An epoxy resin composite material for cables and its preparation method

Abstract

This invention relates to the field of epoxy resin materials technology, specifically to an epoxy resin composite material for cables and its preparation method. This invention overcomes the contradiction between the difficulty in processing highly filled flame-retardant systems and the high brittleness of the resin. The composite material of this application is composed of bisphenol A type epoxy resin prepolymer, phosphorus-containing hyperbranched polyester, carboxyl-terminated polyethersulfone, modified magnesium hydroxide, ionic liquid-modified multi-walled carbon nanotubes, and a curing system. In preparation, the hyperbranched polyester is first used to improve the rheological properties of the system and impart intrinsic flame retardancy to the material. Then, an "island" toughening network is constructed through in-situ reaction of polyethersulfone. Subsequently, dopamine / phosphate-modified magnesium hydroxide and ionic liquid-modified multi-walled carbon nanotubes are added under a stepped mixing process. After vacuum degassing and gradient curing, the resulting material exhibits excellent elongation at break, high flame retardancy rating, and low smoke emission, making it suitable for manufacturing cable insulation and sheathing in harsh dynamic environments such as subway tunnels.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin materials technology, specifically to an epoxy resin composite material for cables and its preparation method. Background Technology

[0002] Epoxy resins, due to their excellent mechanical strength and chemical stability, have become a core matrix material in the field of high-performance electrical insulation. However, epoxy resin compositions applied in complex environments have long faced a trade-off between toughness and flame retardancy. Traditional epoxy resin cured networks are brittle and prone to micro-cracking under laying stress or environmental vibration, leading to insulation failure.

[0003] Currently, the industry commonly uses the addition of inorganic flame-retardant fillers to improve the fire resistance of resins. However, in epoxy resin systems, the introduction of a high proportion of fillers can lead to a drastic decrease in the flow properties of the composition. Excessively high melt viscosity makes it prone to poor plasticization during processing and molding, thus affecting the surface quality and mechanical balance of the final product. Furthermore, while existing modified epoxy resins can achieve self-extinguishing during combustion through additives, they often suffer from problems such as high smoke production and the release of corrosive products, making it difficult to simultaneously achieve low smoke, low toxicity, and high flame retardancy. Existing technologies mostly focus on simple physical modification of the fillers themselves, lacking deep integration of intrinsic modification of the epoxy resin molecular chain and the synergistic mechanism of multiphase filler interfaces. Therefore, developing an epoxy resin composition that possesses both high rheological processing performance and intrinsic flexibility with high smoke suppression and flame retardant properties has become a common challenge in improving the safety level of epoxy resin composites.

[0004] Therefore, an epoxy resin composite material for cables and its preparation method are proposed. Summary of the Invention

[0005] The purpose of this invention is to provide an epoxy resin composite material for cables and a method for preparing the same.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Unless otherwise specified, all parts in this invention are parts by weight.

[0007] This invention provides a method for preparing an epoxy resin composite material for cables, the method being as follows: An epoxy resin prepolymer was obtained by reacting phosphorus-containing hyperbranched polyester and bisphenol A type epoxy resin. A toughened epoxy system was prepared by reacting the epoxy resin prepolymer, carboxyl-terminated polyethersulfone, and triphenylphosphine (as a catalyst). 2.5-3.5 parts of modified multi-walled carbon nanotubes were added to the toughened epoxy system, and the system temperature was maintained at 85℃. A high-shear homogenizer was turned on, and the mixture was dispersed under a high shear force of 1000 rpm for 30 min. The stirring speed was reduced to 300 rpm, and 40-55 parts of modified magnesium hydroxide were added to the system in three equal portions, with each addition spaced 10 min apart. The mixture was continuously stirred and kneaded at a constant temperature for 1 h. Vacuum degassing was performed at 0.095 MPa for 30 min; the system temperature was lowered to 60℃, 20 parts of isophorone diamine curing agent and 1 part of 2-methylimidazole accelerator were added, and the mixture was stirred at 200 rpm for 15 min. Vacuum degassing was then performed again at -0.095 MPa for 30 min to obtain epoxy resin composite melt; the epoxy resin composite melt was injected into a mold and then subjected to gradient curing. First, it was pre-cured at 70-90℃ for 2 h (to stabilize the network structure), and then the temperature was raised to 140-160℃ for post-curing for 4 h (to achieve complete cross-linking and release internal stress) to obtain epoxy resin composite material.

