Method for improving alkali aging resistance of ethylene propylene diene monomer, rubber composition and application of rubber composition

Abstract

The invention discloses a method for improving alkali aging resistance of ethylene propylene diene monomer, a rubber composition and application of the rubber composition, and relates to the technical field of rubber. By adding the modified carbon black into the ethylene propylene diene monomer, the alkali aging resistance of the ethylene propylene diene monomer is improved; the modified carbon black is thermal modified carbon black and / or hydrophobic modified carbon black. Carbon black is subjected to heat treatment, carboxyl on the surface of the carbon black is removed through high temperature, so that the carbon black is prevented from reacting with alkali, and the alkali aging resistance of rubber is further improved; hydrophobic modification is carried out on the carbon black, adsorption of the carbon black to alkali liquor is reduced, then contact between alkali and rubber is reduced, and the alkali resistance of the rubber is improved to a great extent. In conclusion, the surface of the carbon black is subjected to specific chemical modification, and the ethylene propylene diene monomer is filled with the modified carbon black, so that the stability of the ethylene propylene diene monomer in a severe alkaline environment can be improved, and the service life of the ethylene propylene diene monomer serving as an alkaline electrolytic tank sealing element is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of rubber technology, and in particular to a method for improving the alkaline aging resistance of ethylene propylene diene monomer (EPDM) rubber, a rubber composition and applications thereof. Background Art

[0002] The transformation of the global energy structure towards low-carbon and clean energy has become an irreversible development trend. In this context, hydrogen, as an efficient energy carrier, plays a key intermediary role in the utilization and development of renewable energy. It can store, transport or directly utilize electricity, wind energy, solar energy, geothermal energy, etc. Among the many hydrogen production technologies, water electrolysis has attracted much attention due to its environmental friendliness. Among them, alkaline electrolysis cell technology occupies an important position in the field of water electrolysis hydrogen production due to its high maturity, significant cost-effectiveness and good operational stability. However, hydrogen production technology must have excellent sealing to operate efficiently and stably, and the loss of alkaline solution will increase the energy consumption of gas production, which requires the sealing material to have a good ability to resist harsh environments.

[0003] Ethylene propylene diene monomer (EPDM) has many excellent properties: (1) The high saturation of the main chain gives it excellent aging resistance. EPDM products are extremely resistant to ozone, heat, oxygen, and especially ozone, making them excellent in adverse weather conditions and suitable for outdoor applications. (2) The small amount of double bonds in the molecular side chain allows it to be vulcanized with both sulfur and peroxide. (3) It has a low relative density and is the lightest among general-purpose rubbers, allowing it to be filled with a large amount of fillers to reduce costs. (4) It has a wide applicable temperature range of -50°C to 150°C and can maintain good usability. (5) It has excellent electrical insulation and good impact resilience. These excellent aging resistance, chemical stability, and low cost have made it widely used in the sealing of hydrogen electrolytic cells, achieving good sealing effects. However, the electrolyte used in alkaline electrolytic cells is usually a strongly alkaline solution, such as potassium hydroxide (KOH) solution. EPDM rubber, as a sealing material in the electrolytic cell, will directly contact the strongly alkaline electrolyte. The strongly alkaline environment will corrode the molecular structure of the rubber, causing the rubber molecular chain to break and the cross-linking structure to be destroyed, thereby reducing the sealing performance of the rubber. In actual operation, there are safety hazards such as gas leakage or alkali spraying.

[0004] In summary, the current EPDM rubber has poor alkaline aging resistance, resulting in a short service life of the seals. How to improve the alkaline 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 for improving the alkaline aging resistance of EPDM rubber, a rubber composition and its application. The present invention fills the EPDM rubber with modified carbon black to improve its alkaline aging resistance and extend its service life in an alkaline environment, thereby solving the following problems existing in the prior art:

[0006] (1) Insufficient research on the mechanism of alkaline environment's impact on EPDM. Existing technologies lack systematic comparative analysis and are unable to clearly define the main factors affecting EPDM's alkali resistance, such as the influence of alkali solution concentration, temperature, etc. on the material's microstructure, mechanical properties, and chemical stability. This makes it difficult to provide targeted guidance for material modification and performance improvement.

[0007] (2) Research on the mechanism of nanofillers enhancing EPDM’s alkali resistance is scarce, 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 interfacial compatibilizers, and elucidating the relationship between interface structure and material properties are of great significance for the development of EPDM sealing materials with excellent alkali resistance and long service life.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

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

[0010] Adding modified carbon black to EPDM rubber; the modified carbon black is thermally modified carbon black and / or hydrophobically modified carbon black;

[0011] The preparation method of the thermally modified carbon black comprises the following steps: subjecting the carbon black to a heat treatment to obtain the thermally modified carbon black; the heat treatment temperature is 800-900°C;

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

[0013] Preferably, the holding time of the heat treatment 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, the temperature of the acid treatment is 80-90°C, and the time is 8-10 hours;

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

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

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

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

[0019] Preferably, the method further comprises adding an auxiliary agent to the EPDM rubber, wherein the auxiliary agent comprises one or more of an active agent, a plasticizer, an antioxidant, a crosslinking agent and a co-crosslinking agent.

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

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

[0022] Preferably, the rubber composition is composed of the following parts by mass:

[0023] 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, 1 part of co-crosslinking agent;

[0024] The modified carbon black is thermally modified carbon black and / or hydrophobically modified carbon black;

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

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

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

[0028] The sealing component prepared from the EPDM rubber obtained by the method of the present invention can be applied to alkaline working conditions. For example, the O-ring structure is applicable to alkaline working conditions of 4±0.3 MPa and 80-160°C.

[0029] The sealing member prepared from the EPDM rubber obtained by the method of the present invention has a compression permanent deformation rate of ≤17% under frequent start-stop working conditions.

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

[0031] (1) The present invention studies the effects of four different conditions, namely, NaOH concentration, temperature, aging time, and carbon black filling, on the alkali resistance of EPDM. The increase in NaOH concentration, temperature, and aging time will deepen the degree of rubber aging, but the filling of carbon black is an important factor affecting the alkali resistance of rubber. Although the tensile strength and elongation at break of the rubber are improved, after alkaline aging, the performance degradation rate of the sample is about 20% higher than that of the rubber without carbon black filling.

[0032] (2) This study investigated the effects 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 primarily related to carbon black, with the particle size and surface properties of carbon black being the primary factors affecting the alkali resistance of rubber. The carbon black N234, which exhibited the best alkali resistance, was selected, and specific chemical modifications were performed on its surface to improve the stability of the rubber in harsh alkaline environments.

[0033] (3) The present invention has found that the surface of carbon black contains carboxyl groups, which have strong polarity 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 rubber is better. The present invention heat-treats carbon black to remove the carboxyl groups on the surface of carbon black by high temperature, thereby avoiding its reaction with alkali, thereby prolonging the alkali aging resistance of rubber. In addition, carbon black has a large specific surface area and is easy to adsorb alkali solution, which increases the contact between rubber and alkali solution and also causes the alkali resistance of rubber to decrease. The present invention hydrophobically modifies 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, the present invention performs specific chemical modification 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 seal for alkaline electrolytic cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the mass and volume change rate of the rubber after aging at different NaOH concentrations in Example 1;

[0036] Figure 2 The changes in rubber strength and elongation retention after aging at different NaOH concentrations in Example 1;

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

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

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

[0040] Figure 6 is the mass and volume change rate of the rubber after aging at different temperatures in Example 1;

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

[0042] Figure 8 The contact angle changes of the rubber in Example 1 after aging at different temperatures;

[0043] Figure 9 The contact angle changes of the rubber in Example 1 after aging at different temperatures;

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

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

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

[0047] Figure 13 The contact angle changes of the rubber in Example 1 after aging at different aging times;

[0048] Figure 14 The contact angle diagram of the rubber in Example 1 after aging at different aging times;

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

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

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

[0052] Figure 18 The compression set test results of the EPDM rubber filled with seven different carbon blacks at room temperature in Example 2 are as follows;

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

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

[0055] Figure 21 This is the XPS peak diagram of C1s of different types of carbon black in Example 2;

[0056] Figure 22 The micromorphology of EPDM filled with seven carbon blacks (a) N220, (b) N234, (c) N330, (d) N354, (e) N550, (f) N774, and (g) N990 in Example 2 in the original state (1), air aging (2), and alkali aging (3);

[0057] Figure 23 The air aging mass volume change (Figure a) and hardness change (Figure b) of EPDM rubber filled with different carbon blacks in Example 2;

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

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

[0060] Figure 26 The pressure change in the kettle under the variable pressure condition during the alkaline electrolytic cell sealing experiment simulated in Example 3;

[0061] Figure 27 The XPS peak diagram of C1s of modified carbon black gCB, nCB, kCB, and hCB in Example 3;

[0062] Figure 28 The XPS peaks of C1s and N1s of aCB in Example 3 are as follows;

[0063] Figure 29 : FTIR spectra of different modified carbon blacks in Example 3;

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

[0065] Figure 31 The change rates of strength and elongation of EPDM rubber filled with different modified carbon blacks after alkaline aging in Example 3;

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

[0067] Figure 33 The strength and elongation change rates of different O-rings after aging in Example 3. DETAILED DESCRIPTION

[0068] The present invention provides a method for improving the alkaline aging resistance of EPDM rubber, comprising the following steps:

[0069] Modified carbon black is added to EPDM rubber; the modified carbon black is thermally modified carbon black and / or hydrophobically modified carbon black.

