High toughness sheath material for underground cable and preparation method thereof

Abstract

The application discloses a high-toughness sheath material for buried cable and a preparation method thereof, and belongs to the technical field of flame-retardant cable materials. In view of the halogen-free flame-retardant requirement of the polyethylene sheath material of the power cable, a high-efficiency flame-retardant system is constructed by taking the core-shell structure halogen-free flame-retardant microcapsule powder as a core flame-retardant component and taking magnesium hydroxide as an auxiliary flame-retardant component, and the high-efficiency flame-retardant system takes paraffin / aluminum hypophosphite compound as a core material and takes capsaicin grafted polyurethane as a shell layer. The aluminum hypophosphite serves as a phosphorus-based high-efficiency flame retardant, and can play a flame-retardant role through a dual mechanism of gas-phase free radical capture and condensed-phase catalytic carbon formation. After the aluminum hypophosphite is compounded with the traditional inorganic flame retardant magnesium hydroxide, only a low amount of the aluminum hypophosphite needs to be added in the polyethylene matrix, so that the material can meet the halogen-free flame-retardant grade requirement specified in the power cable industry standard under the premise of fully retaining the mechanical strength of the sheath material.

Description

Technical Field

[0001] This invention belongs to the field of flame-retardant cable material technology, specifically a high-toughness sheath material for underground cables and its preparation method. Background Technology

[0002] With the rapid development of new urbanization, urban underground utility tunnel projects, new power systems, and rail transit networks in my country, underground power cables, with their core advantages such as small footprint, high power supply reliability, minimal susceptibility to external environmental interference, and environmental friendliness, have become the core carrier for power transmission in urban power distribution networks, industrial parks, and underground transportation hubs, leading to continuous growth in market demand. As the outermost protective barrier of underground cables, cable sheath material directly determines the cable's service life, operational safety, and adaptability to complex environments, making it a key material for ensuring the core performance of underground cables.

[0003] The underground laying environment is complex and harsh, placing multi-dimensional and high-standard performance requirements on sheathing materials. According to relevant power industry operation and maintenance standards, underground cable sheathing materials not only need to possess excellent electrical insulation and processability, but also must simultaneously meet four core performance requirements: First, high mechanical toughness and deformation resistance, requiring high elongation at break and excellent resistance to environmental stress cracking to cope with soil settlement, geological deformation, and bending, compression, and friction damage during construction and laying; Second, environmentally friendly halogen-free flame retardant performance, requiring low-smoke halogen-free flame retardant requirements to avoid secondary disasters caused by the generation of toxic and corrosive gases in the event of a fire, and to meet the safety protection needs of underground confined spaces; Third, long-term resistance to environmental erosion, requiring excellent water resistance and aging resistance, while also resisting microorganisms, rodent and ant gnawing, and soil chemical corrosion in humid underground environments; Fourth, long-term performance stability, requiring no migration or loss of functional components and no significant attenuation of mechanical and protective properties during long-term underground service.

[0004] Chinese invention patent application CN119431926A discloses a high-strength, high-toughness, low-smoke, halogen-free flame-retardant and rodent-proof cable sheath material and its preparation method. This technical solution uses magnesium hydroxide, aluminum hydroxide, or ammonium polyphosphate as the core inorganic flame-retardant components, aiming to impart corresponding flame-retardant and protective properties to the cable sheath material through these additive flame retardants. However, magnesium hydroxide, aluminum hydroxide, and ammonium polyphosphate inorganic flame retardants generally have the inherent defect of low flame-retardant efficiency, requiring high filler content to achieve the flame-retardant rating required by the power cable industry standards.

[0005] Calculations show that the inorganic flame retardant accounts for as much as 41.45-54.20% of the mass of the above-mentioned technical solution, which is a typical high-filling flame retardant system. Such an ultra-high proportion of inorganic powder filler will directly lead to the deterioration of the interfacial compatibility between the inorganic flame retardant phase and the polymer matrix. This will not only cause a significant decrease in the mechanical properties of the sheath material, but also deteriorate the processing flow properties of the material, making it unable to meet the comprehensive and stringent requirements of underground cable sheath material for high toughness, long-term service stability and extrusion molding processability. Summary of the Invention

