Chemical nature of vat dyes

After treatment of Direct dyes After treatment with developer -Denim(which gets its name from the French city of îmes(de îmes)) is a rugged cotton twill textile. = H 2 H 2 2 2Cl = H 2 H 2 = 2 - Denim has been in American usage since the late 18th century. The word comes from the name of a sturdy fabric called serge, originally made in îmes, France, by the André family. riginally called Serge de îmes, the name was soon shortened to denim. After treatment with cationic activator - Denim was traditionally colored blue with indigo dye to make blue " jeans ", although "jean" formerly denoted a different, lighter cotton textile; C 16 H 33 Br C 16 H 33 Br C 16 H 33 D-S 3 abr - the contemporary use of jean comes from the French word for Genoa, Italy (Gênes), where the first denim trousers were made. 121 122 Vat Dyes Application area : dyeing and printing of all types of cellulosic fiber, and of blends of cotton with polyester. IDIG, probably the oldest dye known to man, is one of the most important members of this group. atural indigo extracted from the plant 'Indigofera tinctorie' was used by the Egyptians in 200 BC. The first synthetic indigo was introduced to the textile trade in 1897 & had the effect of completely replacing the natural product. Chemical nature of vat dyes - The large majority of vat dyes are based on the anthraquinonoid or the indigo (or thioindigo) chromophores. Anthraquinonoid dye (C.I. Vat Yellow 1) Cl CH 3 S S CH 3 Indigoid dye (C.I. Vat ed 6) - Despite their complex molecular structures, vat dyes have one common feature : all contain carbonyl group. Insoluble pigment Alkali reduction Acid oxidation a Solubilized sodium leuco vat 123 - They are insoluble in water & become water soluble when reduced in the presence of an alkali. - After dyeing, the fabric is oxidized & the dye again becomes water insoluble. 124

Chemical nature of vat dyes - Vat dyes have outstanding washfastness and lightfastness as a class. An exception to this rule is the vat dye indigo which has very poor washfastness : awnings, curtains, upholstery, military and naval uniforms, and high quality gabardines Application of vat dyes - Application of vat dyes requires the following steps (a) Preparation of the sodium derivative of the reduced (leuco) compound (vatting) (b) Impregnation of the fibers with the leuco compound (c) xidation in the fibers to the insoluble vat dye (d) insing and soaping - High fastness to bleaching is another strong point of the anthraquinonoid group. : white areas of the pattern can be safely bleached out after weaving. : good-quality shirtings, tablecloths, towels, sportswear, high-quality overall, fabrics for women s and children s clothing and tropical suitings, and yarns and effect threads where repeated washing will be required. riginal (insoluble) Leuco Acid (Leuco Vat dye) (insoluble) Sodium salt of leuco form (soluble) xidized (insoluble) - The biggest disadvantage of vat dyes is their relatively high cost. - The range lacks scarlet, maroon and wine shades. - reduced to leuco forms, whose molecules possess hydroxyl groups. - Although the leuco form is insoluble in water, it can be rendered soluble in alkali and the dissolved material can be oxidized back to the original vat dye. 125 126 Solubilized vat dyes - Because of the time consuming & costly procedure in reducing vat dye into a water-soluble complex, dye manufacturers have produced a stabilized water-soluble vat dye - Although it is possible to isolate the reduced form of the dye, it is too readily oxidized in air for the manufacturer to provide the dyer with the leuco compounds. - It is, however possible, to convert the leuco acid into the leuco ester, a derivative that has greater resistance to oxidation and greater solubility in water. - Such esters can be formed by the reaction of a hydroxyl group of a leuco acid with sulfuric acid, forming a sulfuric ester. Solubilized vat dyes - The sodium salts of such esters are stable and can be stored until required for use. - Since the ester group is only weakly attached to the rest of the dye molecule, it is easily removed by the action of soidum nitrite in dilute sulfuric acid. - The regenerated leuco compound may then be oxidized back to the pigment form - Solubilized vat dyes are less rapidly taken up than are the more conventional vat dyes and are mainly used for the production of pale shades. - An interesting property of solubilized vat dye is their sensitivity to light in solubililzed state. : used for photographic prints on fabric. 127 128

