New material that combines wood and dried sea creatures

A new material that is a combination of wood and an invasive marine invertebrate could lead to improved materials with a range of applications, such as in food packaging, biomedical devices, construction and transport design, according to a team from the National Institute of Standards and Technology (NIST) in the US. As reported in Advanced Functional Materials [Natarajan et al. Adv.Funct. Mater. (2018) DOI: 10.1002/adfm.201800032], the derivatives of wood pulp and dried bits of tunicates were combined to produce a composite material that is flexible, sustainable, non-toxic and UV light-reflective.

Initial interest came from the properties of super-tough natural composites that contain the Bouligand structure, which is commonly found in naturally designed materials. In such a structure, molecules are layered in a rotated microstructure that offers resilience to cracking as the force of any impact is pushed by nanosized twists and turns into a series of detours, with the energy being deflected so that the overall material remains intact and functional.

“The right product, if developed, could be used in everything from aerospace composites to packaging that would keep food fresh”Jeff Gilman
New material that combines wood and dried sea creatures

Although wood does not have a natural Bouligand structure, by washing wood pulp with acid to remove its lignin and amorphous cellulose, a milky solution that dries to form a new material with the structure can be produced. On their own, these Bouligand films are quite brittle and insuffiiently robust to hold much weight. However, when the short wood-derived nanocellulose rods are combined with another natural material with longer rods it produces a material that is both strong and flexible.

For this, the researchers used dried-up tunicates, as they are comprised of extremely long and highly crystalline nanocellulose, quite different from the shorter crystals found in wood. An ingredient in Asian cuisine, tunicates are often found growing in abundance on docks and piers in areas with warm water. The tunicates used here were harvested in Western France, where they are seen as a pest.

Through testing the composite material, it was possible to identify the exact point of greatest toughness. Adding the tunicates meant the nanocrystals twisted in a different way and increased the structure formation in the wood pulp. The resultant pattern was also tighter and denser, making the material UV-reflective. As Jeff Gilman, composites project team leader at NIST, points out, “Many materials begin to degrade if they are exposed to the sun for a long time. This material could potentially be used as a coating on other surfaces in order to reflect light and extend durability.”

The team will continue to explore ways their mixture could help to manufacture composites for use in industry. As Gilman adds, “The right product, if developed, could be used in everything from aerospace composites to packaging that would keep food fresh”.