Natural Rubber

Rubber is a natural polymer and possesses elastic properties. It is also termed as elastomeric polymer. In elastomeric polymers, the polymer chains are held together by the weak intermolecular forces. These weak binding forces permit the polymer to be stretched. A few ‘crosslinks’ are introduced in between the chains, which help the polymer to retract to its original position after the force is released.

Rubber 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 rubber tree (Hevea brasiliensis,) which is found in India, Srilanka, Indonesia, Malaysia and South America. 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.

Natural Rubber -Plant- Rubber latex- isoprene natural rubber structure

Vulcanisation 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 nonpolar 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 between 373 K to 415 K. 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. 

Synthetic rubbers

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

1. Neoprene (GRM)

Neoprene or polychloroprene 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.

2. Buna – N or Nitrile Rubber (GRA)

Buna –N is obtained by the copolymerisation of 1, 3 – buta–1, 3–diene and acrylonitrile in the presence of a peroxide catalyst.

It is used for making tyres, tubes, foam matress, chappals etc. 

3. Buna-S (Styrene Rubber), which is formed by polymerisation of buta–1, 3–diene and styrene is an example of copolymer formed by addition polymerisation.

Buna S is largely used in the manufacture of light duty tyres, hoses and rubber soles.

Difference between Natural Rubber and Synthetic Rubber
(Natural Rubber vs Synthetic Rubber)

Natural Rubber

Synthetic Rubber

Natural Rubber is manufactured from latex is obtained from the rubber tree (Hevea brasiliensis)

It is artificial made polymers under laboratory conditions.

Monomers – cis 1,4 isoprene

Monomers are different in each type

The quality of rubber latex may vary depends upon clone, season, area etc

High quality rubber with very low impurities

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