This paper details a successful synthesis and comparison of a range of tri-metal hydrotalcite-like layered double hydroxides (LDHs) using urea hydrolysis.

BACKGROUND:The influence of different hydrating agents on the pH of the hydrating solutions,

The layered double hydroxide ([Mg 0.667 Al 0.333 (OH) 2 ](CO 3 ) 0.167 ·mH 2 O) (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.

BackgroundThe 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.MethodsThis 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%.ResultsThe 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.ConclusionsBioassay 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.

Comparison of the effect of transition metal modification on the material properties of quintinite synthesised using co-precipitation under the same conditions.