CHANGE OF RICE STRAW LIGNIN WITH NAOH OXYGEN PULPING .2. COMPARISON OF RICE STRAW AND WOOD LIGNINS UPON A NON-STIRRING OXIDATION WITH NAOH OXYGEN

As fundamental research for alkali-oxygen pulping, milled lignins from rice straw (MRL), Japanese beech (Fagus crenata Bl.) (MJL), and Yezo spruce (Picea jezoensis Carr.) (MYL) were dissolved in NaOH solutions and oxidized with oxygen at 5 kg/cm2 under non-stirring conditions, bu t at which oxygen was insufficient although near practical conditions for the pulping, and their reaction behaviors were compared. After the reactions the lignins were fractionationed into precipitates at pH 8 and then pH 2 by centrifugation and extraction from the supernatant wi th organic solvents. Oxidizing degradation of lignin into smaller mole cular weights was greatest for MRL. Next was MJL. This suggested a con densation reaction where molecular weight (M(w)) distributions of acid -precipitated fractions showed the existence of larger Mw parts than t hat in the original materials. It was considered that the conditions o f shortages of oxygen and a great lignin consistency (20%) brought adv antages for the condensation reaction competing with oxidative degrada tion. In macromolecular fractions methoxyl contents larger than those in the original lignins, especially in MJL, suggested that syringyl an d guaiacyl units had great reactivity with the condensation.