Thesis (PhD)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: From the Sasol Fischer- Tropsch process, a variety of different a-olefins are produced. Sasol recently started presenting these a-olefins to polymer producers. To demonstrate the application possibilities of these a-olefins as comonomers for ethylene and propylene polymerization, it was necessary to first synthesize catalysts having a combination of high activity and good comonomer incorporation, and in the case of propylene copolymers, also sufficient stereospecificities. Different methods to produce catalysts conforming to these requirements were investigated and it was found that catalysts produced from a MgCb-support activated by a combination of chemical and mechanical means produced suitable catalysts. The amount of alcohol used during the support activation step and the time allowed for alkylation of the active centers were important. No clear correlation between total titanium content and activity was observed. The degree to which active sites are protected was evaluated from the amount of comonomer present in the final copolymer based on the amount added to the reaction. Cyclopentadiene was used to selectively deactivate the unprotected active sites to determine the ratio between protected and "open" active sites. High activity catalysts are not suitable for gas-phase copolymerization and were consequently "diluted" by dispersion in a pre-formed polymer powder and by prepolymerization. Catalyst activity based on titanium content was substantially decreased, but comonomer incorporation was not. Catalysts for producing crystalline polypropylene require the presence of both an internal and external electron donor. It was shown that isotacticity increased linearly with an increase in external modifier at the expense of catalyst activity and that a double treatment of the support or catalyst before the final TiCl4 fixation was more effective at increasing stereospecificity. The less stereospecific sites are more capable of accepting bulky comonomers in the coordination complex and thus by decreasing the amount of less-stereospecific active sites, the overall capability of the catalyst to incorporate comonomer was decreased. Comonomer sequence distributions and average lamellar thicknesses of different ethylene / a-olefin copolymers were calculated from CH2 dyad concentrations determined by I3C NMR spectroscopy. Ethylene sequences in the I-butene containing copolymers are generally longer than those where a higher a-olefin was used as comonomer which indicates that a more random comonomer distribution is obtained when the higher u-olefins are used. It was shown that an inverse relationship exists between branch size and density. For density, no effect resulting from the comonomer type was observed. This same inverse relationship was also observed for tensile strength. Modulus, hardness and impact strength, on the other hand, did show an effect resulting from the comonomer type. Modulus and hardness were not depressed as much and impact strength improved more than what was expected from calculations based on branch size. Homogeneous copolymers have broad melting peaks. It was shown that at sufficiently high comonomer content, peak broadening occurs when the higher cc-olefins are used as comonomer, which also indicates that more random comonomer distributions are obtained with the higher aolefins. From the chain propagation probabilities calculated it was observed that two types of active sites are present. Those responsible for producing mainly polyethylene have an alternating character while the sites capable of incorporating comonomer have a blocky character. It was expected that the additional introduction of a third a-olefin during ethylene / 1- pentene copolymerization will produce a terpolymer with density and related properties similar to the mathematical average between those of the relevant copolymers. This was only observed for the terpolymers containing l-heptene, 1- octene and l-nonene. The I-butene containing terpolymers have densities well below the expected values while the I-hexene containing terpolymers have values very similar to that of the ethylene / l-hexene copolymer densities, but still below the expected values. Properties related to density, such as tensile strength and modulus, follow this same trend. It is believed that the presence of l-pentene breaks up the tendency of the