A tiny chemical additive could prove to be a big hero in the world of biodegradable polymers. By incorporating small amounts of what they describe as a “masked acid” into polylactic acid (PLA), a team of chemists and chemical engineers have found they can speed up the breakdown of this plastic, which currently takes place only under the hot and humid conditions of industrial composting. The biodegradation boost this additive provides may make PLA suitable for at-home composting (ACS Cent. Sci. 2026, DOI: 10.1021/acscentsci.6c00395).
“If you’ve ever used compostable cutlery, a plastic cup, or any kind of tableware like that, it’s almost certainly PLA,” says Marc A. Hillmyer, a chemistry professor at the University of Minnesota Twin Cities who led the research with chemical engineering colleague Christopher J. Ellison.
Water breaks PLA into lactic acid, thanks to the polymer’s backbone of hydrolyzable ester bonds. But the process is slow—by some estimates it can take 100 years for PLA to degrade at 20 °C and 50% relative humidity. Industrial composting, which operates at higher temperature and humidity, does a better job, but most people don’t have access to these systems. Ellison, Hillmyer, and colleagues discovered that adding scant amounts of cyclic anhydrides—specifically, 2-sulfobenzoic acid cyclic anhydride and phthalic anhydride—speed up the degradation process.
The researchers had previously shown that carboxylic acids, such as salicylic acid, could accelerate PLA degradation, but these acids interfere with PLA’s properties when molding the material. Ellison and Hillmyer’s team found that anhydrides function as masked acids. The anhydrides don’t impact PLA’s properties during molding, but when they’re exposed to water at elevated temperature, the anhydride springs open to reveal two acid moieties. These acids accelerate PLA’s degradation, even if they’re present at just parts-per-million levels.
“We think there’s real commercial viability, because it’s used at such low concentration,” Ellison says.
What’s more, the anhydrides decrease the temperature and humidity required to break down PLA so that it’s within the range of home composting systems. For example, PLA mixed with 2-sulfobenzoic acid cyclic anhydride degraded in 98 days at 45 °C, 49 days faster than plain PLA. And the researchers can dial in the degradation properties based on the anhydride they use. “What this work has taught us is that there’s room to tailor the degradation profile of these materials,” Ellison says.
Sarah-Jeanne Royer, an oceanographer who studies plastic degradation with the Ocean Cleanup and was not involved in the research, says the work is scientifically novel and industrially attractive. “It offers a simple, industrially realistic solution to one of PLA’s biggest limitations: its very slow degradation outside industrial composting,” she says in an email.
But Royer notes that the paper doesn’t establish if the anhydride-modified PLA will behave more favorably in the real world or reduce plastic pollution. “Bridging that gap, from accelerated laboratory degradation to verified environmental outcomes, remains the most important challenge for future research,” she says.
Ellison and Hillmyer say their next steps will be to ensure that anhydride additives don’t have a negative impact on composting systems or other PLA additives. “We have to make sure what we’re doing is making a benefit from the sustainable plastics arena but not compromising something else,” Hillmyer says.
