High-strength insulated HPVC cable protection pipe and preparation method thereof

Abstract

The application discloses a high-strength insulation HPVC cable protection pipe and a preparation method thereof, and belongs to the technical field of cable protection pipe preparation, and is used for solving the technical problem that the insulation performance and mechanical strength of the cable protection pipe in the prior art need to be further improved, and specifically comprises the following components in parts by weight: 90-100 parts of HPVC, 10-15 parts of a thermal stabilizing hydrotalcite composite material, 8-12 parts of epoxy soybean oil and 1-3 parts of auxiliary materials. The application is constructed by a hierarchical composite modification system of a silicon-titanium layer coated ZIF-8 and a fatty acid salt intercalated hydrotalcite, and cooperates with the epoxy soybean oil to effectively inhibit the thermal degradation of the HPVC, improve the processing and thermal stability of the cable protection pipe, synchronously enhance the mechanical strength and the insulation performance through multi-scale barrier and interface densification, and enable the cable protection pipe to have excellent long-term reliability under high voltage and complex service environments.

Description

Technical Field

[0001] This invention relates to the field of cable protection pipe manufacturing technology, specifically to a high-strength insulated HPVC cable protection pipe and its manufacturing method. Background Technology

[0002] HPVC (usually referring to high-performance PVC material made from high-polymerization-degree polyvinyl chloride resin) has the characteristics of high mechanical strength, good dimensional stability, excellent electrical insulation properties and chemical corrosion resistance. It is widely used in the field of power cable protection pipes. With the expansion of power grid construction and the increasingly complex underground laying environment, cable protection pipes not only need to withstand large external mechanical loads and construction impacts during use, but also need to maintain stable mechanical and insulation properties under long-term thermal stress, electric field effects and humid and hot environments. Therefore, higher requirements are placed on the mechanical strength and insulation performance of HPVC cable protection pipes.

[0003] Currently, HPVC cable protection pipes typically use high-polymerization-degree PVC resin as the matrix material and are processed and molded by adding heat stabilizers, lubricants, and processing aids. To improve their overall performance, inorganic fillers such as calcium carbonate, talc, and mica powder are often added to increase stiffness and ring stiffness. Toughening modifiers such as ACR, CPE, and MBS are introduced to improve impact resistance. Organotin or calcium-zinc stabilizers are used in combination with epoxy additives to inhibit the thermal degradation of PVC. However, due to the difficulty in effectively controlling filler agglomeration and thermal degradation products, it is difficult to synergistically improve mechanical strength and insulation performance.

[0004] Meanwhile, while adding inorganic fillers can improve rigidity during the preparation of HPVC cable protection pipes, uneven dispersion can easily lead to interface defects, resulting in stress concentration and enhanced local electric field. Furthermore, the added toughening modifiers, while improving impact performance, reduce the heat resistance and insulation stability of the pipe. Traditional thermal stabilization systems have limited ability to inhibit HCl generated during the thermal degradation of PVC, making it difficult to effectively control the migration and accumulation of acidic small molecules, thus affecting long-term service performance. Therefore, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength insulated HPVC cable protection pipe and its preparation method, which solves the technical problem that the insulation performance and mechanical strength of cable protection pipes in the prior art need to be further improved.

[0006] The objective of this invention can be achieved through the following technical solution: a high-strength insulated HPVC cable protection pipe, comprising the following components by weight: 90-100 parts HPVC, 10-15 parts heat-stabilized hydrotalcite composite material, 8-12 parts epoxidized soybean oil and 1-3 parts auxiliary materials. The thermally stable hydrotalcite composite material is prepared by the following steps: A1. Place aluminum nitrate nonahydrate, calcium nitrate tetrahydrate and decarbonated water in a reaction vessel and stir at room temperature for 15-30 min to obtain a metal salt solution. A2. Stearic acid and ethanol are placed in a reaction vessel and stirred. Sodium hydroxide solution is added. The reaction vessel is heated to 60-70℃ and stirred for 20-30 minutes to obtain a fatty acid salt solution. A3. Place the silicon-titanium layer coated ZIF-8 and decarbonated water in a reaction vessel under nitrogen atmosphere and stir. Heat the reaction vessel to reflux, slowly add metal salt solution and fatty acid salt solution, keep warm and stir for 10-15 min, add sodium hydroxide solution to adjust the pH to 9.8-10.5, keep warm and react for 6-8 h, and then post-process to obtain thermally stable hydrotalcite composite material.

[0007] Furthermore, in step A1, the ratio of aluminum nitrate nonahydrate, calcium nitrate tetrahydrate, and decarbonated water is 6-8g:8-10g:80-100mL; in step A2, the ratio of stearic acid, ethanol, and sodium hydroxide solution is 10-12g:80-100mL:40-60mL, and the sodium hydroxide solution is composed of sodium hydroxide and decarbonated water in a ratio of 3-3.2g:100mL.

