Types of Synthetic Rubber
Neoprene
Neoprene is a polymer of chloroprene. It is also known as Polychloroprene. The Chloroprene
obtained undergoes Polymerization to gives Neoprene. Though no specific catalysts are needed
for this process but the polymerization becomes faster in the presence of Oxygen or peroxide.
Uses of Neoprene
It is used in the manufacture of hoses, gaskets, shoe heels, stoppers, conveyor belts and
printing rollers etc. It is also used as an insulator.
BUNA–S
BUNA–S is a copolymer of a mixture of 1,3- Butadiene and styrene in the ratio of 3:1 in the
presence of sodium (which is polymerizing agent) gives styrene – butadiene copolymer
(styrene – butadiene rubber) or BUNA –S. The name BUNA–S is made up of Bu which indicates
1, 3 – Butadiene, NA is for Sodium (Na) and S indicates Styrene.
Properties of Buna–S
It is very tough and a good substitute for natural rubber.
It possesses high abrasion resistance.
It has high load bearing capacity.
Uses of Buna–S
It is used for manufacturing automobile tyres.
It is used for making floor tiles, footwear components, cable insulation etc.
BUNA – N (Nitrile Rubber)
BUNA–N is obtained by copolymerization of 1, 3 – Butadiene and acrylonitrile in presence of a
peroxide catalyst. The name BUNA–N is made up of Bu which indicates 1, 3 – Butadiene, NA is
for Sodium (Na) and N indicates acrylonitrile.
1, 3-Butadiene reacts with Acrylonitrile to produce Buna – N
Properties of BUNA–N
BUNA-N is resistant to the action of petrol, lubricating oils and organic solvents.
Uses of BUNA–N
BUNA-N It is used in making oil seals, hoses, tank linings etc.
Thiokol
Thiokol is prepared by copolymerization of 1, 2 – dichloroethane (ethylene dichloride) with
Sodium Tetrasulphide (Na2S4) in presence of Magnesium hydroxide.
Properties of Thiokol
Thiokol is resistant to the action of mineral oils, solvents, oxygen & ozone.
Note : Thiokol is also known as polysulphide rubber. It’s tensile strength is slightly less than that
of Natural rubber. It’s different from vulcanized Rubber.
Vulcanized Rubber
Natural rubber is not an important polymer for commercial purpose because of its softness &
tacky (sticky) properties. Softness of natural rubber increases with the increase in temperature
while brittleness increases at low temperature.
Therefore, ideal temperature for using Rubber is 283 – 335K where its elasticity is maintained.
Other properties which decrease the quality of natural rubber are:
It has large water absorption capacity
It has low tensile strength & low resistance to abrasion
It is not – resistant to abrasion
It is easily attacked by organic reagents.
The properties of Natural rubber can be improved by a process called Vulcanization
.Vulcanization is the process of introduction of Sulphur bridges between different chains by
heating raw rubber with Sulphur at 373-415K. In the absence of catalyst the process of
vulcanization is slow. Some additive such as Zinc Oxide is added to accelerate the rate of
Vulcanization.
Difference between Vulcanized rubber and Natural rubber
The new or vulcanized rubber obtained has properties that are just opposite to that of natural
rubber. These properties are
Vulcanized rubber has excellent elasticity.
Low water absorption tendency
It is resistant to the action of organic solvents
It is resistant to attack of oxidizing agents.
Vulcanized Rubber is an improved form of Natural rubber.
In vulcanized rubber, Sulphur bridges are introduced either at their reactive allylic sites or at the
site of double bond. The presence of double bond in the rubber molecule makes it’s highly
reactive as it provides allylic hydrogen that permits formation of Cross links between different
chains. The presence of these cross links increases the toughness, strength and hardness of
rubber. Due to the presence of Sulphur bridges, individual chains can no longer slip over one
another but are locked together in a giant size molecule.
Cross-links being formed between the rubber polymer chains during Vulcanization
Note : Amount of Sulphur used for vulcanization process determines the extent of hardness or
toughness of the rubber.5% Sulphur is used for making tyre rubber, 20 – 25% Sulphur is used
for making Ebonite. 30% of Sulphur is for making Battery Case Rubber.