[0006] The purpose of this invention is to provide a high-toughness sheath material for buried cables and its preparation method. The method uses halogen-free flame-retardant microcapsule powder as the core flame-retardant component and magnesium hydroxide as an auxiliary flame-retardant component. It constructs a core-shell microcapsule flame-retardant system of paraffin / aluminum hypophosphite composite and capsaicin / polyurethane emulsion. Aluminum hypophosphite is a phosphorus-based high-efficiency flame retardant that achieves flame retardancy through a dual mechanism of gas-phase free radical capture and condensed-phase catalytic char formation. Combined with the traditional inorganic flame retardant magnesium hydroxide, only a small amount needs to be added to the polyethylene matrix. This maintains sufficient mechanical strength of the sheath material while ensuring it meets the halogen-free flame-retardant rating required by the power cable industry standards.

[0007] The objective of this invention can be achieved through the following technical solutions: A high-toughness sheathing material for buried cables, comprising the following components by weight: 100-110 parts polyethylene, 4-8 parts halogen-free flame-retardant microcapsule powder, 2-4 parts magnesium hydroxide, 2-4 parts dicumyl peroxide and 0.5-1 parts zinc oxide.

[0008] Furthermore, the high-toughness sheath material for buried cables is prepared through the following steps: Polyethylene, halogen-free flame-retardant microcapsule powder, magnesium hydroxide, dicumyl peroxide and zinc oxide are added to a twin-screw extruder and melt-extruded at 168-170℃. After pelleting, the material is vacuum-dried at 60-70℃ for 1-2 hours to obtain a high-toughness sheath material for underground cables.

[0009] Furthermore, the specific preparation steps of the halogen-free flame-retardant microcapsule powder are as follows: Capsaicin / polyurethane emulsion and paraffin / aluminum hypophosphite composite were added to a reaction vessel and stirred for 20-30 minutes at 70-75℃ and 500-600 r / min. Then ammonium persulfate was added and the reaction was continued for 2-3 hours. After the reaction was completed, the suspension was allowed to stand and naturally cooled to room temperature. It was then refrigerated at 4-5℃ for 12-14 hours. After solid-liquid separation, the excess paraffin floating on the top layer was removed. The mixture was washed 2-4 times with deionized water, filtered, and vacuum dried at 60-70℃ for 1-2 hours to obtain halogen-free flame-retardant microcapsule powder.

[0010] Furthermore, the mass ratio of capsaicin / polyurethane emulsion, paraffin / aluminum hypophosphite composite, and ammonium persulfate is 35-40:24-26:0.6-0.8.

[0011] Furthermore, the specific preparation steps of the capsaicin / polyurethane emulsion are as follows: Polyurethane prepolymer A, polyurethane prepolymer B and 1,4'-butanediol were added to a reactor at a mass ratio of 98-100:12-14:4.2-4.6 and subjected to chain extension reaction at 80-90℃ and 500-600 r / min for 2-3 h to obtain capsaicin / polyurethane emulsion.

[0012] Furthermore, the specific preparation steps for polyurethane prepolymer A are as follows: Polycaprolactone and 4,4'-diphenylmethane diisocyanate were added to a reactor and stirred for 20-30 minutes under a nitrogen atmosphere, at 20-25°C and 500-600 r / min. The mixture was then heated to 80-90°C. As the viscosity of the reaction system increased, N,N-dimethylformamide was added to adjust the viscosity. The reaction was continued for 2-4 hours to obtain polyurethane prepolymer A.

[0013] Furthermore, the ratio of polycaprolactone, 4,4'-diphenylmethane diisocyanate, and N,N-dimethylformamide is 60-62g: 18-20g: 25-30mL.

[0014] Furthermore, the specific preparation steps for polyurethane prepolymer B are as follows: Capsaicin and 4,4'-diphenylmethane diisocyanate were added to a reaction vessel at a mass ratio of 6-8:8.5-9. The mixture was heated to 80-90°C under a nitrogen atmosphere and stirred for 2-4 hours to obtain polyurethane prepolymer B.

[0015] Furthermore, the specific preparation steps of the paraffin / aluminum hypophosphite composite are as follows: The oil phase is added to the aqueous phase and stirred at 80-90℃ and 500-600r / min for 90-100min to obtain the paraffin / aluminum hypophosphite composite.

[0016] Furthermore, the specific preparation steps for the aqueous phase are as follows: After mixing deionized water and Tween-80 at a volume ratio of 10-12:3-4, the mixture was ultrasonically dispersed for 30-40 minutes to obtain the aqueous phase.

