Comparative study of three lignin fractions isolated from mild ball-milled Tamarix austromogoliac and Caragana sepium

Six lignin fractions from mild ball-milled Tamarix austromogoliac (TA) and Caragana sepium (CS) were sequentially isolated with 80% dioxane containing 0.05M HCI at 75 degrees C for 4 h, 50% aqueous ethanol containing 1M triethylamine at 70 degrees C for 4 h, and 8% aqueous NaOH at 45 degrees C for 3 h. The results showed that the successive treatments made it possible to isolate lignin from wood with a high yield and purity, in which 89.4 and 90.6% of the original lignin from TA and CS were released, respectively. The lignin fractions isolated with the three-step method were analyzed with Fourier transform infrared, H-1- and C-13-NMR, alkaline nitrobenzene oxidation, and gel permeation chromatography. It was found that the three lignin fractions isolated from TA were rich in syringyl units, and the molar ratio of the relatively total moles of vanillin, vanillic acid, and acetovanillin to the relatively total moles of syringaldehyde, syringic acid, and acetosyringone decreased from 1 : 2.6 to 1 : 3.2 to 1 : 3.6 in the lignin preparations, whereas this ratio in the corresponding lignin fractions isolated from CS was found to be 1.4 : 1, 1.1 : 1, and I : 1.4, respectively. More importantly, the results revealed that the sequential extractions of the mild ball-milled TA and CS with 80% acidic dioxane, 50% alkaline ethanol, and 8% aqueous NaOH under the conditions used did not significantly cleave the beta-O-4 and alpha-O-4 linkages in lignin macromolecules. (C) 2008 Wiley Periodicals, Inc.