Changes in the Melt Flow Index were related to the shift in the Molecular Weight Distribution Curve (MWD) produced by the thermo-mechanical degradation of polypropylene (PP) during multiprocessing. The degradation was modelled using the Chain Scission Distribution Function (CSDF), which quantifies the shift in the molecular weight distribution curve as a function of the number of extrusions. The effect is normally the reduction of the molecular weight, which means positive values for CSDF and reduction of the polymer melt viscosity. The average molecular weight shift (LogMw(0) - LogMw(D)) calculated from the average weight molecular weight before and after the degradation overlaps the CSDF curve and shows a linear relationship with the MFI values. The thermo-mechanical degradation process of polypropylene can be better visualized when CSDF curves are correlated with MFI values.
Polypropylene; thermo-mechanical degradation; molecular weight distribution; chain scission; melt flow index and chain scission distribution function
