Modified nitrile rubber seal material resistant to hydrogen permeation damage and method of making

Abstract

The application discloses a modified nitrile rubber sealing material resistant to hydrogen permeation damage and a preparation method, and belongs to the field of high polymer rubber sealing materials.The material comprises, in terms of weight parts, nitrile rubber 100 parts, composite nylon 20-35 parts, exfoliated organic montmorillonite 5-15 parts, nano hydrogen-resistant filler 3-8 parts and the like.By introducing the composite nylon as an "inlaid frame", cooperating with the "labyrinth" barrier effect of the exfoliated montmorillonite and the adsorption / quenching effect of the nano filler, a "lamellar barrier-interface anchoring" trinity protection network is constructed, hydrogen permeation and damage are inhibited from the dual mechanisms of physical barrier and chemical adsorption.The preparation adopts a two-stage low-temperature mixing process, the nylon is first blended with the rubber at low temperature, and then the remaining fillers are added at high temperature to ensure dispersion.The material prepared by the method has low hydrogen permeation rate and excellent mechanical properties, and is suitable for sealing elements of hydrogen conveying pipelines.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer rubber sealing materials, specifically a modified nitrile rubber sealing material resistant to hydrogen permeation damage and its preparation method. Background Technology

[0002] Adding a certain proportion of hydrogen to natural gas pipelines can effectively reduce fossil energy consumption and carbon emissions, and is one of the main methods of hydrogen transportation. At the same time, using existing natural gas pipelines for hydrogen transportation is the core technology path for low-carbon transformation of natural gas pipelines and large-scale utilization of hydrogen energy at this stage.

[0003] The sealing structures at the connections of valves, blind flanges, and other components in natural gas pipelines are generally made of rubber. Conventional nitrile rubber matrices contain a large amount of free volume, micropores, and interface defects. Under hydrogen conditions, tiny hydrogen molecules can rapidly penetrate the rubber surface, continuously permeating, diffusing, and accumulating within the matrix. When pipeline pressure fluctuates or gas transmission is started or stopped, the hydrogen dissolved inside the rubber rapidly precipitates, causing blistering, microcrack initiation, and propagation within the material, resulting in typical hydrogen-induced permeation damage. Simultaneously, the expansion of permeated and accumulated hydrogen molecules under pressure fluctuations causes blistering defects, leading to a decrease in the mechanical strength of the sealing material and an increase in permanent compression set. This not only significantly shortens the service life of the seals but also poses a risk of leakage and, if exposed to an ignition source, can easily explode, seriously threatening the safety of pipeline operation.

[0004] To address the issue of insufficient stability of existing nitrile rubber under hydrogen conditions, there is an urgent need to develop modified nitrile rubber sealing materials and their preparation processes that are suitable for hydrogen transportation conditions and possess both hydrogen-blocking and anti-seepage properties. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems and provide a modified nitrile rubber sealing material that resists hydrogen permeation damage. The present invention achieves the optimization of material performance by means of a three-in-one mechanism of "sheet barrier ~ interface anchoring ~ dual network crosslinking" and a specific two-stage low temperature mixing process, while protecting the molecular weight of nylon.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A modified nitrile rubber sealing material resistant to hydrogen permeation damage, comprising the following components by weight: 100 parts of base rubber; 20-35 parts of composite nylon; 5-15 parts of stripped organic montmorillonite; 3-8 parts of nano-hydrogen barrier filler; 5-15 parts of reinforcing agent; 10-20 parts of rigid reinforcing filler; 1-3 parts of interface anchoring agent; 2-5 parts of compound vulcanizing agent; 8-18 parts of auxiliary agents.

[0007] Furthermore, the base rubber is nitrile rubber (NBR) with an acrylonitrile content of 33-40%.

[0008] Furthermore, the composite nylon is a composite system of nylon 12 (PA12) and nylon 6 (PA6) with a ratio of PA12:PA6 = 2:1 to 3:1 and a particle size of 5~20μm. This component serves as an "embedded skeleton". Before use, the component is pre-melted and modified with maleic anhydride grafts to suppress rubber matrix deformation and hydrogen-induced microcrack propagation under high pressure.

[0009] Furthermore, the exfoliated organomontmorillonite is modified by intercalation of dioctadecyl dimethylammonium chloride, with an interlayer spacing ≥2.8 nm. The exfoliated organomontmorillonite is used to construct a maze path for hydrogen molecule permeation.

