Silk has always been an adaptable, flexible fiber. For millennia, it has been spun into satin, jacquard, shimmery Thai silk and rough, absorbent “raw” silk.
Now a team led by Raymond Tu of the City College of New York is working on ways to manipulate silk at an even more basic level, taking it back to a liquid state that can then be re-spun according to precise criteria.
The final goal: better gas masks that can filter out specified gases.
“Silk is very common feedstock material. It’s cheap,” said Tu, an associate professor of chemical engineering at CCNY. It’s also strong, flexible and doesn’t irritate human skin.
“It has traditionally just been used in the fibrous state that comes from the silkworms,” Tu added. “But if you do some fairly simple processing, you can take it from the fibrous state to a liquid state. You can precipitate it, spin it on a surface, or you can do some other tricks.”
Silkworms usually just spin silk to make their cocoons. But silk spinners such as spiders can vary the property of the silk they spin, as needed. They can make it thicker or thinner, sticky or strong. “It’s crazy,” Tu said. “Silk actually transitions from a liquid form into a solid form as they are spinning it. How they spin it, with mixtures of different proteins, affects its properties.”
Tu’s team uses lithium bromide to break down the silk material so that it can be remade into a fabric precisely tuned to filter out particles of certain sizes. The trick is to make a fabric that can filter, while allowing the free flow or air that the wearer needs to breathe.
With the help of the Minority Serving Institutions Science, Technology, Engineering and Mathematics Research and Development Consortium (MSRDC), Tu’s lab won a Department of Defense grant to start the work. He’d like to continue it.
“The DoD has very particular targets and we have a bunch of fundamentals that we would like to explore,” Tu said.
“I don’t know a lot about what they are trying to filter. I don’t know a lot about filtration masks,” he added. But he’s found a route to precisely tune the silk proteins so they have specifically sized pores. It could be mass produced, he said, and the project is providing a valuable learning experience for his students.
“I think that, particularly at a place like CCNY, a lot of the students come from first-generation families,” he said. “Many of our students are the first in their families to go to college, and most are paying (tuition) for themselves,” he added.
“I think those students make for the best researchers. They are driven to be successful. They are on their own, and there is no lifeboat. This is both their first chance and their last chance.”