Wood ink for 3D printers can turn old scraps into new parts

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Wood ink for 3D printers can turn old scraps into new parts

3D printing ink developed from wood waste recombines its natural components back into wooden products

Digitally generated image of wooden twisted shapes

Eugene Mimlin/Getty Images

Wood is one of humanity’s oldest and most versatile building materials, but converting tree trunks into today’s plywood and two-by-fours creates a significant amount of waste.Each year, in the United States alone, approximately 18 million tons A large amount of waste material is generated, of which more than 12 million tons end up in landfills. However, researchers have now discovered a method. Turn some of this waste into “ink” for trees This could eventually be used to 3D print items such as furniture and architectural elements. The findings are described in a study published March 15. scientific progressit looks, feels and smells like natural wood and is physically easy to handle.

Wood-based 3D printing itself is not new. However, existing inks are usually made by mixing sawdust and binder. This produces a wood-like composite material that lacks many of the physical and aesthetic properties that make wood so appealing.In the new process, “we tried to mimic natural wood,” says Rice University materials science researcher. Muhammad Rahmanone of the study’s authors.

Natural wood is primarily composed of organic polymers called cellulose and lignin, along with small amounts of pectin, waxes, and other compounds. To convert wood scraps into ink for 3D printing, the researchers first combined only lignin and cellulose, keeping the proportions of these materials the same as natural wood. Rahman says any type of wood or wood waste can be used for this part of the process. In fact, “it doesn’t even have to be wood,” he added. “you can [use] Plants containing lignin and cellulose [and] Break it down and then mix it up. ”

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The main challenge was creating an ink with precise “flow,” a property scientists call rheology. The 3D printing method they used, called direct ink writing (DIW), involves squeezing liquid ink through microscale nozzles to “draw” the desired structure a little at a time. DIW printers are common in laboratories, used in low-volume production, and, if the ink is manufactured correctly, can print his 3D structures from almost any material, including polymers, ceramics, glass, cement, and metals. Masu. “We need perfect rheology,” says Rahman.

To get that perfect mixture, the researchers experimented with two different forms of cellulose: long chains of molecules called nanofibers, and crystalline structures called nanocrystals in a water-based solution. “Using more nanofibers than nanocrystals either produces thick globules that cannot be printed, or requires very high pressure to print,” explains Rahman. Conversely, too many nanocrystals will make the ink watery and the resulting printed structure will not be able to hold its shape.

The researchers discovered the right combination of cellulose molecules and used lignin to bind them together. It does not contain any of the synthetic additives used in existing types of wood printing, allowing both the ink and the resulting printed structure to be recycled into component parts.

As a proof of concept, the researchers printed miniature furniture, an alphabet, and a honeycomb grid. These structures required additional processing to fully maintain their shape. Air drying would deform the material, so the researchers freeze-dried it in a vacuum at -80 degrees Celsius (-112 degrees Fahrenheit). A heat treatment at 180 °C (356 °F) was then performed to soften the lignin and strengthen the bonds.

Structures printed in this way had mechanical and thermal properties similar to those made from natural hardwood. It could be bent and compressed in a similar way and had comparable fire resistance, Rahman explains. “Our next goal is to further improve the mechanical properties so that we can exceed those of hardwoods,” he says. For example, certain additives can increase the fire resistance of wood.

kevin esterHe, who studies the micro-DIW process at Washington State University, says this new study provides a thorough evaluation of how to fine-tune the effectiveness of wood ink. DIW is “perfect for creating highly complex and customized parts using a wide range of materials,” he says. But he points out that this type of his 3D printing is relatively time-consuming, and questions whether such a process can replace traditional methods of manufacturing wooden parts for furniture and architecture on a large scale. Please, I have my doubts.

Rahman believes further tuning of the rheology of the new wood ink could reduce print times. He and his team are also looking to reduce the energy-intensive post-processing currently required to maintain the shape of printed products. Future research could compare how the energy and costs of recycling methods stack up with traditional wood processing methods.

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