The influence of lignin chemistry and ultrastructure on the pulping efficiency of clonal aspen (Populus tremuloides Michx.)

The variation in wood chemistry among aspen clones of similar age, harvested from a common site in northern British Columbia, Canada, was evaluated. The aspen clones were evaluated for ease of chemical pulping and differed by as much as 4.5% in pulp yield at a common H-factor. The results demonstrate both the need for understanding the resource and the substantial opportunities that exists in natural population of trees for selecting superior clones for reforestation and afforestation. The syringyl/guaiacyl ratio, as determined by nitrobenzene oxidation, was directly correlated with the ease of pulping, whereas thioacidolysis results were not as predictive. These results were supported by quantitative NMR analysis, which demonstrated differences in the amount of beta-O-4/Ar groups and the degree of condensation. Furthermore, it was shown that, in addition to total lignin content, which differed by as much as 5%, structural differences in the lignin may influence pulping efficacy. Among the other parameters evaluated, the distribution of molecular mass and methoxyl content is relevant for pulping. More specifically, among the fractions isolated in this study [milled wood lignin ( MWL), MWELsol, and MWELinsol], the insoluble fraction was the most indicative of the pulping efficiency.