Cleaner Technology Transfer to the Polish Textile ... - Miljøstyrelsen

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3.2 Environmentally friendly recipe in
reactive dyeing of cotton
Hans Henrik Knudsen and Henrik Wenzel,
Institute for Product Development, Denmark.
Abstract
The recipe for reactive dyeing of cotton can be divided into three steps: the
pre-treatment, the dye-bath and the final rinse. The consumption of chemicals
and water in the rinse have been found to be considerable; three quarters of the
total COD-discharge of a recipe have relations to auxiliary chemicals used and
three quarters of the total water consumption have relation to the rinse. The
improvement potentials in the rinsing procedure were found to be considerable,
and the newly developed recipe focuses on improvements in the rinse.
Tests with the new recipe have documented, that neutralization, detergents and
complexing agents can be left out completely with no adverse effect on product
quality. All recognized tests of fastness and shade have been performed
and evaluated in co-operation with the dye-houses.
More than 50 full-scale dyeings have been carried out in jets, overflow and
drum batch machines. These dyeings include 25 different reactive dye-stuffs,
among these – azo, anthrachinon, phtalocyanin and formazan dye-stuffs,
including both monoreactive and bireactive dye-stuffs of which 15 had the
vinyl sulphone as reactive group. The dye-stuffs have been combined in 20
different recipes covering very light to very dark shades.
Hot membrane filtration of the hot rinsing water has been investigated in parallel
projects and it is documented that one new recipe including membrane
filtration, saves chemicals, water, and energy, and implies large savings in production
time as well.
Introduction
Status for the recipe In previous investigations, the consumption of water, energy and chemicals for
the rinse in the reactive dyeing of cotton was found to be of major importance
(D. Fiebig et al., 1985, H. Wenzel et al., 1992). It is common that the rinse has
a water consumption above 200 l/kg textile, or more than 60% of the total
water consumption in the whole refinement process. About 70% of the CODload
from the reactive dyeing process can derive from auxiliary chemicals
used in the rinse.
Status in the dye-houses The dye-houses state that the large consumption of water and chemicals for
the rinse in reactive dyeing of cotton ensures a reliable process. The possible
residual content of salts and/or other chemicals in the cotton textile, which are
not washed out in the pre-treatment, can influence the quality of the product,
and the process is secured by the use of auxiliary chemicals.
Another reason given is, that specific shades require combination of dye-stuffs
with so different chemical and physical properties, and that it is only possible
to control the rinse and obtain the desired shades with the traditional consumption
of water- and chemicals.