Tannic acid derivative antioxidant with main and auxiliary anti-aging structures and multi-mechanism synergistic effect, rubber material prepared from tannic acid derivative antioxidant, preparation method and application of tannic acid derivative antioxidant

Abstract

The invention belongs to the technical field of rubber materials, and particularly relates to a tannic acid derivative antioxidant with a main and auxiliary anti-aging structure and a multi-mechanism synergistic effect, a rubber material prepared from the tannic acid derivative antioxidant, a preparation method and application of the tannic acid derivative antioxidant. According to the preparation method, tannic acid is taken as an antioxidant structure element, epoxy chloropropane is taken as a cross-linking agent, and an aniline group and a thiol group are introduced at the same time, so that the macromolecular polytannic acid derived antioxidant with multiple antioxidant mechanisms is successfully constructed. The polytannic acid-derived antioxidant disclosed by the invention not only can remarkably promote the vulcanization reaction of NBR (nitrile butadiene rubber) and improve the vulcanization rate and crosslinking density, but also shows more excellent thermo-oxidative aging resistance. As a multifunctional antioxidant with a designable structure and a clear synergistic mechanism, the polytannic acid derived antioxidant disclosed by the invention can effectively improve the oxidation resistance, thermal stability, long-term service reliability and other properties of a nitrile rubber composite material, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of rubber material technology, specifically relating to a tannic acid derivative antioxidant with a primary and secondary anti-aging structure and a multi-mechanism synergistic effect, as well as the rubber material prepared therefrom, the preparation method, and the application. Background Technology

[0002] Nitrile butadiene rubber (NBR) possesses excellent oil resistance and mechanical properties, making it widely used in aerospace, oil extraction, and the automotive industry. However, its molecular chain contains numerous unsaturated carbon-carbon double bonds, making it prone to aging under the influence of heat and oxygen. This leads to decreased elasticity, increased hardness, and ultimately, performance degradation or even failure of the finished products. Currently, adding antioxidants remains the simplest and most effective method to improve the aging resistance of rubber.

[0003] Antioxidants commonly used in the rubber industry mainly fall into several categories, including small molecule, macromolecule, and inorganic types. Traditional small molecule antioxidants, such as p-phenylenediamine derivatives (6-PPD, IPPD) and quinoline derivatives (TMQ), are low in cost and fast-acting, but they are prone to migration, volatilization, or extraction, resulting in poor durability and potential environmental pollution and health hazards. Inorganic antioxidants have high thermal stability, but they usually require surface modification to achieve good dispersion, and their dosage significantly affects the mechanical properties of rubber. Macromolecule antioxidants perform excellently in anti-aging; however, their molecular design and synthesis routes are usually complex, and their preparation costs are high, limiting their large-scale industrial application.

[0004] In recent years, the development of polymeric antioxidants using renewable biomass such as chitosan and cellulose as raw materials has become a research hotspot due to their environmentally friendly and sustainable characteristics. Tannic acid (TA), as a widely available natural polyphenol compound, is rich in phenolic hydroxyl groups and crosslinkable active sites, providing an ideal platform for constructing multifunctional antioxidants. Existing studies have shown that the synergy of different structural units within the molecule can enhance anti-aging efficacy. For example, J. Feng et al. (ACSSustainable Chemistry & Engineering, 2017, 5(4), 3399-3408) reported that the intramolecular synergy of aniline and phenol structures can promote hydrogen radical transfer, thereby enhancing antioxidant performance. However, while this type of system captures peroxide radicals to generate hydrogen peroxide, the hydrogen peroxide is prone to further decomposition to generate new oxygen-containing free radicals, which may accelerate polymer chain breakage and limit its long-term stability.

[0005] Therefore, by rationally designing molecules and introducing multiple antioxidant functional groups and stabilizing structures, an antioxidant system that combines primary and secondary aging protection mechanisms with synergistic antioxidant functions can be constructed, which is of great significance for improving the long-term anti-aging performance of rubber materials. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a tannic acid derivative antioxidant with a primary and secondary anti-aging structure and a multi-mechanism synergistic effect, as well as the rubber material prepared from it, the preparation method, and its application.

[0007] This invention provides a polytannic acid-derived antioxidant, which is prepared from raw materials comprising the following parts by weight: Tannic acid 2-50 parts, crosslinking agent A 5-50 parts, aromatic amine molecules 5-50 parts, thiol-based benzimidazole molecules 0-50 parts.

[0008] Preferably, it is made from raw materials comprising the following parts by weight: Tannic acid 2-50 parts, crosslinking agent A 5-50 parts, aromatic amine molecules 5-50 parts, thiol-based benzimidazole molecules 5-50 parts.

[0009] Preferably, the aromatic amine molecule is N-phenyl-p-phenylenediamine, the thiol-benzimidazole molecule is 2-mercaptobenzimidazole, and the crosslinking agent A is epichlorohydrin.

