F.J.W.J. Labuschagne

Layered Double Hydroxide Intercalated with Sodium Dodecyl Sulfate

The study investigates the intercalation of magnesium-aluminum layered double hydroxide with sodium dodecyl sulfate. Monolayer intercalation of the LDH-carbonate was achieved using an acetic acid-assisted ion exchange reaction. The carboxylic acid is believed to assist intercalation of dodecyl sulfate by facilitating the elimination of the carbonate ions present in the anionic clay. Bilayer intercalation was achieved by a coprecipitation method and this resulted in a highly crystalline product. However, in this case the interlayer contains a mixture of dodecyl sulfate anion, sodium dodecyl sulfate and the hydrolysis product dodecanol. The organic phase in the latter product shows an order-disorder transition between 100°C and 120°C, with thermal degradation and volatilization commencing above 170°C.

Metal catalysed intumescence: characterisation of the thermal decomposition of calcium gluconate monohydrate

Calcium gluconate monohydrate is a member of a new class of base-catalysed intumescent compounds. It forms low-density closed-cell carbonaceous foam when exposed to heat. The volume expansion can be as high as two hundred times the original volume. At temperatures above 750°C this foam is transformed into a porous, yet cohesive, structure based on calcium oxide. The latter has only a slightly higher density and shows significant flame-resistance.

Different transition metal combinations of LDH systems and their organic modifications as UV protecting materials for polypropylene (PP)

In this research, the use of layered double hydroxides (LDHs) as ultraviolet (UV) light-protecting additives for PP is explored. Different LDHs, such as ZnTi, ZnSn, ZnGa, ZnCr and CdCr LDHs, were prepared and their UV absorptions were characterized. The ZnTi LDHs showed higher UV absorption than the other four metallic combinations and were further organically modified with dodecylbenzene sodium sulfonate (SDBS) and lauric acid (LA). Nanocomposites of polypropylene (PP) with four different types of LDHs, ZnTi, ZnSn, ZnTi-SDBS and ZnTi-LA, were prepared at concentrations of 5%. The crystallinities and layered structures of all the metallic combinations of LDHs were characterized by wide angle X-ray spectroscopy (WAXS) and ultraviolet visible (UV-vis) absorption spectroscopy, and their crystal morphologies were studied by scanning electron microscopy (SEM). The decomposition and thermal properties of the nanocomposites and pure PP were analyzed by thermogravimetric analysis (TGA) and transmission electron microscopy (TEM) and by their photo-oxidation behavior. The addition of these organically modified and unmodified LDHs showed significant changes in the thermal decomposition of PP. The thermal stability of PP was increased to around 70 °C by the addition of SDBS-modified ZnTi LDHs (5% by weight), and an increase in induction time of about 300% was determined.

Green synthesis of hydrotalcite from untreated magnesium oxide and aluminum hydroxide

ABSTRACT The influence of reaction temperature and time on the hydrothermal dissolution-precipitation synthesis of hydrotalcite was investigated. Untreated MgO, Al(OH)3 and NaHCO3 were used. An industrially beneficial, economically favourable, environmentally friendly, zero effluent synthesis procedure was devised based on green chemistry principles, in which the salt-rich effluent typically produced was eliminated by regenerating the sodium bicarbonate in a full recycle process. It was found that the formation of hydromagnesite dominates at low temperatures independent of reaction time. With an increase in reaction time and temperature, hydromagnesite decomposes to form magnesite. At low temperatures, the formation of hydrotalcite is limited by the solubility of the Al(OH)3. To achieve a hydrotalcite yield of 96%, a reaction temperature of 160°C for 5 h is required. A yield higher than 99% was achieved at 180°C and 5 h reaction time, producing an layered double hydroxide with high crystallinity and homogeneity. GRAPHICAL ABSTRACT

Modelling the Thermal Degradation and Stabilisation of PVC in a Torque Rheometer

Abstract A novel method for simulating the torque and temperature curves from a torque rheometer thermal stability test on poly(vinyl chloride) (PVC) was developed. A mathematical model was proposed which combines the chemical kinetics involved in the thermal degradation and stabilisation process of PVC with heat transfer and viscosity relationships within the torque rheometer. The model coefficients were fitted to data obtained from previous experiments with a program written in the Python programming language using the Levenberg-Marquardt Algorithm (LMA) with multiple starts. The mathematical model fits the torque rheometer data successfully depending on the characteristics of the torque curve. The model fit is successful when the torque curve follows the expected behaviour. An unsuccessful model fit occurs when the torque curve deviates from the expected shape in a very specific way. In the degradation phase the torque curve increases to a local maximum, decreases to a local minimum and then increases again. The exact reason for the dip in torque is unknown.