Fe(II)-based degradative solidification/stabilization (Fe(II)-DS/S) technology is the modification of conventional solidification/stabilization (S/S). Inorganic pollutants are immobilized by Fe(II)-DS/S while organic pollutants are destroyed. Experimental studies were conducted to identify the active agents for Tetrachloroethylene (PCE) degradation as well as the conditions that enhance the formation of the active agents in the Fe(II)-DS/S system. PCE was chosen as a model chlorinated aliphatic hydrocarbon in this study. First, the conditions that lead to maximizing production of the active agents were identified by measuring the ability of various chemical mixtures to degrade PCE. Results showed that Fe(II), Fe(III), Ca, and Cl were the the important elements that affect degradation activity. Elemental compositions of the mixtures and the conditions affecting solid formation might be the important factors in determining how active solids are formed. Second, instrumental analyses (XRD, SEM, SEM-EDS) were used to identify minerals in chemical mixtures that have high activities. Results indicate that active agents for PCE degradation in Portland cement slurries and in cement extracts might be one of several AFm phases. However, systems without cement did not form the same solids as those with cement or cement extract. Ferrous hydroxide was identified as a major solid phase formed in systems without cement. Finally, the effect of using different types of ordinary Portland cement (OPC) on PCE degradation rate during Fe(II)-DS/S was examined and the solids were examined by instrumental analyses (XRD, SEM, SEM-EDS). Four different OPC (Txi, Lehigh, Quikrete, and Capitol) showed different PCE degradation behaviors. Pseudo first-order kinetics was observed for Capitol and Txi OPC and second-order kinetics was observed for Quikrete. In the case of Lehigh cement, pseudo first-order kinetics was observed in cement slurry and second-order kinetics in cement extract. Calcium aluminum hydroxide hydrates dominated solids made with Txi, Quikrete, and Lehigh cements and Friedel’s salt was the major phase found in solids made with Capitol cements. Fe tended to be associated with hexagonal thin plate particles, which were supposed to be a LDH.

Many biopharmaceuticals, already approved for sale or currently under development, are post-translationally modified proteins, such as recombinant monoclonal antibodies or recombinant hormones. These are generally expressed in continuous (stable) mammalian cell lines, which are capable of long-term, commercial-scale production of recombinant proteins of the highest complexity. Yet, the development of a stable cell line capable of expressing heterologous proteins is very costly and can take up to 9–15 months. Therefore, transient gene expression (TGE) in animal cells has become the method of choice for many researchers who wish to obtain small to moderate quantities (1-500 mg) of novel complex recombinant proteins for further functional and structural characterisation within weeks of cDNA discovery. TGE is more cost-effective than the time-consuming establishment of stable cell clones, but a key factor in ensuring that these transient systems have practical application is the availability of efficient and robust transfection agents/methods. While chemical transfection methods currently dominate transient systems, the underlying fundamentals such as the formation of DNA complexes or their mode of function are not fully understood and the characteristics of the complexes and their subsequent ability to transfect cells are variable. This often renders the development of a successful transfection protocol for a new cell line random and researchers frequently have to resort to a trial-and-error approach, testing different media and/or conditions during DNA complex formation, as well as having to fine-tune the cell culture regime pre-, during, and post-transfection. This thesis aimed to explore novel transfection agents and develop DNA complex structure/property—transfection efficiency relationships for these reagents. Two different chemical approaches to transient transfection were investigated: i) a recently suggested inorganic nanoparticle based transfection system which utilises the anion exchange capacity of nanoparticles of a particular family of anionic clays, layered double hydroxides (LDHs), and ii) a modified polyethyleneimine (PEI)-based system, which aimed to reduce the inherent cytotoxicity of high molecular weight (MW) PEI, which is a very effective transfection agent, by constructing high MW mimics from low MW building blocks that are linked to each other via biodegradable linkers such as azomethine groups. While the LDH nanoparticles failed to give satisfactory transfection results for plasmid DNA, they were able to functionally deliver smaller nucleic acids such as siRNA. A mechanism different to that currently accepted for the transfection of mammalian cells with plasmid DNA using LDH nanoparticles as carriers is proposed. The modified polymeric transfection agents were shown to result in significantly less cell death, while maintaining the ability to transfect mammalian cells with almost similar efficiency to that obtained with high MW polyethyleneimine. Generic DNA complex structure/property—transfection efficiency relationships were developed by systematically studying the influence of particle size and zeta potential on transfection results.

