Abstract
aluminum sulfate (alum) as a representative retention aid in papermaking processes was added to pulp suspensions, and the aluminum components adsorbed on the pulp were investigated quantitatively by two types of X-ray elementary analyses with regard to simultaneous changes of their surface charges. X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence analysis (XFA) were applied to determine the aluminum components retained in pulp pads up to ca. 10 nm and 100${\mu}$m depth, respectively. In other words, XPS was utilized to analyze the outermost surface layers of the samples, and XFA was available for measurement of their extensive regions. A particle charge detector (PCD) was used to monitor streaming potentials at various pHs of the pulp mixtures under moderate sharing conditions. At pH 4.5 of pulp suspensions containing alum, surface charges of pulp fibers varied from negative to slight negative (approximately neutral) according to adsorption of aluminum components onto the pulp fibers. Subsequently, when a dilute NaOH solution in limited amounts was added to pulp mixtures, both streaming potentials and surface aluminum content of the pulp fibers increased distinctly although little total aluminum retention increased. Further addition of alkali solutions brought drastic decreases of the surface charges and surface aluminum content, while total aluminum content, on the contrary, increased gradually under neutral conditions. These results indicate that residual aluminum ions remained in pulp suspensions are predominantly adsorbed on surfaces of pulp fibers by adequate alkali additions and they must sufficiently cationize the fiber surfaces with increases of somewhat cationic aluminum complexes formed on the surfaces. On the other hand, aluminum components formed in higher pH ranges have nearly no contribution to improvement of charge properties of the pulp fiber surfaces, even though aluminum retention in pulp pads increases. XPS and XFA analyses combined with streaming potential measurement using a PCD suggest close relationships between aluminum content on the pulp fiber surfaces and their charge properties.