Adhesives are applied for various uses such as bandaging a wound or wrapping a gift. Usually, these sticky substances are made of petroleum-based materials; however, imagine a highly sustainable way to produce them!
At present, a group of engineers from the University of Delaware has devised an innovative process to produce tape from a principal component of plants and trees, known as lignin—a substance usually discarded by paper manufacturers. Besides, their innovation works as good as at least two products that have already hit the market.
The team has recently reported the outcomes of the study in ACS Central Science. They have been studying more ways to recycle plants and scrap wood into “designer materials” for consumer use.
Lignin is a substance found in trees that makes them strong. It is a renewable resource. However, it is not necessary to cut down trees to obtain it since it is abundantly found in the environment. While processing wood, pulp and paper manufacturers discard the lignin, which is normally burned for heat or reaches landfills. Certain companies even willingly deliver a dump truck full of the substance for free since it is a cheaper option than disposing it in a landfill. As lignin is an abundant, cheap, and sustainable material, it offers a fine chance for some scientifically progressive recycling.
Moreover, lignin is a natural polymer, made of very large molecules formed of smaller subunits known as monomers. Certain materials and structural properties of lignin are similar to those of petroleum-based polymers such as polymethyl methacrylate and polystyrene, which are usually used in adhesives and other consumer products, such as packaging materials, cups, and so on.
“One of the thoughts that we have always had is: Can we take lignin and make useful products, and in this case, useful polymers out of it?” stated Thomas H. Epps, III, the Thomas and Kipp Gutshall Professor of Chemical and Biomolecular Engineering, Professor of Materials Science and Engineering at UD, and the corresponding author of the new paper. Specifically, Epps predicted that it is possible to use lignin to make adhesives that have toughness, strength, and scratch resistance similar to those of the petroleum-derived ones.
Before being converted into a product, lignin was broken down by scientists 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, a process that speeds up chemical reactions. For close to 10 years, Vlachos and his colleagues have refined techniques for breaking down certain wood components, such as hemicellulose and cellulose, into useful products. Their goal is to make renewable products that are environment-friendly, with unparalleled performance. Yet, when compared to other wood components, lignin is very tough to handle.
Lignin is very hard, a solid part of the biomass that is the hardest to break down. Developing a catalyst and a process to actually crack these molecules is difficult.
Dionisios Vlachos, Director of CCEI and the Delaware Energy Institute
Vlachos and his team used a commercially available catalyst material to devise a low-temperature, mild process that breaks down lignin into small, molecular fragments — a process known as depolymerization.
Subsequently, Epps used those materials to produce innovative materials by tweaking their properties for application in pressure-sensitive adhesives, substances that stick upon contact.
“We start with a biopolymer, and we end up with another polymer,” stated 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. But we can get better properties, and we can use a much greener source.
Thomas H. Epps, III
The scientists used mechanical tests to ascertain tackiness and adhesion and discovered that the performance of their tape was equivalent to that of the Scotch Magic Tape and the Fisherbrand labeling 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,” stated 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.”
In various tapes, tackifiers are added, which are substances increasing adhesion but could decrease the service life of materials.
From the Lab to Your Home
The scientists used lignin derived from poplar wood; however, they aim to investigate the potential of other plants and other woods with high lignin content, like 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?” stated Epps. Maybe it is possible to reverse engineer the materials to have different levels of stickiness, thereby resulting in products such as electrical tape, bandages, duct tape, sticky notes painter’s tape, and many more.
If I need something that is a little bit tacky, I might use a slightly different tree for that. 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.
Thomas H. Epps, III
Apart from tapes, the applications could also include things such as gaskets and seals, o-rings, rubber bands, or even car tires.
The researchers also plan to advance their processes further to be able to break down more of the lignin and enhance their processes. They also aim to perform further testing to identify the characteristics of their new materials.
Vlachos views the enormous economic potential here. “This could rejuvenate the paper industry because companies could someday sell the lignin to adhesive manufacturers,” he stated. “Or, they could do the first round of processing on site and then sell the molecules to other companies.” The group has filed for a provisional patent on this study.
Collaboration at Its Best
This study illustrates the power of cooperation between UD engineers.
It includes everything from catalyst design to streamlined separations to synthesis and characterization of high performance materials. It covers the gamut of what a chemical engineer does.
Thomas H. Epps, III
Apart from Epps and Vlachos, the authors of the paper are 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.
Funding from the National Science Foundation (CHE-1507010) and the Department of Energy — Basic Energy Sciences (DE-SC0001004) partially supported the study.