Abstract
In commercial processing of wool dyeing using mordant dyestuffs, bichromate has been in use. After chromating it has been a common practice to use potasium bichromate equal to 1/2-1/3% of dyestuffs.
Lately the pressure of chromium in water waste contained in heavy metals came to light as a cause of public nuisance, its amount being in excess beyond the allowance for public safety. As a result of it further investigations has been carried on.
Among the processes directed toward alleviation are to change mordant dyestuffs to some others for instance, such as 1:2 type metal complex dyestuffs; use of reductive agents; application of ion exchange resins to mention the outstanding attempts.
The present paper reports the findings consisted of the following three parts
(1) Amount of chromium in dyebath at the end of dyeing was much influenced by next factors; amount of bichromate and sodium sulfite, chroming temperature and time.
Chromium was hardly detected when potassium bichromate was used less than 0.7% owf under ordinary dyeing conditions.
(2) Purity of dyestuffs in market was investigated and then calculated the stoichiometric chromium amount. Dyeing was practised under this chromium amount and chromium in dyebath was checked. Both change of shade and dyeing fastness properties was also checked.
In the results, it was shown that the minimum amount of bichromate required to develop the dyestuff was nearly the stoichiometric chromium amount.
(3) Application to actual dyeing the stoichiometric chromium amount i.e., to actual dyeing “Potassium bichromate Factor” was considered. Dyeing was practised on the basis of this factor. Actual yarn and piece dyeing tests over six months followed that chromium in waste water was hardly detected and that both fastness properties and reappearance of shade was very satisfied.
