Nanosilica modified zinc oxide synergistic anti-aging EPDM rubber and preparation method thereof

Abstract

The application provides a kind of nano-silica modified zinc oxide synergistic anti-aging EPDM rubber, by mass fraction, main raw materials include: EPDM rubber 80-120 parts, nano-silica 5-15 parts, modified zinc oxide 3-8 parts, antioxidant 1-4 parts, vulcanizing agent 0.8-3 parts, vulcanization accelerator 0.3-2 parts, unsaturated carboxylic acid 2-8 parts, hydroxy acid 1-5 parts, initiator 0.05-0.5 parts;The mass ratio of nano-silica and modified zinc oxide is 1.2-5:1;Modified zinc oxide is nano-zinc oxide modified by silane coupling agent KH560, and the average particle size of modified zinc oxide is less than 50nm, the specific surface area is greater than 40m 2 / g.The application improves the anti-aging property and mechanical property of EPDM rubber by the synergistic effect of modified nano-silica and modified zinc oxide with specific ratio, combined with precise raw material modification and segmented feeding process, and has performance, production and application advantages.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, and in particular relates to a nano-silica-modified zinc oxide synergistic aging-resistant EPDM rubber and its preparation method. Background Technology

[0002] Ethylene propylene diene monomer (EPDM) rubber is widely used in automotive seals (such as headlight seals and glass guide channels), air conditioning duct seals, and vibration damping seals for electronic components due to its excellent compression resilience, chemical stability, and weather resistance. It is particularly consumed in the sealing field. However, EPDM rubber is not self-reinforcing and requires filler reinforcement to meet practical application requirements. Traditional processes often use conventional fillers such as carbon black and silica, which not only require high filler content (often exceeding 50 parts) to improve mechanical properties but also easily lead to decreased processing fluidity. Furthermore, a single filler cannot simultaneously achieve synergistic optimization of aging resistance, heat insulation, and vibration damping. For example, automotive headlight seals, subjected to long-term high temperatures in the engine compartment and outdoor exposure, are prone to stress relaxation and decreased resilience, leading to rainwater leakage and headlight fogging. Air conditioning duct seals, due to the uneven dispersion of traditional fillers, have limited vibration damping and noise reduction effects, and long-term use can easily cause duct rupture, increasing maintenance costs.

[0003] To improve the performance of EPDM, existing technologies have explored various improvement schemes: some schemes involve spraying expanded perlite micron powder thermal insulation paint or silica aerogel coating onto the EPDM surface, which can improve thermal insulation performance, but the adhesion between the coating and the substrate is weak, making it prone to detachment under long-term vibration, and the aging resistance problem of the EPDM itself is not solved; other schemes involve constructing a double cross-linked network (such as introducing graphene or liquid metal hybrid fillers) or adding PTFE / molybdenum disulfide composite powder, which can enhance mechanical properties or reduce the coefficient of friction, but have problems such as complex processes (e.g., ultrasonic dispersion, multi-step cross-linking), high costs, or poor compatibility between inorganic powders and the EPDM matrix, making it difficult to balance performance synergy with the needs of industrial production. In addition, existing aging resistance improvements mostly rely on single antioxidants, without forming a synergistic mechanism between fillers and antioxidants. Under complex operating conditions such as high temperature and humidity, EPDM seals are still prone to aging failure and cannot meet the requirements of long-term service. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a nano-silica-modified zinc oxide synergistic aging-resistant EPDM rubber and its preparation method. Through the synergistic effect of modified nano-silica and modified zinc oxide in a specific ratio, combined with precise raw material modification and segmented feeding processes, the aging resistance and mechanical properties of EPDM rubber are significantly improved. It is suitable for industrial production and can be widely used in automotive, air conditioning, and electronic device sealing applications, possessing advantages in performance, production, and application.

[0005] This invention provides a nano-silica-modified zinc oxide synergistic anti-aging EPDM rubber. By weight, the main raw materials include: 80-120 parts EPDM rubber, 5-15 parts nano-silica, 3-8 parts modified zinc oxide, 1-4 parts antioxidant, 0.8-3 parts vulcanizing agent, 0.3-2 parts vulcanization accelerator, 2-8 parts unsaturated carboxylic acid, 1-5 parts hydroxy acid, and 0.05-0.5 parts initiator. The mass ratio of nano-silica to modified zinc oxide is 1.2-5:1. The modified zinc oxide is nano-zinc oxide modified with silane coupling agent KH560, and the average particle size of the modified zinc oxide is less than 50 nm, with a specific surface area greater than 40 m². 2 / g.

[0006] Furthermore, the nano-silica is fumed silica and is surface-modified with γ-aminopropyltriethoxysilane;

[0007] The modification process is as follows: fumed silica nanoparticles are dispersed in an ethanol-water mixed solvent with a volume ratio of ethanol to water of 4-6:1 and an amount of ethanol-water mixed solvent of 20-50 times the mass of the silica nanoparticles. γ-aminopropyltriethoxysilane is added at an amount of 5%-10% of the silica nanoparticles. The mixture is stirred at 70-85°C for 3-5 hours, centrifuged, and then vacuum dried at 80-90°C for 5-7 hours to obtain surface-modified silica nanoparticles. The surface amino content of the modified silica nanoparticles is 0.8-1.5 mmol / g, and the particle size distribution range is 10-30 nm.

[0008] Furthermore, the antioxidant is a compound system composed of N-phenyl-α-naphthylamine, 2-mercaptobenzimidazole, and N-(4-anilinophenyl)maleimide in a mass ratio of 1-2:1-3:0.5-1.5; the vulcanizing agent is one or more of dicumyl peroxide, bis-tert-butylperoxide, and sulfur; and the vulcanization accelerator is one or more of triallyl isocyanurate and zinc methacrylate.

[0009] Further, the unsaturated carboxylic acid is one or more of acrylic acid, methacrylic acid, and maleic acid; the hydroxy acid is one or more of lactic acid, γ-hydroxybutyric acid, and aspartic acid; and the initiator is one or more of benzoyl peroxide, azobisisobutyronitrile, and di-tert-butyl peroxide.

