Current trends in extruder screw design caused by recent advances in the molecular architecture of polyolefin resins

Recent advances in the evolution of new catalyst technology are influencing current trends in extruder screw design. An experimental investigation into the extrusion performance of a polyolefin plastomer (POP) is used to investigate the effect of screw design and operating conditions. A highly instrumented 63.5 mm 24:1L/D extruder was used to perform the study. The extrusion tests showed that the POP exhibited process instabilities caused by solid bed break-up on a typical cast film barrier screw with a feed section length of 5 L/D. Process variations were observed to increase with increased temperature profile. The causes of the variations were identified as solid bed break-up cause by a large amount of melt generated in the feed section of the extruder due to the high rate of melting of the polymer. A second design was tested that eliminated the instability by adjusting the design to match the melting rate of the POP. Process stability was also observed to be sensitive to barrel temperature set point.