A rare earth complex antioxidant for rubber and its preparation method

Abstract

The present invention discloses a rare earth complex antioxidant for rubber and its preparation method. The chemical composition general formula is REZ 3‑x (OH) x ·mH2O, where RE is one or more of Tb, Dy, Ho, Er, Tm, Yb, Lu, Z is caffeic acid or a caffeic acid derivative, 0 < x ≤ 2, 0 < m ≤ 3; the rare earth complex is prepared by reacting caffeic acid or a caffeic acid derivative with a rare earth salt in a methanol solution under the action of triethylamine and tris(hydroxymethyl)aminomethane, and then successively through filtration, washing and drying. The preparation method of the present invention is simple, the process is easy to control, the raw materials used are non-toxic and environmentally friendly. After adding the prepared rare earth complex antioxidant to styrene-butadiene rubber and aging it for 2 days under hot air at 100 °C, the tensile strength retention rate of the styrene-butadiene rubber can reach up to 95%.

Description

Technical Field

[0001] The invention belongs to the technical field of rubber anti-aging, and relates to a rare earth complex antioxidant used in rubber and a preparation method thereof. Background Art

[0002] During the processing and storage of raw rubber or rubber products, due to the influence of external factors, the structure and organization of rubber products are destroyed and lose their excellent properties. This phenomenon is called rubber aging. The chemical structure of rubber antioxidants can be divided into amine antioxidants, phenolic antioxidants, heterocyclic antioxidants, physical antioxidants and other types of antioxidants. However, with the development of society and the improvement of people's awareness of environmental protection, the disadvantages of traditional antioxidants have become prominent. For example, some amine antioxidants and phenolic antioxidants may irritate human skin and respiratory tract. In addition, antioxidants entering water bodies or soil may have adverse effects on the ecological environment and endanger the survival of aquatic organisms and soil microorganisms. Therefore, it is of great significance to seek a new type of antioxidant to reduce damage to the environment and harm to the human body.

[0003] Caffeic acid, a polyphenol found in many foods, including honey, coffee, apples, etc., is mostly used in medical treatment. Caffeic acid has hemostatic, antibacterial, anti-inflammatory, and anti-cancer effects. Caffeic acid has a strong antioxidant effect, which is mainly related to the two hydroxyl groups on its aromatic ring. Its derivatives (chlorogenic acid, ferulic acid, danshensu) also have the same effect. Because of its low cost, easy availability, non-toxicity and no pollution to the environment, the rare earth complexes formed by rare earth elements and caffeic acid derivatives are currently studied at home and abroad for antibacterial effects on the human body, but there is no literature report on their application in rubber thermal oxidation aging protection.

[0004] Based on this, the present invention aims to solve the problem of thermal oxidation aging of natural rubber and synthetic rubber by using caffeic acid or caffeic acid derivatives in combination with rare earth elements. Summary of the invention

[0005] In view of the above technical problems, the present invention aims to provide a rare earth complex antioxidant for rubber, the chemical composition of which is 3-x (OH) x mH2O, after adding the prepared rare earth complex antioxidant to styrene-butadiene rubber and aging it in hot air at 100℃ for 2 days, the tensile strength retention rate of styrene-butadiene rubber can reach up to 95%;

[0006] The invention also discloses a preparation method of the rare earth complex antioxidant, which comprises reacting caffeic acid or a caffeic acid derivative with a rare earth salt in a methanol solution under the action of triethylamine and trishydroxymethylaminomethane, and then filtering, washing and drying in sequence. The preparation method of the invention is simple, the process is easy to control, the raw materials used are non-toxic, and the antioxidant is environmentally friendly.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A rare earth complex antioxidant used in rubber, the general chemical formula is REZ 3-x (OH) x ·mH2O, wherein RE is one or more of Tb, Dy, Ho, Er, Tm, Yb, and Lu, Z is caffeic acid or a caffeic acid derivative, 0<x≤2, 0<m≤3.

