A composite rubber antioxidant 6PPD for preventing caking and its preparation method

Abstract

This invention belongs to the field of rubber antioxidant technology, and specifically relates to an anti-caking composite rubber antioxidant 6PPD and its preparation method. The anti-caking composite rubber antioxidant 6PPD is prepared by reacting 3-aminoadipic acid with 4-pentenyl isothiocyanate, grafting it onto silica using a silane coupling agent, and complexing it with lanthanum ions to obtain a functional antioxidant. This functional antioxidant is then compounded with a base antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, microcrystalline wax, and an antioxidant to prepare the anti-caking composite rubber antioxidant 6PPD. The prepared anti-caking composite rubber antioxidant 6PPD possesses multiple protective mechanisms—chemical protection, physical barrier, and multi-mechanism synergy—exhibiting excellent aging resistance, good processability, and easy storage due to its anti-caking properties.

Description

Technical Field

[0001] This invention belongs to the field of rubber antioxidant technology, and in particular relates to an anti-caking composite rubber antioxidant 6PPD and its preparation method. Background Technology

[0002] Rubber is a highly elastic polymer material with reversible deformation. It has a low glass transition temperature and is elastic at room temperature, making it widely used in transportation, aerospace, defense, and everyday life. However, the numerous isolated unsaturated double bonds and reactive allyl hydrogens in most rubber molecules make rubber products highly susceptible to damage from heat, oxygen, ozone, light, and stress, leading to performance degradation, or aging. Adding antioxidants is the most convenient and effective way to prevent rubber aging. Among them, the aromatic amine antioxidant 6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) dominates the market due to its excellent aging protection. However, because 6PPD is a small molecule compound, it still suffers from volatilization and migration problems. It performs poorly in terms of thermal stability, extraction resistance, and migration resistance, resulting in a significant decrease in its anti-aging ability. Furthermore, due to its small molecular weight, low melting point, and the presence of polar groups, antioxidant 6PPD is prone to agglomeration during production, transportation, and use.

[0003] Chinese patent CN114044897A discloses a method for preparing antioxidant 6PPD. Using cashew nut shell oil as a raw material, high-temperature decarboxylation distillation yields cashew phenol. Cashew phenol and haloalkanes are then used to synthesize corresponding ether products. These ether products react with antioxidant 6PPD to generate a macromolecular antioxidant 6PPD containing a cashew phenol structure. This method overcomes the shortcomings of existing antioxidant 6PPD, such as easy migration in rubber products, easy extraction in water and solvents, and easy agglomeration at high temperatures. By macromolecularizing and multifunctionalizing antioxidant 6PPD, the method effectively improves the antioxidant's migration resistance, extraction resistance, low toxicity, and compatibility. It is safe, stable, and long-lasting, showing good application prospects. Chinese patent CN112143026A discloses a modified rubber antioxidant, compositions containing the same, and their preparation and application. It uses a long-chain epoxy compound as a raw material and a compound with a traditional p-phenylenediamine-based antioxidant structure to undergo a graft reaction, resulting in a macromolecular-weight antioxidant with better protective effects and better migration resistance. However, using only a single-component antioxidant can easily lead to problems such as poor protective performance, short protective duration, and high cost. Summary of the Invention

[0004] To address the above problems, this invention proposes an anti-caking composite rubber antioxidant 6PPD and its preparation method, which effectively solves the problem of poor performance of single antioxidants.

[0005] In a first aspect, the present invention provides an anti-caking composite rubber antioxidant 6PPD, the following:

[0006] A composite rubber antioxidant 6PPD for preventing caking comprises the following raw materials in parts by weight: 20-30 parts of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 80-100 parts of functional antioxidant, 15-20 parts of microcrystalline wax, and 2-4 parts of antioxidant.

[0007] Furthermore, the antioxidant is a thioester antioxidant.

