Effect of Low Temperature Cyclic Treatments on Modulus of Elasticity of Birch Wood

The modulus of elasticity (MOE) of birch (Betula platyphylla) wood specimens with four different moisture content (MC) levels, i.e., water-saturated, green, air-dried, and oven-dried, were examined under a low temperature condition ranging from -196 °C (liquid nitrogen temperature) to +20 °C (room temperature). Dynamic mechanical analysis (DMA) was used to evaluate the dynamic viscoelastic properties before and after the low temperature treatment, while X-ray diffraction (XRD) was used to analyze the crystalline structure. The results showed that MOE with different MC increased after the low temperature treatment. Specimens with higher MCs were more affected by the treatment than specimens with lower MCs. However, the effect of low temperature treatment (within four times) on MOE was not significant (P > 0.05). Cyclic treatments of liquid nitrogen did not decrease wood MOE. As a structural material, wood has a better residence to low temperatures compared to concrete, in which mechanical properties decreased dramatically after one cycle of low to room temperature.