask and stir. Stir at room temperature for 20min. Add 20g of dopamine hydrochloride to the reaction flask. Heat the reaction flask to 45℃ and keep it at that temperature for 6h. Cool the reaction flask to room temperature, filter, wash the filter cake with purified water until neutral, and then dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain PDA-modified carbon fiber. The concentration of Tris buffer was 0.1mol / L and the pH was 8.3. 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride, 10-undecenoyl chloride and acetone were mixed evenly at a ratio of 1g:1g:15mL to obtain the modified solution; Weigh out 50g of PDA-modified carbon fiber, 300mL of acetone and 10g of triethylamine and add them to the reaction flask. Stir and cool the reaction flask to 5℃. Add 50g of the modification solution to the reaction flask and keep it at this temperature for 5h. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain the reinforcing filler.

[0029] During the preparation process, dopamine in the Tris buffer undergoes oxidative self-polymerization to form a PDA universal adhesion layer containing catechol / amine groups. The PDA is adsorbed onto the carbon fiber, and the coating stability is enhanced by the coordination / chelation effect of catechol on the ZnO surface. Subsequently, the acyl chlorides on 3,5-di-tert-butyl-4-hydroxyphenylpropionyl chloride and 10-undecenoyl chloride undergo acylchlorination reactions with the –NH2 / –OH in the PDA layer to form chemical bonds. This introduces long-chain hydrophobic segments, unsaturated olefins, and hindered phenols at the interface. The long-chain hydrophobic segments can reduce the interfacial tension with HDPE and improve dispersion. The unsaturated olefins provide an interfacial co-reaction entry point for subsequent peroxide radical reactions. The hindered phenol antioxidant structure preferentially terminates the free radical chain reaction near the interface and cooperates with the coated zinc oxide to improve the heat aging resistance of the material.

[0030] Step 3: Preparation of unsaturated modified silicone oil Weigh out 30g of octamethylcyclotetrasiloxane, 10g of vinyldiethoxysilane, 12g of dodecylmethyldiethoxysilane, and 10mL of 2mol / L sulfuric acid and add them to a reaction flask. Stir the mixture and heat it to 80℃. Keep the mixture at this temperature for 60min. Add 6g of tetramethyl-1,3-bis(3-aminopropyl)dimethylsilyl ether to the reaction flask and keep the mixture at this temperature for 2h. Cool the reaction flask to room temperature and add 2wt% sodium bicarbonate solution to adjust the pH of the system to 7. Allow the mixture to stand and separate the liquids. Wash the organic phase three times with purified water and transfer it to a rotary evaporator with a water bath temperature of 80℃. Apply a negative pressure to -0.1MPa and remove low-boiling substances by vacuum evaporation to obtain unsaturated modified silicone oil.

[0031] During the preparation process, under protic acid catalysis, octamethylcyclotetrasiloxane undergoes ring-opening equilibrium polymerization / rearrangement. Simultaneously, the alkoxy groups of vinyldiethoxysilane and dodecylmethyldiethoxysilane undergo hydrolysis-condensation and embedding into siloxane segments, introducing free radical-reactive vinyl and long alkyl hydrophobic side chains. Subsequently, disilicide containing aminopropyl is added as a capping agent to prepare unsaturated modified silicone oil through condensation. The long alkyl side chains reduce the interfacial tension between the silicone oil phase and HDPE, promoting fine and uniform dispersion of the toughening phase and reducing phase migration. The vinyl groups create conditions for subsequent grafting / micro-crosslinking, enabling the toughening phase to form a network of constraints, making it less prone to exudation failure during thermal aging and resulting in better toughness retention after aging.

