Spiders figured out long ago how to make webs with silk that is both strong and flexible. Chemists try to mimic it, and commonly toughen synthetic polymer fibers by mixing in an additive, such as carbon nanotubes. But researchers have found that a combination of additives creates an economical material that exceeds spider silk and Kevlar in toughness.
Steve Down reports for Chemistry World:
The toughest polymer yarn of all time has been made by mixing a polymer with sheets of reduced graphene oxide (RGOF) and carbon nanotubes (CNTs) during spinning. The yarns are much cheaper than those using CNTs as the only additive, producing fibres that can be sewn like threads and coiled into springs.
CNTs can cost up to $90,000 per kilogram, whereas industrial-grade graphene oxide costs about $450 per kilogram.
Natural spider silk is composed of two types of proteins: two-dimensional sheet type and one-dimensional strand type, and their combination is very important to the toughness of the spider silk, Seon Jeong Kim of Hanyang University in Korea explained to Down. Therefore, Kim and his colleagues mixed “sheets” of RGOF and “strands” of single-walled CNT with polyvinyl alcohol (PVA).
To make the fibers from an aqueous solution of PVA, the researchers injected a 1:1 solution of single-walled CNT and wrinkled RGOFs during spinning. The resulting fibers were treated with methanol to increase crystallinity. They confirmed the interconnected structure of the fibers with scanning electron microscopy. Down writes:
The CNT bundles also attached themselves to the edges and surfaces of the RGOF sheets. This alignment led to toughness values up to 970J/g, which are greater than those reported so far for any material.
Down noted that increased hydrogen bonding is responsible for the toughness, and Kim suggested to him that the material may be used to make bullet-proof vests.
Soon Hyung Hong from the Korea Advanced Institute of Science and Technology commented to Chemistry World that the fibers are tough, but that if they were stronger and tougher, they could be used for additional applications such as cables or high-pressure vessels.
Rachel Petkewich is a freelance science writer and editor. She has worked as a research scientist in the chemical industry and spent eight years as a staff writer and editor at various science journals and magazines, including Chemical & Engineering News.