Wood thermodegradation: experimental analysis and modeling of mass loss kinetics

A Pétrissans,M Chaouch,R Younsi,M Pétrissans,P Gérardin

doi:10.4067/s0718-221x2014005000011

Abstract

Wood heat treatment is an attractive alternative to improve decay resistance of low natural durability of wood species. Decay resistance is strongly correlated to thermal degradation of wood cell wall components. Some recent studies proposed the use of wood mass loss during the heat treatment as a valuable marker to predict final properties of the material (Hakkou et al. 2006, Welzbacher et al. 2007). In this study, heat treatment was carried out in a relatively low temperature (230°C). Mass loss kinetics was studied using equipment, specially conceived to measure sample�s mass during the thermal treatment. Laboratory experiments were performed for heating rates of 1°C min-1. Mathematical model for kinetics of pyrolysis process was used and validated. During the pyrolysis of dry wood samples under inert atmosphere, measurements of temperature distribution and dynamic weight loss were performed. Five different wood species Fagus sylvatica (Beech), Populus nigra (Poplar), Fraxinus excelsior (Ash), Pinus sylvestris (Pine) and Abies pectinata (Silver Fir) were investigated. The unsteady-state mathematical model equations were solved numerically using the commercial package Femlab 2.0. A detailed discussion of the computational model and the solution algorithm is given. The validity of different model assumptions was analyzed. Experimental results were compared with those calculated by the model. Acceptable agreement was achieved.

Highlights

Wood is commonly used as building and engineering material
Heat treatment of the wood by mild pyrolysis is used as an alternative to chemically impregnated wood materials
The aim of this work is to build up a kinetic model which could be applied to the industrial wood heat treatment processes, and make recommendations concerning the operating temperature and treatment duration in order to obtain a required mass loss

Summary

Introduction

Wood is commonly used as building and engineering material. Unprotected wood exposed to outdoor conditions undergoes a variety of degradation reactions induced by diverse factors such as light, moisture, heat, oxygen, pollutants (Evans et al 1992). Heat treatment of the wood by mild pyrolysis is used as an alternative to chemically impregnated wood materials. Lignin polymer structure is modified (Zammen et al 2000, Tjeerdsma and Militz 2005, Nguila et al 2006, Nguila et al 2007a, Esteves et al 2008), the ratio between amorphous and crystalline cellulose is changed (Fengel and Wegener 1989, Sivonen et al 2002, Yildiz et al 2006), hemicelluloses are strongly decomposed (Sivonen et al 2002, Nuopponen et al 2004, Gérardin et al 2007), some products precursors of charcoal appear (Nguila et al 2007b).

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