[0008] Further, in step A3, the ratio of the amount of the silicon-titanium layer coating ZIF-8, decarbonated water, metal salt solution and fatty acid salt solution is 1-2g:80-100mL:80-100mL:80-100mL, and the sodium hydroxide solution is composed of sodium hydroxide and decarbonated water in a ratio of 6-8g:100mL. The post-processing steps include: after the reaction is completed, the reaction system is cooled to room temperature, filtered, the filter cake is washed with decarbonated water until neutral, then washed with ethanol 1-2 times, transferred to an oven at 70-80℃, and dried to constant weight to obtain the thermally stable hydrotalcite composite material.

[0009] Furthermore, the method for preparing the decarbonated water is as follows: place deionized water in a reaction vessel, heat the reaction vessel until the deionized water boils, keep the reaction at this temperature for 30-60 minutes, and seal it while it is still hot to obtain decarbonated water.

[0010] Furthermore, the silicon-titanium layer coating ZIF-8 is prepared by the following steps: B1. Place ZIF-8, ethanol, deionized water and ammonia in a reaction vessel and stir. Add tetraethyl orthosilicate solution and stir at room temperature for 4-6 hours. Post-treatment is then performed to obtain silicon-coated ZIF-8. B2. Place the silicon-coated ZIF-8 and ethanol in a reaction vessel and stir. Add triisostearate titanate isopropyl ester and stir at room temperature for 0.5-1 h. Heat the reaction vessel to 45-55℃ and keep it at that temperature for 0.5-1 h. After post-treatment, obtain silicon-titanium coated ZIF-8.

[0011] Further, in step B1, the ratio of ZIF-8, ethanol, deionized water, ammonia, and tetraethyl orthosilicate ethanol solution is 1.5-2.5g:180-200mL:8-10mL:5-7mL:8-10mL, the concentration of ammonia is 25-28wt%, and the tetraethyl orthosilicate solution is composed of tetraethyl orthosilicate and ethanol in a ratio of 1.0-1.2g:10mL. The post-processing steps include: after the reaction is completed, filtration is performed, the filter cake is washed 2-4 times with deionized water and ethanol, transferred to an oven at a temperature of 50-60℃, and dried to constant weight to obtain silicon-coated ZIF-8.

[0012] Furthermore, in step B2, the ratio of the amount of silicon-coated ZIF-8, ethanol, and triisostearate titanate is 1.5-2.5g:80-100mL:0.4-0.6g. The post-processing steps include: after the reaction is completed, the mixture is filtered, the filter cake is washed once with ethanol, transferred to an oven at 60-70℃, and dried to constant weight to obtain silicon-titanium coated ZIF-8.

[0013] Furthermore, the preparation method of ZIF-8 is as follows: zinc nitrate and methanol are placed in a reaction vessel and stirred. The reaction vessel is heated to 55-65℃, 2-methylimidazolium methanol solution is added, and the reaction is kept at the temperature for 8-10 hours. ZIF-8 is obtained by post-treatment.

[0014] Furthermore, the ratio of zinc nitrate, methanol, and 2-methylimidazolium methanol solution is 2-4g:80-100mL:80-100mL, and the concentration of 2-methylimidazolium methanol solution is 0.4-0.6mol / L. The post-processing steps include: after the reaction is completed, the reaction system is cooled to room temperature, filtered, the filter cake is washed with methanol 2-4 times, transferred to an oven at 70-80℃, and dried to constant weight to obtain ZIF-8.

[0015] The present invention also proposes a method for preparing a high-strength insulated HPVC cable protection pipe, comprising the following steps: S1. Add HPVC, heat-stabilized hydrotalcite composite material, epoxidized soybean oil and auxiliary materials into a high-speed homogenizer and mix evenly to obtain a premix. S2. The premixed material is placed in a twin-screw extruder for melt extrusion, and then extruded through the tubular die at the extruder head to form a tube, thus obtaining an HPVC cable protection pipe.

[0016] Further, in step S1, the excipients are composed of lubricant, plasticizer and heat stabilizer in a mass ratio of 3:8:5. The lubricant is one or more of fatty acid amide, oleamide and paraffin wax. The plasticizer is one or more of dibutyl phthalate, diisononyl phthalate and dioctyl sebacate. The heat stabilizer is one or more of di-tert-butyl-p-cresol, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)] and dilauryl thiodipropionate.

[0017] Furthermore, in step S2, the twin-screw extruder is configured with a cooling zone inlet temperature of 170-180℃ and an outlet temperature of 85-95℃.

[0018] The present invention has the following beneficial effects: This invention involves coating the surface of ZIF-8 with a silicon-titanium layer. This allows ZIF-8 to enter HPVC as a dispersed phase with regular micropores and a high-rigidity framework, providing localized rigid support. Simultaneously, its low conductivity and porous structure extend the charge migration path during use, enhancing the insulation performance of the cable protection pipe. The outer layer of ZIF-8 is continuously and densely coated with silicon dioxide, further improving its heat resistance and stability, reducing interface defects during processing and service, and weakening localized electric field concentration. Titanate forms a titanium-containing functional layer on the silicon layer surface, improving the wetting and dispersion of ZIF-8 in the HPVC melt and enhancing interfacial bonding, thereby improving the electrical insulation performance, mechanical strength, and thermal stability of the HPVC cable protection pipe.