[0009] As a limitation of the rare earth complex antioxidant for rubber of the present invention, the caffeic acid derivative is chlorogenic acid or 1,3-dicaffeoylquinic acid.

[0010] As another limitation of the rare earth complex antioxidant for rubber of the present invention, the molecular structural formula of the rare earth complex is:

[0011] ,

[0012] Wherein, R is one of hydroxyl, alkyl and cycloalkyl.

[0013] The present invention also provides a method for preparing a rare earth complex antioxidant for rubber, which is carried out in the following steps in sequence:

[0014] S1. Slowly add the hydrochloric acid solution to the rare earth oxide, stir for 20-40 min, evaporate the solution to dryness at 100-200°C to obtain a white solid, vacuum dry it, grind it to 60 mesh, and then add it to 100-150 mL of methanol to obtain a rare earth salt-methanol solution;

[0015] S2, adding 1.75-3.25 g of caffeic acid or a caffeic acid derivative to 100 mL of water to form a caffeic acid or a caffeic acid derivative solution, then adding 0.15-0.6 g of sodium hydroxide to 75 mL of water to form a sodium hydroxide solution, then slowly dripping the sodium hydroxide solution into the caffeic acid or caffeic acid derivative solution, adding triethylamine, adjusting the pH of the solution to 7.0, reacting for 10 min, adding 0.5 g of tris(hydroxymethyl)aminomethane, stirring evenly with a glass rod, to obtain a sodium salt solution of caffeic acid or a caffeic acid derivative;

[0016] S3. Slowly drop the rare earth salt-methanol solution into the caffeic acid or caffeic acid derivative sodium salt solution, stir and react at 60-80°C for 1-2 h, let the precipitate stand for 24 h and then filter it, wash it with water 5-7 times, and dry it at 40-60°C for 5-12 h to obtain a rare earth complex antioxidant.

[0017] As a limitation of the preparation method of the present invention, in step S1, the rare earth oxide is one or more of terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide, and lutetium oxide.

[0018] As another limitation of the preparation method of the present invention, in step S1, the molar ratio of the hydrochloric acid solution to the rare earth oxide is 1:1.

[0019] As a third limitation of the preparation method of the present invention, in step S1, the vacuum drying temperature is 40-60° C. and the time is 5-12 h.

[0020] As a fourth limitation of the preparation method of the present invention, in step S3, the volume ratio of the rare earth salt-methanol solution to the caffeic acid or caffeic acid derivative sodium salt solution is 1:2.

[0021] In the present invention, the volume ratio of the rare earth salt-methanol solution to the caffeic acid or caffeic acid derivative sodium salt solution is extremely important, which affects the coordination degree and further affects the yield of the final product. Specifically, when the ratio of the two is 1:2, the central atom and the ligand are properly coordinated and the structure is stable. If it is greater than this ratio, it is not conducive to the formation of the complex and affects the structural stability of the complex. If it is less than this ratio, the coordination number is reduced, the structural stability of the complex is reduced, and it is easily affected by external factors such as temperature and solvent, resulting in instability of the complex.

