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Sustainability and 3D printing are prominent themes in modern science as humans strive to make their world a better place. So, it only makes sense that scientists in the University of Akron’s (UA) College of Engineering and Polymer Science are researching these areas.

A Sustainable Future

“There are two approaches we can take to address issues in sustainability — one is a redesign of materials so they’re more recyclable, and the other is recycling materials that already exist,” said Dr. James Eagan, assistant professor of polymer science. “When it comes to recycling existing materials, one of the activities we’re looking at is mechanical recycling.

"Mechanical recycling, or what people think of as conventional recycling, reprocesses materials by grinding or compounding. The plastics then become inherently mixed and, eventually, the processed plastics will phase-separate, like water and oil separating in a container, making the product subpar.

That’s the conflict — if there's an interface between two different polymers that do not adhere, pulling on the materials can cause them to separate, leading to inferior properties and significantly impacting the overall quality of the plastic material.

To combat these challenges, Eagan’s team has developed additives to sprinkle into the recycling process, designed to improve the mechanical properties of plastics. When the two most abundant plastics — polyethylene and polypropylene — are mixed (e.g., Tupperware® mixed with a milk jug) the resulting plastic is brittle.

Eagan and his team are investigating additives, or “compatibilizers,” that would improve the mechanical properties of these plastics to make them more pliable. They’re developing unique nano stitches designed to seamlessly join the interfaces of two polymers without relying on conventional adhesives. This could help manufacturers use more recyclable content and get higher-quality products that are more predictable.

“The endgame is to increase recycling content,” said Eagan. “The manufacturing and production of goods accounts for about one-fifth of the world’s greenhouse gas emissions. If you can reduce process losses or energy intensity, that’s going to significantly impact our missions and goals of net zero.”

The most impacted materials from the additive Eagan is developing would be plastics categorized as 1, 2, 4 and 5— water and pop bottles, shampoo and conditioner bottles, bread bags, bottle caps, straws, plastic take-out containers and more everyday plastic objects.

“Polyethylene and polypropylene account for approximately two-thirds of all plastic production, and you can’t go into the modern world without them,” said Eagan. “So, we’re finding how we can make recycled plastics more durable than current brittle recycled plastics.”

To help with this, undergraduate students involved with UA organizations Zips Precious Plastics and Engineers for a Sustainable World work with Eagan to collect polyethylene and polypropylene plastics to put through the recycling process to make 3D-printed filaments like flowerpots and keychains. The plastic can also be converted to filaments to use for 3D printing, helping play a role in the future of sustainability. These efforts are supported by the Synthomer Foundation.

Investing in 3D Printing

One of the ways in which sustainability can continue improving is through 3D and 4D printing of shape-shifting materials.

“With 3D printing, there’s rapid prototyping and lower capital costs than traditional injection molding,” said Dr. Kevin Cavicchi, professor of polymer engineering. “Studies have shown there is money to be saved with this type of low-scale production for industries that manufacture uniquely made items, like jewelry or body implants.”

Cavicchi’s research group utilizes a 3D printing lab on campus that has been expanded by funds from an Assured Digital Microelectronics Education and Training Ecosystem grant from the Air Force. They are printing in4D, where the fourth dimension is time, meaning that materials respond to stimulus long after they have been printed and change their shape.

“We’re working on shape-memory materials to develop polymers with excellent elasticity that can be misshapen when set into place, and return to their original shape on heating,” said Cavicchi, whose research is the synthesis and characterization of shape memory polymers. “It’s a general property that shows up in polymer processing being applied to 3D printing — if you take a plastic cup that was made by thermoforming and heat it up, it will start to recover back to the shape of the original sheet it was made from.”

With Cavicchi’s research, there’s potential to program other responsive stimuli, like humidity, or fine tune the thermal response to generate complex motion useful for remote deployment of an item without any tools to guide it along.

Like Eagan, Cavicchi is engaging with students and getting the next generation excited about 3D printing and polymers. Through Project SEED with the American Chemical Society, Cavicchi has been working with an Â鶹ÊÓƵAPKPublic Schools student for the last two summers to help 3D print materials and to guide and empower them to explore the world of 3D printing and materials development.

Currently, he is exploring the interaction between heat and 3D-printed polymers to study two-way shape memory. For instance, a bimetallic strip in a thermostat curl and uncurls due to differential thermal expansion, regulating furnace cycles. 3D printing enables layering distinct thermal expansion materials during the printing process, creating dual-memory materials.

“There are exciting opportunities to use these materials as artificial muscles and in soft robotics,” he added.

Cavicchi's pioneering work not only extends the capabilities of shape memory polymers beyond their conventional applications, but it also sets the stage for a new era of smart materials with a myriad of exciting possibilities.

Story by Alex Knisely