- Rubber is a natural polymer and possesses elastic properties.
- It is also termed as elastomer and has a variety of uses.
- It is manufactured from rubber latex which is a colloidal dispersion of rubber in water. This latex is obtained from the bark of rubber tree and is found in India, Sri Lanka, Indonesia, Malaysia and South America.
- Natural Rubber
- Natural rubber may be considered as a linear polymer of isoprene (2-methyl-1, 3-butadiene) and is also called as cis - 1, 4 -polyisoprene.
- The cis-polyisoprene molecule consists of various chains held together by weak van der Waals interactions and has a coiled structure.
- Thus, it can be stretched like a spring and exhibits elastic properties.
Vulcanization of Rubber:-
- Natural rubber becomes soft at high temperature (>335 K) and brittle at low temperatures (<283 K) and shows high water absorption capacity.
- It is soluble in non-polar solvents and is non-resistant to attack by oxidising agents. To improve upon these physical properties, a process of vulcanisation is carried out. This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range 373 K to 415K.
- On vulcanisation, sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened.
- In the manufacture of tyre rubber, 5% of sulphur is used as a crosslinking agent.
- The probable structures of vulcanised rubber molecules are depicted below:
- Synthetic Rubber
- Synthetic rubber is any vulcanisable rubber like polymer, which is capable of getting stretched to twice its length.
- However, it returns to its original shape and size as soon as the external stretching force is released.
- Thus, synthetic rubbers are either homopolymers of 1, 3 - butadiene derivatives or copolymers of 1, 3 - butadiene or its derivatives with another unsaturated monomer.
Preparation of Synthetic Rubbers
- Neoprene or poly chloroprene is formed by the free radical polymerisation of chloroprene.
- It has superior resistance to vegetable and mineral oils.
- It is used for manufacturing conveyor belts, gaskets and hoses.
- Buna –N:-
- Buna –N is obtained by the copolymerisation of 1, 3 – butadiene and acrylonitrile in the presence of a peroxide catalyst.
- It is resistant to the action of petrol, lubricating oil and organic solvents. It is used in making oil seals, tank lining, etc.