The Decoloration Of Direct And Reactive Dyes In Activated Oxygen Bleaching Systems

The fabrics dyed with direct and reactive dyes often display fading and staining inthe washing process, and this problem is more serious during the washing with anactivated oxygen bleach-containing detergent. The fading of direct and reactive dyes inactivated oxygen bleaching systems is worthy of further research, which is of greatsignificance for screening the dyes having a high intrinsic fastness in activated oxygenbleaching systems, and broadening the application range of activated oxygenbleach-containing detergents. In this present work, the activated oxygen bleachingsystems consisted of sodium perborate (PB) or percarbonate (PC), and the activator,tetraacetylethylenediamine (TAED). The effects of oxidants, temperature, time and pHwere systematically discussed, and the dynamics of the decoloration of direct andreactive dyes in solutions were investigated. The main results obtained were as follows:(a) The decoloration of direct and reactive dyes in activated oxygen bleachingsystems was quite different with their different molecular structures. Anthraquinonedyes were stable, and difficult to decoloration; but the dyes with phthalocyanine andtriphenodioxazine structures were highly sensitive to activated oxygen bleaching andshowed rapid decoloration rates; the decoloration of azo dyes varied greatly with theamounts of the anions in their structures and the nature of substituent groups.(b) The decoloration reaction of direct and reactive dyes in solutions was found tofollow the first-order kinetic model, and the nature of reaction was not affected bytemperature and pH. The constant of decoloration rate was observed to increaseobviously with increasing temperature. The decoloration constant of triphenodioxazinedyes was the highest at pH8-9, and those of azo and phthalocyanine dyes at pH9-10.The decoloration of dyes decreased at higher pH. The dependence of the decoloration ofdirect and reactive dyes on various factors had relation to the structures of dyes.(c) The decoloration of direct dyeings was analyzed using the UK-TO test. Theresults showed that the fading of fabrics increased in the case of the addition of the anionic detergent into washing solutions, and the fixation treatment with cationic fixingagents decreased the color fastness to activated oxygen washing. The decoloration ofreactive dyeings was analyzed using the ISO-105-C06/2S test. The results showed thatthe dyeings had the good fastness in terms of staining, indicating that the oxidation ofreactive dyes in solution by activated oxygen could prevent staining.(d) As for the decoloration of direct and reactive dyeings in activated oxygenbleaching systems, the color difference and decoloration percentage increased withincreasing temperature and time, and the effect of temperature was more remarkable.(e) The low fading degree of the fabrics dyed with azo and anthraquinone directand reactive dyes in activated oxygen bleaching systems was observed, and the worstwashing fastness was found when the pH of the washing bath was9-10. The fabricsdyed with phthalocyanine and triphenodioxazine direct dyes exhibited higher fadingdegree with increasing pH of the washing bath, but the reactive dyes of these twostructures on cotton had the significant fading level at pH8~9and pH7~8, respectively.The fading effect of direct and reactive dyeings at the different pHs of washing bathswas related to the parent structures of dyes, and the desorption and hydrolysis degree ofdyes on cotton.