Rheological properties of polymer melts reinforced with small particles

An experimental investigation of rheological properties during both shear and elongational flow and melt spinning characteristics for polystyrene melts reinforced with small rigid particles and high impact polystyrene (HIPs) is reported.

The influences of loading level, particle size and surface treatment were discussed. These systems exhibit yield values for both shear and elongational flow. Experimental values for the ratio of the tensile to the shear yield stress give satisfactory agreement with the production of the von Mises yield criterion. The yield value appears to increase with decreasing particle size and may lower with surface treatment. The first normal stress difference at fixed shear stress decreased with loading level. The spinline elongational viscosity for filled systems shows a strong elongational rate thinning behavior compared with unfilled systems, the same trend as in the steady state elongational viscosity. It has been found that an addition of small particles makes the spinline unstable under both isothermal and nonisothermal conditions.

A theoretical approach to shear viscosity was attempted from a mechanistic viewpoint. A cell theory model of concentrated suspensions involving particle-particle interaction was developed. This theory suggests that a yield stress is related to the particle-particle interaction energy per unit volume. The predicted values give satisfactory agreements with experimental data concerning the effects of particle characteristics on shear viscosity and yield stress. Then, the phenomenological theory of White which is largely consistent with the mechanistic theory was compared with experimental data on both shear and elongational flow. A proposal for flow mechanism was made.