"Biobased" and "biodegradable" are terms that are bandied about universally when discussing solutions to the proliferation of polymer waste, according to Ramani Narayan, distinguished professor at Michigan State University.
But both terms are useless unless people understand what they mean and how they work scientifically, Narayan told his audience in his keynote speech at the International Elastomer Conference in Cleveland 8 Oct.
"It is wrong, misleading and deceptive to use 'biodegradable' in an unqualified way," Narayan said. In fact, careless use of the term in advertising is forbidden by the Federal Trade Commission and the State of California. The latter fined Amazon $1.5m (€1.3m) for advertising bogus "biodegradable" products on its website, he said.
According to Narayan, "biobased" signifies whether the carbon content in any substance comes from organic sources, such as plants and agricultural sources, rather than fossil sources such as oil and coal.
"If the content is 100 years old or less, you can accurately measure its biobased content," he said. There is a value proposition with products made from plant biomass that does not exist with products made from oil or coal, he said.
But just because a product is biobased doesn't make it biodegradable, according to Narayan.
"'Biobased' addresses a product's origins, while 'biodegradable' addresses end-of-life issues," he said. "One does not equate to the other."
"Biodegradable" signifies whether micro-organisms can utilize the molecules of a substance as a food source, according to Narayan.
They do this by transporting the C-substrate inside the cell and converting it to carbon dioxide, he said. Even then, that leaves the question of whether the micro-organisms will consume the substance completely or leave a residue. The more residue they leave, obviously the less acceptable the level of biodegradability, Narayan said.
The question of polymer waste has become a front-page news story, with microplastics leaking into oceans, rivers, soil, air and drinking water, according to Narayan.
A 2015 study, written by Narayan and others, showed the world had between 5 million and 12.7 million tonnes of "mismanaged" plastic waste, most of it in southeast Asia, he said.
If nothing is done to manage the waste, there will be 618.7 million tonnes by 2025, 200 million of which will be in the oceans, he said.
Plastics and other polymers must be diverted from landfills into recovery, recycling, composting and waste-to-energy, according to Narayan. "There is no one solution," he said.
The problem with rubber and plastics, he said, is that they are all long-chain, carbon-carbon backbone polymers.
"They are very hard to biodegrade, because they are built to be strong," he said.
Even more of a problem is the confusion surrounding the word "biodegradable," according to Narayan. "If we can't agree on the definition of 'biodegradable,' how can the public depend on biodegradability?" he said. "We need to get closure on this.
"If you don't have a management system that uses the concept of biodegradability responsibly, you do not have an acceptable system," he said.
Biodegradability cannot be the sole solution to polymer waste, according to Narayan. The solution, he said, lies in a collaboration between chemists and biologists.
"Any plastics that are dumped in the ocean will last there for a very long time," he said. "We need to define the molecular structure, and we also need to define the biological environment."