Carbon fibers derived from liquefied and fractionated poplar lignins: The effect of molecular weight

Lignin recovered from poplar, a key woody biomass resource proposed for lignocellulosic refineries, was investigated for conversion into carbon fibers. Aqueous solutions of ethanol at selected temperatures and compositions, where the requisite solvent and liquefied-lignin phases form, were used to purify and fractionate hybrid poplar (HP) lignin using the Aqueous Lignin Purification with Hot Agents (ALPHA) process. Sugars (<0.1%) and ash (0.01 +/- 0.01%) content of the highest molecular weight fraction (Mw = 52 kDa) approached the limits of detection. This 52 kDa fraction could be dry spun with excellent stability and was subsequently converted into carbon fibers having strength (1.1 +/- 0.2 GPa) and modulus (78 +/- 8 GPa) essentially double those previously achieved with neat poplar and other hardwood lignins. Of equal importance, stabilization times were decreased by a factor of five. Such stabilization and strength/modulus improvements are essential for reducing the overall manufacturing cost of carbon fibers being proposed for cost-sensitive applications.

Automated summary

This study investigates the conversion of lignin from poplar into carbon fibers and its importance. The researchers found that the Aqueous Lignin Purification with Hot Agents (ALPHA) process could effectively purify and fractionate hybrid poplar lignin. The resulting high molecular weight fraction had very low sugar and ash content, and could be spun into stable carbon fibers. The strength and modulus of these carbon fibers were double those achieved with neat poplar lignin, and the stabilization time was reduced by a factor of five.