Dye: Colorant which is homogeneously dispersed in the dye medium Usually soluble Naturally occurring or synthetic organics

Pazyryk carpet (Siberia) 5th century BC Peruvian textile 600-200 B.C.

Medieval Guilds of Master Dyers Formed in Germany in the 12th century Apprentice system Dye recipes were heavily guarded secrets

Development of Trade Routes Textile trade beginnings in 2,000 B.C. the “Silk Road” sea routes from the Americas (15th century) East India Trading Company (17th century) Exchange of not only textiles but also designs, ideas and dyestuffs China Europe

Three Classes of Natural Dyes Substantive dyes Easiest to apply to fibers No need to use other substances to enhance dyeing Vat dyes Involve chemical change of dye through “fermentation” or “chemical reduction” to make it soluble Adjective dyes (Mordant dyes) Require another chemical to develop color and “fix” it to the fiber

Dyes from Snails Tyrian Purple or “Royal Blue” 9000 snails to obtain 1 g of dye Used primarily before 8th century A.D. to dye wool and silk Chemically it is 6,6’-dibromoindigo

Dyes from Bugs Kermes — the most ancient dye in Europe 70,000 female oak beetles produce 1 pound dye Cochineal — Mexico and Central America Mexican cactus beetle

Kermes, Cochineal — Carmine Chemically similar structure, light sensitive Dyed wool and silk — “carmine red”

Dyes From Plants Indigo — used since 2000 B.C. Woad Extracted from Indigofera tinctoria “Navy Blue” of English sailors Blue jeans Insoluble in water Must be chemical reduced to soluble leucoindigo to use as dye Woad Member of the mustard family A common weed in temperate climates Leaves contain same chemical as indigo but in lower amounts Celtic war paint and tattoos Braveheart Blue robes of priests

More Dyes From Plants Madder — “Turkey Red” Root of madder plant found in Europe and Asia Prepared as a “lake” with Al(OH)3 British “Redcoats” Alexander the Great used it to simulate blood Chemically — Alizarin and Pupurin Synthetic alizarin prepared in 1875

Methods of Application Dye and Substrate can interact through... 1. ionic forces 2. hydrogen bonding 3. van der Waals forces 4. covalent bonds Dye Substrate

Types of Dyes by Application Acid Dyes Basic Dyes Mordant Dyes Direct Dyes Fiber-reactive Dyes Vat Dyes

Functional groups for acidic and basic dyes -ROOH acid sulfonic acid, carboxylic acid -NH2 amine base Acid + base = salt (+) (-) -NH2 + -OOH  NH3+ + ROO– from base from acid

Acid Dyes Fiber DYE SO3- Sulfonic acid group NH3+ Basic amine group Acidic dye (-) (+) Basic fiber DYE SO3- Sulfonic acid group Fiber NH3+ Basic amine group Wool, silk, nylon have amine groups

Basic Dyes Fiber Basic Dye (+) (-) Acidic Fiber DYE NH3+ Basic amine group Fiber -OOC Carboxylic acid group Wool, silk, leather, acrylic fibers have carboxylic acid groups

Mordant Dyes Have no natural affinity for fiber Must use a “mordant” to link dye and fiber Dye Fiber Mordant salts of Fe2+, Sn2+, Cr3+, and Cu2+ hydroxides of Al, Mg, Ca, and Ba tannic acid

Direct Dyes Fiber Polar dye Polar Fibers Dye applied from a hot water solution DYE N Fiber HO H Polar group Hydrogen Bond Cotton and cellulose-based fibers Synthetic dyes

Fiber-Reactive Dyes Covalently bonded to fibers R—C—O—fiber R—C—S—fiber R—C—NH—fiber Developed in 1950’s Used primarily on cellulosic and protein fibers

Color Centers in Organic Dyes CHROMOPHORES — “color bearer” structural part of colored molecule which is responsible for its color Conjugated double bond systems Aromatic rings Azo groups —N=N— Carbonyl groups —C=O Quinoid rings

AUXOCHROMES —NH2 —OH —OR “color augmenting” groups functional group with non-bonded electrons which acts to strengthen or deepen the color and hue —NH2 —OH —OR

AZO Dyes first prepared in 1863 R—N = N—R Have widest range of colors of all dyes Contain the AZO Chromophore Generally lightfast R—N = N—R Azo group Brilliant colors ranging from reds to blues Methyl orange, Orange II, etc.

Orange II and Methyl Orange Both are azo dyes Azo Group HO HO 3 S N=N (CH 3 ) 2 N N=N SO 3 - Na + Orange II Methyl Orange

FD & C Food Colors Yellow No. 6 Red No. 40 FD&C Red No. 40 Allura Red Na +- O 3 S OCH CH N = N HO SO - + FD&C Red No. 40 Allura Red

CARBONYL Dyes Anthroquinone Dyes Originate from plants Contain several —C =O groups Multiple aromatic rings Originate from plants Coloring agents in flowers, fruits, vegetables

QUINOIDS Naphthaquinone Anthraquinone Red plant dyes and insect dyes

Alizarin, Cochineal, Kermes All are anthraquinone-based carbonyl dyes O OH CH 3 CO 2 H HO Cochineal Kermes Alizarin

FLAVONOIDS Structure of yellow plant dyes Luteolin (weld or Dyers Weed) OH HO O OH Quercitin (Oak bark) OH OH O

Indigo — a Carbonyl Vat Dye Indigo is insoluble in water Must be chemical reduced to leucoindigo Leucoindigo is soluble Used to dye cellulose fibers

TRIPHENYLENE Dyes Three aromatic rings attached to the same carbon atom C FD&C Blue 2

Fiber-Reactive Dye Structure Chromophore Reactive group Leaving group Mono chlorotriazinyl dye Procion Scarlet H-R, Cibacron Scarlet RP, Chlorine Reactive Red 3

Dichlorotriazinyl Dye Higher reactivity than monochloro dyes Procion Brillian Yellow M-6G, CI Reactive Yellow 1

Fastness in Dyes Stability of dyes towards light Dyes vary greatly in their lightfastness and colorfastness Undergo photo-oxidation and photo-reduction by light — dyes fade and degrade

Effects of Chemicals on Dyes H2O HCl NaOH CaCl2 Chlorox Na2S2O4 Madder Cochineal Orange II Methyl orange

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