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 degrees C. Three equatorial and one meridional d-spacings showed a gradual linear increase with increasing temperature. For temperatures above 180 degrees C, however, the equatorial d-spacing increased dramatically. Thus, the linear and volume thermal expansion coefficients (TECs) below 180 degrees C were determined from the d-spacings. The linear TECs of the a-, b-, and c-axes were: alpha(a) = 13.6 x 10(-5) degrees C-1, alpha(b) = -3.0x 10(-5) degrees C-1, and alpha(c)=0.6x 10(-5) degrees C-1, respectively, and the volume TEC was beta = 11.1x 10(-5) degrees 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.