Plant-based fibers like flax, jute, sisal, hemp, and kenaf are commonly used in the production of biocomposites. Natural fibers have a high strength-to-weight ratio, are non-corrosive, have high fracture toughness, are renewable, and are sustainable, giving them distinct advantages over other materials. Scientists and researchers are interested in developing biocomposites by reinforcing natural fibers because of the environmental benefits and improved mechanical performance.
Plant-derived materials, such as cellulose, are frequently thermally insulating. A new material made from nanoscale cellulose fibers exhibits high thermal conductivity in the opposite direction. This makes it useful in areas where synthetic polymer materials were previously dominant. Because cellulose-based materials have environmental advantages over polymers, research into this area could lead to greener technological applications requiring thermal conductivity.
Cellulose is a structural component of plant cell walls that allows trees to grow to such heights. However, the secret to its material strength lies in its overlapping nanoscopic fibers. Many commercial products have used cellulose nanofiber (CNF) materials in recent years because their strength and durability make them an excellent replacement for polymer-based materials such as plastics, which can be harmful to the environment.
Our main challenge was how to measure the thermal conductivity of such small physical samples and with great accuracy. For this, we turned to a technique called T-type thermal conductivity measurement.
Professor Junichiro Shiomi
But now and for the first time, a research team led by Professor Junichiro Shiomi from the University of Tokyo’s Graduate School of Engineering has investigated previously unknown thermal properties of CNF, and their findings show these materials could be even more useful still.
“If you see plant-derived materials such as cellulose or woody biomass used in applications, it’s typically mechanical or thermally insulating properties that are being employed,” said Shiomi. “When we explored the thermal properties of a yarn made from CNF, however, we found that they show a different kind of thermal behavior, thermal conduction, and it’s very significant, around 100 times higher than that of typical woody biomass or cellulose paper.”
The way CNF yarn is made is what allows it to conduct heat so well. Cellulose fibers are very disorganized in nature, but a process known as flow-focusing combines cellulose fibers, orienting them in the same way, to create CNF. Heat can transfer along this tightly bound and aligned bundle of rod-shaped fibers, whereas a more chaotic structure would dissipate heat more readily.
Plant-derived materials such as cellulose often exhibit thermally insulating properties. A new material made from nanoscale cellulose fibers shows the reverse, high thermal conductivity. This makes it useful in areas previously dominated by synthetic polymer materials. Materials based on cellulose have environmental benefits over polymers, so research on this could lead to greener technological applications where thermal conductivity is needed.
“Our main challenge was how to measure the thermal conductivity of such small physical samples and with great accuracy,” said Shiomi. “For this, we turned to a technique called T-type thermal conductivity measurement. It allowed us to measure the thermal conductivity of the rod-shaped CNF yarn samples which are only micrometers (a micrometer equaling one-thousandth of a millimeter) in diameter. But the next step for us is to perform accurate thermal tests on two-dimensional textilelike samples.”
Shiomi and his colleagues hope that their research and future investigations into the use of CNF as a thermally conductive material will provide engineers with an alternative to some environmentally harmful polymers. Because of the biodegradable nature of CNF and other plant-based materials, it could greatly reduce the consequences of discarded electronic equipment, or e-waste, in applications where heat transfer is important, such as certain electronic or computational components.
