ORNL Researchers Develop Temperature-Controlled Shape-Memory Polymer

A research team from Oak Ridge National Laboratory, Washington State University and the University of Idaho has succeeded in developing a shape-memory polymer that can change from its original shape, through a sequence of temporary shapes, before finally returning back to its initial form. This shape transformation is controlled by temperature variations.

A new plastic developed by ORNL and Washington State University transforms from its original shape (left) through a series of temporary shapes and returns to its initial form.

Malleable thermoplastics are those which can be melted and reused to create products like food containers, while thermosets remain in their final state due to their cross-linking chemical bonds, which tend to provide them with strength for applications such as car tires and golf balls.

Nobody takes a thermoset and recycles it like you would a water bottle,” said Orlando Rios from the Department of Energy’s Oak Ridge National Laboratory. The researchers have succeeded in formulating a technique for reshaping and reusing a thermoset.

The novel plastic is termed as a shape-memory polymer as it is capable of “remembering” its initial shape and returning back to it even after being subjected to deformation by heat or other forces. The polymer material displays triple-shape memory behavior. At a given temperature, it is able to change from one temporary shape to another temporary shape, and subsequently return back to a permanent shape at another temperature.

Rios stated that researchers have been keen to use the shape-memory polymer’s unique features; however, controlling the shape-shifting behavior has been a challenge. “One big issue that has limited their use is controlling the transformation temperatures and their properties,” he said. “We give a recipe where you can adjust the transformation temperature and shift the performance of the material.

Researchers have been able to control the material’s overall properties by altering the ratio of elements. The new technique also use commercial chemicals which can be easily scaled up to produce large quantities of the material.

We’ve taken it from somewhat of a scientific curiosity or fundamental research material to something that can be produced in larger volumes,” Rios said.

Other materials could be blended with the shape-memory polymers to create stiffer and stronger composite materials, or parts which can be recycled or reprocessed at a later stage. For instance, glass fiber composites and recyclable carbon fiber are highly sought after by the automotive industry.

The ability to control the shape-memory behavior of the material provides great design flexibility,” said Yuzhan Li of Washington State University.

It is also possible to use this material as binding glue for novel types of rare earth-free magnets manufactured using powders. Experiments are being conducted by the group involving 3D printing of powder-based magnets with shape-memory polymers.

The applications for these materials are very broad, since the shape-shifting temperatures for these materials can be finely tuned by controlling the ratio of the chemicals used in their synthesis,” said Michael Kessler of Washington State University.

The group have filed for a patent on this technique. Coauthors of the Macromolecules research are Washington State’s Yuzhan Li, Cole Pruitt, Mitch Rock and Michael Kessler; ORNL’s Rios and Jong Keum; and University of Idaho’s Liqing Wei and Armando McDonald.

The researchers used resources at the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility. The project was supported by the Air Force Office of Scientific Research and the Critical Materials Institute, an Energy Innovation Hub funded by the Department of Energy’s Office of Energy Efficiency and Renewable Energy.

The group’s research findings is published journal Macromolecules featuring on the cover of the current issue.

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