Influence of shearing history on the properties of polymer melt. I.

Melt flow behavior was examined using “as polymerized,” mechanically intact polypropylene, and the same polymer after pelletization in a screw extruder. In addition, the polymers were extruded through different capillaries and subsequently tested for melt flow characteristics. Significant differences in shear stress at a given shear rate and shear rate critical to the onset of extrudate roughness were found and compared with the previous shearing history. Both shearing intensity and mode of flow were found to impart long-lasting and short-term effects to the melt flow properties of the polymer. These differences were not explainable on the basis of changed molecular weights, since no significant differences were observed in the molecular weights as a result of the shearing treatments used in this study.