Chitosan-based antioxidant as well as preparation method and application thereof

Abstract

The invention belongs to the field of antioxidants, and particularly relates to a chitosan-based antioxidant as well as a preparation method and application thereof. The chitosan-based antioxidant provided by the invention is prepared by carrying out Michael addition reaction on an antioxidant with a structure as shown in a formula (I) and a biomass raw material and then carrying out amidation reaction with chitosan, the biomass raw material is one or more of itaconic acid, fumaric acid, mesaconic acid, muconic acid, aconitic acid, methacrylic acid, linoleic acid and terpenoids. According to the invention, a specific biomass raw material is taken as a bridging agent, and a small molecular antioxidant is grafted into chitosan through Michael addition reaction and amidation reaction, so that the molecular weight of the antioxidant is increased, and the thermal stability and migration resistance of the antioxidant are improved; meanwhile, a chitosan structure exists in the antioxidant, residual metal ions in the rubber emulsion can be chelated, the catalytic oxidation effect of the metal ions is inhibited, and the oxidation resistance of the antioxidant is improved.

Description

Technical Field

[0001] This invention belongs to the field of antioxidants, and particularly relates to a chitosan-based antioxidant, its preparation method, and its application. Background Technology

[0002] During storage, processing, and use, rubber materials are prone to oxidation under the presence of heat and oxygen, leading to molecular chain degradation or cross-linking. This results in surface defects, hardening and brittleness, and deterioration of performance. Because rubber molecules contain numerous carbon-carbon double bonds (-C=C-) and carbon-oxygen double bonds (-C=O-), its resistance to heat and oxygen aging is its most critical weakness, significantly reducing its service life. To delay or inhibit the aging of rubber materials, the most common method is to add antioxidants. These antioxidants terminate the free radical chain growth reaction during aging, capture free radicals, and form relatively stable substances, thus providing antioxidant protection.

[0003] Antioxidants can be classified into primary antioxidants and secondary antioxidants based on their antioxidant mechanism. Primary antioxidants are characterized by the presence of active hydrogen, enabling them to capture free radicals and block free radical chain reactions. Amine and phenolic antioxidants are commonly used in industry. Secondary antioxidants are characterized by their ability to remove accumulated hydroperoxides in rubber, forming stable alcohols or ketones. Phosphite and organosulfur compound antioxidants are commonly used in industry. However, most commonly used amine and phenolic antioxidants are small molecules. Due to their low molecular weight, they are easily lost from the rubber matrix through migration or volatilization, leading to a decrease in protective efficacy. Furthermore, some amine or phenolic antioxidants may be carcinogenic or ecotoxicological, harming the environment. In addition, in rubber processing (such as vulcanization) or high-temperature environments, small-molecule antioxidants may decompose or volatilize, losing their protective effect. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a chitosan-based antioxidant, its preparation method and application. The chitosan-based antioxidant provided by the present invention has excellent thermal stability, migration resistance and antioxidant properties.

[0005] This invention provides a chitosan-based antioxidant, which is prepared by reacting an antioxidant of formula (I) with biomass raw materials via a Michael addition reaction, followed by an amidation reaction with chitosan;

[0006]

[0007] In formula (I), R is a hydroxyl, amino, methoxy or halogen;

[0008] The biomass raw material is one or more of itaconic acid, fumaric acid, mesocarboxylic acid, mucocarboxylic acid, aconitic acid, methacrylic acid, linoleic acid, and terpenoids.

[0009] This invention provides a method for preparing a chitosan-based antioxidant, comprising the following steps:

[0010] a) Under the presence of a catalyst, an antioxidant of formula (I) is subjected to a Michael addition reaction with biomass feedstock to obtain an intermediate compound;

[0011]

[0012] In formula (I), R is a hydroxyl, amino, methoxy or halogen;

[0013] The biomass raw material is one or more of the following: itaconic acid, fumaric acid, mesoconic acid, mucoconic acid, aconitic acid, methacrylic acid, linoleic acid, and terpenoids.

[0014] b) In the presence of a condensing agent and an activator, the intermediate compound is subjected to an amidation reaction with chitosan to obtain a chitosan-based antioxidant.

[0015] Preferably, in step a), the mass ratio of the antioxidant to the biomass raw material is (0.5-5):1.