[0070] In the present invention, the carbon black used to prepare the thermally modified carbon black and the hydrophobically modified carbon black is preferably N234.

[0071] In the present invention, the preparation method of the thermally modified carbon black includes: heat-treating carbon black to obtain thermally modified carbon black; the temperature of the heat treatment is 800-900°C, specifically 800°C, 850°C or 900°C; the heating rate to the temperature of the heat treatment is preferably 5-10°C / min, and the holding time of the heat treatment 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 tubular furnace; the present invention performs heat treatment under the above conditions, which can remove the carboxyl groups on the surface of the carbon black, reduce the chance of it reacting with alkali solution, and thereby improve the alkali aging resistance of the rubber.

[0072] In the present invention, the preparation method of the hydrophobically modified carbon black comprises:

[0073] treating carbon black with acid to obtain acid-treated carbon black;

[0074] The acid-treated carbon black, a solvent, and dopamine are mixed to perform 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 hydrophobically modified carbon black.

[0076] The present invention treats carbon black with acid to obtain acid-treated carbon black. In the present invention, the acid used in the acid treatment is preferably sulfuric acid, and the concentration of the sulfuric acid is preferably 30% to 70%; the amount ratio of the carbon black to the sulfuric acid is preferably 2g:40 to 50mL; the temperature of the acid treatment is preferably 80 to 90°C, specifically 80°C, 85°C or 90°C, and the time of the acid treatment is preferably 8 to 10 hours, specifically 8 hours, 9 hours or 10 hours; the acid treatment is preferably carried out under stirring; after the acid treatment is completed, the solid product is preferably washed with deionized water to a pH value of 6 to 6.5, and then dried to obtain the acid-treated carbon black; the drying temperature is preferably 40 to 60°C, and the time is preferably 10 to 12 hours.

[0077] After obtaining the acid-treated carbon black, the present invention mixes the acid-treated carbon black, a 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, and the pH value of the Tris buffer is preferably 7.0 to 9.2; the amount ratio of the acid-treated carbon black and the solvent is preferably 1g:50 to 60mL; the mass ratio of the acid-treated carbon black and dopamine is preferably 20:5 to 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, and ultrasonically mixes uniformly before carrying out the first modification reaction; the time of the first modification reaction is preferably 48 to 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 present invention preferably separates the solid product and then washes and dries it. The detergent used for washing is preferably deionized water, the number of washings is preferably 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 the dopamine-modified carbon black, the present invention further comprises mixing the dopamine-modified carbon black, an alkyl isocyanate, polyethylene polyamine, and a solvent to perform a second modification reaction to obtain the hydrophobically 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 isocyanate is preferably 15-20, specifically 15, 16, 18, or 20. Specifically, the alkyl isocyanate is preferably octadecyl isocyanate.

[0079] In the present invention, the polyethylene polyamine is preferably triethylenediamine; the mass ratio of the dopamine-modified carbon black to the polyethylene polyamine is preferably 20:2-5, specifically 20:2, 20:3, or 20:4; the solvent is preferably DMF; the amount ratio of the dopamine-modified carbon black to the solvent is preferably 20g:500mL; the time of the second modification reaction is preferably 40-60°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 the present invention, it is preferred that the dopamine-modified carbon black is first added to a solvent and ultrasonically treated to obtain a dispersion, and then the dispersion is placed in a reaction apparatus, nitrogen is introduced, and then alkyl isocyanate and polyethylene polyamine are added to the reaction apparatus, and the reaction is stirred under a nitrogen environment. After the second modification reaction is completed, the present invention preferably centrifuges the obtained reaction solution to obtain a precipitate, and then dries the precipitate to obtain the hydrophobically modified carbon black; the drying temperature is preferably 40 to 60° C., and the drying time is preferably 48 to 50 hours.

[0080] In the present 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 the present invention, the method for improving the alkaline aging resistance of EPDM rubber also includes adding additives to the EPDM rubber, and the additives preferably include one or more of an active agent, a plasticizer, an antioxidant, a crosslinking agent and a co-crosslinking agent, and more preferably include an active agent, a plasticizer, an antioxidant, a crosslinking agent and a co-crosslinking agent at the same time.

[0082] The present invention has no special requirements for the method of adding modified carbon black and additives to EPDM rubber. The EPDM rubber, modified carbon black and additives are prepared into a rubber mix by methods well known to those skilled in the art, and then vulcanized. The details will be described later.

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

[0084] In the present 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 in the above-mentioned solution and will not be described in detail here.

[0085] In the present 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 the antioxidant RD to the antioxidant MB is preferably 1:1; the cross-linking agent is preferably dicumyl peroxide (DCP); and the auxiliary cross-linking agent is preferably triallyl isocyanurate (TAIC).

[0086] In the present invention, the preparation method of the rubber composition preferably includes: placing the EPDM rubber raw material into an open mill for preliminary thin-pass plasticating, then adding an antioxidant, a plasticizer, an activator, a co-crosslinking agent and modified carbon black to the rubber, and finally adding a vulcanizing agent to obtain the desired mixed rubber; and vulcanizing the mixed rubber to obtain the rubber composition.

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

[0088] The present invention also provides the use of the rubber composition described in the above solution in an alkaline battery seal. The present invention has no special requirements for the specific method of the application, and any method familiar to those skilled in the art can be used.

[0089] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

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

[0091] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0092] The sources of the raw materials and reagents used in the following examples are as follows: ethylene propylene diene monomer (EPDM), brand 4045, LANXESS, Germany; diisopropyl benzene peroxide (DCP), industrial grade (>95%), Shijiazhuang Fate Company; triallyl isocyanurate (TAIC), industrial grade (>95%), Aladdin; carbon black N220, carbon black N234, carbon black N330, carbon black N550, carbon black N774, carbon black N990, industrial grade (>95%), Cabot; active 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 filling on alkali aging resistance of EPDM

[0094] 1. Experimental methods

[0095] 1.1 Rubber formula

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

[0097] Formula of carbon black filled rubber: 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.

[0098] 1.2 Preparation of rubber

[0099] After fully masticating the target amount of EPDM raw rubber on an SK-1608 open mill, the target amounts of processing aid, filler (carbon black; carbon black addition is omitted for unfilled rubber), and crosslinker (DCP) were weighed and added to the raw rubber. The rubber mix was then subjected to multiple thin-pass and triangular tapping procedures to obtain the resulting rubber mix. The vulcanization behavior of the rubber was evaluated at 170°C using a rotorless vulcanizer. The mix was then processed on an XLB flatbed vulcanizer using a Tc90 standard to produce 2 mm thick rubber sheets and 10 mm × 10 mm rubber cylinders. The rubber sheets were cut using a JC-1025 sheet punch to produce standard dumbbell-shaped specimens, which were then marked for subsequent experimental analysis.

