Azo dye location in textiles: a novel UV–vis approach

Abstract

Ultraviolet–visible spectra of Orange II exhibit blue shifts in apolar solvents due to the formation of the azo tautomer. Upon absorption to cotton, Orange II remains as the hydrazone tautomer and, like other phenylazonaphthol dyes or Methyl Orange, exhibits small red spectral shifts. Two superimposed spectra – characteristic of the azo and hydrazone tautomeric forms – are detected when dye 1 (X=p‐MeO) absorbs onto cotton. Only the azo form is observed on nylon; all other dyes, except Orange II, give blue shifts. A model is developed in which the more apolar moiety of the dye binds to pockets formed in the non‐crystalline (amorphous) regions of cotton, with those parts containing the sulphonate group protruding into aqueous pores. In nylon, the binding sites are more apolar with the sulphonate groups bound electrostatically.

New insights into dye chemistry and physics

“…This method was used to examine the environment within cotton and showed that simple monoazo dye encounters both polar and apolar regions in cotton. This would agree with the dye being absorbed on apolar surfaces of crystallites while also interacting with water in amorphous regions .…”

“…This would agree with the dye being absorbed on apolar surfaces of crystallites while also interacting with water in amorphous regions [47]. This method was used to examine the environment within cotton and showed that simple monoazo dye encounters both polar and apolar regions in cotton.…”

“…The azo‐hydrazone tautomerism changes the UV‐vis spectral profile, and this was found to be a useful probe of micropolarity in solution and in microheterogeneous solids . As the micropolarity decreases, the relative height of the shoulder at 430 nm increases, reflecting an increase in the azo fraction relative to the absorption max (λ max ) at 480–485 nm.…”

Synthesis and Application to Polyester and Nylon 6 Fabrics of Hetaryl Bis-Azo Disperse Dyes Based on 6-Amino-2,4-Dihydroxypyrimidine and 4-Methoxy-2-Nitroaniline Moieties

“…This agrees with the view that azo dyes containing electron-withdrawing groups such as -NO 2 ortho to the hydrazo (-N=N-) group, tend to significantly decrease the electron density, and has have been reported to enhance the photostability [19] of dyed polyester fabric. The slightly better photostability of the dyes on polyester fabric [20] could be as a result of the compact crystalline nature of the fibre compared with that of nylon fabrics. The sublimation fastness results gave ratings of 4 to 4/5, which indicates acceptable performance.…”

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“…Passive smart fabrics comprise of first stage productions of smart fabric that offer an extra feature in an inactive manner regardless of the variation of the surrounding [84]. Active-smart fabrics comprise of second level production active smart fabrics have both sensors and actuators that modify their usefulness in altering the environment automatically.…”