[0017] Furthermore, the specific steps for preparing the oil phase are as follows: Solid and liquid paraffin are added to a reactor and melt-blended at 70-75℃ and 500-600r / min for 20-30min. Then, spherical aluminum hypophosphite and Span-80 are added, and the mixture is stirred to obtain the oil phase.

[0018] Furthermore, the ratio of solid paraffin, liquid paraffin, spherical aluminum hypophosphite, and Span-80 is 28-30g: 28-30g: 5-6g: 2-2.8g.

[0019] Furthermore, the specific preparation steps for spherical aluminum hypophosphite are as follows: Aluminum sulfate hexahydrate and aluminum chloride hexahydrate were added to a reaction vessel and stirred for 20-30 minutes at 20-25℃ and 500-600 r / min. Then, deionized water and ethylene glycol were added, and stirring was continued for 1-2 hours until the aluminum sulfate hexahydrate and aluminum chloride hexahydrate were completely dissolved. Sodium hypophosphite solution was then added, and the mixture was heated to 90-92℃ and reacted for another 1-2 hours. The mixture was filtered, and the filter cake was washed 2-4 times with deionized water and anhydrous ethanol. It was then vacuum dried at 60-70℃ for 1-2 hours to obtain spherical aluminum hypophosphite with an average particle size of 3 μm.

[0020] Furthermore, the ratio of aluminum sulfate hexahydrate, aluminum chloride hexahydrate, deionized water, ethylene glycol, and sodium hypophosphite solution is 22.06-23.08g: 2.18-2.26g: 8.75-9.22mL: 8.75-9.53mL: 38-40g.

[0021] The beneficial effects of this invention are: 1. This invention addresses the halogen-free flame retardant requirements of polyethylene sheathing materials for power cables. It constructs a highly efficient flame retardant system with a paraffin / aluminum hypophosphite composite as the core material and capsaicin-grafted polyurethane as the shell, using core-shell structured halogen-free flame retardant microcapsule powder as the core flame retardant component and magnesium hydroxide as an auxiliary flame retardant component. Aluminum hypophosphite, as a phosphorus-based highly efficient flame retardant, exerts its flame retardant effect through a dual mechanism of gas-phase free radical capture and condensed-phase catalytic char formation. When compounded with the traditional inorganic flame retardant magnesium hydroxide, it only needs to be added in low amounts to the polyethylene matrix to fully preserve the mechanical strength of the sheathing material while meeting the halogen-free flame retardant rating requirements stipulated in the power cable industry standards.

[0022] 2. This invention uses capsaicin derived from biomass as a biological repellent component, replacing traditional toxic and harmful chemical ant and rodent repellents, thus meeting ecological and environmental protection requirements and avoiding the pollution of soil and groundwater caused by traditional rodent repellents. Unlike traditional physical blending modification methods, this invention chemically grafts capsaicin into the polyurethane molecular chain, fundamentally solving the problems of easy migration, precipitation, and water loss of small-molecule rodent repellents, enabling the material to maintain stable rodent and ant repellency in complex, damp underground environments for a long period.

[0023] 3. This invention achieves a synergistic unity of flame retardant enhancement and mechanical strengthening through a core-shell structure design. The microcapsule core material adopts a composite structure of paraffin-coated aluminum hypophosphite. Paraffin can rapidly absorb heat from the combustion zone and lower the system temperature through phase change, forming a strong synergistic effect with the flame retardant effect of aluminum hypophosphite, significantly improving flame retardant efficiency. Simultaneously, using capsaicin-grafted polyurethane as a compatible shell layer allows for uniform dispersion of the microcapsules within the polyethylene matrix, avoiding the inherent defects of agglomeration and interfacial stress concentration that easily occur with direct filling of inorganic flame retardant powders. This structure achieves efficient toughening through stress dispersion effect, significantly optimizing the mechanical stability of the sheath material while improving flame retardant performance. Furthermore, the coating effect of the polyurethane shell and the hydrophobicity of capsaicin can isolate the aluminum hypophosphite from direct contact with external water, soil chemical media, and other sources, solving the inherent defects of easy hydrolysis and migration of aluminum hypophosphite, ensuring the long-term stability of the flame retardant performance of the sheath material, and significantly extending the service life of power cables. Detailed Implementation

[0024] 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.