[0019] This invention also constructs a thermally stable hydrotalcite composite material with a hierarchical composite structure by using a silicon-titanium layer-coated ZIF-8 as a solid substrate to induce aluminum and calcium ions to nucleate heterogeneously on its surface and grow hydrotalcite layers, and by synergistically using fatty acid salt intercalation to achieve surface hydrophobicity and inhibit agglomeration. During the HPVC melt processing, the hydrotalcite layered bimetallic hydroxide reacts with HCl generated by the thermal degradation of PVC through the metal sites and hydroxyl groups on the surface and edges of the layers, and fixes chloride ions in the interlayer through anion exchange, thereby inhibiting the autocatalytic degradation process of dechlorination from the source and significantly improving the thermal stability and processing stability of the cable protection pipe.

[0020] The ZIF-8 silicon-titanium layer coating of this invention, through a rigid microporous framework and multi-layer inorganic coating, acts as a solid substrate to induce heterogeneous nucleation during the formation of hydrotalcite, constructing a hierarchical composite structure. This provides a stable growth interface for the hydrotalcite layers and inhibits aggregation. Simultaneously, this structure forms a continuous rigid support and multi-scale barrier interface in the HPVC matrix, extending the migration paths of heat, charge, and small molecules. During processing, the layered hydrotalcite structure neutralizes and exchanges anions with HCl generated from the thermal degradation of HPVC, achieving efficient acid capture. The intercalation of fatty acid salts hydrophobically modifies the inorganic phase, improving its dispersion and interfacial compatibility in HPVC. Epoxidized soybean oil, as an auxiliary heat stabilizer, synergizes with the acid absorption effect of hydrotalcite, further passivating active chlorine and alleviating chain segment breakage. Meanwhile, antioxidants inhibit free radical oxidation reactions, synergistically improving the thermal stability, mechanical strength, and long-term insulation performance of the cable protection pipe. Detailed Implementation

[0021] 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The HPVC used in this invention was purchased from Ningbo Senhong Plastics Co., Ltd., with item number S-80, molecular weight of 18,000-25,000, and product name high-strength polyvinyl chloride. The epoxidized soybean oil used in this invention was purchased from Shandong Shengyong Biotechnology Co., Ltd., with a content of 99%, CAS number 8013-07-8, and the standard implemented is the national standard.

[0023] The stearic acid used in this invention was purchased from Guangzhou Housheng New Materials Co., Ltd., and the model is stearic acid 1801, which conforms to the national standard.

[0024] Example 1 This embodiment provides a method for preparing ZIF-8 coated with a silicon-titanium layer, including the following steps: Step I: Preparation of ZIF-8 Weigh 20g of zinc nitrate and 800mL of methanol and place them in a reaction vessel and stir. Heat the reaction vessel to 55℃ and add 800mL of 0.4mol / L 2-methylimidazolium methanol solution. Keep the reaction vessel at this temperature for 8h. After the reaction is complete, wait for the reaction system to cool to room temperature, filter the mixture, wash the filter cake twice with methanol, transfer it to an oven at 70℃, and dry it to constant weight to obtain ZIF-8.

[0025] Step II: Preparation of silicon-coated ZIF-8 Tetraethyl orthosilicate and ethanol are mixed evenly at a ratio of 1.0 g: 10 mL to obtain a tetraethyl orthosilicate solution for later use. Weigh out 15g of ZIF-8, 1800mL of ethanol, 80mL of deionized water and 50mL of 25wt% ammonia and place them in a reaction vessel and stir. Add 80mL of tetraethyl orthosilicate solution and stir at room temperature for 4 hours. After the reaction is complete, filter the mixture and wash the filter cake twice with deionized water and ethanol. Transfer the cake to an oven at 50℃ and dry it to constant weight to obtain silicon-coated ZIF-8.

[0026] Step III: Preparation of silicon-titanium layer coated ZIF-8 Weigh 15g of silicon-coated ZIF-8 and 800mL of ethanol and place them in a reaction vessel and stir. Add 4g of triisostearate titanate isopropyl ester and stir at room temperature for 0.5h. Heat the reaction vessel to 45℃ and keep it at that temperature for 0.5h. After the reaction is complete, filter the mixture and wash the filter cake once with ethanol. Transfer the cake to an oven at 60℃ and dry it to constant weight to obtain silicon-titanium coated ZIF-8.

[0027] In the reaction, zinc ions undergo coordination self-assembly with 2-methylimidazole to form a zeolite imidazole framework structure ZIF-8 with Zn-N coordination bonds as the backbone. Under ammonia catalysis, tetraethyl orthosilicate undergoes hydrolysis and condensation to generate a Si-O-Si network structure. A continuous thin silicon coating is formed on the surface of ZIF-8 through condensation deposition. The hydroxyl groups on the surface of ZIF-8 coated with the silicon layer undergo coordination exchange and condensation with the titanate ester to introduce a titanium-containing organic functional layer, and a silicon-titanium composite coating structure is further constructed outside the silicon layer.

