Time-temperature-miscibility and morphology of polyolefin blends

Miscibility and crystallization have been studied for polypropylene-polyeth ylene and polyethylene-polyethylene blends. In the case of the polypropylen e blends the composition of interest is 20% polypropylene. At this composit ion the polypropylene has been found to be soluble in linear low density po lyethylene but insoluble in high, low and very low density polyethylenes. T he miscibility has been concluded from the crystallization kinetics and pol arised optical microscopy with a hot stage. Polyethylene-polyethylene blend s have been formed from polymers with similar average branching content but where they have different melting temperatures. Important consequences are to introduce long branches into a polyethylene that only has short branche s, and to modify the morphology of a polyethylenes so that haze, gross and strain hardening are improved. Polyethylene blends must be developed after careful consideration of the branch content and distribution within each of the constituents. It is not sufficient to simply blend polyethylenes, with the desired range of properties, without regard to the miscibility of the blend composition.