Question

Dyestuff suitable for dyeing polyester fabric:

• A. \( \text{Direct dyes} \)
• B. \( \text{Azoic dyes} \)
• C. \( \text{Disperse dyes} \)
• D. \( \text{Metal complex dyes} \)

Hint:

Think of polyester as a "closed door." Disperse dyes are the only ones small and "neutral" enough to squeeze through when the door is opened by heat.

Answer 1

The Correct Option is C

Concept: The chemical compatibility between a dye and a fiber determines how well the color is absorbed and retained. Polyester is a very dense, hydrophobic fiber with no active chemical sites for many traditional dyes.

Step 1: Match dye to fiber type.
Disperse dyes are the only dyes capable of effectively coloring polyester. These dyes are non-ionic (have no electrical charge) and are applied as a fine dispersion in water. Under high heat and pressure, the polyester fiber "opens up," allowing the small dye molecules to diffuse into the fiber and become trapped.

Step 2: Understand other dye applications.

• Direct dyes: Used for cellulosic fibers like cotton.
• Azoic dyes: Used primarily for cotton to get bright reds and oranges.
• Metal complex dyes: Used for protein fibers like wool and silk.