3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Synthesis, development and characterisation of dehydrated castor oil poly (glyceryl phthalate) alkyd resins(1994) Nzeru, Arnold.The dissertation studies the synthesis, formulation development, crosslinking and spectral characterisation of dehydrated castor oil poly(glyceryl phthalate) alkyd resins for use as air-dry surface coating vehicles. Synthesis of alkyd resins involves simultaneous dehydration, alcoholysis and polyesterification reactions. Dehydration of castor oil is achieved in situ under phthalic anhydride catalysis. Alcoholysis of dehydrated castor oil by glycerol is also achieved in situ to form predominantly the monoglyceride. Polyesterification of the resultant mono- and diglycerides is realised through interaction with phthalic anhydride. The reaction is carried out at 280°C for 3 hours and at 225°C for 2 hours under azeotropic distillation with xylene. The parent poly(glyceryl phthalate) alkyd resin is synthesized by reaction of castor oil, glycerol and phthalic anhydride to a predetermined acid value. Formulation development experiments were carried out to study the effect of variations in the dibasic acid to polyol/oil and polyol to oil ratios on alkyd resin properties. Model formulations exhibiting the best alkyd performance were developed. Predictive model formulation equations were derived from model formulation data and their limits of reliability and applicability established. The formulation of water soluble alkyd resins is modified to introduce pendant carboxylic acid groups along the polymer skeleton. Water solubility is achieved by neutralisation of the residual pendant carboxylic acid groups by 'fugitive' amines to yield water soluble alkyd soaps. The effect of variations in the nature and level of incorporation of amine is investigated. Alkyd resin solubilisation and resin acidity guide formulae were studied and developed. Cross-linking chemistry of alkyd resins, both in the reactor (gelation) and on application (film formation) is investigated. Gelation manifested itself in two different forms, thermoplastic and thermosetting. An important alkyd constant, K, was established as an indispensable tool in control of premature gelation and in the prediction of resin drying characteristics. Autooxidation and solvent evaporation are the two competing curing mechanisms encountered in film formation. The nature and influence of each curing mechanism on the rate of cure and film characteristics is highlighted. Catalysis experiments were conducted with metallic driers (Co2 Mn2 and Pb2} to bring the rate of drying of resin films to economically feasible limits and catalyst addition levels were established. New spectral characterisation techniques based on Fourier Transform Infrared spectroscopy were investigated. An extensive study was carried out on FT IR spectral data to establish qualitative and quantitative relationships between transmission peak ratios and alkyd resin composition. Series dependent and series independent correlation equations, useful in quantifying alkyd resin components were derived. A new FT IR spectroanalytic characterisation method for dibasic acids is proposed. The method, if adopted, affords both qualitative and quantitative characterisation of the dibasic acid component in the alkyd resin matrix and it is envisaged the technique will supersede conventional methods in terms of speed and simplicity.'Item Design of novel drug delivery polymeric complexes via innovative crosslinking reactions(2004-04-01) Sibanda, Wilbert, O. L.This thesis presents a multifaceted approach which comprehensively describes the design of novel drug delivery polymeric complexes through the application of innovative crosslinking reactions. These reactions have been built on the statistical and mathematical principles governing the technique of Design of Experiments. At the outset, pertinent aspects covering the importance of rate-controlled drug delivery in achieving superior therapeutics is presented. In addition, the fundamental mechanisms which regulate the complex behaviour of polymeric materials are outlined, placing emphasis on the mathematical models which demonstrate the critical need to be able to synchronize the processes of matrix hydration, relaxation, disentanglement, erosion and dissolution. Initially, the Plackett-Burman Design was evaluated to develop a crosslinked polymeric oilisphere device for the in vitro site-specific delivery of Mentha piperita oil. This design proved to be highly successful in rapidly identifying the appropriate release rate-modifying variables through the application of stepwise regression optimization and Artificial Neural Networks.Item The synthesis, characterization and performance evaluation of polyphelenediamine- and polypyrrole- clay composites for removal of oxo-anionic