Radiation resistant fireproof sealing material and preparation method and application thereof

Abstract

The application relates to a kind of radiation-resistant fireproof sealing materials and preparation method and application thereof, and relates to the technical field of polymer composite sealing material, solves the problem that existing cable sealing material is difficult to consider radiation resistance and fireproof performance and long-term stable sealing performance.A kind of radiation-resistant fireproof sealing material, including ethylene-propylene-diene rubber, radiation-resistant filler, intumescent flame retardant, phosphorus-containing polyphenyl silsesquioxane and crosslinking agent.Radiation-resistant filler includes bismuth oxide, zirconium boride and hydroxylated hexagonal boron nitride;Intumescent flame retardant includes ammonium polyphosphate, pentaerythritol and melamine;Phosphorus-containing polyphenyl silsesquioxane is coated on the surface of radiation-resistant filler and intumescent flame retardant.The application can be directly applied to the batch manufacturing of nuclear power plant cable sheath, nuclear industry facility cable sheath and rail transit fireproof cable sheath.

Description

Technical Field

[0001] This invention relates to the field of polymer composite sealing materials technology, specifically to a radiation-resistant fireproof sealing material, its preparation method, and its application. Background Technology

[0002] With the rapid development of nuclear power plants, nuclear fuel cycle facilities, nuclear waste treatment facilities, and rail transportation, cables are subjected to complex service environments involving high-energy radiation, high temperatures, fire risks, and continuous compression sealing. As a crucial outermost protective component of the cable structure, the cable sheath not only needs excellent mechanical properties and environmental adaptability, but also needs to meet multiple requirements such as long-term radiation resistance, fire resistance, and stable sealing.

[0003] Currently, to improve radiation resistance, some studies have adopted the method of introducing high atomic number inorganic fillers, such as bismuth oxide, tungsten oxide, and lead oxide, into the rubber matrix to utilize the photoelectric effect and Compton effect to attenuate radiation energy. To improve fire resistance, the main approach is to use hydroxide flame retardant systems or intumescent flame retardant systems composed of ammonium polyphosphate / pentaerythritol / melamine, which achieve heat insulation and flame retardant protection by forming an expanded char layer during combustion.

[0004] However, it is widely believed in the art that there is an irreconcilable performance antagonism between high atomic number metal fillers and intumescent flame retardant systems. On the one hand, metal ions in metal oxides are prone to premature decomposition of ammonium polyphosphate through Lewis acid action, causing a mismatch between the gas production rate and the char formation reaction rate. The resulting intumescent char layer has a larger pore size and a looser wall structure, leading to a decrease in flame retardant and heat insulation performance. On the other hand, intumescent flame retardant components are mostly low-density phosphorus and nitrogen compounds. A higher proportion of these compounds dilutes the volume concentration of high atomic number fillers, reducing the intrinsic density and radiation attenuation efficiency per unit volume. Furthermore, the combination of multiple fillers can easily cause interfacial compatibility problems and introduce microscopic defects, further hindering the radiation protection and radiation aging resistance performance. Due to this common understanding, existing technologies typically only optimize radiation resistance or flame retardant performance individually.

[0005] Secondly, the improvement of radiation resistance and flame retardant properties both depend on functional fillers with higher filler content. However, the introduction of a large amount of inorganic fillers will significantly disrupt the continuity of the rubber crosslinking network, resulting in a decrease in elastic recovery ability and making it difficult to meet long-term sealing requirements.

[0006] In addition, most functional fillers in the existing technology exist only in the form of simple physical blending. The interfacial bonding between fillers and between fillers and rubber matrix is ​​weak, which makes it impossible to form a continuous and stable protective structure during combustion or irradiation, resulting in limited improvement in the overall performance of the material.

[0007] Therefore, developing a composite sealing material that can simultaneously achieve radiation resistance, fire retardancy, and long-term sealing performance, and form a stable protective interface in extreme environments, has significant engineering application value and practical significance. Summary of the Invention

[0008] To address the problem that existing cable sealing materials struggle to simultaneously achieve radiation resistance, fire resistance, and long-term stable sealing performance, this invention proposes a radiation-resistant and fire-resistant sealing material, its preparation method, and its application.

