Doron Kam
Researchers from the Hebrew University of Jerusalem have been presenting results of a new 3D printable wood ink from August 21 to 25 at the American Chemical Society (ACS) Fall 2022 event. The material is printed flat, then can self-morph into a complex 3D shape, with the researchers suggesting the potential for furniture or other wooden products to be made this way in the future.
The way the material works is similar to how in nature, plants and some animals can alter their own shapes and textures. Even after a tree is cut down, its wood can change shape as it dries. It shrinks unevenly and warps because of variations in fibre orientation within the wood.
“Warping can be an obstacle,” said Doron Kam, a graduate student who is presenting the work. “We thought we could try to understand this phenomenon and harness it into a desirable morphing.”
Eran Sharon, Ph.D., one of the projects principal investigators spoke about how artificial structures can’t typically shape themselves, but in recent years scientists have begun to print flat sheets that could form into 3D shapes after a stimulus, such as a change in temperature.
Most of the previous self-morphing sheets were made from synthetic materials, such as gels and elastomers. “We wanted to go back to the origin of this concept, to nature, and do it with wood,” said Sharon.
The research began a few years ago, when the team developed an environmentally friendly water-based ink composed of wood-waste microparticles known as wood flour mixed with cellulose nanocrystals and xyloglucan. These are natural binders extracted from plants.
The team soon discovered, after using the ink in a 3D printer, that the way the ink is laid down dictates the morphing behaviour, as the moisture content evaporates from the printed piece.
For example, a flat disc printed as a series of concentric circles, dries and shrinks to form a saddle-like structure similar to a Pringle crisp. A disc printed as a series of rays emanating from a central point turns into a dome or cone-like structure.
The end shape of the object can be controlled by adjusting print speed, because shrinkage occurs perpendicular to the wood fibres in the ink, with print speed changing the degree of alignment in the fibres. A slower rate of printing leaves the particles more randomly oriented, so shrinkage occurs in all directions. Faster printing aligns fibres with one another, making shrinkage more directional.
The team found that stacking two rectangular layers printed in different orientations will yield a helix after drying. The team hopes that in the future, further refinement will allow for the combination of the saddles, domes, helices and other design motifs to produce objects with complicated final shapes, such as a chair.
Ultimately, it could be possible to create wood products that are shipped flat to the end user, reducing shipping volume and costs, then have the product morph into its intended shape when unboxed.
Another goal that Sharon hopes to achieve with the technology is making it feasible to license the technology for home use, enabling customers to design and print their own wooden objects with a 3D printer.
Speaking about the team exploring making the material reversible, Sharon said: “We hope to show that under some conditions we can make these elements responsive, to humidity for example, when we want to change the shape of an object again.”
Desktop Metal delved into wood 3D printing in 2021 when it launched Forust, a new process and subsidiary for the high-volume additive manufacturing of end use wood parts.
