Synergy between conventional phosphorus fire retardants and organically-modified clays can lead to fire retardancy of styrenics

Polystyrene–clay nanocomposites combined with phosphorous-containing fire retardants have been prepared and used to explore the thermal stability and mechanical properties of the polymer formed. The amounts of fire retardants and clay used were varied to study the effect of each on thermal stability and mechanical properties of the polymer. The samples were prepared by bulk polymerization and analyzed by X-ray diffraction, thermogravimetric analysis, cone calorimetry, Fourier Transform infrared spectroscopy and the evaluation of mechanical properties. The thermal stability of the polymers is enhanced by the presence of the phosphorus-containing fire retardants

Enhanced Fire Retardancy of Vinyl Ester Resins by Combination of Additives

In pursuit of fire-retardant materials, vinyl ester resins were combined with commercially available fire retardants at lower loadings than that at which they are usually effective when used alone. The thermal stability and flammability of the various combinations of fire retardants were evaluated by thermogravimetric analysis and cone calorimetric analysis. With some combinations, the 50% degradation temperature was improved by about 5-10ºC Different additives affected the flammability to varying extents and some combinations resulted in an enhanced fire retardancy compared to the additives used alone. The combinations that showed the best reductions in the peak heat release rate (PHRR) were further used to prepare glass reinforced resins and the flammability of those systems was also evaluated using cone calorimetry

The Impact of COVID-19 on Academic Library Service Delivery in Zimbabwe

The higher and tertiary education system was greatly affected by the COVID-19 pandemic leading to tremendous changes in service delivery in academic libraries. All the higher education stakeholders were affected including lecturers, students, researchers, and librarians, and they were forced to adjust accordingly in order to remain relevant. A survey was done using a multiple case study design where online questionnaires were distributed and participant observation were used to collect data from three academic libraries in Zimbabwe. It was discovered that academic libraries changed the way they deliver their services to meet the new demands when teaching and learning was shifted to online as a way of curbing the spreading of the virus. The author recommends that academic librarians should be continuously trained to deal with the skills gap created by the COVID-19 pandemic. There is need to provide appropriate information and communication technology infrastructure and the supporting policies and guidelines for academic libraries to continue supporting the research, teaching and learning activities in the COVID-19 environment

Polystyrene Nanocomposites Based on Quinolinium and Pyridinium Surfactants

In this paper pyridine and quinoline-containing salts were employed to modify montmorillonite. TGA analysis shows that the quinolinium modified clay has a higher thermal stability than the pyridinium modified clay. Polystyrene nanocomposites were prepared by in situ bulk polymerisation and direct melt blending using both clays. The X-ray diffraction and transmission electron microscopy results show the formation of intercalated structures. The 50% degradation temperature of the nanocomposites is increased and so is the amount of char from TGA analysis compared to the virgin polymer. Cone calorimetric results indicate that clay reduces the peak heat release rate and average mass loss rate and thus lowers the flammability of the polymer

Polystyrene Nanocomposites based on Carbazole-Containing Surfactants

New organically-modified clays containing a carbazole unit were prepared and the number of long alkyl chains on the surfactant was varied. The clay was used to prepare polystyrene nanocomposites by both bulk polymerization and melt blending. The dispersion of these clays in the polymer matrix was evaluated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal stability of the clays and the nanocomposites were analyzed by thermogravimetric analysis (TGA) while the fire properties were evaluated by cone calorimetry. If more than two alkyl chains were present, the gallery spacing is apparently overcrowded, leading to poor dispersion. Bulk polymerization gave nanocomposites with better dispersion and reduced flammability when compared to the melt blending process

Styrenic Nanocomposites Prepared using a Novel Biphenyl-Containing Clay

Montmorillonite was organically modified using an ammonium salt containing 4-acetylbiphenyl. This clay (BPNC16 clay) was used to prepare polystyrene (PS), acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS) nanocomposites. Polystyrene nanocomposites were prepared both by in situ bulk polymerisation and melt blending processes, while the ABS and HIPS nanocomposites were prepared only by melt blending. X-ray diffraction and transmission electron microscopy were used to confirm nanocomposite formation. Thermogravimetric analysis was used to evaluate thermal stability and the flammability properties were evaluated using cone calorimetry. By thermogravimetry, BPNC16 clay was found to show high thermal stability, and by cone calorimetry, a decrease in both the peak heat release rate and the mass loss rate was observed for the nanocomposites

