1. Pre-treatment processes (Scouring, Desizing, Bleaching) serve to prepare the textile material for the production of white goods and for the subsequent processing operations, such as dyeing, printing and finishing. These processes are designed to expose the reactive groups of the fibre that were previously blocked by the impurities. The scour is mainly an operation that converts fats and waxes found on the fibres to soaps and then removes the converted product by thoroughly washing the goods; there are also removed proteins, pectin, most ash constituents (for natural fibres), spin finishes, lubricating agents, oil (for synthetic and artificial fibres). A good pre-treatment improves the profitability of the company by ensuring the reproducibility of the effects obtained and thus reducing the losses due to “seconds”.
Fabrics, yarns or fibres can be bleached to be prepared for dyeing or printing or to make them white.
2. Optical Brightening
White can be brightened with fluorescent agents, which can absorb invisible ultra-violet rays and re-emit them within the visible spectrum.
3. Dyeing
Dyestuffs give colour to the material onto which they have been anchored, by selectively retaining some of the wavelengths out of the light upon the surface.
The dyeing process consists of three stages, which are:
Migration of the dye from the solution to the interface accompanied by adsorption on the surface of the fibre.
Diffusion of the dye from the surface towards the centre of the fibre.
Anchoring of the dye molecules by covalent or hydrogen bonds, or other forces of a physical nature.
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...about Preparing & Dyeing Fabrics
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