抄録
The thermal-stability of aqueous solution of the direct dyes was studied to appreciate the suitability for the high temperature dyeing of hydrophobic fibers.
First, the testing method of the thermal-stability was studied.
A Pt-lined autoclave, and a stainless-steel autoclave with or without a glass tube or a quartz tube were used as the vessel for the thermal-stability test. The pH change of distilled water by 180°C-heating in the individual vessel was determined. The grade of pH-change by the heating was remerkably in the glass tube, but was not so much in the stainless-steel and the quartz tube, especially the change in the later tube was negligible.
The aqueous solution of commercial Chlorantine Fast Blue 3 RLL was heated in the stainless-steel autoclave or the quartz tube for 40min. at various temperatures, and the change of absorption spectra and pH of the heat-treated aqueous dye solution was determined. In the stainless-steel autoclave these changes were relatively large and there is no reasonable relation between these variables and treated-temperatures. On the contrary, in the quartz tube the absorption spectra and pH of the heated dye-aqueous solution changed slightly, and their change became gradually larger with the increased of treated temperatures. These results indicate that the quartz tube is the most adequate material for the thermal-stability test of dye aqueous solution.
Then, the thermal-stability of aqueous solution of 16 dyes that belong mainly to direct azo dyes of benzidine series were tested in the quartz tube at 160°C.
Degradation degrees of these dye-aqueous solution were between 0.7% and 7.5y, for 30-minute heating. Therefore it may be said that these dyes have high thermal-stabilities and are more useful for high temperature dyeing.
However, the treatments in the presence of metals causes various changes. The aqueous solutions of commercial Chlorantine Fast Blue 3 RLL and Direct Brown 3G almost completely faded by the heat-treatment (160°C, 30min.) in the presence of iron wire in the quartz tube. In the heattreatment of the aqueous solution of former dye in the presence of copper wire a considerable degradation (26.3%) was recognized, and for the later the change in the color shade was observed. Stainless-steel degrade remarkably either dye-aqueous solution (42% and 36%, each), but no shade change takes place.
Finally, the degradation rate of the aqueous solution (0.5% conc.) of purified Direct Sky Blue 6 B was measured.
In the heat-treatment at 140°C and 150°C the degradation proceeds according to the first order equation during the experimental period (2hours). But in the heat-treatment at above 160°C, the degrees of degradation deviated from calculated values by mean of first order equation based on the degraded value at initial stage, and the deviation becomes larger with the increasing of treating temperature and treating time respectively.
The activation energy of the degradation of Direct Sky Blue 6 B aqueous solution, which is calculated by first order equation, is 23.1 kcal/mol.
