Melt Flow Indexer Evidence of High-Temperature Transitions in Molten High-Density Polyethylenes

A melt flow indexer (MFI) was used to investigate high-temperature transitions in melts of high-density polyethylene (HDPE). The MFI data were obtained in the range 190-230°C. These transitions were found in the MFI at about 210 and 225°C and reproduced in a Haake melt blender. Polystyrene was used in the blender experiment to demonstrate typical amorphous behavior. For HDPE melts, the MFI-temperature behavior and the torque-temperature data of the blender were found to be alternative images of the same anomalous temperature dependency in the range 210-225°C. Also, the Haake melt blender was able to reproduce the 150°C transition observed by Kolnaar and Keller in the extrusion of HDPE. Regardless of the simplicity of the MFI device, results are in agreement with our previous DSC findings.