Fascination Technology Recyclable Ink for 3D Printing

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In our "Fascination Technology" section, we present impressive research and development projects to design engineers every week. Today: a fully recyclable ink for 3D printing made from the industrial by-product lignin.

Additive manufacturing (AM) processes can be used to produce objects with different properties in order to physically produce a digital model. The processes are used for product prototypes and components for vehicles, consumer goods and medical technology applications. One particularly effective AM technique is Direct Ink Writing (DIW), in which objects can be printed at room temperature using specially formulated inks. 
Most of these inks are based on fossil polymers—materials that are often neither recyclable nor biodegradable. Inks made from lignin could be a sustainable solution. However, they usually require high temperatures or irreversible chemical processes to enable reliable 3D printing. This means that the printed objects cannot be reused, making them less sustainable. 
Researchers at the Helmholtz Center Hereon have now changed this: They have developed a fully recyclable ink for 3D printing. Around 70 percent of the ink developed by Hereon consists of lignin, which is a by-product of paper production or is obtained directly from biomass. The ink, presented in the specialist journal ACS Sustainable Chemistry & Engineering, could replace non-recyclable fossil materials. It also enables the printing of objects with excellent resolution, high dimensional stability at temperatures of up to 400 °F and their recycling. During 3D printing, the ink flows easily through the nozzles and then quickly regains its strength when at rest. In contrast to other lignin-based inks, it hardens without chemical or thermal post-treatment.

We wanted to show that even waste materials like lignin can meet the technical requirements of modern 3D printing while simultaneously improving sustainability.

Dr. Maria Balk

On the Road to Sustainable 3D Printing

The team at the Hereon Institute for Functional Materials for Sustainability in Teltow (Germany) was guided by the idea that sustainable materials do not have to be a compromise. "We wanted to show that waste materials such as lignin can also meet the technical requirements of modern 3D printing and improve sustainability at the same time," explains Dr. Maria Balk, one of the lead authors of the study. "To this end, we have converted an industrial waste product into a 3D printing ink that can be completely recycled by simply adding water." 
Prof. Francesca Toma, Head of the Hereon Institute for Functional Materials for Sustainability, emphasizes the overarching context: "Industrial waste streams are an untapped opportunity. Lignin is currently hardly used. Transforming it into a fully recyclable material shows how waste can drive innovation in an industry that urgently needs sustainable solutions."

Complete Recyclability for Circular Production

"One of the most exciting findings is that the printed objects can be recycled several times by adding water without losing performance," explains Balk. "This is rare in additive manufacturing and opens up new perspectives for circular production. CO₂ emissions can be significantly reduced in this way." The current research results open up new possibilities for the sustainable 3D printing of a variety of objects—including customized product prototypes and components for a wide range of technologies. The recyclable ink will now be further optimized and tested to enable a market launch. "We want to scale up the process further and investigate fields of application—especially in areas where low-energy processing and recyclability are important," says Maria Balk.

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