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2026年3月2日
What is differences between Reactive and VAT dyes？
Basic chemistry and fixation Reactive dyes: contain reactive groups (e.g., dichloro-s-triazine, vinylsulfone) that form covalent bonds with fiber functional groups (hydroxyl on cellulose, amino on woo
- Basic chemistry and fixation
- Reactive dyes: contain reactive groups (e.g., dichloro-s-triazine, vinylsulfone) that form covalent bonds with fiber functional groups (hydroxyl on cellulose, amino on wool/nylon) — chemical fixation.
- Vat dyes: water-insoluble reduced (leuco) forms are soluble; they are absorbed into the fiber in the reduced state and then oxidized back to the insoluble pigment inside the fiber — physical entrapment of insoluble dye.
- Typical fibers
- Reactive: cellulosic fibers (cotton, linen), also wool and nylon with proper chemistry.
- Vat: primarily cellulosic fibers (cotton); some use on viscose and blends.
- Dyeing conditions
- Reactive: often done at moderate temperatures (20–60 °C) with alkaline pH (for cellulose) to promote nucleophilic reaction; requires salt to promote exhaustion for many classes.
- Vat: requires strong reducing bath (sodium hydrosulfite or other) under alkaline conditions to solubilize dye, then oxidation (air or chemical) to fix; dyeing often at elevated temperatures depending on process.
- Fixation efficiency and after treatment
- Reactive: covalent bonding yields high wet fastness when fixed; however unfixed (hydrolyzed) dye is washed off — requires thorough soaping, fixation aids (salt/alkali), fixation time.
- Vat: once oxidized inside fiber, dye is insoluble and very difficult to remove — soaping to remove surface dye still needed but overall retention is excellent.
- Fastness properties
- Reactive: generally excellent wash fastness (if well fixed), good light fastness varies by dye class, moderate to good rub fastness.
- Vat: excellent wash and light fastness; very good rub fastness — among best for cellulosics.
- Shade brightness and levelness
- Reactive: can give very bright shades and good levelness with proper process control; hydrolized dye can reduce brightness if fixation poor.
- Vat: deep darks and strong fastness, but some vat dyes give less brilliance than some reactive dyes (depends on dye).
- Process complexity and safety
- Reactive: simpler chemistry (no reducing agents), milder bath chemistry, but requires control of salt, alkali, and fixation times; hydrolysis of dyes creates effluent loading.
- Vat: more complex and hazardous (reducing agents, alkaline conditions), need careful control of reduction/oxidation; equipment and effluent handling more demanding.
- Environmental considerations
- Reactive: unreacted/hydrolyzed dyes and high salt loads in effluent are environmental concerns; treatment and salt reuse strategies used.
- Vat: reducing agents and high COD from vat dyeing effluent; some vat dyes (e.g., indigo) have better-managed processes but overall effluent can be problematic.
- Typical end-use advantages
- Reactive: bright colors, easy application at low/moderate temperatures, good for fashion textiles where softness and brightness matter.
- Vat: superior durability and fastness for workwear, military textiles, denim (indigo is a vat dye), and applications needing long-lasting color.
Summary: Reactive dyes fix by covalent bonding (good brightness, easier process, salt/alkali dependent); vat dyes fix by reduction/oxidation and entrapment as insoluble pigments (harder process but superior wash/light fastness).