[0016] Preferably, in step a), the catalyst is one or more selected from triethylamine, triisopropanolamine, N-methyldiethanolamine, N,N-dimethylethanolamine, sodium amino, triphenylphosphine, dimethylphenylphosphine, bidentate triazolyl telluride compound, cyclic ketone-amine complex, tributylamine, tripropylamine, N,N-diisopropylethylamine, 1,8-diazabicycloundec-7-ene, triethylenediamine, N-ethylmorpholine, bis(2-dimethylaminoethyl) ether, potassium carbonate, and cesium carbonate; the amount of the catalyst is 0.5 to 5 wt% of the total mass of the antioxidant and biomass raw material.

[0017] Preferably, in step a), the Michael addition reaction is carried out at a temperature of 20–120°C for a time of 6–48 h.

[0018] Preferably, in step b), the mass ratio of the intermediate compound to chitosan is (1-5):1.

[0019] Preferably, in step b), the condensing agent is one or more selected from dicyclohexylcarbodiimide, diisopropylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethylurea hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethylurea hexafluorophosphate, and benzotriazol-1-yl-oxytripyrrolidinephosphide hexafluorophosphate; the amount of the condensing agent is 40-80 wt% of the total mass of the intermediate compound and chitosan.

[0020] Preferably, in step b), the activator is one or more of 4-dimethylaminopyridine, 1-hydroxybenzotriazole, propylphosphonic anhydride, ethyl chloroformate, isobutyl ester, ethoxycarbonylethoxydihydroquinoline, trifluoromethanesulfonic anhydride, and trifluoroacetic anhydride; the amount of the activator is 1 to 6 wt% of the total mass of the intermediate compound and chitosan.

[0021] Preferably, in step b), the amidation reaction is carried out at a temperature of 20–80°C for 24–72 h.

[0022] This invention provides a rubber material containing the chitosan-based antioxidant described in the above-described technical solution or the polysaccharide-based antioxidant prepared by the preparation method described in the above-described technical solution.

[0023] Compared with existing technologies, this invention provides a chitosan-based antioxidant, its preparation method, and its application. The chitosan-based antioxidant provided by this invention is prepared by reacting an antioxidant of formula (I) with biomass raw materials via a Michael addition reaction, followed by an amidation reaction with chitosan; in formula (I), R is a hydroxyl, amino, methoxy, or halogen compound; the biomass raw material is one or more of itaconic acid, fumaric acid, mesoconic acid, mucoaconic acid, aconitic acid, methacrylic acid, linoleic acid, and terpenoids. This invention uses specific biomass raw materials as bridging agents, grafting small-molecule antioxidants onto chitosan through Michael addition and amidation reactions, increasing the molecular weight of the antioxidant, thereby improving its thermal stability and migration resistance; simultaneously, the presence of a chitosan structure in the antioxidant allows it to chelate residual metal ions in rubber latex, inhibiting the catalytic oxidation of metal ions and improving the antioxidant's antioxidant properties. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 This is a synthesis route diagram of the chitosan-based antioxidant provided in the embodiments of the present invention. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides a chitosan-based antioxidant, which is prepared by reacting an antioxidant of formula (I) with biomass raw materials via a Michael addition reaction, followed by an amidation reaction with chitosan;

[0028]

[0029] In formula (I), R is a hydroxyl, amino, methoxy or halogen;

[0030] The biomass raw material is one or more of itaconic acid, fumaric acid, mesocarboxylic acid, mucocarboxylic acid, aconitic acid, methacrylic acid, linoleic acid, and terpenoids.

[0031] This invention also provides a method for preparing a chitosan-based antioxidant, comprising the following steps:

[0032] a) Under the presence of a catalyst, an antioxidant of formula (I) is subjected to a Michael addition reaction with biomass feedstock to obtain an intermediate compound;

[0033]

[0034] In formula (I), R is a hydroxyl, amino, methoxy or halogen;

[0035] The biomass raw material is one or more of the following: itaconic acid, fumaric acid, mesoconic acid, mucoconic acid, aconitic acid, methacrylic acid, linoleic acid, and terpenoids.

