The die swell ratio
is defined as ([A.sub.1] - [A.sub.2])/[A.sub.2], where [A.sub.1] denotes the cross-sectional area of the emerging melt stream, and [A.sub.2] is the cross-sectional area of the spinneret die.
The die swell ratio of the composites and the fiber-matrix morphology of the extrudates have also been analyzed.
The variation of die swell ratio [D.sub.e]/D (where [D.sub.e] and D are the diameters of the extrudate and the die) of virgin HDPE, and untreated and treated composites at two different shear rates is represented in Table 3.
Experimental methods for measuring the die swell ratio of polymer melts have involved many difficulties such as draw-down effects, molecular relaxation at the die exit, contraction due to cooling, and crystallization (1).
This can be achieved by knowledge of radial die swell ratio profiles and their dependence on processing conditions.
The radial die swell ratio values ([B.sub.r]) were obtained by comparing the thickness of the colored layer of the extrudate outside the die, for a given reduced radius (r/R) position in the die, to that inside the die as illustrated in Fig.
Die Swell Ratio
of Nylon/NBR Blends (185[degrees]C).
The die swell ratio becomes smaller as the melting temperature and melting residence time are increased.
Wong and Liang demonstrated the relationship between the die swell ratio and melt flow index of high-density polyethylene .
The ratio D/[D.sub.0], where [D.sub.0] is the capillary diameter, is defined as the die swell ratio and used as a measure of die swell.
poly(vinylchloride) whose variation of die swell ratio with shear rate sometimes shows a maximum or a minimum (18).
Figure 7 shows that die swell ratios
D/[D.sub.0] decrease with increasing ultrasonic irradiation power.