A kind of anti-thermal impact MPP cable protection pipe material and its preparation method

Abstract

This invention discloses a heat- and impact-resistant protective conduit for MPP cables and its preparation method, relating to the field of polymer materials technology. The components, by weight, include: 20-22 parts of a toughening dispersion made from anhydrous ethanol and terminally epoxy-terminated hyperbranched polysiloxane; 33-35 parts of a boron-nitrogen co-doped carbon dot made from citric acid, boric acid, and urea, first compounded with phytic acid and piperazine, then compounded with modified zirconium phosphate prepared by hexadecyltrimethylammonium bromide intercalation, and then modified with silane coupling agent KH-560 to form a flame retardant synergist; 12-14 parts of polyolefin elastomer; 2-2.5 parts of magnesium aluminum hydrotalcite; 0.2-0.24 parts of antioxidant; 0.2-0.3 parts of calcium stearate; 0.2-0.3 parts of polyethylene wax; and 100-120 parts of polypropylene. The introduction of the flame retardant synergist and other raw materials in this invention effectively improves flame retardancy, aging resistance, impact resistance, low-temperature resistance, and heat resistance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a heat- and shock-resistant protective tubing for MPP cables and its preparation method. Background Technology

[0002] Cable protection pipes are core components for protecting underground cables in power engineering. Among them, modified polypropylene (MPP) cable protection pipe material has become the mainstream material for power network construction due to its advantages such as light weight, corrosion resistance, ease of processing, and good insulation.

[0003] However, in practical applications, MPP cable protective tubing still suffers from the following performance shortcomings: First, insufficient flame retardancy. High addition levels of conventional halogen-free flame retardant systems significantly degrade mechanical properties, leading to easy melting and dripping during combustion, and poor char layer density and resistance to flame erosion. Second, poor low-temperature impact resistance. Polypropylene has a high glass transition temperature, making it prone to embrittlement in the low temperatures of northern winters, and easily cracking during transportation and construction impacts. Third, insufficient heat resistance. The long-term operating temperature of ordinary MPP tubing generally does not exceed 70℃, and sudden temperature rises during cable overload or short circuits can easily cause the tubing to soften and deform. Fourth, poor UV aging resistance. Long-term exposure to ultraviolet radiation outdoors can cause free radical breakage of polypropylene molecular chains, resulting in rapid degradation of mechanical properties. Therefore, the flame retardancy, aging resistance, low-temperature resistance, and heat resistance of existing MPP cable protective tubing still need improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a heat- and shock-resistant protective tubing for MPP cables and its preparation method, thereby solving the following technical problems: Existing protective tubing materials for MPP cables still suffer from poor flame retardancy, aging resistance, low-temperature resistance, and heat resistance.

[0005] The objective of this invention can be achieved through the following technical solutions: A heat- and impact-resistant protective conduit for MPP cables, comprising, by weight: 20-22 parts of a toughening dispersion made of anhydrous ethanol and terminally epoxy hyperbranched polysiloxane; 33-35 parts of a boron-nitrogen co-doped carbon dot made of citric acid, boric acid, urea, and deionized water, which is first compounded with phytic acid aqueous solution and piperazine to form a carbon dot composite, and then compounded with modified zirconium phosphate prepared by hexadecyltrimethylammonium bromide intercalation, and then modified with silane coupling agent KH-560 to form a flame retardant synergist; 12-14 parts of polyolefin elastomer; 2-2.5 parts of magnesium aluminum hydrotalcite; 0.2-0.24 parts of antioxidant; 0.2-0.3 parts of calcium stearate; 0.2-0.3 parts of polyethylene wax; and 100-120 parts of polypropylene.

[0006] Preferably, the flame retardant synergist is prepared as follows: A1: Citric acid, boric acid, and urea were dissolved in deionized water, and then reacted at 180°C for 6 hours. After cooling, the mixture was filtered, dialyzed for 48 hours, and then freeze-dried to obtain boron-nitrogen co-doped carbon dots. A2: Add piperazine to deionized water and stir until homogeneous. Then add phytic acid aqueous solution dropwise and stir for 30-50 min. Adjust the pH to 6.8-7.2, then add boron-nitrogen co-doped carbon dots and stir in the dark for 1 h. After freeze-drying, the carbon dot complex is obtained. A3: Add α-zirconium phosphate to deionized water and ultrasonically disperse for 1 h, then add hexadecyltrimethylammonium bromide and stir at 80 °C for 24 h, then centrifuge, wash and dry to obtain modified zirconium phosphate; A4: Add carbon dot complex to anhydrous ethanol and stir for 20-30 min. Then add it dropwise to modified zirconium phosphate dispersion and stir for 40-60 min. Then add zinc borate and stir for 30-40 min. Then add silane coupling agent KH-560 and deionized water, stir for 30-40 min, and react at 80℃ for 6 h. Then centrifuge, wash, dry, grind, and pass through a 200-mesh sieve to obtain flame retardant synergist.