[0028] The ZIF-8 zeolite imidazole framework introduces microporous framework particles with regular channels and high rigidity. This structure, as a dispersed phase in the HPVC cable protection pipe material, improves local rigidity and disperses external loads, reducing the risk of stress concentration. Simultaneously, its low conductivity and porous structure extend the charge migration path, enhancing the overall insulation stability of the pipe. A continuous silicon layer is formed on the ZIF-8 surface by a Si-O-Si network. The high bond energy of the silicon-oxygen framework improves the thermal stability and chemical resistance of the particles during processing and use. It also constructs a dense inorganic interface layer, reducing micropores and interface defects in the matrix, which helps reduce local electric field concentration and improve electrical breakdown resistance. Furthermore, titanate is introduced onto the silicon layer surface to form a silicon-titanium composite coating structure. This titanium-containing organic functional layer improves the wetting and dispersion of particles in the HPVC melt, enhancing the interfacial bonding strength between the particles and the polymer matrix. This allows the material to maintain high strength and impact resistance while forming a multi-layered interfacial barrier structure, thereby improving the insulation reliability of the cable protection pipe under high voltage, thermal stress, and humid environments.

[0029] Example 2 This embodiment provides a method for preparing ZIF-8 coated with a silicon-titanium layer, including the following steps: Step I: Preparation of ZIF-8 Weigh out 30g of zinc nitrate and 900mL of methanol and place them in a reaction vessel and stir. Heat the reaction vessel to 60℃ and add 900mL of 0.5mol / L 2-methylimidazolium methanol solution. Keep the reaction vessel at this temperature for 9h. After the reaction is complete, wait for the reaction system to cool to room temperature, filter the mixture, wash the filter cake three times with methanol, transfer it to an oven at 75℃, and dry it to constant weight to obtain ZIF-8.

[0030] Step II: Preparation of silicon-coated ZIF-8 Tetraethyl orthosilicate and ethanol were mixed evenly at a ratio of 1.1g:10mL to obtain a tetraethyl orthosilicate solution for later use. Weigh out 20g of ZIF-8, 1900mL of ethanol, 90mL of deionized water and 60mL of 26.5wt% ammonia and place them in a reaction vessel and stir. Add 90mL of tetraethyl orthosilicate solution and stir at room temperature for 5h. After the reaction is complete, filter the mixture and wash the filter cake three times with deionized water and ethanol. Transfer the cake to an oven at 55℃ and dry it to constant weight to obtain silicon-coated ZIF-8.

[0031] Step III: Preparation of silicon-titanium layer coated ZIF-8 Weigh 20g of silicon-coated ZIF-8 and 900mL of ethanol and place them in a reaction vessel and stir. Add 5g of triisostearate titanate isopropyl ester and stir at room temperature for 1h. Heat the reaction vessel to 50℃ and keep it at that temperature for 1h. After the reaction is complete, filter the mixture and wash the filter cake once with ethanol. Transfer the cake to an oven at 65℃ and dry it to constant weight to obtain silicon-titanium coated ZIF-8.

[0032] Example 3 This embodiment provides a method for preparing ZIF-8 coated with a silicon-titanium layer, including the following steps: Step I: Preparation of ZIF-8 Weigh 40g of zinc nitrate and 1000mL of methanol and place them in a reaction vessel and stir. Heat the reaction vessel to 65℃ and add 1000mL of 0.6mol / L 2-methylimidazolium methanol solution. Keep the reaction vessel at this temperature for 10h. After the reaction is complete, wait for the reaction system to cool to room temperature, filter the mixture, wash the filter cake four times with methanol, transfer it to an oven at 80℃, and dry it to constant weight to obtain ZIF-8.

[0033] Step II: Preparation of silicon-coated ZIF-8 Tetraethyl orthosilicate and ethanol were mixed evenly at a ratio of 1.2g:10mL to obtain a tetraethyl orthosilicate solution for later use. Weigh out 25g of ZIF-8, 2000mL of ethanol, 100mL of deionized water and 70mL of 28wt% ammonia water and place them in a reaction vessel and stir. Add 100mL of tetraethyl orthosilicate solution and stir at room temperature for 6 hours. After the reaction is complete, filter the mixture and wash the filter cake 4 times with deionized water and ethanol. Transfer the cake to an oven at 60℃ and dry it to constant weight to obtain silicon-coated ZIF-8.

[0034] Step III: Preparation of silicon-titanium layer coated ZIF-8 Weigh 25g of silicon-coated ZIF-8 and 1000mL of ethanol and place them in a reaction vessel and stir. Add 6g of triisostearate titanate isopropyl ester and stir at room temperature for 1h. Heat the reaction vessel to 55℃ and keep it at that temperature for 1h. After the reaction is complete, filter the mixture and wash the filter cake once with ethanol. Transfer the cake to an oven at 70℃ and dry it to constant weight to obtain silicon-titanium coated ZIF-8.

[0035] Example 4 This embodiment provides a method for preparing a heat-stabilized hydrotalcite composite material, including the following steps: Step ①: Prepare metal salt solution Deionized water was placed in a reaction vessel, the reaction vessel was heated to boiling point, and the reaction was maintained at this temperature for 30 minutes. The vessel was then sealed while hot to obtain decarbonated water for later use. Weigh out 60g of aluminum nitrate nonahydrate, 80g of calcium nitrate tetrahydrate and 800mL of decarbonated water and place them in a reaction vessel. Stir at room temperature for 15 minutes to obtain a metal salt solution.

