The rubber compound is prone to aging during use, and it is necessary to add a protective system to delay aging and avoid rapid performance degradation. Physical antioxidants are generally light shielding agents or waxes, and chemical antioxidants include compounds such as amines, phenols, and esters. Synthetic rubber needs to add a small amount of antioxidant in the synthesis process, and add a larger amount of antioxidant in the post-processing process.

1. Antioxidant for synthetic rubber

The antioxidant added to synthetic rubber during the synthesis process should be selected according to the synthesis process and product color. For solution-polymerized rubber, you need to choose an antioxidant that is easily soluble in the solvent used in rubber synthesis. For emulsion-polymerized rubber, you need to choose an antioxidant that can form a stable emulsion with the emulsifier used in rubber synthesis. In addition, according to the color of the product, choose pollution type or non-pollution type. type of antioxidant. Polybutadiene rubber (BR), styrene thermoplastic elastomer, isoprene rubber (IR) and other solution-polymerized rubbers used antioxidant BHT (264) in the past, and sometimes combined with phosphite antioxidant TNP (TNPP). Antioxidant TNP is easily hydrolyzed, and its use is prohibited because the nonylphenol produced affects the reproductive health of organisms. Antioxidant BHT has a relatively small molecular weight and is easy to volatilize. Foreign studies believe that its many volatiles are harmful to the environment. Therefore, other phenolic antioxidants are currently used instead. The more common antioxidants are 1076 and 1520. Or use supplementary antioxidants in combination to produce synergistic effects. The phenolic antioxidant styrenated phenol is mostly used in the light-colored latex rubber, and the pollution-type amine antioxidant is used in the dark-colored rubber. Synthetic rubber antioxidants are developing in the direction of environmental protection, large molecular weight, compounding and multi-functionality. The oxidation induction period or oxidation induction temperature of raw rubber can be detected by DSC method, and the performance of antioxidants can also be investigated by thermal oxygen aging performance. Light-colored rubber products also need to investigate thermal oxygen aging resistance and yellowing resistance.

2. Anti-aging agent

a. Physical antioxidant

Synthetic rubber compounds mostly use paraffin as a physical antioxidant that is resistant to ozone and weathering. When the rubber is vulcanized, the paraffin dissolved in it will gradually migrate to the rubber surface after cooling, forming a dense and flexible wax film, thereby isolating ozone in the air and playing a protective role. Compared with ordinary protective wax, modified protective wax has a variety of functional groups (such as carboxyl group, hydroxyl group, etc.) in the molecular structure. The protective ability of modified protective wax is 1.5~3 times higher than that of ordinary protective wax. The use of modified protective wax can reduce the amount of antiozonant.

b. Chemical antioxidants

The antioxidants used in the processing of synthetic rubber are mainly amine and quinoline antioxidants. Common varieties are antioxidants 4020, 4010NA and RD. The dosage of these three anti-aging agents accounts for more than 80% of the current dosage of anti-aging agents in my country.

Our country's anti-aging agent RD has become one of the main anti-aging agents for radial tire compounds. In particular, the dimer has excellent anti-aging properties, so the content of the dimer should be increased as much as possible. Antioxidant RD has excellent anti-oxidative aging performance and has a strong inhibitory effect on metal ions such as copper, but has poor ozone resistance and flex resistance. ) and so on. Anti-aging agent AW can prevent the cracking of rubber products caused by ozone. It is especially suitable for rubber products under dynamic conditions. It can be used in combination with anti-aging agents H, D and 4010 to enhance its performance.

P-phenylenediamine antioxidants are classified into dialkyl p-phenylenediamines, diaryl p-phenylenediamines and alkylaryl p-phenylenediamines according to the groups attached to p-phenylenediamine. The main varieties of dialkyl-p-phenylenediamine antioxidants are antioxidants 4030 and 288. Anti-aging agent 4030 is easy to disperse, has a large solubility in rubber, no blooming problem when the dosage is large, and has the effect of accelerating the vulcanization and shortening the scorch time of the rubber compound; it has excellent anti-aging effect on static ozone, which is obviously better than ozone resistance. Anti-aging agents 4010NA and 4020 with excellent aging performance are especially suitable for outdoor rubber products such as wires and cables, hoses and tapes under static conditions for a long time. The main varieties of alkylaryl-p-phenylenediamine antioxidants are antioxidants 4010, 4010NA, 4020 and H. Anti-aging agent 4020 is a kind of anti-aging agent with a large amount of tire compound at present. It has excellent protective effect on ozone aging and flexural cracking aging, and also has good protective effect on thermo-oxidative aging and weather aging. Passivation, suitable for NR, BR, SBR, NBR and CR, in combination with paraffin waxes (especially mixed or microcrystalline waxes with branched chains) to enhance static protection. Compared with antioxidant 4010NA, antioxidant 4020 has better resistance to water extraction and can achieve long-term protection.

The main varieties of diaryl-p-phenylenediamine antioxidants are antioxidant 3100 and H. Anti-aging agent 3100 is characterized by no spraying, no irritation to the skin, and good protective effect on ozone, oxygen and flex fatigue aging of tires and other rubber products, especially suitable for heavy duty tires and off-road tires with harsh conditions of use. It is also an effective antiozonant for CR. One or two compatibilizing genes are introduced into the benzene rings on both sides of the molecular structure of the anti-aging agent 3100, so its solubility in rubber increases, which can increase the dosage in the rubber compound, and can completely eliminate the application of anti-aging agent 4010NA and The defect of 4020 rubber compound turning red is very good for the protection of harmful metals such as copper and manganese; the disadvantage is that the rubber compound becomes dark brown when exposed to light, and the pollution is serious, so it is only suitable for dark color products.

In recent years, new varieties of rubber antioxidants have been less developed and applied, and with the increasingly stringent environmental protection requirements, antioxidants have gradually developed in the direction of high performance and environmental protection, and the varieties of rubber antioxidants have gradually tended to be concentrated. The varieties are still antioxidant RD and 4020.