MORPHOLOGICAL AND CHEMICAL CHARACTERISTICS OF STEM AND KNOT POPLAR WOOD

摘要

Scanning electron microscopy showed differences in the ultrastructure of stem- and knotwoods. In contrast to stem, knotwood has more compact deformed structure. Its more dark colour is caused by relatively high lignin content as results from the chemical analysis. The lignin extractability of both wood samples was examined by acidolysis in dioxane — water. The chemical character of knots is different from normal stemwood. The characteristics of knotwood lignins, comprising elemental analysis, average molecular weight, polydispersity factor, degree of branching and cross linking density were determined. The results obtained confirm of knotwood lignin exhibits rather higher molecular weight related to stem. The observed lower accesibility of lignin component could explain a negative impact of knots on pulping process.