In this work, a critical extensional stress is proposed as the criterion for the onset of gross melt fracture. This stress is estimated by means of the entrance pressure drop analyses developed by Cogswell and by Binding. This criterion for the onset of gross melt fracture was evaluated for several constrained geometry catalyzed (CGC) and metallocene, linear low, and high density polyethylenes. The presence of a low level of long chain branching in CGC polyethylene enhances the critical extensional stress, as compared to purely linear polyethylene. High density polyethylene blends having large low molecular weight fractions exhibit higher critical extensional stress than blends with lower amounts of low molecular weight material. Finally, a polymer having a broad molecular weight distribution shows a higher critical extensional stress than a narrow molecular weight polymer. The critical extensional stress for the onset of gross melt fracture is independent of temperature.
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