Phase behavior, crystallization, and morphological development in blends of polypropylene (PP) isomers and poly(ethylene -octene) copolymer

Polypropylene is a thermoplastic with a number of desirable properties. However, the poor low temperature impact properties, limit some of its application. In order to achieve improved properties, impact modifiers have been added to PP. Poly(ethylene-octene) copolymer known as polyolefin elastomer (POE) is a material of choice to compete with other impact modifiers such as ethylene-propylene-diene terpolymers. In an attempt to verify the aforementioned concept, a comprehensive study of the morphological development, crystallization and phase behavior in blends of POE and PP isomers (sPP, iPP, ePP) has been undertaken.;Morphological phase diagram of PP/POE blends has been established by means of differential scanning calorimetry, light scattering, optical microscopy, and atomic force microscopy. It has been revealed in the melt crystallization behavior of PP in the blend that the single crystals of PP can be grown even more readily in the blend, in which POE melt acts as a diluent at high temperatures. The development of the crystalline morphology is shown to be strongly dependent on the blend composition and crystallization temperature (supercooling). With decreasing crystallization temperature, the crystalline morphologies gradually change from single crystals through intermediate structure (axialites, etc.) to 2-D spherulitic texture. These crystals exhibit two very unique properties: sectorization and transverse ripples.;Crystallization studies in blends of PP/POE reveal that the crystallization process of PP is affected by the presence of POE and vice-versa. It has been demonstrated how POE accelerates the nucleation and crystal growth mechanisms of PP, this effect being more appreciable at low POE concentration. Analysis of the crystallization kinetics of PP crystals isothermally crystallized at different temperatures in the blend is supported by the morphological observations through OM and the calculated Avrami exponent.;The morphological effects, such as crystallite size, variety of crystalline structures (single crystal, sphenilite, etc.) afforded by the crystallization habit (crystallization rate, supercooling, etc.), and composition of the blends, are correlated with the tensile behavior of the blend. By the addition of small amounts of POE the toughness of the blend improves, whereas with decreasing crystallization temperature the crystal size (length scale) reduces, which promotes high extensibility and tensile strength.