Preparation of lignin and extractive model surfaces by using spincoating technique – Application for QCM-D studies

A method of preparing model lignin and extractive surfaces by using spincoating technique has been developed. The primary aim for the use of these surfaces is adsorption studies performed with the quartz crystal microbalance with dissipation (QCM-D instrument). Milled wood lignin (MWL) was isolated from Norway spruce (Picea abies) and the extractive mixture used was hexane extracted from thermomechanical pulp (TMP) from spruce as well. Both the model films were spincoated on the hydrophobic, polystyrene coated QCM-D crystal. Based on the atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) analyses, smooth and rigid model films were achieved and they were found to be evenly distributed on the polystyrene surface. The stability of the films in aqueous solutions at different ionic strengths (lignin film) and pH (extractive film) were studied using QCM-D. Some water penetrated into the lignin film but no swelling was detected. Extractive film was stable in acidic and neutral conditions but saponification of the fatty and resin acids in basic conditions resulted in an unstable film. Model films were shown to give repeatable results when studying the adsorption of spruce hemicelluloses with QCM-D. It was found that the adsorbed mass, physical properties of the formed layer and the layer formation within the time scale used were all repeatable.