A shape-shifting plastic has promise of a flexible future
With restrictions on space and weight, what would you bring if you were going to Mars? An ideal option might be a single material that can shift shapes into any object you imagine.
In the morning, you could mold that material into utensils for eating. When breakfast is done, you could transform your fork and knife into a spade to tend to your Martian garden. And then when it’s happy hour on the red planet, that spade could become a cup for your Martian beer.
What sounds like science fiction is, perhaps, one step closer to reality. Researchers at the University of Chicago Pritzker School of Molecular Engineering have created a new type of plastic with properties that can be set with heat and then locked in with rapid cooling, a process known as tempering. Unlike classic plastics, the material retains this stiffness when returned to room temperature.
The findings, published in the journal Science on Thursday, could someday change how astronauts pack for space.
“Rather than taking all the different plastics with you, you take this one plastic with you and then just give it the properties you need as you require,” said Stuart Rowan, a chemist at the University of Chicago and an author of the new study.
But space isn’t the only place the material could be useful. Rowan’s team also sees its potential in other environments where resources are scarce — like at sea or on the battlefield. It could also be used to make soft robots and to improve plastics recycling.
“We all depend on plastics in our day-to-day lives,” said Shrayesh Patel, a chemical engineer at the University of Chicago and an author of the new study. But foam cups, trash bags and eyeglass lenses, for example, all require plastics with different properties.
A single material that can be fashioned to different needs, on the other hand, “simplifies how you make plastics,” Patel said. It also would make plastic more sustainable because items could all be processed together when recycling. That plastic must be sorted when recycling contributes to only a small fraction being reused, he explained.
Modern plastics are made of chains of molecules that are permanently bonded, making them difficult to break down. But the Chicago researchers say their new material is “pluripotent” — a term typically used to describe the generic property of stem cells — or made of bonds that can be broken and re-formed using heat.
They were inspired by the way blacksmiths temper, or gradually heat and then rapidly cool, steel in a furnace. 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 stashed it in a freezer to quickly cool it. When tempered 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 rigid enough to scoop peanut butter from a jar and a fork that could pick up cheese. They also made adhesive strong enough to stick two pieces of glass together and a small claw similar to what you might find in a toy machine.
Julia Kalow, a chemist at Illinois’ Northwestern University who was not involved in the study but wrote a perspective on the results for Science, found the idea of a single material that could achieve a variety of properties unique and exciting.
“Now that we know it might be useful to achieve this property, a lot of other researchers will be inspired to find new ways to accomplish that goal,” she said.
There are limitations to the first generation of pluripotent plastic. Though the team has shown that the material can be reprocessed at least seven times and hold its shape for at least a month, there is uncertainty about its shelf life.
“They’re not going to be drop-in replacements for commodity plastics yet,” said Nicholas Boynton, a graduate student at the University of Chicago who led the experiments for the study. The material can’t yet reach the toughness of a plastic bag, for example, nor the elasticity of a rubber band.
“We’re not quite there in those yet, but we’re pretty close,” Boynton said. “I think having one material that can access this huge range is what’s really exciting at this point.”