[0100] 1.3 Preparation of NaOH solution

[0101] Different masses of sodium hydroxide solid with a mass fraction of 96% were weighed, added to deionized water and stirred 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] Measure the original mass, density, and hardness of the rubber dumbbell specimens, as well as the height of the cylindrical specimens. Then, place the specimens in a PTFE hydrothermal reactor and add a 25% by mass NaOH solution, ensuring complete immersion. The reactor is sealed and placed in a DHG-9075A electric constant-temperature forced-air oven for accelerated aging at 160°C for three days. After completion, remove the reactor, cool it to room temperature, open it, remove the specimens, and clean the surface 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. Use a JA3003J electronic balance to measure the mass M of the sample after aging. The formula for the mass change rate 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, and use a solid density balance to measure the volume V of the sample after aging. 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 properties test

[0114] Hardness: Hardness test is carried out in accordance with the national standard GB / T 531.1-2008.

[0115] Tensile strength and elongation at break: According to GB / T 528-2009 “Vulcanized or thermoplastic rubber - Determination of tensile stress-strain properties”, tensile tests were carried out at room temperature using a WDL-10 universal testing machine.

[0116] 2.4 Surface properties determination

[0117] Rubber materials were tested using an OCA15EC contact angle meter, using distilled water as the test liquid. Experiments were conducted under a controlled environment (15°C, 50% relative humidity). The procedure involved turning on the instrument, adjusting the focus, placing the sample, making contact with the droplet, capturing an image, and measuring the contact angle using image analysis software.

[0118] 3. Test results

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

[0120] In order to explore the effect of NaOH concentration on the alkaline aging of EPDM, EPDM rubber without carbon black filling was placed in alkaline solutions with different NaOH concentrations (6.25%, 10%, 25%, 50%) at 140°C and aged 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 shown.

[0123] As shown in Table 1, as the concentration of NaOH increases, the mass, volume and hardness of EPDM gradually decrease. This indicates that the increase in NaOH concentration increases the erosion ability of EPDM and causes a certain degree of breakage of the surface molecular chains, resulting in a decrease in surface hardness. Figure 1 It can be seen that the higher the NaOH concentration, the faster the mass and volume loss. It is speculated that due to the increase in concentration, the probability of interaction between hydroxide ions and rubber molecular chains increases, causing the rubber molecular chains to be destroyed, thereby leading to a decrease in mass and volume.

[0124] Table 1 Hardness change and mass and volume change rate before and after aging at different NaOH concentrations

[0125] Aging conditions Mass 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 mechanical properties of EPDM vulcanizate after aging

[0127] Aging will lead to the decline of rubber mechanical properties, thus making rubber products fail. In order to understand the change of rubber mechanical properties under different NaOH concentrations, a tensile machine was used to test rubber dumbbell specimens. The results are shown in Table 2 and Figure 2 As shown in Table 2 and Figure 2 The results show that in air and low alkali concentrations (6.25% and 10%), the tensile strength and elongation at break of the samples increased after aging. When the NaOH concentration was higher (25% and 50%), the tensile strength and elongation at break of the rubber decreased, and the higher the concentration, the greater the decline in mechanical properties.

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

[0129]

[0130] These experimental results demonstrate that under air aging conditions, the rubber undergoes a certain degree of cross-linking, resulting in a denser cross-linking network and stronger molecular chain interactions. At lower NaOH concentrations, the material's tensile strength and elongation at break slightly increase, indicating that at lower concentrations, the EPDM's aging behavior is consistent with short-term air aging, with cross-linking occurring first. Due to EPDM's excellent alkali resistance, lower concentrations of alkali solution did not cause molecular chain rupture. As the alkali concentration increases, the alkali's force on the rubber's molecular chains gradually increases, accelerating rubber aging and severely damaging the rubber chains, causing them to break, leading to 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 of the rubber. In order to understand the changes in the rubber surface caused by aging with increasing NaOH concentration, contact angle tests were performed on the rubber surface. Figure 3 、 Figure 4 The change of surface contact angle of EPDM before and after aging in different concentrations of NaOH. 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, breaking the molecular backbone, reducing the number of carbon atoms in the backbone, increasing water solubility, increasing the hydrophilicity of the material, and decreasing the contact angle. At the same time, some NaOH may remain on the damaged surface and not be washed away, making the rubber surface more hydrophilic during testing and also causing a smaller contact angle.

[0133] 3.1.4 Compression set of EPDM vulcanizate after aging

[0134] In order to explore the change law of permanent compression deformation of rubber after aging, the rubber cylindrical specimens were tested. The results are as follows: Figure 5 As shown in the figure, it can be seen that with the increase of NaOH concentration, the permanent compression set of rubber shows a trend of first decreasing and then increasing.

[0135] The experimental results show that in low-concentration alkali solutions, rubber primarily undergoes crosslinking. After aging, the crosslinking network becomes denser, with the molecular chains intertwined. However, the compression process does not significantly damage the crosslinking structure, so when the force is removed, the rubber can recover some of its deformation through its own elasticity. As the alkali concentration increases, the rubber's molecular chains degrade and break to a certain extent after aging, reducing the interaction between the molecular chains and making them susceptible to slippage under external forces. Therefore, after the pressure is removed, the rubber cannot recover on its own, resulting in permanent deformation and an increase in the compression set.

[0136] In the subsequent alkaline aging experiments, a sodium hydroxide solution with a mass concentration of 50% was used.

[0137] 3.2 Effect of aging temperature on 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. From the data, we can see that the mass and volume change rate of EPDM shows an upward trend under the condition of rising temperature.

[0140] Table 3 Hardness change and mass and volume change rate before and after aging at different temperatures

[0141] Aging conditions Mass 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 degree of EPDM increases with increasing aging temperature. However, the hardness of EPDM decreases with increasing temperature. It is speculated that on the one hand, the temperature increase causes the rubber additives to precipitate, reducing the reinforcing effect on the rubber compound. On the other hand, the temperature increase makes the reaction more intense, causing the material surface to be corroded and damaged by the alkaline solution, resulting in a decrease in hardness. Figure 6 is the rate of change of rubber mass and volume 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 serious at high temperature.

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

[0144] Table 4 and Figure 7The following are 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 performance loss.

[0145] Table 4 Changes in 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, this is primarily because rising temperature enhances the movement of rubber molecular chains, weakening the intermolecular interactions and making the rubber's molecular structure more susceptible to changes. From the perspective of alkaline solutions, higher temperatures increase the activity of hydroxide ions and their increased reactivity with other substances. Therefore, at high temperatures, rubber molecules in alkaline solutions are more likely to break, generating active substances such as free radicals, which rapidly degrades the rubber's mechanical properties.

[0148] 3.2.3 Surface properties of EPDM vulcanizate after aging

[0149] Figure 8 、 Figure 9 Figure 3 shows the contact angle changes 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 the contact angle.

[0150] This experimental result indicates that high temperatures and high concentrations of strong alkali accelerate the breakage of rubber molecular chains. Furthermore, at high temperatures, the movement and diffusion of these broken molecular chains accelerate, making the surface microstructure more irregular and rougher, leading to a smaller contact angle. Aging also changes the surface energy of rubber, making it easier for water droplets to wet the rubber, resulting in a smaller contact angle.

[0151] 3.2.4 Compression set of EPDM vulcanizate after aging

[0152] Figure 10 The figure shows the change in compression set of EPDM before and after alkaline aging at different temperatures. As can be seen from the figure, the higher the aging temperature, the greater the compression set of the rubber. This experimental result is primarily due to the fact that the cross-linked structure of rubber is easily destroyed at high temperatures, causing the molecular chains to break and shift, weakening the forces between the molecular chains, resulting in a looser structure and difficulty in restoring its original state. Furthermore, higher temperatures increase the intensity of thermal motion of the molecular chains, making them more prone to slippage, causing the rubber material to undergo irreversible plastic deformation. Furthermore, at high temperatures, the additives in the rubber may become ineffective, weakening the rubber's ability to resist deformation and increasing the compression set.

[0153] The aging temperature used in subsequent alkaline aging experiments was 140°C.

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

[0155] In order to explore the effect of different aging times on the alkaline aging of EPDM, EPDM rubber samples without carbon black filling were placed in a 50% by mass NaOH solution at 140°C for 3d, 5d, and 7d, respectively, 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 following are the mass and volume changes of rubber after aging for different aging times. The data show that extending the aging time leads to an increase in the mass and volume change of EPDM, which also indicates that the aging process of EPDM accelerates over time, and the hardness of EPDM gradually decreases with aging time.