[0010] Preferably, it is prepared by the following steps: mixing tannic acid, aromatic amine molecules and / or thiol-based benzimidazole molecules, and adding crosslinking agent A for reaction.

[0011] Preferably, the reaction process includes: reacting at 60-80 °C for 12-24 h; And / or, the mixing process includes: dissolving in an alkaline solution and stirring at 60-80 °C.

[0012] The present invention provides a method for preparing a polytannic acid-derived antioxidant as described in any of the preceding claims, comprising: mixing tannic acid, aromatic amine molecules and / or thiol-based benzimidazole molecules, and adding crosslinking agent A to react.

[0013] The present invention provides the use of polytannic acid-derived antioxidants as described in any of the preceding claims as rubber additives.

[0014] This invention provides a rubber composite material, which is obtained from raw materials comprising the following parts by weight: 90-100 parts of nitrile rubber, 1-3 parts of the polytannic acid-derived antioxidant as described in any one of claims 1-5, and 1-3 parts of crosslinking agent B.

[0015] Preferably, the raw materials for the rubber composite material also include 20-30 parts of reinforcing agent, 1-3 parts of dispersant, and 1-3 parts of accelerator.

[0016] The present invention provides that the reinforcing agent is selected from at least one of carbon black and silicon dioxide, the dispersant is stearic acid, and the accelerator is N-tert-butylbenzothiazole-2-sulfinamide; And / or, the crosslinking agent B is dicumyl peroxide; And / or, the rubber composite material is prepared by the following steps: mixing raw materials, kneading, and vulcanizing.

[0017] Preferably, the rubber composite material described in any of the preceding claims is used in the aerospace, oil extraction, transportation and industrial sectors.

[0018] In this invention, "aromatic amine" refers to a molecule in which at least one aromatic ring (such as benzene, naphthalene, anthracene, pyridine, etc.) is directly linked to an amino group (–NH2).

[0019] The numbers A and B in the terms "crosslinking agent A" and "crosslinking agent B" serve only to distinguish different terms and do not indicate any priority or order, nor do they limit the scope of the technical features described.

[0020] This invention provides a tannic acid derivative antioxidant with a primary and secondary anti-aging structure and multiple synergistic mechanisms, as well as the rubber materials prepared from it, the preparation method, and its applications. Using tannic acid as the structural unit of the antioxidant and epichlorohydrin as the crosslinking agent, this invention successfully constructs a macromolecular polytannic acid derivative antioxidant PTRB with multiple antioxidant mechanisms by simultaneously introducing aniline groups (specifically N-phenyl-p-phenylenediamine) and thiol groups (specifically 2-mercaptobenzimidazole). Compared with many typical commercial antioxidants, PTRB exhibits superior resistance to thermo-oxidative aging, with an aging coefficient improvement of 24%-267%, demonstrating significant advantages. The multiple synergistic antioxidant mechanism of PTRB not only provides a new strategy for the molecular design of high-performance natural polyphenol-based antioxidants but also provides important scientific basis and methodological guidance for the development of highly durable rubber materials. As a multifunctional antioxidant with a designable structure and a clearly defined synergistic mechanism, PTRB can significantly improve the antioxidant performance, thermal stability, and long-term service reliability of NBR composites, showing great application prospects.

[0021] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions, or alterations can be made without departing from the basic technical concept of the present invention.

[0022] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0023] Figure 1 A synthesis route diagram for PTA, PTR, and PTRB; Figure 2 Infrared spectra of PTA, PTR, and PTRB; Figure 3 The figure shows the effect of antioxidants on the thermo-oxidative aging properties of NBR composites; among them, Figure 3 (a) represents the tensile strength of the NBR composite material. Figure 3 (b) shows the relationship between elongation at break and thermal oxidative aging time. Figure 3 (c) shows the relationship between the aging coefficient of the NBR composite material and the thermal oxidative aging time. Figure 3 (d) shows the relationship between the aging coefficient of the BR composite material prepared with commercial antioxidants and the thermal oxidative aging time. Figure 3 (e) represents the growth rate of the aging coefficient of each NBR compound at 120 h; Figure 4 The graph shows the results of the oxidation induction period and the peak temperature of oxidation exothermic reaction of the composite material; among them, Figure 4 (a) is a graph showing the results of the oxidation induction period (OIT). Figure 4 (b) is the peak temperature of the NBR composite material's oxidation exothermic reaction (T). o ); Figure 5 The graph shows the thermal analysis results of the NBR composite material; where, Figure 5 (a) shows the TG curves of NBR composites after adding different antioxidants to N2. Figure 5 (b) shows the DTG curves of NBR composites after adding different antioxidants to N2. Figure 5 (c) shows the TG curves of NBR composite materials after adding different antioxidants to air. Figure 5 (d) DTG curves of NBR composite materials after adding different antioxidants in air; Figure 6 The TGA curves of the composite material in air at different heating rates (10, 20, 30, 40 ℃ / min) are shown; among them, Figure 6 (a) shows the TGA curve of the Neat / NBR composite material. Figure 6 (b) shows the TGA curve of the TA / NBR composite material. Figure 6 (c) shows the TGA curve of the PTA / NBR composite material. Figure 6 (d) shows the TGA curve of the PTR / NBR composite material. Figure 6 (e) is the TGA curve of the PTBR / NBR composite material; Figure 7 The DTG curves of the composite material in air at different heating rates (10, 20, 30, 40 ℃ / min) are shown; among them, Figure 7(a) shows the DTG curve of the Neat / NBR composite material. Figure 7 (b) shows the DTG curve of the TA / NBR composite material. Figure 7 (c) shows the DTG curve of the PTA / NBR composite material. Figure 7 (d) shows the TGA curve of the PTR / NBR composite material. Figure 7 (e) is the DTG curve of the PTBR / NBR composite material; Figure 7 (f) represents ln(β / T) based on the Kissinger method. 2 max ) and 1000 / T max The relationship diagram. Detailed Implementation