[0032] Step 4: Preparation of toughened elastomer Weigh out the following components by weight: 40 parts HDPE, 20 parts unsaturated modified silicone oil, 15 parts reinforcing filler, 0.2 parts diisopropylbenzene peroxide, and 5 parts styrene. Mix them thoroughly and add them to a twin-screw extruder. Set the temperatures of the five sections of the twin-screw extruder to 175℃, 180℃, 180℃, 180℃, and 180℃ respectively. Set the die temperature to 185℃ and the spindle speed to 20 r / min. After melt extrusion, water-cool and pelletize to obtain a toughened elastomer. During the preparation process, dicumyl peroxide decomposes under heating conditions to generate free radicals, which extract hydrogen from the HDPE chain to form macromolecular free radicals. These free radicals undergo addition reactions with the vinyl groups of unsaturated modified silicone oil and the undecenoyl groups on the surface of reinforcing fillers to form grafted structures such as HDPEg silicone oil and HDPE / silicone oilg filler, accompanied by a small amount of HDPE branching / micro-crosslinking. The added styrene can act as a bridging monomer for free radical reactions to improve grafting efficiency and enhance the continuity of the interfacial transition layer.

[0033] Grafted / lightly cross-linked networks restrict the springback and orientation recovery of HDPE chain segments, reducing longitudinal shrinkage. The toughening phase is chemically bound and coupled with the filler / matrix, resulting in cavitation, shear yielding, fiber bridging, and crack deflection during crack propagation. This improves the notched impact strength of the material at low temperatures. At the same time, interfacial chemical bonding reduces fiber pull-out and debonding, allowing stress to be more effectively transferred to the carbon fiber skeleton, thus improving the ring stiffness and tensile strength of the material.

[0034] Step 5: Prepare HDPE cable protection pipe Carbon black, zinc stearate, microcrystalline wax and antioxidant 1010 are mixed evenly in a weight ratio of 2:5:2:1 to obtain the additive. Weigh out the following components by weight: 70 parts HDPE, 25 parts toughening elastomer, 8 parts compatibilizer HDPE-g-MAH, and 2 parts additives. Mix them thoroughly and add them to a twin-screw extruder. Set the temperatures of the five sections of the twin-screw extruder to 165℃, 170℃, 170℃, 170℃, and 170℃ respectively, with the die temperature at 175℃ and the spindle speed at 20 r / min. Melt extrusion is performed in a vacuum sizing box with a vacuum degree of -0.1MPa for sizing. After sizing, the tube is cooled section by section in a water spray cooling box to obtain the HDPE cable protection pipe.

[0035] Example 2 This embodiment provides a method for preparing HDPE cable protection pipes for underground laying of high-voltage cables, specifically including the following steps: Step 1: Preparation of supported carbon fibers 13wt% sodium hydroxide and 20wt% hydrogen peroxide were mixed evenly at a volume ratio of 5:1 to obtain an activation solution; Short carbon fibers and activation solution were added to a reaction flask at a solid-liquid ratio of 1:7.5 and stirred. The reaction flask was heated to 75°C and kept at that temperature for 25 minutes. The reaction flask was then cooled to room temperature and filtered. The filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 75°C and dried to constant weight to obtain activated fibers. Weigh out 50g of activated fiber, 9g of zinc chloride, and 300mL of anhydrous ethanol and add them to a reaction flask. Stir for 35min. At room temperature, add 0.7mol / L sodium hydroxide solution to the reaction flask to adjust the pH of the system to 9.5. Let it stand for 7h for aging. Filter the mixture. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight. Then transfer the fiber material to a tube furnace under argon protection. Heat the tube furnace to 325℃ and calcine it for 135min. Let it cool naturally to room temperature to obtain loaded carbon fiber.

[0036] Step 2: Preparation of reinforcing filler Weigh out 50g of loaded carbon fiber and 1000mL of Tris buffer and add them to a reaction flask. Stir at room temperature for 25min. Add 25g of dopamine hydrochloride to the reaction flask. Heat the reaction flask to 47℃ and keep it at that temperature for 7h. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight to obtain PDA-modified carbon fiber. The concentration of Tris buffer is 0.1mol / L and the pH is 8.3. 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride, 10-undecenoyl chloride and acetone were mixed evenly at a ratio of 1g:1g:15mL to obtain the modified solution; Weigh out 55g of PDA-modified carbon fiber, 300mL of acetone and 10g of triethylamine and add them to the reaction flask. Stir and cool the reaction flask to 7.5℃. Add 50g of the modification solution to the reaction flask and keep it at this temperature for 5.5h. Cool the reaction flask to room temperature, filter it, wash the filter cake with purified water until neutral, and then dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight to obtain the reinforced filler.

