Researchers at Oak Ridge National Laboratory (ORNL) have developed a process that ultimately transforms the lignin byproduct of the pulp and paper industry into a thermoplastic—a polymer that becomes pliable above a specific temperature. An open-access paper on the work is published in the journal Green Chemistry.
The team accomplished this by reconstructing larger lignin molecules either through a chemical reaction with formaldehyde or by washing with methanol. Through these simple chemical processes, they created a crosslinked rubber-like material that can also be processed like plastics.
Instead of using nearly 50 million tons of lignin byproduct produced annually as a low-cost fuel to power paper and pulp mills, the material can be transformed into a lignin-derived high-value plastic. While the lignin byproduct in raw form is worth just pennies a pound as a fuel, the value can potentially increase by a factor of 10 or more after the conversion.
Amit Naskar of Oak Ridge National Laboratory, the leader of the project, noted that earlier work on lignin-based plastics utilized material that was available from pulping industries and was a significantly degraded version of native lignin contained in biomass. This decomposition occurs during harsh chemical treatment of biomass.
Here, however, we attempted to reconstruct larger lignin molecules by a simple crosslinking chemistry and then used it as a substitute for rigid phase in a formulation that behaves like crosslinked rubbers that can also be processed like plastics.—Amit Naskar
Crosslinking involves building large lignin molecules by combining smaller molecules where formaldehyde helps to bridge the smaller units by chemical bonding. Naskar envisions the process leading to lower cost gaskets, window channels, irrigation hose, dashboards, car seat foam and a number of other plastic-like products.
A similar material can also be made from lignin produced in biorefineries.
Tomonori Saito, Rebecca H. Brown, Marcus A. Hunt, Deanna L. Pickel, Joseph M. Pickel, Jamie M. Messman, Frederick S. Baker, Martin Keller and Amit K. Naskar (2012) Turning renewable resources into value-added polymer: development of lignin-based thermoplastic. Green Chem., 14, 3295-3303 doi: 10.1039/C2GC35933B