Abstract: Aiming at the low dye uptake of plant pigment, multiple compositions of tunmeric, rhubarb and gamene were selected to be separated by membrane technology. The relation of molecular status of plant pigment and its dye uptake, colour depth and fastness on silk were studied. The result shows that there is close relationship between molecular status of plant pigment and dye uptake. The rate of dye uptake is only around 10% when the molecular weight of combination of pigment and impurity is more than 10000, while the rate of dye uptake can be up to 30% and 50% when the molecular weight of conbination of pigment and impurity is less than 5000 and 3000. Enzymes can break the combination of plant pigment and impurity. the dissolution rate of plant pigment of which the molecular weight of conbination of pigment and impurity is less than 5000 can increase up to 30% when the combination of amylase and pectinase is applied to treat the extracting solution of plant pigment.

Key words: vegetable dye, membrane separation, enzymatic treatment, dye uptake