Arnebold, André
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Arnebold, André
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Arnebold, André
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Item-typ:Veröffentlichung, Gezielte Einstellung der Morphologie kationisch polymerisierter Epoxidnetzwerke zur Implementierung funktioneller Eigenschaften(2016-11-04); ; ; Material improvements in polymer science are often based on morphology adjustment through incorporation of additives, especially telechelics. For this, a view on natural materials, such as bone, spider silk, human enamel, or nacre reveals that crystallinity is a dominating factor for improved mechanical properties. Furthermore, synthetic materials, e.g. elastomers, thermoplastics, and shape-memory polymers have been pointed out to show functional as well as increased mechanical properties by a defined crystallinity. The use of crystalline domains in thermosets, such as epoxy resins, is only rarely discussed in the literature. This work shows how enhancements in both strength and toughness are achievable in cationically polymerized, epoxy based thermosets due to a semi-crystalline character of the resulting network. Furthermore, functional properties are generated by the materials morphology and composition. The investigations of these materials show combinations of versatile thermo-mechanical properties with moldability, shape-memory behavior, and stress relaxation performance which emphasize them as smart materials. Semi-crystalline polyester polyols, such as poly( -caprolactone) or poly(omega-pentadecalactone), are suitable telechelics to introduce crystalline domains in epoxy networks. Additionally, these telechelics are able to react with the epoxy resin due to a chain transfer reaction known as activated monomer (AM) mechanism. Crystallinity adjustment in epoxy resins is possible by the control of reaction mechanisms and reaction conditions during cationic polymerization. For this, an enhanced segregation into crystalline domains as well as nano-domain formation is observed by suppressing the AM mechanism e.g. by esterification of the polyester polyol end groups or by increased reaction rates due to high curing temperatures. In the last case, the polymerization by epoxide propagation proceeds preferably compared to the AM mechanism. Strong phase separation during polymerization leads to both enhanced strength and toughness, but also to superior adhesion properties when the crystal sizes are small; preferably below one micrometer. Moldability of those crosslinked networks has been observed under certain conditions due to the occurrence of a transesterification reaction. It is shown that reaction conditions and the choice of polyester are responsible for the occurrence of crystallinity and; furthermore, for its unique properties as universal smart material.Dissertation455 407 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Strong and super tough: Layered ceramic-polymer composites with bio-inspired morphology(Wiley, 2018); ; ; ; Bio-inspired layered ceramic-polymer composites with high strength and toughness were prepared from sintered aluminum oxide ceramic sheets and cationically curing epoxy resins toughened with poly(ε-caprolactone) (PCL). The architecture of the composite is inspired by nacre but is arranged on a larger scale. Ceramic sheets with a nominal thickness of 250 μm were assembled into composite plates by adhesive layers with a nominal thickness of 20 μm. Before the manufacturing of the composites, the stress-strain properties of the polymer component were tailored by the variation in the PCL content between 0 and 39 wt%. For composites with 4 and 15 ceramic layers, the bending strengths achieved 327 MPa and 376 MPa, which are higher than that of pure ceramic sheets. Moreover, composites with 15 ceramic layers show a 16 times higher toughness compared to that of the pure ceramic sheets. The results indicate that the toughness of the layered composites increases significantly with the number of layers. Inspired by the geometrical ratio of the natural sheet composite nacre, we have achieved a similar strength but a 2 times higher toughness than nacre by only adding up to 6 vol% of the polymer.Wissenschaftlicher Artikel194 270