Mechanical properties and morphology of isotactic polypropylene/ethylene-propylene copolymer blends F. Coppola, R. Greco* and E. Martuscelli Istituto di Ricerche su Tecnologia dei Polimeri e Reologia del CNR, Arco Felice, Napoli, Italy and H. W. Kammer and C. Kummerlowe Technical University of Dresden, Department of Chemistry, Dresden, GDR (Received 8 April 1986) Mechanical tensile and dynamic mechanical tests have been performed at different temperatures on specimens of polypropylene (iPP)/ethylene-propylene copolymer (EPR) blends, obtained under various crystallization conditions. The initial morphology was observed by optical transmission and scanning electron microscopy. Furthermore the influence of the rubber composition on the neck formation was analysed and the tensile mechanical properties of the fibres evaluated as well. Up to 10% of EPR in the blend, the morphology of iPP was only slightly changed. At higher EPR content, a decrease in spherulite size was observed. The curves of modulus E versus drawing temperature T a exhibited a change in the drawing mechanism at a temperature Ti. This transition temperature increased on enhancing the crystallization temperature Tcand is almost independent of the EPR content. The change in the flowing mechanism was also visible by direct inspection of the specimen fibres which were opaque for Td < Tiand transparent for T d > T i. These features were indicative of a dependence of the drawingmechanisms on the initial morphology and on the testing temperature. The fibre modulus depended strongly on the drawing temperature Ta but not on the crystallization temperature T~. This suggested that an almost complete cancellation of the initial morphology occurred after fibre formation. The effect of the rubber addition was a decrease of the Young's modulus of the fibres in all the blends. A tentative interpretation of the above illustrated features has been provided. (Keywords: blends; morphology; mechanical properties; polyolefms; crystallization; fibres) INTRODUCTION Several noncrystalline polymers like polystyrene and poly(methyl methacrylate) are brittle below their glass transition temperature (T~). Improvement of their mechanical and impact properties has been achieved by embedding a rubbery component into the glassy matrix 1. The toughened behaviour has been interpreted in terms of physical interactions between the soft dispersed phase and the major component whose structure remains substantially unchanged after blending. Multiple craze and shear yielding mechanisms 1 have been invoked to explain the mechanical features of such materials. Analogously, semicrystalline polymers, such as polyamides and polypropylene, show brittleness at temperatures below their Tg (ref. 2). In this case, however, a further problem arises with respect to glassy materials. In fact the matrix itself can be altered by the presence of the rubber, which directly influences the crystallization process. Therefore, recently a number of investigations have been undertaken on binary isotactic polypropylene (iPP)/elastomer blends by some of the authors of the present work to elucidate this aspect 3-s. * To whom correspondence should be addressed The isothermal crystallization behaviour of thin films (10/~m thick) has been studied as a function of composition for various types of rubbers. It was found that during crystallization the pre-existing rubber particles are occluded mainly in intraspherulitic regions. Such a process produces a large modification in the spherulite structure. Moreover, it was observed that the presence of rubber drastically influences the processes of primary and secondary nucleation 3. The mechanical properties of thick films (i-2 mm) ofiPP/polyisobutylene (PIB) blends, obtained by isothermal and nonisothermal crystallization, have been analysed and interpreted in terms of micro- and superstructure by optical and electron microscopy and X-ray diffraction4'5. The present paper is part of such investigations and represents a natural extension of the latter papers utilizing a different kind of rubber, namely an ethylene-propylene copolymer (EPR). Also in this case an attempt to correlate the initial morphology, obtained at certain crystallization temperatures, and the mechanical properties has been made. Furthermore, the influence of rubber addition on the morphological transformation from the initial spherulitic structure to the final fibrillar one of iPP during the cold drawing has been analysed as well. 0032-3861/87/010047-1053.00 © 1987 Butterworth & Co. (Publishers) Ltd. POLYMER, 1987, Vol 28, January 47