Given below are two statements, one is labeled as Assertion (A) and the other is labeled as Reason (R):
Assertion (A): When disperse dyes are applied to polyesters at low temperatures, carriers are required to bring about penetration of the dye molecules into the fiber.
Reason (R): High pressure and high temperature eliminate the need for carriers.
In light of the above statements, choose the correct answer from the options given below:

Correct option is A

· Assertion (A): "When disperse dyes are applied to polyesters at low temperatures, carriers are required to bring about penetration of the dye molecules into the fiber."
· This statement is true because polyester is a hydrophobic fiber with a tightly packed structure, making it difficult for dye molecules to penetrate at low temperatures. Carriers (such as benzyl alcohol or phenols) help open up the fiber structure and allow dye molecules to diffuse.
· Reason (R): "High pressure and high temperature eliminate the need for carriers."
· This statement is also true because at high temperatures (above 120°C) and high pressure, the polyester fiber swells, allowing disperse dyes to diffuse into the fiber without requiring carriers.
Information Booster:
Why Are Carriers Needed at Low Temperatures?
· Polyester fibers are highly crystalline and have a compact molecular structure, making dye penetration difficult at low temperatures.
· Carriers disrupt the polymer structure and enhance dye diffusion by increasing fiber swelling and mobility.
Why Are Carriers Not Needed at High Temperatures?
· When using high-temperature dyeing (HT dyeing) at 120–130°C, polyester fibers expand naturally, allowing dye molecules to enter without chemical assistance.
· The pressure prevents evaporation and ensures efficient dye uptake.