The difficulty in processing filled materials is often a limiting factor in advanced materials development because of the large changes in fluid viscosity observed in these materials. It is widely ...

Model for the Viscosity of Particle Dispersions

An experimental study of the development of phase morphology, rheological properties, and processing behavior of mechanical blends of a polystyrene (PS) and a high density polyethylene (PE) is presented. Phase morphologies were determined by scanning electron microscopy for (i) products prepared in a screw extruder/static mixer system, (ii) samples removed from a cone-plate viscometer, (iii) extrudates, and (iv) melt spun fibers. Disperse phase dimensions were measured. The values varied from 1–5 μm in the products from static mixers. The dimensions of the dispersed phase in the blend products from the cone plate and capillary die were of the same order. The melt-spun fibers exhibited disperse phase dimensions as low as 0.35 μm. Polystyrene was extracted from the blend fibers producing small diameter, PE fibrils, or minifibers. Both the initial melts and the blends were rheologically characterized. The shear viscosity and principal normal stress difference N1 exhibit maxima and minima when plotted as a function of composition. The characteristics of extrudates and melt spinning behavior of the blends were investigated. The shrinkage of extrudates of PE is much greater than PS. Additional small amounts of PE to PS greatly increase its shrinkage. Addition of PE to PS initially increases extrudate swell, though the swell shows maxima and minima when considered as a function of composition. The positions of the maxima and minima correspond to those of N1. The onset of draw resonance has been investigated in isothermal melt spinning. Wide angle X-ray diffraction studies have been carried out on blend fibers and the orientation of the crystalline polyethylene regions has been determined as a function of process conditions. This orientation decreases rapidly with the addition of polystyrene when the melt-spun filaments are compared at the same spinline stress or drawdown ratio.

High density polyethylene/polystyrene blends: Phase distribution morphology, rheological measurements, extrusion, and melt spinning behavior

A study is carried out for characterizing two-phase systems of molten polymers by their viscous and elastic properties. The two-phase systems chosen for study are blends of polystyrene and polypropylene, and blends of polystyrene and high-density polyethylene. For the study, measurements of wall normal stresses are made by use of a capillary melt rheometer described in part I of this series. The concept of the “exit pressure” is used to determine the elastic properties of the two-phase polymer systems. The present study shows anomalous viscous and elastic properties of two-phase systems, which are difficult to predict from knowing the viscous and elastic properties of their individual components. A detailed discussion is given on the state of dispersion of two incompatible polymer systems in the molten state, by presenting pictures of the microstructure of the extrudate samples. The state of dispersion appears to vary depending on the blending ratio, extrusion temperature, melt viscosities of individual components, and blending method.

Rheological properties of molten polymers. II. Two‐phase systems

The effect of viscosity ratio on the morphology of polyamide 66/polypropylene blends was studied, with primary attention to the phase-inversion behavior and the average particle size of the dispersed phase. The relationship between the mechanical properties and the phase-inversion composition was investigated as well. Noncompatibilized and compatibilized blends having five different viscosity ratios were prepared by twin-screw extrusion. Maleic anhydride-grafted polypropylene was used as the compatibilizer to increase the adhesion between the two polymers and to stabilize the blend morphology

The effect of viscosity ratio on the phase inversion of polyamide 66/polypropylene blends

Viscoelastic behavior, phase morphology and flow conditions relationships in polymer/rubber blends have been investigated. The importance of such correlations is illustrated on polymethylmethacrylate (PMMA)/rubber blends subjected to different flow conditions both under small and large deformations. In small-amplitude oscillatory shear (the morphology does not change during the flow) the elastic modulus G′ of the concentrated blends shows a secondary plateau, G′
 p
 , in the low frequency region. This solid-like behavior appears for rubber particle contents beyond the percolation threshold concentration (15%). Morphological observations revealed that for concentrations higher than 15%, the particles are dispersed in a three-dimensional network-type structure. In capillary flow it was found that the network-type structure was destroyed and replaced by an alignment of particles in the flow direction. This morphological modification resulted in a decrease in both viscosity and post-extrusion swell of the blends. Morphological observations revealed that the ordered structure in the flow direction was concentrated only in the skin region of the extrudate, where the shear stress is higher than the secondary plateau, G′
 p
 . A simple kinetic mechanism is proposed to explain the observed morphology. Similarly, steady shear measurements performed in the cone-and-plate geometry revealed alignment of particles in the flow direction for shear stress values higher than G′p.

Rheology/morphology/flow conditions relationships for polymethylmethacrylate/rubber blend

The change in melt flow properties, as determined by melt index measurement, as a function of shear history, has been measured for linear polyethylene. It is shown that a drop in melt index occurs when a polymer sample which has had no previous shear history is melted and subjected to shear mixing. This fact is attributed to a molecular homogenization of a previously unmixed blend. An analytical model of the laminar flow in a pipe of concentric adjacent fluids with different viscosities is presented. The model indicates that the effective viscosity of this non-homogeneous system is much lower than the viscosity of fan intimate blend of the same viscosity of an intimate blend of the same viscosity fluids.

Effect of homogeneity on viscosity in capillary extrusion of polyethylene

The Schulz and Blaschke equation in the rearranged form of Hart was used for reasonably precise calculation of the intrinsic viscosity from a single measured specific viscosity for stereoregular polybutene-1 in Decalin and for a series of alkyl methacrylate polymers in good and poor solvents. A single value of N can be used for each system provided careful measurements are made at specific viscosities somewhat below 1.

Single point determination of intrinsic viscosity

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Effect of homogeneity on viscosity in capillary extrusion of polyethylene

Single point determination of intrinsic viscosity