A modified polypropylene power pipe and a method for preparing the same

Abstract

The application discloses a modified polypropylene electric power pipe and a preparation method thereof, and belongs to the technical field of high-performance polypropylene pipes. The method comprises the following steps: blending, melting, extruding and granulating high-crystalline polypropylene, block copolymerized polypropylene, a nucleating agent, maleic anhydride grafted polypropylene, maleic anhydride grafted polyolefin elastomer, a flame retardant, an antioxidant, a lubricant and modified basalt fibers to obtain modified polypropylene master batches after drying; and extruding and molding the modified polypropylene master batches to obtain the modified polypropylene electric power pipe. The modified basalt fiber is obtained by purifying phosphogypsum powder and dissolving the phosphogypsum powder with acid to obtain a reaction mother liquor; the basalt fiber is immersed in the reaction mother liquor for in-situ mineralization reaction to construct an embedded quaternary ammonium alkali cation and form a calcium carbonate / calcium phosphate salt composite hydrophobic mineralization layer on the surface of the basalt fiber; and the comprehensive performance of the modified polypropylene electric power pipe is improved.

Description

Technical Field

[0001] This invention belongs to the field of high-performance polypropylene pipe technology, specifically relating to a modified polypropylene power pipe and its preparation method. Background Technology

[0002] Currently, modified polypropylene is widely used as the core material for underground pipes in the construction of power grids. With the advancement of ultra-high voltage power transmission projects and the continuous increase in the load of urban underground pipe corridors, the cable laying density and transmission power in underground pipe corridors have increased significantly, and the heat generated during cable operation has increased significantly. Existing ordinary modified polypropylene pipes are prone to softening and deformation under high temperature and long-term service conditions.

[0003] To overcome the aforementioned limitations in mechanical and thermal properties, existing technologies primarily employ two approaches: one is high-filler rigid inorganic modification. For example, patent document CN121652509A enhances the strength of the polypropylene matrix by adding large amounts of inorganic rigid fillers such as talc and calcium carbonate. However, this high-proportion inorganic filler filling method severely disrupts the continuous phase structure of the polypropylene resin matrix, leading to numerous interface defects within the matrix. This significantly weakens the material's low-temperature impact resistance, making the pipe highly susceptible to brittle fracture during low-temperature drop hammer impact tests. Consequently, its resistance to low-temperature impact and external force damage is drastically reduced, making it difficult to adapt to complex applications. The first issue is the use of traditional halogenated flame retardants or halogen-free intumescent flame retardants in underground geological and low-temperature environments. The second issue is the addition of high-load traditional halogenated flame retardants or halogen-free intumescent flame retardants. For example, the patent document with publication number CN121249055A adds halogen-free intumescent flame retardants and anti-dripping additives to polypropylene resin in the form of masterbatch to improve the flame retardant effect. However, high-load flame retardants will break the bonding stability of polypropylene molecular chains, significantly deteriorate the core mechanical properties of the material, and cause a significant reduction in the pipe's resistance to deformation and environmental stress cracking. The pipe is prone to cracking, breakage and other failures during long-term service, which seriously shortens the service life of the power grid and poses a great engineering safety hazard.

[0004] Therefore, in order to overcome the aforementioned mechanical and thermal limitations and meet the long-term safe service requirements of high-load ultra-high voltage power grids and urban underground integrated pipe corridors, it is urgent to develop a balanced modified polypropylene power pipe that combines high heat resistance and flame retardancy, high rigidity, excellent low-temperature impact resistance, and good mechanical properties. Summary of the Invention

[0005] The purpose of this invention is to provide a modified polypropylene power pipe and its preparation method, which improves the high-temperature flame retardant properties, deformation resistance, low-temperature impact resistance and mechanical stability of polypropylene power pipes.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a modified polypropylene power pipe includes the following steps: S1. A blend is prepared by blending highly crystalline polypropylene, block copolymer polypropylene, nucleating agent, maleic anhydride grafted polypropylene, maleic anhydride grafted polyolefin elastomer, flame retardant, antioxidant and lubricant. The blend is then melt-extruded and granulated with modified basalt fiber and dried to obtain modified polypropylene masterbatch. S2. The modified polypropylene masterbatch is fed into a single-screw pipe extruder, and after vacuum sizing, gradient cooling, traction, and cutting, the modified polypropylene power pipe is obtained. The preparation method of the modified basalt fiber includes the following steps: A1. Add purified phosphogypsum powder to hydrochloric acid solution, heat and stir to dissolve, filter, and take the liquid phase to obtain the reaction mother liquor; A2. The basalt fiber is immersed in the reaction mother liquor and treated at a constant temperature. The pH of the system is adjusted to be alkaline by tetrapropylammonium hydroxide, and carbon dioxide is introduced at the same time to carry out the in-situ mineralization reaction. After the reaction is completed, the mineralized basalt fiber is taken out, and after alkali washing and KH-560 modification treatment, the modified basalt fiber is obtained.