Controlled-release formulations for pesticide applications act as depot systems that continuously release the active ingredients into the environment over a speci ed period, usually from months to years. However, some applications require fast-dissolving drug delivery. The interest of this research is in fast-release of water-insoluble pesticides into aquatic environments. This study considered the use of dextrin starch and urea eutectics as fast release, solid dosage carrier forms that contain an active ingredient. The chosen active for this study is an acaricide called amitraz (N-methylbis-(2,4-xylyliminomethyl)- methylamine). The focus is on matrix-based dosage forms such as tablets, granules or bres that either disintegrate or dissolve to release a water-insoluble active. These types of dosage forms can be fabricated using processes such as lyophilisation, spray drying, solvent casting, hot melt extrusion, compression moulding, wet granulation, compaction and electrospinning. A simple melt-casting procedure has been discussed in the present work. Dextrin is a water-soluble form of partially hydrolysed starch and is a promising candidate matrix material for dissolving solid dosage forms. The molecular weight of the dextrin was analysed with MALDI-TOF methods and rheological relations. Glycerolplasticized thermoplastic dextrin-based nanocomposites were prepared with a twin-screw extrusion-compounding process. The nano llers included a layered double hydroxide (LDH), cellulose nano bres (CNF) and stearic acid. The time-dependent retrogradation of the compounds was monitored by X-ray di raction (XRD) and dynamic mechanical thermal analysis (DMA). XRD showed that the inclusion of stearic acid in the formulations led to the formation of an amylose-lipid complex and a stable crystallinity during ageing. Dissolution rates in water for samples containing dextrin starch, were characterised using an iodine indicator and UV-visible spectroscopy. High pressure di erential scanning calorimetry (HPDSC) indicated that the addition of stearic acid led to the formation of amylose-lipid complexes (ALC's). An additive system containing stearic acid and CNF was deemed suitable for compounding with amitraz. Compounding at temperatures above the melting point of the latter led, on dissolution in water, to the release of much ner particles of the acaricide, which was con rmed with particle size analysis (PSA). The addition of the acaricide caused an apparent increase in the dissolution rate of the thermoplastic dextrin. Two eutectic urea systems were considered for casting with amitraz. A eutectic system of urea and acetamide was found to display a melting point of 44 C at a 37 wt.% urea composition. The other system consisting of urea and 1,3-dimethylurea displayed a eutectic point at 32 wt.% urea composition which melted at 59 C. Di erential scanning calorimetry (DSC), however, con rmed a melting point depression due to a high moisture content caused by the compounds high hygroscopicity. The endotherm of the sample containing no excess moisture showed a melting point of 70 C. The 1,3-dimethylurea system was deemed suitable for casting with amitraz. XRD of the eutectic composition indicated a small amount of co-crystallisation. The samples were cast as disks of various diameters while keeping the height of the disks constant. The creation of the cast disks showed automatic generation of a nely dispersed form of the active through the process of melting the deep eutectic solvent, the dissolution of the active and its phase separation on cooling and solidi cation of the eutectic. This implies that ne grinding of the actives might not be necessary. Eutectic casts containing 20 wt.% amitraz dissolved at a slower rate than casts not containing the hydrophobic active ingredient. The advantageous features of these casts were exempli ed using the acaricide incorporated into the urea & 1,3-dimethylurea eutectic. This work provides two safe, biodegradable and water soluble materials for use as a matrix to contain active ingredients. One material, the eutectic organic salt casts, can be produced at low temperatures (<100 C) and can be directly cast into storage containers. The complete dissolution of the cast compounded with a hydrophilic active is rapid (4-6 min). The second material, a thermoplastic dextrin, was melt compounded in an extruder at temperatures not exceeding 120 C. This compound containing 20 wt.% of the active dissolved over a 12 hour period. Dextrin, known to be widely used as an adhesive, will aid in the adhesion of the active ingredient to the surface where it must be used. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2020. / PAMSA / Department of Science and Innovation under Grant DST/CON 0004/2019 / Chemical Engineering / MEng (Chemical Engineering) / Unrestricted

