Page 94 - Shawl Weaving Artisan - TT

Application of direct dyes Stripping: Most direct dyes can be stripped of the use
of stripping salts (Sodium Hydrosulphite) and/or by using
Direct Dye is a class of dyestuffs that are applied
directly to the substrate in a neutral or alkaline bath. a chlorine bleaching agent such as sodium hypochlorite,
The direct dyes are one of the cheapest groups of dyes without harmful effects on the fibers.
used for dyeing cotton and other cellulosic materials. Color fastness properties of direct dyed material:
They produce full shades on cotton and linen without Generally these dyes are used where high wash fastness
mordanting and can also be applied to rayon, silk, and is not required.
wool. Direct dyes give bright shades but exhibit poor Wash fastness: Poor unless treated with suitable dye
wash fastness. Various after treatments are used to fixing agent and/or fastness improving finishing agent.
improve the wash fastness of direct dyes, and such dyes
are referred to as “after treated direct colors”. Direct Light fastness: Good
Dyes are molecules that adhere to the fabric molecules Rubbing fastness: Moderate to Good
without help from other chemicals. Direct dye is defined
as anionic dyes with substantivity for cellulosic fibers, Chemical wash fastness: Poor
normally applied from an aqueous dye bath containing Reactive dyes
an electrolyte, either sodium chloride (NaCl) or sodium
sulfate (Na2SO4). Introduction
Dyeing method of direct dye A dye, which is capable of reacting chemically with a
substrate to form a covalent dye substrate linkage, is
The color is pasted well and dissolved in boiling water to known as reactive dyes.
get a lump free solution. An addition of 0.5–2 g/l sodium
carbonate may be advantageous when applying dyes of Reactive dyes are so called because this is the only type
only moderate solubility in full depths. of dye, which has reactive group, and that reactive group
reacts chemically with fibre polymer molecules and form
• The dye bath is set at 40°C, covalent bond. This covalent bond is formed between
• Raise to the boil at 2oC min, the reactive group and terminal –OH (Hydroxyl) group
of cellulosic fibre and WOOL FIBER or between reactive
• Hold at the boil for 30–45 min, group and terminal -NH2 (Amino) group of polyamide

• During hold add 10–15 g/l of sodium chloride or polymer. The strength of this covalent bond is more than
Glauber’s salt. Light shades are dyed without or lesser ionic bond, hydrogen bond. Thus the reactive group
addition of salt. becomes an integral part of the fibre.
• Improved yields can be achieved when applying full The reactive dyes constitute the most commonly used
depths by cooling to 80°C at the end of the period at class of dyes for dyeing cellulosic textiles, because of
the boil, adding a further 5 g/l salt and rising to the their good all-round properties, such as water solubility,
boil again ease of application, variety of application methods,
availability of different shades, brightness of color shades,
• Dye bath variables which must be considered for level good to excellent wash and light fastness and moderate
dyeing, price. Reactive dyes may have poor fastness to chlorine
1 Temperature of Dyeing and rate of heating bleach.

2 Electrolyte concentration and addition By reactive dyes the following fibres can be dyed
3 Time successfully:
1 Cotton, rayon, flax and other cellulosic fibres.
4 Dye solubility
2 Polyamide and wool fibres.
5 Use of levelling agent
After treatment of direct dyed material 3 Silk and acetate fibres.
It covers a wide range of color spectrum and includes
The wet fastness properties (particularly washing, water
and perspiration) of virtually all dyeing of direct dyes are shades varying from bright to heavy dark like,
inadequate for many end uses but notable improvements • Violet
can be brought about by after treatments.
• Blue
• Diazotisation and development
• Green
• Metal salt treatments • Red

• Cationic fixing agents
• Black
• Formaldehyde treatment
• Yellow etc.
• Cross linking agents and resin treatments

84 Textile & Handloom: Shawl Weaving Artisan : (NSQF - 2024) R.T. Ex.No 1.6.55-65