lower c-olefins to cluster which results in improved randomness. Compared to the copolymers, I-butene and l-hexene containing terpolymers seem to reach the impact strength maximum at a lower total comonomer content than that of the I-pentene copolymers which also indicates an enhanced effect from the combined use of I-pentene with these o-olefins. No substantial difference between impact strengths of co- and terpolymers prepared with higher a-olefins was observed. In general, the melting temperatures of the terpolymers are slightly lower and spread over a wider temperature range than those of the copolymers which can be realized if the comonomer units are less clustered and thus more randomly distributed. Decrease in melting temperature was, however, not as much as for the metallocene catalyzed terpolymers. From sequence length calculations from l3C NMR spectroscopy it was found that the crystallizable ethylene sequences of l-butene containing terpolymers were shorter than those of the corresponding copolymers, which confirms the notion that the introduction of a third comonomer resulted in an increase in randomness. Crystallizable sequence lengths became gradually shorter when higher cc-olefins were used in co- and terpolymers and those of the terpolymers are generally shorter. From the different types of active centers present on a Ziegler-Natta catalyst, it was reasoned that three main types of polymer chains can be present in the terpolymers: (a) ethylene homopolymer, (b) ethylene / lower a-olefin copolymer and (c) ethylene / lower a-olefin / higher a-olefin terpolymer. The ratio between these components in the final terpolymer depends primarily on the size of the higher a-olefin. The larger the third a-olefin becomes, the more active sites will reject it, resulting in a higher amount of ethylene / lower a-olefin copolymer. It was thus suggested that the large decrease in density and the associated change in related properties observed for ethylene / l-pentene / l-butene terpolymers can be related to the combined result of improved random comonomer incorporation together with the decrease in the amount of ethylene homopolymer. The possibilities of using the higher a-olefins having uneven carbon numbers were investigated in random propylene copolymers. Similar to that observed for the ethylene copolymers, less of the higher a-olefins was necessary to achieve a certain level of crystallinity. A good agreement was observed between tensile properties and comonomer type and content and the size of the branch and the resulting defect it causes in the crystal structure is the primary factor affecting tensile strength. For impact strength a close correlation between the size of the comonomer side chain and comonomer content was observed. It was shown that the effect of the heptyl branch derived from a l-nonene unit was 2.3 times that of the propyl group derived from the I-pentene unit. Properties of block copolymers can not be related directly to l-pentene content as is the case with random copolymers, mainly due to the heterogeneity of the block copolymers. The activating effect of hydrogen on catalyst activity was observed. It was also observed that the amount of l-pentene incorporated in the copolymer as well as the copolymer yield were higher in the presence of hydrogen than when the reaction was carried out in the absence of hydrogen. By using DSC it was possible to identify different crystalline phases in the propylene / I-pentene block copolymers due to the differences in their crystallization kinetics. A connection between the low-temperature peak and impact strength was observed. It was found that the presence of the low-temperature peak resulting from thin lamellae formed by chain containing many defects was undesirable when high impact strength is required. It was not possible to quantify the extent to which the intensity of this peak affected mechanical properties of the block copolymers. However, from sequence length calculations it was found that the ratio between the propylene and 1- pentene sequence lengths could be related quantitatively to impact strength, modulus, hardness and tensile strength of the polymers investigated. / AFRIKAANSE OPSOMMING: 'n Verskeidenheid van verskillende «-olefiene word in die Sasol Fischer- Tropsch proses vervaardig. Sasol het onlangs begin om hierdie a-olefiene aan polimeervervaardigers te bied. Om die toepassingsmoontlikhede