Thermal Melting of Lignin Derivatives Prepared from Dried Black Liquor Powder of Softwood Soda-AQ Cooking and Polyethylene Glycol

Softwood lignin prepared by soda-anthraquinone (AQ) cooking does not have thermal melting characteristics. To improve the properties of softwood soda-AQ lignin, we have invented a new method of lignin modification using dried black liquor powder by a spray dryer system and polyethylene glycol (PEG). In this process, black liquor powder was directly treated with PEG under alkaline conditions to produce PEGmodified lignin (alkaline PEG treatment). Dried black liquor powder prepared by a spray dryer was dissolved into PEG and heated at either 120 or 160 C at atmospheric pressure. The modified lignin (alkaline PEGtreated lignin) was precipitated with acid and recovered by filtration. The alkaline PEG-treated lignin showed adequate thermal melting characteristics. The treatment temperature and the molecular weights of PEG considerably affected the thermal properties of the alkaline PEGtreated lignin. There was an addition reaction of the PEG to the lignin hydroxyl group at the alpha-(-) carbon. However, in the acid precipitation step, if the mixture was allowed to set unfiltered for a long time, the PEG bonded with the lignin was hydrolyzed, which yielded the original soda-AQ lignin and PEG polymer.