Conventional and microwave-assisted thermal treatment of dendrocalamus asper bamboo

Abstract

The thermal treatment process of bamboo or wood can be used to improve the mechanical properties and enhance the dimensional stability. The aim of this work was to investigate the mechanical properties of the bamboo Dendrocalamus asper after thermal treatment using a microwave-assisted oven (MO) and a conventional furnace (CF), normally used for this purpose. In the present study, prismatic samples of bamboo were heat treated in the presence of air at the temperatures of 120, 140 and 160°C with heating rate of 1°C/min and isotherm of 10 min. The treatment conditions were evaluated through axial compression tests, density and mass change. The bamboo in the as-received condition showed a mean moisture content of 92.65 %. The experimental results indicated that in average, 51 % more weight loss is observed using the MO than the CF process at the same temperature. However, the compression tests showed similar mechanical resistance after heat treatment in the MO and CF at 120 °C, with a modulus of elasticity MOE of 4.68 GPa and 4.73 GPa and compressive strength MOR of 77.41 MPa and 83.24 MPa respectively. These results suggest an increase of the stiffness and strength after the conducted heat treatments in comparison with the untreated bamboo, which showed a MOE of 3.40 GPa and a MOR of 73.67 MPa. The results of this study showed that the effects of the microwave interfered in the process of removal of compounds with low polarity, without compromising the structure of the material. The performed heat treatments provided materials with similar mechanical characteristics at different treatment temperatures.