Materials that Improve the Ageing of Vulcanizates

The commercial significance of the ingredients used in rubber compounding to improve resistance to ageing accelerated work on the discovery, development, use and manufacture of new products. The development efforts were competitive in nature, each manufacturer claiming superiority of their products over the others. Some of the age retardants are listed below. 

Phenols have definite protective action. Examples are P-hydroxybiphenyl, hydroquinine and pyrogallol, methylene di-b-napthol. 

These were first investigated and used in rubber as accelerators. Their effect in improving the vulcanizing and ageing properties of rubber was utilized for several years. Primary diamines, primary secondary amines and aminophenols are much more active than simple primary amines. Aminophenol and phenolamine salts are effective antidegradents. 

Heat accelerates oxidation. Because oxidation is a chemical reaction, an increase of 10°C in temperature almost doubles the rate of oxidation. This means that the rate of oxidation is at least 28 times 

Falloff in tensile strength, modulus and elongation as the temperature rises is due to accelerated degradation of the rubber. Irrespective of the type of base rubber used, the physical properties of rubber fall as the temperature is increased to above 120°C due to molecular breakdown. Since rubbers lose their physical properties at higher temperature they become weak and as such susceptible to chemical attack. 

---