Micro-morphology of modified and nonmodified blends of polypropylene with linear low density polyethylene

Modified and nonmodified blends of linear low-density polyethylene (PE) and polypropylene (PP) form separated phases of crystalline PP and PE. They fo rm spherulitic crystals in the core, but highly oriented nonspherulitic pha ses at the skin of injection molded test bars. The dimension of the spherul ites decreases with increasing PE content within the blends. Crystallizatio n behavior of both crystalline phases is influenced by the other phase. The crystallization temperature of PP is increased in the presence of the comp atibilizer. Transmission electron micrographs of blends modified by poly(st yrene-block-ethylene/butylene) (SEBS) and stained by OsO4 showed co-continu ous lamellar structure of the blends with a polypropylene phase containing the majority of the modifier. Smaller portions of the modifier can be found on the surface of the two olefinic phases as dispersed spheres, with an av erage diameter of 50-90 nm. The lamellar structure is independent of the sp herulitic structure, and interpenetrates the spherulites. The conclusion of this study is that this block copolymer, while improving the physical prop erties of the blends, is not a true compatibilizer of the system according to the conventional terminology of physical chemistry.