ESCA STUDY OF THE SOLID RESIDUES OF SUPERCRITICAL EXTRACTION OF POPULUS TREMULOIDES IN METHANOL

A systematic ESCA study of the solid residues of supercritical critical extraction of Populus tremuloides prepared in various conditions has been performed. Reference materials also examined by ESCA included the initial wood, Whatman no. 1 paper, and two lignins prepared by different procedures. Interest has been focussed on the C//l//s and O//l//s spectra and on the determination of surface O/C atomic ratio. A difference between bulk O/C values measured by chemical analysis and surface O/C ratios obtained from ESCA data is considered diagnostic of a difference in chemical composition of the bulk and the surface. The O//l//s peak shows also a complex structure with three components in the wood-derived reference materials and four in some of the solid residues. These structures have not been discussed previously in the literature and a tentative assignment for the component peaks is proposed.