[0036] Step 2: Prepare fatty acid salt solution Sodium hydroxide and decarbonated water were mixed evenly at a ratio of 3g:100mL to obtain a sodium hydroxide solution for later use. Weigh out 100g of stearic acid and 800mL of ethanol and place them in a reaction vessel. Stir and add 400mL of sodium hydroxide solution. Heat the reaction vessel to 60℃ and keep it at that temperature for 20min to obtain a fatty acid salt solution.

[0037] Step ③: Preparation of thermally stable hydrotalcite composite material Sodium hydroxide and decarbonated water were mixed evenly at a ratio of 6g:100mL to obtain a sodium hydroxide solution for later use. Weigh 10g of the silicon-titanium layer-coated ZIF-8 prepared in Example 1 and 800mL of decarbonated water and place them in a reaction vessel under nitrogen atmosphere protection and stir. Heat the reaction vessel to reflux and slowly add 800mL of metal salt solution and 800mL of fatty acid salt solution. Keep the mixture warm and stir for 10min. Add sodium hydroxide solution to adjust the pH to 9.8 and keep the reaction warm for 6h. After the reaction is completed, wait for the reaction system to cool to room temperature, filter it, wash the filter cake with decarbonated water until neutral, wash it once with ethanol, transfer it to an oven at 70℃ and dry it to constant weight to obtain the thermally stable hydrotalcite composite material.

[0038] Deionized water is boiled to remove dissolved carbon dioxide, avoiding the introduction of carbonate ions. In this system, aluminum nitrate and calcium nitrate are fully dissolved to form stable aluminum and calcium ion hydrates, providing a metal source for the subsequent formation of layered bimetallic hydroxides. Stearic acid undergoes a neutralization reaction under the action of sodium hydroxide to generate fatty acid salts. Its carboxylate ions can participate in subsequent reactions as organic anions. Aluminum and calcium ions undergo a co-precipitation reaction with hydroxide ions to form a layered bimetallic hydroxide framework. Fatty acid salts are intercalated simultaneously. In this co-precipitation system, the silicon-titanium layer coats ZIF-8 as a solid substrate. Its surface functional structure induces aluminum and calcium ions to undergo heterogeneous nucleation at its interface and grow a hydrotalcite phase, so that the precipitation process is accompanied by the formation of a composite structure, resulting in a thermally stable hydrotalcite composite material.

[0039] The introduction of decarbonated water inhibits carbonate formation and competitive precipitation, allowing aluminum and calcium ions to exist uniformly in a stable hydrated ion form. This reduces impurities and structural defects during the nucleation and growth stages, improving the continuity and density of the hydrotalcite structure. This provides a solid foundation for good mechanical load-bearing continuity and structural maintenance under thermal stress in HPVC. The introduction of fatty acid salts allows their carboxylate ions to insert into the hydrotalcite interlayer and modify the lamellar surface, reducing the surface polarity of the inorganic phase and inhibiting agglomeration. This results in a more uniform filler dispersion and a continuous transition interface, improving stress transmission paths, mitigating interface slippage under thermal loads, and suppressing interface charge accumulation and local field concentration under an electric field. Furthermore, the introduction of a silicon-titanium layer to coat ZIF-8 as a solid substrate induces heterogeneous nucleation of hydrotalcite on its surface and constructs a hierarchical composite structure. This structure forms a stable rigid support and multi-scale barrier interface in HPVC, extending the heat and charge transmission path and improving the mechanical strength, thermal stability, and insulation performance of the HPVC cable protection pipe.

[0040] Example 5 This embodiment provides a method for preparing a heat-stabilized hydrotalcite composite material, including the following steps: Step ①: Prepare metal salt solution Deionized water was placed in a reaction vessel, the reaction vessel was heated to boiling point, and the reaction was maintained at this temperature for 45 minutes. The vessel was then sealed while hot to obtain decarbonated water for later use. Weigh out 70g of aluminum nitrate nonahydrate, 90g of calcium nitrate tetrahydrate and 900mL of decarbonated water and place them in a reaction vessel. Stir at room temperature for 22 minutes to obtain a metal salt solution.

[0041] Step 2: Prepare fatty acid salt solution Sodium hydroxide and decarbonated water were mixed evenly at a ratio of 3.1g:100mL to obtain a sodium hydroxide solution for later use. Weigh out 110g of stearic acid and 900mL of ethanol and place them in a reaction vessel. Stir, add 500mL of sodium hydroxide solution, heat the reaction vessel to 65℃, and stir for 25min to obtain a fatty acid salt solution.

[0042] Step ③: Preparation of thermally stable hydrotalcite composite material Sodium hydroxide and decarbonated water were mixed evenly at a ratio of 7g:100mL to obtain a sodium hydroxide solution for later use. Weigh 15g of the silicon-titanium layer-coated ZIF-8 prepared in Example 2 and 900mL of decarbonated water and place them in a reaction vessel under nitrogen atmosphere protection and stir. Heat the reaction vessel to reflux and slowly add 900mL of metal salt solution and 900mL of fatty acid salt solution. Keep the mixture warm and stir for 12min. Add sodium hydroxide solution to adjust the pH to 10.2 and keep the reaction warm for 7h. After the reaction is completed, wait for the reaction system to cool to room temperature, filter, wash the filter cake with decarbonated water until neutral, wash it twice with ethanol, transfer it to an oven at 75℃ and dry it to constant weight to obtain the thermally stable hydrotalcite composite material.

