Hydrogenated butadiene-acrylonitrile rubber composite material for cryogenic heat preservation and preparation method of hydrogenated butadiene-acrylonitrile rubber composite material

Abstract

The invention discloses a hydrogenated butadiene-acrylonitrile rubber composite material for cryogenic heat preservation and a preparation method thereof in the field of polymer composite materials, and the composite material is characterized in that zirconium-silicon composite modified hydroxyapatite and boron-nitrogen co-doped mesoporous alumina are introduced, so that the mechanical property and heat preservation effect of the material in a low-temperature environment are remarkably improved. The zirconium-silicon oxide network is constructed on the surface of hydroxyapatite by adopting a sol-gel method, and the doped mesoporous structure with the high specific surface area is obtained by adopting alkoxide as a precursor through hydrothermal treatment and calcination. When the rubber is mixed, the functional filler is dispersed at a high temperature, and then the plasticizer is added to ensure uniform distribution of the filler. The obtained composite material has excellent tensile strength, elongation at break and low heat conductivity coefficient at the liquid nitrogen temperature, and is suitable for the cryogenic thermal insulation fields of hydrogen energy storage and transportation, aerospace sealing and the like. All the raw materials are commercially available chemicals, the process is controllable, and industrial production is easy.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a hydrogenated nitrile butadiene rubber composite material for cryogenic insulation and its preparation method. Background Technology

[0002] With the global energy structure shifting towards cleaner and lower-carbon technologies, cryogenic fluids such as liquefied natural gas and liquid hydrogen are increasingly used in energy storage and transportation, aerospace, and superconducting technologies, placing unprecedentedly stringent demands on supporting sealing and insulation materials. Traditional rubber materials generally suffer from hardening, embrittlement, and loss of elasticity in extremely low-temperature environments, making it difficult to meet the reliability requirements for long-term service. Hydrogenated nitrile butadiene rubber (NBR), due to its excellent oil resistance, heat resistance, and high saturation, performs well under normal operating conditions. However, in cryogenic environments approaching liquid nitrogen temperatures, its molecular chain movement is restricted, and its free volume decreases, leading to a sharp decline in mechanical properties. Furthermore, a single matrix cannot simultaneously achieve the dual goals of high strength and low thermal conductivity. Therefore, developing a novel hydrogenated NBR composite material that combines high strength and toughness, low thermal conductivity, and excellent low-temperature stability has become a key technological bottleneck in the field of cryogenic engineering.

[0003] To improve the overall performance of rubber at low temperatures, researchers generally employ filler modification strategies, introducing inorganic fillers to regulate the microstructure and interfacial interactions of the material. However, while conventional carbon black or silica can enhance mechanical properties, their high thermal conductivity often weakens their insulation effect. Some porous fillers, although reducing thermal conductivity, have poor compatibility with the rubber matrix, easily leading to stress concentration and insufficient low-temperature elongation at break. In recent years, functionalized bioceramics such as hydroxyapatite have attracted attention due to their low thermal conductivity, good biocompatibility, and surface activity; however, they lack sufficient chemical stability and interfacial bonding ability, making direct filling difficult to achieve synergistic effects. Meanwhile, mesoporous alumina, with its high specific surface area, tunable pore structure, and low density, shows potential in the field of thermal insulation, but its surface inertness limits its interaction with polymers. If the above fillers can be precisely chemically modified to construct composite systems with strong interfacial bonding, low thermal conductivity pathways, and nano-confinement effects, it is hoped that the performance ceiling of existing materials can be broken.

[0004] To address the aforementioned challenges, existing technologies attempt to modify inorganic fillers through intercalation, coating, or doping, but these methods often suffer from issues such as unreasonable reaction pathways, non-standard raw materials, or uncontrollable processes. For example, direct treatment of hydroxyapatite with strong acids can easily lead to lattice destruction; using insoluble aluminum sources to prepare mesoporous alumina makes it difficult to achieve uniform doping; and during rubber compounding, premature addition of plasticizers or improper dispersion temperatures of functional fillers can severely impair the formation of the filler network. Therefore, a technical solution that optimizes the entire chain from filler design to composite processes is urgently needed: on the one hand, a zirconium-silicon composite oxide shell can be constructed on the surface of hydroxyapatite using a mild and controllable sol-gel method, which protects its crystal structure and enhances its interfacial compatibility with rubber; on the other hand, using soluble alkoxides as precursors, combined with template agents and co-doping strategies, boron-nitrogen co-doped alumina with an ordered mesoporous structure can be prepared, effectively blocking heat conduction pathways. Based on this, the rubber mixing sequence and temperature are reasonably controlled to ensure that the functional fillers are fully dispersed without being interfered with by the plasticizer, and finally a high-performance thermal insulation rubber composite material suitable for cryogenic extreme environments is obtained. Summary of the Invention

[0005] The purpose of this invention is to provide a hydrogenated nitrile butadiene rubber composite material for cryogenic insulation and its preparation method, which solves the technical problems of low strength, brittleness, high thermal conductivity, and uneven dispersion of functional fillers in existing hydrogenated nitrile butadiene rubber under cryogenic conditions.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A method for preparing a hydrogenated nitrile butadiene rubber composite material for cryogenic insulation, comprising the following steps:

