Flame-retardant chlorinated polyvinyl chloride cable protection pipe and preparation method thereof

Abstract

This invention relates to the field of pipe materials and discloses a flame-retardant chlorinated polyvinyl chloride (PVC) cable protection pipe and its preparation method. The cable protection pipe comprises: chlorinated polyvinyl chloride, modified polyvinyl chloride, modified multi-walled carbon nanotubes, and additives. The modified polyvinyl chloride is prepared by grafting a sulfur-containing benzimidazole-based cashew phenol plasticizer onto polyvinyl chloride. The sulfur-containing benzimidazole-based cashew phenol plasticizer is prepared by reacting aldehyde-based cashew phenol with 2-aminobenzimidazole, followed by ring-opening with glycidol, and then reacting sequentially with methyl mercaptopropionate, mercaptopropionic acid, and dimethyl itaconic acid. The modified multi-walled carbon nanotubes are prepared by grafting a polymer of phosphorus-containing acrylate monomers prepared by reacting DOPO, formaldehyde, and acryloyl chloride, maleic anhydride, and butyl acrylate onto the surface of aminated multi-walled carbon nanotubes. The pipe material prepared by this invention has good mechanical properties, thermo-oxidative stability, photo-oxidative stability, heat resistance, and flame-retardant properties.

Description

Technical Field

[0001] This invention belongs to the field of pipe technology, specifically relating to a flame-retardant chlorinated polyvinyl chloride cable protection pipe and its preparation method. Background Technology

[0002] Cable protection pipes are conduits used for laying and protecting cables, providing mechanical protection, insulation, and corrosion resistance. They are suitable for various laying methods, including direct burial, ductwork, and trenchless installation. Chlorinated polyvinyl chloride (PVC) is a product obtained by further chlorination modification of PVC resin. It is an important engineering plastic used in chemical, building materials, shipbuilding, and power industries. Its most widespread application is in pipe manufacturing. The high chlorine content endows PVC with excellent physical and mechanical properties; its corrosion resistance, weather resistance, and flame retardancy are superior to PVC. However, excessively high chlorine content also causes certain performance defects in PVC resin, such as increased susceptibility to thermal decomposition. Chlorination significantly enhances the intermolecular forces, making it difficult for the molecular chains to deform and absorb energy when subjected to external impacts. Increased brittleness and lower impact strength lead to the use of elastic particles such as methyl methacrylate-butadiene-styrene copolymer, chlorinated polyethylene rubber, acrylonitrile-butadiene-styrene copolymer, and methyl methacrylate-acrylate copolymer to mechanically modify chlorinated polyvinyl chloride. This process aims to compensate for its processing or usage defects while maintaining its advantages such as high strength and corrosion resistance. However, the introduction of elastic particles also results in a significant loss of the material's strength, heat resistance, and flame retardancy. Furthermore, it can easily cause the pipe to age during use, leading to a decline in the pipe's mechanical properties and thus limiting the widespread application of the product. Summary of the Invention

[0003] To address the shortcomings mentioned in the background art, the present invention aims to provide a flame-retardant chlorinated polyvinyl chloride cable protection pipe and its preparation method. By adding modified polyvinyl chloride and modified multi-walled carbon nanotubes, the pipe material is endowed with good mechanical properties, thermo-oxidative stability, photo-oxidative stability, heat resistance and flame retardant properties.

[0004] The objective of this invention can be achieved through the following technical solutions: A flame-retardant chlorinated polyvinyl chloride cable protection pipe comprises the following components in parts by weight: 70-85 parts of chlorinated polyvinyl chloride, 10-30 parts of modified polyvinyl chloride, 2-6 parts of modified multi-walled carbon nanotubes, 1.5-3 parts of heat stabilizer, 4-9 parts of toughening agent, and 0.5-2.5 parts of lubricant. The modified polyvinyl chloride (PVC) is prepared by grafting a sulfur-containing benzimidazole-based cashew phenol plasticizer onto PVC. The sulfur-containing benzimidazole-based cashew phenol plasticizer is prepared by introducing an aldehyde group at the ortho position of the phenolic hydroxyl group of cashew phenol using paraformaldehyde. The prepared aldehyde-based cashew phenol is then reacted with 2-aminobenzimidazole via an aldehyde-amine condensation reaction to prepare benzimidazole-based cashew phenol. Then, the cashew phenol benzimidazole-based polyol prepared by the ring-opening reaction of benzimidazole-based cashew phenol with glycidol undergoes a mercapto-olefin click reaction with methyl mercaptopropionate. Next, the prepared sulfur-containing benzimidazole-based cashew phenol undergoes an esterification reaction with mercaptopropionic acid. Finally, the prepared mercapto-based sulfur-containing benzimidazole-based cashew phenol undergoes a mercapto-olefin click reaction with dimethyl itaconic acid. The modified multi-walled carbon nanotubes were prepared by reacting DOPO with formaldehyde to prepare a hydroxymethylated phosphorus-containing intermediate, then reacting the hydroxymethylated phosphorus-containing intermediate with acryloyl chloride via a nucleophilic addition reaction to prepare a phosphorus-containing acrylate monomer, and then preparing aminated multi-walled carbon nanotubes using hydrogen peroxide-ferrous sulfate heptahydrate reagent and 3-aminopropyltriethoxysilane. Finally, the polymer was grafted onto the surface of the aminated multi-walled carbon nanotubes through a polymer reaction of maleic anhydride, phosphorus-containing acrylate monomer and butyl acrylate.

