Question

A : A mixture of raw rubber and sulphur on heating at $373K$ - $415K$ gives vulcanised rubber.
R : ZnO decreases the rate of vulcanisation of rubber.

• A. both A and R are correct and R is the correct explanation of the A
• B. both A and R are correct but R is not the correct explanation of the A
• C. A is correct but R is incorrect
• D. A is incorrect but R is correct

Answer 1

Answer: (C)

A is correct but R is incorrect

Natural rubber becomes soft at high temperature (>335 K) and brittle at low temperatures (<283 K) and shows high water absorption capacity. It is soluble in non-polar solvents and is non-resistant to attack by oxidising agents.

To improve upon these physical properties, a process of vulcanisation is carried out. This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373 K to 415 K. On vulcanisation, sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened.

In sulfur vulcanization of natural rubber, the types of cross-links formed largely depend on the vulcanization system. The vulcanizing agents are zinc oxide (ZnO), stearic acid, accelerators, and sulfur. Conventional ZnO, or micro ZnO, is one of the basic components of rubber compounds and acts as an activator for rubber crosslinking by sulfur or sulfur donors.

Hence, reason given is incorrect. So, option C is correct.