Focus on lignin to help it decay

Bio-based materials may be the new mantra when it comes to replacing petroleum-based, non-biodegradable or synthetic materials. But who would have thought that something natural could become a biodegrading headache, too?

"Everything that is bio-based does not pass the biodegradable test," says Srikanth Pilla, 42, Professor of Material Sciences at Clemson University, U.S.

Lignin, the second-most abundantly found biopolymer after cellulose, can be extremely stubborn when it comes to biodegrading. Often described as "xenobiotic", it adds to its vices by resisting microbial enzyme actions.

The lignin polymer is heterogeneous and complex. In comparison, cellulose consists of repeating chains and is therefore more conducive to breaking down safely.

So, researchers are looking at ways to deal with lignin. The polymer is abundant — 0.5-3.6 billion tonnes of it occur in nature and another 100,000-200,000 tonnes are anthropogenically produced annually, as by-product from bioethanol industries, chiefly paper and pulp.

But microbial mediation can break down lignin into much-in-demand bioplastics, a recent paper states. Another paper looks at chemically recycling lignin-based polyurethanes to extract lignin.

James Sternberg, along with Pilla, recently described in Nature Sustainability their research in extracting lignin from lignin-based foam, through a chemical recycling process that retains the functionality of the molecule so that it can be used in the synthesis of second-generation or recycled polymers. This research followed a previous study, in which the two demonstrated how polyurethane foam was created by using 100% bio-based materials, of which 50% was lignin. Polyurethane is a polymer with multiple uses — ranging from thermal insulation to lingerie.