Effect of Viscosity Ratio and Screw rotational Speed on the Evolution of Morphology in Immiscible Polymer Blends
Anup K. Ghosh, Sandeep Tyagi
Centre for Polymer Science and Engineering, Indian Institute of Technology, Delhi
India

Keywords: Morphology Development, Melt-Mixing, Polymer Blends

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The state of stretching and reorientation of the dispersed domains during melt mixing in the feed section of
the extruder has been characterized in terms of the striation thickness distribution as functions of positions.
The effect of viscosity ratio on the melt-mixing process in terms of striation size and striation size
distribution has also been studied for blends with four selected viscosity ratios. Striation thickness does
depend upon the viscosity ratio and showed sharper decrease along the length of the feed zone when the
viscosities of both the phases were high (PP/EVA blend with viscosity ratio of 0.37). The effect of screw
rotational speed on the morphology development indicates the presence of higher average striation size at
low screw rpm as well as decrease of striations at a much faster rate than that obtained by processing at
relatively higher rpm. A critical size range has been identified as size larger than 100-125 µm for stretching
to be highly effective. Striations having thickness greater than this critical value show sharp decrease in
their size, both in the upper and the lower layer. The total process of morphology development seems to
follow a typical behaviour that has been explained on the basis of two-zone model considering upper layer
as strong zone and lower layer as weak zone.