Development and evaluation of an automated streaming potential measurement device

The streaming potential and other colloidal properties of aqueous suspensions of bleached kraft fibers were evaluated by a new laboratory instrument, the Streaming Potential Jar (SPJ). This device provides precise streaming potential data under moderately high electrical conductivity levels of 0.5–10 mS cm−1. Features of the SPJ include automated operation, rapid acquisition and processing of data, continuous stirring, and applied pressures up to 276 kPa. The SPJ also provides data related to drainage rates and the turbidity of the filtrate. Test results showed a high degree of linearity of the streaming potential signals with applied pressure and little dependence of the results on the solids levels of the fiber slurries. These results, which are consistent with the Helmholtz–Smoluchowski equation, tend to justify the level of applied pressure used in this work. Changes in streaming potential with increasing pH were consistent with expected dissociation of surface-bound carboxyl groups on the fibers. The absolute magnitudes of the streaming potential values of bleached kraft pulps were strongly affected by increasing concentrations of Na2SO4. However, a high repeatability of measurements was obtained throughout the range of conductivities considered; relative standard deviations of streaming potentials were consistently below 3%. Titrations with poly-(diallyldimethylammonium chloride) yielded curves that had shapes similar to those of parallel tests by microelectrophoresis; however, the amount of titrant needed to reach the endpoints was about three times higher in the case of the streaming potential tests. The disagreement between the endpoints determined by the two types of test is attributed to a diffusion process of the titrant into the porous fibers.