Lignin — a component making up 25–35% of woody biomass — is underutilized as a byproduct of biofuels production and paper-making processes.
Because of its abundance, low-cost and sustainability, lignin is being investigated as a raw material for making higher-value chemicals.
Researchers at Oak Ridge National Laboratory (ORNL; Oak Ridge, Tenn.; http://www.ornl.gov) have developed a stretchy material from waste lignin that exhibits self-healing behavior and could be used in adhesives and other industrial applications.
Scientists led by Amit Naskar extracted an oligomer from lignin with acetonitrile using an extraction method that concentrates the regions of lignin that contain carboxylic acid functional groups.
The material is a uniform lignin oligomer with a high degree of carboxylic acid functionalization and a high glass-transition temperature (Tg).
Then the team reacted the lignin oligomer with polyethylene glycol (PEG), forming an elastomeric material with a network of both covalent bonds and hydrogen bonds.
“This network contains both stiff phases, from the lignin, and soft phases, from the PEG,” explains Naskar. The resulting material is highly elastic, with the ability to stretch by over 2,000%, as well as very tough, Naskar says. In addition, the plentiful hydrogen bonds give the material the ability to self-heal if cut.
The new ORNL material is being investigated for a range of industrial applications, such as coatings, glues and hydrogels, where it is a possible bio-based replacement for dihydroxyphenylacetic acid, the derivative compound of dopamine that is responsible for the strong adhesion of mussels.
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