[0005] Preferably, the method for preparing the modified polyvinyl chloride includes the following steps: adding polyvinyl chloride, sulfur-containing benzimidazole cashew phenol plasticizer and potassium carbonate to a reactor, then adding tetrahydrofuran solvent, stirring and reacting at 55~70℃ for 3~5h under a nitrogen atmosphere, cooling to room temperature, precipitating the reaction product in a mixed solution of methanol and deionized water, washing the precipitate multiple times with methanol to remove impurities, and finally vacuum drying to obtain the modified polyvinyl chloride.

[0006] Preferably, the preparation method of the sulfur-containing benzimidazole-based cashew phenol plasticizer includes the following steps: ① Add cashew phenol and toluene to the reactor, stir to dissolve, then add triethylamine and tin tetrachloride, stir for 30 min at room temperature under a nitrogen atmosphere, then add paraformaldehyde and react at 85℃ for 8 h. After the reaction product cools, pour it into deionized water and adjust the pH to 2. Then extract with ethyl acetate, dry the organic layer with anhydrous sodium sulfate, filter and concentrate to dryness, and purify by chromatography to prepare aldehyde-modified cashew phenol. ② Add aldehyde-modified cashew nut powder and 2-aminobenzimidazole to the reactor, pass nitrogen gas through the reaction, then add N,N-dimethylacetamide, stir at 80°C for 5 hours, pour the reaction product into deionized water and stir, precipitate deionized water, let stand overnight, filter and dry to prepare benzimidazole cashew nut powder; ③ Add benzimidazole cashew phenol and glycidol to the reactor, purge the air from the reaction system with nitrogen, heat to 80℃ for 2 hours with stirring, then heat to 100℃ for 4 hours with a heating rate of 10℃ / min, then heat to 120℃ for 2 hours with a heating rate of 10℃ / min, and cool to room temperature after the reaction is completed to prepare cashew phenol benzimidazole polyol; ④ Add cashew phenol benzimidazole polyol, methyl mercaptopropionate and photoinitiator 2-hydroxy-2-methylphenylacetone to the reactor, stir evenly and react for 12 hours, then place under ultraviolet light with a wavelength of 300~350nm and react for 12 hours. Then remove excess methyl mercaptopropionate by rotary evaporation to prepare sulfur-containing benzimidazole cashew phenol. ⑤ Add sulfur-containing benzimidazole cashew phenol, mercaptopropionic acid and catalyst p-toluenesulfonic acid to the reactor, blow nitrogen into the mixture and stir evenly for 20 min to remove air, place it at 90℃ for 4 h, and then remove excess mercaptopropionic acid by rotary evaporation to prepare mercapto-containing sulfur-containing benzimidazole cashew phenol. ⑥ Add thiolized sulfur-containing benzimidazole cashew phenol and photoinitiator 2-hydroxy-2-methylphenylacetone to the reactor, then add dimethyl itaconic acid and stir until homogeneous. React for 12 hours, then place under ultraviolet light with a wavelength of 300~350nm for 12 hours to prepare sulfur-containing benzimidazole cashew phenol plasticizer.

[0007] Preferably, in step ①, the molar ratio of cashew phenol, triethylamine, tin tetrachloride and paraformaldehyde is 1:0.4:0.1:2; and in step ②, the molar ratio of aldehyde-modified cashew phenol and 2-aminobenzimidazole is 1:1.

[0008] Preferably, in step ③, the molar ratio of benzimidazole cashew phenol to glycidol is 1:3; and in step ④, the molar ratio of cashew phenol benzimidazole polyol to methyl mercaptopropionate is 1:1~3.

[0009] Preferably, in step ⑤, the molar ratio of sulfur-containing benzimidazole cashew phenol to mercaptopropionic acid is 1:4; and in step ⑥, the molar ratio of mercapto-modified sulfur-containing benzimidazole cashew phenol to dimethyl itaconic acid is 1:3.

[0010] Preferably, the method for preparing the modified multi-walled carbon nanotubes includes the following steps: (1) DOPO and ethanol were added to the reactor, the temperature was raised to 60°C, and a 37% formaldehyde aqueous solution was slowly added dropwise. Then the temperature was raised to 78°C and refluxed for 5 hours. After the reaction was completed, the hydroxymethylated phosphorus-containing intermediate was prepared by filtration, drying and purification. (2) Add hydroxymethylated phosphorus-containing intermediate, dichloromethane and triethylamine to the reactor, stir and dissolve thoroughly, then add a mixed solution of acryloyl chloride and dichloromethane dropwise at -12℃, and finish the addition within 45 min. Then place it at -5℃ for 12 h. After the reaction is completed, extract with deionized water to remove triethylamine hydrochloride, remove the solvent by rotary evaporation and purify by column chromatography to prepare phosphorus-containing acrylate monomer; (3) Add maleic anhydride, phosphorus-containing acrylate monomer, butyl acrylate and N,N-dimethylformamide to the reactor, heat to 65°C, slowly add a mixture of azobisisobutyronitrile and N,N-dimethylformamide, and after the addition is complete, stir and reflux at 65°C for 10 h to prepare a polymer solution. (4) Multi-walled carbon nanotubes were ultrasonically dispersed in a 16% (w / w) ferrous sulfate heptahydrate aqueous solution. The pH of the solution was adjusted to 3 with dilute sulfuric acid. A 30% (w / w) hydrogen peroxide aqueous solution was slowly added and stirred for 24 h. The solution was filtered and washed until neutral. The solution was then ultrasonically dispersed in ethanol and deionized water. 3-aminopropyltriethoxysilane was added and stirred and refluxed at 70 °C for 10 h. Aminated multi-walled carbon nanotubes were obtained by filtration and washing. The aminated multi-walled carbon nanotubes were ultrasonically dispersed in a polymer solution and stirred for 4 h at room temperature. After the reaction was completed, the solution was filtered, washed, and dried to prepare modified multi-walled carbon nanotubes.

