No description available.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2009. / The study concerns the use of the electrospinning technique for the formation of cellulose acetate hollow nanofibers. These hollow fibers are used to manufacture hollow fiber membranes. Important properties that should be inherent to these hollow-nanofibers include excellent permeability and separation characteristics, and long useful life. They have potential applications in filtration, reverse osmosis, and the separation of liquids and gases. It is apparent from the available literature on electrospinning and co-electrospinning that the diameter and the morphology of the resulting fibers are significantly influenced by variations in the system and process parameters, which include the solution concentration, solvent volatility, solution viscosity, surface tension and the conductivity of the spinning solution. The materials used include cellulose acetate (CA) (concentration = 11~14 wt %), (feed rate = 1~3 ml/h), acetone:dioxane (2:1) and mineral oil (feed rate = 0.5~1 ml/h) with core and shell linear velocity of 2 and 0.7 mm/min respectively. These materials were used as received without further purification. The co-electrospinning setup used comprised a compound spinneret, consisting of two concentric small-diameter capillary tubes/needles, one located inside another (core-shell/co-axial design). The internal and external diameters of the inside and outside needles were 0.3 and 1.2 mm respectively (0.3 mm shell/core gap space). The liquids CA (shell) and mineral oil (core) are pumped to the coaxial needle by a syringe pump, forming a compound droplet at the tip of the needle. A high voltage source is used to apply a potential of several kilovolts over the electrospinning distance. One electrode is placed into the spinning solution and the other oppositely charged (or neutral) electrode attached to a conductive collector. If the charge build up reaches approximately 15 kV the charged compound droplet, (poorly conductive polymer solution) deforms into a conical structure called a Taylor cone. On further increasing, the charge at the Taylor cone to some critical value (unique to each polymer system) the surface tension of the compound Taylor cone is broken and a core-shell jet of polymer solution ejects from the apex of the Taylor cone. This jet is linear over a small distance, and then deviates in a course of violent whipping from bending instabilities brought about by repulsive charges existing along the jet length. The core-shell jet is stretched and solvent is evaporated and expelled, resulting in the thinning and alignment of the fiber. Ultimately dry (most solvent having been removed) submicron fibers are collected in alignment form in a simple collector design (water bath). The shell to core solution flow rate ratio was chosen according to the parameter response of shell-core diameter of the resulting fibers in order to achieve an optimal hollow structure after removal of the mineral oil core. The mineral oil of the dry collected core-shell fibers is removed by immersion in octane. The aforementioned response is determined by measurement of core-shell diameters using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained results showed that the ability of the spinning solution to be electrospun was directly dependent on its concentration and the feed rate of the spinning solution and also parameters such as the spinning distance and type of solvents used. The preferable polymer solution concentration is 14 wt %, shell feed rate of 3 ml/hr, core feed rate of 0.5 ml/hr (2 and 0.7 mm/s core and shell linear velocity respectively), applied voltage of 15 KV, spinning distance of 8 cm and coaxial spinnerets having internal diameters of 0.3 mm and 1.2 mm core and shell needles respectively (0.3 mm shell/core gap space) have been found to make uniform cellulose acetate hollow fibers with an average inside and outside diameter of approximately 495 and 1266 nm, respectively.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Polymeric nanofibrous membranes that act as surfaces offer two compelling properties; they have extremely large surface areas that can be modified and they can offer multiple reactive sites depending on which polymer they were electrospun from. Combining nanofibrous surfaces such as these with photochromic dyes can give remarkable, light responsive materials. In this study, a terpolymer was electrospun and crosslinked (to impart insolubility to the material) to produce a nanofibrous mat that contained surface secondary-hydroxyl units and benzyl chloride units, from which monomers could grow using surface-initiated atom transfer polymerization (SI-ATRP). The surface was further fluorinated though the secondary-hydroxyl moieties to produce a hydrophobic crosslinked nanofibrous surface. n-Butyl acrylate and a photochromic spiropyran dye were copolymerized from the surface using SIATRP, in order to produce a surface that exhibited reversible adhesion towards a water droplet using ultraviolet and visible light as a stimulus to change between the two states. This in principle would allow the droplet to roll off and stick to the surface respectively. Although the surface displayed a colour change when switched, proving that the SI-ATRP had taken place, the droplet of water remained attached to the surface in both states. / AFRIKAANSE OPSOMMING: Polimeriese nanovesel membrane wat dien as oppervlaktes bied twee aantreklike eienskappe; hulle het baie groot oppervlakareas wat gemodifiseer kan word en hulle bied veelvuldige reaktiewe punte, afhangende van die polimeer waarvan hulle ge-elektrospin is. Deur sulke nanovesel oppervlaktes met