Browsing by Author "Magagula, Sifiso Innocent"

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    The effect of controlled rheology on the evolution of chemical composition distribution of commercial Heterophasic Ethylene Propylene Copolymers (HEPCs)
    (Stellenbosch : Stellenbosch University, 2020-03) Magagula, Sifiso Innocent; Van Reenen, Albert Johannes; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: The vis-breaking of heterophasic ethylene-propylene copolymers (HEPCs) is an important industrial process. While the changes in molar mass properties are easy to track using hightemperature size exclusion chromatography (HT-SEC) before and after vis-breaking, changes in the chemical composition are much more challenging due to the complex chemical composition resulting from different ethylene contents and ethylene block lengths. The present work tracks the microstructural changes of three samples with 0 – 10.8 mol.% ethylene content before and after vis-breaking with the aid of molar mass and chemical composition sensitive chromatographic techniques. Bulk sample analyses indicated that the rubber phase, which is ethylene rich was essential in aiding peroxide mobility during vis-breaking as indicated by the narrower dispersities and lower peak molar masses with increasing ethylene content. Preparative temperature rising elution fractionation (p-TREF) and solvent gradient elution fractionation (SGEF) were used to fractionate the non vis-broken and vis-broken HEPC bulk samples into several fractions for further analyses. Upon vis-breaking, the SGEF fractions with high molar mass were observed to diminish after vis-breaking. Furthermore, the increase in ethylene content was observed to reduce the impact of the peroxide on the fraction quantities before and after vis-breaking implying that vis-breaking affects more the polyolefin chains with more PP segments and less those with more ethylene co-monomer. However, SGEF may not be suitable for the fractionation of mixtures of homopolymer and copolymers due to the different solubilities in the solvent/non-solvent mixtures. Furthermore, in-situ solid state NMR experiments revealed the greater sensitivity of copolymers containing short ethylene sequences to peroxide degradation. Long chain ethylene sequences were found to be resistant to radical degradation.
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    The effect of organic peroxides on the molecular composition of heterophasic ethylene-propylene impact copolymers
    (Stellenbosch : Stellenbosch University, 2015-12) Magagula, Sifiso Innocent; Van Reenen, A. J.; Stellebosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Heterophasic ethylene-propylene copolymers, also known as impact polypropylene (PP) copolymers (IPCs) or heterophasic copolymers (HECOs), are a unique group of polyolefins produced through the copolymerisation of ethylene and propylene, with the aim of improving the impact properties of the PP homopolymer at low temperatures. Therefore, this polymer comprises of a PP homopolymer matrix with a dispersed rubbery copolymer phase. Due to their unique properties, HECO polymers have become commercially important materials, with a wide range of applications. Therefore a fundamental understanding of the processes and chemistry that affects their final macroscopic properties needs to be expanded. The main focus of this investigation was to understand why specific organic peroxides influence or interact differently with the various phases of HECO polymers, in order to utilize their properties to obtain HECO polymers with optimal and desired properties. Two HECO polymers with different ethylene contents were fractionated into three fractions (30, 100 and 130 °C), using preparative temperature rising elution fractionation (P-TREF). Each individual TREF fraction was degraded with two different types of organic peroxides, and then characterised using four different analytical tools. The changes in the molecular structures of the different fractions were investigated by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The changes in comonomer sequence distributions were investigated by carbon 13 nuclear magnetic resonance spectroscopy (13C-NMR). Moreover, the degradation of the different fractions was investigated by high temperature size exclusion chromatography (HT-SEC). The investigation showed that the HECO polymers with different ethylene contents were uniquely altered. It was evident that the ethylene content influenced the degradation behaviour of the HECO polymers. The ability of the peroxide to affect certain regions of the HECO polymer more than others is highly dependent upon its miscibility with certain regions of the HECO polymers. The “visbreaking” efficiency of a specific organic peroxide appears to be primarily dependent on the number of “peroxy” groups it contains in its molecular structure. Stellenbosch University https://scholar.sun.ac.za