Ein fundiertes Verständnis der Mechanismen der Gummi-Vulkanisation von Dien-Kautschuken ist noch immer eine der größten Herausforderungen in der Chemie und Technologie der Elastomere. Die Schwefelvulkanisation von Elastomerwerkstoffen ist ein seit langem verwendeter, aber dennoch sehr anspruchsvoller Prozess, mit dessen Hilfe moderne Reifen hergestellt werden. Bei dieser chemischen Reaktion spielt Zinkoxid, zusammen mit den anderen Hilfsstoffen der Schwefelvulkanisation eine entscheidende Rolle. Um die Produkteigenschaften von mit Schwefel vulkanisierten Elastomermaterialien zu verbessern, sollten die Mechanismen der chemischen Vernetzung - und insbesondere auch die Rolle von Zink enthaltenden Verbindungen bei der Vulkanisationsreaktion besser verstanden werden. Zum Beispiel könnte das Eigenschaftsprofil von Reifen durch die Ausbildung von geeigneten Netzwerken aus Schwefel oder anderen Netzknoten optimiert werden. Nitrilkautschke aus der Klasse der Spezialelastomere und die meisten nicht-Tire- Kautschuk in der ganzen Welt eingesetzt, wecken ein großes Interesse der Forschung wegen ihrer einzigartigen Vulkanisationschemie bei der Vernetzung mittels Zinkverbindungen und wegen der besonderen Eigenschaften der dadurch erzeugten Elastomerwerkstoffe. In dieser Arbeit wurde besonderes Augenmerk darauf gelegt, die Rolle von verschiedenen Zinkverbindungen in der Schwefelvulkanisation von carboxylierten Nitrilkautschuken zu verstehen. In der vorliegenden umfangreichen und eingehenden Untersuchung konnte die Ausbildung einer weiteren Polymerphase im Elastomer nachgewiesen werden. Durch dieses Ergebnis kann nun das dynamische mechanische Verhalten von solchen Polymerwerkstoffen besser verstanden werden. Teile dieser Arbeit beschäftigen sich mit der Erforschung der Rolle von Zinkchlorid bei der Vernetzung von Nitrilkautschuken. Hierzu wurde festgestellt, dass Zinkchlorid einen besonderen Einfluss auf die chemische Vernetzung des NBR aufweist, auch in Abwesenheit anderer Vernetzungs- oder Vulkanisationsadditive. Die so vernetzten Elastomere weisen ein stark hydrophiles Verhalten auf, im Gegensatz zu den allgemeinen Eigenschaften solcher Elastomerwerkstoffe. Eine detaillierte Analyse dieser neuartigen Netzwerkstruktur, gebildet durch eine Koordinationsbindung zwischen dem Zinkatom des Zinkchlorids und dem Nitrilkautschuk, wurde durchgeführt. Carboxylierter Nitrilkautschuk (XNBR) wurde ebenfalls eingesetzt, um funktionale Kautschukmischungen mit neuartigen flammhemmenden Eigenschaften zu entwickeln. Zu dieser Thematik wurden Zink enthaltende Doppelhydroxide (Layered Doube Hydroxides, LDH) als multifunktionale Füllstoffe in XNBR-Kautschuk eingesetzt. Neben dem Flammschutzverhalten zeigt LDH einzigartige Eigenschaften als verstärkenden Füllstoff und gleichzeitig als aktivierendes Additiv für die Schwefelvulkanisation. Eine weitere Zink enthaltenden Verbindung, Zinkstearat, wurde eingesetzt um mechanoadaptive elastomere Materialien durch gezieltes Einstellen des kristallinen bzw. amorphen Charakters dieser Verbindung zu entwickeln. Dies könnte einen wichtigen Beitrag zur Entwicklung zukünftiger Reifenmaterialien mit intrinsisch adaptiven Eigenschaften liefern.