[0008] Preferably, the toughened epoxy system is prepared as follows: 115 parts of epoxy resin prepolymer are cooled to 90°C, 10-20 parts of carboxyl-terminated polyether sulfone (CPES) and 0.2 parts of triphenylphosphine are added, and the mixture is pre-reacted at a constant temperature of 400 rpm for 2.5 h to obtain the toughened epoxy system.

[0009] Preferably, the epoxy resin prepolymer is prepared as follows: 100 parts of bisphenol A type epoxy resin (E-51) are heated to 110°C to completely melt it; 8-15 parts of phosphorus-containing hyperbranched polyester are added, the stirring speed is controlled at 300 rpm, and the reaction is carried out at a constant temperature for 2 hours to obtain the epoxy resin prepolymer; in this step, the reaction can proceed stably based on the autocatalytic effect of the residual acid value of the hyperbranched polyester.

[0010] A preferred method for preparing phosphorus-containing hyperbranched polyester is as follows: 10.4 parts of neopentyl glycol are added to a reaction vessel and heated to 130°C to melt. 21 parts of 1,3,5-benzenetricarboxylic acid are added to the melt in batches, along with 0.1 parts of p-toluenesulfonic acid as an esterification catalyst. Under stirring at 200 rpm, the reaction temperature is gradually increased from 130°C to 200°C in a stepwise manner, while nitrogen gas is continuously introduced to remove the byproduct water, thus obtaining a hydroxyl-terminated hyperbranched polyester. The stepwise heating not only avoids the volatilization of oligomers in the early stage of the reaction but also ensures the water removal efficiency under high viscosity conditions in the later stage of the esterification reaction. Diphenylphosphine chloride is added for partial esterification modification, controlling the hydroxyl-terminated modification rate to 35-45%. The product is washed three times with anhydrous ethanol and then placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a phosphorus-containing hyperbranched polyester with an acid value ≤10 mg KOH / g and a weight-average molecular weight of 3800-4500 g / mol.

[0011] The preferred method for preparing modified multi-walled carbon nanotubes is as follows: 3 parts of multi-walled carbon nanotubes (P835724, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) are mixed with 25-35 parts of 1-butyl-3-methylimidazolium hexafluorophosphate (ionic liquid), and 100 parts of anhydrous ethanol are added as a dilution and dispersion medium. The mixture is continuously treated at 60°C using an ultrasonic disperser (400W) for 3-5 hours to achieve surface functionalization of the carbon nanotubes through cation-π non-covalent interactions. After removing most of the anhydrous ethanol by rotary evaporation, excess ionic liquid is removed by filtration, and the mixture is dried in a vacuum drying oven at 80°C for 12 hours to obtain modified multi-walled carbon nanotubes.

[0012] The preferred method for preparing modified magnesium hydroxide is as follows: 50 parts of nano-magnesium hydroxide (average particle size D) are mixed... 50 =50-100nm, specific surface area 10-25m² 2 Magnesium hydroxide (Mg(OH)2, g, purity ≥ 99.0%) was dispersed in 500 parts of Tris-HCl buffer solution with pH 8.5. 0.8-1.5 parts of dopamine hydrochloride were added, and the mixture was reacted at 600 rpm and 25 °C for 12 h to allow dopamine to self-polymerize and form a polydopamine (PDA) coating layer on the surface of magnesium hydroxide. 20 parts of an aqueous solution containing 0.5 parts of sodium phosphate were added dropwise, and the reaction was continued with stirring for 1.5-2.5 h to allow nano-phosphate to be deposited in situ on the PDA layer. The product was filtered, washed three times with deionized water, and dried in a vacuum oven at 80 °C for 12 h to obtain modified magnesium hydroxide.

