A method for improving the alkali aging resistance of ethylene propylene diene rubber, a rubber composition and applications thereof

Abstract

The application discloses a method for improving alkali-resistant aging performance of ethylene-propylene-diene rubber, a rubber composition and application thereof, and relates to the technical field of rubber.The application improves the alkali-resistant aging performance of ethylene-propylene-diene rubber by adding modified carbon black to the ethylene-propylene-diene rubber; the modified carbon black is heat-modified carbon black and / or hydrophobic-modified carbon black.The application carries out heat treatment on the carbon black, removes carboxyl groups on the surface of the carbon black through high temperature, thereby avoiding the reaction of the carbon black with alkali, and further prolonging the alkali-resistant aging performance of the rubber; the application carries out hydrophobic modification on the carbon black, reduces the adsorption of the carbon black to alkali liquor, and further reduces the contact between the alkali and the rubber, thereby greatly improving the alkali resistance of the rubber.In summary, the application carries out specific chemical modification on the surface of the carbon black, and fills the modified carbon black into ethylene-propylene-diene rubber, so that the stability of the ethylene-propylene-diene rubber in a harsh alkali environment can be improved, and the service life of the ethylene-propylene-diene rubber as a sealing piece of an alkali electrolytic cell can be prolonged.

Description

Technical Field

[0001] This invention relates to the field of rubber technology, and in particular to a method for improving the alkali aging resistance of ethylene propylene diene monomer (EPDM) rubber, a rubber composition thereof, and its application. Background Technology

[0002] The global energy structure is transitioning towards low-carbon, clean energy, an irreversible trend. Against this backdrop, hydrogen, as a highly efficient energy carrier, plays a crucial role in the utilization and development of renewable energy, enabling the storage, transportation, or direct use of electricity, wind, solar, and geothermal energy. Among numerous hydrogen production technologies, water electrolysis has garnered significant attention due to its environmental friendliness. Alkaline electrolyzer technology, in particular, holds a prominent position in this field due to its high maturity, cost-effectiveness, and operational stability. However, hydrogen production technologies require excellent sealing for efficient and stable operation, and the loss of alkali solution increases energy consumption in gas production. Both of these factors necessitate sealing materials with strong resistance to harsh environments.

[0003] Ethylene propylene diene monomer (EPDM) rubber has many excellent properties: (1) The high saturation of the main chain gives it excellent aging resistance. EPDM products have strong resistance to ozone, heat, oxygen, and especially ozone, making them perform well in harsh weather conditions and suitable for outdoor applications; (2) The molecular side chains contain a small number of double bonds, allowing it to be vulcanized with sulfur or peroxide; (3) It has a low relative density, making it the lightest of general-purpose rubbers, allowing for the use of a large amount of filler to reduce costs; (4) It has a wide applicable temperature range of -50℃ to 150℃, maintaining good usability; (5) It has excellent electrical insulation and good impact elasticity. These excellent aging resistance, chemical stability, and low cost make it widely used in the sealing of hydrogen electrolysis cells, providing a good sealing effect. However, the electrolyte used in alkaline electrolytic cells is usually a strongly alkaline solution, such as potassium hydroxide (KOH) solution. As a sealing material in the electrolytic cell, EPDM rubber will come into direct contact with the strongly alkaline electrolyte. The strongly alkaline environment will corrode the molecular structure of the rubber, causing the rubber molecular chains to break and the cross-linked structure to be destroyed, which in turn reduces the sealing performance of the rubber. In actual work, there are safety hazards such as gas leakage or alkali spray.

[0004] In summary, the current EPDM rubber has poor alkali aging resistance, resulting in a short service life of seals. How to improve the alkali aging resistance of EPDM rubber is an urgent problem to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention provides a method, a rubber composition, and its application for improving the alkali aging resistance of EPDM rubber. The present invention fills EPDM rubber with modified carbon black, which can improve its alkali aging resistance and extend its service life in alkaline environments, thereby solving the following problems existing in the prior art:

[0006] (1) Insufficient research on the mechanism of alkaline environment on EPDM. Existing technologies lack systematic comparative analysis and cannot clarify the main factors affecting the alkali resistance of EPDM, such as the influence of alkali concentration, temperature, etc. on the microstructure, mechanical properties and chemical stability of the material, making it difficult to provide targeted guidance for material modification and performance improvement.

[0007] (2) Research on the mechanism of nanofillers enhancing the alkali resistance of EPDM is lacking, and research on carbon black / rubber interface regulation and its enhancement mechanism is of great significance. In-depth research on carbon black / rubber interface regulation methods, such as surface modification and interface compatibilizers, and clarifying the relationship between interface structure and material properties are of great significance for developing EPDM sealing materials with excellent alkali resistance and long service life.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] A method for improving the alkali aging resistance of EPDM rubber includes the following steps:

[0010] Modified carbon black is added to ethylene propylene diene monomer (EPDM) rubber; the modified carbon black is heat-modified carbon black and / or hydrophobic modified carbon black.

[0011] The preparation method of the heat-modified carbon black includes the following steps: heat-treating carbon black to obtain heat-modified carbon black; the heat treatment temperature is 800-900℃;

[0012] The preparation method of the hydrophobic modified carbon black includes the following steps: acid treatment of carbon black to obtain acid-treated carbon black; mixing the acid-treated carbon black, solvent and dopamine to carry out a first modification reaction to obtain dopamine-modified carbon black; mixing the dopamine-modified carbon black, alkyl isocyanate, polyethylene polyamine and solvent to carry out a second modification reaction to obtain hydrophobic modified carbon black.

[0013] Preferably, the heat treatment holding time is 2 to 5 hours, and the heating rate to the heat treatment temperature is 5 to 10 °C / min.

[0014] Preferably, the acid used in the acid treatment is sulfuric acid, and the acid treatment temperature is 80-90°C for 8-10 hours;

[0015] The mass ratio of the acid-treated carbon black to the dopamine is 20:5-6; the first modification reaction takes 48-50 hours.

[0016] Preferably, the mass ratio of the dopamine-modified carbon black to the alkyl isocyanate is 20:25-26; the alkyl group in the alkyl isocyanate has 15-20 carbon atoms; the polyethylene polyamine is triethylenediamine; the mass ratio of the dopamine-modified carbon black to the polyethylene polyamine is 20:2-5; and the second modification reaction time is 40-60°C.

[0017] Preferably, the carbon black used to prepare the thermally modified carbon black and the hydrophobic modified carbon black is of type N234.

[0018] Preferably, the modified carbon black is filled at 30-50% of the mass of the EPDM rubber matrix.

[0019] Preferably, the method further includes adding additives to the EPDM rubber, said additives including one or more of activators, plasticizers, antioxidants, crosslinking agents, and co-crosslinking agents.

[0020] The present invention also provides a rubber composition comprising the following components in parts by weight:

[0021] 100 parts EPDM rubber, 30-50 parts modified carbon black, 1-3 parts vulcanizing agent, 0.5-2 parts co-crosslinking agent, 2-5 parts activator, 0.5-1 part plasticizer, and 0.5-2 parts antioxidant;

[0022] Preferably, the rubber composition has the following composition by mass parts:

[0023] 100 parts EPDM rubber, 50 parts modified carbon black, 3 parts activator, 0.5 parts plasticizer, 2 parts antioxidant, 2 parts crosslinking agent, and 1 part co-crosslinking agent;

[0024] The modified carbon black is thermally modified carbon black and / or hydrophobic modified carbon black.

[0025] Preferably, the vulcanizing agent comprises one or two of dicumyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; the co-crosslinking agent comprises one or two of triallyl isocyanurate and triallyl cyanurate; the activator comprises one or two of zinc oxide and calcium carbonate; the plasticizer comprises one or two of stearic acid and polyester; and the antioxidant comprises one or two of 2-mercaptobenzimidazole and 2,2,4-trimethyl-1,2-dihydroquinoline polymer.

[0026] By grafting octadecyl isocyanate onto the surface of carbon black to achieve hydrophobic treatment, the contact between alkali and rubber is reduced, which greatly improves the alkali resistance of rubber.

[0027] By specifically modifying the surface of carbon black, the stability of EPDM rubber in harsh alkaline environments is improved. For example, after aging for 3 days in 25% NaOH solution at 160℃, the tensile strength retention rate of EPDM rubber is ≥92.21%, and the elongation at break retention rate is ≥90.8%.

[0028] The seals made from EPDM rubber obtained by the method of the present invention are suitable for alkaline conditions, such as the O-ring structure which is suitable for alkaline conditions of 4±0.3MPa and 80-160℃.

[0029] The seal made of EPDM rubber obtained by the method of the present invention has a compression set of ≤17% under frequent start-stop conditions.

[0030] The present invention has the following beneficial technical effects:

[0031] (1) This invention studied the effects of four different conditions, namely NaOH concentration, temperature, aging time and carbon black filling, on the alkali resistance of EPDM. Among them, the increase of NaOH concentration, temperature and aging time will deepen the aging of rubber. However, the filling of carbon black is an important factor affecting the alkali resistance of rubber. Although the tensile strength and elongation at break of rubber are improved, the performance decline rate of the sample after alkaline aging is about 20% higher than that of unfilled carbon black rubber.

[0032] (2) This invention investigated the effect of carbon black on the aging behavior of rubber materials under alkaline conditions. Seven different carbon blacks were added to EPDM, and their performance changes before and after air and alkaline aging were compared. The study found that the alkali resistance of rubber is mainly related to carbon black, and the particle size and surface properties of carbon black are the main factors affecting the alkali resistance of rubber. The carbon black N234 with the best alkali resistance was selected, and its surface was specifically chemically modified to improve the stability of rubber in harsh alkaline environments.

[0033] (3) The present invention found that carbon black contains carboxyl groups on its surface, which are highly polar and can promote the dispersion of carbon black in rubber and easily react with alkali. If the content of carboxyl groups on the surface of carbon black is low, the alkali resistance of the rubber is better. The present invention heat-treats carbon black to remove the carboxyl groups on the surface of carbon black at high temperature, thereby avoiding its reaction with alkali and thus extending the alkali resistance aging performance of rubber. In addition, carbon black has a large specific surface area and easily adsorbs alkali solution, which increases the contact between rubber and alkali solution and also leads to a decrease in the alkali resistance of rubber. The present invention performs hydrophobic modification on carbon black to reduce the adsorption of alkali solution by carbon black, thereby reducing the contact between alkali and rubber and greatly improving the alkali resistance of rubber.

[0034] In summary, this invention performs specific chemical modifications on the surface of carbon black and fills the modified carbon black into EPDM rubber, which can improve the stability of EPDM rubber in harsh alkaline environments and extend its service life when used as a sealant in alkaline electrolytic cells. Attached Figure Description

[0035] Figure 1 The changes in mass and volume of rubber after aging with different NaOH concentrations are shown in Example 1.

[0036] Figure 2 The changes in rubber strength and elongation retention after aging with different NaOH concentrations in Example 1 are shown.

[0037] Figure 3 The diagram shows the contact angles of the rubber in Example 1 after aging at different NaOH concentrations.

[0038] Figure 4 The change in contact angle of the rubber after aging at different NaOH concentrations in Example 1;

[0039] Figure 5 The permanent compression set of aged rubber at different concentrations in Example 1;

[0040] Figure 6 The changes in mass and volume of rubber after aging at different temperatures in Example 1 are shown.

