Colour responses of two fast-growing hardwoods to two-step steam-heat treatments

Pedro Henrique G De Cademartori,Darci A Gatto,André L Missio,Bruno D Mattos

doi:10.1590/s1516-14392014005000031

Pedro Henrique G De Cademartori, Darci A Gatto + Show 2 more

Open Access

https://doi.org/10.1590/s1516-14392014005000031

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Abstract

Colour changes by thermal treatments are a good alternative to increase wood quality, especially for non-structural uses. In this study, rose gum (Eucalyptus grandis) and Sydney blue gum (Eucalyptus saligna) woods from Southern Brazil were thermally treated under different conditions (steam pre-treatment in an autoclave at 127 °C for 1 hour and heat treatment in an oven at 180, 200, 200 and 240 °C for 4 hours) and colour changes were investigated using CIEL*a*b* technique. The main findings show that thermal treatments resulted in darkening of the wood, which was more intense at high temperatures. Colour difference after two-step steam-heat treatments was higher than 45 for both species. In general, the influence of the steam pre-treatment was more visible in lower temperatures. Lightness (L*) was the parameter that best described the colorimetric behaviour of rose gum and Sydney blue gum woods. In conclusion, thermal treatments are a great method to improve the market value of wood, especially for aesthetic uses, but it requires a control of process conditions.

Highlights

Thermal treatment is an eco-friendly wood treatment process that aims to expose wood at temperatures higher than 180 °C
Steam pre-treatment in the autoclave influenced the colorimetric parameters, especially lightness (L*) of rose gum wood thermally treated with lower temperatures, which favoured the visualisation of the effect of the autoclave as a steam pre-treatment
Sydney blue gum wood was more susceptible to colorimetric modifications than rose gum wood, mainly in relation to the loss of lightness, which was the parameter that best described colour behaviour during thermal treatments

Summary

Introduction

Thermal treatment is an eco-friendly wood treatment process that aims to expose wood at temperatures higher than 180 °C. This process mainly entails increasing the durability and dimensional stability of wood pieces and has become an important niche in the wood market of some European and North American countries[1,2]. The thermal treatment causes weight loss and, a decrease in mechanical strength[3], which limits the structural use of thermally treated wood. Wood colour modification by thermal treatment is possible and can be worthwhile primarily when the material is chosen based on aesthetic and non-structural factors. According to Todorovic et al.[6], thermal treatment enables many uses and increases the market value of less-valued species

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