[0008] Furthermore, the functional antioxidant is prepared through the following steps: S1, reacting 3-aminohexanoic acid with sodium hydroxide solution to prepare a 3-aminohexanoate solution; S2, adding an ethanol solution of 4-pentenyl isothiocyanate dropwise to the 3-aminohexanoate solution, heating and stirring the reaction, and after purification, obtaining intermediate 1; S3, dissolving intermediate 1 and a silane coupling agent in DMF, adding triethylamine, heating and stirring the reaction, to obtain an intermediate 2 solution; S4, dispersing silica in an ethanol aqueous solution, adjusting the pH to 10-11, ultrasonically dispersing evenly, adding intermediate 2 solution dropwise under an inert gas atmosphere, heating the reaction, and after purification, obtaining intermediate 3; S5, under heating, adding an aqueous solution of lanthanum chloride dropwise to the dispersion of intermediate 3, stirring the reaction, and after purification, obtaining the functional antioxidant.

[0009] Furthermore, the molar ratio of 3-aminoadipic acid to sodium hydroxide is 1:(2.1-2.3).

[0010] Furthermore, the molar ratio of 3-aminoadipate to 4-pentenyl isothiocyanate is 1:(1-1.2).

[0011] Furthermore, the silane coupling agent is one of KH-590, KH-580, KH-581, and KH-582.

[0012] Furthermore, the molar ratio of intermediate 1, silane coupling agent, and triethylamine is 1:(1.2-1.5):(0.3-0.5).

[0013] Furthermore, the mass ratio of silicon dioxide to intermediate 1 is 100:(10-20).

[0014] Furthermore, the molar ratio of lanthanum chloride to intermediate 3 is (1.5-2):1.

[0015] Secondly, the present invention provides a method for preparing an anti-caking composite rubber antioxidant 6PPD, comprising the following steps: (1) heating and melting microcrystalline wax; (2) adding N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, functional antioxidant and antioxidant in batches, and stirring until the system is free of agglomerated particles; (3) transferring to a high-shear emulsifier to further form a uniformly dispersed system; (4) extruding through a twin-screw extruder, water-cooling and pelletizing to obtain the anti-caking composite rubber antioxidant 6PPD.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] This invention prepares an anti-caking composite rubber antioxidant 6PPD by compounding a functional antioxidant with a basic antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, microcrystalline wax, and an antioxidant. This anti-caking composite rubber antioxidant 6PPD has multiple protections of "chemical protection - physical barrier - multi-mechanism synergy", and has the characteristics of excellent anti-aging performance, good processability, anti-caking and easy storage.

[0018] The functional antioxidant prepared in this invention possesses multiple functional groups, including a thiourea structure, a lanthanum ion complex, and a silica-coupled coupling agent. The thiourea structure can effectively decompose the large molecular hydroperoxide ROOH generated in the styrene-butadiene rubber molecular chain due to thermo-oxidative aging in the form of thiols. Sulfur-containing free radicals can terminate active free radicals such as R· and ROO·, and sulfur oxides further decompose ROOH. The ionic metal lanthanum can passivate and terminate active oxygen-containing free radicals ROO·, RO·, and HO·, thereby terminating the thermo-oxidative aging reaction of styrene-butadiene rubber. Grafting a silane coupling agent onto silica increases its dispersibility, migration resistance, and extraction resistance. N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine reacts with free radicals generated by rubber oxidation, consuming initial oxidation products. However, these products are easily lost due to migration and volatilization over time. This functional antioxidant can reduce the loss of 6PPD and extend its action time. Microcrystalline wax forms a physical barrier, creating a wax film on the rubber surface. Antioxidants can form a eutectic structure with the wax, increasing the density of the wax film and isolating oxygen and ozone from contact with the rubber. When the wax film is damaged, the protective gap can be filled by the chemical protection of functional antioxidants, together forming a multi-level protection system of "free radical scavenging - peroxide decomposition - metal ion passivation". Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the preparation process of functional anti-aging agents.

[0020] Figure 2 Infrared spectrum of functional antioxidant.

