most of the emissions are emissions to water. Due to the low vapour pressure of the substances in the dye bath, emissions to air are generally not significant and can be regarded more as problems related to the workplace atmosphere (fugitive emissions from dosing/dispensing chemicals and dyeing processes in "open" machines). A few exceptions are the carrier dyeing, thermosol process, pigment dyeing
In pigment dyeing the substrate is not washed after pigment application and therefore the pollutants are quantitatively released to air during drying Emissions from carriers are to air and water.
Environmental issues related to the substances employed Water-polluting emissions may originate from the dyes themselves (e.g. toxicity, metals, colour) auxiliaries contained in the dye formulation basic chemicals (e.g. alkali, salts, reducing and oxidising agents) and auxiliaries used in dyeing processes contaminants present on the fibre when it enters the process sequence (residues of pesticides on wool are encountered in loose fibre and yarn dyeing and the same occurs with spin finishes present on synthetic fibres). Spent dye baths (discontinuous dyeing), residual dye liquors and water from washing operations
% of non-fixed dye that may be discharged in the effluent for principle classes of dyes
In the drying and curing operation air emissions are produced due to
the volatility of the active substances themselves as well as that of their constituents (e.g. monomers, oligomers, impurities and decomposition by-products).
The emission loads depend on the drying or curing temperature, the quantity of volatile substances in the Finishing liquor
The range of pollutants is very wide and depends on the active substances present in the formulation and on the drying, curing conditions.
Environmental issues associated with discontinuous processes The application of functional finishes in long liquor by means of batch processes is used mainly in varn finishing and in the wool carpet yam industry in particular. For the resulting water emissions, the efficiency exhaustion of the active substance from the liquor to the fibre, influences the emission loads. The efficiency depends on the liquor ratio and on many parameters such as pH, temperature and the type of emulsion (micro- or macro-emulsion).