[0037] Step 3: Preparation of unsaturated modified silicone oil Weigh out 33g of octamethylcyclotetrasiloxane, 12g of vinyldiethoxysilane, 14g of dodecylmethyldiethoxysilane, and 10mL of 2.5mol / L sulfuric acid and add them to a reaction flask. Stir the mixture and heat it to 85℃. Keep the temperature for 70min. Add 7g of tetramethyl-1,3-bis(3-aminopropyl)dimethylsilyl ether to the reaction flask and keep the temperature for 2.5h. Cool the reaction flask to room temperature and add 2.5wt% sodium bicarbonate solution to adjust the pH of the system to 7. Allow the mixture to stand and separate the liquids. Wash the organic phase three times with purified water and transfer it to a rotary evaporator with a water bath temperature of 85℃. Apply a negative pressure to -0.1MPa and remove low-boiling substances by vacuum evaporation to obtain unsaturated modified silicone oil.

[0038] Step 4: Preparation of toughened elastomer Weigh out the following components by weight: 45 parts HDPE, 25 parts unsaturated modified silicone oil, 17 parts reinforcing filler, 0.25 parts dicumyl peroxide, and 6.5 parts styrene. Mix them thoroughly and add them to a twin-screw extruder. Set the temperatures of the five sections of the twin-screw extruder to 175℃, 180℃, 180℃, 180℃, and 180℃ respectively. Set the die temperature to 185℃ and the spindle speed to 23 r / min. After melt extrusion, water-cool and pelletize to obtain a toughened elastomer. Step 5: Prepare HDPE cable protection pipe Carbon black, calcium stearate, microcrystalline wax and antioxidant 1010 are mixed evenly in a weight ratio of 2:5:2:1 to obtain the additive. Weigh out the following components by weight: 75 parts HDPE, 30 parts toughening elastomer, 10 parts compatibilizer HDPE-g-MAH, and 2.5 parts additives. Mix them thoroughly and add them to a twin-screw extruder. Set the temperatures of the five sections of the twin-screw extruder to 165℃, 170℃, 170℃, 170℃, and 170℃ respectively, with the die temperature at 175℃ and the spindle speed at 23 r / min. Melt extrusion is performed in a vacuum sizing box with a vacuum degree of -0.1MPa for sizing. After sizing, the tube is cooled section by section in a water spray cooling box to obtain the HDPE cable protection pipe.

[0039] Example 3 This embodiment provides a method for preparing HDPE cable protection pipes for underground laying of high-voltage cables, specifically including the following steps: Step 1: Preparation of supported carbon fibers 15wt% sodium hydroxide and 20wt% hydrogen peroxide were mixed evenly at a volume ratio of 5:1 to obtain an activation solution; Short carbon fibers and activation solution were added to a reaction flask at a solid-liquid ratio of 1:8 and stirred. The reaction flask was heated to 80°C and kept at that temperature for 30 minutes. The reaction flask was then cooled to room temperature and filtered. The filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 80°C and dried to constant weight to obtain activated fibers. Weigh out 50g of activated fiber, 10g of zinc chloride, and 300mL of anhydrous ethanol and add them to a reaction flask. Stir for 40min. At room temperature, add 0.8mol / L sodium hydroxide solution to the reaction flask to adjust the pH of the system to 10. Let it stand for aging for 8h. Filter the mixture. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 80℃ and dry it to constant weight. Then transfer the fiber material to a tube furnace under argon protection. Heat the tube furnace to 350℃ and calcine it for 150min. Let it cool naturally to room temperature to obtain loaded carbon fiber.