[0008] S1. By weight, 80-120 parts of hydrogenated nitrile butadiene rubber are added to an internal mixer and plasticized at 70-80℃; then 10-20 parts of carbon black N330, 1-2 parts of stearic acid, 3-5 parts of zinc oxide, and 1-2 parts of antioxidant 4020 are added sequentially and mixed to obtain a mixture; the temperature of the mixture is maintained at 70-90℃, and 3-8 parts of zirconium-silicon composite modified hydroxyapatite and 2-6 parts of boron-nitrogen co-doped mesoporous alumina are added first and mixed; then 5-10 parts of dioctyl phthalate are added and mixed again; after the rubber is discharged and cooled to room temperature, it is left to stand to obtain the rubber compound;

[0009] S2. Recycle the rubber compound on a two-roll mill, add 1.5-3.0 parts of dicumyl peroxide and 0.5-1.5 parts of triallyl isocyanurate, and then sheet it to obtain a rubber sheet. Place the rubber sheet in a flat vulcanizing machine and vulcanize it at 165-175℃.

[0010] In this invention, the dispersion behavior of functional fillers and the construction of cross-linking networks jointly determine the final properties during the molding process of hydrogenated nitrile butadiene rubber composites. In the initial mixing stage, the rubber is plasticized at a suitable temperature, and the subsequently added conventional additives initially form the basic compounding system. The key step is the introduction of zirconium-silicon composite modified hydroxyapatite and boron-nitrogen co-doped mesoporous alumina at a higher temperature range. At this temperature, the rubber melt viscosity is moderate, and the high shear force applied by the internal mixer rotor is sufficient to overcome the van der Waals forces between filler particles, allowing them to fully peel off and distribute evenly in the matrix. Because the zirconium-silicon composite modified hydroxyapatite surface is rich in hydroxyl groups and metal oxide active sites, it can form strong interfacial interactions with the rubber molecular chains; while the high specific surface area and surface polarity of the boron-nitrogen co-doped mesoporous alumina also promote its physical anchoring with the matrix. Together, they construct a three-dimensional reinforcing network. The subsequently added plasticizer only plays a softening role and does not interfere with the already formed filler dispersion structure. During the vulcanization stage, peroxides initiate the removal of tertiary hydrocarbons from the rubber backbone, generating free radicals and crosslinking. Triallyl isocyanurate, as a multifunctional monomer, participates in the reaction, forming denser and heat-resistant crosslinking points. The resulting composite material maintains mechanical strength and ductility in cryogenic environments by relying on the filler network, while achieving efficient thermal insulation through its mesoporous structure and interfacial thermal resistance, thus fully meeting the application requirements under extreme low-temperature conditions.

[0011] According to a preferred embodiment of the present invention, in step S1, the time for the glue to be left to stand after cooling to room temperature is 24-30 hours.

[0012] According to a preferred embodiment of the present invention, in step S2, the vulcanization time at 165-175°C is 15-20 min.

[0013] According to a preferred embodiment of the present invention, the preparation method of the zirconium-silicon composite modified hydroxyapatite includes:

[0014] A1. By weight, dissolve 5-7 parts of zirconium oxychloride and 2-6 parts of tetraethyl orthosilicate in a mixed solution of 30-50 parts of anhydrous ethanol, 5-10 parts of deionized water, and 10-20 parts of dilute hydrochloric acid, and stir at 60-70℃ to obtain a zirconium-silicon composite sol; disperse 8-12 parts of hydroxyapatite powder in 100-150 parts of deionized water, and sonicate to obtain a hydroxyapatite suspension; add the zirconium-silicon composite sol dropwise to the hydroxyapatite suspension while stirring, adjust the pH to 8.0-9.0 with ammonia, and continue the reaction at 70-80℃ to obtain a reaction mixture;

[0015] A2. Cool the reaction mixture to room temperature, centrifuge to obtain a precipitate; wash the precipitate with deionized water, then with anhydrous ethanol, dry it under vacuum at 100-110℃, then calcine it at 400-500℃, grind and sieve it.

[0016] In this invention, the preparation of the zirconium-silicon composite modified hydroxyapatite is based on the sol-gel chemistry principle, achieving the directional construction of an inorganic network on the surface of bioceramics through mild and controllable co-hydrolysis and condensation reactions. First, zirconium oxychloride and tetraethyl orthosilicate undergo hydrolysis in a mixture of aqueous ethanol and dilute hydrochloric acid, generating positively charged zirconium hydroxyl species and silanol oligomers. Under acidic catalysis and moderate heating, the two further undergo co-condensation to form a uniform and stable zirconium-silicon composite sol, in which zirconium-oxygen bonds and silanol bonds are cross-linked, constituting an inorganic network precursor with high thermal stability. Subsequently, this sol is introduced into an ultrasonically dispersed hydroxyapatite suspension. Under a weakly alkaline environment (adjusted by ammonia), the sol particles are deposited on the surface of the hydroxyapatite particles due to charge neutralization, and are firmly anchored through coordination or hydrogen bonding between surface hydroxyl groups and phosphate groups. During the subsequent heating reaction, the deposited layer further condenses and densifies, and finally, organic residues are removed by calcination, forming a core-shell structure with hydroxyapatite as the core and zirconium silicon oxide as the shell. This structure not only effectively protects the crystal integrity of hydroxyapatite during high-temperature processing, but also significantly enhances its interfacial compatibility with the rubber matrix and stress transfer efficiency.

