Enhancing asphaltene spinnability through polymer blending
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Carbon fibres are important structural reinforcement materials used in high performance applications where high strength, high stiffness and low weight are required. Carbon fibres are commonly used in the automobile, construction, wind energy, aerospace and defence industries. In the automobiles sector, the demand for carbon fibres is higher as most manufacturers intend to develop fuel-efficient lightweight vehicles because of strict carbon emission regulations imposed by various countries. At present, more than 90% of carbon fibres are made from expensive PAN based precursors and the high cost of precursors limits its application on large scale. Hence, there is a need to look for an alternate low-cost precursors for carbon fibres production. Asphaltenes consists of large polyaromatic and polyaliphatic cyclic systems with low H-to-C ratios. They are suitable for producing carbonaceous materials such as carbon fibres. However, the variation in the viscoelastic properties of asphaltenes due to its source variability is a major limitation in utilizing them for carbon fibre production. In order to achieve the desired viscoelastic properties and also to improve the spinnability of asphaltenes, we attempt to blend asphaltenes with thermoplastic polymers of comparable Hansen solubility parameters. Three weight fractions(5%, 10% and 20%) of polystyrene (PS), polymethylmethacrylate (PMMA), and polyethylene-co-vinyl-acetate (EVA) were added to the pristine asphaltene by commonly used mixing methods: solution mixing and melt blending. All three blends showed improvement in spinnability in comparison to the pristine asphaltene, with EVA resulting in blends that can be melt spun continuously for longer times when compared to other polymer blends. Fibres with smallest diameters are produced from EVA blends of the polymers tested. We link the derived blends microstructure to their rheological properties, as well as the ease of spinnability. The rheological signature of asphaltene is not significantly changed by EVA blending when compared to other polymers and confocal images of the blends reveal better compatibility between EVA and asphaltene. We attribute this phenomenon to the ability of EVA to break down larger asphaltene aggregates into smaller ones, and thereby allow better alignment during spinning. Also, the favourable interactions between vinyl acetate (polar group) in EVA and asphaltenes enhanced the spinnability.