[0013] In another aspect, the present invention provides an epoxy resin composite material for cables, wherein the epoxy resin composite material is prepared by any of the above-described preparation methods.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention introduces phosphorus-containing hyperbranched polyester into an epoxy resin matrix, utilizing the unique three-dimensional spherical molecular structure of hyperbranched polymers. This structure exerts a significant "molecular ball" lubrication effect in the resin melt, fundamentally eliminating the entanglement restrictions between polymer chain segments. This allows the composite system containing a large amount of inorganic flame-retardant fillers to maintain excellent processing fluidity, solving the problems of melt fracture and poor plasticization that easily occur in traditional processes. At the same time, the phosphorus element on the hyperbranched polyester is stably integrated into the cross-linking network through chemical bonds, achieving durable intrinsic flame retardancy and avoiding the migration and precipitation of flame retardants.

[0015] 2. Addressing the industry pain point of high crosslinking density in traditional epoxy resins leading to brittle materials, this invention introduces carboxyl-terminated polyethersulfone for in-situ toughening modification. During prepolymerization, the end groups of the modifier react chemically with the epoxy groups, spontaneously forming a microscale "sea-island" phase separation structure after the matrix cures. When the material is subjected to external laying stress or high-frequency vibration impact, this special flexible network can effectively induce matrix yielding and absorb and dissipate a large amount of impact energy, thereby preventing the initiation and propagation of microcracks. This mechanism ensures that the material significantly improves the elongation at break without losing its inherent high mechanical modulus, meeting the laying requirements under dynamic environments.

[0016] 3. This invention overcomes the limitations of traditional single-layer modification of silane coupling agents, developing a core-shell structure modification process based on biomimetic dopamine and phosphate dual coating. The polydopamine coating not only significantly reduces the surface energy of metal hydroxides, improving their dispersion and interfacial compatibility in organic matrices, but also the phosphorus element deposited on the outer layer and the metal element in the core produce a synergistic effect during combustion. When heated, this system can rapidly promote the dehydration and char formation of the polymer surface, forming a dense and robust heat-insulating and oxygen-barrier char layer, combining gas-phase flame retardancy with condensed-phase flame retardancy.

[0017] 4. To further control the smoke hazard in the early stages of a fire, this invention utilizes ionic liquids to functionalize carbon nanotubes. Ionic liquids not only act as highly efficient dispersion media to prevent the aggregation of carbon nanotubes, but their inherent heteroatoms can also capture free radicals in the gas phase at high temperatures. The uniformly dispersed carbon nanotubes intertwine to form a robust nanoscale network framework during combustion, not only physically blocking the escape of smoke particles but also catalyzing the conversion of combustion products into char residue. This multi-dimensional smoke suppression mechanism overcomes the shortcomings of traditional flame-retardant materials, such as high smoke production and easy release of corrosive gases during combustion.

[0018] 5. This invention develops a dedicated high-shear dispersion, multi-stage step-by-step mixing, and gradient crosslinking molding process. By precisely controlling the temperature and shear force at different mixing stages, it ensures that nano-scale synergists and micron-scale flame-retardant fillers form a uniform three-dimensional dispersion network within the complex polymer matrix. The application of vacuum kneading and degassing technology eliminates microscopic pore defects caused by gas encapsulation in the high-viscosity system; the subsequent gradient curing process allows the material to initially form a stable network at a lower temperature, complete deep crosslinking at a higher temperature, and fully release internal thermal stress, ultimately endowing the composite material with excellent and durable electrical insulation properties. Attached Figure Description

[0019] Figure 1 The graphs show the combustion performance test results of Examples 1-4, Comparative Examples 1-4, and Comparative Example 7 of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figure 1 This invention provides an epoxy resin composite material for cables and its preparation method, the technical solution of which is as follows: Example 1 Three parts of multi-walled carbon nanotubes were mixed with 25 parts of 1-butyl-3-methylimidazolium hexafluorophosphate, and then 100 parts of anhydrous ethanol were added. The mixture was continuously treated at 60°C using an ultrasonic disperser (400W) for 3 hours. After removing most of the anhydrous ethanol by rotary evaporation, excess ionic liquid was removed by filtration, and the mixture was dried in a vacuum drying oven at 80°C for 12 hours to obtain modified multi-walled carbon nanotubes.

