Effect of die temperature on the flow of polymer melts. Part II: Extrudate swell

The effect of die wall temperature on the extrudate swell of polymer melts flowing through dies with single and dual circular channels was studied. Extrudate swell was measured at constant flow rates using an Instron capillary rheometer with a modified die section. It was found that under isothermal conditions, extrudate swell plotted against the average wall shear stress gave rise to a temperature independent correlation for polystyrene. Under non‐isothermal conditions, such a correlation did not exist, which might be due to the change of wall shear stress in the axial direction. The extrudate swell in the non‐isothermal cases can be better correlated with the wall shear stress at die exit. For the two‐hole die, changes of die wall temperature varied both the flow rate ratio and the extru date swell ratio. The latter is, however, much less sensitive to the die wall temperature than the former.