[0021] Figure 3 This is a vulcanization curve diagram of rubber compounds containing different antioxidants.

[0022] Figure 4 The figures show the aging performance test results of vulcanizates containing different antioxidants, where (a) represents the tensile strength retention rate, (b) represents the elongation at break retention rate, and (c) represents the aging coefficient.

[0023] Figure 5 The images show cross-sectional SEM images of vulcanizates containing different antioxidants, where (a) is the blank group, (b) is Comparative Example 1, (c) is Comparative Example 3, (d) is Comparative Example 2, and (e) is Example 1. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] A composite rubber antioxidant 6PPD for preventing caking comprises the following raw materials in parts by weight: 20 kg of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 80 kg of functional antioxidant, 15 kg of microcrystalline wax, and 2 kg of antioxidant.

[0027] In this embodiment, the antioxidant is dilaurate thiodipropionate.

[0028] The functional anti-aging agent in this embodiment is prepared through the following steps (such as...). Figure 1 (as shown)

[0029] S1, 1 mol of 3-aminoadipic acid was mixed with sodium hydroxide solution, heated to 50℃, and reacted for 30 min to prepare 3-aminoadipic acid salt solution; the molar ratio of 3-aminoadipic acid to sodium hydroxide was 1:2.1; the concentration of sodium hydroxide solution was 2.5 mol / L.

[0030] S2, an ethanol solution of 4-pentenyl isothiocyanate was added dropwise to 100 mL of 3-aminoadipate solution, and the mixture was stirred at 50 °C for 5 h. After cooling to room temperature, the mixture was extracted with diethyl ether, and the lower layer was collected. About 0.5 g of hydroquinone was added to the lower layer, and the solvent was removed by rotary evaporation under reduced pressure. The crude product was washed with anhydrous ethanol by centrifugation and then dried under vacuum at 55 °C to obtain intermediate 1. The molar ratio of 3-aminoadipate to 4-pentenyl isothiocyanate was 1:1, and the concentration of the ethanol solution of 4-pentenyl isothiocyanate was 6.5 mol / L.

[0031] S3, under nitrogen protection, 15g of intermediate 1 and silane coupling agent were dissolved in 1.5L of DMF, triethylamine was added, and the mixture was heated to 45℃ and stirred for 4h to obtain intermediate 2 solution; the molar ratio of intermediate 1, silane coupling agent and triethylamine was 1:1.2:0.3; the silane coupling agent was KH-590.

[0032] S4, 100g of silica was dispersed in 1L of ethanol aqueous solution, ammonia was added dropwise to adjust the pH to 10, and the mixture was sonicated for 2h. Under an inert gas atmosphere, intermediate 2 solution was added dropwise at 45℃, and the reaction was stirred for 4h. After cooling to room temperature, the solvent was removed by centrifugation, and unreacted silane coupling agent was removed by washing with tetrahydrofuran. Then, the mixture was vacuum dried at 45℃ to obtain intermediate 3. The mass ratio of silica to intermediate 1 was 100:10, and the volume ratio of alcohol to water in the ethanol aqueous solution was 4:1.

[0033] S5, at 50℃, an aqueous solution of lanthanum chloride was added dropwise to the dispersion of intermediate 3, the mixture was stirred and reacted for 6 hours, cooled to room temperature, filtered, the residue was washed with water, and dried under vacuum at 50℃ to obtain the functional antioxidant; the molar ratio of lanthanum chloride to intermediate 3 was 1.5:1; the concentration of the aqueous solution of lanthanum chloride was 0.5 mol / L; the dispersion of intermediate 3 was obtained by ultrasonic dispersion of intermediate 3 and water at a ratio of 1 g: 10 mL.