[0009] The specific technical solution of the present invention is as follows: A radiation-resistant fireproof sealing material, comprising the following components by weight: 100 parts of EPDM rubber; 25-45 parts of radiation-resistant filler; 15-30 parts of intumescent flame retardant; 1-5 parts of phosphorus-containing polyphenylsilsesquioxane; 2-8 parts of crosslinking agent; The radiation-resistant filler includes bismuth oxide, zirconium boride, and hydroxylated hexagonal boron nitride; The intumescent flame retardant includes ammonium polyphosphate, pentaerythritol, and melamine; The phosphorus-containing polyphenyl silsesquioxane is coated on the surface of the radiation-resistant filler and the intumescent flame retardant.

[0010] Preferably, the mass ratio of bismuth oxide to zirconium boride is (3~5):1, and the mass of hydroxylated hexagonal boron nitride accounts for 10%~30% of the total mass of the radiation-resistant filler.

[0011] Preferably, the mass ratio of ammonium polyphosphate, pentaerythritol and melamine is (2~4):(0.5~2):(0.5~2); the ammonium polyphosphate is a high degree of polymerization ammonium polyphosphate with a degree of polymerization ≥1000.

[0012] Preferably, the crosslinking agent is selected from one or two of dicumyl peroxide and 2,5-dimethyl-2,5-di-tert-butylperoxide.

[0013] Preferably, the phosphorus-containing polyphenylsilsesquioxane is prepared by the following steps: Weigh phenyltriethoxysilane and phenylphosphonic acid in a molar ratio of 3:1, add anhydrous ethanol to prepare a homogeneous solution with a solid content of 30%~40%, and dissolve at room temperature; under the catalysis of 0.1 mol / L dilute hydrochloric acid, hydrolyze and co-condense at 60 ℃, keep warm and stir for 4~6 h, after the reaction is completed, remove ethanol, water and residual small molecules by vacuum distillation, and dry under vacuum to constant weight.

[0014] Preferably, it also includes 3 to 15 parts of functional additives; The functional additives include one or more of the following: reinforcing agents, antioxidants, plasticizers, and processing aids.

[0015] The present invention also provides a method for preparing the above-mentioned radiation-resistant fireproof sealing material, comprising the following steps: S1. Bismuth oxide, zirconium boride, and hydroxylated hexagonal boron nitride are premixed evenly. 70% to 80% of the total amount of phosphorus-containing polyphenyl silsesquioxane is prepared into an ethanol dilution solution, which is then atomized and sprayed into the filler system. The coating reaction is carried out by stirring at 85 to 95°C for 15 to 20 minutes. After removing the solvent by heating, functionalized radiation-resistant filler is obtained. S2. Preheat ammonium polyphosphate to 70~80℃, atomize and spray the remaining 20%~30% of phosphorus-containing polyphenyl silsesquioxane ethanol dilution solution, keep warm and stir for 10~15min to complete the coating, remove the solvent and add pentaerythritol and melamine, mix evenly at low temperature to obtain functionalized intumescent flame retardant filler. S3. Add EPDM rubber to a mixer for plasticizing. First, add functionalized radiation-resistant filler and mix and disperse. Then add functionalized intumescent flame-retardant filler. With or without functional additives, mix evenly and then discharge and cool. S4. Transfer the cooled rubber compound into a two-roll mill, add a crosslinking agent, mix evenly, and then sheet to obtain the compound. S5. After the compounded rubber is extruded or molded, it is vulcanized to obtain a radiation-resistant fireproof sealing material.

[0016] Preferably, the mass fraction of phosphorus-containing polyphenylsilsesquioxane in the ethanol diluent in step S1 is 15%~20%; and the solvent removal temperature is 105~110℃.

[0017] Preferably, in step S3, the plasticizing temperature is 60~80℃ and the plasticizing time is 2~3 min; the mixing temperature does not exceed 130℃, the total mixing time is 8~12 min, the discharge temperature is ≤135℃; and the cooling time is at least 4 h.

[0018] Preferably, in step S5, the vulcanization treatment employs compression vulcanization or continuous extrusion vulcanization: The vulcanization temperature of the compression molding vulcanization is 160~170℃, and the vulcanization pressure is 8~12MPa; The continuous extrusion vulcanization uses a high-pressure steam vulcanization pipeline with a temperature of 155~170℃ and a pressure of 0.8~1.5MPa inside the pipeline.

