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Dyeing and Recent Developments
Published in Asis Patnaik, Sweta Patnaik, Fibres to Smart Textiles, 2019
Prithwiraj Mal, Debojyoti Ganguly
Acid dyes are usually applied to natural protein fibres like wool and silk and polyamide fibres like nylon. These dyes are applicable for those fibres that have amino groups (-NH2-) (Gohl and Vilensky 2005; Roy Choudhury 2011; Lewis 1992). The colour gamut of acid dyes is complete, including greens and blacks. The dyes are available as powders, grains and liquids for continuous dyeing, and as fine dispersions of soluble types. Chemically, these dyes are sodium salt of sulphonic acids (D-SO3Na). Some dyes have carboxylic acid groups in their structure. Due to the presence of sulphonic acid groups, acid dyes have very good solubility in water. These sulphonic acid groups attach with the basic group of protein fibres through ionic bond. Depending upon the concentration of acid used in the dye bath, acid dyes can be classified into four classes, namely levelling acid dyes (pH 2–4), fast acid dyes (pH 4–5), milling acid dyes (pH 5–7) and super milling acid dyes (pH 6–7) (Roy Choudhury 2011).
Bioflocculants Relevant for Water Treatment and Remediation
Published in Sheila Devasahayam, Kim Dowling, Manoj K. Mahapatra, Sustainability in the Mineral and Energy Sectors, 2016
K. A. Natarajan, K. Karthiga Devi
Buthelezi et al. (2012) reported that whale dye was most easily decolorized, followed by mediblue, mixed dyes, and fawn dye, respectively. One explanation for this, according to Pearce et al. (2003), could be the acidic nature of the fawn dye. Acid dyes are the most problematic and difficult to decolorize due to their inert chemical structure and the attached phenyl, methyl, methoxy, nitro, and sulfonate groups. Syafalni et al. (2012) suggested that the removal of color from dye solutions is complex and may be due to the physicochemical processes of coagulation and/or chelation–complexation-type reactions. These techniques decolorize textile wastewater by partially decomposing the dye molecules and thereafter leaving the harmful residues in the effluent. Fang et al. (2010) reported that the removal of dyes (anionic azo-dyes) by flocculants may be attributed to both charge neutralization and bridging effect, with the former being the dominant mechanism. The dye structure appears to be conducive to chelation/complex formation reactions with coagulants leading to the formation of insoluble metal dye complexes that may precipitate from the solution. Color removal could probably be due to aggregation or precipitation and adsorption of coloring substances onto the coagulant species (Karthiga Devi and Natarajan, 2015a,b).
Dyes and their application
Published in Michael Hann, Textile Design, 2020
There are numerous synthetic dyes. Probably the most important are acid dyes; azoic dyes; basic dyes; chrome or mordant dyes; direct dyes; disperse dyes; reactive dyes; sulphur dyes; vat dyes; pigments. The suitability of each to particular fibre types is identified below. Acid dyes can be used in the dyeing of wool, specialty hair fibres, silk and polyamide fibres. Azoic dyes are used mainly for cellulosic fibres. Basic dyes, first developed during the nineteenth century, have particularly pure and brilliant colours on fibres such as silk (and other animal fibres) but have very poor all-round fastness (Storey, 1978: 75) and, by the late-twentieth century, were only used to a limited extent in textile dyeing, especially of acrylics. Chrome dyes are used widely in wool dyeing. They are simple in application and retain good light and wet fastness. Direct dyes are regarded as the simplest class of dyes. They are readily soluble in water and are used mainly to dye natural cellulosic fibres as well as viscose. Fibrous material is simply placed in a weak solution and heated. Exhaustion of the direct dye improves with the presence of common salt, and an increase in temperature can increase the rate of dye uptake. Giles described various after-treatments which would help to improve the wet fastness of direct dyes (Giles, 1971: 61). Disperse dyes are suited to secondary acetate, triacetate and polyamide fibres, as well as acrylic and polyester fibres. Disperse dyes are regarded as the main dye class for synthetic fibres. Reactive dyes are used mainly for cellulosic and wool fibres but have been used with some success in the dyeing of silk also. Further details were provided by Giles (1971: 73). Sulphur dyes are used widely in a soluble form on cottons and provide fast colours. Vat dyes are used mainly for cellulosic fibres and have excellent all-round fastness. Pigments are suited to all fibres and their combinations. A summary of the main dye types and their properties was given in tabular form by Wynne (1997: 259).
Synthesis and characterization of novel water-compatible magnetic molecularly imprinted polymer for tartrazine
Published in Journal of the Chinese Advanced Materials Society, 2018
Sahar Foroughirad, Naghmeh Arabzadeh, Ali Mohammadi, Alireza Khosravi
Water-soluble acid dyes are widely used in many industries including textile, plastics, papers, rubbers, and foodstuffs.[2–4] It is estimated that about 10–15% of waste dyes during dying procedure are released to the environment by wastewater.[3] That is the reason why wastewater treatment for dye removal is one of the important issues in recent centuries.[5] Moreover, using dyes as food color is highly controlled due to their daily intake limits and their allergenic side effects.[6]