[0034] The prepared functional anti-aging agent was tested using an infrared spectrometer, and the results are as follows: Figure 2 As shown. From Figure 2 As can be seen from the spectrum, 468cm -1 780cm -1 and 1042cm -1 An asymmetric absorption peak of Si-O-Si groups appeared at 1550 cm⁻¹. -1 1480cm -1 The characteristic absorption peaks of thiourea, NCN and NC=S, appeared at 1742 cm⁻¹. -1 1428cm -1 Carboxylate C=O and COO appeared at the location. -1 The symmetrical contraction vibration absorption peak is due to both monodentate coordination and bidentate chelation between the carboxyl group and lanthanum, thus some C=O remains; 3341 cm⁻¹ -1 The presence of a large peak at this location is likely due to the mixing of the stretching vibration absorption peaks of NH4+ and OH4+ in thiourea. These characteristic peaks confirm the successful preparation of the target product.

[0035] Example 2

[0036] A composite rubber antioxidant 6PPD for preventing caking comprises the following raw materials in parts by weight: 25 kg of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 90 kg of functional antioxidant, 18 kg of microcrystalline wax, and 3 kg of antioxidant.

[0037] In this embodiment, the antioxidant is distearate thiodipropionate.

[0038] The functional anti-aging agent in this embodiment is prepared through the following steps:

[0039] S1, 1 mol of 3-aminoadipic acid was mixed with sodium hydroxide solution, heated to 525℃, and reacted for 35 min to prepare 3-aminoadipic acid salt solution; the molar ratio of 3-aminoadipic acid to sodium hydroxide was 1:2.2; the concentration of sodium hydroxide solution was 2.5 mol / L.

[0040] S2, an ethanol solution of 4-pentenyl isothiocyanate was added dropwise to 100 mL of 3-aminoadipate solution, and the mixture was stirred at 55 °C for 6 h. After cooling to room temperature, the mixture was extracted with diethyl ether, and the lower layer was collected. About 0.5 g of hydroquinone was added to the lower layer, and the solvent was removed by rotary evaporation under reduced pressure. The crude product was washed with anhydrous ethanol by centrifugation and then dried under vacuum at 55 °C to obtain intermediate 1. The molar ratio of 3-aminoadipate to 4-pentenyl isothiocyanate was 1:1.1, and the concentration of the ethanol solution of 4-pentenyl isothiocyanate was 6.5 mol / L.

[0041] S3, under nitrogen protection, 20g of intermediate 1 and silane coupling agent were dissolved in 1.5L of DMF, triethylamine was added, and the mixture was heated to 48℃ and stirred for 4.5h to obtain intermediate 2 solution; the molar ratio of intermediate 1, silane coupling agent and triethylamine was 1:1.3:0.4; the silane coupling agent was KH-580.

[0042] S4, 100g of silica was dispersed in 1L of ethanol aqueous solution, ammonia was added dropwise to adjust the pH to 11, and the mixture was sonicated for 2.5h. Under an inert gas atmosphere, intermediate 2 solution was added dropwise at 48℃, and the mixture was stirred for 4.5h. After cooling to room temperature, the solvent was removed by centrifugation, and unreacted silane coupling agent was removed by washing with tetrahydrofuran. Then, the mixture was vacuum dried at 45℃ to obtain intermediate 3. The mass ratio of silica to intermediate 1 was 100:15, and the volume ratio of alcohol to water in the ethanol aqueous solution was 4:1.

[0043] S5, at 55℃, an aqueous solution of lanthanum chloride was added dropwise to the dispersion of intermediate 3, and the mixture was stirred for 7 hours. After cooling to room temperature, the mixture was filtered, the residue was washed with water, and dried under vacuum at 50℃ to obtain the functional antioxidant. The molar ratio of lanthanum chloride to intermediate 3 was 1.8:1. The concentration of the aqueous solution of lanthanum chloride was 0.5 mol / L. The dispersion of intermediate 3 was obtained by ultrasonic dispersion of intermediate 3 and water at a ratio of 1 g: 10 mL.

[0044] Example 3

[0045] A composite rubber antioxidant 6PPD for preventing caking comprises the following raw materials in parts by weight: 30 kg of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 100 kg of functional antioxidant, 20 kg of microcrystalline wax, and 4 kg of antioxidant.

