Question

Which of the following group is the reactive group in cotton?

• A. Nitro group
• B. Amino group
• C. Carboxylic group
• D. Hydroxyl group

Hint:

The three hydroxyl (\( -\text{OH} \)) groups per glucose unit are responsible for cotton's high moisture regain (8.5%) and its reactivity with reactive and direct dyes.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The chemical reactivity of a textile fiber depends on the functional groups present along its polymer chain.
These functional groups determine how the fiber interacts with dyes, moisture, finishing agents, and chemical treatments.

Step 2: Detailed Explanation:
Cotton is a natural cellulosic fiber composed of repeating cellobiose units (linked D-glucose units).
Each cellobiose unit contains three reactive hydroxyl groups (\( -\text{OH} \)):
- One primary hydroxyl group on the \( \text{C}_6 \) carbon.
- Two secondary hydroxyl groups on the \( \text{C}_2 \) and \( \text{C}_3 \) carbons.
These hydroxyl groups are highly polar and can form hydrogen bonds with water molecules, making cotton highly hydrophilic.
During dyeing, particularly with reactive dyes, a covalent bond forms between the dye molecule and these active hydroxyl groups.
Other functional groups like amino groups (B) are found in protein fibers (wool, silk), and carboxylic groups (C) are present in acrylics or wool, but not in pure cellulose.
Therefore, the reactive group in cotton is the hydroxyl group.

Step 3: Final Answer:
The reactive functional group present in cotton cellulose is the Hydroxyl group.