The surface composition of explosion pulp and conventional CMP and CTMP underwent ESCA spectroscopy. Explosion pulps exhibited a higher oxygen-to-carbon ratio and less C1 peak areas compared to conventional CMP/CTMP. Based on the theoretical O/C ratios and C1 contents for the main components of wood fibers (i.e., carbohydrates, lignin and extractives), a triangular graph was used to illustrate the relative amounts of the three components on the surface. This analysis indicated that explosion pulps had more carbohydrates exposed on their fiber surface, which may explain their high physical strength. A bulk analysis indicated that these differences could not depend on their bulk compositions, since the latter were similar.
The oxygen (1 s) ESCA peak for aspen explosion pulp consists of two components, O1 and 02. A tentative assignment was made for them. Ol with lower binding energy is assigned to oxygen in lignin; while 02 comes mainly from the oxygen elements in carbohydrates. Thus, an O1 area percentage might be viewed as a measure of lignin exposed on the fiber surface. Sulfur (2p) spectra show that the sulfur on the fiber surface of the pulps studied here is in the form of sulfonate groups. Compared to conventional pulps, the lower percentage of Ol and higher sulfur-to-carbon ratio for explosion pulps imply higher number of hydrophilic groups exposed on their fiber surface.
Steam explosion pulps were studied by means of CP/MAS 13C NMR spectroscopy. The steam explosion treatment of aspen chips with Na2SO3 and Na2SO3 + NaOH led to a loss in hemicellulose and an increase in cellulose crystallinity. No lignin dissolution occurred during explosion pulping, although the lignin structure might have changed to a certain extent. For comparison purposes, conventional CMP and CTMP pulps were also analyzed. The conventional treatments revealed less modification in the spectrum with regard to original wood samples.
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