Since the onset of the COVID-19 pandemic two years ago, the use of face masks has been a major protective measure in reducing the chance of getting infected. This practice, however, has now turned into an environmental catastrophe: disposable, single-use masks are ending up everywhere from street corners to coral reefs, worsening the already serious plastic pollution crisis.
Growing public concerns have forced mask manufacturers to opt for eco-friendly materials such as polylactic acid (PLA)—a low-cost, water-resistant and antimicrobial polymer made from corn starch. However, while much is known about how pure PLA degrades over time, there is a need for more information on how PLA breaks down when woven into fabrics for face masks, especially when mixed with other fossil-based polymers.
“We need to characterise its biodegradation so that we can optimise the rate, such that masks do not degrade during usage, but rapidly do so after being disposed of,” said Xian Jun Loh, Executive Director at A*STAR’s Institute of Materials Research and Engineering (IMRE).
To understand whether biodegradable PLA face masks are truly a greener alternative, Loh and his colleagues performed lab-based simulations to study how they degrade over time. This involved PLA face masks being soaked in a panel of acidic, neutral and basic pH solutions. Pieces from cut-up face masks were also mixed with sewage sludge to recreate how they might break down in a natural setting.
The experiments revealed that despite being marked as eco-friendly, PLA did not degrade completely. Only the masks that were submerged in basic solutions showed any significant signs of disintegration, losing a quarter of their initial weight in a week. In contrast, masks in acidic and neutral solutions remained relatively unchanged.
Images captured using high-powered scanning electron microscopy showed that the thickness of the masks’ PLA fibres influenced their ability to break down. Fibres under 7 micrometres thick degraded the most, while thicker ones remained mostly intact.
Scanning electron microscopy images of the polylactic acid face mask’s meltblown (thinner) and spunbond (thicker) layers degrading in a basic solution over the course of four weeks.
© A*STAR Research
The samples kept in sewage sludge displayed a similar trend. Those with thinner PLA fibres showed extensive degradation, losing more than a quarter of their weight after a month, while thicker fibres disintegrated at half the rate.
“With this knowledge, future mask material should contain PLA material with thinner fibres to increase biodegradation rate,” said Loh, adding that his team has already begun exploring this avenue. “Hopefully we can find an optimum thickness that can easily be mass-produced for future applications.”
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE).
