The insulating properties of cellulose and other plant-based materials are well-known. Nanoscale cellulose fiber, a new material, has the opposite effect, exhibiting high thermal conductivity.
This makes it useful in areas where synthetic polymer materials were previously dominant. Because materials made from cellulose are better for the environment than polymers, research in this area could lead to greener technologies that need good thermal conductivity.
Cellulose is a structural component of plant cell walls that allows tall trees to support themselves. However, the secret to its material strength lies in its overlapping nanoscopic fibers.
100 Times Higher Thermal Conduction
Flow focusing and Cellulose Nanofibers. The apparatus to create thermally conducting CNF using disorganized CNF, water and hydrochloric acid (left). A graph showing how thermal conductivity of the sample changes with its diameter. (right).
Credit: Nano Letters (2022). DOI: 10.1021/acs.nanolett.2c02057
In recent years, cellulose nanofiber (CNF) materials have been used in many commercial products because they are strong and last a long time. This makes them a great replacement for polymer-based materials like plastics, which can be bad for the environment.
Nanofiber cellulose is used, for example, in low-calorie replacements for carbohydrate additives, loudspeaker membranes, battery separators, wound dressing aerogels, and computer components.
But now that researchers under the direction of Professor Junichiro Shiomi from the Graduate School of Engineering at the University of Tokyo have examined previously unresearched thermal properties of CNF, their findings suggest these materials may be even more useful.
“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. 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,”
said Shiomi.
Hydrodynamic Flow Focusing
Because of how it is made, yarn made from CNF has excellent heat conductivity. The cellulose fibers found in nature are incredibly disorganized, but CNF is made by combining cellulose fibers and aligning them in the same direction using a technique known as the flow-focusing method.
Heat can move along this tightly bound and arranged bundle of rod-shaped fibers, whereas in a more disorganized structure, heat would dissipate more quickly.
The main problem was how to accurately measure the thermal conductivity of such small pieces of matter. The scientists used a method called T-type thermal conductivity measurement to do this.
“It allowed us to measure the thermal conductivity of the rod-shaped CNF yarn samples which are only micrometers (a micrometer is one-thousandth of a millimeter) in diameter. But the next step for us is to perform accurate thermal tests on two-dimensional textilelike samples,”
said Shiomi.
Shiomi and his team hope that their research and future work on using cellulose nanofibers as a material that conducts heat will give engineers an alternative to some polymers that are bad for the environment.
Because CNF and other plant-based materials are biodegradable, they could greatly reduce the negative effects of e-waste in places where heat transfer is important, such as in some electronic or computing components.
Reference:
Guantong Wang, Masaki Kudo et al. Enhanced High Thermal Conductivity Cellulose Filaments via Hydrodynamic Focusing. Nano Lett. 2022, DOI: 10.1021/acs.nanolett.2c02057
