Blends

A blend recipe cannot be built around one fibre. The two components want different dyes, different temperatures and different pH; the work is finding the band where neither is damaged.

Why is polyester-cotton dyed in two steps?

The two fibres do not take the same dye. Polyester is dyed with disperse dye near 130 °C under acidic conditions. Cotton is dyed with reactive dye under alkali, at a far lower temperature.

The classic route is therefore two-step: dye the polyester, clear, then dye the cotton. One-bath trials save time and energy but make dye compatibility and shade control harder; each recipe has to be proven separately.

Why can the intermediate clearing not be skipped?

After the polyester is dyed, disperse dye remains stuck on the fibre surface without having entered it. In the second step that dye transfers onto the cotton and leaves a dirty, dull ground — and both shades drift.

Reduction clearing makes that surface dye soluble and takes it into the bath. On elastane blends the alkaline conditions are limited, so special-purpose washing agents that work near neutral are used instead.

Which limit applies in pre-treatment?

The rule is simple: the most sensitive fibre sets the limit. A bleaching condition that is normal for cotton will damage wool or elastane in the blend.

• Cotton-polyester: the cotton bleach governs, and polyester tolerates it.
• Cotton-elastane: alkali and temperature are measured against the elastane.
• Wool-polyester: wool's near-neutral window governs, which makes removing the synthetic's spin finish harder. See the wool page.

Sequestrant and stabiliser choice matters even more inside that narrowed window: uncontrolled peroxide decomposition shows up as a whiteness shortfall in a shortened bleach.

Which faults are more common on blends?

• Dull ground. Insufficient intermediate clearing leaves the cotton side flat.
• Unlevelness. In a two-step process, heating rates have to be controlled separately or the differences accumulate. The unlevelness article covers reading the pattern.
• Creasing. A longer total cycle means more time in the machine; an anti-creasing agent becomes standard here.
• Foam. Two surfactant systems layered on top of each other raise foam. Antifoam choice follows the bath conditions.

Which product groups are used on blends?

Dispersing and levelling agents, washing agents and oil stain removers, sequestering agents and stabilisers, anti-creasing agents, antifoaming agents, fixing agents and finishing agents.