[0024] Unless otherwise specified, all reagents and materials used in the following examples and experimental cases are commercially available.

[0025] Experimental materials: Tannic acid (CAS: 1401-55-4, EINECS No.: 215-753-2, MDL No.: MFCD00066397), nitrile rubber (CAS: 9003-18-3, Ya'an Wanli Rubber & Plastic Sealing Technology Co., Ltd., rubber No. 1051), carbon black (CAS: 1333-86-4, Ya'an Wanli Rubber & Plastic Sealing Technology Co., Ltd., grade N330).

[0026] Example 1: Preparation of tannic acid-derived antioxidant PTA The synthesis route is shown in Figure 1. The specific steps are as follows: 10 g of PTA was dissolved in 250 mL of a 0.125 mol / L sodium hydroxide (NaOH) aqueous solution and stirred at 1000 rpm for 30 min at 80 °C. Then, 18 mL of epichlorohydrin (ECH, density 1.183 g / mL) was slowly added under continuous stirring, and the reaction was carried out at 80 °C for 24 h. After the reaction was complete, the resulting solution was placed in an 80 °C oven to evaporate the moisture and then dried to obtain a viscous PTA. After cooling to room temperature, it solidified into a yellowish-brown blocky solid, which was the PTA product.

[0027] Example 2: Preparation of tannic acid-derived antioxidant PTR The synthesis route is shown in Figure 1. The specific steps are as follows: 10 g of TA and 7.48 g of N-phenyl-p-phenylenediamine (RT) were dissolved in 250 mL of 0.125 mol / L NaOH solution and stirred at 1000 rpm for 30 min at 80 °C. Then, 18 mL of ECH was slowly added, and the reaction was continued at 80 °C for 24 h. The resulting black, viscous crude product was thoroughly dispersed in deionized water at 80 °C, centrifuged at room temperature, and washed 3-5 times to remove unreacted substances. After drying and cooling, a black, blocky PTR product was obtained.

[0028] Example 3: Preparation of tannic acid-derived antioxidant PTRB The synthesis route is shown in Figure 1. The specific steps are as follows: 10 g TA, 7.48 g RT, and 6.1 g 2-mercaptobenzimidazole (MB) were dissolved in 250 mL of 0.125 mol / L NaOH solution and stirred at 1000 rpm for 30 min at 80 °C. Then, 18 mL of ECH was slowly added, and the reaction was continued at 80 °C for 24 h. The resulting black, viscous crude product was thoroughly dispersed in deionized water at 80 °C, centrifuged at room temperature, and washed 3-5 times to remove unreacted substances. After drying and cooling, a black, blocky PTRB product was obtained.

[0029] Example 4: PTA / NBR NBR composite material containing tannic acid-derived antioxidants This embodiment provides a PTA / NBR NBR composite material, which is prepared by the following method: At room temperature, NBR (500g) and carbon black (125g) were added to a two-roll mill with a roll gap of approximately 0.5 mm. Then, silica (SiO2, 25g), stearic acid (SA, 10g), antioxidant (10g, PTA prepared in Example 1), sulfenamide accelerator (specifically N-tert-butylbenzothiazole-2-sulfinamide (NS), 10g), and dicumyl peroxide (DCP, 10g) were added sequentially. The mixture was then kneaded for 10 min to ensure thorough dispersion of the additives and the rubber matrix. After mixing, the compound was left to stand overnight at room temperature.

[0030] The compound rubber was vulcanized using a flat vulcanizing machine (Shanghai Rubber Machinery Factory) under the following conditions: pressure 10 MPa, temperature 150 ℃, and time 30 min.