[0011] Preferably, in step (3), the molar ratio of phosphorus-containing acrylate monomer to butyl acrylate is 3.2:1.

[0012] Preferably, the heat stabilizer is one or more of calcium-zinc stabilizers, organotin stabilizers, and rare earth stabilizers; the toughening agent is one or more of methyl methacrylate-butadiene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, nitrile rubber, ethylene-butyl acrylate copolymer, and methacrylate-acrylate copolymer; and the lubricant is one or more of microcrystalline wax, stearic acid, polyethylene wax, oxidized polyethylene wax, and vinyl distearate.

[0013] 1. The preparation method of the flame-retardant chlorinated polyvinyl chloride cable protection pipe as described above includes the following steps: weigh each raw material according to the weight parts, set the temperature of the high-speed mixer to 60~70℃, add chlorinated polyvinyl chloride, modified polyvinyl chloride, modified multi-walled carbon nanotubes and heat stabilizer, stir and mix for 3~5 minutes, wait for the temperature to rise to 100~120℃, add toughening agent and lubricant and stir and mix evenly, then cool down and discharge the material, add it to the extruder for extrusion and molding to prepare the flame-retardant chlorinated polyvinyl chloride cable protection pipe.

[0014] The beneficial effects of this invention are: This invention uses cashew nut shellac as a bio-based matrix. Aldehyde-containing cashew nut shellac is prepared by introducing an aldehyde group at the ortho position of the phenolic hydroxyl group of cashew nut shellac using paraformaldehyde. Then, benzimidazole-based cashew nut shellac is prepared by reacting the aldehyde-containing cashew nut shellac with 2-aminobenzimidazole via an aldehyde-amine condensation reaction. Subsequently, a ring-opening reaction is conducted between the phenolic hydroxyl group in the benzimidazole-based cashew nut shellac and glycidol to prepare a cashew nut shellac benzimidazole-based polyol containing four alcoholic hydroxyl groups. Then, a mercapto-olefin click reaction is conducted between methyl mercaptopropionate and the side chain of the cashew nut shellac benzimidazole-based polyol to prepare sulfur-containing benzimidazole-based cashew nut shellac. Finally, a mercaptopropionic acid is used to esterify the four alcoholic hydroxyl groups introduced in the sulfur-containing benzimidazole-based cashew nut shellac to prepare mercapto-sulfur-containing benzimidazole-based cashew nut shellac. Phenol is used to prepare a sulfur-containing benzimidazole cashew phenol plasticizer by reacting three of the thiol groups introduced by dimethyl itaconic acid with thiolized sulfur-containing benzimidazole cashew phenol through a thiol-olefin click reaction, resulting in a plasticizer with one remaining thiol group. This plasticizer is then grafted onto polyvinyl chloride (PVC) to prepare self-plasticized modified PVC, achieving plasticization and non-migratory properties, which improves the processing and mechanical properties of PVC. Furthermore, the presence of sulfur in the sulfur-containing benzimidazole cashew phenol plasticizer significantly enhances the thermal stability and flame retardant effect of PVC. Additionally, the introduced benzimidazole group contains two nitrogen-containing antioxidant groups, which impart good thermal and photo-oxidative stability to the material.

[0015] This invention utilizes the reaction of DOPO with formaldehyde to prepare a hydroxymethylated phosphorus-containing intermediate. Then, the hydroxymethylated phosphorus-containing intermediate undergoes a nucleophilic addition reaction with acryloyl chloride to prepare a phosphorus-containing acrylate monomer. Aminated multi-walled carbon nanotubes are then prepared using hydrogen peroxide-ferrous sulfate heptahydrate reagent and 3-aminopropyltriethoxysilane. The polymer is then grafted onto the surface of the aminated multi-walled carbon nanotubes through a reaction with maleic anhydride, the phosphorus-containing acrylate monomer, and butyl acrylate, resulting in modified multi-walled carbon nanotubes. These multi-walled carbon nanotubes possess excellent mechanical properties and a multi-walled tubular structure, serving as a nanoparticle reinforcement. The polymer is grafted onto the surface of the multi-walled carbon nanotubes through strong chemical bonds, resulting in good dispersion and strong interfacial bonding of the multi-walled carbon nanotubes in the substrate, preventing nanoparticle aggregation that could lead to reduced mechanical properties. Simultaneously, the introduced synergistic flame-retardant phosphorus-silicon elements impart excellent flame-retardant properties to the material. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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.

