The thermal expansion of cellulose II and IIIII crystals

Highly crystalline samples of cellulose II and IIIII have been prepared from repeated mercerization of ramie fibers and supercritical ammonia treatment of the mercerized ramie fibers, respectively. The thermal expansion behavior of cellulose II and IIIII was investigated using X-ray diffraction at temperatures ranging from room temperature to 250 degrees C. With increasing temperature, the unit cell of cellulose II expanded in the lateral directions and contracted in the longitudinal direction, with the a and b axes increasing by 0.54 and 3.4%, respectively, and the c axis decreasing by 0.09%. The anisotropic thermal expansion in these three directions was closely related to the crystal structure and the hydrogen bonding in cellulose II. A similar anisotropic thermal expansion was also observed in cellulose IIIII. Cellulose IIIII expanded in the lateral direction but contracted in the longitudinal direction.