[0019] The present invention also provides an application of the above-mentioned radiation-resistant fireproof sealing material in cable sheaths, wherein the cable sheath is a cable sheath for nuclear power plants, a cable sheath for nuclear industrial facilities, or a fireproof cable sheath for rail transit.

[0020] Compared with the prior art, the specific beneficial effects of the present invention are as follows: (1) This invention addresses the common technical bias in the field of premature decomposition of ammonium polyphosphate catalyzed by high atomic number metal fillers and the mutual weakening of the performance of the two when combined. This invention uses phosphorus-containing polyphenylsilsesquioxane to coat the two types of functional fillers in stages, forming an organic-inorganic hybrid isolation layer on the surface of metal fillers such as bismuth oxide, blocking the direct contact between metal ions and ammonium polyphosphate, avoiding premature decomposition of flame retardants caused by Lewis acid catalysis, and making the gas production rate and char formation rate of the expansion system precisely matched. After combustion, a dense, continuous char layer with a high expansion ratio is formed, with an oxygen index of up to 40.1%, and stable vertical combustion passing the V-0 level. At the same time, the coating layer optimizes the dispersion state of the fillers, avoids the volume dilution effect of flame retardant components on high atomic number fillers, and ensures the effective concentration of radiation attenuation components per unit volume. Combined with the photoelectric effect of bismuth oxide, the neutron moderation ability of zirconium boride, and the structural stability of hydroxylated hexagonal boron nitride, synergistic attenuation of γ-rays and neutron rays is achieved, with the tensile strength retention rate after 100kGy irradiation reaching up to 91.3%.

[0021] (2) This invention uses phosphorus-containing polyphenylsilsesquioxane to surface-modify functional fillers. The phenyl and silsesquioxane segments in its molecular structure have excellent compatibility with EPDM rubber, forming a flexible interface transition layer between the filler and the rubber matrix, significantly reducing interfacial tension and solving the problems of poor interfacial compatibility and numerous microscopic defects caused by multi-filler compounding. At the same time, the step-by-step feeding and step-by-step coating process design ensures that the radiation-resistant filler and flame-retardant filler are uniformly dispersed in the matrix, avoiding the damage to the rubber crosslinking network caused by filler agglomeration, and effectively maintaining the continuity and elastic recovery ability of the crosslinking network. The material's compression set can be as low as 17.6%, which can maintain stable contact stress and sealing performance under long-term compression service environment, meeting the long-term sealing requirements of nuclear power, rail transportation and other scenarios.

[0022] (3) Phosphorus-containing polyphenylsilsesquioxane has the dual function of phosphorus-based flame retardancy and silicon-based char formation. When coated on the surface of the filler, it can participate in the char formation reaction during combustion, improving the thermal stability and ablation resistance of the char layer, and forming a synergistic flame retardant effect with the intumescent flame retardant system. At the same time, its hybrid structure can capture free radicals under irradiation, reducing the degradation and damage of rubber molecular chains caused by irradiation. Combined with the high thermal conductivity and irradiation stability of hydroxylated hexagonal boron nitride, it can quickly dissipate heat and reduce material embrittlement caused by irradiation aging. In addition, the high hardness and chemical stability of zirconium boride can improve the wear resistance and media resistance of the material, further broadening the application scenarios of the material.

[0023] The preparation process of this invention uses industry-standard equipment, requires no special production equipment, and is easy to scale up for industrial production. It can be directly applied to the mass production of cable sheaths for nuclear power plants, cable sheaths for nuclear industry facilities, and fire-resistant cable sheaths for rail transit. Detailed Implementation

[0024] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as limiting the present invention.

[0025] The hydroxylated hexagonal boron nitride used in the following examples was prepared using the method described in Example 1 of the published patent CN114956867A.

[0026] Phenylacetoxysilane and phenylphosphonic acid were weighed in a molar ratio of 3:1 and added to anhydrous ethanol to prepare a homogeneous solution with a solid content of 35%. The solution was stirred at room temperature until completely dissolved. 0.1 mol / L dilute hydrochloric acid was added to adjust the pH of the system to 4-5. The temperature was raised to 60°C for hydrolysis and co-condensation. The reaction was carried out with stirring for 5 hours. After the reaction was completed, ethanol, water and residual small molecules were removed by vacuum distillation. The product was dried in a vacuum drying oven at 60°C to constant weight to obtain phosphorus-containing polyphenylsilsesquioxane for later use.

