Dyeing behavior of red rice pigment on silk and polyamide fibers

The structure of acid-modified red rice pigment was investigated by thermal analysis and Fourier-Transform-Infrared,and N-butanol-water two-phase distribution method was used to determine the change in hydrophobicity of the modified red rice pigment as well.The influence of pH,amount of pigment,and temperature on the properties of silk and polyamide fibers dyed with red rice pigment before and after acid-modification was studied.The color fastness of red rice pigment on silk and polyamide fibers was compared between direct dyeing and mordanting.It showed that cyanidin-3-glucoside was conversed into cyanidin under acid condition,and the hydrophobicity of red rice pigment after acid treatment was enhanced.Furthermore modified red rice pigment had better dyeing properties,and suitable for dyeing silk and polyamide fibers in the range of pH 2～4.The color fastnesses to washing and rubbing of red rice pigment on silk and polyamide fibers reached grade 4 or better.The light fastness on polyamide fiber was poor,about grade 2,and on silk,about grade 3.Silk and polyamide fiber dyed with pre-mordant and post-mordant methods had better light fastness.