LSU and two other Louisiana universities are using funds from NASA to research the implementation of vitrimers —a new class of reprocessable polymers — in ultrasonic welding with the intention of revolutionizing space structure assembly.
Genevieve Palardy is leading the project in collaboration with professors from Louisiana Tech University and Southern University and A&M College. Palardy is an associate professor at LSU with a doctoral degree in mechanical engineering from McGill University in Quebec, Canada.
“Vitrimers are in between thermoplastics and thermosets,” Palardy said. “They have advantages from each category. They can be reprocessed and recycled, but they also have mechanical properties and thermal resistance similar to thermosets.”
Thermoplastic, or thermosoftening plastic, is a polymer material that softens under heat, hardens in cooler temperatures and can be repeatedly recycled and reused, like soda bottles or straws. Traditional thermosets are materials that permanently harden after curing and cannot be recycled. Some thermoset examples would be epoxy or polyester.
Palardy’s expertise lies in ultrasonic welding, a process that involves applying a polymer film between two pieces of material, typically carbon fiber. The sonotrode, the ultrasonic welding machine’s welding tool, applies pressure to the joining point of the materials. Then it applies ultrasonic vibrations to the pieces creating friction to melt the polymer and join the pieces together.
“Fiber-reinforced polymers, for example, are interesting because they can further reduce the weights of existing structures or components while maintaining the structural performance,” Palardy said. “So one of the main goals usually is to reduce weight, and then we can, in turn, reduce fuel consumption.”
Guoqiang Li is a mechanical and industrial engineering professor at LSU. He earned his bachelor’s degree from the Hebei University of Technology, his master’s degree from the Beijing Institute of Technology and his doctorate from Southeast University, all in civil engineering. He is collaborating with Palardy on this project using his expertise on polymers and polymer composites.
“A vitrimer is typically a chemically crosslinked polymer network containing dynamic covalent bonds — bonds that can reversibly break and reform,” Li said in an email to the Reveille. “These dynamic bonds allow the material to soften or flow and be reprocessed at temperatures above its glass transition temperature, all while maintaining its overall crosslinked structure.”
The goal of the project is to introduce vitrimers in ultrasonic welding. Because of the polymer’s unique structure and properties, it can be more durable, lighter and cheaper than traditional rivet joints made of metal. The hope is that the welding technique can reduce the weight of space structure assembly by up to 35% and costs by up to 50%.
Li says reusing recyclable materials is critical in deep space explorations. Vitrimers are considered to be greener, more sustainable polymers because they have self-healing, alterable and recyclable properties, unlike traditional thermoset polymers that often turn into solid waste at the end of service life.
“As a result, vitrimers offer significant advantages for NASA missions, for example, serving as matrix materials for fiber-reinforced polymer composites,” Li said.
The project will give undergraduate and graduate students from all three universities hands-on research experience with NASA faculty to better prepare them for careers in manufacturing and space engineering.