[0010] Furthermore, the nano-hydrogen barrier filler is a composite of nano-zinc oxide and nano-titanium dioxide, with a mass ratio of 1:1 to 1:2, and an average particle size of 20-50 nm. The nano-zinc oxide is a functional component, and its surface active sites can adsorb free hydrogen ions (H₂O). + The nano-titanium dioxide inhibits the aggregation of hydrogen molecules in the rubber matrix; it quenches hydrogen free radicals (H·) through photocatalytic effect, blocks hydrogen-induced chain degradation reaction, and synergistically reduces hydrogen permeability.

[0011] Furthermore, the reinforcing agent is carbon black, preferably N330 or N660; the carbon black forms a "physical cross-linking network" in the rubber matrix, and through van der Waals forces, it entangles with the rubber molecular chains, thereby improving the tensile strength, tear strength and abrasion resistance of the material, while also improving the processing fluidity of the rubber compound.

[0012] Furthermore, the rigid reinforcing filler is wollastonite, preferably needle-shaped or fibrous wollastonite, with an aspect ratio of 10 to 20. The wollastonite constructs a three-dimensional network skeleton structure in the rubber matrix, forming a "labyrinthine" hydrogen molecule penetration barrier channel in synergy with the exfoliated organomontmorillonite. At the same time, it transfers the physical support of the embedded skeleton formed by the composite nylon to the rubber matrix, effectively suppressing material creep and hydrogen-induced bulging under high-pressure hydrogen environment.

[0013] Furthermore, the interface anchoring agent is a rare earth element modified titanate coupling agent (NDZ~311W), used to form a chemical bond between the filler and the rubber matrix.

[0014] Furthermore, the composite vulcanizing agent is composed of 1.5 to 2.5 parts of sulfenamide accelerator (CBS) and 0.5 to 2.5 parts of peroxide (DCP) to construct a high- and low-dual-density crosslinking network.

[0015] Furthermore, the auxiliary agent is composed of zinc oxide (3-5 parts), stearic acid (1-3 parts), antioxidant RD (1-3 parts) and plasticizer DOP (3-7 parts); the zinc oxide acts as an activator to activate the sulfenamide accelerator and ensure the efficient construction of the composite vulcanization network.

[0016] The present invention also provides a method for preparing the above-mentioned material, comprising the following steps; S1. First, the pre-modified composite nylon (PA12 / PA6 compound) with maleic anhydride graft is melt-blended and added to an anhydrous ethanol solution in proportion with the interfacial anchoring agent. The mixture is sheared and dispersed in a high-speed mixer at 800-1200 rpm for 10-15 minutes to ensure the rare earth titanate coupling agent is uniformly coated on the surface of the nylon particles. Then, it is dried in a vacuum oven at 80-90℃ for 4-6 hours to completely remove the solvent, obtaining the pretreated composite nylon with interface modification. Finally, the base rubber is fed into a mixing mill for plasticizing. When the rubber compound wraps around the rollers and the temperature stabilizes at 80-90℃, the pretreated composite nylon is added. The rotor speed of the mixing mill is controlled at 30-45 rpm, and the mixture is mixed for 4-5 minutes. During this process, the temperature of the rubber compound is strictly controlled not to exceed 90℃ to prevent thermo-oxidative degradation of the nylon and to ensure its initial compatibility with the rubber. Finally, the rubber is discharged and water-cooled to below 40℃ to obtain the nylon masterbatch.

[0017] S2. After cooling the masterbatch obtained in S1, put it back into the internal mixer and add the peelable organic montmorillonite, rigid reinforcing filler (wollastonite), nano hydrogen barrier filler (ZnO / TiO2 compound), antioxidant and activator in sequence. Heat the internal mixer to 100~110℃, increase the rotor speed to 40~50rpm, and mix for 6~8 minutes to ensure that the inorganic filler with high specific surface area is fully peeled and dispersed in the rubber matrix. After mixing, discharge the rubber and filter it through an 80-mesh filter to remove any possible impurities, clumps and undispersed gel. Then cool it to room temperature with water.

[0018] S3. The compound obtained in S2 is further mixed on a two-roll mill. The compound vulcanizing agent (CBS and DCP) is added, and the roller gap is adjusted to 1-2 mm for thin-pass mixing 6-8 times to ensure that the vulcanizing agent is absolutely uniformly distributed in the rubber compound. Finally, the rubber compound is placed flat into the mold and placed in a flat vulcanizing machine. Under the conditions of a mold cavity temperature of 170℃ and a pressure of 15MPa, it is vulcanized for 15-20 minutes. The air is degassed several times to ensure that there are no air bubbles left. After demolding and cooling, the finished product is obtained.