[0036] b) In the presence of a condensing agent and an activator, the intermediate compound is subjected to an amidation reaction with chitosan to obtain a chitosan-based antioxidant.

[0037] In the preparation method provided by the present invention, in step a), the mass ratio of the antioxidant to the biomass raw material is preferably (0.5-5):1, specifically 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.8:1, 4:1, 4.2:1, 4.5:1, 4.8:1 or 5:1.

[0038] In the preparation method provided by this invention, in step a), the catalyst is preferably one or more of the following: triethylamine, triisopropanolamine, N-methyldiethanolamine, N,N-dimethylethanolamine, sodium amino, triphenylphosphine, dimethylphenylphosphine, bidentate triazolyl telluride compound, cyclic ketone-amine complex, tributylamine, tripropylamine, N,N-diisopropylethylamine, 1,8-diazabicycloundec-7-ene, triethylenediamine, N-ethylmorpholine, bis(2-dimethylaminoethyl) ether, potassium carbonate, and cesium carbonate; the amount of the catalyst is preferably 0.5-5 wt% of the total mass of the antioxidant and biomass raw material, specifically 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%.

[0039] In the preparation method provided by the present invention, in step a), the Michael addition reaction is carried out under a protective gas atmosphere, the protective gas including but not limited to nitrogen.

[0040] In the preparation method provided by the present invention, in step a), the Michael addition reaction is carried out in an organic solvent, preferably one or more of dimethyl sulfoxide, dimethylformamide, acetonitrile, acetone, tetrahydrofuran, hexamethylphosphoric triamine and dichloromethane.

[0041] In the preparation method provided by the present invention, in step a), the Michael addition reaction is preferably carried out under stirring conditions, and the stirring speed is preferably 200-800 r / min, specifically 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, 550 r / min, 600 r / min, 650 r / min, 700 r / min, 750 r / min or 800 r / min.

[0042] In the preparation method provided by the present invention, in step a), the temperature of the Michael addition reaction is preferably 20 to 120°C, specifically 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C.

[0043] In the preparation method provided by the present invention, in step a), the Michael addition reaction time is preferably 6 to 48 hours, specifically 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, or 48 hours.

[0044] In the preparation method provided by the present invention, in step a), after the Michael addition reaction is completed, the intermediate compound (solid) is filtered out and then dried to constant weight.

[0045] In the preparation method provided by the present invention, in step b), the mass ratio of the intermediate compound to chitosan is preferably (1-5):1, specifically 1:1, 1.2:1, 1.5:1, 1.7:1, 2:1, 2.3:1, 2.5:1, 2.7:1, 3:1, 3.2:1, 3.5:1, 3.7:1, 4:1, 4.2:1, 4.5:1, 4.7:1 or 5:1.

[0046] In the preparation method provided by this invention, in step b), the condensing agent is dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethylurea (HATU) of hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethylurea (HBTU) of hexafluorophosphate, and benzotriazolium hexafluorophosphate. One or more of 1-yl-oxytripyrrolidinephosphide (PyBOP); the amount of the condensing agent is preferably 40-80 wt% of the total mass of the intermediate compound and chitosan, specifically 40 wt%, 42 wt%, 45 wt%, 47 wt%, 50 wt%, 52 wt%, 55 wt%, 57 wt%, 60 wt%, 62 wt%, 65 wt%, 67 wt%, 70 wt%, 72 wt%, 75 wt%, 77 wt%, or 80 wt%.

[0047] In the preparation method provided by this invention, in step b), the activator is one or more of 4-dimethylaminopyridine (DMAP), 1-hydroxybenzotriazole (HOBt), propylphosphonic anhydride (T3P), ethyl chloroformate, isobutyl ester, ethoxycarbonylethoxydihydroquinoline (EEDQ), trifluoromethanesulfonic anhydride (Tf2O), and trifluoroacetic anhydride ((CF3CO)2O); the amount of the activator is preferably 1-6 wt% of the total mass of the intermediate compound and chitosan, specifically 1 wt%, 1.2 wt%, 1.5 wt%, 1.7 wt%, 2 wt%, 2.3 wt%, 2.5 wt%, 2.7 wt%, 3 wt%, 3.2 wt%, 3.5 wt%, 3.7 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.7 wt%, 5 wt%, 5.2 wt%, 5.5 wt%, 5.7 wt%, or 6 wt%.

