Question

To the fiber add 85% formic acid at room temperature. Then the fiber dissolves. Identify the fiber.

• A. Acrylic
• B. Wool
• C. Silk
• D. Polyester

Hint:

Fiber identification often uses solubility: Silk → formic acid, Acrylic → DMF, Polyester → phenol, Wool → alkali.

Answer 1

The Correct Option is C

Step 1: Fiber Solubility Tests Overview.
Textile labs use chemical solubility tests to identify fiber types by observing their dissolution in specific solvents.
Step 2: Silk's Solubility.
Silk, a protein fiber (fibroin), uniquely dissolves in 85% formic acid at room temperature, serving as a rapid identification test.
Step 3: Solubility Differences.

• Acrylic: Dissolves in dimethylformamide (DMF), not formic acid.
• Wool: Another protein fiber, but resistant to formic acid; dissolves in chlorine bleach or strong alkali.
• Polyester: A synthetic thermoplastic fiber, insoluble in formic acid; dissolves in phenol or hot chlorinated solvents.

Step 4: Summary.
Only silk dissolves in 85% formic acid at room temperature.