Engineers from the University of Delaware have developed a material to produce pressure-sensitive adhesives while lowering waste going into landfills. Adhesives are typically created out of a petroleum-based material that is not good for the environment. Researchers found that lignin, a substance that helps keep trees strong, can be used to create pressure-sensitive adhesives and limit landfill waste. The lignin-based adhesive performs just as well as two tapes currently on the market.

This is an illustration representing the transformation of trees into tape. Engineers at the University of Delaware have developed a novel process to make tape out of a major component of trees and plants called lignin. Source: University of Delaware/ Illustration by Joy Smoker

Lignin is cheap, abundant and a sustainable source. In paper and pulp producing plants, scrap wood containing the natural polymer lignin is either transported to a landfill or burned. Both of these options are harmful to the environment. The researchers discovered that this wood can be upcycled into sticky materials like adhesives. Lignin has a similar structure to the petroleum-derived polymers that are currently used to create tape and other sticky adhesives.

The researchers broke down the lignin at the Catalysis Center for Energy Innovation (CEI), before the team was able to transform it into an adhesive.

"Lignin is very hard, a solid part of the biomass that is the hardest to break down," said Dionisios Vlachos, director of CCEI and the Delaware Energy Institute and an international expert in catalysis. "Developing a catalyst and a process to actually crack these molecules is difficult."

Because it is so difficult to break down, the team had to create an entirely new process. The team used a commercially available catalysis with a new a mild, low-temperature process called depolymerization. Depolymerization busts the lignin into small, molecular fragments. The materials were then synthesized and pressed to create the pressure-sensitive adhesives that stick when put in contact with a surface.

"We can use the same separation, purification, polymerization, and characterization methods to make these materials as one can use to make the current commercial, and petroleum-based, analogues," said Thomas H. Epps, III, the Thomas and Kipp Gutshall Professor of Chemical and Biomolecular Engineering, Professor of Materials Science and Engineering at UD, "But we can get better properties, and we can use a much greener source."

After creating the lignin pressure-sensitive adhesive, the researchers tested it against two popular tapes currently on the market, Fisherbrand labeling tape and Scotch Magic Tape. The lignin pressure-sensitive adhesive performed just as well as both of the tapes and the researchers believe that it will perform just as well as most brands currently on the market.

The lignin used to create this pressure-sensitive adhesive was pulled from poplar wood but other woods, like switchgrass, could be used. Depending on which wood is used, different levels of residue and stickiness for all kinds of tape ranging from duct tape to Post-It notes.

Pressure-sensitive adhesives aren't the only thing that is lignin could be used to create. The researchers say that lignin could be used to create O-rings, gaskets, seals, tires and more.

The next step for this research is to optimize the process and break down lignin even more. They also want to test the lignin further and see what else they could create out of it.

The paper on this research was published in ACS Central Science.