Influence of solids loading on aqueous injection moulding paste

Model aqueous injection moulding (AIM) pastes were investigated hy capillary rheology at five levels of solids loading. The critical volume fraction of solids ((phi)m) was measured bv water absorption and estimated hy linear and non-linear (where appropriate) extrapolation of the rheological parameters, reciprocal upparent viscosity and reciprocal hulk yield stress. Three models winch consider the influence of volume fraction of solids on relative viscosity were considered: the C hong, German, and Krieger-Dougl-lerty equations. An iterative metlwdfor estimation of (phi)m, dependent on the model used, was also developed for comparison. The German model using the iterative method for estimating (phi)m gave the best prediction of overall rlleological behaviour. The Krieger-Dougherty method using the curve fitted reciprocal, bulk shear stress to find (phi)m also gave low errors and correctly predicted a relative viscosity of unity for the pure binder, suggesting an improved prediction over a wider range of volume fraction of solids than the German equation. The power law exponent n was shown to increase with increasing volume fraction of solids. Tins anomalous behaviour is explained in terms of a change in the flow mechanism from shear flow to slip flow through a transitionary region. BCT/317