[0007] By acid-dissolving purified phosphogypsum powder and then filtering to separate insoluble matter, a reaction mother liquor rich in calcium ions, phosphate ions, and trace amounts of fluoride ions is obtained. The acidic environment of the reaction mother liquor is used to gently etch the surface of basalt fibers, exposing more silanol active sites. As the pH increases, calcium ions react with the introduced carbon dioxide to generate calcium carbonate crystal nuclei and grow epitaxially. At the same time, phosphate ions and calcium ions form a small amount of calcium phosphate salt co-precipitate. During the mineralization process, the cations of organic quaternary ammonium bases are embedded, forming a calcium carbonate / calcium phosphate composite hydrophobic mineralization layer on the surface of basalt fibers. This gives the modified basalt fiber surface hydrophobicity, improves compatibility with the polypropylene system, and exerts flame retardant effect and fiber reinforcement. Simultaneously, the silanol groups after KH-560 hydrolysis condense with the hydroxyl groups of the modified basalt fiber and the surface mineralization layer, introducing epoxy groups. During subsequent extrusion, these epoxy groups undergo ring-opening esterification with the maleic anhydride-grafted polypropylene anhydride, forming covalent coupling bonds, further enhancing the bonding effect between the modified basalt fiber and the polypropylene material. Meanwhile, the nucleating agent NA-21 added to the masterbatch migrates to the fiber surface, growing an α-crystal transcrystalline layer outward with the fiber as the crystal nucleus. This layer has high modulus and excellent heat resistance, allowing stress to be efficiently transferred to the fiber under external force. At the same time, the maleic anhydride-grafted polyolefin elastomer disperses in the matrix to form elastic energy-absorbing points, absorbing a large amount of impact energy. The synergistic effect of both improves the impact resistance of polypropylene power pipes, provided that the Vicat softening point is >150℃.

[0008] As a preferred technical solution of the present invention, in step A1, the mass ratio of the purified phosphogypsum powder to the hydrochloric acid solution is 1:3-5, and the mass fraction of the hydrochloric acid solution is 8%-10%; the heating and stirring dissolution refers to heating and stirring at 70-80℃ for 3-4 hours.

[0009] As a preferred embodiment of the present invention, in step A2, the carbon dioxide gas flow rate is 150-200 mL / min, and the ventilation time is 30-50 min.

[0010] As a preferred embodiment of the present invention, step A2, specifically includes the following steps: alkali washing and KH-560 modification treatment of the mineralized basalt fibers. The mineralized basalt fibers are immersed in a 0.1% sodium hydroxide solution at room temperature for 8-12 minutes, rinsed thoroughly with deionized water until the washing solution is neutral, and then immersed in a 1.5% KH-560 deionized water / ethanol solution at room temperature for 20-40 minutes. After immersion, the fibers are dried at 120℃ for 5-7 hours and then cut into short fibers with a length of 3-6 mm.

[0011] Alkali washing neutralizes and removes any trace chloride ions that may remain in the mineralized layer, eliminating the potential risk of polypropylene degradation. The silanol groups from KH-560 hydrolysis condense with the -OH groups of the mineralized basalt fibers and the surface mineralized layer, introducing epoxy groups. These epoxy groups then undergo ring-opening esterification with the maleic anhydride-grafted polypropylene during subsequent extrusion, forming covalent coupling bonds. This further enhances the bonding between the fiber and the PP material, ultimately achieving efficient dispersion and strong interfacial bonding of the basalt fiber in the PP matrix, resulting in a high-ring-stiffness, halogen-free, flame-retardant modified polypropylene power pipe with excellent mechanical properties. Furthermore, the alkali washing and dechlorination process, followed by epoxy coupling, is simple and efficient, eliminating the risk of polypropylene degradation due to the introduction of initiators. The production process is also free of harmful volatiles, making it more economical and environmentally friendly.

[0012] As a preferred embodiment of the present invention, the specific process conditions for melt extrusion granulation in step S1 are as follows: The temperature in Zone 1 is 175℃, in Zone 2 it is 190℃, in Zones 3 to 5 it is 210℃, in Zones 6 to 8 it is 200℃, the head temperature is 195℃, the main machine speed is 300-400rpm, and after the melt is extruded through the die head, it is granulated by underwater die surface hot cutting, with a circulating water temperature of 40-50℃.

[0013] As a preferred embodiment of the present invention, in step S2, the gradient cooling refers to the pipe being successively cooled by 60°C warm water for 25-35 seconds after vacuum sizing, then transitionally cooled by 30°C warm water for 40-55 seconds, and finally naturally cooled to room temperature in air. This gradual cooling avoids excessive internal and external temperature differences, uneven crystallization, and residual internal stress caused by sudden cooling of the modified polypropylene pipe.

