Printing wood

Author

Neil Baugh
April 10, 2024

TLDR: Mixing two primary components of wood waste, cellulose and lignin, with water gives a 3D printable ink.

You might’ve heard of 3D printing plastics and metals, but what about wood? Big fan of this week’s paper, mostly because they 3D print a tiny wooden desk and chair.

Mini wooden desk made of a cellulose+lignin ink. Credit: MD Thakur, M Rahman, and others, Science Advances, 2024.

Big Takeaways

  1. Making things from wood produces a lot of waste.

  2. Mixing two primary components of wood waste, cellulose and lignin, with water gives a 3D printable ink.

  3. Heating the prints causes the water to evaporate, letting the lignin take its place.

  4. Drying solidifies the prints, letting them take the shape of things like the mini-desk above.

The Problem

Wood is an important building material both inside and outside the home. We use it for buildings, furniture, shelves, and many other things. But we typically process wood by cutting down trees into small pieces and carving out what we want, leaving a ton of waste.

3D printing does the opposite by starting with smaller wood building-blocks and using them to create the structures we want. This avoids waste by printing just the desired shape.

Example prints from this week’s paper. Credit: MD Thakur, M Rahman, and others, Science Advances, 2024.

The Solution

As you might be thinking, it’s probably difficult to 3D print wood. It’s not exactly soft and it doesn’t melt like plastic or metal does, so heating it up won’t help.

The authors of today’s study decided to break down wood into it’s basic building blocks to make it more printable. They used a printing ink made of lignin and cellulose, the two primary components of wood, with some water thrown in for good measure. And importantly, these 2 components are some of the most available wood waste products.

The scientists found that the best combination of lignin and cellulose was similar to that found in natural wood. This combo gave a printable ink when mixed with water while being easy to handle. After printing, the samples were heat-dried, evaporating the water and finalizing the prints.

The cellulose provided stability and stiffness while the lignin played a supporting role. Once heated, the lignin expanded to fill the voids left by the evaporating water, connecting the cellulose regions together. This let the prints maintain their shape and get stronger. Practically speaking, the evaporated water being replaced with lignin turned the prints from a liquid to a solid.

Wood (left), printing mix (right), and a close up comparison of the two (middle). Credit: MD Thakur, M Rahman, and others, Science Advances, 2024.

As you can see from the pictures above, the final prints look super similar to wood, both close up and from a distance. They have good mechanical properties and held up well during use. The paper only shows small-scale prints, but hopefully they’re able to scale up the process to achieve larger structures.

See you next week for more science,

Neil

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