As useful a material as leather is, growing it on the backs of cows isn’t the most environmentally friendly way to get it. Now, engineers at Tufts University have created a new leather-like material out of silk, which can be 3D printed into shape and easily recycled into new products as needed.
Leather has been in wide use for thousands of years, thanks to its versatility and durability, but modern mass production means it has a rather large environmental footprint. Cattle farms take up huge swathes of land and drain lots of water, while the animals themselves belch massive amounts of methane into the atmosphere. And then there are the harsh chemicals involved in processing the material.
Greener, cleaner leather alternatives are in development, made from things like mushrooms. And now, Tufts researchers have shown that silk could be a contender.
Silk and leather seem like pretty distant materials, but the Tufts team developed a new way to process silk to make it tougher, firmer and more durable, while still retaining flexibility and versatility. Better yet, the process requires only mild chemicals and can be done at room temperature, all with the lesser environmental footprint of silk.
The scientists start with regular silk fibers, taken from silkworm cocoons. These fibers are mixed into a slurry, where they’re broken down into their original protein components. Then, the silk fibroin is combined with a plasticizer and a vegetable gum thickener, and the resulting material can be 3D printed – much like how spiders or worms extrude it from their glands.
To strengthen the material further, the team first put down a base layer of chitosan (the material that gives shellfish their tough exoskeletons), mixed with plasticizer and dye.
The team says that the resulting material has similar properties to regular leather. It's able to be folded, pierced, stretched and stitched together to form clothing and accessories normally made of leather. The 3D printing production method can also be tweaked to create patterns and textures to change its function, look and/or feel.
“Our work is centered on the use of naturally-derived materials that minimize the use of toxic chemicals while maintaining material performance so as to provide alternatives for products that are commonly and widely used today,” says Fiorenzo Omenetto, corresponding author of the study. “By using silk, as well as cellulose from textile and agricultural waste and chitosan from shellfish waste, and all the relatively gentle chemistries used to combine them, we are making progress towards this goal.”
To make the material even more sustainable, the team says that the silk-derived leather can be recycled easily. Once a product has reached the end of its useful life, the material can be redissolved back into the silky slurry, and made into a brand new silk-leather product. Even if it ends up in landfill, the material is biodegradable.
The team says that future work will involve testing other ways to produce the material, and better compare how it might stack up against animal-derived leather.
The research was published in the journal Materials & Design. The production process can be seen in action in the video below.
Source: Tufts University
