Browsing by Author "Matthews, Megan Esme"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- ItemCrystallisation behaviour of commercial polyethylenes: a fundamental study(Stellenbosch : Stellenbosch University, 2018-12) Matthews, Megan Esme; Van Reenen, Albert; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Commercial films are generally made of polyolefins, often using a blend of two different polyolefins. Specifically, low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) are blended due to the mechanical strength of LLDPE and the processability of LDPE. However the behaviour of these blends is unpredictable due to the lack of understanding of the underlying processes which determine the final properties. This study focused on developing an understanding of the interactions between LDPE and LLDPE in the blended form through the crystallisation behaviour of the blends. The criteria for co-crystallisation are presented and systematically investigated in order to determine whether the blends meet the criteria. By analysing the blend miscibility in the melt, the crystal structure of the individual blend components as well as the crystallisation kinetics, conclusions can be made about the co-crystallisation potential of LDPE/LLDPE blends. Melt miscibility was investigated by using fluorescent labelling of both polymer components and tracking their movements after the blending process. No isolated domains could be detected with fluorescence microscopy indicating that phase separation did not occur during the melt blending process. However, differential scanning calorimetry (DSC) displayed a number of different crystalline environments which implied that phase separation occurred during the crystallisation process. DSC was also used to verify this through kinetics and showed that the LLDPE crystallised at a faster rate than the LDPE, making co-crystallisation unlikely. Solid state nuclear magnetic resonance (SS NMR) was used to probe the phase separation within the blends and was used to identify a number of different regions which had formed within the amorphous and interfacial areas which seemed to be the cause of the interactions. This disproved the hypothesis that the difference in rate and extent of crystallisation directly affected the ultimate blend properties but rather showed that the amorphous and interfacial regions determine blend behaviour.
- ItemSolid-state interactions of materials: Applications-based solid-state NMR spectroscopy(Stellenbosch : Stellenbosch University, 2022-04) Matthews, Megan Esme; Van Reenen, Albert; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: The solid-state interactions of various polymeric materials were investigated in this study to determine how these interactions affect the macroscopic properties of the solid. The work presented in this dissertation was classified into three commercial problems which were solved using solid-state NMR and a variety of other solid-state techniques. First, vis- breaking was performed in-situ on heterophasic ethylene-propylene copolymers (HEPCs) to determine the effect on HEPCs of increasing ethylene contents. Solution 13C NMR and solid- state NMR was used to determine the effect of the peroxide on the structure and morphology of the HEPCs. The extent of vis-breaking was found to be dependent on the homogeneity of chain sequences. In all cases vis-breaking increased the mobility of the crystalline domains forming a disordered crystal phase within the polypropylene α-structure. Second, the possibility of using impact copolymers as the polymer component of hot-melt adhesives (HMAs) was investigated. A high ethylene-content impact copolymer was blended with three types of waxes and characterised by various solid-state techniques. It was found that the ethylene-rich regions of the impact copolymer displayed strong interactions with the waxes and the extent of the interaction was dependent on the composition of the wax. The bond strength results of the HMAs were found to be comparable to that of an industry standard HMA and the failure mechanism was dependent on the wax type and concentration. Finally, the mechanism of oil entrapment by Fischer-Tropsch (FT) waxes was explored to determine whether wideline NMR is an appropriate method for determination of oil content of waxes. Benchtop solid-state NMR instruments apply wideline methods to determine oil contents commercially in cases where vast differences in mobility exist between phases. Blends of a standard oil and waxes of various melting temperatures were prepared and characterised by various techniques. The higher melting FT waxes were found to trap oil in small pools and limit the mobility of the oil making it difficult to detect by solid-state NMR. Linear correlations could only be obtained by using variable temperature methods and by simplifying the oil composition, however, the accuracy of the correlations was not high. The focus of this study was, therefore, not on the properties of a specific material but on the development of solid-state NMR methods with unique applications to solve industrial problems.