What causes oxidative aging of rubber?

Various external factors, including oxidative agents (such as oxygen), heavy metals, UV rays, ozone, mechanical stress, heat, and aggressive chemicals, etc., could accelerate rubber aging. This review mainly focused on thermo-oxidative aging because it is the most common aging type for rubbers.

Which antioxidants are used in rubber vulcanization?

The amine and phenolic antioxidants are the most widely used rubber antioxidants (Fig. 1 b and c). Generally, the phenolic antioxidants have poor antioxidative efficiency (compared to amine antioxidants) and they can delay vulcanization, but they cause little discoloration problems.

How does rubber antioxidant work?

To prolong the service life of rubber composites by retarding their aging processes, rubber antioxidant initially relies on the use of a coating, such as paraffin, and coal tar, to physically isolate oxygen, but this protective layer would quickly lose the utility due to wear.

Can rubber antioxidants contain rare-earth ions?

The recently reported rubber antioxidants containing rare-earth ions are summarized in Fig. 4, for instance, Sun et al. prepared a novel hindered phenol rare-earth complex (DTSm) (Fig. 4 f) by a simple and green method using 3,5-di-tert-butyl-4-hydroxybenzoic acid (DT) and samarium chloride hexahydrate (SmCl 3 ·6H 2 O) via coordination reaction.

Are rubber antioxidants harmful?

As shown in Table 1, many commonly used rubber antioxidants are damaging to human health and the environment. For example, the antioxidant MB (2-mercaptobenzimidazole), which is widely used in the manufacture of light-colored rubber products, is harmful to aquatic organisms and has a continuous effect.

Are rubber antioxidants a rational design?

The development of medical antioxidants also inspires the rational design of rubber antioxidants. Recently, Sun, et al. synthesized a novel antioxidant (APPT) containing aromatic amine, thiourea and allyl groups by the reaction between N-phenyl-p-phenylenediamine and allyl isothiocyanate (Fig. 3 b) .