[0022] The rare earth complex antioxidant prepared by the present invention uses caffeic acid or caffeic acid derivatives as ligands and rare earth elements as central atoms. The rare earth elements coordinate with oxygen atoms on caffeic acid or caffeic acid derivatives, effectively improving the structural stability in a hot oxygen environment. At the same time, the phenolic hydroxyl group, double bond, and carboxyl group in caffeic acid or caffeic acid derivatives can effectively inhibit the chain reaction of free radicals, thereby solving the problem of hot oxygen aging of natural rubber and synthetic rubber. Specifically, the rare earth complex antioxidant contains hydroxyl groups connected to benzene rings, which are affected by the benzene rings to produce a conjugated effect, making it easier to It is easily oxidized, thus terminating the chain reaction of free radicals. The presence of carboxyl groups has certain reactivity and can also capture free radicals and terminate the chain reaction of free radicals. The double bonds in the ligands can also react with the free radicals generated by the rubber during the aging process. At the same time, due to the special electronic structure of rare earth elements, they can form coordination bonds with the rubber molecular chains to enhance the interaction between the molecular chains. Rare earth elements also have the function of terminating free radical reactions, which can further improve the aging resistance of rubber. Therefore, after the formation of the complex, the phenolic hydroxyl group, carboxyl group, double bond, and rare earth group work synergistically. Due to the large radius of rare earth ions, the complex occupies a large space, forming a steric hindrance, limiting the movement and reaction activity of the ligand so that the ligand is stable. Due to the special electronic structure of rare earth, while absorbing free radicals to achieve the anti-aging effect, the complex can maintain its own structure in a high temperature environment without being destroyed, so that the antioxidant can play a continuous role, and the coordination effect enhances the chemical stability of the ligand. The complex is not easy to react adversely with other additives in the rubber system, ensuring the concentration of the complex in the rubber system, thereby prolonging the aging effect. The formed complex is induced to move the electron cloud, and the electron cloud of the C=O double bond in the carboxyl group moves toward the oxygen atom, the polarity of the C=O double bond is enhanced, and its chemical reaction activity is enhanced, while the stability of the π bond is reduced, and it is easy to break, thereby absorbing free radicals. Similarly, the carbon-carbon double bond connected to the carboxyl group is affected by the polarity of the C=O bond in the carboxyl group, and the stability of the π bond is also reduced, achieving the effect of absorbing free radicals, thereby having a synergistic effect.

[0023] The above technical solution of the present invention is taken as a whole, and each step is closely related and influences each other, which jointly determine the morphological characteristics and performance of the product.

[0024] The above technical solution has the following advantages or beneficial effects:

[0025] 1. The raw materials used in the present invention are widely available. Caffeic acid or caffeic acid derivatives have good compatibility with rare earth salts, are non-toxic, and are environmentally friendly.

[0026] 2. The preparation method of the present invention is simple, the operation process is easy to control, the cost is low, and it is suitable for large-scale batch production;

[0027] 3. The rare earth complex prepared by the present invention has a more obvious anti-thermal oxidative aging effect than the existing antioxidants. When the rare earth complex antioxidant is added to styrene-butadiene rubber and aged in hot air at 100°C for 2 days, the tensile strength retention rate of the styrene-butadiene rubber can reach up to 95%.

[0028] The invention is suitable for preparing a rare earth complex antioxidant used in rubber.

[0029] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is an infrared spectrum of the rare earth complex and the ligand caffeic acid prepared in Example 1 of the present invention;

[0031] Figure 2 XRD diagram of the rare earth complex and ligand caffeic acid prepared in Example 1 of the present invention;

[0032] Figure 3 The thermogravimetric analysis diagrams of the rare earth complex and the ligand caffeic acid prepared in Example 1 of the present invention, wherein (a) is a thermogravimetric analysis diagram, and (b) is a DTG curve diagram;

[0033] Figure 4 This is the infrared spectrum of the rare earth complex and the ligand chlorogenic acid prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0034] The following embodiments are only some embodiments of the present invention, rather than all embodiments. Therefore, the detailed description in the embodiments of the present invention provided below is not intended to limit the scope of the present invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0035] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments are all conventional methods in the art unless otherwise specified. Example

[0036] In this example, TbZ1(OH)2·3H2O (Z is caffeic acid) is prepared, and the preparation process and steps are as follows:

[0037] S1. Slowly add 1 mol hydrochloric acid solution to 1 mol terbium oxide, stir for 20 min, evaporate the solution at 100°C to dryness, obtain a white solid, vacuum dry it at 40°C for 12 h, grind it to 60 mesh, and then add it to 100 mL methanol to obtain a rare earth salt-methanol solution;

