Browsing by Author "Barnard, Johannes Lodewiekus"
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- ItemThe effect of chemical composition and morphology on the properties of polyolefin films(Stellenbosch : Stellenbosch University, 2018-03) Barnard, Johannes Lodewiekus; Van Reenen, A. J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: This thesis consists of three parts, in the first part a preliminary study was conducted pertaining to dunnage bags. Dunnage bags are large inflatable restraining devices used in containers to keep the cargo from toppling over when in transit. Dunnage bags currently in use consist of two materials; one of polyethylene (PE) for air permeability resistance and polypropylene (PP) for strength. In an attempt to create a single layer dunnage bag a material had to be selected having various properties such as high strength, puncture resistance and air permeability resistance. After preliminary testing it was found that high impact polypropylene (HIPP) or heterophasic ethylene-propylene copolymers (HEPCs) conformed to most of the required properties and were therefore selected as ideal candidate materials for further testing. HEPCs are readily available and widely used in various industries. The copolymer consists of an extremely complex composition consisting of PP and PE homopolymers as well as ethylene-propylene copolymers creating rubbery phases. Mechanical properties of this material are well known, but research into how polyethylene inclusion contribute to its permeability properties is still in its infancy. The concepts and problems introduced through answering this problem led to part two. Part two served as the main part of the study and dealt with observation of the finer material properties on a molecular level which related to the macroscopic properties of the final product. The gas permeability of a series of HEPCs with varying ethylene content (sampled by online time-dependent extraction) were investigated and attempts were made to relate this macroscopic property to how ethylene inclusion affects the morphology. This was done by using various analytical techniques such as permeability testing, differential scanning calorimetry (DSC), positron annihilation lifetime spectroscopy (PALS), X-ray diffraction spectroscopy (XRD) and polarizing optical microscopy (POM). Crystal morphology and crystallization kinetics as well as polymer composition turned out to have a contribution towards the final permeability properties. In part three these techniques were employed on a different sample set to substantiate the conclusions made in part two. A HDPE:LDPE blend with varying LDPE composition was studied. Interesting findings were made and substantiated by a PALS experiment. Part three agreed with the findings made in part two and a promising way of predicting the permeability of a polymeric film with varying chemical composition was achieved.
- ItemStructure-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.