Manmade bio-material outperforms steel and spider silk

A team, led by Daniel Söderberg from the KTH Royal Institute of Technology in Stockholm, claims to have used DESY’s (Deutsches Elektronen-Synchrotron) X-ray light source PETRA III to produce the strongest bio-material ever made. The artificial and bio-degradable cellulose fibres (CNF) are stronger than steel and even spider silk, which is usually considered the strongest bio-based material.

Using a novel production method, the researchers have successfully transferred the unique mechanical properties of these nanofibres to a macroscopic, lightweight material that could be used as an eco-friendly alternative for plastic in airplanes, cars, furniture and other products. According to Söderberg, it even has potential for biomedicine since cellulose is not rejected by the body.

The scientists started with commercially available CNF that are just 2 to 5 nanometres in diameter and up to 700 nanometres long. In a process called hydrodynamic focussing, these were suspended in water and fed into a small channel, 1mm wide and milled in steel. Through two pairs of perpendicular inflows additional deionised water and water with a low pH-value entered the channel from the sides, squeezing the stream of nanofibres together and accelerating it.

This process helped to align the nanofibres in the right direction as well as their self-organisation into a macroscopic thread that required no adhesive to hold them together. The nanofibres are held together by supramolecular forces.

With the bright X-rays from PETRA III the scientists could follow and optimise the process. Stephan Roth, head of the Micro- and Nanofocus X-ray Scattering Beamline P03 at DESY, explained: “The X-rays allow us to analyse the detailed structure of the thread as it forms as well as the material structure and hierarchical order in the super strong fibres. We made threads up to 15 micrometres thick and several metres in length.”

Measurements showed a tensile stiffness of 86 gigapascals (GPa) for the material and a tensile strength of 1.57 GPa. Söderberg said: “If you are looking for a bio-based material, there is nothing quite like it. And it is also stronger than steel and any other metal or alloy as well as glass fibres and most other synthetic materials.” The artificial cellulose fibres can be woven into a fabric to create materials for various applications. The researchers estimate that the production costs of the new material can compete with those of strong synthetic fabrics.

The study opens the way for developing nanofibre material that can be used for larger structures while retaining the nanofibres’ tensile strength and ability to withstand mechanical load. The process is also thought be used to control nanoscale assembly of carbon tubes and other nano-sized fibres.

Author
Tom Austin-Morgan

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