RODLIKE PARTICLES IN NON-NEWTONIAN FLUIDS: I. RHEOLOGY AND INJECTION MOLDING OF GLASS-FIBER-FILLED THERMOPLASTICS. II. ORIENTATION AND RHEOLOGY OF RODLIKE PARTICLES IN A SECOND-ORDER FLUID

The shear viscosity of glass-fiber-filled polystyrene and poly- propylene resins has been studied systematically. Effects of fiber concentration and temperature on the shear-viscosity-versus-shear-rate curves have been examined. The viscosity increases with the increase of fiber concentration and with the decrease of temperature. A "wall effect" on the viscosity due to the comparable dimensions of the average fiber length and the capillary die diameter has been found for fiber-filled thermoplastics. This effect is particularly important at lower shear rates and at higher temperatures. It was also found that the rheological properties of glass-fiber-filled thermoplastics can be substantially altered due to fiber breakage during processing. Pressure traces during the cavity filling stage of injection molding experiments have been compared to computer simulation results. It is shown that as long as reliable material properties (i.e. rheological and thermal properties) can be obtained, the simulation results can provide equally good predictions for both glass-fiber-filled and unfilled thermoplastics when tested against experimental results.;A theoretical study of orientation in a dilute suspension of rod-like particles in a second-order fluid is performed to examine the effects of the elasticity of the matrix and of the weak Brownian diffusion of the particle on orientation. The detailed pictures of particle orienta- tions under a simple shear flow have been obtained as a function of a single non-dimensional parameter (beta)* (=(beta)/r(,e)('2)(D/g)) which combines the effects of the particle aspect ratio r(,e), the weak fluid elasticity (beta), and the weak Brownian diffusion coefficient D of the particle. When the fluid elasticity is strong(, )enough to overcome the diffusion effect on the particle motion ((beta)* >(, )0.25), most of the particles will orient close to the vorticity axis. A new shear-thinning mechanism of the shear-viscosity is predicted by the theory for such systems. The theo- retical study has also been extended to systems of rodlike particles with strong Brownian diffusion (e.g. rodlike macromolecules) in a second-order fluid. Both the particle orientation distribution and the rheology of such systems have been investigated.