Yield stress of pulp suspensions The influence of fibre properties and processing conditions

The variation of the yield stress of pulp suspensions was investigated for important process parameters. The measuring device was a standard shear rhe ometer with a rotor body designed as a Rushton type turbine and the cylinde r was modified into a baffled jar. A number of experiments were performed b y varying consistency, freeness, kappa number, pH, temperature and mean fib re length. It was found that the yield stress increases with increasing con sistency, kappa number, pH (slightly), freeness and mean fibre length where as it decreases with increasing temperature. This behaviour may be understo od from underlying physical and chemical characteristics of the interconnec ted fibres. It is suggested that yield stress, and not consistency, should be the relevant parameter in designing equipment along the fibre line of pu lp production.