Binary blends of metallocene polyethylene with conventional polyolefins: Rheological and morphological properties

The rheology and morphology of four sets of binary blends of polyethylene synthesized with metallocene catalysis (metallocene polyethylene: MCPE) with polyolefins prepared using Ziegler-Natta catalysts have been investigated. The blend systems are MCPE with high density polyethylene (MCPE-HDPE), polypropylene (MCPE-PP), poly(propylene-co-ethylene) (MCPE-CoPP), and poly(propylene-co-ethylene-co-1-butylene) (MCPE-TerPP). Cole-Cole plots [storage melt viscosity (η′) versus loss melt viscosity (η″)], plots of the dynamic storage modulus (G′) versus the dynamic loss modulus (G″), and plots of the log melt viscosity (η*, η′, and η″) versus blend compositions were constructed. The morphology of the blends after microtoming and etching was studied. The phase morphology of MCPE-HDPE appeared homogeneous, whereas the other three blends were heterogeneous. Rheological and morphological investigations indicated that the MCPE-HDPE blend was miscible, but the other three blends were immiscible in the melt as well as in the solid state. These observations can be rationalized in terms of the similarity of the chemical structures of the polyolefins.