L’étude cinétique a permis de déterminer le temps d’équilibre atteint lors de la fixation du benzopurpurine 4B sur chaque composé, ainsi que l’ordre de la réaction et la nature du mécanisme de diffusion. Cette adsorption est favorisée par un milieu légèrement basique, et l’augmentation de la température a un effet positif sur l’amélioration des performances maximales de la fixation. L’étude des isothermes d’adsorption de ce colorant, a été établie pour déterminer l’efficacité de cette nouvelle classe d’adsorbants. Ces dernières sont de type L, et les donnés de sorption ont été traitées selon plusieurs modèles, afin de mieux comprendre le mécanisme d'adsorption du colorant sur les différents matériaux. L’analyse des résultats de l’étude thermodynamiques a montré que l’adsorption du colorant sur les différents composés est un phénomène spontané, endothermique et favorable, régie par une adsorption physique pour les matériaux CoFe-CO3/Ec, CoFe-CO3/A et MgAl-CO32- et par une adsorption physico-chimique pour les matériaux CoFe-Ac/p, CoNiFe-Ac/p , et MgAl-500. Ces résultats ont été confirmés par les analyses DRX et IR des différents matériaux avant et après adsorption. En comparant les résultats obtenus pour l’adsorption du colorant sur les différents matériaux, le composé CoNiFe-Ac/p constitue le meilleur adsorbant avec une capacité d’adsorption d’environ 593mg/g. Par conséquent, et compte tenu de l’ensemble des résultats fournis par cette étude, l’hydrolyse forcée en milieu polyol, s’avère une méthode très efficace pour l’élaboration des hydroxydes doubles lamellaire à base de métaux de transition avec une morphologie contrôlée, de taille nanométrique présentant un faible taux d’agglomération, et par conséquent une bonne dispersion de particules et un meilleur pouvoir adsorbant. Ces caractéristiques peuvent être à l’origine de l’application de ces matériaux avec succès dans l’élimination des colorants contenant dans les effluents industriels. / New layered double hydroxides (LDHs) CoFe-Ac, CoNiFe-Ac, ZnNiFe-Ac and ZnCoFe-Acwith MII/MIII molar ratio of 3, and acetate ions in the interlayer region have been preparedusing forced hydrolysis of acetate metallic salts in a polyol medium. The structure,morphology and properties of as-prepared product were investigated by X-ray Diffraction(XRD), FT-IR Spectroscopy, elemental analysis, transmission Electron Microscopy (TEM),Scanning Electron Microscopy (SEM), thermal analysis (DTA, TGA) and V-visibleSpectroscopy: showed that these nanocomposites present the typical features of hydrotalcitelikestructure, exhibit a turbostratic character and the intercalation of acetate anions into theinterlayer domain has been successfully done, giving an interlayer spacing value of 12.70,12.47, 13.64 and 14.69 Å for CoFe-Ac, CoNiFe-Ac, ZnNiFe-Ac and ZnCoFe-Acrespectively.We can note that there is some difference between the interlayer spacing for all synthesizedphases. That can be explained by the arrangement of inserted species (anions + water) indifferent orientation in the interlayer domain.57Fe Mössbauer spectrometry allows concluding the presence of Fe3+ cations which occupyoctahedral sites and confirming the absence of Fe2+ in the as-prepared compounds.In order to check the capacity of our materials synthesized in polyol medium to exchange theacetate anions inserted in their interlamellar space, anionic exchange in aqueous medium waseffected for CoFe-Ac compound as à model of synthesized LDH. All the physicochemicalmethods of analysis (DRX, IR, ATD/ATG and elemental analysis) carried out on the materialCoFe- Ac /EC (exchanged). The comparison with a lamellar phase containing oFeCO3/Asynthesized in aqueous medium, show a layered double hydroxide compound with aturbostratic disorder, and a new interlamellar distance d003 = 7.67Å which correspondsperfectly with the presence of the carbonate anions and the water molecules in the interfeuilletfield.In the second part of this study, we are interested to examine the capacities of these kinds ofmaterials for the adsorption of an anion dye benzopurpurine-4B-. The adsorption of direct red2 by CoFe-Ac, CoNiFe-Ac LDHs has been examined in order to measure the capability ofthis new organic/inorganic nanomaterial to eliminate this highly toxic azoic class of anionicdyes from wastewater. The sorption capacities of LDHs for Benzopurpurine4B are also compared with those of other adsorbents : CoFe- Ac /Ec, CoFeCO3/A (synthesized in aqueous medium), Mg-Al-CO3/A and its calcined product at 500°C “Mg-Al-500”. The quantity of dye eliminated was found to depend on contact time, pH, initial concentration of dye and heating temperature. The thermodynamic parameters ΔG°, ΔH° and ΔS° werecalculated to predict the nature of adsorption. Results suggested that the Benzopurpurine 4B adsorption on different compounds was a spontaneous and endothermic process. Adsorption kinetic data were tested using pseudo-first order, pseudo-second order, Elovitch’sequation and intra-particle diffusion models. Kinetic studies for all cases showed that the adsorption followed a pseudo-second order reaction. Studies revealed that intra-particle diffusion played an important role in the mechanism of dye adsorption by MgAl-500. Theequilibrium data were analyzed using Langmuir, Freundlich, Tempkin, Elovitch, Dubinin-Radushkevich, Redlich-Peterson and Toth isotherm models. [...] Taking these results into account, we can conclude that prepared LDHs by forced hydrolysis in a polyol medium can be used successfully in the removal of anionic dyes from aqueous solutions.

