Cationic Dyeable Polyester (CDP) and Ionic Dyeing
topic
Cationic dyeable polyester (CDP) incorporates 5-sodium sulphoisophthalate (SIIS, 2–3 mol%) during polymerisation, introducing anionic sulphonate groups (SO₃⁻) that electrostatically attract cationic (basic) dyes. CDP dyed with cationic dyes at pH 4–5, 120–130°C. Ionically bonded dye provides excellent wash fastness (rating 4–5). CDP blended with standard PET in same fabric creates differential dyeing effects (heather, melange) with single dye bath.
Role
CDP chemistry and dyeing is a textbook example of molecular engineering for function — modifying polymer chemistry to enable a completely different dyeing mechanism. It is important for understanding differential dyeing, colour design, and ionic bonding in dyeing.
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