Acid Dyes on Plant Fibers

Acid dyes, i.e., azo or anthraquinone dyes containing sulfonic acid groups, were occasionally used for dyeing cotton however, they are no longer important. They do not have sufficient substantivity for cellulose. Only those dyes are usable that can form a metal complex on the fiber when applied together with a metal salt. Excess heavy metal contaminates the wastewater. 

Acid dyes can attach directly to vegetable hard fibers (jute, sisal) by salt formation because the fiber companion substances contain basic groups. 

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