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An Introduction to Textile Processing Auxiliaries Private

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During the dyeing process it has been estimated that the losses of colorants to the environment can reach 10–50%. It is noteworthy that some dyes are highly toxic and mutagenic, and also decrease light penetration and photosynthetic activity, causing oxygen deficiency and limiting downstream beneficial uses such as recreation, drinking water and irrigation.

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Although auxiliaries have been a key component of immersion dyeing processes for many years the precise mode of action of many auxiliaries has not been fully resolved. This part of the paper discusses the various types of auxiliary available and the nature of the assistance they provide in immersion dyeing processes, together with both environmental and financial aspects associated with their use, as well as a discussion of the relationship between liquor ratio and the use of auxiliaries in immersion dyeing.

The purpose of functional additives is to facilitate a textile process and/or increase its efficiency. They serve as sizing materials, lubricants, wetting agents, emulsifiers, agents accelerating or decelerating the dyeing rate, thickeners, binders, etc. often with considerable overlap in the functions and abilities of a specific chemical. Compounds used encompass many different chemical classes, some of which are affected by enzymes and thus can be regarded as substrates, and some of which remain unaffected. Owing to environment and economical concerns, pre-treatment auxiliaries are used as sparingly as possible.

Dyeing and printing auxiliaries may be defined as substances that, when applied to a substrate provide color by a process that alters, at least temporarily, any crystal structure of the colored substances. Such substances with considerable coloring capacity are widely employed in the textile, pharmaceutical, food, cosmetics, plastics, photographic and paper industries. The dyes can adhere to compatible surfaces by solution, by forming covalent bond or complexes with salts or metals, by physical adsorption or by mechanical retention. Dyes are classified according to their application and chemical structure, and are composed of a group of atoms known as chromophores, responsible for the dye color. These chromophore-containing centers are based on diverse functional groups, such as azo, anthraquinone, methine, nitro, arilmethane, carbonyl and others. In addition, electrons withdrawing or donating substituents so as to generate or intensify the color of the chromophores are denominated as auxochromes. The most common auxochromes are amine, carboxyl, sulfonate and hydroxyl.In the textile industry, up to 200,000 tons of these dyes are lost to effluents every year during the dyeing and finishing operations, due to the inefficiency of the dyeing process. Unfortunately, most of these dyes escape conventional wastewater treatment processes and persist in the environment as a result of their high stability to light, temperature, water, detergents, chemicals, soap and other parameters such as bleach and perspiration. In addition, anti-microbial agents resistant to biological degradation are frequently used in the manufacture of textiles, particularly for natural fibers such as cotton. The synthetic origin and complex aromatic structure of these agents make them more recalcitrant to biodegradation. However, environmental legislation obliges industries to eliminate color from their dye-containing effluents, before disposal into water bodies.

During the dyeing process it has been estimated that the losses of colorants to the environment can reach 10–50%. It is noteworthy that some dyes are highly toxic and mutagenic, and also decrease light penetration and photosynthetic activity, causing oxygen deficiency and limiting downstream beneficial uses such as recreation, drinking water and irrigation.

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