Light fastness in cotton and silk with yellow plant dye extracted from Koelreuteria paniculata leaves

Plant dyes are eco-friendly and healthful, while most of them have poor color fastness, especially light fastness. A novel yellow plant dye was extracted from Koelreuteria paniculata leaves and assessed for color fastness to light compared with three typical yellow plant dyes, Sophora japonica , gardenia, and turmeric. The first method used traditional boiling method with distilled water to obtain dye solutions which were treated on woven cotton fabric and silk fabric under conditions with alum mordant and without mordant. The light fastness of dyed fabrics was tested and evaluated. The dyed fabrics demonstrate excellent light and wash color fastness performance with ratings of 4–5 or 4. The K/S reduction values of K. paniculata leaves were all the lowest after light exposure and oxidative bleaching. The second method extracted dyes with ethanol and the dye solutions were subjected to light under the catalyst. The absorbance of four plant dyes before and after lighting was tested and the degradation rates were calculated. K. paniculata leaf dye solution has the lowest degradation rate. Results showed that the stability of plant dyes and the color fastness of dyed fabrics are consistent. K. paniculata leaf dye has the highest light stability and light fastness of dyed fabrics is also superior to the others. This indicates that the light stability of dyes may have a significant impact on the light fastness of dyed fabrics. Because of its excellent light fastness, K. paniculata leaf dye has promising application prospects.