[0014] As a preferred embodiment of the present invention, step A2 further includes the following steps: During the in-situ mineralization reaction with carbon dioxide, polyethylene glycol-2000 (0.3% by mass of phosphogypsum in step A1) is added. The addition of polyethylene glycol-2000 during the in-situ mineralization reaction with carbon dioxide acts as a crystal form regulator and dispersant, making the composite mineralized layer formed on the basalt fiber surface more uniform, dense, and continuous. This further enhances the hydrophobicity of the fiber surface and its interfacial compatibility with the polypropylene matrix, strengthening the fiber reinforcement and flame retardant synergistic effect, ultimately improving the mechanical strength and thermal stability of the modified polypropylene power pipe.

[0015] Another object of the present invention is to provide a modified polypropylene power pipe, wherein the mass ratio of the highly crystalline polypropylene, block copolymer polypropylene, nucleating agent, maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyolefin elastomer, flame retardant, antioxidant, lubricant and modified basalt fiber is 73-77:24-26:0.2-0.4:4-6:3-5:8-10:0.4-0.6:0.5-0.7:10-15.

[0016] As a preferred embodiment of the present invention, the nucleating agent is an organophosphate nucleating agent NA-21; the flame retardant is a halogen-free intumescent flame retardant; the antioxidant includes at least one of BASF Irganox 1010 and BASF Irgafos 168; and the lubricant is pentaerythritol stearate. The product utilizes organophosphate nucleating agent NA-21, which migrates to the surface of basalt fibers and induces the formation of a high-modulus, high-heat-resistant α-crystal transcrystalline structure. This facilitates efficient stress transfer and significantly improves the heat resistance and ring stiffness of the pipe. A halogen-free intumescent flame retardant is selected, offering advantages such as low smoke, non-toxicity, and environmental safety. It also forms a synergistic flame-retardant effect with the calcium carbonate / calcium phosphate mineralization layer on the fiber surface, effectively anchoring the intumescent carbon layer based on the rigid fiber skeleton, thus significantly reducing the amount of flame retardant required. Combined with BASF's Irganox 1010 and Irgafos 168 compound antioxidants, it exerts a synergistic effect of primary and secondary antioxidants, effectively inhibiting the thermo-oxidative degradation of polypropylene during high-temperature processing and long-term use, improving the pipe's aging resistance and service life. Pentaerythritol stearate is used as a lubricant, providing both internal and external lubrication, improving melt processing fluidity and the uniformity of component dispersion. It exhibits good processing thermal stability, no blooming, and does not impair the material's mechanical and flame-retardant properties. The overall formulation demonstrates excellent compatibility, strong process adaptability, and is economical and environmentally friendly.

[0017] As a preferred embodiment of the present invention, the halogen-free intumescent flame retardant includes at least one of ammonium polyphosphate and pentaerythritol.

[0018] The mineralized layer on the surface of the modified basalt fiber decomposes at 300-450℃, releasing water and carbon dioxide, diluting combustible gases and carrying away heat. The residual inorganic phase, together with the basalt fiber body, forms a high-temperature resistant skeleton. The halogen-free intumescent flame retardant in the matrix forms an intumescent carbon layer when heated, which is firmly anchored by the skeleton, forming a dense carbon layer anchoring structure. Thus, only a small amount of flame retardant is needed, and the flame retardant performance can still stably reach UL94 V-0 level (1.6mm), and the material's mechanical properties are well retained.

[0019] The beneficial effects of this invention are: (1) The modified polypropylene power pipe and its preparation method disclosed in this invention are prepared by using purified phosphogypsum acid dissolution filtration to obtain a reaction mother liquor containing calcium, phosphate and trace fluoride ions. The acid mild etching of basalt fibers exposes silanol sites. Alkali is adjusted and carbon dioxide is passed through for in-situ mineralization. Calcium carbonate and calcium phosphate co-precipitate and embed quaternary ammonium alkali cations to construct a calcium carbonate / calcium phosphate composite hydrophobic mineralization layer on the fiber surface, which has hydrophobic compatibility, flame retardant and reinforcing effects. Then, KH-560 silane coupling modification is performed, and covalent interface bonding is formed by the ring-opening esterification of epoxy groups and maleic anhydride grafted polypropylene to strengthen the bond between the fiber and the polypropylene matrix. At the same time, nucleating agent NA-21 induces the generation of a high modulus and high heat-resistant α crystal transcrystalline layer on the fiber surface to achieve efficient stress transfer. Combined with the elastic energy absorption effect of maleic anhydride grafted polyolefin elastomer, it synergistically toughens the pipe, so that the Vicat softening temperature of the pipe reaches above 150°C. This allows the pipe to maintain excellent high-temperature performance while improving the impact resistance of the polypropylene pipe.

[0020] (2) The modified polypropylene power pipe and its preparation method disclosed in this invention embeds tetrapropylammonium hydroxide into the mineralization layer. The quaternary ammonium organic component can be decomposed by heating to generate inert gas, which forms a synergistic smoke suppression and flame retardant effect with the halogen-free intumescent flame retardant system, further improving the limiting oxygen index and flame retardant level of the pipe.

