Masters Degrees (Chemistry)

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Browsing Masters Degrees (Chemistry) by Advisor "Djokovic, V."

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    The effects of peroxide treatment on composites of linear low density polyethylene and short sisal fibre
    (University of the Free State, 2003) Mokoena, Moipone Alice; Luyt, A. S.; Krupa, I.; Djokovic, V.
    In this work sisal fibre (Agave sisalana) was used as reinforcement in LLDPE-sisal fibre reinforced composites. In recent years there has been an increasing interest in finding new applications for sisal fibre as reinforcement in composites. The inherent problem that sisal fibre is hydrophilic in nature and thus absorbs a considerable amount of water, poses a thread towards achieving good interfacial adhesion with hydrophobic thermoplastic materials. Thus it was necessary to consider treatment of the composites. Dicumyl peroxide (DCP) was used for this purpose. The influence of sisal fibre and DCP content on the thermal, mechanical and visco-elastic properties of LLD PE-sisal fibre composites was investigated. Results show a significant decrease in water absorption for the DCP treated samples, changes in the polymer melting behaviour as a result of the presence of sisal as well as cross-linking/grafting in the presence of DCP, and significantly improved stress and strain at break, especially at low sisal contents. The presence of sisal increases the tensile modulus, but DCP treatment does not seem to have much influence on this property. Stress relaxation reduces with increasing sisal content, but again DCP treatment does not seem to have much influence. Although not proved beyond any doubt, there are indications that peroxide treatment, especially at high DCP content, causes grafting between LLDPE and sisal, as well as degradation of LLDPE.
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    Preparation and properties of PVDF based BaTiO3 containing nanocomposites
    (University of the Free State (Qwaqwa Campus), 2014-01) Mofokeng, Tladi Gideon; Luyt, A. S.; Djokovic, V.
    The β-crystallization of PVDF was investigated in this study. Nanocomposites were prepared by melt mixing PVDF, and 80/20 w/w PVDF/PMMA blends, with non-activated and (5 and 10 min) mechanically activated BaTiO3 nanoparticles. The samples were then quenched in ice water followed by annealing at 80 °C for 24 hours. The sizes of the BaTiO3 particles were reduced through mechanical activation prior to mixing, and the activated BaTiO3 nanoparticles interacted better with the polymer matrix. The BaTiO3 nanoparticles were well dispersed in the polymer matrix, but also formed agglomerates. The β-phase was only detected in the blend and the blend nanocomposites. The non-activated BaTiO3 nanoparticles favoured the α-phase crystallization of PVDF/PMMA, while the mechanically activated nanoparticles induced the β-phase. The thermal stabilities of PVDF and the PVDF/PMMA blend decreased with the addition of BaTiO3 nanoparticles. At a fixed filler content, the storage modulus and dielectric constant increased with an increase in activation time. The crystallization and melting temperatures of the matrix were slightly affected by the introduction of activated BaTiO3 particles.