[0007] Preferably, the mass ratio of citric acid, boric acid, urea, and deionized water in A1 is 10:2:5:100-110.

[0008] Preferably, the mass ratio of deionized water, piperazine, phytic acid aqueous solution, and boron-nitrogen co-doped carbon dots in A2 is 150-160:3.6:18.6-19:3; The phytic acid aqueous solution described in A2 has a mass fraction of 50%.

[0009] Preferably, the mass ratio of deionized water, α-zirconium phosphate, and hexadecyltrimethylammonium bromide in A3 is 500-510:10:31.5-32.

[0010] Preferably, the ratio of anhydrous ethanol, carbon dot complex, modified zirconium phosphate dispersion, zinc borate, silane coupling agent KH-560, and deionized water in A4 is 150mL:23.1g:315-335g:3g:0.6g:1.5g; The modified zirconium phosphate dispersion described in A4 is obtained by mixing anhydrous ethanol and modified zirconium phosphate in a mass ratio of 300-320:15.

[0011] Preferably, the preparation method of the terminal epoxy group hyperbranched polysiloxane is as follows: B1: Methyldichlorosilane, methyltrichlorosilane, dimethyldichlorosilane, and trimethylchlorosilane were mixed, and then anhydrous toluene at 0°C was added dropwise under a nitrogen atmosphere. After stirring for 10 min, deionized water was added dropwise at 0°C and stirred for 1 h. The mixture was then reacted at 40°C for 4 h. After discarding the lower aqueous phase, the organic phase was washed, dried with anhydrous magnesium sulfate, filtered, rotary evaporated, and vacuum dried to obtain terminal hydrogen hyperbranched polysiloxane. B2: Under a nitrogen atmosphere, hydrogen-terminated hyperbranched polysiloxane was added to anhydrous toluene and the temperature was raised to 70°C. Then, an isopropanol solution of chloroplatinic acid was added and stirred for 10-15 min. Allyl glycidyl ether was then added dropwise and reacted at 80°C for 6 h. Subsequently, the mixture was rotary evaporated and vacuum dried to obtain epoxy-terminated hyperbranched polysiloxane.

[0012] Preferably, the ratio of methyldichlorosilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, anhydrous toluene, and deionized water in B1 is 23g:12g:7.74g:4.35g:150-155mL:8.3mL.

[0013] Preferably, the ratio of anhydrous toluene, terminal hydrogen hyperbranched polysiloxane, isopropanol solution of chloroplatinic acid, and allyl glycidyl ether in B2 is 50-55 mL: 17 g: 0.5 mL: 23.9 g. The concentration of the isopropanol solution of chloroplatinic acid described in B2 is 0.01 mol / L.

[0014] A method for preparing a heat- and shock-resistant protective tubing for MPP cables includes the following steps: S1: Mix polypropylene, polyolefin elastomer, magnesium aluminum hydrotalcite, antioxidant, calcium stearate, and polyethylene wax for 3-5 minutes. Then spray toughening dispersion and stir for 5-7 minutes. After vacuum drying, feed the mixture into a co-rotating twin-screw extruder through the main feed port for melt extrusion at 170°C in zone 1 (main feed port), 180°C in zone 2, 190°C in zone 3 (side feed port), 200°C in zone 4, 205°C in zone 5, 200°C in zone 6, and 190°C at the die head, with a screw speed of 220 r / min. During the process, add flame retardant synergist at the side feed port in zone 3. Finally, the extruded strip is water-cooled and pelletized to obtain modified granules. S2: Modified granules are extruded using a single-screw pipe extruder. After the pipe is extruded from the die, it first passes through a 120-125℃ pre-cooling sleeve, then enters a 130-135℃ primary stretching sleeve, where it undergoes primary axial stretching with an axial stretching ratio of 1.6 through the traction speed difference. Next, it enters a 125-130℃ secondary stretching sleeve, where it undergoes secondary circumferential stretching with an circumferential stretching ratio of 1.3 through internal air pressure. After cooling and shaping, heat-resistant and impact-resistant protective pipe material for MPP cables is obtained.

[0015] The beneficial effects of this invention are: This invention provides a heat- and impact-resistant protective tubing for MPP cables and its preparation method. The invention simultaneously improves the flame retardancy, aging resistance, impact resistance, low-temperature resistance, and heat resistance of the protective tubing for MPP cables through the following methods.

