Discarded silk yarn can clean up polluted waterways

Cornell researchers have developed an elegant and sustainable way to clean up waterways: reusing one waste product to remove another.

Led by Larissa Shepherd, M.S. '13, Ph.D. '17, assistant professor in the Department of Human Centered Design, in the College of Human Ecology, the team has proposed using discarded silk yarn for the removal of dye and oil from water. Studies on several different forms of silk: fabrics, yarns, and fibers revealed that yarn unraveled from silk fabric, soaked up methylene blue (MB), a common textile dye, from water at a substantially higher rate than other forms of silk they tested.

What's more, the silk yarn can be cleaned and reused. Shepherd's group found that the textile can withstand at least 10 cycles, with minimal loss of functionality.

Shepherd is the corresponding author of "Waste Bombyx Mori Silk Textiles as Efficient and Reuseable Bio-Adsorbents for Methylene Blue Dye Removal and Oil-Water Separation," published Nov. 14 in the journal Fibers. Co-authors are Hansadi Jayamaha, doctoral candidate in the field of fiber science, and Isabel Schorn '26, a fiber science undergraduate.

Jayamaha had been studying properties of silk as part of her doctoral thesis work and developed hollow sphere silk particles in order to test their potential for adsorption - the adhesion of molecules from a gas or liquid to a surface.In doing so, they also tested other forms of silk, including unraveled silk yarn from a textile item.

"Structure is really important in my lab, so we start from the nano scale and work up to that finished textile," Shepherd said. "We were looking for a structure that was optimum for this adsorption, and we initially thought that the silk fabrics coated with particles were going to work best, but we found that just disassembling the fabric itself to the yarn stage actually showed, for the same weight, even faster adsorption."

Jayamaha found that 12 milligrams of silk filament yarn has 90% MB dye removal efficiency within 10 minutes of exposure, for concentrations up to 100 parts per million, substantially greater than the efficiency of other forms - even electrospun fiber mats or fabrics treated with the hollow silk microparticle spheres, which was a surprise, the researchers said.

"By creating the spheres," Jayamaha said, "we were creating a more hydrophilic surface compared to the silk fabric, which is more hydrophobic. But by disassembling the fabric to the yarn stage, we are creating higher surface area, and that improves the adsorption."

The group also tested silk textile adsorption capacity with oil, and found that Noil fabric (a textile that contains silk yarns composed of short fibers, rather than filament) displays oil adsorption capacities three times the initial weight of the fabric for corn oil, and close to twice the weight for gasoline.

Tests on both materials showed that, following a diminishment of function after the first cleaning-reuse cycle, the material maintained its functionality for the subsequent nine cycles.

This intrinsic property of silk as a dye adsorbent, the group found, can be achieved without chemical or other alteration of the material - just deconstructing the textile product.

"When you regenerate silk, you have to use very harsh chemicals," Shepherd said. "In our case, we're just using the fabrics themselves. Yes, we may have to unravel them to get the benefit, but that's much better than putting these harsh chemicals out into the environment."

Shepherd envisions "pillows" containing the silk yarn unraveled from discarded textiles and remnants from the cut and sew operations of the textiles industry as being an effective means of cleaning up spills and waste materials, including MB dye, which is detrimental to agricultural land and waterways when it is accidentally released from textile plants.

"We realized that we can kill two birds with one stone: We can get rid of waste textiles, which is a big issue in the textile industry in general," Shepherd said. "And then we found that it's actually really good at adsorbing, just because of its natural, structural properties."

This work made use of the Cornell Center for Materials Research Shared Facilities, as well as the Cornell NanoScale Science and Technology Facility, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation. This work was partially funded by an American Association of Textiles Chemists and Colorists graduate research grant.

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