[0010] This invention provides a method for preparing the above-mentioned nano-silica modified zinc oxide synergistic aging-resistant EPDM rubber, comprising the following steps:

[0011] (1) Preparation of modified zinc oxide: Disperse nano zinc oxide in an ethanol-water mixed solvent, the amount of ethanol-water mixed solvent being 20-50 times the mass of nano zinc oxide, add silane coupling agent KH560, stir and react at 60-80℃ for 2-4h, centrifuge and then vacuum dry at 80-100℃ for 4-6h to obtain modified zinc oxide;

[0012] (2) Preparation of carboxylated EPDM: Add EPDM rubber to a mixer and melt it at 160-180℃ for 1-2 min. Then add unsaturated carboxylic acid, initiator and hydroxy acid in sequence. Shear reaction at 50-60 r / min for 8-15 min. Remove the rubber to obtain carboxylated EPDM.

[0013] (3) Preparation of composite rubber: Plasticize carboxylated EPDM on a two-roll mill for 1-2 min, and add nano silica and modified zinc oxide in a segmented feeding method: first add 50% nano silica and 50% modified zinc oxide, mix for 1-2 min, then add the remaining nano silica and modified zinc oxide, continue mixing for 2-3 min, and add antioxidant, vulcanizing agent and vulcanization accelerator in sequence, and mix evenly to obtain compound rubber; let the compound rubber stand at room temperature for 12-24 h, and then hot press vulcanize at 150-170℃ and 12-18MPa for 10-25 min to obtain nano silica-modified zinc oxide synergistic aging resistant EPDM rubber.

[0014] Further, in step (1), the volume ratio of ethanol to water in the ethanol-water mixed solvent is 3-5:1; the amount of silane coupling agent KH560 added is 3%-8% of the mass of nano zinc oxide.

[0015] Further, in step (2), the amount of unsaturated carboxylic acid added is 2%-8% of the mass of EPDM rubber; the amount of hydroxy acid added is 1%-5% of the mass of EPDM rubber; and the amount of initiator added is 0.05%-0.5% of the mass of EPDM rubber.

[0016] Furthermore, in step (3), the temperature of the open mill is controlled at 40-60℃; the compound rubber needs to be left at room temperature for 12-24 hours before hot pressing and vulcanization.

[0017] Furthermore, in step (3), the mixing speed of the segmented feeding is controlled at 40-50 r / min.

[0018] This invention provides an application of the above-mentioned nano-silica modified zinc oxide synergistic aging-resistant EPDM rubber in automotive seals, air conditioning duct seals, or vibration damping seals for electronic devices.

[0019] The advantages and positive effects of this invention are:

[0020] 1. This invention significantly improves the aging resistance of EPDM rubber through the synergistic effect of nano-silica and modified zinc oxide, combined with a compound antioxidant system. At the same time, the reinforcing network constructed by the two significantly improves the tensile strength and tear strength of the rubber, solving the problems of easy aging and performance degradation of traditional products.

[0021] 2. This invention employs precise process control, such as segmented feeding, to ensure uniform dispersion of fillers and guarantee stable product quality. The equipment used is conventional in the rubber industry, and key parameters are easily quantifiable and controllable, making it directly adaptable to industrial production and reducing production and debugging costs.

[0022] 3. The rubber material prepared by the technical solution of the present invention is suitable for various scenarios such as automotive seals, air conditioning pipe seals, and vibration damping seals for electronic devices. It can meet the requirements of different application environments for material aging resistance, sealing and vibration damping, and has good practical application value. Detailed Implementation

[0023] The following provides a more comprehensive description of exemplary embodiments of this disclosure. The technical solutions in the embodiments of this disclosure will be clearly and completely described below. Obviously, the described embodiments are merely some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0024] This invention provides a nano-silica-modified zinc oxide synergistic anti-aging EPDM rubber. By weight, the main raw materials include: 80-120 parts EPDM rubber, 5-15 parts nano-silica, 3-8 parts modified zinc oxide, 1-4 parts antioxidant, 0.8-3 parts vulcanizing agent, 0.3-2 parts vulcanization accelerator, 2-8 parts unsaturated carboxylic acid, 1-5 parts hydroxy acid, and 0.05-0.5 parts initiator; the mass ratio of nano-silica to modified zinc oxide is 1.2-5:1; the modified zinc oxide is nano-zinc oxide modified with silane coupling agent KH560, and the average particle size of the modified zinc oxide is less than 50 nm, with a specific surface area greater than 40 m². 2 / g.

[0025] Specifically, the nano-silica is fumed silica, and it is surface-modified with γ-aminopropyltriethoxysilane. The modification process is as follows: fumed silica is dispersed in an ethanol-water mixed solvent with a volume ratio of ethanol to water of 4-6:1 and the amount of ethanol-water mixed solvent is 20-50 times the mass of the nano-silica. γ-aminopropyltriethoxysilane is added at a concentration of 5%-10% of the mass of the nano-silica. The mixture is stirred at 70-85℃ for 3-5 hours, centrifuged, and then vacuum-dried at 80-90℃ for 5-7 hours to obtain surface-modified nano-silica. The surface amino content of the modified nano-silica is 0.8-1.5 mmol / g, and the particle size distribution range is 10-30 nm.

[0026] Specifically, the antioxidant is a compound system composed of N-phenyl-α-naphthylamine, 2-mercaptobenzimidazole, and N-(4-anilinophenyl)maleimide in a mass ratio of 1-2:1-3:0.5-1.5; the vulcanizing agent is one or more of dicumyl peroxide, bis-tert-butylperoxide, and sulfur; and the vulcanization accelerator is one or more of triallyl isocyanurate and zinc methacrylate.

[0027] Specifically, the unsaturated carboxylic acid is one or more of acrylic acid, methacrylic acid, and maleic acid; the hydroxy acid is one or more of lactic acid, γ-hydroxybutyric acid, and aspartic acid; and the initiator is one or more of benzoyl peroxide, azobisisobutyronitrile, and di-tert-butyl peroxide.

[0028] This invention provides a method for preparing the above-mentioned nano-silica modified zinc oxide synergistic aging-resistant EPDM rubber, comprising the following steps:

[0029] (1) Preparation of modified zinc oxide: Disperse nano zinc oxide in an ethanol-water mixed solvent, the amount of ethanol-water mixed solvent being 20-50 times the mass of nano zinc oxide, add silane coupling agent KH560, stir and react at 60-80℃ for 2-4h, centrifuge and then vacuum dry at 80-100℃ for 4-6h to obtain modified zinc oxide;

[0030] (2) Preparation of carboxylated EPDM: Add EPDM rubber to a mixer and melt it at 160-180℃ for 1-2 min. Then add unsaturated carboxylic acid, initiator and hydroxy acid in sequence. Shear reaction at 50-60 r / min for 8-15 min. Remove the rubber to obtain carboxylated EPDM.

