3D printing is a versatile method for producing all kinds of components quickly and precisely. The technology is therefore used in industry and increasingly in the private sector. However, since the inks used are mostly based on petroleum-based plastics, 3D printing is currently only considered sustainable to a limited extent. A research team has now developed a completely recyclable ink, which is largely made from the wood component lignin.
3D printing is one of the additive manufacturing processes (AM), in which digital models are built up layer by layer to form three-dimensional objects. Particularly popular is the so-called “Direct Ink Writing” (DIW), an extrusion process in which inks are pressed through fine nozzles and solidify in the desired shape.
For this to work, these materials must have very specific flow properties: They should deform easily under pressure and quickly solidify after emerging from the nozzle. Inks made from fossil polymers are particularly suitable for this, but are neither recyclable nor biodegradable. In order for 3D printing to work reliably, high temperatures or chemical reactions are usually required that cannot be reversed. The printed objects generally cannot be reused or reprocessed afterwards and are therefore less sustainable than hoped. All of this makes the search for sustainable alternatives difficult.
Waste product gets new life
A research team led by Maria Balk from the Helmholtz Center Hereon has addressed this problem and has now developed a completely recyclable ink for 3D printing. The core component of the new printing ink is lignin, a raw material produced by plants for their woody tissues, which is produced in large quantities as a by-product of paper and wood processing. In contrast to previous lignin-based inks, the newly developed formulation hardens without chemical or thermal post-treatment.
During 3D printing, the material flows easily through the nozzles and then quickly regains its strength when at rest. The ink, which consists of 70 percent of this wood ingredient, enables objects to be printed with excellent resolution and high dimensional stability at temperatures of up to 200 °C. “We wanted to show that waste materials such as lignin can also meet the technical requirements of modern 3D printing and at the same time improve sustainability,” explains Balk. “For this purpose, we converted an industrial waste product into a 3D printing ink that can be fully recycled by simply adding water.”
A promising approach for the future
The newly developed lignin-based 3D printing ink opens up new possibilities for more sustainable 3D printing of a wide range of objects, from customized product prototypes to components for very different technologies, as the team explains. At the same time, according to them, the development shows the great potential of industrial residues. Materials such as lignin, which would otherwise be considered waste, can be recycled. This is a promising approach for an industry that desperately needs more environmentally friendly solutions.
The recyclable ink will now be further optimized and extensively tested in order to prepare for market launch. “We want to further scale the process and investigate areas of application – especially in areas where low-energy processing and recyclability are important,” says Balk.
Source: Helmholtz Center Hereon; Technical article: ACS Sustainable Chemistry & Engineering, doi: 10.1021/acssuschemeng.5c07974