[0016] (1) During pipe combustion, phytic acid in the flame retardant synergist of this invention dehydrates to form polyphosphoric acid, catalyzing the dehydration of polypropylene and its own carbon skeleton into char; piperazine decomposes to release inert gases such as nitrogen, promoting the expansion of the char layer to form a porous foam structure, isolating oxygen and heat, and preventing the spread of flame; the conjugated π structure and surface active groups of carbon dots can catalyze the cross-linking reaction of phytic acid-piperazine with polypropylene to form char, improving the density and thermal stability of the char layer; boron doping promotes the formation of high-temperature resistant BC bond structures in the char layer, and BN synergy helps to reduce the toxicity of flue gas; after intercalation modification, α - The interlayer spacing of zirconium phosphate increases, and under extrusion shearing, it is exfoliated into nanosheets, forming a labyrinth effect that slows down the transfer of combustible gases and heat. At high temperatures, it decomposes to generate a high-temperature resistant zirconium oxide ceramic phase, which combines with the carbon layer to form a ceramicized carbon layer skeleton, improving the mechanical strength and flame erosion resistance of the carbon layer. Zinc borate generates a boron trioxide glassy molten layer and zinc oxide at high temperatures. The boron trioxide covers the carbon layer surface to form a dense oxygen-barrier and heat-insulating film. Zinc oxide can further catalyze carbonization and produce a synergistic effect with phosphorus, nitrogen, boron, and zirconium elements, improving carbonization efficiency. Modified α-zirconium phosphate can load flame-retardant components into the interlayer and surface, reducing the agglomeration of single flame retardants. The methoxy group of the silane coupling agent KH-560 reacts with the hydroxyl group on the surface of inorganic particles, and the epoxy group reacts with the hydroxyl, amino, and terminal epoxy hyperbranched polysiloxane on the carbon dots and phytic acid-piperazine surfaces to form a chemically bonded interface, enhancing the interfacial bonding force. Zirconia and zinc oxide can absorb and reflect ultraviolet light; the boron-nitrogen co-doped carbon dot surface active groups and the layered structure of modified α-zirconium phosphate nanosheets can scatter ultraviolet light and significantly reduce its intensity; good interfacial bonding reduces the penetration channels of oxygen and moisture, thus slowing down the aging process.

[0017] (2) The hyperbranched polysiloxane with terminal epoxy groups of the present invention has a small molecular size and low viscosity, and can be dispersed into uniform nano-elastic microspheres during extrusion. These microspheres, as stress concentration points, can induce a large number of silver crazes and shear bands, dissipating impact energy. The terminal epoxy groups can react with the hydroxyl and amino groups on the surface of the flame retardant synergist at high extrusion temperature. At the same time, epoxy ring-opening crosslinking can also occur between hyperbranched molecules, solving the problem of poor compatibility and easy debonding and pull-out of linear polysiloxanes and polypropylene, and improving toughening efficiency. The Si-O bond of the polysiloxane backbone has excellent flexibility and still maintains high elasticity at -40℃, which can effectively transfer and disperse stress. The covalent bond interface will not become brittle and debonded at low temperature. When the polypropylene matrix enters the glassy state and becomes brittle at -40℃, the dispersed elastomer microspheres can still absorb impact energy through their own deformation, preventing crack initiation. Hyperbranched molecules can affect the crystallization behavior of polypropylene, reduce crystallinity and grain size, and reduce brittle fracture between crystal regions at low temperature. The three-dimensional cross-linked network formed by terminal epoxy groups restricts the thermal movement of polypropylene molecular chains, delaying thermal degradation. During thermal decomposition, silicon components migrate to the material surface, forming a dense silica-silicon carbide ceramic layer that isolates oxygen and heat, prevents the escape of internal combustible gases, and inhibits molten dripping. The ceramic layer can react with phosphorus, nitrogen, and boron components in the system to form a more stable composite ceramic layer. The high bond energy of silicon-oxygen bonds gives it excellent resistance to UV aging. Hyperbranched polysiloxanes can scatter some ultraviolet light. The three-dimensional cross-linked network restricts molecular chain movement, reducing chain breakage under UV irradiation. Simultaneously, due to covalent bonding with flame retardants, hyperbranched polysiloxanes are less prone to precipitation, maintaining long-term performance stability.

[0018] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The embodiments described below 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.

[0020] Unless otherwise specified, the following information pertains to some of the raw materials used in the following embodiments and comparative examples of this invention: The polypropylene was purchased from Hebei Sushang Trading Co., Ltd., grade: Yanshan Petrochemical PPR-C4220; the polyolefin elastomer was purchased from Dongguan Zhonghao New Materials Co., Ltd., grade: Dow 8150.