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

[0159] Aging conditions Mass 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 will cause the rubber molecular chain to break and the internal structure to relax, thereby weakening the intramolecular interaction 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. It is speculated that this is because the molecular chains break and decompose inside the rubber, which causes the mass to decrease after aging. At the same time, the change in the molecular chain structure may cause some cracks and voids in the material, which will increase some space, 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 mechanical properties of EPDM vulcanizate after aging

[0162] Table 6 shows the changes in mechanical properties of rubber after aging at different aging times. Figure 12 The changes of rubber strength and elongation loss rate under different aging time. Figure 12 It can be seen that in high concentration alkali solution, as the aging time increases, the tensile strength and elongation at break of EPDM gradually decrease after aging. Figure 12 It can be seen that the longer the EPDM aging time, the faster the tensile strength and elongation at break decrease.

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

[0164]

[0165] This experimental result is primarily due to the fact that longer aging exposes EPDM to heat and alkali, severely damaging the rubber's internal molecular structure. Furthermore, the rubber is exposed to external factors, such as oxygen, for a longer period of time, further damaging the rubber's molecular structure. Furthermore, with increasing aging time, tiny defects in the EPDM molecular chain gradually accumulate. These defects accumulate and spread over time, accelerating the aging process. Consequently, the rate of rubber performance degradation accelerates with increasing aging time.

[0166] 3.3.3 Surface properties of EPDM vulcanizate after aging

[0167] Figure 13 、 Figure 14 The figure shows the contact angle changes of EPDM before and after aging in alkaline solution for different aging times. 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 due to the fact that as temperature increases, the molecular chain activity increases, making diffusion more likely, and can easily break the rubber molecular chain. This is a rapid process. As aging time increases, the rubber is exposed to alkaline solution for longer periods of time, the main chain continues to break, and the surface roughness gradually increases. This is a gradual and cumulative process.

[0168] 3.3.4 Compression set of EPDM vulcanizate after aging

[0169] Figure 15Figure 3 shows the compression set of rubber after aging at different times. It can be seen that the compression set of EPDM increases with increasing aging time. Compression set of rubber primarily characterizes the resilience of the rubber material. Rubber's elasticity is primarily due to the loose cross-linking structure and intermolecular slip between rubber molecular chains. When subjected to compressive stress, the molecules shift and the chains stretch, creating stress. However, due to the inherent freedom and high degree of alignment of the molecular chains, the rubber exhibits excellent resilience and quickly recovers to its original shape. However, when rubber is subjected to compressive stress for a long time, continuous displacement and slip between the molecular chains occur, leading to molecular rearrangement and repeated structural changes. This causes the rubber molecular chains to become intertwined or constrained, preventing them from fully recovering to their original shape, resulting in permanent deformation, known as compression set. With increasing aging time, these molecular structural changes accumulate and intensify, causing the compression set of the rubber to become increasingly pronounced, ultimately leading to a loss of elasticity and the development of plastic deformation or hardening cracks. Therefore, longer aging results in more structural changes and rearrangements in the rubber's molecular chains, resulting in greater compression set.

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

[0171] 3.4 Effect of carbon black filling 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 without carbon black filling and carbon black filling before and after alkaline aging were tested. The results are shown in Tables 7 and 8.

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

[0175] Aging conditions Mass 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 Hardness change, mass and volume change rate of carbon black filled EPDM rubber after alkaline aging at different temperatures

[0177] Aging conditions Mass 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] According to Tables 7 and 8, the hardness of the rubber increases after filling with carbon black, indicating that the addition of carbon black increases the cross-linking of the rubber and increases the interaction between the rubber molecular chains. However, the mass and volume change rates are not large, indicating that the addition of carbon black mainly plays the role of physical cross-linking points. The rubber molecular chains are not accelerated to decompose. The aging process only weakens the interaction between the rubber and carbon black interfaces.

[0179] 3.4.2 Changes in mechanical properties of EPDM vulcanizate 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 Strength and elongation loss of EPDM rubber without (a) and filled with (b) carbon black after alkaline aging at different temperatures.

[0187] According to the data in Table 9 and Table 10, it can be seen that after filling with carbon black, the tensile strength and elongation at break of EPDM rubber are greatly improved due to the reinforcing effect of carbon black. Figure 16 It can be seen that after soaking in NaOH solution, the tensile strength and elongation at break of the carbon black filled rubber dropped sharply, and the loss of strength and elongation was much greater than that of the unfilled carbon black rubber.

[0188] The above results show that the addition of carbon black greatly affects the alkali resistance of EPDM, making the rubber's alkali resistance worse. The reason may be that there are many oxygen-containing functional groups on the surface of carbon black. Under normal circumstances, these functional groups may react chemically with the rubber matrix to form chemical bonds or rely on physical adsorption to form hydrogen bonds. However, under the action of strong alkali, these carbon black and rubber bonding points will be destroyed, resulting in a weakening of the interfacial force between rubber and carbon black, which in turn affects the reinforcing effect of carbon black on rubber. Therefore, the tensile strength and elongation at break deteriorate after aging. On the other hand, carbon black itself has a large specific surface area and can adsorb chemical substances. The addition of carbon black has an adsorption effect on alkaline substances, thereby increasing the interaction between rubber and alkali and accelerating the aging of rubber.

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

[0190] The compression set properties of EPDM rubber without carbon black filling and carbon black filling before and after alkaline aging were tested. The results are as follows: Figure 17 As shown. Figure 17It can be found that the rubber compression permanent deformation performance can be improved after being filled with carbon black. The porous surface and large specific surface area of ​​carbon black promote its effective bonding with unvulcanized rubber, forming a stable carbon black gel network structure, which has a reinforcing effect on the rubber material. Since the addition of carbon black limits the sliding of the molecular chain, it enhances the mechanical strength, hardness and wear resistance of the vulcanized rubber, resulting in better deformation resistance of the rubber material, which in turn leads to a reduction in permanent deformation under compression. It can also be seen that compared with unfilled carbon black, the change in compression permanent deformation of rubber after filling with carbon black is greater. This is mainly because after the addition of carbon black, the interface between carbon black and rubber will be destroyed under the action of strong alkali, weakening the reinforcing effect of carbon black, resulting in poor rubber deformation resistance and increased compression permanent deformation change.

[0191] 4. Conclusion

[0192] By investigating the effects of four different conditions, namely NaOH concentration, temperature, aging time and carbon black filling, on the alkali resistance of EPDM, the following conclusions were drawn: (1) EPDM undergoes a cross-linking reaction when aged in a low-concentration NaOH solution, which increases the hardness and reduces the compression set. As the NaOH concentration increases, the aging mechanism of EPDM gradually changes from cross-linking to molecular chain scission. The higher the NaOH concentration, the stronger the corrosion to EPDM, and the greater the performance degradation of EPDM after aging. (2) Temperature has a greater impact on the aging of EPDM in an alkaline environment. 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 corroded by NaOH, resulting in an increase in internal defects of EPDM. The continuous accumulation of defects will accelerate the aging of EPDM, resulting in a faster decline in the mechanical properties and surface properties of EPDM. (4) Carbon black has the greatest impact on the alkali resistance of EPDM. Under the same aging conditions, the degree of mechanical property degradation of EPDM without carbon black filling after aging is about 20% less than that of EPDM filled with carbon black, and the higher the temperature, the greater the difference. It is speculated that the interface between carbon black and rubber is destroyed in an alkaline environment, resulting in the weakening of the reinforcing effect of carbon black.

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

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

[0195] 1. Experimental sample preparation

[0196] 1.1 Rubber preparation

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

[0198] 1.2 Basic recipe

[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] Different masses of sodium hydroxide solid with a mass fraction of 96% were weighed, added to deionized water and stirred with a glass rod to prepare NaOH solutions with a mass fraction of 25%.

[0202] 2. Aging resistance test method

[0203] 2.1 Alkaline aging test

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

[0205] 2.2 Air aging test

[0206] The test sample is placed in an electric constant temperature blast oven, and the aging temperature and time are the same as those of alkaline aging.

[0207] 3. Detection method

[0208] 3.1 Quality change rate test

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

[0210] 3.2 Volume change rate test

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

[0212] 3.3 Mechanical properties test

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

[0214] 3.4 Crosslink density test

[0215] The cross-link density is tested using the equilibrium swelling method. First, the rubber is cut into blocks of about 1g and immersed in an acetone solution. After reaching equilibrium, the mass and density are tested. The cross-link density calculation formula is shown below:

[0216]

[0217]

[0218] The quantities in the formula represent the following:

[0219] ve : cross-linking density; χ: interaction parameter between EPDM and cyclohexane; V R : The volume of EPDM itself; V s : molar volume of cyclohexane; M i : The mass of unswollen EPDM; V r : Volume of EPDM after swelling; v sol : Volume of cyclohexane in EPDM after swelling; M f : the total mass of EPDM after swelling; ρ s : Density of cyclohexane.

