Adding value to Alfa grass (Stipa tenacissima L.) soda lignin as phenolic resins - 1. Lignin characterization

Soda lignin from black liquors of Alfa grass was precipitated with hydrochloric acid at pH 2 and 4.5, and with sulfuric acid at pH 4.5. The molecular structures of the lignins were analyzed for the first time. The phenolic structures were studied using UV-visible spectroscopy and P-31-NMR spectrometry. The lignin fragments were also analyzed by size exclusion chromatography and beta-O-4 bond content was determined by thioacidolysis. The total phenolic content was found to be low for annual plant lignin, with more phenolic guaiacyl units than syringyl ones, and with a low proportion of condensed units. The phenolic syringyl elements appear to include beta-O-4 bonds in large proportion in contrast with guaiacyl and p-hydroxyphenyl units. (C) 2002 Elsevier Science Ltd. All rights reserved.