van hierdie aolefiene as komonomere vir etileen en propileen polimerisasie te demonstreer was dit nodig om eerstens 'n katalis met 'n kombinasie van hoë aktiwiteit en goeie komonomeer invoeging te sintetiseer. In die geval van propileen word voldoende stereospesifisiteit ook vereis. Verskillende metodes om kataliste wat aan hierdie vereistes voldoen te vervaardig is ondersoek. Daar is gevind dat kataliste waarvan die MgCb basis deur 'n kombinasie van chemiese- en meganiese metodes geaktiveer is, die vereiste eienskappe besit. Die hoeveelheid alkohol gebruik tydens die basis aktivering stap en die tyd toegelaat vir die alkilering van die aktiewe spesies was belangrik. Geen duidelike verband tussen totale titaan inhoud en aktiwiteit is waargeneem nie. Die mate waartoe aktiewe spesies beskerm is, is bepaal vanaf die hoeveelheid komonomeer teenwoordig in die finale kopolimeer in verhouding met die hoeveelheid bygevoeg tydens die reaksie. Siklopentadieen is gebruik om onbeskermde aktiewe spesies selektief te deaktiveer om die verhouding tussen beskermde en oop aktiewe spesies te bepaal. Hoëaktiwiteit kataliste is nie geskik vir gasfase kopolimerisasie nie en is gevolglik verdun deur dit te versprei in 'n voorafgevormde polimeer poeier en deur prepolimerisasie. Katalis aktiwiteit gebaseer op titaan inhoud was aansienlik laer maar komonomeer invoeging was nie merkbaar beinvloed nie. Kataliste VIr die vervaardiging van kristallyne polipropileen vereis die teenwoordigheid van beide interne- en eksterne elektron donors. Daar is gewys dat isotaktisiteit liniêr verhoog met 'n toename in eksterne modifiseerder ten koste van katalis aktiwiteit en dat 'n dubbele behandeling van die basis of katalis, voor die finale titaan fiksering, meer effektief was om stereospesifisiteit te verhoog. Die spesies met laer stereospesifisiteit is meer bevoeg om bonkige komonomere in die koërdinasie kompleks toe te laat en deur dus die konsentrasie van hierdie spesies te verlaag is die bevoegdheid van die katalis om bonkige komonomeer te inkorporeer, verlaag. Komonomeer reeksverspreiding en gemiddelde lamellêre dikte van verskillende etileen / o-olefien kopolimere is bereken vanaf CH2 diad konsentrasie bepaal deur KMR spektroskopie. Etileen reekse in die kopolimere wat l-buteen bevat is oor die algemeen langer as dié waarin 'n hoër a-olefien as komonomeer gebruik was, wat aandui dat 'n meer egalige komonomeer verspreiding verkry word as hoër «-olefiene gebruik word. Daar is getoon dat 'n inverse verhouding tussen die grootte van die vertakking en digtheid bestaan. Geen effek komende van die komonomeer tipe kon waargeneem word nie. Hierdie soortgelyke inverse verhouding was ook waargeneem vir treksterkte. Modulus, hardheid en impaksterkte aan die ander kant, hét 'n effek komende van die komonomeer tipe getoon. Modulus en hardheid was nie soveel verlaag, en impak sterkte soveel verhoog as wat verwag is vanaf berekeninge gebaseer op vertakking grootte nie. Homogene kopolimere toon breë smeltpieke. Daar is gewys dat by voldoende komonomeer inhoud 'n verbreding van die pieke voorgekom het wanneer hoër a-olefiene as komonomere gebruik is, wat ook aandui dat 'n meer egalige komonomeer verspreiding met hierdie c-olefiene verkry kan word. Vanaf berekening van die ketting voortplantingsmoontlikhede is waargeneem dat twee tipes aktiewe spesies teenwoordig is. Die verantwoordelik vir die vorming van polietileen het 'n alternerende karakter terwyl die sentra wat komonomeer kan inkorporeer 'n blokagtige karakter het. Daar is verwag dat die addisionele byvoeging van 'n derde o.-olefien tydens etileen / I-penteen kopolimerisasie, 'n terpolimeer met digtheid en verwante eienskappe soortgelyk aan die wiskundige gemiddelde tussen dié van die relevante kopolimere tot gevolg sal hê. Dit was egter slegs waargeneem vir terpolimere wat I-hepteen 1- okteen en l-noneen bevat. Die I-buteen bevattende terpolimere het digthede ver onder die verwagte waardes terwyl die I-hekseen bevattende terpolimere waardes soortgelyk aan die etileen / l-hekseen kopolimeer digthede het' wat steeds onder die verwagte waardes is. Eienskappe verwant aan digtheid, soos treksterkte en modulus, volg dieselfde neiging. Dit word geglo dat die teenwoordigheid van l-penteen die neiging van die laer a-olefiene om saam te bondelopbreek wat 'n verbeterde egaligheid in komonomeerverspreiding tot gevolg het. Vergeleke by die kopolimere blyk dit dat die terpolimere