The effect of layer's moisture content and pre-heating by microwave radiation on physical and mechanical properties of laminated veneer lumber

The effect of moisture and pre-heating time by the microwave radiation were studied on the physical and the mechanical properties of laminate veneer lumber (LVL).The variable factors included moisture content of layers in the range of 3, 5 and 8 percentage and the microwave radiation pre-heating times at levels of 0, 120 and 180 seconds. LVLs were made of 9 poplar layers with 2.5 (mm) thickness and bonded together using phenol formaldehyde. The frequency and the power of microwave radiation were 2450 (MHz) and 4000 (W), respectively. The results showed that the physical and mechanical properties of LVL decreased when moisture content of layers increased from 3 to 8 percentage. In contrast, the pre-heating by microwave improved physical and mechanical properties at longer times. The positive impact of pre-heating by microwave radiation was much more evident on the layer with higher moisture content.