RADICAL SULFONATION OF LIGNIN .4. BEHAVIOR OF WATER-SOLUBLE LIGNINS IN AQUEOUS-SOLUTIONS

For the total utilization of lignocellulosic resources, new developmen ts of lignin dispersing agents have been investigeted. Water-soluble l ignins prepared separetly by a radical-sulfonation treatment and an al kali-oxygen treatment of an acid hydrolysis lignin were characterized by gel-filtration chromatography, and adsorption behaviors to kaolin, powdered coal, and veratorole. A most reliable gel-filtration chromato gram was found to be obtainable by the use of a dilute alkali as an el uent. By the addition of a dispersing agent to water-soluble lignins, the lower-molecular weight fractions newly appeared in gel-filtration chromatograms of water-soluble lignins, which strongly indicates the i nteraction of lignin molecules at the hydrophobic parts of lignin surf aces. Water-soluble lignins were adsorbed not only hydrophilic kaolin particles, but also to powdered coal and veratorole. Because the latte r two are hydrophobic materials, the adsorptions of water-soluble lign ins are due to hydrophobic interacrion, which must be very important f or the dispersing ability of water-soluble lignins.