wat l-buteen en I-hekseen bevat, die impaksterkte maksimum by 'n laer totale komonomer inhoud bereik as dié van die 1-penteen polimere. Dit dui ook op 'n verbeterde effek as gevolg van die gekombineerde gebruik van l-penteen met ander a-olefiene. Geen duidelike verskil tussen die impaksterktes van ko- en terpolimere, wat met die hoër a-olefiene berei was, is waargeneem me. In die algemeen is die smeltingstemperature van die terpolimere effens laer, en versprei oor 'n wyer temperatuurgebied as dié van die kopolimere wat verklaar kan word as komonomere minder saamgebondel is en dus meer homogeen versprei is. Die afname in smelt temperatuur was egter nie soveel as dié van die metalloseengekataliseerde terpolimere nie. Vanaf reekslengte berekeninge met behulp van KMR spektroskopie is daar gevind dat die kristalliseerbare etileen reekse van die l-buteen bevattende terpolimere korter was as dié van die ooreenkomstige kopolimere, wat die gevoel dat die byvoeging van 'n derde komonomeer 'n verbeterde komonomeerverspreiding tot gevolg het, bevestig. Vanaf die verskillende aktiewe spesies teenwoordig in 'n Ziegler-Natta katalis is daar geredeneer dat drie hooftipes polimeerkettings in die terpolimere teenwoordig kan wees: (a) etileen hompolimeer, (b) etileen / laer a-olefien kopolimeer en (c) etileen / laer a-olefien / hoër a-olefien terpolimeer. Die verhouding tussen hierdie komponente in die finale terpolimeer hang primêr van die grootte van die hoër aolefien af. Hoe groter die derde a-olefien is, deur hoe meer van die aktiewe spesies sal dit verwerp word wat 'n groter hoeveelheid etileen / laer a-olefien kopolimeer tot gevolg sal hê. Daar word dus voorgestel dat die groot afname in digtheid en die geassosieerde veranderings in die toepaslike eiensappe waargeneem vir etileen / 1- penteen / I-buteen terpolimeere, herlei kan word na die gekombineerde effek van verbeterde komonomeerverspreiding tesame met die afname lil die hoeveelheid etileen homopolimeer. Die moontlikheid om hoër cc-olefiene met onewe koolstofgetalle te gebruik in homogene propileen kopolimere is ondersoek. Soortgelyk aan dit wat waargeneem is vir die etileen kopolimere, was minder van die hoër cc-olefiene nodig om 'n spesifieke vlak van kristalliniteit te bereik. 'n Goeie ooreenkoms tussen trek-eienskappe en . komonomeer tipe- en inhoud is waargeneem en die grootte van die vertakking en die gevolglike defek wat dit veroorsaak in die kristal struktuur is die primêre faktor wat treksterkte beinvloed. Vir impaksterkte is 'n noue verband tusssen die grootte van die vertakking en komonomeer inhoud waargeneem. Daar is aangetoon dat die effek van die heptiel vertakking vanf die l-noneen eenheid 2.3 keer dié van die propiel groep van die l-penteen eenheid is. Eienskappe van blok kopolimere kan nie direk na l-penteen inhoud herlei word soos die geval met die homogene kopolimere was nie, hoofsaaklik as gevolg van die heterogeniteit van die blok kopolimere. Die aktiverende effek van waterstof op katalis aktiwiteit is waargeneem. Daar is ook gesien dat die hoeveelheid l-penteen geïnkorporeer in die kopolimeer, sowel as die kopolimeer opbrengs, hoër was in die teenwoordigheid van waterstof as wanneer die reaksie sonder waterstof uitgevoer is. Deur DSC te gebruik was dit moontlik om verskillende kristallyne fases in die propileen / l-penteen blok kopolimere vanaf die verskille in hulle krisallisasie kinetika, te identifiseer. 'n Verbintenis tussen die lae-temperatuur piek en impaksterkte is waargeneem. Daar is gevind dat die teenwoordigheid van die laetemperatuur piek, komende van die dun lamellas gevorm, deur kettings wat baie defekte bevat, ongewens is wanneer hoë impaksterkte vereis word. Dit was nie moontlik om die bereik waartoe die intensiteit van hierdie piek die meganiese eienskappe van die blok kopolimere affekteer, te kwantifiseer nie. Vanaf reekslengte bepalings is daar gevind dat die verhouding tussen die propileen en I-penteen reekslengtes kwantitiatief herlei kan word na impaksterkte, modulus, hardheid en treksterkte van die ondersoekte polimere.

Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: The study focused on the analysis of a variety o f synthesised tailored copolymers. During the investigation o f the samples new and innovative analytical techniques were developed to be able to identify the presence of certain predicted or expected copolymerisation products. Emphasis was placed on the versatility of CRYSTAF as a method for the analysis of semi-crystalline copolymers. Changes in the crystallisation temperature were used as an indicator, while the type o f method, solvent and sample weight served as variables in the system. The percentage comonomer content distribution for an unknown sample was determined from the standard curve plotted with the aid o f copolymers with known comonomer content. Ethylene/higher a-olefin and propylene/higher a-olefm copolymers were synthesised by means o f a metallocene precatalyst. In both cases, NMR spectroscopy, DSC, GPC, and CRYSTAF were used as analytical tools. In the ethylene series it was shown that the sample mixture was homogenous in the molar mass axis (GPC) but not in the chemical composition axis (CRYSTAF) regarding the comonomer content. For the propylene series, an increase in stereoerrors was observed by NMR and this was correlated with crystallisation on heating a DSC for the range o f copolymers. In the case where ethylene/methyl methacrylate block copolymers were synthesised using metallocene precatalyst, novel detection and separation methods were used and developed. This included the use o f CRYSTAF fitted with a carbonyl filter, high temperature gradient HPLC and high temperature liquid chromatography under critical conditions (LCCC). The last two techniques were the first where separation could be achieved with samples only dissolving at high temperature. All previous mentioned techniques, as well as the coupling of FTIR to GPC and high temperature gradient HPLC via LC-Transform revealed that the samples consisted o f varying ethylene and MMA block lengths. / AFRIKAANSE OPSOMMING: Die doelstelling van die navorsing was die analise van spesiaalvervaardigde kopolimere. Nuwe analitiese tegnieke is vir die bevestiging van sekere voorgestelde kopolimerisasie-produkte ontwikkel. Klem is gelê op die veelsydigheid van CRYSTAF as ’n metode vir die analise van gedeeltelik-kristallyne kopolimere. Veranderinge in die kristallisasie-temperature is as respons gebruik, terwyl die metode van sintese, die oplosmiddel en die hoeveelheid monster as veranderlikes in die sisteem beskou is. ‘n Standaardkurwe vir komonomeerinhoud is opgestel met behulp van kopolimere met ‘n bekende komonomeerinhoud. Hierdie kurwe is gebruik om die komonomeerinhoudsverspreiding van onbekende monsters te bepaal. Etileen/hoër a-olefien- en propileen/hoër a-olefien-kopolimere is met behulp van ‘n metalloseen pre-katalis gesintetiseer. In beide gevalle is KMR spektroskopie, DSC, GPC en CRYSTAF gebruik om die analises uit te uitvoer. Met verwysing na komonomeerinhoud is daar in die geval van die etileenreeks bevind dat die monstermengsel homogeen is met betrekking tot die molere massa, maar nie met betrekking tot die chemiese samestelling nie. Vir die propileenreeks is ’n verhoging in die stereofoute met behulp van KMR waargeneem. Dit is gekorrelleer met kristallisasie weens verhitting tydens DSC-bepalings vir die reeks kopolimere. In die geval van die sinteses van etileen/metielmetakrilaat-blokkopolimere met metalloseen as pre-katalis, moes nuwe waamemings- en skeidingstegnieke ontwikkel word. Dit het die gebruik van CRYSTAF met ’n karbonielfilter, hoetemperatuurgradient- HPLC en hoë-temperatuurvloeistofchromatografie onder kritiese toestande ingesluit. Laasgenoemde twee tegnieke het vir die eerste keer skeiding van monsters wat net by hoe temperature oplos, moontlik gemaak. Bogenoemde tegnieke, sowel as die koppeling van FTIR met GPC en hoë-temperatuur-gradient-HPLC via LC-transformasie het getoon dat die monsters etileen- en MMA-blokke met verskillende lengtes bevat het.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references. Available also in a digital version from Dissertation Abstracts.

