Question

In vulcanization of rubber,
A. Sulphur reacts to form a new compound
B. Sulphur cross links are introduced
C. Sulphur forms a very thin protective layer over rubber
D. All of the above

Answer 1

Hint: In the vulcanization process, the strength of the rubber is improved by heating the rubber at high temperature in the presence of sulfur which results in the formation of a long cross-linked chain.

Complete step by step answer:
The vulcanization of rubber is a process used to improve the elasticity and strength of the rubber by heating in the availability of Sulphur. This results in the formation of three-dimensional cross linking of chain rubber molecules known as polyisoprene which is joined with each other by a Sulphur atom.
The rubber is mainly in two forms.
(1) Natural rubber: Natural rubber is prepared from the latex of the rubber tree. The coagulated latex is converted to soft, plastic and sticky substance which is then further vulcanized. The natural rubber is formed of polyisoprene molecules.
(2) Synthetic rubber: Synthetic rubbers are usually elastomers whose properties are similar with the natural rubber. The composition of synthetic polymers is similar to natural rubber.
In vulcanization, following stages can be seen.
(1) Mixing: The crude rubber is mixed with Sulphur (5-30 %) along with other additives like activators, accelerators, anti-oxidants, softeners etc.
(2) Molding: The rubber is molded in this process as it is required to shape the rubber before the heating stage as cross linking of rubber makes the shaping of rubber impossible.
(3) Heating: In this process the mixture is heated under 250 – 400 degree Fahrenheit.

So, the correct answer is Option B.

Note: The increasing the temperature speed up the vulcanization process which results in fast and complete cross linking. During cross linking the C-S bond is displaced by the C-H bond linking the polyisoprene molecule.