wastewater contaminants(2017) Mdlalose, Lindani MbalenhleContamination of water bodies by numerous pollutants is a worldwide problem that endangers the environment and health of human beings, animals and aquatic life. Hexavalent chromium (Cr(VI)) for example is used in different metal products and processes which makes it a common environmental contaminant. Because of its high mobility in aqueous phase, and improper storage or unsafe disposal practices, leakage of Cr(VI) into water streams and ground water is a common occurrence. While Cr(III) is an essential micronutrient, Cr(VI), however is highly toxic posing serious health risks. Additionally, phosphorus is a limiting nutrient for the growth of organisms in most ecosystems, but, excessive discharge of phosphate ions in water systems leads to profuse algal growth, and is detrimental to both the environment and the ecosystem. This research focused on the development of suitable functional adsorbents for the removal of Cr(VI) complexes and phosphate ions from wastewater. Poly(para-phenylene)- (PpPD) and polypyrrole-based composites were synthesized through chemical oxidation polymerization, and investigated for Cr(VI) remediation. Poly(phenylenediamine) isomers were synthesized through different chemical oxidation methods for the uptake of phosphate ions in wastewater. Transition metals modified bentonite clay adsorbents were developed to remove phosphate ions in aqueous solution.The adsorbents were characterized using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD), Brunauer-Emmett-Teller (BET), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), Thermogravimetric analyzer (TGA) and X-ray photoelectron spectroscopy (XPS) instruments. Adsorption kinetics and isotherm models were investigated. In the first study of this work (paper I), PpPD and PpPD-clay composite were successfully prepared and applied for Cr(VI) removal and reduction in aqueous solution. Characterization by XRD demonstrated that PpPD molecules intercalated into clay galleries. Additionally, PpPD functional groups dominated in the composite even though the signal bands were smaller than the pristine polymer bands indicating that there was a formation of polymeric structure inside the organoclay interlayer spaces. Batch adsorption studies showed that pH, adsorbent dosage, contact time and Cr(VI) concentration affected the degree of adsorption. The Langmuir maximum adsorption capacity for Cr(VI) was 217.4 mg/g and 185.2 mg/g whereas for total Cr it was 193.3 mg/g and 148.8 mg/g for PpPD and PpPD-organoclay, respectively at an optimum pH of 2. Paper II focused on the chemistry of Cr(VI) adsorption by PpPD and adsorbent regeneration. The adsorption mechanism on the material surface was revealed by XPS and FT-IR. Cr(VI) was reduced to Cr(III) which complexed onto the adsorbent surface at the studied pH of 2 and 8. Desorption of the adsorbed Cr was conducted using NaOH (0.05 M) and HCl (0.1 M). The PpPD adsorbent performed optimally for eight cycles and still retained about 80% adsorption efficiency at the 10th cycle using an initial Cr(VI) concentration of 100 mg/L. Treatment with the regenerants showed irreversible oxidation reaction for the adsorbents while still removing Cr(VI) for several cycles. To investigate the toxicological impact on seed germination due to contact with used adsorbents, phytotoxicity test was investigated. Seed germination severely diminished to 35% and 14% (respective to control) in the presence of P-p-PD-MMT and P-p-PD. In paper III polypyrrole-clay composite was synthesized and also proved to be an effective adsorbent for Cr(VI) removal. A percentage Cr(VI) removal of 99% was obtained at pH 2 using adsorbent dosage of 0.15g for 100 mg/L Cr(VI) concentration for 3h in a batch mode. Due to its excellent adsorption properties, the composite was regenerated using different varied concentrations of eluents (NaOH, NH4OH, HCl, NH4Cl and HNO3). Desorption and regeneration using 0.01 M NaOH and 0.5 M HCl gave more regeneration cycles where the first 5 regeneration efficiencies were still greater than 80%. EDX determined the elemental components of the polypyrrole-clay composite before and after Cr(VI) adsorption. It demonstrated a significant decrease of Cl- ions after adsorption which is attributed to ion exchange mechanism between Cl- ions and Cr(VI) during the adsorption process. Investigation of the adsorption behaviour revealed a decrease in thermal stability of the composite after several adsorption cycles while treating the adsorbent with the regenerants as a result of material oxidation and deterioration due to Cr(VI) exposure in acidic medium and the impact of the regenerants. According to FT-IR analysis, polypyrrole-clay bands shifted to a higher wavenumber after Cr(VI) adsorption due to the change in skeletal vibrations as a result of