[0027] Example 1. This embodiment provides a radiation-resistant fireproof sealing material, the specific formula of which is as follows by weight: 500g of EPDM rubber; 175g of radiation-resistant filler; 110g of intumescent flame retardant; 15g of phosphorus-containing polyphenyl silsesquioxane; 20g of crosslinking agent dicumyl peroxide (DCP); 40g of functional additives (15g of carbon black N550, 5g of antioxidant RD, 15g of paraffin oil, and 5g of zinc stearate).

[0028] The radiation-resistant filler consists of 112g of bismuth oxide, 28g of zirconium boride, and 35g of hydroxylated hexagonal boron nitride. The mass ratio of bismuth oxide to zirconium boride is 4:1, and the mass of hydroxylated hexagonal boron nitride accounts for 20% of the total mass of the radiation-resistant filler. The intumescent flame retardant consists of 66g of ammonium polyphosphate, 22g of pentaerythritol, and 22g of melamine, with a mass ratio of 3:1:1.

[0029] The preparation method of the radiation-resistant fireproof sealing material includes the following steps: S1. Weigh bismuth oxide, zirconium boride, and hydroxylated hexagonal boron nitride, and premix them evenly in a high-speed mixer; prepare 75% (11.25g) of the total amount of phosphorus-containing polyphenylsilsesquioxane into an ethanol dilution with a mass fraction of 18%, atomize and spray it into the filler system, control the system temperature at 90℃, and stir for 18min to carry out the coating reaction; then raise the temperature to 108℃, stir to remove the ethanol solvent, and obtain the functionalized radiation-resistant filler, which is then discharged for later use.

[0030] S2. Weigh out ammonium polyphosphate according to the formula, preheat to 75°C and put it into a high-speed mixer; atomize and spray the remaining phosphorus-containing polyphenyl silsesquioxane ethanol dilution solution, keep warm and stir for 12 minutes to complete the coating; after heating to 105°C to remove the solvent, add pentaerythritol and melamine, mix at low speed until uniform, and obtain the functionalized intumescent flame retardant filler, which is then discharged for later use.

[0031] S3. Put EPDM rubber into an internal mixer and plasticize at 70℃ for 2.5 min. First, add all functionalized radiation-resistant fillers and mix and disperse for 4 min. Then add all functionalized intumescent flame-retardant fillers and functional additives and continue mixing for a total time of 10 min. Control the maximum mixing temperature not to exceed 125℃ and the discharge temperature ≤130℃. After discharge, place it at room temperature to cool for 6 h.

[0032] S4. Transfer the cooled rubber compound to the open mill, control the roller temperature at 50~60℃, add the crosslinking agent DCP, and mix evenly after passing through the mill three times. Adjust the roller gap and extrude the compound to obtain the mixed rubber.

[0033] S5. Place the mixed rubber into the mold for molding and vulcanization. The vulcanization temperature is 165℃, the vulcanization pressure is 10MPa, and the vulcanization time is 15min to obtain the radiation-resistant fireproof sealing material.

[0034] Example 2. This embodiment provides a radiation-resistant fireproof sealing material, the specific formula of which is as follows: 500g of EPDM rubber; 125g of radiation-resistant filler; 75g of intumescent flame retardant; 5g of phosphorus-containing polyphenyl silsesquioxane; 10g of crosslinking agent 2,5-dimethyl-2,5-di-tert-butylperoxyhexane (bis(2,5)-5); 15g of functional additives (5g of carbon black N550, 2.5g of antioxidant RD, 5g of paraffin oil, and 2.5g of zinc stearate).

[0035] The radiation-resistant filler consists of 84.375g of bismuth oxide, 28.125g of zirconium boride, and 12.5g of hydroxylated hexagonal boron nitride. The mass ratio of bismuth oxide to zirconium boride is 3:1, and the mass of hydroxylated hexagonal boron nitride accounts for 10% of the total mass of the radiation-resistant filler. The intumescent flame retardant consists of 50g of ammonium polyphosphate, 12.5g of pentaerythritol, and 12.5g of melamine, with a mass ratio of 2:0.5:0.5.