[0025] Example 1: A method for preparing a high-toughness sheath material for buried cables, comprising the following steps: S1: 22.06 g of sodium hypophosphite monohydrate, 8.75 mL of deionized water, and 8.75 mL of ethylene glycol were stirred and mixed to obtain a sodium hypophosphite solution. 22.06 g of aluminum sulfate hexadecahydrate and 2.18 g of aluminum chloride hexahydrate were added to the reaction vessel and stirred for 20 min at 20 °C and 500 r / min. Then, 8.75 mL of deionized water and 8.75 mL of ethylene glycol were added, and stirring was continued for 1 h until the aluminum sulfate hexadecahydrate and aluminum chloride hexahydrate were completely dissolved. Then, 38 g of sodium hypophosphite solution was added, and the mixture was heated to 90 °C and reacted for another 1 h. The mixture was filtered, and the filter cake was washed twice with deionized water and anhydrous ethanol. It was then vacuum dried at 60 °C for 1 h to obtain spherical aluminum hypophosphite with an average particle size of 3 μm.

[0026] Using aluminum sulfate hexahydrate and aluminum chloride hexahydrate as aluminum sources and sodium hypophosphite monohydrate as phosphorus source, a metathesis precipitation method was adopted, combined with a hydrothermal reaction system, to induce the formation of spherical aluminum hypophosphite crystals, thus preparing spherical aluminum hypophosphite. S2: Add 60g of polycaprolactone and 18g of 4,4'-diphenylmethane diisocyanate to a reactor. Stir for 20min at 20℃ and 500r / min under a nitrogen atmosphere. Heat to 80℃. As the viscosity of the reaction system increases, add 25mL of N,N-dimethylformamide to adjust the viscosity. Continue stirring and react for 2h to obtain polyurethane prepolymer A. Add 6g of capsaicin and 8.5g of 4,4'-diphenylmethane diisocyanate to a reactor. Heat to 80℃ under a nitrogen atmosphere and continue stirring and react for 2h to obtain polyurethane prepolymer B. Add 98g of polyurethane prepolymer A, 12g of polyurethane prepolymer B and 4.2g of 1,4'-butanediol to a reactor. Perform chain extension reaction at 80℃ and 500r / min for 2h to obtain capsaicin / polyurethane emulsion.

[0027] Polyurethane prepolymer A was prepared by the addition reaction of polycaprolactone with 4,4'-diphenylmethane diisocyanate. Polyurethane prepolymer B was prepared by the addition reaction of capsaicin with 4,4'-diphenylmethane diisocyanate. Then, the chain was extended by 1,4-butanediol as a chain extender to obtain capsaicin / polyurethane emulsion.

[0028] S3: Add 28g of solid paraffin and 28g of liquid paraffin to a reactor and melt-blend at 70℃ and 500r / min for 20min. Then add 5g of spherical aluminum hypophosphite and 2g of Span-80 and continue stirring to obtain the oil phase. Mix 10mL of deionized water and 3mL of Tween-80 and ultrasonically disperse for 30min to obtain the aqueous phase. Add the oil phase to the aqueous phase and stir at 80℃ and 500r / min for 90min to obtain the paraffin / aluminum hypophosphite composite.

[0029] A paraffin / aluminum hypophosphite composite was obtained by high-temperature melt blending of solid and liquid paraffin, followed by high-temperature shear emulsification to form a stable oil-in-water emulsion using spherical aluminum hypophosphite and Span-80 as the hydrophobic oil phase, and deionized water and Tween 80 as the aqueous phase.

[0030] S4: Add 35g capsaicin / polyurethane emulsion and 24g paraffin / aluminum hypophosphite complex to a reaction vessel, stir for 20min at 70℃ and 500r / min, then add 0.6g ammonium persulfate, continue stirring for 2h. After the reaction is complete, let the suspension stand, cool naturally to room temperature, and refrigerate at 4℃ for 12h. After solid-liquid separation occurs, remove the excess paraffin floating on the upper layer, wash twice with deionized water, filter, and vacuum dry at 60℃ for 1h to obtain halogen-free flame-retardant microcapsule powder.

[0031] Using capsaicin / polyurethane emulsion as the wall material and paraffin / aluminum hypophosphite composite as the core material, ammonium persulfate was used to initiate polymerization and cross-linking, forming a dense polyurethane coating shell on the surface of the core material to obtain halogen-free flame-retardant microcapsule powder.

