Based on current estimates, a bone-dry ton of forest residue can be converted to 59 gallons of isobutanol. What remains is approximately 1450 dry pounds of “waste product”. (Tom Spink presentation at the Idaho Small Log Conference 2013). Approximately 37% of the “waste product” or more technically speaking “co-product residual” is lignin (550 dry pounds) with the remainder being processing acids, unreacted cellulose (polysaccharides), non-fermented sugars, extractives, bark, yeast, and wood ash. The most common commercial use for residual solids is to burn them and produce heat or energy. While this strategy remains a potential option for future conversion sites and depots, NARA researchers are developing new uses for the lignin that may provide a higher value than simple energy production. Creating high-value products from the lignin-rich byproduct is essential to improve profitability of the bio-refinery.
Jinwen Zhang, NARA researcher and associate professor, and Michael Wolcott, NARA co-director and Regents professor, are both affiliated at the Composite Materials and Engineering Center at Washington State University. They lead a team that explores ways to convert lignin into molecules that can used for commercial purposes. Their most recent publication entitled Use of eugenol and rosin as feedstocks for biobased epoxy resins and study of curing and performance properties, featured in the journal Polymer International, explores the use of eugenol, a molecule that can be derived from lignin, as a bio-based source for epoxy resins.
For this work, their group developed a method to convert eugenol into a novel epoxy molecule. Epoxies are a class of molecules that contain at least one functional group known as an epoxide. The epoxide feature allows the molecule to bind or “cross link” to other molecules forming a tight bond. Consequently, epoxy molecules possess strong mechanical properties able to withstand wide temperatures and harsh chemical environments. Epoxies are used commercially in a wide range of applications including use as structural adhesives and as an additive to metal coatings.
When treated with commercially available curing agents and with a curing agent derived from rosin (resin from pines), the eugenol epoxy demonstrates similar mechanical properties and thermal stability to bisphenolA (BPA)-type epoxies that have been in commercial use since the late 1950s.
The authors state in the paper, “ If the highly selective conversion of lignin to aromatic chemicals such as eugenol can be achieved with mass production and cost effectiveness, lignin will bring great value to the chemical industry”. The term “if” looms large here, and making the lignin to eugenol conversion costs competitive with current epoxy resin production is a remaining challenge.
This work indicates that a high-grade epoxy can be synthesized from a lignin-based feedstock and represents a potential direction in converting lignin-based molecules into commercial products.