Fatty acid intercalated layered double hydroxides were used as additives for Jojoba oil and polymer matrices. The first phase of the study was to intercalate carboxylic acids (C14 to C22). These were successfully intercalated into layered double hydroxides (LDHs), with the formula [Mg0.7Al0.3 (OH) 2](CO3)0. 15•0.5H2O. The one-pot synthesis consistently yielded a bilayer intercalated product for the range of acids employed. The intercalated anions had an orientation tilt angle of 55–63°, depending on the length of the fatty acid chain. However, there is an indication that the anion exchange process employed in this study is accompanied by probable dissolution and recrystallisation of the LDH. This is supported by the different growth habits and sizes of platelets observed through scanning electron microscopy (SEM). Moreover, the organo-LDH platelets were found to have varying MII/MIII compositions, ranging from 1.65 to 6, indicating that the one-pot synthesis yields an array of mixed metal hydroxides. Polymer composites, containing 5% and 10 wt.% of stearate intercalated layered double hydroxides (LDH-stearate) and neat layered double hydroxides (LDH-CO3), were prepared via melt-compounding to explore the use of LDHs as an additive. The stearate modified starting material was bilayer-intercalated clay. During melt compounding, excess stearates were released and the clay reverted to a monolayer-intercalated form. Comprehensive characterisation and study of the fatty acid-intercalated LDH showed that these organoclay hybrids exhibit thermotropic behaviour. This behaviour ultimately leads to the exudation of excess fatty acid. The exuded stearates were found to have lubricating and plasticising effects on the poly(ethylene-co-vinyl acetate) (EVA) and linear low density polyethylene (LLDPE) matrices. Strong hydrogen bond interactions between the chains of poly(ethyleneco- vinyl alcohol) (EVAL) and the clay platelet surfaces overwhelmed the lubrication effect and caused an increase in the melt viscosity of this matrix. The notched Charpy impact strength of this composite was almost double that of the neat polymer. It appears that this can be attributed to the ability of the highly dispersed and randomly oriented nanosized clay platelets to promote extensive internal microcavitation during impact loading. The creation of a large internal surface area provided the requisite energy dissipation mechanism. The study also considered fatty acid-intercalated LDH as an argillaceous mineral for potential use as a rheological additive in Jojoba oil. A minimum of 20 wt.% LDH in Jojoba oil formulation was found to be stable, i.e. it did not form separate layers on standing. The viscosity of the neat Jojoba oil demonstrated Newtonian behaviour, whereas the modified LDH/Jojoba oil formulation shear thinned, which is a typical non-Newtonian behaviour. Viscosity as a function of temperature showed complex rheological behaviour for the long chain fatty acids C16 to C22. The viscosity increase is assumed to be due to a combination of three events, which include the formation and changes of LDH microstructures within the oil, the loss of excess fatty acids into the oil matrix, and the formation of fatty acid crystal networks. Shear action also induced some delamination of the clay platelets. / Thesis (PhD(Eng))--University of Pretoria, 2012. / Chemical Engineering / unrestricted

Surfactant-mediated intercalation of aliphatic fatty acids into a commercial,layered double hydroxide (LDH) with the approximate composition of [Mg0.689Al0.311(OH2)] (CO3)0.1569nH2O was explored. The reactions were conducted at elevated temperatures with the LDH powder suspended in a fatty acid oil-water emulsion. The acidic fatty acid, e.g. stearic acid, reacts with the basic carbonate anions from LDH-CO3. In the process, CO2 is released as a gas and the fatty acids are intercalated as a bilayer. A high concentration of anionic or non-ionic surfactants, i.e. sodium dodecylsulphate or Tween 60, facilitates the intercalation process by emulsifying the molten fatty acids and dispersing the LDH particles. The presence of carboxylate anions in the interlayer region was confirmed by the carboxylate absorption peaks observed in the region 1700–1000 cm-1 on Fouriertransform infrared spectroscopy (FT-IR). Several bands were observed, i.e. ionised and non-ionised. An increase in the d-spacing of the d003 plane of the brucite-like LDH layers was observed on X-ray diffraction (XRD) analysis of all the LDH intercalates. The d-spacing increased linearly with the length of the carboxylic acid chain. Sharp reflection peaks were obtained on XRD, showing the high crystallinity of the LDH intercalates. The thermal decomposition of these materials was explored on thermogravimetric or differential thermogravimetric analysis (TGA/DTA) and temperature-scanned XRD. The mole ratio of Mg to Al was obtained by XRF and the morphology by scanning electron microscopy (SEM). The present method works well with long-chain aliphatic fatty acids at temperatures above or at the melting point of the desired acid. Temperature proved to be the most important parameter to control during the preparation process, i.e. at low temperatures incomplete reactions were obtained. The method is convenient, economical and environmentally friendly. It employs the readily available carbonate form of LDH as a starting reagent, water is used as medium rather than organic solvents, there are no high-temperature calcinations, and an inert atmosphere is not required. Copyright / Dissertation (MSc)--University of Pretoria, 2008. / Chemistry / unrestricted

