1 reactive dyes
- 1. TEX 3101, WPT-II NUB FR 1 REACTIVE DYES Introduction: Reactive dyes are so called because their molecules react chemically with the polymers of some fibres to form a covalent bond between the dye molecule and fibre polymer. Reactive dyes are most readily used to dye cellulosic fibres like cotton, viscose etc. but it can be used to dye synthetic Nylon, and natural protein fibres. Cell-OH + HO- Cell- O- + H2O Cell- O- + Dye-Cl Cell-O-Dye + Cl- Where Cell-OH is the cellulose with a reactive hydroxyl group, Dye-Cl is the dye with its reactive chlorine atom, and Cell-O-Dye, the dye linked to the cellulose by a covalent bond. The role of the alkali is to cause acidic dissociation of some of the hydroxyl groups in the cellulose, and the cellulosate ion (Cell-0- ) reacts with the dye. General Dye Features: W-D- W: Solubilising group / Auxochrome group (-NH2, -NH-CH3, -OH, -COOH, -NO2) D: Chromogen Q: Bridge link (-NH-, -NHCO-, -NHSO2-, -NCH3-) X: Leaving Group (-Cl, -Br, -SH, -OCH) RG: Reactive groups (Vinyl Sulphone, Monochlorotriazine, Dichlorotriazine) The auxochrome/water solubilising group has the expected effect of improving the solubility, since reactive dyes must be in solution for application to fibres. Auxochomes intensify the hue of the dye molecule’s colour, makes the dye molecule more water soluble, and improves the colourfastness properties of the dyed or printed fibre. The bridging group links the chromogen and the fibre-reactive group. Frequently the bridging group is an amino, -NH-, group. This is usually for convenience rather than for any specific purpose. RGQ X
- 2. TEX 3101, WPT-II NUB FR 2 The reactive group is the only part of the molecule able to react with the fibre. Properties of Reactive Dyes: Dyes are soluble in water and anionic in nature. Makes covalent bonds with the fibre. A certain amount of dye is hydrolysed during dyeing (10-60%). Dyeing is carried out in alkaline conditions (PH = 10.5-12). Fastness to wash, rubbing, light, and perspiration are generally good. Easily applicable to cellulose as well as protein fibres (Wool and Silk). Comparatively cheap. Al kinds of shades are found. The mechanism of reaction of reactive dyes with cellulose is generally classified into two types- Nucleophilic addition reaction (Vinyl sulphone). Dye-SO2-CH =CH2 + Cell-OH Dye-SO2-CH2-CH2-O- Cell Nucleophilic substitution reaction (Monochlorotriazine). Cell- O- + Dye-Cl Cell-O-Dye + Cl- Classification of Reactive dyes: Classification of reactive dyes based on functional group: 1. Mono - functional 2. Bi - functional a) Homo - bi functional b) Hetero - bi functional 3. Tri – functional 4. Tetra – functional 5. Penta – functional Mono functional reactive dyes: DCT (Dichlorotriazine) MCT (Monochlorotriazine) MFT (Monofluorotriazine) TCP (Trichloropyrimidine) DFCP (Difluorochloropyrimidine) Vinylsulphone (VS) N N N Dye-HN Cl Cl N N N Cl Dye-HN NHR N N N Dye-HN Cl F N N Dye-HN Cl Cl Cl N N Dye-HN F Cl Cl Dye-SO2-CH=CH2 NHR
- 3. TEX 3101, WPT-II NUB FR 3 Classification of Reactive Dyes based on Application: The reactive groups of the various types of reactive dyes have different chemical structures and show a wide range of reactivity. They were originally divided into cold- and hot-dyeing types but many current ranges would be better called warm dyeing. The most reactive types, such as DCT reactive dyes only require a weak alkali such as NaHCO3 or Na2CO3 for fixation. The less reactive types such as MCT dyes need stronger alkalis such as Na2CO3 plus NaOH. Dyes Brand Fixation Temp˚ C Cold <40 Warm 40-80 Hot >80 Classification of Reactive Dyes based on Reactivity: Type PH Highly Reactive Dyes 10 Medium Reactive Dyes 10.5-11 Lower Reactive Dyes 11-12 Recipe: Reactive Dye(s) : 2% OWF (on the weight of fabric) Wetting Agent : 1 g/L Sequestering Agent : 1.5 g/L Anti-creasing Agent : 0.75 g/L Levelling Agent : 1.5 g/L Anti-Foaming Agent : 0.5 g/L Salt (NaCl/Na2SO4) : 40 g/L Soda Ash (Na2CO3)/NaOH/Mixed (PH =11) : 5 g/L M:L : 1:10 Temperature : 60°C The Three-Step Exhaust Dyeing Process: 1. The Initial Exhaustion Phase: Dyeing is started in neutral solution so that there is little likelihood of the dye reacting with the cellulose. During this stage of dyeing, some reactive dye will be absorbed by the fibres, the amount depending upon its substantivity power. This dye is capable of promoting level dyeing. Sodium chloride or sulphate will often be present initially or be added gradually to the dye bath during this phase to promote exhaustion. 2. The Fixation Phase: After the initial exhaustion phase, the PH of the dye bath is increased by complete or gradual addition of the appropriate type and amount of alkali. This causes dissociation of some of the hydroxyl groups in the cellulose and the nucleophilic cellulosate ions began to react with the
