Write a note on vulcanization of rubber.

Explanation

(i) The process of mixing natural rubber with sulphur is called vulcanization. (ii) Natural rubber is mixed with 3-5% sulphur and heated at `100-150^@` C causes cross linking of the cis-1,4-polyisoprene chains through disulphide (-S-S-) bonds. (iii) The physical properties of rubber can be altered by controlling the amount of sulphur that is used for vulcanization. (iv) In sulphur rubber, made with about 1 to 3% sulphur is soft and stretchy. (v) When 3 to 10% sulphur is used the resultant rubber is somewhat harder but flexible.