Vegetable dyes: molecular status vs dyeing ability

Aiming at the problem of low dye uptake of vegetable dyes,tunmeric,madder,and rhubarb were selected and their dye components were separated by membrane technology.The molecular status of vegetable dyes in the solution was investigated as well as its relationship with the dye uptake,color depth and color fastness on silk.The results showed that close relationship exists between the molecular status of coloring material and the dye uptake.The dye uptake is only around 10% as showed by the bonding of coloring material with the impurities when the molecular weight is more than 10 000;and while the dye uptake can be up to 30% and 50% when the molecular weight is lower than 5 000 and 1 000,respectively.Bio-enzymes can break the bonding of coloring material with the impurities.The dissolution rate of vegetable coloring material with the molecular weight lower than 5 000 can be increased by more than 30% if the coloring material extract is treated by amylase and pectinase.