[0032] S5: Add 100g polyethylene, 4g halogen-free flame-retardant microcapsule powder, 2g magnesium hydroxide, 2g dicumyl peroxide and 0.5g zinc oxide to a twin-screw extruder, melt extrude at 168℃, then pelletize and vacuum dry at 60℃ for 1h to obtain high-toughness sheath material for underground cables.

[0033] Example 2: A method for preparing a high-toughness sheath material for buried cables, comprising the following steps: S1: 22.57 g of sodium hypophosphite monohydrate, 8.985 mL of deionized water, and 9.14 mL of ethylene glycol were stirred and mixed to obtain a sodium hypophosphite solution. 22.57 g of aluminum sulfate hexadecahydrate and 2.22 g of aluminum chloride hexahydrate were added to the reaction vessel and stirred for 25 min at 22.5 °C and 550 r / min. Then, 8.985 mL of deionized water and 9.14 mL of ethylene glycol were added, and stirring was continued for 1.5 h until the aluminum sulfate hexadecahydrate and aluminum chloride hexahydrate were completely dissolved. Then, 39 g of sodium hypophosphite solution was added, and the mixture was heated to 91 °C and reacted for another 1.5 h. The mixture was filtered, and the filter cake was washed three times with deionized water and anhydrous ethanol. It was then vacuum dried at 65 °C for 1.5 h to obtain spherical aluminum hypophosphite with an average particle size of 3 μm.

[0034] S2: 61g of polycaprolactone and 19g of 4,4'-diphenylmethane diisocyanate were added to a reactor and stirred for 25min at 22.5℃ and 550r / min under a nitrogen atmosphere. The mixture was then heated to 85℃. As the viscosity of the reaction system increased, 27.5mL of N,N-dimethylformamide was added to adjust the viscosity. The reaction was continued for 3h with stirring to obtain polyurethane prepolymer A. 7g of capsaicin and 8.75g of 4,4'-diphenylmethane diisocyanate were added to a reactor and heated to 85℃ under a nitrogen atmosphere. The reaction was continued for 3h with stirring to obtain polyurethane prepolymer B. 99g of polyurethane prepolymer A, 13g of polyurethane prepolymer B, and 4.4g of 1,4'-butanediol were added to a reactor and subjected to a chain extension reaction at 85℃ and 550r / min for 2.5h to obtain a capsaicin / polyurethane emulsion.

[0035] S3: Add 29g of solid paraffin and 29g of liquid paraffin to a reactor and melt-blend at 72.5℃ and 550r / min for 25min. Then add 5.5g of spherical aluminum hypophosphite and 2.4g of Span-80 and continue stirring to obtain the oil phase. Mix 11mL of deionized water and 3.5mL of Tween-80 and ultrasonically disperse for 35min to obtain the aqueous phase. Add the oil phase to the aqueous phase and stir at 85℃ and 550r / min for 95min to obtain the paraffin / aluminum hypophosphite composite.

[0036] S4: Add 37.5g capsaicin / polyurethane emulsion and 25g paraffin / aluminum hypophosphite composite to a reaction vessel, stir for 25min at 72.5℃ and 550r / min, then add 0.7g ammonium persulfate, and continue stirring for 2.5h. After the reaction is complete, let the suspension stand, cool naturally to room temperature, and refrigerate at 4.5℃ for 13h. After solid-liquid separation occurs, remove the excess paraffin floating on the upper layer, wash three times with deionized water, filter, and vacuum dry at 65℃ for 1.5h to obtain halogen-free flame-retardant microcapsule powder.

[0037] S5: Add 105g polyethylene, 6g halogen-free flame-retardant microcapsule powder, 3g magnesium hydroxide, 3g dicumyl peroxide and 0.75g zinc oxide to a twin-screw extruder, melt extrude at 169℃, then pelletize and vacuum dry at 65℃ for 1.5h to obtain high-toughness sheath material for underground cables.