[0041] Figure 7 The changes in rubber strength and elongation loss after aging at different temperatures in Example 1 are shown.

[0042] Figure 8 The contact angle of the rubber in Example 1 after aging at different temperatures is shown.

[0043] Figure 9 The contact angle of the rubber in Example 1 after aging at different temperatures is shown.

[0044] Figure 10 The permanent compression deformation of rubber at different aging temperatures in Example 1;

[0045] Figure 11 The change rate of rubber mass and volume after aging for different aging times in Example 1;

[0046] Figure 12 The changes in rubber strength and elongation loss rate under different aging times in Example 1;

[0047] Figure 13 The contact angle of the rubber in Example 1 after aging at different aging times is shown.

[0048] Figure 14 The diagram shows the contact angles of the rubber in Example 1 after aging at different aging times.

[0049] Figure 15 The permanent compression deformation of rubber under different aging times in Example 1;

[0050] Figure 16 The strength and elongation loss of EPDM without carbon black (Figure a) and with carbon black filled (Figure b) in Example 1 after aging in NaOH solution at different temperatures are shown.

[0051] Figure 17 The compression set of unfilled and filled carbon black rubbers in Example 1 after aging in NaOH solution at different temperatures;

[0052] Figure 18 The results of the compression set test at room temperature for EPDM rubber filled with seven different types of carbon black in Example 2;

[0053] Figure 19 The changes in mass and volume (a) and hardness (b) of EPDM rubber filled with seven different types of carbon black in Example 2 after alkaline aging;

[0054] Figure 20 XPS spectra of different types of carbon black in Example 2;

[0055] Figure 21 XPS peak diagrams of C1s for different types of carbon black in Example 2;

[0056] Figure 22 The microstructures of EPDM filled with seven types of carbon black (a) N220, (b) N234, (c) N330, (d) N354, (e) N550, (f) N774, and (g) N990 in Example 2 are shown in their original state (1), air aging (2), and alkali aging (3).

[0057] Figure 23 Figure a shows the changes in mass volume (Figure a) and hardness (Figure b) of EPDM rubber filled with different carbon blacks under air aging in Example 2.

[0058] Figure 24 The states of carbon black in water before and after surface hydrophobic modification (aCB) in Example 3;

[0059] Figure 25 This is a physical image of the O-ring seal simulation mold used in Example 3;

[0060] Figure 26 The pressure change in the reactor during the simulated alkaline electrolysis cell sealing experiment in Example 3;

[0061] Figure 27 XPS peak diagrams of C1s for modified carbon blacks gCB, nCB, kCB, and hCB in Example 3;

[0062] Figure 28 The XPS peak diagrams of C1s and N1s of aCB in Example 3 are shown.

[0063] Figure 29 Fourier transform infrared spectra of different modified carbon blacks in Example 3;

[0064] Figure 30 The strength and elongation changes of EPDM rubbers filled with different modified carbon blacks in Example 3 after hot air aging;

[0065] Figure 31 The changes in strength and elongation of EPDM rubber filled with different modified carbon blacks after alkaline aging in Example 3 are shown.

[0066] Figure 32 The O-rings before and after experimental aging in Example 3;

[0067] Figure 33 The values ​​represent the changes in strength and elongation of different O-rings after aging in Example 3. Detailed Implementation

[0068] This invention provides a method for improving the alkali aging resistance of ethylene propylene diene monomer (EPDM) rubber, comprising the following steps:

[0069] Modified carbon black is added to ethylene propylene diene monomer (EPDM) rubber; the modified carbon black is heat-modified carbon black and / or hydrophobic modified carbon black.

[0070] In this invention, the preferred carbon black type used to prepare both the thermally modified carbon black and the hydrophobic modified carbon black is N234.

[0071] In this invention, the method for preparing the heat-modified carbon black includes: heat-treating carbon black to obtain heat-modified carbon black; the heat treatment temperature is 800-900℃, specifically 800℃, 850℃, or 900℃; the heating rate to the heat treatment temperature is preferably 5-10℃ / min; the heat treatment holding time is preferably 2-5h, specifically 2h, 3h, 4h, or 5h; the heat treatment is preferably carried out in a protective atmosphere; the protective atmosphere is preferably nitrogen; the heat treatment is preferably carried out in a tube furnace; under the above conditions, the present invention can remove the carboxyl groups on the surface of carbon black, reduce the chance of it reacting with alkali solution, and thus improve the alkali aging resistance of rubber.

[0072] In this invention, the preparation method of the hydrophobic modified carbon black includes:

[0073] Carbon black is acid-treated to obtain acid-treated carbon black.

[0074] The acid-treated carbon black, solvent, and dopamine are mixed to carry out a first modification reaction to obtain dopamine-modified carbon black;

[0075] The dopamine-modified carbon black, alkyl isocyanate, polyethylene polyamine, and solvent are mixed to carry out a second modification reaction to obtain hydrophobic modified carbon black.

[0076] This invention involves acid treatment of carbon black to obtain acid-treated carbon black. In this invention, the acid used for acid treatment is preferably sulfuric acid, with a concentration preferably between 30% and 70%; the preferred ratio of carbon black to sulfuric acid is 2g:40-50mL; the preferred temperature for acid treatment is 80-90℃, specifically 80℃, 85℃, or 90℃; the preferred treatment time is 8-10 hours, specifically 8 hours, 9 hours, or 10 hours; the acid treatment is preferably carried out under stirring conditions; after the acid treatment, the solid product is preferably washed with deionized water to a pH of 6-6.5, followed by drying to obtain acid-treated carbon black; the preferred drying temperature is 40-60℃, and the preferred drying time is 10-12 hours.

[0077] After obtaining acid-treated carbon black, the present invention mixes the acid-treated carbon black, solvent, and dopamine to carry out a first modification reaction to obtain dopamine-modified carbon black. In the present invention, the solvent is preferably tris(hydroxymethyl)aminomethane hydrochloride (Tris) buffer solution, and the pH value of the Tris buffer solution is preferably 7.0-9.2; the volume ratio of acid-treated carbon black to solvent is preferably 1g:50-60mL; the mass ratio of acid-treated carbon black to dopamine is preferably 20:5-6, specifically 20:5, 20:5.5, or 20:6; the present invention preferably first disperses the acid-treated carbon black in the solvent, then adds dopamine, mixes it evenly by ultrasonication, and then carries out the first modification reaction; the time of the first modification reaction is preferably 48-50h, specifically 48h, 49h, or 50h, and the first modification reaction can be carried out at room temperature. After the first modification reaction is completed, the solid product is preferably separated and then washed and dried. The washing agent is preferably deionized water, the washing is preferably repeated 3 to 4 times, the drying temperature is preferably 40 to 60°C, and the drying time is preferably 48 to 50 hours.

[0078] After obtaining dopamine-modified carbon black, the present invention mixes the dopamine-modified carbon black, alkyl isocyanate, polyethylenepolyamine, and solvent to carry out a second modification reaction to obtain hydrophobic modified carbon black. In the present invention, the mass ratio of the dopamine-modified carbon black to the alkyl isocyanate is preferably 20:25-26; the number of carbon atoms in the alkyl ester of the isocyanate is preferably 15-20, specifically 15, 16, 18, or 20, and more specifically, the alkyl isocyanate is preferably octadecyl isocyanate.

[0079] In this invention, the polyethylene polyamine is preferably triethylenediamine; the mass ratio of dopamine-modified carbon black to polyethylene polyamine is preferably 20:2 to 5, specifically 20:2, 20:3, or 20:4; the solvent is preferably DMF; the ratio of dopamine-modified carbon black to solvent is preferably 20g:500mL; the second modification reaction time is preferably 40 to 60°C, specifically 40°C, 50°C, or 60°C; the second modification reaction can be carried out at room temperature; the second modification reaction is preferably carried out in a protective atmosphere, preferably nitrogen. In a specific embodiment of this invention, it is preferable to first add dopamine-modified carbon black to a solvent and sonicate it to obtain a dispersion, then place the dispersion in a reaction apparatus, introduce nitrogen gas, and then add alkyl isocyanate and polyethylene polyamine to the reaction apparatus, and stir the reaction under nitrogen atmosphere. After the second modification reaction is completed, the present invention preferably centrifuges the obtained reaction solution to obtain a precipitate, and dries the precipitate to obtain the hydrophobic modified carbon black; the drying temperature is preferably 40-60℃, and the drying time is preferably 48-50h.

[0080] In this invention, the filling amount of the modified carbon black is preferably 30-50% of the mass of the EPDM rubber matrix, specifically 30%, 40%, 45% or 50%.

[0081] In this invention, the method for improving the alkali aging resistance of EPDM rubber further includes adding additives to EPDM rubber. The additives preferably include one or more of activators, plasticizers, antioxidants, crosslinking agents and co-crosslinking agents, and more preferably include activators, plasticizers, antioxidants, crosslinking agents and co-crosslinking agents simultaneously.

[0082] This invention does not have any special requirements for the method of adding modified carbon black and additives to EPDM rubber. The method is well known to those skilled in the art. The EPDM rubber, modified carbon black and additives are prepared into a compound and then vulcanized. The following is a detailed description.

[0083] The present invention also provides a rubber composition comprising the following components in parts by weight: 100 parts of EPDM rubber, 50 parts of modified carbon black, 3 parts of activator, 0.5 parts of plasticizer, 2 parts of antioxidant, 2 parts of crosslinking agent, and 1 part of co-crosslinking agent.

[0084] In this invention, the modified carbon black is thermally modified carbon black and / or hydrophobically modified carbon black; the preparation methods of the thermally modified carbon black and hydrophobically modified carbon black are the same as those described above, and will not be repeated here.

[0085] In this invention, the active agent is preferably zinc oxide; the plasticizer is preferably stearic acid (SA); the antioxidant includes 2-mercaptobenzimidazole (antioxidant MB) and 2,2,4-trimethyl-1,2-dihydroquinoline polymer (antioxidant RD), and the mass ratio of antioxidant RD to antioxidant MB is preferably 1:1; the crosslinking agent is preferably dicumyl peroxide (DCP); and the co-crosslinking agent is preferably triallyl isocyanurate (TAIC).

[0086] In this invention, the preferred method for preparing the rubber composition includes: placing ethylene propylene diene monomer (EPDM) rubber raw material into a two-roll mill for preliminary thin-pass plasticizing; subsequently adding antioxidant, plasticizer, activator, crosslinking agent and modified carbon black to the rubber; and finally adding a vulcanizing agent to obtain the desired compound; and vulcanizing the compound to obtain the rubber composition.

[0087] In this invention, the vulcanization temperature is preferably 170°C.

[0088] This invention also provides the application of the rubber composition described above in alkaline battery seals. The specific method of application is not particularly important; any method well-known to those skilled in the art is acceptable.