[0022] 50 parts of nano-magnesium hydroxide were dispersed in 500 parts of Tris-HCl buffer solution with a pH of 8.5, and 0.8 parts of dopamine hydrochloride were added. The mixture was reacted at 600 rpm and 25 °C for 12 h. 20 parts of an aqueous solution containing 0.5 parts of sodium phosphate were added dropwise, and the mixture was stirred for another 1.5 h. The product was filtered, washed three times with deionized water, and dried in a vacuum oven at 80 °C for 12 h to obtain modified magnesium hydroxide.

[0023] 20.8 parts of neopentyl glycol were added to the reactor and heated to 130°C to melt. 21 parts of 1,3,5-benzenetricarboxylic acid were divided into three equal portions and added to the melt in batches, with 20-minute intervals between each batch. Simultaneously, 0.1 parts of p-toluenesulfonic acid were added as an esterification catalyst. Under stirring at 200 rpm, the reaction temperature was gradually increased from 130°C to 200°C in a stepwise manner, with nitrogen continuously purging to remove the byproduct water. The first stage was carried out at a constant temperature of 130°C for 1.5 hours (including the feeding time) to ensure thorough mixing of the monomers and the initiation of preliminary esterification. In the second stage, the temperature was increased to 170℃ at a rate of 1.5℃ / min and kept at a constant temperature for 2.0h. In the third stage, the temperature was increased to 200℃ at a rate of 2℃ / min and kept at a constant temperature for 1.5h. At this time, a slight vacuum (-0.05MPa) was applied to promote the removal of residual moisture, and the hydroxyl-terminated hyperbranched polyester was obtained. Diphenylphosphine chloride was added for partial esterification modification, and the hydroxyl-terminated modification rate was controlled at 35%. The product was washed three times with anhydrous ethanol and then placed in a vacuum drying oven and dried at 60℃ for 24h to obtain phosphorus-containing hyperbranched polyester.

[0024] 100 parts of 4,4'-dichlorodiphenyl sulfone, 93 parts of bisphenol S, and 55 parts of anhydrous potassium carbonate were added to a reactor equipped with nitrogen protection, a stirrer, and a water separator. 500 parts of NMP were added to dissolve the solid, and 100 parts of toluene were added as a dehydrating agent. Stirring was started at 300 rpm, and the temperature was raised to 145°C. The mixture was refluxed for 2 hours until no more water was generated in the water separator. The temperature was then raised and the toluene was distilled off, increasing the reactor temperature to 200°C. The reaction was maintained at this temperature for 5 hours. The system temperature was then lowered to 125°C, and 14 parts of trimellitic anhydride and 0.5 parts of pyridine were added as a promoter. The reaction was carried out at 250 rpm for 4 hours. After the reaction, the hot reaction solution was slowly poured into 7 times its volume of a weakly acidic aqueous solution (containing 1% hydrochloric acid) to precipitate the solid. The precipitated fibrous solid was mechanically pulverized until D... 50 The sample was less than 150 μm in size. It was then repeatedly washed with boiling water until the washing solution was neutral and no chloride ions were detected. It was then vacuum dried at 100 °C for 24 h to obtain carboxyl-terminated polyethersulfone with a number average molecular weight of 5000 g / mol, a polydispersity index (PDI) of 1.6, and a carboxyl-terminated value of 0.40 mmol / g determined by titration.