[0019] Compared with the prior art, the beneficial effects of this invention are as follows: Nylon is used as an embedded skeleton, while the synergistic effect of exfoliated montmorillonite and nano-hydrogen barrier filler is utilized to further prevent hydrogen permeation; a two-stage mixing process is adopted, with the first stage at low temperature to protect the nylon from thermo-oxidative degradation, and the second stage at high temperature to ensure the dispersion of filler, solving the processing problem of blending rigid plastics and rubber; rare earth modified coupling agents form "molecular bridges" between nylon and rubber, improving the interfacial bonding energy and effectively preventing high-pressure hydrogen from accumulating at the interface. Detailed Implementation

[0020] Example: The modified nitrile rubber sealing material provided in this embodiment of the invention is composed of the following specific components by weight.

[0021] 100 parts of nitrile butadiene rubber (NBR, grade N240S) with an acrylonitrile content of 38% were selected.

[0022] 30 parts of composite nylon are selected. Furthermore, the composite nylon is composed of nylon 12 (PA12) and nylon 6 (PA6) in a mass ratio of 2:1 (i.e., 6 parts of PA12 and 3 parts of PA6), and the particle size is controlled at 15 μm. This component serves as an "embedded skeleton" to suppress matrix deformation under high pressure.

[0023] Eight portions of exfoliated organomontmorillonite were selected. Furthermore, the montmorillonite was modified by intercalation of dioctadecyl dimethylammonium chloride, with an interlayer spacing ≥2.8 nm, to construct a labyrinthine pathway for hydrogen molecule permeation.

[0024] Four parts of a compound of nano zinc oxide and nano titanium dioxide were selected, with a mass ratio of 1:1 and an average particle size of 30 nm. The hydrogen permeability was reduced through the synergistic effect of adsorption and quenching.

[0025] The reinforcing agent selected is 10 parts of carbon black, and further, the carbon black type is N330, which is used to form a physical cross-linking network in the rubber matrix.

[0026] Fifteen parts of needle-shaped wollastonite were selected, and the aspect ratio of the wollastonite was 15, to construct a three-dimensional mesh framework, which worked in conjunction with montmorillonite to block hydrogen permeation.

[0027] Furthermore, two parts of a rare earth element modified titanate coupling agent (NDZ~311W) were selected.

[0028] Furthermore, a compound consisting of 1.8 parts of sulfenamide accelerator (CBS) and 0.8 parts of peroxide (DCP) was selected.

[0029] Furthermore, the auxiliary agents include 4 parts zinc oxide, 1 part stearic acid, 2 parts antioxidant RD, and 4 parts plasticizer DOP, which are used to activate the vulcanization system and improve processing fluidity.

[0030] Based on the above formula, the preparation method of this embodiment includes the following steps: S1. Place the composite nylon in a vacuum oven at 90℃ and dry for 5 hours; disperse the dried nylon and rare earth titanate coupling agent in anhydrous ethanol at high speed for 15 minutes, and dry at 80℃ to complete the surface pretreatment; then put the nitrile rubber into a mixer for plasticizing, and after the rollers are smooth, add the pretreated composite nylon; control the rotor temperature of the mixer at 80~85℃, the average rotor speed at 30~40rpm, mix for 4 minutes, discharge the glue and cool it with water to below 40℃ to obtain the nylon masterbatch. This step aims to achieve uniform dispersion of nylon at low temperature and avoid thermo-oxidative degradation.

[0031] S2. Put the cooled masterbatch back into the internal mixer, and add the peelable organic montmorillonite, wollastonite, nano hydrogen barrier filler, carbon black N330 and auxiliary agents in sequence; heat to 0.5℃, with an average rotor speed of 45rpm, and mix for 6 minutes; after discharging the masterbatch, filter impurities through an 80-mesh filter and cool to room temperature with water.

[0032] S3. Add the mixed rubber and compound vulcanizing agent to the open mill, adjust the roller gap to 1mm and pass through the mill 6 times. Then place it in a flat vulcanizing machine and vulcanize it for 15 minutes at 170℃ and 15MPa. Degas the material 3 times, remove it from the mold and cool it to obtain the finished product.

[0033] Comparative Example: The comparative sample provided in this invention is a conventional NBR composite material without added toughening support skeleton. The difference between this comparative example and the embodiment is that the composite nylon component is completely removed and no alternative reinforcing skeleton is introduced. The specific types, specifications and amounts of the remaining components are consistent with those of the embodiment.

