Charge and the dry-strength performance of polyampholytes. Part 1: Handsheet properties and polymer solution viscosity

Paper strength was increased by adding random terpolymers having a fixed ratio of basic to acidic monomeric groups to bleached kraft fibre slurries over a wide range of pH. Subsequent treatment of the fibre slurries with polyaluminum chloride (PAC) increased tensile breaking length further. By contrast, PAC tended to reduce the dry-strength contribution of a cationic polyelectrolyte having the same mass and cationic monomer content as one of the polyampholytes. The reason for adding the PAC last to the mixture was to evaluate possible interactions of fresh, highly cationic aluminum species with the polymers as well as with the fibre surfaces. It is proposed that the observed effects are due to the influence of pH and ionic aluminum species on the molecular conformations, as well as to the electrokinetic behaviour of the solids exposed to the polyampholytes. Results of solution viscosity tests indicated more expanded polyampholyte conformations resulting from PAC addition, especially in those cases where dry strength advantages of PAC addition were observed.