The effect of incorporation two clays; layered double hydroxides (LDH) and montmorillonite layered silicates (MLS) in linear low density polyethylene (PE) matrix was investigated. MLS and LDH were added of 5, 15, 30 and 60 weight percent in the PE and compounded using a Brabender. Ground pellets were subsequently compression molded. Dispersion of the clays was analyzed using optical microscopy, SEM and XRD. Both the layered clays were immiscible with the PE matrix and agglomerates formed with increased clay concentration. The thermal properties were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Both clays served as nucleation enhancers increasing recrystallization temperatures in the composites. Flame retarding properties were determined by using the flammability HVUL-94 system. LDH indicated better flame retarding properties than MLS for PE. The char structure was analyzed by environmental scanning electron microscopy. Mechanical properties were studied by tensile testing and Vickers microhardness testing apparatus.

Content: The wastewater of leather industry contains pollution loads which includes anionic contaminants such as chloride, sulfate and phosphate. Different treatment technologies for tannery wastewater have been investigated. Adsorption is a promising technique due to its greater selectivity, simple operation, faster regeneration kinetics and high uptake capacity even at trace levels. In the present study, Mg-Al and Zn-Al Layered Double Hydroxides were synthesized by the co-precipitation method at variable pH through a semi-batch system. The prepared material was characterized by XRD, BET surface area determination, TGDTA and FTIR. The chloride, sulfate and phosphate adsorption properties onto Mg-Al and Zn-Al Layered Double Hydroxides from aqueous solutions were evaluated. The adsorption experiments of chloride, sulfate and phosphate were investigated through batch studies at initial concentrations of 100 mg/L of these anions as NaCl, K2SO4 and KH2PO4, respectively. The experiments were carried out separately for each anionic specie by mixing 10 ml of solution with 1 g/L of adsorbent for 5 h. Mixing was performed on a thermostatic shaker at 200 rpm and at room temperature (25 °C). The effect of co-existing anions on the adsorption capacity were also analyzed. After ion adsorption, chloride, sulfate and phosphate concentrations were measured by ion chromatography. The results showed a removal ratio for Mg-Al Layered Double Hydroxide of 24% and 51% for sulfate and phosphate, respectively, while chloride was not removed from the solution. For the adsorbent Zn-Al Layered Double Hydroxide, the removal ratio of sulfate, phosphate and chloride reached 12.76 %, 69.07 % and 6.34%, respectively. Take-Away: Both adsorbents exhibited a satisfactory removal ratio of phosphate. Therefore, Mg–Al and Zn–Al LDHs can be used as effective adsorbents for phosphate removal from industrial wastewaters.