[0021] Example 1: A method for preparing a heat- and shock-resistant protective tubing for MPP cables is as follows: S1: Dissolve 10g citric acid, 2g boric acid, and 5g urea in 100mL deionized water, then react at 180℃ for 6h. After cooling, filter through a 0.22μm filter membrane, then dialyze through a dialysis bag (molecular weight cutoff of 3500Da) for 48h (replace deionized water every 6h), and freeze-dry to obtain boron-nitrogen co-doped carbon dots; S2: Add 3.6g piperazine to 150mL of deionized water and stir for 20min. Then, while stirring, dropwise add 18.6g of 50% phytic acid aqueous solution and stir for 30min. Adjust the pH to 6.8 with phytic acid or piperazine. Then add 3g of boron-nitrogen co-doped carbon dots and stir in the dark for 1h. After freeze-drying, the carbon dot complex is obtained. S3: Add 10g of α-zirconium phosphate to 500mL of deionized water and sonicate for 1h. Then add 31.5g of cetyltrimethylammonium bromide and stir at 80℃ for 24h. Then centrifuge and wash the precipitate with deionized water until there are no bromide ions in the filtrate (tested with 0.1mol / L silver nitrate aqueous solution, no white precipitate is found). Finally, vacuum dry at 80℃ for 12h to obtain modified zirconium phosphate. S4: Add 15g of modified zirconium phosphate to 300g of anhydrous ethanol and ultrasonically disperse for 30min to obtain a modified zirconium phosphate dispersion. S5: Add 23.1g of carbon dot complex to 150mL of anhydrous ethanol and stir for 20min. Then add it dropwise to 315g of modified zirconium phosphate dispersion and stir for 40min. Then add 3g of zinc borate and stir for 30min. Then add 0.6g of silane coupling agent KH-560 and 1.5g of deionized water. After stirring for 30min, react at 80℃ for 6h. Centrifuge and wash the precipitate three times with anhydrous ethanol. Then vacuum dry at 100℃ for 12h. Finally grind and pass through a 200-mesh sieve to obtain the flame retardant synergist. S6: Mix 23g of methyldichlorosilane, 12g of methyltrichlorosilane, 7.74g of dimethyldichlorosilane, and 4.35g of trimethylchlorosilane until homogeneous. Then, under a nitrogen atmosphere, add 150mL of anhydrous toluene at 0℃ at a rate of 0.8g / min and stir for 10min. Then, add 8.3mL of deionized water at 0℃ at a rate of 0.25g / min and stir for 1h. Then, react at 40℃ for 4h. After discarding the lower aqueous phase, wash the organic phase with saturated sodium bicarbonate solution until neutral, then wash three times with deionized water. Then, dry with anhydrous magnesium sulfate for 12h. After filtration, remove toluene and low-boiling-point impurities by rotary evaporation. Finally, dry under vacuum at 80℃ for 12h to obtain terminal hydrogen hyperbranched polysiloxane. S7: Under a nitrogen atmosphere, 17 g of terminal hydrogen hyperbranched polysiloxane was added to 50 mL of anhydrous toluene and the temperature was raised to 70 °C. Then, 0.5 mL of isopropanol solution with a concentration of 0.01 mol / L chloroplatinic acid was added and stirred for 10 min. Then, 23.9 g of allyl glycidyl ether was added dropwise at 0.2 g / min and reacted at 80 °C for 6 h. Subsequently, toluene and excess allyl glycidyl ether were removed by rotary evaporation. Finally, the product was dried under vacuum at 85 °C for 12 h to obtain terminal epoxy hyperbranched polysiloxane. S8: Add 4g of terminal epoxy hyperbranched polysiloxane to 16g of anhydrous ethanol and ultrasonically disperse for 15min to obtain toughened dispersion. S9: Mix 100g polypropylene, 12g polyolefin elastomer, 2g magnesium aluminum hydrotalcite, 0.1g antioxidant 1010, 0.1g antioxidant 168, 0.2g calcium stearate, and 0.2g polyethylene wax for 3 minutes. Then spray 20g toughening dispersion and stir for 5 minutes. Then vacuum dry at 80℃ for 1.5 hours. Then feed the mixture into a co-rotating twin-screw extruder (L / D ratio L / D=44, screw diameter 35mm) through the main feed port for melt extrusion treatment at 170℃ (main feed port), 180℃ (secondary diameter), 190℃ (side feed port), 200℃ (fourth diameter), 205℃ (fifth diameter), 200℃ (sixth diameter), 190℃ (die head), and 220r / min screw speed. During the treatment, add 33g flame retardant synergist at the side feed port in the third zone. Finally, the extruded strip is water-cooled and pelletized to obtain modified granules. S10: Modified granules are extruded using a single-screw pipe extruder (feeding / zone 175℃, zone 2 185℃, zone 3 195℃, zone 4 200℃, die 200℃, screw speed 30r / min). After extrusion from the die, the pipe first passes through a 2m long 120℃ pre-cooling sleeve (to uniformly transform the pipe from a molten state to a highly elastic state), then enters a 130℃ primary stretching sleeve, where it undergoes primary axial stretching with an axial stretching ratio of 1.6 through the traction speed difference. Next, it enters a 125℃ secondary stretching sleeve, where it undergoes secondary circumferential stretching with an internal air pressure with a circumferential stretching ratio of 1.3. Finally, it undergoes vacuum cooling and shaping at a water temperature of 25℃ to obtain heat-resistant and impact-resistant protective pipe material for MPP cables.

