Before the lignin could be transformed into a product, it was broken down by researchers at the Catalysis Center for Energy Innovation (CCEI), a multi-institutional research center at UD established by a grant from the U.S. Department of Energy.

Dionisios Vlachos, director of CCEI and the Delaware Energy Institute, is an international expert in catalysis, processes that accelerate chemical reactions. For nearly a decade, Vlachos and his team have perfected methods to break down some wood components, cellulose and hemicellulose, into useful products. They aim to make renewable products that are better for the environment, with unmatched performance. However, compared to other wood components, lignin presents a tougher challenge.

“Lignin is very hard, a solid part of the biomass that is the hardest to break down,” said Vlachos. “Developing a catalyst and a process to actually crack these molecules is difficult.”

Using a commercially available catalyst material, Vlachos and his colleagues developed a mild, low-temperature process that busts the lignin into small, molecular fragments—a process called depolymerization.

Then, Epps used those materials to synthesize new materials, adjusting their properties for use in pressure-sensitive adhesives, materials that stick upon contact.

“We start with a biopolymer, and we end up with another polymer,” said Vlachos.

“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 Epps. “But we can get better properties, and we can use a much greener source.”

Using mechanical tests to determine adhesion and tackiness, the researchers found that their tape performed on par with Fisherbrand labeling tape and Scotch Magic Tape.

“We were expecting it to be competitive because we knew that if we could form well-defined polymers, we could engineer them to have similar performance,” said Epps. “The thing that we found a bit surprising and interesting is that our materials gave similar performance to Scotch tape and Fisherbrand tape without any additional formulation or other additives that are typically used in commercial materials to improve their performance.”

Many tapes have added tackifiers, substances that increase adhesion but can also decrease the lifetime of materials.

From the lab to your home

The research team utilized lignin sourced from poplar wood, but they plan to explore the potential of other woods and other plants with high lignin content, such as switchgrass.

“Let’s say we change to a birch tree, oak tree or pine tree, can we make these same designer materials, but with slightly different properties?” said Epps. Perhaps the materials could be reverse engineered to have varying levels of stickiness, yielding products from duct tape to electrical tape to painter’s tape to bandages to sticky notes and more.

“If I need something that is a little bit tacky, I might use a slightly different tree for that,” said Epps. “If I want something that is less tacky and leaves less residue, I might use a different tree. There is a lot of opportunity to use biodiversity to finetune the end product.”

The applications could also extend beyond tapes to include things like rubber bands, o-rings, gaskets and seals, or even car tires.

The team also aims to develop their processes further so that they can break down more of the lignin and optimize their processes. They plan to do additional testing to characterize the properties of their new materials.

Vlachos sees tremendous economic potential here.

“This could rejuvenate the paper industry because companies could someday sell the lignin to adhesive manufacturers,” he said. “Or, they could do the first round of processing on site and then sell the molecules to other companies.”

The research team has filed for a provisional patent on this work.

Collaboration at its best

This research exemplifies the power of collaboration between UD engineers.

“It includes everything from catalyst design to streamlined separations to synthesis and characterization of high performance materials,” said Epps. “It covers the gamut of what a chemical engineer does.”

In addition to Epps and Vlachos, the paper’s authors include Shu Wang, a former postdoctoral associate at UD who is now a materials scientist at Bridgestone Americas; Li Shuai, a former postdoctoral associate at UD who is now an assistant professor in the Department of Sustainable Biomaterials at Virginia Tech University; and Basudeb Saha, associate director of CCEI.

The work was partially supported by funding from the National Science Foundation (CHE-1507010) and the Department of Energy - Basic Energy Sciences (DE-SC0001004).