Oak Ridge National Laboratory, Tenn., reports that its scientists have developed a method for making a renewable, leathery shape-memory material that is coated with a thin layer of silver nanoparticles to activate electrical conductivity. The solvent-free process involves mixing rubber with lignin, the byproduct of woody plants in biofuels.
"We cross-linked lignin macromolecules with an acrylonitrile–butadiene rubbery melt in high quantities ranging from 40 to 60 wt%, and processed the resulting thermoplastics into thin films. Chemical and physical networks within the polymeric materials significantly enhanced key characteristics such as mechanical stiffness, strain fixity, and temperature-stimulated recovery of shape." (From the abstract of “An Acrylonitrile–Butadiene–Lignin Renewable Skin with Programmable and Switchable Electrical Conductivity for Stress/Strain-Sensing Applications,” in Macromolecules)
They fashioned the leathery material into small strips, which were then stretched or curled. The strips were then frozen as part of the process to program the material to return to its intended shape, which occurs after the application of low heat. This process may offer a low-cost alternative to conventional conductors for applications in sensors and robotics.
"The performance of this polymer can be tuned further," says ORNL's Amit Naskar. "Variant lignins can be used at different ratios, which determines the material's pliability."
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http://pubs.acs.org/doi/full/10.1021/acs.macromol.7b02336
Video: https://www.youtube.com/watch?time_continue=1&v=CGGkJo6WJJc
