Post extrusion swelling of polyethylene

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Abstract
When polymers are extruded from a reservoir through a capillary the extrudate diameter is generally greater than the capillary diameter. Experiments with polyethylene show that the extent of this extrudate swelling depends, at constant shear stress, on the length‐to‐radius ratio of the capillary even though the viscosity does not. Consideration of this result at various shear stresses indicates that the degree of swelling depends on the total shear strain imposed on the melt. The same factor also governs the amount of extrudate distortion observed when melt fracture occurs.