Lignin is the second most abundant renewable carbon source, making up about 30% of the non-fossil fuel-based carbon on Earth. It is in all vascular plants, where it forms cell walls and provides plants with rigidity. Lignin allows trees to stand, gives vegetables their firmness and makes up about 20%–35% of the weight of wood. The material holds great promise as a precursor for biobased materials and fuels, but it is also notoriously difficult to extract from plants.
The material is usually separated during papermaking and biorefining, but these processes often contaminate and significantly alter lignin's chemical and physical properties, decreasing its value. So most lignin is either burned to produce fuel and electricity or used in low-value products, such as for cement additives or as a binder in animal feed. Producing a more homogenous lignin provides the opportunity to pursue high-value material development to replace petroleum-derived plastics and polymers.
"Because of its heterogeneity, lignin can't be used as a valuable material despite centuries of effort," said Zhang, who holds a joint appointment with Pacific Northwest National Laboratory. "The saying has been that 'you can make anything out of lignin, except money.' There's so much heterogeneity in the molecules that nobody can reliably make things out of it."
In their work, the researchers used a solvent to separate the lignin from wheat straw and were able to preserve and control its key properties, producing a more uniform molecule with a consistent molecular weight that makes it more useful for industry. The lignin extracted was light-colored, which is more like the lignin that exists in nature.
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