[0040] Step 2: Preparation of reinforcing filler Weigh out 50g of loaded carbon fiber and 1000mL of Tris buffer and add them to a reaction flask. Stir at room temperature for 30min. Add 30g of dopamine hydrochloride to the reaction flask. Heat the reaction flask to 50℃ and keep it at that temperature for 8h. Cool the reaction flask to room temperature, filter, wash the filter cake with purified water until neutral, and then dry it. Transfer the filter cake to a drying oven at 80℃ and dry it to constant weight to obtain PDA-modified carbon fiber. The concentration of Tris buffer is 0.1mol / L and the pH is 8.3. 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride, 10-undecenoyl chloride and acetone were mixed evenly at a ratio of 1g:1g:15mL to obtain the modified solution; Weigh 60g of PDA-modified carbon fiber, 300mL of acetone and 10g of triethylamine and add them to the reaction flask. Stir and cool the reaction flask to 10℃. Add 50g of the modification solution to the reaction flask and keep it at this temperature for 6 hours. Cool the reaction flask to room temperature and filter. Wash the filter cake with purified water until neutral and then dry it. Transfer the filter cake to a drying oven at 80℃ and dry it to constant weight to obtain the reinforcing filler.

[0041] Step 3: Preparation of unsaturated modified silicone oil Weigh out 36g of octamethylcyclotetrasiloxane, 14g of vinyldiethoxysilane, 16g of dodecylmethyldiethoxysilane, and 10mL of 3mol / L sulfuric acid and add them to a reaction flask. Stir the mixture and heat it to 90℃. Keep the temperature for 80min. Add 8g of tetramethyl-1,3-bis(3-aminopropyl)dimethylsilyl ether to the reaction flask and keep the temperature for 3h. Cool the reaction flask to room temperature and add 3wt% sodium bicarbonate solution to adjust the pH of the system to 7. Allow the mixture to stand and separate the liquids. Wash the organic phase three times with purified water and transfer it to a rotary evaporator with a water bath temperature of 90℃. Apply a negative pressure to -0.1MPa and remove low-boiling substances by vacuum evaporation to obtain unsaturated modified silicone oil.

[0042] Step 4: Preparation of toughened elastomer Weigh out the following components by weight: 50 parts HDPE, 30 parts unsaturated modified silicone oil, 20 parts reinforcing filler, 0.3 parts dicumyl peroxide, and 8 parts styrene. Mix them thoroughly and add them to a twin-screw extruder. Set the temperatures of the five sections of the twin-screw extruder to 175℃, 180℃, 180℃, 180℃, and 180℃ respectively. Set the die temperature to 185℃ and the spindle speed to 25 r / min. After melt extrusion, water-cool and pelletize to obtain a toughened elastomer. Step 5: Prepare HDPE cable protection pipe Carbon black, barium stearate, microcrystalline wax and antioxidant 1010 are mixed evenly in a weight ratio of 2:5:2:1 to obtain the additive. Weigh out the following components by weight: 80 parts HDPE, 35 parts toughening elastomer, 12 parts compatibilizer HDPE-g-MAH, and 3 parts additives. Mix them thoroughly and add them to a twin-screw extruder. Set the temperatures of the five sections of the twin-screw extruder to 165℃, 170℃, 170℃, 170℃, and 170℃ respectively, with the die temperature at 175℃ and the spindle speed at 25 r / min. Melt extrusion is performed in a vacuum sizing box with a vacuum degree of -0.1MPa for sizing. After sizing, the tube is cooled section by section in a water spray cooling box to obtain the HDPE cable protection pipe.

[0043] Comparative Example 1 The difference between this comparative example and Example 3 is that the activated fiber in step 1 is used instead of the loaded carbon fiber in step 2.

[0044] Comparative Example 2 The difference between this comparative example and Example 3 is that the PDA-modified carbon fiber in step 2 is used instead of the reinforcing filler in step 4.

[0045] Comparative Example 3 The difference between this comparative example and Example 3 is that dodecylmethyldiethoxysilane was not added in step 3.

