The influence of lignin content and structure on hemicellulose alkaline extraction for non-wood and hardwood lignocellulosic biomass

The extractability of hemicellulose from different lignocellulosics depends on the source of biomass. Differences in hemicellulose extractability are believed to be due to plant-specific hemicellulose arrangement alongside lignin within the cell wall. In this research, six biomasses were used to probe hemicellulose alkaline extractability as a function of the native lignin within the biomasses. Quantitative 2D-HSQC and 13C NMR analysis were performed to determine the S/G (S: syringyl, G: guaiacyl) and lignin-carbohydrate complex (LCC) linkages of milled wood lignin isolated from these biomasses. A strong negative correlation was observed between total lignin content and hemicellulose extractability, demonstrating that a greater presence of lignin in the original material results in lower xylan solubilization. In addition, a correlation between S/G of lignin and xylan dissolution was found within a group of hardwoods and within a group of non-woods. This suggests that monomeric constituency also influences xylan’s propensity for dissolution in 10% NaOH. Although there is some uncertainty in the quantification of LCC linkages, both non-woods and hardwoods exhibited negative correlations between alkaline-stable LCC linkages content and xylan extractability. This suggests that alkaline-stable LCC structures are associated with a decrease in the alkaline extractability of hemicellulose.