Washington State University researchers have used advanced manufacturing techniques to develop super light, strong, and porous foams that could someday be used for a large variety of applications ranging from component materials in batteries to a sponge to absorb pollutants.
The foams have an intricate honeycomb-like architecture with excellent structural, mechanical, and electrical properties. The work is reported in the high-impact journal, Advanced Functional Materials.
“This is very meaningful work,” said Kaiyan Qiu, Berry Family Assistant Professor in the School of Mechanical and Materials Engineering and lead author on the paper. “It can provide a foundation of advanced manufacturing for porous materials and gives us a pathway to create very light materials with unique geometries, strong mechanical properties, and excellent electrical properties for a variety of applications.”
Qiu and his co-author, Ulrike G. K. Wegst, a professor at Northeastern University, used a technique called freeze casting to create the foam materials from bacterial cellulose, a unique type of cellulose made by bacterial fermentation. Plant cellulose is the most common biopolymer on Earth. Bacterial cellulose has the same molecular makeup as plant cellulose, which is what makes up the cell walls of plants, but it’s purer, more porous, doesn’t include lignin, the woody part of plants that can be troublesome in manufacturing, and is more crystalline.
The researchers used liquid nitrogen to directionally freeze at a controlled cooling rate an aqueous suspension of milled bacterial cellulose and a binder made from seaweed. The frozen material, an ice-polymer composite with a lamellar structure, was put in a freeze dryer, which removes the ice by sublimation and reveals the remnant — extremely lightweight foams that possess a beautiful and intricate architecture of tiny micrometer to nanometer-sized pores. When Qiu heated these foams to high temperatures in a vacuum oven, the materials were converted to carbon, rendering them able to conduct electricity well while maintaining good strength. They could potentially be used as lightweight electrodes and other components for supercapacitors, LEDs, and batteries.
While Qiu is pleased with the properties of the foam materials, he said the work also highlighted possibilities at the fundamental level of the manufacture of new materials by freeze casting and specialized heating methods for creating porous and functional materials. The foam properties also aligned well with predictions from related mathematical models, he said.
“This can be an important supplementary advanced manufacturing method to the 3D printing, for creating porous, light structures and for manufacturing many unique and complex materials with excellent properties for different applications,” he said.
The work was funded by the Department of Energy, the National Institute of Health, and the National Science Foundation. The work also received support from researchers at Dartmouth College and Lawrence Berkeley National Lab.