Question

The HTHP (High Temperature High Pressure) dyeing of polyester is carried out at the temperature of __________ for effective dye penetration.

• A. $70^{\circ}C$
• B. $80^{\circ}C$
• C. $130^{\circ}C$
• D. $50^{\circ}C$

Hint:

Think of $130^{\circ}C$ as the "magic number" for polyester. Without this high heat or the use of chemical "carriers," the dye would simply sit on the surface and wash right off.

Answer 1

The Correct Option is C

Concept: Polyester is a highly crystalline and hydrophobic fiber with a high glass transition temperature ($T_g$). Standard dyeing at $100^{\circ}C$ is often insufficient for disperse dyes to penetrate the fiber structure effectively.

Step 1: Overcoming the Glass Transition Barrier.
At temperatures below its $T_g$, the molecular chains of polyester are tightly packed, leaving very little "free volume" for dye molecules to enter. Dyeing polyester typically requires increasing the temperature well above the $T_g$ in a pressurized vessel to prevent the water from boiling away.

Step 2: Standard HTHP Conditions.
The industry standard for HTHP dyeing of polyester is $130^{\circ}C$. At this temperature, the polymer chains gain enough thermal energy to move, creating sufficient space (pores) for the disperse dye molecules to diffuse rapidly into the fiber core, ensuring deep and level coloration.