[0220] 3.5 Micromorphology Characterization

[0221] The micromorphology of EPDM cross-sections before and after aging was observed using a SU8010 cold field emission scanning electron microscope (SEM). Because the sample is a polymer with poor conductivity, it required gold coating. The SEM sample preparation method was as follows: using liquid nitrogen freeze-fracture technology, the film was immersed in liquid nitrogen for 5 minutes to promote fracture. The sample was then quickly fractured using tweezers in the liquid nitrogen environment. Subsequently, the sample was fixed to a sample holder with the fracture surface facing up and gold coating was applied to 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, and stick them on a sample plate. Use an AMICUS X-ray photoelectron spectrometer to test the binding mode and element content of the carbon black surface groups before and after modification.

[0224] 4. Experimental results

[0225] 4.1 Effects of different types of carbon black filled rubber on physical and mechanical properties

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

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

[0228] Iodine absorption 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] The data in Tables 11 and 12 show that N990, due to its large particle size and small specific surface area, is 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, the greater the specific surface area, and the stronger its reinforcing effect on rubber.

[0233] Compression set can effectively measure the elasticity of rubber materials and the degree of recovery of rubber molecules after deformation. Figure 18 The following are the test results of the compression permanent deformation performance of rubber at room temperature after filling with 50 parts of seven different carbon blacks. Figure 18 It can be seen that N990 carbon black has the smallest compression set. This is mainly due to the large particle size and small specific surface area of ​​N990 carbon black, which results in less interaction between the carbon black particles and the rubber matrix. This results in less heat generation, lower viscosity, and lower shear forces during processing. Therefore, the rubber molecular chains are not damaged during processing, maintaining good elasticity. This results in a low compression set, but its reinforcement effect is poor, resulting in poor overall performance. Secondly, N234 carbon black has the smallest compression set. Considering its tensile strength and hardness, N234 carbon black has better reinforcement properties.

[0234] 4.2 Effect of carbon black type on EPDM alkali resistance

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

[0236] Aging will cause changes in the molecular structure of rubber, resulting in a certain degree of change in mass, volume and hardness. This is to explore the changes in the sample after aging. Figure 19 The changes in mass, volume and hardness of rubber filled with different types of carbon black after alkali aging.

[0237] according to Figure 19 It can be seen that the N234 carbon black-filled rubber has the smallest change in mass and volume, showing good alkali resistance. As the particle size increases, the mass change basically shows a phenomenon of first increasing and then decreasing. From the perspective of particle size, this is mainly because the smaller the particle size, the larger the specific surface area of ​​the carbon black, the stronger the binding ability to the rubber matrix, and the alkaline environment causes less damage to the interface between the carbon black and the rubber matrix. As the particle size increases, the binding ability of the carbon black particles to the rubber matrix weakens, and the degree of alkali damage to the carbon black and rubber interface increases. When the particle size increases to a certain extent, the carbon black can no longer reinforce the rubber matrix (such as N990). At this time, the interfacial bonding ability of the carbon black particles and the rubber matrix is ​​very weak without external damage, so the change in the mass and volume of the rubber after alkali aging is not large. With the exception of N990, the hardness changes of various 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. Table 13 shows that the mechanical properties of the N234 carbon black-filled rubber change relatively little after alkaline aging. Combined with the 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 and smaller specific surface areas, resulting in a weaker reinforcing effect. This suggests 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 superior alkali resistance to N200, indicating that the type and number of groups on the carbon black surface also affect the alkali resistance of the rubber after carbon black filling.

[0240] Table 13 Comparison of mechanical properties of seven carbon black filled EPDM rubbers 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 Strength 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 / % -16.14 -15.01 -25.84 -22.05 -25.34 -22.82 -18.92

[0242] 4.2.3 X-ray photoelectron spectroscopy

[0243] In order to explore the effect of carbon black surface properties on alkali resistance, XPS tests were carried out on different carbon blacks. Figure 20 Table 14 shows the full XPS spectra and surface elemental content of different carbon blacks. It can be seen that starting with N330, the number of surface oxygen groups increases with increasing particle size. Compared to N220, N234 has a lower oxygen content. Therefore, all other conditions being equal, fewer surface oxygen groups means fewer active sites on the carbon black surface that can react with alkali, resulting in greater alkali resistance.

[0244] Table 14 Element contents of seven kinds 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] In order to study the types and composition ratios of surface functional groups of different carbon black samples in detail, Figure 20 The C1s spectrum in the figure was fitted with peaks, and the corresponding peak distribution and quantitative results were shown in Figure 21 As shown in Table 15, it can be seen that the types of groups on the surfaces of the various carbon blacks are essentially the same. In addition to the C-C bond with a binding energy of approximately 284.8 eV, the main groups are carboxyl groups at approximately 288.8 eV and hydroxyl groups at approximately 286.5 eV. The group content varies among the various carbon blacks, with N234 carbon black having the lowest surface carboxyl content. Therefore, when other conditions are similar, the lower the surface carboxyl content, the greater the alkali resistance of the vulcanized rubber.

[0247] Table 15 Surface group content of 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 crosslink density

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

[0251] Table 16 Changes in crosslink density of seven carbon black filled EPDM rubbers after alkali 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 analysis and infrared spectroscopy, indicates that the reduction in crosslink density is primarily due to a weakening of the interfacial interaction between carbon black and rubber. In carbon black-filled EPDM rubber systems, carbon black primarily adsorbs EPDM molecular chains on its surface, forming an EPDM layer and acting as a physical crosslinking point. In an alkaline environment, the active sites on the carbon black surface are destroyed by the base, weakening the carbon black's ability to adsorb EPDM molecular chains and preventing the formation of a dense crosslinked network, resulting in a decrease in crosslink density. Therefore, the decrease in crosslink density reflects a weakening of the rubber network structure, which can lead to a decrease in the rubber's mechanical properties.

[0254] 4.2.5 Micromorphological changes

[0255] Scanning electron microscopy (SEM) was used to analyze the microstructure of EPDM aged samples after liquid nitrogen brittle fracture treatment. Figure 22 These are the micromorphologies of EPDM rubber filled with different carbon black in the original state, after air aging and alkali aging, where a1 to g1 are the micromorphologies of EPDM rubber filled with N220, N234, N330, N354, N550, N774 and N990 in the original state, a2 to g3 are the micromorphologies of EPDM rubber filled with N220, N234, N330, N354, N550, N774 and N990 after air aging, and a3 to g3 are the micromorphologies of EPDM rubber filled with N220, N234, N330, N354, N550, N774 and N990 after alkaline aging.

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

[0257] Unaged sample: 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 increases slightly, and microscopic defects such as holes begin to appear, indicating that air aging has damaged the rubber surface. However, the degree of damage is not large and the impact on the performance of the rubber is not significant.

[0259] Alkaline-aged samples: The surface roughness of the samples increased, and the number of holes and defects increased significantly. As the carbon black particle size increased, the hole diameter also increased accordingly. The surface roughness of the EPDM filled with N234 carbon black was relatively low, and no substantial defects were found, indicating that the carbon black filler still maintained a relatively strong bond with the rubber matrix, indicating that the sample had good alkali resistance. In comparison, although the number of holes in the rubber filled with N220 carbon black was small, the surface roughness was relatively high. For the N330 and N354 carbon black filled rubbers, the number of holes increased, indicating that the interface between the carbon black and the rubber matrix was destroyed by alkali, and the rubber's alkali resistance was weakened, resulting in an increase in defects and a decrease in performance. The increase in the size and number of large holes observed in the N550, N774, and N990 carbon black filled rubbers indicates that the interface between the larger carbon black particles and the rubber matrix was significantly weakened, further weakening the reinforcement effect of the carbon black and seriously affecting 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, high temperature aging has an impact on the performance of rubber. In order to exclude the possibility that high temperature causes the significant decline in performance of rubber after aging, the present invention conducted a hot air aging experiment. Figure 23 Table 17 is a comparison of the mechanical properties of EPDM rubber filled with seven kinds of carbon black after air aging. Figure 23 As shown in Table 17, the strength and hardness of each sample increased after hot air aging, while the elongation at break decreased. This indicates that the aging reaction caused by hot air aging is primarily cross-linking of the rubber. Compared with aging experiments in an alkaline environment, hot air aging did not cause a significant decrease in rubber properties.

