Question

Explain the purpose of vulcanization of rubber.

Answer 1

Hint:Natural rubber is a polymer of isoprene. Its properties can be enhanced by addition of certain substances to it.

Complete step by step answer:
Natural rubber, also known as latex, is a polymer of organic compound isoprene and some other impurities and water. It is harvested from rubber trees as latex. It is usually sticky, milky colloid form. The stretch ratio of rubber is large. It has high resilience and is waterproof too.
Apart from its advantages, it has its drawbacks. These are
-It is very soft and sticky at room temperature. At high temperatures its softness increases and at low temperature it is brittle. So, in order to maintain its elasticity, natural rubber should be used in the temperature range of 238K-335K.
-Large amounts of water can be absorbed by natural rubber.
-It has low resistance to abrasion and tensile strength is also low.
-Soluble in nonpolar solvents.
-Can be easily attacked by oxidizing agents.
In order to overcome all these drawbacks of natural rubber, it is modified by the process called vulcanisation.
Vulcanization is the range of processes for hardening rubbers. It is mainly treating natural rubber with sulphur. Other additives are also used to enhance its properties. Vulcanised rubber can be heated at a temperature between 373K and 415K. Some additives are added to accelerate the process of vulcanization such as zinc oxide. In this process, sulphur cross-links are formed and make the rubber hard, tough with a greater tensile strength. The elasticity of natural rubber is increased by vulcanisation, has low water absorption and is resistant to oxidising agents and organic solvents.

Note:
Vulcanised rubber has higher wear and tear resistance than natural rubber. But both have the same solubility in solvents such as ether, carbon tetrachloride etc. Basically vulcanised rubber is a superior form of natural rubber.