[0048] In the preparation method provided by the present invention, in step b), the amidation reaction is carried out under a protective gas atmosphere, the protective gas including but not limited to nitrogen.

[0049] In the preparation method provided by the present invention, in step b), the amidation reaction is carried out in an organic solvent, which includes, but is not limited to, dimethyl sulfoxide.

[0050] In the preparation method provided by the present invention, in step b), the Michael addition reaction is preferably carried out under stirring conditions, and the stirring speed is preferably 200-800 r / min, specifically 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, 550 r / min, 600 r / min, 650 r / min, 700 r / min, 750 r / min or 800 r / min.

[0051] In the preparation method provided by the present invention, in step b), the temperature of the amidation reaction is preferably 20 to 80°C, specifically 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C.

[0052] In the preparation method provided by the present invention, in step b), the amidation reaction time is preferably 24 to 72 h, specifically 24 h, 27 h, 30 h, 33 h, 36 h, 39 h, 42 h, 45 h, 48 h, 51 h, 54 h, 57 h, 60 h, 63 h, 66 h, 69 h or 72 h.

[0053] In the preparation method provided by the present invention, in step b), after the amidation reaction is completed, the reaction product is post-processed. The post-processing process preferably includes: filtering the reaction solution to collect the filtrate, adding excess diethyl ether to the filtrate, collecting the lower layer solution, adding the collected bottom layer solution to excess deionized water to generate a precipitate, and drying the precipitate to constant weight to obtain a pure chitosan-based antioxidant.

[0054] The present invention also provides a rubber material containing the chitosan-based antioxidant described in the above technical solution or the polysaccharide-based antioxidant prepared by the preparation method described in the above technical solution.

[0055] The technical solution provided by this invention uses specific biomass raw materials as bridging agents to graft small molecule antioxidants into chitosan through Michael addition and amidation reactions, thereby increasing the molecular weight of the antioxidant and improving its thermal stability and migration resistance. At the same time, the presence of chitosan structure in the antioxidant can chelate residual metal ions in rubber latex, inhibit the catalytic oxidation of metal ions, and improve the antioxidant's antioxidant performance.

[0056] For clarity, the following examples will be used to provide a detailed description.

[0057] Examples 1-10

[0058] according to Figure 1 The synthetic route shown is used to prepare chitosan-based antioxidants. The specific steps are as follows:

[0059] 1) Michael addition reaction: A quantitative amount of the compound with structure I and biomass feedstock (itaconic acid) were added to a three-necked flask containing solvent. A quantitative amount of catalyst solution was added dropwise. The flask was sealed, and nitrogen gas was introduced to replace the air. The mixture was then heated and stirred at a constant speed (500 r / min) to generate an intermediate. After the reaction was completed, the reaction solution was poured into a beaker and excess deionized water was slowly added. The mixture was stirred until a precipitate was formed. The precipitate was filtered out and dried under vacuum at 40°C until the solid reached constant weight to obtain the intermediate compound with structure II.

[0060] 2) Amide reaction: The product obtained above was quantitatively added to a three-necked flask, and a quantitative amount of chitosan (n = 0.95, Mn = 150000 Da) was added. Then, dimethyl sulfoxide solvent was added to dissolve it. A quantitative amount of condensing agent and activator solution was added dropwise. The mixture was heated under nitrogen protection and stirred at a constant speed (500 r / min) to carry out the reaction.

[0061] 3) Purification: After the amidation reaction is completed, the reaction solution is filtered to collect the filtrate. Excess diethyl ether is added to the filtrate through a separatory funnel, and the lower layer solution is collected. The collected bottom layer solution is slowly added to excess deionized water under mechanical stirring to produce a precipitate. The precipitate is dried to constant weight under vacuum at 40°C to obtain the chitosan-based polymeric antioxidant with the structure shown in Formula III.

[0062] In Examples 1-10 provided by this invention, compounds of Formula I with R representing a hydroxyl group are specifically selected. Their chemical name is 2-mercaptobenzimidazole-hydroxyl, also known as antioxidant MB-A. Other raw material selections, amounts of raw materials, and reaction conditions in Examples 1-10 are detailed in Table 1.