[0038] Example 3: A method for preparing a high-toughness sheath material for buried cables, comprising the following steps: S1: 23.08 g of sodium hypophosphite monohydrate, 9.22 mL of deionized water, and 9.53 mL of ethylene glycol were stirred and mixed to obtain a sodium hypophosphite solution. 23.08 g of aluminum sulfate hexadecahydrate and 2.26 g of aluminum chloride hexahydrate were added to the reaction vessel and stirred at 25 °C and 600 r / min for 30 min. Then, 9.22 mL of deionized water and 9.53 mL of ethylene glycol were added, and stirring was continued for 2 h until the aluminum sulfate hexadecahydrate and aluminum chloride hexahydrate were completely dissolved. Then, 40 g of sodium hypophosphite solution was added, and the mixture was heated to 92 °C and reacted for another 2 h. The mixture was filtered, and the filter cake was washed four times with deionized water and anhydrous ethanol. It was then vacuum dried at 70 °C for 2 h to obtain spherical aluminum hypophosphite with an average particle size of 3 μm.

[0039] S2: Add 62g of polycaprolactone and 20g of 4,4'-diphenylmethane diisocyanate to a reactor, stir for 30min at 25℃ and 600r / min under a nitrogen atmosphere, heat to 90℃, and add 30mL of N,N-dimethylformamide to adjust the viscosity as the viscosity of the reaction system increases. Continue stirring and react for 4h to obtain polyurethane prepolymer A; Add 8g of capsaicin and 9g of 4,4'-diphenylmethane diisocyanate to a reactor, heat to 90℃ under a nitrogen atmosphere, and continue stirring and react for 4h to obtain polyurethane prepolymer B; Add 100g of polyurethane prepolymer A, 14g of polyurethane prepolymer B, and 4.6g of 1,4'-butanediol to a reactor, and perform chain extension reaction at 90℃ and 600r / min for 3h to obtain capsaicin / polyurethane emulsion.

[0040] S3: Add 30g of solid paraffin and 30g of liquid paraffin to a reactor and melt-blend at 75℃ and 600r / min for 30min. Then add 6g of spherical aluminum hypophosphite and 2.8g of Span-80 and continue stirring to obtain the oil phase. Mix 12mL of deionized water and 4mL of Tween-80 and ultrasonically disperse for 40min to obtain the aqueous phase. Add the oil phase to the aqueous phase and stir at 90℃ and 600r / min for 100min to obtain the paraffin / aluminum hypophosphite composite.

[0041] S4: Add 40g capsaicin / polyurethane emulsion and 26g paraffin / aluminum hypophosphite complex to a reaction vessel, stir for 30min at 75℃ and 600r / min, then add 0.8g ammonium persulfate, continue stirring for 3h. After the reaction is complete, let the suspension stand, cool naturally to room temperature, refrigerate at 5℃ for 14h. After solid-liquid separation occurs, remove the excess paraffin floating on the top layer, wash 4 times with deionized water, filter, and vacuum dry at 70℃ for 2h to obtain halogen-free flame-retardant microcapsule powder.

[0042] S5: Add 110g of polyethylene, 8g of halogen-free flame-retardant microcapsule powder, 4g of magnesium hydroxide, 4g of dicumyl peroxide and 1g of zinc oxide to a twin-screw extruder, melt extrude at 170℃, then pelletize and vacuum dry at 70℃ for 2h to obtain high-toughness sheath material for underground cables.

[0043] Comparative Example 1: Based on Example 3, the polyurethane prepolymer B in step S2 was replaced with capsaicin, the raw material in step S2, while the other steps remained unchanged, to prepare a high-toughness sheath material for underground cables.

[0044] Comparative Example 2: Based on Example 3, the paraffin / aluminum hypophosphite composite in step S4 was replaced with the spherical aluminum hypophosphite prepared in step S1, while the other steps remained unchanged, to prepare a high-toughness sheath material for buried cables.

[0045] Comparative Example 3: Based on Example 3, the spherical aluminum hypophosphite in step S3 was removed, and a paraffin core material was prepared to replace the paraffin / aluminum hypophosphite composite in the original step S3. The remaining steps remained unchanged, and a high-toughness sheath material for buried cables was prepared.

[0046] In the examples and comparative examples: Sodium hypophosphite monohydrate was purchased from Dongguan Xunye Chemical Reagent Co., Ltd., CAS No.: 10039-56-2.

[0047] Polycaprolactone was purchased from Hubei Watson Chemical Technology Co., Ltd., CAS No.: 24980-41-4, molecular weight: 114.142.

