Molecular Characterization of Alkalilignin-1M30C: a Valid Alternative Preparation to the Björkman Lignin in the Analytical Study of Wheat Straw Lignin

Bjorkman lignin, obtained by extensive grinding and dioxane extraction, is considered one of the most suitable standard preparations close to the native lignin from lignocellulosic materials. In this study, alkalilignin extracted with 1 M NaOH at 30 °C (AL-1M30C), and the Bjorkman lignin from wheat straw (Triticum aestivum) were compared using spectroscopic and degradative techniques. The very small chemical differences between the two preparations are mainly that the Bjorkman method yields a lignin with slightly higher proportion of p-hydroxyphenyl units, and some co-extracted aliphatic fractions. The AL-1M30C preparation, on the other hand, showed a somewhat higher proportion of syringyl units, as well as the probable effects of the selective removal of structures associated with ester carbonyl groups. The evident similarity between both lignin samples suggests that AL-1M30C produced from wheat straw may represent a convenient alternative to Bjorkman lignin preparation for analytical purposes. These results also point towards the possibility of producing suitable lignin preparations from other Gramineae plants showing high solubility in alkaline reagents.