One way to help our planet is by using more sustainable materials, such as those made from bio-based materials, but the problem is that these are not yet common enough to be economically sound. Researchers from the University of Delaware and CanmetENERGY in Canada put it best by explaining that if the cost of milk goes up to $20 a gallon because the bio-based jug was so expensive to make, no one’s going to buy that milk. The collaborators recently published a paper about their method of turning industrially processed lignin—waste from making paper products—into sustainable high-performance plastics, like bio-based 3D printing resins, more efficiently.
The abstract states, “Here, we provide the first report of an intensified reactive distillation–reductive catalytic deconstruction (RD-RCD) process to concurrently deconstruct technical lignins from diverse sources and purify the aromatic products at ambient pressure. We demonstrate the utility of RD-RCD bio-oils in high-performance additive manufacturing via stereolithography 3D printing and highlight its economic advantages over a conventional reductive catalytic fractionation/RCD process.”
In the natural world, lignin is a part of trees and plants that offers stiffness and strength to help them stand up, but in the paper and pulp industry, it’s considered unusable, except for adding to tires as filler or burning it for heat; not very sustainable options. About 100 million tons of technical lignin waste a year is generated from paper and pulp mills, and the researchers believe that the material could be put to much more use. With funding from the National Science Foundation Growing Convergence Research (NSF GCR) program, they set out to economically upcycle biomass into new products.
Professor Thomas H. Epps, III, the Allan and Myra Ferguson Distinguished Professor of Chemical and Biomolecular Engineering, leader of UD’s NSF GCR efforts, and also a professor in the Department of Materials Science and Engineering, said, “The ability to take something like technical lignin and not only break it down and turn it into a useful product, but to do it at a cost and an environmental impact that is lower than petroleum materials is something that no one has really been able to show before.”
It’s costly and tough to scale when upgrading lignin, plus most of the necessary processes involve high pressures. So instead of using methanol as a solvent to deconstruct the lignin, this team went with glycerin, an everyday, inexpensive ingredient often used in lotions, soaps, liquid cosmetics, and shampoos. Not only did this choice keep costs down, but due to its high boiling point, glycerin also allowed the process to happen at ambient atmospheric pressure, which is much safer, faster, and easier to scale.
Glycerin breaks down lignin into chemical building blocks that can help make bio-based products, such as antioxidants, various plastics, and 3D printing resins. The material offered the same chemical functionality as methanol would, but a closed system wasn’t needed because glycerin requires much lower vapor pressure, allowing the team to perform the reaction and separation steps at the same time.
The team spent about a year developing the process and ensuring that it was consistent and repeatable; CanmetENERGY gave them technical lignin waste from different pulping processes to use. One of the co-lead authors and a 2021 UD Honors graduate student, Paula Pranda, looked at available data sets to see what products they could create, and estimated the physical properties of the materials they’d need. This made it possible for chemical engineering doctoral student Yuqing Luo, from Professor Marianthi Ierapetritou’s group, to analyze if the system was practical from an economic point of view. Through economical modeling, Luo determined that the cost of producing a pressure-sensitive, bio-based adhesive from softwood Kraft lignin decreased by 60% when comparing the team’s low-pressure method to a typical high-pressure one.
“We knew we could physically do it, but we needed to know whether it actually made any financial sense to do it at the scale of the chemical plant,” said lead author Robert O’Dea, a doctoral student in the Epps lab. “Yuqing’s analysis showed it does.”
In the analysis, Luo looked at upstream costs such as feedstock price or yield to see how they might impact the economics of the process later on, and found that because of reduced capital costs and the ultimate creation of valuable co-products, the cost of operating the team’s low-pressure process was much less than conventional methods. Luo also performed a life-cycle assessment to see how much greenhouse gas emissions the materials production would create, and found that the team’s approach was still competitive with other similar petroleum-based products.
Luo explained, “We were trying to capture the bigger picture, not just the costs of the process, but also the environmental impacts across the entire operation.”
To demonstrate their new RD-RCD lignin oils, the team added acrylated nonwood, acid-precipitated soda lignin (SNWA) bio-oil—because of its high syringol content—into a Peopoly SLA resin. After designing a printable version of the university’s logo in Fusion 360 software, they 3D printed the material on a commercially available Peopoly Moai 200 SLA printer.
“The complete 3D printing formulation contained 40 wt% acrylated bio-oil obtained directly from the RD-RCD products generated in this work, 40 wt% lignin-derivable vanillyl alcohol diacrylate, 15 wt% Peopoly resin, and 5 wt% photoinitiator. The diacrylate and Peopoly resin were added to improve overall print quality,” the researchers wrote. “A second resin was prepared from the acrylated bio-oil and vanillyl alcohol diacrylate without Peopoly resin, and the material was cured following the same procedure. However, the print without Peopoly exhibited breaking/flaking after several minutes.”
The researchers have a patent pending on their ambient pressure process.
“It shows there is a lot of potential for using renewable resources to make different types of plastics,” Pranda said about the low-pressure method. “You don’t have to use fossil fuels, plastics from renewable resources can be economically feasible, too.”
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