[0048] 4,4'-Diphenylmethane diisocyanate was purchased from Wuhan Hongde Yuexin Pharmaceutical Technology Co., Ltd.

[0049] The performance of the high-toughness sheathing materials for underground cables prepared in Examples 1-3 and Comparative Examples 1-3 was tested, and the results are shown in Table 1: Table 1 Performance Test Table of High-Toughness Sheath Material for Underground Cables As shown in Table 1, in Comparative Example 1, capsaicin did not chemically bond to the polyurethane molecular chain through an addition reaction, but was physically dispersed in the system as a small molecule. Small molecule capsaicin is very easy to migrate inside the material and precipitate to the surface. In damp underground environments, it will also be leached away by water. The small amount of capsaicin that remains will also quickly become ineffective, ultimately resulting in extremely poor rodent-repellent performance. Unreacted small molecule capsaicin will destroy the regularity and cross-linking density of the polyurethane shell, resulting in a decrease in the film-forming properties and density of the shell. At the same time, free capsaicin small molecules form a large number of interface defects and stress concentration points in the polyethylene matrix, reducing the density of the polyurethane shell and weakening the coating and protection effect on the core material aluminum hypophosphite. Aluminum hypophosphite is prone to hydrolysis and migration, resulting in the continuous loss of flame-retardant components and a decrease in the limiting oxygen index.

[0050] In Comparative Example 2, the synergistic flame-retardant effect of paraffin phase change endothermic and cooling flame suppression is lost. Relying solely on aluminum hypophosphite as a single component, the flame-retardant efficiency is significantly reduced. At the same time, paraffin can inhibit combustion dripping through melting and film formation. Without paraffin, aluminum hypophosphite alone cannot inhibit the molten dripping generated by polyethylene combustion, which easily leads to secondary combustion. The limiting oxygen index decreases, and the efficient toughening effect of paraffin as a flexible core material is lost. The interfacial compatibility between pure inorganic aluminum hypophosphite and the polyurethane shell and polyethylene matrix is ​​greatly reduced, making it easy for interfacial delamination and powder agglomeration to occur. A large number of stress concentration points are formed in the matrix. Without the pre-coating and isolation of aluminum hypophosphite by paraffin, aluminum hypophosphite powder is easy to agglomerate in the core material. The polyurethane shell cannot achieve uniform and dense coating, and some aluminum hypophosphite particles are directly exposed, which is prone to hydrolysis and migration. The flame-retardant performance continues to decline during long-term service.

[0051] In Comparative Example 3, the microcapsules themselves lost their flame-retardant function and relied solely on magnesium hydroxide as an auxiliary flame retardant. The flame-retardant efficiency was extremely low, and it could not inhibit the combustion of polyethylene. Although the capsaicin structure in the shell was not destroyed, the overall strength of the material decreased, making it more susceptible to being eaten by rodents and ants. At the same time, the migration and precipitation of paraffin would cause the capsaicin in the shell to be lost simultaneously, resulting in a significant decrease in the long-term rodent-repellent effect.

[0052] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A high-toughness sheath material for buried cables, characterized in that, By mass, it includes the following components: 100-110 parts polyethylene, 4-8 parts halogen-free flame-retardant microcapsule powder, 2-4 parts magnesium hydroxide, 2-4 parts dicumyl peroxide and 0.5-1 parts zinc oxide; The specific preparation steps of the halogen-free flame-retardant microcapsule powder are as follows: Capsaicin / polyurethane emulsion and paraffin / aluminum hypophosphite composite were added to a reaction vessel and stirred for 20-30 minutes at 70-75℃ and 500-600 r / min. Then ammonium persulfate was added and the reaction was continued for 2-3 hours. After the reaction was completed, the suspension was allowed to stand and naturally cooled to room temperature. It was then refrigerated at 4-5℃ for 12-14 hours. After solid-liquid separation, the excess paraffin floating on the top layer was removed. The mixture was washed 2-4 times with deionized water, filtered, and vacuum dried at 60-70℃ for 1-2 hours to obtain halogen-free flame-retardant microcapsule powder.

2. The high-toughness sheath material for buried cables according to claim 1, characterized in that, The mass ratio of capsaicin / polyurethane emulsion, paraffin / aluminum hypophosphite composite and ammonium persulfate is 35-40:24-26:0.6-0.

8.

