Synchrotron X-ray fiber diffraction study on the thermal expansion behavior of cellulose crystals in tension wood of Japanese poplar in the low-temperature region

The thermal expansion behavior of tension wood cellulose obtained from Populus maximowiczii A. Henry was investigated by synchrotron X-ray fiber diffraction at temperatures ranging from 100 to 300 K. Three equatorial and one meridional d-spacings indexed as 1 (1) over bar0, 110, 200, and 004 showed a gradual linear increase with increasing temperature. Unit-cell parameters calculated from the changes in these d-spacings showed anisotropic thermal expansion behavior in the three axial directions related to the crystal structure and hydrogen-bonding system of cellulose I(beta). The linear thermal expansion coefficients (TECs) of the a-, b-, and c- axes were: alpha(a) = 5.2 x 10(-5) K(-1), alpha(b) = 2.1 x 10(-5) K(-1), and alpha(c) = 0.4 x 10(-5) K(-1), respectively. The volume TEC was beta = 7.8 x 10(-5) K(-1), which was approximately 70% of previously reported values in the high-temperature region from room temperature to 250 degrees C.