[0046] Performance testing: The ring stiffness and tensile strength of the HDPE cable protection pipe samples prepared in Examples 1-3 and Comparative Examples 1-3 were determined in accordance with the standard DL / T 802.1-2023 "Technical Conditions for Power Cable Conduits Part 1: General Rules". The longitudinal shrinkage rate of the HDPE cable protection pipe samples prepared in Examples 1-3 and Comparative Examples 1-3 was determined in accordance with the standard GB / T 6671-2001 "Determination of longitudinal shrinkage rate of thermoplastic pipes". Referring to Method B.1 of standard GB / T 18743.1-2022 "Determination of impact strength of simply supported beams for thermoplastic pipes - Part 1: General test methods", the notched impact strength of HDPE cable protection pipe samples prepared in Examples 1-3 and Comparative Examples 1-3 was determined at 23℃ and -30℃. The HDPE cable protection pipe samples prepared in Examples 1-3 and Comparative Examples 1-3 were placed in an environment with a temperature of 100°C for 100 days for heat aging treatment. Then the notched impact strength of the samples was measured. The specific test data are shown in Table 1 below.

[0047] Table 1 - Performance Test Data of Samples Data Analysis: The HDPE cable protection pipe prepared by this invention has a ring stiffness of 22.3-22.7 kN / m. 2 The tensile strength reaches 23.4-23.7 MPa, the longitudinal shrinkage rate decreases to 0.82-0.86%, and the notched impact strength at 23℃ reaches 42.5-43.1 kJ / m. 2 The notched impact strength at -30℃ reaches 38.3-38.6 kJ / m. 2 The notched impact strength after heat aging reaches 37.6-38.0 kJ / m. 2 The performance test data of the present invention are all superior to those of the comparative example, indicating that the present invention activates short-cut carbon fibers with an alkali / oxidation system and loads ZnO on its surface in situ. After constructing a universal adhesion layer by PDA self-polymerization, long alkyl hydrophobic segments, unsaturated alkenyl groups and sterically hindered phenolic structures are introduced into the PDA layer by acyl chloride reaction, thereby obtaining a reinforcing filler with dispersion stability, interfacial reaction connection and interfacial antioxidant capacity. At the same time, unsaturated modified silicone oil containing vinyl and long alkyl side chains is prepared. Toughened elastomer is prepared using HDPE, unsaturated modified silicone oil and reinforcing filler as raw materials under dicumyl peroxide initiation conditions. The toughened elastomer is then blended with HDPE, HDPE-g-MAH and additives and extruded into tubes. This improves the ring stiffness and tensile strength of HDPE cable protection pipe samples while reducing longitudinal shrinkage, and significantly improves the retention rate of notched impact performance of HDPE cable protection pipe samples after low temperature and thermal aging.

[0048] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high-voltage cable buried protection pipe, comprising HDPE, toughening elastomer, compatibilizer and additives, thoroughly mixed, and obtained by melt extrusion, sizing and cooling, characterized in that, It also includes mixing HDPE, unsaturated modified silicone oil, reinforcing filler, dicumyl peroxide, and styrene evenly and then adding them to a twin-screw extruder. After melt extrusion, the mixture is water-cooled and pelletized to obtain a toughened elastomer. In this process, octamethylcyclotetrasiloxane, vinyldiethoxysilane, dodecylmethyldiethoxysilane and sulfuric acid are mixed, the reaction system is heated to 80-90℃ and kept at this temperature for 60-80 min, tetramethyl-1,3-bis(3-aminopropyl)dimethylsilyl ether is added to the reaction system, and the reaction is kept at this temperature for 2-3 h. After post-treatment, unsaturated modified silicone oil is obtained. Furthermore, zinc oxide-loaded carbon fibers and Tris buffer were mixed and stirred at room temperature for 20-30 min. Dopamine hydrochloride was added to the reaction system, the temperature was raised to 45-50℃, and the reaction was maintained for 6-8 h. After post-treatment, PDA-modified carbon fibers were obtained. Under an inert gas atmosphere, PDA-modified carbon fibers, acetone, and triethylamine were mixed and stirred. The reaction system was cooled to 5-10℃, the modification liquid was added to the reaction system, and the reaction was maintained for 5-6 h. After post-treatment, the reinforcing filler was obtained. By weight, 70-80 parts HDPE, 25-35 parts toughening elastomer, 8-12 parts compatibilizer, and 2-3 parts additives are thoroughly mixed, and then melt-extruded, sized, and cooled to obtain the HDPE cable protection pipe for underground laying of high-voltage cables.