[0017] According to a preferred embodiment of the present invention, in step A1, the reaction continues at 70-80°C for 4-6 hours.

[0018] According to a preferred embodiment of the present invention, in step A2, the calcination time at 400-500°C is 2-3 hours.

[0019] According to a preferred embodiment of the present invention, the method for preparing the boron-nitrogen co-doped mesoporous alumina includes:

[0020] B1. Dissolve 15-20 parts by weight of aluminum isopropoxide in 100-150 parts by weight of anhydrous ethanol, add 2-4 parts by weight of hexadecyltrimethylammonium bromide, and stir. Then add 0.6-2 parts by weight of boric acid and 1.5-4 parts by weight of urea, and continue stirring to obtain a mixed sol. Transfer the mixed sol to a reaction vessel and perform a hydrothermal reaction at 90-110°C to obtain a reaction mixture. B2. After cooling the reaction mixture, filter to obtain a solid. Wash the solid with anhydrous ethanol and dry it under vacuum at 60-80°C. Then place it in a muffle furnace, heat it to 500-600°C, calcine it, and grind and sieve it after natural cooling.

[0021] In this invention, the synthesis of boron-nitrogen co-doped mesoporous alumina relies on a sol-gel combined hydrothermal crystallization and template agent self-assembly mechanism. Aluminum isopropoxide, as a soluble aluminum source, is completely dissolved in anhydrous ethanol and forms a microemulsion system with the surfactant hexadecyltrimethylammonium bromide. The latter acts as a structure-directing agent, inducing the ordered arrangement of inorganic precursors around it through the self-assembly behavior of its long-chain alkyl groups and polar head groups. Based on this, boric acid and urea are simultaneously introduced as dopant sources: during hydrolysis, boric acid partially replaces aluminum in the aluminum-oxygen tetrahedra, forming boron-oxygen bonds and regulating the local electronic structure and thermal vibration modes; urea slowly decomposes during hydrothermal processes to produce ammonia, allowing nitrogen atoms to enter the alumina lattice in a substitutional or interstitial form, while the gas produced by its decomposition also contributes to pore expansion. Under medium-temperature hydrothermal conditions, aluminum species gradually hydrolyze, condense, and grow around the template agent, forming a precursor with a highly ordered mesoporous structure. Subsequently, the organic template agent was removed by calcination, yielding mesoporous alumina with high specific surface area, uniform pore size distribution, and boron-nitrogen co-doping characteristics. The abundant nanopores within this material effectively scatter phonons, significantly reducing thermal conductivity, while the doping elements further suppress lattice thermal vibrations, synergistically achieving excellent thermal insulation performance.

[0022] According to a preferred embodiment of the present invention, in step B1, the hydrothermal reaction time at 90-110°C is 18-24 hours.

[0023] According to a preferred embodiment of the present invention, in step B2, the calcination time at 500-600°C is 3-5 hours.

[0024] The present invention also provides a hydrogenated nitrile butadiene rubber composite material for cryogenic insulation prepared according to the preparation method of the hydrogenated nitrile butadiene rubber composite material for cryogenic insulation.

[0025] The beneficial effects of this invention are as follows:

[0026] The hydrogenated nitrile butadiene rubber composite material provided by this invention exhibits superior comprehensive performance in cryogenic environments, significantly outperforming similar materials in existing technologies. By synergistically introducing two functional fillers—zirconium-silicon composite modified hydroxyapatite and boron-nitrogen co-doped mesoporous alumina—the material achieves excellent elongation at break and extremely low thermal conductivity while maintaining high tensile strength. The former constructs a stable zirconium-silicon oxide network on the surface of hydroxyapatite, effectively protecting its crystal structure from thermodynamic shocks during processing and significantly enhancing the interfacial bonding with the rubber matrix, thus suppressing the initiation and propagation of microcracks at low temperatures. The latter, with its highly ordered mesoporous structure and boron-nitrogen co-doping effect, forms numerous nanoscale thermal barrier interfaces within the material, significantly extending the phonon heat transfer path and effectively suppressing heat conduction. The synergistic effect of these two fillers enables the composite material to maintain good elasticity and structural integrity even at liquid nitrogen temperatures, meeting the stringent requirements of cryogenic sealing and insulation.

[0027] In terms of the preparation process, this invention fundamentally solves the industry problem of uneven dispersion of functional fillers by precisely controlling the mixing sequence and temperature window. High specific surface area inorganic fillers are added in a higher temperature range, taking full advantage of the moderate viscosity and sufficient shear stress of the rubber melt at this temperature. This ensures that the filler particles are fully wetted and uniformly distributed in the matrix, avoiding agglomeration. Subsequently, a plasticizer is introduced, preserving the high shear dispersion effect of the initial step while imparting necessary flexibility to the material. Furthermore, the vulcanization system uses a combination of peroxide and a crosslinking agent, completing the crosslinking reaction under precisely controlled temperature and time to form a dense and stable three-dimensional network structure, further improving the material's low-temperature aging resistance and dimensional stability. The entire process has clearly defined parameters and is highly operable. All raw materials are commercially available chemicals, requiring no special equipment or complex post-processing, and possesses excellent prospects for industrial scale-up.

