Enhanced Dispersion and Mechanical Behavior of Polypropylene Composites Compounded Using Extension-Dominated Extrusion

The process of dispersing filler in polymer matrix is vital to the behavior of polymer composites. The current study involves understanding the extent of dispersion of filler by only varying the nature of mixing during the process. Identical polymer composite materials are processed via two different kinds of mixing sections on the screw in a twin-screw extruder, differing in the type and amount of stress they impose on the filler agglomerate. An aggressive (900) Kneading Block (KB) mixing section is compared with recently developed Extensional Mixing Elements (EMEs), which impart extension dominated mixing while KB imparts shear dominated mixing. Various EME geometries of different levels of aggressiveness were computationally studied and validated. Composites obtained from KB are compared with composites processed using five different EME geometries. Three composites of Polypropylene (PP) filled with carbon black, graphene nano platelets and carbon nanotubes were studied independently. Composites processed through EMEs display about an order of magnitude better dispersion of filler agglomerate over the composites processed through KB. In addition, enhanced modulus and yield stress is observed for composites processed through EMEs. An improvement of 63% to 266% in the strain achieved for EME processed composites is seen under biaxial film stretching.