Lignin as a Material Platform for High Value-Added Macromolecules

Our envisioned material platform will utilize lignin as a precursor for high value-added fibers, fuel emulsifiers and reactive intermediates for use as proppants (a necessary component in the hydraulic fracturing process). While lignin is the second most abundant polymer found in nature, its complex chemical structure and poor thermal stability limit its application-use to low-profit fillers and adhesives. Our central hypothesis is that lignin's limitations in higher cost margin materials can be reduced with surface modification by thermally stable silicon-containing precursors which impart unique surface properties. The current methodologies to modify lignin surfaces include acetylation, methylation, and carboxylation processes. In contrast, the Willoughby lab has developed a highly efficient disilazane reaction to covert the -hydroxy and -methoxy groups on lignin to -ene components. The -ene groups provide lignin a reactive group for subsequent modification to tune its hydrophilic/ liphophilic balance for tailoring surfactant properties, perform "click" or thiol-ene chemistry, or induce radical polymerization. Of significant importance is that the simple disilazane reaction (moderate temperature, atmospheric pressure) solubilizes lignin in organic solvents. This enhancement in solubility promises 1) greater compatibility with current wet and melt fiber spinning processes and 2) the ability to filter damaging inorganic contaminants from the modified lignin prior to processing. In this proposed two-year project, we intend to exploit our initial findings by partnering with the University of Kentucky's Center for Applied Energy Research (UK-CAER) to utilize their expertise in carbon fiber processing and lignin deconstruction. The objectives of this proposal are 1) to implement our reaction scheme using UK-CAER's switchgrass lignin and its oligomers, 2) combine our solubilized lignin with traditional polyacrylonitrile (PAN) for a step change in raw material costs for carbon fiber manufacture, 3) define polymerization routes with the modified "silazane" lignin for use in resins for proppants and as precursors for silicon carbide fibers; higher value products than carbon fiber alone and 4) conduct a preliminary economic analysis focusing on the use of our modified lignin in the stated material platforms. Currently, there is limited process chemistry for converting lignin to profitable advanced materials. The results of this proposal will establish the reaction parameters and surface chemistry modifications necessary for shifting the paradigm of low-profit lignin products to the utilization of lignin in high value, energy-related applications. A rich interplay between the forest biomaterials and silicon chemistry communities will be established through a fundamentally different surface modification of lignin with silicon-containing precursors. The results are expected to impart thermal stability and surface-activity enhancement to lignin macromolecules. If successful, this work will provide biorefineries in the Southeastern Sun Grant region with processing options for deriving increased value from lignocellulosic biomass. More broadly, providing value-added applications for bio-derived materials can reduce our dependence on fossil fuels, increase rural income and help to solve environmental issues caused by the use of non-renewable resources. This proposal seeks to address the USDA-NIFA and the SGP-SER priority areas of improving preprocessing for high quality feedstock from biomass from switchgrass (primary) and pine (benchmarked from our current work with Indulin AT). At the end of year 1 we will modify and characterize lignin extracted from switchgrass via the silizane method. Characterization will include neutron magnetic resonance, thermal gravitional analysis, and surface chemistry obtained via contact angle and electrokinectic analysis. These results will be compared with lignin derived from pine. At the end of year 2, the modified lignin will be processed with PAN for solution spinning fiber formation, conversion to carbon fiber and characterization. The modified lignin will also be formulated in proppant-type resin formulations. Finally, based on the final performance of the products, a preliminary cost to benefit ratio will be determined.