Generalized Newtonian Fluid (GNF) Models

As discussed in Chapter 2, most polymers exhibit shear thinning, temperature and pressure dependent viscosities. The shear thinning effect is defined as the reduction in viscosity at high rates of deformation. This phenomenon is explained by the fact that the molecular chains are disentangled and stretched out at high rates of deformation and can therefore slide past each other with more ease, which in turn lowers the bulk viscosity of the melt. Figure 3.1 clearly shows the shear thinning behavior and temperature dependence of the viscosity of a general purpose polystyrene.