[0063] Table 1. Raw material information and reaction conditions for Examples 1-10

[0064]

[0065]

[0066] The product yields of Examples 1-10 are detailed in Table 2.

[0067] Table 2 Product Yield Table for Examples 1-10

[0068]

[0069]

[0070] Example 11

[0071] The antioxidant MB-A, a commonly used antioxidant on the market, was compared with the antioxidant prepared in Example 1 of this invention in terms of its effectiveness. The specific experimental procedure is as follows:

[0072] (1) Sample preparation:

[0073] Vulcanized rubber sample 1: First, 160g of bio-based itaconic acid ester rubber was placed in a mixer, and 72g of silica VN3, 2.88g of silane coupling agent Si-69, 8g of zinc oxide, 4g of stearic acid, 1.6g of paraffin wax, 6.4g of polyethylene glycol PEG4000, 1.6g of rubber accelerator ACT, and 3.2g of antioxidant MB-A were added and mixed. The specific mixing conditions and process are as follows: The mixer was set at 85℃ and 70rpm. Rubber was added and mixed for 1 minute. Then, the small amount of raw materials and 1 / 3 of silica were added. The speed was adjusted according to the temperature rise, and the mixture was mixed for 1 minute. Then, 1 / 3 of silica was added and mixed for 1 minute. Then, 1 / 3 of silica was added and mixed for 1 minute. After mixing for 7 minutes, the rubber was discharged at a discharge temperature of 130℃. In a Banbury mixer at 70℃ and 65 rpm, a first-stage compound, 1.6 g of rubber accelerator DM, 0.8 g of rubber accelerator D, and 2.4 g of sulfur were added and mixed for 3 minutes, then discharged. After cooling, the compound was passed through a two-roll mill at 0.5 mm thickness 6 times, and then sheeted at 2 mm thickness. After resting for 8 hours, the compound was vulcanized on a hydraulic flat vulcanizing machine at 160℃ for the optimal vulcanization time, measured using a rotorless vulcanizing apparatus.

[0074] Vulcanized rubber sample 2: First, 160g of bio-based itaconic acid ester rubber was placed in a mixer, and then 72g of silica VN3, 2.88g of silane coupling agent Si-69, 8g of zinc oxide, 4g of stearic acid, 1.6g of paraffin wax, 6.4g of polyethylene glycol PEG4000, 1.6g of rubber accelerator ACT, and 3.2g of antioxidant synthesized in Example 1 were added and mixed. The specific mixing conditions and process are as follows: The mixer was set at 85℃ and 70rpm. Rubber was added and mixed for 1min; small components and 1 / 3 silica were added, and the speed was adjusted according to the temperature rise, and mixed for 1min; 1 / 3 silica was added and mixed for 1min; 1 / 3 silica was added and mixed for 1min; after mixing for 7min, the rubber was discharged at a discharge temperature of 130℃. In a Banbury mixer at 70℃ and 65 rpm, a first-stage compound, 1.6 g of rubber accelerator DM, 0.8 g of rubber accelerator D, and 2.4 g of sulfur were added and mixed for 3 minutes, then discharged. After cooling, the compound was passed through a two-roll mill at 0.5 mm thickness 6 times, and then sheeted at 2 mm thickness. After resting for 8 hours, the compound was vulcanized on a hydraulic flat vulcanizing machine at 160℃ for the optimal vulcanization time, measured using a rotorless vulcanizing apparatus.

[0075] Blank vulcanized rubber sample: Refer to the preparation process of vulcanized rubber samples 1 and 2, the only difference being that no antioxidant is added.

[0076] Raw rubber sample 1: Based on the determined solid content of the bio-based itaconic acid ester latex, the latex and antioxidant MB-A were mixed at a ratio of 0.5% of the latex solid content. The mixture was stirred for 15 minutes at 160 rpm using a cantilever electric stirrer to ensure uniform dispersion. A 0.3% calcium chloride solution was prepared and stirred for 15 minutes at 160 rpm using a cantilever electric stirrer. The bio-based itaconic acid ester latex containing antioxidant MB-A was then added dropwise to the 0.3% calcium chloride solution at a rate of approximately 3 drops / s. The flocculated solids were cut into pieces approximately 1 cm in size and washed three times with deionized water to remove impurities from the surface of the bio-based itaconic acid ester raw rubber. The mixture was then dried in a constant temperature drying oven at 100°C for 3 hours.