[0043] Example 6 This embodiment provides a method for preparing a heat-stabilized hydrotalcite composite material, including the following steps: Step ①: Prepare metal salt solution Deionized water was placed in a reaction vessel, the reaction vessel was heated to boiling point, and the reaction was maintained at this temperature for 60 minutes. The vessel was then sealed while hot to obtain decarbonated water for later use. Weigh out 80g of aluminum nitrate nonahydrate, 100g of calcium nitrate tetrahydrate and 1000mL of decarbonated water and place them in a reaction vessel. Stir at room temperature for 30 minutes to obtain a metal salt solution.

[0044] Step 2: Prepare fatty acid salt solution Sodium hydroxide and decarbonated water were mixed evenly at a ratio of 3.2g:100mL to obtain a sodium hydroxide solution for later use. Weigh out 120g of stearic acid and 1000mL of ethanol and place them in a reaction vessel. Stir, add 600mL of sodium hydroxide solution, heat the reaction vessel to 70℃, and keep it at this temperature while stirring for 30min to obtain a fatty acid salt solution.

[0045] Step ③: Preparation of thermally stable hydrotalcite composite material Sodium hydroxide and decarbonated water were mixed evenly at a ratio of 8g:100mL to obtain a sodium hydroxide solution for later use. Weigh 20g of the silicon-titanium layer-coated ZIF-8 prepared in Example 3 and 1000mL of decarbonated water and place them in a reaction vessel under nitrogen atmosphere protection and stir. Heat the reaction vessel to reflux and slowly add 1000mL of metal salt solution and 1000mL of fatty acid salt solution. Keep the mixture warm and stir for 15min. Add sodium hydroxide solution to adjust the pH to 10.5 and keep the reaction warm for 8h. After the reaction is completed, wait for the reaction system to cool to room temperature, filter, wash the filter cake with decarbonated water until neutral, wash it twice with ethanol, transfer it to an oven at 80℃ and dry it to constant weight to obtain the thermally stable hydrotalcite composite material.

[0046] Example 7 This embodiment provides a method for preparing a high-strength insulated HPVC cable protection pipe, including the following steps: Step 1: Preparation of premix Oleamide, diisononyl phthalate and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)] were mixed evenly at a mass ratio of 3:8:5 to obtain the excipient for later use. Weigh out the following by weight: 90 parts HPVC, 10 parts heat-stabilized hydrotalcite composite material prepared in Example 4, 8 parts epoxidized soybean oil and 1 part auxiliary material, add them to a high-speed homogenizer and mix evenly to obtain a premix.

[0047] Step 2: Prepare HPVC cable protection pipe The premixed material is placed in a twin-screw extruder for melt extrusion, and then extruded through a tubular die at the extruder head to form a tube, thus obtaining an HPVC cable protection pipe. The twin-screw extruder is equipped with a cooling zone with an inlet temperature of 170°C and an outlet temperature of 85°C.

[0048] During the HPVC melt extrusion process, the HCl generated from the thermal degradation of PVC first undergoes an acid-base neutralization reaction with the metal and hydroxyl sites on the surface and edges of the thermally stable layered hydroxide sheets. Simultaneously, the generated chloride ions are fixed by entering the interlayer of the layered hydroxide through anion exchange, reducing the concentration of free acid in the system and weakening the catalytic effect of HCl on the breaking of C-Cl bonds, thus inhibiting the autocatalytic cycle of dehydrochlorination. The fatty acid anions introduced into the interlayer hydrophobically modify the surface of the layered hydroxide sheets, reducing the polarity of the inorganic phase, weakening sheet aggregation, and reducing defects at the interface between the filler and the matrix. This makes it difficult for acidic small molecules to accumulate at the interface and form local acidic hot spots. The silicon-titanium layer coating ZIF-8 constitutes a continuous and dense inorganic coating structure. By increasing the tortuosity of the diffusion path and producing adsorption and retention effects on polar small molecules, it regulates the migration rate and direction of HCl and other low molecules around the filler, making them easier to be neutralized or exchanged and fixed in the vicinity of the filler. This improves the thermal stability and processing stability of the HPVC cable protection pipe, while also improving the mechanical strength and insulation performance.

[0049] Example 8 This embodiment provides a method for preparing a high-strength insulated HPVC cable protection pipe, including the following steps: Step 1: Preparation of premix Oleamide, diisononyl phthalate and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)] were mixed evenly at a mass ratio of 3:8:5 to obtain the excipient for later use. Weigh out the following by weight: 95 parts HPVC, 12 parts heat-stabilized hydrotalcite composite material prepared in Example 5, 10 parts epoxidized soybean oil and 2 parts auxiliary materials, add them to a high-speed homogenizer, mix them evenly to obtain a premix.