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Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2008. / This study involved (a) the development and testing of a solution turbidity fractionation analyser (TFA) and (b) the investigation of possible molecular weight effects on solution crystallisation. To investigate the latter highly isotactic polypropylene was polymerised with a C2 symmetric metallocene catalyst. Blends were made of these homopolymers. The homopolymers as well as the blends were fractionated by means of temperature rising elution fractionation (TREF). The fractionated and unfractionated homopolymers as well as the fractionated blends were characterised by 13C NMR, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The TFA was successfully developed and helped in explaining the shifting of solution crystallisation temperature that was seen when blending of the homopolymers occurred. This was done performing analyses on the machine of blends of the homopolymers. Fractions, of the homopolymers and blends, obtained from TREF were also done. Subsequent runs of blends made from the fractions obtained from TREF were also done. In the end it was shown that the shift of the solution crystallisation temperature is either due to the tacticity or the molecular weight depending on the sample.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Isotactic polypropylene (iPP) exists in four different crystalline phases: α-, β-, γ- and the mesomorphic (smectic) form. The α-phase is probably the most predominant form of iPP with a monoclinic unit cell, whereas the unit cell of the γ-phase is orthorhombic. The aim of this study was to examine the ability of AFM to identify the α and γ crystalline forms of polypropylene and polypropylene copolymers that were not especially treated. Spherulites imaged on propylene-ethylene random copolymer surfaces had diameters ranging from 10-30μm and predominantly radial lamellae. The cross-hatching phenomenon of isotactic polypropylene was observed for samples containing both the α- and γ-phase. Two types of γ-phase spherulites were observed, namely a featherlike form for samples with a high content of the γ-phase and a bundle-like form with varying sizes, which is typical for the mixed structure of both α- and γ-forms. In some images of polypropylene-ethylene copolymer sample lozenge-shaped structures could be observed between the γ-spherulites, which might be single polyethylene crystals. Both the α- and γ-phase of iPP were successfully imaged and identified with AFM without prior treatment of the surface. The degree of crystallinity obtained from AFM images was calculated as a percentage of the surface area exhibiting regular structures. The results compared well to X-ray results.

Thesis (DSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Unstabilised polyolefins are susceptible to degradation when exposed to molecular oxygen, heat, irradiation as well as chemical and mechanical stimuli. Oxidation leads to changes in molecular properties such as molecular weight, molecular weight distribution, chemical composition, chemical composition distribution and crystallisability. Conventional analytical techniques are of limited use when studying the degradation of heterogeneous materials such as impact polypropylene copolymers (ICPP). These copolymers consist of a number of components of different monomer contents, isotacticity and crystallinity, ranging from amorphous EPR to highly crystalline polypropylene. The individual components are affected differently by degradation, leading to heterogeneity within the degradation of impact copolymers. Novel analytical approaches that acknowledge the heterogeneity in sample composition are needed to study the degradation behaviour of such heterogeneous materials. This study describes the combination of fractionation and hyphenated techniques with conventional analyses for extensive structural characterisation of complex impact copolymers as well as their degradation behaviour. Temperature rising elution fractionation (TREF) coupled to conventional techniques such as size exclusion chromatography (SEC), Fourier-Transform infrared spectroscopy (FTIR), Carbon-13 nuclear magnetic resonance (13C-NMR) and differential scanning calorimetry (DSC) indicated the ICPPs in question to consist of four main components, namely ethylene-propylene random copolymers (EPR), isotactic PP (iPP), as well as semi-crystalline ethylene-propylene copolymers (EPC) and lower isotacticity PP. The degradation of an ICPP was studied by a multi-component analysis procedure consisting of TREF coupled to SEC, 13C-NMR, as well as SEC-FTIR. Results obtained by this procedure indicated the change in crystallisability of the bulk sample observed by TREF, crystallisation analysis fractionation (CRYSTAF) and DSC to be the result of the preferential degradation of the iPP phase. Degradation of ICPPs initiates within this phase where chain scission and carbonyl group insertion leads to a change in the crystallisability of iPP chains. During TREF of degraded bulk ICPPs, the