Abstract
For structural elucidation of native lignin, native lignins of Western hemlock (Tsuga heterophylla), Birch (Betula papyrifera marsh) and Rice straw (Oryza sativa) were converted to lignin-based polymers, lignophenols, through the phase-separation system. The lignophenols were divided into ether soluble (ESL) and insoluble (EIL) fractions. Their structural features were analyzed by GPC, UV-Vis, FT-IR and 1H-NMR. The weight ratio of ESL to EIL from Rice straw (grass plant) was higher than those from Western hemlock (softwood) and Birch (hardwood), indicating the difference in the growth of primary lignin chains resulted from random radical coupling of precursors. The FT-IR spectra of ESL showed higher absorption at 815 cm-1 due to C-H out of plane skeletal vibration of aromatic ring, suggesting higher frequency of grafted p-cresol, which was supported by 1H-NMR.
