Browsing by Author "Makan, Ashwell Craig"

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    Asymmetric flow field flow fractionation (AF4) of polymers with focus on polybutadienes and polyrotaxanes
    (Stellenbosch : Stellenbosch University, 2012-03) Makan, Ashwell Craig; Pasch, H.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Over the past two decades, field flow fractionation (FFF), as a polymer characterization technique, has become cutting edge technology. The demand for molar mass and size characterisation of complex polymer systems has increased, especially in cases where classical calibration techniques such as size exclusion chromatography (SEC) has shown several shortcomings. FFF is a technique resembling chromatography. It has several significant advantages over SEC, especially for the characterisation of ultrahigh molar mass (UHMM), branched and gel-containing polymers. In this study, polybutadienes, which often contain the abovementioned species, were analysed by SEC and asymmetric flow field flow fractionation (AF4). Both separation techniques were coupled to refractive index and multi-angle laser light scattering detection. Similarly, polyrotaxanes, which are polymers with complex and unique molecular architectures, were also investigated. Results showed that AF4 can explicitly be used as a superior tool over SEC. In the case of UHMM polybutadienes, much higher molar masses could be detected by AF4, due to the absence of shear degradation which is often encountered in SEC. Gel-containing species could be detected by AF4 as no filtering is required prior to injection. Abnormal retention behaviour, a phenomenon often encountered in UHMM branched polymers, was observed in SEC analysis of the polyrotaxanes materials. AF4 provided sufficient separation from low to high molar masses, without out any irregularities.
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    Novel characterization of decorative coatings using field-flow fractionation and a multi-detector approach
    (Stellenbosch : Stellenbosch University, 2017-03) Makan, Ashwell Craig; Pasch, Harald; Stellenbosch University. Faculty of Sciences. Dept. Chemistry and Polymer Science.
    ENGLISH ABSTRACTION: Decorative coatings are present and fulfil and important role in all industry forms from aesthetics, construction, medicine, textiles, manufacturing, packaging and timber. The raw materials used in coatings have an important role to perform and impart various functions, e.g. finishing and feel (gloss or matt), ultraviolet protection against colour fading, resistance against scratches, stains and cracking. Water-based decorative coatings were critically characterized using classical size exclusion chromatography (SEC) and field-flow fractionation (FFF). Various physico-chemical properties were investigated in order to explore potential links between the observed findings and the physical properties of the resultant coating. Particle size of latices and inorganic additives used in decorative coatings were studied using various FFF techniques coupled to an array of detectors, refractive index (RI), dynamic light scattering (DLS), multiangle laser light scattering (MALLS), ultraviolet (UV) and mass spectrometry (MS). Average particle size and particle size distribution from flow FFF (AF4) and sedimentation (SdFFF) had correlations with each other in comparison to DLS. Additional particle populations, which may be due to secondary reactions during synthesis of these particles, could be identified. Mixtures of latex and TiO2 particles were tested with an online AF4 - Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) system to investigate the separation power of AF4. The organic latex particles and the inorganic TiO2 particles could be separated with high resolution using AF4 coupled to UV, MALLS, and ICP-MS. Molar mass, branching and gel-content of latices used in decorative coatings were explored by comparing SEC and AF4. The outcome pointed towards AF4 having more information-rich outcomes compared to SEC. Larger molar masses were observed using AF4 in comparison to SEC. Conformational plots provided more information on branching within acrylic and styrene-acrylic latices as a function of time during free radical polymerization. An interaction study between latices and TiO2 particles using AF4 were conducted to investigate opportunities to minimize TiO2 content in a typical decorative coating formulation. An in-house synthesized sample were compared against a supplier sample focusing on various latex – to – TiO2 ratios, as well as the effect of ultrasonication on the retention time of latex and TiO2 fractograms. Fractionation into narrow fractions and coupling to detection to ICP-MS indicated that the chemical nature of the latex particles as well as the ratio between latex and TiO2 particles has an effect on the overall quantity of the detected TiO2 particles. Furthermore, ultrasonication prior to FFF analyses resulted in latex and TiO2 peaks shifting to earlier retention times, an indication that sonication assist in breaking up large particle agglomerates into smaller and uniform particle populations.