[0262] Therefore, the significant performance degradation of carbon black-filled EPDM samples in alkaline environments is primarily due to corrosion from the alkaline medium. High-temperature hot air aging, while increasing the crosslink density of the rubber matrix, leads to increases in hardness and strength, but does not cause the same significant performance degradation observed in alkaline environments. Therefore, it is clearly confirmed that the presence of alkali has a significant negative effect on the performance of carbon black-filled rubber.

[0263] Table 17 Comparison of mechanical properties of seven carbon black filled EPDM rubbers 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 Strength 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 / % -12.06 -9.48 -15.31 -21.94 -1.29 -10.55 4.15

[0265] 5. Conclusion

[0266] This example compares the effects of seven different types of carbon black on rubber's alkali resistance, explaining why carbon black affects rubber's alkali resistance. The particle size and structure of carbon black significantly influence its reinforcing effect, which in turn influences rubber's alkali resistance. Experimental data shows that even materials with similar particle size and specific surface area (such as N220 and N234) exhibit varying alkali resistance, with N234 demonstrating superior alkali resistance, highlighting the influence of surface groups on rubber's alkali resistance.

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

[0268] It can be seen from Example 2 that 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, the alkali resistance of rubber can be further improved by surface modification of N234 using six different methods.

[0269] 1. Experimental sample preparation

[0270] 1.1 Rubber preparation

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

[0272] 1.2 Basic recipe

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

[0274] 1.3 Preparation of NaOH solution

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

[0276] 1.4 Carbon black modification

[0277] (1) High-temperature treatment: Weigh 20 g of carbon black and put it into a quartz boat. Place the quartz boat in a tube furnace and heat it to 900 °C at a rate of 5 °C / min under a nitrogen environment for 2 h. Then cool it down and mix it into rubber. It is named gCB.

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

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

[0280] (4) KOH activation treatment: Weigh 20g of carbon black and 60g of potassium hydroxide, add appropriate amount of deionized water and ethanol, mix them ultrasonically, and place them 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. Keep the temperature constant for 0.5h, then continue to heat it to 800℃ and keep the temperature constant for 2h. Wash the treated carbon black repeatedly with deionized water until the pH remains unchanged, filter it, and dry it in a 60℃ oven until it is dried. It is named kCB.

[0281] (5) Hydrogen bond or ionic bond: Weigh 20 g of carbon black and 2 g of 4-dimethylaminopyridine, mix them evenly, put them in a 140 °C oven for 4 h, and then take them out. The mixture is named 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 the pH is 6 and place in a 40℃ oven to dry for 12h. Disperse the dried carbon black in 1000ml of Tris, add 5g of DA and mix evenly with ultrasound. Stir and react at room temperature for 10h, then wash with deionized water 3-4 times and place in a 40℃ oven to dry for 48h. After drying, add it to 500ml of DMF and ultrasonicate for 30min. Pour it into a three-necked round-bottom flask, pass 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. It is named aCB.

[0283] Figure 24 The state of carbon black in water before and after hydrophobic modification. Figure 24 It can be seen that the unmodified carbon black sinks to the bottom of the water in a dispersed particle state, while the hydrophobically modified carbon black floats on the water surface and does 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 method

[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] Use O-ring to seal the simulation mold (such as Figure 25 As shown), the O-ring is squeezed and sealed, and placed in an autoclave, and NaOH solution is added into the autoclave to simulate the alkaline environment during actual use.

[0291] 1) Simulation of constant pressure conditions in the kettle

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

[0293] 2) Simulation of pressure change conditions in the kettle

[0294] Nitrogen was used to pressurize the autoclave to simulate the process of starting the machine, and the shutdown process was simulated by venting the pressure. The autoclave was frequently vented and deflated every day for 3 days. The pressure in the autoclave was as follows: Figure 26 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 Crosslink density test

[0301] Same as Example 2.

[0302] 4.4 Physical and mechanical properties test

[0303] Same as Example 2.

[0304] 4.5 Fourier transform infrared spectroscopy (FTIR) characterization

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

[0306] 4.6 Micromorphology 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 the ASAP2460 BET specific surface area test system. The sample was placed in a nitrogen medium for isothermal adsorption and desorption testing. The test data was fitted and calculated to obtain the specific surface area of ​​the sample.

[0312] 5. Experimental results

[0313] 5.1 Specific surface area and pore size analysis

[0314] In order to explore the changes in the specific surface area of ​​carbon black after modification, the N2 adsorption specific surface area of ​​carbon black was measured using BET, see Table 18.

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

[0316] N234 gB kC hB nB 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] Table 18 shows that the specific surface area of ​​carbon black (gCB) decreases slightly after high-temperature treatment, likely because high-temperature sintering causes carbon black to adhere to each other, resulting in larger carbon black particles and a decrease in specific surface area. The specific surface area of ​​carbon black (kCB) increases significantly after high-temperature treatment with KOH. This is primarily due to KOH's ability to activate carbon black, chemically reacting with it, and causing partial vapor etching at high temperatures, forming more micropores and mesoporous structures, thereby increasing the specific surface area. The increase in specific surface area of ​​carbon black (hCB) after nitric acid treatment is primarily due to the fact that nitric acid treatment removes impurities from the carbon black surface and, as a strong oxidant, oxidizes functional groups on the carbon black surface, increasing the number of oxygen-containing functional groups and micropores, thereby increasing the specific surface area. The specific surface area of ​​carbon black (nCB) treated with NaOH changes slightly, likely because the alkaline treatment removes some impurities from the carbon black surface, increasing the specific surface area. The reason for the decrease in the specific surface area of ​​pCB may be that after the formation of hydrogen bonds or ionic bonds, the pyridine groups will cover the surface of carbon black, filling some of the pores of carbon black, resulting in a decrease in specific surface area. The significant decrease in the specific surface area of ​​aCB is mainly because octadecyl isocyanate is a relatively long alkyl chain compound. When it reacts with the active sites on the surface of carbon black, the long alkyl chain will cover the surface of carbon black, causing the original pores on the surface of carbon black to be largely blocked, making the original rough surface smooth, thereby reducing the surface area. And after the long-chain molecules are grafted, the carbon black particles may aggregate through hydrophobic interactions (or other non-polar interactions), thereby forming larger particle agglomerates, which will also lead to a decrease in specific surface area.

[0318] 5.2X photoelectron spectroscopy

[0319] In order to verify whether the content of carboxyl groups on the surface of carbon black affects the alkali resistance of rubber, the XPS data of modified carbon black were subjected to peak separation to obtain the types and contents of surface groups of modified carbon black. The results are as follows: Figure 27 As shown. Figure 27 As can be seen from the graph, the carboxyl content on the gCB surface decreased by 2.51% and the hydroxyl content decreased by 4.07% compared to unmodified carbon black, demonstrating that high-temperature treatment can reduce 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%, demonstrating that NaOH treatment reduces the number of carboxyl groups on the carbon black surface and simultaneously introduces some hydroxyl groups, increasing the total amount of oxygen-containing groups on the carbon black surface. C=O groups appeared on the kCB surface, and the carboxyl content increased, demonstrating that KOH high-temperature activation treatment not only increases the specific surface area of ​​carbon black but also reacts with carbon black surface groups to generate ketone groups and other groups. The figure shows a significant increase in the carboxyl and hydroxyl content on the hCB surface, with the carboxyl content increasing by 4.37% and the hydroxyl content increasing by 14.05%, demonstrating that nitric acid treatment oxidizes the carbon black surface and increases the number of oxygen-containing groups on the carbon black surface.

[0320] Figure 28 The C1s and N1s peaks of aCB are shown below. The C1s peak shows a CN peak at 288.43 eV, indicating that the nitrogen element primarily originates from DA and octadecyl isocyanate. In the N1s peak, the peaks at 399.5 eV and 400.2 eV likely represent the amine reaction between DA or octadecyl isocyanate and DA. The -N=N- peak at 402.15 eV also indicates successful grafting of the alkylamine onto the carbon black. Overall, the XPS data demonstrate the successful carbon black modification and provide valuable support for subsequent experimental results.