degraded iPP molecules elute at lower elution temperatures, depending on their degree of degradation. The other components of the copolymer were degraded to a lesser extent. Degradation products were also found to be heterogeneously distributed across the molecular weight distribution of each fraction, with a higher concentration appearing at the low molecular weight side. The multi-component analysis procedure was also used to study the difference in degradation behaviour between ICPPs of different comonomer content, isotacticity and crystallinity. The spatial heterogeneity of degradation within ICPPs was studied by Fourier-Transform infrared microspectroscopy (FTIR-μS). A heterogeneous distribution of degradation products was found across the depth of thicker sample specimens. These results were compared to those obtained by conventional layer-by-layer milling followed by SEC, FTIR and CRYSTAF. The principles of degradation within thick samples were similar to that observed for thin films, although additional contributions by sample morphology and oxygen diffusion were detected.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Solution electrospinning is a technique used to produce polymer micro- or nanofibres. Recently a great deal of research has been done on the application of polymer nanofibres produced by this method. The solution electrospinning of polyolefins have not been researched in-depth mainly due to the difficulty in dissolving these polymers in suitable electrospinning solvents. We managed to electrospin polypropylene copolymers at room temperature, obtaining both polymer micro- and nanofibres. A suitable solvent system was developed (cyclohexane/DMF/acetone) that allowed for the room temperature solution electrospinning of these crystalline polypropylene copolymers. It was also shown that using propylene-1-alkene copolymers with a low comonomer content was a facile way of producing crystalline polyolefins nano – and microfibers. Similar attempts to electrospin isotactic polypropylene were unsuccessful, even though lower molecular weight materials were used than in the case of the copolymers. This lead to an investigation of solution melting temperature by SCALLS. The copolymers showed great variance in their solution melting temperatures despite the fact that they all had more or less the same crystallinity and amount of comonomer, indicating that the type of comonomer played an important role in the solubility of the copolymer. The effect of different collectors was investigated, but in the end it was found that between spinning unto ice, foil on ice of just foil, foil still seemed to be the best collector. Comparing crystallinity of the polymer powders with that of the polymer fibres by DSC and WAXD, it was found that there is a difference in the crystallinity of the fibres and the powders. EVOH is a polymer with excellent properties and electropspinning of this polymer is relatively easy due to the fact that it dissolves quite easily in conductive solvents. DMF, Isopropanol/water and DMSO were all tested as suitable solvents and the morphology was compared through the use of SEM. The morphology of the fibres indicated that DMSO was the best solvent. The influence of the spinning parameters was determined for both systems of DMF and DMSO. These nanofibres were used as reinforcement in LDPE matrix and the mechanical properties of the LDPE matrix was improved with the addition of both aligned and unaligned fibres. The next step was the electrospinning of EVOH fibres containing MWCNT. TEM, FE-SEM and TGA were used to confirm the presence of the MWCNT as well as determine the distribution of the MWCNT inside the nanofibres. The nanotubes were distributed through the fibres; however agglomeration of the nanotubes did still take place. The nanofibres containing MWCNT were also used to make composites where the fibres were melted, leaving the MWCNT behind in the polymer matrix. This was done in both LDPE and EVOH matrices. The LDPE/MWCNT composites did not give positive results, on the other hand the EVOH/MWCNT composite showed an improvement in the mechanical properties compared to pure EVOH. The attachment of fluorescent dye molecules to the surface of the MWCNT was attempted and through fluorescent microscopy and the dispersion of the nanotubes inside the fibres as well as the composite could be seen. This study proved that polyolefin nanofibres