fotochromiese kleurstowwe te kombineer, kan uitstekende lig reagerende materiale verkry word. In hierdie studie is ‘n terpolimeer ge-elektrospin en daarna gekruisbind (om die materiaal onoplosbaar te maak) om ‘n nanovesel web te kry wat oppervlak sekondêre-hidroksiel en benzielchloried eenhede bevat. Monomere kan dan vanaf hierdie eenhede groei deur middel van oppervlak-geïnisieerde atoomoordrag polimerisasie (OI-AOPR). Die oppervlak was verder gefluorineer via die sekondêre-hidroksiel eenhede om ‘n hidrofobiese, gekruisbinde nanovesel oppervlak te vorm. n-Butielakrilaat en ‘n fotochromiese spiropiraan kleurstof is gekopolimeriseer vanaf die oppervlak deur middel van OI-AORP om sodoende ‘n oppervlak te skep wat omkeerbare adhesie van ‘n water druppel gee as ultraviolet en sigbare lig as stimulus gebruik word om tussen die twee toestande te wissel. In beginsel sal die water druppel vanaf die oppervlak kan afrol én daaraan vassit, afhangende van die toestand van die oppervlak. Alhoewel die oppervlak van kleur verander het met die wisseling tussen die twee toestande, wat as bewys dien dat OI-AORP wel plaasgevind het, het die druppel water bly vassit aan die oppervlak in beide toestande.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Needle-electrospinning is an uncomplicated and highly versatile nanofiber (fiber diameter of 50 to 500 nm) production technique. Nevertheless the process can only produce 0.01 to 1.0 g/h/m2 of nanofibers, unpractical for large-scale productions. Bubble-electrospinning, in the presence of surfactants, is a novel nanofiber mass-production technique developed at Stellenbosch University.[1] The technique is similar to needle-electrospinning only that the surface area of a bubble surpasses that of a solution droplet, making it possible for multiple jets to form on the bubble surface at high field strengths. Thus far little research has been done on the influence of solution properties on the bubble-electrospinning technique. During electrospinning the solution experiences three competing forces, namely, surface tension (contracting force), charge repulsion (expanding force), and viscosity (resistance to flow). The first aim of this study was to obtain better understanding on the influence of three significant solution properties (viscosity, conductivity and surface tension) on bubble-electrospinning in terms of bubble lifetime, bubble size, average number of jets and the resultant fibers. The solution properties were varied using a range of polymer and surfactant concentrations. A second aim was to obtain better understanding on the comparison of the bubble-electrospinning process between two polymer solutions, namely Polyvinyl alcohol (PVOH) solutions containing sodium lauryl ether sulphate (SLES) surfactant, and Polyacrylonitrile (PAN) solutions containing silicone surfactant. Results indicated that the solution viscosity and conductivity increased with increasing polymer concentrations for both polymer solutions. In addition, both the solution surface tensions were not influenced by polymer concentration. With regards to bubble-electrospinning of PVOH solutions, results indicated that the average number of jets per bubble was influenced by the polymer concentration. Regarding PAN solutions, bubble lifetime and the average number of jets was influenced by polymer concentration. Results indicated that the solution viscosity increased and surface tension decreased with increasing surfactant concentration for both polymer solutions. PVOH solution conductivity increased whilst PAN solution conductivity decreased with increasing surfactant concentrations. With regards to bubble-electrospinning of PVOH solutions, the bubble lifetime and bubble size was significantly influenced by the SLES concentration. Regarding PAN solutions, the silicone surfactant concentration had no significant effect on the bubble-electrospinning process. Overall, PVOH fiber diameters decreased with increasing surfactant concentration. There was no common trend between the bubble-electrospinning of PVOH and PAN solutions in relation to their solution properties. It was concluded that solution viscosity, conductivity and surface tension are not the only significant contributing parameters to the bubble-electrospinning process. / AFRIKAANSE OPSOMMING: Die naald-elektrospinproses is 'n eenvoudige, hoogsaanpasbare tegniek wat gebruik word vir die maak van nanovesels. Nanovesels het tipies 'n deursnee van 50nm tot 500nm. Ongelukkig is dit onprakties vir grootskaalse produksie omdat die uitset daarvan beperk is tot 0.01 tot 1.0 g/h/m2. Die borrel-elektrospinproses, waar elektrospinstrale gespin word vanaf die oppervlak van borrels op die oppervlak van die spinoplossing en waar die borrels gestabiliseer is m.b.v. sepe, is 'n nuwe tegniek wat ontwikkel is by die Universiteit van Stellenbosch. [1]. Die tegniek is soortgelyk aan die naald-elektrospinproses in dié sin dat die elektrospinstraal vorm vanaf 'n gelaaide halfsfeervormige oppervlak in die spinoplossing, maar die aansienlik groter oppervlakarea van die borrel in die borrel-elektrospinproses maak dit moontlik om verskeie elektrospinstrale gelyktydig op die oppervlak van die borrel te onderhou. Dit lei tot baie hoër doeltreffendheid in die saamgroeppering van die strale en gevolglik tot hoër nanoveseluitsette. Tot dusver is daar weinig navorsing aangaande die invloed van oplossingseienskappe op die borrel- elektrospintegniek gedoen. Tydens die elektrospinproses ervaar die oplossing drie kompeterende kragte, naamlik: oppervlakspanning (sametrekkende krag), elektrostatiese afstoting (afstotende krag) en viskositeit (vertragende effek op vloei van die oplossing). Die hoofdoelwit van hierdie