Carbon fibers represent a class of materials with enormous potential for many material and other engineering applications for our society. There are projections that by 2020 the actual demand for carbon fibers will be such that the traditional poly-acrylonotrile precursors used today will not be enough to address the projected demand. Consequently, it is imperative that new precursors based on the foundations of Green Chemistry need be developed. Technical lignins present us with formidable challenges but also with enormous opportunities and they are to be explored in detail during this presentation. In our earlier effort, we have embarked in discussing the importance of propargylation chemistry on lignin to synthesize lignin macromonomers for thermal polymerization <i>via</i> Claisen rearrangement. We have also discussed that molecular weight and glass transition temperatures of the thermally polymerized lignin improves significantly. The intricate polymer structure created within lignin as a result of the benzopyran thermal polymerization chemistry (see Scheme 1) is offering a regular covalently linked framework from which, after carbonization, a carbon fiber material could be produced. As such, thermally polymerized propargylated softwood lignin emerges as a prospective material for the synthesis of bio-based Carbon Fiber precursor. Various reactivity considerations were addressed by a series of experiments where initially Acetone Soluble Kraft Lignin (ASKL) was propargylated, thus occupying readily accessible and highly reactive phenolic–OHs, followed by methylation of the remaining phenolic OH’s to limit phenoxy radical induced thermal polymerization. As anticipated, the installation of the propargyl groups in more reactive positions, more readily prone to Claisen rearrangement and thermal polymerization events, offered much better developed molecular weights able to offer Carbon Fibers.

Toward carbon fibers from single component Kraft lignin systems: An application of green chemistry with forest biomaterials

255th National Meeting (2018)

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