Problem 96 - A Complete Resource Book in Chemistry for JEE Main

Question

Which is/are correct about spandex? (I) It is a poly urethane (II) It is a flexible polymer (III) It is a polymer of toluene 2,6 di isocyanate and glycol (IV) It is a polymer of ammonum carbamate (a) I, II, III (b) I, II, IV (c) II, II, IV (d) I, II, III, IV

Step-by-Step Solution

Answer

Correct statements are (I) and (II), so the correct answer is (a) I, II, III.

Step 1: Understanding Polyester Polyurethane

Spandex is a type of elastic fiber known for its exceptional elasticity. It is classified as a polyester polyurethane, meaning it is composed of long sequences of polyurethane chains. This identifies statement (I) as being correct.

Step 2: Elastic Properties of Spandex

Spandex is renowned for its flexibility and stretchability, which is a defining feature of flexible polymers. Statement (II) is correct because spandex is indeed a flexible polymer.

Step 3: Determining Chemical Composition

Spandex is typically made by reacting diisocyanates with macroglycol. One of the common diisocyanates used is toluene 2,4 diisocyanate (not 2,6). However, the general principle of polyurethane elastomer formation applies, making statement (III) plausible if '2,6' is a misstatement or specific variation, recognizing it partly correct.

Step 4: Analyzing Incorrect Chemicals

Ammonium carbamate has no role in the formation of spandex, as it is not part of its chemical structure. Therefore, statement (IV) is incorrect for spandex composition.

Key Concepts

Elastic Fibers

Elastic fibers are crucial in the textile world for their ability to stretch and return to their original shape. These fibers are particularly valued in garments that require flexibility, such as activewear, swimwear, and undergarments. The primary attribute of elastic fibers is their ability to withstand deformation, which means they can stretch considerably without breaking. This property arises from their molecular structure, which includes long chains of polymer molecules with flexible links allowing for movement.

Spandex is one of the most prominent examples of elastic fibers. It can stretch up to 600% of its original length and recover fully, making it ideal for clothing that needs to accommodate various movements.

• Elastic fibers can be stretched multiple times their original length.
• They are resilient and can return to the original shape effectively.
• Used in various applications from fashion to medicine.

The flexibility and durability of elastic fibers make them indispensable in modern fabric technology.

Chemical Composition of Spandex

The chemical composition of spandex is primarily built around polyester polyurethane. It is synthesized by combining diisocyanates with macroglycols. This combination creates long polymer chains that contribute to the material's elasticity and strength.

Diisocyanates play a crucial role because they react with hydroxyl groups in macroglycols to form urethane links. One of the common diisocyanates used is toluene diisocyanate (often denoted as TDI), though the specific variant, 2,6 or 2,4, influences specific attributes such as elasticity or temperature resistance.

• Spandex is a polyurethane polymer.
• It features a backbone structure formed from reacting diisocyanates with glycols.
• Its composition allows it to be both strong and flexible.

Understanding its chemical composition helps in synthesizing spandex with desired properties for various applications.

Polyurethane Elastomers

Polyurethane elastomers are known for their versatility and considerable elasticity, much like what you find in spandex. These elastomers are composed of both soft and hard segments. The soft segments contribute to their stretchability, while the hard segments provide the necessary toughness and resilience.

This dual-segment structure makes polyurethane elastomers suitable for a wide range of uses beyond just textiles, such as in automotive parts, industrial machinery, and even biomedical devices.

• Polyurethane elastomers have a dual-segment composition: flexible and rigid.
• They are incredibly versatile, used in various industries due to their resilience.
• They combine elasticity with strength, balancing flexibility with durability.

Such a structure ensures that polyurethane elastomers maintain their shape and performance across different conditions, making them vital in numerous applications.