A small amount (1 wt%) of organoclay-modified thermotropic liquid crystalline polymer (TLCP) acting as a viscosity reduction agent in high molecular mass polyethylene (HMMPE) was characterized and compared with purified TLCP (I wt%) in HMMPE at 190 degrees C and 230 degrees C, respectively, where the TLCP displayed nematic and nematic-isotropic biphase structures. In the TLCP/PE blend at 190 degrees C and 230 degrees C, dramatic reductions in viscosity were observed with significant improvement in extrudate surface smoothness and an enlarged processing window. For the organoclay-modified TLCP in PE, the viscosity reduction ability of TLCP was further enhanced with viscosity dropped by up to >98.5% and >97.4% at 190 degrees C and 230 degrees C and processing window enlarged to >700 s(-1) and >900 s(-1) respectively in comparison to that of PE. Moreover, yielding stress, initial transition shear rate and transition region decreased to lower magnitudes than those of the TLCP/PE blend. A phenomenological model was applied to elucidate the mechanism of organoclay, TLCP and PE conformation before and after yielding in the confined capillary environment. A binary flow pattern model was applied to successfully predict the rheological behavior of the blends at 190 degrees C. (C) 2009 Elsevier Ltd. All rights reserved.