Classification of Dyes PDF

Prepared by: TS. DR. MOHD AZLIN MOHD NOR/ CLASSIFICATION MIAK OF DYES  Color arises from the way in which colorants interact with light. Colored organic compounds contain groups of atoms whose bonds are unsaturated, such as C=C...

Prepared by: TS. DR. MOHD AZLIN MOHD NOR/ CLASSIFICATION MIAK OF DYES  Color arises from the way in which colorants interact with light. Colored organic compounds contain groups of atoms whose bonds are unsaturated, such as C=C (carboxyl group), C=O (carbonyl group), N=N (azo group), NO (nitro group), and NO2 (nitryl group). These groups are called chromophores, i.e. the color carrier or color-carrying groups in dye molecule or electron acceptor. It is important as a link, bridge or corner pillar. The presence of chromophores in chemical compounds produces color (chromogen i.e. color producer). In other words, chromophore is the groups which introduced a potentiality for color.  This potentiality was then developed by weak salt- forming groups e.g. –OH (hydroxyl group), -NH2 (amino group), - NHR (mono alkyl amino group) and –NR2 (dialkyl amino group) which acts as a “color intensifier” and also confers affinity for textile fibers. These groups are called auxochrome. A dye is obtained and has affinity for the fiber when both auxochrome (electron donor) and a chromophore (electron acceptor) are present. Chromophore + Auxochrome Dyestuff (Cationic) NO2 + -NH2 H2N NO2 Pale yellow Deep yellow-orange - not fiber adherent -fiber adherent CLASSIFICATION OF DYES By application By ionic class By chemical class  By Application The names of application class are an important guide as to the method of use. Therefore, acid dyes are applied from acidic dyebaths, reactive dyes chemically bond to the fiber and basic dyes form basic cations in acidic media.  Fiber Types Application Class Cellulosic Protein Polyamide Polyester Acrylic Acetate Direct Reactive Vat Sulphur Azoic Acid Mordant Basic Disperse Fibers for which the dye is usually employed Fibers for which the dye has a possible application  By Ionic Class Dyes are molecularly-designed to be soluble in water, since water is the usual dyeing medium used to transport the dye onto the fibers from the dyebaths. Certain dyes posses appropriate molecular groupings on their structure to aid their solubility in water. These solubilizing groups ionize in water during dyeing, to create either positive or negatively-charged dye ions, i.e. cations or anions respectively. Solubilizing groups able to form dye ions include the sodium carboxylate (-COONa) or more usually the sodium sulphonate (-SO3Na) radicals. Therefore, the dye molecule (depicted as below) containing one or more of these groups were readily dissociate into colored anion within the dyebath, as follows:- SO3Na SO3- H2O D D + 2Na+ SO3Na SO3-  Similarly, the quaternary ammonium group (-NR3) when bonded to halogen atom (Cl or Br) forms a useful dye solubilizing group, which will create a colored dye cation within the dyebath; this is simplified below CH3 CH3 H2O _ D N CH3 D N+ CH3 + Br Br CH3 CH3 Dye molecule Dye cation  The success of water as a solubilizing medium for dye is due to its highly polar character. Oxygen’s high tendency to attract electrons (i.e. its high electronegativity) compared to hydrogen means that the covalent bonding electrons within water are unequally shared between oxygen and hydrogen atoms. They are drawn or polarized towards to oxygen atom, giving the latter a somewhat negative δ- character compared to hydrogen atoms’ electropositive character δ+ as shown below: δ- O δ+ δ+ H H  The positive or negative dye ions will therefore each be surrounded by a sheath of water molecules attracted to the charged site, as in the following diagram: O H H H HH O H _ or D N+R 3 O D SO3 O H H O H H O H H  This so-called water ‘molecule of solvation’ are attracted to other water molecules by hydrogen bonding and the net result is that the dye ions are kept apart. They are therefore prevented from aggregating (or coming together), which would tend to cause the dye to come out of solution. Essentially, the greater the number of solubilizing groups on the dye molecule, the greater the number of molecules of salvation and the greater the dye’s solubility.  Depending upon their ionic character, dyes can be classed as being either anionic or cationic in type, i.e. forming dye anions or cations in solution. However, there are a number of dyes which possess no ionizing groups on their structure and which are unable to form dye ionions or cations within the dye bath. These nonionic dyes include the type of dyes called ‘disperse dyes’ and as the name implies, these forms dispersions within the dyebath rather than solution. Although such dyes have no ionic solubiliszing groups, they do often have other substituents on their molecular structure which aid solubility.  Consequently, hydroxyl (-OH) and amino (- NH2) groups which may present can produce limited but significant solubility of these nonionic dye molecules. The uptake of nonionic dyes by the fiber depends upon a small number of dye molecules coming out of dispersion and dissolving in the dyebath prior to being adsorbed by the fiber. Dye type (Solubility/ Fibre affinity Fastness properties End-uses ionic character) Direct Water soluble Cellulosics Light-poor/good Low quality apparel (anionic) (cotton, viscose) Washing-poor Fabrics/linings/curtains Acid Water soluble Protein fibres Light- Carpet yarns, dress goods, leveling (anionic) (wool, silk) good/moderate Suitings, overcoats, knitting Washing-poor yarns Acid milling Water soluble Polyamide fibres Light-good Carpet yarns, dress goods, (anionic) (nylon), Wool Washing-good Suitings, overcoats, knitting yarns Vat Insoluble in Cellulosics Light-excellent High quality curtains, water (cotton, viscose) Washing-excellent furnishing, shirts, towels, (nonionic) sewing threads Reactive Water soluble Cellulosics (also Light-good/excellent Curtains, furnishings, apparel (anionic) protein and Washing-excellent fabrics, towelling, sewing polyamide threads fibres) Basic Water soluble Acrylics (also Light- Furnishings, apparel fabrics (cationic) occasionally good/moderate protein fibres) Washing-good Disperse Insoluble in All synthetics Apparel fabrics, bed sheets, water carpets (nonionic)  By Chemical Class This classification is based on the chemical structure of the dyes and the nature of their chromogen. This classification is very useful in predicting some of the properties of dyes relating to their behavior in dyeing process (solubility, substantivity, etc.) and in normal use (fastness to sunlight, bleaching, etc.).  The Azo Chromophore Azo dyes contain one or more azo groups (- N=N-) i.e. the chromophoric parts of such dyes. They form an important classification of dyes and can be found represented in most of the different application classes. The shade gamut provided by these dyes encompasses the yellow, orange, red and scarlet in colors. The azo groups may be containing mono azo, diazo or etc.  NH2 NaO3S NHOC N=N OH Mono azo OH NaSO3 NH2 N=N N=N NaSO3 OH Diazo The Anthraquinonoid Chromophore Although not as numerous as azo dyes and more expensive to manufacture, O anthraquinone dyes can still be found in most of the major application classes. They provide shades primarily in the violet, blue O and green parts of the spectrum, which are usually of good fastness to washing.  The Triarylmethane Chromophore Dyes in this type are often CH3 CH3 extremely bright O HO (sometimes fluorescent) and include red, blue and HOOC C COOH green shades. Unfortunately, their light fastness can be poor. Acid, direct, basic and N(C2H5)2 mordant dyes include examples of this chromophoric type.  The Indigoid Chromophore Originally extracted from plants. Is a useful blue dye still employed in the dyeing of cotton yarn for denim fabrics. O H O H Cl Cl C N C N C=C C=C N C N C Cl Cl H H O O Indigo An Indigoid Dye indigo is now manufactured synthetically and can form the source of a number of blue-based indigoid dye derivaties