F.J.W.J. Labuschagne

University of Pretoria, Πρετόρια/Πόλη του Ακρωτηρίου, Gauteng, South Africa

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Publications (13)17.13 Total impact

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    ABSTRACT: The layered double hydroxide ([Mg0.667Al0.333(OH)2](CO3)0.167·mH2O) (LDH) has found application as a heat stabiliser for PVC. Derivatives of this compound were synthesised using a hydrothermal method. Emulsion grade PVC was plasticised with 100 phr diisononyl phthalate and stabilised with 30 phr of the LDH filler additives. Heat stabilities were determined at 200 °C. The dynamic heat stability tests were performed on the plastisols using the torque rheometer method. Static heat stability was evaluated on the fused compounds. It was evaluated from discoloration profiles of strips exposed for various lengths of time to heat in a Metrastat oven. The time dependence of hydrogen chloride evolution was followed with a Metrohm Thermomat instrument. The conventional LDH provided the best dynamic heat stability. However, partial replacement of the magnesium with copper significantly delayed the release of volatile HCl. If instead the replacement was done using zinc, better colour retention was achieved.
    No preview · Article · Mar 2015 · Polymer Degradation and Stability
  • W.W. Focke · L. Moyo · F.J.W.J. Labuschagne · N.G. Hoosen · S. Ramjee · M. Saphiannikova
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    ABSTRACT: Stearate intercalated layered double hydroxide was synthesized by reacting the corresponding carbonate form with a large excess of stearic acid. Thermal analysis, FTIR, XRD and SEM-EDS characterization indicated the formation of a highly crystalline bilayer-intercalated product. The composition of the inorganic portion showed high variability in the Al:Mg atom ratio. This suggests that the crystals comprised stacks of randomly interstratified layers that varied in compositions from one close to magnesium stearate to one similar to aluminium distearate. The rheology of the jojoba oil suspensions containing this material showed strong shear thinning behaviour and also an anomalous temperature dependence.
    No preview · Article · Feb 2014 · Colloids and Surfaces A Physicochemical and Engineering Aspects
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    Full-text · Dataset · May 2013
  • L. Moyo · W. W. Focke · D. Heidenreich · F.J.W.J. Labuschagne · H.-J. Radusch
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    ABSTRACT: Carbonate and stearate intercalated layered double hydroxides were used as fillers to prepare polymer micro- and nanocomposites, respectively. The stearate modified starting material was bilayer-intercalated clay. During melt compounding excess stearates were released and the clay reverted to a monolayer-intercalated form. The exuded stearate acted as a lubricant lowering the melt viscosity of poly(ethylene-co-vinyl acetate) and linear low density polyethylene matrices. Strong hydrogen bond interactions between the chains of poly(ethylene-co-vinyl alcohol) and the clay platelet surfaces overwhelmed the lubrication effect and caused an increase in the melt viscosity of this matrix. The notched Charpy impact strength of this composite is almost double that of the neat polymer. It appears that this can be attributed to the ability of the highly dispersed and randomly oriented nano-sized clay platelets to promote extensive internal micro-cavitation during impact loading. The creation of a large internal surface area provided the requisite energy dissipation mechanism.
    No preview · Article · Mar 2013 · Materials Research Bulletin
  • Lumbidzani Moyo · Walter W. Focke · Frederick J. W. J. Labuschagne · Sabine Verryn
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    ABSTRACT: The study investigates the intercalation of magnesium-aluminum layered double hydroxide with sodium dodecyl sulfate. Monolayer intercalation of the LDH-carbonate was achieved using an acetic acid-assisted ion exchange reaction. The carboxylic acid is believed to assist intercalation of dodecyl sulfate by facilitating the elimination of the carbonate ions present in the anionic clay. Bilayer intercalation was achieved by a coprecipitation method and this resulted in a highly crystalline product. However, in this case the interlayer contains a mixture of dodecyl sulfate anion, sodium dodecyl sulfate and the hydrolysis product dodecanol. The organic phase in the latter product shows an order-disorder transition between 100°C and 120°C, with thermal degradation and volatilization commencing above 170°C.
    No preview · Article · Apr 2012 · Molecular Crystals and Liquid Crystals
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    L. Moyo · W.W. Focke · F.J.W. Labuschagne · S.C. Verryn

