engleski

The Use of Ultrasound in Textile Bleaching and Dyeing

Textile wet processes are usually not economically and ecologically favorable. They consume too much energy, water and produce enormous amounts of textile wastewater which is heavily charged with unconsumed dyes and other chemicals. In order to overcome these problems novel processes are being introduced or studied. Although several studies on ultrasound have been performed since a long time, it is considered only in recent years as a possible serious alternative to the conventional methods for accelerating mass transfer in textile materials and as pretreatment of textile surface materials. It is to point out that the same or better results were obtained than with existing techniques under less extreme conditions, i.e. lower temperature and lower chemical concentration. In this paper, an application of high frequency ultrasound on textile bleaching and dyeing is discussed. Ultrasound treatment has the potential for use in bleaching due to localized high temperatures and pressures, and formation of highly active oxidizing species such as hydroxyl radicals (HO•), hydrogen radicals (H•), hydroperoxyl radicals (HO2•) and H2O2. Cotton and polyester fabrics were bleached at pH 7 using 279 kHz and 817 kHz. The significant effect of high frequency ultrasound on bleaching of cotton and polyester fabric is obtained for the first time. It is interesting to note, that high whiteness degrees are achieved in ultrasonic bleaching without any addition of hydrogen peroxide. According to variance analysis, there is significant impact of ultrasound frequency on whiteness degree. Comparison between conventional and low frequency ultrasound (20 kHz) assisted dyeing of wool, polyamide and cotton was performed and found that US assisted dyeing results in greater dye exhaustion under the same experimental conditions as conventional dyeing in a shorter time and so we are dealing with process intensification. More, spent dyebath presents lower ecological parameters values, what means that US assisted dyeing contribute to the reduction of water pollution.

Ultrasound; Textile; Bleaching; Dyeing

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