Photodegradation of CI Acid Orange 60 and CI Acid Green 25 in an Amide Environment

Abstract

Photodegradation, in solution and in nylon 66 fiber, of two automotive acid dyes (CI acid orange 60 and CI acid green 25) for nylon carpet has been investigated. Photofading in solution was done in dimethylformamide (DMF) with the aid of a 254-nm light source, and the work in nylon fiber used the xenon arc light of an Atlas CI 65 weatherometer. The results show that these dyes fade via a photoreduction process under both sets of conditions, and they suggest that DMF is a suitable model for nylon in characterizing the photodegradation of acid dyes. The structures of the degradation products of the two dyes were determined with the aid of fast atom bombardment and desorption chemical ionization mass spectrometry and by HPLC and TLC comparisons with authentic samples.Although it has been more than one hundred years since Bancroft [14] ] reported that the light-induced fading of dyes proceeds by oxidation at times and by reduction at other times, the photodegradation of synthetic dyes continues to be a commercially important problem and therefore the subject of many presentday research reports. In as much as others [8] have already summarized a large proportion of the work in this area since the early studies of Bancroft and later Gebhard [ 23 ] , we will not repeat the intimate details of prior studies here. It is worthwhile to mention, however, that the many published papers indicate among other things that light stability of dyes depends not only on various structural factors but also on (a) the physical state of the absorbed dye, which includes the size and location of associated particles, (b) the nature of the polymer, (c) the extent of penetration of the dye and its concentration, (d) the ease of diffusion of air, moisture, and gasses, (e) the energy of the incident radiation, and (f) the relative ease with which transient reactive species are formed upon absorption of light [ 2-7, 9-11, 16, 17, 24, 33, 34, 38 ] . It is also clear from previous reports that much of the work pertaining to the characterization of the processes by which dyes undergo photodegradation was done in solution [ 1,12,27,30,35 ], although work has also been done in a polymer matrix [3,13,25,28,36,37] ] to better simulate the environment of dyes in commercial applications requiring high lightfastness.The presence of metal ions such as Cr, Cu, or Co often improves the lightfastness of textile dyes. As a consequence, 1:2 Cr ( III ) and 1:2 Co ( II ) complexes of certain azo dyes are widely used in dyeing polyamide and protein fibers. Interestingly, there are very few published reports describing the photofading of these important compounds [ 20,26 ] .A key objective of this investigation is to determine the process by which the widely used automotive acid dye Cl acid orange 60 ( 1 ) undergoes photodegradation in nylon fiber and to compare the results with information derived from experiments done in an amide ,a

Physico-Chemical Principles of Color Chemistry

“…More recently, Freeman et al 136 have investigated the photodegradation of c.1. Acid Green 25 (35), in dimethylformamide and on nylon 66…”