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11	β-nucleated isotactic polypropylene with different thermomechanical histories investigated by synchrotron X-ray Chen, Jianhong 10 March 2015 (has links) Isotactic polypropylene (iPP), as one of the most versatile commodity thermoplastic polymers, is a polymorphic material having several crystal modifications, among which the β-form exhibits higher performance including excellent impact strength and improved elongation at break.Up to now, the effective and convenient way to prepare the iPP with high content of β-phase has been successfully achieved by addition of certain β-nucleating agent. Since the coexistence of β-nucleating agent and flow (shear flow, extensional flow or mixed), which usually exists in common industrial processing, makes the crystallization process more complex, their combined effect on the structure evolution of polymers, especially in the early stage of crystallization is still not well understood. The mechanical properties of iPP depend strongly on its crystallinity, crystal orientation and morphology determined by the conditions during preparation. On the other hand, the mechanical properties of polymers can also be modulated by deformation processing, which is directly related to the deformation-induced structure transition. However, the transition mechanism of different crystal forms and structure-property correlation still remain unclear. In this thesis, time-resolved synchrotron X-ray scattering was firstly used for the in-situ study of the structural and morphological developments of β-nucleated iPP during shear-induced crystallization. It was found that the crystallization process was strongly influenced by the concentration of β-nucleating agent, shear rate and shear temperature. Then extension-induced crystallization was investigated by a novel melt draw experiment, where a different crystallization mechanism compared to the shear-induced crystallization was found. Subsequently, β-nucleated iPP samples with different thermomechanical histories were scanned by synchrotron X-ray microbeam to construct their overall morphological distributions, including distributions of crystallinity, lamellar thickness, orientation, etc. Finally, these morphology-identified samples were investigated by in-situ synchrotron X-ray measurements coupled with mechanical testing to follow the structure evolution during deformation at elevated temperature. It was found that the deformation behaviour of β-nucleated iPP was closely associated with its initial morphology, its subsequent variation during stretching as well as the stretching conditions including the stretching rate and stretching temperature. The current study would not only contribute to the development of crystallization and deformation theory but also be beneficial for the material design. info:eu-repo/classification/ddc/620 ddc:620
12	Glättungsmechanismen beim Ionenbeschuss rauer amorpher Oberflächen / Smoothing mechanisms due to ion bombardment of rough amorphous surfaces Vauth, Sebastian 11 October 2007 (has links) No description available. 530 Physik RD RV000 RVI000 RVI210 RVI220 RVQ450 RVQ500 RVQ700 RVQ820 RVS500 RVT500 RJM000 RJM200 RJM300 RJM320 RQI000 RQI900 RQL200 RTF500 Mathematics and Natural Science Oberflächen Ionenbestrahlung Strukturentwicklung getriebene Systeme Transportphänomene amorphe Systeme Gläser Metalle Halbleiter Rastertunnelmikroskopie Molekulardynamik-Simulationen stochastische Ratengleichungen surfaces ion bombardment structure evolution driven systems transport phenomena amorphous systems glasses metals semiconductors scanning tunneling microscopy molecular dynamics simulations stochastic rate equations 33.60 33.66 33.68 33.28 33.05 33.06

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β-nucleated isotactic polypropylene with different thermomechanical histories investigated by synchrotron X-ray

Glättungsmechanismen beim Ionenbeschuss rauer amorpher Oberflächen / Smoothing mechanisms due to ion bombardment of rough amorphous surfaces