Weighted-Power-Mean mixture model for the Gibbs energy of fluid mixtures

A continuous family of excess Gibbs free energy expressions is derived based on the double-weighted power mean mixture model and concepts from cubic equations of state. This family has two types of parameters: The model form is determined by two power indices, whereas the matrix of binary coefficients characterizes pure component behavior and binary interactions. It is shown that the Porter, Margules, and Wassiljewa composition dependence are but special forms of this more general expression. In particular, the Wassiljewa Gibbs free energy form turns out to have the same composition dependence as the nonrandom two-liquid (NRTL) equation.Financial support for this research from the THRIP program of the Department of Trade and Industry and the National Research Foundation of South Africa as well as Xyris Technology is gratefully acknowledged.http://pubs.acs.org/journals/iecred/index.htm

Polypropylene-based long-life insecticide-treated mosquito netting

Malaria causes approximately one million deaths a year and more than 300 million cases of severe illness. The World Health Organization (WHO) regards insecticide-treated nets (ITNs) as an important component in its efforts to roll back malaria.Sasol ChemCityhttp://www.degruyter.com/view/j/polyeng?rskey=fISiih&result=222&q=am201

Surface resistivity and mechanical properties of rotationally molded polyethylene/graphite composites

Antistatic polymers are required to dissipate static charges safely from component surfaces. Our overall objective has been to develop cost-effective flame-retarded and antistatic polyethylene compounds suitable for rotomolding. This communication considers the surface resistivity and mechanical properties of rotationally molded linear low-density polyethylene (LLDPE)/graphite composites containing natural Zimbabwean graphite, expandable graphite, or expanded graphite. Dry blending and melt compounding were employed to obtain antistatic composites at the lowest graphite contents. Dry blending was found to be an effective mixing method for rotomolding antistatic LLDPE/graphite composites, thereby eliminating an expensive compounding step. Dry-blended Zimbabwean graphite composites showed the lowest surface resistivity at all graphite contents, with a surface resistivity of 105 Ω/square at 10 wt% loading. Although rotomolded powders obtained following the melt compounding of Zimbabwean graphite exhibited higher resistivity values, the variability was much lower. Injection molding resulted in surface resistivity values above 1014 Ω/square for all compositions used. The rotomolded composites exhibited poor mechanical properties, in contrast to injection-molded composites. The Halpin-Tsai model showed good fits to the tensile modulus data for injection-molded Zimbabwean and expandable graphite.Institutional Research Development Programme (IRDP) of the National Research Foundation of South Africa and Xyris Technology CC.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1548-0585hb201

Development of an insecticide impregnated polymer wall lining for malaria vector control

This study explored the effectiveness of inexpensive monofilament mesh linings produced by extruding insecticide impregnated polyethylene and poly(ethyleneco-vinyl acetate) (EVA) directly into a net format.From Challanges in malaria research: Core science and innovation Oxford, UK. 22-24 September 2014http://www.malariajournal.comam201

Trapping citronellal in a microporous polyethylene matrix

The Flory–Huggins theory was used to model the phase behaviour of linear low density polyethylene– citronellal binary mixtures. The model parameters were obtained from fitting the bimodal phase envelope using data points from cloud point determinations. This allowed the prediction of the melting point depression curve as well as the location of the spinodal region. A microporous polyethylene matrix was obtained by quenching homogeneous liquid mixtures at temperatures well below the spinodal phase boundary. This strategy makes it possible to trap, and effectively solidify, large amounts of citronellal in a polyethylene (LLDPE) matrix. This has potential implications for the development of long-lasting insect repellent bracelets and anklets.Dr Leo Braack, the Centre for Sustainable Malaria Control at University of Pretoria and the National Research Foundation of South Africa.http://www.elsevier.com/locate/tca2016-08-10hb201

Thermo-mechanical properties of urea-based pattern molding compounds for investment casting

Urea is a low cost material with thermal and mechanical properties suitable for use in investment casting pattern molding compounds. Conventional compounds are made by a “cooking” process wherein the urea is added to and dissolved in an aqueous solution of a water soluble polymer followed by evaporation of the water. Here we describe novel formulations based on either polyvinyl alcohol (PVOH) plasticized by glycerol or ethylene vinyl acetate (EVA) resins together with wax that can be prepared by a facile twin-screw compounding process. The thermo-mechanical properties of these compounds were characterized using differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), dynamic mechanical analysis (DMA) and three bend point tests. The PVOH-based molding compounds featured better mechanical properties than those based on EVA. Increasing the polymer content produced weaker but tougher molding compounds. Increasing wax content improved stiffness but resulted in a loss of toughness. The TG results showed that both compounds decomposed readily at elevated temperatures and left less than 3 wt. % ash at 800°C.Financial support for this research from Xyris Technology, Ceracast and the THRIP program of the Department of Trade and Industry and the National Research Foundation of South Africa is gratefully acknowledged.www.polymer-process.co