[0022] Example 2: A method for preparing a heat- and shock-resistant protective tubing for MPP cables is as follows: S1: Dissolve 10g citric acid, 2g boric acid, and 5g urea in 105mL of deionized water, then react at 180℃ for 6h. After cooling, filter through a 0.22μm filter membrane, then dialyze through a dialysis bag (molecular weight cutoff of 3500Da) for 48h (replace deionized water every 6h), and freeze-dry to obtain boron-nitrogen co-doped carbon dots; S2: Add 3.6g piperazine to 155mL of deionized water and stir for 25min. Then, while stirring, dropwise add 18.8g of 50% phytic acid aqueous solution and stir for 40min. Adjust the pH to 7 with phytic acid or piperazine. Then add 3g of boron-nitrogen co-doped carbon dots and stir in the dark for 1h. After freeze-drying, the carbon dot complex is obtained. S3: Add 10g of α-zirconium phosphate to 505mL of deionized water and sonicate for 1h. Then add 31.7g of cetyltrimethylammonium bromide and stir at 80℃ for 24h. Then centrifuge and wash the precipitate with deionized water until there are no bromide ions in the filtrate (tested with 0.1mol / L silver nitrate aqueous solution, no white precipitate is found). Finally, vacuum dry at 80℃ for 13h to obtain modified zirconium phosphate. S4: Add 15g of modified zirconium phosphate to 310g of anhydrous ethanol and ultrasonically disperse for 35min to obtain a modified zirconium phosphate dispersion. S5: Add 23.1g of carbon dot complex to 150mL of anhydrous ethanol and stir for 25min. Then add it dropwise to 325g of modified zirconium phosphate dispersion and stir for 50min. Then add 3g of zinc borate and stir for 35min. Then add 0.6g of silane coupling agent KH-560 and 1.5g of deionized water. After stirring for 35min, react at 80℃ for 6h. Centrifuge and wash the precipitate 4 times with anhydrous ethanol. Then vacuum dry at 100℃ for 13h. Finally grind and pass through a 200-mesh sieve to obtain the flame retardant synergist. S6: Mix 23g of methyldichlorosilane, 12g of methyltrichlorosilane, 7.74g of dimethyldichlorosilane, and 4.35g of trimethylchlorosilane until homogeneous. Then, under a nitrogen atmosphere, add 153mL of anhydrous toluene at 0℃ at a rate of 0.8g / min and stir for 10min. Then, add 8.3mL of deionized water at 0℃ at a rate of 0.25g / min and stir for 1h. Then, react at 40℃ for 4h. After discarding the lower aqueous phase, wash the organic phase with saturated sodium bicarbonate solution until neutral, then wash with deionized water 4 times. Then, dry with anhydrous magnesium sulfate for 13h. After filtration, remove toluene and low-boiling point impurities by rotary evaporation. Finally, dry under vacuum at 80℃ for 12h to obtain terminal hydrogen hyperbranched polysiloxane. S7: Under a nitrogen atmosphere, 17 g of terminal hydrogen hyperbranched polysiloxane was added to 53 mL of anhydrous toluene and the temperature was raised to 70 °C. Then, 0.5 mL of isopropanol solution with a concentration of 0.01 mol / L chloroplatinic acid was added and stirred for 13 min. Then, 23.9 g of allyl glycidyl ether was added dropwise at 0.2 g / min and reacted at 80 °C for 6 h. Subsequently, toluene and excess allyl glycidyl ether were removed by rotary evaporation. Finally, the mixture was dried under vacuum at 87 °C for 12 h to obtain terminal epoxy hyperbranched polysiloxane. S8: Add 4g of terminal epoxy hyperbranched polysiloxane to 17g of anhydrous ethanol and ultrasonically disperse for 18min to obtain toughened dispersion. S9: Mix 110g polypropylene, 13g polyolefin elastomer, 2.3g magnesium aluminum hydrotalcite, 0.11g antioxidant 1010, 0.11g antioxidant 168, 0.25g calcium stearate, and 0.25g polyethylene wax for 4 minutes. Then spray 21g toughening dispersion and stir for 6 minutes. Then vacuum dry at 80℃ for 1.8 hours. Then feed it into a co-rotating twin-screw extruder (L / D ratio L / D=44, screw diameter 35mm) through the main feed port for melt extrusion treatment at 170℃ (main feed port), 180℃ (L / D ratio L / D=44), 190℃ (side feed port), 200℃ (Zone 1), 205℃ (Zone 5), 200℃ (Zone 6), 190℃ (die head), and 220r / min screw speed. During the treatment, add 34g flame retardant synergist at the side feed port in Zone 3. Finally, the extruded strip is water-cooled and pelletized to obtain modified granules. S10: Modified granules are extruded using a single-screw pipe extruder (feeding / zone 1 175℃, zone 2 185℃, zone 3 195℃, zone 4 200℃, die 200℃, screw speed 30r / min). After extrusion from the die, the pipe first passes through a 2.2m long 123℃ pre-cooling sleeve (to uniformly transform the pipe from a molten state to a highly elastic state), then enters a 133℃ primary stretching sleeve, where it undergoes primary axial stretching with an axial stretching ratio of 1.6 through the traction speed difference. Next, it enters a 128℃ secondary stretching sleeve, where it undergoes secondary circumferential stretching with an internal air pressure with a circumferential stretching ratio of 1.3. Finally, it undergoes vacuum cooling and shaping at a water temperature of 25℃ to obtain heat-resistant and impact-resistant protective pipe material for MPP cables.