[0089] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0090] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0091] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0092] The sources of the raw materials and reagents used in the following examples are as follows: Ethylene propylene diene monomer (EPDM) rubber, grade 4045, Lanxess GmbH, Germany; Dicumyl peroxide (DCP), industrial grade (>95%), Shijiazhuang Fate Company; Triallyl isocyanate (TAIC), industrial grade (>95%), Aladdin; Carbon black N220, N234, N330, N550, N774, and N990, industrial grade (>95%), Cabot; Activated zinc oxide (ZnO), analytical grade (>99.5%), Shijiazhuang Pinbai Company; Stearic acid (SA), analytical grade (>99.5%), Tianjin Guangfu Company; 2,2,4-Trimethyl-1,2-dihydroquinoline polymer (antioxidant RD) ), Industrial grade (>95%), Aladdin; 2-mercaptobenzimidazole (antioxidant MB), Industrial grade (>95%), Aladdin; Sodium hydroxide (NaOH), potassium hydroxide (KOH), Analytical grade (>99.5%), Fuchen Company; Sulfuric acid (H2SO4), 98%, Beijing Chemical Plant; 4-Dimethylaminopyridine, Analytical grade (>99.5%), Maclean; Tris(hydroxymethyl)aminomethane hydrochloride (Tris), Reagent grade (≥99.0%), Aladdin; Dopamine (DA), 98%, Aladdin; N,N-Dimethylformamide (DMF), Analytical grade (>99.5%), Aladdin; Triethylenediamine (TEDA), 98%, Maclean; Octadecyl isocyanate, 90%, Aladdin.

[0093] Example 1: Effect of carbon black filler on the alkali aging resistance of ethylene propylene diene monomer (EPDM) rubber.

[0094] 1. Experimental Methods

[0095] 1.1 Rubber Formulation

[0096] The formulation of unfilled carbon black rubber is as follows: 100 parts EPDM; 3 parts ZnO; 0.5 parts SA; 1 part RD; 1 part MB; 2 parts DCP; 1 part TAIC.

[0097] The formulation of carbon black-filled rubber is as follows: 100 parts EPDM; 50 parts carbon black; 3 parts ZnO; 0.5 parts SA; 1 part RD; 1 part MB; 2 parts DCP; 1 part TAIC.

[0098] 1.2 Preparation of Rubber

[0099] After fully plasticizing the target amount of EPDM raw rubber on an SK-1608 open mill, the target amounts of processing aids, fillers (carbon black; carbon black is omitted for unfilled rubber), and crosslinking agent (DCP) were weighed and added to the raw rubber for mixing. Multiple thin-pass and triangular-wrap cutting processes were performed to obtain the compound. The vulcanization behavior of the rubber was evaluated at 170℃ using a rotorless vulcanizer. Using Tc90 as the standard, the compound was processed in an XLB-type flat vulcanizing machine to prepare 2mm thick rubber sheets and Φ10mm×10mm rubber cylinders. The rubber sheets were cut using a JC-1025 punching machine to produce standard dumbbell-shaped samples, which were then marked for subsequent experimental analysis.

[0100] 1.3 Preparation of NaOH solution

[0101] Weigh out different masses of 96% sodium hydroxide solid, add them to deionized water and stir with a glass rod to prepare NaOH solutions with mass fractions of 6.25%, 10%, 25%, and 50%, respectively.

[0102] 1.4 Alkaline aging test

[0103] The original mass, density, and hardness of the dumbbell-shaped rubber specimens and the height of the cylindrical specimens were measured. Then, the specimens were placed in a PTFE hydrothermal reactor, and a 25% (w / w) NaOH solution was added to ensure complete immersion. The reactor was then sealed and placed in a DHG-9075A electric thermostatic oven for accelerated aging at 160°C for 3 days. After completion, the reactor was removed, and after cooling to room temperature, it was opened, the specimens were removed, and the surfaces were cleaned in preparation for subsequent performance analysis.

[0104] 2. Detection Method

[0105] 2.1 Mass Change Rate Test

[0106] Remove the aged sample and clean it. Measure the mass M of the sample after aging using a JA3003J electronic balance. The formula for the rate of mass change is as follows:

[0107]

[0108] Where M0 is the original mass of the sample.

[0109] 2.2 Volume Change Rate Test

[0110] Remove the aged sample and clean it. Measure the volume V of the sample after aging using a solid density balance. The formula for the volume change rate is as follows:

[0111]

[0112] Where V0 is the original volume of the sample.

[0113] 2.3 Mechanical Performance Testing

[0114] Hardness: Hardness test was conducted in accordance with the national standard GB / T 531.1-2008.

[0115] Tensile strength and elongation at break: The tensile test was conducted at room temperature using a WDL-10 universal testing machine in accordance with GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanizates or thermoplastic rubbers".

[0116] 2.4 Surface property determination

[0117] The OCA15EC contact angle meter was used to test rubber materials, with distilled water as the test liquid. The experiment was conducted under controlled conditions (15℃, 50% relative humidity). The operation procedure is as follows: turn on the equipment, adjust the focus, place the sample, allow the droplet to contact, capture the image, and measure the contact angle using image analysis software.

[0118] 3. Test Results

[0119] 3.1 Effect of NaOH concentration on the alkali resistance of EPDM rubber

[0120] To investigate the effect of NaOH concentration on the alkaline aging of EPDM, unfilled EPDM rubber was placed in alkaline solutions with different NaOH concentrations (6.25%, 10%, 25%, and 50%) at 140℃ for three days and the changes in the rubber after aging were observed.

[0121] 3.1.1 Changes in volume, mass, and hardness of EPDM vulcanizate after aging

[0122] The test results are shown in Table 1 and Figure 1 As shown.

[0123] Table 1 shows that as the NaOH concentration increases, the mass, volume, and hardness of EPDM gradually decrease, indicating that the increased NaOH concentration enhances the corrosive effect on EPDM, causing a certain degree of breakage in the surface molecular chains, leading to a decrease in surface hardness. Figure 1 It can be seen that the higher the NaOH concentration, the faster the loss of mass and volume. It is speculated that the increase in concentration increases the probability of interaction between hydroxide ions and rubber molecular chains, causing the rubber molecular chains to be destroyed, which in turn leads to a reduction in mass and volume.

[0124] Table 1. Changes in hardness and mass / volume changes before and after aging with different NaOH concentrations.

[0125] Aging conditions Quality change rate / % Volume change rate / % hardness Not aged -- -- 55 Air -1.74 -1.85 55 6.25% NaOH -0.25 -0.18 55 10% NaOH -0.54 -0.43 54 25% NaOH -0.68 -0.79 53 50% NaOH -1.28 -1.18 53

[0126] 3.1.2 Changes in the mechanical properties of EPDM vulcanizates after aging

[0127] Aging leads to a decline in the mechanical properties of rubber, thereby causing rubber products to fail. To understand the changes in the mechanical properties of rubber under different NaOH concentrations, a tensile testing machine was used to test dumbbell-shaped rubber samples. The results are shown in Table 2 and... Figure 2 As shown in Table 2 and... Figure 2 The results showed that the tensile strength and elongation at break of the aged samples increased under air and low-concentration alkali (6.25%, 10%) conditions. When the NaOH concentration was higher (25%, 50%), the tensile strength and elongation at break of the rubber decreased, and the higher the concentration, the greater the decrease in mechanical properties.

[0128] Table 2 Comparison of mechanical properties before and after aging at different NaOH concentrations

[0129]

[0130] The above experimental results demonstrate that under air aging conditions, rubber undergoes a certain degree of cross-linking, resulting in a denser cross-linked network and enhanced molecular chain interactions. At lower NaOH concentrations, the tensile strength and elongation at break of the material slightly increase, indicating that at lower concentrations, the aging behavior of EPDM is consistent with short-term air aging, with cross-linking occurring first. Due to EPDM's good alkali resistance, lower concentrations of alkali solution do not cause molecular chain breakage. As the alkali concentration increases, the alkali's force on the rubber molecular chains gradually increases, accelerating rubber aging and severely damaging the rubber molecular chains, leading to breakage and a gradual decrease in rubber strength and elongation.

[0131] 3.1.3 Surface properties of EPDM vulcanizate after aging

[0132] Aging can cause irreversible damage to the rubber surface, thereby increasing the surface roughness. To understand the changes in the rubber surface caused by the increase of NaOH concentration after aging, contact angle tests were conducted on the rubber surface. Figure 3 , Figure 4 The change in surface contact angle of EPDM before and after aging in different concentrations of NaOH was determined based on... Figure 3 and Figure 4 It can be seen that the contact angle of the material surface decreases with increasing NaOH concentration, indicating that the material surface is corroded in the alkaline solution, the molecular backbone breaks down, resulting in a decrease in the number of carbon atoms in the backbone, increased water solubility, increased hydrophilicity of the material, and a decreased contact angle. Simultaneously, some NaOH may remain on the damaged surface and not be washed away, making the rubber surface more hydrophilic during testing, which also leads to a smaller contact angle.

[0133] 3.1.4 Compression set of EPDM vulcanizate after aging

[0134] To investigate the changes in compression set of rubber after aging, cylindrical rubber samples were tested, and the results are as follows: Figure 5 As shown in the figure, it can be seen that as the NaOH concentration increases, the compression set of rubber first decreases and then increases.

[0135] Experimental results show that in low-concentration alkaline solutions, rubber mainly undergoes cross-linking. After aging, the cross-linked network becomes denser, with molecular chains intertwined. The compression process does not significantly damage the cross-linked structure, so when the force is removed, the rubber can recover some deformation through its own elasticity. As the alkaline concentration increases, the rubber molecular chains undergo a certain degree of degradation and breakage after aging, resulting in weaker interactions between the chains. Under external forces, they easily slip, and therefore cannot recover on their own after the pressure is removed, leading to permanent deformation and increased permanent compression set.

[0136] In subsequent alkaline aging experiments, a 50% sodium hydroxide solution was used.

[0137] 3.2 Effect of aging temperature on the alkali resistance of EPDM rubber

[0138] 3.2.1 Changes in volume, mass, and hardness of EPDM vulcanizate after aging

[0139] Table 3 shows the changes in mass, volume, and hardness of rubber after aging under different temperature conditions. The data shows that the rate of change in mass and volume of EPDM increases with increasing temperature.

[0140] Table 3. Changes in hardness and mass / volume change rates before and after aging at different temperatures.

[0141] Aging conditions Quality change rate / % Volume change rate / % hardness Not aged -- -- 55 95℃ -0.803 -0.92 55 120℃ -0.86 -0.97 54 140℃ -1.28 -1.18 53 160℃ -1.53 -1.47 51

[0142] This result indicates that the aging process of EPDM intensifies with increasing aging temperature. The hardness of EPDM gradually decreases with increasing temperature, suggesting that, on the one hand, higher temperatures cause additives to precipitate out of the rubber, reducing their reinforcing effect; on the other hand, higher temperatures intensify the reaction, causing corrosion and damage to the material surface by alkaline solutions, leading to a decrease in hardness. Figure 6 The graph shows the rate of change in mass and volume of rubber after aging. As the temperature increases, the slope of the graph gradually increases, indicating that the aging rate gradually accelerates with increasing temperature, and the damage to the material is more severe at high temperatures.

[0143] 3.2.2 Changes in the mechanical properties of EPDM vulcanizates after aging

[0144] Table 4 and Figure 7The data present experimental data on the mechanical properties of rubber after aging at different aging temperatures. It can be seen that in a concentrated alkaline environment, the tensile strength and elongation of EPDM gradually decrease with increasing temperature, and the higher the temperature, the faster the rubber properties are lost.

[0145] Table 4 Changes in the mechanical properties of rubber under aging at different temperatures

[0146]

[0147] This result can be analyzed from the following perspectives: From the perspective of the material itself, the increased temperature enhances the movement of rubber molecular chains and weakens the intermolecular forces, making the molecular structure of rubber materials more susceptible to changes. From the perspective of alkaline solutions, the higher the temperature, the more reactive the hydroxide ions become, and the easier it is for them to react with other substances. Therefore, rubber molecules at high temperatures are more likely to break down in alkaline solutions, generating free radicals and other reactive substances, leading to a rapid decline in the mechanical properties of rubber.