[0028] From an application perspective, the composite material produced by this invention is particularly suitable for high-end fields such as sealing rings for liquefied natural gas storage tanks, insulation layers for liquid hydrogen pipelines, and protection of cryogenic components in spacecraft. It exhibits high strength, high elasticity, and ultra-low thermal conductivity at extreme low temperatures, effectively solving the technical bottleneck of traditional rubber materials being prone to brittle fracture and insulation failure in cryogenic environments. Simultaneously, the material retains the inherent oil resistance, ozone resistance, and chemical corrosion resistance of hydrogenated nitrile rubber, extending its service life and reducing maintenance costs. More importantly, this invention abandons the unreasonable approach of relying on strong acid treatment or non-standard precursors, employing a mild and controllable sol-gel and hydrothermal synthesis method to ensure the integrity of the filler structure and batch-to-batch consistency. This technical solution not only possesses outstanding practicality and innovation but also provides a completely new approach and paradigm for the design of high-performance cryogenic rubber composite materials. Detailed Implementation

[0029] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0030] Example 1

[0031] Zirconium-silicon composite modified hydroxyapatite was prepared. 6.00 g of zirconium oxychloride and 4.00 g of tetraethyl orthosilicate were added to a mixed solution of 40.00 g anhydrous ethanol, 8.00 g deionized water, and 15.00 g of 0.30 mol / L dilute hydrochloric acid. The solution was hydrolyzed at 65.0 °C and 500 rpm for 2.50 h to obtain a clear zirconium-silicon composite sol. Separately, 10.00 g of hydroxyapatite powder was dispersed in 120.00 g of deionized water and sonicated at 40 kHz and 300 W for 30.0 min to obtain a homogeneous hydroxyapatite suspension. Under continuous vigorous stirring, the zirconium-silicon composite sol was slowly added dropwise to the hydroxyapatite suspension at a rate of approximately 2 mL / min using a constant-pressure dropping funnel. After the addition was complete, the pH of the mixture was slowly adjusted to 8.5 using a 25% (w / w) ammonia solution. The reaction system temperature was then raised to 75.0℃, and the reaction was continued with stirring at this temperature for 5.00 h to obtain a white suspension reaction mixture. The reaction mixture was cooled to 25℃ and centrifuged at 8000 rpm for 10 min to collect the precipitate. The precipitate was repeatedly washed with deionized water until the conductivity of the washing solution was less than 10 μS / cm, and then washed twice with anhydrous ethanol. The washed product was placed in a vacuum drying oven and dried at 105℃ and -0.095 MPa for 7.00 h. The dried powder was then transferred to a muffle furnace and heated to 450℃ at a programmed heating rate of 2.5℃ / min in air atmosphere, and calcined at this temperature for 2.50 h. After calcination, the powder was allowed to cool naturally to room temperature in the furnace, then removed, ground, and passed through a 200-mesh standard sieve to obtain the final product, zirconium-silicon composite modified hydroxyapatite powder.

[0032] Prepared boron-nitrogen co-doped mesoporous alumina. 18.00 g of aluminum isopropoxide was dissolved in 120.00 g of anhydrous ethanol. 3.00 g of hexadecyltrimethylammonium bromide was added under magnetic stirring, and the mixture was stirred continuously at 25 °C for 0.50 h to ensure thorough mixing and pre-hydrolysis. Subsequently, 1.20 g of boric acid and 2.80 g of urea were added to the system, and stirring was continued for 1.50 h until a homogeneous and transparent mixed sol was formed. This mixed sol was transferred to a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, with the filling degree controlled at 70%. The reactor was placed in an oven and subjected to a hydrothermal reaction at 100.0 °C for 20.0 h. After the reaction, the reactor was allowed to cool naturally to room temperature. The reaction product was then opened and filtered to obtain a white solid. This solid was washed three times with 50 mL of anhydrous ethanol each time. The washed solid was placed in a vacuum drying oven and dried at 70 °C and -0.095 MPa for 12.0 h. The dried precursor powder was placed in an alumina crucible and then placed in a muffle furnace. The temperature was programmed to reach 550°C at a rate of 1.5°C / min under air atmosphere and held at this temperature for 4.00 h to completely remove the template agent and complete crystallization and doping. After calcination, the powder was allowed to cool naturally to room temperature in the furnace, then removed, ground, and passed through a 200-mesh standard sieve to obtain the final product, boron-nitrogen co-doped mesoporous alumina powder.

[0033] Hydrogenated nitrile butadiene rubber composite was prepared. 100.0 g of hydrogenated nitrile butadiene rubber was added to a Banbury mixer (initial temperature of the mixing chamber set to 75℃) and plasticized at 75℃ for 3.0 min until the rubber completely wrapped the rollers. Then, 15.0 g of carbon black N330, 1.5 g of stearic acid, 4.0 g of zinc oxide, and 1.5 g of antioxidant 4020 were added sequentially, and the mixer rotor speed was maintained at 50 r / min for 4.00 min. The mixture temperature was controlled at 80℃, and 5.00 g of the zirconium-silicon composite modified hydroxyapatite and 4.00 g of the boron-nitrogen co-doped mesoporous alumina prepared above were added, and mixing continued at 50 r / min for 3.00 min. Then, 8.0 g of dioctyl phthalate was added, and mixing continued at 50 r / min for 1.50 min. After mixing, the rubber compound was discharged and cooled on a 25°C metal plate, then left to stand in a dry environment for 24.0 hours to obtain a homogeneous compound. The rested compound was then re-milled on an open mill (roll temperature set to 50°C). After the rolls wrapped around the compound, 2.2g of dicumyl peroxide and 1.0g of triallyl isocyanurate were added. The mixture was then cut with left and right cutters and passed through a thin tube 6 times to ensure uniform dispersion of the vulcanizing agent before sheeting, resulting in a sheet with a thickness of approximately 2.5mm. The sheet was cut to appropriate sizes and placed in a preheated flat vulcanizing machine for vulcanization at 170°C and 10.0MPa pressure for 18.0 minutes. After vulcanization, the sample was quickly removed, yielding the hydrogenated nitrile butadiene rubber composite material for cryogenic insulation.

