Researchers at the University of Tokyo and KTH Royal Institute of Technology in Stockholm have developed a new sustainable thermal management material from nanoscale cellulose fiber that offers high thermal conductivity. The material could become an environmentally friendly alternative to synthetic polymer-based materials such as nylon and polyester, and lead to greater use of plant fibers to dissipate heat within or from electronic devices.
Cellulose, an important structural component of the walls of plant cells, gets its material strength, durability and flexibilityfrom overlapping nanoscopic fibers, with plant-derived materials being used primarily for their thermally insulating properties. For instance, nanocellulose is found in insulating wall and roof cavities, and in noise reduction and draft protection, as well as being applied in ink dispersants for ballpoint pens, disposable diapers and aerogels.
This is the first proper examination of previously unknown thermal properties of such fibers. Studies into enhancing the thermal conductivity of polymers have used microscopic alignment, and here the concept was applied to CNF. However, as reported in Nano Letters [Wang et al. Nano Lett. (2022) DOI: 10.1021/acs.nanolett.2c02057], alignment was insufficient and it was crucial to also increase the crystalline domain size by hydrogen bonding between the CNFs and prevent excess molecular deformation.
On investigating a yarn produced from CNF, it was discovered to offer thermal conduction of about 100 times greater than cellulose paper or typical woody biomass. The yarn conducts heat so efficiently because cellulose fibers are very disorganized, but a process called the flow-focusing method works to combine the fibers, orientating them into tightly bound and aligned bundle of rod-shaped fibers to produce CNF.
This allows heat to transfer along the bundle, as opposed to the more chaotic structure which is more likely to dissipate heat. Here, it was key to measure the thermal conductivity of small physical samples with accuracy, which was achieved using T-type thermal conductivity measurement to assess the thermal conductivity of the rod-shaped CNF yarn samples.
Where heat transfer is important, the material could much reduce the impact of discarded electronic equipment due to the biodegradable nature of CNF and other plant-based materials. Since this process is not yet optimized, there is plenty of room for further improvement. Team leader Junichiro Shiomi told Materials Today, “What we have found so far is a high thermal conductivity filament and the clear next step is to scale it up”. They now hope to perform accurate thermal tests on 2D textile-like samples and to integrate the filaments into a film, or even spin the filaments into a ribbon and knit them to form a fabric.
“What we have found so far is a high thermal conductivity filament and the clear next step is to scale it up”Junichiro Shiomi
Yarn produced from CNF offers high thermal conduction