Cr(VI) species adsorbed onto its surface Paper (IV) described synthesized adsorbents for phosphate removal. The study presented the development and performance of two sets of poly(phenyelenediamine) (PPD) isomers synthesized from ammonium persulphate ((NH4)2S2O8) and potassium dichromate (K2Cr2O7) as oxidants. The chemical structure of the adsorbents were determined using FT-IR, TGA and XRD. Amorphous morphology dominated in all the polymers with poly(m-phenylenediamine) PmPD being more amorphous and PpPD was the least. Batch adsorption studies showed improved adsorption capacity for K2Cr2O7 synthesized polymers. K2Cr2O7 oxidant played a major role in providing trivalent chromium metal which improved the phosphate uptake. This is attributed to the Lewis acid-base interaction where trivalent chromium acts as an acid and phosphate ions serve as a base. Batch adsorption results showed that solution pH, contact time and initial concentration influenced phosphate adsorption with the maximum adsorption capacities of 143 mg/g, 217 mg/g and 69.0 mg/l for PoPD, PmPD and and PpPD adsorbents, respectively. Adsorption reached equilibrium at about 300 min at an optimum pH of 2.0. The adsorption isotherms were described by Langmuir isotherm and the kinetic data were described better by pseudo-second order kinetic rate model implying adsorption onto homogeneous surfaces and the mechanism of adsorption was attributed to chemisorption. Desorption was conducted on the meta substituted PPD using NaOH (0.05 M) which displayed effective desorption capacity and exhibited commendable adsorption for re-use. The adsorbent also proved to be selective to phosphate ions at the background of much higher concentrations of sulphate and nitrate anions due to the presence of Coulombic and Lewis-acid-base interactions. In paper (V), remediation of phosphate ions was examined using modified bentonite clay as an adsorbent. Modification was achieved by incorporating Fe, Ni and Co metal salts using precipitation method. Adsorbents were characterized by FT-IR and XRD. The results showed significant amorphosity for metal modified bentonite compared to the parent bentonite. The adsorption capacity for all studied bentonite-based materials increased with increasing initial phosphate concentration and adsorption mechanisms were influenced by the solution pH. The maximum adsorption capacity of 6.57 mg/g, 20.88 mg/g, 29.07 mg/g and 46.95 mg/g were obtained for Bent, Fe-Bent, Ni-Bent and Co-Bent, respectively. The adsorption rate fitted pseudo-second order for all adsorbents. Langmuir isotherm model described the phosphates removal for all adsorbents at an optimum pH of 3.Item Analytical techniques in polymer chemistry with special reference to urea-formaldehyde resins(1993) Ferg, Ernest EduardOne of the greatest environmental drives in the synthetic resins field has been to decrease the formaldehyde emission from cured urea formaldehyde (UF) resins, without adversely affecting their excellent technical performance. [Abbreviated Abstract. Open document to view full version]Item Pre-treatment processing of household plastic packaging waste(2016) Blackstock, RossThe purpose of this investigation was to investigate whether or not it would be possible to separate blow moulded and injection moulded waste plastics using two techniques; air classification and ballistic separation. Air classification and ballistic separation are two techniques that separate different types of material according to size, shape and density. Previous research, together with new measurements, has suggested that blow mould plastics tend to be thinner in terms of wall thickness than injection moulded plastics meaning that air classification could be used to separate each type of plastic. The material used for the study was supplied by a Romanian recycler and was a mixture of High Density Polyethylene and polypropylene. Two additional samples, one Polyethylene rich and the other polypropylene rich, were also included in the research. The first part of the study involved measuring different characteristics of the material to determine how to go about performing the different air classification experiments. The second part of the study focused on separating the different material samples using different air classifier systems and a ballistic separation system. The third part of the study focused on processing the samples from part 2 (air classification) into test specimens for further mechanical and melt flow property measurements. After measuring the mechanical and melt flow properties of the different samples it was found that air classification did not substantially improve the mechanical or melt flow properties of the material. The study did, however, show that there is a strong correlation between polymer type and melt flow properties. High Density polypropylene