[0017] Example 1: A method for preparing a sulfur-containing benzimidazole-based cashew phenol plasticizer includes the following steps: ① Add 3.02 g of cashew nut shellac and 20 mL of toluene to the reactor, stir to dissolve, then add 0.55 mL of triethylamine and 0.26 g of tin tetrachloride. Stir for 30 min at room temperature under a nitrogen atmosphere, then add 0.66 g of paraformaldehyde and react at 85 °C for 8 h. After the reaction product cools, pour it into deionized water and adjust the pH to 2. Then extract with ethyl acetate, dry the organic layer with anhydrous sodium sulfate, filter and concentrate to dryness, and purify by chromatography (using silica and hexane as eluent) to prepare aldehyde-modified cashew nut shellac. ② Add 13.2g of aldehyde-modified cashew nut powder and 5.33g of 2-aminobenzimidazole to the reactor. Purge the reaction with nitrogen gas, then add 150mL of N,N-dimethylacetamide. Stir the reaction at 80℃ for 5h. After the reaction product cools, pour it into deionized water and stir. After the deionized water is precipitated, allowed to stand overnight, filtered, and dried, benzimidazole-modified cashew nut powder is prepared. ③ Add 8.9g of benzimidazole cashew phenol and 4.45g of glycidol to the reactor, purge the air from the reaction system with nitrogen, heat to 80℃ under stirring and react for 2h, then heat to 100℃ at a rate of 10℃ / min and react for 4h, then heat to 120℃ at a rate of 10℃ / min and react for 2h, and finally cool to room temperature after the reaction is complete to prepare cashew phenol benzimidazole polyol; ④ Add 13.35g of cashew phenol benzimidazole polyol, 4.81g of methyl mercaptopropionate and 0.36g of photoinitiator 2-hydroxy-2-methylphenylacetone to the reactor, stir evenly and react for 12h, then place under ultraviolet light at a wavelength of 350nm and react for 12h. Subsequently, remove excess methyl mercaptopropionate by rotary evaporation to prepare sulfur-containing benzimidazole cashew phenol; ⑤ Add 18.14g of sulfur-containing benzimidazole cashew phenol, 8.49g of mercaptopropionic acid and 0.53g of catalyst p-toluenesulfonic acid to the reactor, blow nitrogen into the mixture and stir evenly for 20min to remove air, place it at 90℃ for 4h, and then remove excess mercaptopropionic acid by rotary evaporation to prepare mercapto-containing sulfur-containing benzimidazole cashew phenol; ⑥ Add 25.19g of mercapto-modified sulfur-containing benzimidazole cashew phenol and 0.48g of photoinitiator 2-hydroxy-2-methylphenylacetone to the reactor, then add 9.49g of dimethyl itaconic acid and stir until homogeneous. React for 12 hours, then place under 350nm ultraviolet light for 12 hours to prepare sulfur-containing benzimidazole cashew phenol plasticizer.

[0018] Example 2 A method for preparing modified polyvinyl chloride includes the following steps: 7.5 g of polyvinyl chloride, 22.19 g of the sulfur-containing benzimidazole cashew phenol plasticizer prepared in Example 1, and 2.64 g of potassium carbonate were added to the reactor. Then, 250 mL of tetrahydrofuran solvent was added, and the mixture was stirred at 65 °C for 4 h under a nitrogen atmosphere. After cooling to room temperature, the reaction product was placed in a 1:1 mixture of methanol and deionized water for precipitation. The precipitate was washed repeatedly with methanol to remove impurities. Finally, it was vacuum dried to obtain modified polyvinyl chloride.

[0019] Example 3 A method for preparing modified multi-walled carbon nanotubes includes the following steps: (1) Add 10.81g DOPO and 80mL ethanol to the reactor, heat to 60℃, slowly add 5.03g of 37% formaldehyde aqueous solution, and finish adding within 30min. Then heat to 78℃ and reflux for 5h. After the reaction is completed, filter, dry and purify to prepare hydroxymethylated phosphorus-containing intermediate. (2) Add 4.94 g of hydroxymethylated phosphorus-containing intermediate, 20 mL of dichloromethane and 4.34 mL of triethylamine to the reactor and stir to dissolve. Then, control the temperature at -12 °C and add a mixed solution of 2.17 g of acryloyl chloride and 10 mL of dichloromethane dropwise. The addition is completed within 45 min. Then, place the reactor at -5 °C and react for 12 h. After the reaction is completed, extract with deionized water to remove triethylamine hydrochloride. Remove the solvent by rotary evaporation and purify by column chromatography (with ethyl acetate as the mobile phase) to prepare phosphorus-containing acrylate monomer. (3) Add 1.18g maleic anhydride, 9.61g phosphorus-containing acrylate monomer, 1.28g butyl acrylate and 80mL N,N-dimethylformamide to the reactor, heat to 65℃, slowly add 0.12g azobisisobutyronitrile and 40mL N,N-dimethylformamide mixed solution, and after the addition is complete, stir and reflux at 65℃ for 10h to prepare polymer solution; (4) Take 5g of multi-walled carbon nanotubes and ultrasonically disperse them in 250mL of 16% ferrous sulfate heptahydrate aqueous solution. Adjust the pH of the solution to 3 with dilute sulfuric acid. Slowly add 300mL of 30% hydrogen peroxide aqueous solution and stir for 24h. Filter and wash until neutral. Then ultrasonically disperse them in 190mL of ethanol and 10mL of deionized water. Add 30g of 3-aminopropyltriethoxysilane and stir and reflux at 70℃ for 10h. After filtration and washing, aminated multi-walled carbon nanotubes are obtained. Ultrasonically disperse the aminated multi-walled carbon nanotubes in 150g of polymer solution and stir for 4h at room temperature. After the reaction is completed, filter, wash and dry to prepare modified multi-walled carbon nanotubes.