navorsing was om 'n beter begrip te kry van die invloed van drie gemete oplossingswaardes, d.w.s. viskositeit, elektriese geleidingsvermoë en oppervlakspanning op die borrel-elektrospinproses. Die impak van hierde waardes is spesifiek geëvalueer in terme van borrellewensduur, borrelgrootte, gemiddelde hoeveelheid elektrospinstrale per borrel en die morfologie van die vesels wat in die proses gevorm is. Die tweede doelwit van die studie was om 'n vergelyking te tref tussen die mees optimale oplossingswaardes in die borrel-elektrospinproses van twee baie uiteenlopende polimeerspinoplossings, naamlik polivinielalkohol (PVOH), met natrium dodesieletersulfaat (SLES) as die borrelstabiliserende seep en poliakrilonitriel (PAN) oplossing, met 'n silikoonseep as die borrelstabiliserende seep. Resultate het getoon dat die viskositeit en elektriese geleidingsvermoë toeneem met toename in polimeerkonsentrasie vir beide PVOH- en PAN-oplossings. Verder is oppervlakspanning in beide gevalle nie beduidend beïnvloed deur die polimeerkonsentrasie nie. In die geval van die borrel-elektrospin van die PVOH-oplossings het resultate daarop gedui dat die gemiddelde aantal elektrospinstrale per borrel moontlik beïnvloed kon word deur die polimeerkonsentrasie. In die geval van borrel-elektrospin van PAN-oplossing is bevind dat polimeerkonsentrasie die borrelleeftyd en die gemiddelde aantal elektrospinstrale per borrel beïnvloed. Resultate het ook getoon dat die viskositeit vermeerder en die oppervlakspanning afneem met toename in die konsentrasie van die sepe in beide die polimeeroplossings. Die PVOH-oplossing se elektriese geleidingsvermoë het vermeerder terwyl dit verminder in die geval van die PAN-oplossings met 'n toename in die seepkonsentrasie. Tydens borrel-elektrospin van die PVOH-oplossings is beide borrelleeftyd en borrelgrootte beduidend beïnvloed deur die SLES konsentrasie. By die borrel-elektrospin van PAN-oplossings het die silikoonseepkonsentrasie nie 'n beduidende invloed gehad op die borrelleeftyd en borrelgrootte nie. Oor die algemeen het die gemiddelde PVOH veseldeursnee afgeneem met toename in seepkonsentrasie. Geen algemene tendens kon waargeneem word tussen die optimale oplossingswaardes vir borrel-elektrospin van die PVOH- en die PAN-oplossings onderskeidelik nie. Die gevolgtrekking is dat die viskositeit, elektriese geleidingsvermoë en oppervlakspanning nie die enigste beduidende waardes is wat bepaal of die borrel-elektrospinproses sal werk vir 'n spesifieke polimeeroplossing nie.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Two series of poly(methyl methacrylate)-graft-poly(dimethylsiloxane) copolymers were synthesized via conventional free radical copolymerization of methylmethacrylate and monomethacryloxypropyl terminated PDMS macromonomers of different lengths. It is shown how these copolymers can be electrospun to produce the copolymer nanofibers. The affects of copolymer compositions, the electrospinning tip-to-collector (TCD) distance and the concentration of the polymer solution on the fiber morphology are discussed. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to establish the surface topography as well as the fiber morphology of the electrospun copolymer nanofibers. It is also shown that these nanofibers produce superhydrophobic surfaces where the preferential surface segregation of the PDMS component is combined with the roughness of the nanofiber surface. It is shown that after exposure of these nanofiber surfaces to corona discharge, the initial superhydrophobic surfaces become easily wettable. The samples show the phenomena of hydrophobicity recovery after corona exposure. The rate and extent of this recovery depends on the PDMS content of the nanofibers as well as the time of corona treatment. The hybrid copolymer nanofibers were evaluated as potential reinforcing fillers for cross linked polydimethylsiloxane compounds. The fibers show a remarkably good distribution in the PDMS matrix and show a dramatic improvement in the mechanical properties of the composites.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The work presented in this dissertation describes the use of coaxial electrospinning of two miscible polymer solutions in the preparation of core-shell fibres with a semicrystalline core of poly(L-lactic acid) and an amorphous shell of poly(D,L-lactic acid). Additionally it describes using these fibres in the production of single polymer composite yarns and films. These materials can potentially be used in applications that require biodegradable and fibre-reinforced composite materials e.g. suture yarns. Traditional methods, such as TEM, when used to analyse the core-shell fibre structure were not successful with the polymer system used. A method was developed to validate core-shell fibre structure by selective dissolution of the shell material and correlating analyses of the separated components using differential scanning calorimetry (DSC) and optical rotation. The effects of solution concentration and flow rate on resultant core-shell fibre diameters were investigated. Core-solution flow rate was shown to be the most significant variable affecting the core and core-shell fibre diameters. A thermal processing window exists between the glass transition temperature of the amorphous PDLLA shell material and the crystalline melting temperature of the semicrystalline PLLA core material. Heating these core-shell fibres within this processing window resulted in flow and fusion of overlapping shells of these core-shell fibres at their surfaces while the fibrous core components remained intact and reinforced the resulting composite material. This approach was used to produce single polymer composite