The reduction clearing of dyed polyester. Part 1: Colour strength

An alternative after treatment has been devised for polyester which has been dyed with disperse dyes. A comparison of colorimetric data obtained for dyeings which had been treated using a traditional, sodium dithionite-based reduction clearing process with those secured for dyeings which had been washed-off for 15 min at 98 °C with detergent-based process showed that the colour strength of the washed-off samples was slightly lower than that of the reduction cleared samples but there was no difference between the λmax of the washed-off and reduction cleared dyeings; in addition, there was little difference between the hue and chroma of the reduction cleared and washed-off dyeings. The washed-off dyeings displayed higher fastness to washing at 60 °C than their reduction cleared counterparts. Thus, in terms of fastness and colorimetric characteristics, the traditional reduction clearing treatment can be replaced by a single, non-dithionite-based wash-off at 98 °C for 15 min. This enabled a major reduction to be achieved in terms of the BOD, COD and TOC that are typically generated as a result of the traditional reduction clearing of disperse dyes on polyester; it also offers the potential of avoiding the environmentally unacceptable generation of aromatic amines.