[0046] In this embodiment, the antioxidant is 2,2'-thiobis(4-methyl-6-tert-butylphenol).

[0047] The functional anti-aging agent in this embodiment is prepared through the following steps:

[0048] S1, 1 mol of 3-aminoadipic acid was mixed with sodium hydroxide solution, heated to 55℃, and reacted for 40 min to prepare 3-aminoadipic acid salt solution; the molar ratio of 3-aminoadipic acid to sodium hydroxide was 1:2.2; the concentration of sodium hydroxide solution was 2.5 mol / L.

[0049] S2, an ethanol solution of 4-pentenyl isothiocyanate was added dropwise to 100 mL of 3-aminoadipate solution, and the mixture was stirred at 60 °C for 7 h. After cooling to room temperature, the mixture was extracted with diethyl ether, and the lower layer was collected. About 0.5 g of hydroquinone was added to the lower layer, and the solvent was removed by rotary evaporation under reduced pressure. The crude product was washed with anhydrous ethanol by centrifugation and then dried under vacuum at 55 °C to obtain intermediate 1. The molar ratio of 3-aminoadipate to 4-pentenyl isothiocyanate was 1:1.2, and the concentration of the ethanol solution of 4-pentenyl isothiocyanate was 6.5 mol / L.

[0050] S3, under nitrogen protection, 25g of intermediate 1 and silane coupling agent were dissolved in 1.5L of DMF, triethylamine was added, and the mixture was heated to 50℃ and stirred for 5h to obtain intermediate 2 solution; the molar ratio of intermediate 1, silane coupling agent and triethylamine was 1:1.5:0.5; the silane coupling agent was KH-581.

[0051] S4, 100g of silica was dispersed in 1L of ethanol aqueous solution, ammonia was added dropwise to adjust the pH to 11, and the mixture was sonicated for 3h. Under an inert gas atmosphere, intermediate 2 solution was added dropwise at 50℃, and the reaction was stirred for 5h. After cooling to room temperature, the solvent was removed by centrifugation, and unreacted silane coupling agent was removed by washing with tetrahydrofuran. Then, the mixture was dried under vacuum at 45℃ to obtain intermediate 3. The mass ratio of silica to intermediate 1 was 100:20, and the volume ratio of alcohol to water in the ethanol aqueous solution was 4:1.

[0052] S5, at 60℃, an aqueous solution of lanthanum chloride was added dropwise to the dispersion of intermediate 3, and the mixture was stirred for 8 hours. After cooling to room temperature, the mixture was filtered, the residue was washed with water, and dried under vacuum at 50℃ to obtain the functional antioxidant. The molar ratio of lanthanum chloride to intermediate 3 was 2:1. The concentration of the aqueous solution of lanthanum chloride was 0.5 mol / L. The dispersion of intermediate 3 was obtained by ultrasonic dispersion of intermediate 3 and water at a ratio of 1 g: 10 mL.

[0053] A method for preparing an anti-caking composite rubber antioxidant 6PPD includes the following steps: (1) heating and melting microcrystalline wax; (2) adding N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, functional antioxidant and antioxidant in batches, and stirring until the system is free of agglomerated particles; (3) transferring to a high-shear emulsifier to further form a uniformly dispersed system; (4) extruding through a twin-screw extruder, water-cooling and pelletizing to obtain the anti-caking composite rubber antioxidant 6PPD.

[0054] Comparative Example 1

[0055] Similar to Example 1, except that no functional antioxidant is added in the preparation of the anti-caking composite rubber antioxidant 6PPD.

[0056] Comparative Example 2

[0057] Similar to Example 1, except that intermediate 3 was directly used in place of the functional antioxidant in the preparation of the anti-caking composite rubber antioxidant 6PPD.