[0023] Example 3: A method for preparing a heat- and shock-resistant protective tubing for MPP cables is as follows: S1: Dissolve 10g citric acid, 2g boric acid, and 5g urea in 110mL deionized water, then react at 180℃ for 6h. After cooling, filter through a 0.22μm filter membrane, then dialyze through a dialysis bag (molecular weight cutoff of 3500Da) for 48h (replace deionized water every 6h), and freeze-dry to obtain boron-nitrogen co-doped carbon dots; S2: Add 3.6g piperazine to 160mL of deionized water and stir for 30min. Then, while stirring, dropwise add 19g of 50% phytic acid aqueous solution and stir for 50min. Adjust the pH to 7.2 with phytic acid or piperazine. Then add 3g of boron-nitrogen co-doped carbon dots and stir in the dark for 1h. After freeze-drying, the carbon dot complex is obtained. S3: Add 10g of α-zirconium phosphate to 510mL of deionized water and ultrasonically disperse for 1h. Then add 32g of hexadecyltrimethylammonium bromide and stir at 80℃ for 24h. Then centrifuge and wash the precipitate with deionized water until there are no bromide ions in the filtrate (tested with 0.1mol / L silver nitrate aqueous solution, no white precipitate is found). Finally, vacuum dry at 80℃ for 14h to obtain modified zirconium phosphate. S4: Add 15g of modified zirconium phosphate to 320g of anhydrous ethanol and ultrasonically disperse for 40min to obtain a modified zirconium phosphate dispersion. S5: Add 23.1g of carbon dot complex to 150mL of anhydrous ethanol and stir for 30min. Then add it dropwise to 335g of modified zirconium phosphate dispersion and stir for 60min. Then add 3g of zinc borate and stir for 40min. Then add 0.6g of silane coupling agent KH-560 and 1.5g of deionized water. After stirring for 40min, react at 80℃ for 6h. Centrifuge and wash the precipitate 5 times with anhydrous ethanol. Then vacuum dry at 100℃ for 14h. Finally grind and pass through a 200-mesh sieve to obtain the flame retardant synergist. S6: Mix 23g of methyldichlorosilane, 12g of methyltrichlorosilane, 7.74g of dimethyldichlorosilane, and 4.35g of trimethylchlorosilane until homogeneous. Then, under a nitrogen atmosphere, add 155mL of anhydrous toluene at 0℃ at a rate of 0.8g / min and stir for 10min. Then, add 8.3mL of deionized water at 0℃ at a rate of 0.25g / min and stir for 1h. Then, react at 40℃ for 4h. After discarding the lower aqueous phase, wash the organic phase with a saturated sodium bicarbonate aqueous solution until neutral, then wash with deionized water 5 times. Then, dry with anhydrous magnesium sulfate for 14h. After filtration, remove toluene and low-boiling point impurities by rotary evaporation. Finally, dry under vacuum at 80℃ for 12h to obtain terminal hydrogen hyperbranched polysiloxane. S7: Under a nitrogen atmosphere, 17 g of terminal hydrogen hyperbranched polysiloxane was added to 55 mL of anhydrous toluene and the temperature was raised to 70 °C. Then, 0.5 mL of isopropanol solution with a concentration of 0.01 mol / L chloroplatinic acid was added and stirred for 15 min. Then, 23.9 g of allyl glycidyl ether was added dropwise at 0.2 g / min and reacted at 80 °C for 6 h. Subsequently, toluene and excess allyl glycidyl ether were removed by rotary evaporation. Finally, the product was dried under vacuum at 90 °C for 12 h to obtain terminal epoxy hyperbranched polysiloxane. S8: Add 4g of terminal epoxy hyperbranched polysiloxane to 18g of anhydrous ethanol and ultrasonically disperse for 20min to obtain toughened dispersion. S9: Mix 120g polypropylene, 14g polyolefin elastomer, 2.5g magnesium aluminum hydrotalcite, 0.12g antioxidant 1010, 0.12g antioxidant 168, 0.3g calcium stearate, and 0.3g polyethylene wax for 5 minutes. Then spray 22g toughening dispersion and stir for 7 minutes. Then vacuum dry at 80℃ for 2 hours. Then feed it into a co-rotating twin-screw extruder (L / D ratio L / D=44, screw diameter 35mm) through the main feed port for melt extrusion treatment at 170℃ (main feed port), 180℃ (L / D ratio L / D=44), 190℃ (side feed port), 200℃ (Zone 1), 205℃ (Zone 5), 200℃ (Zone 6), 190℃ (die head), and 220r / min screw speed. During the treatment, add 35g flame retardant synergist at the side feed port in Zone 3. Finally, the extruded strip is water-cooled and pelletized to obtain modified granules. S10: Modified granules are extruded using a single-screw pipe extruder (feeding / zone 1 175℃, zone 2 185℃, zone 3 195℃, zone 4 200℃, die 200℃, screw speed 30r / min). After extrusion from the die, the pipe first passes through a 2.5m long 125℃ pre-cooling sleeve (to uniformly transform the pipe from a molten state to a highly elastic state), then enters a 135℃ primary stretching sleeve, where it undergoes primary axial stretching with an axial stretching ratio of 1.6 through the traction speed difference. Next, it enters a 130℃ secondary stretching sleeve, where it undergoes secondary circumferential stretching with an circumferential stretching ratio of 1.3 through internal air pressure. Finally, it undergoes vacuum cooling and shaping at a water temperature of 25℃ to obtain heat-resistant and impact-resistant protective pipe material for MPP cables.

