Browsing by Author "Siebert, Piere-Andre John"
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- ItemElectrospun carbon nanotube filled composite nanofibers by non-covalent compatibilization(Stellenbosch : Stellenbosch Univesity, 2016-03) Siebert, Piere-Andre John; Mallon, Peter E.; Stellenbosch University. Faculty of Engineering. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: This study covers the successful production of poly(acrylonitrile) (PAN)/multi-walled-carbon-nanotube (MWCNT) fibrous composites by the incorporation of noncovalently functionalized MWCNTs in various loading fractions. In maintaining the sp2 hybridization as opposed to the conventional covalent functionalization, the conjugated MWCNT structure is maintained and in doing so preserves the mechanical and conductive properties commonly associated with these fillers. This allows for the optimum transference of desired property/properties to the produced composite assuming sufficient filler dispersion. MWCNTs are functionalized by polymeric compatibilizers of mono- and multi pyrene functional character. The pyrene moiety allows for the noncovalent 𝜋-𝜋 stacking interaction to the conjugated surface of MWCNTs by strong van der Waals forces. Mono pyrene functional poly(acrylonitrile) (Py-PAN) polymers were synthesized via Atom Transfer Radical Polymerization (ATRP) from presynthesized pyrene functional initiators namely 1-pyrenemethyl-2-bromoisobutyrate and 1-pyrenebutyl-2-bromoisobutyrate respectively. The synthesis of PAN polymers of α-chain end pyrene functionality was also attempted by the relatively unexplored redox initiated polymerization by catalytic cerium ammonium nitrate (CAN) from 1-pyrenemethanol and 1-pyrenebutanol initiators respectively. The synthesis proved challenging from the proposed initiators and with relatively low yields even after an extensive method development in an effort to achieve optimum reaction conditions. Multi pyrene functional PAN polymers (PAN-co-PyMMP) was successfully prepared via Conventional Free Radical (CFR) copolymerization of conventional acrylonitrile (AN) monomers and presynthesized (1-pyrene)methyl-2-methyl-2-propenoate (PyMMP) macromonomers in producing a PAN based polymers of protruding pyrene moieties along the polymer chain. The multi pyrene functional copolymer is successfully prepared to three predetermined PyMMP compositions (or mol% functionality) by variation of the monomer feed ratio. The synthesized initiators as well as the monomer and functional polymers were analyzed by 1H-NMR analysis confirming the isolation of the hypothesized products. 1H-NMR was also implemented to determine the average composition of the pyrene moiety incorporated into both of the structurally alternate functional PAN polymers presented as the mol% pyrene functionality. Mono- and multi-functional variations of the PAN polymer were exposed to increasing amounts of MWCNTs and analyzed by 1H-NMR following reported instances of a quenching phenomenon being seen in the 1H-NMR spectra of signals representing protons taking part in 𝜋-𝜋 stacking interactions (protons protruding from the pyrene moiety). The analysis produced a quenching trend of the polymers as the MWCNT loading is increased. These trends are confirmed by the more common method of tracking these noncovalent 𝜋-𝜋 stacking interactions by the quenching phenomenon apparent from the UV-fluorescence analysis of the pyrene moieties. Trends observed are presented to be linear as the mono-functional polymer is exposed to increasing amounts of MWCNTs where as the multi-functional polymer shows a greater initial quenching followed by what seems to be an inversion point at a 20 wt% to 30 wt% MWCNT composition after which a linear trend emerges upon a further increase of MWCNT loadings comparable to what is seen for the mono-functional polymer. The quenching analysis suggests a stronger MWCNT/functional-polymer interaction for the multi-functional polymers at similar mol% pyrene functionalities. As envisioned, electrospinning is used to prepare the fibrous composite PAN/MWCNT materials that were prepared by the noncovalent functionalization of pristine MWCNTs via the mono and multi pyrene functional PAN compatibilizers. This lead to the successful dispersion of the MWCNT filler throughout the fiber matrix in an aligned state along the fiber axis, as shown by scanning electron microscopy (SEM) and transition electron microscopy (TEM) analysis. A preliminary study was undertaken to produce PAN/graphene fibrous nanocomposites using the novel compatibilizers, synthesized in this study. Association analysis with compatibilizers indicated weaker 𝜋- 𝜋 stacking interactions when compared to the MWCNT fillers. Further analysis sugest poor graphite exfoliation and filler dispersion within the fibrous matrix. The carbonization of noncovaently funtionalized fibrous MWCNT/PAN composites was sucsessful as shown by SEM analysis.