Rheological properties and morphology of compatibilized, poly(butylene terephthalate)/linear low-density polyethylene alloy

The rheological behavior of PBT/LLDPE and PBT/LLDPE-g-AA blends [where PBT is poly(butylene terephthalate), LLDPE is linear low-density polyethylene, and AA is acrylic acid] under a capillary flow was investigated with a capillary rheometer. The Utracki equation was used to describe the viscosity-composition dependence of PBT/LLDPE and PBT/LLDPE-g-AA blends at low shear stresses. However, at high shear stresses, this equation was not suitable for these blending systems. There existed a maximum on the curves of the entrance pressure drop versus the blending compositions, and the interlayer slip factor beta in the Utracki equation was related not only to the shear stress but also to the elasticity difference of the two blending components. Morphological observations indicated that at high shear rates, there existed two different morphologies at different positions of the extruclates, and this was the reason that the Utracki equation failed. Near the wall of the capillary, low-viscosity PBT stratified, and this resulted in an additional decrease in the viscosities of the blending systems. (C) 2003 Wiley Periodicals, Inc.