2. The HDPE cable protection pipe for underground laying of high-voltage cables according to claim 1, characterized in that, The compatibilizer is HDPE-g-MAH.

3. The HDPE cable protection pipe for underground laying of high-voltage cables according to claim 1, characterized in that, The weight ratio of HDPE, unsaturated modified silicone oil, reinforcing filler, dicumyl peroxide, and styrene is 40-50:20-30:15-20:0.2-0.3:5-8. The temperatures of the five sections of the twin-screw extruder are 175℃, 180℃, 180℃, 180℃, and 180℃ respectively, the die temperature is 185℃, and the spindle speed is 20-25 r / min.

4. The HDPE cable protection pipe for underground laying of high-voltage cables according to claim 1, characterized in that, The ratio of the amounts of octamethylcyclotetrasiloxane, vinyldiethoxysilane, dodecylmethyldiethoxysilane, sulfuric acid, and tetramethyl-1,3-bis(3-aminopropyl)dimethylsilyl ether is 15-18g:5-7g:6-8g:5mL:3-4g, and the concentration of the sulfuric acid is 2-3mol / L.

5. The HDPE cable protection pipe for underground laying of high-voltage cables according to claim 1, characterized in that, The ratio of the loaded carbon fiber, Tris buffer, 4-aminomethyl-2,2,6,6-tetramethylpiperidine, and dopamine hydrochloride is 5g:100mL:2-3g, and the concentration of the Tris buffer is 0.1mol / L with pH=8.

3. The ratio of the PDA-modified carbon fiber, acetone, triethylamine, and 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride solution is 5-6g:30mL:1g:5g, and the modification solution is composed of 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride, 10-undecenoyl chloride, and acetone in a ratio of 1g:1g:15mL.

6. The HDPE cable protection pipe for buried high-voltage cables according to claim 1, characterized in that, Loaded carbon fibers are obtained through the following steps: B1. Mix and stir the chopped carbon fibers and the activation solution, heat the reaction system to 70-80℃, keep it at the temperature for 20-30 minutes, and then perform post-treatment to obtain activated fibers. B2. Mix and stir the activated fiber, zinc chloride, and anhydrous ethanol for 30-40 minutes. At room temperature, add sodium hydroxide solution to the reaction system to adjust the pH of the system to 9-10. Let it stand for aging for 6-8 hours, and then perform post-treatment to obtain the loaded carbon fiber.

7. The HDPE cable protection pipe for underground laying of high-voltage cables according to claim 6, characterized in that, In step B1, the solid-liquid ratio of the chopped carbon fibers and the activation solution is 1:7-8, and the activation solution is composed of 10-15wt% sodium hydroxide and 20wt% hydrogen peroxide in a volume ratio of 5:1; in step B2, the ratio of the activated fiber, zinc chloride, and anhydrous ethanol is 5g:0.8-1g:30mL, and the concentration of the sodium hydroxide solution is 0.6-0.8mol / L.

8. A method for preparing an HDPE cable protection pipe for underground laying of high-voltage cables as described in any one of claims 1-8, characterized in that, The process includes the following steps: HDPE, toughening elastomer, compatibilizer and additives are mixed evenly and then added to a twin-screw extruder. The mixture is melt-extruded into a vacuum sizing box with a vacuum degree of -0.1MPa for sizing and forming. After sizing, the mixture is cooled in stages by a water spray cooling box to obtain HDPE cable protection pipe.

9. A method for preparing an HDPE cable protection pipe for underground laying of high-voltage cables according to claim 8, characterized in that, The additives consist of pigment, dispersant, lubricant and antioxidant in a weight ratio of 2:5:2:1; the pigment is carbon black, the dispersant is stearate, the lubricant is microcrystalline wax and the antioxidant is antioxidant 1010.

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