Extractives on fiber surfaces investigated by XPS, ToF-SIMS and AFM

Abstract

The composition, nanostructure and distribution of extractives on fiber surfaces of a birch bleached kraft pulp (BKP) and a recycled deinked pulp (DIP) was investigated using X-ray photoelectron spectroscopy (XPS or ESCA), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and atomic force microscopy (AFM). Effects of different extraction methods on the fiber surfaces were also investigated, in addition to the analyses of extractives by gas chromatography (GC). Traces of surface extractives were observed by XPS, ToF-SIMS and AFM in the BKP after extraction using an acetone–phosphate method (AcP). This method improved the extraction yield of palmitic and stearic acids in DIP, but the removal of surface extractives was not as effective as for BKP. Contaminants, identified as siloxanes and phthalates by ToF-SIMS were observed for DIP and BKP, even after AcP extraction. Stearic acid and its calcium salts were found to form aggregates with a diameter of 100–500 nm, while oleic acid formed a uniform layer. Estimations of extractive surface coverage by XPS were consistent with qualitative observations by ToF-SIMS and AFM. The combinations of different techniques strengthen the value of XPS, ToF-SIMS and AFM for fiber surface investigation.