Accidental discovery depolimizes commercial plexiglass | Research

A new process for chemical recycling of commercially available polymetacrylates under visible light has been discovered serendipitiv by chemists in Switzerland. The researchers have shown that the process, which does not require specially designed polymers, could work on commercial plexiglas samples.

About 4 million tons of poles (methyl metacrylate) (PMMA) are produced every year, for applications, from Perspex for spectacle lenses to plexiglass for breaking windows. Physical recycling degrades PMMA properties, while pyrolysis – the standard recycling method – requires temperatures above 400 ° C and partially decompose functional groups before interruption of the carbon -carbon spine, which leaves the contaminants in the recycled material.

Researchers have “designers” polymers synthesized with pre -installed weak ties or final groups that allow the polymer chain to be discharged under specific conditions. However, most PMMA used commercially do not have these specialized groups, as they tend to compromise the stability of the polymer during use.

Athina Anastasaki And her colleagues from Eth Zurich investigated the opportunity to perform similar chemistry on PMMA without pre -installed final groups. “Commercial polymers, such as plexiglass, do not have a specialized final group, so that meant we cannot activate the reaction,” explains Anastasaki. “Our idea was to come with a way to do multiple activations along the spine, so that we can break it down to several locations. To achieve this, we had to come up with ways to make a hydrogen atom transfer reaction. ‘

While trying to perform the reaction under light using a catalyst, the researchers were puzzled to find that it took place in their control experiment in which the catalyst was not present. Finally, they resolved that the transfer of hydrogen atom was triggered not by the catalyst, but by the chlorine radicals released from the 1,2-dictorobenzene solvent. The researchers confirmed this, showing that it worked in other chlorinated solvents, such as 1,2,4-tarorobenzene, but not in unpublished solvents.

At 150 ° C, the researchers obtained the complete depolymerization of almost all types of PMMA they have tested, regardless of the specific synthesis method and the final group, simply using 415nm LED light. They also obtained the successful depolymerization of the different commercial tests of plexiglas, despite the presence of unidentified and variable impurities.

Yutan Getzler At Kenyon College in Ohio, the US is impressed by chemistry. “In the world of PMMA recycling, I think this is a truly significant advance,” he says. However, it is worried about industrial feasibility of reactions based on halogenic solvents, which are usually regulated carcinogenic. “Probably some of them are related to the types of things we see here in the proposed mechanism, which is that you can get photo generated radicals that then leave and make chemistry in ecosystems.” He also notes that PMMA is a tiny fraction of the 400 million tonnes of plastic produced each year, which limits the potential impact that the new process could have on the general plastic waste.

Anastasaki says that researchers are investigating the possibility of eliminating the chlorate solvent, but that they have already received interest from several companies that want to market the process.