[0321] 5.3 Infrared Spectroscopy

[0322] In order to investigate the changes in the surface groups of different modified carbon blacks, Fourier transform infrared spectroscopy tests were performed on different modified carbon blacks. The results are as follows: Figure 29 . Figure 29 Medium, 3432cm -1 The peak at 3217 cm is the -OH stretching vibration peak. -1 The stretching vibration of the C-H bond on the benzene ring is 1656 cm -1 and 1400cm -1 The -OH and C=O peaks of gCB are weakened after treatment, indicating that the oxygen-containing groups are reduced after high temperature treatment. -1 The peak at 1656 cm -1 The peak ratio at 3217 cm-1 increases, indicating that the oxygen-containing groups on the carbon black surface increase after nitric acid treatment.-1 The peak at 3432 cm-1 is reduced, indicating that the structure of carbon black is destroyed after activation treatment, and the number of -CH is reduced. -1 The peak at 1656 cm -1 The peak decreases, indicating that the carboxyl content of carbon black surface decreases and the hydroxyl content increases after NaOH treatment. -1 and 2845cm -1 The peaks at 1469 cm-1 are the -CH2 and -CH3 symmetrical stretching vibration peaks of octadecyl isocyanate. -1 The -CH3 vibration peak of the alkyl long chain is 721 cm -1 The skeleton vibration of -(CH2)n- is at 3340cm -1 and 1573cm -1 The peak at 1611 cm is the stretching vibration and bending vibration of the NH bond in the reaction, which is attributed to the amide group or carbamate. -1 The stretching vibration of C=O in -CONH- is 1240 cm -1 The characteristic peak of -COOR is at , and it can be seen from the infrared spectrum results that octadecyl isocyanate has been successfully grafted onto carbon black.

[0323] 5.4 Mechanical properties analysis

[0324] The mechanical properties test results 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 blacks

[0326] N234 gB kC hB nB 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] Table 19 shows that the modified carbon black exhibits improved elongation at break, reaching 945.69% for aCB. However, the tensile strength decreases significantly. This is primarily because, while the grafting of octadecyl isocyanate improves its dispersion in the rubber, the presence of long chains weakens the interfacial interaction between the carbon black and the rubber, resulting in a less dense and robust carbon black network and a reduction in the overall strength of the rubber. The increase in elongation at break is primarily due to the enhanced interactions between the molecular chains on the carbon black surface after grafting, which complicates the spatial structure between the molecules and leads to entanglement, resulting in a more stable structure. When the rubber is subjected to stress, the molecular chains can pull against each other, preventing them from breaking even under high strains, resulting in an increase in elongation at break. The high-temperature treatment of gCB is intended to reduce the number of oxygen-containing groups on the carbon black surface. This reduction weakens the interaction between the rubber and the carbon black, making it easier for these carbon black particles to migrate or be pulled out of the rubber under external forces, resulting in a decrease in rubber strength. Carbon black kCB treated with KOH high-temperature activation exhibits increased tensile strength but improved elongation at break. This is primarily due to high-temperature activation destroying the carbon black surface structure, increasing surface pores and specific surface area. This provides more surface area for bonding with the rubber, thereby strengthening the interfacial interaction between the rubber and carbon black. Carbon black hCB treated with nitric acid oxidation exhibits increased tensile strength and elongation at break. This is because nitric acid oxidation increases the carbon black's specific surface area and the number of surface oxygen groups, improving its dispersion in the rubber and enhancing its reinforcing effect. The tensile strength of nCB decreases while its elongation at break increases, primarily because the treatment reduces the number of carboxylic acid groups on the carbon black surface and increases the number of hydroxyl groups. This weakens the strong interaction between the carbon black and the rubber, making the carbon black network less compact and reducing tensile strength. During stretching, the molecular chains in the rubber can move and stretch more freely, resulting in an increase in elongation at break. Carbon black pCB treated with pyridine groups exhibits decreased tensile strength but increased elongation at break. This is primarily due to the formation of hydrogen or ionic bonds between the pyridine groups and the carbon black, which enhances the rubber's resistance to deformation and increases elongation at break.

[0328] 5.5 Analysis of mechanical properties after hot air aging

[0329] In order to investigate the difference in aging failure results between EPDM filled with different modified carbon blacks under hot air conditions and alkaline conditions, hot air aging experiments were carried out on different EPDMs in a 160℃ oven for 3 days.

[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 black after hot air aging

[0332] N234 gB kC hB nB pCB aCB Tensile strength / MPa 24.41 21.23 26.46 23.88 23.01 22.36 10.58 Strength 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 / % -9.48 -11.78 -8.72 -7.52 -11.83 -17.67 4.65

[0333] Figure 30 The change rate of strength and elongation of EPDM rubber filled with different modified carbon black after hot air aging. Figure 30 It can be seen that the change rates of strength and elongation of the samples after hot air aging are smaller than those after alkaline aging.

[0334] The experimental results above indicate that gCB, due to the removal of surface oxygen groups, 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 in a hot-oxidative environment, leading to an increase in crosslinking. kCB and hCB, due to the increased surface oxygen groups present in their kCB and hCB, strengthen the interfacial interaction between rubber and carbon black, making the rubber chains more resistant to hot-oxidative environments. Furthermore, the increased carboxyl content enhances carbon black's adsorption of free radicals or molecular chains, mitigating chain breakage or crosslinking caused by thermal oxidation. nCB, due to the reduced surface carboxyl content and increased hydroxyl content, can adsorb free radicals to a certain extent and resist crosslinking caused by hot-oxidative reactions. However, the hydrogen bonds formed between the hydroxyl groups and the rubber matrix may be disrupted by hot-oxidative reactions, reducing the mechanical properties of the rubber. pCB primarily interacts with rubber through hydrogen or ionic bonds, which are easily broken by hot-oxidative reactions. Therefore, when hydrogen bonds are broken, the resulting active sites are more susceptible to reaction with free radicals, increasing the degree of crosslinking. Because aCB is grafted with long-chain octadecyl isocyanate, it reduces the surface energy difference between carbon black and rubber through hydrophobic interaction, enhancing overall structural stability. The long chains also cover the active sites on the carbon black surface, reducing its adsorption of oxygen. The covered long chains also form a barrier, reducing the diffusion of heat and oxygen, thereby weakening crosslinking caused by aging.

[0335] This example not only compares the different failure mechanisms of rubber under alkaline aging and air aging conditions, eliminates the influence of the thermal oxidative environment on the alkaline aging experiment, but also obtains the change pattern of the modified carbon black filled rubber performance after thermal oxidative aging.

[0336] 5.6 Analysis of mechanical properties after alkaline aging

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

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

[0339] N234 gB kC hB nB pCB aCB Tensile strength / MPa 19.46 18.87 20.65 17.43 20.62 19.7 9.23 Strength 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 / % -15.01 -14.5 -19.29 -21.43 -17.58 -22.14 -9.2

[0340] Test results show that EPDM filled with aCB exhibits high alkali resistance. This is primarily due to the hydrophobic structure formed on the surface of the modified carbon black, which reduces direct contact between the strong alkaline solution and the rubber. This effectively reduces the damage caused by the NaOH solution to the rubber-carbon black interface and improves the alkali resistance of the EPDM.

[0341] EPDM containing modified carbon black (gCB) with a high-temperature surface treatment exhibited minimal degradation in mechanical properties in alkaline solutions. Compared to unmodified carbon black, the strength change rate decreased by 12.58%, while the elongation at break decreased by only 0.51%. This result is primarily due to the reduction of surface oxygen groups, which reduces the number of active sites susceptible to alkali attack. Although this modification resulted in a decrease in the initial mechanical properties of the EPDM composite, it reduced the magnitude of the change in mechanical properties before and after aging, thereby enhancing the material's alkali resistance.

[0342] EPDM containing modified carbon black (kCB) activated at high temperature with KOH exhibits a greater decrease in strength and elongation after alkaline aging than unmodified carbon black. This is primarily due to the increased number of surface pores in the activated carbon black, which enhances the adsorption capacity of the NaOH solution. This, in turn, increases the contact area between the alkali and the rubber, weakening the interfacial forces between the carbon black and the EPDM, potentially leading to damage to the rubber's main molecular chain.