[0021] (3) The modified polypropylene power pipe and its preparation method disclosed in this invention remove residual chloride ions by alkaline washing of mineralized basalt fibers to avoid polypropylene degradation, and then introduce epoxy groups by KH-560 coupling modification, so that they can be combined with maleic anhydride-grafted polyacrylic anhydride ring-opening esterification to form a covalent interface bond, thereby achieving uniform dispersion and strong interfacial bonding of basalt fibers in polypropylene matrix, and significantly improving the mechanical strength of modified polypropylene power pipe.

[0022] (4) The modified polypropylene power pipe and its preparation method disclosed in this invention achieves efficient stress transfer by inducing the formation of α crystal transcrystalline layer on the surface of basalt fiber using nucleating agent NA-21. Combined with the elastic energy absorption of maleic anhydride-grafted polyolefin elastomer, it enhances the heat resistance and impact resistance of the pipe. At the same time, the mineralized layer on the fiber surface is pyrolyzed to reduce temperature and suppress flame, and it is anchored with the basalt fiber skeleton to expand the flame-retardant carbon layer, which greatly reduces the amount of flame retardant used. It achieves excellent flame retardancy while taking into account excellent mechanical properties. Detailed Implementation

[0023] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0024] Details of some of the raw materials used in this invention are as follows: High crystallinity polypropylene, Hanwha Total BI452, Shanghai Fuyi International Trading Co., Ltd.; Block copolymer polypropylene, Yanshan Petrochemical B8101, Beijing Kunpeng Chemical Co., Ltd.; Maleic anhydride-grafted polypropylene, Nanjing Sutai Polymer Technology Co., Ltd. Maleic anhydride-grafted polyolefin elastomer, Dow AMPLIFY GR 216, Shanghai Wangsu Import & Export Co., Ltd.; Ammonium polyphosphate, Zhenjiang Xingxing Flame Retardant Co., Ltd.; Phosphogypsum, Guizhou Guicheng Industrial (Group) Co., Ltd.

[0025] Example 1 Add phosphogypsum to deionized water at a solid-liquid ratio of 1:2 (by mass), stir and wash for 10 minutes, filter, repeat twice, dry the filter cake at 90℃, grind to 800 mesh to obtain purified phosphogypsum powder, add the purified phosphogypsum powder to 10wt% hydrochloric acid solution at a solid-liquid ratio of 1:3, heat and stir at 70℃ for 3 hours, filter, and take the liquid phase to obtain the reaction mother liquor.

[0026] Continuous basalt fiber yarn was drawn and immersed in the reaction mother liquor and heated at a constant temperature of 65°C. 25wt% tetrapropylammonium hydroxide solution was slowly added to adjust the pH of the system to 9.5. At the same time, carbon dioxide gas with a flow rate of 150mL / min was introduced to carry out an in-situ mineralization reaction for 50min. After the reaction, the mineralized basalt fiber was taken out and immersed in a 0.1% sodium hydroxide solution at room temperature for 8min. It was then rinsed thoroughly with deionized water until the washing solution was neutral. It was then immersed in a 1.5% KH-560 deionized water / ethanol solution (the volume ratio of deionized water to ethanol was 1:4) at room temperature for 20min. It was then taken out, dried at 120°C for 5h, and cut into short fibers with a length of 3mm to obtain modified basalt fiber.

[0027] The mixture comprises 73 parts by weight of highly crystalline polypropylene, 24 parts by weight of block copolymer polypropylene, 0.2 parts by weight of nucleating agent, 4 parts by weight of maleic anhydride-grafted polypropylene, 3 parts by weight of maleic anhydride-grafted polyolefin elastomer, 6 parts by weight of flame retardant ammonium polyphosphate, 4 parts by weight of flame retardant pentaerythritol, 0.2 parts by weight of antioxidant BASF Irganox 1010, and 0.3 parts by weight of antioxidant BASF Irgafos. 168 parts by weight and 0.5 parts by weight of pentaerythritol stearate lubricant were added to a high-speed mixer and mixed at 500 rpm for 7 minutes to obtain a premix, which was then fed into a twin-screw extruder through the main feed port. 15 parts by weight of modified basalt fiber were added to the twin-screw extruder through the side feed port of zone 5. The temperature settings of the twin-screw extruder were as follows: zone 1 175℃, zone 2 190℃, zones 3 to 5 210℃, zones 6 to 8 200℃, die head 195℃, main extruder speed 300 rpm. After the melt was extruded through the die, it was granulated by underwater die hot cutting with circulating water at 40℃ and centrifugally dried to obtain modified polypropylene masterbatch.

[0028] Modified polypropylene masterbatch is fed into a single-screw pipe extruder with a barrel temperature of 190℃. After vacuum sizing, 60℃ warm water shaping and cooling for 25s, 30℃ warm water transition cooling for 40s, natural air cooling to room temperature, traction, and cutting, modified polypropylene power pipe is obtained.