[0031] (3) Preparation of composite rubber: Plasticize carboxylated EPDM on a two-roll mill for 1-2 min, and add nano silica and modified zinc oxide in a segmented feeding method: first add 50% nano silica and 50% modified zinc oxide, mix for 1-2 min, then add the remaining nano silica and modified zinc oxide, continue mixing for 2-3 min, and add antioxidant, vulcanizing agent and vulcanization accelerator in sequence, and mix evenly to obtain compound rubber; let the compound rubber stand at room temperature for 12-24 h, and then hot press vulcanize at 150-170℃ and 12-18MPa for 10-25 min to obtain nano silica-modified zinc oxide synergistic aging resistant EPDM rubber.

[0032] In step (1), the volume ratio of ethanol to water in the ethanol-water mixed solvent is 3-5:1; the amount of silane coupling agent KH560 added is 3%-8% of the mass of nano zinc oxide.

[0033] In step (2), the amount of unsaturated carboxylic acid added is 2-8% of the mass of EPDM rubber; the amount of hydroxy acid added is 1-5% of the mass of EPDM rubber; and the amount of initiator added is 0.05-0.5% of the mass of EPDM rubber.

[0034] In step (3), the temperature of the open mill is controlled at 40-60℃; the compound rubber needs to be left at room temperature for 12-24 hours before hot pressing and vulcanization.

[0035] In step (3), the mixing speed of the segmented feeding is controlled at 40-50 r / min.

[0036] This invention provides an application of the above-mentioned nano-silica modified zinc oxide synergistic aging-resistant EPDM rubber in automotive seals, air conditioning duct seals, or vibration damping seals for electronic devices.

[0037] Raw materials and equipment

[0038] EPDM rubber: grade Keltan5149, ethylene content 50%, Mooney viscosity ML1+4 (125℃) = 50, purchased from Arlanxon High Performance Elastomers (Changzhou) Co., Ltd.

[0039] Vapor phase nano-silica: Grade AEROSIL200, original particle size 12nm, specific surface area 200±25m² 2 / g, purchased from Degussa (China) Investment Co., Ltd.;

[0040] Nano zinc oxide: average particle size 30nm, specific surface area 50±5m² 2 / g, purity ≥99.5%, purchased from Jining Bora Carbon Materials Co., Ltd.;

[0041] Silane coupling agent KH560: γ-glycidyl etheroxypropyltrimethoxysilane, purity ≥98%, Jiangsu Tengda Additives Co., Ltd.;

[0042] γ-aminopropyltriethoxysilane (KH550): purity ≥97%, refractive index 1.418-1.422, Jiangsu Tengda Additives Co., Ltd.

[0043] Antioxidant N-phenyl-α-naphthylamine (antioxidant A): industrial grade, melting point 58-63℃, purity ≥95%, purchased from Jiangsu Tengda Additives Co., Ltd.

[0044] Antioxidant 2-mercaptobenzimidazole (antioxidant MB): industrial grade, melting point 290-295℃, purity ≥98%, purchased from Jiangsu Tengda Additives Co., Ltd.

[0045] Antioxidant N-(4-anilinephenyl)maleimide (antioxidant MC): industrial grade, melting point 200-205℃, purity ≥98%, purchased from Jiangsu Tengda Additives Co., Ltd.

[0046] The vulcanizing agent, dicumyl peroxide (DCP), has a purity of 98% and a half-life of 160℃ / 1min. It was purchased from Jiangsu Tengda Additives Co., Ltd.

[0047] The vulcanizing agent, bis-tert-butyl peroxide isopropylbenzene (BIPB), has a purity of 98% and a half-life of 170℃ / 1min. It was purchased from Jiangsu Tengda Additives Co., Ltd.

[0048] Sulfur for vulcanizing: Industrial grade, particle size 100 mesh, purity ≥99.5%, purchased from Jiangsu Tengda Additives Co., Ltd.

[0049] Vulcanization accelerator triallyl isocyanurate (TAIC): industrial grade, purity ≥95%, refractive index 1.503-1.507, purchased from Jiangsu Tengda Additives Co., Ltd.

[0050] Zinc methacrylate (ZDMA), vulcanization accelerator: industrial grade, particle size 500 mesh, purity ≥98%, purchased from Jiangsu Tengda Additives Co., Ltd.

[0051] Unsaturated carboxylic acid (methacrylic acid): purity ≥99%, density 0.954 g / cm³ 3 (20℃), purchased from Shanghai Yan'an Oil & Chemical Co., Ltd.;

[0052] Unsaturated carboxylic acid (maleic acid): purity ≥99%, melting point 138-141℃, purchased from Shanghai Yan'an Oil & Chemical Co., Ltd.

[0053] Unsaturated carboxylic acid (acrylic acid): purity ≥99%, density 1.0511 g / cm³ 3 (20℃), purchased from Shanghai Yan'an Oil & Chemical Co., Ltd.;

[0054] Hydroxy acid (aspartic acid): food grade, L-type, melting point 270℃ (decomposes), purity ≥98%, purchased from Shanghai Yan'an Oil & Chemical Co., Ltd.

[0055] Hydroxy acid (lactic acid): Food grade, 85% aqueous solution, density 1.209 g / cm³ 3 (20℃), purchased from Shanghai Yan'an Oil & Chemical Co., Ltd.;

[0056] Hydroxy acid (γ-hydroxybutyric acid): purity ≥99%, melting point 48-50℃, liquid at room temperature (must be sealed and moisture-proof), non-aqueous solution, purchased from Shanghai Yan'an Oil & Chemical Co., Ltd.

[0057] Initiator benzoyl peroxide (BPO): purity 98%, melting point 103-106℃, active oxygen content 6.9%, purchased from Shandong Yanggu Huatai Chemical Co., Ltd.

[0058] Initiator azobisisobutyronitrile (AIBN): purity 98%, melting point 102-104℃, half-life 64℃ / 10h, purchased from Shandong Yanggu Huatai Chemical Co., Ltd.

