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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Polymer - Sepiolite Clay Nanocomposites

Author: BILOTTI, Emiliano

Year: 2009

Supervisor(s): Ton Peijs

In the last two decades, polymer-clay nanocomposites have attracted great interests because of the remarkable enhancements in mechanical and physical properties with minute amount of nano-filler, promising to eliminate the typical compromise that exists between properties and processability of composite materials. Despite the expectations created by nano-clays in the academic and industrial communities, their success has so far been limited. The reasons can be ascribed to the poor dispersion of nano-clays in polymer matrices, to the often weak interfacial interaction with polymers, and to the lack of control of nano-clay orientation. In this thesis, all the aspects above will be tackled, studying the potential of sepiolite, a nano-clay with a peculiar needle-like shape, in two thermoplastic polymers: polypropylene (PP) and polyamide 6 (PA6). After an extensive literature survey, the experimental part of the thesis starts with the characterisation of sepiolite (Chapter 5). The dimensions of the nano-filler are evaluated, as well as the specific surface area, the thermal properties and the stiffness of individual nano-needles with novel nano-mechanical tests. Chapter 6 deals with improving the dispersion and interaction of nano-clay in PP, by employing three compatibilisers and by surface functionalisation of the clay. In order to align the fibrous nano-filler, thin PP/sepiolite tapes are prepared by solid-state drawing (Chapter 7). It is shown that in these oriented nanocomposite tapes, small amounts of clay (<2.5wt%) are able to improve the mechanical performances, due to a better reinforcement efficiency of the nanofiller and to a higher orientation induced crystallinity, but also the thermal resistance and barrier properties. Finally (Chapter 8-9), PA6/sepiolite nanocomposites were prepared both by melt compounding and in situ polymerisation. Sepiolite is well dispersed in PA6 without any need of compatibilisers or clay surface functionalisation. The simple and environmentally friendly melt-compounding process turns out to be as efficient as the in situ polymerisation route for what concerns the dispersion state of nano-filler, making it a good candidate for industrial and commercial applications. In conclusion, sepiolite shows promising credentials as nanofiller for thermoplastic polymers (i.e. PA6), and in particular for oriented tapes, ultimately creating a 1D nanocomposite reinforced by a 1D nanofiller.

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