Discuss the main purpose of vulcanisation of rubber.

Answer

Natural rubber has the following disadavantages :
(i) It is solid and sticky and becomes even more so at high temperature and brittle at low temperatures. Therefore, rubber is generally used in a narrow temperature range `(283-335 K)` where its elasticity is maintained.
(ii) It has large water absorption capacity, has low tensile strength and low resistance to abrasion,
(iii) It is not resistant to the action of organic solvents
(iv) It is easily attacked by oxygen and other oxidising agents.
To improve all these properties, natural rubber is vulcanised by heating it with about `5%` sulphur at `375-415 K`. The valcanized rubber thus obtained has excellent elasticity over a large range of temperature, has low water absorption tendency, is resistant to the action of organic solvents and oxidising agents.

Explanation

Fehling solution on reaction with aldehyde, gives red coloured solution.