Comparative study on topochemistry of delignification from Japanese cedar and Japanese beech by hydrothermal treatment

Abstract

The difference in decomposition behavior of lignin from Japanese cedar (Cryptomeria japonica) as softwood and Japanese beech (Fagus crenata) as hardwood treated by hot-compressed water was investigated. The obtained residual lignin was then evaluated by the alkaline nitrobenzene oxidation analysis, the relative proportion of ether type linkages had decreased for both species as the hot-compressed water treatment was prolonged. Furthermore, the microscopic observation of the residual lignin indicated that lignin in tracheid cell walls was removed to a greater extent than that in middle lamella in Japanese cedar. Similarly in Japanese beech, lignin in fiber cell walls was removed more extensively, with middle lamella lignin remaining after two-step treatment. Such observation was supported by a result obtained from the methoxyl content analysis per C9 unit of the residual lignin. Based on these lines of evidence, lignin in middle lamella must be rich in condensed type, and these differences between softwood and hardwood can be attributed to the intrinsic characteristics of the original lignin and its topochemistry in woods.