Eutrophication, caused by phosphate, can be detrimental both for the aquatic environment and human health. This research aims to provide deep knowledge about the adsorption properties of low-cost Fe/Mg layered double hydroxide modified biochar (LDHBC) for removal of phosphate from aqueous solution. Firstly, Fe/Mg layered double hydroxide (LDH) was synthesized by mixing FeCl3 and MgCl2. 6H2O salts in water, followed by NaOH treatment (coprecipitation method). For LDHBC, FeCl3, and MgCl2. 6H2O salts were dissolved in water, and Douglas fir biochar was added to the salts mixture to make a slurry, followed by NaOH treatment. The surface chemistry and elemental composition of both adsorbents and phosphate-laden adsorbents were characterized using Elemental analysis, BET, PZC, TGA, DSC, XRD, SEM, and TEM. Adsorption ability of LDH and LDHBC was studied by pH effects, kinetics, and the highest capacity for the analyte.

The presented research report deals with the investigation of magnesium aluminum based layered double hydroxide (LDH) as a potential nanofiller and flame-retardant for polymers with special reference to polyethylene. LDH is a mixed hydroxide of di- and trivalent metal ions that crystallizes in the form of mineral brucite. The basic reason for selecting LDH or more specifically magnesium-aluminum based LDH (Mg-Al LDH) is their typical metal hydroxide-like chemistry and conventional clay-like layered crystalline structure. The former is helpful in the direct participation in flame inhibition through endothermic decomposition and stable char formation. On the other hand, the later makes LDH suitable for polymer nanocomposite preparation, which can address the poor dispersibility problem associated with conventional metal hydroxide type fillers in polyolefin matrix. Besides, unlike layered silicate type clays (often reported for their capability to improve flame retardancy of polymers), LDH being reactive during combustion has higher efficiency to reduce the heat released during combustion of the composites. LDH clay with fixed Al:Mg ratio was synthesized using urea hydrolysis method and characterized. The organic modification of Mg-Al LDH using anionic surfactants has been studied in details. The main purpose of such modification is to enlarge the interlayer distance and to render it more organophilic. The surfactants were selected based on their functionality, chain length, etc and the modification was carried out by regeneration method. In the modified LDHs, the surfactants anions are arranged as a monolayer in the interlayer region and expand the interlayer distance according to their tail size. PE/LDH nanocomposites were prepared by melt-compounding method using a co-rotating tightly intermeshed twin-screw extruder and the morphological, mechanical and flammability properties of the nanocomposites were investigated in details. The X-ray diffraction analysis and electron microscopic analysis show a complex LDH particle morphology with hierarchy of particle size and shape starting from exfoliated particles fragments to particle aggregates over few hundred nm size. The exfoliated LDH platelets are distributed both in the vicinity of large particles and also in the bulk matrix. The melt rheological characterization of the nanocomposites also reflects the similar complex particle morphology. The dynamic oscillatory shear experiments showed that with increasing LDH concentration, the rheological behavior of the nanocomposite melts deviates strongly from that of the unfilled polyethylene. Thermogravimetric analysis (TGA) shows that LDH significantly improves the thermal stability of the polymer matrix in comparison to the unfilled polymer. The flammability studies of the PE/LDH nanocomposites have been reported in terms of various standard methods, like limited oxygen index (LOI), cone-calorimetry and UL-94 vertical and horizontal burn tests. The cone-calorimetric investigation shows that the nanocomposites have significantly lower burning rate and heat released during combustion. With increasing concentration of LDH though the LOI value of the nanocomposite increases marginally, the burning behavior, like dripping, rate of burning, etc are significantly improved. The flammability performance of LDH in combination with other commonly used flame-retardant (magnesium hydroxide) was also investigated. It has been observed that in polyethylene, a 50 wt% combination filler (4:1 weight ratio of magnesium hydroxide and LDH) can provide similar flammability ratings (like V0 rating in UL94 test, no dripping, etc) as that observed with 60 wt% magnesium hydroxide alone.

