Browsing by Author "Human, Chantelle"

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    Facile method for producing silicon containing porous carbon nanofibres from amphiphilic copolymers and controlling precursor fibre morphology
    (Stellenbosch : Stellenbosch University, 2015-12) Human, Chantelle; Mallon, Peter Edward; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Amphiphilic graft copolymers PAN-g-PDMS were synthesized via a conventional free radical polymerization. The dispersities and molecular weights are typical of that of conventional free radical polymerizations. From the relative integration of NMR peaks it was found that the copolymer composition present could be varied by variation of the PDMS feed ratio. Subsequently, precursor fibres have been produced from the PAN-g-PDMS copolymers series by single needle electrospinning. SEM analysis revealed an increase in fibre diameter and a change in porous structure as the PDMS content increased which could be explained by self-assembly of the amphiphilic molecules. With the addition of MWCNTs, a drastic decrease in fibre diameter was apparent due to the conductive nature of the MWCNTs. TEM images showed that the MWCNTs are distributed and aligned inside the electrospun fibres. Surprisingly, despite the wide use of PAN to produce polymer nanofibres by solution electrospinning, there are no reports on the effect of solution ageing on this process. The investigation revealed an increase in fibre diameter and viscosity for the PAN and grafted copolymers when dissolved in DMF. The effect is more exaggerated for the homo-PAN than the graft copolymers, which is indicative that the effect is caused by PAN rather than PDMS. UV-VIS and XRD results showed the formation of dipole-dipole interaction aggregates in solution accompanied by a decrease in crystallinity in the fibres with an increase in ageing time. Precursor films were also prepared and found to be porous. The precursor fibres and films were subjected to a carbonization process in order to obtain silicon containing porous carbon nanomaterial as stated above. The carbonized samples were analysed with SEM, FE-SEM, EDX, XRD, DSC, BET and TEM to quantify the effect of the thermal treatment. The carbonizations led to major mass loss of the samples and thus a decrease in fibre diameter. FE-SEM and TEM analysis showed that the porous morphology is still present after carbonization. The subsequent carbonized fibres and films consisted largely of carbon, but contained silicon and oxygen from the PDMS. It was found that the carbonization mechanism is similar to that of PAN, but that the PDMS grafts retard the cyclization of the PAN in the stabilization step as shown by DSC. The results also show a comparable difference between the fibres and films. This was attributed to the non-equilibrium morphology present in the electrospun fibres. A possible application of the porous carbon nanofibres was also investigated. The sorption capacity for various oils and organic solvents was found to be higher than that of other carbon-silica nanofibre membranes. PAN-g-PEO and PAN:PEO blends were electrospun and carbonized as an alternative method for porous carbon fibre production. The results showed successful carbonization where porosity of the carbon fibres was strongly dependant on the size of the sacrificial PEO domains. Lastly, an alternative method for more efficient production of precursor fibres was utilized. The ball electrospinning process showed the same trend with regards to the PDMS content and porosity as the single needle technique, but with a throughput rate of 36 times faster.
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    The physicochemical properties and stability of aspalathin in micro- and nanoencapsulated green rooibos extract formulations
    (Stellenbosch : Stellenbosch University, 2019-04) Human, Chantelle; De Beer, D.; Joubert, E.; Sigge, G. O.; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Green rooibos extracts with high aspalathin content have potential as nutraceutical food ingredients based on their properties relating to the prevention of metabolic syndrome. However, delivery of green rooibos extracts in convenient beverage products is a challenge due to poor stability of aspalathin in the presence of moisture. Thus, the development of alternative ingredients and convenience products is required. Microencapsulation of a green rooibos extract (GRE) with maltodextrin as control carrier and inulin and chitosan as low kilojoule functional alternatives was achieved by spray-drying. Spray-dried GRE and powders containing maltodextrin or inulin had similar yields (>76%), moisture content (<3.5%) and aspalathin retention (>95%), whereas microencapsulation with chitosan resulted in lower yields (<66%), higher moisture content (>3.4%) and lower aspalathin retention (<83%). Accelerated stability tests (40 °C/75% relative humidity (RH)) revealed similar aspalathin degradation rates (based on fractional conversion model) for GRE, inulin and maltodextrin formulations, but significantly higher degradation rates for chitosan formulations. Given the low incompatibility between GRE and inulin, inulin-microencapsulated GRE (1:1 ratio; IN50) was selected as the most suitable green rooibos nutraceutical beverage ingredient. IN50 was added to iced tea powder formulations, which contained various food grade ingredients (sucrose, xylitol, citric acid and ascorbic acid). Shelf-life trials (30 °C and 40 °C/65% RH for 5–12 months) in different packaging materials (semi-permeable vs impermeable) revealed more aspalathin degradation (based on first order reaction rates), more discolouration and clumping after the addition of crystalline ingredients. These changes were more pronounced at 40 °C and for powders stored in the semi-permeable packaging. The formulation containing IN50, xylitol and citric acid, which showed the most drastic physical and chemical changes during storage, was subjected to descriptive sensory analysis, which confirmed significant changes also in its sensory profile. Nanoencapsulation of an aspalathin-rich fraction (GRAF) prepared from green rooibos was also investigated. Combinations of natural (chitosan and lecithin) and synthetic [poly(lactide-co-glycolide) and Eudragit S100® (ES100)] polymers with suitable conventional methods and electrospraying were investigated. Overall, ES100 electrosprayed particles had the best combination of properties, i.e. encapsulation efficiency (EE, 55.4%), loading capacity (LC, 11.1%), release rate at pH 7.4 (1.67 h-1) and size (190 nm). Further optimisation of the ES100-GRAF loaded nanoparticles was achieved using a central composite design. Responses included yields between 78.2–78.3%, EE between 73.9–76.4% and LC between 9.9–12.9%. Pure aspalathin was subsequently encapsulated using the optimal conditions, resulting in a similar yield, EE, LC, particle size and particle morphology to that of GRAF loaded nanoparticles. The stability of the aspalathin and GRAF loaded nanoparticles was investigated at fixed pH-time combinations. Nanoencapsulation offered a more stable environment for aspalathin. Overall, pure aspalathin was less stable than when in GRAF. Even though intestinal permeability could theoretically be improved with nanoencapsulation, the parallel artificial membrane permeability assay and Caco-2 cell model indicated that pure aspalathin and aspalathin nanoparticles both have equally low permeability. These methods offered an alternative for the production of GRE convenience products and ingredients, whilst providing insight on the effects of encapsulation and ingredients of powder formulations.