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Thermal Conductivity of Cellulose Fibers in Different Size Scales and Densities
Department of Physics, Umeå University, SE-90187 Umeå, Sweden.
Department of Physics, Umeå̊ University, SE-90187 Umeå, Sweden.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.ORCID iD: 0000-0002-6247-5963
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.ORCID iD: 0000-0003-4762-2854
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2021 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 22, no 9, p. 3800-3809Article in journal (Refereed) Published
Abstract [en]

Considering the growing use of cellulose in various applications, knowledge and understanding of its physical properties become increasingly important. Thermal conductivity is a key property, but its variation with porosity and density is unknown, and it is not known if such a variation is affected by fiber size and temperature. Here, we determine the relationships by measurements of the thermal conductivity of cellulose fibers (CFs) and cellulose nanofibers (CNFs) derived from commercial birch pulp as a function of pressure and temperature. The results show that the thermal conductivity varies relatively weakly with density (ρsample = 1340–1560 kg m–3) and that its temperature dependence is independent of density, porosity, and fiber size for temperatures in the range 80–380 K. The universal temperature and density dependencies of the thermal conductivity of a random network of CNFs are described by a third-order polynomial function (SI-units): κCNF = (0.0787 + 2.73 × 10–3·T – 7.6749 × 10–6·T2 + 8.4637 × 10–9·T3)·(ρsample0)2, where ρ0 = 1340 kg m–3 and κCF = 1.065·κCNF. Despite a relatively high degree of crystallinity, both CF and CNF samples show amorphous-like thermal conductivity, that is, it increases with increasing temperature. This appears to be due to the nano-sized elementary fibrils of cellulose, which explains that the thermal conductivity of CNFs and CFs shows identical behavior and differs by only ca. 6%. The nano-sized fibrils effectively limit the phonon mean free path to a few nanometers for heat conduction across fibers, and it is only significantly longer for highly directed heat conduction along fibers. This feature of cellulose makes it easier to apply in applications that require low thermal conductivity combined with high strength; the weak density dependence of the thermal conductivity is a particularly useful property when the material is subjected to high loads. The results for thermal conductivity also suggest that the crystalline structures of cellulose remain stable up to at least 0.7 GPa.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2021. Vol. 22, no 9, p. 3800-3809
Keywords [en]
Nanofibers, Crystallinity, Carbon nanomaterials, Thermal conductivity, Cellulose
National Category
Bio Materials
Research subject
Wood and Bionanocomposites
Identifiers
URN: urn:nbn:se:ltu:diva-86775DOI: 10.1021/acs.biomac.1c00643ISI: 000696378100014PubMedID: 34510907Scopus ID: 2-s2.0-85114373514OAI: oai:DiVA.org:ltu-86775DiVA, id: diva2:1586485
Funder
Magnus Bergvall FoundationThe Kempe FoundationsBio4EnergyKnut and Alice Wallenberg Foundation
Note

Validerad;2021;Nivå 2;2021-09-21 (alebob);

Forskningsfinansiär: Wallenberg Wood Science Center

Available from: 2021-08-20 Created: 2021-08-20 Last updated: 2023-09-05Bibliographically approved

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Berglund, LinnOksman, Kristiina

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