Creating a new sustainable plastic using physics

Over the past three years, a Ph.D. Candidate Sophie van Lange has dedicated herself to a clear goal: to produce plastic that is both hard and durable. The plastics we use today are either recyclable or strong and hard, but not both. Van Lange has moved away from traditional chemical approaches to producing plastic and developed a completely new method to create durable, reusable plastic in a whole new way. The trick? Physical strengths.

The process begins with a seemingly simple setup: yellow powder in one dish and white powder in another. By dissolving and combining these two solutions, and subjecting them to heat and pressure in a hot press, Van Lange turns these substances into a rectangular piece of plastic measuring two centimeters by half a centimeter in two weeks.

Under normal conditions, the resulting plastic is sturdy and hard but becomes reformable when heated. She describes these innovative plastics as “compleximers”. Van Lange and his colleagues discuss this in Scientists progress.

Sustainable plastic processing

Plastics are omnipresent in our daily lives, used as packaging for peppers and cucumbers in the supermarket or as packaging for new toys. “But plastic is also incorporated into the shoes on my feet and into the glasses on my nose,” says Van Lange, pointing to his pink frames. Yet we rarely think about what happens to these materials after the shoes break or you need new glasses.

“You can take your old objects to a recycling point, but almost no one knows exactly what happens to them afterwards,” explains the young researcher. Take the example of a shoe sole, which is also a type of plastic. After use, we can’t do anything with it except burn or grind it. Other plastics, like the bag around a pepper or the liner of a milk carton, can be recycled.

“It would be great if we could process all plastics sustainably,” says Van Lange. She is motivated by her love for sustainable materials and works on this innovative plastic within the Physics Chemistry and Soft Matter chair group. “I think sustainable materials are really cool,” she says.

“At the molecular level, plastics are made of long chains,” explains Van Lange. In traditional hard plastics, these chains are connected by chemical bonds for strength. However, these cross-links are so robust that recycling becomes almost impossible. That’s why Van Lange redesigned these plastics without chemical crosslinking, this time using adjustable physical forces.

Force of attraction

“Half of the chains that make up our plastic are positively charged,” says Van Lange.

“The other half is negatively charged.” When you contact them correctly, they attract each other, just like two magnets. This holds the chains together without the need for chemical cross-links. When heated, the attraction between the parts weakens, allowing the entire material to reshape itself. “This makes it possible to reuse the plastic or, for example, to repair a hole or other damage in the plastic with heat,” explains Van Lange.

So far, Ph.D. The candidate produced about three grams of the new plastic. “It took a while before my colleagues and I got the plastic we wanted,” she says. It all came down to attraction: in nature, positive and negative particles strongly attract each other. This makes the materials brittle and almost impossible to warp when heated. “The innovation lies in weakening this load sufficiently,” explains Van Lange.

She achieved this thanks to a sort of “molecular umbrella” which partially protects the positive and negative charges of the plastic. “This is how we obtained a perfect attractive force and, as a result, a plastic that is easily deformable when heated,” explains the doctoral student. candidate. Additionally, these umbrellas are water-repellent, ensuring that the plastic remains sturdy when exposed to water. A shoe sole made from the new plastic stays strong when you step into a puddle. “Charged materials are almost always sensitive to water, so achieving this is very special,” adds Van Lange.

More flexibility

The new plastic isn’t quite ready yet. For example, the material is not yet flexible enough, according to Van Lange: “We demonstrate that the concept works, but now we need to find a way to give it more rubber-like properties.” The researcher hopes to achieve this by reducing the load of complexing agents, perhaps by adjusting the building blocks of the chains that make up the plastic.

“An alternative could be to expand the molecular umbrellas,” says Van Lange. She is also considering changing the type of channels. “We currently use polystyrene, a rigid molecule,” explains the doctoral student. candidate. “If we replace it with a more flexible variant, we could already get a more flexible plastic.”

Although plastic is not yet ready for the market, the Ph.D. The candidate hopes that her work will inspire other researchers. His research demonstrates that thinking outside the box can lead to entirely new materials. “I want to motivate other scientists to look at materials differently and use them in unconventional ways,” concludes Van Lange.