[0029] Example 2 Add phosphogypsum to deionized water at a solid-liquid ratio of 1:3 (by mass), stir and wash for 20 minutes, filter, repeat twice, dry the filter cake at 90℃, grind to 800 mesh to obtain purified phosphogypsum powder, add the purified phosphogypsum powder to 9wt% hydrochloric acid solution at a solid-liquid ratio of 1:4, heat and stir at 75℃ for 3.5 hours, filter, and take the liquid phase to obtain the reaction mother liquor.

[0030] Continuous basalt fiber yarn was drawn and immersed in the reaction mother liquor and heated at a constant temperature of 65°C. 25wt% tetrapropylammonium hydroxide solution was slowly added to adjust the pH of the system to 10.0. At the same time, carbon dioxide gas with a flow rate of 180mL / min was introduced to carry out an in-situ mineralization reaction for 40min. After the reaction, the mineralized basalt fiber was taken out and immersed in a 0.1% sodium hydroxide solution at room temperature for 10min. It was then rinsed thoroughly with deionized water until the washing solution was neutral. It was then immersed in a 1.5% KH-560 deionized water / ethanol solution (the volume ratio of deionized water to ethanol was 1:4) at room temperature for 30min. It was then taken out, dried at 120°C for 6h, and cut into short fibers with a length of 4.5mm to obtain modified basalt fiber.

[0031] The mixture comprises 75 parts by weight of highly crystalline polypropylene, 25 parts by weight of block copolymer polypropylene, 0.3 parts by weight of nucleating agent, 5 parts by weight of maleic anhydride-grafted polypropylene, 4 parts by weight of maleic anhydride-grafted polyolefin elastomer, 6 parts by weight of flame retardant ammonium polyphosphate, 3 parts by weight of flame retardant pentaerythritol, 0.25 parts by weight of antioxidant BASF Irganox 1010, and 0.25 parts by weight of antioxidant BASF Irgafos. 168 parts by weight and 0.6 parts by weight of pentaerythritol stearate lubricant were added to a high-speed mixer and mixed at 800 rpm for 6 minutes to obtain a premix, which was then fed into a twin-screw extruder through the main feed port. 13 parts by weight of modified basalt fiber were added to the twin-screw extruder through the side feed port of zone 5. The temperature settings of the twin-screw extruder were as follows: zone 1 175℃, zone 2 190℃, zones 3 to 5 210℃, zones 6 to 8 200℃, die head 195℃, and main extruder speed 350 rpm. After the melt was extruded through the die, it was granulated by underwater die hot cutting with circulating water at 45℃ and centrifugally dried to obtain modified polypropylene masterbatch.

[0032] Modified polypropylene masterbatch is fed into a single-screw pipe extruder at a barrel temperature of 200℃. After vacuum sizing, 60℃ warm water shaping and cooling for 30 seconds, 30℃ warm water transition cooling for 50 seconds, natural air cooling to room temperature, traction, and cutting, modified polypropylene power pipe is obtained.

[0033] Example 3 Add phosphogypsum to deionized water at a solid-liquid ratio of 1:4 (by mass), stir and wash for 30 minutes, filter, repeat twice, dry the filter cake at 90℃, grind to 800 mesh to obtain purified phosphogypsum powder, add the purified phosphogypsum powder to 8wt% hydrochloric acid solution at a solid-liquid ratio of 1:5, heat and stir at 80℃ for 4 hours, filter, and take the liquid phase to obtain the reaction mother liquor.

[0034] Continuous basalt fiber yarn was drawn and immersed in the reaction mother liquor and heated at a constant temperature of 65°C. 25wt% tetrapropylammonium hydroxide solution was slowly added to adjust the pH of the system to 10.5. At the same time, carbon dioxide gas with a flow rate of 200mL / min was introduced to carry out an in-situ mineralization reaction for 30min. After the reaction, the mineralized basalt fiber was taken out and immersed in a 0.1% sodium hydroxide solution at room temperature for 12min. It was then rinsed thoroughly with deionized water until the washing solution was neutral. It was then immersed in a 1.5% KH-560 deionized water / ethanol solution (the volume ratio of deionized water to ethanol was 1:4) at room temperature for 40min. It was then taken out, dried at 120°C for 7h, and cut into short fibers with a length of 6mm to obtain modified basalt fiber.

