The Thermal Expansion of Wood Cellulose Crystals

We have investigated tension wood cellulose obtained from Populus maximowiczii using X-ray diffraction at temperatures from room temperature to 250 °C. Three equatorial and one meridional d-spacings showed a gradual linear increase with increasing temperature. For temperatures above 180 °C, however, the equatorial d-spacing increased dramatically. Thus, the linear and volume thermal expansion coefficients (TECs) below 180 °C were determined from the d-spacings. The linear TECs of the a-, b-, and c-axes were: α _a = 13.6 × 10⁻⁵ °C⁻¹, α _b = −3.0× 10⁻⁵ °C⁻¹, and α _c =0.6× 10⁻⁵ °C⁻¹, respectively, and the volume TEC was β = 11.1× 10⁻⁵ °C⁻¹. The anisotropic thermal expansion in the three coordinate directions was closely related to the crystal structure of the wood cellulose, and it governed the macroscopic thermal behavior of solid wood.