Investigation on mechanical and thermal properties related to hygroscopicity of two African hardwoods

This paper aims to study the mechanical, thermal and hygroscopic behavior of Okan ( Cylicodiscus gabunensis ) and Ayous ( Triplochiton scleroxylon ), two African hardwood species grown in southern Cameroon. The mechanical characterization of wood at 10%, 15%, 20%, 25% and 30% was investigated using tensile and bending tests. The thermal parameters were measured at the same moisture content levels by using the asymmetrical hot plate method. Sorption isotherms were obtained using the static gravimetric method. Mechanical properties decreased with moisture content. Okan wood, which Guitard and Brazilian models was not suitable for, presented very good properties compared to Ayous wood. Its flexural strength varied between 100 and 140 MPa and was 2.5 times higher than Ayous wood. Thermal conductivity increased with moisture content and was ranged from 0.1 to 0.56 W/mK. There was no significant difference between the radial thermal conductivities of the two species. The volumetric heat capacity was not influenced by the heat flow and the species. Experimental data showed a good fitting with the GAB model concerning sorption isotherms. Okan wood was less hygroscopic than Ayous wood. The annual equilibrium moisture content of the two species was determined and the cities of Bafoussam and Douala presented the best stabilization trend.