[0059] Initiator di-tert-butyl peroxide: purity ≥98%, half-life at 180℃ approximately 0.1 h, purchased from Shandong Yanggu Huatai Chemical Co., Ltd.

[0060] The models, manufacturers, and corresponding uses of the equipment used in this specific embodiment are as follows:

[0061] Internal mixer: Model XSM500, manufactured by Shanghai Rubber Machinery Factory No. 1, mainly used for the preparation of carboxylated EPDM and the premixing of raw materials;

[0062] Opening mill: Model XK160, manufactured by Shanghai Rubber Machinery Factory No. 1, its function is to mix compound rubbers;

[0063] Vacuum drying oven: Model DZF6050, manufactured by Shanghai Jinghong Experimental Equipment Co., Ltd., used for drying modified zinc oxide and modified nano-silica;

[0064] High-speed centrifuge: Model TGL16M, manufactured by Hunan Xiangyi Laboratory Instrument Development Co., Ltd., is used to separate modified zinc oxide from modified nano-silica.

[0065] Hot press vulcanizing machine: Model XLBD400×400, manufactured by Qingdao Yadong Rubber Machinery Co., Ltd., mainly used for vulcanization molding of composite rubber;

[0066] Electronic universal testing machine: Model WDW50, manufactured by Jinan TestJin Group Co., Ltd., used to test the tensile strength and elongation at break of samples;

[0067] Shore hardness tester: Model LXA, manufactured by Shanghai Liuling Instrument Factory, its function is to measure the Shore hardness of a sample;

[0068] Thermo-oxidative aging test chamber: Model 401A, manufactured by Shanghai Experimental Instrument Factory Co., Ltd., used to conduct thermo-oxidative aging performance tests on samples.

[0069] Stress relaxation tester: Model RLX200, manufactured by Changchun Intelligent Instrument Equipment Co., Ltd., is mainly used to test the stress relaxation coefficient of samples;

[0070] Surface amino content analyzer: Model TOCL, manufactured by Shimadzu Enterprise Management (China) Co., Ltd., used to determine the amino content on the surface of nano-silica;

[0071] Laser particle size analyzer: Model Mastersizer3000, manufactured by Malvern Instruments Ltd., used to test the particle size of modified zinc oxide and nano silica;

[0072] Specific surface area analyzer: Model ASAP2460, manufactured by McMurray Instruments (Shanghai) Co., Ltd., used to determine the specific surface area of ​​modified zinc oxide.

[0073] Ultrasonic dispersion equipment: adjustable power 1200-2000W, frequency 20kHz, used for dispersion of nano-silica.

[0074] Example 1

[0075] I. Preparation of Modified Zinc Oxide

[0076] Weigh 3g of nano-zinc oxide and add it to a 500mL three-necked flask. Pour 200mL of an ethanol-water mixture (ethanol to water volume ratio 3:1) into the flask. Turn on a mechanical stirrer at 300r / min and a constant temperature water bath, and slowly heat to 60℃. Weigh 0.09g of silane coupling agent KH560 (3% of the nano-zinc oxide mass), dilute it with 10mL of anhydrous ethanol, and slowly add it dropwise to the three-necked flask at a rate of 1 drop / s. After the addition is complete, maintain the reaction temperature at 60℃ and continue stirring for 4 hours. After the reaction is complete, transfer the mixture in the flask to a centrifuge tube and centrifuge at 3000r / min for 10 minutes. Discard the supernatant. Collect the solid material at the bottom of the centrifuge tube, wash it three times with deionized water (50mL each time), and then wash it once with 50mL of anhydrous ethanol. The washed solid was placed in a vacuum drying oven and dried under vacuum at 80℃ and 0.09MPa for 6 hours. After drying, the solid was removed and gently ground in a mortar to obtain modified zinc oxide. Testing showed that the modified zinc oxide had an average particle size of 45nm and a specific surface area of ​​45m². 2 / g.

[0077] II. Preparation of Surface-Modified Nano-Silica

[0078] Weigh 5g of fumed silica nanoparticles and add them to a 500mL three-necked flask. Add 200mL of an ethanol-water mixture (ethanol to water volume ratio of 4:1) to the flask. Turn on an ultrasonic dispersion device with a power of 1200W and a frequency of 20kHz and ultrasonically disperse the mixture for 30min to form a uniform dispersion. Weigh 0.25g of γ-aminopropyltriethoxysilane (5% of the mass of the fumed silica nanoparticles) and add it to the dispersion prepared above. Turn on a mechanical stirrer at 300r / min and a constant temperature water bath, slowly raise the temperature to 70℃, and maintain this temperature while stirring for 3h. After the reaction is complete, transfer the dispersion to a centrifuge tube and centrifuge at 4000r / min for 8min. Discard the supernatant. Collect the solid material at the bottom of the centrifuge tube, wash it three times with deionized water (50mL each time), and then wash it once with 50mL of anhydrous ethanol. The washed solid was placed in a vacuum drying oven and dried under vacuum at 80℃ and 0.09MPa for 5 hours. After drying, the solid was taken out and gently ground with a mortar to obtain surface-modified nano-silica. The surface amino content of the surface-modified nano-silica was found to be 0.8 mmol / g, and the particle size distribution range was 10-25 nm.

[0079] III. Preparation of Carboxylated EPDM

[0080] Turn on the internal mixer and set the equipment temperature to 160℃ and the rotation speed to 50 r / min. Weigh 80g of EPDM rubber and add it to the mixing chamber of the internal mixer. After the rubber melts for 1 minute, add 2% (by weight of the EPDM rubber) of unsaturated carboxylic acid (methacrylic acid), totaling 1.6g, and mix for 1 minute. Then add 0.05% (by weight of the EPDM rubber) of initiator BPO, totaling 0.04g, and mix for 3 minutes. Finally, add 1% (by weight of the EPDM rubber) of hydroxy acid (aspartic acid), totaling 0.8g, and maintain a rotation speed of 50 r / min for a shear reaction for 15 minutes. After the reaction is complete, open the discharge port of the internal mixer and collect the carboxylated EPDM. The carboxyl grafting rate of the carboxylated EPDM is tested by acid-base titration. The results show that the carboxyl grafting rate is 1.2 mmol / g, indicating that carboxyl groups have been successfully introduced into the EPDM molecular chain.