[0058] Comparative Example 3

[0059] Similar to Example 1, except that the functional anti-aging agent is prepared by the following steps: S1, 1 mol of 3-aminoadipic acid is mixed with sodium hydroxide solution, heated to 50°C, and reacted for 30 min to prepare 3-aminoadipic acid salt solution; the molar ratio of 3-aminoadipic acid to sodium hydroxide is 1:2.1; the concentration of sodium hydroxide solution is 2.5 mol / L.

[0060] S2, an ethanol solution of 4-pentenyl isothiocyanate was added dropwise to 100 mL of 3-aminoadipate solution, and the mixture was stirred at 50 °C for 5 h. After cooling to room temperature, the mixture was extracted with diethyl ether, and the lower layer was collected. About 0.5 g of hydroquinone was added to the lower layer, and the solvent was removed by rotary evaporation under reduced pressure. The crude product was washed with anhydrous ethanol by centrifugation and then dried under vacuum at 55 °C to obtain intermediate 1. The molar ratio of 3-aminoadipate to 4-pentenyl isothiocyanate was 1:1, and the concentration of the ethanol solution of 4-pentenyl isothiocyanate was 6.5 mol / L.

[0061] S3, at 50℃, an aqueous solution of lanthanum chloride was added dropwise to the dispersion of intermediate 1, and the mixture was stirred for 6 hours. After cooling to room temperature, the mixture was filtered, the residue was washed with water, and dried under vacuum at 50℃ to obtain the functional antioxidant. The molar ratio of lanthanum chloride to intermediate 1 was 1.5:1. The concentration of the aqueous solution of lanthanum chloride was 0.5 mol / L. The dispersion of intermediate 1 was obtained by ultrasonic dispersion of intermediate 1 and water at a ratio of 1 g: 10 mL.

[0062] I. Following standard GB / T16584-1996, the vulcanization performance of the blank group and the styrene-butadiene rubber compounds containing the antioxidants prepared in Example 1 and Comparative Examples 1-3 were tested using a rotorless vulcanizing apparatus. The test temperature was 158℃, the frequency was 1.66Hz, and the swing angle was ±1°. The components and their weight percentages are shown in Table 1 ("-" indicates no addition, SA is stearic acid, NS is N-tert-butyl-2-benzothiazole sulfenamide, DM is 2,2'-benzothiazole disulfide, and S is sulfur). The preparation method of the styrene-butadiene rubber compound is as follows: First, the styrene-butadiene rubber was plasticized on a two-roll mill. Then, SiO2, ZnO / SA, NS / DM, antioxidants, and sulfur were added sequentially, and the mixture was mixed for 15 minutes to obtain the styrene-butadiene rubber compound. The measured vulcanization curves are shown in Table 1. Figure 3 As shown.

[0063] Table 1. Components and dosage of styrene-butadiene rubber compound

[0064] Styrene-butadiene rubber <![CDATA[SiO2]]> ZnO / SA NS / DM S Anti-aging agents Example 1 100 - 5 / 2 2 / 0.6 2 35 Comparative Example 1 100 32 5 / 2 2 / 0.6 2 3 Comparative Example 2 100 - 5 / 2 2 / 0.6 2 35 Comparative Example 3 100 32 5 / 2 2 / 0.6 2 3 Blank group 100 32 5 / 2 2 / 0.6 2 -

[0065] from Figure 3 As can be seen, compared with the blank group of rubber compound without antioxidant, the addition of antioxidants prepared in Example 1, Comparative Examples 1-3 significantly shortened the vulcanization time of the rubber compound, increased the maximum torque and torque difference, and promoted the vulcanization effect. Among them, Example 1 showed the best improvement in vulcanization effect, followed by: Comparative Example 3 > Comparative Example 2 > Comparative Example 1 > Blank Group.