[0031] Example 5: PTR / NBR NBR composite material containing tannic acid-derived antioxidants This embodiment provides a PTR / NBR composite material containing PTR, which is prepared in the same way as in Example 4, except that the antioxidant is changed to the PTR prepared in Example 2.

[0032] Example 6: NBR composite material PTRB / NBR containing tannic acid-derived antioxidants This embodiment provides a PTRB / NBR NBR composite material containing PTRB, which is prepared in the same way as in Example 4, except that the antioxidant is changed to PTRB prepared in Example 3.

[0033] Comparative Example 1 This comparative example provides an NBR composite material TA / NBR with added antioxidant TA. The preparation method is the same as in Example 4, except that the antioxidant is changed to TA.

[0034] Comparative Example 2 This comparative example provides an NBR composite material PTA / RTNBR with added composite antioxidant PTA / RT. The preparation method is the same as in Example 4, except that the type of antioxidant is changed to PTA and RT, and the dosage is adapted according to the formulation in Table 1.

[0035] Table 1. Basic Formulation (phr) of NBR Composite Materials Note: The amounts of NBR, SiO2, SA, NS and DCP used to prepare all samples were 100, 5, 2, 2 and 2 parts by weight (phr), respectively, and the amount of NBR used was 500g.

[0036] Comparative Example 3 This comparative example provides an NBR composite material PTA / RT / MBNBR with added composite antioxidant PTA / RT / MB. The preparation method is the same as in Example 4, except that the types of antioxidants are adjusted to PTA, RT and MB, and the dosage is adapted according to the formulation in Table 1.

[0037] The technical solution of the present invention will be further explained through experiments below. The samples PTA, PTR, PTRB, TA / NBR, PTA / NBR, PTR / NBR, PTRB / NBR, PTA / RTNBR, and PTA / RT / MBNBR tested in the following experimental examples were all prepared by the methods of the above embodiments and comparative examples.

[0038] Experimental Example 1: Structural Characterization of Antioxidants I. Experimental Methods 1. Fourier Transform Infrared Spectroscopy (FTIR) Test The FTIR tests were performed using a NICOLET 5 spectrometer from Thermo Fisher Scientific (China) Co., Ltd., employing the KBr pellet method to measure TA, PTA, PTR, and PTRB, with a scanning range of 400 cm⁻¹. -1 ~4000 cm -1The number of scans was 32, and the resolution was 4cm. -1 The infrared absorption spectrum of the sample was obtained, and its functional group structural characteristics were analyzed.

[0039] II. Experimental Results The infrared spectra of PTA, PTR, and PTRB are as follows: Figure 2 As shown. For TA, at 3300-3400 cm -1 A broad and strong absorption peak appears within the range, corresponding to the O–H stretching vibrations of the numerous phenolic hydroxyl groups in the molecule; 1198 cm⁻¹ -1 The absorption peak at 1198 cm⁻¹ is attributed to the stretching vibration of COC in the aromatic ether bond or ester group, which is a major manifestation of the characteristic structure of the TA molecule. PTA crosslinked with ECH has an absorption peak at 1198 cm⁻¹. -1 The significantly enhanced COC stretching vibration peak indicates that ECH was successfully introduced into the TA molecules via etherification to form a cross-linked structure. Compared to PTA, PTR showed a stronger peak at 1514 cm⁻¹. -1 A new absorption peak appears at 993 cm⁻¹, which is attributed to the NH₄⁺ bending vibration, indicating that the amino group of 4-aminodiphenylamine (RT) has been successfully grafted onto the PTA molecule. Furthermore, PTRB shows an absorption peak at 993 cm⁻¹. -1 A distinct CS stretching vibration absorption peak was observed, confirming that 2-mercaptobenzimidazole (MB) had undergone covalent bonding with PTA. FTIR characterization results fully demonstrate that this invention successfully prepared a novel tannic acid antioxidant possessing both aniline and thioether groups.

[0040] Experimental Example 2: Effect of Antioxidants on the Thermo-Oxidative Aging Properties of NBR Composites I. Experimental Methods To evaluate the effects of different antioxidants on the thermo-oxidative aging behavior of NBR, this experimental example conducted an accelerated aging test on NBR and NBR composite materials at 121 °C for 120 h, and tested their tensile strength and elongation at break at different aging time points (0, 24 h, 72 h, 120 h).

[0041] 1. Tensile property testing methods for NBR composite materials According to GB / T528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber", a CMT6104 microcomputer-controlled electronic universal testing machine controlled by Meters Industries (China) Co., Ltd. was used to test the mechanical properties of dumbbell-shaped specimens of NBR composite materials containing different antioxidants. The tensile rate was 200 mm / min. Three specimens were used in each test group, and the average value was taken as the final test result.

