Peroxydicarbonate modification of polypropylene and extensional flow properties

Long chain branches (LCB) were added to initially linear polypropylene (PP) using reactive extrusion in the presence of selected organic peroxydicarbonates (PODIC). The LCB structure was confirmed by high temperature size exclusion chromatography combined with on-line intrinsic viscosity measurements. Compared to the initial linear PP, the branched samples showed distinct strain hardening of the elongational viscosity, slightly lower Melt Flow Index, increased extrudate swelling and improvement of the melt strength by up to a factor of two. All elastic properties increased with the degree of branching. The efficiency of PODIC with varying structure for the LCB modification of PP was evaluated. PODIC with non-linear or large linear alkyl groups resulted in modified PP with the highest degree of branching and the fastest strain hardening.