Scientists from the Woods Hole Oceanographic Institution in the United States, some with association to Eastman, have found that changing the surface area of a product, not just the material it is made from, can affect how fast it biodegrades in ocean water.
The academics focused on single use drinking straws, which are ubiquitous on beaches and pose danger to biodiversity. To combat plastic pollution, countries across the world have restricted fossil-based polymers, such as polypropylene (PP), in drinking straws. These policies have led to a growing market for single-use items made from paper or bioplastics. However, replacement materials need to retain functionality, so they don’t flop over whilst being used but nevertheless fall apart later if they end up in soil, fresh water, or salt water.
The scientists noted that data on biodegradation rates and environmental lifetimes for materials such as cellulose diacetate (CDA), polyhydroxyalkanoates (PHA), and polylactic acid (PLA) are limited. To fill this gap, they incubated commercial drinking straws made of CDA, PHA, PLA, PP, and (coated and uncoated) paper for 16 weeks. The team cut inch-long pieces of each straw and suspended them on wires in large thanks with room temperature seater flowing through.
Results show that paper, CDA, and PHA straws lost 25% to 50% of their initial weights after the 16 weeks. The researchers projected that these straws should fully disintegrate in coastal oceans within 10 months for paper, 15 months for PHA, and 20 months for CDA.
PP and PLA straws didn’t have measurable weight changes, which suggests they could persist for years in ocean water. In particular, the PHA straw degraded approximately eight times slower than 58 days (2 months) advertised by the manufacturer, called Phade.
“This variation in environmental lifetimes underscores the need for transparent reporting of experimental conditions used to test biodegradable plastic products,” the scientists wrote.
Using the same experimental conditions, the researchers then examined how changing the CDA material’s form from solid to a foam, and thereby increasing its surface area, impacted its environmental lifetime. They observed that the CDA foam broke down at least twice as fast as the solid version, and they estimated that a straw made from the prototype foam would disintegrate in seawater in eight months — the shortest lifetime of any material tested.
“Notably, the projected environmental lifetime of the foamed bioplastics CDA straw was ~2 and ~5 months shorter than those of uncoated and coated paper straws, respectively,” the scientists wrote.
The team concluded that foaming materials is a promising strategy to reduce the persistence of biodegradable plastics in marine environments.
They shared their findings in “Strategies to Reduce the Environmental Lifetimes of Drinking Straws in the Coastal Ocean,” recently published in ACS Sustainable Chemistry & Engineering