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How Bound Water Regulates Wood Drying

Hélène Penvern, Meng Zhou, Benjamin Maillet, Denis Courtier-Murias, Mario Scheel, Jonathan Perrin, Timm Weitkamp, Sandrine Bardet, Sabine Caré, and Philippe Coussot
Phys. Rev. Applied 14, 054051 – Published 20 November 2020
Physics logo See Focus story: Watching Wood Dry

Abstract

For most wood-based product uses it is essential to remove a large part of the water content from wet or green (fresh-cut) wood, to reduce further dimensional variations under varying humidity conditions, improve its mechanical characteristics, and protect it from biological attacks. However, the internal mechanisms of drying are not fully described. Here we observe drying at different scales using macroscopic measurements (weighing), nuclear magnetic resonance measurements allowing to distinguish bound- and free-water contents, and x-ray computed tomography images of air-liquid interfaces at the smallest pore scale (wood lumens). We show that during wood drying, even well above the fiber saturation point, bound-water diffusion in cell walls (instead of capillary effects) ensures the extraction of liquid water from pores and its transport towards the surface of evaporation, and thus controls the drying rate. The distribution of bound-water content (uniform or heterogeneous) along the main sample axis and the drying-rate evolution depend on the competition between the external conditions and a characteristic rate of transport due to bound-water diffusion. For sufficiently slow drying this distribution remains homogenous until free water is fully extracted. An original physical phenomenon is thus at work, which plays a major role in regulating water extraction, in that it maintains a constant drying rate and a homogeneous distribution of the (mean) water content throughout the material. These results provide sound concepts for modeling and controlling drying properties of wood materials. They open the way to the understanding or control of the properties of many other materials containing two water types in food or civil-engineering applications. Our results complete recent observations that bound-water diffusion also controls imbibition in hardwood and finally show that transfers between bound and free water play a major role in the interaction of plantlike systems with water.

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  • Received 20 June 2020
  • Revised 4 September 2020
  • Accepted 9 October 2020

DOI:https://doi.org/10.1103/PhysRevApplied.14.054051

© 2020 American Physical Society

Physics Subject Headings (PhySH)

Interdisciplinary Physics

Focus

Key Image

Watching Wood Dry

Published 20 November 2020

Combining x-ray and MRI techniques leads to a microscopic explanation for the process by which water escapes from wood.

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Authors & Affiliations

Hélène Penvern1, Meng Zhou1, Benjamin Maillet1, Denis Courtier-Murias1,2, Mario Scheel3, Jonathan Perrin3, Timm Weitkamp3, Sandrine Bardet4, Sabine Caré1, and Philippe Coussot1,*

  • 1Laboratoire Navier, Ecole des Ponts, Université Gustave Eiffel, CNRS, 77420 Marne la Vallée, France
  • 2GERS-LEE, Université Gustave Eiffel, IFSTTAR, F-44344 Bouguenais, France
  • 3Synchrotron SOLEIL, 91192 Gif-sur-Yvette, France
  • 4LMGC, Université Montpellier, CNRS, 34090 Montpellier, France

  • *philippe.coussot@univ-eiffel.fr

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Vol. 14, Iss. 5 — November 2020

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