[0020] Example 4 A flame-retardant chlorinated polyvinyl chloride cable protection pipe, comprising the following components in parts by weight: 72 parts of chlorinated polyvinyl chloride, 11 parts of modified polyvinyl chloride prepared in Example 2, 2.3 parts of modified multi-walled carbon nanotubes prepared in Example 3, 1.6 parts of calcium-zinc stabilizer, 4.4 parts of toughening agent methyl methacrylate-butadiene-styrene copolymer, and 0.7 parts of lubricant polyethylene wax.

[0021] The preparation method of the above-mentioned flame-retardant chlorinated polyvinyl chloride cable protection pipe includes the following steps: weigh each raw material according to the weight parts, set the temperature of the high-speed mixer to 65°C, add chlorinated polyvinyl chloride, modified polyvinyl chloride, modified multi-walled carbon nanotubes and heat stabilizer, stir and mix for 5 minutes, wait for the temperature to rise to 120°C, add toughening agent and lubricant and stir and mix evenly, then cool down and discharge the material, add it to the extruder for extrusion and molding, and prepare the flame-retardant chlorinated polyvinyl chloride cable protection pipe.

[0022] Example 5 A flame-retardant chlorinated polyvinyl chloride cable protection pipe, comprising the following components in parts by weight: 78 parts of chlorinated polyvinyl chloride, 20 parts of modified polyvinyl chloride prepared in Example 2, 4.4 parts of modified multi-walled carbon nanotubes prepared in Example 3, 2.3 parts of calcium-zinc stabilizer, 6.8 parts of toughening agent methyl methacrylate-butadiene-styrene copolymer, and 1.5 parts of lubricant polyethylene wax.

[0023] The preparation method of the flame-retardant chlorinated polyvinyl chloride cable protection pipe is the same as in Example 4.

[0024] Example 6 A flame-retardant chlorinated polyvinyl chloride cable protection pipe, comprising the following components in parts by weight: 84 parts of chlorinated polyvinyl chloride, 28 parts of modified polyvinyl chloride prepared in Example 2, 5.7 parts of modified multi-walled carbon nanotubes prepared in Example 3, 2.8 parts of calcium-zinc stabilizer, 8.5 parts of toughening agent methyl methacrylate-butadiene-styrene copolymer, and 2.3 parts of lubricant polyethylene wax.

[0025] The preparation method of the flame-retardant chlorinated polyvinyl chloride cable protection pipe is the same as in Example 4.

[0026] Comparative Example 1: A method for preparing a sulfur-containing cashew phenol plasticizer includes the following steps: ① Add 6.04 g cashew nut alcohol and 4.45 g glycidol to the reactor, purge the air from the reaction system with nitrogen, heat to 80 °C for 2 h with stirring, then heat to 100 °C for 4 h at a heating rate of 10 °C / min, then heat to 120 °C for 2 h at a heating rate of 10 °C / min, and cool to room temperature after the reaction is complete to prepare cashew nut alcohol polyol; ② Add 10.48g of cashew nut polyol, 4.81g of methyl mercaptopropionate and 0.36g of photoinitiator 2-hydroxy-2-methylphenylacetone to the reactor, stir evenly and react for 12h, then place under ultraviolet light at a wavelength of 350nm and react for 12h. Then remove excess methyl mercaptopropionate by rotary evaporation to prepare sulfur-containing cashew nut polyol. ③ Add 15.29g of sulfur-containing cashew phenol, 8.49g of mercaptopropionic acid and 0.53g of catalyst p-toluenesulfonic acid to the reactor, blow nitrogen into the mixture and stir evenly for 20min to remove air, place it at 90℃ for 4h, and then remove excess mercaptopropionic acid by rotary evaporation to prepare mercapto-sulfur-containing cashew phenol. ④ Add 22.34g of mercapto-sulfur-containing cashew phenol and 0.48g of photoinitiator 2-hydroxy-2-methylphenylacetone to the reactor, then add 9.49g of dimethyl itaconic acid and stir until homogeneous. React for 12 hours, then place under 350nm ultraviolet light for 12 hours to prepare sulfur-containing cashew phenol plasticizer.

[0027] Comparative Example 2: A method for preparing modified polyvinyl chloride includes the following steps: 7.5 g of polyvinyl chloride, 22.19 g of sulfur-containing cashew phenol plasticizer prepared in Comparative Example 1, and 2.64 g of potassium carbonate were added to the reactor, followed by 250 mL of tetrahydrofuran solvent. The mixture was stirred at 65 °C for 4 h under a nitrogen atmosphere. After cooling to room temperature, the reaction product was placed in a 1:1 mixture of methanol and deionized water for precipitation. The precipitate was washed repeatedly with methanol to remove impurities. Finally, the product was vacuum dried to obtain modified polyvinyl chloride.

