Disperse dyes are essentially non – ionic, exhibit poor solubility in water, and they can be used in the form of water dispersion. Polyester fibres are resistant to dilute aqueous acids and alkaline solutions and pH value does not provide a crucial impact on the dyeing mechanism; however, many disperse dyes undergo degradation if the pH is uncontrolled during aqueous dyeing. In order to minimize the possibility of dye hydrolysis, the dyeing is carried out in a slightly acidic medium, and pH is usually adjusted with acetic acid. In this work, the quantity of disperse dyes (Sinten Gelb P-5GL and Sinten Scharlach P-3GL) applied to polyester knitwear was investigated as a function of pH. The sorption capacity of polyester knitwear was monitored by using reflection curves and CIELab system, according to Swiss software Sandoz (based on spectrophotometry). The acetic acid was used for dyebath pH adjustment. The results showed that the maximum uptake of Sinten Gelb P-5GL and SintenScharlach P-3GL dyes by polyester knitwear occurred at pH 4.64 (0.2924%) and 6.20 (0.1860%), respectively. According to reflection curves in the range (max = 400-700 nm), the effect of pH on the sorption of Sinten Gelb P-5GL was more significant than one for Sinten Scharlach P-3GL, when concentration of dye is constant (0.4%). The CIELab values for three illuminants (daylight, light – bulb and incandescent) showed a significant dependence between pH float and hue and intensity of polyester knitwear dyeing with disperse dyes

Milena Miljković, Sandra S. Konstantinović, Vojkan M. Miljković, Milena Nikodijević and Dušan Trajković