[0038] S2, adding 2.7 g of caffeic acid to 100 mL of water to form a caffeic acid solution, then adding 0.6 g of sodium hydroxide to 75 mL of water to form a sodium hydroxide solution, then slowly dripping the sodium hydroxide solution into the caffeic acid solution, then adding triethylamine, adjusting the pH of the solution to 7.0, reacting for 10 min, adding 0.5 g of tris(hydroxymethyl)aminomethane, stirring evenly with a glass rod, to obtain a sodium caffeic acid salt solution;

[0039] S3. Slowly drop 50 mL of rare earth salt-methanol solution into 100 mL of sodium caffeate solution, stir and react at 60°C for 2 h, let the precipitate stand for 24 h and then filter it. Wash it with water 5 times and dry it at 60°C for 12 h to obtain a rare earth complex antioxidant.

[0040] The rare earth complex antioxidant prepared in this example is in the form of gray powder, and the yield is 95%.

[0041] The rare earth complex antioxidant prepared in this example, antioxidant MB, and antioxidant 4010NA were added to styrene-butadiene rubber to test the anti-aging performance. The experiment was divided into three groups, among which group A added rare earth complex as antioxidant, group B added MB as antioxidant, and group C added 4010NA as antioxidant, as follows:

[0042] The basic formulas of the three groups of experiments to test the anti-aging performance of styrene-butadiene rubber are:

[0043]

[0044] Mixing and vulcanization process of styrene-butadiene rubber: first, knead the styrene-butadiene rubber in an open mill for 5 minutes, add other compounding ingredients according to the conventional mixing method, and finally add sulfur, mix for 5 minutes, thin it, and sheet it. The mixed rubber is placed at room temperature for 24 hours to remove internal stress, and the rubber is vulcanized on a flat vulcanizer at 143°C, 10 MPa, and positive vulcanization time T90 to obtain styrene-butadiene rubber vulcanizate.

[0045] The styrene-butadiene rubber vulcanizates prepared from Group A, Group B and Group C were placed in a hot air aging test chamber at a test temperature of 100°C for aging experiments, and their tensile strength retention rates were tested. The specific data are shown in the following table:

[0046] Table 1 Tensile strength retention of styrene-butadiene rubber vulcanizate after hot air aging at 100℃

[0047]

[0048] It can be seen from the above table that the styrene-butadiene rubber vulcanizate prepared in group A has the highest tensile strength retention rate after 2 days of aging, which is significantly better than that of groups B and C. The reason why the styrene-butadiene rubber vulcanizate in group A can still maintain a high tensile strength after 2 days of aging is that the rare earth has a larger ionic radius and a higher charge, which enables the caffeic acid ligand to more stably bind to the rare earth ions, thereby improving the stability of the complex and prolonging the aging effect.

[0049] Figure 1 This is the infrared spectrum of the rare earth complex and the ligand caffeic acid prepared in this example. It can be concluded from the figure that the characteristic band generated by the stretching vibration peak of the carbonyl (C=O) in caffeic acid exists at 1649cm -1 , 1606cm -1 , which coincides with the stretching vibration band of the C=C group. The figure also shows that the -1 The characteristic band of the hydroxyl vibration on the aromatic ring is at 3425cm -1 , 3235cm -1 , the stretching vibration peak of hydroxyl was observed; in the rare earth complex graph, the spectral bands related to the bending vibration of hydroxyl disappeared or weakened, which is due to the participation of hydroxyl in the coordination of metal cations. In addition, new characteristic bands related to the vibration of carboxylic acid anions appeared in the spectrum of rare earth complexes. These make the symmetrical stretching vibration of COO- in rare earth complexes exist at 1513cm -1 , 1442cm -1 .

[0050] Figure 2 The XRD diagram of the rare earth complex and the ligand caffeic acid prepared in this example shows that caffeic acid has a regular crystal structure. ° , 25-30 ° There are five obvious sharp diffraction peaks at 10-40 ° There are also some diffraction peaks with smaller intensity, indicating that caffeic acid has a regular crystal structure, while rare earth complexes only have 10-30 ° The appearance of diffraction peaks with smaller intensity is because the rare earth elements affect the structural regularity of the complex, making the complex close to an irregular structure.