The presented research report deals with the investigation of magnesium aluminum based layered double hydroxide (LDH) as a potential nanofiller and flame-retardant for polymers with special reference to polyethylene. LDH is a mixed hydroxide of di- and trivalent metal ions that crystallizes in the form of mineral brucite. The basic reason for selecting LDH or more specifically magnesium-aluminum based LDH (Mg-Al LDH) is their typical metal hydroxide-like chemistry and conventional clay-like layered crystalline structure. The former is helpful in the direct participation in flame inhibition through endothermic decomposition and stable char formation. On the other hand, the later makes LDH suitable for polymer nanocomposite preparation, which can address the poor dispersibility problem associated with conventional metal hydroxide type fillers in polyolefin matrix. Besides, unlike layered silicate type clays (often reported for their capability to improve flame retardancy of polymers), LDH being reactive during combustion has higher efficiency to reduce the heat released during combustion of the composites. LDH clay with fixed Al:Mg ratio was synthesized using urea hydrolysis method and characterized. The organic modification of Mg-Al LDH using anionic surfactants has been studied in details. The main purpose of such modification is to enlarge the interlayer distance and to render it more organophilic. The surfactants were selected based on their functionality, chain length, etc and the modification was carried out by regeneration method. In the modified LDHs, the surfactants anions are arranged as a monolayer in the interlayer region and expand the interlayer distance according to their tail size. PE/LDH nanocomposites were prepared by melt-compounding method using a co-rotating tightly intermeshed twin-screw extruder and the morphological, mechanical and flammability properties of the nanocomposites were investigated in details. The X-ray diffraction analysis and electron microscopic analysis show a complex LDH particle morphology with hierarchy of particle size and shape starting from exfoliated particles fragments to particle aggregates over few hundred nm size. The exfoliated LDH platelets are distributed both in the vicinity of large particles and also in the bulk matrix. The melt rheological characterization of the nanocomposites also reflects the similar complex particle morphology. The dynamic oscillatory shear experiments showed that with increasing LDH concentration, the rheological behavior of the nanocomposite melts deviates strongly from that of the unfilled polyethylene. Thermogravimetric analysis (TGA) shows that LDH significantly improves the thermal stability of the polymer matrix in comparison to the unfilled polymer. The flammability studies of the PE/LDH nanocomposites have been reported in terms of various standard methods, like limited oxygen index (LOI), cone-calorimetry and UL-94 vertical and horizontal burn tests. The cone-calorimetric investigation shows that the nanocomposites have significantly lower burning rate and heat released during combustion. With increasing concentration of LDH though the LOI value of the nanocomposite increases marginally, the burning behavior, like dripping, rate of burning, etc are significantly improved. The flammability performance of LDH in combination with other commonly used flame-retardant (magnesium hydroxide) was also investigated. It has been observed that in polyethylene, a 50 wt% combination filler (4:1 weight ratio of magnesium hydroxide and LDH) can provide similar flammability ratings (like V0 rating in UL94 test, no dripping, etc) as that observed with 60 wt% magnesium hydroxide alone.