yarns and films. Thermal treatments on yarns were shown to increase crystallinity of the cores and therefore the modulus and yield strength of the fibres when compared to untreated yarns. / AFRIKAANSE OPSOMMING: Die werk wat in hierdie tesis voorgelê word, beskryf die gebruik van koaksiale elektro-spinnery van twee wedersydsoplosbare polimeeroplossings in die vervaardiging van kern-skilvesels met ‘n gedeeltelik-kristallyne kern van poli-Lmelksuur (PLLA) en ‘n amorfe skil van poli-D,L-melksuur (PDLLA). Verder beskryf dit die gebruik van hierdie vesels in die vervaardiging van enkel-polimeer saamgestelde-materiaalgarings en -films. Hierdie materiale kan moontlik gebruik word in toepassings wat bio-afbreekbare en veselversterkte saamgestelde materiale vereis, soos byvoorbeeld chirurgiese steke. Die polimeervesels wat in hierdie studie gebruik is, kon nie gekaraktiseer word met behulp van transmissie-elektronmikroskopie (TEM), wat gewoonklik gebruik word in die bestudering van kern-skilvesels, nie. ‘n Alternatiewe karakteriseringsmetode is ontwikkel om te bevestig dat die gevormde vesels wel ‘n kern-skilstruktuur het. Hierdie metode het behels dat die skil van die kern-skilvesel selektief opgelos is, waarna beide komponente (d.i. kern en skilmateriale) bestudeer is met behulp van differensiële skanderingskalorimetrie en optiese rotasie. Die invloed van polimeeroplossingskonsentrasie en –vloeitempo op die gevormde kern-skilvesels is daarna ondersoek en die vloeitempo van die kernoplossing is geïdentifiseer as die prosesinsetwaarde wat die mees beduidende invloed het op die deursnee van die vesels. Daar bestaan ‘n temperatuurinterval tussen die glasoorgangstemperatuur van die amorfe PDLLA skilmateriaal en die kristallyne smeltpunt van die gedeeltelikkristallyne PLLA kernmateriaal. Verwerking van die kern-skilvesels by ‘n temperatuur binne hierdie interval het gelei tot vervloeiing en samesmelting van die oorvleuelende skille van die kern-skilvesels, terwyl die veselagtige kernkomponente van die vesels heel gebly het en opgetree het as versterking binne-in die saamgestelde materiaal wat gevorm het. Hierdie benadering is gebruik om enkelpolimeersaamgestelde- materiaalgarings en –films te vervaardig. ‘n Vergelykende studie tussen onbehandelde en hitte-behandelde enkel-polimeer-saamgesteldemateriaalgarings het aangetoon dat die hittebehandeling gelei het tot ‘n verhoging in die kristalliniteit van die veselkerne en daarom ook ‘n verhoging in die modulus en breeksterkte van die garings tot gevolg gehad het.

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Novel silicone nanocomposites were prepared using poly(acrylonitrile) (PAN) based reinforcing fibres as well as multi-walled carbon nanotubes (MWCNTs). Compatibility of the fibre fillers with the silicone matrix required the synthesis of novel amphiphilic, organic–inorganic graft copolymers of PAN and poly(dimethylsiloxane) (PAN-g-PDMS). These fibre precursor materials were synthesised via the “grafting through” technique using conventional free radical copolymerisation. The PDMS macromonomer content in the feed was varied from 5 wt% to 25 wt% and the molecular weights of the macromonomer were 1000 g.mol-1 and 5000 g.mol-1. The solvent medium of the precipitation reaction was optimised at a volume ratio of 98% benzene to 2% dimethylformamide (DMF). Successful incorporation of PDMS yielded graft copolymer blend materials of PAN-g-PDMS, blended with PAN homopolymer and unreacted PDMS macromonomer. A gradient elution profile was developed to track the successful removal of the PDMS macromonomer via hexane extraction. The gradient profile showed that as the PDMS content in the feed increased, the number of graft molecules in the blend increased relative to the number of PAN homopolymer molecules. The crystallisability of the PAN segments was shown to decrease as the PDMS content increased. The synthesised polymer was used as precursor material for the electrospinning of fibre fillers. The electrospinning of the precursor material was successfully achieved using 100% DMF as electrospinning solution medium. The amphiphilic nature of the precursor material in DMF resulted in self-assembled aggregate structures in the electrospinning solution. An increasing PDMS content was shown to affect the aggregation of the precursor material, and resulted in an increase in the solution viscosity. The “gel-like” solutions limited the achievable fibre morphological control when altering conventional electrospinning parameters such as voltage, tip-to-collector distance, and solution concentrations. The rapid evaporation and stretching of the solution during electrospinning, combined with the phase segregated amphiphilic molecules in solution and the crystallisation of the PAN segments resulted in (non-equilibrium morphology) fully porous fibres. The crystallinity was shown to decrease after electrospinning of the fibre precursor materials. Successful incorporation of surface oxidised MWCNTs into the electrospun fibres was achieved. The content of nanotubes was varied from 2 wt% to 32 wt%. The MWCNTs reduced the mean fibre diameters by acting as cross-linkers between the PAN segments and increasing the solution conductivity. The nanotubes dispersed well throughout the porous structure of the fibres and aligned in the direction of the fibre axis. Fabrication of silicone composites containing nonwoven and aligned fibre mats (with 8 wt% MWCNTs in the fibres, and without) was successfully achieved. The compatibilisation of the PDMS surface segregated domains allowed excellent dispersion and interaction of the PAN based fibre fillers with the silicone matrix. Mechanical analysis showed improved properties as the