Extrusion-blended and injection-molded PEI/PBT blends were found to be misc
ible whatever the composition. The processability of the blends clearly imp
roved with the presence of PET. The melt pressure at the exit was seen to b
e a parameter as representative of the processability of the blends as the
torque of blending. In the blends with 80 and 90% PET, a positive volume of
mixing and the maintenance of the crystallinity of PET were seen. However,
in the rest of the blends, negative volumes of mixing and important decrea
ses in the crystallinity of PET were found. These solid state features gave
rise to a ductility similar to that of the pure PEI and to a synergism of
the modulus of elasticity and of the yield stress in the 90/10 and 80/20 bl
ends such that the values were higher than those of either of the pure comp
onents. (C) 2001 John Wiley & Sons, Inc.