could be obtained, giving rise to more applications for these versatile polymers. It also confirmed the importance of nanofibres as reinforcement and the use of nanofibres as a way to incorporate MWCNT in a polymer matrix. / AFRIKAANSE OPSOMMING: Elektrospin in ‘n oplosmiddel is ‘n tegniek wat gebruik word om polimeer mikro- en nanovesels te produseer. Die afgelope tyd word baie navorsing gedoen oor die aanwending van polimeer nanovesels wat geproduseer word op hierdie manier. Daar is nog min navorsing gepubliseer wat handel oor die elektrospin van poliolefiene uit ‘n oplosmiddel, deels oor hoe moeilik dit is om ‘n geskikte elektrospin oplosmiddel te vind vir hierdie polimere. In hierdie studie het ons mikro- en nanovesels verkry deur polipropileen kopolimere te elektrospin by kamertemperatuur. Die polimere is opgelos in ‘n oplosmiddel sisteem wat bestaan uit sikloheksaan/dimetielformamied/asetoon, by hoë temperatuur en het toegelaat dat die polimere in oplossing bly by kamertemperatuur. Hierdie diverse kopolimere het verskillende resultate gegee, sommige polimere het mikrovesels produseer, waar ander nanovesels geproduseer het. Die vessel morfologie is ondersoek deur die gebruik van Skandering Elektron Mikroskopie (SEM) en daar is gevind dat die vesels nie ‘n gladde voorkoms het nie, maar dat daar kraalvormige morfologie gesien kon word. Om dit te voorkom is sout by die oplosmiddel sisteem gevoeg. Die invloed van die verskillende parameters op die vesels se deursnit is ondersoek vir al die kopolimere. Die byvoeging van sout het gelei tot ‘n meer gladde vesel morfologie. Die effek van die gebruik van verskillende oppervlaktes om die vesels op te vang is ondersoek en die die kristalliniteit van die polimeer poeiers is vergelyk met die kristalliniteit van die polimeer vesels met die hulp van DSC en WAXD. ‘n Poging is aangewend om isotaktiese polipropileen te elektrospin uit oplossing, maar ons kon nie daarin slag om die polimeer op te los nie, al was die molekulêre gewig minder as die van die kopolimere. Dit het gelei tot die ondersoek van die smeltpunt temperatuur in oplossing deur die gebruik van oplossing kristallisasie-analise deur laser lig verstrooing (SCALLS). Al die kopolimere het min of meer dieselfde kristalliniteit en hoeveelheid komonomer bevat, tog het hulle smeltpunt temperatuur in oplossing baie verskil. Dit het gedui op die feit dat die tipe komonomeer ‘n groot rol speel in die oplosbaarheid van die kopolimeer. Die elektrospin van etileen-ko-vinielalkohol (EVOH) is ook ondersoek. DMF, Isopropanol/Water en Dimetielsulfoksied (DMSO) is getoets as geskikte oplosmiddels en die morfologie van die vesels is vergelyk deur die gebruk van SEM. Die tyd wat die polimeer in oplossing gebly het asook die morfologie van die vesels, het aangedui dat DMSO die mees geskikte oplosmiddel was. Die invloed van die elektrospin parameters was vasgestel vir beide DMF en DMSO sisteme. Hierdie nanovesels is gebruik as versterking in ‘n LDPE matriks en die meganiese eienskappe van die LDPE matriks is verbeter deur die toevoeging van beide nie-geweefde en gerigte veselsopppervlakte. Die volgende stap was die elektrospin van EVOH vesels wat multi-ommuurde koolstof nanobuisies (MWCNT) bevat. TEM, FE-SEM en TGA was gebruik om te bevestig dat die vesels wel MWCNT bevat asook om die verspreiding van MWCNT in die vesels aan te dui. Die nanobuisies was versprei deur die vesels, maar bundels nanobuisies het tog voorkom in sommige plekke. Die nanovesels wat MWCNT bevat is ook gebruik om nanosamestellings te maak, waar die vesels gesmelt is om net MWCNT agter te laat in die polimeer matriks. Hierdie was gedoen in beide LDPE en EVOH matrikse. Geen positiewe resultate is verkry vir die LDPE/MWCNT nanosamestelling nie, maar die EVOH/MWCNT nanosamestelling het aan die anderkant ‘n groot verbetering getoon in die meganiese eienskappe in vergelyking met EVOH sonder MWCNT. ‘n Poging was aangewend om fluoreseerende molekules aan die oppervlak van MWCNT te voeg en deur fluoresensie mikroskopie kon die verspreiding van die MWCNT in die vesels asook in die nanosamestellings gesien word. Hierdie studie het bewys dat poliolefien nanovesels gemaak kan word wat lei tot die aanwending van hierdie polimere in nog meer toepassings. Dit het ook die belangrikheid van die gebruik van nanovesels as versterking in nanosamestellings bevestig asook die gebruik van nanovesels as ‘n manier om MWCNT in ‘n matriks te plaas.