Fatty acid intercalated layered double hydroxides as additives for Jojoba oil and polymer matrices

Fatty acid intercalated layered double hydroxides were used as additives for Jojoba oil and polymer matrices. The first phase of the study was to intercalate carboxylic acids (C14 to C22). These were successfully intercalated into layered double hydroxides (LDHs), with the formula [Mg0.7Al0.3 (OH) 2](CO3)0. 15•0.5H2O. The one-pot synthesis consistently yielded a bilayer intercalated product for the range of acids employed. The intercalated anions had an orientation tilt angle of 55–63°, depending on the length of the fatty acid chain. However, there is an indication that the anion exchange process employed in this study is accompanied by probable dissolution and recrystallisation of the LDH. This is supported by the different growth habits and sizes of platelets observed through scanning electron microscopy (SEM). Moreover, the organo-LDH platelets were found to have varying MII/MIII compositions, ranging from 1.65 to 6, indicating that the one-pot synthesis yields an array of mixed metal hydroxides. Polymer composites, containing 5% and 10 wt.% of stearate intercalated layered double hydroxides (LDH-stearate) and neat layered double hydroxides (LDH-CO3), were prepared via melt-compounding to explore the use of LDHs as an additive. 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. Comprehensive characterisation and study of the fatty acid-intercalated LDH showed that these organoclay hybrids exhibit thermotropic behaviour. This behaviour ultimately leads to the exudation of excess fatty acid. The exuded stearates were found to have lubricating and plasticising effects on the poly(ethylene-co-vinyl acetate) (EVA) and linear low density polyethylene (LLDPE) matrices. Strong hydrogen bond interactions between the chains of poly(ethyleneco- vinyl alcohol) (EVAL) 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 was almost double that of the neat polymer. It appears that this can be attributed to the ability of the highly dispersed and randomly oriented nanosized clay platelets to promote extensive internal microcavitation during impact loading. The creation of a large internal surface area provided the requisite energy dissipation mechanism. The study also considered fatty acid-intercalated LDH as an argillaceous mineral for potential use as a rheological additive in Jojoba oil. A minimum of 20 wt.% LDH in Jojoba oil formulation was found to be stable, i.e. it did not form separate layers on standing. The viscosity of the neat Jojoba oil demonstrated Newtonian behaviour, whereas the modified LDH/Jojoba oil formulation shear thinned, which is a typical non-Newtonian behaviour. Viscosity as a function of temperature showed complex rheological behaviour for the long chain fatty acids C16 to C22. The viscosity increase is assumed to be due to a combination of three events, which include the formation and changes of LDH microstructures within the oil, the loss of excess fatty acids into the oil matrix, and the formation of fatty acid crystal networks. Shear action also induced some delamination of the clay platelets.Thesis (PhD(Eng))--University of Pretoria, 2012.Chemical Engineeringunrestricte

A critical assessment of the methods for intercalating anionic surfactants in layered double hydroxides

The intercalation of surfactant anions, namely sodium dodecyl sulphate, sodium benzene sulphonate and lauric acid, into commercial layered double hydroxides (LDH-CO3) with approximate composition [Mg0.654AI0.346 (OH)2](CO3)0.173.0.5H2O] was explored. LDH-CO3 is commercially available in bulk form owing to its large scale applications as a PVC stabiliser and acid scavenger in polyolefins. It is therefore of interest to investigate intercalation methods using LDH-CO3 as starting material. The intercalation method used was compared with the pre existing procedures, for instance the co-precipitation, ion exchange and regeneration methods. Due to the tenacity with which the carbonate ion is held in LDH-CO3, direct ion exchange is an intricate matter. Hence, in the regeneration method the carbonate ion is removed by thermal treatment and the LDH-surfactant is obtained by reaction of the LDH and surfactant in an aqueous medium. Nevertheless, the resulting products are impure and poorly crystallised, and only partial intercalation is achieved. The underlying principle of the current method is protonation of the carbonate anion to a monovalent anion that is easily exchanged with surfactant anions. Improved results were obtained when water-soluble organic acids were used, the most suitable being lower aliphatic carboxylic acids, e.g. acetic, butyric and hexanoic acid. In contrast, higher linear aliphatic carboxylic acids are preferentially intercalated to the anionic surfactants. In both cases the carboxylic acids are assumed to assist intercalation by facilitating the elimination of the carbonate ions present in the anionic clay galleries. X-ray diffraction analysis, thermal analysis and infrared spectroscopy confirmed the monolayer intercalation of LDH-dodecyl sulphate and LDH-dodecylbenzene sulphonate. In contrast, LDH-laurate featured a bilayer structure.Dissertation (MSc)--University of Pretoria, 2009.Chemistryunrestricte