[0024] Comparative Example 1: Compared with Example 1, this comparative example only did not add "boron-nitrogen co-doped carbon dots" in the preparation process of S2. All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, heat-resistant and shock-resistant protective tubing for MPP cables is obtained.

[0025] Comparative Example 2: Compared with Example 1, this comparative example only omits the addition of a "flame retardant enhancer" during the preparation process of S9. All other steps and parameters are the same, and will not be repeated here. The final product is a heat-resistant and impact-resistant protective tubing for MPP cables.

[0026] Comparative Example 3: Compared with Example 1, this comparative example only omits the addition of "toughening dispersion" during the preparation process of S9. All other steps and parameters are the same, and will not be repeated here. The final product is a heat-resistant and impact-resistant protective tube for MPP cables.

[0027] Performance testing: Determination of flame retardancy: Referring to GB / T 2408-2021 standard, the vertical burning flame retardancy rating of the 127mm×13mm×3mm samples made from the heat-resistant and impact-resistant MPP cable protective tubing prepared in Examples 1-3 and Comparative Examples 1-3 of this invention was determined. The test results are shown in Table 1.

[0028] Determination of aging resistance: Referring to GB / T 1040.2-2022 standard, the heat- and shock-resistant protective tubing materials for MPP cables prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were used to prepare Type 1A dumbbell-shaped specimens (total length 150 mm, parallel section width 10 mm, thickness 3 mm). The specimens were then tested under a UVB-313 fluorescent ultraviolet lamp at a temperature of 0.71 W / (m²). 2 The tensile strength (MPa) before and after exposure to UV radiation at 310 nm and a spacing of 150 mm for 168 h (one cycle consists of 4 h of UV irradiation at 60℃ and 4 h of condensation at 50℃, with alternating cycles) is shown in Table 1.