[0028] Comparative Example 3: A flame-retardant chlorinated polyvinyl chloride cable protection pipe, comprising the following components in parts by weight: 78 parts of chlorinated polyvinyl chloride, 20 parts of modified polyvinyl chloride prepared in Comparative Example 2, 4.4 parts of modified multi-walled carbon nanotubes prepared in Example 3, 2.3 parts of calcium-zinc stabilizer, 6.8 parts of toughening agent methyl methacrylate-butadiene-styrene copolymer, and 1.5 parts of lubricant polyethylene wax.

[0029] The preparation method of the flame-retardant chlorinated polyvinyl chloride cable protection pipe is the same as in Example 4.

[0030] Comparative Example 4: A flame-retardant chlorinated polyvinyl chloride cable protection pipe, comprising the following components in parts by weight: 78 parts of chlorinated polyvinyl chloride, 20 parts of polyvinyl chloride, 4.4 parts of modified multi-walled carbon nanotubes prepared in Example 3, 2.3 parts of calcium-zinc stabilizer, 6.8 parts of toughening agent methyl methacrylate-butadiene-styrene copolymer, and 1.5 parts of lubricant polyethylene wax.

[0031] The preparation method of the flame-retardant chlorinated polyvinyl chloride cable protection pipe is the same as in Example 4.

[0032] Comparative Example 5: A flame-retardant chlorinated polyvinyl chloride cable protection pipe, comprising the following components in parts by weight: 78 parts of chlorinated polyvinyl chloride, 20 parts of modified polyvinyl chloride prepared in Example 2, 4.4 parts of multi-walled carbon nanotubes, 2.3 parts of calcium-zinc stabilizer, 6.8 parts of toughening agent methyl methacrylate-butadiene-styrene copolymer, and 1.5 parts of lubricant polyethylene wax.

[0033] The preparation method of the flame-retardant chlorinated polyvinyl chloride cable protection pipe is the same as in Example 4.

[0034] Performance testing The cable protection tubes prepared in Examples 4-6 and Comparative Examples 3-5 were subjected to performance testing: (1) Tensile property test: The sample was injection molded into a standard dumbbell-shaped specimen with a thickness of 4 mm. The tensile properties were tested using a universal testing machine according to GB / T 1040.2-2022. The tensile speed was 5 mm / min. The data results are shown in Table 1.

[0035] (2) Impact resistance test: The sample was injection molded into a sample with a thickness of 4mm, a width of 10mm and a length of 80mm. The impact strength test was carried out in accordance with GB / T 1843-2008. The sample size was 80mm×10mm×4mm. The data results are shown in Table 1.

[0036] (3) Thermo-oxidative aging test: The sample was placed in a thermo-oxidative aging chamber and aged at 100℃ for 72 hours. The tensile strength reduction rate was measured and the data results are shown in Table 1.

[0037] (4) Xenon lamp aging test: A xenon lamp weathering test chamber was used for light aging test. The sample was placed in the test chamber and aged for 48 hours according to GB / T 16422.2-2022. The tensile strength reduction rate was measured. UVA-340 was used as the light source and the irradiance was 0.51W / m². 2 The black label temperature was cycled at 65℃ and 100℃, with an exposure cycle of 102 min drying and 18 min spraying. The data results are shown in Table 1.

[0038] (5) Heat resistance test: Accurately weigh 3~5mg of sample and place it in a crucible, place it in a thermogravimetric analyzer, test temperature range: 30~600℃, heating rate: 10℃ / min, nitrogen atmosphere, flow rate 50ml / min, and the data results are shown in Table 1.

[0039] (6) Flame retardant performance test: Refer to GB / T 2406.1-2008, the sample size is 150mm×10mm×10mm, and the test is conducted using an oxygen index tester. The data results are shown in Table 1.

[0040] Table 1 Sample performance test results As shown in Table 1, the pipes prepared in Examples 4-6 of this invention possess good mechanical properties, thermo-oxidative stability, photo-oxidative stability, heat resistance, and flame retardant properties. In Comparative Example 3, the modified polyvinyl chloride was prepared by replacing benzimidazole-based cardiophenol with an equimolar amount of cardiophenol. Comparative Example 4 did not undergo any modification treatment of the polyvinyl chloride. The tensile strength measured after thermo-oxidative aging and xenon lamp aging in Comparative Examples 3-4 was significantly lower than that in Examples 4-6, indicating that the introduction of nitrogen-containing heterocyclic benzimidazole groups is beneficial to improving the thermo-oxidative and photo-oxidative stability of the material. Furthermore, the tensile strength, impact strength, initial thermal decomposition temperature, and limiting oxygen index measured in Comparative Example 4 were lower than those in Examples 4-6, indicating that grafting with sulfur-containing benzimidazole-based cardiophenol plasticizers can further improve… The mechanical properties, heat resistance, and flame retardancy of the material were improved. In Comparative Example 5, no modification treatment was performed on the multi-walled carbon nanotubes. The measured tensile strength, impact strength, initial thermal decomposition temperature, and limiting oxygen index were lower than those of Examples 4-6. This is because the grafting of polymers is beneficial to improving the dispersion and interfacial bonding of multi-walled carbon nanotubes in the substrate, so that the mechanical properties of multi-walled carbon nanotubes can be fully utilized. At the same time, it promotes the dissipation of heat in the substrate, thereby further improving the thermal stability of the material. In addition, the introduction of synergistic flame-retardant phosphorus-silicon elements is beneficial to improving the flame retardancy of the material to a certain extent.