Properties of layered double hydroxide micro- and nanocomposites

Carbonate and stearate intercalated layered double hydroxides were used as fillers to prepare polymer micro- and nanocomposites, respectively. The stearate modified starting material was bilayerintercalated 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.The National Research Foundation (NRF) and the Bundesministerium fur Forschung (BMBF)http://www.elsevier.com/locate/matresbuhj2013ai201

Anomalous shear viscosity-temperature behaviour of jojoba oil/LDH-stearate suspensions

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 SEMEDS 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.The National Research Foundation (NRF) and the Bundesministerium für Forschung (BMBF).http://www.elsevier.com/locate/colsurfahb2014ai201

Degradation of insecticides used for indoor spraying in malaria control and possible solutions

BACKGROUND: 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. METHODS: 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%. RESULTS: 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. CONCLUSIONS: 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.The Bill & Melinda Gates Foundation through the Grand Challenges Exploration Initiative.http://www.malariajournal.com

Degradation of insecticides used for indoor spraying in malaria control and possible solutions

BACKGROUND: 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. METHODS: 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%. RESULTS: 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. CONCLUSIONS: 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.The Bill & Melinda Gates Foundation through the Grand Challenges Exploration Initiative.http://www.malariajournal.com

A critical assessment of the methods for intercalating anionic surfactants in layered double hydroxides

Anionic surfactant intercalated layered double hydroxides (LDH) of high purity are easily prepared via direct coprecipitation and also by the ion exchange method provided that the precursor contains a monovalent anion, e.g., LDH–Cl or LDH–NO3. However, LDH–CO3 is an attractive starting material as it is commercially available in bulk form owing to large-scale applications as a PVC stabilizer and acid scavenger in polyolefins. Thus, intercalation of dodecyl sulfate and dodecylbenzenesulfonate into a commercial (LDH) with approximate composition [Mg0.654Al0.346(OH)2](CO3)0.173 • 0.5H2O] was explored. Direct ion exchange is difficult as the carbonate is held tenaciously. In the regeneration method it is removed by thermal treatment and the surfactant form obtained by reaction with the layered double hydroxide that forms in aqueous medium. Unfortunately the resulting products are impure, poorly crystallized and only partial intercalation is achieved. Better results were obtained using water-soluble organic acids, e.g., acetic, butyric, or hexanoic acid, to aid decarbonation of LDH–CO3. Intercalation proceeded at ambient temperatures with the precursor powder suspended in an aqueous dispersion of the anionic surfactant. The carboxylic acids are believed to assist intercalation by facilitating the elimination of the carbonate ions present in the anionic clay galleries

Thermal properties of lauric- and stearic acid intercalated layered double hydroxides

A commercial layered double hydroxide (LDH) with nominal composition [Mg0.689A10.311(OH)2](CO3)0.156.zH2O was intercalated with lauric and stearic acid using a surfactant-assisted method. X-ray diffraction, thermal analysis and infrared spectroscopy confirmed that bilayer-intercalated compounds were formed and that the surfactant (sodium dodecyl sulfate) was not co-intercalated. These compounds shows interesting thermal behavior with two phase transformations observed at elevated temperatures. At temperatures that are significantly higher than the melting points of the corresponding free acids, the alkyl chains assume a disordered liquid-like state within the clay galleries. However, at even higher temperatures the materials become completely amorphous like true melts