Circular ink Upcycled lignin becomes a reusable 3D printing ink that recycles with water

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Researchers at Helmholtz-Zentrum Hereon have created a water-based, room-temperature 3D printing ink made mostly from upcycled lignin that needs no heat curing. Printed parts can be recycled simply by adding water, enabling repeated reuse and a potential step toward circular additive manufacturing.

Additive manufacturing (AM) methods, such as 3D printing, enable the realization of objects with different geometric properties, by adding materials layer-by-layer to physically replicate a digital model. These methods are now widely used to rapidly create product prototypes, as well as components for vehicles, consumer goods and medical technologies. A particularly effective AM technique, called direct ink writing (DIW), entails the 3D printing of objects at room temperature using inks with various formulations. Most of these inks are based on fossil-derived polymers, materials that are neither recyclable nor biodegradable. Recently introduced lignin-derived inks could be a more sustainable alternative. However, they typically need to be treated at high heat or undergo permanent chemical bonding processes to reliably support 3D printing. This prevents them from being re-utilised after objects are printed, limiting their sustainability.

Moving towards sustainable 3D printing

The team at Hereon’s Institute of Functional Materials for Sustainability in Teltow was inspired by the idea that sustainable materials should not be a compromise and could be the primary structural components of inks for 3D printing. “We wanted to demonstrate that waste-derived materials like lignin can meet the technical demands of modern 3D printing while improving sustainability,” explains Dr Maria Balk, one of the lead authors of the paper. “To do this, we transformed an industrial waste product into a water-based 3D printing ink that can be fully recycled simply by adding water.”

Prof Francesca Toma, corresponding author of the manuscript, highlights the broader context: “Industrial waste streams are an untapped opportunity. Lignin is one of the most abundant components of wood, yet largely underused. Turning it into a fully recyclable material shows how waste can drive innovation in an industry that urgently needs sustainable solutions.” Approximately 70 percent of the printable ink created by Dr Balk and her colleagues consists of lignin. Lignin is produced during paper-making processes or can directly be extracted from biomass. While it is generally treated as waste, the researchers used it to create their recyclable ink for 3D printing.

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The new ink was found to easily flow through 3D printer nozzles when pressure is applied to it, rapidly recovering its strength after printing. In contrast with most lignin-based inks introduced in the past, it solidifies to create desired objects without the need for any chemical or heat treatments. “One of the most exciting findings is that the printed objects can be recycled multiple times through rehydration without losing performance,” says Dr Balk. “This is still very rare in additive manufacturing and could offer a realistic pathway toward circular manufacturing in 3D printing, where materials can be reused instead of discarded, significantly reducing waste and CO₂ emissions.”

The recent efforts by these scientists could open new possibilities for the sustainable 3D printing of a wide range of objects, including customised product prototypes and components for various technologies. The team’s recyclable ink could soon be improved and tested further to facilitate its future commercialisation. “We are now interested in scaling the process and exploring real-world applications, particularly in areas where low-energy processing and recyclability are crucial,” adds Balk.

Cutting-edge research for a changing world

Helmholtz-Zentrum Hereon`s scientific research aims at preserving a world worth living in. To this end, around 1000 employees generate knowledge and research new technologies for greater resilience and sustainability - for the benefit of the climate, the coast and people. The path from idea to innovation leads through a continuous interplay between experimental studies, modeling and AI to digital twins that map the diverse parameters of climate and coast or human biology in the computer. This is an interdisciplinary approach that spans from the fundamental scientific understanding of complex systems to scenarios and practical applications. As an active member of national and international research networks and the Helmholtz Association, Hereon supports politics, business and society in shaping a sustainable future by transferring the expertise it has gained.

Original Article: Room-Temperature, Aqueous-Based 3D Printing of Fully Recyclable Wood-like Inks from Upcycled Lignin; ACS Sustainable Chemistry & Engineering; DOI:10.1021/acssuschemeng.5c07974

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