Three purified sodium lignosulfonate (SL) samples with various molecular weights were prepared by fractionation using ultrafiltration.The structural characteristics of SL samples and its effect on performance of dye are investigated by means of gel permeation chromatography

ultraviolet spectrophotometry

electrolytic titration and high temperature dying process. The results show that

with increase of molecular weight

the color of SL becomes darker

its purity increases

and the content of guaiacyl increases while phenolic hydroxyl

carboxyl and sulfonic decrease. The SL with high molecular weight is of good dispersibility and high temperature stability for dispersing dyestuff

and the dyeing rate of dyestuff increases also with increase of SL molecular weight. The staining of SL for fiber could be weakened when its molecular weight is larger and its concentration is higher. In addition

the reduction destruction of SL for dyestuff depends on molecular weights and the content of phenolic hydrophilic group. The SL fraction with molecular weight above 2.5?103 can make dyestuff the most excellent levelling property and the lowest reduction effect

the reduction and hydrolysis rate reduce from 26.0% of unpurified SL to 6.9%.