In what could form the basis of petroleum-free plastics that are both entirely recyclable and biodegradable, chemists have found a polymer that can be synthesized into useful materials and then broken down into its original building blocks to be given a new life.
Though some of the plastic society churns through every day makes it to recycling facilities and can be re-cast as useful items, much of it also ends up in landfill and the ocean. Plastics that can biodegrade in certain environments, such as polylactic acid (PLA), have come to offer a more eco-friendly alternative, but these too have their downside. Though recycling is an option as a means of prolonging the material's lifecycle, it cannot be broken down into its original molecular state without producing other unwanted byproducts.
In search of a plastic that is completely recyclable and biodegradable, researchers at Colorado State University (CSU) were eyeing off a molecule derived from a biomass compound, which the US Department of Energy had rated as one of the 12 most suited to replace petrochemicals. Known as gamma-butyrolactone (GBL), earlier scientific literature had ruled the molecule out as a potential building block for advanced plastics. Its was apparently unable to polymerize (combine into a chain of repeating monomers to form a plastic) due to its thermal stability.
"'Don't even bother with this monomer,'" says professor of chemistry at CSU, Eugene Chen, referring to the conclusions in of previous researchers. "'You cannot make a polymer out of it because the measured reaction thermodynamics told you so. We suspected that some of the previous reports were probably incorrect."
So Chen and postdoctoral fellow Miao Hong got to work, discovering a way to not only build a polymer using GBL, but to do so in a way where the polymer could form different shapes, such as linear and cyclic. This involved both metal-based and metal-free catalysts, resulting in a polyester they have dubbed poly(GBL). The pair then found that it could reset the poly(GBL) back to the original monomer state by heating it for one hour at 220 degrees Celsius for a linear polymer and 300 ° C for cyclic polymer (428 and 572 ° F).
The team says that poly(GBL) is chemically equivalent to a commercial bioplastic called P4HB. But because P4HB is derived from bacteria it is more expensive and complicated than most plastics to produce, so the team therefore hopes that its cheaper version could come to offer a more practical path forward.
The research was published in the journal Nature Chemistry.
Source: Colorado State University