[0034] Example 2

[0035] The specific implementation method is the same as in Example 1, except that zirconium-silicon composite modified hydroxyapatite is prepared. 5.00 g of zirconium oxychloride and 2.00 g of tetraethyl orthosilicate are added to a mixed solution of 30.00 g anhydrous ethanol, 5.00 g deionized water, and 10.00 g of 0.10 mol / L dilute hydrochloric acid. The solution is stirred at 500 rpm for 2.00 h at 60.0 °C to obtain a clear zirconium-silicon composite sol. Separately, 8.00 g of hydroxyapatite powder is dispersed in 100.00 g of deionized water and ultrasonicated at 40 kHz and 300 W for 25.0 min to obtain a homogeneous hydroxyapatite suspension. Under continuous vigorous stirring, the zirconium-silicon composite sol is slowly added dropwise to the hydroxyapatite suspension at a rate of approximately 1.5 mL / min using a constant pressure dropping funnel. After the addition is complete, the pH of the mixture is slowly adjusted to 8.0 using a 25% (w / w) ammonia solution. The reaction system temperature was then raised to 70.0℃, and the reaction was continued at this temperature with stirring for 4.00 h to obtain a white suspension reaction mixture. The reaction mixture was cooled to 25℃ and centrifuged at 8000 rpm for 10 min to collect the precipitate. The precipitate was repeatedly washed with deionized water until the conductivity of the washing solution was less than 10 μS / cm, and then washed twice with anhydrous ethanol. The washed product was placed in a vacuum drying oven and dried at 100℃ and -0.095 MPa for 6.00 h. The dried powder was then transferred to a muffle furnace and heated to 400℃ at a programmed heating rate of 2.0℃ / min in air atmosphere, and calcined at this temperature for 2.00 h. After calcination, the powder was allowed to cool naturally to room temperature in the furnace, then removed, ground, and passed through a 200-mesh standard sieve to obtain the final product, zirconium-silicon composite modified hydroxyapatite powder.

[0036] Prepared boron-nitrogen co-doped mesoporous alumina. 15.00 g of aluminum isopropoxide was dissolved in 100.00 g of anhydrous ethanol. 2.00 g of hexadecyltrimethylammonium bromide was added under magnetic stirring, and the mixture was stirred continuously at 25 °C for 0.50 h to ensure thorough mixing and pre-hydrolysis. Subsequently, 0.60 g of boric acid and 1.50 g of urea were added to the system, and stirring was continued for 1.00 h until a homogeneous and transparent mixed sol was formed. This mixed sol was transferred to a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, with the filling degree controlled at 65%. The reactor was placed in an oven and subjected to a hydrothermal reaction at 90.0 °C for 18.0 h. After the reaction, the reactor was allowed to cool naturally to room temperature. The reaction product was then opened and filtered to obtain a white solid. This solid was washed three times with 50 mL of anhydrous ethanol each time. The washed solid was placed in a vacuum drying oven and dried at 60 °C and -0.095 MPa for 12.0 h. The dried precursor powder was placed in an alumina crucible and then placed in a muffle furnace. The temperature was programmed to reach 500°C at a rate of 1.0°C / min under air atmosphere and held at this temperature for 3.00 h to completely remove the template agent and complete crystallization and doping. After calcination, the powder was allowed to cool naturally to room temperature in the furnace, then removed, ground, and passed through a 200-mesh standard sieve to obtain the final product, boron-nitrogen co-doped mesoporous alumina powder.

[0037] Prepare hydrogenated nitrile butadiene rubber composite material. 80.0 g of hydrogenated nitrile butadiene rubber was added to a Banbury mixer (initial temperature of the mixing chamber set to 70℃) and plasticized at 70℃ for 2.5 min until the rubber completely wrapped the rollers. Then, 10.0 g of carbon black N330, 1.0 g of stearic acid, 3.0 g of zinc oxide, and 1.0 g of antioxidant 4020 were added sequentially, maintaining the Banbury mixer rotor speed at 40 r / min for 3.00 min. The mixture temperature was controlled at 70℃, and 3.00 g of the zirconium-silicon composite modified hydroxyapatite and 2.00 g of the boron-nitrogen co-doped mesoporous alumina prepared above were added, continuing to mix at 40 r / min for 2.00 min. Then, 5.0 g of dioctyl phthalate was added, and mixing continued at 40 r / min for 1.00 min. After mixing, the rubber compound was discharged and cooled on a 25°C metal plate, then left to stand in a dry environment for 24.0 hours to obtain a homogeneous compound. The rested compound was then re-milled on an open mill (roll temperature set to 50°C). After wrapping around the rolls, 1.5g of dicumyl peroxide and 0.5g of triallyl isocyanurate were added. The mixture was then cut with left and right cutters and passed through a thin tube 6 times to ensure uniform dispersion of the vulcanizing agent before sheeting, resulting in a sheet with a thickness of approximately 2.5mm. The sheet was cut to appropriate sizes and placed in a preheated flat vulcanizing machine for vulcanization at 165°C and 10.0MPa pressure for 15.0 minutes. After vulcanization, the sample was quickly removed, yielding the hydrogenated nitrile butadiene rubber composite material for cryogenic insulation.

