Thermal degradation of commercially available woods in South Asia: a study on physical properties

Abstract

ABSTRACT The influential effects of thermal treatment on material density, hardness, colour and microstructure of three commercially available woods in South Asia are evaluated. Wood specimens are isochronally annealed 120 min at different temperatures up to 250°C and isothermally annealed at 100°C, 150°C and 225°C up to 480 min under atmospheric pressure. Heat treatments cause density loss, hardness loss, darkening and microstructure frailer of woods, as the maximum temperature was increased. However, thermal treatment up to the temperature around 150°C shows lower values for the case of density, higher values for hardness and no remarkable changes in colour of wood specimens. Higher temperature treated samples are found to recover through absorbing water (moisture); however, chemically bonded water and thermally lost substances cannot be recovered. The diffuse reflectances of all the wooden samples decrease with the increase of annealing temperature, especially at colour band of higher wave length. The negative effects of the high-temperature thermal treatment on the properties of all the woods are observed due to removal of the free, loosely and chemically bonded water of woods, along with higher thermal degradation of cellulose, hemicelluloses and lignin. The SEM microstructures of the wood samples also comply with the present investigation showing the damage structure of fibres and pores.