Microplastics are a growing environmental problem, but a new study could help cut out a decent chunk of them. The authors showed that silk could be a biodegradable replacement for microbeads and plastic particles that are often added to cosmetics, paints and other products.
Studies continually show that there are few places on Earth untouched by microplastic pollution. These tiny fragments have been detected in oceans, rivers, farmland, ice and snow from the Arctic to the Antarctic, and from the top of Mount Everest to the deepest trenches of the sea. They’ve been detected in living molluscs, crustaceans, fish, turtles, seals, birds, small land mammals, livestock and humans, and are linked to an increasing range of health problems.
Most of these microplastics form as larger plastic products break down in the environment, but as if the problem wasn’t bad enough, we’ve been adding our own microplastic particles to other products for decades. They show up in laundry detergents, cosmetics, toothpaste, shampoo, paints, and other chemicals. They give paints a nice sparkle, make facial scrubs abrasive, and can help control the timing of release of chemicals like herbicides.
Estimates suggest these primary microplastics make up between 10 and 15% of those in the environment, and these are the ones that the new study is aiming to address.
“We cannot solve the whole microplastics problem with one solution that fits them all,” said Benedetto Marelli, corresponding author of the study. “Ten percent of a big number is still a big number. … We’ll solve climate change and pollution of the world one percent at a time.”
For the new study, the team suggests a surprisingly simple alternative to plastic beads – silk. This common material can not only serve the same function by encapsulating substances until needed, but will biodegrade quickly and safely when it’s done.
Textile-quality silk requires silkworm cocoons to be meticulously unraveled, but to make these microbeads, the cocoons can be dissolved in water in a process that’s simple, scalable and can be done using existing infrastructure, the team says. Better yet, it can make use of low-grade silk that currently goes to waste in large amounts. The resulting silk coatings can be processed in ways that allow it to have different properties based on the intended use, like whether it attracts or repels water.
The team tested the silk coating material in the lab using existing spray-based manufacturing equipment, to make a herbicide contained in silk capsules that dissolve in water to release the product over time. When this was tested on corn in a greenhouse, the silk-encapsulated herbicide worked as well as existing products but reduced crop damage significantly – down to 0.8%, compared to 25% from herbicide that wasn’t encapsulated.
The team says that this silk coating could replace primary microplastics in most applications – not just in chemicals like the herbicide, but in cosmetics or even medicines, since the silk breaks down in the body too.
“There is a strong need to achieve encapsulation of high-content actives to open the door to commercial use,” said Marelli. “The only way to have an impact is where we can not only replace a synthetic polymer with a biodegradable counterpart, but also achieve performance that is the same, if not better.”
The research was published in the journal Small.
Source: MIT
