Effects of fatty acid components present in AKD wax on emulsion stability and paper sizing performance

Commercial alkylketene dimer (AKD) waxes generally contain 80-90% AKD, and the rest of the components are by-products such as fatty acids, fatty acid anhydrides, and AKD oligomers. In this article, the effects of fatty acid components present in AKD waxes on AKD emulsion stability and paper sizing performance were studied using AKD emulsions, which were prepared from an AKD wax mixed with 0-12% stearic and palmitic acids. Repeated temperature shock treatments revealed that the fatty acids-containing AKD emulsions became most unstable at 3% fatty acid content, whereas those with 12% fatty acids were rather stable. When the addition level of fatty acids was increased up to 12%, zeta potentials of the AKD emulsion particles increased from +1.4 mV to +4.4 mV with increasing fatty acid content. This increase in zeta potential may be one of the factors that lead to a decrease in AKD retention ratios in handsheets. Thus, fatty acid components present in AKD waxes not only decrease the pure AKD content in the waxes but also have negative impacts on emulsion stability and paper sizing performance. These results show that fatty acid content in AKD waxes must be sufficiently controlled as low as possible to keep a standard level of the AKD wax quality.