Visco-elastic behaviour at the nano-level of a commonly used polymer (PET) is characterised using atomic force microscopy (AFM) at a range of temperatures. The modulus, indentation creep and relaxation time of the PET film (thickness = 100 m) is highly sensitive to temperature over an experimental temperature range of 22¿175 ¿C. The analysis showed a 40-fold increase in the amount of indentation creep on raising the temperature from 22 ¿C to 100 ¿C, with the most rapid rise occurring above the glass-to-rubber transition temperature (Tg = 77.1 ¿C). At higher temperatures, close to the crystallisation temperature (Tc = 134.7 ¿C), the indentation creep reduced to levels similar to those at temperatures below Tg. The calculated relaxation time showed a similar temperature dependence, rising from 0.6 s below Tg to 1.2 s between Tg and Tc and falling back to 0.6 s above Tc. Whereas, the recorded modulus of the thick polymer film decreases above Tg, subsequently increasing near Tc. These visco-elastic parameters are obtained via mechanical modelling of the creep curves and are correlated to the thermal phase changes that occur in PET, as revealed by differential scanning calorimetry (DSC).

Safripol is a South African polymer company producing mainly high density polyethylene and polypropylene for the South African market. Safripol used to be part of a global chemical company Dow Chemicals. Dow Chemical's divested in South Africa in 2006 and Safripol lost all the advantages of being part of a global corporate enterprise. The company is faced with a unique situation in that it is receiving monomer from Sasol, which is also its main competitor in the polymer market. The price of monomer and its low availability is putting pressure on Safripol's product margins, with a negative effect on the company's sustainability. The above was also defined as the research problem that threatens to undermine the company's competitive edge in the polymer market. It was clear from this research study that monomer and specifically propylene was the biggest burning point for Safripol regarding the price and availability thereof. Research into the South African polymer market has shown that Safripol will lose significant market share if the company is not showing additional growth in the market. The research problem is investigated through interviews, monomer availability investigations, plant capacity increasing and potential technology partner's discussions. A specific scenario planning process was also followed to help Safripol identify potential present and future scenarios that the company can investigate. The research problem was addressed by developing a strategy for Safripol to address the research objectives. Recommendations were done regarding the following: 1) Recommendations for additional propylene supply. 2) Recommendations to increase the polypropylene plant capacity. 3) Recommendations with regards to technology partners. 4) Recommendations regarding the scenario planning process. / Thesis (M.Ing. (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2011. (Mag eers in 2014 gepubliseer word)

Increasing environmental awareness over the past decade as well as stringent environmental laws forced all factories to invest in water treatment processes for effluent treatment before discharge or re-use. Most of these effluent treatment processes utilize membranes as the physical. barrier for separation. The membranes used in water applications are expensive and alternative materials and production techniques will increase the viability of membrane separation processes. Experiments conducted on irradiated polyethylene showed that some of its properties were enhanced while others deteriorated. However, the enhanced properties make the polyethylene, in particular ultra-high molecular weight polyethylene, an ideal membrane material. The manufactured membranes were tested in extraction experiments, and satisfactory results were obtained. Permeation studies on the membranes compared favourably with similar studies done on commercially available membranes. An extraction rate of 1.08 g/(m2h) nickel was achieved. A preliminary cost evaluation showed that these membranes can be manufactured at a low cost (R13.45/m2). and can be applied as supported liquid membranes. Future research should focus on methods to decrease the brittleness and stiffness of the membranes. / Thesis (MIng)--PU for CHE, 1999

Safripol is a South African polymer company producing mainly high density polyethylene and polypropylene for the South African market. Safripol used to be part of a global chemical company Dow Chemicals. Dow Chemical's divested in South Africa in 2006 and Safripol lost all the advantages of being part of a global corporate enterprise. The company is faced with a unique situation in that it is receiving monomer from Sasol, which is also its main competitor in the polymer market. The price of monomer and its low availability is putting pressure on Safripol's product margins, with a negative effect on the company's sustainability. The above was also defined as the research problem that threatens to undermine the company's competitive edge in the polymer market. It was clear from this research study that monomer and specifically propylene was the biggest burning point for Safripol regarding the price and availability thereof. Research into the South African polymer market has shown that Safripol will lose significant market share if the company is not showing additional growth in the market. The research problem is investigated through interviews, monomer availability investigations, plant capacity increasing and potential technology partner's discussions. A specific scenario planning process was also followed to help Safripol identify potential present and future scenarios that the company can investigate. The research problem was addressed by developing a strategy for Safripol to address the research objectives. Recommendations were done regarding the following: 1) Recommendations for additional propylene supply. 2) Recommendations to increase the polypropylene plant capacity. 3) Recommendations with regards to technology partners. 4) Recommendations regarding the scenario planning process. / Thesis (M.Ing. (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2011. (Mag eers in 2014 gepubliseer word)

