The TuFF Age

The TuFF Age

UD researchers tackle new task in making complex material more viable for building aircraft

TuFF — Tailored Universal Feedstock for Forming — is a strong, highly aligned, short-fiber composite material that can be made from many fiber and resin combinations. Created at the University of Delaware’s Center for Composite Materials (CCM), it can be stamped into complex shapes, just like sheet metal, and features high-performance and stretchability up to 40%.

Since its introduction, CCM researchers have explored applications for TuFF, from materials for repairing our nation’s pipelines to uses in flying taxis of the future.

Now, armed with $13.5 million in funding from the U.S. Air Force, UD mechanical engineers and co-principal investigators Suresh Advani and Erik Thostenson along with industry collaborators Composites Automation and Maher and Associates are working on ways to improve manufacturing methods for TuFF.

“I am really excited at the opportunity to mature the TuFF pre-pregging process and demonstrate high-throughput composite thermoforming for Air Force relevant components,” said David Simone of the U.S. Air Force.

The goal is to enable lighter-weight composites to become cost-competitive with aluminum for creating small parts found in air vehicles.

Advani explained that when it comes to making aircraft materials more cost-efficient, reducing a material’s weight even a mere kilogram, just 2.2. pounds, will reduce fuel consumption and emissions and can result in thousands of dollars in savings over time.

This is because aircraft are heavy. A Boeing 747, for example, weighs a whopping 404,600 pounds. A B2 Stealth Bomber in the U.S. Air Force, meanwhile, tips the scale at over 43,000 pounds.

“In general, the aerospace industry wants to reduce weight and replace metals,” said Advani, George W. Laird Professor of Mechanical Engineering. TuFF is a good option because the material can achieve properties equivalent to the best continuous fiber composites used in aerospace applications.

Advancing TuFF thermosets

Until now, most of the work around TuFF has focused on thermoplastic composite materials that melt when heated, becoming soft and pliable, which is useful for forming. By contrast, TuFF thermosets have a higher temperature threshold, making them useful for aerospace applications. But TuFF thermosets have manufacturing challenges, too, including the long manufacturing times necessary to make a part.

In this new project, Thostenson and Advani will work on ways to improve the viability of thermoset TuFF composites. To start, the researchers will characterize the starting materials’ mechanical properties to understand how to make TuFF thermosets reliably and consistently. The research team will explore whether they can make the material in a new way, using thin resin films and liquid resins. They will test the limits of how the material forms and behaves under pressure and temperature, too.

“How does it stretch during forming in a mold? What shapes can we make? When does it tear or thin or develop voids that can compromise material integrity?” said Advani.

Having a database for such properties and behaviors will be useful in understanding TuFF material capabilities and limits, and to inform efforts to model and design parts with TuFF.

Thostenson, professor of mechanical engineering, is an expert in structural health monitoring of materials. He will advance ways to embed sensor technology into TuFF thermosets. This would allow the researchers to see from the inside how the material is forming and curing during its manufacture, in hopes of being able to gauge—and improve— the material’s damage tolerance.

It’s intricate work. To give you an idea of scale, a single layer of TuFF material is approximately 100 microns thick, about the diameter of the average human hair. The carbon-nanotube sensors Thostenson plans to integrate into the material are smaller still—one billionth the width of a human hair.

“This would allow us to do health monitoring for the materials and parts during service life, but you could also imagine using sensor technology to detect a defect during manufacturing,” said Thostenson.

While it remains to be seen whether this is possible, Thostenson said having this ability could result in real cost savings for manufacturing methods, where real-time knowledge of how a material is curing could help the researchers speed up production. Additionally, if there is a material failure, such as a tear, the sensors could point the researchers where to look in the process.

The research team also plans to develop a virtual modeling system to refine the material-forming process through computer simulation instead of by trial and error. In this way, the team will better understand each step in the material-forming process, enhancing the team’s ability to make TuFF materials consistently and reliably — a must for aerospace applications.

“I am hoping this work will allow us finally to make composites cost competitive with the metal industry,” said Advani.

In addition to Thostenson and Advani, the team includes, from CCM, Jack Gillespie, Dirk Heider, Shridhar Yarlagadda, Thomas Cender, John Tierney and Pavel Simacek, along with four to five graduate students.

Cracking the Code

Cracking the Code

UD researchers explore methods to turn biomass into sunscreens, shoe soles and more

Lignin is a major waste product of the pulp and paper industry that can be converted into chemical building blocks to create other materials. It comes from trees, grasses and other biomass.