PDMS content in the fibre increased. The highest PDMS content fibres did, however, exhibit decreased properties. This was ascribed to increased PDMS (soft and weak) content, decreased crystallinity and increased fibre diameter (lower interfacial area). Dramatic improvements in strength, stiffness, strain and toughness were achieved. The most significant result was an increase in strain of 470%. The mechanical results correlated with results of SEM analysis of the fracture surfaces. The dramatic improvements in properties were a result of the fibre strength and ductility, as well as the mechanism of composite failure. / AFRIKAANSE OPSOMMING: Nuwe silikonnanosamestellings is berei deur gebruik te maak van poli(akrilonitriel) (PAN) gebaseerde versterkende vesels wat multi-ommuurde koolstof nanobuisies bevat het. Versoenbaarheid van die vesels met die silikonmatriks het die sintese van nuwe amfifiliese, organies–anorganiese ent-kopolimere van PAN en poli(dimetielsiloksaan) (PAN-g-PDMS) benodig. Die vesel voorlopermateriaal is deur middel van ‘n “ent-deur” vryeradikaalkopolimerisasie gesintetiseer. Die inhoud van die PDMS makromonomeer in die reaksie het gewissel vanaf 5% tot 25%. Die gebruik van twee verskillende molekulêre massas makromonomere is bestudeer (1000 en 5000 g.mol-1). Die optimale oplosmiddelmengsel vir die neerslagreaksie was 'n volume verhouding van 98% benseen tot 2% dimetielformamied (DMF). Suksesvolle insluiting van PDMS het versnitmateriale van PAN-g-PDMS kopolimere gemeng met PAN homopolimere en ongereageerde PDMS makromonomere gelewer. 'n Gradiënteluering- chromatografiese profiel is ontwikkel om die suksesvolle verwydering van die PDMS makromonomere via heksaanekstraksie te bepaal. Die gradiëntprofiel het aangetoon dat indien die PDMS inhoud in die reagense verhoog is, die aantal entmolekules relatief tot PAN homopolimeermolekules ook verhoog het. 'n Toename in PDMS inhoud het egter 'n afname in kristallisasie van die PAN segmente tot gevolg gehad. Die gesintetiseerde polimeer is gebruik as die beginmateriaal vir die elektrospin van veselvullers. Die elektrospin van die beginmateriaal was suksesvol wanneer 100% DMF as elektrospinoplosmiddel gebruik is. Die amfifiliese aard van die beginmateriaal in DMF lei tot outokonstruksie van aggregaatstrukture in die elektrospinoplossing. Toenemende PDMS inhoud beïnvloed die outokonstruksie van die molekules in oplossing en het gelei tot 'n toename in die oplossings se viskositeit. Die "gelagtige" oplossings beperk die haalbare vesel se morfologiese beheerbaarheid wanneer konvensionele elektrospin parameters soos elektriese spanning, punt-tot-versamelaar afstand, en oplossingkonsentrasies gewysig word. Die vinnige verdamping en strek van die oplossing tydens elektrospin, gekombineer met die fase-geskeide amfifiliese molekules in oplossing en die kristallisasie van die PAN segmente, het gelei tot (nie-ewewig morfologie) volledige poreuse vesels. Die kristalliniteit van die veselbeginmaterial het afgeneem nadat elektrospin toegepas is. Die insluiting van die oppervlak-geoksideerde multi-ommuurde koolstof nanobuisies in die elektrogespinde vesels was suksesvol. Die inhoud van die nanobuisies het gewissel van 2 wt% tot 32 wt%. Die MWCNTs het die gemiddelde veseldeursnit verminder deur op te tree as kruisbinders tussen die PAN segmente van die molekules. Die nanobuisies was goed versprei deur die poreuse struktuur van die vesels en dit was gerig in die rigting van die vesel-as. Bereiding van die silikonsamestellings bestaande uit nie-geweefde en gerigte veseloppervlakke (met en sonder 8 wt% multi-ommuurde koolstof nanobuisies in die vesel) was suksesvol. Die versoenbaarheid tussen die oppervlak van die PDMS-geskeide gebiede en die silikonmatriks laat uitstekende verspreiding en interaksie van die PAN-gebaseerde veselvullers met die silikonmatriks toe. Meganiese analise het aangetoon dat die fisiese eienskappe verbeter het namate die PDMS inhoud in die vesel vermeerder het. Die vesels met die hoogste PDMS inhoud het egter verswakte eienskappe getoon. Dit is toegeskryf aan ‘n verhoogde PDMS inhoud (sag en swak), ‘n afname in kristalliniteit en ‘n verhoogde veseldeursnit (laer grensoppervlakke). Dramatiese verbeterings in sterkte, styfheid, verlengbaarheid, vervorming en taaiheid is bereik. Die mees betekenisvolle gevolg was 'n toename in die verrekking van 470%. Die meganiese resultate is gekorreleer met SEM ontleding van die brekingsoppervlakke. Die veselkrag en vervormbaarheid, sowel as die meganisme van die splyting van die samestellings, het tot die dramatiese verbeterings in die meganiese eienskappe gelei.

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The main objective of this study was to develop electrospun nanofibres with both antimicrobial and antibiofouling properties for possible application in water filtration. To do this, two routes were investigated: firstly, the use of biocides and bactericidal copper salts to introduce bactericidal properties on electrospun nanofibres. Secondly, the modification of polymers using furanone compounds to obtain nanofibres with the ability to repel microbial attachment. Fabrication of biocide-containing PVA nanofibres was successful. This was achieved through direct doping of PVA solutions with AquaQure which is an aqueous biocide comprising of mainly Cu2+ and Zn2+, prior to the electrospinning process coupled with chemical crosslinking using glyoxal. The conventional needle based electrospinning technique was used to fabricate these nanofibrous mats. The presence of the constituents of AquaQure on surfaces of PVA/AquaQure nanofibrous mats was confirmed using energy dispersive x-ray analysis (EDX). ATR/FTIR, XRD, TGA, DSC and SEM