Engineers develop solid lubricant to replace toxic materials in farming

Researchers have developed a new class of nontoxic, biodegradable solid lubricants that can be used to facilitate seed dispersal using modern farming equipment, with the goal of replacing existing lubricants that pose human and environmental toxicity concerns. The researchers have also developed an analytical model that can be used to evaluate candidate materials for future lubricant technologies.

Modern farming makes use of various machines to accurately and efficiently plant seeds in the ground. However, it can be difficult to prevent the seeds from jamming in these machines. To keep the seeds flowing smoothly, farmers use solid lubricants that prevent the seeds from clumping up or sticking together. Unfortunately, commercially available lubricants make use of talc or microplastics, and can pose threats to farmers, farmland and pollinators.

“Lubricants are essential to modern farming, but existing approaches are contributing to toxicity in our farmlands that affect farmer health, soil health and pollinators that are essential to our food supply,” says Dhanush Udayashankara Jamadgni, co-lead author of a paper on the work and a Ph.D. student at North Carolina State University. “We’ve developed a new class of safe solid lubricants that are effective and nontoxic.”

“There is a growing body of research that suggests microplastics are problematic for both human and environmental health, and we wanted to create a new lubricant that was safe and biodegradable,” says Martin Thuo, co-corresponding author of the paper and a professor of materials science and engineering at NC State. “We ended up with something that is also relatively inexpensive, efficient, and makes use of sustainable, readily available materials.”

The new lubricant is derived from cellulose, a biodegradable, plant-based material. Specifically, the lubricant consists of millions of tiny fibers measuring 0.2-2 millimeters long and 10-40 microns across. The surface of these fibers is grafted with hydrophobic particles, which repel water. To the naked eye, the collection of engineered fibers resembles a powder.

When this powder is mixed with seeds, it reduces friction in two ways. First, the surface of the fibers is smoother than the surface of the seeds. As the fibers slip between the seeds, they reduce mechanical friction that occurs when seeds rub against each other. Second, the hydrophobic particles on the surface of the fibers repels adsorbed water on the surface of the seeds, making the fibers even more slippery. This allows seeds to travel through the farm equipment without jamming or clustering.

In proof-of-concept testing and field trials with corn and soybean seeds, the new lubricant performed at least five times better than the best commercial talc lubricants and 25 times better than microplastic lubricants.

“And the new lubricant outperforms commercial lubricants by even more when using smaller seeds, such as mustard and canola, or when there is high humidity,” says Udayashankara Jamadgni.

And that point about humidity is important.

“Right now, it is difficult for farmers to sow their fields when there is high humidity or wet weather, because this moisture causes the seeds to stick together and clog the machinery,” says Thuo. “We’ve tested our cellulose-derived lubricant in wet conditions – up to 80% humidity – and it works beautifully. That was confirmed by farmers who used our new lubricant in blind field testing.

“Our lubricant handles wet conditions so well because the hydrophobic particles repel water on the surface of the seeds and stay slick,” Thuo explains. “In addition, water vapor in the air can seep through the gaps between hydrophobic particles on the surface of the fibers and be absorbed by the cellulose, which does two things. First, it reduces the amount of moisture that is available to make the seeds stick together. Second, as the cellulose absorbs water vapor, it swells the fibers and makes them softer. Then, as the seeds and fibers are agitated in the farming machinery, the water is squeezed back out of the fibers – where it comes into contact with the hydrophobic particles, making them even more slippery.”

“We also found an additional benefit that we were not expecting at all,” says Udayashankara Jamadgni. “It has to do with the fact that most seeds used in crop agriculture are covered with a thin coat of nutrients and pesticides. When planting with conventional lubricants, some of this coating is scraped off. Pieces of seed coating that are scraped off are released in the exhaust system from the planting machinery – creating a toxic cloud that poses risks for pollinators, birds and farmers.

“We were surprised to find that our cellulose-derived lubricant drastically reduces this problem – very little of the seed coating is scraped off,” says Udayashankara Jamadgni. “This is actually the topic of our next paper.”

“In addition, we found that we are able to filter out the cellulose-derived fibers in the lubricant from the vacuum system used in farming machinery to plant the seeds,” says Thuo. “This means that very little of the lubricant itself is released into the environment – and the lubricant can actually be reused or properly disposed of. That will be in the next paper, too.”

While developing the new lubricant, the research team also developed a tool that will be useful for developing new lubricants in the future. Specifically, Thuo and Udayashankara Jamadgni collaborated with graph theory experts from the University of Michigan and the University of Southern California.

“Essentially, we’ve been able to define a parameter space that provides an analytical model using graph-based mathematical techniques to simplify what is an incredibly complex system,” Thuo says. “And that model can help researchers quickly identify promising candidates for solid lubricant applications.”

The paper, “Graph Theory Based Bioderived Solid Lubricant,” will be published Oct. 7 in the journal Matter. Co-lead author of the paper is Paul Gregory of Iowa State University. Co-corresponding authors of the paper are Paul Bogdan, an associate professor of electrical and computer engineering at the University of Southern California; and Nicholas Kotov, the Joseph B. and Florence V. Cejka Professor of Chemical Engineering at the University of Michigan. The paper was co-authored by Andrew Martin and Alana Pauls, postdoctoral researchers at NC State; Souvik Banerjee and Boyce Chang of Iowa State University; Xiong Ye Xiao and Kien Nguyen of USC; and Anastasia Visheratina and Nancy Muyanja, of Michigan.

This work was done with support from John Deere. The work also received support from the Center for Complex Particle Systems (COMPASS), which is funded by the National Science Foundation under grant 2243104 and is headquartered at the University of Michigan.

Multiple patents have been filed worldwide with regard to this technology; some have been granted (solid dry-type lubricant U.S. patent No. 11613630 and 12122901; European EP4012009B1) and others are pending (specialty seed lubricant U.S. provisional patent No. 63/837,885; network disruptor U.S provisional patent No. 63/869,643). Thuo, Udayashankara Jamadgni, Kotov, Gregory and Chang are all listed as inventors on the U.S. patents.