The main role of Diphenylamine as a Rubber Antioxidant

The main role of Diphenylamine as a rubber antioxidant

1. Anti-oxidation effect

Rubber will inevitably be affected by oxygen during processing and use. Oxygen reacts with unsaturated double bonds in rubber molecules to generate peroxide free radicals. These free radicals will trigger a series of chain reactions, causing the rubber molecular chain to break and cross-link, making the rubber hard, brittle, and lose elasticity. This is the oxidative aging process of rubber.

Diphenylamine can capture these free radicals and react with them to generate relatively stable compounds. For example, the amino group (-NH₂) in the diphenylamine molecule has a lone pair of electrons, which is easy to combine with free radicals, preventing the free radicals from further inducing the oxidation reaction of rubber. This effectively slows down the oxidative aging rate of rubber and extends the service life of rubber products.

2. Anti-thermal oxygen aging effect

In high temperature environments, the oxidation rate of rubber will accelerate. When rubber products are used under high temperature conditions, such as automobile tires that generate heat due to friction with the ground during long-term driving, or rubber seals working near high-temperature components such as engines, the combined action of heat and oxygen will accelerate the aging of rubber.

Diphenylamine can play a stabilizing role in this thermal oxidation environment, and can still effectively inhibit the generation and reaction of free radicals at high temperatures, reducing the degree of rubber degradation due to thermal oxidation. The benzene ring structure in its molecular structure is relatively stable, and can withstand high temperature environments to a certain extent. It can also interact with rubber molecules at high temperatures to prevent rubber from thermal oxidation aging.

3. Anti-flex aging effect

During use, rubber products are often subjected to repeated deformation actions such as bending and stretching. For example, tires are constantly deformed during driving. This repeated flexing action will cause internal stress concentration in the rubber and weaken the bonding force between rubber molecular chains.

Diphenylamine can enhance the bonding force between rubber molecular chains, reduce the formation and expansion of microcracks caused by flexing, and play the role of a "bridge" between rubber molecular chains. When rubber is flexed and deformed, diphenylamine molecules can help disperse stress, thereby improving the rubber's anti-flex fatigue performance, so that rubber products can still maintain good physical properties during frequent deformation.

4. Prevent metal aging and ozone cracking

When rubber products come into contact with metal, electrochemical factors and other factors may accelerate the aging of rubber. Diphenylamine can form a protective film at the contact interface between rubber and metal, preventing metal ions from catalyzing the oxidation of rubber and slowing down the aging of rubber near the metal.

Ozone (O₃) is a strong oxidant that can react with double bonds in rubber molecules, causing cracking on the rubber surface. Diphenylamine can react with ozone, consume ozone or change the surface properties of rubber molecules, making it difficult for ozone to react with rubber double bonds, thereby playing a certain role in preventing ozone cracking of rubber products.