[0050] Step 2: Prepare HPVC cable protection pipe The premixed material is placed in a twin-screw extruder for melt extrusion, and then extruded through a tubular die at the extruder head to form a tube, thus obtaining an HPVC cable protection pipe. The twin-screw extruder is equipped with a cooling zone with an inlet temperature of 175°C and an outlet temperature of 90°C.

[0051] Example 9 This embodiment provides a method for preparing a high-strength insulated HPVC cable protection pipe, including the following steps: Step 1: Preparation of premix Oleamide, diisononyl phthalate and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenylpropionic acid)] were mixed evenly at a mass ratio of 3:8:5 to obtain the excipient for later use. Weigh out the following amounts by weight: 100 parts HPVC, 15 parts heat-stabilized hydrotalcite composite material prepared in Example 6, 12 parts epoxidized soybean oil, and 3 parts auxiliary materials. Add them to a high-speed homogenizer and mix evenly to obtain a premix.

[0052] Step 2: Prepare HPVC cable protection pipe The premixed material is placed in a twin-screw extruder for melt extrusion, and then extruded through a tubular die at the extruder head to form a tube, thus obtaining an HPVC cable protection pipe. The twin-screw extruder is equipped with a cooling zone with an inlet temperature of 180°C and an outlet temperature of 95°C.

[0053] Comparative Example 1 The difference between this comparative example and Example 9 is that, in step ③, when preparing the thermally stable hydrotalcite composite material, ZIF-8 is used in an equal amount to replace the silicon-titanium layer to coat ZIF-8.

[0054] Comparative Example 2 The difference between this comparative example and Example 9 is that the fatty acid salt solution was omitted in step ③ when preparing the thermally stable hydrotalcite composite material.

[0055] Comparative Example 3 The difference between this comparative example and Example 9 is that, in step (1) when preparing the premix, commercially available hydrotalcite is used in an equal amount to replace the thermally stabilized hydrotalcite composite material.

[0056] Performance testing: Random samples were taken from the head, middle, and tail of the HPVC cable protection pipes prepared in Examples 7-9 and Comparative Examples 1-3. After crushing, the samples were passed through a 2mm standard sieve to obtain HPVC cable protection pipe samples with a particle size of 0.5-2mm. The thermal stability of the HPVC cable protection pipe samples was tested according to standard GB / T 2917.1-2002 "Determination of the release of hydrogen chloride and any other acidic products at high temperature from blends and products mainly composed of vinyl chloride homopolymers and copolymers" (Congo Red method). The thermal stability of the HPVC cable protection pipe samples was characterized by the Congo Red test color change time. The longer the Congo Red test color change time, the better the thermal stability of the HPVC cable protection pipe. Referring to standard GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics", the HPVC cable protection pipes prepared in Examples 7-9 and Comparative Examples 1-3 were cut into specified Type 1A dumbbell-shaped specimens (gauge length 50 mm), and the tensile strength and elongation at break of the specimens were tested. The tensile strength and elongation at break were used to characterize the mechanical strength of the HPVC cable protection pipe specimens. The higher the tensile strength and elongation at break of the specimens, the better the mechanical strength of the HPVC cable protection pipe. Slice-shaped specimens were cut from the defect-free area in the middle of the HPVC cable protection pipes prepared in Examples 7-9 and Comparative Examples 1-3. The dielectric breakdown strength and volume resistivity of the HPVC cable protection pipe specimens prepared in Examples 7-9 and Comparative Examples 1-3 were tested in accordance with the standards GB / T 1408.1-2016 "Electrical Strength Test Methods for Insulating Materials - Part 1: Tests at Power Frequency" and GB / T 31838.2-2019 "Dielectric and Resistance Properties of Solid Insulating Materials - Part 2: Resistance Properties (DC Method) - Volume Resistivity and Volume Resistivity". The dielectric breakdown strength and volume resistivity were used to characterize the insulation performance of the HPVC cable protection pipe specimens. The higher the dielectric breakdown strength and volume resistivity of the HPVC cable protection pipe specimens, the better the insulation performance of the HPVC cable protection pipe specimens. Specific data are shown in Table 1.

[0057] Table 1 - Performance Test Data for Each Sample Data Analysis: Comparative analysis of the data in Table 1 above shows that the high-strength insulated HPVC cable protection pipe prepared by this invention exhibits the following characteristics: Congo Red color change time of 35 min, tensile strength of 38.2 MPa, elongation at break of 28.7%, and dielectric breakdown strength of 21.6 kV·mm. -1 At the same time, the volume resistivity is 1.3×10 14 The Ω·m values ​​are all superior to those of the comparative example, indicating that the present invention constructs a hierarchical composite modification system by introducing a silicon-titanium layer to coat ZIF-8 and fatty acid salt intercalated hydrotalcite, and forms a synergistic stabilizing effect with auxiliary materials such as epoxidized soybean oil. This not only effectively delays the thermal degradation process of HPVC and significantly improves the thermal and processing stability of the cable protection pipe, but also enhances the mechanical strength and insulation performance simultaneously through multi-scale barrier interfaces and interface densification effects. This enables the cable protection pipe to maintain excellent comprehensive performance and long-term reliability under high voltage, thermal stress and complex service environments.