[0035] The mixture comprises 77 parts by weight of highly crystalline polypropylene, 26 parts by weight of block copolymer polypropylene, 0.4 parts by weight of nucleating agent, 6 parts by weight of maleic anhydride-grafted polypropylene, 5 parts by weight of maleic anhydride-grafted polyolefin elastomer, 6 parts by weight of flame retardant ammonium polyphosphate, 4 parts by weight of flame retardant pentaerythritol, 0.3 parts by weight of antioxidant BASF Irganox 1010, and 0.3 parts by weight of antioxidant BASF Irgafos. 168 and 0.7 parts by weight of pentaerythritol stearate lubricant were added to a high-speed mixer and mixed at 1000 rpm for 5 minutes to obtain a premix, which was then fed into a twin-screw extruder through the main feed port. 10 parts by weight of modified basalt fiber were added to the twin-screw extruder through the side feed port of zone 5. The temperature settings of the twin-screw extruder were as follows: zone 1 175℃, zone 2 190℃, zones 3 to 5 210℃, zones 6 to 8 200℃, die head 195℃, main extruder speed 400 rpm. After the melt was extruded through the die, it was granulated by underwater die hot cutting with circulating water at 50℃ and centrifugally dried to obtain modified polypropylene masterbatch.

[0036] Modified polypropylene masterbatch is fed into a single-screw pipe extruder with a barrel temperature of 210℃. After vacuum sizing, 60℃ warm water shaping and cooling for 35s, 30℃ warm water transition cooling for 55s, natural air cooling to room temperature, traction, and cutting, modified polypropylene power pipe is obtained.

[0037] Example 4 Add phosphogypsum to deionized water at a solid-liquid ratio of 1:3 (by mass), stir and wash for 20 minutes, filter, repeat twice, dry the filter cake at 90℃, grind to 800 mesh to obtain purified phosphogypsum powder, add the purified phosphogypsum powder to 9wt% hydrochloric acid solution at a solid-liquid ratio of 1:4, heat and stir at 75℃ for 3.5 hours, filter, and take the liquid phase to obtain the reaction mother liquor.

[0038] Continuous basalt fiber yarn was drawn and immersed in the reaction mother liquor and heated at a constant temperature of 65°C. 25wt% tetrapropylammonium hydroxide solution was slowly added to adjust the pH of the system to 10.0. At the same time, carbon dioxide gas with a flow rate of 180mL / min was introduced to carry out an in-situ mineralization reaction for 40min. After the reaction, the mineralized basalt fiber was taken out and immersed in a 0.1% sodium hydroxide solution at room temperature for 10min. It was then rinsed thoroughly with deionized water until the washing solution was neutral. It was then immersed in a 1.5% KH-560 deionized water / ethanol solution (the volume ratio of deionized water to ethanol was 1:4) at room temperature for 30min. It was then taken out, dried at 120°C for 6h, and cut into short fibers with a length of 4.5mm to obtain modified basalt fiber.

[0039] The mixture comprises 76 parts by weight of highly crystalline polypropylene, 24.5 parts by weight of block copolymer polypropylene, 0.32 parts by weight of nucleating agent, 5.5 parts by weight of maleic anhydride-grafted polypropylene, 4.2 parts by weight of maleic anhydride-grafted polyolefin elastomer, 6 parts by weight of flame retardant ammonium polyphosphate, 3 parts by weight of flame retardant pentaerythritol, 0.25 parts by weight of antioxidant BASF Irganox 1010, and 0.25 parts by weight of antioxidant BASF Irgafos. 168 and 0.6 parts by weight of pentaerythritol stearate lubricant were added to a high-speed mixer and mixed at 800 rpm for 6 minutes to obtain a premix, which was then fed into a twin-screw extruder through the main feed port. 11.78 parts by weight of modified basalt fiber were added to the twin-screw extruder through the side feed port of zone 5. The temperature settings of the twin-screw extruder were as follows: zone 1 175℃, zone 2 190℃, zones 3-5 210℃, zones 6-8 200℃, die head 195℃, and main extruder speed 350 rpm. After the melt was extruded through the die, it was granulated by underwater die hot cutting with circulating water at 45℃ and centrifugally dried to obtain modified polypropylene masterbatch.

[0040] Modified polypropylene masterbatch is fed into a single-screw pipe extruder at a barrel temperature of 200℃. After vacuum sizing, 60℃ warm water shaping and cooling for 30 seconds, 30℃ warm water transition cooling for 50 seconds, natural air cooling to room temperature, traction, and cutting, modified polypropylene power pipe is obtained.

[0041] Example 5 The difference from Example 2 is that the preparation method of this modified basalt fiber includes the following steps: A1. Add phosphogypsum to deionized water at a solid-liquid ratio of 1:3 (by mass), stir and wash for 20 minutes, filter, repeat twice, dry the filter cake at 90℃, grind to 800 mesh to obtain purified phosphogypsum powder, add the purified phosphogypsum powder to 9wt% hydrochloric acid solution at a solid-liquid ratio of 1:4, heat and stir at 75℃ for 3.5 hours, filter, and take the liquid phase to obtain the reaction mother liquor; A2. Continuous basalt fiber yarn is drawn and immersed in the reaction mother liquor and heated at a constant temperature of 65°C. 25wt% tetrapropylammonium hydroxide solution is slowly added to adjust the pH of the system to 10.0. At the same time, carbon dioxide with a gas flow rate of 180mL / min is introduced. Polyethylene glycol-2000 with a mass of 0.3% of the original phosphogypsum is added to carry out an in-situ mineralization reaction for 40min. After the reaction is completed, the mineralized basalt fiber is taken out and immersed in a sodium hydroxide solution with a mass fraction of 0.1% for 10min at room temperature. It is then rinsed thoroughly with deionized water until the washing solution is neutral. It is then immersed in a deionized water / ethanol solution with a mass fraction of 1.5% KH-560 (volume ratio of deionized water to ethanol is 1:4) for 30min at room temperature. It is then taken out, dried at 120°C for 6h, and cut into short fibers with a length of 4.5mm to obtain the product.

