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The mechanical properties of semi-crystalline polymers depend extremely on their
morphology, which is dependent on the crystallization during processing. The aim of
this research is to determine the effect of various nanoparticles on morphology
formation and tensile mechanical properties of polypropylene under conditions
relevant in polymer processing and to contribute ultimately to the understanding of
this influence.
Based on the thermal analyses of samples during fast cooling, it is found that the
presence of nanoparticle enhances the overall crystallization process of PP. The results
suggest that an increase of the nucleation density/rate is a dominant process that
controls the crystallization process of PP in this work, which can help to reduce the
cycle time in the injection process. Moreover, the analysis of melting behaviors
obtained after each undercooling reveals that crystal perfection increases significantly
with the incorporation of TiO2 nanoparticles, while it is not influenced by the SiO2
nanoparticles.
This work also comprises an analysis of the influence of nanoparticles on the
microstructure of injection-molded parts. The results clearly show multi-layers along
the wall thickness. The spherulite size and the degree of crystallinity continuously
decrease from the center to the edge. Generally both the spherulite size and the degree
of crystallinity decrease with higher the SiO2 loading. In contrast, an increase in the
degree of crystallinity with an increasing TiO2 nanoparticle loading was detected.
The tensile properties exhibit a tendency to increase in the tensile strength as the core
is reached. The tensile strength decreases with the addition of nanoparticles, while the
elongation at break of nanoparticle-filled PP decreases from the skin to the core. With
increasing TiO2 loading, the elongation at break decreases.
Cyanobacteria are the only prokaryotes with the ability to conduct oxygenic photosynthesis,
therefore having major influence on the evolution of life on earth. Their diverse morphology
was traditionally the basis for taxonomy and classification. For example, the genus
Chroococcidiopsis has been classified within the order Pleurocapsales, based on a unique
reproduction modus by baeocytes. Recent phylogenetic results suggested a closer
relationship of this genus to the order Nostocales. However, these studies were based
mostly on the highly conserved 16S rRNA and a small selection of Chroococcidiopsis
strains. One aim of this present thesis was to investigate the evolutionary relationships of
the genus Chroococcidiopsis, the Pleurocapsales and remaining cyanobacteria using
16S rRNA, rpoC1 and gyrB gene. Including the single gene, as the multigene analyses of
97 strains clearly showed a separation of the genus Chroococcidiopsis from the
Pleurocapsales. Furthermore, a sister relationship between the genus Chroococcidiopsis
and the order Nostocales was confirmed. Consequently, the monogeneric family
Chroococcidiopsidaceae Geitler ex. Büdel, Donner & Kauff familia nova is justified. The
phylogenetic analyses also revealed the polyphyly of the remaining Pleurocapsales, due to
the fact that the strain Pleurocapsa PCC 7327 was always separated from other strains.
This is supported by differences in their metabolism, ecology and physiology.
A second aim of this study was to investigate the thylakoid arrangement of
Chroococcidiopsis and a selection of cyanobacterial strains. The investigation of 13 strains
with Low Temperature Scanning Electron Microscopy revealed two unknown thylakoidal
arrangements within Chroococcidiopsis (parietal and stacked). This result revised the
knowledge of the thylakoid arrangement in this genus. Previously, only a coiled
arrangement was known for three strains. Based on the data of 66 strains, the feature
thylakoid arrangement was tested as a potential feature for morphological identification of
cyanobacteria. The results showed a strong relationship between the group assignment of
cyanobacteria and their thylakoid arrangements. Hence, it is in general possible to
conclude from this certain phenotypic character the affiliation to a particular family, order
or genus.
The third aim of this study was to investigate biogeographical patterns of the worldwide
distributed genus Chroococcidiopsis. The phylogenetic analysis suggested that the genus do not have biogeographical patterns, which is in contrast with a recent study on hypolithic
living Chroococcidiopsis strains and the majority of phylogeographic analysis of
microorganisms. Further analysis showed no separation of different life-strategies within
the genus. These results could be related to the genetic markers utilized, which may not
contain biogeographical information. Hence the present study can neither exclude nor
prove the possibility of biogeographic and life-strategy patterns in the genus
Chroococcidiopsis.
Future research should be focused on finding appropriate genetic markers investigate of
evolutionary relationships and biogeographical patterns within Chroococcidiopsis.