Sulfur dyes The first Sulfur dye was discovered in France in 1873, & further work done by aymond Videl enabled the manufacture of 'Videl black". Its outstanding fastness to light, washing & boiling far surpassed any cotton black known at that time. The general disadvantage of the Sulfur dyes that they produce dull shades & lack a red. ne of the earliest and best-known sulfur dyes is CI Sulphur Black 1, which is a popular black with good fastness properties still in use today educed and applied as soluble leuco compounds that need to be kept under alkaline conditions, but sulfur dyes need only sodium sulfide to act as both alkali and reducing agent. Ar-S-S-Ar reduction with a 2 S Ar-S- Ar-S- Sulfur dyes The main advantage lays in their cheapness, ease of application & good wash-fastness. The use of Sulfhur dyes is restricted to dull brown, Khaki & avy shades, where a good wash but not boil-fastness is required. Most Khaki & avy overalls are dyed with Sulfur dyes. An outstanding member of this family is Sulfur black. It dyes all cellulose fibers, but particularly linen & jute, to a lustrous & deep black with excellent wash & light fastness. ne disadvantage of black sulfur dyes is that dyed material stored under conditions of high humidity and temperature can lose its natural strength, probably due to inadequate washing-off after dyeing ( generation of sulfuric acid in the fiber, arising from the presence of sulfur) Heavy drill fabrics, corduroys, overalls, denims, awnings and canvas 129 130 Sulfur dyes - Use Sulfur dyes are dyed from a dye bath containing Sodium Sulfide & common or Glauber Salt, & are oxidized by airing or with some oxidizing agents (Sodium dichromate or hydrogen peroxide) in a fresh bath. After exhausting the dyebath for approximately 1 hour at 60-90 the fabric is thoroughly rinsed and exposed to the atmosphere, where oxidation generates the mechanically entrapped insoluble pigments The word 'Azoic' is the distinguishing name given to insoluble azo dyes that are not applied directly as dyes, but are actually produced within the fiber itself. This is done with impregnating the fiber with one component of the dye, followed by treatment in another component, thus forming the dye within the fiber. Complicated application; limited color range (red, orange, navy among the best); bright shade at moderate cost; generally good wet fastness but moderate to poor dry cleaning & rubbing fastness CH 3 Azoic dyes H2 2 H C H 131 132

Azoic dyes 1) Dissolving coupling components and Impregnation H ah a 2) Coupling with Developer Acid Dyes and Their Application to Polyamide 1 a 1 1 2 X H 2 2 Cl 2 X HCl 2 2 2 1 = H, CH 3 X = BF 2 = H, Cl, CH 3, ZnCl 2, aphthalenesulfonic acid 3 H H H 2 1 = = = 2 2 a 3 S S 3 a 133 134 Acid dyes Acid dyes : structures - The AATCC Buyers Guide lists more than 1000 acid dye products. About 70 of these C.I names are for products used almost exclusively by the leather industry (40 are browns and 10 are blacks). - The color gamut is extremely broad (eds 26%, Blues 22% and Yellows 17%): the reason fiber reactive dyes have such a wide color gamut is that they are based on many of the same acid dye molecular structures. - Acid dye molecules provide a wide range of colors covering several different chromophoric systems, based on anthraquinone(a), azo(b), premetallized(c) and triphenylmethane(d) structures - These dyes comprise a large number of dyes used for the dyeing of wool, silk & nylon. - Most of the acid dyes are sulfonic acid salts, but there are a few containing carboxyl groups. - They vary considerably in their basic chemical structure, but have one common feature - Acid dyes are sufficiently soluble to allow direct application from an aqueous solution and they dye from an acid dye bath. a 3 S = CI Acid Yellow 23 Pyrazolone (High light fastness) Ca S 3 a 135 136