[0148] 3.2.3 Surface properties of EPDM vulcanizates after aging

[0149] Figure 8 , Figure 9 The figure shows the change in contact angle of EPDM before and after aging in alkaline solutions at different temperatures. It can be seen that as the temperature increases, the contact angle of the sample surface gradually decreases, and the higher the temperature, the greater the decrease in contact angle.

[0150] The results of this experiment indicate that high temperature and high concentration of strong alkali accelerate the breakage of rubber molecular chains. Furthermore, the movement and diffusion of the broken molecular chains are faster at high temperatures, resulting in a more irregular microstructure and increased surface roughness, leading to a smaller contact angle. Aging also alters the surface energy of rubber, making it easier for water droplets to wet the rubber, thus further reducing the contact angle.

[0151] 3.2.4 Compression set after aging of EPDM vulcanizate

[0152] Figure 10 The graph shows the changes in compression set of EPDM before and after alkali aging at different temperatures. As can be seen from the graph, the higher the aging temperature, the greater the compression set of the rubber. This result is mainly because the cross-linked structure of the rubber is easily destroyed at high temperatures, causing molecular chains to break and transfer, weakening the intermolecular forces, and making the rubber structure more loose and difficult to return to its original state. Furthermore, the higher the temperature, the more intense the thermal motion of the molecular chains, and the easier it is for the molecular chains to slip, causing plastic deformation in the rubber material that cannot be recovered. At the same time, at high temperatures, additives in the rubber may become ineffective, weakening the rubber's resistance to deformation, which also increases the compression set.

[0153] In subsequent alkaline aging experiments, the aging temperature was 140℃.

[0154] 3.3 Effect of aging time on the alkali resistance of EPDM rubber

[0155] To investigate the effect of different aging times on the alkaline aging of EPDM, unfilled EPDM rubber samples were placed in a 50% NaOH solution at 140℃ for 3 days, 5 days, and 7 days of aging, and the changes in rubber properties before and after aging were compared.

[0156] 3.3.1 Changes in volume, mass, and hardness of EPDM vulcanizate after aging

[0157] Table 5 shows the changes in mass, volume, and hardness of rubber after aging at different aging times. Figure 6 The data shows the rate of change in mass and volume of EPDM after aging for different aging times. The data indicates that extending the aging time leads to an increase in the rate of change in both mass and volume, suggesting that the aging process of EPDM intensifies over time. Furthermore, the hardness of EPDM gradually decreases with increasing aging time.

[0158] Table 5. Changes in rubber hardness and mass / volume change rates at different aging times.

[0159] Aging conditions Quality change rate / % Volume change rate / % hardness Not aged 55 3d -1.16 -1.16 53 5d -1.47 -1.68 52 7d -1.82 -2.04 52

[0160] This indicates that long-term aging leads to the breakage of rubber molecular chains and the relaxation of the internal structure, thereby weakening intramolecular interactions and reducing the overall hardness of the material. Figure 11 It can be seen that the mass loss rate of EPDM after aging is greater than the volume loss rate. This is presumably because the molecular chains inside the rubber break and decompose, resulting in a decrease in mass after aging. At the same time, changes in the molecular chain structure may cause some cracks and voids in the material, which will increase some space, thus making the measured volume larger than the actual volume, resulting in a smaller calculated volume loss degree and loss rate.

[0161] 3.3.2 Changes in the mechanical properties of EPDM vulcanizates after aging

[0162] Table 6 shows the changes in the mechanical properties of rubber after aging at different aging times. Figure 12 The changes in rubber strength and elongation loss rate at different aging times are shown in Table 6. Figure 12 It can be seen that in high-concentration alkaline solutions, the tensile strength and elongation at break of EPDM gradually decrease with prolonged aging time. Figure 12 It can be seen that the longer the aging time of EPDM, the faster the tensile strength and elongation at break decrease.

[0163] Table 6. Changes in the mechanical properties of rubber at different aging times.

[0164]

[0165] This experimental result is primarily due to the fact that longer aging times result in longer exposure of EPDM to temperature and alkali, leading to severe damage to the internal molecular structure of the rubber. Simultaneously, the exposure of the rubber to external factors such as oxygen also increases, further damaging the rubber's molecular structure. Secondly, with increasing aging time, microscopic defects generated in the EPDM molecular chains gradually accumulate. These defects, through long-term accumulation and diffusion, accelerate the aging process of the rubber. Therefore, the rate of performance degradation in rubber increases rapidly with aging time.

[0166] 3.3.3 Surface properties of EPDM vulcanizates after aging

[0167] Figure 13 , Figure 14 The changes in the contact angle of EPDM before and after aging in alkaline solution for different times are shown. It can be seen that the rubber contact angle gradually decreases with increasing aging time. Compared with the results in 3.2.3, it can be seen that aging temperature has a more significant impact on rubber properties than aging time. This phenomenon is mainly because as temperature increases, the activity of the molecular chains increases, making diffusion easier and facilitating the breakage of rubber molecular chains—a rapid process. In contrast, as aging time increases, the rubber is exposed to alkaline solution for a longer period, leading to continuous breakage of the main chain and a gradual increase in surface roughness—a gradual, cumulative process.

[0168] 3.3.4 Compression set after aging of EPDM vulcanizate

[0169] Figure 15The compression set of rubber after aging at different aging times is shown. It can be seen that the compression set of EPDM increases with prolonged aging time. Compression set primarily characterizes the resilience of rubber materials. Rubber's elasticity is mainly due to the loose cross-linking structure between rubber molecular chains and the resulting intermolecular slippage. When rubber is subjected to compressive stress, displacement occurs between molecules, stretching the molecular chains and creating stress. However, due to the inherent freedom and high degree of arrangement of the molecular chains, rubber exhibits good resilience and quickly returns to its original shape. However, when rubber is subjected to compressive stress for a prolonged period, continuous displacement and slippage occur between the molecular chains, leading to rearrangement and repeated structural changes. This results in the intertwining or confinement of rubber molecular chains, preventing them from fully returning to their original shape, resulting in permanent deformation, i.e., compression set. With increasing aging time, these changes in molecular structure accumulate and intensify, leading to increasingly pronounced compression set and ultimately causing the rubber material to lose its original elasticity, exhibiting plastic deformation or hardening cracks. Therefore, the longer the aging time, the more accumulated changes and rearrangements occur in the molecular chain structure of the rubber material, resulting in greater compression set.

[0170] The aging time in the subsequent alkaline aging experiments was 3 days.

[0171] 3.4 Effect of Carbon Black Filler on Alkali Resistance of EPDM Rubber

[0172] 3.4.1 Changes in volume, mass, and hardness before and after alkaline aging

[0173] The changes in volume, mass, and hardness of EPDM rubber before and after alkaline aging were tested for both unfilled and carbon black-filled materials. The results are shown in Tables 7 and 8.

[0174] Table 7. Hardness changes and mass and volume change rates of unfilled carbon black EPDM rubber after alkaline aging at different temperatures.

[0175] Aging conditions Quality change rate / % Volume change rate / % hardness Not aged -- -- 55 120℃ -0.56 -0.64 54 140℃ -0.68 -0.79 53 160℃ -0.78 -0.83 52

[0176] Table 8. Changes in hardness and mass / volume change rates of carbon black-filled EPDM rubber after alkaline aging at different temperatures.

[0177] Aging conditions Quality change rate / % Volume change rate / % hardness Not aged -- -- 59 120℃ -0.56 -0.64 59 140℃ -0.69 -0.79 60 160℃ -0.66 -0.77 59

[0178] As can be seen from Tables 7 and 8, the hardness of rubber increases after carbon black is added, indicating that the addition of carbon black increases the cross-linking of rubber and increases the interaction between rubber molecular chains. However, the change rate of mass and volume is not large, indicating that the addition of carbon black mainly acts as a physical cross-linking point, and the rubber molecular chains are not accelerated to decompose. The aging process only weakens the interaction between the rubber and carbon black interface.

[0179] 3.4.2 Changes in the mechanical properties of EPDM vulcanizates after alkaline aging

[0180] The changes in mechanical properties of unfilled and carbon black-filled EPDM rubber before and after alkaline aging were tested, and the results are shown in Tables 9 and 10.

[0181] Table 9 Mechanical properties of unfilled carbon black EPDM rubber before and after alkaline aging at different temperatures

[0182]

[0183] Table 10 Mechanical properties of carbon black-filled EPDM rubber before and after alkaline aging at different temperatures

[0184]

[0185]

[0186] Figure 1 The strength and elongation loss of EPDM rubbers without carbon black (a) and filled with carbon black (b) after alkaline aging at different temperatures.

[0187] As can be seen from the data in Tables 9 and 10, the tensile strength and elongation at break of EPDM rubber are significantly improved after being filled with carbon black due to the reinforcing effect of the carbon black. Combined with... Figure 16 It can be seen that after soaking in NaOH solution, the tensile strength and elongation at break of carbon black-filled rubber decreased sharply, and the loss in strength and elongation was much greater than that of unfilled carbon black rubber.

[0188] The above results indicate that the addition of carbon black significantly affects the alkali resistance of EPDM, leading to a decrease in the alkali resistance of the rubber. One possible reason is that carbon black has many oxygen-containing functional groups on its surface. Under normal circumstances, these functional groups may react chemically with the rubber matrix to form chemical bonds or form hydrogen bonds through physical adsorption. However, under the influence of strong alkalis, these carbon black-rubber bonding points are disrupted, weakening the interfacial forces between the rubber and carbon black, thus affecting the reinforcing effect of carbon black on the rubber. Consequently, the tensile strength and elongation at break deteriorate after aging. Another reason is that carbon black itself has a large specific surface area and can adsorb chemical substances. The addition of carbon black adsorbs alkaline substances, increasing the chance of interaction between the rubber and the alkali, thus accelerating the aging of the rubber.

[0189] 3.4.3 Changes in compression set of EPDM vulcanizate before and after alkaline aging

[0190] The compression set properties of unfilled and carbon black-filled EPDM rubbers were tested before and after alkaline aging. The results are as follows: Figure 17 As shown. According to Figure 17It can be observed that adding carbon black improves the compression set of rubber. The porous surface and large specific surface area of ​​carbon black promote its effective bonding with uncured rubber, forming a stable carbon black gel network structure, which reinforces the rubber material. Because the addition of carbon black restricts the sliding of molecular chains, it enhances the mechanical strength, hardness, and abrasion resistance of the vulcanized rubber, resulting in superior resistance to deformation and consequently reduced permanent deformation under compression. It can also be seen that the change in compression set of rubber is greater after carbon black filling compared to unfilled rubber. This is mainly because the addition of carbon black, under the action of strong alkali, disrupts the carbon black-rubber interface, weakening the reinforcing effect of carbon black, leading to poorer resistance to deformation and a greater change in compression set.

