A new study shows that plastic bottles and bags can be vaporized and converted into their building blocks, and then create new plastics with the properties of the starting material. There are still hurdles to overcome, but the new process is a big step towards a circular plastics economy.
Some five billion tons of plastic have been buried in landfills since the 1950s, and recycling efforts account for only 9 percent of our production. With current techniques, plastic is degraded in each round of recycling and after several cycles of this process, it eventually ends up in a landfill.
According to New Scientist, John Hartwig of the University of California, Berkeley and his colleagues had previously developed a process that breaks down plastic waste and turns it into its constituent parts, but this method required expensive metal catalysts such as iridium, ruthenium and palladium, which during the process They are lost and not recycled.
Hartwig says the technique is fine for an academic paper, but not industrializable. Now his team has found an improved process that works on polyethylene, the material most plastic bags are made of, as well as polypropylene, a material used to make tougher items, and relies on catalysts that are abundant and inexpensive.
Plastics are made up of large molecules called polymers, and polymers are made up of smaller units called monomers. Catalysts break the chemical bonds of polymers and convert them into gaseous monomers from which plastic with basic properties can be produced.
In their experiments, researchers used two catalysts, sodium on aluminum oxide and tungsten oxide on silicon, to convert a mixture of polyethylene and polypropylene into propylene and isobutylene monomers with an efficiency of about 90%.
Benjamin Ward of Cardiff University in the UK, who was not involved in the new research, says recycling plastics is difficult because of the thousands of additives such as dyes, flame retardants and plasticizers. These components can make up to a third of the final product and contaminate the product after recycling. Ward believes the new method solves the problem of additives, because breaking the material down to its constituent gaseous monomers also removes the additives.
Hartwig cautions that there are still many hurdles, and their process has only been tested in the presence of a small number of common additives. There are additives that can inhibit the performance of the catalyst. Consequently, we either need to find a way to separate them or develop different catalyst structures or compositions that are more resistant to some of those additives. This issue is an important challenge in the development and improvement of recycling technologies.
Even when we have a process that can break down plastic into its constituent parts and is resistant to additives, there are still concerns, says Cressida Boyer of the University of Portsmouth in the UK.
As Boyer explains, in the recycling process, attention must be paid to issues related to toxicity and how to dispose of the end products of recycling, such as catalysts and additives. These may have negative impacts that outweigh the potential benefits of recycling technologies.
Recycling should not be seen as a way to continue or encourage the production of more unnecessary and single-use plastics. Moreover, recycling should not be considered as a justification for the continuation of the “take-make-dispose” economic model that wastes natural resources and produces a lot of waste.