3. The high-toughness sheath material for buried cables according to claim 1, characterized in that, The specific preparation steps of the capsaicin / polyurethane emulsion are as follows: Polyurethane prepolymer A, polyurethane prepolymer B and 1,4'-butanediol were added to a reactor at a mass ratio of 98-100:12-14:4.2-4.6 and subjected to chain extension reaction at 80-90℃ and 500-600 r / min for 2-3 h to obtain capsaicin / polyurethane emulsion.

4. The high-toughness sheath material for buried cables according to claim 3, characterized in that, The specific preparation steps for polyurethane prepolymer A are as follows: Polycaprolactone and 4,4'-diphenylmethane diisocyanate were added to a reaction vessel and stirred for 20-30 minutes under a nitrogen atmosphere, at 20-25°C and 500-600 r / min. The mixture was then heated to 80-90°C. As the viscosity of the reaction system increased, N,N-dimethylformamide was added to adjust the viscosity. The reaction was continued for 2-4 hours to obtain polyurethane prepolymer A. The ratio of polycaprolactone, 4,4'-diphenylmethane diisocyanate, and N,N-dimethylformamide is 60-62g: 18-20g: 25-30mL.

5. The high-toughness sheath material for buried cables according to claim 3, characterized in that, The specific preparation steps for the polyurethane prepolymer B are as follows: Capsaicin and 4,4'-diphenylmethane diisocyanate were added to a reaction vessel at a mass ratio of 6-8:8.5-9. The mixture was heated to 80-90°C under a nitrogen atmosphere and stirred for 2-4 hours to obtain polyurethane prepolymer B.

6. The high-toughness sheath material for buried cables according to claim 1, characterized in that, The specific preparation steps of the paraffin / aluminum hypophosphite composite are as follows: The oil phase was added to the aqueous phase and stirred for 90-100 min at 80-90℃ and 500-600 r / min to obtain the paraffin / aluminum hypophosphite composite. The specific steps for preparing the aqueous phase are as follows: After mixing deionized water and Tween-80 at a volume ratio of 10-12:3-4, the mixture was ultrasonically dispersed for 30-40 minutes to obtain the aqueous phase.

7. The high-toughness sheath material for buried cables according to claim 6, characterized in that, The specific steps for preparing the oil phase are as follows: Solid paraffin and liquid paraffin are added to a reaction vessel and melt-blended at 70-75℃ and 500-600r / min for 20-30min. Then, spherical aluminum hypophosphite and Span-80 are added, and the mixture is stirred to obtain the oil phase. The ratio of solid paraffin, liquid paraffin, spherical aluminum hypophosphite, and Span-80 is 28-30g: 28-30g: 5-6g: 2-2.8g.

8. The high-toughness sheath material for buried cables according to claim 7, characterized in that, The specific preparation steps for the spherical aluminum hypophosphite are as follows: Aluminum sulfate hexahydrate and aluminum chloride hexahydrate were added to a reaction vessel and stirred for 20-30 minutes at 20-25℃ and 500-600 r / min. Then, deionized water and ethylene glycol were added, and stirring was continued for 1-2 hours until the aluminum sulfate hexahydrate and aluminum chloride hexahydrate were completely dissolved. Sodium hypophosphite solution was then added, and the mixture was heated to 90-92℃ and reacted for another 1-2 hours. The mixture was filtered, and the filter cake was washed 2-4 times with deionized water and anhydrous ethanol. It was then vacuum dried at 60-70℃ for 1-2 hours to obtain spherical aluminum hypophosphite with an average particle size of 3 μm.

9. A high-toughness sheath material for buried cables according to claim 8, characterized in that, The ratio of the amounts of aluminum sulfate hexahydrate, aluminum chloride hexahydrate, deionized water, ethylene glycol, and sodium hypophosphite solution is 22.06-23.08 g : 2.18-2.26 g : 8.75-9.22 mL : 8.75-9.53 mL : 38-40 g.

10. The method for preparing a high-toughness sheath material for buried cables according to claim 1, characterized in that, The high-toughness sheath material for buried cables is prepared through the following steps: Polyethylene, halogen-free flame-retardant microcapsule powder, magnesium hydroxide, dicumyl peroxide and zinc oxide are added to a twin-screw extruder and melt-extruded at 168-170℃. After pelleting, the material is vacuum-dried at 60-70℃ for 1-2 hours to obtain a high-toughness sheath material for underground cables.

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