    Full-text · Article · Jan 2012 · Molecular Crystals and Liquid Crystals
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    ABSTRACT: The insecticide dichloro-diphenyl-trichloroethane (DDT) is widely used in indoor residual spraying (IRS) for malaria control owing to its longer residual efficacy in the field compared to other World Health Organization (WHO) alternatives. Suitable stabilization to render these alternative insecticides longer lasting could provide a less controversial and more acceptable and effective alternative insecticide formulations than DDT. This study sought to investigate the reasons behind the often reported longer lasting behaviour of DDT by exposing all the WHO approved insecticides to high temperature, high humidity and ultra-violet light. Interactions between the insecticides and some mineral powders in the presence of an aqueous medium were also tested. Simple insecticidal paints were made using slurries of these mineral powders whilst some insecticides were dispersed into a conventional acrylic paint binder. These formulations were then spray painted on neat and manure coated mud plaques, representative of the material typically used in rural mud houses, at twice the upper limit of the WHO recommended dosage range. DDT was applied directly onto mud plaques at four times the WHO recommended concentration and on manure plaques at twice WHO recommended concentration. All plaques were subjected to accelerated ageing conditions of 40°C and a relative humidity of 90%. The pyrethroids insecticides outperformed the carbamates and DDT in the accelerated ageing tests. Thus UV exposure, high temperature oxidation and high humidity per se were ruled out as the main causes of failure of the alternative insecticides. Gas chromatography (GC) spectrograms showed that phosphogypsum stabilised the insecticides the most against alkaline degradation (i.e., hydrolysis). Bioassay testing showed that the period of efficacy of some of these formulations was comparable to that of DDT when sprayed on mud surfaces or cattle manure coated surfaces. Bioassay experiments indicated that incorporating insecticides into a conventional paint binder or adsorbing them onto phosphogypsum can provide for extended effective life spans that compare favourably with DDT's performance under accelerated ageing conditions. Best results were obtained with propoxur in standard acrylic emulsion paint. Similarly, insecticides adsorbed on phosphogypsum and sprayed on cattle manure coated surfaces provided superior lifespans compared with DDT sprayed directly on a similar surface.
    Full-text · Article · Oct 2011 · Malaria Journal
  • L. Moyo · D. Heidenrich · F.J. Labuschagne · R. Androsch · W. W. Focke

    No preview · Conference Paper · Jan 2011
  • L.Moyo · D. Heidenrich · F.J.W. Labuschagne · R. Androsch · W. W. Focke

    No preview · Conference Paper · Jan 2010
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    Walter W. Focke · Dan Molefe · F. J. W. Labuschagne · Shatish Ramjee
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    ABSTRACT: Hydrated filler-type flame retardants were coated with approximately a monolayer of stearic acid using a solvent technique. Compared to the uncoated powders, the BET surface area was lower, the powder packing density was improved, and the thickening effect on white oil was significantly reduced. The latter two observations are rationalized in terms of a reduction in the attractive interactions between the powder particles. The viscosity of white oil slurries containing 25wt% solids showed shear-thinning non-Newtonian behavior. The coated powders showed significantly lower viscosities at low shear rates although the difference diminished at high shear rates. The lower viscosities shown by the coated powders indicate that the surface modification facilitated the break-up of agglomerates and the dispersion of individual particles in the fluid.
    Full-text · Article · Nov 2009 · Journal of Materials Science
  • F. J. W. J. Labuschagné · S. M. C. Verryn · W. W. Focke
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    ABSTRACT: The compound ammonium D-gluconate (C6H11O7−NH4+) has been studied by X-ray powder diffraction. The powder diffraction pattern and data obtained at room temperature are presented (cell data and powder data summary).
    No preview · Article · Jun 2003
  • F. J. W. J. Labuschagné · W. W. Focke
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    ABSTRACT: Calcium gluconate monohydrate is a member of a new class of base-catalysed intumescent compounds. It forms low-density closed-cell carbonaceous foam when exposed to heat. The volume expansion can be as high as two hundred times the original volume. At temperatures above 750C this foam is transformed into a porous, yet cohesive, structure based on calcium oxide. The latter has only a slightly higher density and shows significant flame-resistance.
    No preview · Article · Feb 2003 · Journal of Materials Science
  • W. W. Focke · F. J. W. Labuschagne · C. A. Strydom
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    ABSTRACT: In this study, potassium bitartrate and pentaerythritol mixtures were ground together using a mortar and pestle until the blends appeared homogeneous. Thermogravimetric (TG) and differential scanning calorimetric (DSC) data were obtained in an air atmosphere using a Netzsch STA 409 simultaneous TG/DSC instrument.
    No preview · Article · Apr 2000 · Journal of Materials Science Letters