The influence of branching efficiency on the rheology and morphology of melt state long-chain branched polypropylene/polybutene-1 blends

In this study, the compatibility of polypropylene (PP)/polybutene-1 (PB-1) homopolymer blends before and after a long-chain branching process was studied. The blends were prepared and long-chain branched directly via a reactive extrusion process in the presence of a free radical initiator and trimethylolpropane trimethacrylate (TMPTMA) poly functional monomer. The optimum percentage of TMPTMA and PB-1 resin was determined by measuring the grafting efficiency and by studying the rheological behavior in steady state shear and transient extensional mode and the morphology of samples was investigated by scanning electron microscopy (SEM). The morphology observations, which were also approved by rheological data, demonstrated an enhanced compatibility for the blend branched with 1.5wt% of TMPTMA and 10wt% of PB-1 resin. The highest grafting efficiency of 37% and branch index of 5.2 were achieved for this blend composition. The zero-shear viscosity (η0) of PP increased from 4500 Pa.s to 6800 Pa.s after branching process, and further enhanced to 2400 Pa.s by using 10 wt% PB-1 resin. The long-chain branched structure of blend resulted in a prominent higher zero-shear viscosity, a longer relaxation time and a pronounced strain-hardening behaviors. The branch index of blend samples were determined, and their branching behavior was quantified using extensional viscosity data.