[0066] Preparation of rubber vulcanizates: Following the preparation method and component amounts of styrene-butadiene rubber (SBR) compounds (the component amounts in Examples 2 and 3 were the same as in Example 1), blank groups and SBR compounds containing the antioxidants prepared in Examples 1-3 and Comparative Examples 1-3 were prepared. The SBR compounds were then subjected to vulcanization on a flat vulcanizing machine at 158°C, 12 MPa, and t... 90 The rubber was vulcanized under +2 min conditions to obtain a rubber vulcanizate, which was then used for the following tests.

[0067] 2. In accordance with standard ASTM D412-15a, the blank group and the rubber vulcanizates containing the antioxidants prepared in Examples 1-3 and Comparative Examples 1-3 were cut into dumbbell-shaped rubber vulcanizate strips. The mechanical properties of the rubber vulcanizate strips were tested using a universal testing machine with a tensile rate of 300 mm / min. Five strips were used for each test group, and the average value was taken as the final test result.

[0068] III. Resistance to extraction

[0069] The blank group and the rubber vulcanizates containing the antioxidants prepared in Examples 1-3 and Comparative Examples 1-3 were cut into dumbbell-shaped rubber vulcanizate strips. Using methanol as a solvent, the rubber vulcanizate strips were placed in a Soxhlet extractor for extraction. After extraction for 48 hours, the strips were removed and dried in a vacuum drying oven at 65°C to constant weight. The methanol extraction resistance of the antioxidant was evaluated based on the mass loss of the strips before extraction. The mass loss rate (%) = (m1-m2) / m1 × 100%, where m1 and m2 are the masses of the strips before extraction, respectively. The results are shown in Table 2.

[0070] Table 2. Performance Test Results

[0071] Tensile strength (MPa) Stress at 100% strain (MPa) Stress at 300% strain (MPa) Elongation at break (%) Quality loss rate (%) Example 1 20.8 2.13 12.13 415 2.83 Example 2 20.6 2.13 12.12 418 2.85 Example 3 20.5 2.14 12.15 419 2.86 Comparative Example 1 17.8 1.93 8.38 381 3.76 Comparative Example 2 19.7 2.10 11.68 410 3.03 Comparative Example 3 18.9 2.04 10.31 387 3.42 Blank group 15.8 2.01 8.72 402 2.70

[0072] As can be seen from Table 2, compared with the blank group and Comparative Examples 1-3, the rubber vulcanizate samples with added antioxidant prepared in this application have the best mechanical properties and strong resistance to extraction.

[0073] IV. Accelerated thermo-oxidative aging tests were conducted using an accelerated thermo-oxidative aging test chamber, referring to ASTM D573-04 (2015). The blank group and the rubber vulcanizates containing the antioxidants prepared in Example 1 and Comparative Examples 1-3 were cut into dumbbell-shaped tensile test strips and suspended at intervals on the rotating frame of the thermo-oxidative aging chamber. The aging temperature was 100℃. The strips were removed after the set aging time, and their mechanical properties were tested according to standard ASTM D412-15a. The tensile strength retention rate Rt was calculated as follows: Rt = Ta / Tu × 100%, where Tu and Ta are the tensile strengths before and after aging, respectively; the elongation at break retention rate Rg was calculated as follows: Rg = Ea / Eu × 100%, where Eu and Ea are the elongation at break before and after aging, respectively; and the anti-aging coefficient k was calculated as follows: f = T × E, k = fa × fu, where f is the tensile product, T is the tensile strength, E is the elongation at break, and fu and fa are the tensile products before and after aging, respectively. The results are as follows: Figure 4 As shown.

[0074] from Figure 4 As can be seen, during the 9-day thermo-oxidative aging process at 100℃, the retention rate of mechanical properties of almost all rubber vulcanizates decreased with increasing aging time. The trend of the aging coefficient with aging time was basically the same as the trend of the tensile strength retention rate. The blank group, due to the absence of antioxidants, consistently had the lowest aging coefficient, mainly because no antioxidants were added during the aging process, resulting in a decline in the performance of the rubber vulcanizates. Example 1 showed the best anti-aging effect, and the anti-aging effect from strongest to weakest was: Example 1 > Comparative Example 3 > Comparative Example 2 > Comparative Example 1 > Blank Group.

