Speciality Chemicals

Cationic-dyeable polyester behaves differently from standard polyester. Basic dye bonds fast to the anionic groups in the fibre and tends to pile up at the surface. A penetrating agent helps the dye move on into the fibre instead of stopping there.

What is cationic-dyeable polyester?

Standard polyester carries no ionic groups for dye to bind to, which is why it is dyed with disperse dye by diffusion. Cationic-dyeable polyester (CDP) is modified during polymerisation with sulphonate groups on the chain. Those anionic groups bind basic dye ionically.

The result is bright, clean colour. The price is speed: basic dye attaches to those sites very quickly.

Why is a fast strike a problem?

The dye fills the binding sites at the fibre surface first. Once the surface saturates, further progress depends on diffusion, and diffusion is slower than binding.

Two things follow. The first is ring dyeing: the outside of the fibre cross-section is coloured while the core stays pale. Rub fastness drops and the fabric starts to look washed out in wear. The second is unlevelness; the area the dye reaches first comes out darker, and because migration is limited with this dye class it does not correct itself.

What does the penetrant do?

A penetrating agent loosens the dye's hold at the fibre surface slightly and makes it easier for it to move through the cross-section. In practice it earns its place in three situations: on tight, heavy constructions, on microfilament fabrics, and in package dyeing where the dye struggles to get into the yarn.

There is a side effect on the bath as well. When dye is distributed evenly through the cross-section, less dye is needed for the same visual depth and less is left in the liquor.

How does it differ from a carrier?

A carrier swells the amorphous regions of polyester to speed up the diffusion of disperse dye, and is classically used in atmospheric dyeing below 100 °C. A penetrant does not alter the fibre structure; it works on how the dye distributes.

The two address different faults. A carrier is used when diffusion is too slow, a penetrant when distribution is uneven. Conditions of use for the Derin Kimya product are on its page: pending from the client.

How does it enter the recipe?

The product is dosed into the dye bath before the dye. In a bath running basic dyes there is a risk that anionic auxiliaries precipitate with the dye, so the ionic character of everything else in the bath is checked first. Any new recipe starts at lab scale.

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