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Accelerated photooxidation under ultraviolet (UV) test of polyamide 11 (PA11) films filled with unmodified vermiculite clay at 5 wt% was investigated up to 600 h. Film samples of ~60-[micro]m thick were prepared by melt compounding using a cast extruder and exposed to UV light irradiation at [lambda] > 295 nm. Fourier transform infrared (FTIR) spectra indicated similar structural changes occurring in both PA11 and PA11 /unmodified vermiculite nanoclay (UVMC) nanocomposite along the photooxidation process, resulting in imides and carboxylic acids as the main carbonyl products. It was however observed that the formation rate of carbonyls in the PA11 /UVMC nanocomposite was slower than neat PA11. This behavior is consistent with the yellowing index evolution determined by ultraviolet-visible (UV-vis) spectroscopy. Further, the photooxidation stability of the samples was also evaluated by the onset oxidation temperature determined by differential scanning calorimetry. The results indicated a better stability of the nanocomposite film than neat PA11, corroborating well the data obtained by FTIR and UV-vis techniques., INTRODUCTION Polyamide 11 (PA11) is a bio-based engineering thermoplastic derived from a renewable resource (castor oil) [1]. It is biocompatible and has the advantage of being less hydrophilic than the [...]

Coal fly ash (FA), an aluminum silicate by-product and environmental pollutant which is generated during the combustion of coal in coal-fired power stations, was used as an electrode modifier for the determination of Cd(II) in aqueous solutions. In this work, graphite/polyurethane-based composites containing different amounts of FA were prepared and characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) thermogravimetry (TGA), and derivative thermogravimetry (DTG). The graphite/polyurethane composite electrodes (GPUE), with and without FA modifier, were evaluated with regard to their performance as voltammetric electrodes in the determination of metallic cations, using Cd(II) as a probe. After optimizing solution and instrumental parameters affecting the peak current, a differential pulse anode stripping voltammetry (DPASV) procedure was developed for GPUE modified with 5% FA (m/m), resulting in a linear response for Cd(II) from 2.0 x 10−7 to 1.0 x 10−6 mol L−1 with a detection limit (LOD) of 6.6 x 10−8 mol L−1. Cd(II) was added to natural water samples and determined at the 10−7 mol L−1 level with a mean recovery of 99%. It was also extracted from exhausted rechargeable Ni-Cd batteries and diluted to ca. 0.2 µmol L−1 and determined with the same electrode, with recoveries of 98.7% when compared to FAAS. These results serve as a proof of concept that FA is a useful electrode modifier. [ABSTRACT FROM AUTHOR]

BACKGROUND: The effectiveness of mosquito repellents, whether applied topically on the skin or released from a wearable device, is determined by the evaporation rate. This is because a repellent has to be present in the form of a vapour in the vicinity of the exposed skin that needs protection. Therefore, gravimetric techniques were used to investigate the direct evaporation of selected liquid repellents, their permeation through polymer films, and their release from a microporous polyethylene matrix. RESULTS: Evaporation of a repellent into quiescent air is determined by its air permeability. This is a product of the vapour pressure and the diffusion coefficient, i.e. SA=PAsatDA. It was found that repellents could be ranked in terms of decreasing volatility as: ethyl anthranilate > citriodiol > dimethyl phthalate > N,N‐diethyl‐meta‐toluamide (DEET) > decanoic acid > ethyl butylacetylaminopropionate > Icaridin. Experimental SA values, at 50 °C, ranged from 0.015 ± 0.008 mPa m2 s−1 for the least volatile repellent (Icaridin) to 0.838 ± 0.077 mPa m2 s−1 for the most volatile (ethyl anthranilate). The release rate from microporous polyethylene strands, produced by extrusion‐compounding into ice water baths followed a similar ranking. These strands featured an integral skin‐like membrane that covered the extruded strands and controlled the release of the repellent at a low effective rate. CONCLUSION: The high thermal and thermo‐oxidative stability together with the low volatility of the mosquito repellents ethyl butylacetylaminopropionate and Icaridin make them attractive candidates for long‐lasting wearable mosquito‐repellent devices. Such anklets/bracelets may have utility for outdoor protection against infective mosquito bites in malaria‐endemic regions. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Before 100,000 years ago, during the Middle Stone Age (MSA) of South Africa, silica varieties of minerals and rocks were sometimes heated during tool making in order to improve their knapping properties. If the heating and cooling process is not controlled, failure results and the nodules fracture. Recently, we postulated that the reversible α- to β-phase transition may play a role in causing silcrete, a type of rock often used to make stone tools in the Western Cape, to fracture. In this new study, we analyse the thermal behaviour (520–620 °C) of silcrete and compare it to that of two chalcedony samples from different origins, together with samples of chert, agate and flint. These minerals and rocks were commonly used to make stone tools. Differential scanning calorimetry (DSC) measurements show that the α- to β-phase transformation is prominent in silcrete, agate and one of the chalcedony samples, weaker in chert and the second chalcedony sample, but non-existent in flint. X-ray fluorescence (XRF), thermogravimetric analysis (TG) and carbon and sulphur analyses show differences in elemental composition between the rocks and minerals. X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy highlight differences in microstructure. These small differences in chemical composition and structure contribute to a variety of chemical reactions and phase transformations that can take place in rocks and minerals, which in combination determine their stability upon heating and show that care should be taken when generalising thermal behaviour. [ABSTRACT FROM AUTHOR]