Molecular simulations and supercomputers lead to breakthrough in energy-efficient biomaterials

The method, which uses a solvent of sodium hydroxide and urea in water, could significantly reduce the cost of producing nanocellulose fibers—a strong, lightweight biomaterial ideal as a composite for 3D printing structures such as sustainable homes and vehicle assemblies. The findings support the development of a circular economy in which renewable, biodegradable materials replace petroleum-based resources, decarbonizing the economy and reducing waste.

Colleagues from ORNL, the University of Tennessee, Knoxville, and the University of Maine’s Process Development Center collaborated on a project that aims to more efficiently produce the highly desirable material. Nanocellulose, a form of natural polymer cellulose found in plant cell walls, is up to eight times stronger than steel.

The researchers sought to make fibrillation more efficient: the process of separating cellulose into nanofibrils, a traditionally energy-intensive, high-pressure mechanical process that takes place in an aqueous pulp suspension. The researchers tested eight candidate solvents to determine which one would work as a better pretreatment for cellulose. They used computer models that mimic the behavior of atoms and molecules in solvents and cellulose as they move and interact. The approach simulated about 0.6 million atoms, giving the researchers an understanding of the complex process without the need for the initial, time-consuming physical work in the lab.

The simulations, developed by researchers at the UT-ORNL Center for Molecular Biophysics, or CMB, and ORNL’s Chemical Sciences Division, were run on the Frontier exascale computing system—the world’s fastest supercomputer for open science. Frontier is part of the Oak Ridge Leadership Computing Facility, a DOE Office of Science user facility at ORNL.

“These simulations, taking into account every single atom and the forces between them, provide detailed information not only about whether the process works, but also why exactly it works,” said project manager Jeremy Smith, director of the CMB and chairman of the UT-ORNL board of governors.

After identifying the best candidate, the researchers conducted pilot experiments that confirmed that solvent pretreatment saved 21% energy compared to using water alone, as described in Proceedings of the National Academy of Sciences.

With the winning solvent, the researchers estimated the electricity-saving potential at about 777 kilowatt-hours per metric ton of cellulose nanofibers, or CNFs, roughly equivalent to the amount needed to power a home for a month. Testing of the resulting fibers at the Center for Nanophase Materials Science, a DOE Office of Science user facility at ORNL and U-Maine showed similar mechanical strength and other desirable characteristics compared with conventionally produced CNFs.

“We focused on the separation and drying process because it is the most energy-intensive step in making nanocellulose fibers,” said Monojoy Goswami of ORNL’s Carbon and Composites group. “With these molecular dynamics simulations and our high-performance computing at Frontier, we were able to quickly accomplish what would have taken us years in trial-and-error experiments.”

The right mix of materials, production

“When we combine our expertise in computational, materials science, manufacturing, and nanoscience tools at ORNL with our knowledge of forest products at the University of Maine, we can take some of the guesswork out of science and develop more focused experimental solutions,” said Soydan Ozcan, group leader for Sustainable Manufacturing Technologies at ORNL.

The project is supported by both the Department of Energy’s Office of Energy Efficiency and Advanced Materials and Manufacturing Technologies Office (AMMTO) and a partnership between ORNL and the University of Maine known as the Hub & Spoke Sustainable Materials & Manufacturing Alliance for Renewable Technologies Program (SM2ART).

The SM2ART program is focused on developing the infrastructure of the factory of the future, where sustainable, carbon-storing biomaterials are used to build everything from homes, ships and cars to clean energy infrastructure such as wind turbine components, Ozcan said.

“Creating durable, affordable and carbon-neutral 3D printing materials gives us an advantage in solving problems like the housing shortage,” Smith said.

It typically takes about six months to build a house using conventional methods. But with the right combination of materials and additive manufacturing, manufacturing and assembling the sustainable, modular housing units could take just a day or two, the researchers added.

The team continues to explore additional paths to more cost-effective nanocellulose production, including new drying processes. Further research is expected to use simulations to predict the best combination of nanocellulose and other polymers to create fiber-reinforced composites for advanced manufacturing systems, such as those being developed and refined at DOE’s Manufacturing Demonstration Facility (MDF) at ORNL. The MDF, supported by AMMTO, is a nationwide consortium of collaborators working with ORNL to innovate, inspire and catalyze the transformation of U.S. manufacturing.

Other scientists contributing to the solvent project include Shih-Hsien Liu, Shalini Rukmani, Mohan Mood, Yan Yu, and Derya Vural of the UT-ORNL Center for Molecular Biophysics; Katie Copenhaver, Meghan Lamm, Kai Li, and Jihua Chen of ORNL; Donna Johnson of the University of Maine; Micholas Smith of the University of Tennessee; Loukas Petridis, now at Schrödinger; and Samarthya Bhagia, now at PlantSwitch.