By Izzie Gall. Photography by Shawn Poynter.
Composite polymer extrusion is an extremely versatile manufacturing technique. Resins are fed into the long barrels of twin-screw extruders, where they are mixed with fillers that give the final product favorable characteristics like strength or chemical resistance. The finished polymers can be injection-molded into all sorts of shapes and used in the food, automotive, construction, and toy industries, among others.
But there are limits to resins’ versatility.
“With composite materials, adding more fillers also increases the viscosity and makes it harder to extrude,” said Ria Corder, an assistant professor in the Department of Chemical and Biomolecular Engineering (CBE).
Corder is a rheologist, studying how materials flow and change under different circumstances. She earned her PhD in chemical engineering at North Carolina State University at the same time as Amber Hubbard, a polymer processing and composites expert in the Sustainable Manufacturing Technologies Group at Oak Ridge National Laboratory (ORNL).
Thanks to a grant from the UT-Oak Ridge Innovation Institute (UT-ORII), Corder and Hubbard are collaborating to improve resin extrusion by integrating state-of-the-art processes, novel rheological protocols, and more sustainable inputs.
UT-ORII Supports New Collaborations
This fall, Corder and Hubbard received $95,970 from UT-ORII to fund their polymer extrusion research. The one-year grant is the first joint project between CBE and ORNL’s Manufacturing Demonstration Facility (MDF). The MDF, supported by the US Department of Energy’s Advanced Materials and Manufacturing Technologies Office, is a nationwide consortium of collaborators working with ORNL to innovate, inspire, and catalyze the transformation of US manufacturing.
“One of the things that’s really great about UT-ORII is that it allows for the initiation of new collaborations, especially between early-career researchers,” said Hubbard, who has worked at ORNL for just over two years. Corder joined CBE in January of 2024.
The funding will allow Corder to hire a graduate student and two undergraduates, who she says will also benefit from the collaboration.
“My students will have the opportunity to see what we do on the gram scale in our lab, then go to the MDF and watch it be tested at an industrially relevant scale,” Corder said. “It’ll be a really great way to see our work translated.”
Safely Harnessing Reactive Extrusion
The first step in Corder and Hubbard’s plan is utilizing a newer approach to resin compounding: reactive extrusion.
“As you’re heating the polymer and mixing in a filler, you can also initiate a reaction along the barrel of the extruder,” Hubbard explained. “A lot of reaction-based systems require batch processing, but reactive extrusion allows us to get those same high-performance or functional polymer composites in a fast, continuous process.”
Extruders are currently “black boxes” where reactions take place unobserved. Testing new reactive polymer recipes inside one could lead to poor mixing and a low-quality final product, or even to lead to safety concerns if a reaction creates unexpected volume or pressure changes.
Instead, the researchers will mix small batches of new reactive formulas in Corder’s rheometer, a tool that measures changes in a material’s viscosity under different conditions.
“We’re using the rheometer as a tool to mimic what is happening in the extruder,” Corder said. “We need to develop heating, mixing, and measurement protocols that mimic what’s happening as the materials are heated, spend a certain amount of time in the extruder while the reaction takes place, and then come out the nozzle.”
Improving and Decarbonizing Composite Materials
The team’s new rheological protocols will also streamline the creation of new resin recipes. Corder and Hubbard plan to start by exploring biologically based (bio-based) polymers and fillers.
The most common resin in use, polylactic acid (PLA), is derived from bio-based materials like corn starch and is fully recyclable. However, many other resin systems, and most of the fillers used to increase the strength of composites, are derived from petroleum.
To reduce the industry’s carbon footprint, Corder and Hubbard will be investigating different shapes and sizes of wood fillers for their effectiveness in strengthening multiple bio-based resins, including PLA.
“Testing the different wood materials allows us to keep chemical interactions between the filler and polymers the same but isolate how particle size and shape affects the rheology,” Corder explained.
The researchers hope to find a formulation that stands up to the standards of the automotive, marine, and construction industries, which have so far been unable to switch to more sustainable materials.
“You don’t want your car, for example, to be made out of something that isn’t flame retardant,” Hubbard pointed out. “If you can get to the point where reactively extruded materials have these added functionalities, now you can actually start to see market penetration.”
Facilitating Long-Term Improvements
Corder and Hubbard hope their standardized protocols will enable rheologists and manufacturers to quickly discover and implement high-performance, reactively extruded resins.
“We’re going to be promoting the manufacturing of bio-based composite materials, developing new formulations so we can make materials that haven’t been made before, and predicting their manufacturing behavior so they can arrive to market more quickly,” Corder said.
They also look forward to identifying multiple bio-based resins that meet industry standards. Hubbard emphasized that even a small shift away from petroleum-based materials is a step in the right direction—and can stack up quickly at the industry scale.
“Think about the number of cars in Knoxville, and in the US, and in the world,” she said. “If we find a way to use a natural fiber to displace just 10% of the synthetic plastic that would have been in a car, it has a huge impact.”