ERC to fundamentally understand more sustainable plastic recycling

Assistant professor Ina Vollmer received an ERC Starting Grant for her plastic recycling research. The main goal of the five-year project is to gain fundamental insight into the innovative process of breaking down plastics to its chemical building blocks, the monomers, by using force. Using force, instead of heat, is more sustainable and yields higher quality building blocks for new plastic products. The fundamental knowledge that Vollmer aims to acquire is needed to optimize and upscale these kinds of recycling methods.

Current plastic recycling involves washing, melting and reshaping the plastic. This process generates plastic of inferior quality, due to unwanted chemical changes that cannot be avoided in this process. Another recycling technique is to break down plastics at very high temperatures to something similar to crude oil, the primary raw material for plastics. This requires a lot of energy and many refinery steps to produce monomers and then plastic again.

Plastic building blocks

Instead, Vollmer uses force instead of heat to break down plastic. This way, the long polymer chains that make up plastics can be converted to monomers directly, without the many refinery steps. These chemical building blocks can then be used to produce new high-quality polymers. The method could be more sustainable as it requires less process steps, makes use of renewable energy such as mechanical energy from wind- or hydropower and could even allow for fast startup and shutdown of the conversion process, in case the wind does not blow and the sun does not shine. Traditionally, this takes one or two days.

Marbles in a ball mill

Vollmer and her team have already shown that the idea works in the lab. They did so with a groundbreaking experiment involving marbles. These marbles - made of a super strong diamond simulant (zirconia) – were put in a ball mill, together with pieces of plastic that needed to be recycled, for instance pieces of a plastic blueberry container from the grocery store. When the mill rotates, the marbles grind the plastic until all that is left is a bit of white powder and a gas containing the monomers that can be reused to produce new plastics.

“Our experiments show that the idea works, but we don’t know exactly how. With this grant, we want to understand the fundamental chemistry underlying it”

Trick

“However”, Vollmer says, “we don’t know exactly how this works. With this grant, we want to understand the fundamental chemistry underlying it.” This is important for optimizing and upscaling the process so that it can be used for industrial purposes. Vollmer will focus specifically on polyethylene and polypropylene, used to make, for example, shampoo bottles and yoghurt containers.

One important aspect of the project is looking at the marbles interacting with the plastic using spectroscopy. This interaction is both physical and chemical. “The marbles grind, but also act as a chemical catalyst, because we chemically treat the surface of the balls”, Vollmer says. “That is the trick.”