Dye fiber interaction

In exhaustion dyeing, the dye, which is at least partially soluble in the dyebath, is transported to the fiber surface by motion of the dye liquor or the textile. It is then adsorbed on the fiber surface and diffuses into the fiber. Finally, depending on the dye-fiber interaction, it is fixed chemically or physically. The dye can be applied to the textile discontinuously from a dilute solution (exhaustion dyeing from a long liquor) or continuously by immersing the textile in a concentrated bath and squeezing-off excess liquor (padding), followed by separate steps for diffusion and fixation in the fiber. 

The dyeing of fiber from an aqueous dye bath depends on the dye-fiber interaction. Depending on the nature of dye and the nature of fiber, the dye is fixed onto the fiber chemically or physically. Table 8.1 shows the methods of apphcation for various dye classes and principal substrates [7]. 

Oprea, T.I., Kurunczi, L. and Timofei, S. (1997) QSAR studies of disperse azo dyes. Towards the negation of the pharmacophore theory of dye-fiber interaction Dyes S, Pigments, 33, 41-64. 

We have analyzed the nature of the dye-fiber interaction for 27 disperse azo dyes by means of several QSAR methodsbased on the pharmacophore theory of dye-fiber interaction. Hydrophobic effects were excluded because CLOGP gave a limited correlation, = 0.32. MTD (r = 0.924) and CoMFA (j-2 = 0.925 and = 0.776, LOO) results emphasized the importance of steric contributions for enhancing the affinity to cellulose fiber. CoMFA results apparently confirm the validity erf the pharmacophore theory of dye-fiber interaction. This was not surprising because similar results between CoMFA and MTD were reported in 1993. ... 

Disperse Azo Dyes. Towards the Negation of the Pharmacophore Theory of Dye-Fiber Interaction ... 

De Clerck K., Rahier H., Van Mele B., Westbroek P., Kiekens P. (2007), Dye-Fiber Interactions in PET Fibers Hydrogen Bonding Studied by IR-Spectroscopy Journal of Applied Polymer Science, 106, 3,1648-58. 

Direct dyes are anionic colorants that have affinity for cellulosic fibers.17 They were the first dyes that could be used to dye cotton in the absence of a mordanting agent, giving rise to the term direct-cotton dyes. Like acid dyes, direct dyes contain one or more -SOjNa groups, making them water-soluble. Unlike acid dyes, they interact with cellulose (Cell-OH) chains via secondary valency forces (e.g., H-bonding and dipole-dipole interactions), as illustrated in... 

ACID DYES Commercial acid dyes contain one or more sulfonate groups, thereby providing solubility in aqueous media. These dyes are apphed in the presence of organic or mineral acids (pH 2—6). Such acids protonate any available cationic sites on the fiber, thereby making possible bonding between the fiber and the anionic dye molecule. Wool, an animal fiber, is an amphoteric coUoid, possessing both basic and acidic properties because of the amino and carboxylic groups of the protein stmcture. In order to dye such a system, coulombic interactions between the dye molecule and the fiber must take place ie, H2N" -wool-COO + H2N" -wool-COOH. The term acid dye is appHed to those that are capable of such interactions. Acid dyes... 

The force of attraction between a dye and fiber results from the usual electronic interactions. 

Ion-Dipole Forces. Ion-dipole forces bring about solubihty resulting from the interaction of the dye ion with polar water molecules. The ions, in both dye and fiber, are therefore surrounded by bound water molecules that behave differently from the rest of the water molecules. If when the dye and fiber come together some of these bound water molecules are released, there is an increase in the entropy of the system. This lowers the free energy and chemical potential and thus acts as a driving force to dye absorption. 

Hydrophobic Interaction. This is the tendency of hydrophobic groups, especially alkyl chains such as those present in synthetic fibers, and disperse dyes to associate together and escape from the aqueous environment. Hydrophobic bonding is considered (7) to be a combination of van der Waals forces and hydrogen bonding taking place simultaneously rather than being a completely new type of bond or intermolecular force. 

Internal and External Phases. When dyeing hydrated fibers, for example, hydrophUic fibers in aqueous dyebaths, two distinct solvent phases exist, the external and the internal. The external solvent phase consists of the mobile molecules that are in the external dyebath so far away from the fiber that they are not influenced by it. The internal phase comprises the water that is within the fiber infrastmcture in a bound or static state and is an integral part of the internal stmcture in terms of defining the physical chemistry and thermodynamics of the system. Thus dye molecules have different chemical potentials when in the internal solvent phase than when in the external phase. Further, the effects of hydrogen ions (H" ) or hydroxyl ions (OH ) have a different impact. In the external phase acids or bases are completely dissociated and give an external or dyebath pH. In the internal phase these ions can interact with the fiber polymer chain and cause ionization of functional groups. This results in the pH of the internal phase being different from the external phase and the theoretical concept of internal pH (6). 

Chromoionophores, 20 517-518 Chromonema fibers, 17 612 Chromonic liquid crystals, 15 101 Chromophore interaction, in dye molecules, 20 511-512... 

Light that is transmitted through the fiber surface can interact with the molecular structure, e.g. dye molecules, and thereby change its spectral character before being emitted back through the surface... 

Contrary to other synthetic fiber materials, polypropylene fibers cannot be colored by contacting them with an aqueous solution or dispersion of organic dyes. Due to its highly apolar nature, polypropylene is not able to interact with conventional dye molecules, so that it cannot take up any dye from the dye bath. 

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