[0038] Example 3

[0039] The specific implementation method is the same as in Example 1, except that zirconium-silicon composite modified hydroxyapatite is prepared. 7.00 g of zirconium oxychloride and 6.00 g of tetraethyl orthosilicate were added to a mixed solution of 50.00 g anhydrous ethanol, 10.00 g deionized water, and 20.00 g of 0.50 mol / L dilute hydrochloric acid. The solution was stirred at 70.0 °C and 500 rpm for 3.00 h to obtain a clear zirconium-silicon composite sol. Separately, 12.00 g of hydroxyapatite powder was dispersed in 150.00 g of deionized water and sonicated at 40 kHz and 300 W for 35.0 min to obtain a homogeneous hydroxyapatite suspension. Under continuous vigorous stirring, the zirconium-silicon composite sol was slowly added dropwise to the hydroxyapatite suspension at a rate of approximately 2.5 mL / min using a constant pressure dropping funnel. After the addition was complete, the pH of the mixture was slowly adjusted to 9.0 using a 25% (w / w) ammonia solution. The reaction system temperature was then raised to 80.0℃, and the reaction was continued with stirring at this temperature for 6.00 h to obtain a white suspension reaction mixture. The reaction mixture was cooled to 25℃ and centrifuged at 8000 rpm for 10 min to collect the precipitate. The precipitate was repeatedly washed with deionized water until the conductivity of the washing solution was less than 10 μS / cm, and then washed twice with anhydrous ethanol. The washed product was placed in a vacuum drying oven and dried at 110℃ and -0.095 MPa for 8.00 h. The dried powder was then transferred to a muffle furnace and heated to 500℃ at a programmed heating rate of 3.0℃ / min in air atmosphere, and calcined at this temperature for 3.00 h. After calcination, the powder was allowed to cool naturally to room temperature in the furnace, then removed, ground, and passed through a 200-mesh standard sieve to obtain the final product, zirconium-silicon composite modified hydroxyapatite powder.

[0040] Prepared boron-nitrogen co-doped mesoporous alumina. 20.00 g of aluminum isopropoxide was dissolved in 150.00 g of anhydrous ethanol. 4.00 g of hexadecyltrimethylammonium bromide was added under magnetic stirring, and the mixture was stirred continuously at 25 °C for 0.50 h to ensure thorough mixing and pre-hydrolysis. Subsequently, 2.00 g of boric acid and 4.00 g of urea were added to the system, and stirring continued for 2.00 h until a homogeneous and transparent mixed sol was formed. This mixed sol was transferred to a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, with the filling degree controlled at 75%. The reactor was placed in an oven and subjected to a hydrothermal reaction at 110.0 °C for 24.0 h. After the reaction, the reactor was allowed to cool naturally to room temperature. The reaction product was then opened and filtered to obtain a white solid. This solid was washed three times with 50 mL of anhydrous ethanol each time. The washed solid was placed in a vacuum drying oven and dried at 80 °C and -0.095 MPa for 12.0 h. The dried precursor powder was placed in an alumina crucible and then placed in a muffle furnace. The temperature was programmed to reach 600℃ at a heating rate of 2.0℃ / min under air atmosphere, and then calcined at this temperature for 5.00 h to completely remove the template agent and complete crystallization and doping. After calcination, the powder was allowed to cool naturally to room temperature in the furnace, removed, ground, and passed through a 200-mesh standard sieve to obtain the final product, boron-nitrogen co-doped mesoporous alumina powder.

[0041] Hydrogenated nitrile butadiene rubber composite was prepared. 120.0 g of hydrogenated nitrile butadiene rubber was added to a Banbury mixer (initial temperature of the mixing chamber set to 80℃) and plasticized at 80℃ for 3.5 min until the rubber completely wrapped the rollers. Then, 20.0 g of carbon black N330, 2.0 g of stearic acid, 5.0 g of zinc oxide, and 2.0 g of antioxidant 4020 were added sequentially, and the mixer rotor speed was maintained at 60 r / min for 5.00 min. The mixture temperature was controlled at 90℃, and 8.00 g of the zirconium-silicon composite modified hydroxyapatite and 6.00 g of the boron-nitrogen co-doped mesoporous alumina prepared above were added, and mixing continued at 60 r / min for 4.00 min. Then, 10.0 g of dioctyl phthalate was added, and mixing continued at 60 r / min for 2.00 min. After mixing, the rubber compound was discharged and cooled on a 25°C metal plate, then left to stand in a dry environment for 30.0 hours to obtain a homogeneous compound. The rested compound was then re-milled on an open mill (roll temperature set to 50°C). After wrapping around the rolls, 3.0g of dicumyl peroxide and 1.5g of triallyl isocyanurate were added. The mixture was then cut with left and right cutters and passed through a thin tube 6 times to ensure uniform dispersion of the vulcanizing agent before sheeting, resulting in a sheet with a thickness of approximately 2.5mm. The sheet was cut to appropriate sizes and placed in a preheated flat vulcanizing machine for vulcanization at 175°C and 10.0MPa pressure for 20.0 minutes. After vulcanization, the sample was quickly removed, yielding the hydrogenated nitrile butadiene rubber composite material for cryogenic insulation.

