Modern Concepts of The Theory of Dyeing

The general theory of dyeing explains the interaction between dye, fiber, water and dye auxiliary. But the modern concept are some difference from general concept which are given below. It appears that the mechanism of dyeing depends on the nature of both the dye and the fibre. Textile fall into two main groups : vegetable and animals vegetable fibre is cellulose fibre, e.g. cotton, lined, flax, hemp and jute. Animal fibres are protein fibre, e.g. wool, silk and leather.

There is also a third type of fibres, the artificial and synthetic fibres e.g. rayon’s (cellulose-type) and nylons (protein-type).

Dyeing was already practiced inn ancient times and has undergo many changes in its development. The first hypothesis of purely mechanical character attempting to explain the processes underlying dyeing was advanced in 1740-41. According to this hypothesis the fibre has pores which particles of dyes penetrate at high temperature; when the dye bath cools, the pores of the fibre contract, thus fastly retaining the dye. The problem of the different behavior of dyes in respect to various kinds of the fibre was not referred to.

For about one and half a century, the dyeing process was considered was only from the mechanical stand point without paying due regard to chemical essence o the process, only at the end of the 19th century, when chemistry was developed, the chemical nature of dyeing process was revealed.

New theories is come replace the old erroneous ones. thus, as a result of the work carried out by two groups of English chemist-S Neale collaborators and J. Belton, it was found that inn the process of dyeing, the was first absorbed by the external surface of the fibrous materials and than started to diffuse inside in the molecular-disperse state. this was the determining feature of the kinetics of the process.

At organic fibres, cellulose,, protein and synthetic have one feature in common; they are all macromolecules having a linear structure and more or less oriented along the fibre axis. Macromolecules contain a great number of identical or similar atoms linked by covalent bond. Most high polymers from which the fibres are composed contain active functional groups, such as hydroxyl, carboxyl, nitrile and amino groups. In cross longitudinal directions, macromolecules are interconnected by the force of intermolecular attraction and in separated cases, by chemical bonds (wool keratin). The super molecular structure of the fibrous polymer is characterized y chain having in some portion a very regular arrangement crystalline region) and a maximum density of packing and in other portions, regions with less regular arrangement (amorphous region) and a maximum density of packing and in other portions, regions with less regular arrangement (amorphous region) with loose structure. 
 
 
 

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