The network strength of non-flocculated fibre suspensions

The influencies of concentration acid of fibre length distribution on the network strength of nylon and pulp fibre suspensions has been studied experimentally and theoretically. A new model for non-flocculated suspensions is proposed, which postulates that the network strength is a product of the number of contact points per unit shearing surface, N-ss, and the average frictional force per contact point. An expression for N-ss has been derived for fibre suspensions with continuous length distributions. A modification of the model was also proposed, which takes the end-effects of the fibres into account by omitting m contact points at the ends. The network strength was measured with a concentric cylinder rheometer. Attempts have been made to achieve a non-flocculated suspension by dewatering a 0.25 wt % fibre suspension directly in the rheometer. It was found that mixing a small amount of long fibres into a short fibre suspension increased the network strength significantly more than could be explained by the increase in average fibre length. The proposed model performed well when using m=3 for nylon fibre suspensions and m=0 for pulp fibres. The measured values of F-o (normal force independent contribution to friction) seems to be larger than the corresponding forces in a suspension by a factor of 5. As well as being a predictive model, the new network model yielded better data fitting, when compared to the power-law models, for both pulp and nylon suspensions. Measurements of flocculated suspensions show significantly lower network strength as compared to non-flocculated suspensions. Further theoretical work is needed to account for flocculation.