[0042] 2. Aging coefficient K The formula for calculating the aging factor K is as follows: K = (Tensile strength after aging × Elongation at break after aging) ÷ (Tensile strength before aging × Elongation at break before aging) II. Experimental Results The results of tensile strength and elongation at break are as follows: Figure 3 As shown in a-3b and Table 3-4, the mechanical properties of Neat / NBR degrade rapidly with aging time. Its tensile strength drops to only 12.27 MPa after 5 days of aging, and its elongation at break decreases to 71.96%, exhibiting significant thermo-oxidative embrittlement behavior. The system containing TA and PTA also shows a clear trend of performance decline during aging, and its strength and elongation retention are similar to those of Neat / NBR, further illustrating that the antioxidants TA and PTA have very limited effect on inhibiting rubber aging.

[0043] Table 3. Tensile strength (MPa) of NBR composites with different antioxidant systems at 121 °C for different aging times. Table 4. Elongation at break (%) of NBR composites with different antioxidant systems at 121 °C for different aging times In comparison, the grafted antioxidant systems PTR and PTRB exhibited significantly better aging resistance than the aforementioned systems. When RT was grafted onto PTA, the aging performance of the resulting PTR / NBR was significantly improved. After 120 h of aging, its tensile strength and elongation at break retention rates increased significantly from 48.58% and 20.12% of PTA / NBR to 97.80% and 49.95%, respectively, representing increases of 101.32% and 148.26% compared to PTA / NBR. This result indicates that the aniline structure in RT can form a synergistic stabilizing effect with the phenolic hydroxyl groups of PTA, achieving more efficient hydrogen radical transfer and release, thereby enhancing the capture of oxidative free radicals. Further introduction of MB into PTA / RT further enhanced the aging resistance of PTRB / NBR. After 120 h of aging, its tensile strength and elongation at break retention rates reached as high as 99.96% and 65.00%, respectively, the best among all samples. After 5 days of aging, the tensile strength of PTRB / NBR remained at 24.04 MPa, showing almost no decline; the elongation at break was still 321.93%, significantly better than other samples, demonstrating excellent antioxidant stability. Furthermore, while the physically blended systems PTA / RT and PTA / RT / MB delayed the degradation of mechanical properties to some extent, their long-term stability was still inferior to that of the covalently grafted PTR and PTRB.

[0044] In summary, both sets of data show that: (1) using TA or PTA alone has limited contribution to improving the thermo-oxidative stability of NBR; (2) PTR containing aniline structure significantly improves the mechanical properties after aging; (3) PTRB, a multi-mechanism antioxidant integrating aniline and thioether structures, performs best in all systems and can maintain the highest strength and elongation retention rate under long-term thermo-oxidative aging conditions, further verifying its unique advantages as a high-performance antioxidant.

[0045] To more comprehensively evaluate the antioxidant effect, this experimental example introduces the aging coefficient K as a key evaluation indicator. Figure 3 c). The results showed that the K values ​​of TA and PTA decreased sharply with aging time, indicating that their long-term antioxidant capacity was limited; while the decrease in K values ​​of PTR and PTRB was significantly slower, and their long-term stability was significantly improved. After aging at 121 °C for 72 h, the aging coefficients of PTR and PTRB were 0.67 and 0.78, respectively; after aging for 120 h, they were 0.49 and 0.65, respectively, which were significantly better than those of TA and PTA.

[0046] To further demonstrate the advantages of PTRB, this experimental example compares it with several commercial antioxidants such as 4010NA, MBMTB, TMQ, and RT. Figure 3 d). The results showed that PTRB had significantly better long-term antioxidant performance than the aforementioned traditional antioxidants.

[0047] This experimental example further demonstrates the superior performance of PTRB through literature comparison. Previous studies have shown that COS-UC-MC-MPA has a K-value of 0.48 after aging at 100 °C for 120 h, while COS-GMMP has a K-value below 0.6. In contrast, the PTRB of this invention maintains an aging coefficient as high as 0.65 even at a higher aging temperature (121 °C), exhibiting superior antioxidant stability.

[0048] Finally, this experimental example further demonstrates the synergistic antioxidant mechanism between the aniline structure RT and the phenol structure PTA based on the aging coefficient. Figure 3 e). Under the same RT content (8.63 wt%), RT alone can improve the antioxidant performance of NBR by 320%; while covalently grafted PTR and PTRB can improve it by 390% and 550%, respectively, with performance far exceeding the theoretical additive effect. This result fully demonstrates that the synergistic effect between the phenolic hydroxyl group and the aniline structure significantly improves the migration efficiency of hydrogen free radicals, enabling PTRB to achieve antioxidant capacity superior to traditional antioxidants.

[0049] In summary, the multi-mechanism antioxidant PTRB prepared by this invention exhibits excellent long-term stability in high-temperature oxidative environments, significantly delaying the thermo-oxidative aging process of NBR, and its performance is superior to conventional small-molecule antioxidants and some reported macromolecular antioxidants, thus possessing significant theoretical and application value.