[0081] IV. Preparation of Composite Rubber

[0082] Turn on the open mill and set the equipment temperature to 40℃ and the roll gap to 2mm. Weigh the carboxylated EPDM prepared above and add it to the open mill. Perform a plasticizing treatment for 2 minutes to fully soften the rubber compound. Add fillers in stages: First, add 2.5g of surface-modified nano silica and 1.5g of modified zinc oxide (both 50% of the total amount of the two fillers). Mix for 1 minute and then perform a venting operation (the venting height is 20% of the open mill roll gap). Continue mixing for 1 minute. Then add the remaining 2.5g of surface-modified nano silica and 1.5g of modified zinc oxide. Mix for 2 minutes and then perform another venting operation. Continue mixing for 1 minute. Subsequently, 1g of antioxidant (composed of 0.4g N-phenyl-α-naphthylamine, 0.4g 2-mercaptobenzimidazole, and 0.2g N-(4-anilinephenyl)maleimide in a mass ratio of 1:1:0.5), 0.8g of vulcanizing agent DCP, and 0.3g of vulcanization accelerator TAIC were added sequentially, and the mixture was continuously mixed for 5 minutes until the rubber compound was homogeneous. The compound was then sheeted to obtain the rubber compound. The rubber compound was placed in an environment with a room temperature of 23℃ and a relative humidity of 40% for 24 hours. After that, the rubber compound was placed in the mold of a hot press vulcanizing machine, and the temperature was set to 150℃ and the pressure to 12MPa for 25 minutes of hot press vulcanization. After vulcanization, the product was allowed to cool naturally to room temperature, and the nano-silica modified zinc oxide synergistic aging-resistant EPDM rubber was obtained.

[0083] Example 2

[0084] I. Preparation of Modified Zinc Oxide

[0085] Weigh 5g of nano-zinc oxide and add it to a 500mL three-necked flask. Pour 250mL of an ethanol-water mixture (ethanol to water volume ratio 4:1) into the flask. Turn on a mechanical stirrer at 300r / min and a constant temperature water bath, and slowly heat to 70℃. Weigh 0.25g of silane coupling agent KH560 (5% of the nano-zinc oxide mass), dilute it with 15mL of anhydrous ethanol, and slowly add it dropwise to the three-necked flask at a rate of 1 drop / s. After the addition is complete, maintain the reaction temperature at 70℃ and continue stirring for 3 hours. After the reaction is complete, transfer the mixture in the flask to a centrifuge tube and centrifuge at 4000r / min for 8 minutes. Discard the supernatant. Collect the solid material at the bottom of the centrifuge tube, wash it three times with deionized water (50mL each time), and then wash it once with 50mL of anhydrous ethanol. The washed solid was placed in a vacuum drying oven and dried under vacuum at 90℃ and 0.09MPa for 5 hours. After drying, the solid was removed and gently ground in a mortar to obtain modified zinc oxide. Testing showed that the modified zinc oxide had an average particle size of 40nm and a specific surface area of ​​48m². 2 / g.

[0086] II. Preparation of Surface-Modified Nano-Silica

[0087] Weigh 10g of fumed silica nanoparticles and add them to a 1000mL three-necked flask. Add 500mL of an ethanol-water mixture (ethanol to water volume ratio of 5:1) to the flask. Turn on an ultrasonic dispersion device with a power of 1500W and a frequency of 20kHz and ultrasonically disperse the mixture for 40min to form a uniform dispersion. Weigh 0.8g of γ-aminopropyltriethoxysilane (8% of the mass of the fumed silica nanoparticles) and add it to the dispersion prepared above. Turn on a mechanical stirrer at 300r / min and a constant temperature water bath, slowly raise the temperature to 80℃, and maintain this temperature while stirring for 4h. After the reaction is complete, transfer the dispersion to a centrifuge tube and centrifuge at 4500r / min for 7min. Discard the supernatant. Collect the solid material at the bottom of the centrifuge tube, wash it three times with deionized water (80mL each time), and then wash it once with 80mL of anhydrous ethanol. The washed solid was placed in a vacuum drying oven and dried under vacuum for 6 hours at a temperature of 85℃ and a pressure of 0.09MPa. After drying, the solid was taken out and gently ground with a mortar to obtain surface-modified nano-silica. The surface amino content of the surface-modified nano-silica was found to be 1.2 mmol / g, and the particle size distribution range was 12-28 nm.

[0088] III. Preparation of Carboxylated EPDM

[0089] Turn on the internal mixer and set the equipment temperature to 170℃ and the rotation speed to 55 r / min. Weigh 100g of EPDM rubber and add it to the mixing chamber of the internal mixer. After the rubber melts for 1.5 min, add 5g of unsaturated carboxylic acid (maleic acid) at 5% of the EPDM rubber mass, and mix for 1.5 min. Then add 0.2g of initiator BPO at 0.2% of the EPDM rubber mass, and mix for 3 min. Finally, add 3g of hydroxy acid (lactic acid) at 3% of the EPDM rubber mass, and maintain the rotation speed at 55 r / min for a shear reaction for 12 min. After the reaction is complete, open the discharge port of the internal mixer and collect the carboxylated EPDM. The carboxyl grafting rate of the carboxylated EPDM is tested by acid-base titration. The results show that the carboxyl grafting rate is 1.6 mmol / g, indicating that carboxyl groups have been successfully introduced into the EPDM molecular chain.

[0090] IV. Preparation of Composite Rubber

[0091] Turn on the open mill and set the equipment temperature to 50℃ and the roll gap to 2mm. Weigh the carboxylated EPDM prepared above and add it to the open mill. Perform a plasticizing treatment for 1.5 minutes to fully soften the rubber compound. Add fillers in stages: First, add 5g of surface-modified nano silica and 2.5g of modified zinc oxide (both 50% of the total amount of the two fillers), mix for 1 minute, and then perform a venting operation (the venting height is 25% of the open mill roll gap). Continue mixing for 0.5 minutes. Then add the remaining 5g of surface-modified nano silica and 2.5g of modified zinc oxide, mix for 2 minutes, perform another venting operation, and continue mixing for 0.5 minutes. Subsequently, 2g of antioxidant (0.67g N-phenyl-α-naphthylamine, 1g 2-mercaptobenzimidazole, and 0.33g N-(4-anilinephenyl)maleimide, compounded in a mass ratio of 2:3:1), 1.5g of vulcanizing agent (compounded from 0.75g dicumyl peroxide (DCP) and 0.75g sulfur in a mass ratio of 1:1), and 1g of vulcanization accelerator zinc methacrylate (ZDMA) were added sequentially. The mixture was continuously mixed for 6 minutes until the rubber compound was homogeneous, and then sheeted to obtain the compound. The compound was placed in an environment with a room temperature of 23℃ and a relative humidity of 50% for 18 hours. After that, the compound was placed in the mold of a hot press vulcanizing machine, and the temperature was set to 160℃ and the pressure to 15MPa for 18 minutes of hot press vulcanization. After vulcanization, the product was naturally cooled to room temperature, and the nano-silica modified zinc oxide synergistic aging-resistant EPDM rubber was obtained.