[0036] The preparation method of the radiation-resistant fireproof sealing material includes the following steps: S1. Weigh out bismuth oxide, zirconium boride, and hydroxylated hexagonal boron nitride according to the formula, and premix them evenly in a high-speed mixer; prepare 70% (3.5g) of the total amount of phosphorus-containing polyphenylsilsesquioxane into a 15% ethanol dilution, atomize and spray it into the filler system, control the system temperature at 85℃, and stir for 15min to carry out the coating reaction; then raise the temperature to 105℃, stir to remove the ethanol solvent, and obtain the functionalized radiation-resistant filler, which is then discharged for later use.

[0037] S2. Weigh out ammonium polyphosphate according to the formula, preheat to 70°C and put it into a high-speed mixer; atomize and spray in the remaining 30% of the phosphorus-containing polyphenyl silsesquioxane ethanol dilution (i.e. 1.5g of active ingredient), keep warm and stir for 10 minutes to complete the coating; after heating to 105°C to remove the solvent, add pentaerythritol and melamine, mix at low speed until uniform, and obtain the functionalized intumescent flame retardant filler, which is then discharged for later use.

[0038] S3. Put EPDM rubber into an internal mixer and plasticize at 60℃ for 2 minutes. First, add all functionalized radiation-resistant fillers and mix and disperse for 3 minutes. Then add all functionalized intumescent flame-retardant fillers and functional additives and continue mixing for a total time of 8 minutes. Control the maximum mixing temperature to not exceed 120℃ and the discharge temperature to ≤135℃. After discharge, place it at room temperature to cool for more than 4 hours.

[0039] S4. Transfer the cooled rubber compound to the open mill, control the roller temperature at 50~60℃, add the crosslinking agent bis(2,5)5, ​​and mix evenly after passing through the mill three times. Adjust the roller gap and extrude the compound to obtain the mixed rubber.

[0040] S5. Place the compounded rubber into the mold for molding and vulcanization. The vulcanization temperature is 160℃, the vulcanization pressure is 8MPa, and the vulcanization time is 18min to obtain the radiation-resistant fireproof sealing material.

[0041] Example 3. This embodiment provides a radiation-resistant fireproof sealing material, the specific formula of which is as follows: 500g of EPDM rubber; 225g of radiation-resistant filler; 150g of intumescent flame retardant; 25g of phosphorus-containing polyphenyl silsesquioxane; 40g of compound crosslinking agent (20g of DCP and 20g of bis(250)-5-dimethylsiloxane, mass ratio 1:1); 75g of functional additives (25g of carbon black N550, 10g of antioxidant RD, 30g of paraffin oil, and 10g of zinc stearate).

[0042] The radiation-resistant filler consists of 131.25g of bismuth oxide, 26.25g of zirconium boride, and 67.5g of hydroxylated hexagonal boron nitride. The mass ratio of bismuth oxide to zirconium boride is 5:1, and the mass of hydroxylated hexagonal boron nitride accounts for 30% of the total mass of the radiation-resistant filler. The intumescent flame retardant consists of 75g of ammonium polyphosphate, 37.5g of pentaerythritol, and 37.5g of melamine, with a mass ratio of 4:2:2.

[0043] The preparation method of the radiation-resistant fireproof sealing material includes the following steps: S1. Weigh out bismuth oxide, zirconium boride, and hydroxylated hexagonal boron nitride according to the formula, and premix them evenly in a high-speed mixer; prepare 20g of 20% ethanol dilution with 80% of the total amount of phosphorus-containing polyphenylsilsesquioxane, atomize it into the filler system, control the system temperature at 95℃, and stir for 20min to carry out the coating reaction; then raise the temperature to 110℃, stir to remove the ethanol solvent, and obtain the functionalized radiation-resistant filler, which is then discharged for later use.

