We performed three-dimensional viscoelastic analysis of multi-layer polymer flow by numerical simulation, and investigated the effects of the elongational properties on the encapsulation phenomenon in the coextrusion process. The K-BKZ model with multiple relaxation times was used as viscoelastic constitutive equation, and the PSM type damping function was used for this model. This model is convenient to investigate the effects of the elongational properties, because the parameter b in this model can control only the elongational properties. Also we can extract the effects only of the elongational properties, because the second normal stress difference in this model is zero. In this study, we assumed that multi-layer polymer flow of Fluid I (less viscous) and Fluid II (more viscous) flows in three kinds of channels with different taper angle (parallel, tapered contraction and tapered expansion). As a result, by increasing the b ratio between Fluid I and Fluid II (βI/βII) from 0.1 to 10.0, the degree of encapsulation (DE) hardly changed at confluence, increased at contraction part and decreased at expansion part. These results mean that the elongational properties clearly influence the encapsulation phenomenon especially at contraction part and expansion part.
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