Effect of heat treatment on colour changes of black alder and beech veneers

Abstract

In the present study, colour changes in black alder (Alnus glutinosa L. Gaertn.) and beech (Fagus sylvatica L.) wood veneers subjected to heat treatment at 190 °C for different time spans were investigated. The potential of CIELab system and near infrared (NIR) spectroscopy were used to evaluate the colour changes. The changes in colour appeared mostly by the reduction in lightness which is related to the degradation of hemicelluloses during heat treatment in both wood species. It was found that black alder discoloured much more than beech veneers under same treatment conditions. NIR spectra revealed that the dark colour that wood veneers get under heat exposure is due to the chemical decomposition of lignin and hemicelluloses. Heat treatment could, therefore, enhance the use of such veneers for value added products in furniture manufacturing as an alternative to expensive tropical species.