Rubber is a resilient elastic polymer that is obtained from natural and synthetic sources. Rubber is widely used in tyres, seals, footwear, hoses etc.
Rubber is a resilient elastic polymer that is obtained from natural and synthetic sources. Rubber is widely used in tyres, seals, footwear, hoses etc.
What are the types of rubber?
Depending on the source from which it is obtained, rubber can either natural or synthetic. Natural rubber originates naturally from the sap of a tree, while Synthetic rubber is made from components of crude oil, bonded together through chemical processes to form a synthetic polymer.
How is Natural Rubber Made?
Natural Rubber or NR comes from extracting the liquid sap called latex, from certain trees – especially Hevea Brasiliensis trees.
Step 1: Latex is extracted by first making a cut in the bark of the tree, and collecting the runny sap in cups. This process is known as tapping.
Step 2: In cases where uncoagulated latex is required, ammonia is added to prevent the raw latex from solidifying.
Step 3: In other cases, the latex is coagulated with formic acid or acetic acid, whereupon the coagulum rises to the surface as a white, doughy material.
Step 4: It is then milled into thin crepe sheets, to remove the moisture.
Step 5: The sheets of rubber are hung over racks in a smokehouse or left to air dry.
Step 6: Several days later, it is then folded into bales and is ready for processing.
Where does Synthetic Rubber come from?
Synthetic rubber is made from the catalyzation of monomers from cracked hydrocarbons. They are polymerized to form long chains. The different forms of synthetic rubbers are produced by the copolymerization of the carbon chain with styrene, butadiene, isoprene, chloroprene etc.
The various rubber compounds have their desirable characteristics through the addition of fillers, protectants, plasticizers, curatives, and other chemicals in various ratios to produce specific physical and chemical properties.
Rubber Processing:
Natural and Synthetic rubber needs to be processed further with additives to achieve desirable physical and chemical characteristics.
Chemical substances (additives) are added during the blending process to ensure that the eventual rubber produced has the specific properties required.
Vulcanisation Process:
The process of adding sulphur to the compound to create cross links between the long polymer chain.
Adding Pigments & Plasticizers:
Pigments: Solid materials that are added into gum rubber, except for those used as vulcanizing agents, are called pigments. There are 2 types of pigments:
- Reinforcing pigment – These improve the properties of the compound
- Filler – These act as diluents that can be added into compounds to improve processing capabilities and reduce cost.
Soot and silica are two examples of fillers; these enhance the firmness of the rubber.
Colouring agents: these give the rubber a certain colour.
Preservatives: these protect the eventual rubber product from ageing and ozone.
Plasticizers: these are oily substances which make the rubber end product softer.
