<p>A strategic research area today is development of polymericproducts made from renewable sources. The ways of utilizingrenewable sources studied in this thesis are using 1)prepolymers obtained by steam treatment of wood and 2) monomersobtainable by fermentation of agricultural products.</p><p>Novel hemicellulose-based hydrogels were prepared by usingprepolymers obtained from steam treatment of spruce.Hemicellulose was first modified with well-defined amounts ofmethacrylic functions. Hydrogels were then prepared by radicalpolymerization with 2-hydroxyethyl methacrylate orpoly(ethylene glycol) dimethacrylate to form hydrogels. Theradical polymerization reaction was carried out in water usinga redox initiator system. The hydrogels were in generalelastic, soft and easily swollen in water. Frequency sweeptests indicated that the hydrogel system displayed prevailingsolid-like behavior. Comparison of the hemicellulose-basedhydrogels with pure poly(2-hydroxyethyl methacrylate)-basedhydrogels showed that it was possible to preparehemicellulose-based hydrogels with properties similar to thoseof pure poly(2-hydroxyethyl methacrylate)-based hydrogels.</p><p>Polyester-based materials were prepared by using themonomers 1,3- propanediol and succinic acid obtainable byfermentation. α,ω-Dihydroxyterminatedoligomeric polyesters produced by the thermal polycondensationof 1,3-propanediol and succinic acid were chain-extended toobtain sufficiently high molecular weight. Depending on thechain-extension technology adopted, poly(ester carbonate)s orpoly(ester urethane)s were obtained. In the case of poly(estercarbonate)s, the chain-extended products ofα,ω-dihydroxyterminated oligomeric copolyesters werealso produced using 1,3-propanediol/1,4-cyclohexanedimethanol/succinic acid mixtures toimprove thermal and mechanical properties. Segmented poly(esterether carbonate)s fromα,ω-dihydroxyterminated oligo(propylenesuccinate)s and poly(ethylene glycol) were also synthesized toincrease the hydrophilicity.</p><p>Molecular weights and polydispersity were analyzed by SECfor all materials. Their structures were also identified by NMRspectroscopy (1H NMR and 13C NMR). All characterizations werein agreement with the proposed structures. Thermal parameterswere characterized by DSC. Tensile testing anddynamic-mechanical tests were performed and in additionpreliminary processing trials were carried out in some cases.The results demonstrate the feasibility of using monomersderived from renewable sources to build up new polymericstructures endowed with a variety of physical and mechanicalproperties.</p>

