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

Abstract 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 31 P-NMR spectrometry. The lignin fragments were also analyzed by size exclusion chromatography and β- 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 β- O -4 bonds in large proportion in contrast with guaiacyl and p- hydroxyphenyl units.