[0044] S2. Weigh out ammonium polyphosphate according to the formula, preheat to 80°C and put it into a high-speed mixer; atomize and spray in the remaining 20% ​​of phosphorus-containing polyphenyl silsesquioxane ethanol dilution (i.e. 5g of active ingredient), keep warm and stir for 15 minutes to complete the coating; after heating to 108°C to remove the solvent, add pentaerythritol and melamine, mix at low speed until uniform, and obtain the functionalized intumescent flame retardant filler, which is then discharged for later use.

[0045] S3. Put EPDM rubber into an internal mixer and plasticize at 80℃ for 3 minutes. First, add all functionalized radiation-resistant fillers and mix and disperse for 5 minutes. Then add all functionalized intumescent flame-retardant fillers and functional additives and continue mixing for a total time of 12 minutes. Control the maximum mixing temperature to not exceed 130℃ and the discharge temperature to ≤135℃. After discharge, place it at room temperature to cool for more than 8 hours.

[0046] S4. Transfer the cooled rubber compound to the open mill, control the roller temperature at 50~60℃, add the compounding crosslinking agent, and mix evenly after passing through the mill three times. Adjust the roller gap and extrude the compound to obtain the mixed rubber.

[0047] S5. Place the mixed rubber into the mold for molding and vulcanization. The vulcanization temperature is 170℃, the vulcanization pressure is 12MPa, and the vulcanization time is 12min to obtain the radiation-resistant fireproof sealing material.

[0048] Example 4. This embodiment provides a radiation-resistant fireproof sealing material, the specific formula of which is as follows: 500g of EPDM rubber; 175g of radiation-resistant filler; 110g of intumescent flame retardant; 15g of phosphorus-containing polyphenyl silsesquioxane; 20g of crosslinking agent dicumyl peroxide (DCP); no functional additives added.

[0049] The radiation-resistant filler consists of 112g of bismuth oxide, 28g of zirconium boride, and 35g of hydroxylated hexagonal boron nitride. The mass ratio of bismuth oxide to zirconium boride is 4:1, and the mass of hydroxylated hexagonal boron nitride accounts for 20% of the total mass of the radiation-resistant filler. The intumescent flame retardant consists of 66g of ammonium polyphosphate, 22g of pentaerythritol, and 22g of melamine, with a mass ratio of 3:1:1.

[0050] The preparation method of the radiation-resistant fireproof sealing material includes the following steps: S1. Weigh bismuth oxide, zirconium boride, and hydroxylated hexagonal boron nitride according to the formula, and premix them evenly in a high-speed mixer; prepare 75% (i.e., 11.25g) of the total amount of phosphorus-containing polyphenylsilsesquioxane into an ethanol dilution with a mass fraction of 18%, atomize and spray it into the filler system, control the system temperature at 90℃, and stir for 18min to carry out the coating reaction; then raise the temperature to 108℃, stir to remove the ethanol solvent, and obtain the functionalized radiation-resistant filler, which is then discharged for use.

[0051] S2. Weigh out ammonium polyphosphate according to the formula, preheat to 75°C and put it into a high-speed mixer; atomize and spray in the remaining 25% of phosphorus-containing polyphenyl silsesquioxane ethanol dilution (i.e. 3.75g of active ingredient), keep warm and stir for 12 minutes to complete the coating; after heating to 105°C to remove the solvent, add pentaerythritol and melamine, mix at low speed until uniform, and obtain the functionalized intumescent flame retardant filler, which is then discharged for later use.

[0052] S3. Put EPDM rubber into an internal mixer and plasticize at 70℃ for 2.5 min. First, add all functionalized radiation-resistant fillers and mix and disperse for 4 min. Then add all functionalized intumescent flame-retardant fillers and continue mixing until the total time is 10 min. Control the maximum mixing temperature to not exceed 125℃ and the discharge temperature to ≤130℃. After discharge, place it at room temperature to cool for more than 6 hours.

[0053] S4. Transfer the cooled rubber compound to the open mill, control the roller temperature at 50~60℃, add the crosslinking agent DCP, and mix evenly after passing through the mill three times. Adjust the roller gap and extrude the compound to obtain the mixed rubber.

[0054] S5. Place the mixed rubber into the mold for molding and vulcanization. The vulcanization temperature is 165℃, the vulcanization pressure is 10MPa, and the vulcanization time is 15min to obtain the radiation-resistant fireproof sealing material.

