Rheology of unsaturated polyester resins. III. Effects of filler and low‐profile additive on the thickening behavior of unsaturated polyester resin

An investigation was made of the rheological behavior of unsaturated polyester resin during thickening in the presence of filler or low‐profile additive alone and, also, in the presence of both filler and low‐profile additive. For the study, two different types of filler (CaCO3 and clay) and two different types of low‐profile additive (PMMA and PVAc) were evaluated. Compared to the resin/thickener system, the resin/filler/thickener system exhibits shear‐thinning behavior as thickening progresses, and gives rise to smaller normal stress effects. On the other hand, the resin/low‐profile additive/thickener system exhibits two distinct Newtonian regimes in the viscosity‐shear stress curves and gives rise to larger normal stress effects. The viscosity behavior of the resin/filler/low‐profile additive/thickener system was found to be very similar to that of the resin/low‐profile additive/thickener system. In all cases, when the first normal stress difference was plotted against the shear stress, a correlation was obtained which was independent of thickening period. This behavior was exactly the same as for thickening polyester resin alone, as discussed in Part II of this series.