[0041] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0042] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A flame-retardant chlorinated polyvinyl chloride cable protection pipe, characterized in that, It includes the following components by weight: 70-85 parts of chlorinated polyvinyl chloride, 10-30 parts of modified polyvinyl chloride, 2-6 parts of modified multi-walled carbon nanotubes, 1.5-3 parts of heat stabilizer, 4-9 parts of toughening agent, and 0.5-2.5 parts of lubricant; The modified polyvinyl chloride (PVC) is prepared by grafting a sulfur-containing benzimidazole-based cashew phenol plasticizer onto PVC. The sulfur-containing benzimidazole-based cashew phenol plasticizer is prepared by introducing an aldehyde group at the ortho position of the phenolic hydroxyl group of cashew phenol using paraformaldehyde. The prepared aldehyde-based cashew phenol is then reacted with 2-aminobenzimidazole via an aldehyde-amine condensation reaction to prepare benzimidazole-based cashew phenol. Then, the cashew phenol benzimidazole-based polyol prepared by the ring-opening reaction of benzimidazole-based cashew phenol with glycidol undergoes a mercapto-olefin click reaction with methyl mercaptopropionate. Next, the prepared sulfur-containing benzimidazole-based cashew phenol undergoes an esterification reaction with mercaptopropionic acid. Finally, the prepared mercapto-based sulfur-containing benzimidazole-based cashew phenol undergoes a mercapto-olefin click reaction with dimethyl itaconic acid. The modified multi-walled carbon nanotubes were prepared by reacting DOPO with formaldehyde to prepare a hydroxymethylated phosphorus-containing intermediate, then reacting the hydroxymethylated phosphorus-containing intermediate with acryloyl chloride via a nucleophilic addition reaction to prepare a phosphorus-containing acrylate monomer, and then preparing aminated multi-walled carbon nanotubes using hydrogen peroxide-ferrous sulfate heptahydrate reagent and 3-aminopropyltriethoxysilane. Finally, the polymer was grafted onto the surface of the aminated multi-walled carbon nanotubes through a polymer reaction of maleic anhydride, phosphorus-containing acrylate monomer and butyl acrylate.

2. The flame-retardant chlorinated polyvinyl chloride cable protection pipe according to claim 1, characterized in that, The method for preparing the modified polyvinyl chloride includes the following steps: adding polyvinyl chloride, sulfur-containing benzimidazole cashew phenol plasticizer and potassium carbonate to a reactor, then adding tetrahydrofuran solvent, stirring and reacting at 55~70℃ for 3~5h under a nitrogen atmosphere, cooling to room temperature, precipitating the reaction product in a mixed solution of methanol and deionized water, washing the precipitate multiple times with methanol to remove impurities, and finally vacuum drying to obtain the modified polyvinyl chloride.

3. The flame-retardant chlorinated polyvinyl chloride cable protection pipe according to claim 2, characterized in that, The preparation method of the sulfur-containing benzimidazole-based cashew phenol plasticizer includes the following steps: ① Add cashew phenol and toluene to the reactor, stir to dissolve, then add triethylamine and tin tetrachloride, stir for 30 min at room temperature under a nitrogen atmosphere, then add paraformaldehyde and react at 85℃ for 8 h. After the reaction product cools, pour it into deionized water and adjust the pH to 2. Then extract with ethyl acetate, dry the organic layer with anhydrous sodium sulfate, filter and concentrate to dryness, and purify by chromatography to prepare aldehyde-modified cashew phenol. ② Add aldehyde-modified cashew nut powder and 2-aminobenzimidazole to the reactor, pass nitrogen gas through the reaction, then add N,N-dimethylacetamide, stir at 80°C for 5 hours, pour the reaction product into deionized water and stir, precipitate deionized water, let stand overnight, filter and dry to prepare benzimidazole cashew nut powder; ③ Add benzimidazole cashew phenol and glycidol to the reactor, purge the air from the reaction system with nitrogen, heat to 80℃ for 2 hours with stirring, then heat to 100℃ for 4 hours with a heating rate of 10℃ / min, then heat to 120℃ for 2 hours with a heating rate of 10℃ / min, and cool to room temperature after the reaction is completed to prepare cashew phenol benzimidazole polyol; ④ Add cashew phenol benzimidazole polyol, methyl mercaptopropionate and photoinitiator 2-hydroxy-2-methylphenylacetone to the reactor, stir evenly and react for 12 hours, then place under ultraviolet light with a wavelength of 300~350nm and react for 12 hours. Then remove excess methyl mercaptopropionate by rotary evaporation to prepare sulfur-containing benzimidazole cashew phenol. ⑤ Add sulfur-containing benzimidazole cashew phenol, mercaptopropionic acid and catalyst p-toluenesulfonic acid to the reactor, blow nitrogen into the mixture and stir evenly for 20 min to remove air, place it at 90℃ for 4 h, and then remove excess mercaptopropionic acid by rotary evaporation to prepare mercapto-containing sulfur-containing benzimidazole cashew phenol. ⑥ Add thiolized sulfur-containing benzimidazole cashew phenol and photoinitiator 2-hydroxy-2-methylphenylacetone to the reactor, then add dimethyl itaconic acid and stir until homogeneous. React for 12 hours, then place under ultraviolet light with a wavelength of 300~350nm for 12 hours to prepare sulfur-containing benzimidazole cashew phenol plasticizer.

