(413b) Tailoring the Molecular Weight of Purified Lignins for Materials Applications
Lignin is like any other polymer in that the molecular weight (MW) can have a dramatic impact on its suitability for a given application. Furthermore, polymer purity can be an equally important factor if the desired materials properties are to be achieved. Two large and growing markets have been identified for lignin use, where both MW and purity can play an important role: (1) high-performance carbon fibers for automotive applications and (2) rigid polyurethane foams for spray insulation for buildings. In both cases, we hypothesize that todayâs commercial lignins have too broad a molecular weight (MW) distribution and are too low in purity to give acceptable performance. Preliminary results with lignins of controlled MW and high purity are encouraging. For example, very clean, high-MW lignins isolated via ALPHA were converted into carbon fibers almost 40% stronger than any previously reported from lignin. For rigid polyurethane foams, preliminary data suggest that very clean lignins of low molecular weight and polydispersity with high hydroxyl content would be ideal as a replacement for polyols. The Aqueous Lignin Purification with Hot Agents (ALPHA) process is being investigated for controlling the MW and polydispersity, purity, and chemical functionality of lignin fractions. Hot aqueous solutions of acetic acid and acetone are each being investigated as the renewable solvents for effecting the desired separations. NMR is being used to quantify the effect of ALPHA solvent and operating conditions on the chemical functionality of the fractions being isolated.