[0050] Experimental Example 3: Oxidation Induction Period and Oxidation Exothermic Peak Temperature of Composite Materials I. Experimental Methods To further evaluate the effects of different antioxidants on improving the thermo-oxidative stability of NBR, this experimental example used DSC to determine the oxidation induction time (OIT) and oxidation exothermic peak temperature (T) of the NBR composite material under an O2 atmosphere. o This test method can characterize the material's oxygen susceptibility delay and the change in the activation energy of the oxidation reaction under oxidative conditions, and is a reliable means of evaluating antioxidant performance.

[0051] The oxidation induction period test method is as follows: According to GB / T19466.6-2009 "Differential Scanning Calorimetry (DSC) for Plastics - Part 6, Determination of Oxidation Induction Time (Isothermal OIT) and Oxidation Induction Temperature (Dynamic OIT)," a NETZSCH 204F1 differential scanning calorimeter (Germany) was used to test the oxidation induction period of NBR composite samples containing different antioxidants. First, approximately 8 mg of sample was weighed and kept at 30 °C for 5 min in a N2 atmosphere. Then, the temperature was increased to 200 °C at a rate of 20 °C / min and held for 5 min. Subsequently, the N2 atmosphere was switched to oxygen (O2), and the temperature was maintained at 200 °C until the sample exhibited an exothermic oxidation peak. The oxidation induction period is the interval between the onset of the exothermic oxidation peak and the initial oxygen inlet time. The onset of the exothermic oxidation peak was obtained using NETZSCH thermal analysis software.

[0052] The method for testing the oxidation exothermic peak temperature is as follows: The DSC curve of the NBR composite material was determined using a differential scanning calorimeter (model 204F1) from NETZSCH GmbH, Germany. Approximately 5 mg of the NBR composite material sample was weighed and heated from room temperature to 350 °C at a heating rate of 10 K / min in air.

[0053] II. Experimental Results The results are as follows Figure 4 As shown in Table 5. Figure 4 As shown in figure a, the OIT of Neat / NBR is only 1.81 min, indicating its weak initial oxidation resistance. In contrast, the OIT of TA / NBR further decreases to 1.61 min, while the OIT of PTA only increases to 2.66 min. Oxidation exothermic peak temperature (To) o ) Consistent with the changing trend of OIT ( Figure 4b). After the introduction of RT and MB, the oxidation stability of PTR / NBR and PTRB / NBR is significantly enhanced. Although physical blending systems such as PTA / RT and PTA / RT / MB can improve OIT and T to some extent, o However, its synergistic effect is significantly weaker than that of PTR and PTRB. Specifically, the OIT of PTR / NBR increased to 4.84 min, 2.67 times that of pure NBR; the OIT of PTRB / NBR reached an even more impressive 7.62 min, an improvement of 421%. The corresponding T... o The oxidation temperatures were also increased by 8.59 °C and 13.44 °C, respectively. Such significant delayed oxidation behavior indicates that the synergistic effect between the aniline structure of RT and the phenolic hydroxyl group of PTA can effectively promote the migration and release of hydrogen free radicals, thereby efficiently scavenging oxidative free radicals; while the thioether structure of MB can catalyze the conversion of hydrogen peroxides into stable products, further inhibiting the propagation of the oxidation chain reaction.

[0054] Table 5. Oxidation induction time (OIT) and oxidation exothermic peak temperature (T) of NBR composites with different antioxidant systems o ) Example 4: Kinetic Analysis of Thermal Oxidative Degradation and Decomposition of NBR Composite Materials I. Experimental Methods 1. Thermogravimetric analysis (TGA) test (1) Thermogravimetric test of antioxidant Thermal degradation tests were conducted on different antioxidants using a TG209F1 thermogravimetric analyzer from Netzsch GmbH, Germany. The tests were performed under a nitrogen (N2) atmosphere at a gas flow rate of 50 mL / min, a heating rate of 20 °C / min, a temperature range of 25–800 °C, and a sample mass of 7–8 mg.

[0055] (2) Thermal degradation test of composite materials The test conditions were exactly the same as those in (1) for the thermal degradation test of the antioxidant, to investigate the thermal decomposition behavior of the composite material under an inert atmosphere.

[0056] (3) Thermo-oxidative degradation test of composite materials The test conditions were similar to (1), except that the atmosphere was changed to air, and the heating rates were 10, 20, 30 and 40 K / min, respectively.

[0057] (4) Analysis and testing of thermo-oxidative degradation kinetics of composite materials The thermo-oxidative degradation kinetics of NBR composites with different antioxidants were analyzed using the Kissinger equation (Equation 1). ln ( β / T 2 max ) for 1000 / T max Plot the graph and calculate the activation energy of thermo-oxidative degradation of the sample by fitting the slope of the straight line. E .

