Physico-Mechanical Properties of Thermally Modified Gmelina arborea (Roxb.) Wood

Jacob M. Owoyemi, Henry H. Adebayo, and John T. Aladejana

Department of Forestry and Wood Technology, Federal University of Technology, Nigeria

Abstract: The major problem of wood in service is dimensional instability caused by varying relative humidity of the surrounding environment. This study investigated the effect of thermal modification on the physical and mechanical properties of Gmelina arborea wood. Freshly felled Gmelina arborea trees were machined and trimmed to standard size of 20×20×60 mm for the determination of physical properties (colour, volumetric shrinkage, swelling and water absorption) and 20×20×300 mm for mechanical properties (Modulus of Rupture and Modulus of Elasticity) assessment. Thermal modifications were performed in several batches using 160, 180 and 200oC at 1, 2 and 3 hours. Visual observation of treated samples showed that wood colour changed from light yellowish to very dark brown with increasing treatment temperature. Water absorption, shrinkage and swelling values decreased with increase in treatment duration and temperature. At a treatment time of 3hrs, compared with the control, mean values of the thermally treated samples for volumetric swelling ranged from 2.65% at 160°C to 1.94% at 200°C. Mean values of the thermally treated samples for volumetric shrinkage ranged from 6.58% at 160oC to 3.65% at 200°C. Mean values of the thermally treated samples for water absorption ranged from 33.40% at 160°C to 26.8% at 200°C. The MOE of heat treated Gmelina arborea wood varied from 4012.25 N/mm2 at 160°C to 12415.87 N/mm2 at 180°C. The MOR varied from 38.30 N/mm2 at 200°C to 100.91 N/mm2 at 160°C. MOR was significantly reduced while there were no significant effects on the MOE as a result of heat treatment. The result showed reduction in the hygroscopic properties of Gmelina arborea wood making it suitable for use in high moisture prone areas in construction.

Key words: dimensional stability, hygroscopicity, colour change, moisture content