Trees and other plants lead the way: they produce cellulose themselves and use it to build complex structures with extraordinary mechanical properties. That makes cellulose attractive to materials scientists who are seeking to manufacture sustainable products with special functions. However, processing materials into complex structures with high cellulose content is still a big challenge for materials scientists.
A group of researchers at ETH Zurich and Empa have now found a way to process cellulose using 3D printing so as to create objects of almost unlimited complexity that contain high levels of cellulose particles.
Print first, then densify
To do this, the researchers combined printing via direct ink writing (DIW) method with a subsequent densification process to increase the cellulose content of the printed object to a volume fraction of 27 percent. Their work was recently published in the Advanced Functional Materials journal.
The ETH and Empa researchers are admittedly not the first to process cellulose with the 3D printer. However, previous approaches, which also used cellulose-containing ink, have not been able to produce solid objects with such a high cellulose content and complexity.
The composition of the printing ink is extremely simple. It consists only of water in which cellulose particles and fibres measuring a few hundred nanometres have been dispersed. The cellulose content is in between six and 14 percent of the ink volume.
Solvent bath densifies cellulose
The ETH researchers used the following trick to densify the printed cellulose products: After printing a cellulose-based water ink, they put the objects in a bath containing organic solvents. As cellulose does not like organic solvents, the particles tend to aggregate. This process results into shrinkage of the printed part and consequently to a significant increase in the relative amount of cellulose particles within the material.