Pulp charge determination by different methods: effect of beating/refining

Total and surface charge of unbleached and bleached softwood kraft pulps of different levels of freeness were determined using three different techniques—potentiometric titrations, conductometric titrations (with NaOH and NaHCO3 separately) and polyelectrolyte titrations using a particle charge detector (PCD). Each method gave different charge values but the relative levels were similar for each pulp. The surface charge as determined by titration with poly-DADMAC was highly dependent on the degree of beating but the total fibre charge as given by potentiometric titration or conductometric titration with NaOH remained constant after beating. Conductometric titration with sodium hydroxide gave a slightly higher value for total charge than the potentiometric titration. Conductometric titrations with 0.05 M NaOH gave higher values of pulp charge than similar titrations with 0.05 M NaHCO3.