[0025] 100 parts of bisphenol A type epoxy resin (E-51) were heated to 110℃ until completely melted. 8 parts of phosphorus-containing hyperbranched polyester were added, and the stirring speed was controlled at 300 rpm. The mixture was reacted at a constant temperature for 2 hours to obtain an epoxy resin prepolymer. All the epoxy resin prepolymer obtained above was cooled to 90℃, and 10 parts of carboxyl-terminated polyethersulfone and 0.2 parts of triphenylphosphine were added. The mixture was pre-reacted at a constant temperature of 400 rpm for 2.5 hours to obtain a toughened epoxy system. 2.5 parts of modified multi-walled carbon nanotubes were added to the toughened epoxy system. The system temperature was maintained at 85℃, and a high-shear homogenizer was turned on. The mixture was dispersed under a high shear force of 1000 rpm for 30 minutes. The stirring speed was then reduced to 300 rpm. Forty parts of modified magnesium hydroxide were added to the system in three equal portions, with each addition spaced 10 minutes apart. After continuous constant temperature stirring and kneading for 1 hour, the mixture was vacuum degassed at -0.095 MPa for 30 minutes. The system temperature was then lowered to 60°C, and 20 parts of isophorone diamine curing agent and 1 part of 2-methylimidazole accelerator were added. The mixture was stirred at 200 rpm for 15 minutes, and then vacuum degassed again at -0.095 MPa for 30 minutes to obtain an epoxy resin composite melt. The epoxy resin composite melt was injected into a mold and then subjected to gradient curing. First, it was pre-cured at 70°C for 2 hours, and then post-cured at 140°C for 4 hours to obtain an epoxy resin composite material.

[0026] Example 2 Referring to the preparation method and parameters of Example 1, the differences are as follows: when preparing modified multi-walled carbon nanotubes, the amount of 1-butyl-3-methylimidazolium hexafluorophosphate is 35 parts, and the ultrasonic treatment time is 5 hours; when preparing modified magnesium hydroxide, the amount of dopamine hydrochloride is 1.5 parts, and the reaction time after adding sodium phosphate aqueous solution is 2.5 hours; when preparing phosphorus hyperbranched polyester, the terminal hydroxyl modification rate is 45%; the amount of phosphorus-containing hyperbranched polyester added is 15 parts, the amount of carboxyl-terminated polyethersulfone added is 20 parts, and the amount of modified multi-walled carbon nanotubes added is 3.5 parts; the amount of modified magnesium hydroxide added is 55 parts, the pre-curing temperature is 90℃, and the post-curing temperature is 160℃.

[0027] Example 3 Referring to the preparation method and parameters of Example 1, the differences are as follows: when preparing modified multi-walled carbon nanotubes, the amount of 1-butyl-3-methylimidazolium hexafluorophosphate is 30 parts, and the ultrasonic treatment time is 4 hours; when preparing modified magnesium hydroxide, the amount of dopamine hydrochloride is 1.3 parts, and the reaction time after adding sodium phosphate aqueous solution is 2.0 hours; when preparing phosphorus hyperbranched polyester, the terminal hydroxyl modification rate is 40%; the amount of phosphorus-containing hyperbranched polyester added is 12 parts, the amount of carboxyl-terminated polyethersulfone added is 15 parts, and the amount of modified multi-walled carbon nanotubes added is 3.0 parts; the amount of modified magnesium hydroxide added is 48 parts, the pre-curing temperature is 80℃, and the post-curing temperature is 150℃.

[0028] Example 4 Referring to the preparation method and parameters of Example 1, the differences are as follows: when preparing modified multi-walled carbon nanotubes, the amount of 1-butyl-3-methylimidazolium hexafluorophosphate is 32 parts, and the ultrasonic treatment time is 4.5 h; when preparing modified magnesium hydroxide, the amount of dopamine hydrochloride is 1.0 part, and the reaction time after adding sodium phosphate aqueous solution is 2.0 h; when preparing phosphorus hyperbranched polyester, the terminal hydroxyl modification rate is 42%; the amount of phosphorus-containing hyperbranched polyester added is 10 parts, the amount of carboxyl-terminated polyethersulfone added is 18 parts, and the amount of modified multi-walled carbon nanotubes added is 2.8 parts; the amount of modified magnesium hydroxide added is 50 parts, the pre-curing temperature is 85℃, and the post-curing temperature is 155℃.

[0029] Comparative Example 1 The preparation method and parameters were the same as in Example 1, except that unmodified multi-walled carbon nanotubes were used.

