Sizing mechanism of emulsion rosin size-alum systems was studied in terms of chemical structures of rosin size components in handsheets prepared under various conditions. Extraction of handsheets and cellulase-treated residues of the handsheets with dioxane-water revealed that at least 80 % of the rosin size molecules were present in the sheet as free acid structures without forming aluminum salts for both cured and non-cured handsheets. Since no sizing features appeared on the extracted handsheets, the rosin size molecules having free acid structures contributed to the appearance of sizing features. Thermal behavior of the cellulase-treated residues also supported that no aluminum rosinates were formed in the sheet at least by curing treatments, although sizing degrees of the cured handsheets were clearly higher than those of non-cured ones. Scanning electron microscopic observations of surfaces of cured and non-cured handsheets, and X-ray diffraction analysis of the cellulase-treated residues showed that melting of rosin size molecules having free acid structures and their spreading over pulp fiber surfaces was the primary reason for the curing effect. Although the presence of aluminum compounds in the sheet was necessary for the efficient appearance of sizing features, this effect must be explained in terms of some mechanisms other than the simple aluminum rosinate formation.
All Science Journal Classification (ASJC) codes
- General Materials Science