A brief introduction to the current state of research in the Origins of Life field is given in Part I of this work. Part II covers original research performed by the author and co-workers. Layered Double Hydroxide (LDH) systems are anion-exchanging clays that have the general formula M(II)xM(III)(OH)(2x+2)Y, where M(II) and M(III) are any divalent and trivalent metals, respectively. Y can be nearly any anion, although modern naturally occuring LDH systems incorporate carbonate (CO32-), chloride (Cl-), or sulfate (SO42-) anions. Intercalated cobalticyanide anion shows a small yet observable deviation from local Oh symmetry causing small differences between its oriented and non-oriented infrared spectra. Nitroprusside is shown to intercalate into 2:1 Mg:Al LDH with decomposition to form intercalated ferrocyanide and nitrosyl groups of an unidentified nature. The [Ru(CN)6]4- anion is shown to intercalate into layered double hydroxides in the same manner as other hexacyano anions, such as ferrocyanide and cobalticyanide, with its three-fold rotational axis perpendicular to the hydroxide sheets. The square-planar tetracyano-nickelate(II), -palladate(II), and platinate(II) anions were intercalated into both 2:1 and 3:1 Mg:Al layered double hydroxides (LDH). The basal spacings in the 2:1 hosts are approximately 11 Å, indicating that the anions are inclined approximately 75 degrees relative to the hydroxide layers, while in the 3:1 hosts the square-planar anions have enough space to lie more nearly parallel to the LDH cation layers, giving basal spacings of approximately 8 Å. It has been found that the LDH Mg2Al(OH)6Cl catalyzes the self-addition of cyanide, to give in a one-pot reaction at low concentrations an increased yield of diaminomaleonitrile and in addition, at higher ($0.1M) concentrations, a purple-pink material that adheres to the LDH. We are investigating whether this reaction also occurs with hydrotalcite itself, what is the minimum effective concentration of cyanide, and what can be learned about the products and how they compare with those reported at high HCN concentrations in the absence of catalyst.

The primary aim of this thesis is to explore the immunostimulatory properties of a family of layered, crystalline, inorganic materials known as layered double hydroxides (LDHs). <strong>Chapter One</strong> provides an introduction to relevant aspects of the immune system, and the context for investigating the immunostimulatory properties of inorganic materials in terms of vaccine/adjuvant formulations. The possible mechanisms of action of commercial adjuvant materials are also reviewed, and the structure, synthesis methods and applications of LDHs are discussed. <strong>Chapter Two</strong> details the controlled synthesis and characterisation of LDHs in specific particle sizes. A series of MgAl-CO3 LDHs with precisely controlled particle sizes ranging from 20 to 10000 nm were successfully synthesised, then the techniques used were extended to other compositions to create a panel of LDHs for use in subsequent Chapters. In <strong>Chapter Three</strong>, the responses of monocyte-derived dendritic cells (Mo-DC) to the LDH particle sizes discussed in Chapter Two are assessed in terms of viability, surface molecule expression, and cytokine secretion. A statistical modelling approach using the physicochemical properties of the LDHs as explanatory variables for immune responses was employed to evaluate the validity of the model formulated in the previous work, and to establish if particle size could be used to improve its predictive ability. It was found that strong relationships between LDH particle size and certain Mo-DC responses exist, and that these responses could be predicted with a high degree of accuracy. <strong>Chapter Four</strong> is concerned with the investigation of T cell responses to LDH-stimulated allogeneic Mo-DC. Various methods were used for assessing T cell division and proliferation, and a protocol for intracellular cytokine staining was developed to probe T cell polarisation. Five LDHs, which have elicited potentially interesting T cell responses in previous work, were selected for investigation. However, using the assays described, no discernible improvement in proliferation or polarisation was observed with any of the LDHs tested. <strong>Chapter Five</strong> presents an initial exploration of the interactions between LDH particles and cells. Experiments have shown that LDH particles both adhere to and are internalised by Mo-DC. Variations in the extent of internalisation with both particle size and composition were highlighted by confocal microscopy studies. Through investigations into interactions between LDH particles and the plasma membrane using protease enzymes, it was revealed that adhesion of LDH particles is partly protein-dependent. Further studies have also demonstrated a pH-dependent element to particle association with Mo-DC. Details of the experimental procedures employed are included in <strong>Chapter Six</strong>. Supplementary information referred to in the main thesis may be found in the <strong>Appendices</strong>.