[0191] 4. Conclusion

[0192] By investigating the effects of four different conditions—NaOH concentration, temperature, aging time, and carbon black filling—on the alkali resistance of EPDM, the following conclusions were drawn: (1) In low-concentration NaOH solution, EPDM mainly undergoes cross-linking reaction during aging, resulting in increased hardness and decreased compression set. As the NaOH concentration increases, the aging mechanism of EPDM gradually changes from cross-linking to molecular chain breakage. The higher the NaOH concentration, the stronger the corrosiveness to EPDM, and the greater the performance degradation after aging. (2) Temperature has a significant impact on the aging of EPDM in alkaline environments. The higher the temperature, the faster the aging rate of EPDM, the rougher the surface, and the greater the compression set. (3) The longer the aging time, the longer the EPDM is subjected to NaOH corrosion, leading to an increase in internal defects. The continuous accumulation of these defects accelerates the aging of EPDM, resulting in a faster decline in the mechanical and surface properties of EPDM. (4) Carbon black has the greatest impact on the alkali resistance of EPDM. Under the same aging conditions, the mechanical properties of EPDM without carbon black filling decrease by about 20% less after aging than those of EPDM with carbon black filling, and the difference is greater at higher temperatures. It is speculated that the interfacial interaction between carbon black and rubber is disrupted under alkaline conditions, which weakens the reinforcing effect of carbon black.

[0193] The above experiments show that carbon black is the biggest factor affecting the alkali resistance of EPDM. Modifying carbon black to improve the alkali aging resistance of rubber is of great practical significance for improving the stability of alkaline electrolytic cells and extending the service life of seals.

[0194] Example 2: The effect of carbon black type on the aging of EPDM rubber under alkaline conditions

[0195] 1. Preparation of experimental samples

[0196] 1.1 Rubber Preparation

[0197] The preparation method is the same as that in Example 1, Section 1.2.

[0198] 1.2 Basic Formula

[0199] EPDM 100 parts; Carbon black 50 parts; ZnO 3 parts; SA 0.5 parts; RD 1 part; MB 1 part; DCP 2 parts; TAIC 1 part.

[0200] 1.3 Preparation of NaOH solution

[0201] Weigh out different masses of 96% sodium hydroxide solid, add them to deionized water and stir with a glass rod to prepare NaOH solutions with a mass fraction of 25%.

[0202] 2. Aging Resistance Test Methods

[0203] 2.1 Alkaline aging test

[0204] The experimental method is the same as that in Example 1, Section 1.4.

[0205] 2.2 Air Aging Test

[0206] The test sample was placed in an electric constant temperature drying oven, and the aging temperature and time were the same as those for alkaline aging.

[0207] 3. Detection Method

[0208] 3.1 Mass Change Rate Test

[0209] The test method is the same as that in Example 1, Section 2.1.

[0210] 3.2 Volume Change Rate Test

[0211] The test method is the same as that in Example 1, Section 2.2.

[0212] 3.3 Mechanical Performance Testing

[0213] The test method is the same as the test method in 2.3 of Example 1.

[0214] 3.4 Crosslinking density test

[0215] The crosslinking density was tested using the equilibrium swelling method. First, the rubber was cut into pieces of approximately 1g each and immersed in an acetone solution. After equilibrium was reached, the mass and density were measured. The formula for calculating the crosslinking density is shown below:

[0216]

[0217]

[0218] The quantities in the formula are represented as follows:

[0219] ve Crosslinking density; χ: Interaction parameter between EPDM and cyclohexane; V R : The volume of the EPDM itself; V s : Molar volume of cyclohexane; M i : Mass of unswollen EPDM; V r : Volume of EPDM after swelling; v sol : Volume of cyclohexane in EPDM after swelling; M f : Total mass of EPDM after swelling; ρ s : Density of cyclohexane.

[0220] 3.5 Microscopic Morphology Characterization

[0221] The microstructure of the EPDM rubber cross-section before and after aging was observed using a SU8010 cold field emission scanning electron microscope (SEM). Due to the poor conductivity of the polymer material, gold sputtering was required. The sample preparation method for the SEM was as follows: The thin film was immersed in liquid nitrogen for 5 minutes to promote fracture using liquid nitrogen cryogenic fracture technology. Then, the sample was rapidly fractured using tweezers in a liquid nitrogen environment. Subsequently, the fractured surface was fixed to the sample holder with the fractured surface facing upwards, and gold sputtering was performed on the surface.

[0222] 3.6 X-ray photoelectron spectroscopy (XPS)

[0223] Take appropriate amounts of dried carbon black, press them into tablets on a tablet press, attach them to a sample tray, and use an AMICUS X-ray photoelectron spectroscopy instrument to test the bonding mode and elemental content of the surface groups of the carbon black before and after modification.

[0224] 4. Experimental Results

[0225] 4.1 Influence of different types of carbon black on the physical and mechanical properties of rubber

[0226] To understand the differences in physical and mechanical properties of EPDM rubber filled with different types of carbon black, mechanical property tests were conducted on EPDM rubber samples filled with different types of carbon black. Table 11 shows the relevant parameters for different grades of carbon black, and Table 12 shows the performance changes of EPDM rubber after being filled with seven different types of carbon black.

[0227] Table 11 Relevant parameters of different grades of carbon black

[0228] Iodine uptake value (g / kg) <![CDATA[Oil absorption value / (10 -5 m 3 / kg)]]> Particle size / nm <![CDATA[Nitrogen adsorption specific surface area / (m 2 / g)]]> N220 121 114 20 118 N234 120 125 22 128 N330 82 102 30～50 81 N550 43 121 50～150 44 N774 29 72 80～170 34 N990 10 43 280 9

[0229] Table 12 Comparison of Mechanical Properties of EPDM Rubber Filled with Different Carbon Blacks

[0230]

[0231]

[0232] As can be seen from the data in Tables 11 and 12, N990 has a large particle size and a small specific surface area, making it a non-reinforcing rubber. Therefore, its tensile strength, elongation at break, and hardness are generally lower than those of other carbon blacks. Furthermore, the smaller the carbon black particle size and the larger the specific surface area, the stronger its reinforcing effect on the rubber.

[0233] Compression set is an effective measure of the elasticity of rubber materials and the degree of recovery of rubber molecules after deformation. Figure 18 The results of compression set tests on rubber filled with 50 parts of seven different carbon blacks at room temperature are presented. Figure 18 It can be seen that N990 carbon black has the lowest compression set. This is mainly because N990 carbon black has a large particle size and small specific surface area, resulting in less interaction between the carbon black particles and the rubber matrix. This leads to less heat generation and lower viscosity during processing, resulting in lower shear forces. Therefore, the processing does not damage the rubber molecular chains, maintaining the rubber's good elasticity and resulting in a low compression set. However, its reinforcing effect is poor, and its overall performance is not good. Secondly, N234 carbon black has the lowest compression set. Considering tensile strength and hardness, N234 carbon black possesses better reinforcing properties.

[0234] 4.2 Effect of Carbon Black Type on Alkali Resistance of EPDM

[0235] 4.2.1 Changes in mass, volume, and hardness

[0236] Because aging causes changes in the molecular structure of rubber, resulting in changes in mass, volume, and hardness to a certain extent, this study aims to investigate the changes that occur in samples after aging. Figure 19 The changes in mass, volume, and hardness of rubber after alkali aging were shown after being filled with different types of carbon black.

[0237] according to Figure 19 It can be seen that N234 carbon black exhibits the smallest change in the mass and volume of rubber filled with it, demonstrating good alkali resistance. Furthermore, the mass change generally shows a pattern of first increasing and then decreasing with increasing particle size. From the perspective of particle size, this is mainly because smaller particle sizes result in a larger specific surface area of ​​carbon black, leading to stronger bonding with the rubber matrix and less damage to the carbon black-rubber matrix interface under alkaline conditions. As the particle size increases, the bonding ability between carbon black particles and the rubber matrix weakens, and the degree of alkali-induced damage to the carbon black-rubber interface increases. When the particle size increases to a certain extent, carbon black can no longer reinforce the rubber matrix (e.g., N990). At this point, the interfacial bonding ability between carbon black particles and the rubber matrix is ​​already very weak without external damage, so the change in the mass and volume of rubber after alkali aging is not significant. Except for N990, the hardness changes of all carbon blacks are similar.

[0238] 4.2.2 Changes in mechanical properties

[0239] Table 13 compares the mechanical properties of EPDM rubber filled with different types of carbon black after alkaline aging. As shown in Table 13, N234 carbon black-filled rubber exhibits relatively small changes in mechanical properties after alkali aging. Combined with changes in mass, volume, and hardness, this indicates that N234 carbon black has the best alkali resistance. Compared to N220 and N234, the other carbon blacks have larger particle sizes, smaller specific surface areas, and weaker reinforcing effects, suggesting that increased particle size and specific surface area may lead to decreased alkali resistance. While N220 and N234 have similar particle sizes and specific surface areas, N234 exhibits better alkali resistance than N200, indicating that the type and number of functional groups on the carbon black surface also affect the alkali resistance of the filled rubber.

[0240] Table 13 Comparison of Mechanical Properties of Seven Types of Carbon Black-Filled EPDM Rubber After Alkali Aging

[0241] N220 N234 N330 N354 N550 N774 N990 Tensile strength / MPa 17.01 19.46 18.1 18.54 16.5 15.6 9.31 Intensity change rate / % -18.69 -18.23 -26.18 -16.67 -25.57 -28.63 -18.76 Elongation at break / % 455.84 443.77 380.29 518.97 319.06 366.73 380.49 Elongation change rate / % -16.14 -15.01 -25.84 -22.05 -25.34 -22.82 -18.92

[0242] 4.2.3 X-ray photoelectron spectroscopy

[0243] To investigate the effect of carbon black surface properties on alkali resistance, XPS tests were conducted on different types of carbon black. Figure 20 Tables 1 and 14 show the XPS full spectrum and surface element content of different carbon blacks. It can be seen that starting from N330, the number of oxygen-containing groups on the surface increases with increasing particle size. Compared with N220, N234 has a lower oxygen content. Therefore, under the same conditions, the fewer oxygen-containing groups on the surface, the fewer active sites on the carbon black surface that can react with alkali, and the stronger the alkali resistance.

[0244] Table 14 Elemental Content of Seven Types of Carbon Black

[0245] Element content / % N220 N234 N330 N354 N550 N774 N990 C 94.39 96.83 97.72 97.06 96.45 95.26 92.37 O 5.61 3.17 2.28 2.94 3.55 4.74 7.63

[0246] To investigate in detail the types and proportions of functional groups on the surface of different carbon black samples, the following studies were conducted: Figure 20 Peak fitting was performed on the C1s spectrum, and the corresponding peak distribution and quantitative results were obtained. Figure 21 As shown in Table 15, it can be seen that the types of functional groups on the surface of each carbon black are basically the same. Besides the C-C bonds with a binding energy of approximately 284.8 eV, the main functional groups are carboxyl groups with a binding energy of approximately 288.8 eV and hydroxyl groups with a binding energy of approximately 286.5 eV. The content of functional groups varies among the carbon blacks; N234 carbon black has the lowest carboxyl group content. Therefore, under similar conditions, the lower the surface carboxyl group content, the stronger the alkali resistance of the vulcanizate.

[0247] Table 15 Content of surface functional groups in different carbon blacks

[0248] CC / % C-OH / % OC = O / % N220 76.39 13.16 10.45 N234 81.81 11.44 6.75 N330 79.49 11.12 9.39 N354 78.98 11.98 9.04 N550 79.98 8.75 11.27 N774 77.43 10.81 11.76 N990 80.83 10.84 8.33

[0249] 4.2.4 Changes in crosslinking density

[0250] Table 16 shows the changes in crosslinking density of vulcanized EPDM rubber with different carbon black fillers before and after alkaline aging. The results in Table 16 show that the crosslinking density of all carbon black-filled rubbers decreased.

