Disprsion in high viscosity ratio polyolefin blends

The dispersion of polyethylene and polyropylene in a polypropylene matrix using a co‐rotating twin screw extruder has been investigated. Poymer pairs were selected to study the effect of viscosity ratio, defined as the viscosity of the minor component over that of the matrix, in the range 0.1 to 900. The dispersion quality was defined by determining the number of “gels,”i.e., large undispersed particles, present in thin films and by conventional microscopy techniques. The gel numbers were found to increase steadily with the viscoty ratio. It was also observed that particle size distributions in the high viscosity ratio blends was very broad, with particles as large as a hundred microns coexisting with much finer ones in the sub‐micron range. For a given polymer blend, the re‐processing was found to have and important effect on gel reduction. The effect of rotation speed, flow rate minor phase feeding position was aso investigated and is discussed in the paper.