[0051] Figure 3The thermogravimetric analysis diagrams of the rare earth complex and the ligand caffeic acid prepared in this embodiment, wherein (a) is the thermogravimetric analysis diagram and (b) is the DTG curve diagram. It can be seen from the diagram that the initial decomposition temperature of caffeic acid is 170.7°C, and the maximum weight loss rate is reached at 222.9°C, and the final mass residual is 13.78%. The rare earth complex has three obvious weight loss steps. The weight loss in the range of 30°C-169.36°C is the removal of adsorbed water and crystal water of the complex, and the weight loss is about 14%. When the temperature continues to rise, the ligand begins to decompose. The weight loss in the range of 170°C-293.09°C and 300°C-457.48°C is mainly the decomposition of the ligand. When the temperature rises to 800°C, the mass of the complex remains basically unchanged, and its mass residual rate is 48.21%. At this time, a relatively stable rare earth complex is obtained. Example 2

[0052] In this embodiment, ErZ2(OH)·2H2O (Z is chlorogenic acid) is prepared, and the preparation process and steps are as follows:

[0053] S1. Slowly add 1 mol hydrochloric acid solution to 1 mol erbium oxide, stir for 30 min, evaporate the solution at 150°C to dryness, obtain a white solid, vacuum dry it at 50°C for 9 h, grind it to 60 mesh, and then add it to 120 mL methanol to obtain a rare earth salt-methanol solution;

[0054] S2. Add 3.25 g of chlorogenic acid to 100 mL of water to form a chlorogenic acid solution, then add 0.3 g of sodium hydroxide to 75 mL of water to form a sodium hydroxide solution, then slowly drip the sodium hydroxide solution into the chlorogenic acid solution, then add triethylamine, adjust the pH of the solution to 7.0, react for 10 min, add 0.5 g of tris(hydroxymethyl)aminomethane, stir evenly with a glass rod to obtain a chlorogenic acid sodium salt solution;

[0055] S3. Slowly drop 50 mL of rare earth salt-methanol solution into 100 mL of chlorogenic acid sodium salt solution, stir and react at 70°C for 1.5 h, let stand for 24 h after the precipitate is formed, filter it, wash it with water 6 times, and dry it at 50°C for 10 h to obtain a rare earth complex antioxidant.

[0056] The rare earth complex antioxidant prepared in this example is in the form of green powder with a yield of 96%.

[0057] The rare earth complex antioxidant prepared in this example, antioxidant MB, and antioxidant 4010NA were added to styrene-butadiene rubber to test the anti-aging performance. The experiment was divided into three groups, among which group A added rare earth complex as antioxidant, group B added MB as antioxidant, and group C added 4010NA as antioxidant. The details are as follows:

[0058] The basic formulas of the three groups of experiments to test the anti-aging performance of styrene-butadiene rubber are:

[0059]

[0060] The mixing and vulcanization process of styrene-butadiene rubber is the same as that of Example 1. Then, the styrene-butadiene rubber vulcanizates prepared in Group A, Group B and Group C are placed in a hot air aging test box at a test temperature of 100° C. for aging experiments, and their tensile strength retention rates are tested. The specific data are shown in the following table:

[0061] Table 2 Tensile strength retention of styrene-butadiene rubber vulcanizate after hot air aging at 100℃

[0062]

[0063] As can be seen from the above table, the styrene-butadiene rubber vulcanizate prepared in group A has the highest tensile strength retention rate after aging for 2 days, which can reach 95%, which is significantly better than groups B and C.

