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8/8/2019 Yellowing of Wool in Dye Bath4
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Yellowing of Wool In Dye
Bath
BY : Hemant GhanGhor&
Patanjal Kumar
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.1 Introduction2.
.3 Types of yellowing4.
.5 Causes of yellowing
6..7 Mechanism8.
.9 Effect of various parameter pH temperature
time
.6 Effect of bleaching and whitening7.
.8 Prevention of yellowing9.
.10 Measurement of yellowing
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Introduction Wool dyeing
It is carried out at boil= -Ph 2 7
For prolonged time
Due to which wool fibre is modified in several ways
Modification or damage results in unacceptable level of yellowing
During bleaching and whitening process also the strength of wool fibre. ,is lost When bleached and whitened fibres are dyed at boil due to dye
bath heat wool fibre are.further damaged and result in yellowing of wool Yellowing of wool
.also occurs during sun drying
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ypes of yellowingYellowing of wool
Hydrothermal yellowing photo yellowing
( )Occurs during dyeing hydrolysis of peptide bonds depanding on the condition
,exposure sunlightmay either yellow wool or
bleach it
254 nm UV light 331 nm UV light 398 nm UV light
Irradiation in ambient conditions UV below 331 nm increases visible light above
.Causes wool to appear green Wool yellowness 398 nm induces( )due to formation of two chromophores photobleaching
Fade rapidly in post irradiation reactionsTo leave a residual yellow colour
Thermal yellowing
:-occurs duringExtended dyeing at boilIn setting with superheated steam ( > )Drying for extended time Ph 7
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auses of yellowingDamage of wool fibre
.1 ( )Photo oxidation of CYS cystine is the most damaging reaction
.2 (Hydrolysis of peptide bonds in hot acidic liquors particularly at aspartic)acid residues
.3 Few carbonyl groups are detachable when wool is wet show pronouncedyellowing
.4 In dry state due to irradiation of wool minor amount of -keto acids becomesdetachable
Wool
Protein fibres containing cystine bonds
Protein are long polymers of amino acids bonded by peptide linkage
amino acids peptide bonds
cystinebonds cell membrane complexAnd other non keratinous
region cleavage of the peptide
-N Cbond produces soluble proteins
fibrestrength loss known as wool gelatins
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Amino acids of wool
Acidic amino acids and their - ( . ,amides eg Aspartic acid glutamic)acid etc
Lysine Basic amino acids Histidine Tryptophan
Serine
Amino acids with hydroxyl groups in the side chainThreonine
Tyrosine
( , ,sulphur containing amino acids cystine cysteine methionine.)etc
Amino acids without reactive groups in the side chain
Proline
Isoleucine
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The residues of amino acids extensively damaged by prolonged exposure tosunlight are
, , , , , , , .TRP PHE THR MET ILEU LEU PRO HIS etcMechanismR R
R R h CH C NH CH C CHC NH 2 + C C
O O O O O
This reaction is implicated both with fibre strenght loss and.subsequent susceptibility to hydrothermal yellowing
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ffect of various parameters
Y e
l l
o w
n e
s s
I n
d e x
pH
Effect ofpH
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Ye
ll
own
ess
In
dex
Temperature
fect of temperature
ffect of various parameters
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/Time h
Ye
ll
ow
ness
in
dex
Effect oftime
At ph 3
ffect of various parameters
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hotostability of wool:-Natural wool more photo stability
Ox datively bleached with H2O 2 :-stability furtherreduced
:-FWA treated wool it yellows wool rapidly in sunlight
Principal factors which influences the observed colourchange of wool when exposed toradiation :-
Wavelength distribution of incident light Presence of oxygen presence of water processing history the wool
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ffect of bleaching and whitening
whitened
bleached
natural
whitened
bleached
natural
(Exposure time days) (Exposure time days)
C h
a n
g e
i n
y e
l l
o w
n e s s
i n
d e x
C h
a n g
e
i n
y e
l l
o w
n e s s
i n
d e x
0
10
20
0
10
20
0 2 4 0 2 4
DRY WET
.1 > >Decreasing order or strength of wool fibre natural bleachedwhitened
.2 :Disappointing aspect of wool bleaching and whitening the products are lessstable in colour than before
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Commercial bleaching of wool
ffect of bleaching and whitening
Oxidative process(Using alkalineH2O2)
Reductiveprocess(using hydros or
thiourea dioxide)
Double bleaching process(First oxidative H2O 2bleaching then reductive
sodium dithionite)bleaching
Whitest wool isobtained
To further improve whitenessWA treatment
( it is carried out either after oxidative bleaching or after reductivebleaching )
It absorbs UV light and emits bluefluorescence( ) Wool appears much brighter
,Yellow rapidly when expose to sunlight specially in wet:-Cause superoxide generation via photo induced electron transfer
:-Example FWA Sulphonated stilbene
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revention of wool dye bath yellowingMethods of prevention
.1 Pretreatment with HA
.2 By adding sodium bisulphite to dyebath
.3 Addition of H2O 2 to dyebath after exhaustion
retreatment with HA( )In mildly acidic dye bath
( . % )Add HA 0 2
% - %50 70 reduction
+ . +HA carbonyl gr Aldoximes ketoximes
-retreatment of wool with HA only transient protection
retreatment with HA neutral medium dyeing no yellowing
cidic conditions predominate in wool dyeing so HA must be present at an.dequate amount to minimize hydrothermal yellowing
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easurement of yellowness( - ) .It is measured in the term of Y Z value
( - ) (To summarize Y Z yellowness measurements will usually rank between 0 very) - ( )good whiteness to 8 12 very yellow and
= . + . + . + . Weighted average of yellowness 3 5 2 6 2 3 5 5 1 4 5 4
10= .4 9
LOT Clean wt .(tonnes)
Yellowness (Y-Z)
A 2 3.5
B 3 6.2
C 1 5.5D 4 4.5
WA 10 4.9
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THANKS