Introduction of dyeing Basic knowledge
- 1. INTRODUCTION OF DYEING Tonmoy Textile 36th Batch University Of South Asia Tonmoymollick78@gmail.com
- 2. Dye:- A dye or a dyestuff is usually a colored organic compound or mixture that may be used for imparting color to a substrate such as cloth, paper, plastic or leather in reasonably permanent fashion. All colored compounds are not dye:- A dye is a colored substane but all colored substances are not dyes. Thus a dye should fix itself on the substrate to give it a permanent colored appearance. Thus azo benzene is not a dye even though it has red color as it can not be attached to substrate. However congo red is a dye as it can be applied on cotton and retained by it. Thus the dyes should have certain groups which help the attachment to the fiber. 1. Azo Benzene
- 3. Pigment:- Pigment is a substance that can absorb light and reflect some lights to show color but it is water insoluble substances. Normally it is used for printing (with the presence of binder). Fig. Anthocyanine Pigment
- 4. Chromophore:- A chromophore is the part of a molecule responsible for its color . It is that part of the molecule which when exposed to visible light will absorb and reflect a certain color. Auxochrome:- Auxochrome is a Greek word arising from two word roots; ‘auxo’ meaning “to increase” and ‘chrome’ meaning “color”. Auxochrome is a group of atoms which will impart a particular color when attached to a chromophore but when present alone, will fail to produce that color. Chromogen:- Chromogen is a substance which can be readily converted into dye or other colored compound. In other words, it can also be defined as any substance found in organic fluids that forms color when oxidized. The presence of the entire three produces intense color and the whole compound is called chromogen.
- 5. LIST OF CHROMOPHORESGroup Structure • Carbonyl > C = O • Azo -N = N- • Nitro -N=O • Thioketone -C =S • Nitrite -NO2 • Conjugated Diene -C=C-C=C- • Conjugated Triene -C=C-C=C-C=C- • Conjugated Tetraene -C=C-C=C-C=C-C=C- • Benzene
- 6. THEORY OF DYEING Migration of the dye from the solution to the interface accompanied by the adsorption on the surface of the fiber. Diffusion of the dye from the surface towards the center of the fiber. The anchoring of the dye molecules by covalent bond or H- bond or other forces of a physical nature.
- 7. Forces in the dye bath:- Two forces are produced in the dyebath- a. Forces of repulsion which are developed between the dye molecule and water. b. Forces of attraction which are developed between the dye molecules and fiber.
- 8. BONDS FORMED BETWEEN DYE MOLECULES AND FIBER 1. Ionic interaction:- These arise from ionic sites of opposite charge in the fiber and the dye molecules. For example, the dyeing of wool with acid dyes of the leveling type is mainly due to the formation of salt type chemical links between dye anions and cationic groups in that fiber. Wool-NH2 + H+ Wool-NH3 + Wool polymer Hydrogen Wool polymer with with amino group or acid ion positively charged amino group Then Wool-NH3 + + DSO3 - Wool –NH3 +-SO3D
- 9. 2. Hydrogen Bonds:- These interactions are weak and are formed by sharing a lone pair of electrons on nitrogen, oxygen or fluorine in a molecule with covalently bonded hydrogen atom. The hydrogen bonds are involved in dyeing of wool, silk and manmade fibers. 3. Vander Waal’s interaction:- These interactions are weak and mainly arise due to interactions between molecules close to one another. Vander waal’s interactionbs become stronger between similar group, e.g. Alkyl, aryl in polyester dyes. 4. Covalent Bonds:- These bonds are formed between dye and fiber molecules due to the reaction between a reactive dye and a group such as –OH. Such reactive dyes were first introduced by ICI in 1956 under the name Procion dyes.
- 10. Factors influences the dyeing:- 1. Temperature 2. Pressure 3. Time 4. PH in the dye bath 5. M:L ratio 6. Dye auxiliaries. Auxiliaries used in Dyeing:- 1. Wetting agent 2. Dispersing Agent 3. Acid/Alkali 4. Antifoaming agent 5. Carriers 6. Electrolytes 7. Levelling Agents
- 11. Aggregation of dyes • Dye-dye self association in solution is called dye aggregation, which is important phenomenon where dye molecules or ion takes part. In general, the term aggregation is used for dye-dye interaction and dye association for interaction of dyes with other compounds e.g. polymers. • Generally dye molecules form aggregation in aqueous solution at room temperature and to an extent which depend on i. Size of dye molecules ii. No of solubilizing groups in the dye molecules • In dye aggregation multiple equilibrium need to be considered i.e. diametric, trimetric etc, aggregates are formed. • Prevention of aggregation 1. By raising the temperature of dye bath 2. Liberation and existence of monomers by circulations or stirring and keep concentration below 10-5 mole/L of dye.
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