[0092] Example 3

[0093] I. Preparation of Modified Zinc Oxide

[0094] Weigh 8g of nano-zinc oxide and add it to a 1000mL three-necked flask. Pour 400mL of an ethanol-water mixture (ethanol to water volume ratio 5:1) into the flask. Turn on a mechanical stirrer at 300r / min and a constant temperature water bath, and slowly heat to 80℃. Weigh 0.64g of silane coupling agent KH560 (8% of the nano-zinc oxide mass), dilute it with 20mL of anhydrous ethanol, and slowly add it dropwise to the three-necked flask at a rate of 1 drop / s. After the addition is complete, maintain the reaction temperature at 80℃ and continue stirring for 2 hours. After the reaction is complete, transfer the mixture in the flask to a centrifuge tube and centrifuge at 5000r / min for 5 minutes. Discard the supernatant. Collect the solid material at the bottom of the centrifuge tube, wash it three times with deionized water (100mL each time), and then wash it once with 100mL of anhydrous ethanol. The washed solid was placed in a vacuum drying oven and dried under vacuum at 100℃ and 0.09MPa for 4 hours. After drying, the solid was removed and gently ground in a mortar to obtain modified zinc oxide. Testing showed that the modified zinc oxide had an average particle size of 35nm and a specific surface area of ​​52m². 2 / g.

[0095] II. Preparation of Surface-Modified Nano-Silica

[0096] Weigh 15g of fumed silica nanoparticles and add them to a 1500mL three-necked flask. Add 800mL of an ethanol-water mixture (ethanol to water volume ratio of 6:1) to the flask. Turn on an ultrasonic dispersion device with a power of 2000W and a frequency of 20kHz and ultrasonically disperse the mixture for 50min to form a uniform dispersion. Weigh 1.5g of γ-aminopropyltriethoxysilane (10% of the mass of the fumed silica nanoparticles) and add it to the dispersion prepared above. Turn on a mechanical stirrer at 300r / min and a constant temperature water bath, slowly raise the temperature to 85℃, and maintain this temperature while stirring for 5h. After the reaction is complete, transfer the dispersion to a centrifuge tube and centrifuge at 5000r / min for 6min. Discard the supernatant. Collect the solid material at the bottom of the centrifuge tube, wash it three times with deionized water (120mL each time), and then wash it once with 120mL of anhydrous ethanol. The washed solid was placed in a vacuum drying oven and dried under vacuum for 7 hours at a temperature of 90℃ and a pressure of 0.09MPa. After drying, the solid was taken out and gently ground with a mortar to obtain surface-modified nano-silica. The surface amino content of the surface-modified nano-silica was found to be 1.5 mmol / g, and the particle size distribution range was 15-30 nm.

[0097] III. Preparation of Carboxylated EPDM

[0098] Turn on the internal mixer and set the equipment temperature to 180℃ and the rotation speed to 60 r / min. Weigh 120 g of EPDM rubber and add it to the mixing chamber of the internal mixer. After the rubber melts for 1 minute, add 9.6 g of unsaturated carboxylic acid (acrylic acid) at 8% of the EPDM rubber mass and mix for 1 minute. Then add 0.6 g of initiator di-tert-butyl peroxide at 0.5% of the EPDM rubber mass and mix for 3 minutes. Finally, add 6 g of hydroxy acid (γ-hydroxybutyric acid) at 5% of the EPDM rubber mass and maintain the rotation speed at 60 r / min for a shear reaction for 8 minutes. After the reaction is complete, open the discharge port of the internal mixer and collect the carboxylated EPDM. The carboxyl grafting rate of the carboxylated EPDM is tested by acid-base titration. The results show that the carboxyl grafting rate is 2.0 mmol / g, indicating that carboxyl groups have been successfully introduced into the EPDM molecular chain.

[0099] IV. Preparation of Composite Rubber

[0100] Turn on the open mill and set the equipment temperature to 60℃ and the roll gap to 2mm. Weigh the carboxylated EPDM prepared above and add it to the open mill. Perform a plasticizing treatment for 1 minute to fully soften the rubber compound. Add fillers in stages: First, add 7.5g of surface-modified nano silica and 4g of modified zinc oxide (both 50% of the total amount of the two fillers), mix for 1 minute, and then perform a venting operation (the venting height is 30% of the roll gap of the open mill). Continue mixing for 0.5 minutes. Then add the remaining 7.5g of surface-modified nano silica and 4g of modified zinc oxide, mix for 2 minutes, perform another venting operation, and continue mixing for 0.5 minutes. Subsequently, 4g of antioxidant (composed of 1.33g N-phenyl-α-naphthylamine, 2g 2-mercaptobenzimidazole, and 0.67g N-(4-anilinephenyl)maleimide in a mass ratio of 2:3:1), 3g of sulfur vulcanizing agent, and 2g of zinc methacrylate (ZDMA) vulcanizing accelerator were added sequentially. The mixture was continuously mixed for 7 minutes until the rubber compound was homogeneous, and then sheeted to obtain the compound. The compound was placed in an environment with room temperature of 23℃ and relative humidity of 60% for 12 hours. After that, the compound was placed in the mold of a hot press vulcanizing machine, and the temperature was set to 170℃ and the pressure to 18MPa for 10 minutes of hot press vulcanization. After vulcanization, the product was naturally cooled to room temperature, and the nano-silica modified zinc oxide synergistic aging-resistant EPDM rubber was obtained.

