rubber compounding

In developing a rubber compound, it is  essential to mix the raw dry rubber with various compounding ingredients.  The process of sequentially adding the ingredients into the raw rubber is termed ‘compounding’ and the resulting final homogeneous mix is referred to as the ‘rubber compound’. 

The most common  compounding ingredients  added into the rubber are vulcanizing agents, vulcanization accelerators, activators for the accelerators, fillers, processing aids, softeners, antidegradants and other miscellaneous ingredients for specific purposes.  Each compounding ingredient has specific role in the compound and some give significant effects on the final properties of the resulting products.Therefore a rubber compound has to be formulated with an expectation to incorporate the desired properties required in the finished rubber product as well as in the production process.  In view of this, the important factors that need to be considered when designing a rubber compound are price, processability and functional properties. 

      There are 5 main ingredients in a rubber compound formula and each are measured in parts per hundred (phr):

1.       Rubber/Polymer

2.       Filler

3.       Protectant

4.       Processing Aid

5.       Curing System

Below is an example of a compounding recipe.

A typical rubber formation based on parts per hundred is:

Polymer          100 phr

Filler                30 – 60 phr
Antioxidant     1 – 3 phr
Antiozonants    1 – 3 phr
Oil                       5 – 30 phr
Cure                  5 – 10 phr