Discuss the improvement in the drawbacks of natural rubber after vulcanization.

FE > Semester 1 > Applied Chemistry 1

Marks : 05

Years : DEC 2015

Vulcanization or vulcanisation is a chemical process for converting natural rubber or related polymers into more durable materials by the addition of sulfuror other equivalent.These additives modify the polymer by forming cross-links (bridges) between individual polymer chains. Vulcanized materials are less sticky and have superior mechanical properties.

Reaction-

Improvement in the drawbacks of natural rubber after vulcanization is-

1) Cross-linking increases the elasticity and the strength of rubber by about ten-fold, but the amount of cross-linking must be controlled to avoid creatin a brittle and inelastic substance.

2) Rubber is a polymer (long chain made of repeating units) of isoprene. Natural rubber is relatively reactive, and is especially vulnerable to oxidation.

3) In the process of vulcanization, the added sulfur allows some C-H bonds to be broken and replaced by C-S bonds. The process of vulcanization cross-links the chains or polyisoprene to each other. The cross-linked molecules create a three-dimensional network of rubber. Each cross-link is a chain of about eight sulfur atoms between two long chains of polyisoprene.

4) Vulcanized rubber is about 10 times stronger than natural rubber and is also about 10 times more rigid. However, it is still very elastic, which means that is can be stretched reversibly. Polymers that are elastic are sometimes called elastomers. The optimum amount of sulfur to be added to the rubber is about 10% by weight. Adding an excess of sulfur produces a very brittle and inelastic substance called ebonite. Man-made or synthetic rubber can also be vulcanized, and the process is similar.