Effect of polydispersity on the thermo-mechanical degradation of HDPE polymerized using a chromium catalyst

The thermo-mechanical degradation of chromium-catalyst polymerized high-density polyethylene was studied during the first pelletizing of the polymer. Twin-screw technology was used at mechanical mixing energies and melt temperatures characteristic for polymer production. Polydispersity affects sensitivity to degradation. Increase in polydispersity increases the end-vinyl content and decreases the mechanical energy needed for processing. These two competitive factors result in a degradation maximum at a D value ( M w M n ) between 7 and 9. Extensive long-chain branching or high-molecular-weight tailing of the MWD was not observed as has been reported for processing under low shear over longer residence times.