Since the 1990s, Michael Kessler has worked on refining polymers with healing agents and catalysts that seal microcracks caused by moisture getting into the polymer and degrading the material.
As reported earlier this year on the website of ASM International, the materials-focused information and training association, Kessler’s process mixes catalysts and microcapsules with a liquid healing agent into the polymer. Microcracks eventually rupture the capsules and release the healing agent, which then interacts with the catalyst to form a polymer chain that fills the cracks.
Over the course of his research, Kessler—an associate professor of materials science and engineering at Iowa State University—has experimented mostly with petroleum-based healing agents and various catalysts such as copper. More recently, though, he’s been developing biorenewable polymers with healing properties from vegetable oils.
During the past five years, working with Richard Larock, a distinguished professor of chemistry at the university’s Ames Laboratory, Kessler has created polymer materials with healing agents made from corn and linseed and tung oils. “As you know, there’s a big push towards ‘green,’ and what we’ve been experimenting with comes from renewable sources that are available in large quantities,” he tells Builder.
Kessler sees potential applications for self-healing polymers in products such as adhesives and caulking. A number of companies already have emerged that use this process, such as Autonomic Materials in Champaign, Ill., which makes self-healing coatings. And Kessler himself is conducting research funded by an Iowa-based window manufacturer to develop a vegetable oil–based alternative to that supplier’s line of glass-fiber pultruded window frames. (Kessler thinks this process might be perfected within five years.)
He notes, however, that healing agents won’t improve the imperviousness of a product’s exterior surface to environmental exposure. The healing efficiency of biorenewable polymers is still below that of standard composites.
He sees a “bigger opportunity” in the next step his research has taken, one that might play a quicker commercial role: the further development of oil-based resins. “We’ve been trying different strategies to polymerize these components.” For example, he’s taken DDGS—distiller’s dried grains with solubles, which is a coproduct when ethanol is produced—and wheat straw, and reduced that mixture to vegetable-based material that can be pressed into a board-like substance.
“We’ve made samples, and have published our findings,” says Kessler, who intimates that this process might be closer to realization than the healing-agent science.