Over 70 million tons of lignin is left over annually as a byproduct of pulp and paper manufacturing processes. Biorefineries and paper manufacturers currently burn lignin for heat or discard it in landfills. This inefficient use of a potentially valuable raw material is a massive economic, environmental and societal stressor that needs a renewable solution.

With a $3.69 million grant from the National Science Foundation, University of Delaware’s Thomas H. Epps, III and an interdisciplinary team of experts will unlock new routes to sustainably develop materials from lignin. The funding is part of a broader NSF effort to support research driven by specific and compelling problems, in this case materials life cycle management, which includes everything from how materials are developed and created to how they are disposed of at the end of their useful life. The UD work is among the first cohort of awards in the new Growing Convergence Research initiative — one of NSF’s 10 Big Ideas.

Epps, the Thomas and Kipp Gutshall Professor of Chemical and Biomolecular Engineering at UD, is the project’s principal investigator. He has assembled a team of researchers with expertise in catalysis, polymer chemistry, polymer engineering, environmental toxicity and ecohydrology to tackle this problem.

The research team aims to develop and evaluate comprehensive strategies to convert lignin into more valuable products, such as lubricants, sunscreens and adhesives, or impact-resistant materials, from rubber bands, gaskets and shoe soles to car tires, dashboards or bumpers.

The project leverages UD’s institutional strengths in catalysis, energy and polymeric materials, and it involves faculty from three of UD’s eight colleges: the College of Engineering, the College of Earth, Ocean and Environment and the College of Agriculture and Natural Resources.

Major faculty participants and co-principal investigators (PI) on the project include Dion Vlachos, director of the Delaware Energy Institute and the Catalysis Center for Energy Innovation, and the Allan and Myra Ferguson Professor of Chemical and Biomolecular Engineering; Delphis Levia, professor of ecohydrology and chair of geography; Aditya Kunjapur, assistant professor of chemical and biomolecular engineering; Changqing Wu, associate professor of food toxicology; and LaShanda Korley, Distinguished Associate Professor of Materials Science and Engineering.

Recyclable, friendly materials

One major challenge is that lignin traditionally is the hardest part of the biomass to break down. Additionally, different kinds of biomass (trees, grasses) have different chemistries, which can influence the types of molecules and materials that can be generated from the lignin.

The researchers plan to develop a roadmap that links environmental factors, such as where the biomass comes from and how it grows, to how the end products created from the biomass perform, while also considering the downstream impacts of biomass use.

“One of the big problems that we want to address is sustainability,” said Epps, who also holds a joint appointment in materials science and engineering and directs the Center for Research in Soft Matter and Polymers at UD. “Not just thinking about whether we can make new polymers or catalysts from biomass, but understanding the impact of these polymers on the environment, in terms of toxicity and in terms of the resources.”

An exploratory aspect of the work involves looking at whether these molecules can be broken down into their original components after their useful life is over. Epps explained that when polymer materials are reused, the new material’s properties, such as strength or flexibility, are normally not as robust as the original polymer. A material’s performance typically degrades each time it is reprocessed.

Instead, the UD research team is exploring ways to break materials back into their chemical building blocks so that they can be regenerated in a way that retains the full properties of the original material.

“This regeneration would make things that are infinitely recyclable,” Epps said. “If we could break polymer materials back into their monomer building blocks, we would have a blank slate. We could build the exact same thing or maybe something even better.”

Each member of the research team brings knowledge and experience critical to driving forward sustainable materials development. For example, Vlachos’ extensive expertise in catalysis — processes that accelerate chemical reactions — lends itself nicely to creating the molecules that Epps and others need to make polymer materials. Similarly, Epps’ monomers and polymer designs can help Korley develop polymer networks with specific mechanical properties, like toughness. These skills, Epps said, can help other scientists and engineers turn polymers and other materials into functional items like toy action figures or airplane wings.

Meanwhile, Levia’s hydrology and forest ecology know-how can help the research team explore noninvasive methods to predict the chemistry in trees so that they can design ways to make materials from biomass that are not only better, but also environmentally friendly and nontoxic. Wu can lend a hand here, too, by providing the research team with information about how different structures lead to more or less toxicity in materials, which can inform Kunjapur’s work engineering different enzymes and organisms to make specific molecules.

Six graduate students from across the project’s three collaborating colleges will work as an integrated team to link stem flow chemistry in forests to the structural properties (strength, impact resistance) that the researchers are finding in polymers being developed out of the biomass.

“This interdisciplinary work has potential to drive forward a circular economy that eliminates waste and encourages the continued reuse of resources. UD can be a leader in this area,” said Dion Vlachos, director of the Delaware Energy Institute and a co-PI on the project.