[0343] hCB-type modified carbon black has improved surface polarity due to the increase in surface oxygen groups, thus improving its dispersibility in EPDM. However, under the influence of high temperature and 25% NaOH solution, the oxygen groups on the carbon black surface may react with alkali, which weakens the interfacial forces between the carbon black and EPDM and may cause damage to the carbon black structural network, reducing the EPDM's resistance to deformation and causing a significant decrease in tensile strength and elongation at break. Rubber containing nCB has a reduced surface carboxyl 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, which improves the rubber's alkali resistance.

[0344] The tensile strength and elongation at break of pCB type modified carbon black decreased after alkaline corrosion. The main reason was that the alkaline environment caused the hydrolysis or deprotonation of the pyridine group, weakening its interfacial bonding with the rubber molecular chain and inducing carbon black agglomeration and stress concentration.

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

[0346] 5.7.1 Mechanical properties analysis under constant pressure in the reactor

[0347] The gas pressure in the autoclave was maintained at 4 MPa, and the mechanical properties of the O-rings in compressed and uncompressed states before and after aging were tested, see Tables 22 and 23.

[0348] The test results show that the uncompressed O-ring exhibited greater aging than the compressed O-ring, and the same pattern as the laboratory dumbbell specimens indicates that both were in the chain scission aging stage. However, the compressed O-ring was in the crosslinking stage, which differs from the expected higher aging under compression. Possible reasons for this are: 1) In the laboratory, the EPDM and the uncompressed O-ring were completely immersed in the alkali solution, resulting in extensive contact with the solution. Under compression, however, the O-ring was squeezed by the mold, pressing against the mold wall, reducing its contact area with the alkali solution. 2) Under compression, the internal structure of the EPDM may become more compact, potentially enhancing the rubber's barrier properties and reducing the rate at which alkaline media enter the material. 3) Compression may promote crosslinking within the rubber, increasing the crosslink density. Rubber with a higher crosslink density exhibits greater chemical stability and improved resistance to alkali. 4) The stress condition may alter the orientation and alignment of the EPDM molecular chains. This orientation may, to some extent, alter the diffusion pathways, thereby affecting the diffusion of alkaline substances.

[0349] Table 22 Mechanical properties of uncompressed O-ring before and after constant pressure aging in the kettle

[0350]

[0351] Table 23 Mechanical properties of compressed O-ring before and after constant pressure aging in the kettle

[0352]

[0353] 5.7.2 Mechanical properties analysis under variable pressure conditions in the kettle

[0354] Because the actual working conditions of the laboratory experiment are different from those of the laboratory experiment, such as frequent start-up and shutdown, will occur during the industrial electrolysis of water to produce hydrogen, resulting in different laboratory aging conditions from the actual aging conditions. Therefore, in order to simulate the start-up and shutdown working conditions of the alkaline electrolysis cell, the experiment simulated the start-up process by pressurizing the autoclave with nitrogen and relieving the pressure by venting to simulate the shutdown process. Figure 32 shown.

[0355] Depend on Figure 32 It can be seen that after aging, the surface of the O-ring has lost its luster and has undergone severe permanent deformation. When the electrolyzer is operating, the gas generated by the electrolysis of water generates high pressure, squeezing the O-ring and causing it to deform. When the electrolyzer is shut down, the pressure in the electrolyzer decreases, and the deformation of the O-ring gradually recovers. If this continues for a long time, the deformation of the squeezed O-ring cannot be restored in time, and the sealing effect will be reduced when the gas is generated the next time the electrolyzer is turned on, which may cause the electrolyzer to leak.

[0356] Table 24 shows the mechanical properties of different O-rings after alkaline aging. Figure 33 The strength and elongation change rates of different O-rings after aging are shown in Table 24 and Figure 33 It can be seen that the alkali resistance of different O-rings is the same under laboratory aging and constant pressure conditions in the autoclave. N234 carbon black and modified aCB still have good alkali resistance, but the degree of aging of the O-rings is greater than that of the O-rings under constant pressure and compression in the autoclave. The main reasons for this are as follows: 1) The gas pressure remains constant, providing a stable environment, thereby making the chemical and physical aging processes experienced by the rubber O-rings relatively stable. 2) When the pressure in the autoclave changes cyclically, the O-rings experience additional physical stress, including changes in compression and tension. This cyclical pressure change can cause 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-rings after alkali aging

[0358]

[0359] 6. Conclusion

[0360] This embodiment improves the stability of rubber in harsh alkaline environments by performing specific chemical modifications on the surface of carbon black. The surface of carbon black contains carboxyl groups, 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 will be better. The large specific surface area of ​​carbon black easily leads to the adsorption of excessive alkali solution, which increases the contact between the rubber and the alkali solution. Thermal modification or hydrophobic modification of carbon black can reduce the carboxyl groups on the surface of carbon black and reduce the chance of it reacting with alkali solution, thereby improving the alkali aging resistance of the rubber; hydrophobically modified carbon black can slow down the corrosion of alkaline solution on the carbon black-rubber interface, thereby improving the alkali resistance stability of the rubber.

[0361] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for improving the alkaline aging resistance of EPDM rubber, characterized in that: The following steps are involved: Adding modified carbon black to EPDM rubber; The modified carbon black is thermally modified carbon black and / or hydrophobically modified carbon black; The preparation method of the thermally modified carbon black comprises the following steps: subjecting the carbon black to a heat treatment to obtain the thermally modified carbon black; the heat treatment temperature is 800-900°C; The preparation method of the hydrophobically modified carbon black comprises the following steps: subjecting carbon black to acid treatment to obtain acid-treated carbon black; mixing the acid-treated carbon black, a solvent and dopamine to carry out a first modification reaction to obtain dopamine-modified carbon black; and mixing the dopamine-modified carbon black, an alkyl isocyanate, polyethylene polyamine and a solvent to carry out a second modification reaction to obtain hydrophobically modified carbon black.

2. The method according to claim 1, characterized in that 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.

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

4. The method according to any one of claims 1 to 3, characterized in that The mass ratio of the dopamine-modified carbon black to the alkyl isocyanate is 20:25-26; the number of carbon atoms of the alkyl group in the alkyl isocyanate is 15-20; the polyethylene polyamine is triethylenediamine; the mass ratio of the dopamine-modified carbon black to the polyethylene polyamine is 20:2-5; and the temperature of the second modification reaction is 40-60°C.

5. The method according to any one of claims 1 to 4, characterized in that The carbon black used to prepare the thermally modified carbon black and the hydrophobically modified carbon black is of model N234.

6. The method according to any one of claims 1 to 5, characterized in that The filling amount of the modified carbon black is 30-50% of the mass of the EPDM rubber matrix.

7. The method according to any one of claims 1 to 6, characterized in that The method further comprises the step of adding an auxiliary agent to the EPDM rubber, wherein the auxiliary agent comprises one or more of an active agent, a plasticizer, an antioxidant, a crosslinking agent and a co-crosslinking agent.

8. A rubber composition, characterized in that The composition includes the following parts by weight: 100 parts of EPDM rubber, 30-50 parts of modified carbon black, 1-3 parts of vulcanizing agent, 0.5-2 parts of co-crosslinking agent, 2-5 parts of activating agent, 0.5-1 parts of plasticizer, 0.5-2 parts of antioxidant; The modified carbon black is thermally modified carbon black and / or hydrophobically modified carbon black; The preparation method of the thermally modified carbon black comprises the following steps: subjecting the carbon black to a heat treatment to obtain the thermally modified carbon black; the heat treatment temperature is 800-900°C; The preparation method of the hydrophobically modified carbon black comprises the following steps: subjecting carbon black to acid treatment to obtain acid-treated carbon black; mixing the acid-treated carbon black, a solvent and dopamine to carry out a first modification reaction to obtain dopamine-modified carbon black; and mixing the dopamine-modified carbon black, an alkyl isocyanate and polyethylene polyamine to carry out a second modification reaction to obtain hydrophobically modified carbon black.

9. The rubber composition according to claim 8, characterized in that The vulcanizing agent is one or both of dicumyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; the auxiliary cross-linking agent is one or both of triallyl isocyanurate and triallyl cyanurate; the activating agent is one or both of zinc oxide and calcium carbonate; the plasticizer is one or both of stearic acid and polyester; and the antioxidant is one or both of 2-mercaptobenzimidazole and 2,2,4-trimethyl-1,2-dihydroquinoline polymer.

10. Use of the rubber composition according to claim 8 or 9 in alkaline electrolytic cell seals.

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