Commercial photochromic and thermochromic colorants that change rapidly and reversibly from colorless to colored state when activated by stimuli like ultraviolet irradiation, temperature or pH are well established class of colorants for manufacturing of niche products. Use of photochromic and thermochromic systems in applications like medical thermography, plastic strip thermometers, photochromic lenses, food packaging and nondestructive testing of engineered articles and electronic circuitry is well documented. However, in the last few years, the research on application of these systems on textiles has picked up significantly which has the potential to unlock commercially significant nascent high-tech applications. This review paper presents a summary of the chemistry, mechanism, application on textiles and evaluation procedure of performance, other technical features, current and potential application areas as well as challenges encountered in wider acceptance of photochromic and thermochromic colorants on textiles.
Commercial thermochromic colorants were applied to a conductive cotton fabric prepared by using nichrome/cotton core‐spun yarns in weft and 100% cotton in warp. The fabrics were pretreated and coloured with thermochromic pigments in isolation, in combination with each other, or in a mixture with a non‐thermochromic pigment. The weft yarns were joined to allow passage of current through the fabric to enable ohmic heat generation to increase fabric temperature. The heat generation and temperature rise could be controlled by monitoring the voltage applied. The colour of the samples changed gradually with an increase in temperature, and significantly so when the temperature of the fabric rose beyond the activation temperature of the thermochromic colorant. The temperature‐dependent properties of commercial thermochromic colorants were determined using a spectrophotometer. Wash fastness of the samples was found to be fair in all cases except with the yellow colorant. Predetermined colour effects, such as camouflage or novel design, can be produced by combining thermochromic colorants with conventional pigments or thermochromic colorants with different activation temperatures.
Mercerization, the treatment of cotton with concentrated sodium hydroxide under tension, is performed to enhance absorption, luster, strength and dimensional stability. After mercerization, the unreacted sodium hydroxide is neutralized with acids. Neutralization with polycarboxylic
acids (PCAs) is likely not only to crosslink the cellulose molecules, but to also enhance other functional attributes like crease recovery behavior, flame retardancy, and soil release properties. In this research, four PCAs with different functional groups were used for fabric neutralization
to merge mercerization and poly- functional finishing into one continuous process. The PCA treated fabrics were then assessed for their performance. All four PCAs were effective in improving crease recovery and soil release properties, and reducing the flammability, of the treated cotton fabric.
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