Low shear rheological behaviour of two-phase mesophase pitch

The low shear rate rheology of two phase mesophase pitches derived from coal tar pitch has been investigated. Particulate quinoline insolubles (QI) stabilised the mesophase spheres against coalescence. Viscosity measurements over the range 10–106 Pa s were made at appropriate temperature ranges. Increasing shear thinning behaviour was evident with increasing mesophase content. At low mesophase contents the dominant effect on the near Newtonian viscosity was temperature but at higher contents it was the shear rate; temperature dependence declined to near zero. The data indicated that agglomeration could be occurring at intermediate mesophase volume fractions, 0.2–0.3. The Krieger– Dougherty function and its emulsion analogue indicated that in this region the mesophase pitch emulsions actually behaved like ‘hard’ sphere systems and the effective volume fraction was estimated as a function of shear rate illustrating the change in extent of agglomeration. At the higher volume fractions approaching the maximum packing fraction, which could only be measured at higher temperatures, the shear thinning behaviour changed in character and it is considered that this is possibly due to shear induced deformation and breakup of dispersed drops in the shear field.South African Research Chairs Initiative of the Department of Science and Technology (DST) and the National Research Foundation (NRF).http://www.elsevier.com/locate/carbon2016-02-28hb201

Stabilizing sunflower biodiesel with synthetic antioxidant blends

Biodiesel was prepared using base catalyzed methanolysis of sunflower oil. The oxidative stability of the neat biodiesel, as well as samples spiked with 0.15 wt% antioxidant was quantified by induction periods (IP) obtained with the Rancimat method according to the tangent method. The neat stabilizers, binary blends and a ternary mixture of poly(1,2-dihydro-2,2,4-trimethylquinoline) (Orox PK), tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane (Anox 20), and tris(nonylphenyl)phoshite (Naugard P) were tested. Of these, Anox 20 was the most effective stabilizer while Naugard P proved ineffective for the sunflower biodiesel. Synergistic improvement of oxidative stability was observed on partial substitution of this phenolic-based compound with the Orox PK. Combinations of the latter amine-based stabilizer with other phenolic antioxidants did not show any synergy, with perhaps the exception of DTBHQ. At a dosage of 0.15 wt%, only TBHQ, propyl gallate and pyrogallol, as well as their 2:1 blends with Orox PK, provided IP values that exceeded 8 h as required by the European Standard EN 14,214 for biodiesel.The Energy Institutional Research Theme of the University of Pretoriahttp://www.elsevier.com/locate/fuel2019-05-01hj2018Chemical Engineerin

Correlating multicomponent surface tension data with Padé approximants. Part I. Surface tension

DATA AVAILABILITY : Data will be made available on request.Please read abstract in the article.The Deutsche Forschungsgemeinschaft (DFG) and the German Academic Exchange Service (DAAD).https://www.elsevier.com/locate/molliqhj2024Chemical EngineeringNon

Surfactant-free dimer fatty acid polyamide/montmorillonite bio-nanocomposites

Polyamide bio-nanocomposites were successfully prepared using a surfactant-free approach. The clay morphology was fixed by dispersing the ammonium ion-exchanged clay in acetic acid. This was mixed with an acetic acid solution of the polyamide and the composite was recovered by precipitation with water. The composites featured a mixed morphology containing some exfoliated clay sheets together with nano-sized clay tactoids. Bio-nanocomposites containing as much as 27.5 wt.% clay were obtained. At this filler level, and depending on the temperature, the modulus was up to nine times higher than that of the parent polymer. Addition of clay also increased the glass transition temperature by as much as 5 °C. This indicates that the high interfacial surface area, presented by the clay platelets dispersed in the matrix, significantly impaired the polymer chain mobility.Institutional Research Development Programme (IRDP) and the South Africa/Mozambique Collaboration Programme of the National Research Foundation (NRF)http://link.springer.com/journal/396hb201