Research reveals thermal conductivity of cellulose fibres

Cellulose is a key structural component of plant cell walls, and its material strength is derived from overlapping nanoscopic fibres. In recent years, many commercial products have used cellulose nanofibre (CNF) materials because their strength and durability make them a good replacement for polymer-based materials such as plastics.

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.

“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,” Shiomi said in a statement. “When we explored the thermal properties of a yarn made from CNF, however, we found that they show a different kind of thermal behaviour, thermal conduction, and it’s very significant, around 100 times higher than that of typical woody biomass or cellulose paper.”

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According to the University of Tokyo, CNFs conduct heat because of the way they are made. Cellulose fibres in nature are very disorganised, but a process called the flow-focusing method combines cellulose fibres, orientating them in the same way to create CNF. It is this tightly bound and aligned bundle of rod-shaped fibres that allows heat to transfer along the bundle, whereas in a more chaotic structure it would dissipate heat more readily.

“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 micrometres in diameter. But the next step for us is to perform accurate thermal tests on two-dimensional textilelike samples.”

Shiomi and his team hope that their investigation and future explorations into the use of CNF as a thermally conductive material could give engineers an alternative to some environmentally damaging polymers.

In applications where heat transfer is important, such as certain electronic or computational components, it could greatly reduce the consequences of e-waste, thanks to the biodegradable nature of CNF and other plant-based materials.

The team’s findings have been published in Nano Letters.