This document discusses direct dyes, which are anionic dyes used for cellulosic fibers. Most direct dyes have an azo or phthalocyanine structure and provide bright colors ranging from yellow to blue. The document describes the chemical classification and properties of various direct dyes, including their decomposition during dyeing and use in assessing cotton maturity. It also covers classifying dyes based on dyeing properties and treating dyed fabrics with metal salts or cationic fixing agents to improve wet fastness.

1. DDyyeeiinngg wwiitthh DDiirreecctt DDyyeess
TTeexxttiillee CChheemmiissttrryy
1144 JJuullyy 22000055
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2. iinnttrroodduuccttiioonn
 DDiirreecctt ddyyeess aarree ddeeffiinneess aass aanniioonniicc ddyyeess wwiitthh
ssuubbssttaannttiivviittyy ffoorr cceelllluulloossiicc ffiibbeerrss
 SSiimmppllee ddyyeeiinngg pprroocceessss
 NNeeeedd aafftteerrttrreeaattmmeenntt ttoo eennhhaannccee wweett ffaassttnneessss
 AAllssoo uussee iinn lleeaatthheerr ddyyeeiinngg aanndd ccoolloorraattiioonn ooff
ppaappeerr
 DDyyeess hhaavvee bbeeeenn rreeppllaacceedd bbyy rreeaaccttiivvee ddyyeess,, wwhhiicchh
hhaavvee bbeetttteerr wweett ffaassttnneessss aanndd bbrriigghhtteerr sshhaaddeess iinn
mmaannyy hhuueess
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3. SSttrruuccttuurree aanndd pprrooppeerrttiieess ooff
ddiirreecctt ddyyeess
 MMoorree tthhaann 7755%% aarree uunnmmeettaalllliisseedd aazzoo ssttrruuccttuurree,,
mmaaiinnllyy aarree ddiissaazzoo aanndd ppoollyyaazzoo ttyyppeess
 DDiissaazzoo ==>>bbrriigghhtt yyeellllooww ttoo bblluuee
 PPoollyyaazzoo ==>> dduullll ggrreeeennss,, bbrroowwnnss
 CCooppppeerr--ccoommpplleexx ddiirreecctt ==>> dduullll vviioolleett,, nnaavvyy,, bblluuee
bbllaacckk
 SSttiillbbeennee && tthhiiaazzooll ==>> yyeellllooww ttoo rreedd
 PPhhtthhaallooccyyaanniinnee ==>> bbrriigghhtt bblluuee
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4. CChheemmiiccaall ccllaassssiiffiiccaattiioonn
5500%% ooff aallll ddiirreecctt ddyyeess aarree
ddiissaazzoo ssttrruuccttuurree
CCII DDiirreecctt BBlluuee 11
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5. CChheemmiiccaall ccllaassssiiffiiccaattiioonn
Copper complexes only possible with direct
dyes containing o,o’-di-hydroxy-azo
CI Direct Blue 76
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6. CChheemmiiccaall ccllaassssiiffiiccaattiioonn
Phthalocyanine direct dyes
are mainly in the form of
sulphonated copper
phthalocyanine
 Give brilliant turquoise
blue colours
 High light fastness
 Poor wet fastness
 Poor exhaustion
 Dyeing temp at about 95oc
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7. CChheemmiiccaall ccllaassssiiffiiccaattiioonn
The most significant breakthroughs of direct dyes
made by Sandoz, Indosol SF
 Use with Indosol fixing agent
 Comprise of 12 dyes
 All copper complexes selected from Solar range
Indosol Violet SF-B CI Direct Violet 66
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8. DDeeccoommppoossiittiioonn ooff ddiirreecctt
ddyyeess dduurriinngg ddyyeeiinngg
 Prolonged dyeing time can cause dye decomposition
by the reduction of azo linkage, especially in alkali
condition
 Buffering to pH 6 with ammonium sulphate is
preferred
 Mild oxidizing agent such as sodium m-nitro
benzene sulphonate are occasionally useful
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9. DDiirreecctt ddyyee aass ccoottttoonn
mmaattuurriittyy aasssseessssmmeenntt
 The Red-Green test ; the mixture of
 CI Direct Red 81 and
 CI Direct Green 26
 The Red-Blue test ; the mixture of
 CI Direct Red 151 and
 CI Direct Blue 10
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10. CCllaassssiiffiiccaattiioonn aaccccoorrddiinngg ttoo
ddyyeeiinngg pprrooppeerrttiieess
Based on four parameters – migration (or leveling
power), salt controllability, influence of
temperature and liquor on exhaustion
Direct dyes are classified as follow:
Class A self-leveling, dyes of good migration or
leveling properties
Class B not self-leveling, but can be controlled by
addition of salt to give level result; described as salt-controllable
Class C not self-leveling, high sensitive to salt, the
exhaustion can be controlled by addition of salt and
control of temperature; described as temperature-controllable
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11. Aftertreatment of direct
dyes
Metal salt treatment
 Treatment with solution of 0.25-2% copper sulphate
and 1% acetic acid for 20-30 mins at 60c
Cationic fixing agent
 Improved wet fastness at temp below 60c
 Hue changes may occur
 Light fastness may be reduced
 Chemicals are quaternary ammonium, pyridinum
compound, melamine derivatives etc
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