Layered double hydroxides (LDHs) are clay-like minerals commonly referred to as anionic clays" with a wide range of physical and chemical properties. LDHs often find application in pharmaceuticals, as polymer additives, as additives in cosmetics, as nanomaterial's and in catalysis. This is due to having variable layer charge density, reactive interlayer space, ion exchange capabilities, a wide range of chemical compositions and rheological properties (Forano et al., 2006). Various techniques exist for the synthesis of layered double hydroxides. These include co-precipitation, the urea method, induced hydrolysis, sol-gel and hydrothermal methods. Many of these produce environmentally unfriendly effluents or by-products, are energy intensive, make use of metallic salts or require inert synthesis environments (Rives, 2001). Limitations associated with these existing processes make LDH synthesis at an industrial level expensive or difficult to achieve. The need for 'green', affordable and repeatable synthesis methods are therefore often sought after. Recently the use of mechanochemistry as an alternative synthesis technique has gained wide-spread attention. Mechanochemistry involves the breaking and forming of chemical bonds due to an induced mechanical force. Various mechanochemical techniques for the synthesis of LDH materials exist or have been explored. These include methods such as single-step, two-step and mechano-hydrothermal grinding techniques. Grinding methods can be conducted dry, wet or collectively (Qu, Zhang, et al., 2015a). Mechanochemistry has further been used in conjunction with micro-wave energy and ultrasonic irradiation. The use of mechanochemistry as a synthesis method has proven to be promising with successful and unique LDHs produced. Intercalation of unique or complex anions within the interlayer has further been proven possible. The versatility and robust nature of this synthesis method makes it ideal for industrial application. Although many studies exist it was noted that limited research has been conducted on single-step wet grinding for LDH synthesis and warrants further investigation (Qu, Zhang, et al., 2015a) (Iwasaki,Yoshii, et al., 2012). This was due to factors such as incomplete conversion, difficulties associated with grinding and morphological imperfections. Single step wet milling could be benifi cial as a synthesis procedure as it eliminates hazards associated with dry powder, contains less process steps and is therefore possibly more cost effective and can be conducted batch, semi-batch or continuously due to fluid flow. Throughout the literature research conducted it was further noted that not many different milling devices have been explored. Ball mills, mixer mills and manual grinding were the most common methods used to supply mechanical energy to a system. The study therefore aims to expand on single-step wet synthesis of LDH materials by making use of a different milling device, namely a Netzsch LME 1 horizontal bead mill. The selected mill is designed for wet grinding application and can easily be up-scaled to a commercial batch, semi-batch or continuous process. Raw materials selected were a combination of oxides, hydroxides and basic carbonates. This would eliminate hazardous salt by-products and effluent, promoting 'green' synthesis of LDH materials. It was noted that the synthesis of LDH with the use of these materials have previously proven to be challenging (Qu, Zhang, et al., 2015a). The study was divided up into two sections namely a 'parameter study' and a 'versatility study'. The 'parameter study' involved exploring the in influence of milling and experimental parameters, such as rotational speed, retention time, solids loading, bead size and jacket water temperature, on the synthesis of Mg-Al LDH. The raw materials selected were MgO and Al(OH)3 combined at a divalent to trivalent cationic ratio of 2:1. The parameters were individually investigated, with the exception of jacket water temperature as it was varied with a change in retention time and a change in rotational speed. Unless stated otherwise or under investigation, parameters were investigated at a set speed of 2000 rpm, jacket water temperature of 30 °C, solids loading of 10 %, retention time of 1 h and with 2 mm yttrium stabilised zirconia beads. Therefore when investigating a specific c parameter, the others remained as stated above. Comparatively the 'versatility' study further explores the synthesis of Mg-Al, Ca-Al, Cu-Al and Zn-Al LDH by adapting optimal synthesis conditions, derived from existing mechanochemical techniques and methods, to the selected process. These were related to the divalent to trivalent cationic ratio and selected starting materials. Ageing of the samples obtained through the 'versatility study' were further explored to determine if the potential for a two-step commercial process exists. The study was investigated at a set speed of 2000 rpm, jacket water temperature of 30 °C, solids loading of 10 %, retention time of 1 h and with 2 mm yttrium stabilised zirconia beads. Half of the sample collected was subjected to ageing at 80 °C for 24 h under atmospheric conditions. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2020. / This research was funded by Techsparks (Pty) Ltd and the Technology and Human Resources for Industry Programme (THRIP) administered by the Department of Trade and Industry, South Africa, (grant number THRIP/133/31/03/2016) / Chemical Engineering / MEng (Chemical Engineering) / Unrestricted

