Effects of electrolytes, pH and surface tension on dewatering, dry and wet web properties

Speed of paper machines is often limited by the drainage rate of the furnish and the mechanical properties of the wet web, i.e. the tension and relaxation properties. The conductivity of the water was adjusted to 1 mS/cm with CaCl2 and the pH was 6.5 in order to mimic conditions on a fine paper machine. Addition of a non-ionic surfactant at concentrations below critical micelle concentration (cmc) decreased dewatering time and increased dry content. Tensile strength and residual tension at 2% strain of the wet web increased until cmc, primarily due to the increased dry content after wet pressing. Density, air permeability and tensile strength increased for dry sheets. Lowering of pH from 6.5 to 5, decreased dry content after wet pressing and air permeability of dry sheets. Adjustment of conductivity with NaCl caused a decrease in both tensile strength and residual tension for wet sheets and increased dewatering time.