Driven by the huge environmental burden, scientists are constantly looking for new ways to make plastic materials easier to recycle, and researchers at the Massachusetts Institute of Technology now claim a major breakthrough in the field. By modifying the composition of a common plastic, the team produced an equivalent lying version that was more easily broken down after use and could be rebuilt and recycled.
The work, carried out by chemical researchers at the Massachusetts Institute of Technology, focused on a class of major plastics called thermoset plastics. Separated from thermoplastics that make up plastic bags and food packaging paper, thermosolid plastics include epoxy resins, polyurethanes and rubber, and are often used in automotive parts and electrical appliances.
Thermoset plastics are manufactured in slightly different ways than thermoplastics, which means they are less easy to recycle. This is because thermoplastics can melt into liquids and reshape them into new shapes, but the bonds inside thermoset plastics are difficult to break down, meaning they often burn under heat rather than returning to liquid form.
“Once they’re set to a given shape, they’ll keep that shape for the rest of their lives, ” he says. “There’s usually no easy way to recycle them.”
The team may have found a way to solve this challenge by intervening during the formative phase of the material. It builds on some of its early work on biodegradable polymers, in which the bonds in the material are decomposed by the addition of a sialale ether monomer.
Applying this method to their plastic studies, the scientists found that by adding the silicone ether monomer to a liquid precursor that forms a thermoplastic called polycyclic polycycline (pDCPD), the team found that in a solution with concentrations between 7.5% and 10%, it not only retained the original mechanical strength, but was easily reduced to powder form through exposure to fluorine ions after use.
This means that scientists can now make pDCPD materials biodegradable without compromising their useful mechanical properties. The team was then able to use the powder to form a new pDCPD thermoset material by dissolving it in the precursor solution. This material is commonly used for body panels for trucks and buses, but importantly, the team believes it can also be used for other types of thermoset materials.
“This work reveals a basic design principle that we believe is common to any thermoset material with this basic architecture,” said Jeremiah Johnson, a professor of chemistry at the Massachusetts Institute of Technology and senior author of the study.
The study was published in the journal Nature.