- 4. TEX 3101, WPT-II NUB FR 4 dye. The fixation process then results in additional dye absorption, to re-establish the dyeing equilibrium. Dye absorption from solution and reaction with the fibre then progress until no further dye is taken up. 3. The Post-Dyeing Washing-off: The rinsed dyeing contains dye bonded to the cellulose, absorbed but unreacted dye, as well as hydrolysed dye. There will also be residual salt and alkali. These are removed by successive rinsing in cold and then warm water. As much unfixed dye as possible must be washed out of the dyeing. If this is not done, desorption of this dye during washing by the consumer can cause staining of other material in the wash. Some unfixed dye is eliminated during the initial rinsing that removes salt and alkali. Thorough washing of the dyeing using a boiling detergent solution (soaping) eliminates the remainder. Soaping must often be repeated for deep dyeings. Colour Fastness properties of reactive dyes: Colour fastness to wash: Reactive dyes on cellulosic fibres give dyeings with good to very good fastness to washing and other wet processes. Apparent inferior fastness to washing is usually because of incomplete removal of unreacted and hydrolysed dye from the material by washing after dyeing. Colour fastness to light: Textile material coloured with reactive dye has a moderate to good light fastness and a rating is about 5-6.There are some reactive dyes with only fair light fastness. Colour fastness to Perspiration: Reactive dyes have good perspiration fastness with rating 4-5. Colour fastness to rubbing: Textiles dyed with reactive dyes have moderate rubbing fastness. Perspiration is slightly acidic and may affect textile materials coloured with reactive dyes and result in some fading. Colour Fastness to chlorine: When reactive dyes were first introduced, it was found that bleaches which contained chlorine, adversely affected some of these dyes. Problems/ Disadvantages in dyeing with Reactive Dyes: o One of the major problems in exhaust dyeing with many reactive dyes is the rather low level of fixation, particularly when using a high liquor ratio. Often less than 70% of the original dye reacts with the fibre. o Low level of fixation results in appreciable dye concentration in the dye house effluent. This environmental problem is compounded if high salt concentrations are also present. o If the amount of unfixed dye remaining in the goods is significant, there is a risk of the precipitated dye-auxiliary complex rubbing-off, particularly on wet abrasion. o Dyeings with a few red DCT reactive dyes on cotton are prone to increased colour bleeding because of the dye-fibre bond.
- 5. TEX 3101, WPT-II NUB FR 5 o There is always a risk of anionic reactive dyes being precipitated by calcium, magnesium or heavy metal ions in the water supply, or of the formation of insoluble hydroxides of these metals under the alkaline dyeing conditions. Trade Names of Reactive Dyes: Trade Name Company Country Procion I.C.I. UK Cibacron Ciba-Geigy Switzerland Drimarene Sandoz Switzerland Livafix F.Bayer Germany Remazol F.Hoechst Germany Cavalite Dupont USA Printing with Reactive Dyes A) The Choice of Thickeners: Sodium alginate. Starch. CMC (Carboxy-methyl Cellulose). Natural gums. British gums. Gum Tragacanth, etc. B) Fabric Preparation prior to printing: Fabric should be bleached or mercerized. Fabric should not be in neutral or slightly alkaline condition. No residual starch in the fabric. C) Different process sequences of printing: A) Steaming process (All in method): Print with alkali Dry Steam Wash-off Dry B) Dry heat process: Print with alkali Dry Cure Wash-off Dry C) Alkali-pad printing process (Two Phase Method): Print Without alkali Dry Pad with Alkali Steaming Wash-off Dry D) Air Development process: Print with alkali/ Print without alkali on alkali padded fabric Hang in Air Wash-off Dry
- 6. TEX 3101, WPT-II NUB FR 6 Steaming Process (All in Method): Recipe: Reactive Dyes : 10gm Thickener (Sodium alginate) : 500g (6% Paste) Urea : 200gm Sodium bi-carbonate : 20gm Sodium m-nitrobenzene sulphonate : 10gm Water : 260gm Total : 1 kg Printing of Cotton fabric by Two Phase Method: The fabric is pre-treated. Printed with a paste containing only dye, thickener and water. After drying, passing through an alkaline solution of high electrolyte content. Fixing by steaming at about 120°C for 30-60 seconds without intermediate drying. Then soaping and washing is carried out. 1. Recipe for print paste: Reactive Dyes : 30-50gm Thickener Paste (6% Na-Alginate) : 470-450gm Water : 500g Total : 1 kg 2. Recipe for pad-liquor (Treated with 70% pickup) Common Salt (NaCl) : 150gm Potassium Carbonate (K2CO3) : 100gm Sodium Hydroxide (68°Tw) : 30ml Water : 720ml Total : 1 L