A COMPARISON OF BLENDS OF LINEAR WITH BRANCHED POLYETHYLENES PREPAREDBY MELT MIXING AND BY SOLUTION BLENDING

Blends of a linear and a lightly branched polyethylene were prepared b y solution blending and in the melt, by mixing in a screw extruder, an d the phase morphologies were compared. First, the melt phase behaviou r of the solution-blended system was studied by differential scanning calorimetry and transmission electron microscopy. A loop of liquid-liq uid phase separation was found at low linear-polyethylene content. Thr ee melt-mixed blends were then prepared and characterized, again by di fferential scanning calorimetry and transmission electron microscopy. The general pattern of phase behaviour of these melt-mixed blends was similar to that obtained by solution blending the same pair of polymer s (i.e. a region of phase separation was again found at low linear-pol yethylene content). Where the phase behaviour allowed mixing, the scre w extruder produced blends with uniform composition throughout the sam ple. The morphologies of the melt-mixed materials showed enhanced nucl eation, compared with the solution-blended materials, and orientation effects particularly at low linear-polyethylene content.