Simulation viscoelastic coextrusion

Figure4.21 Simulation ofextrudate swell from viscoelastic properties of the melts, hence coextrusion circular dies for a combination of different stress ratio, Sr. Viscoelastic HDPE and PS melts (PS/HDPE = inner/outer). simulations with the K-BKZ integral model A different configuration produces different (Eq. (4.12)) [46]. swelling for the same flow rate due to different...

Interlayer adhesion between a polycarbonate (PC) layer and a PC-ABS blend layer, in 3-layer films made by melt coextrusion in a multi-manifold die, was analyzed using nonlinear viscoelastic (NLVE) die-flow simulations with POLYFLOW. These simulations showed significant extensional stresses in the interface vicinity where the two melt layers come into contact for the first time. A Viscosity Normalized Nonlinearity Ratio parameter was defined to correlate the simulated interfacial melt stresses and the observed adhesion behavior. Larger deviation of this parameter from a value of 1.0 (large disparities in melt extensional configuration across the interface) corresponded to poorer observed peel strength. 

Viscoelastic effects during coextrusion have been extensively studied in the past primarily from the point of view of predicting interfacial instability. A TNSD sign criterion has been developed to predict instability based on local layer stretching, as assessed by simulated normal stresses [5],... 

Figure 5b First normal stress difference in PC and PC-ABS layers near the developing interface. Obtained from PTT viscoelastic simulation of the Cap-PC-PCABS-1 film coextrusion.

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