[0030] Comparative Example 2 Following the preparation method and parameters of Example 1, the difference was the use of silane coupling agent KH-560 to modify magnesium hydroxide. The modification steps were as follows: 50 parts of nano-magnesium hydroxide were dispersed in a mixed solution of 200 parts of anhydrous ethanol and water with a volume ratio of 9:1; the pH of the system was adjusted to 4.5 with glacial acetic acid; 1.0 part of KH-560 was added dropwise, and the mixture was stirred at 600 rpm for 2 hours in a water bath at 70°C; the product was filtered, washed three times with anhydrous ethanol, and dried in a vacuum oven at 80°C for 12 hours to obtain modified magnesium hydroxide.

[0031] Comparative Example 3 The preparation method and parameters of Example 1 are the same, except that only polydopamine coating is performed when preparing modified magnesium hydroxide.

[0032] Comparative Example 4 The preparation method and parameters are the same as in Example 1, except that no phosphorus-containing hyperbranched polyester is added.

[0033] Comparative Example 5 The preparation method and parameters are the same as in Example 1, except that no carboxyl-terminated polyethersulfone is added.

[0034] Comparative Example 6 Referring to the preparation method and parameters of Example 1, the difference is that the carboxyl-terminated polyethersulfone is directly physically mixed without a 90°C pre-reaction. The reaction steps are as follows: the temperature of the epoxy resin prepolymer system is adjusted to 75°C, and 10 parts of carboxyl-terminated polyethersulfone, 2.5 parts of modified multi-walled carbon nanotubes, and 40 parts of modified magnesium hydroxide are added to the system simultaneously; a high-shear homogenizer is turned on, and mechanical dispersion is performed at 1000 rpm and 75°C for 40 min to achieve only physical dispersion in the matrix (without chemical ring-opening grafting). Then, vacuum degassing is performed directly, and a curing agent is added for subsequent curing and molding steps.

[0035] Comparative Example 7 The preparation method and parameters of Example 1 are the same, except that no modified multi-walled carbon nanotubes are added.

[0036] Comparative Example 8 The preparation method and parameters of Example 1 are the same, except that the curing process is changed to direct curing at 140°C for 6 hours.

[0037] Comparative Example 9 The preparation method and parameters of Example 1 are the same, except that the modified magnesium hydroxide is added to the system all at once.

[0038] Experiment Example 1: Combustion Performance Test Oxygen Index (LOI): The test was conducted in accordance with GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics", with a sample size of 80mm×10mm×4mm. Smoke density: Tested in accordance with GB / T 8323.2-2008 "Plastic smoke generation - Part 2: Test method for determination of smoke density by single chamber method", and expressed as specific optical density Ds; The results are shown in Table 1.

[0039] Table 1 Combustion performance tests of Examples 1-4 and Comparative Examples 1-4 and Comparative Example 7 Experiment Example 2: Mechanical Property Testing Tensile strength and elongation at break: Referring to GB / T 1040.2-2006 "Determination of tensile properties of plastics", the tensile speed was set to 50 mm / min; the results are shown in Table 2.

[0040] Table 2 Mechanical property tests of Examples 1-4 and Comparative Examples 2, 4-6, and 8-9 Experiment Example 3 Electrical Performance Test Dielectric strength: Refer to GB / T 1408.1-2016 "Electrical strength test method for insulating materials - Part 1: Test at power frequency"; the cured composite material was processed into circular specimens with a diameter of 100±1mm and a thickness of 1.0±0.1mm, with a smooth surface, no mechanical damage, and no bubbles; before testing, the specimens were placed in an environment of 23±2℃ and 50±5% relative humidity for 24h to equilibrate, and the continuous voltage increase method was used with an AC voltage of 50Hz and a voltage increase rate of 2.0kV / s until the specimen broke down; the results are shown in Table 3.

[0041] Table 3 Electrical performance tests of Examples 1-4 and Comparative Examples 4 and 8 Experiment Example 4: Corrosion and Toxicity Test Halogen acid gas release: The test was conducted in accordance with GB / T 17650.1-1998 "Test method for gases released during combustion of materials derived from cables or optical fibers"; the results are shown in Table 4.