[0251] Table 16 Changes in crosslinking density of EPDM rubber filled with seven types of carbon black under alkaline aging.

[0252] <![CDATA[Before aging (×10 -4 )]]> <![CDATA[After aging (×10 -4 )]]> N220 2.06 1.66 N234 2.41 2.03 N330 2.32 1.47 N354 1.87 1.26 N550 3.19 2.13 N774 2.56 1.52 N990 2.89 2.05

[0253] This result, combined with XPS and infrared spectroscopy analysis, indicates that the decrease in crosslinking density is mainly due to the weakened interaction between carbon black and rubber. In carbon black-filled EPDM rubber systems, carbon black primarily forms an EPDM layer by adsorbing EPDM molecular chains on its surface, acting as physical crosslinking points. Under alkaline conditions, the active sites on the carbon black surface are destroyed by the alkali, weakening the carbon black's ability to adsorb EPDM molecular chains and preventing the formation of a dense crosslinked network, thus leading to a decrease in crosslinking density. Therefore, the decrease in crosslinking density reflects the weakening of the rubber network structure, which results in a decline in the mechanical properties of the rubber.

[0254] 4.2.5 Microscopic morphological changes

[0255] The microstructure of the EPDM aged samples after liquid nitrogen embrittlement treatment was analyzed using scanning electron microscopy (SEM). Figure 22 The images show the microstructures of EPDM rubber filled with different carbon blacks in its original state, after air aging, and after alkali aging. a1–g1 represent the original microstructures of EPDM rubber filled with N220, N234, N330, N354, N550, N774, and N990; a2–g3 represent the air aging microstructures of EPDM rubber filled with N220, N234, N330, N354, N550, N774, and N990; and a3–g3 represent the alkali aging microstructures of EPDM rubber filled with N220, N234, N330, N354, N550, N774, and N990.

[0256] contrast Figure 22 The following changes can be observed in the microstructure of the unaged and aged samples:

[0257] Unaged samples: The rubber surface was observed to be relatively smooth with low roughness and few defects, indicating a good interfacial interaction between carbon black and the rubber matrix.

[0258] Air-aged samples: The surface roughness of the material increased slightly and micro-defects such as pores began to appear, indicating that air aging damaged the rubber surface. However, the degree of damage was not significant and the impact on the rubber's performance was not yet significant.

[0259] Alkaline aging samples: The surface roughness of the samples increased, and the number of pores and defects increased significantly. As the carbon black particle size increased, the pore diameter also increased accordingly. N234 carbon black-filled EPDM showed relatively low surface roughness and no substantial defects were found, indicating that the carbon black filler maintained a relatively strong bond with the rubber matrix, suggesting good alkali resistance. In contrast, N220 carbon black-filled rubber, although having fewer pores, exhibited relatively high surface roughness. For N330 and N354 carbon black-filled rubbers, the increased number of pores indicated that the interfacial interaction between the carbon black and the rubber matrix was disrupted by alkali, weakening the rubber's alkali resistance, leading to increased defects and decreased performance. The increased size and number of large pores observed in N550, N774, and N990 carbon black-filled rubbers indicated a significant weakening of the interfacial interaction between larger carbon black particles and the rubber matrix, further weakening the reinforcing effect of the carbon black and severely impacting the overall performance of the rubber material.

[0260] 4.2.6 Hot air aging

[0261] Since the experiment was conducted in a high-temperature environment, and high-temperature aging affects the performance of rubber, in order to rule out that high temperature is the cause of the significant decline in rubber performance after aging, this invention conducted a hot air aging experiment. Figure 23 Table 17 shows the mass and volume changes (a) and hardness changes (b) of EPDM rubber filled with different carbon blacks after air aging; Table 18 compares the mechanical properties of EPDM rubber filled with seven different carbon blacks after air aging. Figure 23 As shown in Table 17, the strength and hardness of all samples increased after hot air aging, while the elongation at break decreased, indicating that the aging reaction induced by hot air aging mainly manifests as cross-linking of the rubber. Compared with aging experiments under alkaline conditions, hot air aging did not lead to a significant decrease in rubber properties.

[0262] Therefore, the significant performance degradation observed in carbon black-filled EPDM samples under alkaline conditions is primarily due to the corrosive effects of the alkaline medium. High-temperature hot air aging increases hardness and strength by enhancing the crosslinking density of the rubber matrix, but does not cause the severe performance degradation observed under alkaline conditions. Therefore, it can be clearly confirmed that the presence of alkali has a significant negative impact on the performance of carbon black-filled rubber.

[0263] Table 17 Comparison of Mechanical Properties of Seven Types of Carbon Black-Filled EPDM Rubber After Air Aging

[0264] N220 N234 N330 N354 N550 N774 N990 Tensile strength / MPa 22.84 24.41 22.38 22.30 23.55 22.6 15.71 Intensity change rate / % 11.03 2.56 -8.72 0.22 6.22 3.38 37.08 Elongation at break / % 478.08 472.62 434.32 519.58 421.79 425.07 488.76 Elongation change rate / % -12.06 -9.48 -15.31 -21.94 -1.29 -10.55 4.15

[0265] 5. Conclusion

[0266] This embodiment compares the effects of seven different types of carbon black on the alkali resistance of rubber, revealing the reasons why carbon black affects the alkali resistance of rubber. The particle size and structure of carbon black significantly influence its reinforcing effect, which in turn relates to the alkali resistance of rubber. Experimental data shows that even carbon blacks with similar particle size and specific surface area (such as N220 and N234) exhibit differences in alkali resistance, with N234 demonstrating superior alkali resistance, indicating the influence of surface groups on the alkali resistance of rubber.

[0267] Example 3: Effect of carbon black / rubber interface regulation on the aging of EPDM rubber under alkaline conditions

[0268] As shown in Example 2, among the seven carbon blacks, the alkali resistance of EPDM filled with N234 carbon black is better than that of the other six carbon blacks. Therefore, by performing surface modification on N234 using six different methods, the alkali resistance of rubber can be further improved.

[0269] 1. Preparation of experimental samples

[0270] 1.1 Rubber Preparation

[0271] The preparation method is the same as that in Example 1, Section 1.2.

[0272] 1.2 Basic Formula

[0273] The preparation method is the same as that in Example 2, 1.2.

[0274] 1.3 Preparation of NaOH solution

[0275] The preparation method is the same as that in Example 2, 1.3.

[0276] 1.4 Carbon Black Modification Treatment

[0277] (1) High temperature treatment: Weigh 20g of carbon black and put it into a quartz boat. Place the quartz boat into a tube furnace and heat it to 900℃ for 2 hours in a nitrogen environment at a heating rate of 5℃ / min. Then cool it down and mix it into the rubber. Name it gCB.

[0278] (2) NaOH treatment: Weigh 20g of carbon black and add it to a 1mol / L sodium hydroxide solution. Stir and react at 90℃ for 12h. Wash the treated carbon black with deionized water until the pH remains unchanged. After filtration, dry it in a 90℃ oven for 48h and name it nCB.

[0279] (3) Nitric acid oxidation: Weigh 20g of carbon black into a round bottom flask, add 500ml of nitric acid, and stir in a 60℃ water bath for 8h. Then wash the treated carbon black with deionized water until the pH remains unchanged, filter, and dry in a 40℃ oven for 48h. Name it hCB.

[0280] (4) KOH activation treatment: Weigh 20g of carbon black and 60g of potassium hydroxide, add appropriate amounts of deionized water and ethanol, and ultrasonically mix evenly. Place the mixture in a 60℃ oven for drying. Then, place the dried sample in a tube furnace and heat it to 400℃ at a rate of 3℃ / min under nitrogen atmosphere. Hold the temperature for 0.5h, then continue heating to 800℃ and hold for 2h. Wash the treated carbon black repeatedly with deionized water until the pH remains constant. After filtration, dry it in a 60℃ oven until completely dry, and name it kCB.

[0281] (5) Hydrogen bond or ionic bond: Weigh 20g of carbon black and 2g of 4-dimethylaminopyridine, mix them evenly, put them in an oven at 140℃ for 4h, and then take them out and name them pCB.

[0282] (6) Surface hydrophobic treatment: Weigh 20g of carbon black and add it to 400ml of sulfuric acid. Stir and react at 90℃ for 8h. After the reaction, wash with deionized water until pH 6, and dry in a 40℃ oven for 12h. Disperse the dried carbon black in 1000ml of Tris, add 5g of DA, and mix evenly by sonication. Stir and react at room temperature for 10h, wash 3-4 times with deionized water, and dry in a 40℃ oven for 48h. After drying, add it to 500ml of DMF, sonicate for 30min, pour into a three-necked round-bottom flask, purge with nitrogen, and then gradually add 25g of octadecyl isocyanate and 2.5g of TEDA. Stir and react at room temperature under nitrogen for 24h. After the reaction, centrifuge, and dry the precipitate in a 40℃ oven for 48h, naming it aCB.

[0283] Figure 24 The states of carbon black in water before and after hydrophobic modification. According to... Figure 24 As can be seen, the unmodified carbon black sank to the bottom of the water and was in a dispersed particle state, while the hydrophobically modified carbon black floated on the water surface and did not come into contact with the water. This indicates that the modified carbon black is in a hydrophobic state and can isolate the NaOH solution to a certain extent.

[0284] 3. Aging resistance test methods

[0285] 3.1 Alkaline aging test

[0286] Same as Example 2.

[0287] 3.2 Air Aging Test

[0288] Same as Example 2.

[0289] 3.3 Simulated alkaline electrolytic cell sealing experiment

[0290] Using O-rings to seal simulated molds (such as Figure 25 As shown, the O-ring is squeezed and sealed, then placed in an autoclave. NaOH solution is added to the autoclave to simulate the alkaline environment in actual use.

[0291] 1) Simulation of constant pressure working condition inside the vessel

[0292] Nitrogen gas was introduced into the autoclave to simulate the gas environment generated during the operation of an alkaline electrolytic cell. The gas pressure inside the autoclave was maintained at 4 MPa, and the autoclave was sealed at 160°C for 3 days.

[0293] 2) Simulation of internal pressure variation conditions

[0294] Nitrogen gas was used to pressurize the autoclave to simulate the machine startup process, and venting gas to release pressure simulated the shutdown process. The autoclave was frequently vented and released daily for three days, with the pressure inside the autoclave being as follows: Figure 26 As shown.

[0295] 4. Sample Characterization and Analysis Methods

[0296] 4.1 Quality Change Rate Test

[0297] Same as Example 2.

[0298] 4.2 Volume Change Rate Test

[0299] Same as Example 2.

[0300] 4.3 Crosslinking density test

[0301] Same as Example 2.

[0302] 4.4 Physical and mechanical property testing

[0303] Same as Example 2.

[0304] 4.5 Fourier Transform Infrared Spectroscopy (FTIR) Characterization

[0305] The infrared spectra of rubber sheets before and after aging were measured using a Tensor II FTIR spectrometer to study the changes in functional groups before and after aging. Test parameters: After drying the samples, the ATR mode was used for testing, with a wavelength range of 400–4000 cm⁻¹. -1 .

[0306] 4.6 Microscopic Morphology Characterization

[0307] Same as Example 2.

