ThinKing November 2020: From wood to organic ink for 3D-printed lightweight components.



Printing technological components from wood-based biopolymers might sound like science fiction, but researchers at the University of Freiburg and the Freiburg Material Research Center have now succeeded in developing a wood-based biopaste using green engineering principles – with outstanding sustainability credentials. Woodmimetics3D can be used to 3D-print even lightweight components – making this production method energy-efficient and competitively priced.

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The State Lightweight Construction Agency of Baden-Württemberg is presenting this innovation as its November 2020 ThinKing. Each month, Leichtbau BW GmbH awards this title to innovative products or services in lightweight construction from Baden-Württemberg.

At a glance:

  • Pure sustainability: biodegradable, renewable organic material
  • High potential for lightweight construction: light material with good mechanical properties for additive manufacturing
  • Climate-friendly: CO2-neutral material
  • Energy efficient: additive manufacturing at room temperature
  • Inexpensive: Raw materials with industrial availability

“We call the new material bio-ink because we can print with it. But we’re printing in three-dimensions, instead of on paper,” explains Lisa-Sophie Ebers, doctoral student at the University of Freiburg. “The new material, which is a polymer paste, can be processed to make lightweight components using direct ink writing,” Ebers continues.
She is writing her dissertation on the wood-based material Woodmimetics 3D1), which has outstanding potential for lightweight construction. It is being developed based on a bionic approach.

Material for cradle-to-cradle manufacturing
“We expect Woodmimetics3D to have an advantageous ecological footprint, since it uses raw materials that are renewable, and since the materials are also biodegradable at the end of their life cycle,” says Prof. Marie-Pierre Laborie, Professor of Forest Biomaterials at the University of Freiburg.
The organic substance is made exclusively of the wood-based raw materials lignin and hydroxypropyl cellulose – an additive frequently used in the pharmaceutical, cosmetics and food industry (E463) – as well as water, ethanol and acetic acid as a solvent.
Because of this, the material is not only bio-based, but also 100% biodegradable. The biodegradability was tested using fungi, with results comparable to the biodegradability of PLA (polylactides). This means that the components can be returned to the materials cycle after the end of their useful lives.
Compared to the few commercial lignin-based products available, Woodmimetics3D has a fairly high percentage, up to 50% of lignin. Since this raw material is produced as a waste product in paper manufacturing, and since currently 98% of it is burned, the biopaste creates a new way to recycle. Woodmimetics could play a key role in the bio-economy, especially in Baden-Württemberg. Thanks to its wealth of forests and its commitment to wood as a raw material, Baden-Württemberg is one of Germany's most important hubs for the wood and paper industry.

Inexpensive and energy-efficient processing
Another economic benefit is that processing the material takes very little energy. Woodmimetics3D has particularly advantageous rheological properties for direct ink writing.
“In 3D printing, the viscosity of the material drops solely due to shear stress during the process. Because of this, we can process the material at room temperature,” says Ebers.
In addition, the adhesion of filaments within the material plays a key role for technical components made of the wood-based raw material. This adhesion is key to determining the mechanical properties of the component. The ratio between solvents and solid materials can be adjusted in Woodmimetics3D to modify this parameter.

Lightweight construction potential - à la carte
Woodmimetics3D has outstanding potential for semi-structural and structural applications in the lightweight construction field. Its biggest advantage is its low relative density of 0.7 kg/m3. That makes the material lighter than many metals or oil-based polymers. In addition, the biopaste can be used to 3D print lattice structures to further reduce component weight.
This makes it a sustainable alternative in many different lightweight construction applications, thanks to the design flexibility offered by 3D printing. It could be used, for instance, to connect components in lightweight structures, or as molded parts for use in consumer goods or in the automotive and aerospace industries. Thanks to its material properties, it could also be used for protective equipment, such as individually molded helmets.
In addition, parts made of Woodmimetics3D could replace certain oil-based molded parts in automotive and airplane interiors, in order to reduce a product’s CO2 footprint.
The desired Woodmimetics3D structure can be developed digitally based on the desired shape and function, without any investment costs for production materials. The research team is now seeking an industry partner for potential applications, in order to advance technological development together.

1) Their work is financed by the Sustainability Performance Center of Freiburg, as part of the project “Using lignin materials for bio-based plastic,” funded by the Ministry of Science, Research and Art of Baden-Württemberg.

About the Department of Forest Biomaterials at the University of Freiburg

The Forest Biomaterials at the University of Freiburg is the product of the 2013 restructuring of the former Institute for Forest Management and Forestry Sciences. It is part of the department of Environment and Natural Resources, and is housed under the Institute for Geoscience and Environmental Sciences. Prof. Marie-Pierre Laborie is a member of the Freiburg Material Research Center. The department concentrates on researching natural materials and developing new kinds of biomaterials. Its research is by nature highly interdisciplinary, ranging across a wide variety of different scientific areas, from wood research to the synthesis of biomacromolecules, polymer physics and nanotechnology to material technology.