Note that the above polymers are made in multi-million pound polymerisation plants where monomers such as styrene and butadiene are reacted under pressure to produce rubber (Styrene Butadiene Rubber or SBR in this example). Every polymer has its own monomers and polymerisation chemistry. Each is made with a specific molecular weight (or Mooney Viscosity), balancing the physical properties and the processing required.
Polymers on their own, without the addition of other ingredients, find little use. The notable exception is oil modification. Polymers can be added to oil in order to maintain a constant viscosity with increasing temperatures, with a prime example of this being motor oil. Most polymers are used in the cured or vulcanised state to obtain the optimum physical properties required for the application and service life.
Fillers are added to reinforce the polymer for improved physical properties, better processing and bulking out the polymer for cost-effectiveness. The vast majority of rubber applications are black. This is due to the use of a reinforcing, organic filler called carbon black. They are available in many grades that each impart their own unique set of properties to the polymer and subsequently the resulting compound and final product.
Many non-reinforcing fillers are used in polymers to make non-black rubber goods for industries, such as shoe soles, food, medical and pharmaceutical products. The only reinforcing non-black filler is silica. Fillers in this category are inorganic, such as whiting (calcium carbonate), talc (magnesium silicate), clay and silica (silicon dioxide) to name but a few. Specialist fillers for flame retardancy and other properties are also available.
Polymers need the addition of some fillers to make them process better. Fillers tend to increase the hardness and produce stiff compounds and eventually harder parts. To counterbalance this effect, plasticisers or oils are used.
The most common types include:
These are widely used and provide good processing rubber compounds. They can be used in commodity rubbers within limits. For oil resistant and specialist rubbers, synthetic oils are used. These tend to be of the ester type and are used for their application-specific properties. For instance, providing flexibility at sub-zero temperatures, flame retardancy or antistatic properties.
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