4. The flame-retardant chlorinated polyvinyl chloride cable protection pipe according to claim 3, characterized in that, In step ①, the molar ratio of cashew phenol, triethylamine, tin tetrachloride, and paraformaldehyde is 1:0.4:0.1:2; in step ②, the molar ratio of aldehyde-modified cashew phenol and 2-aminobenzimidazole is 1:

1.

5. The flame-retardant chlorinated polyvinyl chloride cable protection pipe according to claim 3, characterized in that, In step ③, the molar ratio of benzimidazole cashew phenol to glycidol is 1:3; in step ④, the molar ratio of cashew phenol benzimidazole polyol to methyl mercaptopropionate is 1:1~3.

6. The flame-retardant chlorinated polyvinyl chloride cable protection pipe according to claim 3, characterized in that, In step ⑤, the molar ratio of sulfur-containing benzimidazole cashew phenol to mercaptopropionic acid is 1:4; in step ⑥, the molar ratio of mercapto-modified sulfur-containing benzimidazole cashew phenol to dimethyl itaconic acid is 1:

3.

7. The flame-retardant chlorinated polyvinyl chloride cable protection pipe according to claim 1, characterized in that, The method for preparing the modified multi-walled carbon nanotubes includes the following steps: (1) DOPO and ethanol were added to the reactor, the temperature was raised to 60°C, and a 37% formaldehyde aqueous solution was slowly added dropwise. Then the temperature was raised to 78°C and refluxed for 5 hours. After the reaction was completed, the hydroxymethylated phosphorus-containing intermediate was prepared by filtration, drying and purification. (2) Add hydroxymethylated phosphorus-containing intermediate, dichloromethane and triethylamine to the reactor, stir and dissolve thoroughly, then add a mixed solution of acryloyl chloride and dichloromethane dropwise at -12℃, and finish the addition within 45 min. Then place it at -5℃ for 12 h. After the reaction is completed, extract with deionized water to remove triethylamine hydrochloride, remove the solvent by rotary evaporation and purify by column chromatography to prepare phosphorus-containing acrylate monomer; (3) Add maleic anhydride, phosphorus-containing acrylate monomer, butyl acrylate and N,N-dimethylformamide to the reactor, heat to 65°C, slowly add a mixture of azobisisobutyronitrile and N,N-dimethylformamide, and after the addition is complete, stir and reflux at 65°C for 10 h to prepare a polymer solution. (4) Multi-walled carbon nanotubes were ultrasonically dispersed in a 16% (w / w) ferrous sulfate heptahydrate aqueous solution. The pH of the solution was adjusted to 3 with dilute sulfuric acid. A 30% (w / w) hydrogen peroxide aqueous solution was slowly added and stirred for 24 h. The solution was filtered and washed until neutral. The solution was then ultrasonically dispersed in ethanol and deionized water. 3-aminopropyltriethoxysilane was added and stirred and refluxed at 70 °C for 10 h. Aminated multi-walled carbon nanotubes were obtained by filtration and washing. The aminated multi-walled carbon nanotubes were ultrasonically dispersed in a polymer solution and stirred for 4 h at room temperature. After the reaction was completed, the solution was filtered, washed, and dried to prepare modified multi-walled carbon nanotubes.

8. The flame-retardant chlorinated polyvinyl chloride cable protection pipe according to claim 7, characterized in that, In step (3), the molar ratio of phosphorus-containing acrylate monomer and butyl acrylate is 3.2:

1.

9. The flame-retardant chlorinated polyvinyl chloride cable protection pipe according to claim 1, characterized in that, The heat stabilizer is one or more of calcium-zinc stabilizers, organotin stabilizers, and rare earth stabilizers; the toughening agent is one or more of methyl methacrylate-butadiene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, nitrile rubber, ethylene-butyl acrylate copolymer, and methacrylate-acrylate copolymer; the lubricant is one or more of microcrystalline wax, stearic acid, polyethylene wax, oxidized polyethylene wax, and vinyl distearate.

10. A method for preparing a flame-retardant chlorinated polyvinyl chloride cable protection pipe according to any one of claims 1 to 9, characterized in that, The process includes the following steps: Weigh each raw material according to the weight proportions, set the temperature of the high-speed mixer to 60~70℃, add chlorinated polyvinyl chloride, modified polyvinyl chloride, modified multi-walled carbon nanotubes and heat stabilizer, stir and mix for 3~5 minutes, wait for the temperature to rise to 100~120℃, add toughening agent and lubricant and stir and mix evenly, then cool down and discharge the material, add it to the extruder for extrusion and molding, and prepare flame-retardant chlorinated polyvinyl chloride cable protection pipe.