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The thermo-hydro-mechanical processing of wood.
EPFL, École Polytechnique Fédérale de Lausanne.
Linnaeus University, Faculty of Science and Engineering, School of Engineering. (Virkeslära)
2012 (English)Book (Refereed)
Abstract [en]

The fabrication of wood-derived products is numerous and is continuously being developed thanks to its unique advantages: widespread availability, natural renewal, favorable ecological assessment and its flexibility of implementation. Moreover, the polymeric components of wood together with its porous structure confer to it a faculty for transformation exceeding that of other materials.

Since the dawn of civilization wood has been used in its natural state. Only recently has wood been developed to form a range of products that are increasingly functional, based on a combination of performance and sustainability requirements.

Since the beginning of the last century, the advance of knowledge on this topic has been constant, mainly through the efforts of systematic scientific research and new types of applications.

Around the middle of the last century the preliminary work addressing the science and technology of wood was published. The current success in the understanding of its material properties, chemistry, physics and advances obtained in materials science, together with modeling techniques, provided the means for engineers and researchers to be able to engineer wood as a material and to produce new materials and products under controlled processing conditions.

The intention to overcome difficulties in the processing technologies, as related to wood, requires an interdisciplinary approach. A close co-operation between scientific disciplines such as the anatomy of wood, physics, chemistry and mechanics makes it possible for each to contribute a constructive and complementary part in order to evolve, together, the technologies that relate to the various wood treatments, such as, for example - conservation, drying, machining, shaping and joining, etc.

One of the emerging eco-friendly treatment methods is the combined use of temperature, moisture and mechanical action, the so called Thermo-Hydro-Mechanical (THM) treatment.  THM processing is implemented to improve the intrinsic properties of wood, to produce new materials, and in order to acquire a form and functionality desired by engineers without changing the eco-friendly nature of the material. These processes can be divided into two major categories; Thermo-Hydro (TH) treatments and Thermo-Hydro-Mechanical (THM) treatments.

As we pointed out above, wood consists of natural polymeric chains, connecting to each other by hydrogen bands, and in certain parts by covalent bonds. The hydrogen bond is at the origin of its properties to transformation. For example, when wood is put under thermo-hydrous conditions, allowing for the softening of its amorphous components, it can easily deform which makes it possible to consider the application of a large number of industrial processes such as molding, densification, surface densification, bending, shaping, drying at high temperature, etc. Nevertheless, the application of high temperature, however, with or without moisture can damage mechanically, and modify chemically, the polymeric components of wood.

The intention to gather together in one book the key elements of the chemical degradation of wood constituents under TH processing, the Thermo-Hydro, the Thermo-Hydro-Mechanical behavior, as well as a selection of the principal technologies implemented in TH/THM treatments, constitutes the primary reason of this edition. This work is intended for researchers, professionals of timber construction, as well as students studying the science of materials, wood technology and processing, civil engineering and architecture. This work is not exhaustive or a reference, but intends to deliver an outline of the scientific disciplines necessary to apprehend the technologies of wood THM and its behavior during treatment, as well as during its use.

This work consists of 11 chapters. The first chapter is devoted to the reasons for TH/THM processing.  The ancient treatments of wood by THM processing are discussed in the second chapter. It is shown that different heat treatment processes have been used to improve the performance of wood and that the use of these processes dates back many thousands of years. The description of the structure and the chemical composition of the components of wood are given in the third chapter. In the fourth chapter, the explanation and modeling of certain THM behaviors of wood is presented. In the first part, the small and large deformations of wood are described, and the constitutive equations of elastic linear, as well as elastic nonlinear behavior of wood, are derived. In the second part the viscoelastic behavior of wood under ambient temperature, constant and variable humidity is described. In the chapter five, the behavior of THM of wood under variable moisture and temperatures (as high as 200°C), is examined by considering that during the processing, at high temperatures, the components of wood undergo certain chemical modifications. In this chapter the effects of the processing parameters: temperature, moisture content and time, on the THM wood characteristics are discussed. The sixth chapter is devoted to the processing of wood densification by THM treatment. In the first part of this chapter various THM wood densification processing methods are discussed and the machines that have been developed in different countries corresponding to open, closed, and mixed processing, are illustrated. In the rest of this chapter the origin and mechanisms of the shape memory and fixation of compression-set by THM treatment are discussed. Chapters seven and eight are devoted respectively to the wood welding by friction techniques and wood surface densification techniques. In both chapters different techniques are discussed and the problems related to these different ‘open systems’ are explained.

In the recent decades developments in the area of heat treatment have accelerated considerably. At the present time many countries have developed their own wood TH treatments. In chapter nine most of these processing methods are presented and discussed. In chapter ten different wood bending processes: bending of solid-wood, laminated wood bending and other methods like green wood bending and kerfing are presented and different techniques discussed. Also, the theory of solid wood bending is explained. This chapter gives a demonstration of solid wood bending in the laboratory and at industrial levels. Finally, a selection of technologies is presented in the eleventh chapter on the fabrication of reconstituted wood, namely: Fiberboards, Particle boards and panels made of veneers.

For the benefit wood engineers and other people with an interest in this fascinating industry, we hope that the availability of this material as printed book will provide an understanding of all the fundamentals involved in TH and THM processing of wood.

Place, publisher, year, edition, pages
Lausanne: EPFL Press distr by CRC Press , 2012, 1. , 376 p.
Keyword [en]
wood processing, bending, densification, welding, panels, EWP, wood structure
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
URN: urn:nbn:se:lnu:diva-18842ISBN: 9781439860434 (print)OAI: oai:DiVA.org:lnu-18842DiVA: diva2:528214
Note

EPFL Press Distributed by CRC Press

Available from: 2012-08-27 Created: 2012-05-24 Last updated: 2016-01-27Bibliographically approved

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