[0101] Comparative Example 1

[0102] Preparation of modified zinc oxide: Same as in Example 2, 8g of nano zinc oxide was weighed to prepare an average particle size of 38nm and a specific surface area of ​​50m². 2 / g of modified zinc oxide.

[0103] Preparation of carboxylated EPDM: Same as in Example 2, with a carboxyl grafting rate of 1.7 mmol / g.

[0104] Preparation of compound rubber: On a two-roll mill set to 50℃ and 2mm roll gap, carboxylated EPDM was added and plasticized for 1.5 min. Modified zinc oxide was added in stages: first, 4g was added and mixed for 1 min, then the vent was lifted (height 25% of the roll gap), and mixing continued for 0.5 min; then another 4g was added and mixed for 2 min, followed by a second venting and another 0.5 min of mixing. Then, 2g of antioxidant, 1.5g of vulcanizing agent, and 1g of vulcanization accelerator ZDMA were added sequentially, and the mixture was mixed for 6 min before sheeting. The compound was left to stand at 23℃ and 55% relative humidity for 18 h, then hot-pressed at 165℃ and 15MPa for 18 min, and cooled to obtain the rubber.

[0105] Comparative Example 2

[0106] Preparation of surface-modified nano-silica: Same as in Example 2, 15g of fumed nano-silica was weighed to prepare surface-modified nano-silica with a surface amino content of 1.3mmol / g and a particle size distribution of 13-27nm.

[0107] Preparation of carboxylated EPDM: Same as in Example 2, with a carboxyl grafting rate of 1.7 mmol / g.

[0108] Preparation of compound rubber: On a two-roll mill set to 50℃ and 2mm roll gap, carboxylated EPDM was added and plasticized for 1.5 min. 15g of surface-modified nano-silica was added in stages: first, 7.5g was added and mixed for 1 min, then the vent was lifted (height 25% of the roll gap), and mixing continued for 0.5 min; then another 7.5g was added and mixed for 2 min, followed by a second venting and another 0.5 min of mixing. 2g of antioxidant, 1.5g of vulcanizing agent, and 1g of vulcanization accelerator ZDMA were added sequentially, and mixing continued for 6 min before sheeting. The compound was left to stand at 23℃ and 55% relative humidity for 18 h, then hot-pressed at 165℃ and 15MPa for 18 min, and cooled to obtain the rubber.

[0109] Comparative Example 3

[0110] Preparation of carboxylated EPDM: Same as in Example 2, with a carboxyl grafting rate of 1.7 mmol / g.

[0111] Preparation of compound rubber: On a two-roll mill set to 50℃ and 2mm roll gap, carboxylated EPDM was added and plasticized for 1.5 min. Then, 10g of raw fumed silica and 5g of raw nano zinc oxide were added at once, and the mixture was kneaded at 40 rpm for 6 min. Next, 2g of antioxidant, 1.5g of vulcanizing agent, and 1g of vulcanization accelerator ZDMA were added sequentially, and the mixture was kneaded for 6 min before sheeting. The compound was left to stand at 23℃ and 55% relative humidity for 18 h, then hot-pressed at 165℃ and 15MPa for 18 min, and cooled to obtain the rubber.

[0112] Detection methods

[0113] (a) Raw material performance testing

[0114] Performance testing of modified zinc oxide

[0115] Average particle size: According to GB / T19077-2016 "Particle size analysis by laser diffraction", the sample was tested using a laser particle size analyzer (Mastersizer3000). The sample was dispersed in anhydrous ethanol (concentration 0.1%-0.5%) and ultrasonically dispersed for 10 min.

[0116] Specific surface area: According to GB / T19587-2017 "Determination of specific surface area of ​​solid substances by gas adsorption BET method", a specific surface area analyzer (ASAP2460) was used, nitrogen adsorption method, and the sample was degassed at 105℃ for 4h.

[0117] Performance testing of surface-modified nano-silica

[0118] Surface amino content: The surface amino content was determined using a surface amino content analyzer (TOCL) and acid-base titration method. After the sample was dissolved, it was titrated with standard hydrochloric acid, referring to the principle of GB / T30714-2014.

[0119] Particle size distribution: Same as the particle size determination method for modified zinc oxide (GB / T19077-2016).

[0120] Carboxyl grafting rate of carboxylated EPDM: According to GB / T28191-2011 "Determination of carboxyl content in rubber", acid-base titration method, the sample is dissolved in toluene-ethanol (1:1), phenolphthalein is used as indicator, and standard KOH ethanol solution is used for titration.

[0121] (II) Performance Testing of Composite Rubber

[0122] Mechanical property testing

[0123] Tensile strength and elongation at break: According to GB / T528-2009, electronic universal testing machine (WDW50), dumbbell-shaped specimen, tensile speed 500mm / min, 5 tests and averaged.

[0124] Tear strength: According to GB / T529-2008, electronic universal testing machine, trouser-shaped specimen, tensile speed 500mm / min, 5 tests and average.

[0125] Shore hardness: According to GB / T531.1-2008, Shore hardness tester (LXA), 5 points were measured at room temperature and the average was taken.

[0126] Rebound rate: According to GB / T1681-2009, using a falling ball rebound hammer, the average of 5 measurements were taken at room temperature.

[0127] Aging resistance test

[0128] Hot air aging performance: According to GB / T3512-2014, aging in a thermo-oxidative aging chamber (401A) at 100℃ for 96 hours, and after being placed at room temperature for 24 hours, the tensile strength and elongation at break were measured, and the retention rate was calculated.

[0129] Stress relaxation coefficient: Calculated by measuring stress change over 96 hours at 100℃ and initial compression rate using a stress relaxation tester (RLX200) according to GB / T1685-2019.

[0130] Filler dispersibility test: According to GB / T33834-2017, SEM (SU8010) was used to observe the frozen fracture surface, and the agglomeration was observed after gold sputtering treatment.

[0131] Test results

[0132]

[0133] in conclusion

[0134] The tensile strength (10.2-14.3 MPa), tear strength (48.5-62.3 kN / m), and performance retention rate after heat aging (tensile strength retention rate 88%-95%) of Examples 1-3 (nano silica-modified zinc oxide synergistic system) were significantly higher than those of Comparative Example 1 (modified zinc oxide only, tensile strength 8.1 MPa, heat aging tensile strength retention rate 75%) and Comparative Example 2 (nano silica only, tensile strength 7.8 MPa, heat aging tensile strength retention rate 72%), demonstrating that the two have a synergistic effect and can jointly improve the mechanical and aging resistance properties of EPDM rubber.

