1. The Shear Stress is the preferred design characteristic for a "Self Cleaning" die design. 2. A nominal design value of 30 kPa appears to work for most polyolefin materials. Absolute minimum value is probably around 15 - 20 kPa, below which stagnation at the wall is more likely. 3. Elongational deformation should be avoided to minimize the effect of elongational viscosity. 4. Don't arbitrarily select materials; compare shear viscosity. 5. Thin, high viscosity layers should be avoided.
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