[0077] Raw rubber sample 2: Based on the determined solid content of the bio-based itaconic acid ester latex, and according to the antioxidant synthesized in Example 1 accounting for 0.5% of the latex solid content, the latex and antioxidant were mixed and stirred at 160 r / min for 15 min using a cantilever electric stirrer to ensure uniform dispersion. A 0.3% calcium chloride solution was prepared and stirred at 160 r / min for 15 min using a cantilever electric stirrer. The bio-based itaconic acid ester latex containing the antioxidant synthesized in Example 1 was uniformly dropped into the 0.3% calcium chloride solution at a rate of approximately 3 drops / s. The flocculated solids were cut into pieces of approximately 1 cm and washed three times with deionized water to remove impurity ions from the surface of the bio-based itaconic acid ester raw rubber. It was then dried in a constant temperature drying oven at 100°C for 3 h.

[0078] Raw rubber blank sample: Refer to the preparation process of raw rubber samples 1 and 2, the only difference being that no antioxidant is added.

[0079] (2) Mechanical property testing:

[0080] Mechanical properties were tested on the blank vulcanized rubber sample, vulcanized rubber sample 1, and vulcanized rubber sample 2. The results are shown in Table 3.

[0081] Table 3 Mechanical property test results

[0082]

[0083] As shown in Table 3, the tensile strength of the bio-based itaconic acid ester rubber vulcanizate is 17.20 MPa without the addition of antioxidants. When the antioxidant prepared in Example 1 of this invention is added, the tensile strength of the bio-based itaconic acid ester rubber vulcanizate is the highest, at 19.5 MPa. When antioxidant MB-A is added, the tensile strength of the bio-based itaconic acid ester rubber vulcanizate is 18.6 MPa. This indicates that the antioxidant prepared in Example 1 of this invention has superior tensile properties to the bio-based itaconic acid ester rubber vulcanizate compared to antioxidant MB-A. Furthermore, with the addition of antioxidants, the elongation at break, tear strength, and hardness of the rubber all show different changes. As shown in Table 3, the antioxidant prepared in Example 1 of this invention exhibits superior mechanical properties to the bio-based itaconic acid ester rubber vulcanizate compared to antioxidant MB-A. Therefore, the antioxidant prepared in Example 1 of this invention can more effectively delay rubber aging and extend the service life of the rubber.

[0084] (3) Resistance to thermo-oxidative aging test:

[0085] Accelerated thermo-oxidative aging tests were conducted on the blank sample, sample 1, and sample 2 of vulcanized rubber. The accelerated thermo-oxidative aging test was carried out according to GB / T 3512-2014, with an aging temperature of 100±1℃ and an aging time of 48 hours. After 48 hours of aging, the retention rate of tensile strength and elongation at break of the blank sample, sample 1, and sample 2 were tested respectively. The tensile properties were determined according to GB / T 528-2009, with a tensile rate of 500 mm / min.

[0086] Meanwhile, differential scanning calorimetry (DSC) was used to test the oxidation induction period of raw rubber blank sample, raw rubber sample 1 and raw rubber sample 2. The test conditions were: air atmosphere, air flow rate: 50 mL / min, sample size 5-10 mg, heating rate: 10℃ / min, temperature: 160℃.

[0087] The results of the thermo-oxidative aging resistance test are shown in Table 4.

[0088] Table 4 Results of thermo-oxidative aging resistance test

[0089] sample Oxidation induction period / min Tensile strength retention rate / % Elongation at break retention rate / % Aging coefficient blank sample 7.6 86.47 62.39 58.24 Sample 1 28.7 91.62 70.24 67.73 Sample 2 39.2 95.49 76.32 75.65