[0308] 4.7 X-ray photoelectron spectroscopy (XPS)

[0309] Same as Example 2.

[0310] 4.8 Specific Surface Area Analysis (BET)

[0311] The specific surface area of ​​the material was measured using an ASAP2460 BET specific surface area testing system. The sample was placed in a nitrogen medium for isothermal adsorption-desorption testing. The test data were then fitted and calculated to obtain the sample's specific surface area.

[0312] 5. Experimental Results

[0313] 5.1 Specific surface area and pore size analysis

[0314] To investigate the changes in the specific surface area of ​​modified carbon black, the N2 adsorption specific surface area of ​​carbon black was measured using BET, as shown in Table 18.

[0315] Table 18 Nitrogen adsorption specific surface area of ​​different modified carbon black

[0316] N234 gCB kCB hCB nCB pCB aCB <![CDATA[Specific surface area m 2 / g]]> 128.57 121.01 369.58 205.63 129.56 113.68 21.47 Aperture nm 36.08 33.31 32.83 35.61 34.85 38.29 43.38

[0317] As shown in Table 18, the specific surface area of ​​carbon black (gCB) decreased slightly after high-temperature treatment. This is likely because high-temperature sintering causes adhesion between carbon black particles, increasing their size and thus reducing the specific surface area. The specific surface area of ​​carbon black (kCB) significantly increased after high-temperature treatment with KOH. This is mainly because KOH activates the carbon black, reacting chemically and promoting partial vapor-phase etching under high temperature, forming more micropores and mesopores, thereby increasing the specific surface area. The increased specific surface area of ​​carbon black (hCB) after nitric acid treatment is primarily due to the removal of impurities from the carbon black surface and the oxidation of functional groups on the surface by nitric acid, increasing the number of oxygen-containing functional groups and micropores, thus increasing the specific surface area. The slight change in specific surface area of ​​carbon black (nCB) after NaOH treatment is likely due to the removal of some impurities from the carbon black surface by the alkali treatment, leading to an increase in the specific surface area. The decrease in the specific surface area of ​​pCB may be due to the formation of hydrogen or ionic bonds, which cause pyridine groups to coat the carbon black surface, filling some of the pores and thus reducing the specific surface area. The significant decrease in the specific surface area of ​​aCB is mainly because octadecyl isocyanate is a long alkyl chain compound. When it reacts with the active sites on the carbon black surface, the long alkyl chain coats the surface, significantly blocking the original pores and smoothing the rough surface, thereby reducing the surface area. Furthermore, after grafting long-chain molecules, carbon black particles may aggregate through hydrophobic interactions (or other nonpolar interactions), forming larger particle aggregates, which also leads to a decrease in specific surface area.

[0318] 5.2X photoelectron spectroscopy

[0319] To verify whether the content of carboxyl groups on the carbon black surface affects the alkali resistance of rubber, the XPS data of the modified carbon black were subjected to peak splitting to obtain the types and contents of surface functional groups. The results are as follows: Figure 27 As shown. From Figure 27 As can be seen from the figure, the carboxyl content on the gCB surface decreased by 2.51% and the hydroxyl content decreased by 4.07% compared to unmodified carbon black, proving that high-temperature treatment can lead to a reduction in the number of oxygen-containing groups on the carbon black surface. Although the carboxyl content on the nCB surface decreased by 1.93%, the hydroxyl content increased by 9.34%, proving that NaOH treatment reduces the carboxyl groups on the carbon black surface while introducing some hydroxyl groups, thus increasing the total number of oxygen-containing groups on the carbon black surface. C=O groups appeared on the kCB surface, and the carboxyl content increased, proving that KOH high-temperature activation treatment not only increases the specific surface area of ​​carbon black but also reacts with the carbon black surface groups to generate ketone groups and other groups. As can be seen from the figure, the carboxyl and hydroxyl content on the hCB surface increased significantly, with the carboxyl content increasing by 4.37% and the hydroxyl content increasing by 14.05%, proving that nitric acid treatment oxidizes the carbon black surface, increasing the number of oxygen-containing groups on the carbon black surface.

[0320] Figure 28 The C1s and N1s peak profiles of aCB are shown. In the C1s profile, a CN peak appears at 288.43 eV, where the nitrogen mainly originates from DA and octadecyl isocyanate. In the N1s profile, the peaks at 399.5 eV and 400.2 eV likely represent the amine reaction between DA or octadecyl isocyanate and DA. The presence of a -N=N- peak at 402.15 eV indicates successful grafting of alkylamines onto carbon black. In conclusion, the XPS data demonstrate the success of the carbon black modification and provide valid evidence for subsequent experimental results.

[0321] 5.3 Infrared Spectroscopy

[0322] To investigate the changes in surface functional groups of different modified carbon blacks, Fourier transform infrared spectroscopy was performed on different modified carbon blacks, and the results are as follows: Figure 29 . Figure 29 Middle, 3432cm -1 The peak at 3217 cm⁻¹ is the -OH stretching vibration peak. -1 The point is the stretching vibration of the CH bond on the benzene ring, 1656 cm⁻¹. -1 and 1400cm -1 The peaks at 3432 cm⁻¹ represent the C=O and -CH₃ vibration peaks, respectively. It can be seen that the -OH and C=O peaks of gCB weakened after treatment, indicating a reduction in oxygen-containing groups after high-temperature treatment. Meanwhile, hCB shows a peak at 3432 cm⁻¹. -1 The peak at 1656cm -1 The increased peak percentage at 3217 cm⁻¹ indicates an increase in oxygen-containing groups on the carbon black surface after nitric acid treatment. kCB at 3217 cm⁻¹-1 The decrease in the peak at 3432 cm⁻¹ indicates that the activation treatment disrupted the structure of the carbon black, resulting in a reduction of -CH₂. nCB at 3432 cm⁻¹... -1 The peak increases at 1656 cm⁻¹ -1 The decrease in peak size indicates that the carboxyl content on the carbon black surface decreases and the hydroxyl content increases after NaOH treatment. This can be seen in the infrared spectrum of aCB at 2918 cm⁻¹. -1 and 2845cm -1 The peaks at 1469 cm⁻¹ represent the -CH₂ and -CH₃ symmetric stretching vibrations of octadecyl isocyanate. -1 The peak at 721 cm⁻¹ represents the -CH₃ vibration of the alkyl long chain. -1 The skeletal vibration is -(CH2)n- at 3340 cm⁻¹. -1 and 1573cm -1 The peak at 1611 cm⁻¹ represents the stretching and bending vibrations of the NH bond, which are attributed to the amide group or carbamate in the reaction. -1 The point is a tensile vibration of C=O in -CONH-, 1240cm. -1 The characteristic peak at this point is -COOR. The infrared spectroscopy results show that octadecyl isocyanate has been successfully grafted onto carbon black.

[0323] 5.4 Mechanical Property Analysis

[0324] The mechanical properties of EPDM rubber filled with different modified carbon blacks are shown in Table 19.

[0325] Table 19 Comparison of Mechanical Properties of EPDM Rubber Filled with Different Modified Carbon Black

[0326] N234 gCB kCB hCB nCB pCB aCB Tensile strength / MPa 23.8 20.52 25.87 24.21 22.47 21.32 10.41 Elongation at break / % 522.17 509.63 496.57 780.56 541.78 583.48 945.69

[0327] As shown in Table 19, the elongation at break of modified carbon black was improved, with aCB achieving an elongation at break of 945.69%. However, the tensile strength decreased significantly. This is mainly because while grafting octadecyl isocyanate improved its dispersion in rubber, the presence of long chains weakened the interfacial interaction between carbon black and rubber, resulting in a less dense and robust carbon black network structure, thus reducing the overall strength of the rubber. The increase in elongation at break is primarily due to the stronger interaction of molecular chains on the carbon black surface after grafting, leading to a more complex spatial structure between molecules and resulting in entanglement and a more stable structure. Under stress, the molecular chains can pull against each other, preventing breakage even under high strain, thus increasing the elongation at break. High-temperature treatment of gCB aims to reduce the oxygen-containing groups on the carbon black surface. This reduction weakens the interaction between rubber and carbon black, making these carbon black particles more prone to movement or being pulled out of the rubber under external force, leading to a decrease in rubber strength. KOH-activated carbon black (kCB) exhibits increased tensile strength but also higher elongation at break. This is primarily because high-temperature activation disrupts the carbon black's surface structure, increasing surface pores and specific surface area. This provides more surface area for bonding with rubber, enhancing the interfacial interaction between the two. Nitric acid-oxidized carbon black (hCB) shows improved tensile strength and elongation at break. This is because nitric acid oxidation increases the specific surface area and the number of oxygen-containing groups on the surface, improving its dispersibility in rubber and enhancing its reinforcing effect. nCB shows decreased tensile strength but increased elongation at break. This is mainly because treatment reduces carboxylic acid groups and increases the number of hydroxyl groups on the carbon black surface, weakening the strong interaction between carbon black and rubber and making the carbon black network less compact, thus reducing tensile strength. During stretching, the molecular chains in the rubber can move and extend more freely, resulting in increased elongation at break. Pyridine-treated carbon black (pCB) shows decreased tensile strength but increased elongation at break. This is mainly because pyridine groups form hydrogen or ionic bonds with the carbon black, increasing the rubber's resistance to deformation and thus increasing elongation at break.

[0328] 5.5 Mechanical property analysis after hot air aging

[0329] To investigate the differences in aging failure results of EPDM filled with different modified carbon black under hot air and alkaline conditions, different EPDMs were placed in a 160℃ oven for 3 days of hot air aging experiment.

[0330] Table 20 shows the mechanical properties of EPDM filled with different modified carbon black after hot air aging. It can be seen that after hot air aging, the tensile strength of each EPDM sample increased, while the elongation at break decreased.

[0331] Table 20 Comparison of mechanical properties of EPDM filled with different modified carbon blacks after hot air aging

[0332] N234 gCB kCB hCB nCB pCB aCB Tensile strength / MPa 24.41 21.23 26.46 23.88 23.01 22.36 10.58 Intensity change rate / % 2.56 3.46 2.28 1.37 2.4 4.88 1.63 Elongation at break / % 472.62 449.58 453.25 721.84 477.67 480.35 989.66 Elongation change rate / % -9.48 -11.78 -8.72 -7.52 -11.83 -17.67 4.65

[0333] Figure 30 The strength and elongation changes of EPDM rubber filled with different modified carbon blacks after hot air aging. Figure 30 It can be seen that the strength and elongation change rate of the sample after hot air aging are both less than those of the sample after alkaline aging.