[0058] 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-strength insulated HPVC cable protection pipe, comprising HPVC, heat-stabilized hydrotalcite composite material, epoxidized soybean oil, and auxiliary materials, which are fully mixed and then extruded, characterized in that, The process also includes placing aluminum nitrate nonahydrate, calcium nitrate tetrahydrate, and decarbonated water in a reaction vessel and stirring at room temperature for 15-30 minutes to obtain a metal salt solution. Then, stearic acid and ethanol are placed in the reaction vessel and stirred. Sodium hydroxide solution is added, and the reaction vessel is heated to 60-70°C and stirred for 20-30 minutes to obtain a fatty acid salt solution. Then, ZIF-8 coated with silicon titanium layer and decarbonated water are placed in a reaction vessel under nitrogen atmosphere and stirred. The reaction vessel is heated to reflux, and the metal salt solution and fatty acid salt solution are slowly added dropwise. The mixture is stirred for 10-15 minutes, and sodium hydroxide solution is added to adjust the pH to 9.8-10.

5. The reaction is kept at the temperature for 6-8 hours, and the post-treatment yields a thermally stable hydrotalcite composite material. The high-strength insulated HPVC cable protection pipe is obtained by extrusion molding after being fully mixed with 90-100 parts of HPVC, 10-15 parts of heat-stabilized hydrotalcite composite material, 8-12 parts of epoxidized soybean oil, and 1-3 parts of auxiliary materials, by weight.

2. The high-strength insulated HPVC cable protection pipe according to claim 1, characterized in that, The ratio of aluminum nitrate nonahydrate, calcium nitrate tetrahydrate, and decarbonated water is 6-8g:8-10g:80-100mL; the ratio of stearic acid, ethanol, and sodium hydroxide solution is 10-12g:80-100mL:40-60mL, and the sodium hydroxide solution is composed of sodium hydroxide and decarbonated water in a ratio of 3-3.2g:100mL.

3. The high-strength insulated HPVC cable protection pipe according to claim 1, characterized in that, The ratio of the amount of ZIF-8 coated with the silicon-titanium layer, decarbonated water, metal salt solution and fatty acid salt solution is 1-2g:80-100mL:80-100mL:80-100mL, and the sodium hydroxide solution is composed of sodium hydroxide and decarbonated water in a ratio of 6-8g:100mL.

4. The high-strength insulated HPVC cable protection pipe according to claim 1, characterized in that, The silicon-titanium layer coated ZIF-8 was prepared by the following steps: First, ZIF-8, ethanol, deionized water, and ammonia were placed in a reaction vessel and stirred. Then, tetraethyl orthosilicate solution was added and stirred at room temperature for 4-6 hours. After post-treatment, ZIF-8 with a silicon layer was obtained. Next, ZIF-8 with a silicon layer and ethanol were placed in a reaction vessel and stirred. Then, isopropyl triisostearate titanate was added and stirred at room temperature for 0.5-1 hour. The reaction vessel was heated to 45-55℃ and kept at that temperature for 0.5-1 hour. After post-treatment, ZIF-8 with a silicon-titanium layer was obtained.

5. A high-strength insulated HPVC cable protection pipe according to claim 4, characterized in that, The ratio of ZIF-8, ethanol, deionized water, ammonia, and tetraethyl orthosilicate ethanol solution is 1.5-2.5g:180-200mL:8-10mL:5-7mL:8-10mL, the concentration of ammonia is 25-28wt%, and the tetraethyl orthosilicate solution is composed of tetraethyl orthosilicate and ethanol in a ratio of 1.0-1.2g:10mL; the ratio of silicon layer coating ZIF-8, ethanol, and triisostearate titanate isopropyl ...

6. A high-strength insulated HPVC cable protection pipe according to claim 4, characterized in that, The preparation method of ZIF-8 is as follows: zinc nitrate and methanol are placed in a reaction vessel and stirred. The reaction vessel is heated to 55-65℃, 2-methylimidazolium methanol solution is added, and the reaction is kept at the temperature for 8-10 hours. ZIF-8 is obtained by post-treatment.

7. A high-strength insulated HPVC cable protection pipe according to claim 6, characterized in that, The ratio of zinc nitrate, methanol, and 2-methylimidazolium methanol solution is 2-4 g: 80-100 mL: 80-100 mL, and the concentration of 2-methylimidazolium methanol solution is 0.4-0.6 mol / L.

8. A method for preparing a high-strength insulated HPVC cable protection pipe as described in any one of claims 1-7, characterized in that, Includes the following steps: First, HPVC, heat-stabilized hydrotalcite composite material, epoxidized soybean oil and auxiliary materials are added to a high-speed homogenizer and mixed evenly to obtain a premix. Then, the premix is ​​placed in a twin-screw extruder for melt extrusion and extruded through a tubular die at the extruder head to form an HPVC cable protection pipe.

9. The method for preparing a high-strength insulated HPVC cable protection pipe according to claim 8, characterized in that, The auxiliary materials consist of lubricant, plasticizer and heat stabilizer in a mass ratio of 3:8:5.

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