[0090] As shown in Table 4, compared with the bio-based itaconic acid rubber vulcanizate without added antioxidant, the vulcanizate with the antioxidant prepared in Example 1 of this invention or antioxidant MB-A has a much higher retention rate of tensile strength and elongation at break, indicating that both the antioxidant prepared in Example 1 of this invention and antioxidant MB-A can effectively inhibit the thermo-oxidative aging of bio-based itaconic acid rubber. After aging for 48 hours, the bio-based itaconic acid rubber vulcanizate with the antioxidant prepared in Example 1 of this invention has a higher retention rate of tensile strength and elongation at break than the vulcanizate with antioxidant MB-A, indicating that the antioxidant prepared in Example 1 of this invention has better thermo-oxidative aging resistance to rubber than the antioxidant MB-A without chitosan grafting. The reason may be as follows: the antioxidant prepared in Example 1 of this invention has hindered phenol and amide / thioether groups in its molecular structure, among which the amide and thioether groups have the function of co-antioxidants and can produce a synergistic antioxidant effect with the hindered phenol. Furthermore, the antioxidant prepared in Example 1 of this invention has a chitosan structure, and chitosan can react with metal ions (such as Fe) in rubber. 3+ Cu 2+ (etc.) Combined, it inhibits the catalytic oxidation reaction of metal ions. In addition, the decomposition temperature of chitosan is usually above 200℃, which can prevent its decomposition during the sulfidation process and prevent the antioxidant from volatilizing due to heat.

[0091] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A chitosan-based antioxidant, characterized by, The antioxidant of formula (I) is subjected to Michael addition reaction with a biomass raw material, and then subjected to amidation reaction with chitosan to prepare; In formula (I), R is hydroxyl, amino, methoxy or halogen; The biomass raw material is one or more of itaconic acid, fumaric acid, mesaconic acid, muconic acid, aconitic acid, methacrylic acid, linoleic acid and terpenoids.

2. A method for preparing a chitosan-based antioxidant, characterized by, The method comprises the following steps: a) Michael addition reaction of an antioxidant of formula (I) with a biomass raw material in the presence of a catalyst to obtain an intermediate compound; In formula (I), R is hydroxyl, amino, methoxy or halogen; The biomass raw material is one or more of itaconic acid, fumaric acid, mesaconic acid, muconic acid, aconitic acid, methacrylic acid, linoleic acid and terpenoids. b) amidation reaction of the intermediate compound with chitosan in the presence of a condensing agent and an activating agent to obtain a chitosan-based antioxidant.

3. The method of claim 2, wherein, In step a), the mass ratio of the antioxidant to the biomass raw material is (0.5-5):

1.

4. The preparation method according to claim 2, characterized in that, In step a), the catalyst is one or more of triethylamine, triisopropanolamine, N-methyldiethanolamine, N,N-dimethylethanolamine, sodium amide, triphenylphosphine, dimethylphenylphosphine, bidentate triazolyl tellurium compound, cyclic ketone-amine complex, tributylamine, tripropylamine, N,N-diisopropylethylamine, 1,8-diazabicycloundec-7-ene, triethylenediamine, N-ethylmorpholine, bis(2-dimethylaminoethyl) ether, potassium carbonate and cesium carbonate; the amount of the catalyst is 0.5-5wt% of the total mass of the antioxidant and the biomass raw material.

5. The preparation method according to claim 2, characterized in that, In step a), the temperature of the Michael addition reaction is 20-120℃, and the time is 6-48h.

6. The preparation method according to claim 2, characterized in that, In step b), the mass ratio of the intermediate compound to chitosan is (1-5):

1.

7. The preparation method according to claim 2, characterized in that, In step b), the condensing agent is one or more of dicyclohexyl carbodiimide, diisopropyl carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate and benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate; the amount of the condensing agent is 40-80wt% of the total mass of the intermediate compound and chitosan.

8. The preparation method according to claim 2, characterized in that, In step b), the activating agent is one or more of 4-dimethylaminopyridine, 1-hydroxybenzotriazole, propylphosphonic anhydride, ethyl chloroformate, isobutyl chloroformate, ethoxycarbonyl ethoxydihydroquinoline, triflic anhydride and trifluoroacetic anhydride; the amount of the activating agent is 1-6wt% of the total mass of the intermediate compound and chitosan.

9. The preparation method according to claim 2, characterized in that, In step b), the temperature of the amidation reaction is 20-80℃, and the time is 24-72h.

10. A rubber material characterized by, The rubber material contains the chitosan-based antioxidant of claim 1 or the chitosan-based antioxidant prepared by the method of any one of claims 2-9.

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