Megan Robertson, assistant professor of chemical and biomolecular engineering at the University of Houston Cullen College of Engineering, has won a $100,000, two-year Norman Hackerman Advanced Research Program (NHARP) grant from the Texas Higher Education Coordinating Board to develop fruit and vegetable-based materials for wind turbines. Out of 45 proposals submitted for the NHARP grant, only 11 received funding. The purpose of the NHARP grant program is to encourage and provide support for basic research in biomedicine, energy and the environment.
Robertson will be working with a class of polymers (which are long, chain-like molecules made up of repeating units) called epoxy resins, a type of adhesive material you can buy in any hardware store. Epoxy resins are very commonly used for a wide variety of applications, from coating floors and countertops to structural composites – and, more recently, for wind turbine blades.
Traditional epoxy resins are partially derived from a compound called bisphenol A, a petroleum-derived molecule commonly referred to as BPA. BPA has garnered media attention in recent years for its possible toxicity and harmful effect on humans, spurring more research into using alternative, non-petroleum-derived molecules to replace BPA in plastics and resins.
But BPA-based epoxy resins have desirable traits such as high strength and stiffness, which is why these traditional polymers are so vital to producing wind turbines and other structural components that must undergo constant mechanical and environmental stress.
However, like all materials, current petroleum-based epoxy resins also have some deficiencies. Although strong and stiff, epoxy resins are also very brittle, and after being exposed to stresses for long periods of time – such as the wind shear against wind turbine blades that are constantly turning – the material will become fatigued and eventually fail. Robertson is hoping to enhance the performance and durability of these materials so they can withstand environmental and mechanical stress for a much longer time – and to make these wind turbine materials much “greener” in the process.
“One goal of this project is to make materials that will be more ductile and tough compared to current materials, and another major goal is to make materials that are sustainable and environmentally friendly,” Robertson said. “There’s really two components to this research: we want to move away from petroleum as a source for polymers, and we want these new materials to have superior properties as well.”
If anyone is capable of finding a stronger and more desirable material than petroleum-based polymers for wind turbines, it’s Robertson. Her laboratory specializes in studying plant-based products for plastics and rubbers. Robertson’s research into plant-based polymers even won her the much-coveted National Science Foundation’s (NSF) CAREER Award last January, one of the most prestigious grants given to young investigators.
Applying her plant-based polymer expertise to the field of wind energy made wonderful sense, said Robertson, especially since the University of Houston has its very own offshore wind technology center, the National Wind Energy Center, which received a $2.3 million grant from the U.S. Department of Energy in 2010. “The state of Texas is also investing in wind as an energy source, so it seems very relevant to be working on materials for that alternative energy source here in Houston,” said Robertson.
For epoxy resins, Robertson’s group is looking into replacing BPA with phenolic acids – compounds found in fruits and vegetables. “We can incorporate nontoxic, fully renewable materials which will ideally have a lower environmental impact than petroleum derived materials, but will also be strong, stiff and tough, and will perform really well in this specific application for wind turbines,” Robertson explained. The primary reason Robertson’s team chose phenolic acids to replace BPA-derived molecules in traditional epoxy resins is because of the materials’ similar molecular structures, which Robertson said should result in biobased epoxy resins with similar properties to the BPA-based resins
Robertson’s group is also investigating the incorporation of vegetable oils into epoxy resins, which will make the materials biodegradable, providing additional end-of-life options such as disposal in a compost facility. “We want to look at the full lifecycle of a material – not only what the source of the material is, but what happens to the material after the end of its lifecycle,” Robertson explained. Currently, no epoxy resins can be recycled, but Robertson believes this shouldn’t be the case. Her group’s uniquely holistic approach to developing alternative, sustainable materials for wind turbines is quite a bit more compelling once you take into consideration the sheer size of the wind turbine blades that will need to be disposed of: many can be as large as a football field.
Once the wind turbine is no longer usable, its enormous mechanical components must be disposed of somehow, somewhere. Whether the blades are incinerated, buried in a land fill, or ground up into smaller pieces, all of that non-recyclable waste is going to end up somewhere and is going to cause some amount of environmental damage. “So, if we invest further in wind technology, waste will be a problem,” Robertson said. However, with the plant-based epoxy resins Robertson and her team are developing, wind turbine blades could simply be dropped off at an industrial compost facility to undergo normal biodegradation, causing no additional harm to the environment.
In addition to synthesizing plant-based polymers, Robertson’s research group seeks to characterize the properties of these newly developed polymers in order to better understand the correlations between the molecular structure of materials and their properties. In doing so, Robertson’s hope is that their findings will help other polymer researchers identify not only the plant-based polymers with the best mechanical properties, but those that make the most sense in terms of sustainability and environmental impact.
Once all of the research results are in, Robertson and her lab group will incorporate their findings into an outreach program she’s developed in conjunction with North Shore Senior High School located in the Houston’s Galena Park suburb. The program, called “Materials Day at UH,” takes place annually and is currently in its third year. “We bring high school students here to campus and many engineering professors participate,” Robertson explained. “The students do lab experiments and other hands-on projects, and the goal is to introduce them to engineering in a fun way so they can see if they are interested in pursuing engineering as a career.”