Factors Influencing the Morphology of a Polymer Blend

Single-screw extruders have been widely used for blend preparation however, they do not offer sufficiently high stress levels to improve mixing thus, special designs of screws have been developed such as those with mixing heads or barrier zones that increase residence time and enhance blend mixing. 

A theory for the break up of individual droplets for Newtonian fluids has been developed and a relationship has been established between the capillary number (Ca), which is a ratio of shear to interfacial forces, and the viscosity ratio rj rj = rj /rj = dispersed phase viscosity/matrix phase viscosity), where G is shear rate, D is the diameter of the droplet, and y is interfacial tension. 

The predicted drop size for a simple field is proportional to interfacial tension and inversely proportional to shear rate and matrix phase viscosity. Although Newtonian systems are relatively well understood, there are many limitations to this theory for predicting the morphology of a multiphase polymer system. Other difficulties in comparison with such ideal systems may include the complex shear fields applied in processing and the relatively high concentrations of the dispersed phase in most commercial polymer blends. 

Viscosity ratio is the ratio between viscosity of the dispersed phase and the viscosity of the matrix. This 

For a given A-B blend, the composition of each component will define a specific region (i) a region for which phase A is dispersed in matrix B, (ii) an intermediate region of phase inversion for which both A and B are cocontinuous, and (iii) a region in which the phase has been inverted in which now phase B is dispersed in matrix A (Fig. 27.7). 

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