Ein fundiertes Verständnis der Mechanismen der Gummi-Vulkanisation von Dien-Kautschuken ist noch immer eine der größten Herausforderungen in der Chemie und Technologie der Elastomere. Die Schwefelvulkanisation von Elastomerwerkstoffen ist ein seit langem verwendeter, aber dennoch sehr anspruchsvoller Prozess, mit dessen Hilfe moderne Reifen hergestellt werden. Bei dieser chemischen Reaktion spielt Zinkoxid, zusammen mit den anderen Hilfsstoffen der Schwefelvulkanisation eine entscheidende Rolle. Um die Produkteigenschaften von mit Schwefel vulkanisierten Elastomermaterialien zu verbessern, sollten die Mechanismen der chemischen Vernetzung - und insbesondere auch die Rolle von Zink enthaltenden Verbindungen bei der Vulkanisationsreaktion besser verstanden werden. Zum Beispiel könnte das Eigenschaftsprofil von Reifen durch die Ausbildung von geeigneten Netzwerken aus Schwefel oder anderen Netzknoten optimiert werden. Nitrilkautschke aus der Klasse der Spezialelastomere und die meisten nicht-Tire- Kautschuk in der ganzen Welt eingesetzt, wecken ein großes Interesse der Forschung wegen ihrer einzigartigen Vulkanisationschemie bei der Vernetzung mittels Zinkverbindungen und wegen der besonderen Eigenschaften der dadurch erzeugten Elastomerwerkstoffe. In dieser Arbeit wurde besonderes Augenmerk darauf gelegt, die Rolle von verschiedenen Zinkverbindungen in der Schwefelvulkanisation von carboxylierten Nitrilkautschuken zu verstehen. In der vorliegenden umfangreichen und eingehenden Untersuchung konnte die Ausbildung einer weiteren Polymerphase im Elastomer nachgewiesen werden. Durch dieses Ergebnis kann nun das dynamische mechanische Verhalten von solchen Polymerwerkstoffen besser verstanden werden. Teile dieser Arbeit beschäftigen sich mit der Erforschung der Rolle von Zinkchlorid bei der Vernetzung von Nitrilkautschuken. Hierzu wurde festgestellt, dass Zinkchlorid einen besonderen Einfluss auf die chemische Vernetzung des NBR aufweist, auch in Abwesenheit anderer Vernetzungs- oder Vulkanisationsadditive. Die so vernetzten Elastomere weisen ein stark hydrophiles Verhalten auf, im Gegensatz zu den allgemeinen Eigenschaften solcher Elastomerwerkstoffe. Eine detaillierte Analyse dieser neuartigen Netzwerkstruktur, gebildet durch eine Koordinationsbindung zwischen dem Zinkatom des Zinkchlorids und dem Nitrilkautschuk, wurde durchgeführt. Carboxylierter Nitrilkautschuk (XNBR) wurde ebenfalls eingesetzt, um funktionale Kautschukmischungen mit neuartigen flammhemmenden Eigenschaften zu entwickeln. Zu dieser Thematik wurden Zink enthaltende Doppelhydroxide (Layered Doube Hydroxides, LDH) als multifunktionale Füllstoffe in XNBR-Kautschuk eingesetzt. Neben dem Flammschutzverhalten zeigt LDH einzigartige Eigenschaften als verstärkenden Füllstoff und gleichzeitig als aktivierendes Additiv für die Schwefelvulkanisation. Eine weitere Zink enthaltenden Verbindung, Zinkstearat, wurde eingesetzt um mechanoadaptive elastomere Materialien durch gezieltes Einstellen des kristallinen bzw. amorphen Charakters dieser Verbindung zu entwickeln. Dies könnte einen wichtigen Beitrag zur Entwicklung zukünftiger Reifenmaterialien mit intrinsisch adaptiven Eigenschaften liefern.

1 Abstract The aim of the study was to evaluate the numbers, severity and causes of accidents, occurring in the households due to the cleaning products. Among the groups of potentially dangerous cleaning products, the highest proportion of accidents was caused by cleaning products containing sodium hypochloride (37 %), descalers containing acids (29 %) and dishwasher tablets (25 %). A lower percentage of inquiries appeared due to hydroxides containing drain cleaning products (7 %). In the year 2009, there were 251 inquiries to the Toxicological Information Centre due to cleaning products in defined categories studied. Among them, there were 133 children and 118 adult patients, who ingested cleaning product accidentally (86%) or for suicidal purposes (3%); inhaled (9%) or had an eye contact with the product (2%). There were 23% children and 27% adults hospitalized; the children most frequently due to accidental ingestion of hydroxides (92%), the adults due to the inhalation of irritant vapors (64%). Among them 14% children (86% due to the ingestion of cleaning products containing hydroxides) have been examined using the endoscopy (in the total anesthesia), in addition to 5% adults. The study has shown that the most common cause of the accidents in children is the distraction of the adults; nevertheless, the...

