Eco-Friendly Lignin Glue Binds Carpet

Lignin is a cross-linked phenolic polymer that serves as a reinforcing matrix to hold cellulose fibers together in plants. But as an inert waste product of paper and biofuel production, lignin is usually burned to generate heat and electricity. Researchers in Spain have now developed a process to repurpose waste lignin by using laccase enzymes produced by plants and fungi to convert it to a biodegradable adhesive for wool carpeting (Green Chem. 2014, DOI: 10.1039/c4gc00063c). Styrene-butadiene latex adhesives currently used to bind carpet fibers to a rigid backing material are inexpensive. But the synthetic cross-linked polymer adhesive makes it difficult to separate the fiber from the backing for recycling. So most carpeting is disposed of in landfills or burned. As a possible solution, Tzanko Tzanov and coworkers at Polytechnic University of Catalonia have been treating lignin with laccases. The enzymes oxidize phenolic groups to partially depolymerize lignin and form reactive quinone groups. The degraded lignin then self-polymerizes and the quinone groups cross-link with amines in the wool. Tzanov’s team is working with the European joint venture Erutan to use the new adhesive in all-natural wool carpet production. Instead of being incinerated in its afterlife, Tzanov notes, the fully biodegradable carpet can be shredded and mixed with soil for agricultural uses.