[0042] Comparative Example 1 The difference from Example 2 is that the preparation method of this modified basalt fiber includes the following steps: A1. Add phosphogypsum to deionized water at a solid-liquid ratio of 1:3 (by mass), stir and wash for 20 minutes, filter, repeat twice, dry the filter cake at 90℃, grind to 800 mesh to obtain purified phosphogypsum powder, add the purified phosphogypsum powder to 9wt% hydrochloric acid solution at a solid-liquid ratio of 1:4, heat and stir at 75℃ for 3.5 hours, filter, and take the liquid phase to obtain the reaction mother liquor; A2. Continuous basalt fiber yarn is drawn and immersed in the reaction mother liquor and heated at a constant temperature of 65°C. A 0.1 mol / L sodium hydroxide solution is slowly added to adjust the pH of the system to 10.0. At the same time, carbon dioxide gas with a flow rate of 180 mL / min is introduced to carry out an in-situ mineralization reaction for 40 min. After the reaction is completed, the mineralized basalt fiber is taken out and immersed in a 0.1% sodium hydroxide solution at room temperature for 10 min. It is then rinsed thoroughly with deionized water until the washing solution is neutral. It is then immersed in a 1.5% KH-560 deionized water / ethanol solution (the volume ratio of deionized water to ethanol is 1:4) at room temperature for 30 min. After that, it is taken out and dried at 120°C for 6 h. The fiber is then cut into short fibers with a length of 4.5 mm.

[0043] Comparative Example 2 The difference from Example 2 is that the preparation method of this modified basalt fiber includes the following steps: A1. Add phosphogypsum to deionized water at a solid-liquid ratio of 1:3 (by mass), stir and wash for 20 minutes, filter, repeat twice, dry the filter cake at 90℃, grind to 800 mesh to obtain purified phosphogypsum powder, add the purified phosphogypsum powder to 9wt% hydrochloric acid solution at a solid-liquid ratio of 1:4, heat and stir at 75℃ for 3.5 hours, filter, and take the liquid phase to obtain the reaction mother liquor; A2. Continuous basalt fiber yarn is drawn and immersed in the reaction mother liquor and heated at a constant temperature of 65°C. 25wt% tetrapropylammonium hydroxide solution is slowly added to adjust the pH of the system to 10.0. At the same time, carbon dioxide gas with a flow rate of 180mL / min is introduced to carry out in-situ mineralization reaction for 40min. After the reaction is completed, the mineralized basalt fiber is taken out and immersed in a 0.1% sodium hydroxide solution. It is soaked at room temperature for 10min. It is then rinsed thoroughly with deionized water until the washing solution is neutral. It is dried at 120°C for 6h and cut into short fibers with a length of 4.5mm to obtain the product.

[0044] Comparative Example 3 The difference from Example 2 is that the preparation method of this modified basalt fiber includes the following steps: A1. Add phosphogypsum to deionized water at a solid-liquid ratio of 1:3 (by mass), stir and wash for 20 minutes, filter, repeat twice, dry the filter cake at 90℃, grind to 800 mesh to obtain purified phosphogypsum powder, add the purified phosphogypsum powder to 9wt% hydrochloric acid solution at a solid-liquid ratio of 1:4, heat and stir at 75℃ for 3.5 hours, filter, and take the liquid phase to obtain the reaction mother liquor; A2. Continuous basalt fiber yarn is drawn and immersed in the reaction mother liquor and heated at 65°C for 40 minutes. The immersed basalt fiber is then removed and immersed in a 0.1% sodium hydroxide solution at room temperature for 10 minutes. It is then thoroughly rinsed with deionized water until the washing solution is neutral. The fiber is then immersed in a 1.5% KH-560 deionized water / ethanol solution (the volume ratio of deionized water to ethanol is 1:4) at room temperature for 30 minutes. The fiber is then removed, dried at 120°C for 6 hours, and cut into short fibers with a length of 4.5 mm.

