Masters Degrees (Chemistry and Polymer Science)

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

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    The 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.