Phase separation in polypropylene and metallocene polyethylene blends

Blends of a metallocene linear low density polyethylene (m-LLDPE) and polypropylene random copolymer (PP) have been prepared using a twin screw extruder and characterized by thermal analysis, mechanical properties, and wide angle X-ray scattering to determine their degree of compatibility. The blends were either directly quenched in water from the melt- or slow-cooled to room temperature. In both cases, the two components formed separate phases and crystallized independently. The slow-cooled specimens had higher yield stress, tensile modulus, and lower elongation at break consistent with higher degree of crystallinity. The elongation to break also varied with composition reaching a minimum at 50% consistent with the incompatible nature of the blends. Crystallization kinetics and melting studies confirm that the two components formed separate phases and crystallized independently.