Increasing environmental awareness over the past decade as well as stringent environmental laws forced all factories to invest in water treatment processes for effluent treatment before discharge or re-use. Most of these effluent treatment processes utilize membranes as the physical. barrier for separation. The membranes used in water applications are expensive and alternative materials and production techniques will increase the viability of membrane separation processes. Experiments conducted on irradiated polyethylene showed that some of its properties were enhanced while others deteriorated. However, the enhanced properties make the polyethylene, in particular ultra-high molecular weight polyethylene, an ideal membrane material. The manufactured membranes were tested in extraction experiments, and satisfactory results were obtained. Permeation studies on the membranes compared favourably with similar studies done on commercially available membranes. An extraction rate of 1.08 g/(m2h) nickel was achieved. A preliminary cost evaluation showed that these membranes can be manufactured at a low cost (R13.45/m2). and can be applied as supported liquid membranes. Future research should focus on methods to decrease the brittleness and stiffness of the membranes. / Thesis (MIng)--PU for CHE, 1999

Environmental stress cracking (ESC) is one of the main, and probably the most common, failure mechanisms involved in polymer fractures. This type of failure is critically important as it occurs suddenly, without any visible pre-fracture deformation. Such failure can be catastrophic and costly in cases where structural integrity is required. In polyethylene (PE), ESC occurs through a slow crack growth mechanism. Cracks initiate from stress-concentrated imperfections, propagate through the bulk of PE, and ultimately result in a brittle fracture. In order to predict the environmental stress cracking resistance (ESCR) of PE, it is necessary to fully understand the molecular structure of the resin. In this thesis, attempts were made to find relationships between molecular structure characteristics and material responses, mainly inter-lamellar entanglements and strain hardening behaviour of PE resins, through mechanical and rheological experiments. Inter-lamellar entanglements are believed to be the main factor controlling slow crack growth of PE. Extent of entanglements and entanglement efficiency were investigated by monitoring the strain hardening behaviour of PE resins in the solid state through a uniaxial tensile test, and in the melt state, through extensional rheometry. ESCR is usually assessed by unreliable and time consuming testing methods such as the notch constant load test (NCLT) on notched PE specimens in the presence of an aggressive fluid and elevated temperatures. In this thesis, a practical, yet reliable, tensile test was developed for the evaluation and prediction of ESCR. The developed test offers a more reliable and consistent ESCR picture without the drawbacks of the subjective notching process and presence of aggressive fluids. Through this test, a factor called ???corrected hardening stiffness (cHS)??? was developed, which can easily be used for a relative ranking of ESCR of different PE resins. Studies were next extended to the melt state via shear and extensional rheometry. Through studies in the shear mode, a molecular weight-normalized average characteristic relaxation time (??N) was found to be efficient in predicting the extent of chain entanglements in resins. This provided a potential melt indicator for a relative measure of ESCR, for linear low density polyethylene (LLDPE), with different short chain branching levels. Extensional studies were conducted to evaluate the strain hardening behaviour in the melt state. An inverse correlation was obtained between ESCR and the melt strain hardening coefficient (MSHC), found from Sentmanat Extensional Rheometry (SER). This indicated an inverse relationship between ESCR and chain extensibility in the melt. In addition, a new factor called ???melt hardening stiffness (mHS)??? was developed from the slope of a stress-strain line, obtained from SER. This factor, analogous to cHS, can be used for a practical and reliable ranking of ESCR of PEs. ESCR is usually associated with classical crystalline phase property indicators, such as crystallinity and lamella thickness. In this thesis, the effect of processing and post processing temperature on the extent of inter-lamellar entanglements were investigated, evaluated, and correlated to ESCR. Also, analysis of the lamella surface area (LSA) was pursued since LSA reflects changes in phase interconnectivity more precisely. The focus of this part of the study was on the effect of temperature on LSA to identify the optimum processing and post-processing conditions which yield a higher LSA. It was reasonable to presume that PE with larger lamella lateral surface areas will have more inter-lamellar entanglements, hence higher ESCR. Finally, a well-controlled ultraviolet (UV) photoinitiated reactive extrusion (REX) process was developed for selective formation of long chain branches in the PE structure. This was conducted to impose restrictions against stretching of the polymer chain, which consequently enhanced ESCR.

