Dyeing processes problems

Natural dyes processed for the market do not undergo any chemical operations. Those operations iavolved are purely physical, such as grinding, spray or vacuum dryiag, and water or solvent extractions. None of these operations create any great environmental problems. 

In the course of his studies of the dyeing process, he became deeply interested in the structure of natural fibers, and most of his efforts were directed toward this new field of research, with the help of able associates, among them R. Brill, M. Dunkel, G. von Susich, and E. Valkd. His investigation of various aspects of the problem utilized physical means (for example, x-ray diffraction, optical properties, and viscosity) and the purely chemical approach. A young scientist, H. Mark, who later became an authority in the field of high polymers, was appointed head of the physical chemistry laboratory. 

Besides an optimization of the dyestuff and the dyeing processes with regard to improved dyebath, exhaustion, the problem of colored wastewater released from dyehouses, has led to numerous technical developments proposed to overcome it. 

The major problem with dye wastewater is the color produced by residual dyes during the dyeing process. If the concentration of dyes in wastewater increases, then the color of the streams will grow darker. The transparency of streams will then be reduced, causing plants to perish and ecosystems to suffer. Several amino-substituted azo dyes are mutagenic and carcinogenic. 

The afterchroming dyes have also lost their former importance because of the considerable amount of time required by the dyeing process and because of effluent problems, but they are still used in wool dyeing because of their low price. 

Perkin sent a sample of the new compound to a firm of dyers. Their assessment was very favourable, so at the early age of eighteen Perkin left the Royal College of Chemistry and raised sufficient capital to build a factory for the manufacture of mauve. Before mauve could be used as a dye, Perkin had to solve several technological problems connected with the dyeing process. His most significant innovation was the use of tannin as a mordant to bind the dye to the cotton. 

One manufacturer has found a way to overcome the lead-time problems so as to be able to quickly respond to fashion. Benetton, an Italian apparel manufacturer makes sweaters in bulk, but delays the dyeing process until after initial sales figures are received from the retailers. In other words, colour choices are made after the manufacture. This approach has increased the cost of production by 10 per cent but has resulted in improved forecasts, less surplus stock and due to quick response to customer demand higher sales which has more than compensated for the inCTease in production cost. Major retailers are responding to challenges of lean and agile supply chain (see Chapter 13) as the following case example of Tesco illustrates. 

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