Question: 56: Which statement regarding polymers is not correct?
(1) Thermoplastic polymers are capable of repeatedly softening and hardening on heating and cooling respectively
(2) Thermosetting polymers are reusable
(3) Elastomers have polymer chains held together by weak intermolecular forces
(4) Fibers possess high tensile strength
Answer: Option (2)
Explanation:
Polymers are classified into different types based on their structure and physical properties such as thermoplastics, thermosetting polymers, elastomers, and fibres.
Thermoplastic polymers consist of linear or slightly branched chains. On heating, the intermolecular forces between chains weaken, allowing the polymer to soften.
On cooling, these forces are restored, causing the polymer to harden again.
Therefore, thermoplastics can be repeatedly softened and hardened.
Thermosetting polymers form a rigid, highly cross-linked three-dimensional network during heating.
Once this network is formed, the polymer cannot be softened again on reheating.
Hence, thermosetting polymers cannot be reused, making the statement that they are reusable incorrect.
Elastomers have long polymer chains with weak intermolecular forces between them.
This allows the chains to stretch easily when stress is applied and return to their original shape when the stress is removed.
Fibres have strong intermolecular forces such as hydrogen bonding or dipole–dipole interactions.
These strong forces result in high tensile strength, making fibres suitable for making ropes and fabrics.