Decolourization of vat dyes on cotton fabric with infrared laser light

A method for the decolourization of coloured cotton fabric dyed with vat dyes, based on exposure to infrared laser light, has been tested. Pulsed CO₂ laser has been used for all experiments. To detect changes in colour shade, reflection data of original and dyed cotton irradiated at various fluency of infrared laser light were measured on a UV–VIS spectrophotometer, and then colour intensity was calculated for each vat dye. To observe changes in chemical composition and morphology of fiber surfaces, an analysis was performed by X-ray photoelectron spectroscopy and scanning electron microscopy due to thermal effects. Thermal stability of vat dyes and cotton fabric was determined with differential scanning calorimetry method to simulate the heating process during exposure of samples to the infrared laser irradiation.