Differences between crystallization of LDPE and iPP in EPDM matrix

Supermolecular structure of blends made of low density polyethylene (LDPE) or isotactic polypropylene (iPP) and ethylene-propylene-diene rubber (EPDM) was studied with X-ray diffraction (WAXS and SAXS), differential scanning calorimetry (DSC) and positron annihilation spectroscopy. Experimental data reveals different behaviour of the plastomers in the elastomer matrix. The crystalline phase of LDPE is to some extent solvated by the amorphous EPDM , whereas addition of iPP enhances the degree of the blend's crystallinity. This additional crystalline phase is of imperfect nature and probably orig inates from cocrystallization of propylene monomer units from EPDM onto IPP particles. LDPE recrystallizes in the blends with EPDM at a lower temperat ure, the higher the plastomer content. Contrary to this, iPP recrystallizes in the rubber matrix at higher temperature. The blend's composition influe nces the morphology of the crystalline phase. Interlamellar amorphous layer thickness slightly increases with an increase of LDPE content, being simul taneously accompanied by a slight decrease of the crystalline lamella thick ness. The longs period values remain practically constant. In the case of i PP/EPDM blends, the crystalline lamella thickness increases with an increas e of the plastomer content, whereas the interlamellar amorphous layer remai ns constant, which results in an increase of the long period. The reversed tendency, observed for high-filled samples containing greater than or equal to 50 phr of iPP, is likely to be associated with too many nucleation cent res, finally reducing the spherulite size. Despite annihilation taking plac e in the amorphous as well as the crystalline phase of polymers, the positr on lifetime data stays in good agreement with the postulated supermolecular structure of the blends.