[0055] Comparative Example 1. The only difference between this comparative example and Example 1 is that: phosphorus-containing polyphenylsilsesquioxane is not added to the formulation, the radiation-resistant filler and the intumescent flame retardant are not coated, and all components are directly blended with EPDM rubber; all other aspects are consistent with Example 1.

[0056] Comparative Example 2. The only difference between this comparative example and Example 1 is that the phosphorus-containing polyphenyl silsesquioxane is not subjected to stepwise coating treatment, but is directly added to the internal mixer along with the other components for physical blending; all other aspects are consistent with Example 1.

[0057] Comparative Example 3. The only difference between this comparative example and Example 1 is that no intumescent flame retardant is added to the formulation; all other aspects are consistent with Example 1.

[0058] Comparative Example 4. The only difference between this comparative example and Example 1 is that no radiation-resistant filler is added to the formulation; all other aspects are consistent with Example 1.

[0059] Example of results. The sealing materials prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests, and the test methods are as follows: Mechanical properties: Tensile strength and elongation at break were tested according to GB / T 528-2009; Radiation resistance: using 60 The Co-γ ray irradiation test was conducted with a total irradiation dose of 100 kGy. After irradiation, the mechanical properties were tested, and the tensile strength retention rate and elongation at break retention rate were calculated. Flame retardant performance: Oxygen index is tested according to GB / T 10707-2008, and vertical burning rating is tested according to GB / T 2408-2008; Compression set: Tested according to GB / T 7759.1-2015, the test conditions are 100℃×22h, compression rate 25%, calculate the compression set rate, the lower the value, the better the sealing resilience performance; The test results are shown in the table below:

[0060] Examples 1-4 of this invention were subjected to 100kGy 60 After Co-γ irradiation, the tensile strength retention rate was over 87%, and the elongation at break retention rate was over 80%, which was far superior to Comparative Example 1 without coating modification and also superior to Comparative Example 2 with direct blending of coating agent. Its radiation resistance was comparable to or even better than Comparative Example 3 with only radiation-resistant filler added, and far superior to Comparative Example 4 with only flame retardant system added. This proves that the surface coating of phosphorus-containing polyphenylsilsesquioxane can significantly improve the interfacial bonding between filler and rubber matrix, reduce microscopic defects, and capture irradiated free radicals and inhibit molecular chain degradation. Moreover, after compounding with intumescent flame retardant, the radiation resistance effect was not weakened by volume dilution effect, but rather the performance loss caused by multi-filler compounding was compensated by interface optimization.

[0061] The oxygen index and vertical combustion rating of Examples 1-4 were superior to those of the comparative examples. This indicates that the stepwise coating and isolation with phosphorus-containing polyphenylsilsesquioxane can effectively block the Lewis acid catalytic decomposition of ammonium polyphosphate by metal ions such as bismuth oxide, enabling precise matching of the gas generation rate and char formation rate of the intumescent flame retardant system. During combustion, a dense, continuous, and structurally complete intumescent char layer can be formed, fully exerting the flame retardant effect of heat insulation and oxygen barrier. The high atomic number radiation-resistant filler did not degrade the flame retardant performance; the two achieved synergistic effect.

[0062] The test results of compression set show that surface coating modification significantly improves the interfacial compatibility between inorganic fillers and EPDM rubber matrix, reduces interfacial tension, reduces the damage of filler agglomeration to rubber crosslinking network, effectively maintains the continuity and elastic recovery ability of crosslinking network, and solves the technical problem of decreased material elasticity and long-term sealing performance failure caused by high-filler functional fillers.

[0063] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A radiation-resistant fireproof sealing material, characterized in that, By weight, it includes the following components: 100 parts of EPDM rubber; 25-45 parts of radiation-resistant filler; 15-30 parts of intumescent flame retardant; 1-5 parts of phosphorus-containing polyphenylsilsesquioxane; 2-8 parts of crosslinking agent; The radiation-resistant filler includes bismuth oxide, zirconium boride, and hydroxylated hexagonal boron nitride; The intumescent flame retardant includes ammonium polyphosphate, pentaerythritol, and melamine; The phosphorus-containing polyphenyl silsesquioxane is coated on the surface of the radiation-resistant filler and the intumescent flame retardant.

