Researchers recycle lignin for sustainable 3D printing with economy in mind

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Researchers at the University of Delaware (UD) have released a new research paper exploring ways to economically recycle biomass into new 3D printing materials.

Funded by the National Science Foundation’s Growing Convergence Research (NSF GCR) program, the paper focuses on lignin, a waste product resulting from the manufacture of paper products, and demonstrates that it can be efficiently transformed into resins. bio-based 3D printing in an approach they claim is competitive with similar petroleum-based products.

“The ability to take something like technical lignin and not just break it down and turn it into a useful product, but do it at a lower cost and environmental impact than petroleum-based materials is something no one has. was really able to do.” show before,” said Thomas Epps, NSF GCR manager at UD.

One of the end products that UD researchers and colleagues are investigating is the creation of bio-resins for 3D printing. Photo via Paula Pranda.

Reuse lignin for 3D printing

Lignin is a chemical that gives strength and rigidity to plant cell walls and is endlessly produced by plants to protect themselves from predators. As such, lignin is a widely available resource, with approximately 100 million tons of technical lignin waste generated each year in pulp and parts mills around the world, according to UD. Although the researchers say their research is unique, several other universities and 3D printing companies have also made progress in this area.

In 2020, researchers from the University of Friborg combined lignin with cellulose calls to develop their own eco-friendly wood-based 3D printing material. The biosynthetic polymer has potential uses in lightweight construction or industrial applications.

Elsewhere, MIT scientists have developed their own lab-grown wood cells containing lignin-reinforced walls that could form the basis of a new, more durable 3D-printable biomaterial. Although still in its infancy, research may in the future lend itself to 3D printing eco-friendly furniture or producing synthetic woods to tackle the growing global deforestation crisis.

Perhaps the most notable development in this area to date is Desktop Metal’s new Forust wood 3D printing technology launched in the middle of last year. The process transforms wood waste by-products, such as lignin and sawdust, to create sustainable 3D printing materials compatible with its binder jetting technology.

The Freiburg researchers used a DIW 3D printing technique (photo) to test their new biomaterial.  Image via Lisa Ebers, University of Fribourg.
Researchers from the University of Friborg used a DIW 3D printing technique (pictured) to test their new eco-friendly wood-based 3D printing material. Image via Lisa Ebers, University of Fribourg.

Economic recovery of lignin

What sets UD’s research apart from others in the field is that it focuses on the economics of the scaling process. One of the main disadvantages of lignin beneficiation is that many existing processes operate at very high temperatures, and are therefore expensive and difficult to scale. Today’s industrial techniques still come with the safety issues, capital costs and energy consumption associated with traditional solvents, temperatures or pressures.

To address these challenges, the UD research team replaced methanol, a traditional solvent used in lignin deconstruction, with glycerin to allow the process to take place at normal atmospheric pressure. Glycerin is an inexpensive ingredient typically used in liquid cosmetics, soaps and shampoos for its moisturizing benefits, but can also be used to break down lignin into its chemical building blocks, from which a wide range of bio-based products like 3D printing resins can be done.

Replacing methanol with glycerin provided the same chemical functionality but at a much lower vapor pressure, eliminating the need for a closed system. This allowed researchers to simultaneously complete the reaction and separation stages of the process, leading to a more cost-effective system.

According to the researchers, running at atmospheric pressure is not only safer, but also provides a simple route to scale the method from small batches to continuous runtime, which they believe will create more material cheaper, faster and with less manual work.

'UD' 3D printed using SLA resin in a commercially available SLA printer.  Picture via UD.
‘UD’ 3D printed using SLA resin in a commercially available SLA printer. Picture via UD.

Economic viability assessment

The method was developed over the course of a year to ensure its repeatability and consistency, and during this time the economic feasibility of the process was also assessed.

The team researched datasets on the types of products the team could create with their new SLS 3D printing materials and estimated their physical properties. This allowed the team to model the system to see if the materials created would be economically viable.

The models assessed technical waste lignin from various pulping processes obtained from project partner CanmetENERGY in Canada. This allowed them to examine how upstream costs, such as raw material price or yield, would impact the economics of the method further down the process.

According to models, UD’s low-pressure method could reduce the cost of producing a bio-based pressure-sensitive adhesive from softwood Kraft lignin by up to 60% compared to a conventional high-pressure process. Although the scientists acknowledge that the cost advantage was less pronounced for the other types of technical lignins used in the study, softwood Kraft lignin is one of the most common types of technical lignin generated by the woodworking industry. pulp and paper.

The researchers’ analysis demonstrated that while yield plays a major role in plant economics, the operating cost of the new low-pressure process was significantly lower than the conventional process “in all cases”, offering reduced investment costs and the generation of valuable co-products. The team also carried out a life cycle analysis (LCA) to determine the amount of greenhouse gas emissions generated by the process, the data from which can be used in the future to explore other ways to optimize the process.

With a patent currently pending for their ambient pressure process, the researchers believe the method has “a lot of potential” for using renewable resources to make various types of plastics in favor of fossil fuels.

Further information on the study can be found in the document entitled: “Upgrading Lignin at Ambient Pressure to High-Performance Polymers by Intensified Reductive Catalytic Deconstruction”, published in the journal Science Advances. The article was co-authored by R. O’Dea, P. Pranda, Y. Luo, A. Amitrano, E. Ebikade, E. Gottlieb, O. Ajao, M. Benali, D. Vlachos, M. Ierapetritou , T .Epps.

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Featured image shows one of the end products that UD researchers and colleagues are studying is the creation of bio-resins for 3D printing. Photo via Paula Pranda.

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