Mechanism of Light Fading of Azo Dyes on Polyvinyl Chloride and Poly(ethylene Terephthalate)

Abstract

A series of monoazo compounds based on phenyl azo-β-naphthol and phenyl azo-8-hydroxyquinoline were applied to polyvinyl chloride and poly(ethylene terephthalate), respectively. From the relation between the electron attracting or withdrawing properties of the substituents in the benzene nucleus and relative fading rates, the conclusion was that the fading reaction in both the dye-fiber systems is probably oxidative. This conclusion agrees with that from an earlier analysis of fading products of anthraquinone disperse dyes on polyester. It is therefore clear that both polyvinyl chloride and poly(ethylene terephthalate) conform with the general observation that fading on any nonprotein is oxidative, provided the oxygen has access to the dye.Lightfastness of phenyl azo-β-naphthol dyes on polyvinyl chloride and that of phenyl azo-8-hydroxyquinoline dyes on poly(ethylene terephthalate) was very low. Also, in both the systems, the dyes in the substrate were in the form of a collection of particles of many different sizes.The fading of dyed materials by light has long been a subject of investigation, yet surprisingly little is known of the fundamental photochemical reactions involved [ 10,12,13], mainly because of the complex nature of dye-fiber systems. The reactions are not necessarily the same as those of dyes in solution [9], which are probably simpler and have been more widely studied [9,10,12,19]. Calvert and Pitts [4] have stated that &dquo;In general ... solid-phase photochemistry has not received the amount of quantitative effort afforded the liquid and gaseous systems,&dquo; and they have suggested that one reason for this neglect lies in the difficulty of dealing with the very high light absorption of many solids.This difficulty can be overcome if dyes are adsorbed in transparent films of solid polymers and changes caused by irradiation readily measured spectrophotometrically. Even then, however, many complicating factors are present, e.g., the physical state of the adsorbed dye, that is, the size and location of its associated particles, structure of the dye, extent of penetration of the dye, diffusion of air, moisture, gases, etc. Because of these and many other factors, the lightfastness of a dye differs when applied to different textile substrates.A dye may show very good lightfastness on one fiber and poor on another one. For example, the same anthraquinone dyes show moderate to good lightfastness on nylon and cellulose acetate but poor on polyester [ 13]. A number of studies have attempted to account for such variations in lightfastness. One line of work has ascertained the nature of chemical reactions taking place during fading of dyes, mainly to show oxidation and reduction, and another has reported on the physical state of dyes in fibers. Kienle et al. [ 16] were probably the first to study quantitatively the fading rates of a series of benzene azo-R-acid dyes on wool and gelatin. They found that electron attracting groups (e.g., -N02) accelerate fading and electron repelling ones (e.g., ...

Fading phenomena of azo oil dye in anionic-nonionic surfactant solutions III. The effect of solubilizates on the fading behavior of azo oil dye in mixed surfactant systems

“…Griffith and Hawkins [1,2] investigated the photochemical oxidation of arylazonaphthols in methanol; Kuramoto and Kitao [3] studied the photofading of some dyes in organic solvents, such as methanol, acetone, dichloromethane or benzene; Shah andJain [4] reported the light fading of azo dye on poly(vinyl chloride) and poly(ethylene terephthalate); Mustroph and co-workers [5] carried out the photofading of 1-phenylazo-2-naphthol in cellulose acetate. However, these studies have been done in organic solvents and on polymer substrates, but not in a mixed surfactant solution.…”

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

“…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.…”

Photolytic Behavior of Some Popular Disperse Dyes on Polyester and Nylon Substrates

“…More recently, Acoria et al reported [4] that the photolysis of certain monoazo disperse dyes in amide solvents follows zero-order kinetics when done under nitrogen. They concluded that a reducing species was formed photochemically from the solvent which then interacted with the dye, and that the photofading rate increased with increasing solvation of the dye.A few papers have been published [3,5,15,17,23,25] describing work resulting from the fading of dyed films or fabrics. These papers include the recent work of Acoria [5], which suggested that a reductive pathway was involved when nine azo dyes were irradiated on nylon films at 254 nm in the presence or absence of air.…”

“…A few papers have been published [3,5,15,17,23,25] describing work resulting from the fading of dyed films or fabrics. These papers include the recent work of Acoria [5], which suggested that a reductive pathway was involved when nine azo dyes were irradiated on nylon films at 254 nm in the presence or absence of air.…”