[0042] Table 4 Corrosion and toxicity tests of Examples 1-4, Comparative Examples 2-4, and Comparative Example 7 As shown in Tables 1-4, in Comparative Example 1, unmodified multi-walled carbon nanotubes were used. These unmodified nanotubes easily aggregated in the resin, failing to form a uniform barrier network. This not only led to easy dispersion of smoke particles during combustion and a significant increase in specific optical density, but also created localized leakage paths in the matrix, resulting in a substantial decrease in electric field strength. In Comparative Example 2, magnesium hydroxide was modified using the silane coupling agent KH-560. KH-560 only improved physical compatibility, lacking the synergistic "phosphorus-magnesium" char formation mechanism constructed by polydopamine and phosphate during combustion. This resulted in a significant decrease in the oxygen index, and the conventional modification, due to the loose char layer, had extremely low "filtering" efficiency for acidic gases. Furthermore, the weak interfacial bonding of the single silane layer reduced tensile strength. In Comparative Example 3, when preparing modified magnesium hydroxide, only dopamine was used for coating, without sodium phosphate. Although polydopamine improved dispersibility, the lack of condensed-phase catalytic char formation by the outer nano-phosphate layer prevented the construction of a dense, heat-insulating char layer, resulting in an oxygen index of only 30.8%, lower than the example. Furthermore, its char formation rate and char layer strength were insufficient to completely seal the acidic flue gas generated during combustion. The lack of phosphorus disrupted the complete cycle mechanism of "char formation-heat insulation-smoke suppression," and the release of halogen acid also increased. In Comparative Example 4, without the addition of phosphorus-containing hyperbranched polyester, the lack of rheological regulation by the hyperbranched polymer led to a sharp increase in viscosity of the high-filler system, generating numerous internal processing defects. This resulted in a decrease in tensile strength and elongation at break, and the residual microbubbles caused severe electric field distortion. Simultaneously, the lack of intrinsic phosphorus-based flame-retardant groups not only caused a sharp drop in the oxygen index but also, due to the absence of phosphorus condensed-phase char formation catalysis, incomplete combustion of the resin matrix occurred, releasing a large amount of acidic decomposition products, leading to a significant increase in corrosivity. In Comparative Example 5, without the addition of carboxyl-terminated polyethersulfone, the inherently high crosslinking density of the epoxy resin resulted in an extremely brittle material. Although the tensile strength was slightly higher, it was completely unable to withstand the dynamic laying and vibration stress of the cable in the tunnel, and was extremely prone to cracking. In Comparative Example 6, the carboxyl-terminated polyethersulfone was directly physically mixed without pre-reaction. The end groups of the carboxyl-terminated polyethersulfone could not form chemical bonds with the epoxy groups, resulting in severe phase separation on a macroscopic scale rather than a microscopic "sea-island" structure. The interface debonding prevented the effective transfer of stress under load, significantly weakening the toughening effect and tensile strength. Furthermore, the macroscopic phase separation caused the interface layer to become a weak electrical breakdown point, resulting in unstable dielectric strength. In Comparative Example 7, without the addition of modified multi-walled carbon nanotubes, the system lost the gas-phase trapping ability of the ionic liquid and the physical framework support of the carbon nanotubes during combustion. Combustion products were largely released with the hot gas flow, and the specific optical density increased. Moreover, during a fire, the multi-walled carbon nanotubes could work synergistically with the free radical trapping effect generated by the ionic liquid to intercept acidic gases in the condensed phase. Without this component, smoke and corrosive gases lost their physical barrier and were largely released with the hot gas flow, increasing the release of halogen acid.In Comparative Example 8, the curing process was changed to direct curing at 140℃ for 6 hours. Direct high-temperature rapid cross-linking leads to the generation of huge internal thermal stress that cannot be released, causing a large number of microcracks. This not only reduces the elongation, but also causes the electric field lines to concentrate at the crack tips under a strong electric field, resulting in electric field distortion. In Comparative Example 9, magnesium hydroxide was added all at once. The large-scale addition of powder at once leads to severe local agglomeration and "gas encapsulation" phenomena. Vacuum degassing is also unable to completely eliminate microbubbles. These agglomerates and pores become stress concentration points, leading to a decrease in tensile strength.

