Dyes may be
classified in two ways:
a. according to
the chemical constitution of the dye molecule, or;
b. according to
the method of application of the dye.
Acid dyes
Acid dyes are
so called because they are usually applied under acidic conditions The fibres most
readily coloured with acid dyes are man-made, synthetic, nylon fibres and the
natural protein fibres (mohair, silk, wool, etc)
DSO3-Na+
the generalized formula for the acid dye molecule
D the colour
radical or component of the acid dye molecule
DSO3-
the dye anion
Na+
the sodium ion
H+
the hydrogen Ion
nylon the nylon
polymer
wool the wool
polymer
The application
of acid dyes to protein fibres results in an ionic or salt link between the dye
molecule and the fibre polymer. The point of the fibre polymer at which the dye
is attached is termed the dye site. In wool the dye sites are the many amino
groups of the fibre. Under dyeing conditions, the amino group becomes
positively charged and attracts the negatively charged dye anion. This can be
represented as follows:
wool-NH2 + H+ → wool-NH3+
wool
polymer hydrogen wool polymer with
with amino
group or acid ion positively charged amino group
then
wool-NH + DSO3- →
wool-NH3+-SO3D
wool polymer dye ionic link formed
with positively
anion between positively
charged amino
group charged amino group
on
wool polymer and dye anion
Properties of acid dyes
Light-fastness: Dyed and printed acid colours have
good light-fastness.
Wash-fastness: Dyed and printed acid colours have
poor wash fastness.
Reactive dyes
Reactive dyes
are so called because their molecules react chemically with the fibre polymers
of some fibres to form a covalent bond between the dye molecule and fibre
polymer.
The fibres most
readily coloured with reactive dyes are the man-made and natural cellulose
fibres, synthetic nylon, and natural protein fibres.
The application
of reactive dyes involves the formation of a covalent bond between the dye
molecule and the polymer of the particular fibre. The process of applying
reactive dyes is considered below for protein fibres.
Reactive
dyes are applied to protein fibres under slightly acid conditions.
Printing with reactive dyes
Reactive dyes
can be used for printing textile materials such as cellulosics and wool.
Figure 2: The vinyl
sulphone sodium sulphate radical of a Remazol-type reactive dye molecule and
how it attaches itself, by way of covalent bonding, to fibre polymers.
Properties
of reactive dyes
Washing-off: Textile materials which are coloured
with reactive dyes have to be thoroughly rinsed and scoured.
If the products you look for are not in our catalog we would be pleased to offer our custom synthesis service. TDAF
ReplyDelete