[0135] Filler modification and process necessity: The tensile strength of Example 2 (modified filler + segmented feeding) is 12.5 MPa and the stress relaxation coefficient is 0.89, which is much better than that of Comparative Example 3 (unmodified filler + one-time feeding, tensile strength 6.5 MPa and stress relaxation coefficient 0.58). Moreover, Comparative Example 3 has serious filler agglomeration, indicating that nano-silica surface modification, zinc oxide KH-560 modification and segmented feeding process can improve filler dispersibility and interfacial compatibility.

[0136] Reasonable selection of raw materials: The fumed silica (modified with γ-aminopropyltriethoxysilane), modified zinc oxide (KH-560 modified) and compound antioxidant system used in the examples make the rubber have excellent comprehensive properties.

[0137] Application compatibility: The mechanical properties (Shore hardness 68-75 Shore A, resilience 32%-38%) and aging resistance (stress relaxation coefficient 0.85-0.93) of Examples 1-3 meet the requirements of automotive seals and air conditioning pipe seals for material strength, elasticity and temperature aging resistance.

[0138] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent protection scope of the present invention.

Claims

1. A nano-silica-modified zinc oxide synergistic aging-resistant EPDM rubber, characterized in that, The raw materials, by weight, include: 80-120 parts EPDM rubber, 5-15 parts nano-silica, 3-8 parts modified zinc oxide, 1-4 parts antioxidant, 0.8-3 parts vulcanizing agent, 0.3-2 parts vulcanization accelerator, 2-8 parts unsaturated carboxylic acid, 1-5 parts hydroxy acid, and 0.05-0.5 parts initiator; the mass ratio of nano-silica to modified zinc oxide is 1.2-5:1; the modified zinc oxide is nano-zinc oxide modified with silane coupling agent KH560, and the average particle size of the modified zinc oxide is less than 50 nm, and the specific surface area is greater than 40 m². 2 / g; The nano-silica is fumed silica, and is surface-modified with γ-aminopropyltriethoxysilane. The modification process is as follows: fumed silica is dispersed in an ethanol-water mixed solvent with a volume ratio of ethanol to water of 4-6:1, and the amount of ethanol-water mixed solvent is 20-50 times the mass of the nano-silica. γ-aminopropyltriethoxysilane is added, with an addition amount of 5%-10% of the mass of the nano-silica. The mixture is stirred at 70-85℃ for 3-5 hours, centrifuged, and then vacuum-dried at 80-90℃ for 5-7 hours to obtain surface-modified nano-silica. The surface amino content of the modified nano-silica is 0.8-1.5 mmol / g, and the particle size distribution range is 10-30 nm. The antioxidant is a compound system composed of N-phenyl-α-naphthylamine, 2-mercaptobenzimidazole, and N-(4-anilinophenyl)maleimide in a mass ratio of 1-2:1-3:0.5-1.5; the vulcanizing agent is one or more of dicumyl peroxide, bis-tert-butyl peroxide, and sulfur; and the vulcanization accelerator is one or more of triallyl isocyanurate and zinc methacrylate.

2. The nano-silica-modified zinc oxide synergistic aging-resistant EPDM rubber according to claim 1, characterized in that, The unsaturated carboxylic acid is one or more of acrylic acid, methacrylic acid, and maleic acid; the hydroxy acid is one or more of lactic acid, γ-hydroxybutyric acid, and aspartic acid; and the initiator is one or more of benzoyl peroxide, azobisisobutyronitrile, and di-tert-butyl peroxide.

3. A method for preparing nano-silica-modified zinc oxide synergistic aging-resistant EPDM rubber as described in any one of claims 1-2, characterized in that, Includes the following steps: (1) Preparation of modified zinc oxide: Disperse nano zinc oxide in an ethanol-water mixed solvent, the amount of ethanol-water mixed solvent being 20-50 times the mass of nano zinc oxide, add silane coupling agent KH560, stir and react at 60-80℃ for 2-4h, centrifuge and then vacuum dry at 80-100℃ for 4-6h to obtain modified zinc oxide; (2) Preparation of carboxylated EPDM: Add EPDM rubber to a mixer and melt it at 160-180℃ for 1-2 min. Then add unsaturated carboxylic acid, initiator and hydroxy acid in sequence. Shear reaction at 50-60 r / min for 8-15 min. Remove the rubber to obtain carboxylated EPDM. (3) Preparation of composite rubber: Plasticize carboxylated EPDM on a two-roll mill for 1-2 min, and add nano silica and modified zinc oxide in a segmented feeding method: first add 50% nano silica and 50% modified zinc oxide, mix for 1-2 min, then add the remaining nano silica and modified zinc oxide, continue mixing for 2-3 min, and add antioxidant, vulcanizing agent and vulcanization accelerator in sequence, and mix evenly to obtain compound rubber; let the compound rubber stand at room temperature for 12-24 h, and then hot press vulcanize at 150-170℃ and 12-18MPa for 10-25 min to obtain nano silica-modified zinc oxide synergistic aging resistant EPDM rubber.

4. The preparation method according to claim 3, characterized in that, In step (1), the volume ratio of ethanol to water in the ethanol-water mixed solvent is 3-5:1; the amount of silane coupling agent KH560 added is 3-8% of the mass of nano zinc oxide.

5. The preparation method according to claim 3, characterized in that, In step (2), the amount of unsaturated carboxylic acid added is 2-8% of the mass of EPDM rubber; the amount of hydroxy acid added is 1%-5% of the mass of EPDM rubber; and the amount of initiator added is 0.05-0.5% of the mass of EPDM rubber.

6. The preparation method according to claim 3, characterized in that, In step (3), the temperature of the open mill is controlled at 40-60℃; the compound rubber needs to be left at room temperature for 12-24 hours before hot pressing and vulcanization.

7. The preparation method according to claim 3, characterized in that, In step (3), the mixing speed of the segmented feeding is controlled at 40-50 r / min.

8. The application of the nano-silica-modified zinc oxide synergistic aging-resistant EPDM rubber as described in any one of claims 1-2 in automotive seals, air conditioning duct seals, or vibration damping seals for electronic devices.

Images