A green synthesis method for the synthesis of hydrotalcite has been previously developed but this process has not yet been optimised. The main focus of this dissertation was on aluminium-based LDHs. The purpose of this investigation were; to determine optimum synthesis conditions for the formation of hydrotalcite using the dissolution-precipitation method and to determine the possibility of partial substituting the divalent metal species in hydrotalcite and hydrocalumite with other metal species. During the optimisation process for the formation of hydrotalcite using the dissolution precipitation method, the formation of hydromagnesite was proved to be dominant reaction at lower reaction temperatures. With the increase in reaction time and temperature the decomposition of hydromagnesite occurred to form magnesite. At low temperatures the formation of Mg-Al-CO3 LDH is limited due to the low solubility of gibbsite. Mg-Al-CO3 LDH formation of 80 % was achieved at 140 oC after 2 hours reaction time, but crystallinity was low. To achieve an Mg-Al-CO3 LDH conversion higher than 96 % a reaction temperature of 160 oC for a minimum of 4 hours is required, but is achieved within 1 hour at 180 oC. A 99.37 % conversion was achieved at 180 oC for 5 hours with a high crystallinity and homogeneity. The surface area for Mg-Al-CO3 LDH at 180 oC after 5 hours reaction time proved to be 9.19 m2/g. The average particle size obtained for a high crystalline LDH was in the range of approx. 3 μm and 6.8 μm at temperatures of 160 oC and above for a minimum of 3 hours reaction time. The following are recommended for future work:  Determine the effect of mixing speed on the shape of the platelets.  Determine the difference between freshly precipitated metal oxides/hydroxides as reagents compared to aged metal oxides/hydroxides. The presence of Mg(OH)2 and Ca(OH)2 in solution (respectively) did increase the pH enough for the dissolution of gibbsite and most of the Mx+ metal species. A reaction time and temperature of 5 hours at 180 oC in a carbonate environment proved to be close to the ideal conditions for the formation of Mg/Mo-Al-CO3 LDH and Mg/Zn-Al-CO3 LDH. The results for the formation of Mg/Ti-Al-CO3 LDH were inconclusive. Isolation of the possible Mg/Ti-Al-CO3 LDH is recommended to determine the degree of substitution. The conditions for the dissolution of the metal species for the following experiments were proven to be successful:  Ca/Mn(lV)-Al  Ca/Mo-Al  Ca/Ni-Al  Ca/Ti-Al The following recommendations are made for the improvement on the formation of an Mx+-impregnated LDH/precursor:  Determine the effect of different reaction time and temperature.  Determine the effect of adding the carbonate source at temperatures above 100 oC under pressure.  Determine the effect of synthesising at different pH conditions. Cobalt and tin showed no/negligible amount of possible solubility. / Dissertation (MSc)--University of Pretoria, 2014. / Chemical Engineering / MSc / Unrestricted

The fate of ring-14C labeled triphenyltin hydroxide was studied in a model ecosystem consisting of soiI, water, and channel catfish (Ictalurus punctatus). Two initial levels of triphenyltin hydroxide concentration in soiI, 1.0 and 0.010 ppm, were compared. The soiI showed a gradual loss of 20 to 30% of the total 14C residues. Only about 33% of the remaining soil residues could be extracted and almost all of these were triphenyltin hydroxide. Total residues in the water were very low. Catfish muscle and viscera accumulated 14C residues continually throughout the treatment portion of the experiment. When the catfish were transferred to untreated aquaria the total residues in the catfish remained at a steady plateau. In the catfish muscle, extractable residues accounted for less than 10% of the total residues and essentially all were triphenyltin hydroxide. Approximately 80% of the total residues in the entire model ecosystem remained bound, mainly in the soiI and catfish. Of the extractable residues from the soiI, water, and catfish muscle the greatest percentage was found to be triphenyltin hydroxide.

No description available.