Global scientists are turning waste from plywood and lumber manufacturing into “ink,” which, after heat treatment, can be used to “3D-print” the next generation of furniture that looks like real timbers – now targeted by global governments looking to introduce circular economies into building supply chains.
That is according to a new study, Three-dimensional Printing of Wood, published in Science Advances, which supports research by MIT scientists last year showing that 3D printing of biomaterials can produce “lab-grown” timbers in high-value furniture.
Now, researchers have shown that water-based ink, free of additives and derived from lignin and cellulose, can 3D-print various building products. The method, known as direct ink writing, holds significant promise for sustainable construction. They are confident that the new technology could be scaled up to compete with traditional wood processing.
“The resulting printed structures closely resemble the visual, textural, olfactory and macro-anisotropic properties, including mechanical properties, of natural wood,” according to Muhammad Rahman, one of the study’s researchers from Rice University. He added, “The results pave the way for 3D-printed wooden construction with a sustainable pathway to upcycle/recycle natural wood.”
Until now, the recycling or upcycling of timbers has been limited to traditional uses, namely used in fuel, mulch, filler for particleboards, sewage sludge fill medium, compost, and animal bedding.
“However, it is essential to recognise that waste wood has untapped potential as it can be deconstructed into its fundamental building blocks,” the researchers said, adding that lignin and cellulose are the secret weapons for creating new biobased products.
“We are exploring the prospect of recombining these bio-based materials (lignin and cellulose nanomaterials), abundantly available in waste wood, to fabricate wood structures in a bottom-up approach.”
Using additive manufacturing, the scientists used 3D printing to build objects layer by layer, reducing waste and providing unprecedented design freedom to create highly intricate architected structures.
According to Mr Rahman, this process “mimics natural wood.” He adds that until now, 3D-printed timbers have been creating “inks” by mixing sawdust with a binder—creating wood-like composites lacking many of natural wood’s physical and aesthetic properties.
However, the new method, which uses an equal ratio of lignin and cellulose, can unlock the potential for using any wood. In fact, “it does not even need to be wood,” he adds. “You can [use] any plant that has lignin and cellulose [and] deconstruct it and then mix it.”
The main challenge was creating an ink with the right “flow,” a property scientists call rheology. A 3D printing method known as direct ink writing (DIW) involves squeezing liquid inks through a microscale nozzle to “draw” the desired structure slightly at a time.
DIW printers, standard in laboratories and used in low-volume manufacturing, can print 3D structures from almost any material—including polymers, ceramics, glass, cement or metals—providing the correct ink is used.
“You need a perfect rheology,” Mr Rahman said, adding that the researchers experimented with different cellulose types to get the perfect mix: long strands of molecules called nanofibers and crystallised structures called nanocrystals in a water-based solution.
“If you use more nanofiber than nanocrystal, you get chunky globules that you cannot print, or you need very high pressures to print that,” Mr Rahman said. Conversely, too much nanocrystal makes the ink watery, and the resulting printed structures don’t hold their shape.
As a result, researchers found the perfect combination of cellulose molecules and lignin, which correctly bound together – and because they did not use synthetic additives, the ink and printing structures can be recycled back into their parts and upcycled into new structures.
As a proof of concept, the researchers printed miniature furniture, letters of the alphabet and a honeycomb lattice. These structures needed some additional processing to maintain their shape fully: Air-drying deformed them, so the research team freeze-dried them at −80 degrees Celsius (-112 degrees Fahrenheit) in a vacuum. Next, they were subjected to heat treatment at 180 degrees C (356 degrees F), which caused the lignin to soften and bind better.
According to Mr Rahman, structures printed this way had mechanical and thermal properties that resembled those of natural hardwood:
“They bent and compressed similarly and had comparable fire resistance. Our next goal is to increase the mechanical properties further so that they surpass the properties of hardwood. For example, certain additives can make the wood more fire-resistant.”
Kevin Estelle researches micro-DIW processes at Washington State University and says the new study thoroughly assesses ways to tweak wood ink’s efficacy. DIW “is best used to create highly complex and customised parts with a broad range of materials,” he told Scientific American last week. However, he notes that this type of 3D printing is small-scale and questions whether it could be scaled up to meet future demand.
For Mr Rahman, the solution to scaling up could lie in the new ink’s rheology, allowing quicker printing times. He added that global scientists are now working to reduce the energy-intensive postprocessing required for printing products to take shape.
3D-printed wooden furniture could transform the timber supply
Last year, Wood Central reported that the market for reclaimed timber is expected to grow 20% over the next five years to US $74 billion, with the furniture segment leading the international market with a share of 31% and is expected to multiply – with the global government’s pushing for greater circularity in supply chains.
In 2022, Australia became the first country in the world to commit to a fully circular economy by 2030, with Forest and Wood Products Australia (FWPA) revealing to Wood Central the importance of recycled timber in various applications, such as construction, furniture, and decoration, helping to minimise waste and driving the aims.
Last year, Ashley Beckwith and Claudia Pianica founded FORAY, using bioscience to manufacture “tree-free” wooden furniture using cells of a flowering plant known as Zinnia elegans.
Foray claims that it can produce tree-free alternatives and superior supplies for traditionally tree-sourced goods – with improved yields, reduced processing requirements and the capacity for on-site production anywhere in the world.
Rather than cultivate and destroy an entire tree to yield as little as half a litre of usable product, Foray’s bioreactors will grow only the valuable parts.
“When we have this discrepancy in total plant matter versus target product, that’s where we can make a huge impact,” according to Ms Beckwith, who said high-value furniture is among a range of products that could benefit from the new technology.
“Wouldn’t it be better if we could just grow wood in the shape that we needed, without having to grow and then remove all the extraneous bits?” she said.
- For more information about 3D printing and how it can produce “tree-free” wood, visit Wood Central’s special feature.
