An investigation of the performance of photochromic dyes and their application to polyester and cotton fabrics
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Six commercial photochromic dyes were applied to polyester and, to a lesser extent, cotton fabrics by different dyeing and printing methods. The photochromic performance of the dyed and printed fabrics was investigated in terms of the degree of photocoloration, background colour, fading characteristics, fatigue resistance and storage stability. A traditional aqueous-based disperse dyeing method was used to apply the photochromic dyes to polyester fabric. Solvent-based dyeing methods also were investigated for application of the photochromic dyes to polyester fabric. Solvent-based inks were formulated and applied to polyester and cotton fabrics by digital inkjet printing. The photochromic performance and colour fastness to light and washing of the photochromic fabrics were evaluated and comparison made. UV/visible spectra of the commercial photochromic dyes in a range of solvents were obtained and interpreted in terms of solvent polarity. On the basis of this study, the photochromic performance of the fabrics was improved by selecting the appropriate application solvents which transferred minimum background colours onto the fabrics. A new method of evaluating lightfastness of photochromic fabrics was established, aimed at replacing the conventional method by an instrumental method. This method was based on comparing the decrease in the degree of photocoloration of photochromic fabrics after light exposure with measured values of the colour differences of the blue wool references after fixed periods of light exposure. Two photochromic dyes were synthesized by azo coupling of a spironaphtho[2,1-b]oxazine with diazonium salts obtained from p-nitroaniline, and m-nitroaniline. Molecular modeling of the new photochromic systems, which are referred to as azospirooxazine dyes, showed that the dyes were predicted to have the potential to show photochromism. Thus, the photochromism of the azospirooxazine dyes in a range of solvents was investigated. The investigations showed that the dyes performed differently in different solvents in terms of the hue, the rate of the photochromic colour change and the colour reversibility.