A shape-changing plastic with a flexible future

What would you take with you if you went to Mars, given the space and weight limitations? An ideal option could be a single material that can change shapes into any object you can imagine.

In the morning you could mold that material into eating utensils. Once breakfast is ready, you can turn your fork and knife into a shovel to tend your Martian garden. And when it's happy hour on the red planet, that shovel can become a cup for your Mars beer.

What sounds like science fiction may be one step closer to reality. Researchers at the University of Chicago's Pritzker School of Molecular Engineering have created a new type of plastic with properties that can be set by heat and then locked in by rapid cooling, a process known as tempering. Unlike classic plastics, the material retains this stiffness when brought to room temperature.

The findings, published in the journal Science on Thursday, could one day change the way astronauts pack for space.

“Instead of taking all these different types of plastic, you take this one plastic and give it the properties you need,” says Stuart Rowan, a chemist at the University of Chicago and author of the new study. .

But space isn't the only place where the material can be useful. The team of Dr. Rowan also sees its potential in other environments where resources are scarce, such as at sea or on the battlefield. It can also be used to create soft robots and improve plastics recycling.

“We all depend on plastic in our daily lives,” said Shrayesh Patel, a chemical engineer at the University of Chicago and author of the new study. But for example, foam cups, garbage bags and glasses all require plastics with different properties.

In contrast, a single material that can be adapted to different needs “simplifies the way you make plastics,” said Dr. Patel. It would also make plastic more sustainable because the products can all be processed together when recycled. That plastic needs to be sorted while recycling helps ensure that only a small portion is reused, he explained.

Modern plastics are made of chains of molecules that are permanently bonded together, making them difficult to break down. But the Chicago researchers say their new material is “pluripotent” — a term commonly used to describe the generic property of stem cells — or made of bonds that can be broken and reformed using heat.

They were inspired by the way blacksmiths temper steel in a furnace, or gradually heat it and then cool it quickly. But unlike metal, plastics are lightweight and can be molded at temperatures achievable with an oven or stovetop.

The researchers heated the reddish, translucent plastic to temperatures between 140 and 230 degrees Fahrenheit and then put it in a freezer to cool it quickly. When tempering at lower temperatures, more molecular bonds formed, making the plastic stiffer. But at higher temperatures the material became softer and stickier.

The team molded the plastic into a spoon stiff enough to scoop peanut butter from a jar, and a fork that could pick up cheese. They also made glue strong enough to stick two pieces of glass together, and a small claw similar to what you would find in a toy machine.

Julia Kalow, a chemist at Northwestern University who was not involved in the study but wrote one perspective Based on the results for Science, I found the idea of ​​a single material that could achieve a variety of properties unique and exciting. “Now that we know that achieving this property can be useful, many other researchers will be inspired to find new ways to achieve that goal,” she said.

There are limitations to the first generation pluripotent plastic. Although the team has shown that the material can be reprocessed at least seven times and retain its shape for at least a month, there is uncertainty about its shelf life.

“They won't be a direct replacement for commodity plastics yet,” said Nicholas Boynton, a graduate student at the University of Chicago who led the experiments for the study. The material cannot yet achieve the toughness of, for example, a plastic bag, nor the elasticity of a rubber band.

“We're not quite there yet, but we're pretty close,” Mr Boynton said. “I think it's really exciting right now to have one material that can access this enormous reach.”