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Heterophasic copolymers comprised of polypropylene (PP) matrix and ethylene-propylene copolymer (EPC) dispersed phase were investigated with respect to the dispersed phase composition, i.e., ethylene/propylene ratio. The rheological properties, morphology, as well as thermal and mechanical relaxation behavior were studied to describe the structure evolution and phase interactions between the components of the PP copolymers. Decrease of the ethylene content of the EPC leads to a higher matrix-dispersed phase compatibility, as evaluated by the shift of the glass transition temperatures of EPC and PP towards each other. At ethylene content of EPC of 17 wt %, the glass transition temperatures of the both phases merged into a joint relaxation. The effect of the EPC composition on the internal structure of the dispersed domains and on the morphology development of the heterophasic copolymers was demonstrated. Decreasing ethylene content was found to induce a refinement of the dispersed phase with several orders of magnitude down to 0.18 m for propylene-rich EPC. Optical microscopy observations showed that the dispersed propylene-rich phase is preferably rejected at the interlamellar regions of the spherulites and/or at the interspherulitic regions, while the ethylene-rich domains are engulfed within the PP spherulites. Both of these processes impose an additional energetic barrier and influence the spherulite growth rate of the heterophasic materials.

The orientation behavior of isotactic polypropylene (iPP) in ␣and ␤-crystal form was investigated by rheo-optical Fourier transformed infrared (FTIR) spectroscopy. This method enabled quantification of the degree of orientation as a feature of structural changes during uniaxial elongation in not only the crystalline phase but also the amorphous one. Molecular orientation mechanisms can be successfully derived from experimental results. Generally, three mechanisms were detected for iPP: (1) interlamellar separation in the amorphous phase, (2) interlamellar slip and lamellar twisting at small elongations, and (3) intralamellar slip at high elongations. The third mechanism was favored by ␣-PP, whereas ␤-PP favored the second mechanism, which, in fact, was responsible for the different mechanical properties of both materials at the macroscopic level. On the other hand, crystallization conditions may have significantly affected the amorphous orientation. Nevertheless, for both iPP types the chains in the amorphous phase always oriented less than did those in the crystalline phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4478 -4488, 2004

Two samples of isotactic polypropylene (iPP) representing the crystalline α‐ and β‐modifications are compared with regard to their semicrystalline morphology and the resulting micromechanical mechanisms. Processes at room temperature (23°C) and at −40°C have been investigated by means of different microscopic techniques. Good results can be achieved by the application of a chemical etching technique to the deformed samples prior to scanning electron microscopy inspection. The toughness enhancement that is measured for the β‐iPP is attributed to micromechanical mechanisms initiated within the intercrystalline, amorphous phase. It is shown that the specific nanostructure (lamellar arrangement) causes significant changes in the mechanical behaviour of the materials.

Hydroxyapatite has become the most common material to replace bone or to guide its regeneration. Nanocrystalline hydroxyapatite suspension had been introduced in the clinical use recently under the assumption that small dimension of crystals could improve resorption. We studied the resorption and osteointegration of the nanocrystalline hydroxyapatite Ostim in a rabbit model. The material was implanted either alone or in combination with autogenic or allogenic bone into distal rabbit femora. After survival time of 2, 4, 6, 8 and 12 weeks the implants had been evaluated by light and electron microscopy. We observed a direct bone contact as well as inclusion into soft tissue. But we could observe no or only marginal decay and no remarkable resorption in the vast majority of implants. In situ the nanocrystalline material mostly formed densely packed agglomerates which were preserved once included in bone or connective tissue. A serious side effect was the initiation of osteolysis in the femora far from the implantation site causing extended defects in the cortical bone.

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International audienceChevron morphology was observed using transmission electron microscopy in various semicrystalline polymers deformed in tensile experiments. The morphological and mechanical prerequisites for chevron structure formation in semicrystalline polymers were revealed. It was demonstrated that chevron folding is a common deformation mode which can appear in real, i.e. globally unoriented or partially oriented samples, in areas where the lamellar stacks are oriented perpendicular to the deformation direction. Similarities with the behaviour of other layered systems were found. The mechanisms of chevron formation is discussed in the light of the fundamental statements of the folding theories and is related to the specific microstructure of the polymers. The effect of the boundary conditions, deformation temperature and macroscopic strain on the characteristics of the chevron structure is described