The purpose of this research work was to develop novel continuous bio-composite fibres with a combination of wood pulp or lignin and synthetic polymers, using continuous electrospinning and extrusion processes. The electrospun composite fibres have potential application in filtration, wound dressing, non-woven fabrics and support of thin polymeric separation membranes. Lignin fibres could be used for the development of carbon fibres. Two types of polyethylene oxide electronspun composite fibres (300-600 nm in diameter) were formulated using treated and untreated wood fibre. The optimum polymer solution concentration (7 wt.%) and addition of 5 wt.% wood pulp were found to produce uniform composite fibres. Superior dispersion and orientation were obtained with acetylated wood pulp as compared to untreated fibres. Similarly, wood pulp and nylon 6,6 based bio-composite fibres were generated successfully by electrospinning process. In this study solution concentration was found to be a critical parameter in regulating the diameter of fibres. Bio-composite fibres were developed from wood pulp and polypropylene (PP) by an extrusion process and subsequently characterized by various techniques. Tensile properties of composite fibres were improved by addition of maleated polypropylene (MAPP) and wood pulp. Fourier transform infrared spectroscopy provided the nature of chemical interaction between wood pulp reinforcement and PP matrix. Scanning electron microscopy results revealed that MAPP treatment was effective in increasing reinforcing fibre-matrix compatibility. X-ray computed tomography showed that the fibre becomes more aligned along the length axis possibly due to compression and die geometry of the extruder. Finally, blended lignin fibres (hardwood lignin/polyethylene oxide) were successfully developed by an extrusion process. Softening temperature and glass transition temperature of lignin were measured by differential scanning calorimetry which was helpful in selecting an optimal temperature profile for the extrusion process. Rheological studies provided information about the viscosity of hardwood lignin which was useful in producing lignin fibres.

The composition of orthopaedic wear testing lubricants used to mimic synovial fluid (SF) is known to significantly affect in vitro polyethylene (PE) wear; however, some wear testing standards may be promoting the use of lubricants that are not clinically relevant. The present thesis evaluated the biochemical composition of human osteoarthritic and periprosthetic SF in order to propose changes to lubricant specifications in current wear testing standards. Using this data, pin-on-disc wear tests were conducted to explore the effects of more clinically relevant lubricants on PE wear. Results showed that wear decreased using a more clinically relevant lubricant. Samples of these lubricants were biochemically evaluated and compared to the SF results previously obtained, which showed that current standards for wear testing lubricants are biochemically different from SF. The findings from the present thesis encourage the modification of standardized lubricant specifications to improve wear testing protocols and guarantee clinically relevant wear testing.

The purpose of this research work was to develop novel continuous bio-composite fibres with a combination of wood pulp or lignin and synthetic polymers, using continuous electrospinning and extrusion processes. The electrospun composite fibres have potential application in filtration, wound dressing, non-woven fabrics and support of thin polymeric separation membranes. Lignin fibres could be used for the development of carbon fibres. Two types of polyethylene oxide electronspun composite fibres (300-600 nm in diameter) were formulated using treated and untreated wood fibre. The optimum polymer solution concentration (7 wt.%) and addition of 5 wt.% wood pulp were found to produce uniform composite fibres. Superior dispersion and orientation were obtained with acetylated wood pulp as compared to untreated fibres. Similarly, wood pulp and nylon 6,6 based bio-composite fibres were generated successfully by electrospinning process. In this study solution concentration was found to be a critical parameter in regulating the diameter of fibres. Bio-composite fibres were developed from wood pulp and polypropylene (PP) by an extrusion process and subsequently characterized by various techniques. Tensile properties of composite fibres were improved by addition of maleated polypropylene (MAPP) and wood pulp. Fourier transform infrared spectroscopy provided the nature of chemical interaction between wood pulp reinforcement and PP matrix. Scanning electron microscopy results revealed that MAPP treatment was effective in increasing reinforcing fibre-matrix compatibility. X-ray computed tomography showed that the fibre becomes more aligned along the length axis possibly due to compression and die geometry of the extruder. Finally, blended lignin fibres (hardwood lignin/polyethylene oxide) were successfully developed by an extrusion process. Softening temperature and glass transition temperature of lignin were measured by differential scanning calorimetry which was helpful in selecting an optimal temperature profile for the extrusion process. Rheological studies provided information about the viscosity of hardwood lignin which was useful in producing lignin fibres.

Computational quantum mechanics in the frame work of density functional theory (DFT) was used to investigate the effect of chemical impurities on high field conduction in polyethylene (PE). The impurity states in the band gap caused by common chemical impurities were characterized in terms of their “depth”, i.e. energy relative to their relevant band edge (valence band or conduction band), and in terms of the extent to which their wavefunctions were localized to a single polymer chain or extended across chains. It was found that impurity states can affect high field phenomena by providing “traps” for carriers, the depths of which were computed from first principle in agreement with estimates in literature. Since the square of the wavefunction is proportional to the spatial electron probability density, transfer of charge between chains requires wavefunctions which are extended across chains. Impurity states which are extended between chains can facilitate the inherently limited interchain charge transfer in PE, as the DFT study of iodine doped PE revealed. The introduction of iodine into PE increases conductivity by several orders of magnitude, increases hole mobility to a much greater extent than electron mobility, and decreases the activation energy of conduction from about 1 eV to about 0.8 eV. These characteristics were explained in terms of the impurity states introduced by iodine and wavefunctions of those states. Understanding the effect of iodine on conduction in PE provided a basis for understanding the effect of common chemical impurities on conduction therein. In particular, carbonyl and vinyl impurities create states which should promote hole mobility in a manner very similar to that caused by iodine. It was demonstrated that in the context of high field conduction in PE, besides the traditional focus on the depth of impurity states, it is important to study the spatial features of the states wavefunctions which are neither discussed nor accounted for in present models.