Prof. Dr. PhD Marie-Pierre Laborie
Professorship of Forest Biomaterials, University of Freiburg
Lignin and Tannin-based Materials
Prof. Dr. Marie-Pierre Laborie, University of Freiburg
If you take a closer look at wood under the microscope, you will see that the cell wall contains mainly three polymers: cellulose, hemicellulose and lignin. Cellulose and hemicellulose form a scaffold in which lignin is embedded as a kind of putty, thus solidifying the cell wall.
To make paper and other hygiene products, cellulose is extracted from wood. This also produces lignin as a by-product, most of which is burned to produce energy. Lignin has many positive functions in wood, such as antibacterial and antifungal properties that protect against pests, and is essential for the tree as it gives it strength. Therefore the aim of our work is to use lignin in inks for 3D printing.
The wood cell wall
© Jin et al. 2015
© Jin et al. 2015
Schematic representation of Direct Ink Writing
© Forest Biomaterials Group, Lisa Ebers
© Forest Biomaterials Group, Lisa Ebers
3D printing has been gaining in importance for many years. The advantage of this method is that objects can be printed and individualised quickly. Since only material is printed that is also needed for the object, less waste is generated than with conventional methods.
In our laboratory we use the method of "Direct Ink Writing". Here the ink to be printed is filled into a cartridge and extruded from the needle by compressed air. The object is printed layer by layer on a platform by lifting the cartridge.
To design inks for Direct Ink Writing, two things are especially important: the flow behaviour through the needle and the viscosity of the ink. When the ink is extruded from the needle, a filament should be created so that 3D objects can be printed. If droplet extrusion occurs, the ink is not suitable as it is not possible to form uniform filaments. By simple tests with syringes this flow behaviour can be investigated and suitable inks can be found. The viscosity of the inks can be determined by rheological measurements.
The ink is placed between two plates, the upper one of which rotates during the measurement. This causes the sample to flow and the viscosity is determined, which describes the viscosity of the inks. Viscosity is essential for 3D printing. If it is too high, the ink cannot be extruded. If it is too low, the material melts and 3D objects are difficult to shape. Therefore, all inks should first be checked for flow and viscosity before 3D printing.
3D printed cylinder
© Forest Biomaterials Group, Lisa Ebers
© Forest Biomaterials Group, Lisa Ebers
Cellulose derivative, lignin and a 3D-printed film
© Forest Biomaterials Group, Lisa Ebers
© Forest Biomaterials Group, Lisa Ebers
The ink we have designed contains only lignin and a cellulose derivative. Both solids are dissolved in a mixture of solvents. After or during printing, the solvent evaporates and thus three-dimensional objects can be produced that are completely made of bio-based materials.
After 3D printing, the films are tested. Important here are mechanical tests to examine the elasticity and strength of the films. One of our findings is that samples with a higher lignin content have a higher strength. Thus, we were able to determine that lignin also gives strength to materials outside the tree.
More information on: