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Congratulations to Mr. D. G. Papageorgiou for successfully defending his PhD Thesis!

Category: news Published on Friday, 23 May 2014

Congratulations to Mr. D. G. Papageorgiou for successfully defending his PhD Thesis on 29/04/2014!

Thesis Title: High performance polypropylene nanocomposites, with enhanced thermal properties



Polymers are generally considered versatile materials, which present interesting properties such as low density, easy processibility, high flexibility and low price. However, the continuous progress of research and technology demands materials with improved properties, able to withstand extreme conditions and wear. According to these specifications, polymer nanocomposites were developed in order to achieve a significant enhancement of the physicochemical properties of neat polymers with the introduction of small amount of fillers in the nanodimension. Almost all types of polymers such as thermoplastics, thermosets and elastomers have been used to produce polymer nanocomposites and one of the most popular polymers is polypropylene. Towards this direction, three fillers with different structural and geometrical characteristics were used in the current thesis (silica nanoparticles, multi walled carbon nanotubes and montmorillonite clays) for their insertion into a polypropylene matrix and ultimately the production and in-depth study of their final properties.

Initially, the polypropylene matrix that was used, exhibited complex structure due to the presence of ethylene units which disrupted the sequence of the main macromolecular chains and the insertion of a β-nucleating agent. Furthermore, different preparation methods and techniques were applied for each set of nanocomposites in order to observe their effect on the dispersion and adhesion of the fillers into the polymeric matrix. Neat and surface-modified fillers were prepared and compatibilizers were added in different sets of samples. Each filler affected in different aspects the nanocomposite material and the study was focused on the structural characteristics and modifications caused by the fillers, the thermal stability and the thermal degradation kinetics, along with the nucleation effects and the influence of each filler on the crystallization temperature and kinetics. Empasis was given to the structure-property relationships and especially the mechanical properties in comparison with the transmission electron microscopy images and x-ray diffraction characteristics. Various micromechanical models were applied on the experimental data in order to export conclusions regarding the interfacial interactions between the matrix and the fillers. Finally, an in-depth study was performed on the thermal degradation kinetics for all the prepared samples and isoconversional and model-fitting procedures were followed for the calculation of the respective activation energies.