Aims:
1. To apply a vat dye dispersion to a fabric by padding
2. To apply a vat dye to cotton fabric using a pre-pigmentation method
3. To observe the changes a vat dye undergoes during application to a fabr
4. To determine the effect of soaping on a vat dye
5. To practice pad-bath calculations.
Theory:
The simplest arrangement for dyeing fabric is to pull the textile material through the
dyebath so that the dye can exhaust on to the fabric surface. Low liquor ratios and the
addition of common salt or Glauber's salt both promote such exhaustion. In some cases,
the addition of acid also promotes exhaustion. If the dye is only partially soluble in water
and likely to be exhausted unevenly, the addition of soap or sodium carbonate may
promote leveling. A dyeing is considered to be level if all parts of all fibers have been
penetrated evenly and completely. Machines for this type of dyeing are called batch
machines.
• Package and beam machines for yarns.
• Jigs for open width fabrics
• Winches for woven and knitted fabrics in rope form
• Jet dyeing machines for knitted fabrics in rope form.
• Paddle machines for sewn products like bedspreads
• Smith drums for nylon hosiery or special machines for nylon hosiery
If a dye is not soluble in water, as is the case with vats, it may be applied to the fabric as a
dispersion by a padder. Once the insoluble vat dye has been uniformly applied to the
fabric surface, usually with the aid of special dispersing agents (detergents), it can be
solubilized by reaction with a reducing agent, e.g., sodium hydrosulfite ("hydros",
Na2S2O4) in dilute NaOH. Once it has been converted to its soluble (LEUCO) form, the
vat dye can penetrate into the cotton fibers. After adequate time for penetration to occur,
the fabric is withdrawn from the bath and oxidized by air or an oxidizing agent such as
sodium perborate or hydrogen peroxide. This process is schematically represented below.
pad hydros
vat dye (insol) → on fabric surface → LEUCO form (soluble)
NaOH
air oxidation
vat dye
(insolublized inside. fibers)
Before chemical reducing agents were readily available, vat dyes were converted to their
soluble leuco form by fermentation of organic matter in wood tubs called vats. This
method of reduction and application is the source of the name for this class of dyes.
Once the vat dyes have been regenerated inside the fiber, they are very insoluble. This
accounts for their excellent wash fastness.
Because they can be applied as a dispersion by padding, solubilized by reduction, and
finally reoxidized when inside the fibers, vats are well- suited to continuous dyeing
operations. Such treatments exhibit a number of advantages:
a) very efficient use of the dye. All that is made up can be applied.
b) the insoluble vat is very evenly distributed over the fabric surface, leading
to level dyeings
c) continuous processes are normally more economical processes than batch
processes
Equipment and Chemicals:
Bleached 100% cotton (8" x 24")
C. I. Vat Green 1 (20 g/L) Indanthrene Green FFG
Dispersing agent (10 g/L)
Alginate NVS (sodium alginate, 1 g/L)
Soap solution (50 g/L)
NaOH solution (100 g/L)
Sodium hydrosulfite (hydros) (100 g/L) ..
Sodium chloride solution (100 g/L)
The diagram below illustrates how your fabric is to be labeled and cut for testing.
CAUTION -WEAR SAFETY GLASSES AT ALL TIMES DURING THIS DYEING!
1. To apply a vat dye dispersion to a fabric by padding
2. To apply a vat dye to cotton fabric using a pre-pigmentation method
3. To observe the changes a vat dye undergoes during application to a fabr
4. To determine the effect of soaping on a vat dye
5. To practice pad-bath calculations.
Theory:
The simplest arrangement for dyeing fabric is to pull the textile material through the
dyebath so that the dye can exhaust on to the fabric surface. Low liquor ratios and the
addition of common salt or Glauber's salt both promote such exhaustion. In some cases,
the addition of acid also promotes exhaustion. If the dye is only partially soluble in water
and likely to be exhausted unevenly, the addition of soap or sodium carbonate may
promote leveling. A dyeing is considered to be level if all parts of all fibers have been
penetrated evenly and completely. Machines for this type of dyeing are called batch
machines.
• Package and beam machines for yarns.
• Jigs for open width fabrics
• Winches for woven and knitted fabrics in rope form
• Jet dyeing machines for knitted fabrics in rope form.
• Paddle machines for sewn products like bedspreads
• Smith drums for nylon hosiery or special machines for nylon hosiery
If a dye is not soluble in water, as is the case with vats, it may be applied to the fabric as a
dispersion by a padder. Once the insoluble vat dye has been uniformly applied to the
fabric surface, usually with the aid of special dispersing agents (detergents), it can be
solubilized by reaction with a reducing agent, e.g., sodium hydrosulfite ("hydros",
Na2S2O4) in dilute NaOH. Once it has been converted to its soluble (LEUCO) form, the
vat dye can penetrate into the cotton fibers. After adequate time for penetration to occur,
the fabric is withdrawn from the bath and oxidized by air or an oxidizing agent such as
sodium perborate or hydrogen peroxide. This process is schematically represented below.
pad hydros
vat dye (insol) → on fabric surface → LEUCO form (soluble)
NaOH
air oxidation
vat dye
(insolublized inside. fibers)
Before chemical reducing agents were readily available, vat dyes were converted to their
soluble leuco form by fermentation of organic matter in wood tubs called vats. This
method of reduction and application is the source of the name for this class of dyes.
Once the vat dyes have been regenerated inside the fiber, they are very insoluble. This
accounts for their excellent wash fastness.
Because they can be applied as a dispersion by padding, solubilized by reduction, and
finally reoxidized when inside the fibers, vats are well- suited to continuous dyeing
operations. Such treatments exhibit a number of advantages:
a) very efficient use of the dye. All that is made up can be applied.
b) the insoluble vat is very evenly distributed over the fabric surface, leading
to level dyeings
c) continuous processes are normally more economical processes than batch
processes
Equipment and Chemicals:
Bleached 100% cotton (8" x 24")
C. I. Vat Green 1 (20 g/L) Indanthrene Green FFG
Dispersing agent (10 g/L)
Alginate NVS (sodium alginate, 1 g/L)
Soap solution (50 g/L)
NaOH solution (100 g/L)
Sodium hydrosulfite (hydros) (100 g/L) ..
Sodium chloride solution (100 g/L)
The diagram below illustrates how your fabric is to be labeled and cut for testing.
CAUTION -WEAR SAFETY GLASSES AT ALL TIMES DURING THIS DYEING!
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