ENGLISH ABSTRACT: Electrospinning is a simple yet versatile method used for producing nanofibers from various materials, including natural and synthetic polymers, polymer blends, ceramics and metals. The high specific surface areas, high aspect ratios (length/diameter), and the biomimicking nature of nanofibers make them ideally suited for application in diverse areas, including high-performance filtration, biomedical materials for tissue engineering scaffolds, wound dressings and controlled drug release, fiber-reinforced composites and highly sensitive nano-sensors. Two of the main requirements that need to be met for electrospun nanofiber materials to become commercially viable are: (1) a process for manufacturing continuous aligned nanofiber yarns, and (2) a drastic increase in the fiber production rate of the electrospinning process. The objectives of this study were to develop a scalable process for making continuous yarns of aligned electrospun nanofibers, and to develop a needleless electrospinning method for the high-throughput production of nanofibers. Three novel processes were developed while exploring innovative ways for making yarns from electrospun fibers. Finally, a fourth process, the so-called the NanoCaterpillar process, was developed. This process can be used as a scalable method for obtaining continuous yarns of aligned nanofibers. Advantages of the process include the requirement for relatively simple equipment, the simple process variations required for obtaining yarns of different linear densities, and the fact that, as a 'dry' process, it can be used to manufacture yarns from most materials that can be electrospun. The second goal of this study was to develop a needle-less electrospinning process, capable of making nanofibers at commercially viable throughput rates. The phenomenon of bubble electrospinning was discovered and developed further. Initial exploratory studies showed that bubble electrospinning could be employed to produce nanofibers from polymers in aqueous as well as organic solutions, and that the process follows similar trends to classic electrospinning such as the dependence of fiber diameter on polymer solution concentration and the possibility of including substances in the formed fibers by including them in the spin solution. A second, more in-depth study of the bubble electrospinning process revealed that fibers could be produced at very high rates with estimates, under ideal spinning conditions, reaching 5 kg/h per square meter of bubble bath surface. Furthermore it was found that fiber yield did not depend on the size or the lifetime per bubble. Investigations into several interesting aspects of bubble and jet behaviour during bubble electrospinning, such as child bubble formation and jet-splitting, led to predictive multiple linear regression models being fitted to the experimental data to describe process variables like yield per bubble, number of jets per bubble and fiber diameters.
AFRIKAANSE OPSOMMING:
Die elektrospintegniek is 'n eenvoudige, dog veelsydige metode wat gebruik word om nanovesels van verskeie materiale, insluitend natuurlike en sintetiese polimere, polimeermengsels, keramieke, en ook metale te vervaardig. Die hoë spesifieke oppervlakareas, hoë lengte tot deursnee verhoudings en bio-naboodsende eienskappe van nanovesels maak hulle ideaalgeskik vir toepassing in uiteenlopende velde soos filtrasie, biomediese materiale vir weefselingenieurswese, wondbedekkings en beheerde vrystelling van geneesmiddels, veselversterkte saamgestelde materiale en hoogs-sensitiewe nanosensors. Twee van die hoofvereistes waaraan voldoen moet word, voordat elektrogespinde nanovesels kommersieël-lewensvatbaar kan word, is: (1) 'n proses vir die vervaardiging van kontinuë garings van gerigte nanovesels, en (2) 'n drastiese toename in die vervaardigingstempo van die elektrospinproses. Die doelwitte van hierdie studie was om 'n skalleerbare proses te ontwikkel vir die vervaardiging van kontinuë garings van gerigte nanovesels, en om 'n naaldlose elektrospinmetode te ontwikkel vir die hoë-uitset vervaardiging van nanovesels.
Drie nuwe prosesse is ontwikkel tydens ondersoeke na innoverende maniere om garings van elektrogespinde nanovesels te vervaardig. Laastelik is 'n vierde proses, die sogenaamde NanoCaterpillar proses ontwikkel. Hierdie proses kan gebruik word as 'n skalleerbare metode vir die vervaardiging van kontinuë garings van gerigte nanovesels. Voordele van die proses sluit in dat relatief eenvoudige toerusting benodig word om die konsep toe te pas, dat slegs eenvoudige veranderinge aan die proses benodig word om garings van verskillende liniêre digthede te verkry, en dat die proses, synde 'n 'droë' proses, gebruik kan word om garings te maak van meeste materiale wat gespin kan word met die elektrospintegniek.
Die tweede doelwit van hierdie studie was om 'n naaldlose elektrospinproses te ontwikkel wat nanovesels kon vervaardig teen kommersieël-lewensvatbare tempo's. Die borrelelektrospin verskynsel is ontdek en verder ontwikkel. Aanvanklike ondersoeke het getoon dat die borrelelektrospinproses gebruik kon word om nanovesels te vervaardig van polimere in water- sowel as organiese oplossings. Dit het ook getoon dat die proses soortgelyke tendense toon as die klassieke elektrospintegniek, soos die afhanklikheid van veseldeursnee aan polimeeroplossingkonsentrasie en die moontlikheid om ander stowwe in die gevormde vesels in te sluit deur dit aanvanklik in die spinoplossing in te sluit.
'n Verdere indiepte ondersoek van die borrelelektrospinproses het onthul dat vesels, onder geïdealiseerde omstandighede, vervaardig kon word teen baie hoë tempo's, na beraming 5 kg/h per vierkante meter borrelbadoppervlakarea. Verder is bevind dat die veselopbrengs nie afhanklik was van die borrelgrootte of -lewensduur nie. Ondersoeke na verskillende aspekte van die borrel- en polimeerstraalgedrag tydens die borrelelektrospinproses, soos die vorming van kind-borrels en polimeerstraalsplitsing, het gelei tot die passing van voorspellende meerfoudige liniêre regressiemodelle op die eksperimentele data, ten einde prosesveranderlikes soos opbrengs per borrel, aantal polimeerstrale, en vesels deursnee te kan beskryf.
