WEST LAFAYETTE, IN—Engineers at Purdue University are developing new types of adhesives that are sustainable. They’re turning to nature for inspiration.

“Our current adhesives create all sorts of environmental problems,” says Jonathan Wilker, Ph.D., a professor of chemistry. “Almost all glues are petroleum-based and do not degrade. The bonded materials in our products stay stuck together.

“Consequently, we cannot recycle many of the materials that we put into our recycling bins,” explains Wilker. “Discarded products will sit in landfills for centuries and, sometimes, contribute to ocean microplastics.

“Those volatile petrochemicals in these glues can be toxic, which is a further problem with current technologies,” warns Wilker. “By studying how nature makes adhesives, we are learning how to design new technologies for our future society.”

After a series of experiments on a range of different biologically sourced and sustainable ingredients, the engineers settled on epoxidized soy oil for a main component. Epoxidized soy oil is already produced globally on a massive scale.

Wilker and his colleagues added the epoxidized soy oil to malic acid, a compound known for giving apples their tart flavor. Then, they added tannic acid to provide an aspect of the chemistry that mussels use for attaching themselves to rocks and each other. Tannic acid is a component of tannins, common in trees, red wine and black tea.

Those three ingredients add up to an adhesive that is inexpensive, effective, scalable, practical to produce and completely sustainable.

“If you combine these components under the right conditions, adhesives can be made that are as strong as epoxies,” claims Wilker. “All of the components are bio-based, safe and already available [in bulk quantities]. A bonus is that the adhesive is easy to make. Basically, you can mix and heat the components.”

Other bio-based compounds can also be used with epoxidized soy oil, generating an entire family of new sustainable adhesives.

To test the adhesive’s performance, the engineers bonded together objects made out of wood, plastic and metal and then used an instrument for breaking the bonds and measuring forces. In many cases, their new adhesives held up well, sometimes performing similarly to, or even better than, traditional toxic adhesives such as cyanoacrylate and epoxy.