[0075] V. The morphology of the cross-sections of the blank group and the rubber vulcanizates containing the antioxidants of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 was observed using a scanning electron microscope. The results are as follows: Figure 5 As shown.

[0076] from Figure 5 As can be seen, in the blank group without added antioxidant, the silica was unevenly dispersed and agglomerated over a large area; in Comparative Example 1, the silica was still unevenly dispersed and agglomerated severely; in Comparative Example 3, the silica showed small agglomeration and was evenly dispersed; and the silica was most evenly dispersed in Comparative Example 2 and Example 1.

[0077] VI. Anti-caking test

[0078] The antioxidants prepared in Examples 1-3 and the commercially available antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine were placed in an environment with a temperature of 30°C and an air humidity of 75% for 10 days, and the agglomeration phenomenon was observed. It was found that the commercially available antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine agglomerated severely, while the antioxidants prepared in Examples 1-3 did not show any agglomeration phenomenon.

[0079] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite rubber antioxidant 6PPD for preventing caking, characterized in that: The raw material comprises the following components in parts by weight: 20-30 parts of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 80-100 parts of functional antioxidant, 15-20 parts of microcrystalline wax, and 2-4 parts of antioxidant; the functional antioxidant is prepared by the following steps: S1, reacting 3-aminohexanoic acid with sodium hydroxide solution to prepare 3-aminohexanoate solution; S2, adding an ethanol solution of 4-pentenyl isothiocyanate dropwise to the 3-aminohexanoate solution, heating and stirring the reaction, and after purification, obtaining intermediate 1; S3, mixing intermediate 1 with silicon... The silane coupling agent is dissolved in DMF, triethylamine is added, and the mixture is heated and stirred to obtain intermediate 2 solution; S4, silica is dispersed in an ethanol aqueous solution, the pH is adjusted to 10-11, ultrasonically dispersed evenly, and intermediate 2 solution is added dropwise under an inert gas atmosphere, heated to react, and purified to obtain intermediate 3; S5, under heating, an aqueous solution of lanthanum chloride is added dropwise to the dispersion of intermediate 3, stirred to react, and purified to obtain a functional antioxidant; the silane coupling agent is one of KH-590, KH-580, KH-581, and KH-582.

2. The anti-caking composite rubber antioxidant 6PPD according to claim 1, characterized in that: The antioxidant is a thioester antioxidant.

3. The anti-caking composite rubber antioxidant 6PPD according to claim 1, characterized in that: The molar ratio of 3-aminoadipic acid to sodium hydroxide is 1:(2.1-2.3).

4. The anti-caking composite rubber antioxidant 6PPD according to claim 1, characterized in that: The molar ratio of 3-aminoadipate to 4-pentenyl isothiocyanate is 1:(1-1.2).

5. The anti-caking composite rubber antioxidant 6PPD according to claim 1, characterized in that: The molar ratio of intermediate 1, silane coupling agent, and triethylamine is 1:(1.2-1.5):(0.3-0.5).

6. The anti-caking composite rubber antioxidant 6PPD according to claim 1, characterized in that: The mass ratio of silicon dioxide to intermediate 1 is 100:(10-20).

7. The anti-caking composite rubber antioxidant 6PPD according to claim 1, characterized in that: The molar ratio of lanthanum chloride to intermediate 3 is (1.5-2):

1.

8. The preparation method of the anti-caking composite rubber antioxidant 6PPD as described in any one of claims 1-7, characterized in that: Includes the following steps: (1) Heat the microcrystalline wax to melt and liquefy it; (2) Add N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, functional antioxidant and antioxidant in batches, and stir until there are no agglomerated particles in the system; (3) Transfer it to a high-shear emulsifier to further form a uniformly dispersed system; (4) Extrude it through a twin-screw extruder, and cut it into pellets by water cooling to obtain anti-caking composite rubber antioxidant 6PPD.

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