[0334] The experimental results show that gCB, due to the removal of oxygen-containing groups on its surface, weakens the interfacial interaction between carbon black and rubber, thereby increasing oxygen penetration into the rubber and making it more susceptible to free radical attack under thermo-oxidative conditions, leading to increased cross-linking. kCB and hCB, after treatment, increase the number of oxygen-containing functional groups on their surfaces, enhancing the interfacial interaction between rubber and carbon black, making the rubber molecular chains more resistant to thermo-oxidative environments. Simultaneously, the increased carboxyl content enhances the adsorption of free radicals or molecular chains by carbon black, mitigating chain breakage or cross-linking caused by thermal oxidation. nCB, with its reduced carboxyl content and increased hydroxyl content, can adsorb free radicals to a certain extent, resisting cross-linking caused by thermo-oxidation. However, the hydrogen bonds formed between the hydroxyl groups and the rubber matrix may be broken under thermo-oxidative conditions, reducing the mechanical properties of the rubber. pCB mainly interacts with rubber through hydrogen bonds or ionic bonds, which are easily broken under thermo-oxidative conditions. Therefore, when hydrogen bonds are broken, the resulting active sites readily react with free radicals, increasing the degree of cross-linking. Because aCB is grafted with long-chain octadecyl isocyanate, it reduces the surface energy difference between carbon black and rubber through hydrophobic interactions, thereby enhancing the overall structural stability. The long chains also cover the active sites on the carbon black surface, reducing the adsorption of oxygen by the carbon black. At the same time, the covered long chains also form a barrier, reducing the diffusion of heat and oxygen, thus weakening cross-linking caused by aging.

[0335] This embodiment not only allows for a comparison of the different failure mechanisms of rubber under alkaline aging and air aging conditions, eliminating the influence of thermo-oxidative environment on alkaline aging experiments, but also reveals the changing patterns of the properties of modified carbon black-filled rubber after thermo-oxidative aging.

[0336] 5.6 Mechanical property analysis after alkaline aging

[0337] The changes in the mechanical properties of EPDM rubber filled with different modified carbon blacks after alkaline aging were tested, and the results are shown in Table 21. Figure 31 As shown.

[0338] Table 21 Comparison of mechanical properties of EPDM rubber filled with different modified carbon blacks after alkali aging

[0339] N234 gCB kCB hCB nCB pCB aCB Tensile strength / MPa 19.46 18.87 20.65 17.43 20.62 19.7 9.23 Intensity change rate / % -18.23 -5.65 -20.17 -28.01 -8.23 -3.71 -7.79 Elongation at break / % 443.77 435.56 400.76 613.27 446.49 454.25 875.56 Elongation change rate / % -15.01 -14.5 -19.29 -21.43 -17.58 -22.14 -9.2

[0340] The test results show that EPDM filled with aCB exhibits higher alkali resistance. This is mainly because the modified carbon black surface forms a hydrophobic structure, reducing the direct contact between strong alkaline solutions and rubber. This effectively reduces the damaging effect of NaOH solution on the rubber-carbon black interfacial interaction, thus improving the alkali resistance of EPDM.

[0341] EPDM containing surface-treated modified carbon black (gCB) exhibits less degradation of mechanical properties in alkaline solutions. Compared to unmodified carbon black, the rate of change in strength is reduced by 12.58%, while the elongation at break is reduced by only 0.51%. This result is primarily due to the reduction in surface oxygen-containing groups, leading to a decrease in the number of active sites susceptible to alkali corrosion. Although this modification results in a slight decrease in the initial mechanical properties of the EPDM composite, it reduces the magnitude of changes in mechanical properties before and after aging, thus enhancing the material's alkali resistance.

[0342] EPDM containing KOH-activated modified carbon black (kCB) exhibits a greater decrease in strength and elongation after alkaline aging compared to unmodified carbon black. This is primarily due to the increased number of pores on the activated carbon black surface, which enhances the adsorption capacity of NaOH solution on the carbon black. This, in turn, increases the contact area between the alkali and the rubber, weakening the interfacial forces between the carbon black and EPDM, potentially leading to damage to the rubber macromolecular backbone.

[0343] hCB-type modified carbon black exhibits improved surface polarity due to the increased number of oxygen-containing groups, thus enhancing its dispersibility in EPDM. However, under high temperature and 25% NaOH solution exposure, the oxygen-containing groups on the carbon black surface may react with the alkali, weakening the interfacial forces between carbon black and EPDM and potentially damaging the carbon black structural network. This reduces the EPDM's resistance to deformation, resulting in a significant decrease in tensile strength and elongation at break. In contrast, nCB-containing rubber has a reduced surface carboxyl group content and introduces a large number of hydroxyl groups. Although carboxyl groups are more polar than hydroxyl groups, hydroxyl groups are more resistant to alkali corrosion, thus improving the rubber's alkali resistance.

[0344] After alkaline corrosion, the tensile strength and elongation at break of pCB-type modified carbon black decrease. This is mainly because the alkaline environment causes the pyridine groups to hydrolyze or deprotonate, which weakens their interfacial bonding force with the rubber molecular chain and also causes carbon black agglomeration and stress concentration.

[0345] 5.7 Effects of O-ring aging under simulated alkaline electrolytic cell sealing conditions

[0346] 5.7.1 Mechanical property analysis under constant pressure conditions inside the vessel

[0347] The gas pressure inside the reactor was kept at 4 MPa. The mechanical properties of the O-rings before and after aging were tested under compressed and uncompressed conditions, as shown in Tables 22 and 23.

[0348] The test results show that the uncompressed O-rings exhibit a higher degree of aging compared to the compressed state, and this is consistent with the test pattern of the dumbbell-shaped samples in the laboratory, both being in the chain-splitting aging stage. The compressed O-rings, however, are in the cross-linking stage, which differs from the expected higher aging degree under compression. The reasons for this may be: 1) In the laboratory environment, both the EPDM and the uncompressed O-rings are completely immersed in the alkaline solution, ensuring full contact with it. Under compression, the O-rings are squeezed by the mold, pressed against the inner wall of the mold, reducing the contact area with the alkaline solution. 2) Under pressure, the internal structure of EPDM may become more compact, potentially enhancing the rubber's shielding properties and reducing the rate at which alkaline media enter the material. 3) Compression may promote cross-linking in the rubber, increasing the cross-linking density. Rubber with higher cross-linking density exhibits better chemical stability and stronger resistance to alkalis. 4) The stress state may cause changes in the orientation and arrangement of molecular chains in EPDM. This orientation may, to some extent, alter the diffusion pathway, thus affecting the diffusion of alkaline substances.

[0349] Table 22 Mechanical properties of uncompressed O-rings before and after constant pressure aging in the autoclave.

[0350]

[0351] Table 23 Mechanical properties before and after constant pressure aging in the O-ring reactor.

[0352]

[0353] 5.7.2 Mechanical property analysis under variable pressure conditions inside the vessel

[0354] Because industrial water electrolysis for hydrogen production involves frequent start-ups and shutdowns, differing from laboratory conditions, the aging process in the laboratory differs from the actual aging process. Therefore, to simulate the start-up and shutdown of an alkaline electrolysis cell, the experiment used nitrogen gas in a high-pressure reactor to simulate the machine start-up process, and then released the gas to simulate the shutdown process. The O-rings before and after aging are shown in the image. Figure 32 As shown.

[0355] Depend on Figure 32 As can be seen, the surface of the O-rings lost its luster and underwent severe permanent deformation after aging. During electrolysis, the gas generated from water electrolysis produces high pressure that compresses the O-rings, causing them to deform. When the electrolysis cell shuts down, the pressure inside decreases, and the O-rings gradually recover from their deformation. However, if this process continues for a long time, the deformation of the compressed O-rings cannot be recovered in time, resulting in a decreased sealing effect when gas is generated again upon startup, potentially leading to leaks in the electrolysis cell.

[0356] Table 24 shows the mechanical properties of different O-rings after alkaline aging. Figure 33 To determine the strength and elongation changes of different O-rings after aging, refer to Table 24 and... Figure 33 It can be seen that the alkali resistance of different O-rings is the same as that under laboratory aging and constant pressure conditions in the reactor. N234 carbon black and modified aCB still have good alkali resistance, but the aging degree of the O-rings is greater than that of the O-rings under constant pressure compression conditions in the reactor. The main reasons are as follows: 1) The constant gas pressure provides a stable environment, thus making the chemical and physical aging processes of the rubber O-rings relatively stable. 2) When the pressure in the reactor changes periodically, the O-rings will experience additional physical stress, including changes in compression and tension. This periodic pressure change can lead to changes in the microstructure of the rubber material, thereby affecting the overall performance of the material.

[0357] Table 24 Comparison of mechanical properties of different O-type caustic sodas after aging

[0358]

[0359] 6. Conclusion

[0360] This embodiment improves the stability of rubber in harsh alkaline environments by specifically chemically modifying the surface of carbon black. Carbon black contains carboxyl groups, which are highly polar and promote dispersion in rubber, readily reacting with alkalis. Lower carboxyl group content on the carbon black surface results in better alkali resistance in the rubber. The large specific surface area of ​​carbon black easily leads to excessive adsorption of alkali solutions, increasing the contact between the rubber and the alkali. Thermal or hydrophobic modification of carbon black reduces the number of carboxyl groups on its surface, decreasing its interaction with alkali solutions and thus improving the alkali aging resistance of the rubber. Hydrophobic modification of carbon black can slow down the corrosive effect of alkali solutions on the carbon black-rubber interface, thereby enhancing the alkali resistance stability of the rubber.

[0361] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving the alkali aging resistance of ethylene propylene diene monomer (EPDM) rubber, characterized in that: Includes the following steps: Modified carbon black was added to ethylene propylene diene monomer (EPDM) rubber. The modified carbon black is a hydrophobic modified carbon black; The preparation method of the hydrophobic modified carbon black includes the following steps: acid treatment of carbon black to obtain acid-treated carbon black; mixing the acid-treated carbon black, solvent and dopamine to carry out a first modification reaction to obtain dopamine-modified carbon black; mixing the dopamine-modified carbon black, alkyl isocyanate, polyethylene polyamine and solvent to carry out a second modification reaction to obtain hydrophobic modified carbon black. The mass ratio of the dopamine-modified carbon black to the alkyl isocyanate is 20:25~26; the alkyl group in the alkyl isocyanate has 15~20 carbon atoms; the polyethylenepolyamine is triethylenediamine; the mass ratio of the dopamine-modified carbon black to the polyethylenepolyamine is 20:2~5; the temperature of the second modification reaction is 40~60℃; The type of carbon black used in the preparation of the hydrophobic modified carbon black is N234; The modified carbon black is filled at a rate of 30-50% of the mass of the EPDM rubber matrix.

2. The method according to claim 1, characterized in that: The acid used in the acid treatment is sulfuric acid, and the acid treatment temperature is 80~90℃, and the time is 8~10h; The mass ratio of acid-treated carbon black to dopamine is 20:5~6; the first modification reaction takes 48~50 hours.

3. The method according to claim 1 or 2, characterized in that: It also includes the step of adding additives to the EPDM rubber, the additives including one or more of activators, plasticizers, antioxidants, crosslinking agents and co-crosslinking agents.

4. A rubber composition prepared by the method for improving the alkali aging resistance of EPDM rubber as described in any one of claims 1-3, characterized in that: The components include the following parts by mass: 100 parts EPDM rubber, 30-50 parts modified carbon black, 1-3 parts vulcanizing agent, 0.5-2 parts crosslinking agent, 2-5 parts activator, 0.5-1 part plasticizer, and 0.5-2 parts antioxidant.

5. The rubber composition according to claim 4, characterized in that: The vulcanizing agent is one or two of dicumyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; the co-crosslinking agent is one or two of triallyl isocyanurate and triallyl cyanurate; the activator is one or two of zinc oxide and calcium carbonate; the plasticizer is one or two of stearic acid and polyester; and the antioxidant is one or two of 2-mercaptobenzimidazole and 2,2,4-trimethyl-1,2-dihydroquinoline polymer.

6. The use of the rubber composition according to claim 4 or 5 in seals for alkaline electrolytic cells.

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