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This will help you alot in under standing about leuco dye and its modern applications
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CHEMISTRY AND APPLICATION OF LEUCO DYES
PRESENTED BY:
ASMA MUQADASROLL # 7632
Contents
Dyes Natural & synthetic Dyes Leuco Dyes Application Method Properties Two forms of Leuco Dyes Classes of Leuco Dyes Applications Limitations References
Dyes
The colored, ionizing and aromatic organic
compound to which it is being applied. Dyes are applied to numerous substrates
e.g. textile, ,plastic, paper, etc. Certain kind of dyes can be toxic,
carcinogenic or mutagenic and can pose as
a hazard to health. Dyes are the larges group that can easily
be influence to our liking.
Natural and Synthetic Dyes Natural dyes are get from natural resources such as plants, invertebrates and minerals. The first synthetic organic dye, mauveine, by William Henry Perkin in 1856.Synthetic dyes replaced the natural dyes.Cost less, range of new colors.Imparted better properties to the dyed materials. Special and high technology application .
Dyes Give Colors Due to the presence of Chromophore. Chromophores are the groups which imparts color.
Leuco Dyes
Certain leuco Dyes insoluble in water.The term Leuco, meaning white and was
applied to the reduced form of vat dyes. Change color on oxidation or with
fluctuating of temperatures. The products found in forms of slurry,
powder, solvent-based ink, epoxy, master
batch, etc.
Method of Application
These dyes are insoluble in water. Reduce with sodium hydrosulphite yield
alkali soluble forms (Leuco-compounds). It is in this form they are introduced into the
fabric. The reducing operation carried out in
wooden vats.
…………… After the reduction, dye has been absorbed in
the fiber. The original insoluble colored dye is
reformed by oxidation with air or chemical. These dyes are used to dye
cotton etc. Very fast because of their
insolubility in water. e.g. Indigo
Forms of Leuco dyes
Colorless. Colored when changing temp.
e.g.
Spiro form Oxazine form
Classes of Leuco Dyes
1.Triphenyle
methane2.Sulfur Dyes
3.Indigo
Dyes
1.TriphenylemethaneAniline green, malachite green, or china green Synthesis
Applications of Malachite Green
Used pharmaceutically in dilute solution as a local antiseptic. Effective against fungi and gram-positive bacteria. In the fish-breeding industry it has been used to control the fungus Saprolegnia . Used as a dye for silk ,wool, jute, leather and to dye cotton that has been mordanted with tannin.
Sulfur Dyes
Inexpensive complex reaction mixtures
of selected aromatic compounds with
sodium polysulfide.
SynthesisSulfur black
2
NH2
R1
2S
S
N
R1
R2
H
R2
R1
S
NaOHR2
-H2S
-NH3
S
N S
S
N
R1
R2
H
R3
H
R4 R4
R2
R1
8C4HBr
C4H9OH
S
N S
S
N
R6
R9
R7
R9
R8 R8
R6
R5
8HBr
R5
R7
Applications
Used for black, blue, brown, khaki and green colors.
Applied to cellulosic fibers and blends of cellulosics with polyester, nylon and acrylics.
Excellent results at a relatively low cost. With good application methods, sulfur dyes
are extremely wash-fast. Not fast to chlorine bleaching.
…..…..
Dark and medium colors are most common Light colors can be produced by special
procedures involving:• Blended reducing agents. • Blends of surfactants. • Controlled oxidation.• Preparation methods like
Mercerizing and bleaching.
Indigo Dyes
Indigo dye is an organic compound with a distinctive blue color.
Natural indigo get from a plant ‘indigofera tinctorie’.
1st Synthetic indigo replace natural product in textile trade in 1897.
Synthesis
Indigo Dye
Application of Indigo Dyes Use as a dye for cotton yarn, for the
production of denim cloth for blue jeans. Use for dyeing wool and silk. ’Qing Dai’’ a Chinese name for Indigo
natural it has a salty taste and cooling properties.
Application of Other Leuco Dyes A wide range of organic leuco dyes are
available changing color between -5 °C and 60 °C.
Application wherever sharpness of the temperature change is not important.
Novelties such as bath toys, color changing spoons, mugs and cups.
Microwave temperature indicators on food packaging
Color Changing Cups
Thermal paper
Hair Color
Battery status indicators The Duracell indicator makes use of leuco dyes applied to a resistive strip indicating the heating temperature of the strip that is related to the battery's current deliver.
Color Changing Ducks
The color changing ducks are covered with a layer of leuco dyes.
Cold
Hot
Flat Thermometer
MicroencapsulationProcess in which tiny particles are surrounded by a coating to give small capsules of many useful properties. Leuco Dyes require a special system i.e.
combination of chemicals. This process is effectively shown in the
photo-microgh.
Thermo chromic inks
These are very high temperature uses Leuco Dyes change color with changes in temperature.
LD's are reversible.
It takes about a 5ºF (3ºC) temperature change for the LD to change color.
Cold Activated Thermo chromic Ink
It is used on labels and packaging to create a color change when cooled. (Clear to Color at 15ºC / 59ºF).
Touch Activated Thermochromic Ink:
• It will vanish when rubbed or touched to reveal an image or another color printed beneath. (ColortoClearat31ºC/88ºF).
High Temperature Thermo chromic InkIt is designed to change color just below the pain threshold alerting consumers and users to a safety hazard - Too Hot! (Color to Clear at 47ºC / 117ºF).
References 1. Chemistry and Applications of Leuco Dyes by Ramaiah Muthyala
Springer, 30-Jun-1997. 2. Industrial Dyes, Chemistry, Properties, Application by Klaus Hunger 3. Kolorjet Chemicals Pvt. Ltd. 4. LCR Hall crests Thermodynamic Leuco Dyes. 5. Gilbert N. Lewis, Jacob Bigeleisen J. Am. Chem. Soc.,
Photochemical Reactions of Leuco Dyes in Rigid Solvents. Quantum Efficiency of Photo-oxidation., 1943, 65 (12), pp. 2419–2423
6. Thermochromism in commercial products" M A White & M LeBlanc 7. Journal of Chemical Education, Vol 76, No 9, P 1201, Sept 1999. 8. en.wikipedia.org/wiki/ Leuco _dye. 9. Marjan Kooroshnia The Swedish School of Textiles, University of
Boras, Boras Sweden. [email protected]
THANK YOU