techniques were used to do chemical and thermal analysis of the nanofibres in comparison with pristine PVA nanofibres. These nanofibres demonstrated antimicrobial activity of up to 5 log against the Gram-positive strain S. aureus Xen 36 and Gram-negative strains E. coli Xen 14, S. typhimurium Xen 26, P. aeruginosa Xen 5 and K. pneumoniae Xen 39. Because of crosslinking, these fibres also demonstrated good water stability. Leaching of the ions constituting AquaQure was limited and compared with South African national standards for drinking water, the water filtered through these nanofibress was deemed safe for human consumption. Bioluminescence imaging and fluorescence microscopy were used to confirm antimicrobial activity results obtained from plate counting. These nanofibres demonstrated satisfactory antimicrobial efficiency but did not repel microbial attachment. The second part of this study entailed the investigation of copper-doped PVA and SMA nanofibres for antimicrobial activity. Although bactericidal properties of copper are well documented, its selection was based on the fact that it is the main constituent of the AquaQure. Bubble electrospinning was used instead of needle electrospinning to upscale nanofibre production. Similar techniques as those used in PVA/AquaQure nanofibres were used to characterize the copper functionalized nanofibres. Even though these nanofibres demonstrated exceptional antimicrobial efficacy (up to 5 log) for all the strains, bioluminescence imaging indicated a trend for these cells to enter a dormant state on contact with the copper containing-nanofibres. The last part of this project involved testing of free furanone compounds as well as surface-tethered furanone-modified nanofibres for their antibiofouling potentials. To do this, blends of 2,5-dimethyl-4-hydroxy-3(2H)furanone (DMHF) (5% wt/vol) with PVA (10% wt/vol) were prepared and electrospun to produce PVA/DMHF nanofibres. The free furanones and furanone-modified nanofibres demonstrated not only antibiofouling properties but also antimicrobial activity. Other furanone compounds with 3(2H) and 2(5H) cores were synthesized. The synthesis of these furanone compounds (5-(2-(2-aminoethoxy)ethoxy)methyl)-2(5H)furanone and 4-(2-(2-aminoethoxy)-2,5-dimethyl-3(2H)-furanone) was successful. Their structures and molar masses were confirmed using 1H NMR and ES mass spectroscopy. These furanones were then covalently immobilized on the SMA backbone. To test their antimicrobial and antibiofouling activity, the furanone-modified polymer was dissolved in an ethanol and methanol mixture (1:1) and electrospun to produce nanofibres. The free furanone and furanone-modified SMA nanofibres derived from 4-(2-(2-aminoethoxy)-2,5-dimethyl-3(2H)-furanone demonstrated high antibiofouling and antimicrobial efficiency against the Gram-positive strain S. aureus Xen 36 and Gram-negative strains E. coli Xen 14, S. typhimurium Xen 26, P. aeruginosa Xen 5 and K. pneumoniae Xen 39. The 2(5H) furanone on the other hand had limited activity against the strains. These nanofibres were also characterized and compared with their pristine polymer counterparts and leaching experiments were conducted using GC-MS. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie studie was om nanovesel filtrasie nanofibre met beide antimikrobiese en aanpakwerende eienskappe te ontwikkel. Twee verskillende metodes is ondersoek. Eerstens is biosiede en bakteriee-dodende koper soute gebruik om antimikrobiese nanovesels te lewer. Tweedens is nanovesels met furanoon samestellings gemodifiseer om nanovesels te lewer wat mikrobiese aanhegting voorkom. Die fabrisering van biosied-bevattende PVA nanovesel nanofibre was suksesvol. AquaQure, ‟n biosied wat hoofsaaklik uit Cu2+ en Zn2+ bestaan, is direk by PVA oplossings gevoeg voor die elektrospin proses, en is gevolg deur chemiese kruisbinding deur middel van “glyoxal”. Die nanovesels is neergele in ‟n ongeweefde mat deur middel van die konvensionele naald-gebasseerde elektrospin proses. Verspreidings X-staal analises (EDX) is gebruik om die teenwoordigheid van AquaQure komponente in en op die oppervlakte van die PVA/aquaqure nanovesel matte te bevestig. ATR/FTIR, UV-Vis, XRD, TGA, DSC en SEM tegnieke is gebruik vir chemiese en termiese analises om sodoende PVA/aquacure nanovesels met ongemodifiseerde PVA nanovesels te vergelyk. PVA/aquacure nanovesels het ‟n antimikrobiese aktiwiteit van tot 5 log reduksie getoon teen Gram-positiewe S. aureus Xen 36 en Gram-negatiewe E. coli Xen 14, S. typhimurium Xen 26, P. aeruginosa Xen 5 en K. pneumoniae Xen 39. Die vesels was stabiel in water na kruisbinding. Slegs beperkte uitloging van Aquaqure Cu2+ en Zn2+ ione is waargeneem, en water wat deur die PVA/aquacure nanovesels gefiltreer is, is volgens Suid Afrikaanse Nasionale Standaarde vir drinkwater steeds veilig vir menslike gebruik. Behalwe vir die plaat-tellingsmetode het bio-lumiserende fotos en fluoroserende mikroskopie ook die antimikrobiese aktiwiteit van die vesels bevestig. Die vesels het bevredigende antimikrobiese efektiwiteit getoon, maar kon nie mikrobiese aanhegting voorkom nie. In die tweede gedeelte van die werk is die antimikrobiese aktiwiteit van PVA en SMA vesels wat met koper verreik is, ondersoek. Alhoewel die bakteriee dodende eienskappe van koper reeds goed gedokumenteer is, is hierdie ondersoek gedoen op grond van die feit dat koper een van die hoof komponente van aquaqure is. Nanovesels is uit koper-verreikte oplossings van PVA en SMA deur middel van die borrel-gebasseerde elektrospin tegniek gefabriseer, ten einde die opbrengs van nanovesels te verhoog. Fisiese kruisbinding deur middel van hitte behandeling is toegepas ten einde die stabiliteit