Question

One bath dyeing of P/C blends calls for use of

• A. High temperature resistant reactive dyes
• B. High viscosity disperse dyes
• C. Low temperature disperse dyes
• D. Low viscosity reactive dyes

Hint:

• P/C blends (Polyester/Cotton) Require two dye classes. Disperse for polyester, reactive (or other cellulosic dyes) for cotton.
• One-bath dyeing method Aims to dye both fibers in a single bath. Common approach is HT (High Temperature) method.
• In HT one-bath method:
  • Disperse dyes are applied for polyester at high temperature (e.g., 130$^\circ$C).
  • High temperature resistant reactive dyes} are used for cotton, which can withstand these conditions and fix on cellulose.
• This ensures both fiber components are dyed with good fastness properties.

Answer 1

The Correct Option is A

Dyeing Polyester/Cotton (P/C) blends typically requires two different classes of dyes because polyester (a synthetic fiber) and cotton (a cellulosic fiber) have very different dyeing properties.

• Polyester is usually dyed with disperse dyes at high temperatures (e.g., 130-135$^\circ$C under pressure, called HT dyeing) or with a carrier chemical at boil (100$^\circ$C).
• Cotton is commonly dyed with reactive dyes, vat dyes, direct dyes, sulfur dyes, etc. Reactive dyes form covalent bonds with cellulose and are known for good fastness.

One-bath dyeing of P/C blends aims to dye both fiber components simultaneously in the same dyebath to save time, energy, and water compared to a two-bath process (dyeing one fiber, then clearing, then dyeing the other). This requires careful selection of dyes and dyeing conditions. A common one-bath method for P/C blends involves using: 
Option (A) Disperse dyes for the polyester component. 
Option (B) Reactive dyes for the cotton component. 

The challenge is that these two dye classes typically require different dyeing conditions (pH, temperature, electrolytes). For a one-bath process, one approach is the High Temperature (HT) one-bath method:

• Both disperse dyes and reactive dyes are applied simultaneously.
• The dyeing is carried out at high temperatures (e.g., 120-135$^\circ$C) suitable for fixing disperse dyes on polyester.
• Special reactive dyes are needed that are stable and can fix onto cotton under these HT conditions, usually with an alkali like sodium carbonate or bicarbonate added at the HT phase or during cooling. These are often called HT-stable reactive dyes or high-temperature resistant reactive dyes.

Let's look at the options:

• (a) High temperature resistant reactive dyes: This fits the requirement for one-bath HT dyeing of P/C blends, where reactive dyes must withstand the high temperatures needed for disperse dyeing of polyester and still be able to fix on cotton.
• (b) High viscosity disperse dyes: Viscosity of the dye itself is not the primary characteristic for this application, but rather its dyeing properties (sublimation fastness, stability at HT). "High viscosity" is not a standard descriptor in this way for dye selection.
• (c) Low temperature disperse dyes: These are disperse dyes designed for dyeing polyester at lower temperatures (e.g., with a carrier). If used in a one-bath HT process, they might not be optimal or could have issues with fastness. The process often goes to HT for the polyester part.
• (d) Low viscosity reactive dyes: Similar to (b), viscosity is not the key property here. "High temperature resistant" is crucial.

Therefore, for one-bath dyeing of P/C blends, particularly by an HT method, the use of compatible disperse dyes for polyester and high temperature resistant reactive dyes for cotton is essential. \[ \boxed{\text{High temperature resistant reactive dyes}} \]