pH Dependence of the Color of Pigments in Naturally Colored Cotton

摘要

Naturally colored cotton (NCC) is a kind of environmental friendly natural fiber,which has been successfully bred in many countries.The instability of the color of NCC based products has been the concern for their further development.In this paper,the pH dependence of the color of NCC was investigated,and LAB color space was used to evaluate the color properties of the NCC.The color of the NCC is highly pH dependent.The L value (lightness) is polynomially decreased with increasing pH value of the treatment,indicating the intensifying of the color when pH of the treatment is increased,for both the brown and green cotton.The a value and b value of the color properties are also decreased with increasing pH of the treatment solution.Such phenomena are attributed to the new chemical equilibrium and also consequently the new pigment forms formed when the concentration of H+ or OH-was changed as the pH value changed.The detergent treatment has generally stronger action on the intensifying of the color than that having same pH value but no detergent present,indicating that all kinds of chemicals in detergent formulation could probably additionally intensify the color besides the reason of the alkali nature of the detergent solution.Chemical reactions between different ions in different detergents and the pigments in NCC change the color properties.The pH dependence of the color of NCC fiber also suggests that a weak alkali wash finishing may be applied for the NCC based product so as to improve its color property,especially its shade depth.