[0042] Comparative Example 1

[0043] The specific implementation method is the same as in Example 1, except that zirconium-silicon composite modified hydroxyapatite and boron-nitrogen co-doped mesoporous alumina are not added when preparing the rubber composite material. The remaining steps, raw material amounts, and process parameters are consistent with those in Example 1.

[0044] Comparative Example 2

[0045] The specific implementation method is the same as in Example 1, except that only 5.00g of zirconium-silicon composite modified hydroxyapatite is added when preparing the rubber composite material, and boron-nitrogen co-doped mesoporous alumina is not added. The remaining steps, raw material amounts, and process parameters are consistent with those in Example 1.

[0046] Comparative Example 3

[0047] The specific implementation method is the same as in Example 1, except that only 4.00g of boron-nitrogen co-doped mesoporous alumina is added when preparing the rubber composite material, and zirconium-silicon composite modified hydroxyapatite is not added. The remaining steps, raw material amounts, and process parameters are consistent with those in Example 1.

[0048] Performance testing

[0049] The hydrogenated nitrile butadiene rubber composites for cryogenic insulation prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following method, which included the following steps: all tests were conducted in a standard laboratory environment (temperature 23±2℃, relative humidity 50±5%).

[0050] Tensile strength and elongation at break tests: Type I dumbbell-shaped specimens were used, with a thickness of 2.0 ± 0.2 mm, a narrow parallel section width of 6.0 mm, and a length of 25.0 mm. Before testing, the specimens were completely immersed in liquid nitrogen at -196°C and kept at this temperature for 30.0 min in a dedicated cryogenic container to ensure uniform internal temperature reaching the test temperature. Subsequently, the tests were conducted using an electronic universal testing machine equipped with a liquid nitrogen cooling jacket and cryogenic tensile fixtures. After the specimens were removed from the liquid nitrogen, they were clamped into the fixtures within 15 s, with an initial clamping distance of 50.0 mm. Tensile strength was applied at a constant beam speed of 500 mm / min until the specimen broke. The maximum tensile force and the change in gauge length at break were recorded, and the tensile strength and elongation at break were calculated. Five valid specimens were tested in parallel for each formulation, and the results were taken as the arithmetic mean.

[0051] Thermal conductivity testing: The transient planar heat source method was used. The material was vulcanized and molded into a disc-shaped sample with a diameter of 50.0 mm and a thickness of 5.0 ± 0.1 mm, and the upper and lower surfaces were polished smooth. Before testing, the sample was placed in a sealed cryogenic chamber cooled by liquid nitrogen vapor and held at -196℃ for 1.0 h. During testing, a 10.0 mm diameter planar probe was clamped at the center of two identical samples, and a constant low-power step heat flux was applied to the probe. The thermal conductivity of the material was directly calculated by recording the probe temperature change curve over time. Each sample was measured three times at -196℃, and the average value was taken as the final test result. The above method systematically characterized the mechanical integrity and thermal insulation performance of the material under cryogenic conditions. The specific test results are shown in the table below.

[0052] Test results:

[0053] Table 1: Test results of each embodiment and comparative example

[0054] As can be seen from Table 1, firstly, the tensile strength of Comparative Example 1 at -196℃ is only 9.5MPa, the elongation at break is 150%, and the thermal conductivity is 0.152W / (m·K). This directly confirms the inherent technical problems of existing pure hydrogenated nitrile rubber in cryogenic environments, namely low strength, poor toughness (easy to become brittle), and high thermal conductivity.

[0055] Secondly, comparative examples 2 and 3 were modified with zirconium-silicon composite hydroxyapatite or boron-nitrogen co-doped mesoporous alumina, respectively. Although their performance was improved compared with comparative example 1, the tensile strength of comparative example 2 increased to 13.0 MPa and the thermal conductivity decreased to 0.120 W / (m·K), but it was still significantly lower than that of all examples. This proves that the effect of a single filler is limited and cannot fully solve the above problems.

[0056] Crucially, Examples 1-3 simultaneously introduced zirconium-silicon composite modified hydroxyapatite and boron-nitrogen co-doped mesoporous alumina, resulting in a significant performance improvement. Taking the optimal Example 1 as an example, its tensile strength reached 16.2 MPa, an increase of 70.5% compared to Comparative Example 1; its elongation at break reached 215%, an increase of 43.3%; and its thermal conductivity was as low as 0.098 W / (m·K), a decrease of 35.5%. This is attributed in two ways: firstly, the zirconium-silicon composite modified hydroxyapatite and boron-nitrogen co-doped mesoporous alumina constructed a robust multi-element network in the rubber matrix, significantly enhancing the material's rigidity at low temperatures and suppressing brittle fracture through stress transfer and pinning effects; secondly, the unique multi-scale structure (such as surface modification and mesoporous characteristics) of the zirconium-silicon composite modified hydroxyapatite and boron-nitrogen co-doped mesoporous alumina greatly increased the phonon scattering path, synergistically endowing the material with excellent thermal insulation properties.

