Superior plant based carbon fibers from electrospun poly-(caffeyl alcohol) lignin

Plant-sourced carbon has a valuable impact on zero carbon footprint materials for automotive, aerospace, water filtration and other applications. A new lignin, poly-(caffeyl alcohol) (PCFA, also known as C-lignin), has recently been discovered in the seeds of the vanilla orchid (Vanilla planifolia). In contrast to all known lignins which are comprised of polyaromatic networks, the PCFA lignin is a linear polymer derived almost totally from caffeyl alcohol monomers linked head to tail into benzodioxane chains via the ‘endwise’ radical coupling reactions that typify lignification. In this paper we investigate carbon fiber formed from this linear C-lignin and compare it to a Kraft lignin. The PCFA was extracted and electrospun into fibers without additional modification or blending of polymers. Nanoindentation shows an increase in transverse and axial modulus for PCFA carbon by around 250% and 25% respectively as compared to Kraft lignin carbon. Raman spectroscopy results indicate higher graphitic structure for PCFA carbon than that from Kraft lignin, as seen from G/D ratios of 1.92 vs 1.15 which was supported by XPS and TEM results. Size exclusion chromatography indicates a polydispersity index (PDI) for PCFA of 1.6 as compared to 2.6 for Kraft lignin and Zeta potential measurements show higher ionic conductivity for Kraft lignin as compared to PCFA reflecting higher impurities. The results indicate a new bio-source for carbon fibers based on this newly identified linear lignin.