This project began in 2008 when Dr. Matt Davis, a scientist in the group I led at the Naval Air Warfare Center, Weapons Division, began to think about new ways to make useful materials from bio-based sources. A particular source of interest was the neutraceutical trans-resveratrol, which is a well-known anti-oxidant found in red wine and is associated with anti-aging. The chemical structure of trans-resveratrol is quite similar (but not exactly the same — and that turns out to be very important) to many of the building blocks of the plastics used in high-performance applications, including airplanes, space probes, battery housings, and the circuit boards inside a smartphone.
At that time it was recognized that there was a need for substitutes for petroleum-based materials (because people feared oil would be in short supply), but it was generally believed that such substitutes would have inferior performance, and that for any application with highly demanding performance requirements, the substitution would not work. This was a logical assumption because the switch away from bio-based materials to petroleum-based plastics early in the 20th century brought about great improvements in performance, so bio-based plastics were seen as a necessary retreat back down the performance curve.
When Matt and I first discussed these issues, we realized that for Navy applications (which we were interested in), backing down on performance would not be acceptable. (Imaging having to explain that a ship sank or a plane crashed because we didn’t want to use a petroleum-based products to build it.) But we saw a way around this issue. We knew that, for many applications, there were petroleum-based products that performed significantly better than needed when built with certain chemical functionalities. We figured that if we started at the high end and somehow minimized the “hit” from using a substitute for petroleum, we might end up with performance that was still acceptable.
To see if this idea would be feasible, we needed to find a way to extract a starting material from a renewable resource and literally make a little piece of an airplane out of it, then test it to see how well it performed. Although we could get some already-made trans-resveratrol, we wanted to use a real plant source to prove it could be done. Unfortunately, it takes a lot of grapes (or seaweed) to make resveratrol, and in the desert where we lived, we weren’t going to get much of either any time soon. So we literally turned to something in our backyard. A college intern, Ms. Jessica Cash, volunteered to go harvest the needles of creosote bushes from her backyard and try to extract a usable ingredient for us. In the Mojave high desert, creosotes are everywhere, and they are known for producing a fire-resistant oil, so we quickly got our hands on some extract and started working with it.
Those initial experiments worked well enough to convince the Strategic Environmental Research and Development Program (SERDP) to give us a grant to further explore the possibilities in 2009. That same year, I transferred from the Naval Air Warfare Center to the Air Force Research Laboratory, leaving the project behind (temporarily). To help fill the gap, I invited Dr. Benjamin Harvey at the Naval Air Warfare Center to take over my role. Dr. Harvey was an expert on creating fuels from bio-based resources, and had some great ideas about to extend his work to the area we were now working on, so he fit perfectly into the role.
In my new role at the Air Force Research Laboratory, I continued to investigate new high-performance materials for space launch vehicles. In late 2010, our laboratory was shut down for asbestos remediation for a few weeks, so I convinced my management that rather than simply sit and wait for the lab to re-open, I could at least get some collaborative work done with my former colleagues at the Navy to help them move the bio-based materials project along, and that because that project was showing some promise, doing so might help us identify some interesting new high-performance materials for rockets. As a result, I was able to return to the Naval Air Warfare Center and do the first measurements that confirmed at least one of the materials developed as part of the project was good enough for many Navy and Air Force applications. As a result of the success of those initial efforts, more project funds were secured, and the Air Force took a formal role in the effort along with the Navy.
During the next few years, the project team (now quite extensive) built and tested many new materials based on renewable resources. Our efforts won us a 2016 SERDP Project of the Year award in the Weapons and Platforms category. Not only did we find that we could minimize the performance “hit” from avoiding petroleum, we found there really was no “hit” at all. In fact, in some cases, we saw levels of performance that exceeded anything we had ever seen before … which brings us back to: resveratrol.
Once the project was well-established and we could examine many different kinds of materials, we went back and checked on our original thoughts. We made a structural material from resveratrol and were surprised to see how stable it was at elevated temperatures. We were so impressed that we contacted the Federal Aviation Administration, which is always on the lookout for new flame-resistant materials, and gave them a sample. They tested it and were also highly impressed with the results.
The important part of this discovery, however, was not the performance of the resveratrol-based material. The important part was that we were surprised by how well it performed. In other words, our expectations for the performance of bio-based materials were too low. It wasn’t simply possible to minimize the “hit” in performance, it was possible get better performance. But why?
Recall that the chemical structure of resveratrol is similar to, but not quite the same, as the petroleum-based materials. Although those differences are small, they are, from a chemical standpoint, unique. The uniqueness arises because, when chemicals are made from petroleum, the sequence of events used to make those chemicals follows one of only a few routes, determined by the economics of petroleum refining. Nature, however, uses a much wider variety of routes to make the molecules it needs, having nothing to do with petroleum refining. As a result, “nature-made” molecules have structures that are almost never seen in petroleum-based materials. For materials science, “never-seen” often means “not important enough to bother with or spend the effort to obtain”, which means that almost all of the science of studying how the properties of organic materials relate to their structure is confined to only those kinds of structures found in petroleum-based materials.
Until recently, we would have assumed that such small differences in structure really did not matter all that much, but in fact, they can matter a lot. As we began to build a database of a large number of bio-based materials for our research project, we found that we were looking at a much wider variety of chemical structures than normal for the purposes of studying performance. Because of this, the performance was more difficult to predict than anticipated (see the publications page) for more details. Yet, also because of this, the possibilities for both highly tailored and overall improved performance are much greater than expected. We now realize that our initial study has only scratched the surface.
Interestingly, what started out as a concern about the availability of petroleum has in fact matured into a concern about the limitations of petroleum for generating high-performance materials. In the future, as more renewable and sustainable sources are employed to substitute for petroleum-based products, we can expect not only to match, but also to exceed, the performance of those petroleum-based products, which gives us a compelling reason to investigate them further.