van die vesels in water te verbeter. Dieselfde karakteriseringstegnieke wat gebruik is vir die PVA/aquacure vesels is op hierdie vesels toegepas. Alhoewel die vesels uitstekende antimikrobiese aktiwiteit van tot 5 log reduksie gedemonstreer het, het bio-lumiserende beeldvorming getoon dat die selle ‟n dormante stadium binnegaan na kontak met hierdie vesels. In die laaste gedeelte van die projek is vrye furanoon samestellings en nanofibre met oppervlak-gehegde furanone getoets vir aanpakwerende potensiaal. Om dit te bewerkstellig was „n mengsel van 2,5 – dimethyl-4-hydroxy-3(2H) furanone (DMHF) (5% wt/vol) en PVA (10% wt/vol) voorberei en gebruik om PVA/DMHF nanovesel filtrasie nanofibre te produseer deur middel van die elektrospin proses. Die vrye furanone en furanoon-gemodifiseerde nanofibre het nie alleen aanpak weerstandbiedende einskappe gedemonstreer nie maar ook antimikrobiese eienskappe. DMHF was gebruik as die begin material om furanoon samestellings te produseer met 3(2H) en 2(5H) kerne. Die sintesis van hierdie furanone se samestellings (5-(2-(2-aminoethoxy)ethoxy)methyl)-2(5H)furanone en 4-(2-(2-aminoethoxy)-2,5-dimethyl-3(2H)-furanone) was suksesvol. Hulle strukture en molere massas was bevestig met 1H NMR en ES massa spektrometrie. Hierdie furanone is daarna kovalent ge-immobiliseer op die SMA rugbeen. Om hulle antimikrobiese en aanpakwerende aktiwitiet te toets, is die furanoon-gemodifiseerde polimeer opgelos in „n etanol en metanol mengsel (1:1) en ge-elektrospin om nanovesel filtrasie nanofibre te produseer. Die furanone en furanoon-gemodifiseerde nanovesel filtrasie nanofibre afkomstig van 4-(2-(2-aminoethoxy)-2,5-dimethyl-3(2H)-furanone het hoe aanpakwerende en antimibrobiese effektiewitiet getoon teenoor die Gram-positiewe S. aureus Xen 36 en Gram-negatiewe E. coli Xen 14, S. typhimurium Xen 26, P. aeruginosa Xen 5 and K. pneumoniae Xen 39. Hierdie nanovesel filstrasie nanofibre is ook gekarakteriseer en vergelyk met die ongemodifiseerde polimeer. „n Uitlogings eksperiment is uitgevoer deur gebruik te maak van GC-MS.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Antimicrobial fibers are very useful in various fields such as air and water purification, wound dressings and protective bandages, where sterile environments are essential. The nonwoven nanofiber mats or membranes are able to filter out microorganisms and potentially kill several threatening pathogenic bacteria. In this thesis, a variety of styrene-maleimide copolymer derivatives were prepared based on the modification of poly(styrene-co-maleic anhydride with various primary amine compounds. All prepared copolymer derivatives were electrospun to nanofiber mats using the needle electrospinning technique. For the characterization, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the thermal properties of the electrospun fiber mats. Scanning electron microscopy (SEM) was carried out to observe fiber dimensions and morphology. The antibacterial activity of electrospun fiber mats was evaluated against different bacteria including Staphylococcus aureus (Gram-positive), Escherichia coli and Pseudomonas aeruginosa (Gram-negative). The evaluation study utilized different tools to test for antibacterial activity and mode of cell death, including bioluminescent imaging, fluorescence imaging and the viable cell counting method. Excellent antimicrobial activity was obtained against the different strains especially against Staphylococcus aureus. Fiber mats containing tertiary amino groups, phenol or quaternary ammonium groups had the strongest antimicrobial properties. / AFRIKAANSE OPSOMMING: Antimikrobiese vesels is baie nuttig in verskeie toepassingsgebiede, soos lug- en watersuiwering, wondbedekkings en beskermende verbande, waar ‘n steriele omgewing noodsaaklik is. Die ongeweefde nanovesel matte of membrane is in staat om mikroorganismes te verwyder deur filtrasie, maar kan ook verskeie patogeniese bakterieë doodmaak. In hierdie proefskrif is ‘n verskeidenheid stireen-maleimied kopolimeer afgeleides gesintetiseer, gebaseer op die modifikasie van poli(stireen-ko-maleïne anhidried) met verskeie primêre amien verbindings. Nanovesel matte van al die gesintetiseerde kopolimeer afgeleides is gemaak deur gebruik te maak van die naald-elektrospin tegniek. Die termiese eienskappe van hierdie nanovesel matte is bestudeer deur gebruik te maak van differensiële skandeer kalorimetrie (DSK) en termogravitasie analiese (TGA) as karakteriseringsmetodes. Die vesel dimensies en morfologie is bestudeer deur skandeer elektronmikroskopie as karakteriseringsmetode te gebruik. Die antibakteriële aktiwiteit van die gespinde vesel matte is geëvalueer teen verskillende bakterieë, naamlik Staphylococcus aureus (Gram-positief), Escherichia coli en Pseudomonas aeruginosa (Gram-negatief). Die evalueringstudie het verskillende instrumente gebruik om vir antibakteriële aktiwiteit en meganisme van seldood te toets, insluitend bioluminiserings beelding, fluoressensie beelding en die lewensvatbare sel tellingsmetode. Uitstekende antimikrobiese aktiwiteit is verkry teen die verskillende rasse, veral teen Staphylococcus aureus. Vesel matte met tersiêre aminogroepe, fenol of kwaternêre ammoniumgroepe het die sterkste antimikrobiese eienskappe gehad.

