Discuss the main purpose of vulcanisation.

Explanation

To improve upon various physical properties of natural rubber, raw rubber is heated with Iphur and some suitable additives at 375 K-415K. This process is called vulcanization.
Improvement in various physical properties of natural rubber on vulcanization are discussed
(i) Natural rubber has a narrow useful temperature range (280-335K). Below 280 K it. becomes brittle and above 335 K it becomes soft and sticky. On vulcanisation its useful temprature range becomes 230 K to 375 K.
(ii) Natural rubber shows high water absorption capacity. On vulcanisation it becomes almost water-proof.
(iii) Natural rubber is non-resistant to the attack of oxidising agents. On vulcanisation it becomes quite resistant to oxidation.
(iv) Low degree of vulcanisation (upto 5% S). improves elasticity but vulcanisation with more than 5% sulphụr(upto 30%) makes rubber stiff.
(v) Vulcanisation reduces the solubility or rubber in non-polar organic solvents.