Fire Retardancy of Vinyl Ester Nanocomposites: Synergy with Phosphorus-Based Fire Retardants

Vinyl ester (PVE) nanocomposites were prepared using both clay and polyhedral oligosilsesquioxanes (POSS) as the nano-dimensional material. From cone calorimetric data, it was shown that both POSS and clay affect the flammability of the nanocomposites to the same extent. To improve on the flame retardancy, the nanocomposites were combined with phosphorous-containing fire retardants (FRs) and the result compared to the benchmark halogen-containing system. The use of the cone calorimeter to investigate the fire properties of these nanocomposites showed a great reduction in peak heat release rate (PHRR) in the presence of phosphate and slight improvements in average mass loss rate (AMLR) while thermogravimetric analysis showed improvement in char yield in the presence of phosphate. Several different organically modified clays were used and they affected the flammability to different extents. The time that the resin and clay were mixed and the atmosphere in which the reaction was carried out do not have an effect on the flammability and thermal stability of the nanocomposites. The effect of curing temperature on the clay dispersion and flammability was also investigated

Dynamics and mechanism studies of nonlinear chemical systems

The kinetics and mechanisms of oxidation of selected thiocarbamides (tetra-methylthiourea, trimethylthiourea, phenylthiourea, and 2-aminoethanethiolsulfuric acid) by chlorite in aqueous acidic media are investigated using UV/Vis, NMR, Stopped-flow techniques, and qualitative analysis. The reactions were extremely complex, with reaction dynamics strongly influenced by the pH of the reaction medium and formation of stable intermediates (sulfonic acids). Results revealed that oxidations of substituted thioureas do not always proceed via a stepwise oxidation of the sulfur center. Instead, reactions occurred in two stages: S-oxygenation of the sulfur center to yield the sulfinic acid, which then reacts in the second phase predominantly through an initial hydrolysis to produce a urea-type residue and the sulfoxylate anion. The sulfoxylate anion, a highly reducing species, is then rapidly oxidized to sulfate.;Experimental and numerical studies of local periodic forcing on an excitable Belousov-Zhabotinsky (BZ) medium in a thin gel layer are reported. Rather than the traditional suprathreshold perturbations giving rise to a local oscillatory state, waves were initiated in an excitable system via localized small amplitude variations in light intensity, without crossing into the oscillatory regime of the autonomous system. Initiation of waves in the initially quiescent medium was possible when the frequency of the sinusoidal perturbation was suitably tuned to that of the autonomous system. The region in phase space where wave initiation was possible depended on the parameter values of the perturbation, namely forcing frequency and forcing amplitude, and on the inherent properties of the autonomous system. Resonance patterns are found by relating the period between two waves to the period of the sinusoidal perturbation.;Experimental and theoretical studies of the peroxidase-oxidase (PO) reaction are reviewed. Numerical investigations into the initiation of trigger waves in an oscillatory one-dimensional PO reaction-diffusion system are presented. Trigger waves are initiated in the oscillatory system via localized perturbations in the concentration of one of the variables using the extended BFSO model. The chemical waves traveled with a sharp front and were not able to penetrate barriers to diffusion, which are properties characteristic of trigger waves

Synergy Between Nanocomposite Formation and Low Levels of Bromine on Fire Retardancy in Polystyrenes

An organically-modified clay has been prepared using ammonium salts which contain an oligomeric material consisting of vinylbenzyl chloride, styrene and dibromostyrene. The presence of dibromostyrene enhances the flame retardancy of polystyrene nanocomposites compared to both the virgin polymer and polystyrene nanocomposites prepared from non-halogen-containing organically-modified clays. The nanocomposites were prepared both by bulk polymerization and melt blending and they were evaluated by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry measurements. Bulk polymerization produced nanocomposites with reduced peak heat release rate, reduced total heat release and improved thermal stability. It is noteworthy that all these improvements were obtained with clay loading as low as 3% and bromine content less than 4%