Utilization of temperature kinetics as a method to predict treatment intensity and corresponding treated wood quality: Durability and mechanical properties of thermally modified wood

K Candelier,A Pétrissans,P Gérardin,S Dumarçay,R Collet,S Hannouz,M Pétrissans,M Elaieb

doi:10.4067/s0718-221x2015005000024

Abstract

Wood heat treatment is an attractive alternative to improve decay resistance of wood species with low natural durability. However, this improvement of durability is realized at the expense of the mechanical resistance. Decay resistance and mechanical properties are strongly correlated to thermal degradation of wood cells wall components. Mass loss resulting from this degradation is a good indicator of treatment intensity and final treated wood properties. However, the introduction of a fast and accurate system for measuring this mass loss on an industrial scale is very difficult. Nowadays, many studies are conducted on the determination of control parameters which could be correlated with the treatment conditions and final heat treated wood quality such as decay resistance. The aim of this study is to investigate the relations between kinetics of temperature used during thermal treatment process representing heat treatment intensity, mass losses due to thermal degradation and conferred properties to heat treated wood. It might appear that relative area of treatment temperature curves is a good indicator of treatment intensity. Heat treatment with different treatment conditions (temperature-time) have been performed under vacuum, on four wood species (one hardwood and three softwoods) in order to obtain thermal degradation mass loses of 8, 10 and 12%. For each experiment, relative areas corresponding to temperature kinetics, mass loss, decay resistance and mechanical properties have been determined. Results highlight the statement that the temperature curves’ area constitutes a good indicator in the prediction of needed treatment intensity, to obtain required wood durability and mechanical properties such as bending resistance and Brinell hardness.

Highlights

Wood heat treatment by mild pyrolysis is used to improve wood properties such as its decay resistance and dimensional stability (Rowell et al 2009, Poncsak et al 2010)
The aim of this study is to investigate the relations between the heat treatment intensity and the thermal degradation kinetics, mass losses and the final properties conferred to the heat treated wood
Heat treatment was performed at 220°C

Summary

Introduction

Wood heat treatment by mild pyrolysis is used to improve wood properties such as its decay resistance and dimensional stability (Rowell et al 2009, Poncsak et al 2010). These improved properties result from the wood cell polymers’ chemical modifications occurring during treatment (Esteves et al 2013), which confer the new wood properties (Tjeerdma and Militz 2005). Previous studies have shown that the wood thermal degradation mass loss is a good indicator for the treatment intensity directly related to the temperature and the duration of the heat treatment (Welzbacher et al 2007, Pétrissans et al 2014). The global treatment duration by comparison with a process using a nitrogen atmosphere (Candelier et al 2013a) is reduced, because re-condensation and thermal reticulation of wood degradation products are avoided

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Conclusion