Currently, the global annual production of PMMA is about 3.9 million tons. Due to its lightweight and durability, this acrylic plastic continues to see increased application in the aerospace and automotive industries. Image source: ROBERTO/ISTOCK VIA GETTY IMAGES

Quite a number of scientific discoveries have been made by accident—some famous examples include Velcro, vulcanized rubber, and polytetrafluoroethylene (PTFE) under the brand name Teflon. Thanks to researchers from ETH Zürich, we can now add an almost complete method of recycling PMMA to that list.

This acrylic plastic, known by various names such as clear resin glass (Plexiglass) and clear synthetic resin (Lucite), is composed of carbon atom chains and various side groups or branches. According to a press release from ETH Zürich, the uniform carbon chains present an almost insurmountable chemical challenge for targeted cleavage into monomers, as they do not provide specific attack points for the cleavage reaction.

A team of scientists led by Athina Anastasaki at the Polymer Materials Laboratory of the Swiss research university discovered a method to almost completely break down the organic glass into its monomer building blocks. Using additives, these building blocks can be easily purified through distillation and used as starting materials for synthesizing new organic glass polymers. Anastasaki says the recycling process is surprisingly simple and represents a significant breakthrough compared to existing technologies.

Issues with Pyrolysis

Pyrolysis is currently the only industrial method available for fully decomposing uniform carbon chains. This involves thermally breaking down the carbon chains at temperatures around 400°C. However, these reactions are non-specific and produce a mixture of various cleavage products. According to ETH Zürich, the high energy requirements of this process and the associated costs of purifying the resulting mixture severely limit the economic viability of pyrolysis.

Many researchers have been experimenting with modified polymers that have easily separable molecular groups at the ends of the polymer chains, which then initiate the breakdown from the chain ends. This approach yields over 90% efficiency but has some drawbacks:
- This material must be integrated into existing plastic production processes;
- The reactive end groups significantly limit the thermal stability of the polymer, thereby limiting its potential applications;
- Many commonly used plastic additives reduce the yield, resulting in even lower outputs for the long chains common in commercial plastics.