Acid dyes : structures Dyeing principle of acid dyes H H H 3 CHCH H 2 CHCH H 2 CHC Acid H atural H Base 1) Step 1 HA H A Isoelectric point :ph 4.9 (Wool) [C] A Et 2 Et 2 D-S 3 a D-S 3 2) Step 2 a Time D-S 3 H CI Acid Blue 1 S 3 a 3 S C 2 H 5 CH 2 C CH 3 CH 3 Cl C 2 H 5 CH 2 S 3 - Di-sulfonated monoanionic triphenylmethane dyes (C.I. Acid Green 22) A H 2 CHCH H A H 3 CHCH D-S 3 a A H 3 CHCH D-S 3 H 3 CHCH aa 137 138 - Charges and substantivity variation with ph H- H 3 (X) CH H 3 (X) C H H 2 (X) C - H- H Charges and substantivity variation with ph ex. Approximate states of nylon 6,6 ph -CH -C - -H 3 -H 2 1.35 90.91 9.09 100 0 2.35 50 50 100 0 3.35 9.09 90.91 100 0 4.35 0.99 99.01 100 0 7.78 0 100 99.01 0.99 8.78 0 100 90.91 9.09 9.78 0 100 50 50 The attractiveness of anions for those positive charges within protein and polyamide fibers, which are not neutralized by the carboxylate anions within the fiber will increase rapidly with the increasing acidity in the fiber. 139 H3 CH CH nylon 6,6 fibre ph < 3.5 H 3 - C - C nylon 6,6 fibre ph 3.5-10 H 2 - C - C nylon 6,6 fibre ph > 10 140

Dye uptake of acid dye on nylon 6,6 Dye uptake of acid dye on nylon 6,6 Dye S 3 - H 3 Dye Dye Dye Dye - S 3 H 3 - S 3 - S 3 - S 3 H 3 H 3 H 3 Ionic interaction molecular glue increasing dye uptake verdyeing H 3-CH-CH H 3-CH-C - H H - H2-CH-C - ylon 6,6 fibre Water / high temperature / high ph increases dye mobility. Hydrophobic aftertreatment minimises dye mobility 141 rapid dyeing isoelectric point ph 2 ph 4 ph 6 ph 7 ph 8 142 Classification of acid dyes - Acid dyes were subdivided into groups which reflect the wool processing technology: the strongly acidic, leveling (equalizing) acid dyes), the half milling dyes and the super milling(neutral dyeing) dyes. - The word milling refers to the processes by which wool fabrics were converted into felts by mechanical beating treatments in alkaline solutions. - Dyes which could be applied to the wool fabric prior to milling and which survived the alkaline treatment were fast to milling. Classification of acid dyes The connection between the leveling properties of the dyes and their subsequent fastness to wet treatments allows acid dyes to be classified into groups according to the application proceduresa. Levelling (Equalizing) acid dyes : level well but have poor fastness to wet treatments. Sulfuric acid is incorporated into the dye bath. b. Milling acid dyes : have poorer leveling properties but better fastness to wet treatments. They are applied using a weaker acid such as methanoic or ethanoic acid. c. Super milling acid dyes : Their leveling properties are poor but their fastness to wet treatments is excellent. 143 144

a. Levelling acid dyes: These dyes produce bright dyeing. The main feature is their good leveling properties. They are dyed from a dye bath containing strong acids (Sulfuric or formic acid to give ph of 2.5-3.5 which promotes exhaustion and sodium sulfate aids leveling by providing sulfate ions). These dyes exhibit low wash & light fastness. b. Milling acid dyes: Selected because of their high & light fastness & are extensively used for dyeing woolen fabrics that are subsequently milled. Adequate leveling through the controlled formation of ionic links using a strongly acidic dyebath is no longer possible, because the overall attractive forces are too strong. For these dyes the dominance of ionic forces then needs to be suppressed by reducing the acidity to a ph of 4.5~5.5 using acetic acid instead of sulfuric acid, and aggregation is controlled by raising the temp. These dyes require great care in application because uneven dyeing are difficult or impossible to rectify. 145 146 Dyeing theory of milling acid dyes As a rule the milling type acid dyes have larger molecules and also a high planarity, so that they present abundant opportunities for hydrogen bonding and van der waals forces to come into play. c. Super milling acid dyes : have long hydrocarbon chains ( C 12 H 25 ) induced into their dye molecules. H HC H H 2 = = = C 12 H 25 CH S 3 H 3 a 3 S S 3 a Action of electrolytes -2-2 D-S 3 H 3 -W 2a S 4 S 4 H 3 -W 2a D-S 3 The presence of electrolytes reduces the negative potential of the fiber, making easier the approach of the dye ion to within the zone of influence of the retaining forces. The highest standard of wet fastness are usually obtained using these super milling acid dyes, a group that includes dyes able to withstand the very severe wet milling processes associated with the preparation of wool fabric. 147 148