Composition of lignocellulosic surfaces: comments on the interpretation of XPS spectra

The surface compositions of lignocellulosic materials are critical to their end use performance. X-ray photoelectron spectroscopy (XPS) measures the elemental composition sampling of a very thin surface layer, and has long been used to assess the surface composition of dry lignocellulosic materials. The method is based on the quantification of carbon and oxygen XPS peak sizes and shapes, but care is necessary to minimize the effects of surface contamination and degradation. We review the XPS method, and present a simplified approach to estimate the surface lignin content of extractive-free samples. The approach corrects for surface contamination and degradation by measuring the XPS signal of a cellulose standard under the same conditions as the lignin-containing samples. The method is illustrated using XPS results for a series of extracted softwood kraft pulps.