[0057] Furthermore, the comprehensive performance of the examples, which is significantly superior to the comparative examples of any single filler, directly confirms that the present invention effectively solves the problem of uneven dispersion of functional fillers through specific preparation processes (such as optimized mixing temperature and sequence), promotes the synergistic effect of the two fillers rather than a simple addition, and thus jointly overcomes the technical bottleneck of the difficulty in simultaneously achieving strength, toughness and thermal insulation performance of cryogenic insulating rubber at the molecular-nano-micron multi-level.

[0058] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing hydrogenated nitrile butadiene rubber composite material for cryogenic insulation, characterized in that the steps include... include: S1. By weight, 80-120 parts of hydrogenated nitrile rubber are put into an internal mixer and plasticized at 70-80℃. Then, add 10-20 parts of carbon black N330, 1-2 parts of stearic acid, 3-5 parts of zinc oxide, and 1-2 parts of antioxidant 4020 in sequence, and mix to obtain a mixture; keep the temperature of the mixture at 70-90℃, first add 3-8 parts of zirconium-silicon composite modified hydroxyapatite and 2-6 parts of boron-nitrogen co-doped mesoporous alumina, and mix; then add 5-10 parts of dioctyl phthalate, and continue mixing; after removing the glue and cooling to room temperature, let it stand to obtain the rubber compound; S2. Recycle the rubber compound on a two-roll mill, add 1.5-3.0 parts of dicumyl peroxide and 0.5-1.5 parts of triallyl isocyanurate, and then sheet it to obtain a rubber sheet. Place the rubber sheet in a flat vulcanizing machine and vulcanize it at 165-175℃.

2. The method for preparing hydrogenated nitrile butadiene rubber composite material for cryogenic insulation according to claim 1, characterized in that, In step S1, the time for the glue to be left to stand after cooling to room temperature is 24-30 hours.

3. The method for preparing hydrogenated nitrile butadiene rubber composite material for cryogenic insulation according to claim 1, characterized in that, In step S2, the vulcanization time at 165-175℃ is 15-20 minutes.

4. The method for preparing the hydrogenated nitrile butadiene rubber composite material for cryogenic insulation according to claim 1, characterized in that, The preparation method of the zirconium-silicon composite modified hydroxyapatite includes: A1. By weight, dissolve 5-7 parts of zirconium oxychloride and 2-6 parts of tetraethyl orthosilicate in a mixed solution of 30-50 parts of anhydrous ethanol, 5-10 parts of deionized water, and 10-20 parts of dilute hydrochloric acid, and stir at 60-70℃ to obtain a zirconium-silicon composite sol; disperse 8-12 parts of hydroxyapatite powder in 100-150 parts of deionized water, and sonicate to obtain a hydroxyapatite suspension; add the zirconium-silicon composite sol dropwise to the hydroxyapatite suspension while stirring, adjust the pH to 8.0-9.0 with ammonia, and continue the reaction at 70-80℃ to obtain a reaction mixture; A2. Cool the reaction mixture to room temperature, centrifuge to obtain a precipitate; wash the precipitate with deionized water, then with anhydrous ethanol, dry it under vacuum at 100-110℃, then calcine it at 400-500℃, grind and sieve it.

5. The method for preparing the hydrogenated nitrile butadiene rubber composite material for cryogenic insulation according to claim 4, characterized in that, In step A1, the reaction continues at 70-80℃ for 4-6 hours.

6. The method for preparing the hydrogenated nitrile butadiene rubber composite material for cryogenic insulation according to claim 4, characterized in that, In step A2, the calcination time at 400-500℃ is 2-3 hours.

7. The method for preparing hydrogenated nitrile butadiene rubber composite material for cryogenic insulation according to claim 1, characterized in that, The method for preparing the boron-nitrogen co-doped mesoporous alumina includes: B1. Dissolve 15-20 parts by weight of aluminum isopropoxide in 100-150 parts by weight of anhydrous ethanol, add 2-4 parts by weight of hexadecyltrimethylammonium bromide, and stir; then add 0.6-2 parts by weight of boric acid and 1.5-4 parts by weight of urea, and continue stirring to obtain a mixed sol; transfer the mixed sol to a reaction vessel and perform a hydrothermal reaction at 90-110°C to obtain a reaction mixture; B2. After cooling the reaction mixture, filter to obtain a solid; wash the solid with anhydrous ethanol and dry it under vacuum at 60-80℃; then place it in a muffle furnace, heat it to 500-600℃ and calcine it, then grind and sieve it after natural cooling.

8. The method for preparing hydrogenated nitrile butadiene rubber composite material for cryogenic insulation according to claim 7, characterized in that, In step B1, the hydrothermal reaction time is 18-24 hours at 90-110℃.

9. The method for preparing the hydrogenated nitrile butadiene rubber composite material for cryogenic insulation according to claim 7, characterized in that, In step B2, the calcination time at 500-600℃ is 3-5 hours.

10. A hydrogenated nitrile butadiene rubber composite material for cryogenic insulation, characterized in that, The hydrogenated nitrile butadiene rubber composite material for cryogenic insulation is prepared by the method according to any one of claims 1-9.

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