Effect of plasticizers and polymer blends for processing softwood kraft lignin as carbon fiber precursors
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ORIGINAL RESEARCH
Effect of plasticizers and polymer blends for processing softwood kraft lignin as carbon fiber precursors Ali Ayoub . Trevor Treasure . Luke Hansen . Tiina Nypelo¨ . Hasan Jameel . Saad Khan . Hou-min Chang . Martin A. Hubbe . Richard A. Venditti
Received: 24 June 2020 / Accepted: 1 November 2020 Ó Springer Nature B.V. 2020
Abstract Plasticizers depress the glass transition temperature (Tg) of polymers and produce a flowable material at lower temperatures. The use of plasticizers to depress Tg of lignin is important, since at high processing temperatures lignin crosslinks, making it intractable. The goal of this study was to assess plasticizers and polymer blends for the ability to retard a commercial softwood kraft lignin from crosslinking and also serve as thermal and rheological property modifiers during thermal processing in the attempt to produced moldable and spinnable lignin for lignin and carbon fiber products. The Tg of the lignin and the lignin mixed with various amounts of plasticizers and with different thermo-mechanical mixing were determined using differential scanning calorimetry. The Tg and the change in heat capacity at the glass transition
(DCp) decreased and increased, respectively, about linearly within this plasticizers range with increased plasticizer weight percentage. Gel permeation chromatography results for extruded lignin as well as extruded lignin-plasticizer blends with glycerol, N-allyurea, citric acid with and without sodium hypophosphite, and oleic acid indicate that the presence of these materials reduced the rate of molecular weight increase at temperatures between 100 and 200 °C. Continuous, homogenous films and fibers could be produced by thermal processing with plasticized lignin samples and plasticized lignin-polymer blends, but not with lignin alone. These fibers could be carbonized, yielding up to about 50% of carbon. The present findings have shown the advantages of plasticizers in thermally processing a commercial softwood kraft lignin.
A. Ayoub T. Treasure L. Hansen H. Jameel H. Chang M. A. Hubbe R. A. Venditti (&) Department of Forest Biomaterials, College of Natural Resources, North Carolina State University, Raleigh, NC 27695-8005, USA e-mail: [email protected]
Keywords Softwood kraft lignin Extrusion Plasticizers Carbon fiber Glass transition temperature Polymer blends
T. Treasure S. Khan Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695-7905, USA T. Nypelo¨ Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden
Introduction Lignin is the greatest natural source of aromatic and phenolic functional groups and is the second most abundant natural terrestrial polymer next to cellulose (Adler 1977). Regardless of the source and type, lignin
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Cellulose
Fig. 1 Structural softwood lignin model
is a complex polymer that exhibits numerous structures and bonding betwe
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