[0058] (Equation 1) In the formula, β It is the heating rate of the thermogravimetric test. T max It is the absolute temperature corresponding to the maximum rate of thermal weight loss. A It refers to the pre-factor. R It is the ideal gas constant. R Take 8.314 J / (mol·K).

[0059] II. Experimental Results 1. Thermogravimetric analysis results The results are as follows Figure 5 As shown in Table 6, under a N2 atmosphere, all systems exhibited obvious single-stage or multi-stage thermogravimetric processes, corresponding to the breakage and degradation of rubber molecular chains. Compared with Neat / NBR, the composite materials with added antioxidants all showed an increased initial thermal degradation temperature, indicating that the phenolic hydroxyl groups in PTA and the aniline structure in RT can effectively capture free radicals generated during thermal degradation, thereby delaying the chain breakage reaction and improving the initial thermal stability of the materials.

[0060] Table 6. Temperature characteristics of thermal decomposition and thermal oxidative decomposition of NBR composites under nitrogen and air atmospheres for different antioxidants. Note: a T onset The initial temperature at which the sample begins to decompose; b T 5% The temperature at which a 5% mass loss occurs; c T max Temperature corresponding to the maximum mass loss rate.

[0061] Further comparison of TA / NBR and PTA / NBR reveals that TA / NBR degrades rapidly at around 550 °C, while the mass loss trend of PTA / NBR is relatively gradual. This result indicates that unmodified TA, under thermo-oxidative conditions, negatively impacts the structural integrity of NBR, while the cross-linked structure of PTA can partially offset this negative effect.

[0062] From the characteristic weightlessness temperature (T) 5% T 10%According to the results, under N2 atmosphere, all samples containing antioxidants showed a higher T than Neat / NBR. 5% and T 10% As the temperature further increases, PTA's adsorption capacity with the filler is weaker than that of TA due to the reduction of some oxygen functional groups during the modification process. Therefore, the Tg of PTA / NBR... 10% Slightly lower than TA / NBR.

[0063] In summary, thermogravimetric analysis results show that: (1) TA is prone to migration and has insufficient structural stability, which has an adverse effect on thermal degradation behavior; (2) PTA improves structural stability, but its high-temperature adsorption capacity is slightly weaker; (3) Both covalently grafted PTR and PTRB can significantly delay the thermal degradation process; (4) Especially PTRB, its T 5% The characteristic temperature was significantly increased, exhibiting the most stable thermal degradation behavior. This result further demonstrates the effectiveness of the multi-mechanism synergistic antioxidant system in improving the thermal stability of NBR.

[0064] 2. TGA Test Results and Analysis To further investigate the effects of different antioxidant systems on the thermo-oxidative stability of NBR composites, this experimental example underwent TGA testing at various heating rates, and the thermo-oxidative degradation kinetic parameters were analyzed based on the Kissinger method. Figure 6 The TGA curves of each system at different heating rates are shown. The apparent activation energy (E) of thermo-oxidative degradation of the composite material can be calculated by linearly fitting ln(β / T²max) and 1000 / Tmax using the Kissinger equation. The relevant results are listed in Table 7. The DTG curves at different heating rates are shown below. Figure 7 As shown, all samples exhibited similar mass loss behavior in air atmosphere, indicating that their thermo-oxidative decomposition process was consistent.

[0065] Table 7. DTG curves and thermal oxidation activation energy (E) of NBR composites with different antioxidants calculated by Kissinger. max Fitting the experimental data to the Kissinger equation reveals that the coefficient of determination (R²) of the fitted curves for all samples is [missing information]. 2 The apparent activation energy (E) of all samples was above 0.99 (Table 7), indicating that the kinetic analysis of this experimental example has high reliability. The activation energy (E) is an important parameter for measuring the ease of thermo-oxidative degradation of a material. The larger the E value, the more difficult the material structure is to be damaged by thermo-oxidative processes, and the better its resistance to thermo-oxidative aging. As shown in Table 7, PTRB / NBR has the highest apparent activation energy, reaching 246.15 kJ·mol⁻¹. -1 It is significantly higher than other antioxidant systems.

[0066] Experimental Example 5: Extraction Resistance Analysis of Antioxidants I. Experimental Methods To clarify the migration resistance of antioxidants, this experimental example uses NBR composite material for ethanol extraction experiments instead of migration behavior testing, aiming to quantify the mass loss of antioxidant components.