Polymer composites containing nanosized fillers have generated explosive interest since the early 1980's. Many recent studies have been conducted incorporating nano-fillers into polymer matrices to design and synthesize materials with tunable mechanical, thermal, and optical properties. Conventional filled polymers, where the reinforcement is on the order of microns, have been replaced by composites with discrete nanosized fillers. Gradually, theories that predicted that composite properties are independent of particle size in the micron range were challenged by nanocomposites. Rather, nanocomposite properties are greatly influenced by the surface area of the. All of this is complicated by the fact that nanoparticles are inclined to aggregate or migrate to interfaces. Much effort has been devoted to optimize dispersion of nanofillers in the polymer matrices, as polymer-nanoparticle interactions and adhesion greatly influence performance of the material. A well- dispersed composite system with various noncovalent interactions such as those that arise from hydrogen bonding, electrostatic attractions and π-π interactions between the filler and the matrix, can transfer stress and the interface will stop the development of cracks and impede stress concentrations. Overall, large reinforcement increases are noted at low nanoparticle loadings. Additionally, functional properties such as thermal, electrical conductivity and porosity can be tailored for specific applications. The design of high performance composites requires optimizing dispersion, nanoparticle-polymer noncovalent interactions and the chemistry of the materials. Therefore polymer composites with different types of nanofillers were investigated to prove various noncovalent interaction and to improve the mechanical, thermal and electrical properties in this study. Poly (methyl methacrylate) (PMMA) with BaTiO3 and Bi2O3 composites were fabricated by two different methods; sonication of fillers in PMMA and in situ polymerization. Samples were irradiated in air via a JL Shepherd Mark I cesium-137 source. The dose rate was 985 rads/min and the total dose was 2.0 Mrad. The polymer sonication (PSON) method has a greater effect than in situ polymerization on sample uniformity. With the PSON method there was a slight improvement in rad hardness in the barium titanate composites. This is the case with and without MWNTs and coupling agents. The storage modulus and loss modulus were measured via Dynamic Mechanical Analyzer (DMA) under the tension film mode using a heating rate of 5 °C min-1 from -150 °C to 200 °C and a scanning frequency range of 1-100 Hz. Scanning electron microscopy (SEM) provided images of the polymer-nanocomposites. An aliphatic isocyanate, polyether, polyol thermoplastic polyurethane, Tecoflex® SG-85A, was solution processed with the varying amounts of silica nanowire. A new grade polyurethane, Tecoflex®, was synthesized from the aliphatic 4,4-methylene dicyclohexyl diisocyanate (H12MDI) with polytetramethylene ether glycol. Despite Tecoflex®'s longevity and wide use, this polymer's dielectric behavior has not been widely studied. Therefore, the dielectric response of neat PU, Tecoflex®, and PU composites with silica nanowire from -150 to 150 °C is presented. The mechanism of nanowire growing with diameters ranging from 50 to 500 nm has been established to follow the vapour liquid solid (VLS) model via the PtSi phase acting as the catalyst. Our previous thermal stability study of PU nanowire composites have yielded increased heat stability to 330 °C. In comparison, neat PU only maintains thermal stability in temperatures that range to 250 °C. The onset of decomposition temperature was measured by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) provided images of the polymer-nanocomposites. A series of PMMA-dodecyloxy NB and PHEMA-dodecyloxy NB composites were synthesized in situ and characterized. The dodecyl groups significantly alter the solubility of the nanoballs, imparting hydrophobicity to the surface of the nanoball. A comparison study was made between the PMMA-NB and PHEMA-NB nanocomposites. Structure property relations are discussed in terms of interactions between the polymer matrices and nanoball surfaces and interiors. These OC12 NB and the hydroxyl NB polymer composites are the first studies to date that probe relaxations and conductivity in discrete polyhedral metal-organic polymer composites. A novel ultra-flexible polycarbonate-polyurethane (PCPU) was synthesized with methylene bis(4-cyclohexylisocyanate), 1,4 butanediol as a chain extender and a polycarbonate polyol containing 1,6-hexanediol and 3-methyl-1,5-pentanediol. Through the techniques of water coagulation, the synthesis of self-healing PCPU with various concentrations of SWNT (Single-Walled Nanotubes) is possible. The resulting features of this synthesized rubber-like substance are to be evaluated to determine glass transition temperature. This novel type of polyurethane material targets growing markets for biocompatible polymers. Also, a secondary goal of this project is to obtain information useful to determining whether PCPU-carbon nanotube composites would be good candidates for use as a gel electrolyte in polymer batteries. All nanocomposites were characterized by differential scanning calorimetry (DSC) to determine glass transition temperatures. The dielectric permittivity (ε’) and loss factor (ε”) were also measured via Dielectric Analysis (DEA) in the frequency range 1Hz to 100 kHz and between the proper temperatures in all polymer composite. The electric modulus formalism was used to reveal structural relaxations including conductivity relaxation. The activation energies for the relaxations are presented.

<p>In the presented work, immunosensors for detection of Aflatoxin B1 based on different immobilization platforms were studied. Synthesis of an electroactive hydrogel was also carried out. Aflatoxins are a group of mycotoxins that have deleterious effects on humans and are produced during fungal infection of plants or plant products. Electrochemical immunosensor for the determination of Aflatoxin B1 (AFB1) was developed with anti-aflatoxin B1 antibody immobilized on Pt electrodes modified with polyaniline (PANi) and polystyrene sulphonic acid (PSSA). Impedimetric analysis shows that the electron transfer resistances of Pt/PANi-PSSA electrode, Pt/PANi-PSSA/AFB1-Ab immunosensor and Pt/PANi-PSSA/AFB1-Ab incubated in BSA were 0.458, 720 and 1066 k&Omega / , respectively. These results indicate that electrochemical impedance spectroscopy (EIS) is a suitable method for monitoring the change in electron-transfer resistance associated with the immobilization of the antibody. Modelling of EIS data gave equivalent circuits which showed that the electron transfer resistance increased from 0.458 k&Omega / for Pt/PANi-PSSA electrode to 1066 k&Omega / for Pt/PANi-PSSA/AFB1-Ab immunosensor, indicating that immobilization of the antibody and incubation in BSA introduced an electron transfer barrier. The AFB1 immunosensor had a detection limit of 0.1 mg/L and a sensitivity of 869.6 k &Omega / L/mg.</p>

Philosophiae Doctor - PhD / In the presented work, immunosensors for detection of Aflatoxin B1 based on different immobilization platforms were studied. Synthesis of an electroactive hydrogel was also carried out. Aflatoxins are a group of mycotoxins that have deleterious effects on humans and are produced during fungal infection of plants or plant products. Electrochemical immunosensor for the determination of Aflatoxin B1 (AFB1) was developed with anti-aflatoxin B1 antibody immobilized on Pt electrodes modified with polyaniline (PANi) and polystyrene sulphonic acid (PSSA). Impedimetric analysis shows that the electron transfer resistances of Pt/PANi-PSSA electrode, Pt/PANi-PSSA/AFB1-Ab immunosensor and Pt/PANi-PSSA/AFB1-Ab incubated in BSA were 0.458, 720 and 1066 kΩ, respectively. These results indicate that electrochemical impedance spectroscopy (EIS) is a suitable method for monitoring the change in electron-transfer resistance associated with the immobilization of the antibody. Modelling of EIS data gave equivalent circuits which showed that the electron transfer resistance increased from 0.458 kΩ for Pt/PANi-PSSA electrode to 1066 kΩ for Pt/PANi-PSSA/AFB1-Ab immunosensor, indicating that immobilization of the antibody and incubation in BSA introduced an electron transfer barrier. The AFB1 immunosensor had a detection limit of 0.1 mg/L and a sensitivity of 869.6 kΩL/mg. / South Africa