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Polyacrylonitrile, (PAN), polymers are of interest due to their many unique characteristics in comparison to most other fibre forming polymers. The focus of this study was the effect of electrospinning variables and additives on their unusual thermal properties and internal molecular morphology with the objective of improving the performance of this fibre in industrial application, or at least contributing to the understanding of how the fibre processing variables affect the thermal performance. The process of electrospinning was used to process samples of PAN fibres with additives in order to determine their effect on the molecular orientation and crystallinity of the resultant nano- and micronsized fibres. The effect of additives in the forms of low molecular weight oligomers, blends of conductive polymers and nanoparticles and conductive salts (mainly copper and lithium based) on the molecular structure and thermal properties is reported. In addition the effect of certain electrospinning processing variables such as the PAN polymer grade, the type of solvent, the temperature, the spinning voltage and the spinning distance were evaluated in terms of their effect on the resultant fibre molecular structure. The crystallinity and molecular orientation are quantified using various analytical techniques including: Fourier-Transform Infra-Red Spectroscopy (FTIR); Differential Scanning Colorimetry; (DSC) Thermal Gravimetric Analysis, TGA, Scanning and Transmission Electron Microscopy; Wide-Angle X-ray Diffractometry, XRD, Small-angle Neutron Scattering; SANS, Solid-state 13C Nuclear Magnetic Resonance Spectroscopy; NMR, and Electron-spin Resonance Spectroscopy, ESR. The researcher has ascertained in this study that the orientation of electrospun PAN is comparable to that in commercial wet-spun fibres when the electrospinning field strength is greater than 0,75 kV per cm. The process of electrospinning leads to chemical degradation of the PAN polymer only previously noted by other fibre scientists after heating PAN fibres to more than 280 C. This is due to the high mechanical stress on the high surface area electospun fibres spun into an oxygen rich air atmosphere. The addition of certain salts, particularly lithium chloride and copper nitrate, to the PAN electrospinning dope by the researchers produced fibres with improved thermal stability in comparison to the control PAN samples with no additives. In addition these salts lower the endotherm for the production of carbonized fibres from PAN fibres and will therefore make more structured, stronger, high tenacity carbon fibres. The XRD revealed that through the addition of certain salts to disrupt the dipole interations in PAN, that fibres with a 2D hexagonal crystal structure can be electrospun and have a structure similar to wet spun PAN. It is shown that fibres in a non-aligned electrospun mat have a 3D crystal structure and lower molecular orientation that wet spun fibres. Some industrial applications of electrospinning using PAN fibres are developed and reported. / AFRIKAANSE OPSOMMING: Polyakrilonitrielpolimere (PAN) is van belang weens die baie unieke eienskappe wat hulle het in vergelyking met die meeste ander vesel-vormende polimere. Die fokus van hierdie studie op die effek van verskeie veranderlikes en byvoegmiddels op hul buitengewone termiese eienskappe en interne molekulêre morfologie, met die doel om die werksverrigting van hierdie vesel in industriële toepassings te verbeter, of ten minste by te dra tot die begrip van hoe die vesel-prosesveranderlikes die termiese werksverrigting beïnvloed. Die elektrospinproses is gebruik om monsters van PAN met bymiddels te prosesseer om vas te stel wat die effek sou wees op die molekulêre oriëntering en kristalliniteit van die gelewerde nano- en mikrongrootte vesels. Verslag word gelewer oor die effek van bymiddels in die vorm van oligomere met „n lae molekulêre gewig, mengsels van geleidende polimere en verskillende nano-partikels en geleidende soute (meestal koper- en litium-gebaseerd). Die effek van sekere veranderlikes in die elektrospinproses, soos die PAN polimeer-graad, die temperatuur, die tipe oplosmiddel, die spin-spanning en spin-afstand, is geëvalueer in terme van hulle effek op die vesels wat gelewer word. Die kristalliniteit en molekulêre oriëntering word gekwantifiseer deur verskeie analitiese tegnieke te gebruik, onder meer: Fourier-Transform Infrarooispektroskopie; Differensiële Skandeerkolorimetrie; Termiese Gravimetriese Ontleding; Skandeeringelektronmikroskopie; Transmissie Elektron Mikroskopie; Wye-hoek X-straal Diffraktometrie; Klein-hoek Neutronstrooiing; Vaste-toestand 13C Kern Magnetiese Resonansiespektroskopie; en Elektronspin Resonansiespektroskopie. Dit is in hierdie studie vasgestel dat die oriëntering van elektro-gespinde PAN vergelykbaar is met kommersiële nat-gespinde vesels as die elektro-spin veldsterkte groter is as 0,75 kV per cm. Die elektro-spin proses lei tot chemiese degradasie van die PAN polimeer, wat voorheen slegs deur ander vesel-wetenskaplikes waargeneem is nadat PAN tot meer as 280 C verhit is. Dit word veroorsaak deur die hoë meganiese spanning op die hoë-oppervlakarea vesels wat in „n suurstofryke lug-atmosfeer gespin word. Die byvoeging van sekere soute, veral litiumchloried en kopernitraat, by die PAN elektro-spin spinlak (dope) deur die navorser het vesels gelewer met verbeterde termiese stabiliteit in vergelyking met die kontrole PAN-monsters sonder bymiddels. Verder verlaag hierdie soute die endoterm vir die produksie van gekarboniseerde vesels uit PAN-vesels, en dit sal daarom meer gestruktureerde, sterker koolstofvesels met hoë taaiheid lewer. X-straaldiffraksieanalise het gewys dat gewone elekrospin vesels ‟n driedimensionele struktuur het maar as gevolg van die byvoeging van sekere soute, wat die dipoolinteraksies in PAN opbreek, dat vesels wat 'n soortgelyke tweedimensionele struktuur het as dié van groot skaalse kommersiële nat-spin vesels, maklik d.m.v. die elektrospinproses berei kan word. Enkele nywerheidstoepassings van elektrospin is ontwikkel, en beskryf.