is generally used for blow mould applications whereas polypropylene is generally used for injection mould applications. Separating the material according to polymer type therefore means that the material is, to an extent, also sorted according to melt flow properties.Item Preparation of phenolic resins from Sasol phenosolvan pitch(2012-04-20) Stephanou, AndreasItem Development and application of polymeric materials for heavy metal ions recovery from industrial and mining wastewaters(2012-02-01) Saad, DaliaContamination of water bodies by heavy metals and metalloids is an established problem and several studies have been conducted to deal with it. South Africa is amongst those countries whose water systems are most affected as a result of intensive mining activities. This research was dedicated to the development of insoluble chelating polymers for use as adsorbents to abstract heavy metal ions from mining and industrial wastewater. Branched polyethylenimine (PEI), well known for its metal chelating potential, was cross linked by epichlorohydrin in order to convert it into a water-insoluble form. The water-insoluble property gives the advantage of being used in situ and a possibility of regeneration and re-use, making it a more feasible and cost-effective method. Its surface was also modified for selective removal of specifically-targeted heavy metal and metalloid ions. The binding affinity of the synthesized materials to heavy metal and metalloid ions has been determined as well as their ability to be regenerated for reuse. These processes demonstrated that cross-linked polyethylenimine (CPEI) exhibited good complexation ability with high affinity to Cr and some divalent metal ions such as Fe, Zn, and Ni. On the other hand, it showed very poor ability to bind oxo-anions such as SeO32- and AsO2- which has been attributed to the unavailability of suitable functional groups to interact with these ions. The observed order of complexation was: Cr > Zn> Fe >> Ni > Mn > Pb >> As > U > Se. The phosphonated polyethylenimine (PCPEI) showed high selectivity for As, Mn and uranyl ions. The observed order of removal was: U > Mn> Ni > Zn > As >> Cr > Pb > Fe >> Hg > Se; whereas the suffocated polyethylenimine (SCPEI) exhibited high affinity to Se, and Hg. The observed order of adsorption was: Hg > Se >> U > Zn >Pb > Ni >> As > Cr > Fe. v The adsorption behaviour of these polymeric materials involved more than one mechanism such as complexation, normal surface charge exchange, and anion replacement and all these mechanisms are governed by the functional groups. The nitrogen atom on the chelating group (-NH) in the cross-linked polyethylenimine; the phosphorus atom on the chelating group (-PO3H2) in phosphonated cross-linked polyethylenimine; and sulphur atom on the chelating group (-SO3H) in suffocated cross-linked polyethylenimine act as Lewis bases and donate electrons to metal cations which are considered Lewis acids. The existence of the chelating groups in SCPEI and PCPEI facilitate the removal of oxo-anions through anion replacement since they exist as bases in solution and hence cannot be electron acceptors. Thus, the expected mechanism is the normal anion replacement. This mechanism can explain the high removal of Se by SCPEI since Se has similar chemical behaviour as sulphur and are in the same group in the periodic table. As such they can easily replace each other. Sulphur is released from the polymer into the solution by replacing the selenium ions in the polymer. Similar behaviour occurs between phosphorus in PCPEI and arsenic ions as As and P belong to the same group in the periodic table and hence have similarities in their chemical behaviour. The Langmuir and Freundlich isotherm models were used to interpret the adsorption nature of the metal ions onto synthesized polymers. The Freundlich isotherm was found to best fit and describe the experimental data describing the adsorption process of metal and metalloid ions onto the synthesized polymeric materials The kinetic rates were modelled using the pseudo first-order equation and pseudo second-order equation. The pseudo second-order equation was found to explain the adsorption kinetics most effectively implying chemisorption. vi The thermodynamic study of the adsorption of metals and metalloids by the synthesized CPEI, PCPEI and SCPEI resulted in high activation energies > 41 KJ mol-1 which confirm chemisorption as a mechanism of interaction between adsorbate and adsorbent. So far, the developed polymeric materials showed good results and have potential to be applied successfully for remediation of heavy metal-polluted waters, and they have potential for use in filter systems for household use in communities that use borehole water impacted by mining and industrial waste waters. The desorbed metals can be of use to metal processing industries.