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

Kukjin Yoon, Shiho Takahashi, ThiThi Nge, Olov Karlsson, Akiko Nakagawa-izumi, Hiroshi Ohi, Yasumitsu Uraki, Tatsuhiko Yamada


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 PEG-modified 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 PEG-treated 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 PEG-treated 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.


Alkaline PEG treatment; Dried black liquor powder; Thermal melting; Polyethylene glycol; Softwood soda-AQ lignin

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