Doctoral Degrees (Chemistry and Polymer Science)

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Browsing Doctoral Degrees (Chemistry and Polymer Science) by Author "Barnard, Johannes Lodewiekus"

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    Structure-property relationships in PVC-lubricant compounds
    (Stellenbosch : Stellenbosch University, 2021-03) Barnard, Johannes Lodewiekus; Van Reenen, A. J.; Robertson, D. D.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: This thesis was constructed with the aim of developing and improving current methods for tracking lubricants during the single screw extrusion of unplasticized polyvinyl chloride (uPVC). First a set of commercial waxes were selected to develop this method. These waxes were sourced from industries making use of different production technologies and therefore varied widely in chemical composition and morphology. The lubricant behaviour was monitored over three stages. In stage 1, it was essential to fully characterize the waxes according to their chemical composition and morphological properties. During stage 2, it was necessary to evaluate any inherent chemical or physical association interactions between any of the components within a uPVC formulation. For stage 3, full uPVC formulations were extruded using a single screw Brabender extruder and subsequently analysed. In stage 1 the waxes were characterized using various analytical techniques such as High-temperature size exclusion chromatography (HT-SEC), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, 13C nuclear magnetic resonance (13C-NMR) spectroscopy, solid state NMR (SS-NMR), differential scanning calorimetry (DSC) and, X-ray diffraction (XRD) spectroscopy. In stage 2, uPVC formulations were hot-melt mixed at high speed and evaluated using scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDS). This allowed for the effective determination of additive positions before extrusion. In stage 3 the extrudates were also analysed using SEM-EDS. This technique helped to establish the additive positions after PVC fusion, effectively tracking additive migration. At this point it was established that calcium stearate (CaSt) facilitated the dispersion of the nonpolar wax across the surface of a PVC particle and that there exists a competition effect between polar waxes and CaSt. The extrudates showed some interesting results such as a complete phase separation for formulations containing CaSt and a polar wax. The method was further refined using a screw-freezing technique which allowed in-extruder sampling to be done. The method was applied to a second set of polar and nonpolar waxes (Wax set 2). No trends could be observed at this stage due to the waxes differing too much in chemical composition and morphology. It was therefore decided to synthesize a new set of polar waxes and fully characterize them. A new set of waxes were successfully synthesized by ozonolysis of FT (Fischer-Tropsch) waxes. These waxes were fully characterized, and an attempt was made to track the lubricants’ migration. Migration could not be track and the samples were subjected to commercial testing. Through combining the stage 3 experiments and commercial fusion studies a deeper understanding of the currently accepted model for lubricant migration was gained. Additionally, the model was expanded to include the effect of oxidized waxes.