What is fixation?
Fixation is basically how much the dye reacts with the
fabric. It depends on how much dye is fixed onto the fabric after considering
all the washes.
For the measurement of fixation one can do the same as for
exhaustion and also measuring the absorbance of all the washes and then he can find
out easily the fixation for the fixation.
Formula will be:
Fixation % = [{C0-(C1+CW1+CW2+..)}/C0] x 100 C0 =
concentration of dye initially C1= Concentration of dye after dyeing CW1, CW2
are concentrations of the dye in each wash.
What types of reactive dyes are there?
There are three main types of reactive dyes: vinylsulphones
(VS), monochlorotriazines (MCT) and hetero-bifunctional groups that are a mixture
of both VS and MCT.
What is a vinyl sulphone dye?
These dyes are moderately reactive. The dyeing temperature
is 600C and pH 11.5 is used by utilising a mixture of soda ash and caustic
soda. These dyes show excellent fixation efficiency under the correct alkaline
conditions. Remazol dyes which contains 2-Sulphatoethyl sulphonamide. This is capable
of either reaction with cellulose or hydrolysis to the hydroxyethylsulphonamide
according to the usual nuchleophilic addition mechanism.
What is a monochlorotriazine dye?
These dyes are less reactive than vinylsulphone dyes. They
require more energetic reaction conditions, typically 800C and pH 10.5, are necessary
for fixation on cellulosic fibres.
What is a bi-functional dye?
A bi-functional dye is a reactive dye that has more than one
type of reactive group in the molecule. These reactive dyes are designed to
have the ability to react with the fibre in more than one way. This increases
how much of the dye in the bath is actually fixed to the fibre, rather than
being wasted through hydrolysis.
Bi functional dyes contain two reactive systems of the same
type or different type. The objective to produce these dyes for exhaust dyeing
was for higher substantivity exhaustion and fixation values. Homo bifunctional
dyes contain two of the same reactive group.
What are hot brand, medium brand and cold brand dyes?
It is not common practice to specify dye types in this
manner, for example, monochlorotriazine dyes have been given the name 'hot
brand' whilst vinyl sulphone dyes have been termed 'warm brand' using this
system it is not possible to give a term to mixed bi-functional dyes since
they have one monochlorotriazine group and one vinyl sulphone group.
The batch wise dyeing temperature of these dyes for optimal
fixation is 300C to 400C. These dyes are very much reactive and show high fastness
properties. These dyes require very careful control and should only be used
where full automation of the dyeing process is possible. Examples of cold brand
dyes include: Dichlrotriazines ometimes these dyes are called "M" dyes.
Typical Brand name for these dye types are Procion MX.
- Warm or medium brand dyes
Recommended dyeing temperature of these dyes for the maximum
fixation for exhaust dyeing is 600C. The reactive groups for these types of
dyes are of vinyl sulphone. The required pH for these dyes is 11.5. Typical brand
names of these dyes are Remazol (HOE).
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