[0034] The preparation method for this comparative example is as follows: S1. Directly add 100 parts of NBR into an internal mixer for plasticizing. When the rubber compound wraps around the rollers and the temperature stabilizes at 80~85℃, add the peelable organic montmorillonite, wollastonite, nano hydrogen barrier filler, carbon black N330, and auxiliary additives (zinc oxide, stearic acid, antioxidant RD, plasticizer DOP) in sequence. Control the rotor speed to 30~40 rpm and mix for 5 minutes to initially disperse the inorganic filler in the rubber matrix. Discharge the rubber and cool it with water to below 40℃.

[0035] S2. Put the cooled rubber compound back into the internal mixer, heat it to 100~105℃, increase the rotor speed to 40~50rpm, and continue mixing for 5 minutes to ensure that the inorganic filler is fully peeled off and dispersed; after discharge, filter impurities through an 80-mesh filter screen and cool it to room temperature for later use.

[0036] S3. The final rubber compound is further mixed on a two-roll mill, and the composite vulcanizing agent (CBS and DCP) is added. The roll gap is adjusted to 1-2 mm and the mixture is passed through the mill 6 times. Then the rubber compound is flattened and placed in a mold, and placed in a flat vulcanizing machine. It is vulcanized for 15 minutes at a mold cavity temperature of 170°C and a pressure of 15 MPa. The air is degassed 3 times. After demolding and cooling, the comparative sample of the present invention is obtained.

[0037] The samples prepared in the above examples and comparative examples were subjected to performance tests. It is worth noting that the NBR system has a fast / slow dual-channel diffusion characteristic due to the presence of carbon black filler. The apparent diffusion coefficients listed in this table are measured based on the concentration-time curve using the time lag method, which is an equivalent single exponential fit. The test conditions and the data obtained for the test items are compared in Table 1 below.

[0038] Table 1 Performance comparison between comparative examples and embodiments .

[0039] As shown in the table above, this invention successfully prepared a sealing material with both ultra-low hydrogen permeability and good mechanical properties by introducing composite nylon as an embedded skeleton into nitrile rubber and working synergistically with the lamellar barrier effect of montmorillonite through a two-stage mixing process. The comparative example without nylon has high hydrogen permeability due to the lack of skeleton support; while the example containing nylon forms a dense barrier network, significantly reducing hydrogen permeability to 10%. ~11 It achieves speeds on the order of m² / s while simultaneously increasing material strength.

[0040] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A modified nitrile rubber sealing material resistant to hydrogen permeation damage, characterized in that, By weight, it includes the following components: 100 parts of base rubber; 20-35 parts of composite nylon; 5-15 parts of stripped organic montmorillonite; 3-8 parts of nano-hydrogen barrier filler; 5-15 parts of reinforcing agent; 10-20 parts of rigid reinforcing filler; 1-3 parts of interface anchoring agent; 2-5 parts of compound vulcanizing agent; 8-18 parts of auxiliary agents.

2. The modified nitrile rubber sealing material according to claim 1, characterized in that, The composite nylon is a composite system of nylon 12 (PA12) and nylon 6 (PA6) with a mass ratio of PA12:PA6 = 2:1 to 3:1 and a particle size of 5~20μm. It is pre-modified by melt blending with maleic anhydride grafts.

3. The modified nitrile rubber sealing material according to claim 1, characterized in that, The exfoliated organomontmorillonite is montmorillonite modified by intercalation of dioctadecyl dimethylammonium chloride, with an interlayer spacing ≥2.8 nm.

4. The modified nitrile rubber sealing material according to claim 1, characterized in that, The interface anchoring agent is a rare earth element modified titanate coupling agent.

5. A method for preparing the modified nitrile butadiene rubber sealing material resistant to hydrogen permeation damage as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Masterbatch preparation: The interface anchoring agent is mixed with the composite nylon in a solvent, and the composite nylon is surface pretreated and dried; After the base rubber is plasticized, the pretreated composite nylon is added at 80~90℃, mixed evenly, and then cooled to obtain nylon masterbatch. S2. Filler mixing: After cooling the nylon masterbatch, put it back into the mixing equipment, and add the peelable organic montmorillonite, rigid reinforcing filler, nano hydrogen barrier filler and auxiliary agents in sequence. Heat to 100~110℃ for mixing to fully disperse the filler. Then cool and filter to obtain the final rubber. S3. Vulcanization molding: Add a composite vulcanizing agent to the final rubber compound, mix well, place in a mold, and vulcanize at 170°C and 15MPa for 15-20 minutes to obtain the sealing material.