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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