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Blown Film Characterization of Binary Blends of Metallocene-Catalyzed LLDPES

We have explored the effects of blending metallocene-catalyzed linear low-density polyethylenes (LLDPE) of reasonably differing molecular weights on the performance and orientation characteristics of blown films. The presence of relatively longer molecules in a metallocene-catalyzed LLDPE resulted in blown films with relatively lower machine direction (MD) tear resistance, lower impact strength and higher transverse direction (TD) tear resistance. While all of the blown films investigated displayed the Keller-Machin “row” structure, the degree of orientation was observed to increase with increasing concentration of long molecules (or high molecular weight blend component). The observed influence of orientation in the crystalline and non-crystalline phases on the Elmendorf tear resistance of the blown films was observed to be consistent with previous investigations on a wide spectrum of commercial LLDPE blown films [15]. Morphological investigations of the blend films indicated the potential significance of microstructural anisotropy on blown film impact performance. This calls into question the wide-spread notion that co-monomer distribution profile is largely responsible for distinguishing the impact performance of various classes of LLDPE blown films.