By utilizing the novel liquid–liquid phase behavior that exists between lignin and hot aqueous ethanol, agriculturally based bulk lignins derived from hybrid poplar (HP) and corn stover (CS) have been simultaneously fractionated, cleaned, and solvated for conversion to higher-value bioproducts. This unusual liquid–liquid phase behavior forms the basis for a process that we refer to as Aqueous Lignin Purification with Hot Agents, or ALPHA. Finally, ALPHA has the added advantage of using only aqueous bioethanol, the primary product of a lignocellulosic biorefinery, for the solvent system.<br/><br/>The focus of this effort has been on the conversion of fractionated and purified "ALPHA" lignins into three high-volume, higher-value co-products, namely carbon fibers, polyurethane (PU) foams, and activated carbon. Lignin is like any other polymer in that both the molecular weight (MW) and purity can have a dramatic impact on its suitability for a given application. Thus, high MW, HP lignins isolated via ALPHA could be stabilized 5X faster than either the bulk lignin or lower MW fractions, significantly enhancing commercial viability. Furthermore, the drawdown ratio for these ultraclean, high-MW lignins was also excellent (i.e., approaching 8), resulting in 7 μm dia. fibers. Thus, tensile strength and modulus values for the final carbon fibers substantially exceeded the previous best values for a hardwood lignin. Initial results for higher-MW ALPHA lignins derived from corn stover were also encouraging, with good drawdown ratios and rapid stabilization rates producing carbon fiber 7 μm in dia., having tensile properties significantly exceeding previously reported work.<br/><br/>Our work with PU foams indicates that the low MW cuts derived from ALPHA, whether obtained from HP or CS lignin, can replace the polyols at levels significantly exceeding 50%. Foam derived from both HP and CS lignin beat the "no-lignin" control in most property categories, and readily exceeded all ASTM property requirements. In particular, density and thermal resistance requirements were met, and compressive strengths matched those of the control. This application for lignin thus nicely complements the lignin needs for carbon fibers, and makes possible the conversion of a substantial fraction of lignin carbon into higher-value products.

Upgrading agriculturally based lignins with hot aqueous ethanol solutions: Precursor design for carbon fibers, polyurethane foams, and activated carbons

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