[0043] In summary, this application constructs a multi-dimensional deep synergistic network. As shown in Comparative Examples 4 and 5, relying solely on fillers cannot solve the processing disasters and intrinsic brittleness caused by high filler content. This application combines "rheological / intrinsic flame retardant synergy of phosphorus-containing hyperbranched polyester" with "in-situ semi-interpenetrating toughening of polyethersulfone," overcoming the impossible triangle of "high flame retardancy-high rheology-high toughness" at the molecular scale. Furthermore, the performance degradation of Comparative Examples 2, 3, and 7 confirms the bottleneck of single flame retardant effectiveness. The "polydopamine / phosphate bilayer coating" and "ionic liquid functionalized carbon nanotubes" designed in this application spontaneously form a three-dimensional flame retardant and smoke-suppressing barrier of "gas phase capture-condensed phase catalysis-physical framework shielding" during combustion. Combined with a stepped temperature control process, microscopic defects are eliminated, greatly improving the overall performance of the material.

[0044] 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 alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for the preparation of an epoxy resin composite material for cables, characterized in that: The preparation method is as follows: phosphorus-containing hyperbranched polyester and bisphenol A type epoxy resin are reacted to obtain epoxy resin prepolymer; the epoxy resin prepolymer, carboxyl-terminated polyethersulfone and triphenylphosphine are reacted to obtain toughened epoxy system; modified multi-walled carbon nanotubes are added to the toughened epoxy system for shear dispersion. Modified magnesium hydroxide was added to the system in three batches and stirred and kneaded, followed by vacuum degassing. After the temperature was lowered, isophorone diamine and 2-methylimidazole were added and mixed and stirred, followed by vacuum degassing again to obtain an epoxy resin composite melt. The epoxy resin composite melt was injected into a mold and then subjected to gradient curing to obtain the epoxy resin composite material. The modified multi-walled carbon nanotubes were prepared by reacting multi-walled carbon nanotubes with 1-butyl-3-methylimidazolium hexafluorophosphate. The modified magnesium hydroxide was prepared by reacting nano-magnesium hydroxide, Tris-HCl buffer solution, dopamine hydrochloride, and sodium phosphate.

2. The method for preparing an epoxy resin composite material for cables according to claim 1, characterized in that: The toughened epoxy system is prepared as follows: the epoxy resin prepolymer is cooled and then the carboxyl-terminated polyethersulfone and the triphenylphosphine are added, and the toughened epoxy system is obtained by isothermal pre-reaction.

3. The method for preparing an epoxy resin composite material for cables according to claim 2, characterized in that: The epoxy resin prepolymer is prepared as follows: the bisphenol A type epoxy resin is heated to melt; the phosphorus-containing hyperbranched polyester is added, and the reaction is carried out at a constant temperature to obtain the epoxy resin prepolymer.

4. The method for preparing an epoxy resin composite material for cables according to claim 3, characterized in that: The preparation method of the phosphorus-containing hyperbranched polyester is as follows: neopentyl glycol is added to a reaction vessel and heated to melt, and 1,3,5-benzenetricarboxylic acid is added in batches to react and obtain hydroxyl-terminated hyperbranched polyester. Diphenylphosphoyl chloride is added for partial esterification modification, and the product is washed and dried to obtain the phosphorus-containing hyperbranched polyester.

5. The method for preparing an epoxy resin composite material for cables according to claim 1, characterized in that: The modified multi-walled carbon nanotubes are prepared as follows: the multi-walled carbon nanotubes are mixed with 1-butyl-3-methylimidazolium hexafluorophosphate, anhydrous ethanol is added, the mixture is ultrasonically treated, filtered and dried to obtain the modified multi-walled carbon nanotubes.

6. The method for preparing an epoxy resin composite material for cables according to claim 1, characterized in that: The modified magnesium hydroxide is prepared as follows: the nano magnesium hydroxide is dispersed in the Tris-HCl buffer solution, and the dopamine hydrochloride is added to react; an aqueous solution containing the sodium phosphate is added dropwise, the reaction is continued by stirring, and the product is filtered, washed, and dried to obtain the modified magnesium hydroxide.

7. An epoxy resin composite material for electric cables, characterized by: The epoxy resin composite material is prepared by the preparation method according to any one of claims 1-6.

Images