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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/3996 |
| Date | 03 1900 |
| Creators | Greyling, Corinne Jean |
| Contributors | Sanderson, Ronald D., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Rights | University of Stellenbosch |
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