Anisotropy is generally observed in the machine direction (MD) and transverse direction (TD) tear strength properties of polyethylene blown films prepared at high draw-down ratios. This study investigates the tear strength of blown films prepared from different linear low density polyethylenes (LLDPE) at different draw-down ratios. Conventional Zeigler-Natta catalyzed (Z-N LLDPE) and single-site catalyzed (sLLDPE) resins were used. The films were analyzed using Raman spectroscopy, optical microscopy and wide-angle X-ray scattering (WAXS) for pole figures analysis. We observed that the TD tear strength correlated with crystalline phase orientation in the films, and MD tear strength correlated with orientation in both the crystalline and the amorphous phases. The Z-N LLDPE blown films showed higher MD orientation of crystalline and amorphous phases at higher draw-down ratio. The sLLDPE blown films showed higher crystalline MD orientation at higher draw-down but the overall orientation was higher in TD. This anomalous orientation behavior in sLLDPE blown films resulted in unusually high TD and MD tear properties at higher draw down.
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