2. The radiation-resistant fireproof sealing material according to claim 1, characterized in that, The mass ratio of bismuth oxide to zirconium boride is (3~5):1, and the mass of hydroxylated hexagonal boron nitride accounts for 10%~30% of the total mass of the radiation-resistant filler.

3. The radiation-resistant fireproof sealing material according to claim 1, characterized in that, The mass ratio of ammonium polyphosphate, pentaerythritol, and melamine is (2~4):(0.5~2):(0.5~2); the ammonium polyphosphate is a high degree of polymerization ammonium polyphosphate with a degree of polymerization ≥1000.

4. The radiation-resistant fireproof sealing material according to claim 1, characterized in that, The crosslinking agent is selected from one or two of dicumyl peroxide and 2,5-dimethyl-2,5-di-tert-butylperoxide.

5. The radiation-resistant fireproof sealing material according to claim 1, characterized in that, The phosphorus-containing polyphenylsilsesquioxane is prepared by the following steps: Weigh phenyltriethoxysilane and phenylphosphonic acid in a molar ratio of 3:1, add anhydrous ethanol to prepare a homogeneous solution with a solid content of 30%~40%, and dissolve at room temperature; under the catalysis of 0.1 mol / L dilute hydrochloric acid, hydrolyze and co-condense at 60 ℃, keep warm and stir for 4~6 h, after the reaction is completed, remove ethanol, water and residual small molecules by vacuum distillation, and dry under vacuum to constant weight.

6. The radiation-resistant fireproof sealing material according to claim 1, characterized in that, It also includes 3 to 15 parts of functional additives; The functional additives include one or more of the following: reinforcing agents, antioxidants, plasticizers, and processing aids.

7. A method for preparing a radiation-resistant fireproof sealing material as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Mix bismuth oxide, zirconium boride, and hydroxylated hexagonal boron nitride evenly. Prepare phosphorus-containing polyphenyl silsesquioxane into an ethanol dilution solution. Atomize 70% to 80% of the total amount into the filler system. Stir at 85 to 95°C for 15 to 20 minutes to carry out the coating reaction. After heating to remove the solvent, functionalized radiation-resistant filler is obtained. S2. Preheat ammonium polyphosphate to 70~80℃, atomize and spray the remaining 20%~30% of phosphorus-containing polyphenyl silsesquioxane ethanol dilution solution, keep warm and stir for 10~15 minutes to complete the coating, remove the solvent and add pentaerythritol and melamine, mix evenly to obtain functionalized intumescent flame retardant filler. S3. Add EPDM rubber to a mixer for plasticizing. First, add functionalized radiation-resistant filler and mix and disperse. Then add functionalized intumescent flame-retardant filler. With or without functional additives, mix evenly and then discharge and cool. S4. Transfer the cooled rubber compound to a two-roll mill, add a crosslinking agent, mix evenly, and then sheet to obtain the compound. S5. After the compounded rubber is extruded or molded, it is vulcanized to obtain a radiation-resistant fireproof sealing material.

8. The method for preparing the radiation-resistant fireproof sealing material according to claim 7, characterized in that, The mass fraction of phosphorus-containing polyphenylsilsesquioxane in the ethanol diluent in step S1 is 15%~20%; the solvent removal temperature is 105~110℃; In step S3, the plasticizing temperature is 60~80℃ and the plasticizing time is 2~3 min; the mixing temperature does not exceed 130℃, the total mixing time is 8~12 min, and the discharge temperature is ≤135℃; the cooling time is at least 4 h.

9. The method for preparing the radiation-resistant fireproof sealing material according to claim 7, characterized in that, In step S5, the vulcanization process employs either compression vulcanization or continuous extrusion vulcanization. The vulcanization temperature for compression molding is 160~170℃, and the vulcanization pressure is 8~12MPa; The continuous extrusion vulcanization uses a high-pressure steam vulcanization pipeline with a temperature of 155~170℃ and a pressure of 0.8~1.5MPa inside the pipeline.

10. The application of a radiation-resistant fire-retardant sealing material as described in any one of claims 1 to 6 in cable sheaths, characterized in that, The cable sheath is a cable sheath for nuclear power plants, a cable sheath for nuclear industry facilities, or a fire-resistant cable sheath for rail transit.

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