Philosophiae Doctor - PhD / In the presented work, immunosensors for detection of Aflatoxin B1 based on different immobilization platforms were studied. Synthesis of an electroactive hydrogel was also carried out. Aflatoxins are a group of mycotoxins that have deleterious effects on humans and are produced during fungal infection of plants or plant products. Electrochemical immunosensor for the determination of Aflatoxin B1 (AFB1) was developed with anti-aflatoxin B1 antibody immobilized on Pt electrodes modified with polyaniline (PANi) and polystyrene sulphonic acid (PSSA). Impedimetric analysis shows that the electron transfer resistances of Pt/PANi-PSSA electrode, Pt/PANi-PSSA/AFB1-Ab immunosensor and Pt/PANi- PSSA/AFB1-Ab incubated in BSA were 0.458, 720 and 1066 kΩ, respectively. These results indicate that electrochemical impedance spectroscopy (EIS) is a suitable method for monitoring the change in electron-transfer resistance associated with the immobilization of the antibody. Modelling of EIS data gave equivalent circuits which showed that the electron transfer resistance increased from 0.458 kΩ for Pt/PANi-PSSA electrode to 1066 kΩ for Pt/PANi- PSSA/AFB1-Ab immunosensor, indicating that immobilization of the antibody and incubation in BSA introduced an electron transfer barrier. The AFB1 immunosensor had a detection limit of 0.1 mg/L and a sensitivity of 869.6 k ΩL/mg. In the second platform an immunosensor based on gold nanoparticles (AuNP) and polythionine-modified glassy carbon electrode (GCE) for the determination of aflatoxin B1 (AFB1) was developed. Aflatoxin B1-BSA conjugate was immobilised on the modified GCE. Horseradish peroxidase (HRP) or Bovine serum albumin (BSA) were used to block sites against non-specific binding of the AFB1- conjugate with other compounds such as the salts used in preparing the buffer when the antibody interacts with the AFB1 conjugate and free AFB1. Competition reaction was allowed to take place between the free AFB1 and AFB1-conjugate for the binding sites of the anti-aflatoxin B1 antibody. Cyclic voltammetry (CV) was employed to characterize the electrochemical properties of the modified process. The peak separation of the immunosensor (ΔEp) was 62 mV indicating a quasi reversible process. Differential pulse voltammetry (DPV) was used to monitor the analytical signal. The response decreased with an increase in AFB1 concentration in the range of 0.6-2.4 ng/mL with a limit of detection of 0.07 and 0.16 ng/mL for HRP and BSA blocked immunosensors respectively. Significantly the low detection limit of 0.07 ng/mL is within the limits set by worl health organization (WHO) for AFB1 and its derivatives which is 2 ng/mL The proposed method eliminates the use of secondary antibody enzymatic labels. Synthesis and characterization of (p-(HEMA)-polyaniline hydrogels were investigated. The hydrogels were synthesized using: 2-Hydroxyeththyl methacrylate (HEMA), N-Tris (hydroxymethyl) methyl] acrylamide, 3- Sulfopropyl methacrylate potassium salt, Tetraethylene glycol diacrylate, Poly-(2- hydroxyethyl methacrylate), 2, 2-Dimethoxy-2-phenylacetophenone and aniline by UV irradiation. Two sets of the hydrogels were prepared using water / 1, 3, 3, 3-(tetramethyl butyl phenyl polyethylene glycol [Triton X-100] and water / ethylene glycol as the solvent. Scanning electron microscopy (SEM) revealed a more uniform pore size when Triton X 100 (TX-100 HG) was used as compared to ethylene glycol (EG-HG). Thermogravimetric analysis (TGA) showed that both hydrogels were stable up to 270 oC. Fourier transform-Infra red (FTIR) spectrum confirmed the incorporation of polyaniline (PANi) and HEMA in the composite. Electrochemical properties of the hydrogels evaluated using Cyclic Voltammetry and Electrochemical Impedance Spectroscopy (EIS) demonstrated the electroactivity and conductivity.

Hydrogel, semi-interpenetrating polymer network, poly(2-hydroxyethyl methacrylate), diffusion