[0029] Impact resistance testing: Referring to GB / T 1043.1-2008 standard, the heat- and impact-resistant protective tubing materials for MPP cables prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were tested. The specimens, made into Type A notched samples (notch bottom radius 0.25 mm) with dimensions of 80 mm × 10 mm × 4 mm, were measured at 25°C under conditions of pendulum energy of 2.75 J (kJ / m²). 2 The measurement results are shown in Table 1.

[0030] Low temperature resistance test: Referring to GB / T 1043.1-2008 standard, the heat- and impact-resistant protective tubing materials for MPP cables prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were tested. Specimens with A-type notches (notch bottom radius 0.25 mm) measuring 80 mm × 10 mm × 4 mm were prepared and stored at -40°C for 24 hours. The impact strength (kJ / m²) under the conditions of -40°C and a pendulum energy of 2.75 J was then measured. 2 The measurement results are shown in Table 1.

[0031] Determination of heat resistance: Referring to GB / T 1634.1-2019 standard, the heat distortion temperature (°C) of 80mm×10mm×4mm specimens made of heat-resistant and shock-resistant MPP cable protective tubing prepared in Examples 1-3 and Comparative Examples 1-3 of this invention was measured at 1.82MPa. The results are shown in Table 1.

[0032] Table 1: Performance test results of Examples 1-3 and Comparative Examples 1-3

[0033] Data Analysis: As can be seen from Table 1, the heat-resistant and impact-resistant protective tubing for MPP cables prepared according to the embodiments of the present invention also has excellent flame retardancy, aging resistance, impact resistance, low temperature resistance and heat resistance.

[0034] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A heat- and shock-resistant protective tubing material for MPP cables, characterized in that, The components, by weight, include: 20-22 parts of anhydrous ethanol and a toughening dispersion made of terminal epoxy hyperbranched polysiloxane; 33-35 parts of boron-nitrogen co-doped carbon dots made of citric acid, boric acid, urea, and deionized water, which are first compounded with phytic acid aqueous solution and piperazine to form a carbon dot complex, and then compounded with modified zirconium phosphate prepared by hexadecyltrimethylammonium bromide intercalation, and then modified with silane coupling agent KH-560 to form a flame retardant synergist; 12-14 parts of polyolefin elastomer; 2-2.5 parts of magnesium aluminum hydrotalcite; 0.2-0.24 parts of antioxidant; 0.2-0.3 parts of calcium stearate; 0.2-0.3 parts of polyethylene wax; and 100-120 parts of polypropylene.

2. The heat-resistant and shock-resistant protective tubing for MPP cables according to claim 1, characterized in that, The mass ratio of anhydrous ethanol to terminal epoxy hyperbranched polysiloxane is 16-18:

4.

3. The heat-resistant and shock-resistant protective tubing for MPP cables according to claim 1, characterized in that, The mass ratio of citric acid, boric acid, urea, and deionized water is 10:2:5:100-110.

4. The heat-resistant and shock-resistant protective tubing for MPP cables according to claim 1, characterized in that, The mass ratio of piperazine, phytic acid aqueous solution, and boron-nitrogen co-doped carbon dots is 3.6:18.6-19:

3.

5. The heat-resistant and shock-resistant protective tubing for MPP cables according to claim 4, characterized in that, The phytic acid aqueous solution has a mass fraction of 50%.

6. The heat-resistant and shock-resistant protective tubing for MPP cables according to claim 1, characterized in that, The mass ratio of zirconium phosphate to hexadecyltrimethylammonium bromide is 10:31.5-32.

7. The heat-resistant and shock-resistant protective tubing for MPP cables according to claim 1, characterized in that, The mass ratio of the carbon dot complex, modified zirconium phosphate dispersion, zinc borate, and silane coupling agent KH-560 is 23.1:315-335:3:0.

6.

8. The heat-resistant and shock-resistant protective tubing for MPP cables according to claim 7, characterized in that, The modified zirconium phosphate dispersion was obtained by mixing anhydrous ethanol and modified zirconium phosphate in a mass ratio of 300-320:

15.

9. A method for preparing a heat-resistant and impact-resistant protective tubing for MPP cables according to any one of claims 1-8, characterized in that, Includes the following steps: S1: Polypropylene, polyolefin elastomer, magnesium aluminum hydrotalcite, antioxidant, calcium stearate and polyethylene wax are mixed evenly, then toughening dispersion is sprayed and stirred evenly, then vacuum dried, followed by melt extrusion treatment. Flame retardant synergist is added during the treatment process, and finally modified granules are obtained after post-treatment. S2: After the modified granules are extruded, they are first pre-cooled at 120-125℃, and then subjected to axial stretching, circumferential stretching, and cooling to obtain heat-resistant and impact-resistant protective tubing for MPP cables.

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