Photophysical processes in poly(hexamethylene adipamide)–acid dye complexes: Energetics of nylon 66 phototendering

Abstract

synopsisThe mechanism of dye-sensitized photo-oxidative degradation of nylon 66 was investigated.A .known phototendering dye, C.I. Acid Blue 40 (l-amino4(paminoacetanilide)-2-anthraquinone sodium sulfonate), was used for this study. Excitation and emission spectra of the dyed and undyed nylons indicated that a ground-state complex between the dye and the polyamide waa formed upon dyeing. The energy level of the complex's electronic states favor triplet-triplet energy transfer from the nylon to the complex. Quenching studies show that the energy transfer occurs efficiently with a rate constant of 45.8 1. mole-' sec-l. An additional energy transfer occurs between the excited free dye and the complex by either a singlet-triplet or a triplet-triplet mechanism. Kinetic analysis of the nylon-complex energy transfer suggests that the triplet energy of nylon migrates 24 to 33 A along the amide chromophores in an exciton fghion until an energy trapping complex is reached. Energy is then transferred by an exchange mechanism. Photo-oxidative studies verify that the dye-nylon complex sensitizes the polyamide photo-oxidative degradation at its own expense without dye photobleaching.

Effect of Dye-Bath pH on Photostability of Dyed Nylon 66

“…Samples dyed at pH 3.0 to 7.0 show the same extent of photo-oxidation. Neat samples showed more photo-oxidation than those dyed above [2] also observed that the samples containing 0.52 and 0.83% dye (C. I. Acid Blue 40) degraded much less than the undyed nylon.…”

“…[1,2] Photo-oxidation of polyamides in the presence of oxygen, impurities, dyes, pigments and delustrants is also well reported. [3 -5] However, the mechanistic aspects of dye sensitized photo-oxidative degradation of polyamides remains an important area of research for textile chemists and polymer scientists.…”

“…Koenig and Roberts [2] investigated a ground state complex formation between the dye and the polyamide using photoluminescence technique. They observed that the energy level of electronic states of this complex favored triplet-triplet energy transfer from the nylon to the complex.…”

Progress in the Area of Degradation and Stabilization of Nylon 66

“…The 2-aminoanthraquinone and 2-hydroxy anthraquinone gave strong transient absorption on flash photolysis in 2-propanol due to the formation of dye radical anion (AA~), whereas 2-amino-3-hydroxyanthraquinone gave strong transient absorption due to the semiquinone radical (AH) [37]. This difference causes higher lightfastness of the latter in the polymer.…”

“…These carbonyl species, on further exposure to thermal/photochemical treatments, decompose to diketones and dialdehydes, which are precursors to the pyrrole compound formation [36]. Koening and Roberts [37] studied the mechanism of dye-sensitized photodegradation of nylon 66 by means of excitation and emission spectra of polymer dyed with C.I. acid blue 40.…”