Using compostable forks and spoons might soothe an environmentalist’s soul, but the reality is that most of this cutlery ends up in landfills, where it sits around just like conventional petroleum-based plastics.
Researchers have now found a way to turn these plastics into foam that can be used for building insulation. By offering a way to repurpose compostable plastics, the advance reported in the journal Physics of Fluids could create enough value for discarded single-use plastic cutlery to keep it out of landfills.
Compostable cutlery is typically made of polylactic acid (PLA), a plastic that is derived from the starch in corn or sugar cane. Unlike petroleum-based plastics, PLA is designed to break down into harmless substances. But that only happens in industrial composters. In landfills and the environment, it can last for years even though it is often called biodegradable. And because these plastics are meant to be degradable, they cannot be recycled because they lose their strength during the recycling process.
Chemical engineers at the University of Canterbury in New Zealand placed PLA cutlery into a chamber that they filled with carbon dioxide. As they increased the pressure in the chamber, the gas infused into the plastic.
Then they quickly release the pressure, which expands the gas, and the plastic along with it, making it foamy. The researchers liken this to popping open a soda can, which releases the carbon dioxide.
By changing the pressure in the chamber, the researchers could vary the structure and porosity of the foams. The materials could find different uses, with the finer-pored foams used in housing insulation and the bulkier foams with more larger air pockets being used in flotation devices.
The researchers say the technique could be applied to other materials as well. Eventually, they hope that this technique could help keep plastics out of the environment and reduce the need to make new virgin plastics and foams, all with the goal of curbing plastic pollution.
Source: Lilian Lin, Young Lee, and Heon E. Park. Recycling and rheology of poly(lactic acid) (PLA) to make foams using supercritical fluid. Physics of Fluids, 2021.
Photo: Paul Ferguson via flickr