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Dissertation
Synthesis of new sustainable poly(ethylene)-like precursors for carbon fibres
Authors: --- ---
Year: 2017 Publisher: Leuven KU Leuven. Faculteit Wetenschappen

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Abstract

Carbon fibres are very useful building blocks for the construction of lightweight materials. Due to their light weight, they can reduce the fuel consumption of cars, but due to their high price they are not yet used on a large scale for automobile construction. The current fabrication of these fibres is expensive and also has a severe environmental impact. Therefore, a lot of research has aimed to find alternative precursor materials for these fibres such as cellulose, lignin, poly(ethylene) and so on. The downside of these precursor materials is that the performance of the resulting carbon fibres is inferior to the current carbon fibres limiting their applicability. In this work an alternative route to carbon fibre precursors is investigated by functionalising poly(olefins). The polymers were produced using ring-opening metathesis polymerisation so that double bonds remain present in the polymer. These functionalities can be used to crosslink the polymer chains after extrusion to ensure mechanical stability during carbonisation. The functionalities investigated in this work are azides, epoxides and a photoinitiator moiety. By copolymerising these functionalised monomers with non-functionalised monomers in different ratios the effect of the degree of copolymerisation on the properties of the resulting polymers can be investigated. Upon characterisation of these polymers a decrease of the melting point and crystallinity with increasing comonomer content was noticed. As well as a dependence of both these properties on the initiator used for the polymerisation. The temperature at which thermal crosslinking is induced however is a lot higher than the melting point of any of the polymers. Thermal decomposition in an inert atmosphere unfortunately did not yield any carbon, but tests with an oxidative stabilisation step yielded promising results.

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Dissertation
Synthesis of new furan-based polymers for carbon fiber production
Authors: --- --- ---
Year: 2018 Publisher: Leuven KU Leuven. Faculteit Wetenschappen

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The high strength to weight ratio of carbon fibers is of special interest for the auto-motive industry as it offers a way to reduce the weight and thus fuel consumption of a vehicle without a loss in crash worthiness. The use of carbon fibers in vehicles presents a great market opportunity with the prospects of a greener future. However, the automotive industry is reluctant to make the transition due to the high price tag associated with the present-day production of the carbon fibers. In the production procedure, a polymeric precursor is spun into a fiber form which is then converted via a heat-treatment into a fiber of at least 92 wt% carbon, termed carbon fiber. The current market is dominated by carbon fibers derived from a poly(acrylonitrile) precursor. The petroleum based nature of poly(acrylonitrile) and the complications encountered in its processing, make the carbon fiber production expensive with a severe environmental impact. Therefore, research is often aimed to realize carbon fibers with performances similar to that of poly(acrylonitrile)-based carbon fibers from a more sustainable and low-cost precursor. This work directed its focus towards the potential of a polymeric precursor derived from renewable furan-based chemicals. Because both spinnability and carbon yield of the polymer dictate its viability as carbon fiber precursor, this work was guided towards the potential of the linear structure of poly(furfuryl alcohol). However, the structure of poly(furfuryl alcohol) is not linear but rather a polymeric network which proves detrimental to its spinnability. The network formation of poly(furfuryl alcohol) was bypassed through a slight alteration of the monomer. However, polymerization of the furfuryl alcohol analogue yielded oligomers with molecular weights that were too low to ensure spinnability. The degree of polymerization could not be increased through variations in the polymerization procedure. The carbon yields of the oligomers increased with the molecular weight and did show the potential of the furan-based structure. In addition, a modification of the polycondensation between furan and acetone was attempted in which the furan would be replaced by a bifuran. However, multiple attempts to synthesize the bifuran monomer were unsuccessful.

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Dissertation
Furaan precursorpolymeer voor duurzaam, bio-gebaseerde koolstofvezel productie

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De interesse in koolstofvezel werd aangewakkerd door hun superieure fysische en chemische eigenschappen. Koolstofvezels zijn zeer sterke maar tegelijk ook lichte vezels waardoor toepassing in duurzaamheidsprojecten zoals uitstootvermindering van auto's mogelijk is. Maar de moderne koolstofvezels bezitten ook nadelen. Het productieproces van de vezel is enorm duur waardoor koolstofvezels enkel gebruikt worden voor de meest hoogwaardige doeleinden. Bovendien is de productie van koolstofvezels toxisch en schadelijk voor het milieu. Onderzoek naar meer duurzame koolstofvezelprecursoren zoals cellulose vezels werd reeds uitgevoerd. Maar deze vezels bleken kwalitatief minderwaardig te zijn. Binnen deze studie zijn we op zoek gegaan naar de productie van alternatieve, furaangebaseerde precursorpolymeren voor duurzamere koolstofvezel- productie. Als startmateriaal van de polymeren vertrekken we van het biogebaseerde hydroxymethylfurfural (HMF) dat geoxideerd wordt tot 2,5-diformylfuraan (DFF). DFF wordt gepolymeriseerd via een condensatiereactie gebruikmakend van een N-heterocyclische carbeenkatalysator tot precursorpolymeer. Bij de karakterisatie van de precursorpolymeren bleek uit TGA-waarden dat het polymeer thermisch niet volledig degradeert en dus carbonisatie een mogelijkheid is. Maar de molaire massa van het polymeer was te laag voor (koolstof)vezelproductie. Daarom hebben we het moleculaire gewicht proberen te verhogen door middel van een koppelingsreagens dat de polymeerketens onderling verbindt.

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