[0067] Ethanol extraction experiment: Extraction resistance assessment of antioxidants was conducted according to ISO 1407:2023. NBR composite samples with different antioxidants were subjected to Soxhlet extraction with ethanol as solvent, and recovered in batches after 6, 12, 24, and 48 hours of extraction. The samples were then dried to constant weight in a 60°C vacuum oven. The mass loss rate of the antioxidants was calculated using the following formula: Where P represents the percentage of mass loss of the sample due to extraction, and m1 and m2 represent the sample mass before and after extraction, respectively; W represents the percentage of mass loss of the antioxidant due to extraction, and P1 and P2 are the extraction-induced mass loss percentages of the samples with and without added antioxidants, respectively; Q is the mass percentage of antioxidant in the formulation.

[0068] II. Experimental Results As shown in Table 8, the commercial antioxidant 4010NA in the NBR composite exhibited significant mass loss during solvent extraction. A mass loss of 23.58% was recorded after only 6 hours, and this figure further increased to 69.11% after 48 hours of extraction. This significant leaching ability in ethanol indicates poor migration resistance of 4010NA, which will inevitably lead to a gradual decline in its antioxidant efficacy over long-term use.

[0069] Table 8. Percentage of mass loss of NBR composite material samples and percentage of mass loss of antioxidants after ethanol extraction. In contrast, the composites containing low-molecular-weight tannic acid (TA) exhibited significantly reduced extraction loss. Notably, high-molecular-weight derivatives (PTA, PTR, and PTRB) demonstrated superior migration resistance. Specifically, the PTRB system showed only a 25.36% mass loss after 48 hours of extraction.

[0070] As can be seen from the above embodiments and experimental examples, this invention provides a tannic acid derivative antioxidant with a primary and secondary anti-aging structure and a multi-mechanism synergistic effect, as well as the rubber materials prepared from it, the preparation method, and its applications. This invention uses tannic acid as the structural unit of the antioxidant and epichlorohydrin as the crosslinking agent. By simultaneously introducing aniline groups (specifically N-phenyl-p-phenylenediamine) and thiol groups (specifically 2-mercaptobenzimidazole), a macromolecular polytannic acid derivative antioxidant PTRB with multiple antioxidant mechanisms was successfully constructed. Compared with many typical commercial antioxidants, PTRB exhibits superior resistance to thermo-oxidative aging, with an aging coefficient improvement of 24%-267%, showing significant advantages. The multiple synergistic antioxidant mechanism of PTRB not only provides a new strategy for the molecular design of high-performance natural polyphenol-based antioxidants but also provides important scientific basis and methodological guidance for the development of high-durability rubber materials. As a multifunctional antioxidant with a designable structure and a clearly defined synergistic mechanism, PTRB can significantly improve the antioxidant performance, thermal stability, and long-term service reliability of NBR composite materials, showing great application prospects.

Claims

1. A polytannic acid-derived antioxidant, characterized in that, It is made from the following raw materials in parts by weight: Tannic acid 2-50 parts, crosslinking agent A 5-50 parts, aromatic amine molecules 5-50 parts, thiol-based benzimidazole molecules 0-50 parts.

2. The polytannic acid-derived antioxidant according to claim , characterized in that, It is made from the following raw materials in parts by weight: Tannic acid 2-50 parts, crosslinking agent A 5-50 parts, aromatic amine molecules 5-50 parts, thiol-based benzimidazole molecules 5-50 parts.

3. The polytannic acid-derived antioxidant according to claim 2, characterized in that, The aromatic amine molecule is N-phenyl-p-phenylenediamine, the thiol-benzimidazole molecule is 2-mercaptobenzimidazole, and the crosslinking agent A is epichlorohydrin.

4. The polytannic acid-derived antioxidant according to any one of claims 1-3, characterized in that, It is prepared by the following steps: mixing tannic acid, aromatic amine molecules and / or thiol-based benzimidazole molecules, and adding crosslinking agent A for reaction.

5. The polytannic acid-derived antioxidant according to claim 3, characterized in that: The reaction process includes: reacting at 60-80 ℃ for 12-24 h; And / or, the mixing process includes: dissolving in an alkaline solution and stirring at 60-80 °C.

6. The method for preparing the polytannic acid-derived antioxidant according to any one of claims 1-5, characterized in that, It includes: Tannic acid, aromatic amine molecules and / or thiol-based benzimidazole molecules are mixed and reacted with crosslinking agent A.

7. Use of the polytannic acid-derived antioxidant according to any one of claims 1-5 as a rubber additive.

8. A rubber composite material, characterized in that, It is made from the following raw materials in parts by weight: 90-100 parts of nitrile rubber, 1-3 parts of the polytannic acid-derived antioxidant as described in any one of claims 1-5, and 1-3 parts of crosslinking agent B.

9. The rubber composite material according to claim 8, characterized in that: The raw materials for rubber composites also include 20-30 parts of reinforcing agent, 1-3 parts of dispersant, and 1-3 parts of accelerator.

10. The application of the rubber composite material of claim 8 or 9 in aerospace, oil extraction, transportation and industrial fields.

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