[0064] Figure 4 The infrared spectra of the rare earth complex and ligand chlorogenic acid prepared in this example are shown in FIG. 1 . As can be seen from the figure, in the spectrum of the ligand chlorogenic acid, the characteristic vibration peak of the benzene ring of the ligand is at 1636 cm -1 、1602cm -1 、1513cm -1 and 1439cm -1 , the characteristic vibration peak of unsaturated carboxylic acid is 1685cm -1 , hydroxyl vibration peak 3461cm -1 and 3315cm -1 ; The characteristic vibration peak of the benzene ring of the rare earth complex is at 1591cm -1 、1519cm -1 、1444cm -1 and 1371cm -1 A broad peak appears, and the characteristic vibration peak of the carboxyl group is at 1681cm -1 , hydroxyl vibration peak 3275cm -1 , the carboxyl vibration peak in the rare earth complexes changes from 1685cm -1 Red shifted to 1681 cm -1 Therefore, it can be judged that the metal ions are coordinated by carboxylic acid anions. In the spectrum of rare earth complexes, the stretching vibration band of the CO group obviously shifts to 1264 cm -1 , while in the spectrum of chlorogenic acid, it is located at 1283 cm -1 , which indicates additional metal coordination and weakened CO bond strength via catechol. Example 3

[0065] In this example, LuZ2(OH)·H2O (Z is 1,3-dicaffeoylquinic acid) is prepared, and the preparation process and steps are as follows:

[0066] S1. Slowly add 1 mol hydrochloric acid solution to 1 mol lutetium oxide, stir for 40 min, evaporate the solution to dryness at 200°C to obtain a white solid, dry it in vacuum at 60°C for 5 h, grind it to 60 mesh, and then add it to 150 mL methanol to obtain a rare earth salt-methanol solution;

[0067] S2, adding 1.75 g of 1,3-dicaffeoylquinic acid to 100 mL of water to form a 1,3-dicaffeoylquinic acid solution, then adding 0.15 g of sodium hydroxide to 75 mL of water to form a sodium hydroxide solution, then slowly dripping the sodium hydroxide solution into the 1,3-dicaffeoylquinic acid solution, then adding triethylamine to adjust the pH of the solution to 7.0, reacting for 10 min, adding 0.5 g of tris(hydroxymethyl)aminomethane, stirring evenly with a glass rod to obtain a 1,3-dicaffeoylquinic acid sodium salt solution;

[0068] S3. Slowly drop 50 mL of rare earth salt-methanol solution into 100 mL of 1,3-dicaffeoylquinic acid sodium salt solution, stir and react at 80°C for 1 h, let stand for 24 h after forming a precipitate, filter it, wash it with water 7 times, and dry it at 40°C for 5 h to obtain a rare earth complex antioxidant.

[0069] The rare earth complex antioxidant prepared in this example is in the form of white powder, and the yield is 96%.

[0070] The rare earth complex antioxidant prepared in this example, antioxidant MB, and antioxidant 4010NA were added to styrene-butadiene rubber to test the anti-aging performance. The experiment was divided into three groups, among which group A added rare earth complex as antioxidant, group B added MB as antioxidant, and group C added 4010NA as antioxidant. The details are as follows:

[0071] The basic formulas of the three groups of experiments to test the anti-aging performance of styrene-butadiene rubber are:

[0072]

[0073] The mixing and vulcanization process of styrene-butadiene rubber is the same as that of Example 1. Then, the styrene-butadiene rubber vulcanizates prepared in Group A, Group B and Group C are placed in a hot air aging test box at a test temperature of 100° C. for aging experiments, and their tensile strength retention rates are tested. The specific data are shown in the following table:

[0074] Table 3 Tensile strength retention of styrene-butadiene rubber vulcanizate after hot air aging at 100℃

[0075] Comparative Example

[0076] In order to explore the influence of different substances in the preparation process of the present invention on the performance of the product of the present invention, the following comparative experiment was carried out. Different antioxidants were prepared in the following comparative examples, as follows:

[0077] Comparative Example 1

[0078] This comparative example prepares an antioxidant similar to that of Example 1, except that, during the preparation process, no ligand caffeic acid is added, and only terbium oxide is used as the antioxidant.

