What is a Rubber Compound
The addition of various chemicals to raw rubber to impart desirable properties is termed as rubber compounding. The process includes adding additives, reinforcements or fillers to polymer material in a homogeneous polymer mixture in order to upgrade properties to meet a set of specifications and requirements. The quantity of additives varies on the weight and the choice of additive or polymer used, in accordance with the properties to be achieved by the finished good. The important compounding ingredients include:
- Polymer – It is the most important ingredient in the rubber compounds. Polymers give the fundament for physical and chemical properties.
- Anti-degradants – oxygen and ozone can react with elastomer and alter the network structure by causing cross-linking. Antioxidants and antiozonants help supress these reactive component of air. PPDs (paro-phenylenediamines) and wax are effective in reducing ozone. Antioxidants help prevent the compound from high temperature and employ slow oxidation. They can be categorized as: a) chain breaking oxidants b) preventive oxidants.
- Vulcanization- vulcanization or curing is the process in which the chains are chemically linked together to form a network, transforming the material from a viscous liquid to a tough elastic solid. The most widely used vulcanizing agents are sulphur or peroxide.
- Accelerator- Accelerators boost the rate of crosslinking reaction and decreases the sulphur content in order to achieve optimum vulcanising properties.
- Fillers- fillers are used to reinforce and increase strength properties. It gives colour to the material. Carbon black is one of the most common filler. It improves the durability and strength and is predominant reinforcing filler. It also aggregates the size, shape and structure, surface activity, particle size, and porosity.
- Processing aids- the role of processing aids in rubber compound is to scale down the frictional heating of ingredients during the process. They are additives that lower the viscosity and thus enable a rubber compound to fabricate less energy. They increase melt stability so that the rate of processing can be increased.
There are many other ingredients that can be used to give different properties. Because of all the combinations not all are same. It can take hundreds of variations and hours of testing to perfect the mechanical properties while maintaining good processing.