Physico-chemical characterisation of TMP resin and related model mixtures

Abstract

Abstract A set of model resin mixtures were prepared to simulate Norway spruce thermomechanical pulp (TMP) resin at different conditions, such as in winter or summer, or after lipase and/or steryl esterase treatments. The resin samples were analysed on their viscosity, tackiness, wettability and surface energy; properties which may be related to the deposition tendency of wood resin. During production of mechanical pulps, large amounts of wood resin are dispersed into the process waters, which may later on aggregate and deposit onto paper machine equipment or the formed sheet, thus affecting the runnability of the paper machine as well as the quality of the paper. It is, therefore, important to understand which physico-chemical properties of the wood resin may influence its deposition tendency. The results showed that resin acids, steryl esters, and especially sterols had a much stronger effect on resin viscosity than the lower-viscosity fatty acids and triglycerides. The surface energy measurements showed that steryl esters and triglycerides were the most hydrophobic components. The resin acids, fatty acids and sterols gave the highest value for the acid-base (AB) component of the work of adhesion ( W a ). Model resin mixtures with high amounts of one or more of these three components also showed a higher AB component of the W a . In light of this, a model for the wood resin droplet was proposed. Colloidal droplets released from spruce TMP tend to form a two-layered droplet structure. The hydrophobic steryl esters and triglycerides form the core and main body of the resin droplets, while the resin acids, fatty acids and sterols, are enriched at the outer surface with the carboxyl and hydroxyl groups extending into the water. Because of the high viscosity of resin acids and sterols, the exterior part may be a viscous film. Although the exterior part is much thinner than the interior, it probably plays a much more important role in determining resin properties, such as chemical reactivity, charge, colloidal stability and pitch deposition tendency.