[0079] Comparative Example 2

[0080] This comparative example prepares an antioxidant similar to that of Example 1, except that, during the preparation process, terbium oxide is not added, and only caffeic acid is used as the antioxidant.

[0081] Comparative Example 3

[0082] This comparative example prepares an antioxidant similar to that of Example 2, except that, during the preparation process, erbium oxide is not added, and only chlorogenic acid is used as the antioxidant.

[0083] The antioxidants prepared in Comparative Examples 1-3 were added to styrene-butadiene rubber for aging experiments. The mixing and vulcanization process of the styrene-butadiene rubber and the hot air aging experimental process were the same as those in Example 1. The following table shows the tensile strength retention rate of the styrene-butadiene rubber vulcanizate after hot air aging at 100°C with the antioxidants prepared in Comparative Examples 1-3.

[0084]

[0085] It can be seen from the above table that the antioxidants prepared in Comparative Examples 1-3 have a tensile strength retention rate that drops below 70% after two days of aging. The tensile strength retention rates of Comparative Examples 1 and 3 are only 60%. Compared with the rare earth complexes prepared in Examples 1-3, the tensile strength retention rate drops significantly. This is mainly because rare earths have a higher ionic radius and a higher charge, which enables the ligands to be more stably bound around rare earth ions, thereby improving the stability of the complex. However, the stability of caffeic acid and chlorogenic acid alone is not strong, so it drops quickly. Although rare earth oxides have empty orbitals, they absorb limited free radicals and the effect is not outstanding.

[0086] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A rare earth complex antioxidant for rubber, characterized in that: The molecular structural formula of the rare earth complex antioxidant is: ， Wherein, R is a hydroxyl group; RE is one or more of Tb, Dy, Ho, Er, Tm, Yb, and Lu; The method for preparing the rare earth complex antioxidant is carried out in the following steps in sequence: S1. Slowly add the hydrochloric acid solution to the rare earth oxide, stir for 20-40 min, evaporate the solution to dryness at 100-200°C to obtain a white solid, vacuum dry it, grind it to 60 mesh, and then add it to 100-150 mL of methanol to obtain a rare earth salt-methanol solution; S2, adding 1.75-3.25 g of caffeic acid or a caffeic acid derivative to 100 mL of water to form a caffeic acid or caffeic acid derivative solution, then adding 0.15-0.6 g of sodium hydroxide to 75 mL of water to form a sodium hydroxide solution, then slowly dripping the sodium hydroxide solution into the caffeic acid or caffeic acid derivative solution, wherein the caffeic acid derivative is chlorogenic acid or 1,3-dicaffeoylquinic acid, adding triethylamine, adjusting the pH of the solution to 7.0, reacting for 10 min, adding 0.5 g of tris(hydroxymethyl)aminomethane, stirring evenly with a glass rod, and obtaining a sodium salt solution of caffeic acid or a caffeic acid derivative; S3. Slowly drop the rare earth salt-methanol solution into the caffeic acid or caffeic acid derivative sodium salt solution, stir and react at 60-80°C for 1-2 h, let the precipitate stand for 24 h and then filter it, wash it with water 5-7 times, and dry it at 40-60°C for 5-12 h to obtain a rare earth complex antioxidant.

2. The rare earth complex antioxidant for rubber according to claim 1, characterized in that: In step S1, the rare earth oxide is one or more of terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide, and lutetium oxide.

3. The rare earth complex antioxidant for rubber according to claim 1, characterized in that: In step S1, the molar ratio of the hydrochloric acid solution to the rare earth oxide is 1:

1.

4. The rare earth complex antioxidant for rubber according to claim 1, characterized in that: In step S1, the vacuum drying temperature is 40-60°C and the time is 5-12 h.

5. The rare earth complex antioxidant for rubber according to claim 1, characterized in that: In step S3, the volume ratio of the rare earth salt-methanol solution to the caffeic acid or caffeic acid derivative sodium salt solution is 1:2.

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