[0045] Performance testing The properties of the polypropylene materials prepared in Examples 1-5 and Comparative Examples 1-3 were tested, and the results are shown in Table 1 below: Table 1

[0046] As shown in Table 1, the polypropylene power pipes prepared in Examples 1-5 of this invention have better high-temperature deformation resistance, low-temperature impact resistance, and flame retardant properties than the comparative examples. In contrast, the performance of Comparative Example 1 (which did not embed organic quaternary ammonium cations into basalt fibers), Comparative Example 2 (which did not undergo KH-560 modification treatment on basalt fibers), and Comparative Example 3 (which did not undergo surface mineralization treatment on basalt fibers) all showed a significant decline due to the lack of key process steps.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a modified polypropylene power pipe, characterized in that, Includes the following steps: S1. A blend is prepared by blending highly crystalline polypropylene, block copolymer polypropylene, nucleating agent, maleic anhydride grafted polypropylene, maleic anhydride grafted polyolefin elastomer, flame retardant, antioxidant and lubricant. The blend is then melt-extruded and granulated with modified basalt fiber and dried to obtain modified polypropylene masterbatch. S2. The modified polypropylene masterbatch is fed into a single-screw pipe extruder, and after vacuum sizing, gradient cooling, traction, and cutting, the modified polypropylene power pipe is obtained. The preparation method of the modified basalt fiber includes the following steps: A1. Add purified phosphogypsum powder to hydrochloric acid solution, heat and stir to dissolve, filter, and take the liquid phase to obtain the reaction mother liquor; A2. The basalt fiber is immersed in the reaction mother liquor and treated at a constant temperature. The pH of the system is adjusted to be alkaline by tetrapropylammonium hydroxide, and carbon dioxide is introduced at the same time to carry out the in-situ mineralization reaction. After the reaction is completed, the mineralized basalt fiber is taken out, and after alkali washing and KH-560 modification treatment, the modified basalt fiber is obtained.

2. The method for preparing a modified polypropylene power pipe according to claim 1, characterized in that, In step A1, the mass ratio of phosphogypsum to deionized water is 1:2-4; the mass ratio of purified phosphogypsum powder to hydrochloric acid solution is 1:3-5, and the mass fraction of hydrochloric acid solution is 8%-10%; the heating and stirring dissolution refers to heating and stirring at 70-80℃ for 3-4 hours.

3. The method for preparing a modified polypropylene power pipe according to claim 1, characterized in that, In step A2, the carbon dioxide gas flow rate is 150-200 mL / min, and the ventilation time is 30-50 min.

4. The method for preparing a modified polypropylene power pipe according to claim 1, characterized in that, In step A2, the alkali washing and KH-560 modification treatment of the mineralized basalt fibers specifically includes the following steps: The mineralized basalt fibers are immersed in a 0.1% sodium hydroxide solution at room temperature for 8-12 minutes, rinsed thoroughly with deionized water until the washing solution is neutral, and then immersed in a 1.5% KH-560 deionized water / ethanol solution at room temperature for 20-40 minutes. After immersion, the fibers are dried at 120℃ for 5-7 hours and then cut into short fibers with a length of 3-6 mm.

5. The method for preparing a modified polypropylene power pipe according to claim 1, characterized in that, In step S1, the specific process conditions for melt extrusion granulation are as follows: The temperature in Zone 1 is 175℃, in Zone 2 it is 190℃, in Zones 3 to 5 it is 210℃, in Zones 6 to 8 it is 200℃, the head temperature is 195℃, the main machine speed is 300-400rpm, and after the melt is extruded through the die head, it is granulated by underwater die surface hot cutting, with a circulating water temperature of 40-50℃.

6. The method for preparing a modified polypropylene power pipe according to claim 1, characterized in that, In step S2, the gradient cooling refers to the process where the pipe is vacuum sizing followed by sequential cooling with 60°C warm water for 25-35 seconds, transition cooling with 30°C warm water for 40-55 seconds, and finally natural cooling to room temperature in the air.

7. The method for preparing a modified polypropylene power pipe according to claim 1, characterized in that, Step A2 also includes the following steps: When carbon dioxide is introduced for in-situ mineralization reaction, polyethylene glycol-2000 is added at a mass of 0.3% of the phosphogypsum in step A1.

8. A modified polypropylene power pipe prepared by the method of any one of claims 1-7, characterized in that, The mass ratio of the highly crystalline polypropylene, block copolymer polypropylene, nucleating agent, maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyolefin elastomer, flame retardant, antioxidant, lubricant, and modified basalt fiber is 73-77:24-26:0.2-0.4:4-6:3-5:8-10:0.4-0.6:0.5-0.7:10-15.

9. The modified polypropylene power pipe according to claim 8, characterized in that, The nucleating agent is organophosphate nucleating agent NA-21; the flame retardant is a halogen-free intumescent flame retardant; the antioxidant includes at least one of BASF Irganox 1010 and BASF Irgafos 168; and the lubricant is pentaerythritol stearate.

10. The modified polypropylene power pipe according to claim 9, characterized in that, The halogen-free intumescent flame retardant includes at least one of ammonium polyphosphate and pentaerythritol.

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