6. Implementation

6.1 Formulation and blending

Like most rubbers, natural rubber is formulated with fillers, mainly carbon black, plasticizers, a mostly sulfur-based vulcanization system and a protection system.

When natural rubber is not a constant viscosity (CV) rubber, a mechanical or chemical plasticization (peptization) operation must be carried out prior to the mixing operation to bring the viscosity down to the desired value for mixing. This operation is generally carried out by tire manufacturers.

The mixing operation then takes place in an internal mixer, where all the ingredients are added, in an order determined by the designer, except for part of the vulcanization system. This part is introduced either into a second internal mixer, or into...