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Lamellae Formation and Deformation of Isotactic Polypropylene due to Push-Pull Processing

Like all thermoplastic materials, the mechanical performance of isotactic polypropylene (i-PP) depends strongly on morphology. Using techniques such as push-pull processing or SCORIM (Shear Controlled Orientation in Injection Moulding), it is possible to obtain i-PP with an oriented lamellae structure via injection moulding. Due to an overall shear induced crystallisation and molecular alignment both the amorphous and the crystalline phases are oriented. The orientation can be visualised using X-ray-diffraction methods (WAXD, SAXS) and Raman-Spectroscopy techniques as well as light and electron microscopy (SEM, TEM). Although the molecular chains are oriented parallel to the flow direction (and so the c-axis in the crystallites) lamellae are oriented perpendicular. Results for DSC measurements and micro-hardness over the cross-section of injection-moulded plates accompany the microscopical investigations. This lamellar structure has been deformed under tensile and shear load. The results are discussed with reference to mechanical tests and microscopic investigations. The deformation on a structural level shows a fibrillar, crazed structure that is examined using SEM and plasma etching preparation techniques.