Quantitative analysis of synthetic sizing agents (ASA/AKD) using NIR spectroscopy

The purpose of this work was to develop a fast and easy-to-use method for the quantification of synthetic sizing agents. The investigations have shown that a quantitative determination of synthetic sizing agents (ASA/AKD) is possible using NIR spectroscopy. With the help of multivariate data analysis and PLS regression, mainly the region of the CH,bands around 4300 cm(-1) and 5750 cm(-1) are evaluated. The prediction error (RMSEP) for the determination of AKD is 0.01% and 0.013% for ASA both calibrated for a copy paper system. Even an analysis of the percentage of bound and unbound ASA/AKD is possible by NIR spectroscopy of extracted paper samples. Thus, a fast and detailed investigation of mechanisms as regards sizing is possible. It has been shown that sizing agents adsorbed onto fillers do not significantly affect the water absorption (penetration) but they can increase the surface hydrophobicity (wetting). However, sizing agents adsorbed at highly anionic polyelectrolytes can contribute to (internal) sizing to a large extent, when they are retained in the paper. The percentage of extractable ASA depends mainly on the used solvent. The best extraction yields were obtained with polar solvents, such as acetone or methanol. There is a good correlation between the sizing level and the extracted amount of sizing agent, thus showing that extractable (not-bound) ASA contributes to sizing to a large extent and that the formation of ester bonds with the cellulose plays a lesser role in the development of sizing. The determination of sizing agents using NIR spectroscopy might even be available as an online application for the pulp and paper industry.