The weak photostability of photochromic dyes applied to textile substrates is one of the disadvantages of the broader use of photochromic dyes in the textile industry. Therefore, the influence of optical brightener concentration on both the photocoloration and photostability of cotton fabric coated with photochromic microcapsules using a pad-dry-cure process, as well as the physical-mechanical properties and colorfastness properties, were studied in this research. Coated samples were subjected to different tests according to valid EN ISO standards; namely mass per unit area, fabric stiffness, breaking force and elongation, air permeability, and different colorfastness properties (rubbing, domestic and commercial laundering, and light). Results showed that the coated fabric had higher mass per unit area, stiffness, breaking force and elongation and lower air permeability compared to uncoated fabric, irrespective of the padding bath composition. Coated fabric has better colorfastness to wet than dry rubbing. The colorfastness to washing decreases with the increased number of washing cycles. The use of optical brightener decreases the photocoloration of coated fabric and increases the photostability of coated fabric after the exposure of samples to a Xenotest apparatus for longer than 12 h.
Keywords: cotton; optical brightening agent; pad-dry-cure process; photochromic microcapsules; photocoloration.