Buna-S Rubber

Several synthetic rubbers have captured the natural rubber market. Now a days we can use tailorable elastomers for any desired specific purpose. Buna-S rubber is one of the commonly used synthetic rubber.



Synthetic scheme of Buna-S Rubber



Buna-S Rubber:

It is a random co-polymer formed by the emulsion polymerisation of a mixture of 1:3 butadiene and styrene in the presence of peroxide catalyst at 5 degree Celsius and therefore the product is called as cold rubber.  The rubber obtained is also called Styrene butadiene rubber (SBR).

In Buna-S, Bu stands for butadiene and, Na for sodium and S for styrene. It is vulcanised with sulfur. The rubber is slightly inferior to natural rubber in its physical properties.



Application of Buna-S



Applications: It finds application due to its high resistance to abrasion.



• It is used for the manufacture of passenger car tyres and treads,motor cycle and scooter tyres,cycle tyres and tubes.

• They are also used for the manufacture of conveyor belts,foot-wares, shoe soles,hoses and electrical insulation.

Natural Rubber and its deficiencies

Natural rubber is obtained from rubber trees which are grown in tropical regions. The tree is known for storing milky white latex behind the bark of the tree. Natural rubber is an example for addition polymer formed by the repeated union of monomer called cis-isoprene. Natural rubber is the ciss somer while the trans isomer is called gutta -percha. Natural rubber exhibit large number of deficiencies, which are

 


Isoprene

• Hard and brittle at low temperature but soft and sticky ant high temperature.
• It undergoes air oxidation and develops bad odour.
• Soluble in many organic solvents.
• Natural rubber is highly hygroscopic in nature.
• Low chemical resistance towards chemicals like acids, bases, oxidising and reducing agents.
• It has low tensile strength, wear and tear resistance.
 
 

Elastomers

Elastomers are high molecular weight polymers with great stretching property. They can stretch easily by several times their length when subjected to an external force but it regains their original shape when the force is just removed. Rubbers are the great example for elastomers. The linear polymer having glass transition temperature below the working temperature range of the rubber is an example for a elastomer.

Elasticity of a rubber polymer is mainly due to the uncoiling and recoiling of the molecule chain by the application of external force. For the polymer to exibit elasticity property the individual chains should not break on prolonged stretching.

Example for Elastomers are

• Natural rubber , Neoprene Rubber, Butyl Rubbers, Buna Rubbers